The "quasi-thermal" mechanism for electron beam damage of n-paraffins

Electron diffraction patterns from epitaxially grown microcrystals of n-hexatriacontane, which are slightly damaged by the electron beam, strongly resemble those from the same material when it is warmed just below the pre-melt hexagonal phase. The identity of these diffraction patterns, which display a marked attenuation of lamellar 001 reflections but much less alteration of the strongest reflections, implies that both processes occur via the induction of chain defects which, in turn, generate chain-end voids in the crystal packing. Such defects, however, need not be identical for the two events. With warming they are probably the gtg-1 kink and the gauche chain conformers identified by infrared spectroscopy. The creation of trans vinylene groups during radiation damage will also increase chain flexibility, and perhaps induce the production of gtg-1 kinks.

Thermal decomposition of amorphous beta-lactam antibacterials

Thermal decomposition rates for amorphous samples of penicillin G potassium, cephalothin sodium, cefamandole sodium, and cefamandole nafate were determined as a function of water content and temperature. Even when rigorously dry, amorphous cephalosporins were at least one order of magnitude less stable than the corresponding unsolvated crystalline form. Absorbed water generally increased both the number of decomposition products and the net decomposition rate. Reaction kinetics were usually apparent first order, but an anomalously high effective reaction order was observed in several systems. Nonlinear Arrhenius plots were observed, and a qualitative model based on molecular relaxation in glayses is proposed. Although decomposition rates at 25 degrees were small for dry samples, even slight decomposition produced visually detectable changes. Thus, the unsolvated crystalline form was noticeably more stable, even at 25 degrees.