Synthesis and structure of the 2-(chlorophenylazo)pyridine chelated tricarbonylrhenium(I) complex and its anion radical derivatives <Emphasis Type="Italic">via</Emphasis> electrochemical reduction

Reacting Re(CO)₅Cl with the azopyridine ligand (1) (L) in boiling benzene afford the complex Re(CO)₃Cl(L), (2) in excellent yield [L=2-(p-Cl-C₆H₄NN)C₅H₄N]. The chelation of the azopyridine ligand accompanied by displacement of the two carbon monoxide ligands furnish a five-membered chelate ring. Structure determination of complex (2) has revealed a distorted octahedral ReC₃N₂Cl coordination sphere. The Re–N(pyridine) and, Re–N(azo) distances are 2.158(3) and 2.153(6) Å respectively, and the N–N length [1.273(4) Å], implicate relatively weak Re-azo(π*) back–bonding. The Re(CO)₃Cl(L) lattice consists of C–H...Cl hydrogen bonding and Cl...O non-bonded interactions constituting a supramolecular network. Extended Hückel calculations reveal that the LUMO of Re(CO)₃Cl(L) is Ca. 57% azo in character. One-electron quasireversible electrochemical reduction of the complex occurs near −0.3 V versus Saturated Calomel electrode(s.c.e.) The redox orbital is believed to belong to the above noted LUMO. Electrogenerated Re(CO)₃Cl(L^•–) underwent spontaneous solvolytic chloride displacement in MeCN, resulting in the isolation of Re(CO)₃(MeCN)(L^•–). The latter complex in turn reacted with imidazole and triphenylphosphine, furnishing Re(CO)₃(C₃H₄N₂)(L^•–) and Re(CO)₃(PPh₃)(L^•–), respectively. The pattern of carbonyl stretching frequencies of these radical anion complexes is similar to that of Re(CO)₃Cl(L) but with shifts to lower frequencies by 10–20 cm⁻¹. All three radical anion systems are one-electron paramagnetic (1.7–1.8 μ_B). The unpaired electron is primarily localized on the azoheterocycle ligand in a predominantly azo-π* orbital, but a small metal contribution (^{185, 187}Re, I=5/2) is also present. Thus Re(CO)₃(MeCN)(L^•–) and Re(CO)₃(C₃H₄N₂)(L^•–) display six-line e.p.r. spectra (A ˜ 28 G). The line shapes and intensities are characteristic of the presence of g-strain. In the case of Re(CO)₃(PPh₃)(L^•–) seven nearly equispaced lines are observed due to virtually equal coupling between the metal and ³¹P (I=&frac;) nuclei. The g-values of the radical species are slightly higher than the free-electron value of 2.0023.     

New block copolymers V. Synthesis,characterization and morphological studies of poly(pentamethylene terephthalate)-b-(acrylonitrile butadiene rubber)

A block copolymer was prepared by low temperature polycondensation between (acid chloride)-terminated poly(pentamethylene terephthalate) as the hard block, and amine-terminated acrylonitrile-butadiene rubber, as the soft block. The polymer was characterized by nitrogen analysis, IR and NMR spectroscopy. The polymer showed two glass transition temperatures (T _g ) and exhibited two-phase morphology.     

Structurally characterized acylruthenium organometallics bearing a pendant aldehyde function

By reacting [Ru(RL¹)(PPh₃)₂(CO)Cl], (1) (R = C₆H₄Me, Et) with an excess of CNBu^t in the presence of NH₄PF₆, organometallics of the type [Ru(RL²)(PPh₃)₂(CNBu^t)₂]PF₆, (2) have been isolated in excellent yield [RL¹ = C₆H₂O-2-CHNHR(p)-3-Me-5, RL² = C₆H₂(CO)-O-2-CHNHR(p)-3-Me-5]. These organometallics, on controlled hydrolysis, produce [Ru(L³)(PPh₃)₂(CNBu^t)₂], (3) in very good yield (L³ = C₆H₂(CO)-O-CHO-3-Me-5). In both ([2(C₆H₄Me)] · 2H₂O) and ([3] · 2CH₂Cl₂) the two phosphine ligands lie in trans positions. In ([2(C₆H₄Me)] · 2H₂O) the Ru(C₆H₄MeL²) fragment, excluding the pendant tolyl ring, is a near perfect plane (mean dev ~ 0.02Å) which makes a dihedral angle of 5.2° with the tolyl plane. The acyl chelate ring in ([2(C₆H₄Me)] · 2H₂O) is excellently planar with a mean deviation of 0.006°. In ([3] · 2CH₂Cl₂) the Ru(L³) fragment defines a crystallographic plane of symmetry, the coordinates of the atom being of the type x, 1/4z. The complex ([2C₆H₄Me)] · 2H₂O) displays N–HȮFO (iminium-phenolato) hydrogen bonding while in ([3] · 2CH₂Cl₂) C–H...O hydrogen bonding is present. Characteristic spectral data (u.v.–vis, i.r. and ¹H n.m.r.) of the complexes are reported. A notable feature is that an allowed band near 500 nm due to the t_2g → π^*(azomethine) charge transfer transition, which is diagnostic of the coordinated iminium-phenolato function, is present in (3) but this band is absent in the aldehydic acyl complex (2). In the ¹H n.m.r. spectrum the N⁺–H signal in (2) (near 13.5 ppm) is split into a doublet due to transcoupling with the azomethine proton. The aldehydic proton of (3) resonates as a sharp singlet near 10 ppm. In CH₂Cl₂ solution (2) and (3) display quasireversible a Ru^III/Ru^IIcyclic voltammetric response with E_1/2 near 0.9 and 0.5 V versuss.c.e. The conversion (2) → (3) is accompanied by the nucleophilic attack of water. The complex (3) is also obtained directly from (1) by reaction with CNBu^t in the presence of H₂O. The aldehyde function in (3) is deactivated by the existing acyl moiety; as a result further decarbonylation does not take place.     

Fabrication of polyvinyl alcohol/chitosan oligosaccharide hydrogel: physicochemical characterizations and in vitro drug release study

Abstract

Hydrogel composites from polyvinyl alcohol and chitosan have been developed by various researchers as a function of their composition for various medical applications. Although, the solubility of chitosan in acidic solvents may limit its wide bioengineering applications. In this article, we demonstrate that polyvinyl alcohol-chitosan oligosaccharide (water soluble) to develop cross-linked hydrogel network using chemical cross linker. X ray diffraction, Fourier transform infrared spectroscopy, and wettability study of these hydrogels were also performed. Lomefloxacin drug was loaded into the hydrogels and its release profile was studied.     

Real time band selective F1‐decoupled proton NMR for the demixing of overlay spectra of chiral molecules

The small chemical shift dispersion and complex multiplicity pattern in proton NMR limit quantifications, for instance the determination of enantiomeric excess (ee) for an enantiomeric mixture. Herein, we present a simple proton–proton correlation experiment with band selective homonuclear (BASH) decoupling in both F₁ and F₂ dimensions, for the removal of scalar and residual dipolar couplings to provide collapsed singlet for each chemical site. The method has been demonstrated to separate the severely overlapped spectra of enantiomers using both chiral isotropic and anisotropic phases as well as a small biomolecule, particularly for the diastereotopic protons and also for the determination of ee. Copyright © 2016 John Wiley & Sons, Ltd.     

K2PdCl4 catalyzed efficient multicomponent synthesis of α-aminonitriles in aqueous media

An efficient, mild and environmentally friendly method has been developed for the Strecker reaction to synthesize α-aminonitriles in the presence of K₂PdCl₄ as a catalyst. The three-component one-pot condensation of an aldehyde, amine and trimethylsilyl cyanide proceeded smoothly in water to afford the corresponding product in high yield with short reaction times.     

Structure of marsileagenin a; A new hexahydroxy triterpene from marsilea minuta linn

The crude saponin obtainable from Marsilea minuta Linn on acid hydrolysis yielded a mixture of sapogenols. The major sapogenol named Marsileagenin A was found to be a hexahydroxy triterpene of oleanene series. From a study of various spectrometric data together with chemical reactions the structure of this sapogenol has been assigned as olean-12-ene-2α, 3β, 16β, 21β, 22α, 28-hexol (1a).     

Mixed equilibrium problems with relaxed \alpha -monotone mapping in Banach spaces

Using the KKM mapping technique, we obtain existence results for the mixed equilibrium problem (under the relaxed \(\alpha \)-monotonicity assumption on the bi-function) in a reflexive Banach space. Several examples are given to show that our definition of \(\alpha \)-monotonicity and, hence, our results are more general than that in the existing literature.