Hydrogen Maleates Research Articles

The advanced treatment of hydrogen bonding in quantum crystallography.

Although hydrogen bonding is one of the most important motifs in chemistry and biology, H-atom parameters are especially problematic to refine against X-ray diffraction data. New developments in quantum crystallography offer a remedy. This article reports how hydrogen bonds are treated in three different quantum-crystallographic methods: Hirshfeld atom refinement (HAR), HAR coupled to extremely localized molecular orbitals and X-ray wavefunction refinement. Three different compound classes that form strong intra- or intermolecular hydrogen bonds are used as test cases: hydrogen maleates, the tripeptide l-alanyl-glycyl-l-alanine co-crystallized with water, and xylitol. The differences in the quantum-mechanical electron densities underlying all the used methods are analysed, as well as how these differences impact on the refinement results.

Structural Variety of Alkali Hydrogen Maleates at High Pressure

The effect of pressure on the structure of pharmaceutical inactive excipients, such as hydrogen maleates, can provide useful information about their stability in the formulation and overall chemica...

Features of the Thermolysis of Fe(II), Co(II), Ni(II), and Cu(II) Salts of Maleic and Phthalic Acids with the Formation of Metal Nanoparticles

A relationship is established between the structural and thermoanalytical characteristics of the decomposition of hydrogen maleates and phthalates of Fe(II), Co(II), Ni(II), Cu(II). The temperatures of the onset of the first and second stages of decomposition grow in the series of both hydrogen maleates Cu ≤ Fe < Co < Ni and phthalates Fe ≤ Co < Ni < Cu, while the lengths of M– $${{{\text{O}}}_{{{{{\text{H}}}_{2}}{\text{O}}}}}$$ and M–Oanion bonds shrink in these structures. At the third stage, the temperature of the onset of the decarboxylation of hydrogen maleates and phthalates falls in the order Fe > Co > Ni > Cu. The size of metal nanoparticles additionally contained in a polymer or graphene shell grows from 3.5 to 5 nm (Co) and from 4.5 to 7 nm (Ni) upon moving from composites obtained through the decomposition of hydrogen maleates to hydrogen phthalates. Polymeric conglomerates containing shell-less copper nanoparticles, the average size of which ranges from 7.5 to 50 nm, are incorporated into a polymer matrix of composites obtained via the thermolysis of Cu(II) hydrogen maleate and phthalate.

How the H-Bond Layout Determines Mechanical Properties of Crystalline Amino Acid Hydrogen Maleates

The stiffness tensor and elastic anisotropy characteristics for the crystalline hydrogen maleates of l-isoleucinium, l-leucinium, and l-norvalinium with l-norvaline have been calculated using the periodic DFT calculations and atom-centered basis sets. The H-bond orientations have been compared with spatial directions of the minimum and maximum values of Young’s modulus, shear modulus, and linear compressibility. In spite of the similar layered structures, l-isoleucinium and l-leucinium hydrogen maleates show significant difference in elastic moduli anisotropy. The flexibility of l-leucinium hydrogen maleate is explained by the relatively high universal elastic anisotropy index and the large anisotropy ratios of elastic moduli. In its turn, this index is determined by the almost coincidental Young’s modulus maximum direction and the orientation of the strongest H-bonds.

Thermal decomposition of solid solutions in systems of Fe(II), Co(II), and Ni(II) hydrogen maleates with the formation of bimetallic nanoparticles

XRD phase analysis and thermal analysis are used to confirm the formation of a continuous series of solid solutions in which one cation is substituted for another in the systems Co(II) hydrogen maleate–Ni(II) hydrogen maleate; Fe(II) hydrogen maleate–Co(II) hydrogen maleate; and Fe(II) hydrogen maleate–Ni(II) hydrogen maleate. The unit cell volume of these solid solutions is shown to depend linearly on their composition. The linear character of changes in the initial temperatures of dehydration and thermal decomposition is established. Using the example of the first of these systems, it is shown that when heated, bimetallic nanoparticles embedded in the polymeric matrix of composites obtained via the thermal decomposition of solid solutions of hydrogen maleates undergo a second-order phase transition, resulting in decomposition of the solid solutions of metals at the Curie temperature.

New 1:1 and 2:1 salts in the `DL-norvaline–maleic acid' system as an example of assembling various crystal structures from similar supramolecular building blocks

Molecular salts and cocrystals of amino acids have potential applications as molecular materials with nonlinear optical, ferroelectric, piezoelectric, and other various target physical properties. The wide choice of amino acids and coformers makes it possible to design various crystal structures. The amino acid-maleic acid system provides a perfect example of a rich variety of crystal structures with different stoichiometries, symmetries and packing motifs built from the molecular building blocks, which are either exactly the same, or differ merely by protonation or as optical isomers. The present paper reports the crystal structures of two new salts of the DL-norvaline-maleic acid system with 1:1 and 2:1 stoichiometries, namely DL-norvalinium hydrogen maleate, C5H12NO2+·C4H3O4-, (I), and DL-norvalinium hydrogen maleate-DL-norvaline, C5H12NO2+·C4H3O4-·C5H11NO2, (II). These are the first examples of molecular salts of DL-norvaline with an organic anion. The crystal structure of (I) has the same C22(12) structure-forming motif which is common for hydrogen maleates of amino acids. The structure of (II) has dimeric cations. Of special interest is that the single crystals of (I) which are originally formed on crystallization from aqueous solution transform into single crystals of (II) if stored in the mother liquor for several hours.

Transition-metal bimaleates and their solid solutions: Synthesis, structural, and thermoanalytical study

Transition-metal hydrogen maleates of composition M(C4H3O4)2 · 4H2O, where M = Mn, Fe, Co, and Ni, and their solid solutions were synthesized and characterized by X-ray crystallography, IR spectroscopy, mass spectrometry, and thermal analysis. X-ray crystallography and IR spectroscopy showed that both intramolecular and intermolecular H-bonds exist in these compounds. The generation of continuous substitutional solid solutions with cation substitution in these compounds was studied. The thermolysis mechanism was studied for both transition-metal hydrogen maleates and their solid solutions. The composite produced by thermolysis is stable up to 1200°C in flowing helium.

Kinetic and Theoretical Studies on the Mechanism of Intramolecular Catalysis in Phenyl Ester Hydrolysis

The kinetic study of the hydrolysis reaction of Z-substituted phenyl hydrogen maleates (Z = H, m-CH3, p-CH3, m-Cl, p-Cl and m-CN) was carried out in aqueous solution, and the results were complemented with theoretical studies. Under some experimental conditions, two kinetic processes were observed. One of them was ascribed to maleic anhydride formation and the other to the anhydride hydrolysis. The Brönsted-type plot for the leaving-group dependence was linear with slope beta(lg) = -1. The experimental results are consistent with a mechanism that involves significant bond breaking in the rate-limiting transition state (alpha(lg) = 0.64). Theoretical results for the reaction in the gas phase showed an excellent Brönsted-type dependence with a beta(lg) of -1.03. A tetrahedral intermediate (TI) could not be found through DFT gas-phase studies (B3LYP/6-311+G*). Calculations carried out within a continuous solvation model or with discrete water molecules failed to find a stable TI. With both models, a flat region on the potential-energy surface is found and a tight optimization of the structures led back to starting materials. The theoretical results do not discard the possible existence of an unstable intermediate on the free-energy surface, but the analysis of the whole body of results compared with other acyl transfer reactions lead us to suggest that an enforced concerted mechanism is the most appropriate to describe these reactions.

Hydrolysis of aryl hydrogen maleate esters mediated by cyclodextrins — Effect on the intramolecular catalysis

Kinetic studies of the hydrolysis of Z-aryl hydrogen maleates (Z = H, p-CH3, m-CH3, p-Cl, m-Cl) were carried out in the presence and absence of hydroxypropyl-β-cyclodextrin (HPCD) at variable pH from 1.00 to 3.00. The reaction involves the formation of maleic anhydride as an intermediate and the rate of its formation is strongly dependent on the pH. This is because the neighboring carboxylate group is a better catalyst than the carboxylic group. The rate constant for the formation of maleic anhydride decreases as the HPCD concentration increases in a nonlinear fashion. The results were interpreted in terms of the formation of a 1:1 inclusion complex of the esters with HPCD. The neutral (HA) and anionic (A) species of the substrate have different association constants (K[Formula: see text] and K[Formula: see text]). In all cases studied,K[Formula: see text] is higher than K[Formula: see text] for the same substrate. This difference is responsible for a decrease in the amount of the anionic substrate (reactive species) in the presence of HPCD, which results in a diminution of the observed rate constant. Besides, the rate constant for the reaction of the complexed substrate is smaller than that in the bulk solution indicating that the transition state of the cyclodextrin mediated reaction is less stabilized than the anionic substrate. The values of ΔΔG‡are almost independent of the substituent on the aryl ring and range within 0.48 and 1.05 kcal mol–1(1 cal = 4.184 J). There is no correlation between KTSand the association constant of the substrate indicating that the factors stabilizing the transition state are different from those that stabilize the substrate. Key words: cyclodextrins, intramolecular catalysis, hydrolysis, inhibition.

Synthesis of monomoraprenyl- and monodolichylsuccinates and maleates

The reactions of moraprenol and dolichol with succinic and maleic anhydrides in the presence of pyridine or triethylamine were studied, and the conditions were found for the efficient synthesis of moraprenyl and dolichyl hydrogen succinates and maleates. These may be of interest as analogues of moraprenyl and dolichyl hydrogen phosphates with modified anionic groups. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 2; see also http://www.maik.ru.

Potential Antagonists of Excitatory Amino Acids and Anticonvulsants: Some Heterocyclic (±)-Pyrrolidine-2-carboxamides

The benzylpyrrolidine amides 1a-1d, 3a-3e, 5a, and 5b were prepared from N-benzyl-L-proline methyl ester with corresponding diamines. Compounds 2a-2d, 4b, and 4e have similarly been synthesized from L-proline methyl ester and the corresponding diamines in refluxing methanol. In both cases, the reactions were accompanied by racemization. Prepared amides were transformed to salts, suitable for pharmacological testing (hydrogen maleates, hydrogen oxalates and hydrochlorides). The products were tested by selected methods of biochemical and behavioural pharmacology.

Structures of the silver(I) complexes with maleic and fumaric acids: silver(I) hydrogen maleate, silver(I) maleate and silver(I) fumarate

Abstract A series of silver(I) complexes with the unsaturated isomeric dicarboxylic acids, maleic and fumaric, has been prepared and the structures of three of these, silver(I) hydrogen maleate, (1), silver(I) maleate, (2) and silver(I) fumarate, (3), were determined by X-ray diffraction. All three structures are polymeric, with (1) and (2) based on bis(carboxylato-O,O′) dimers. With (1), a strong intramolecular hydrogen bond is found [O … O, 2.494(2) Å], involving the acidic proton and the cis-related carboxylate group. In this respect it is similar to maleic acid and other hydrogen maleates. With (2), a unique feature is the presence of an ethylene-Ag π-bond to one of the independent silver ions [Ag–C, 2.448(5) Å] giving angle distortion about the dimer unit. The polymeric structure of (3) is based on an unusual cyclic, open figure-eight Ag4 complex unit involving four different carboxylato-(O,O′) interactions. This results in three separate Ag … Ag contacts [2.924(1) Å, 2.925(1) Å, 3.090(1) Å].

ChemInform Abstract: Potential Cerebral Stimulants: Esters of 2‐Dimethylaminoethanol with Some Lipophilic Carboxylic Acids.

AbstractThe title compounds (III) are converted to crystalline salts (hydrogen fumarates, hydrogen maleates, hydrochlorides) for pharmacological evaluation.

Potential antidepressants: 2-(6,11-Dihydrodibenzo[b,e]thiepin-11-yl)-4,5-dihydroimidazoles

Reactions of 2-substituted 11-chloro-6,11-dihydrodibenzo[b,e]thiepins with trimethylsilyl cyanide in dichloromethane in the presence of stannic chloride afforded nitriles IIb-IId in high yields. Heating of IIa-IId with 2-aminoethylammonium toluene-4-sulfonate to 200 °C gave the title compounds Ia-Id which were transformed to hydrogen maleates. Compound Ic (hydrogen maleate VÚFB-17 092) showed in several tests a clear thymoleptic (potential antidepressant) character.

17O and 2H quadrupole double resonance in potassium hydrogen maleate and related compounds

2 H, 17O, 39K and 85,87Rb quadrupole resonance signals have been recorded in potassium and rubidium hydrogen maleates and several related compounds by double resonance methods. The 17O signals were detected in natural abundance by a novel technique of high sensitivity based on the “solid effect” and thermal mixing. The symmetric hydrogen bonds in potassium hydrogen maleate and chloromaleate are shown to have characteristic values of the 17O and 2H quadrupole coupling constants which can be used to identify this kind of bonding in other related compounds. The orientation of the quadrupole tensor within the bonding system is also discussed.