Structural Investigations on Poly(4-hydroxy-L-proline). 2. Physicochemical Studies

We report experimental studies which confirm our prediction, namely that the ordered structure of poly(hydroxypro1ine) in solution corresponds to a left-handed helical structure with intrachain hydrogen bonds. The CD studies show that the poly(hydroxypro1ine) molecule has essentially the same conformation in aqueous solution and in the film obtained subsequently by evaporation. X-ray diffraction patterns of the sample in this form (B form) have been recorded at different relative humidities. The patterns recorded at relative humidities over 66% can be interpreted in terms of a helical structure with intrachain hydrogen bonds. These results lead us to conclude that the ordered conformation of poly(hydroxypro1ine) in solution is form B and not form A. This offers a simple explanation for the greater stability of the poly(hydroxypro1ine) helix in solution as compared to the poly(pro1ine) form I1 helix and also for the absence of mutarotation for poly(hydroxypro1ine).

Structural Investigations on Poly(4-hydroxy-L-proline). 1. Theoretical Studies

Model building studies on poly(hydroxypro1ine) indicate that in addition to the well-known helical structure of form A, a left-handed helical structure with trans peptide units and with h = 2.86 A and n = 2.67 (i.e., 8 residues in 3 turns) is also possible. In this structure which is shown to be in agreement with X-ray data of the form B in the next paper, the y-hydroxyl group of an (i + 1)th Hyp residue is hydrogen bonded to the carbonyl oxygen of an (i - 1)th residue. The possibility of a structure with cis peptide units is ruled out. It is shown that both forms A and B are equally favorable from considerations of intramolecular energies. Since form B is further stabilized by intrachain hydrogen bonds, we believe that this is likely to be the ordered conformation for poly(hydroxypro1ine) in water.

Miscibility of poly(phenyl acrylate) with acrylonitrile/styrene copolymers

The Blase transition and phase behavior of blends of poly(pheny1 acrylate) with poly(acrylonitri1eco-styrene) was studied by differential scanning calorimetry. It was found that poly(pheny1 acrylate) is miscible with poly(acrylonitri1e-co-styrenes) within a specific range of copolymer composition. The segmental interaction parameters were estimated and found to be positive for all three pairs. The miscibility in thissystem appears to be the consequence of the intramolecular repulsion between styrene and acrylonitrile units.

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.

Nuclear-quadrupole resonance in coordination chemistry- identification of bridiging and therminal chlorines in the mercuric chloride-4-picoline n-oxide complex

The temperature dependence of the chlorine-35 n.q.r. in the mercuric chloride-4-picoline N-oxide complex has been studied from 77 K to room temperature, and the results are used to assign the observed frequencies to terminal and bridging chlorines.

New methods for the Preparation of Nitrosyl Chloride

A pure sample of nitrosyl chloride has been prepared either by reaction of phosphorus trichloride with concentrated nitric acid or by reaction of phosphorus trichloride with sodium nitrate in presence of water. The nitrosyl chloride gas has been characterized by i.r. spectral data and elemental analysis.

New Concepts for PVC Detection

A new scheme is proposed for the detection of premature ventricular beats, which is a vital function in rhythm monitoring of cardiac patients. A transformation based on the first difference of the digitized electrocardiogram (ECG) signal is developed for the detection and delineation of QRS complexes. The method for classifying the abnormal complexes from the normal ones is based on the concepts of minimum phase and signal length. The parameters of a linear discriminant function obtained from a training feature vector set are used to classify the complexes. Results of application of the scheme to ECG of two arrhythmia patients are presented.

Poly propyl ether imine (PETIM) dendrimer: A novel non-toxic dendrimer for sustained drug delivery

In the present study, an attempt was made to study the acute and sub-acute toxicity profile of G3-COOH Poly (propyl ether imine) PETIM] dendrimer and its use as a carrier for sustained delivery of model drug ketoprofen. Drug-dendrimer complex was prepared and characterized by FTIR, solubility and in vitro drug release study. PETIM dendrimer was found to have significantly less toxicity in A541 cells compared to Poly amido amine (PAMAM) dendrimer. Further, acute and 28 days sub-acute toxicity measurement in mice showed no mortality, hematological, biochemical or histopathological changes up to 80 mg/kg dose of PETIM dendrimer. The results of study demonstrated that G3-COOH PETIM dendrimer can be used as a safe and efficient vehicle for sustained drug delivery. (C) 2010 Elsevier Masson SAS. All rights reserved.

Mesoporous Carbon and Poly(3,4-ethylenedioxythiophene) Composite as Catalyst Support for Polymer Electrolyte Fuel Cells

In situ polymerization of 3,4-ethylenedioxythiophene with sol-gel-derived mesoporous carbon (MC) leading to a new composite and its subsequent impregnation with Pt nanoparticles for application in polymer electrolyte fuel cells (PEFCs) is reported. The composite exhibits good dispersion and utilization of platinum nanoparticles akin to other commonly used microporous carbon materials, such as carbon black. Pt-supported MC-poly(3,4-ethylenedioxythiophene) (PEDOT) composite also exhibits promising electrocatalytic activity toward oxygen reduction reaction, which is central to PEFCs. The PEFC with Pt-loaded MC-PEDOT support exhibits 75% of enhancement in its power density in relation to the PEFC with Pt-loaded pristine MC support while operating under identical conditions. It is conjectured that Pt-supported MC-PEDOT composite ameliorates PEFC performance/durability on repetitive potential cycling. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3486172] All rights reserved.

Estimation Of Charge Transport Parameters And Equivalent Circuit For Poly Alkyl Thiophene Field-Effect Transistors

The small signal ac response is measured across the source-drain terminals of organic field-effect transistors (OFET) under dc bias to obtain the equivalent circuit parameters of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) and poly(3-hexyl thiophene) (P3HT) based devices. The numerically simulated response based on these parameters is in good agreement with the experimental data for PBTTT-FET except at low frequencies, while the P3HT-FET data show significant deviations. This indicates that the interface with the metal electrode is rather complex for the latter, involving additional circuit elements arising from contact impedance or charge injection processes. Such an investigation can help in identifying the operational bottlenecks and to improve the performance of OFETs.

Chemical toughening of epoxies. I. Structural modification of epoxy resins by reaction with hydroxy-terminated poly (butadiene-co-acrylonitrile)

In an attempt to toughen the epoxy resin matrix for fiber-reinforced composite applications, a chemical modification procedure of a commercially available bisphenol-A-based epoxy resin using reactive liquid rubber HTBN [hydroxy-terminated poly(butadiene-co-acrylonitrile)] and TDI (tolylene diisocyanate) is described. The progress of the reaction and the structural changes during modification process are studied using IR spectroscopy, viscosity data, and chemical analysis (epoxy value determination). The studies support the proposition that TDI acts as a coupling agent between the epoxy and HTBN, forming a urethane linkage with the former and an oxazolidone ring with the latter. The chemical reactions that possibly take place during the modification are discussed.

Kinetics of sono-photooxidative degradation of poly(alkyl methacrylate)s

The mechano-chemical degradation of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and poly(n-butyl methacrylate) (PBMA) using ultrasound (US), ultraviolet (UV) radiation and a photoinitiator (benzoin) has been investigated. The degradation of the polymers was monitored using the reduction in number average molecular weight (M-n) and polydispersity (PDI). A degradation mechanism that included the decomposition of the initiator, generation of polymer radicals by the hydrogen abstraction of initiator radicals, reversible chain transfer between stable polymer and polymer radicals was proposed. The mechanism assumed mid-point chain scission due to US and random scission due to UV radiation. A series of experiments with different initial M-n of the polymers were performed and the results indicated that, irrespective of the initial PDI, the PDI during the sono-photooxidative degradation evolved to a steady state value of 1.6 +/- 0.05 for all the polymers. This steady state evolution of PDI was successfully predicted by the continuous distribution kinetics model. The rate coefficients of polymer scission due to US and UV exhibited a linear increase and decrease with the size of the alkyl group of the poly(alkyl methacrylate)s, respectively. (C) 2010 Elsevier B.V. All rights reserved.