And form vs. content

Duplessix et al. used water vapor pressure isotherm (i.e., water uptake vs external relative humidity) data combined with simultaneous isotherm differential microcalorimeter analysis to determine the average heat of absorption per water molecule for 1200 EW acid form samples. Hysteresis was seen between sorption and subsequent desorption curves at 25 °C, and nonzero water content remained at zero relative humidity, indicating the presence of tightly... 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

Polymeric materials also form in Miller-Urey reactions, by both spark discharge (Miller, 1955) and UV irradiation (Sagan and Khare, 1979). These materials have not been studied in detail, but the elemental" analyses show high N contents (36% and 11%, vs. 2.4% for Murchison and 1.23% for FTT polymer). The H/C ratios also are higher (1.28 and 1.23, vs. 0.70 and 0.78), suggesting a predominantly aliphatic and/or alicyclic, rather than aromatic, structure. 

In a subsequent study, van Hal et al. [40] reported that a decrease in cholesterol content in liquid state bilayers, which increases bilayer fluidity, resulted in an increase in estradiol transport across SC. With confocal laser scanning microscopy, Meuwissen et al. examined the diffusion depth of gel- vs. liquid-state liposomes labeled with fluorescein-dipalmitoylphosphatidylethanolamine (fluorescein-DPPE) with human skin in vitro [41] (Figure 3) and rat skin in vivo [42] and found that the lipophilic label when applied in liquid-state bilayers onto the skin penetrated deeper into the skin than when applied in gel-state liposomes. Recently, Fresta and Puglisi [43] reported that corticosteroid dermal delivery with skin-lipid liposomes was more effective than delivery with phospholipid vesicles, both with respect to higher drug concentrations in deeper skin layers and therapeutic effectiveness. This is a very surprising result, because skin lipid liposomes are rigid and form stacks of lamellae on the surface of the skin [44]. From the previously mentioned studies it seems clear that the thermodynamic state of the bilayer plays a crucial role in the effect of vesicles on dmg transport rate across skin in vitro. 

Initial velocity studies were conducted in the presence of a number of dead-end inhibitors of NAD and DNA binding. Nicotinamide, a product of the reaction which acts as a dead-end inhibitory analog of NAD, is competitive vs NAD (Fig. 2, cf. [3]) and noncompetitive vs DNA (not shown). NADH exhibits similar kinetic properties and is competitive vs NAD (not shown) and noncompetitive vs DNA (Fig. 3). Both monomeric and polymeric dead-end inhibitory analogs of DNA behaved similarly. Thymidine (Fig. 4) and poly(dT) (data not shown) are both competitive vs DNA. The polymeric form is seven times more effective as an inhibitor based on total thymine content (Kj values of 5 juM vs 35 juM)- On a per molecule of inhibitor basis the difference is even more striking, the poly(dT) being more than 1000 times more effective than thymidine. Both poly(dT) (Fig. 5) and thymidine (data not shown, cf [3]) also exhibited competitive kinetics vs NAD. 

For Cr-containing catalysts, the stabilizing effect of Ce and La is not so evident, since Cr ions appeared to be weak mineralizations at their content less than 10% and the temperatures below 1273 K [8]. When Cr is supported on Ce-containing alumina, the stabilizing effect of cerium is enhanced by Cr. The quantity of a-Al203 formed vs Cr concentration with respect to the absolute value becomes comparable with La effect (Fig.l, A, B). 

The validity of the conclusion regarding the reaction scheme can be verified from Figure 5, which plots relative moles of each species vs time. There is a rapid rise in monoadduct and diadduct content initially. Shortly after initial mixing, a rapid decrease in monoadduct with a significantly slower decline in diadduct content is seen. Triadduct is slow to form and slow to react. 

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