Solid-state acid-base interactions in complexes of heterocyclic bases with dicarboxylic acids: crystallography, hydrogen bond analysis, and 15N NMR spectroscopy

A cancer candidate, compound 1, is a weak base with two heterocyclic basic nitrogens and five hydrogen-bonding functional groups, and is sparingly soluble in water rendering it unsuitable for pharmaceutical development. The crystalline acid-base pairs of 1, collectively termed solid acid-base complexes, provide significant increases in the solubility and bioavailability compared to the free base, 1. Three dicarboxylic acid-base complexes, sesquisuccinate 2, dimalonate 3, and dimaleate 4, show the most favorable physicochemical profiles and are studied in greater detail. The structural analyses of the three complexes using crystal structure and solid-state NMR reveal that the proton-transfer behavior in these organic acid-base complexes vary successively correlating with Delta pKa. As a result, 2 is a neutral complex, 3 is a mixed ionic and zwitterionic complex and 4 is an ionic salt. The addition of the acidic components leads to maximized hydrogen bond interactions forming extended three-dimensional networks. Although structurally similar, the packing arrangements of the three complexes are considerably different due to the presence of multiple functional groups and the flexible backbone of 1. The findings in this study provide insight into the structural characteristics of complexes involving heterocyclic bases and carboxylic acids, and demonstrate that X-ray crystallography and 15N solid-state NMR are truly complementary in elucidating hydrogen bonding interactions and the degree of proton transfer of these complexes.     

Synthesis and Crystal Structure of Isosteviol Derivatives

Isosteviol (ent-16-ketobeyeran-19-oic acid, I) is a tetracyclic diterpenoid with a beyerane skeleton obtained by acid hydrolysis of stevioside.1 Several tetracyclic diterpenoids, specially the kaurenes, have important biological activities. Recent studies on the microbial transformation of isosteviol have revealed that it is metabolized by Cunninghamella bainieri, Actinoplanes sp., Mucor recurvatus, and Cunninghamella blackesleeana to yield five new metabolites.2 The hydroxylation pattern of these bioactive compounds may influence their binding on to the receptors, as was proposed for the Rabdosia diterpenoids. Therefore, the introduction of hydroxyl groups or unsaturated bonds in saturated and non-hydroxylated diterpenoids, like isosteviol, may enhance existing properties or lead to new biological activities. Although some beyeranes have been subjected to biotransformations by fungi,4 there are few report in the literature related the chemical transformation of Isosteviol. In the present study, we try to develop the chemical transformation of isosteviol and other beyeranes in order to obtaining some bioactive compounds with beyerane skeleton. Seven isosteviol derivatives, Ⅱ-Ⅷ, were therefore synthesized and characterized. The X-ray crystal strcture of H(R = H) was also determined.     

Organylthiochloroacetylenes: IV. Reaction with Thiourea

Alkylthiochloroacetylenes react with thiourea in acetone to form S-(alkylthioethynyl)isothiuronium chlorides and N-[1-(alkylthio)ethylidene]thioureas; phenylthiochloroacetylene reacts with thiourea to give 4-(phenylthio)-2-imino-1,3(3H)-thiazole hydrochloride.     

Metal Complexes of Phthalocyanine Structural Analogs with Oxygen- or Nitrogen-containing Heterorings. Synthesis and Properties

Nucleophilic substitution of the bromine atom and nitro group in 4-bromo-5-nitrophthalodinitrile and reduction of 4-benzoylamino-5-nitrophthalodinitrile gave, respectively, tribenzo[b,e,g][1,4]dioxocine-7,8-dicarbonitrile and 2-phenylbenzimidazole-5,6-dicarbonitrile. These compounds were used to synthesize new structural analogs of phthalocyanine, having oxygen- and nitrogen-containing heterorings, (tetratribenzo[b,e,g][1,4]dioxocino[7,8-b,g,l,q]-5,10,15,20-tetraazaporphyrinato)copper(II) and (23,73,123,173-tetraphenyl-tetrabenzimidazolo[5,6-b,g,l,q]-5,10,15,20-tetraazaporphyrinato)cobalt(II). Spectral properties of the resulting complexes were studied.     

Branched-chain nature of hydrogen combustion in the detonation mode

Minor admixtures of the simplest hydrocarbons can prevent detonation and break down a steady-state detonation wave in hydrogen-air mixtures at atmospheric and higher pressures. Therefore, the determining role in the appearance and propagation of the detonation wave is played by the branched mechanism and, accordingly, by the competing chain branching and termination reactions. Without taking into account these reactions, combustion theory cannot explain the basic regularities of the process, including the concentration limits of detonation.     

Synthesis and properties of magnetite-poly(aminopropylsiloxane) composites

A method is developed for the synthesis of nanosized Fe₃O₄-(SiO₂) _x [NH₂(CH₂)₃SiO_3/2] _y magnetic composites with varied SiO₂: NH₂(CH₂)₃SiO_3/2, weight/weight, ratios. The structure, texture, morphology, and magnetic properties of the obtained materials are studied by several physicochemical methods. It is shown that the composites represent systems of magnetite nanoparticles coated with poly(aminopropylsiloxane). The specific surface areas, pore volumes, and saturation magnetizations of the composites are in the ranges of 21–27 m²/g, 0.03–0.04 cm³/g, and 59–62 G cm³/g, respectively.     

Nucleophilic substitution in 4-bromo-5-nitrophthalodinitrile: XI. Preparation,properties, and prediction of mesomorphism in mixed-substituted phthalocyanines containing aryloxy and benzotriazole fragments

Stepwise nucleophilic substitution of bromine and nitro group in 4-bromo-5-nitrophthalodinitrile has led to a series of phthalonitriles containing benzotriazole and aryloxy fragments; basing on them, the mixed-substituted phthalocyanines have been prepared. The spectral properties of products have been studied. According to simulation of columnar mesomorphism only one of the products is not capable of mesomorphism characteristic of discotic mesogens; the result has been confirmed with the experiment.     

Resolving sequences of operators for linear ordinary differential and difference systems of arbitrary order

We introduce the notion of a resolving sequence of (scalar) operators for a given differential or difference system with coefficients in some differential or difference field K. We propose an algorithm to construct, such a sequence, and give some examples of the use of this sequence as a suitable auxiliary tool for finding certain kinds of solutions of differential and difference systems of arbitrary order. Some experiments with our implementation of the algorithm are reported.     

A nonlocal problem for singular linear systems of ordinary differential equations

A system of linear ordinary differential equations is examined on an infinite half-interval. This system is supplemented by the boundedness condition for solutions and a nonlocal linear condition specified by the Stieltjes integral. A method for approximating the resulting problem by a problem posed on a finite interval is proposed, and the properties of the latter are investigated. A numerically stable method for solving this problem is examined. This method uses an auxiliary boundary value problem with separated boundary conditions.     

Dipole emission of a nanostructure system composed of two atoms and dimensional resonances

A stationary solution is obtained for the joint system of equations for atomic and field variables for two different atoms with dipole-dipole interaction in the radiation field taking into account the common radiative friction. The atoms are treated as an Lorentz oscillator with one isolated resonance. The interaction of atoms in the radiation field forms four dimensional resonances at frequencies that are substantially different from the natural frequencies of isolated atoms. Two of the four dimensional resonances are characterized by negative dispersion, and the intensity of dipole emission at these frequencies may be increased with respect to the intensity of emission at the frequencies of natural atomic resonances by a factor of about 10¹².