Re: [ccp4bb] Confusion about space group nomenclature
@ Ian: Not quite, here's a table giving the complete list of the 3 types: http://pd.chem.ucl.ac.uk/pdnn/symm3/allsgp.htm Yes, this Table is known and agrees with what I wrote. I still do not like, to the point of vehement opposition, the use of enantiomorphic for the entire 65 because of the point made below @Jens @ Boaz: the most general, analytical, mathematical one-word definition of this 65 sg's or something that will bring the message as clearly (in the practical sense) to students Yes. One word. Succinct. Clear. Context-insensitive. Un-mis-interpretable. …wishful thinking. @ Jens: I think the precise and correct term applicable to the 65 should be pro-chiral spacegroups. They are not chiral by themselves, but addition of something /allows/ for the creation of a chiral object (i.e. the crystal). For a moment I though we have it…. but then the rest would be anti-chiral? Again, if we care about structure, then the word should address what the space group does (or does not) to the motif. This clashes already with the fact that the members of an enantiomorphic pair are themselves called enantiomorphic or chiral, because they do not morph the subject. This was the point in my original post, and we are not any closer. I give up. But not without throwing another one: What are we supposed to do with the poor 3 space groups that are their own enantiomorph? Are they bi-enant? Or trans-enant? Enough of this thread. Over and out, BR
Re: [ccp4bb] Confusion about space group nomenclature
After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature …. Enough of this thread. Over and out, BR
Re: [ccp4bb] Confusion about space group nomenclature
Or space gRupps? From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Jim Pflugrath Sent: Friday, May 02, 2014 8:36 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UKmailto:CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Enough of this thread. Over and out, BR
Re: [ccp4bb] Confusion about space group nomenclature
You guys are enantioqueer. BR From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Keller, Jacob Sent: Freitag, 2. Mai 2014 15:43 To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Or space gRupps? From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Jim Pflugrath Sent: Friday, May 02, 2014 8:36 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim _ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature .. Enough of this thread. Over and out, BR
Re: [ccp4bb] Confusion about space group nomenclature
I actually meant enantioweird. From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Keller, Jacob Sent: Freitag, 2. Mai 2014 15:43 To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Or space gRupps? From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Jim Pflugrath Sent: Friday, May 02, 2014 8:36 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim _ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature .. Enough of this thread. Over and out, BR
Re: [ccp4bb] Confusion about space group nomenclature
Dear all, It is nice to see this rather high-brow thread end with some verbal humour, but I think the subject might deserve a better treatment than it has received. Three-dimensional crystallographic space groups were classified by 3 different people as far back as the 19th century, and questions such as those that have been discussed are ultra-classical in group theory - so if this thread is to lead us towards the spool rather than the ragged end, we should look towards those sources. It has perhaps been an unfortunate side effect of the creation of the International Tables that we have tended to consider such topics as being part of our private microcosm and folklore, all compiled between the covers of a single book. Perhaps we should be a little less flippant: if we are to identify the actual ultimate authorities on this topic, we may have to look further than colleagues who can be contacted by e-mail and come up with an answer within a day. Happy weekend to all, Gerard. -- On Fri, May 02, 2014 at 01:42:36PM +, Keller, Jacob wrote: Or space gRupps? From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Jim Pflugrath Sent: Friday, May 02, 2014 8:36 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UKmailto:CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Enough of this thread. Over and out, BR
Re: [ccp4bb] Confusion about space group nomenclature
In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George On 05/02/2014 02:35 PM, Jim Pflugrath wrote: After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim *From:* CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] *Sent:* Friday, May 02, 2014 3:04 AM *To:* CCP4BB@JISCMAIL.AC.UK *Subject:* Re: [ccp4bb] Confusion about space group nomenclature …. Enough of this thread. Over and out, BR -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582
Re: [ccp4bb] Confusion about space group nomenclature
I agree with George. Sohnke is only six letters and it's been used for a long time to label these groups. Ron On Fri, 2 May 2014, George Sheldrick wrote: In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George On 05/02/2014 02:35 PM, Jim Pflugrath wrote: After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim __ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature …. Enough of this thread. Over and out, BR -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582
Re: [ccp4bb] Confusion about space group nomenclature
Dear George My student class would not find that IUCr dictionary definition helpful. What they do find helpful is to state that they cannot contain an inversion or a mirror. To honour Sohnke is one thing but is it really necessary as a label? You're from Huddersfield I am from Wakefield ie let's call a spade a spade (not a 'Black and Decker'). Cheers John Prof John R Helliwell DSc On 2 May 2014, at 17:01, George Sheldrick gshe...@shelx.uni-ac.gwdg.de wrote: In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George On 05/02/2014 02:35 PM, Jim Pflugrath wrote: After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature …. Enough of this thread. Over and out, BR -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582
Re: [ccp4bb] Confusion about space group nomenclature
It well-known in the mathematics community to refer to these as Sohnke groups, or even Jordan-Sohnke groups. Camille Jordan identified them in 1868-1869, and L. A. Sohnke in 1879. William Barlow derived all 230 space groups by adding reflection operations to Sohnke's 65 groups in 1894-1989. On May 2, 2014, at 11:42 AM, Jrh Gmail wrote: Dear George My student class would not find that IUCr dictionary definition helpful. What they do find helpful is to state that they cannot contain an inversion or a mirror. To honour Sohnke is one thing but is it really necessary as a label? You're from Huddersfield I am from Wakefield ie let's call a spade a spade (not a 'Black and Decker'). Cheers John Prof John R Helliwell DSc On 2 May 2014, at 17:01, George Sheldrick gshe...@shelx.uni-ac.gwdg.de wrote: In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George
Re: [ccp4bb] Confusion about space group nomenclature
Dear John, What is wrong with honouring Sohnke by using his name for something that he first saw a point in defining, and in investigating the properties resulting from that definition? Why insist that we should instead replace his name by an adjective or a circumlocution? What would we say if someone outside our field asked us not to talk about a Bragg reflection, or the Ewald sphere, or the Laue method, but to use instead some clever adjective or a noun-phrase as long as the name of a Welsh village to explain what these mean? Again, I think we should have a bit more respect here. When there are simple adjectives to describe a mathematical properties, the mathematical vocabulary uses it (like a normal subgroup). However, when someone has seen that a definition by a conjunction of properties (i.e. something describable by a sentence) turns out to characterise objects that have much more interesting properties than just those by which they were defined, then they are often called by the name of the mathematician who first saw that there is more to them than what defines them. Examples: Coxeter groups, or Lie algebras, or the Leech lattice, or the Galois group of a field, the Cayley tree of a group ... . It is the name of the first witness to a mathematical phenomenon, just as we call chemical reactions by the name of the chemist who saw that mixing certain chemicals together led not just to a mixture of those chemicals. So why don't we give Sohnke what belongs to him, just as we expect other scientists to give to Laue, Bragg and Ewald what we think belongs to them? Maybe students would not be as refractory to the idea as might first be thought. With best wishes, Gerard. -- On Fri, May 02, 2014 at 05:42:34PM +0100, Jrh Gmail wrote: Dear George My student class would not find that IUCr dictionary definition helpful. What they do find helpful is to state that they cannot contain an inversion or a mirror. To honour Sohnke is one thing but is it really necessary as a label? You're from Huddersfield I am from Wakefield ie let's call a spade a spade (not a 'Black and Decker'). Cheers John Prof John R Helliwell DSc On 2 May 2014, at 17:01, George Sheldrick gshe...@shelx.uni-ac.gwdg.de wrote: In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George On 05/02/2014 02:35 PM, Jim Pflugrath wrote: After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature …. Enough of this thread. Over and out, BR -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582
Re: [ccp4bb] Confusion about space group nomenclature
Bernhard et al, @ Jens: I think the precise and correct term applicable to the 65 should be pro-chiral spacegroups. They are not chiral by themselves, but addition of something /allows/ for the creation of a chiral object (i.e. the crystal). For a moment I though we have it…. but then the rest would be anti-chiral? I never thought about it that way but actually, yes! You put something chiral into their AU and those little buggers go on and invert it. They are really anti-chiral. So we have the three groups chiral, prochiral and antichiral. I like the suggestion of calling the chiral and prochiral groups the Sohncke groups (beware everybody misspelled that poor guy, he has a ck in his last name). That keeps the history of our field in the expressions we use and might even inspire people to look up who the people were on whose shoulders we stand. Jens PS: I had to laugh when I looked him up on Wikipedia: Leonhard Sohncke (22 February 1842 Halle – 1 November 1897 München) was a German mathematician who classified the 65 chiral space groups, sometimes called Sohncke groups. The German Wikipedia entry is much more complete. Also, I guess inspired by this thread, anonymous created an entry in Wikipedia L.A. Sonke - about 3h ago...
Re: [ccp4bb] Confusion about space group nomenclature
Dear Jens, I hope I can make a couple more remarks, and then I will keep quiet. The first is that your suggestion that we do use Sohncke's name in relation to these groups may still leave the impression that, as John put it earlier, this name is just a label. This is where I want to point out what it is exactly that we owe Sohncke. It is not the bland definition of a list of groups of Euclidean transformations with certain properties, printed in some section of IT-A: it is a classification result, namely that if you look for all the groups with those properties, there are only 65 types of them, and here they are. So it is in that 65, that we take for granted because we read it in the ITs, that Sohncke's contribution lies. A second remark is about wanting to find where the attribute of chirality (or pro-chirality) resides. As was pointed out, it is not the groups themselves that have these attributes: it is objects in space on which the groups act. A sensible adjective might therefore exist to designate the 65, namely chirality-preserving. With best wishes, Gerard. -- On Fri, May 02, 2014 at 12:36:59PM -0700, Jens Kaiser wrote: Bernhard et al, @ Jens: I think the precise and correct term applicable to the 65 should be pro-chiral spacegroups. They are not chiral by themselves, but addition of something /allows/ for the creation of a chiral object (i.e. the crystal). For a moment I though we have it…. but then the rest would be anti-chiral? I never thought about it that way but actually, yes! You put something chiral into their AU and those little buggers go on and invert it. They are really anti-chiral. So we have the three groups chiral, prochiral and antichiral. I like the suggestion of calling the chiral and prochiral groups the Sohncke groups (beware everybody misspelled that poor guy, he has a ck in his last name). That keeps the history of our field in the expressions we use and might even inspire people to look up who the people were on whose shoulders we stand. Jens PS: I had to laugh when I looked him up on Wikipedia: Leonhard Sohncke (22 February 1842 Halle – 1 November 1897 München) was a German mathematician who classified the 65 chiral space groups, sometimes called Sohncke groups. The German Wikipedia entry is much more complete. Also, I guess inspired by this thread, anonymous created an entry in Wikipedia L.A. Sonke - about 3h ago...
Re: [ccp4bb] Confusion about space group nomenclature
Dear Gerard I am duly reprimanded . You are quite correct . Have a good weekend John Prof John R Helliwell DSc On 2 May 2014, at 18:16, Gerard Bricogne g...@globalphasing.com wrote: Dear John, What is wrong with honouring Sohnke by using his name for something that he first saw a point in defining, and in investigating the properties resulting from that definition? Why insist that we should instead replace his name by an adjective or a circumlocution? What would we say if someone outside our field asked us not to talk about a Bragg reflection, or the Ewald sphere, or the Laue method, but to use instead some clever adjective or a noun-phrase as long as the name of a Welsh village to explain what these mean? Again, I think we should have a bit more respect here. When there are simple adjectives to describe a mathematical properties, the mathematical vocabulary uses it (like a normal subgroup). However, when someone has seen that a definition by a conjunction of properties (i.e. something describable by a sentence) turns out to characterise objects that have much more interesting properties than just those by which they were defined, then they are often called by the name of the mathematician who first saw that there is more to them than what defines them. Examples: Coxeter groups, or Lie algebras, or the Leech lattice, or the Galois group of a field, the Cayley tree of a group ... . It is the name of the first witness to a mathematical phenomenon, just as we call chemical reactions by the name of the chemist who saw that mixing certain chemicals together led not just to a mixture of those chemicals. So why don't we give Sohnke what belongs to him, just as we expect other scientists to give to Laue, Bragg and Ewald what we think belongs to them? Maybe students would not be as refractory to the idea as might first be thought. With best wishes, Gerard. -- On Fri, May 02, 2014 at 05:42:34PM +0100, Jrh Gmail wrote: Dear George My student class would not find that IUCr dictionary definition helpful. What they do find helpful is to state that they cannot contain an inversion or a mirror. To honour Sohnke is one thing but is it really necessary as a label? You're from Huddersfield I am from Wakefield ie let's call a spade a spade (not a 'Black and Decker'). Cheers John Prof John R Helliwell DSc On 2 May 2014, at 17:01, George Sheldrick gshe...@shelx.uni-ac.gwdg.de wrote: In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George On 05/02/2014 02:35 PM, Jim Pflugrath wrote: After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature …. Enough of this thread. Over and out, BR -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582
Re: [ccp4bb] Confusion about space group nomenclature
Fellows, my apologies for having sparked that space war. I wish to interject than in my earlier postings to this thread to Howard I did give credit to the '65 sons of Sohnke' (albeit sans c). If we honor him, we ought to spell him right. http://reference.iucr.org/dictionary/Sohnke_groups Sohnke (IUCr) Sohncke (same page, IUCr) Sohncke (Wikipedia and German primary sources): http://www.deutsche-biographie.de/sfz80497.html Ron posted the Sohncke link to me off-line right away and I admit that I realized the same by googling 'chiral space groups' which immediately leads you to Wikipedia's space group and Sohncke entry. It also shows (in addition to an interesting 74-group page...) my own web list, which imho erroneously used the improper (no pun intended) adjective 'chiral' for the 65 Sohncke groups. No more. Nonetheless, this does not necessarily discredit my quest for a descriptive adjective, and the absence of such after this lively engagement might indicate that the question was not quite as illegitimate as it might have appeared even to the cognoscenti at first sight. Nonetheless, a toast to Sohncke! BR -Original Message- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Gerard Bricogne Sent: Friday, May 02, 2014 7:17 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Dear John, What is wrong with honouring Sohnke by using his name for something that he first saw a point in defining, and in investigating the properties resulting from that definition? Why insist that we should instead replace his name by an adjective or a circumlocution? What would we say if someone outside our field asked us not to talk about a Bragg reflection, or the Ewald sphere, or the Laue method, but to use instead some clever adjective or a noun-phrase as long as the name of a Welsh village to explain what these mean? Again, I think we should have a bit more respect here. When there are simple adjectives to describe a mathematical properties, the mathematical vocabulary uses it (like a normal subgroup). However, when someone has seen that a definition by a conjunction of properties (i.e. something describable by a sentence) turns out to characterise objects that have much more interesting properties than just those by which they were defined, then they are often called by the name of the mathematician who first saw that there is more to them than what defines them. Examples: Coxeter groups, or Lie algebras, or the Leech lattice, or the Galois group of a field, the Cayley tree of a group ... . It is the name of the first witness to a mathematical phenomenon, just as we call chemical reactions by the name of the chemist who saw that mixing certain chemicals together led not just to a mixture of those chemicals. So why don't we give Sohnke what belongs to him, just as we expect other scientists to give to Laue, Bragg and Ewald what we think belongs to them? Maybe students would not be as refractory to the idea as might first be thought. With best wishes, Gerard. -- On Fri, May 02, 2014 at 05:42:34PM +0100, Jrh Gmail wrote: Dear George My student class would not find that IUCr dictionary definition helpful. What they do find helpful is to state that they cannot contain an inversion or a mirror. To honour Sohnke is one thing but is it really necessary as a label? You're from Huddersfield I am from Wakefield ie let's call a spade a spade (not a 'Black and Decker'). Cheers John Prof John R Helliwell DSc On 2 May 2014, at 17:01, George Sheldrick gshe...@shelx.uni-ac.gwdg.de wrote: In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George On 05/02/2014 02:35 PM, Jim Pflugrath wrote: After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature . Enough of this thread. Over and out, BR -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582
Re: [ccp4bb] Confusion about space group nomenclature
namely chirality-preserving. enantiostatic ;-) ? BR
Re: [ccp4bb] Confusion about space group nomenclature
Bernhard On 2 May 2014 21:51, Bernhard Rupp hofkristall...@gmail.com wrote: Nonetheless, this does not necessarily discredit my quest for a descriptive adjective, and the absence of such after this lively engagement might indicate that the question was not quite as illegitimate as it might have appeared even to the cognoscenti at first sight. Nonetheless, a toast to Sohncke! I second that, but while not intending in any way to belittle Sohncke's contribution to the subject, I would point out that Sohncke is a noun (of kind proper noun) and most definitely not an adjective (of any kind). I say that because I have been working all along on the assumption that your quest was for an adjective (i.e. as you say above, a descriptor of a noun). In the English language at least, adjectives come in 5 different flavours: 1) attributive (the good book), 2) predicative (this book is good), 3) absolute (this book, good though it is, won't win the Booker, 4) nounal adjective (the good, the bad and the ugly), and 5) postpositive (adjective follows noun: mostly archaic usage in English though common syntax in other languages). Of course nouns can also function as adjectives (adjectival noun) but only in a very limited way. In particular nouns can only function as attributive adjectives (a Sohncke space group). You can't use a noun as a predicative adjective (this space group is Sohncke just doesn't sound right), or use an adjectival noun in any of the other 3 ways; it can only function as the attribute of another noun. A true adjective can be used in all 5 ways without breaking the syntactical rules, e.g. the attributive a centrosymmetric space group and the predicative this space group is centrosymmetric are both valid syntax (I hesitate to use the e word again having had it ruled totally out of contention). Exceedingly descriptive though it is, chirality-preserving is technically also not an adjective (it's an adjectival phrase), though of course that's no reason to rule it out. Some proper nouns (mostly names of mathematicians for some reason!) have been transformed into real adjectives (e.g. Hessian in honour of Ludwig Otto Hesse, Wronskian for Józef Hoene-Wronski, and several others). Sadly Sohncke is not one of those in common, or indeed any, usage in adjectival form (I would hesitate to suggest Sohnckian as the adjective derived from the proper noun). As an aside, strangely many of these name-derived adjectives have made the reverse journey and now double as true nouns themselves, having dropped the nouns to which they were originally attached. Hessian as a true noun (i.e. not even a nounal adjective) is of course now used in preference to and is a synonym for the original Hessian matrix, Wronskian is used instead of Wronskian determinant, etc. Enough of this drivel. You can tell it's the weekend, and that none of us have anything better to do ... Cheers -- Ian
Re: [ccp4bb] Confusion about space group nomenclature
Bernhard is giving me too much credit. I just told him I'd seen someone's name associated with the 65 space groups, but that's the only information I provided. Ron On Fri, 2 May 2014, Bernhard Rupp wrote: Fellows, my apologies for having sparked that space war. I wish to interject than in my earlier postings to this thread to Howard I did give credit to the '65 sons of Sohnke' (albeit sans c). If we honor him, we ought to spell him right. http://reference.iucr.org/dictionary/Sohnke_groups Sohnke (IUCr) Sohncke (same page, IUCr) Sohncke (Wikipedia and German primary sources): http://www.deutsche-biographie.de/sfz80497.html Ron posted the Sohncke link to me off-line right away and I admit that I realized the same by googling 'chiral space groups' which immediately leads you to Wikipedia's space group and Sohncke entry. It also shows (in addition to an interesting 74-group page...) my own web list, which imho erroneously used the improper (no pun intended) adjective 'chiral' for the 65 Sohncke groups. No more. Nonetheless, this does not necessarily discredit my quest for a descriptive adjective, and the absence of such after this lively engagement might indicate that the question was not quite as illegitimate as it might have appeared even to the cognoscenti at first sight. Nonetheless, a toast to Sohncke! BR -Original Message- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Gerard Bricogne Sent: Friday, May 02, 2014 7:17 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Dear John, What is wrong with honouring Sohnke by using his name for something that he first saw a point in defining, and in investigating the properties resulting from that definition? Why insist that we should instead replace his name by an adjective or a circumlocution? What would we say if someone outside our field asked us not to talk about a Bragg reflection, or the Ewald sphere, or the Laue method, but to use instead some clever adjective or a noun-phrase as long as the name of a Welsh village to explain what these mean? Again, I think we should have a bit more respect here. When there are simple adjectives to describe a mathematical properties, the mathematical vocabulary uses it (like a normal subgroup). However, when someone has seen that a definition by a conjunction of properties (i.e. something describable by a sentence) turns out to characterise objects that have much more interesting properties than just those by which they were defined, then they are often called by the name of the mathematician who first saw that there is more to them than what defines them. Examples: Coxeter groups, or Lie algebras, or the Leech lattice, or the Galois group of a field, the Cayley tree of a group ... . It is the name of the first witness to a mathematical phenomenon, just as we call chemical reactions by the name of the chemist who saw that mixing certain chemicals together led not just to a mixture of those chemicals. So why don't we give Sohnke what belongs to him, just as we expect other scientists to give to Laue, Bragg and Ewald what we think belongs to them? Maybe students would not be as refractory to the idea as might first be thought. With best wishes, Gerard. -- On Fri, May 02, 2014 at 05:42:34PM +0100, Jrh Gmail wrote: Dear George My student class would not find that IUCr dictionary definition helpful. What they do find helpful is to state that they cannot contain an inversion or a mirror. To honour Sohnke is one thing but is it really necessary as a label? You're from Huddersfield I am from Wakefield ie let's call a spade a spade (not a 'Black and Decker'). Cheers John Prof John R Helliwell DSc On 2 May 2014, at 17:01, George Sheldrick gshe...@shelx.uni-ac.gwdg.de wrote: In my program documentation I usually call these 65 the Sohnke space groups, as defined by the IUCr: http://reference.iucr.org/dictionary/Sohnke_groups George On 05/02/2014 02:35 PM, Jim Pflugrath wrote: After all this discussion, I think that Bernhard can now lay the claim that these 65 space groups should really just be labelled the Rupp space groups. At least it is one word. Jim From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Bernhard Rupp [hofkristall...@gmail.com] Sent: Friday, May 02, 2014 3:04 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature . Enough of this thread. Over and out, BR -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582
Re: [ccp4bb] Confusion about space group nomenclature
I'm watching the periphery of this, having just taught something about The Sixty-Five Space Groups a few days ago, but my impression is that you guys have too much time on your hands. If you'd like something really interesting (and perhaps useful) to spend your time on, let us know. We'll put you to work. BS From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Ian Tickle [ianj...@gmail.com] Sent: Friday, May 02, 2014 7:42 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Bernhard On 2 May 2014 21:51, Bernhard Rupp hofkristall...@gmail.commailto:hofkristall...@gmail.com wrote: Nonetheless, this does not necessarily discredit my quest for a descriptive adjective, and the absence of such after this lively engagement might indicate that the question was not quite as illegitimate as it might have appeared even to the cognoscenti at first sight. Nonetheless, a toast to Sohncke! I second that, but while not intending in any way to belittle Sohncke's contribution to the subject, I would point out that Sohncke is a noun (of kind proper noun) and most definitely not an adjective (of any kind). I say that because I have been working all along on the assumption that your quest was for an adjective (i.e. as you say above, a descriptor of a noun). In the English language at least, adjectives come in 5 different flavours: 1) attributive (the good book), 2) predicative (this book is good), 3) absolute (this book, good though it is, won't win the Booker, 4) nounal adjective (the good, the bad and the ugly), and 5) postpositive (adjective follows noun: mostly archaic usage in English though common syntax in other languages). Of course nouns can also function as adjectives (adjectival noun) but only in a very limited way. In particular nouns can only function as attributive adjectives (a Sohncke space group). You can't use a noun as a predicative adjective (this space group is Sohncke just doesn't sound right), or use an adjectival noun in any of the other 3 ways; it can only function as the attribute of another noun. A true adjective can be used in all 5 ways without breaking the syntactical rules, e.g. the attributive a centrosymmetric space group and the predicative this space group is centrosymmetric are both valid syntax (I hesitate to use the e word again having had it ruled totally out of contention). Exceedingly descriptive though it is, chirality-preserving is technically also not an adjective (it's an adjectival phrase), though of course that's no reason to rule it out. Some proper nouns (mostly names of mathematicians for some reason!) have been transformed into real adjectives (e.g. Hessian in honour of Ludwig Otto Hesse, Wronskian for Józef Hoene-Wronski, and several others). Sadly Sohncke is not one of those in common, or indeed any, usage in adjectival form (I would hesitate to suggest Sohnckian as the adjective derived from the proper noun). As an aside, strangely many of these name-derived adjectives have made the reverse journey and now double as true nouns themselves, having dropped the nouns to which they were originally attached. Hessian as a true noun (i.e. not even a nounal adjective) is of course now used in preference to and is a synonym for the original Hessian matrix, Wronskian is used instead of Wronskian determinant, etc. Enough of this drivel. You can tell it's the weekend, and that none of us have anything better to do ... Cheers -- Ian
Re: [ccp4bb] Confusion about space group nomenclature
On Tue, 2014-04-29 at 16:12 +0200, Bernhard Rupp wrote: Response to off-board mail: How about [calling them] non-centro-symmetric space groups, as I often tell my students? Almost, but not exact enough. The 65 are only a subset of non-centrosymmetric space groups: Not all enantiogenic (not elements of the 65-set) space groups are centrosymmetric. Simplest example Pm. According to above definition Pm (and many more lacking a center of inversion) would be a ok space group for chiral motifs. (when a space group has the 'center at ' annotation in the Tables, it has a coi and is a centrosymmetric space group). This implies that there are actually three types of crystal structures (cf. Flack): (a) chiral (non-centrosymmetric) crystal structures (b) centrosymmetric crystal structures (c) achiral non-centrosymmetric crystal structures And just as a reminder, the substructure inversion for 3 members of the 65 is not about the origin (0,0,0): I41, I4122, F4132 are their own enantiomorph, so for them there is no enantiomorphic pair (eg. I41 and I43), in fact no separate space group I43 is even necessary - look at the SG diagram #80 - both, 41 and 43 axes appear in the same SG. (2005 Erice paper of George explains more) Enough yet? Cheers, BR Not quite, here's a table giving the complete list of the 3 types: http://pd.chem.ucl.ac.uk/pdnn/symm3/allsgp.htm The table heading states: Space groups possessing a point of inversion are termed *centrosymmetric*; these are shown in the table in red. Some space groups have no symmetry element that can change the handedness of an object; these are termed *enantiomorphic* space groups and are shown in magenta. i.e. your (a) set are the magenta ones, your (b) set are the red ones and your (c) set are the remaining black ones. -- Ian
Re: [ccp4bb] Confusion about space group nomenclature
Hi Fellows, I have bugged now the ultimate authorities including Howard Flack (of Flack parameter fame), and alas, there is no official descriptive adjective for these 65 Söhnke space groups. Chiral is definitely wrong, and so is enantiomorphic, although 22 of the nameless form 11 enantiomorphic pairs. Thou shallst not use those descriptors for SGs, only for structures. So the contest for a proper descriptive adjective is still open. Best, BR PS: Otherwise it is a bit like saying 'You know, that thing, the one where you see stuff moving and it is not black and white' instead of simply 'color TV' - almost as old as space groups
Re: [ccp4bb] Confusion about space group nomenclature
Response to off-board mail: How about [calling them] non-centro-symmetric space groups, as I often tell my students? Almost, but not exact enough. The 65 are only a subset of non-centrosymmetric space groups: Not all enantiogenic (not elements of the 65-set) space groups are centrosymmetric. Simplest example Pm. According to above definition Pm (and many more lacking a center of inversion) would be a ok space group for chiral motifs. (when a space group has the 'center at ' annotation in the Tables, it has a coi and is a centrosymmetric space group). This implies that there are actually three types of crystal structures (cf. Flack): (a) chiral (non-centrosymmetric) crystal structures (b) centrosymmetric crystal structures (c) achiral non-centrosymmetric crystal structures And just as a reminder, the substructure inversion for 3 members of the 65 is not about the origin (0,0,0): I41, I4122, F4132 are their own enantiomorph, so for them there is no enantiomorphic pair (eg. I41 and I43), in fact no separate space group I43 is even necessary - look at the SG diagram #80 - both, 41 and 43 axes appear in the same SG. (2005 Erice paper of George explains more) Enough yet? Cheers, BR
Re: [ccp4bb] Confusion about space group nomenclature
Bernhard The term enantiomorphic pair is used consistently in ITC-A to mean one of the 11 pairs of what you previously called chiral space groups. PersonalIy I would never use the term chiral in this context even though it is synonymous with enantiomorphic (I would reserved chiral for single objects like hands, screws, mollusc shells and molecules - actually pretty well everything in Nature is chiral, natural achiral objects are in the minority). You say Thou shalt not use those descriptors for SGs, only for structures but enantiomorphic in the sense above is being used in ITC-A exactly to describe a SG, so on which tablet of stone is this commandment inscribed? Certainly not in ITC. Also on my CCP4 web page that I referred to earlier I used enantiomorphic to describe a structure (or to be precise a crystal), not a SG (43 enantiomorphic SGs are not enantiomorphic if it refers to the SG). I accept that nowhere does ITC use enantiomorphic in the way I'm using it but you wanted a suitable descriptor and I don't see any alternative candidates. As you said the only distinction ITC makes is between centrosymmetric and non-centrosymmetric (presumably having centrosymmetry leads to great simplication of the structure-factor equations in that you only have to worry about 2 alternative values for the phase), but that's not the description you're seeking for the reasons you gave. The only apparent inconsistency here is that the same adjective is being used to describe two different things. But is that really an inconsistency? Can't I use black to describe both crows and blackboards? Cheers -- Ian On 29 April 2014 10:32, Bernhard Rupp hofkristall...@gmail.com wrote: Hi Fellows, I have bugged now the ultimate authorities including Howard Flack (of Flack parameter fame), and alas, there is no official descriptive adjective for these 65 Söhnke space groups. Chiral is definitely wrong, and so is enantiomorphic, although 22 of the nameless form 11 enantiomorphic pairs. Thou shallst not use those descriptors for SGs, only for structures. So the contest for a proper descriptive adjective is still open. Best, BR PS: Otherwise it is a bit like saying 'You know, that thing, the one where you see stuff moving and it is not black and white' instead of simply 'color TV' - almost as old as space groups
Re: [ccp4bb] Confusion about space group nomenclature
Dear Bernhard (and others), I was looking for catchy combinations of chiral or enantio and Latin or Greek words for support or allow -- until I realized there is already a name for this very concept, used widely in chemistry: I think the precise and correct term applicable to the 65 should be pro-chiral spacegroups. They are not chiral by themselves, but addition of something /allows/ for the creation of a chiral object (i.e. the crystal). Cheers, Jens On Tue, 2014-04-29 at 16:12 +0200, Bernhard Rupp wrote: Response to off-board mail: How about [calling them] non-centro-symmetric space groups, as I often tell my students? Almost, but not exact enough. The 65 are only a subset of non-centrosymmetric space groups: Not all enantiogenic (not elements of the 65-set) space groups are centrosymmetric. Simplest example Pm. According to above definition Pm (and many more lacking a center of inversion) would be a ok space group for chiral motifs. (when a space group has the 'center at ' annotation in the Tables, it has a coi and is a centrosymmetric space group). This implies that there are actually three types of crystal structures (cf. Flack): (a) chiral (non-centrosymmetric) crystal structures (b) centrosymmetric crystal structures (c) achiral non-centrosymmetric crystal structures And just as a reminder, the substructure inversion for 3 members of the 65 is not about the origin (0,0,0): I41, I4122, F4132 are their own enantiomorph, so for them there is no enantiomorphic pair (eg. I41 and I43), in fact no separate space group I43 is even necessary - look at the SG diagram #80 - both, 41 and 43 axes appear in the same SG. (2005 Erice paper of George explains more) Enough yet? Cheers, BR
Re: [ccp4bb] Confusion about space group nomenclature
actually, I'll have to amend that: Dear Bernhard (and others), I was looking for catchy combinations of chiral or enantio and Latin or Greek words for support or allow -- until I realized there is already a name for this very concept, used widely in chemistry: I think the precise and correct term applicable to the 65 should be the 22 chiral (aka 11 enantiomorphic paris) and the 43 pro-chiral spacegroups. They are not chiral by themselves, but addition of something /allows/ for the creation of a chiral object (i.e. the crystal). Cheers, Jens On Tue, 2014-04-29 at 16:12 +0200, Bernhard Rupp wrote: Response to off-board mail: How about [calling them] non-centro-symmetric space groups, as I often tell my students? Almost, but not exact enough. The 65 are only a subset of non-centrosymmetric space groups: Not all enantiogenic (not elements of the 65-set) space groups are centrosymmetric. Simplest example Pm. According to above definition Pm (and many more lacking a center of inversion) would be a ok space group for chiral motifs. (when a space group has the 'center at ' annotation in the Tables, it has a coi and is a centrosymmetric space group). This implies that there are actually three types of crystal structures (cf. Flack): (a) chiral (non-centrosymmetric) crystal structures (b) centrosymmetric crystal structures (c) achiral non-centrosymmetric crystal structures And just as a reminder, the substructure inversion for 3 members of the 65 is not about the origin (0,0,0): I41, I4122, F4132 are their own enantiomorph, so for them there is no enantiomorphic pair (eg. I41 and I43), in fact no separate space group I43 is even necessary - look at the SG diagram #80 - both, 41 and 43 axes appear in the same SG. (2005 Erice paper of George explains more) Enough yet? Cheers, BR
Re: [ccp4bb] Confusion about space group nomenclature
Hi Fellows, thanks for the comments. Some of them agree with what I found through more (small mol) literature search. Let me explain why I am pestilent about this: If people who are already in the know use a weird term but have common understanding what it means, be it. If I introduce it in a textbook or introductory article, not so. It needs to make sense to someone who hears this term the first time. As it stopped making sense to me, I guess they’d be confused too. An important point made, was to distinguish between objects that can be chiral (i.e. have a certain defined handedness, χείρ cheir, hand), and space groups, which inherently are just a mathematical concept and in essence a set of instructions of how to deal with an object, and not chiral themselves. Ian’s space group diagrams, in contrast, are objects and they can display chirality and not be superimposable (i.e. superimpossible?). Space groups just act upon objects, be they chiral or not. So the point is to use a meaningful qualifier that, applied as an adjective to a space group, describes what happens if that space group acts on a chiral object. Now the ‘enantio’ creeps in: enantio means other, opposite, and morphos, gestalt, form or so. (Where is Tassos when you need him…) so: The adjective of those 65 who are not possessing improper rotations as enantiomorphic, is completely illogical. They are exactly the ones which do NOT change the ‘morph’ of any ‘enantio’. They, logically I maintain, are ‘non-enantiogen’ because they generate no opposite. The 11 pairs of non-enantiogenic SGs that that exist however indeed form enantiomorphic pairs, even as groups in absence of the need to act on a (chiral) object. One then can argue, as Ian did, that they form chiral pairs. However, that is not necessarily a justification to call these individual SGs themselves chiral. To me, the only satisfactory statement is that the 65 space groups “not possessing improper rotations” are non-enantiogenic, and 22 of them form enantiomorphic pairs. None of them change the handedness of a chiral object. Common use seems to be illogically “enantiomorphic” for the 65, and semi-illogical, “chiral” for the 22 forming the 11 em pairs. Is that what everybody including IUCr agrees upon? What does the ACA Standards commission have to say? Who has an authoritative answer? Let there be light. Cheers, BR From: Ian Tickle [mailto:ianj...@gmail.com] Sent: Sunday, April 20, 2014 4:52 PM To: b...@hofkristallamt.org Cc: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Confusion about space group nomenclature Hi Bernhard My understanding, gleaned from ITC-A and ITC-B is that the 65 space groups listed here: http://www.ccp4.ac.uk/dist/html/alternate_origins.html that I assume you are referring to, are enantiomorphic, which is defined as not possessing improper rotations (see http://pd.chem.ucl.ac.uk/pdnn/symm2/enantio1.htm). The non-superposable mirror image of a chiral object is called its enantiomorph, from Latin meaning opposite form. The chiral object by itself is one of a pair of enantiomers, each being the enantiomorph of the other. You need to be clear when talking about chirality whether you are referring to the space-group (or point-group) diagrams or to the contents of the unit cell. Not all the 65 enantiomorphic space group diagrams are chiral, even though the unit cells may be (you can have a non-enantiomorphic molecule crystallising in an enantiomorphic space group, but not vice versa). For example no triclinic, monoclinic or orthorhombic enantiomorphic SG diagrams are chiral (they are superposable on their mirror images), so enantiomorphic space group diagrams such as those of P1, P2, P21, P222, P212121 etc. do not have enantiomorphs (they can be regarded as their own enantiomorphs). However enantiomorphic space group diagrams containing 3, 4 or 6-fold screw axes are all chiral so do have enantiomorphs, e.g. there are enantiomorphic pairs P31 P32, P41 P43, P41212 P43212 etc. HTH! Cheers -- Ian On 20 April 2014 00:35, Bernhard Rupp hofkristall...@gmail.com wrote: Hi Fellows, because confusion is becoming a popular search term on the bb, let me admit to one more: What is the proper class name for the 65 space groups (you know, those): Are (a)these 65 SGs the chiral SGs and the 22 in the 11 enantiomorphic pairs the enantiomorphic SGs? Or (b) the opposite? In other words, is (a) enantiomorphic a subclass of chiral or (b) chiral a subclass of enantiomorphic? Small molecule crystallography literature seems to tend to (b) whereas in macro I often find (in terms of number of class members) chiral enantiomorphic. Interestingly, did not find an authoritative definition in ITC-A. Logical is neither. The 65 are perhaps enantiostatic because they do not change handedness (as opposed to enantiogen), and the 22 are enantiodyadic (or so). I am sure
Re: [ccp4bb] Confusion about space group nomenclature
On 21 April 2014 21:57, Bernhard Rupp hofkristall...@gmail.com wrote: So the point is to use a meaningful qualifier that, applied as an adjective to a space group, describes what happens if that space group acts on a chiral object. Now the ‘enantio’ creeps in: enantio means other, opposite, and morphos, gestalt, form or so. (Where is Tassos when you need him…) so: The adjective of those 65 who are not possessing improper rotations as enantiomorphic, is completely illogical. They are exactly the ones which do NOT change the ‘morph’ of any ‘enantio’. They, logically I maintain, are ‘non-enantiogen’ because they generate no opposite. The 11 pairs of non-enantiogenic SGs that that exist however indeed form enantiomorphic pairs, even as groups in absence of the need to act on a (chiral) object. One then can argue, as Ian did, that they form chiral pairs. However, that is not necessarily a justification to call these individual SGs themselves chiral. To me, the only satisfactory statement is that the 65 space groups “not possessing improper rotations” are non-enantiogenic, and 22 of them form enantiomorphic pairs. None of them change the handedness of a chiral object. Bernhard, Sorry ignore previous empty message (must have accidentally hit a keyboard shortcut for 'Send': Gmail should make it much harder to hit Send accidentally!). I was going to say that I didn't quite follow your argument. The point I was making in my reply was that 'enantiomorphic' refers to the unit cell contents, _not_ to merely the unit cell including its space-group symmetry elements, which is what I meant by 'space-group diagram'. The latter of course possesses the symmetry of the Cheshire group which has additionally symmetry elements, e.g. additional inversion centre and translational elements in many cases. 'Enantiomorphic' means that for which an enantiomorph (non-superposable mirror image) exists. So the 65 space groups, including their unit-cell contents, are enantiomorphic by that definition, because there exists for each one an enantiomorph of the unit cell contents. We are after all talking only about a mirror-inverted image of an object not the mirror-inverted object (one can argue about whether an image in a mirror 'exists' since it's merely a mathematical construct). In fact in this sense there's no difference between enantiomorphic and chiral (since that also means having a non-superposable mirror image). The fact that the enantiomorph (i.e. with D-amino acids and left-handed alpha helices) can't actually exist in Nature is irrelevant, the point is that it's only a mathematical construct. As I said there's really no distinction between 'enantiomorphic' and 'chiral'. However in the sense in which 'chiral' is being used to described the 11, it is clearly being applied to the space-group diagram only, so the space-group diagrams for P1, P21, P212121, P4, P622 etc. are achiral (and non-enantiomorphic in this limited sense), whereas those for P31, P41212 etc are chiral (and enantiomorphic). The unit-cell contents are in all these cases enantiomorphic in the wider sense defined above. This is why I said you need to take care about what objects the words are describing: enantiomorphic and chiral mean the same but they are being used to desscribe 2 different objects! Cheers -- Ian
Re: [ccp4bb] Confusion about space group nomenclature
Upon further contemplation: Someone who builds a right-handed helix into a left-handed map is an enantiopath. Enantiopathy can be treated with Enantiomab ® although some people prefer a daily dose of enantiostatins. These generics are made by Irratiopharm. BR
Re: [ccp4bb] Confusion about space group nomenclature
Hi Bernhard My understanding, gleaned from ITC-A and ITC-B is that the 65 space groups listed here: http://www.ccp4.ac.uk/dist/html/alternate_origins.html that I assume you are referring to, are enantiomorphic, which is defined as not possessing improper rotations (see http://pd.chem.ucl.ac.uk/pdnn/symm2/enantio1.htm). The non-superposable mirror image of a chiral object is called its enantiomorph, from Latin meaning opposite form. The chiral object by itself is one of a pair of enantiomers, each being the enantiomorph of the other. You need to be clear when talking about chirality whether you are referring to the space-group (or point-group) diagrams or to the contents of the unit cell. Not all the 65 enantiomorphic space group diagrams are chiral, even though the unit cells may be (you can have a non-enantiomorphic molecule crystallising in an enantiomorphic space group, but not vice versa). For example no triclinic, monoclinic or orthorhombic enantiomorphic SG diagrams are chiral (they are superposable on their mirror images), so enantiomorphic space group diagrams such as those of P1, P2, P21, P222, P212121 etc. do not have enantiomorphs (they can be regarded as their own enantiomorphs). However enantiomorphic space group diagrams containing 3, 4 or 6-fold screw axes are all chiral so do have enantiomorphs, e.g. there are enantiomorphic pairs P31 P32, P41 P43, P41212 P43212 etc. HTH! Cheers -- Ian On 20 April 2014 00:35, Bernhard Rupp hofkristall...@gmail.com wrote: Hi Fellows, because confusion is becoming a popular search term on the bb, let me admit to one more: What is the proper class name for the 65 space groups (you know, those): Are (a)these 65 SGs the chiral SGs and the 22 in the 11 enantiomorphic pairs the enantiomorphic SGs? Or (b) the opposite? In other words, is (a) enantiomorphic a subclass of chiral or (b) chiral a subclass of enantiomorphic? Small molecule crystallography literature seems to tend to (b) whereas in macro I often find (in terms of number of class members) chiral enantiomorphic. Interestingly, did not find an authoritative definition in ITC-A. Logical is neither. The 65 are perhaps enantiostatic because they do not change handedness (as opposed to enantiogen), and the 22 are enantiodyadic (or so). I am sure Tassos will enlighten us on that one…. So, (a) or (b) or ? Happy Easter, BR
