Metal Chelates in Vinyl Polymerization: Kinetics and Mechanism of Acrylonitrile Polymerization Initiated by Cu(I1) Imine Complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(I1) 4-anilino 3-pentene 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(I1) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCld), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 22 at two different temperatures and in different solvents. The square-root dependence of R, on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formatign was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

Stereochemistry of Peptides Containing 1-AminocyclopentanecarboxylicA cid ( Am5): Solution and Solid-state Conformations of Boc-Acc '-Acc'-NHMe

The conformational analysis of a protected homodipeptide of 1-aminocyclopentanecarboxylic acid (Acc5) has been carried out. 1H-nmr studies establish a -turn conformation for Boc-Acc5-Acc5-NHMe in chloroform and dimethylsulfoxide solutions involving the methylamide NH in an intramolecular hydrogen bond. Supportive evidence for the formation of an intramolecular hydrogen bond is obtained from ir studies. X-ray diffraction studies reveal a type III -turn conformation in the solid state stabilized by a 4 1 hydrogen bond between the Boc CO and methylamide NH groups. The , values for both Acc5 residues are close to those expected for an ideal 310-helical conformation ( ± 60°, ±30°).

Solid-State Acyl Migration In Salicylamides - An X-Ray Study Of The Ortho-Propionyl And Normal-Propionyl Derivatives

In recent years there has been an upsurge of interest in the study of organic reactions in the solid state. It is now realised that the crystalline matrix provides an extra-ordinary spatial control on the initiation and progress of these reactions. Electronic and dipolar effects which are important in solution are replaced by structural and geometric effects in solids. These 'spatial' or 'topochemical' aspects are important in understanding the mechanistic details of the reaction. In our laboratory, the thermally induced acyl migration in salicylamides from 0- to N- position in the solid state has been under study (Scheme 1). The structures of the acetyl and benzoyl derivatives (Ia,IIa, Ib and IIb) have been reported.

Conformations of the amino aterminal tetrapeptide of emerimicins and antiamoebins in solution and in the solid state

The conformations of Boc-l-Phe-(AiB)3-OH (1) and Boc-l-Phe-(Aib)3-OMe (2) which correspond to the amino terminal sequence of the emerimicins and antiamoebins have been studied in solution using 270 MHz 1H n.m.r. In dimethyl sulphoxide solution both peptides show the presence of two strongly solvent shielded Aib NH groups, consistent with a consecutive β-turn conformation, involving the Aib(3) and Aib(4) NH groups in intramolecular 4 → I hydrogen bonds. This folded conformation is maintained for 2 in chloroform solution. Nuclear Overhauser effect studies provide evidence for a Type II Phe-Aib β-turn. An X-ray diffraction study of Boc-(d,l)-Phe-(Aib)3-OH establishes a single type III(III′) β-turn conformation with Aib(2)-Aib(3) as the corner residues. A single intramolecular 4 → I hydrogen bond between Phe(I) CO and Aib(4) NH groups is observed in the crystal. The solution conformation may incorporate a consecutive type II-III′ structure for the Phe(1)-Aib(2)-Aib(3) segment, with the initial type II β-turn being destabilized by intermolecular interactions in the solid state.

Crystallization kinetics of poly(l-lactic acid)

The morphology and crystal growth of poly(l-lactic acid), PLLA have been studied from the melt as a function of undercooling and molecular weight using hot stage microscopy. Attention has been given to the application of growth rate equation on the growth rate data of PLLA and thus various nucleation parameters have been calculated. The criteria of Regime I and Regime II types of crystallization has been applied for the evaluation of substrate lengths.

An infrared spectroscopic study of the phase transitions of crystalline aromatic donor-acceptor complexes involving a pseudoplastic state

Variable temperature i.r. spectroscopic studies of weak pi-donor-pi-acceptor complexes in the crystalline state indicate that the complexes undergo order-disorder transitions, the disorder being caused by molecular motion. Thermodynamic data on the phase transitions along with the spectral data suggest that the high-temperature crystalline forms of the complexes are likely to be pseudoplastic.

Lead-acid batteries for partial-state-of-charge applications

2 V/40 Ah valve-regulated lead-acid (VRLA) cells have been constructed with negative plates employing carbon black as well as an admixture of carbon black fumed silica as additives in negative active material for partial-state-of-charge (PSoC) applications. Electrical performance of such cells is compared with conventional 2 V/40 Ah VRLA cells for PSoC operation. Active material utilization has been found to be higher for carbon-black fumed-silica mixed negative plates while formation is faster for cells with carbon-black mixed negative plates. Both faradaic efficiency and percentage capacity delivered have been found to be higher for cells with carbon-black + fumed-silica mixed negative plates. However, a high self-discharge rate is observed for cells with carbon-black + fumed-silica mixed negative plates.

Constitutive modeling of shape memory alloy wire with non-local rate kinetics

A constitutive modeling approach for shape memory alloy (SMA) wire by taking into account the microstructural phase inhomogeneity and the associated solid-solid phase transformation kinetics is reported in this paper. The approach is applicable to general thermomechanical loading. Characterization of various scales in the non-local rate sensitive kinetics is the main focus of this paper. Design of SMA materials and actuators not only involve an optimal exploitation of the hysteresis loops during loading-unloading, but also accounts for fatigue and training cycle identifications. For a successful design of SMA integrated actuator systems, it is essential to include the microstructural inhomogeneity effects and the loading rate dependence of the martensitic evolution, since these factors play predominant role in fatigue. In the proposed formulation, the evolution of new phase is assumed according to Weibull distribution. Fourier transformation and finite difference methods are applied to arrive at the analytical form of two important scaling parameters. The ratio of these scaling parameters is of the order of 10(6) for stress-free temperature-induced transformation and 10(4) for stress-induced transformation. These scaling parameters are used in order to study the effect of microstructural variation on the thermo-mechanical force and interface driving force. It is observed that the interface driving force is significant during the evolution. Increase in the slopes of the transformation start and end regions in the stress-strain hysteresis loop is observed for mechanical loading with higher rates.

Partial purification and properties of a transamidinase from Lathyrus sativus seedlings. Involvement in homoarginine metabolism and amine interconversions

A transamidinase was purified 463-fold from Lathyrus sativus seedlings by affinity chromatography on homoarginine--Sepharose. The enzyme exhibited a wide substrate specificity, and catalysed the reversible transfer of the amidino groups from donors such as arginine, homoarginine and canavanine to acceptors such as lysine, putrescine, agmatine, cadaverine and hydroxylamine. The enzyme could not be detected in the seeds, and attained the highest specific activity in the embryo axis on day 10 after seed germination. Its thiol nature was established by strong inhibition by several thiol blockers and thiol compounds in the presence of ferricyanide. In the absence of an exogenous acceptor, it exhibited weak hydrolytic activity towards arginine. It had apparent mol.wt. 210000, and exhibited Michaelis--Menten kinetics with Km 3.0 mM for arginine. Ornithine competitively inhibited the enzyme, with Ki 1.0 mM in the arginine--hydroxylamine amidino-transfer reaction. Conversion experiments with labelled compounds suggest that the enzyme is involved in homoarginine catabolism during the development of plant embryo to give rise to important amino acids and amine metabolites. Presumptive evidence is also provided for its involvement in the biosynthesis of the guanidino amino acid during seed development. The natural occurrence of arcain in L. sativus and mediation of its synthesis in vitro from agmatine by the transamidinase are demonstrated.

Enzyme-catalysed non-oxidative decarboxylation of aromatic acids: I.Purification and spectroscopic properties of 2,3 dihydroxybenzoic acid decarboxylase from Image Image

In order to understand the molecular mechanism of non-oxidative decarboxylation of aromatic acids observed in microbial systems, 2,3 dihydroxybenzoic acid (DHBA) decarboxylase from Image Image was purified to homogeneity by affinity chromatography. The enzyme (Mr 120 kDa) had four identical subunits (28 kDa each) and was specific for DHBA. It had a pH optimum of 5.2 and Km was 0.34mM. The decarboxylation did not require any cofactors, nor did the enzyme had any pyruvoyl group at the active site. The carboxyl group and hydroxyl group in the Image -position were required for activity. The preliminary spectroscopic properties of the enzyme are also reported.

Cyclic Peptide Disulfides - Solution And Solid-State Conformation Of Boc-Cys-Pro-Aib-Cys-S-S-Bridge-Nhme,A Disulfide-Bridged Peptide Helix

The solution and solid-state conformations of the peptide disulfide Boc-Cys-Pro-Aib-Cys-NHMe have been determined by NMR spectroscopy and X-ray diffraction. The Cys(4) and methylamide NH groups are solvent shielded in CDCI3 and (CD,),SO, suggesting their involvement in intramolecular hydrogen bonding. On the basis of known stereochemical preferences of Pro and Aib residues, a consecutive @-turn structure is favored in solution. X-ray diffraction analysis reveals a highly folded 310 helical conformation for the peptide, with the S-S bridge lying approximately parallel to the helix axis, linking residues 1 and 4. The backbone conformational angles are Cys(1) 4 = -121.1', $ = 65.6"; Pro(2) 4 = -58.9', 4 = -34.0'; Aib(3) 4 = -61.8', $ = -17.9'; Cys(4) 4 = -70.5', $ = -18.6'. Two intramolecular hydrogen bonds are observed between Cys(1) CO--HN Cys(4) and Pro(2) CO--HNMe. The disulfide bond has a right-handed chirality, with a dihedral angle (xss) of 82'.

Estrogen modulation of retinol-binding protein in immature chicks: Comparison with riboflavin carrier protein

The kinetics of estrogen (E) modulation of retinol-binding protein (RBP) production in the liver of immature chicks were compared with those governing de novo induction of riboflavin carrier protein (RCP) in the same tissue. A single dose of E markedly enhanced the plasma levels of RBP without any detectable lag period to reach peak value by 24 h and this was followed by a decline to attain the baseline by 4 days. There was no amplification of the response during secondary stimulation unlike the case with RCP induction. With multiple E administration, the 4-fold increased plasma RBP concentrations were sustained at a steady state during both primary and secondary stimulations, whereas concomitant RCP concentration progressively increased with each hormone administration and this response was further amplified during secondary stimulation. Unlike RCP induction, enhanced RBP accumulation was not strictly E dose dependent although a minimal threshold level of the steroid was required to elicit measurable response. Progesterone (P) could neither modulate nor substitute for E in enhancing plasma levels of either of the 2 proteins while the anti-estrogens, en- and zuclomifene citrate severely suppressed the production of both the proteins. RCP induction was completely inhibited by both α-amanitin and cycloheximide for prolonged periods while E-stimulated RBP production was affected only partially by α-amanitin. Likewise, cycloheximide inhibition of RBP accumulation followed a pattern similar to that of hepatic general protein synthesis.

Enzymic synthesis of sym-homospermidine in Lathyrus sativus (grass pea) seedlings

An enzyme catalysing the synthesis of sym-homospermidine from putrescine and NAD+ with concomitant liberation of NH3 was purified 100-fold from Lathyrus sativus (grass pea) seedlings by affinity chromatography on Blue Sepharose. This thiol enzyme had an apparent mol.wt. of 75000 and exhibited Michelis-Menten kinetics with Km 3.0mM for putrescine. The same enzyme activity could also be demonstrated in the crude extracts of sandal (Santalum album) leaves, but with a specific activity 15-fold greater than that in L. sativus seedlings.

Kinetics of Extraction of Iron(II1) by Bis(2-ethylhexyl Phosphate in a Laminar Liquid-Liquid Jet Reactor

The kinetics of iron(II1) extraction by bis(Zethylhexy1) phosphate (HDEHP, HA) in kerosene from sulfuric acid solutions has been studied in a liquid-liquid laminar jet reactor. The contact time of the interface in this reacting device is of the same order of magnitude as the surface renewal time in dispersion mixing and much less than that obtained in the relatively quiescent condition of the Lewis cell. Yet the analysis of the data in this study suggested a rate-controlling step involving surface saturation quite in conformity with that obtained in the Lewis cell and not with that in dispersion mixing as reported in the literature. Further, the mechanism suggested a weaker dependence of the rate on hydrogen ion concentration which was reported by other workers.