First and Second Dissociation Enthalpies in Bi-Component Crystals Consisting of Maleic Acid and L-Phenylalanine

The energetics of the stepwise dissociation of a A:B2 bi-component crystal, according to A:B2(cr) → A:B(cr) + B(cr) and A:B(cr) → A(cr) + B(cr), was investigated using MA:Phe2 and MA:Phe (MA = maleic acid; Phe = L-phenylalanine) as model systems. The enthalpy changes associated with these sequential processes and with the overall dissociation reaction A:B2(cr) → A(cr) + 2B(cr) were determined by solution calorimetry. It was found that they are all positive, indicating that there is a lattice enthalpy gain when MA:Phe2 is formed, either from the individual precursors or by adding Phe to MA:Phe. Single-crystal X-ray diffraction (SCXRD) analysis showed that MA:Phe2 is best described as a protic salt containing a maleate anion (MA−) and two non-equivalent L-phenylalanine units, both linked to MA− by NH···O hydrogen bonds (H-bond): one of these units is protonated (HPhe+) and the other zwitterionic (Phe±). Only MA− and HPhe+ molecules are present in the MA:Phe lattice. In this case, however, NH···O and OH···O H-bonds are formed between each MA− unit and two HPhe+ molecules. Despite these structural differences, the enthalpy cost for the removal of the zwitterionic Phe± unit from the MA:Phe2 lattice to yield MA:Phe is only 0.9 ± 0.4 kJ mol−1 higher than that for the dissociation of MA:Phe, which requires a proton transfer from HPhe+ to MA− and the rearrangement of L-phenylalanine to the zwitterionic, Phe±, form. Finally, a comparison of the dissociation energetics and structures of MA:Phe and of the previously reported glycine maleate (MA:Gly) analogue indicated that parameters, such as the packing coefficient, density, hydrogen bonds formed, or fusion temperature, are not necessarily good descriptors of dissociation enthalpy or lattice enthalpy trends when bi-component crystals with different molecular composition are being compared, even if the stoichiometry is the same.

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Orientability of Rigid Rodlike Molecules in Solution and Controlled Preparation of Model Systems

MRS Proceedings ◽

10.1557/proc-134-223 ◽

1988 ◽

Vol 134 ◽

Cited By ~ 2

Author(s):

Jeffrey A. Odell ◽

Andrew Keller ◽

Edward D.T. Atkins ◽

Miklos J. Nagy ◽

Jose Luis Feijoo ◽

...

Keyword(s):

Rotational Diffusion ◽

Model Systems ◽

Specific Reference ◽

X Ray Diffraction ◽

Rigid Rods ◽

Colloid Science ◽

Rigid Rod ◽

Separate Line ◽

The Individual ◽

Controlled Preparation

ABSTRACTA survey is presented of our works on orientability of poly(p-phenylene-benzbisthiazole) (PBT) as a model for rigid rods. It starts with the solid state with specific reference to diffraction by the individual molecule. It is followed by behaviour in semidilute solutions, demonstrating increase of orientability with increasing rod alignment, with vastly higher absolute values (as expressed by rotational diffusion coefficient) than anticipated from existing theory. The origin of the discrepancy, as identified by simulations, lies in the inappropriateness of the application of mean constraints, a recognition which should have wider implications. The relaxation from the highly oriented state, also in solution, has been followed and the elementary rotational jump of rods identified, with a new method relying on in situ (synchrotron) X-ray diffraction. As a separate line, we are announcing a new model system, ellipsoidal latices of predesigned axial ratios, with wide ranging potential for the study of rigid rod behaviour in polymer and colloid science.

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Two closely related 2-(benzofuran-2-yl)-2-oxoethyl benzoates: structural differences and C—H...O hydrogen-bonded supramolecular assemblies

Acta Crystallographica Section E Crystallographic Communications ◽

10.1107/s2056989017009422 ◽

2017 ◽

Vol 73 (7) ◽

pp. 1087-1091

Author(s):

Li Yee Then ◽

C. S. Chidan Kumar ◽

Huey Chong Kwong ◽

Yip-Foo Win ◽

Siau Hui Mah ◽

...

Keyword(s):

Hydrogen Bonds ◽

Carbonyl Group ◽

Phenyl Ring ◽

Molecular Structures ◽

X Ray Diffraction ◽

Compound I ◽

Torsion Angles ◽

Molecular Conformations ◽

Structural Differences ◽

Compound Ii

The compounds 2-(1-benzofuran-2-yl)-2-oxoethyl 2-nitrobenzoate, C17H11NO6(I), and 2-(1-benzofuran-2-yl)-2-oxoethyl 2-aminobenzoate, C17H13NO4(II), were synthesized under mild conditions. Their molecular structures were characterized by both spectroscopic and single-crystal X-ray diffraction analysis. The molecular conformations of both title compounds are generally similar. However, differentortho-substituted moieties at the phenyl ring of the two compounds cause deviations in the torsion angles between the carbonyl group and the attached phenyl ring. In compound (I), theortho-nitrophenyl ring is twisted away from the adjacent carbonyl group whereas in compound (II), theortho-aminophenyl ring is almost co-planar with the carbonyl group. In the crystal of compound (I), two C—H...O hydrogen bonds link the molecules into chains propagating along thec-axis direction and the chains are interdigitated, forming sheets parallel to [20-1]. Conversely, pairs of N—H...O hydrogen bonds in compound (II) link inversion-related molecules into dimers, which are further extended by C—H...O hydrogen bonds into dimer chains. These chains are interconnected by π–π interactions involving the furan rings, forming sheets parallel to theacplane.

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Modellsysteme für die Gallium-Extraktion, I. Struktur und Moleküldynamik von Aluminium- und Galliumtris(oxinaten) / Model Systems for Gallium Extraction, I. Structure and Molecular Dynamics of Aluminium and Gallium Tris(oxinates)

Zeitschrift für Naturforschung B ◽

10.1515/znb-1991-0709 ◽

1991 ◽

Vol 46 (7) ◽

pp. 901-911 ◽

Cited By ~ 74

Author(s):

Hubert Schmidbaur ◽

Josef Lettenbauer ◽

Dallas L. Wilkinson ◽

Gerhard Müller ◽

Otto Kumberger

Keyword(s):

Ammonium Acetate ◽

Elevated Temperatures ◽

Model Systems ◽

X Ray Diffraction ◽

Metal Chlorides ◽

H Nmr ◽

Lower Temperature ◽

The Individual ◽

Influence Of Substituents ◽

Steric Influence

Tris(oxinato) complexes of aluminium(III) and gallium(III) have been prepared from 8-oxyquinoline (OxH) and its six C-methylated derivatives from aqueous solutions of the metal chlorides or nitrates and an ammonium acetate buffer. Crystalline monohydrates or (upon precipitation with methanol) mono-methanol adducts are obtained. Single crystal X-ray diffraction studies reveal a meridional tris(chelate) structure for the two (isomorphous) tris(oxinates) Al(Ox)3 · MeOH and Ga(Ox)3 · MeOH with distinct differences in the individual dimensions. (The MeOH molecules form strong hydrogen bonds with one of the oxygen atoms.) For these species and those of the substituted ligands 3-MeOx, 4-MeOx, 5-MeOx, 6-MeOx, and 7-MeOx a similar meridional structure was confirmed by low temperature 1H NMR spectroscopy, which showed three inequivalent sets of ligands in each case. The collaps of these signals at elevated temperatures indicates a ligand-equilibrating process, with the mechanism probably comprising a dissociation of a pyridine function from the metal, to give a fluctional pentacoordinate species with free rotation about the intact M—O bond, and an M—N recombination at a random octahedral site. For the 2-MeOx ligands, however, the facial structure is preferred at lower temperature, but with the meridional isomer present as a component of an equilibrium. This indicates the strong steric influence of substituents in 2-position of the 8-oxy-quinoline.

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Acemetacin cocrystals and salts: structure solution from powder X-ray data and form selection of the piperazine salt

IUCrJ ◽

10.1107/s2052252514004229 ◽

2014 ◽

Vol 1 (2) ◽

pp. 136-150 ◽

Cited By ~ 37

Author(s):

Palash Sanphui ◽

Geetha Bolla ◽

Ashwini Nangia ◽

Vladimir Chernyshev

Keyword(s):

Hydrogen Bonds ◽

Dissolution Rate ◽

Aqueous Medium ◽

Acid Amide ◽

Three Dimensional ◽

X Ray Diffraction ◽

Reference Drug ◽

X Ray ◽

Time Period ◽

Solid Form

Acemetacin (ACM) is a non-steroidal anti-inflammatory drug (NSAID), which causes reduced gastric damage compared with indomethacin. However, acemetacin has a tendency to form a less soluble hydrate in the aqueous medium. We noted difficulties in the preparation of cocrystals and salts of acemetacin by mechanochemical methods, because this drug tends to form a hydrate during any kind of solution-based processing. With the objective to discover a solid form of acemetacin that is stable in the aqueous medium, binary adducts were prepared by the melt method to avoid hydration. The coformers/salt formers reported are pyridine carboxamides [nicotinamide (NAM), isonicotinamide (INA), and picolinamide (PAM)], caprolactam (CPR),p-aminobenzoic acid (PABA), and piperazine (PPZ). The structures of an ACM–INA cocrystal and a binary adduct ACM–PABA were solved using single-crystal X-ray diffraction. Other ACM cocrystals, ACM–PAM and ACM–CPR, and the piperazine salt ACM–PPZ were solved from high-resolution powder X-ray diffraction data. The ACM–INA cocrystal is sustained by the acid...pyridine heterosynthon and N—H...O catemer hydrogen bonds involving the amide group. The acid...amide heterosynthon is present in the ACM–PAM cocrystal, while ACM–CPR contains carboxamide dimers of caprolactam along with acid–carbonyl (ACM) hydrogen bonds. The cocrystals ACM–INA, ACM–PAM and ACM–CPR are three-dimensional isostructural. The carboxyl...carboxyl synthon in ACM–PABA posed difficulty in assigning the position of the H atom, which may indicate proton disorder. In terms of stability, the salts were found to be relatively stable in pH 7 buffer medium over 24 h, but the cocrystals dissociated to give ACM hydrate during the same time period. The ACM–PPZ salt and ACM–nicotinamide cocrystal dissolve five times faster than the stable hydrate form, whereas the ACM–PABA adduct has 2.5 times faster dissolution rate. The pharmaceutically acceptable piperazine salt of acemetacin exhibits superior stability, faster dissolution rate and is able to overcome the hydration tendency of the reference drug.

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Crystal structure of 3-benzyl-2-[(E)-2-(furan-2-yl)ethenyl]-2,3-dihydroquinazolin-4(1H)-one and 3-benzyl-2-[(E)-2-(thiophen-2-yl)ethenyl]-2,3-dihydroquinazolin-4(1H)-one from synchrotron X-ray diffraction

Acta Crystallographica Section E Crystallographic Communications ◽

10.1107/s2056989017017479 ◽

2018 ◽

Vol 74 (1) ◽

pp. 10-14

Author(s):

Flavien A. A. Toze ◽

Vladimir P. Zaytsev ◽

Lala V. Chervyakova ◽

Elisaveta A. Kvyatkovskaya ◽

Pavel V. Dorovatovskii ◽

...

Keyword(s):

Crystal Structure ◽

Hydrogen Bonds ◽

Axial Position ◽

Isatoic Anhydride ◽

X Ray Diffraction ◽

X Ray ◽

Bond Angles ◽

Pyramidal Geometry ◽

Three Component Reaction ◽

Racemic Crystals

The chiral title compounds, C21H18N2O2, (I), and C21H18N2OS, (II) – products of the three-component reaction between benzylamine, isatoic anhydride and furyl- or thienyl-acrolein – are isostructural and form isomorphous racemic crystals. The tetrahydropyrimidine ring in (I) and (II) adopts a sofa conformation. The amino N atom has a trigonal–pyramidal geometry [sum of the bond angles is 347.0° for both (I) and (II)], whereas the amido N atom is flat [sum of the bond angles is 359.3° for both (I) and (II)]. The furyl- and thienylethenyl substituents in (I) and (II) are planar and the conformation about the bridging C=C bond isE. These bulky fragments occupy the axial position at the quaternary C atom of the tetrahydropyrimidine ring, apparently, due to steric reasons. In the crystals, molecules of (I) and (II) form hydrogen-bonded helicoidal chains propagating along [010] by strong intermolecular N—H...O hydrogen bonds.

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Crystal and molecular structure of diorganoammonium oxalatotrimethylstannate, [R2NH2][Me3Sn(C2O4)] (R=i-Bu, cyclohexyl)

Main Group Metal Chemistry ◽

10.1515/mgmc-2011-0018 ◽

2011 ◽

Vol 34 (5-6) ◽

pp. 127-130 ◽

Cited By ~ 3

Author(s):

Yaya Sow ◽

Libasse Diop ◽

Kieran C. Molloy ◽

Gabrielle Kociok-Köhn

Keyword(s):

Molecular Structure ◽

Hydrogen Bonds ◽

Diffraction Study ◽

Crystal And Molecular Structure ◽

X Ray Diffraction ◽

X Ray ◽

Trigonal Bipyramidal ◽

Trans Complex ◽

A Chain ◽

Distorted Trigonal Bipyramidal

Abstract The title compounds [R2NH2][C2O4SnMe3](R=i-Bu, Cy), in which tin atoms adopt a distorted trigonal bipyramidal configuration, have been prepared and submitted to an X-ray diffraction study. These compounds have been obtained from the reaction of (Cy2NH2)2C2O4·H2O or (i-Bu2NH2)2C2O4 with SnMe3Cl. In both [R2NH2][C2O4SnMe3] compounds, the trans complex has an almost regular trigonal bipyramidal geometry around the tin atom. The SnMe3 residues are connected as a chain with bridging oxalate anions in a trans-SnC3O2 framework, the oxygen atoms being in axial positions. The cations connect linear adjacent chains through NH…O hydrogen bonds giving layered structures.

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Structure Based Grading of Kinematic Chains

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.575.501 ◽

2014 ◽

Vol 575 ◽

pp. 501-506 ◽

Cited By ~ 1

Author(s):

Shubhashis Sanyal ◽

G.S. Bedi

Keyword(s):

Structural Properties ◽

Structural Property ◽

Kinematic Chain ◽

Degree Of Freedom ◽

Kinematic Chains ◽

Structural Differences ◽

The Individual ◽

Independent Loops

Kinematic chains differ due to the structural differences between them. The location of links, joints and loops differ in each kinematic chain to make it unique. Two similar kinematic chains will produce similar motion properties and hence are avoided. The performance of these kinematic chains also depends on the individual topology, i.e. the placement of its entities. In the present work an attempt has been made to compare a family of kinematic chains based on its structural properties. The method is based on identifying the chains structural property by using its JOINT LOOP connectivity table. Nomenclature J - Number of joints, F - Degree of freedom of the chain, N - Number of links, L - Number of basic loops (independent loops plus one peripheral loop).

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Strain Measurement by X-ray Diffraction Methods

Aeronautical Quarterly ◽

10.1017/s0001925900000160 ◽

1949 ◽

Vol 1 (3) ◽

pp. 211-224

Author(s):

G. B. Greenough

Keyword(s):

Strain Measurement ◽

Plastic Anisotropy ◽

Stress And Strain ◽

Routine Method ◽

X Ray Diffraction ◽

Strain Measurements ◽

X Ray ◽

The Past ◽

Polycrystalline Metals ◽

The Individual

SummaryMany papers have been written on the measurement of strain by X-ray diffraction methods and on the interpretation of these strains in terms of stresses. Whereas, during the past few years, the experimental methods of determining the strains have. remained largely unchanged, research has shown that the older techniques for calculating stresses from strains are not always valid.In this paper an attempt is made to describe some of the principles of strain measurement by X-ray diffraction methods to those who are unfamiliar with the methods. The types of stress and strain systems which may exist in polycrystalline metals are then considered, particular attention being paid to the effect of the elastic and plastic anisotropy of the individual crystals. Some indication is given as to how the earlier methods of interpreting X-ray strain measurements should be modified, but no rigid routine method is proposed for use in a general case.

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Salts of purine alkaloids caffeine and theobromine with 2,6-dihydroxybenzoic acid as coformer: structural, theoretical, thermal and spectroscopic studies

Acta Crystallographica Section C Structural Chemistry ◽

10.1107/s2053229621010883 ◽

2021 ◽

Vol 77 (11) ◽

Author(s):

Mateusz Gołdyn ◽

Anna Komasa ◽

Mateusz Pawlaczyk ◽

Aneta Lewandowska ◽

Elżbieta Bartoszak-Adamska

Keyword(s):

Hydrogen Bonds ◽

Water Solubility ◽

Theoretical Calculations ◽

Spectroscopic Studies ◽

X Ray Diffraction ◽

Dihydroxybenzoic Acid ◽

Scanning Calorimetry ◽

X Ray ◽

Purine Alkaloids ◽

Vis Spectroscopy

The study of various forms of pharmaceutical substances with specific physicochemical properties suitable for putting them on the market is one of the elements of research in the pharmaceutical industry. A large proportion of active pharmaceutical ingredients (APIs) occur in the salt form. The use of an acidic coformer with a given structure and a suitable pK a value towards purine alkaloids containing a basic imidazole N atom can lead to salt formation. In this work, 2,6-dihydroxybenzoic acid (26DHBA) was used for cocrystallization of theobromine (TBR) and caffeine (CAF). Two novel salts, namely, theobrominium 2,6-dihydroxybenzoate, C7H9N4O2 +·C7H5O4 − (I), and caffeinium 2,6-dihydroxybenzoate, C8H11N4O2 +·C7H5O4 − (II), were synthesized. Both salts were obtained independently by slow evaporation from solution, by neat grinding and also by microwave-assisted slurry cocrystallization. Powder X-ray diffraction measurements proved the formation of the new substances. Single-crystal X-ray diffraction studies confirmed proton transfer between the given alkaloid and 26DHBA, and the formation of N—H...O hydrogen bonds in both I and II. Unlike the caffeine cations in II, the theobromine cations in I are paired by noncovalent N—H...O=C interactions and a cyclic array is observed. As expected, the two hydroxy groups in the 26DHBA anion in both salts are involved in two intramolecular O—H...O hydrogen bonds. C—H...O and π–π interactions further stabilize the crystal structures of both compounds. Steady-state UV–Vis spectroscopy showed changes in the water solubility of xanthines after ionizable complex formation. The obtained salts I and II were also characterized by theoretical calculations, Fourier-transform IR spectroscopy (FT–IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and elemental analysis.

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Two types of Ln2Cu2 hydroxo-trimethylacetate complexes with 0D and 1D motifs: synthetic features, structural differences, and slow magnetic relaxation

Dalton Transactions ◽

10.1039/d1dt01161h ◽

2021 ◽

Author(s):

Anna Bovkunova ◽

Evgeniya S. Bazhina ◽

Igor Evstifeev ◽

Yulia V. Nelyubina ◽

Maxim Shmelev ◽

...

Keyword(s):

Magnetic Relaxation ◽

X Ray Diffraction ◽

Metal Core ◽

X Ray ◽

Trimethylacetate Complexes ◽

Structural Differences ◽

Slow Magnetic Relaxation ◽

New Compounds

Two series of heterometallic LnIII−CuII compounds containing a butterfly-like tetranuclear metal core were synthesized and characterized by X-ray diffraction and magnetometry. The structures of the new compounds were shown to...

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