A colorimetric method for determination of pyrocatechol and related substances

A colorimetric assay for the quantitative determination of catecholic compounds was developed. The method was based on the observation that a red color was formed when nitrite was added to a solution containing pyrocatechol and sodium tungstate. Aromatic amines interfere with the reaction but this could be overcome by the addition of formaldehyde. When interfering substances are present along with pyrocatechol, it can be readily separated by paper chromatography and estimated after elution from the filter paper.

Stabilisation and characterisation of N,N′-dibenzylidene-o-phenylenediamine as a copper(I) perchlorate complex

QUITE OFTEN, metal ions profoundly affect the condensation of carbonyl compounds with primary amines to form Schiff bases as well as their subsequent reactions[I-4]. Condensation of benzaldehyde with o-phenylenediamine (opd) in glacial acetic acid[5] or in absolute alcohol[6] gives benzimidazole derivative, 1-benzyl-2-phenylbenzimidazole (bpbi). In this reaction, the Schiff base N,N'-dibenzylidene-o-phenylenedianfme (dbpd) has been postulated as an intermediate, which cyclises to give bpbi. It was found that the reaction of opd in presence of copperO1) perchlorate with benzaldehyde gave dbpd complex of copper(l) perchlorate instead of bpbi.

Dipole moments and structure of organophosphine and organoarsine compounds

The formal charge distributions in and the dipole moments of some organophosphines and arsines have been calculated, and the dipole moments of (p-chlorophenyl)dichlorophosphine (2.28 D) and (p-bromophenyl)dichlorophosphine (2.04 D) have been determined in benzene at 35° C. The differences between the observed and the calculated moments are explained in terms of dπ---pπ back-bonding and hyperconjugative effects in alkylhaloarsines. The mesomeric effects operating in the aromatic systems are evaluated by comparing the moments with those for the corresponding aliphatic systems. In unsaturated compounds the differences are attributed to mesomeric effects involving the expansion of arsenic valence shell.

Click chemistry inspired synthesis of ferrocene amino acids and other derivatives

This work reports the synthesis of a wide range of ferrocenyl-amino acids and other derivatives in excellent yield. Diverse amino acid containing azides were synthesized and ligated to ferrocene employing click reaction to access ferrocenyl amino acids. Chiral alcohols, esters, diols, amines containing azido group were tagged to ferrocene via click reaction to generate ferrocene derived chiral derivatives. A novel strategy for direct incorporation of ferrocene into a peptide and a new route to 1, 1′disubstituted ferrocene amino acid derivative are reported.

Dipole moments and structure of organophosphine and organoarsine compounds

The formal charge distributions in and the dipole moments of some organophosphines and arsines have been calculated, and the dipole moments of (p-chlorophenyl)dichlorophosphine (2.28 D) and (p-bromophenyl)dichlorophosphine (2.04 D) have been determined in benzene at 35° C. The differences between the observed and the calculated moments are explained in terms of dπ---pπ back-bonding and hyperconjugative effects in alkylhaloarsines. The mesomeric effects operating in the aromatic systems are evaluated by comparing the moments with those for the corresponding aliphatic systems. In unsaturated compounds the differences are attributed to mesomeric effects involving the expansion of arsenic valence shell.

X-Ray structure of a ternary complex, copper(II)–lnosine 5-monophosphate–benzimidazole. The first example for the absence of direct metal–nucleotide interaction

The unprecedented absence of direct metal–nucleotide interaction has been observed in the X-ray structure of the ternary metal nucleotide system [Cu(bzim)(H2O)5]2+[IMP]2–·3H2O [IMP = inosine 5-monophosphate(2–), bzim = benzimidazole). The complex crystallizes in the space group P21 with a= 7.013(2), b= 13.179(9), c= 14.565(9)Å, = 94.82(4)°, and Z= 2. The structure was solved by the heavy-atom method and refined by full-matrix least squares on the basis of 1 761 observed (I? 3i) reflections to final R and R values of 0.034 and 0.036 respectively. The CuII has a distorted octahedral co-ordination with a nitrogen of the bzim ligand [Cu–N 1.947(5)Å] and three oxygens of water molecules in the basal plane [mean Cu–O 2.017(3)Å] and two more water oxygens at axial positions [Cu–O 2.194(6) and 2.732(5)Å]. The nucleotide base stacks with the bzim ligand at an average distance of 3.5 Å and an angle of 22°. In the lattice, N(7) of the base is linked to a lattice water through a hydrogen bond, while all the phosphate oxygens are involved in hydrogen bonds with co-ordinated as well as lattice water molecules. The co-ordination behaviour of IMP to CuII is compared in structures containing different -aromatic amines in order to assess the influence of the ternary ligand in complex formation. The present results indicate that, apart from the commonly observed phosphate binding, other modes of co-ordination are possible, these being influenced mainly by the -accepting properties of the ternary ligand.

A Novel Synthetic Route For The Preparation Of Ammonium And Alkali-Metal Tetrafluoroborates And Alkyl Substituted Ammonium Tetrafluoroborates Using Pyridinium Tetrafluoroborate As The Precursor

Ammonium and alkali metal tetrafluoroborates have been prepared by the cation exchange reaction of pyridinium tetrafluoroborate with the corresponding hydroxides/halides. The reaction of pyridinium tetrafluoroborate with primary, secondary and tertiary alkyl amines at room temperature gives rise to mono-, di- and tri-alkylammonium tetrafluoroborates, respectively. The yields are good and the samples are of high purity. The products have been characterised by elemental analysis, IR and PMR spectroscopy. The spectral data for most of the compounds are reported for the first time.

Spectroscopic, microscopic and first rheological investigations in charge-transfer interaction induced organogels

This article describes two-component charge-transfer interaction mediated organogels (CT-gels) derived from anthracene carboxamides obtained from 2-amino 2-hydroxymethyl-1,3-propanediol (TRIS), and 2,3-dialkoxyanthracenes as donors, with 2,4,7-trinitrofluorenone (TNF) as the common acceptor. We demonstrate the versatility of TNF as an electron acceptor in the formation of these gels. The effect of subtle changes in the donor structure on the gelation ability has been investigated by varying the alkyl chain length in the dialkoxyanthracene donors, and by varying the position of the TRIS substituent in the anthracene carboxamide donors. Distinct differences have been observed in the nature of the CT-gels based on these two kinds of anthracene donors. It has been reported in the literature that 2,3-dialkoxyanthracenes form gels on their own in various aliphatic hydrocarbons and alcohols for linear alkyl chains bearing at least 6mcarbon atoms (C-6). In the present study, it is shown that themCT-complex of these molecules with TNF is able to gel many alcoholic and a few hydrocarbon solvents. Also, in the presence of TNF, the 2,3-dialkoxyanthracenes (C-4-C-5) which were non-gelators on their own at ambient temperatures, form CT-gels in a number of alcohols. The other series of gelators discussed, the anthracene carboxamides, require the mandatory presence of TNF to form gels. This donor-acceptor complex forms gels in various aliphatic alcohols. Interestingly, the formation of these CT-gels requires rapid cooling in most of the cases. Thermal stability studies with both types of CT-gels indicate an optimum stoichiometry of 1 : 1 between the donor and the acceptor. Dynamic rheological experiments reveal these gels as viscoelastic soft materials, with the mechanical strength of these gels depending on the amount of TNF present. This provides a means to tune the strength of the gel by varying the doping concentration of the acceptor.

Molecular Complexes of Alprazolam with Carboxylic Acids, Boric Acid, Boronic Acids, and Phenols. Evaluation of Supramolecular Heterosynthons Mediated by a Triazole Ring

A series of molecular complexes, both co-crystals and salts, of a triazole drug-alprazolam-with carboxylic acids, boric acid, boronic acids, and phenols have been analyzed with respect to heterosynthons present in the crystal structures. In all cases, the triazole ring behaves as an efficient hydrogen bond acceptor with the acidic coformers. The hydrogen bond patterns exhibited with aromatic carboxylic acids were found to depend on the nature and position of the substituents. Being a strong acid, 2,6-dihydroxybenzoic acid forms a salt with alprazolam. With aliphatic dicarboxylic acids alprazolam forms hydrates and the water molecules play a central role in synthon formation and crystal packing. The triazole ring makes two distinct heterosynthons in the molecular complex with boric acid. Boronic acids and phenols form consistent hydrogen bond patterns, and these are seemingly independent of the substitutional effects. Boronic acids form noncentrosymmetric cyclic synthons, while phenols form O-H center dot center dot center dot N hydrogen bonds with the triazole ring. (C) 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3743-3753, 2010.

Purification and properties of 4-hydroxyphenylacetic acid 3-hydroxylase from pseudomonas putida

4-Hydroxyphenylacetic acid 3-hydroxylase is a key enzyme in the pathway for the microbial degradation of phenylalanine, tyrosine and many aromatic amines. This enzyme was purified to homogeneity from Image by affinity chromatography. The protein had a molecular weight of 91,000 and was a dimer of identical subunits. It was a typical external flavoprotein monooxygenase and showed an absolute requirement of NADH for activity. The enzyme had a pH optimum of 7.5 and the Km values for 4-hydroxyphenylacetic acid and NADH were 2×10−4 M and 5.9×10−5 M respectively. It was strongly inhibited by heavy metal ions and thiol reagents, suggesting the possible involvement of -SH group(s) in enzyme reaction.

Complexation of siRNA with Dendrimer: A Molecular Modeling Approach

This paper reports the structural behavior and thermodynamics of the complexation of siRNA with poly(amidoamine) (PAMAM) dendrimers of generation 3 (G3) and 4 (G4) through fully atomistic molecular dynamics (MD) simulations accompanied by free energy calculations and inherent structure determination. We have also done simulation with one siRNA and two dendrimers (2 x G3 or 2xG4) to get the microscopic picture of various binding modes. Our simulation results reveal the formation of stable siRNA-dendrimer complex over nanosecond time scale. With the increase in dendrimcr generation, the charge ratio increases and hence the binding energy between siRNA and dendrimer also increases in accordance with available experimental measurements. Calculated radial distribution functions of amines groups of various subgenerations in a given generation of dendrimer and phosphate in backbone of siRNA reveals that one dendrimer of generation 4 shows better binding with siRNA almost wrapping the dendrimer when compared to the binding with lower generation dendrimer like G3. In contrast, two dendrimers of generation 4 show binding without siRNA wrapping the den-rimer because of repulsion between two dendrimers. The counterion distribution around the complex and the water molecules in the hydration shell of siRNA give microscopic picture of the binding dynamics. We see a clear correlation between water. counterions motions and the complexation i.e. the water molecules and counterions which condensed around siRNA are moved away from the siRNA backbone when dendrimer start binding to the siRNA back hone. As siRNA wraps/bind to the dendrimer counterions originally condensed onto siRNA (Na-1) and dendrimer (Cl-) get released. We give a quantitative estimate of the entropy of counterions and show that there is gain in entropy due to counterions release during the complexation. Furthermore, the free energy of complexation of IG3 and IG4 at two different salt concentrations shows that increase in salt concentration leads to the weakening of the binding affinity of siRNA and dendrimer.

Chiral gels derived from secondary ammonium salts of (1R, 3S)-(+)-camphoric acid

In order to have access to chiral gels, a series of salts derived from (1R, 3S)-(+)-camphoric acid and various secondary amines were prepared based on supramolecular synthon rationale. Out of seven salts prepared, two showed moderate gelation abilities. The gels were characterized by differential scanning calorimetry, table top rheology, scanning electron microscopy, single crystal and powder X-ray diffraction. Structure property correlation based on X-ray diffraction techniques remain inconclusive indicating that some of the integrated part associated with the gelation phenomena requires a better understanding.

Physicochemical behaviour of polyperoxide

Polymeric peroxides are equimolar alternating copolymers formed by the reaction of vinyl monomers with oxygen. Physicochemical studies on the microstructure and chain dynamics of poly(styrene peroxide) PSP were first carried out by Cais and Bovey. We have found that polyperoxides are formed as main intermediates in solid-propellant combustion by the interaction of the monomer and oxygen generated by the decomposition of the polymeric binder and the oxidizer ammonium perchlorate. The experimentally determined heat of degradation and that calculated from thermochemical considerations reveal that polyperoxides undergo highly exothermic primary degradation, the rate-controlling step being the O-O bond dissociation. A random-chain scission mechanism for the thermal degradation of polyperoxides has been proposed. The prediction of unusual exothermic degradation of polyperoxides has resulted in the discovery of an interesting new phenomenon of 'autopyrolysability' in polymers. Several new polyperoxides based on vinyl naphthalene have been synthesized. We have also found that PSP, in conjunction with amines, can be used as initiator at ambient temperature for the radical polymerization of vinyl monomers.

Oxidation of aromatic substrates with hydrogen peroxide and hydrochloric acid

Chloroquinones are prepared conveniently from phenol, naphthols and aromatic amines.

Lewis Acid-Lewis Base Mediated Metal-Free Hydrogen Activation and Catalytic Hydrogenation

Organocatalysis, the use of organic molecules as catalysts, is attracting increasing attention as one of the most modern and rapidly growing areas of organic chemistry, with countless research groups in both academia and the pharmaceutical industry around the world working on this subject. The literature review of this thesis mainly focuses on metal-free systems for hydrogen activation and organocatalytic reduction. Since these research topics are relatively new, the literature review also highlights the basic principles of the use of Lewis acid-Lewis base pairs, which do not react irreversibly with each other, as a trap for small molecules. The experimental section progresses from the first observation of the facile heterolytical cleavage of hydrogen gas by amines and B(C6F5)3 to highly active non-metal catalysts for both enantioselective and racemic hydrogenation of unsaturated nitrogen-containing compounds. Moreover, detailed studies of structure-reactivity relationships of these systems by X-ray, neutron diffraction, NMR methods and quantum chemical calculations were performed to gain further insight into the mechanism of hydrogen activation and hydrogenation by boron-nitrogen compounds.