Assignment of absolute configuration of holadyson by computed NMR chemical shifts

The unassigned configurations of holadyson in the C8, C9, C13, C14, and C17 were assigned as S, S, R, S, and S, respectively. In this assignment, the extensive density functional theory calculations followed by chemical shift predictions were employed. Predicted chemical shifts were correlated to experimental ones to find the correct configuration, shown here.     

Determination of gauche and trans proton vicinal coupling constant Jg and Jt for 1,2-dichloropropane as a model compound for 1,2-disubstituted and 1,2,3-trisubstituted profanes

Variations in temperature and nature of solvent lead to changes in the population of the three rotamers of the title compounds in solution. The medium can be adjusted in this way so that either equality in the population of the three rotamers is reached, or the population of the conformer with two gauche interactions is decreased to near zero. These two limits are used to calculate J_t and J_g, for 1,2-dichloropropane.     

Neutron scattering studies of the structure of a highly tetrahedral form of amorphous carbon

The structure of amorphous carbon prepared by plasma-arc deposition has been determined by neutron scattering and analysed to estimate the fraction of tetrahedrally and trigonally bonded carbon. The mean value of the nearest neighbour C-C distance is close to that of crystalline diamond and a fit to the data for the first interatomic distance gives about 86% tetrahedral bonding. This form of diamond-like carbon therefore appears to be the structural equivalent of a-Si and a-Ge. A somewhat different interpretation is obtained from an analysis of the measured first and second peak coordination numbers and an attempt is made to reconcile the two approaches.     

Effects of monomer structure and imidization degree on mechanical properties and viscoelastic behavior of thermoplastic polyimide films

Two thermoplastic polyimides based on a common diamine (3,4′-ODA) were synthesized using different dianhydrides, namely ODPA and BPDA by a two step method. Molecular weight was controlled by using PA as an end capping agent. Effects of imidization degree on the mechanical properties and viscoelastic behavior of thermoplastic polyimide films were investigated. Film samples with varying degrees of imidization were characterized using FTIR, DMTA and tensile properties testing. It was found that two polyimides have different rates of imidization because of difference in monomer reactivity and molecular structure. It was observed that with an increase in imidization degree there was a decrease in thermoplastic response and a change in viscoelastic behavior from liquid-like to solid-like. With increase in imidization degree the tensile modulus and tensile strength of the films were increased, whereas elongation at break and tensile breaking energy were found to decrease after a certain imidization temperature.     

Sorption and thermodynamic behavior of zinc(II)-thiocyanate complexes onto polyurethane foam from acidic solutions

The uptake of Zn(II)-SCN complex onto polyurethane foam (PUF) has been investigated in detail with respect to different composition and variable concentration of electrolyte, zinc, thiocyanate ions and PUF, and equilibration time. The sorption data followed both Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms over the entire concentration range of zinc investigated whereas Freundlich sorption isotherm is obeyed upto 13.6^.10^-3M concentration. The Langmuir constants Q = 202±7 mmole^.g^-1 and of b = (1.78±0.31.10⁴ dm^3.mole^-1 and of D-R paraneter X _m = 493±1 mmole^.g^-1, b = activity coefficient = -0.028±0.0002 and of sorption energy E = 13.2±0.5 kJ^.mole^-1 and Freundlich constants 1/n = 0.42±0.03 and c _m = 6.47±1.7 mmole^.g^-1 were evaluated. The influence of temperature variation on sorption have yielded DH = -77.5±2.9 kJ^.mole^-1, DS = -5±0.09 J^.mole^-1.K^-1 and DG = -6.67±0.05 kJ^.mole^-1. The effect of common anions and cations on the sorption has been examined. Sulphate, ascorbate and bromide ions enhances the sorption to some extent whereas nitrite, Pb(II), Fe(III), Al(III), Cu(II) and Co(II) decrease to sorption significantly. A possible mechanism has been envisaged for Zn(II)-SCN sorption onto PUF.     

Benzohydrazides,benzothiohydrazides, and benzamidrazones as sources of 1,3,4(2H)-oxadiazolenones, 1,3,4(2H)-thiadiazolenones,and 1,2,4(5H)-triazolenones

Benzohydrazides, benzothiohydrazides, and benzamidrazones have been converted to 1,3,4(2H)-oxadiazolenones, 1,3,4(2H)-thiadiazolenenones, and 1,2,4(5H)-triazolenones respectively by reaction with ethyl chloroformate, with ethyl thiolchloroformate, and with phenyl isocyanate. In some reactions, a carbamate or urea has been isolated as intermediate.     

Characterization of copolymer hydroxybutyrate/hydroxyvalerate from saponified vernonia,soybean, and "spent" frying oils

Poly(beta-hydroxyalkanoate)s (PHAs) were biosynthesized by Ralstonia eutropha (formerly known as Alcaligenes eutrophus) by using saponified soybean, vernonia, and "spent" frying oils. These PHAs were isolated and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), gas chromatography/mass spectrometry (GC/MS), proton nuclear magnetic resonance spectrometry (1H NMR), and 2-dimensional homonuclear (1H-1H) correlation spectroscopy (COSY). The analytical results revealed that the PHAs produced from saponified vernonia and soybean oils were copolymers of hydroxybutyrate (HB) and hydroxyvalerate (HV), that is, P(HB/HV)s, whereas the saponified "spent" frying oil produced only poly(beta- hydroxybutyrate) (PHB) homopolymer. MALDI-MS, GC/MS, and NMR independently confirmed the composition of the PHAs. Saponified soybean oil and vernonia oil PHAs contained approximately 4 and 1% HV units, respectively. For comparison, commercial PHB and P(HB/HV), produced by R. eutropha by using glucose and a cosubstrate of glucose and propionic acid, respectively, as carbon sources, were similarly characterized.     

A facile synthesis of cytogenin (8‐hydroxy‐3‐hydroxymethyl‐6‐methoxyisocoumarin)

A facile and straightforward synthesis of cytogenin 1 (8‐hydroxy‐3‐hydroxymethyl‐6‐methoxyisocoumarin) metabolite of Streptoverticillium eurocidicum and Certocystis fimbriata has been achieved. Condensation of chloroacetyl chloride with 3,5‐dimethoxyhomophthalic acid 2 directly furnished 3‐chloromethyl‐6,8‐dimethoxyisocoumarin 3 which was hydrolyzed to 6,8‐dimethoxy‐3‐hydroxymethylisocoumarin 4 using 0.05% aqueous sodium hydroxide in THF. Regioselective demethylation of 4 yielded cytogenin 1 . In model experiments, 3‐chloromethylisocoumarin was prepared and converted into 3‐hydroxymethyl isocoumarin.