Novel materials for non‐ablative optical recording

Abstract

Communications polyelectrolytes including poly-L-glutamate, can be explained on the basis of the model proposed by Addadi et al.L4I These authors demonstrated that the P-sheet structure of the polyaspartate adsorbed on solid substrate is essential in order to induce (001)-oriented calcite nucleation by matching the charged groups of the polymer and the intercationic distances in the crystal lattice of the salt. It follows that the [3-sheet structure should be assumed by the exposed stretches of poly-L-aspartate on the surface of the gelatin films, while for the other polyelectrolytes considered the electrostatic interactions do not seem to be dictated by structural factors.Gelatin containing polyelectrolytes can be considered a versatile system for the planning of new films with tailor made surfaces. In fact, this system overcomes the compatibility problem between inert matrix and water-soluble polyelectrolytes or protein generally associated with biological mineralization. Furthermore, the nature, density and structural disposition of the charged groups on the surface can be regulated in a simple way by changing the kind and the amount of the polyelectrolytes in the film. ExperimentalType A gelatin from porcine skin was used (G-2500). The sodium salts of poly-L-aspartic acid (P-5387, average M.w. = 9900), poly-L-glutamic acid (P-4636, average M.Iv. = 6100). sulfate chondroitine A (C-8529) and C (C-4384) and carrageenan K (C-1263) were supplied by Sigma Co.3.0mlofa2% aqueousgelatinsolutioncontainingfrom5x 10-'to5 x lo-' weight percent (relative to gelatin) of polyelectrolyte was used to fill a Petri dish (diameter = 5 cm) on the bottom of which the film was obtained after water evaporation at room temperature. 5.0 ml of a 5 % glutaraldehyde solution in phosphate buffer (pH = 7.5) were placed on the film for 24 h. The films kept on the bottom of the dishes were thoroughly washed three times with water, dialyzed for 24 h against 3.0 ml of a l mM CaC1, solution to obtain calcium salts, and then washed again with water and dried. The air-dried films were 22 pm thick.Calcite crystals were grown, as reported by Addadi et a1.[4], at a temperature of 18 _+2 "C by very slow diffusion of (NH,),CO, vapor in the dishes, containing 2.9 ml of a 7.5 mM CaCI, solution. The crystals obtained after different times, up to four days, were examined by optical and scanning electron microscopy and X-ray powder diffraction. Crystals were counted under a microscope ( x 40) and nucleation density (crystals per cm2) was averaged over the total surface of the film (19.6 cm'). The (001) oriented crystals were identified by the hexagonal symmetry in two dimensional projection down the c axis.

Positive Halogens from Halides and Hydrogen Peroxide with Organotellurium Catalysts

“…However, the addition of cyclohexene to the mixture containing 8 does not lead to regeneration of the starting catalyst 3 with the formation of 4b and 5b in the time frame of the bromide experiments above. Studies of the thermal reductive elimination of halogen from 7 and 8 have shown that the Te−Cl bond is stronger than the Te−Br bond. , The poorer catalysis observed in the chloride reactions may be due to competitive formation of chlorine oxidative-addition products, which only slowly regenerate the Te(II) state of the catalyst.…”

Chalcogen(IV)−Chalcogen(II) Redox Cycles. 1. Halogenation of Organic Substrates with Dihaloselenium(IV) and -tellurium(IV) Derivatives. Dehalogenation of Vicinal Dibromides with Diaryl Tellurides

“…Experimental verification of these predictions has come from reductive elimination and halogen exchange reactions. The bond strengths of Te(IV) dihalides have been measured by the rates of reductive elimination of halogen from Te(IV) dihalides 23 and 24 . , In these reactions, the Arrhenius energy of activation, E A , for reductive elimination of bromine from 23 is 4 kcal mol -1 lower than E A for reductive elimination of chlorine from 24 . The rates of tellurium−halogen exchange between diphenyltellurium dihalides and diphenyl telluride suggest that the bond strengths of the Te−X bonds decrease in the following order: Te−F > Te−Cl > Te−Br > Te−I .…”

Correlation of Structure with Crystalline to Amorphous Phase Transitions of 1,3,6-Substituted Fulvene-Derived Molecular Glasses

“…For example, amorphous solid dispersions, drug formulations composed of active pharmaceutical ingredients dispersed in an amorphous glassy matrix, have been shown to improve important variables of biological drug efficacy such as transport and dissolution. − The value of the glassy state has also been exploited for incorporating liquid crystal mesogens into low molecular weight matrices for information storage materials . Randomly organized, glassy materials have also been used as host matrices to lock in chromophore guests in the design of optoelectronic materials. − More recently, small molecules have been designed for well-defined fluorescent glasses, nonlinear optics, charge transporting devices, and radioluminescence . Related to fulvenes of interest to this work, it has been reported that 1,2,3,4-tetraphenyl substituted fulvenes exhibited T g ’s of over 100 °C, and correlate with the nature of the 6-substituent (Figure ).…”