Thermally stimulated luminescence and conductivity — Additional tools for thermal analysis of polymers

The physical phenomena underlying thermally stimulated luminescence and conductivity measurements, logically considered as complementary to conventional thermal analysis measurements, are outlined. The equipment and samples required to make such measurements are briefly described, and the basic concepts underpinning the interpretation of the data sketched. Some recent experimental data, chosen to reflect the sensitivity of thermally stimulated luminescence and conductivity to doping of the sample and changes in its morphology, are presented and discussed.

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Zusammenfassung Es werden diejenigen physikalischen Erscheinungen umrissen, auf denen Messungen von thermisch stimulierter Lumineszenz und Leitfähigkeit basieren, die logisch als ergänzend zu herrkömmlichen thermoanalytischen Messungen betrachtet werden. Zur Durchführung von Messungen dieser Art benötigte Einrichtungen und Proben werden kurz beschrieben und Grundbegriffe für die Interpretierung der experimentellen Ergebnisse skizziert. Einige frühere experimentelle Daten, die ausgewählt wurden, um die Empfindlichkeit der thermisch stimultierten Lumineszenz und Leitfähigkeit gegenüber Dopen der Probe bzw. Vernäderungen in ihrer Morphologie zu verdeutlichen, werden vorgestellt und diskutiert.

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This review was written during my stay at the Institute for Molecular Science as Visiting Professor. I wish to thank Professors Y. Maruyama and H. Inokuchi for their thoughtful hospitality, and the Japanese Ministry of Education Science and Culture for financial assistance.     

Pre-irradiation treatments for CR-39 detectors

The production of track-spots in CR-39 detectors for alpha particles and the subsequent optical counting of the detectors are often influenced by foreign substances deposited on the surface of the detectors. The removal of these substances can be achieved using chemicals for pre-irradiation treatment. Two methods of pre-irradiation treatment were studied in the present experiments. One of them involves the dipping of the detectors in ethanol. In the other method, the detectors were treated in 6N KOH etchant prior to exposure. It was found that prolonged treatment could only produce a reduction in the track density of less than 20%.     

A Convenient One-Step Gingerol Synthesis

Racemic 6-gingerol can be obtained in a one-pot reaction by hexanal addition to the dianion of zingerone at low temperature. Similarly, addition of octanal or decanal to the dianion provides 8-gingerol or 10-gingerol, respectively. Acid treatment of the gingerols allows for formation of the corresponding shogaols.     

Synthesis and anticancer properties of RGD peptides conjugated to nitric oxide releasing functional groups and abiraterone

A series of analogues of the integrin binding aspartic acid-glycine-arginine (RGD) peptide sequence were synthesised conjugated to nitric oxide (NO) donating functional groups. Also the cytotoxicity of abiraterone, a prostate cancer drug, was explored when it was conjugated in three part constructs to RGD sequences and NO releasing heterocycles. In general the analogues showed integrin binding affinity comparable to RGD reference compounds, and all released NO by the Griess test assay. Two analogues exhibited significant cytotoxic effects against PC3 and MCF7 cell lines.     

Electrical Conductivity in Poly(vinyl Chloride)

Conductivity and Seebeck coefficient measurements have been made on commerically-available molded PVC samples containing a range of impurities and on much purer specimens recast from tetrahydrofuran solution. Activation energies measured in the latter materials were not very reproducible; it seems likely that the evaporation of gold electrodes thermally initiates a dehydrochlorination reaction which renders the samples unstable. A range of activation energies from 1.4 to 1.8 eV was observed in the impure samples. The Seebeck coefficient measurements indicated that the majority carriers were negatively charged; the linearity of the current-voltage relationship up to applied field strengths of 80,000 V/cm then suggested an electronic conduction mechanism, although considerable polarization effects were observed in both pure and impure samples. The Seebeck coefficient results also showed that even the purest PVC obtainable is unlikely to be an intrinsic semiconductor, and that the electron transport mechanism probably corresponds more closely to the small polaron hopping model than to the conventional energy-band formation model commonly applied to inorganics.     

Prediction of Heat Shield Performance in Terms of Epoxy Resin Structure

Abstract

High-strength, readily processable, char-forming, insulative materials are being sought for application in ablative heat shields for re-entry vehicles. Toward this end, the family of epoxy resins has been evaluated. The structure of epoxy resins and curing agents in terms of their functionality, aromaticity, and chemical nature is discussed in relation to its effect on ablative properties. The concept of controlled, constructive thermal degradation is extremely important in ablative epoxide compositions. Bridged Diels-Alder adducts based upon cyclic dienes and maleic anhydride perform well as epoxy resin curing agents in this respect. The mechanism of thermal ablative degradation of these systems is discussed in terms of in situ thermal control and char-forming reactions. The position of attachment of glycidyl groups, as well as the nature and position of other sub-stituents around the aromatic nucleus, has little effect in general upon the ablative properties of epoxy resins. Thermal and ablative data of both benzene and naphthalene derivatives are given. A new epoxy resin based upon 2-nitro resorcinol has been synthesized. This resin gives significant char increases, both quantitatively and qualitatively, over conventional epoxides. The unusual mechanism of polymerization and thermal degradation of this resin is discussed.     

Membrane Proteins Have Distinct Fast Internal Motion and Residual Conformational Entropy

The internal motions of integral membrane proteins have largely eluded comprehensive experimental characterization. Here the fast side‐chain dynamics of the α‐helical sensory rhodopsin II and the β‐barrel outer membrane protein W have been investigated in lipid bilayers and detergent micelles by solution NMR relaxation techniques. Despite their differing topologies, both proteins have a similar distribution of methyl‐bearing side‐chain motion that is largely independent of membrane mimetic. The methyl‐bearing side chains of both proteins are, on average, more dynamic in the ps–ns timescale than any soluble protein characterized to date. Accordingly, both proteins retain an extraordinary residual conformational entropy in the folded state, which provides a counterbalance to the absence of the hydrophobic effect. Furthermore, the high conformational entropy could greatly influence the thermodynamics underlying membrane‐protein functions, including ligand binding, allostery, and signaling.     

beta-Siloxy unsaturated nitriles: stereoselective cyclizations to cis- and trans-decalins

[formula: see text] beta-Siloxy unsaturated nitriles are excellent precursors to enolate and nitrile anions that cyclize to cis- and trans-decalins, respectively. The stereoelectronic requirements of endocyclic enolates and exocyclic nitrile anions are complementary, providing cis- and trans-decalins from a common intermediate. This cyclization allows the synthesis of diastereomeric cis- and trans-decalins containing a contiguous array of quaternary-tertiary-quaternary stereocenters.