[ { "id": "authors:zmsyt-jnj19", "collection": "authors", "collection_id": "zmsyt-jnj19", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-094928604", "type": "article", "title": "Effects of pH on the Structure and Function of Carboxypeptidase A: Crystallographic Studies", "author": [ { "family_name": "Shoham", "given_name": "G.", "clpid": "Shoham-G" }, { "family_name": "Rees", "given_name": "D. C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lipscomb", "given_name": "W. N.", "clpid": "Lipscomb-W-N" } ], "abstract": "High-resolution crystal structures are described for carboxypeptidase A (EC 3.4.17.1) in crystals grown at pH 8.5, 9.0, and 9.5 and compared with the structure at pH 7.5. The comparison shows that in the pH range of 7.5-9.5 the enzyme structure is practically unchanged, and, most importantly, that the flexible side chain of Tyr-248 remains exclusively in the \"up\" position, away from the Zn atom, throughout the pH range. There is no evidence for binding of Tyr-248 to Zn at any of these pH values. We conclude that the interaction of Tyr-248 with Zn is not an essential part of the mechanism of carboxypeptidase A and that its occurrence is an artifact of chemical modification of Tyr-248. It is also suggested that Tyr-248 is not uniquely associated with the observed high pK of the enzymatic hydrolysis.", "pmcid": "PMC392233", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1984-12-01", "series_number": "24", "volume": "81", "issue": "24", "pages": "7767-7771" }, { "id": "authors:wn6vq-j8804", "collection": "authors", "collection_id": "wn6vq-j8804", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-095029990", "type": "article", "title": "Crystal and Molecular Structure of S-Deoxo[Ile^3]amaninamide: A Synthetic Analog of Amanita Toxins", "author": [ { "family_name": "Shoham", "given_name": "G.", "clpid": "Shoham-G" }, { "family_name": "Rees", "given_name": "D. C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lipscomb", "given_name": "W. N.", "clpid": "Lipscomb-W-N" }, { "family_name": "Zanotti", "given_name": "G.", "clpid": "Zanotti-G" }, { "family_name": "Wieland", "given_name": "Th.", "clpid": "Wieland-T" } ], "abstract": "The crystal structure of S-deoxo[Ile^3]amaninamide, a nontoxic synthetic derivative of the Amanita phalloides mushroom\ntoxins (amatoxins), has been determined by single-crystal X-ray diffraction. The crystals are monoclinic, space group P2_1,\nwith 2 formula units per unit cell. Cell dimensions are a = 12.147 \u00c5, b = 11.250 \u00c5, c = 19.267 \u00c5, and (\u03b2 = 92.41\u00b0. The\nstructure was determined by molecular replacement methods and refined by least-squares techniques to a final R value of\n0.065 for 3894 independent observations. Six intramolecular hydrogen bonds hold the bicyclic octapeptide in a compact\nconformation, which is very similar to the conformation of the naturally occurring (and toxic) amatoxin, (\u03b2-amanitin. The\nstudy demonstrates that the 30-fold reduction in binding affinity to RNA polymerase B of the title amatoxin, and probably\nof most of the other amatoxin analogues with altered side chain 3, is not due to alteration of backbone conformation. The\nthree water molecules and two ethanol molecules, crystallized with the amatoxin, form a strong and extensive intermolecular\nhydrogen-bonding system.", "doi": "10.1021/ja00328a051", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1984-08", "series_number": "16", "volume": "106", "issue": "16", "pages": "4606-4615" }, { "id": "authors:x8ar8-m8777", "collection": "authors", "collection_id": "x8ar8-m8777", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-095316855", "type": "article", "title": "Crystallographic Studies on Apocarboxypeptidase A and the Complex with Glycyl-L-Tyrosine", "author": [ { "family_name": "Rees", "given_name": "D. C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lipscomb", "given_name": "W. N.", "clpid": "Lipscomb-W-N" } ], "abstract": "The crystal structures of zinc-free carboxypeptidase A (apocarboxypeptidase A) and the complex of glycyl-L-tyrosine with apocarboxypeptidase A are described and compared to the corresponding structures of the zinc-containing enzyme. Only small conformational changes in the zinc ligands accompany removal of the metal. Interactions between the tyrosine residue of glycyl-L-tyrosine and apocarboxypeptidase A are similar to those observed in the complex with the holoenzyme. However, in the absence of zinc, the carbonyl oxygen of the glycyl moiety now receives a hydrogen bond from the side chain of arginine-127. Although not as yet observed, a similar shift of the carbonyl oxygen of a susceptible bond from the zinc to arginine-127 could stabilize tetrahedral intermediates generated during the hydrolysis of substrates by carboxypeptidase.", "pmcid": "PMC390011", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1983-12-01", "series_number": "23", "volume": "80", "issue": "23", "pages": "7151-7154" }, { "id": "authors:xpfwq-92e50", "collection": "authors", "collection_id": "xpfwq-92e50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-095701909", "type": "article", "title": "Refined Crystal Structure of Carboxypeptidase A at 1.54\u00c5 Resolution", "author": [ { "family_name": "Rees", "given_name": "D. C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lewis", "given_name": "M.", "clpid": "Lewis-M" }, { "family_name": "Lipscomb", "given_name": "W. N.", "clpid": "Lipscomb-W-N" } ], "abstract": "The crystal structure of bovine carboxypeptidase A (Cox) has been refined at 1\u202254 \u00c5 resolution using the restrained least-squares algorithm of Hendrickson & Konnert (1981). The crystallographic R factor (R = \u03a3||F_o| \u2212 |F_c||/\u03a3|F_o|) for structure factors calculated from the final model is 0\u2022190. Bond lengths and bond angles in the carboxypeptidase A model have root-mean-square deviations from ideal values of 0\u2022025 \u00c5 and 3\u20226\u00b0, respectively. Four examples of a reverse turn like structure (the \"Asx\" turn) requiring an aspartic acid or asparagine residue are observed in this structure. The Asx turn has the same number of atoms as a reverse turn, but only one peptide bond, and the hydrogen bond that closes the turn is between the Asx side-chain CO group and a main-chain NH group. The distributions of CO-N and NH-O hydrogen bond angles in the \u03b1-helices and \u03b2-sheet structures of carboxypeptidase A are centered about 156\u00b0. A total of 192 water molecules per molecule of enzyme are included in the final model. Unlike the hydrogen bonding geometry observed in the secondary structure of the enzyme, the CO-O(wat) hydrogen bond angle is distributed about 131\u00b0, indicating the role of the lone pair electrons of the carbonyl oxygen in the hydrogen bond interaction. Twenty four solvent molecules are observed buried within the protein. Several of these waters are organized into hydrogen-bonded chains containing up to five waters. The average temperature factor for atoms in carboxypeptidase A is 8 \u00c5^2, and varies from 5 \u00c5^2 in the center of the protein, to over 30 \u00c5^2 at the surface.", "doi": "10.1016/S0022-2836(83)80024-2", "issn": "0022-2836", "publisher": "Elsevier", "publication": "Journal of Molecular Biology", "publication_date": "1983-08-05", "series_number": "2", "volume": "168", "issue": "2", "pages": "367-387" }, { "id": "authors:718d5-xrm42", "collection": "authors", "collection_id": "718d5-xrm42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-100044543", "type": "article", "title": "Refined Crystal Structure of the Potato Inhibitor Complex of Carboxypeptidase A at 2.5 \u00c5 Resolution", "author": [ { "family_name": "Rees", "given_name": "D. C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lipscomb", "given_name": "W. N.", "clpid": "Lipscomb-W-N" } ], "abstract": "The exopeptidase carboxypeptidase A forms a tight complex with a 39 residue inhibitor protein from potatoes. We have determined the crystal structure of this complex, and refined the atomic model to a crystallographic R-factor of 0.196 at 2.5 \u00c5 resolution. The structure of the inhibitor protein is organized around a core of disulfide bridges. No \u03b1-helices or \u03b2-sheets are present in this protein, although there is one turn of 3_(10) helix. The four carboxy-terminal residues of the inhibitor protein bind in the active site groove of carboxypeptidase A, defining binding subsites S\u2032_1, S_1, S_2 and S_3 on the enzyme. The carboxy-terminal glycine of the inhibitor is cleaved from the remainder of the inhibitor in the complex, and remains trapped in the back of the active site pocket. Interactions between the inhibitor and residues Tyr248 and Arg71 of carboxypeptidase A resemble possible features of binding stages for substrates both prior and subsequent to peptide bond hydrolysis. Not all of these interactions would be available to different types of ester substrates, however, which may be in part responsible for the observed kinetic differences in hydrolysis between peptides and various classes of esters. With the exception of residues involved in the binding of the inhibitor protein (such as Tyr248), the structure of carboxypeptidase A as determined in the inhibitor complex is quite similar to the structure of the unliganded enzyme (Lipscomb et al., 1968), which was solved from an unrelated crystal form.", "doi": "10.1016/0022-2836(82)90309-6", "issn": "0022-2836", "publisher": "Elsevier", "publication": "Journal of Molecular Biology", "publication_date": "1982-09-25", "series_number": "3", "volume": "160", "issue": "3", "pages": "475-498" }, { "id": "authors:xzszg-a8h77", "collection": "authors", "collection_id": "xzszg-a8h77", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-100229261", "type": "article", "title": "Binding of Ligands to the Active Site of Carboxypeptidase A", "author": [ { "family_name": "Rees", "given_name": "D. C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lipscomb", "given_name": "W. N.", "clpid": "Lipscomb-W-N" } ], "abstract": "We compare the detailed binding modes of the 39-amino acid inhibitor from potatoes, glycyl-L-tyrosine, the ester analogue CH_3OC_6H_4(CO)CH_2CH(CO_2(-))C_6H_5, and indole acetate to the exopeptidase carboxypeptidase A (EC 3.4.17.1). In the potato inhibitor, cleavage of the COOH-terminal glycine-39 leaves a new carboxylate anion of valine-38 having one oxygen on zinc and the other as a receptor of a hydrogen bond from tyrosine-248 of carboxypeptidase. Tyrosine-248 also receives a hydrogen bond from the amide proton of the originally penultimate peptide bond between tyrosine-37 and valine-38. This hydrogen bond suggests product stabilization which is available to peptides and depsipeptides but not to esters lacking an equivalent peptide bond (nonspecific esters). Also, this structure may represent the intermediate binding step for the uncleaved substrate as it moves along the binding subsites. In particular, this may be the binding mode for the substrate after association of the COOH-terminal region of the substrate with the residues at binding subsite S_2 (tyrosine-198, phenylalanine-279, and arginine-71) and preceding entry into the catalytic site S_1'. These stabilized complexes allow some understanding of the effect of indole acetate, shown here to bind in the pocket at S_1', as a competitive inhibitor for esters (for which entry into S_1' precedes the rate-determining catalytic step for hydrolysis) and as a noncompetitive inhibitor for peptides (for which entry into S_1' is rate limiting). These results, including the binding mode of the ester analogue, are consistent with the original proposal from x-ray studies that both esters and peptides are cleaved with the carboxy terminus at S_1', although not necessarily by the same chemical steps.", "doi": "10.1073/pnas.78.9.5455", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1981-09", "series_number": "9", "volume": "78", "issue": "9", "pages": "5455-5459" }, { "id": "authors:wg21b-3t924", "collection": "authors", "collection_id": "wg21b-3t924", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-100313332", "type": "article", "title": "Zinc Environment and cis Peptide Bonds in Carboxypeptidase A at 1.75\u00c5 Resolution", "author": [ { "family_name": "Rees", "given_name": "D. C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lewis", "given_name": "M.", "clpid": "Lewis-M" }, { "family_name": "Honzatko", "given_name": "R. B.", "clpid": "Honzatko-R-B" }, { "family_name": "Lipscomb", "given_name": "W. N.", "clpid": "Lipscomb-W-N" }, { "family_name": "Hardman", "given_name": "K. D.", "clpid": "Hardman-K-D" } ], "abstract": "The structure of the metalloenzyme carboxypeptidase A (peptidyl-L-amino-acid hydrolase, EC 3.4.17.1) has been refined at 1.75 \u00c5 by a restrained least-squares procedure to a conventional crystallographic R factor of 0.162. Significant results of the refined structure relative to the catalytic mechanism are described. In the native enzyme, the zinc coordination number is five (two imidazole N delta 1 nitrogens, the two carboxylate oxygens of glutamate-72, and a water molecule). In the complex (at 2.0-\u00c5 resolution) of carboxypeptidase A with the dipeptide glycyl-L-tyrosine, however, the water ligand is replaced by both the carbonyl oxygen and the amino nitrogen of the dipeptide. The amino nitrogen also statistically occupies a second position near glutamate-270. Consequently, the coordination number of zinc may vary from five to six in carboxypeptidase A-substrate complexes. Implications of these results for the catalytic mechanism of carboxypeptidase A are discussed. In addition, three cis peptide bonds, none of which involves proline as the amino nitrogen donor, have been located fairly near the active site.", "pmcid": "PMC319577", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1981-06", "series_number": "6", "volume": "78", "issue": "6", "pages": "3408-3412" }, { "id": "authors:5pjpc-waa97", "collection": "authors", "collection_id": "5pjpc-waa97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-100406855", "type": "article", "title": "Structure of the Potato Inhibitor Complex of Carboxypeptidase A at 2.5\u00c5 Resolution", "author": [ { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lipscomb", "given_name": "William N.", "clpid": "Lipscomb-W-N" } ], "abstract": "The structure of the complex between the proteolytic enzyme carboxypeptidase A (peptidyl-L-amino-acid hydrolase, EC 3.4.17.1) and the 39-amino-acid carboxypeptidase A inhibitor from potatoes has been determined at 2.5-\u00c5 resolution. A combination of multiple isomorphous replacement, molecular replacement, and noncrystallographic symmetry averaging techniques was used to solve the structure. The chain trace of the inhibitor and details of the binding interactions in the complex are described. A surprising aspect of the complex is that the carboxy-terminal peptide bond of the inhibitor has been hydrolyzed, and the carboxy-terminal glycine is trapped in the binding pocket of carboxypeptidase A. Consequently, the complex resembles a stage in the catalytic mechanism after hydrolysis of the peptide bond. The ring of tyrosine-248, which is known to undergo large conformational changes upon substrate binding, is in the \"down\" position and interacts with the inhibitor in the complex.", "pmcid": "PMC349899", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1980-08", "series_number": "8", "volume": "77", "issue": "8", "pages": "4633-4637" }, { "id": "authors:5z5sj-nx290", "collection": "authors", "collection_id": "5z5sj-nx290", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-100541503", "type": "article", "title": "The Structure of an Actively Exchanging Complex between Carboxypeptidase A and a Substrate Analogue", "author": [ { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Honzatko", "given_name": "Richard B.", "clpid": "Honzatko-R-B" }, { "family_name": "Lipscomb", "given_name": "William N.", "clpid": "Lipscomb-W-N" } ], "abstract": "An x-ray diffraction study at 2.8 \u00c5 resolution has yielded the structure of a complex between bovine carboxypeptidase A (peptidyl-L-amino-acid hydrolase, EC 3.4.17.1) and (-)-2-benzyl-3-p-methoxybenzoylpropionic acid. This substrate is an analogue of N-(p-methoxy)-benzoylphenylalanine, in which the amide NH is replaced by CH_2. T. Sugimoto and E T. Kaiser (1979) J. Am. Chem. Soc. 101, 39469--3951] have shown that this complex catalyzes stereospecific exchange of that proton of the CH_2 group which is in the R configuration. Our structure of this complex suports the model proposed by Sugimoto and Kaiser and is very similar to the productive peptide binding mode suggested by Lipscomb et al. [Lipscomb, W. N., Hartsuck, J. A., Reeke, G. N., Quiocho, F. A., Bethge, P. A., Ludwig, M. L., Steitz, T. A., Muirhead, H. & Coppola. J. C. (1968) Brookhaven Symp. Biol. 21, 24--90]. The proposed roles of glutamic acid 270 in the proton exchange and the interaction of zinc with the carbonyl group of the substrate are consistent with the observed structure.", "pmcid": "PMC349600", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1980-06", "series_number": "6", "volume": "77", "issue": "6", "pages": "3288-3291" }, { "id": "authors:rx6w6-36984", "collection": "authors", "collection_id": "rx6w6-36984", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-100728083", "type": "article", "title": "Structure of Potato Inhibitor Complex of Carboxypeptidase A at 5.5\u00c5 Resolution", "author": [ { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Lipscomb", "given_name": "William N.", "clpid": "Lipscomb-W-N" } ], "abstract": "The complex of the 39-amino inhibitor (potato) of bovine carboxypeptidase A (carboxypeptidase; peptidyl-L-amino-acid hydrolase, EC 3.4.12.2) was crystallized in space group P3_2. There are two protein-inhibitor complexes in the asymmetric unit. These crystals exhibited pseudo-P32_21 symmetry due to twinning about the a_3 axis. Heavy atom difference Patterson maps and rotation functions indicated, however, that the noncrystallographic twofold axis that relates these two complexes is nearly coincident with the a_3 axis. Consequently, to a good approximation at low resolution, the space group of the complex is P3_221 and the effects of twinning may be ignored. The structure was solved by using multiple isomorphous replacement and molecular replacement techniques. At 5.5-\u00c5 resolution, the multiple isomorphous replacement map was readily interpretable in terms of the known native carboxypeptidase A structure plus extra density around the active site. The position of this extra density is consistent with the binding mode for extended substrate proposed from earlier model building studies with the native enzyme (Lipscomb, W.N., Hartsuck, J.A., Reeke, G.N., Quiocho, F.A. Bethge, P.H., Ludwig, M.L., Steitz, T.A., Muirhead, H. & Coppola, J.C. (1968) Brookhaven Symp. Biol. 21, 24-90).", "doi": "10.1073/pnas.77.1.277", "pmcid": "PMC348252", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1980-01", "series_number": "1", "volume": "77", "issue": "1", "pages": "277-280" }, { "id": "authors:fntks-qq146", "collection": "authors", "collection_id": "fntks-qq146", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:DONjcp47", "type": "article", "title": "The crystal structure of hydrazinium dichloride, N2H6Cl2", "author": [ { "family_name": "Donohue", "given_name": "Jerry", "clpid": "Donohue-J" }, { "family_name": "Lipscomb", "given_name": "William N.", "clpid": "Lipscomb-W-N" } ], "abstract": "Accurate values of the two parameters in the structure of crystalline hydrazinium dichloride have been determined by the x-ray diffraction method, with the use of one and two dimensional Fourier syntheses. The NN separation in this crystal is 1.42A, and is equal to that in hydrazinium difluoride. This NN distance is 0.05A shorter than in gaseous hydrazine. Each chloride ion forms hydrogen bonds with three nitrogen atoms, the structure consisting of a three dimensional network of NH\u00b7\u00b7\u00b7Cl bonds. The angle NNH\u00b7\u00b7\u00b7Cl is 100\u00b0. The configuration of the N2H ions is trans. The differences between this structure and that of hydrazinium difluoride probably arise from the greater coordinating ability of the chloride ion as compared with that of the fluoride ion. The shortening of the NN distance may be caused in part by the formal charges on the nitrogen atoms, although it seems certain that this formal charge effect is not of general validity.", "doi": "10.1063/1.1746438", "issn": "0021-9606", "publisher": "Journal of Chemical Physics", "publication": "Journal of Chemical Physics", "publication_date": "1947-03-01", "series_number": "3", "volume": "15", "issue": "3", "pages": "115-119" }, { "id": "authors:js012-svh53", "collection": "authors", "collection_id": "js012-svh53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LIPjap47", "type": "article", "title": "An Investigation of a Method for the Analysis of Smokes According to Particle Size", "author": [ { "family_name": "Lipscomb", "given_name": "William N.", "clpid": "Lipscomb-W-N" }, { "family_name": "Rubin", "given_name": "T. R.", "clpid": "Rubin-T-R" }, { "family_name": "Sturdivant", "given_name": "J. H.", "clpid": "Sturdivant-J-H" } ], "abstract": "An electrical precipitation method for the analysis of smokes according to particle size has been investigated. A thin stream of smoke particles moving under laminar conditions in a wind tunnel of rectangular cross section is electrically charged in a small region. The charged particles are then precipitated by the uniform field existing between the charged upper plate and the grounded lower plate of the wind tunnel as a long track along the lower plate. The size-frequency distributions of the particles precipitated at various points on the lower plate were determined from measurements on enlargements of electron-microscope photographs of samples of the smoke precipitated at various points. The agreement between theory and experiment is fair, but the range of sizes of the particles precipitated at a given point is rather large.", "doi": "10.1063/1.1697555", "issn": "0021-8979", "publisher": "Journal of Applied Physics", "publication": "Journal of Applied Physics", "publication_date": "1947-01-01", "series_number": "1", "volume": "18", "issue": "1", "pages": "72-79" }, { "id": "authors:9gzzv-13y36", "collection": "authors", "collection_id": "9gzzv-13y36", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170330-123356461", "type": "article", "title": "The Crystal Structure of Methylammonium Chloride", "author": [ { "family_name": "Hughes", "given_name": "Edward W.", "clpid": "Hughes-E-W" }, { "family_name": "Lipscomb", "given_name": "William N.", "clpid": "Lipscomb-W-N" } ], "abstract": "Values of the carbon-nitrogen single-bond distance in various compounds are of special interest because of the occurrence of this bond in amino acids, proteins and related substances. Numerous electron diffraction studies of gas molecules have yielded values of about 1.47 \u00c5, which are consistent with the usual table of covalent radii. On the other hand, distances ranging from 1.39 to 1.49 \u00c5. have recently been reported in X-ray crystal structure investigations of compounds containing tetracovalent nitrogen. Because of these many different values it was thought desirable to investigate the carbon-nitrogen distance in a simple crystal in which a minimum number of parameters needed determination; methylammonium chloride appeared to be such a crystal.", "doi": "10.1021/ja01214a029", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1946-10", "series_number": "10", "volume": "68", "issue": "10", "pages": "1970-1975" }, { "id": "authors:bnede-4n495", "collection": "authors", "collection_id": "bnede-4n495", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LIPjcp46", "type": "article", "title": "An Electron Diffraction Investigation of Dimethylketene Dimer", "author": [ { "family_name": "Lipscomb", "given_name": "William N.", "clpid": "Lipscomb-W-N" }, { "family_name": "Schomaker", "given_name": "Verner", "clpid": "Schomaker-V" } ], "abstract": "An electron diffraction investigation of dimethylketene dimer confirms the 2,2,4,4-tetramethylcyclobutadione-1,3 structure. The following parameters were determined for the symmetrical model: C[Single Bond]C (ring)=1.56\u00b10.05A, C[Single Bond]CH3=1.54\u00b10.05A, C[Double Bond]O=1.22\u00b10.04A, [angle]C[Single Bond]CO[Single Bond]C=93\u00b0\u00b16\u00b0, and [angle]CH3[Single Bond]C[Single Bond]CH3=111\u00b0\u00b16\u00b0. The limits of error assigned to the angles apply only if simultaneous variation is excluded; otherwise much larger limits must be assigned. A notable feature of the structure is the large temperature factor which must be ascribed to the interatomic distances greater than 3A. The relation of this temperature factor to the unusually large atom polarization is discussed in terms of the probable amplitudes of the pertinent modes of vibration of the molecule.", "doi": "10.1063/1.1724176", "issn": "0021-9606", "publisher": "American Institute of Physics", "publication": "Journal of Chemical Physics", "publication_date": "1946-08", "series_number": "8", "volume": "14", "issue": "8", "pages": "475-479" } ]