1,720,973 research outputs found
Co-crystallization of racemic amino acids with ZnCl2: An investigation of chiral selectivity upon coordination to the metal centre
Full text linkThe amino acids alanine, valine, proline, isoleucine, serine, asparagine, tyrosine, and threonine in their racemic forms have been reacted with ZnCl2 under different preparative conditions (grinding and LAG, both manual and ball milling, and co-crystallization from solvent). In most cases, relatively stable (from days to months) oils were obtained; only in those cases for which single crystals could grow from oils, structural characterisation was possible via X-ray diffraction. Aim of the work has been the investigation of the occurrence of chiral selectivity upon the formation of tetrahedral metal coordination complexes or polymers. It has been shown that co-crystallization reactions lead, in the majority of cases, to crystals of racemic-AA2ZnCl2, formed by 0D homochiral complexes of formula l-AA2ZnCl2 and d-AA2ZnCl2. With the dl-amino acid threonine, however, crystals of meso-AA2ZnCl2 have also been obtained, made of 0D heterochiral complexes of formula dl-AA2ZnCl2. With dl-proline, both the known racemic and the new meso-AA2ZnCl2 solids were obtained. Formation of 1D coordination polymers has been observed in the cases of dl-asparagine and dl-tyrosine with alternating d and l amino acids along the polymeric chain. This journal i
Ionic Cocrystals of Levodopa and Its Biological Precursors l-Tyrosine and l-Phenylalanine with LiCl
No full textIonic cocrystals (ICCs) of LiCl with levodopa and its biological precursors l-tyrosine and l-phenylalanine, namely, l-phe·LiCl·nH2O, l-tyr·LiCl, and l-dopa·LiCl·H2O, were synthesized by mechanochemical mixing of the reactants in the presence of a small quantity of ethanol. In the case of l-dopa, a polymorph of l-dopa·LiCl·H2O was also obtained from solution crystallization. All compounds were investigated by solid state methods, and the structures were determined either from single crystal or from powder diffraction data
Chiral Resolution via Cocrystallization with Inorganic Salts
Full text linkcrystal engineering, cocrystals, chiralityThe coordination mode to lithium, magnesium, calcium and zinc cations of racemic vs. enantiopure amino acids and racetam APIs is analysed and its effect on chiral selection critically reviewed. It is shown that chiral resolution in the solid state can be obtained via cocrystallization of racemic compounds with an achiral inorganic salt coformer, such as LiX (X=Cl, Br, I) or ZnCl2, which favour tetrahedral coordination in the solid state. The chiral selection may take the form of conglomerate crystal formation or of selective homochiral aggregation in racemic crystals. When cocrystallization involves alkaline earth metal cations, such as Ca2+ and Mg2+, which favour octahedral coordination, heterochiral complexation is observed in most cases, with formation of racemic crystals
Embroidering Ionic Cocrystals with Polyiodide Threads: The Peculiar Outcome of the Mechanochemical Reaction between Alkali Iodides and Cyanuric Acid
Full text linkWe report here the preparation and structural characterization of a series of new crystalline materials obtained by mechanochemical mixing of cyanuric acid (CA) and alkali halides (LiI, NaI, and KI) in the presence of molecular iodine, namely, the isomorphous catena-poly[tetra(cyanuric acid)·lithium tetraiodide], n[CA4·LiI4], and catena-poly[tetra(cyanuric acid)·sodium tetraiodide], n[CA4·NaI4], featuring three-dimensional (3D) cationic frameworks able to segregate linear, infinite n[I4-] chains in their squared open channels and the layered solid [CA·KI3]2·I2·2H2O characterized by alternating sheets of (i) hydrated potassium cations and CA molecules and (ii) I3- anions and discrete I2 molecules. The combination of X-ray diffraction (XRD), Raman spectroscopy, and thermal analyses allowed us to elucidate the compound's structural features and to discuss the effect of cation size on the stoichiometry and architecture of the three ionic cocrystals (ICCs)
Ionic co-crystals of enantiopure and racemic histidine with calcium halides
No full textIonic co-crystals (ICCs) of l- and dl-histidine with CaCl2, CaBr2 and CaI2 were prepared by mechanochemical and solution methods and were structurally characterized by either single crystal or powder X-ray diffraction methods. The l-histidine molecules bridge Ca2+ cations forming enantiopure ribbons in the homochiral crystals (l-His)2·CaX2·nH2O (X = Cl and Br n = 3, X = I n = 4), as well as in the partial dehydration product of (l-His)2·CaI2·4H2O, namely (l-His)2·CaI2·3H2O. In the racemic (dl-His)2·CaX2·4H2O cases (X = Cl, Br, X = I), molecules of both chiralities are accommodated in the coordination sphere of the Ca2+ cation forming ribbons with homochiral rims as in the enantiopure crystals. Intrinsic dissolution rate measurements show that the histidine-CaCl2 co-crystals have a much higher IDR with respect to both enantiopure and racemic histidine solids
Solvent Effect on the Preparation of Ionic Cocrystals of dl -Amino Acids with Lithium Chloride: Conglomerate versus Racemate Formation
Full text linkThe hydrophobic dl-amino acids alanine, valine, leucine, and isoleucine have been cocrystallized with LiCl via solid-state and solution methods, and the effect of preparation conditions and solvent choice on the racemic versus conglomerate formation has been investigated. For the sake of comparison, enantiopure l-amino acids have also been reacted with LiCl in the same experimental conditions. With dl-alanine only, a racemic ionic cocrystal of formula dl-alanine·LiCl·H2O is obtained, irrespective of the preparation conditions, while the amino acids dl-valine and dl-leucine undergo spontaneous chiral resolution when MeOH is used in ball milling conditions, yielding monohydrated conglomerates, which at ambient conditions convert over time into the racemic ionic cocrystals dl-Val·LiCl·H2O and dl-Leu·LiCl·1.5H2O; these racemic ionic cocrystals (ICCs) are otherwise obtained in a single step if water is employed instead of MeOH, both in ball milling and solution conditions. dl-Isoleucine behaves differently, and product characterization is complicated by the presence of dl-alloisoleucine (dl-aIle) in the commercial starting material; solution crystallization in the presence of excess LiCl, however, unexpectedly results in the formation of the alloisoleucine conglomerate d-aIle·LiCl·H2O and l-aIle·LiCl·H2O, together with unreacted dl-isoleucine. Solid-state syntheses of the ionic cocrystals proceed in most cases via formation of intermediate metastable polymorphs; phase identification and structural characterization for all ICCs have been conducted via single crystal and/or powder X-ray diffraction
Proflavine and zinc chloride “team chemistry”: combining antibacterial agentsviasolid-state interaction
Full text linkCo-crystallization of the antibacterial agent proflavine (PF) with the inorganic salt ZnCl2by mechanochemical and solution methods results in the formation of novel compounds ZnCl3(HPF) (1) and [HPF]2[ZnCl4]·H2O (2), both containing the proflavinium cation (HPF)+. Both compounds show a 50-125% enhanced antimicrobial activity with respect to a reference standard of AgNO3, and a 25-50% enhancement to the behaviour of the separate components against pathogen indicator strains ofPseudomonas aeruginosa,Staphylococcus aureus, andEscherichia coli. In terms of crystal structure, both compounds ZnCl3(HPF) and [HPF]2[ZnCl4]·H2O are characterized by extensive π-stacking interactions between the proflavine moieties. The same interaction is predominant in the previously unknown crystal structures of neutral proflavine (PF), as well as in that of its dihydrated monochloride salt, [HPF]Cl·2H2O, which are also described in this paper
Mechanochemical preparation of molecular and ionic co-crystals of the hormone melatonin
No full textTwo co-crystals of melatonin with piperazine and (1,4-diazabicyclo[2.2.2]octane), DABCO, and a hydrated ionic co-crystal with CaCl2 were obtained directly in the solid-state via kneading of the solid mixtures with a few drops of ethanol. The structure of the DABCO co-crystal, mel2·DABCO, was determined by single crystal X-ray diffraction, while those of the piperazine co-crystal, mel2·pip, isomorphous with the DABCO one, and the ionic co-crystal, mel2·CaCl2·2H2O, were determined from powder data. In the case of the ionic co-crystal with CaCl2, solubility measurements indicate that melatonin solubility in water increases by an order of magnitude with respect to the pure substance
Ionic co-crystals of enantiopure and racemic histidine with calcium halides
No full textIonic co-crystals (ICCs) of L- and DL-histidine with CaCl2, CaBr2
and CaI2 were prepared by mechanochemical
and solution methods and were structurally characterized by either single crystal or powder X-ray
diffraction methods. The L-histidine molecules bridge Ca2+ cations forming enantiopure ribbons in the
homochiral crystals (L-His)2·CaX2·nH2O (X = Cl and Br n = 3, X = I n = 4), as well as in the partial dehydration
product of (L-His)2·CaI2·4H2O, namely (L-His)2·CaI2·3H2O. In the racemic (DL-His)2·CaX2·4H2O cases (X
= Cl, Br, X = I), molecules of both chiralities are accommodated in the coordination sphere of the Ca2+
cation forming ribbons with homochiral rims as in the enantiopure crystals. Intrinsic dissolution rate measurements
show that the histidine-CaCl2 co-crystals have a much higher IDR with respect to both enantiopure
and racemic histidine solids
Ionic Cocrystals of Racemic and Enantiopure Histidine: An Intriguing Case of Homochiral Preference
No full textIonic cocrystals (ICC) of l- and dl-histidine with lithium halides (LiCl, LiBr, LiI) have been prepared by solid state and solution methods, and structurally characterized in order to compare the behavior of enantiopure and racemic crystals in the interaction with inorganic salts. It has been shown that the lithium cations interact selectively with enantiomers of one handedness only, to the extent that the crystals obtained with racemic dl-histidine can be described as a special type of cocrystals made of enantiopure l-histidine and d-histidine chains of the same type as those obtained with enantiopure l-histidine. This chiral preference is even more noticeable in the ICC obtained from dl-histidine and LiI, which is actually a conglomerate of l- and d-ICCs. It is also reported that attempts to prepare ICCs with other alkali/alkaline earth halides invariably yield crystals of the less stable polymorph of l-histidine
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