Stereochemical studies on medicinal agents. 19. The x-ray crystal structures of two (+-)-allylprodine diastereomers. Role of the allyl group in conferring high stereoselectivity and potency at analgetic receptors

1976 ◽  
Vol 19 (1) ◽  
pp. 55-57 ◽  
Author(s):  
Philip S. Portoghese ◽  
Eli Shefter
Keyword(s):  
Crystal Structures ◽  
X Ray ◽  
High Stereoselectivity

Novel X-ray sequences and crystal structures of Persian and Starry sturgeon methemoglobins: Highlighting the role of heme pocket waters in causing autoxidation

2019 ◽  
Vol 1867 (6) ◽  
pp. 586-594 ◽  
Author(s):  
Arefeh Seyedarabi ◽  
Shohreh Ariaeenejad ◽  
Ali A. Moosavi-Movahedi ◽  
Saeed Rayati ◽  
Najmeh Poursasan ◽  
...  
Keyword(s):  
Crystal Structures ◽  
X Ray ◽  
Heme Pocket ◽  
Ray Sequences

scholarly journals Continuous mutual improvement of macromolecular structure models in the PDB and of X-ray crystallographic software: the dual role of deposited experimental data

2014 ◽  
Vol 70 (10) ◽  
pp. 2533-2543 ◽  
Author(s):  
Thomas C. Terwilliger ◽  
Gerard Bricogne
Keyword(s):  
Crystal Structures ◽  
Paradigm Shift ◽  
Large Scale ◽  
Data Bank ◽  
Small Scale ◽  
Macromolecular Structure ◽  
X Ray ◽  
Rapid Pace ◽  
Very High

Accurate crystal structures of macromolecules are of high importance in the biological and biomedical fields. Models of crystal structures in the Protein Data Bank (PDB) are in general of very high quality as deposited. However, methods for obtaining the best model of a macromolecular structure from a given set of experimental X-ray data continue to progress at a rapid pace, making it possible to improve most PDB entries after their deposition by re-analyzing the original deposited data with more recent software. This possibility represents a very significant departure from the situation that prevailed when the PDB was created, when it was envisioned as a cumulative repository of static contents. A radical paradigm shift for the PDB is therefore proposed, away from the static archive model towards a much more dynamic body of continuously improving results in symbiosis with continuously improving methods and software. These simultaneous improvements in methods and final results are made possible by the current deposition of processed crystallographic data (structure-factor amplitudes) and will be supported further by the deposition of raw data (diffraction images). It is argued that it is both desirable and feasible to carry out small-scale and large-scale efforts to make this paradigm shift a reality. Small-scale efforts would focus on optimizing structures that are of interest to specific investigators. Large-scale efforts would undertake a systematic re-optimization of all of the structures in the PDB, or alternatively the redetermination of groups of structures that are either related to or focused on specific questions. All of the resulting structures should be made generally available, along with the precursor entries, with various views of the structures being made available depending on the types of questions that users are interested in answering.

Molecular reorientation in a dehydration process of an organic polar salt of 2,4-diaminotoluene/L(+)-tartaric acid

2017 ◽  
Vol 32 (1) ◽  
pp. 15-22
Author(s):  
Weicai Ju ◽  
Simin Qiu ◽  
Yaqiu Tao ◽  
Xiaodong Shen ◽  
Zhigang Pan
Keyword(s):  
Crystal Structures ◽  
Tartaric Acid ◽  
Variable Temperature ◽  
Ethanol Dehydration ◽  
X Ray Diffraction ◽  
Molecular Reorientation ◽  
X Ray ◽  
Hydrate Crystal ◽  
Dehydration Behavior

An organic polar hydrate was obtained through cocrystallization of 2,4-diaminotoluene (2,4-DAT) and L(+)-tartaric acid (TA) from ethanol. Dehydration behavior of the obtained hydrate was investigated using variable temperature powder X-ray diffraction (PXRD) and thermal analysis. Proton transfer from L(+)-TA to 2,4-DAT in both hydrate and dehydrated form was revealed via Fourier transform infrared spectroscopy. The crystal structures of both forms were determined using PXRD techniques. The similarities and differences between two crystal structures were analyzed and the role of water in the hydrate crystal structure was demonstrated.

scholarly journals Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides

2001 ◽  
Vol 57 (2) ◽  
pp. 213-220 ◽  
Author(s):  
Artem Evdokimov ◽  
A. Joseph Gilboa ◽  
Thomas F. Koetzle ◽  
Wim T. Klooster ◽  
Arthur J. Schultz ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Crystal Structures ◽  
Critical Role ◽  
Chair Conformation ◽  
Geometrical Analysis ◽  
X Ray ◽  
Wide Range ◽  
First Time ◽  
Ring Conformations

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl α-D-arabinofuranoside (1), methyl β-D-arabinofuranoside (2), methyl α-D-lyxofuranoside (3), methyl β-D-ribofuranoside (4) and methyl α-D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C 1 chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations.

Hydrogen-bond directionality and symmetry in [C(O)NH](N)2P(O)-based structures: a comparison between X-ray crystallography data and neutron-normalized values, and evaluation of reliability

2021 ◽  
Vol 77 (3) ◽  
Author(s):  
Maryam Taherzadeh ◽  
Mehrdad Pourayoubi ◽  
Banafsheh Vahdani Alviri ◽  
Samad Shoghpour Bayraq ◽  
Maral Ariani ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Crystal Structures ◽  
X Ray Diffraction ◽  
X Ray ◽  
Maximum Percentage ◽  
Bond Lengths ◽  
X Ray Crystallography ◽  
Percentage Difference ◽  
Structural Database

For [C(O)NH](N)2P(O)-based structures, the magnitude of the differences in the N—H...O, H...O=P and H...O=C angles has been evaluated when the N—H bond lengths, determined by X-ray diffraction, were compared to the neutron normalized values and the maximum percentage difference was obtained, i.e. about 3% for the angle even if the N—H bond lengths have a difference of about 30% (0.7 Å for the X-ray and 1.03 Å for the neutron-normalized value). The symmetries of the crystals are discussed with respect to the symmetry of the molecules, as well as to the symmetry of hydrogen-bonded motifs, and the role of the most directional hydrogen bond in raising the probability of obtaining centrosymmetric crystal structures is investigated. The work was performed by considering nine new X-ray crystal structures and 204 analogous structures retrieved from the Cambridge Structural Database.

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