Equivalent electric circuit analyses of ionic thermocurrent in sodium-doped CaF2 crystals

The characteristics of high-temperature ionic thermocurrent (HT ITC) in CaF₂ doped with different sodium concentrations were studied by the Teflon-insulated electrode ITC method. It was shown that, with increasing sodium concentration, the HT ITC band moved toward a Na⁺-F_V dipole band with a peak at 162 K. The results of analyses of the HT ITC spectra using an equivalent electric circuit proved that the activation energy of space charge migration related to HT ITC was also strongly dependent on the doped sodium concentrations if varied from 0.94 to 0.46 eV with increasing sodium concentration in our ITC study. In addition, the broadening of the Na⁺-F_V dipole band was observed in 3 nominal mole% NaF-doped CaF₂, which was accompanied by a considerable decrease of the activation energy from 0.46 to 0.29 eV without showing marked temperature shifts of the peak ITC bands.     

Direct measurement of electron transport features in cytochrome c via V–I characteristics of STM currents

The morphology of and electron tunneling through single and cluster cytochrome c molecules deposited on self-assembled dodecanthiol monolayer film on a gold substrate have been studied experimentally using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. STM images of a single cytochrome c molecule revealed a globular structure with a diameter of 4 nm and height of 1.5 nm. A spectroscopic study obtained by recording tunneling current–bias voltage (V–I) curves revealed that the STM current increases stepwise at asymmetric threshold sample bias voltages of +100 mV and –200 mV.     

Conformational behavior on 2,2,3-trisubstituted 1,2,3,4-tetrahydroquinoline alkaloids,virantmycin, benzastatins,and their congeners,evaluated by semi-empirical molecular orbital calculations

The conformational behaviors on ring inversion between two half-chair conformers a and b in physiologically active 2,2,3-trisubstituted 1,2,3,4-tetrahydroquinoline alkaloids, virantmycin ( 1 ), benzastatin C ( 6 ), benzastatin D ( 7 ), and their congeners 2–5 , which were revealed by their nmr studies have been quantitatively evaluated by semi-empirical molecular orbital calculations (PM3). The geometries of respective half-chair conformers a and b in compounds 1–7 were optimized and it was found that their thermodynamic distributions are approximately valid in comparison with the coupling constants observed in their nmr experiments. Furthermore, these calculations estimated the energy barriers for ring inversion in compounds 1–7 in the range of ca. 4.86–11.13 kcal/mol, which were compatible with rapid interconversions between a and b at room temperature.     

Effects of manifold components on peak profiles in flow-injection analysis

The effects of pumps, mixing coils and joints on the peak profiles in flow-injection analysis are described. Four reciprocating pumps, three peristaltic pumps, single coils and double coils with helix diameters of 0.4–3 cm and two types of mixing joint were examined. When pumps yielding small pulsations and double coils with small helix diameter were used, well defined and reproducible peaks were obtained and the effects of mixing joints were small.     

Magnetic behavior and Mossbauer spectra of spin-crossover pyrazolate bridged dinuclear diiron(II) complexes: X-ray structures of high-spin and low-spin [(Fe(NCBH3)(py))2(mu-bpypz)2

The synthesis and characterization of new spin-crossover pyrazolato bridged dinuclear [(FeII(NCS)(py))2(mu-bpypz)2] and the corresponding cyanotrihydroborato-kappaN complexes are described together with the X-ray crystal analysis of the latter in both the high-spin and low-spin states as well as the variable temperature magnetic susceptibility and/or Mossbauer spectra demonstrating the spin-crossover which exhibits an one-step process, but not a two-step one characteristic of the known bpym bridged dinuclear complexes.     

Enhanced transdermal delivery of zidovudine in rats and human skin

Zidovudine (azidothymidine, AZT), a potent antiviral agent acting on acquired immunodeficiency syndrome virus, was examined with regard to permeation through rat and human skin. A steady state plasma concentration of AZT after transdermal application in rats estimated from both pharmacokinetics data after i.v. administration and penetration rate through excised rat skin from 10% oleic acid (OA) aqueous solution shows penetration about 85 times higher compared to that from 10% OA would be needed for therapeutic efficacy. A mixed-solvent system consisted of 5% Sefsol-318 (S-318), 10% OA, 10% N-methyl-2-pyrrolidone (MP), 20% propylene glycol (PG) and water showed promising characteristics as a vehicle in terms of permeability of AZT through excised rat skin. The maximum flux of 0.41 mumol/cm2/h was observed in excised human skin after application of a gel formulation including S-318, OA, MP and PG. The result suggests a possible use of the gel formulation to gain an effective plasma concentration in humans.     

Surface tension of polymer solutions II. Poly- γ-benzyl-L-glutamate in N,N-dimethylformarnide,dioxane and dichloracetic acid solutions

Summary The time, dependence of the surface tension of poly--benzyl-L-glutamate in dimethylformamide, dioxane, and dichloracetic acid solutions was measured. A comparison of the initial and final surface tension value permits conclusions for models of PBLG molecules present in the surface. DMF and dioxane solutions show a peak in the -concentration curve which can be explained by a transition. Coils of PBLG molecules in dichloracetic acid solution are unable to extend on the surface.

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Zusammenfassung Es wurde die Zeitabhängigkeit der Oberflächenspannung von Poly--benzyl-L-glutamat in Dimethyl-formamid-, Dioxan- und Dichloressigsäurelösungen gemessen. Ein Vergleich der Anfangs- und Endwerte der Oberflächenspannung gestatter Modellvorstellungen für die PBLG-Moleküle in der Oberfläche. DMF-und Dioxanlösungen zeigen ein Maximum in der -Konz.-Kurve, das auf einen Übergang hinweist. Knäuel von PBLG-Molekülen in Dichloressigsäurelösung Können sich nicht in der Oberfläche ausstrecken.

     

On the heat of solution of polymer with solvent: Polydimethylsiloxane–solvent systems

Heats of mixing and excess volumes at infinite dilution have been obtained at 25°C. for polydimethylsiloxane or its lower oligomers in various solvents by using a twin conduction microcalorimeter and from the pycnometric specific volumes. From those values, excess energies ΔE^M_v at constant volume have been determined. The prediction on intramolecular conformation contributions to the heat of solution as proposed by Bianchi has been evaluated by the values of ΔE^M_v. The heat of solution in the polymer–solvent systems was interpreted by the expression for ΔE^M_v derived from the Van Laar-Hildebrand work on simple liquid mixtures with the solubility parameters of polymers obtained from indirect measurements. The values of conformational intramolecular energy change calculated from dilute solution properties were difficult to rationalize with our results. Our present results suggest that systems in a nonideal state can not be distinguished for certain from those in the ideal state. This conclusion based on apparent values does not deny the possible effect of the conformational energy change.