Studies on pre-hump and main fractions of cellulose-2,5-acetate in acetone

Technical cellulose-2.5-acetates (CA 2.5) were characterized regarding their carbohydrate composition in comparison to the raw material. The association of the CA 2.5 samples in acetone was studied by size exclusion chromatography (SEC) using various acetone grades and styrene divinylbenzene copolymer columns. In HPLC grade acetone with and without addition of 1% water up to three different pre-humps eluted in front of the main fraction of the polymer. The evaluation of the main peak by light scattering measurements resulted in high molar masses indicating that for these technical CA 2.5 samples even the main fraction is not dissolved without association. No pre-humps or association phenomena were observed after addition of 1 ppm LiBr to HPLC grade acetone or with p.a. grade acetone. In addition pre-hump enriched and pre-hump free fractions were isolated by fractionated precipitation. The carbohydrate composition of these fractions was determined and correlated with their association pattern in SEC investigations.     

Zur Berechnung Stekloffscher Eigenwerte

Zusammenfassung Es wird ein neues Verfahren zur numerischen Berechnung des ersten nichttrivialen Stekloffschen Eigenwertes beschrieben. Dieses Verfahren arbeitet nur mit oberen Schranken.

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We describe a new procedure for the numerical evaluation of the first nontrivial Stekloff eigenvalue. This procedure works only with upper bounds.

     

Susceptibility to Effects of UVB Irradiation on Induction of Contact Sensitivity, Relevance of Number and Function of Langerhans Cells and Epidermal Macrophages

Sensitization on skin exposed to acute low-dose UVB irradiation separates normal humans into two phenotypically distinct groups: One group, following sensitization on UVB-irradiated skin, develops contact sensitivity, designated UVB resistant (UVB-R) and the second group, following sensitization on UVB-irradiated skin, fails to develop contact sensitivity, designated UVB susceptible (UVB-S). To investigate whether UVB susceptibility in humans is related to antigen-presenting activity in the skin we studied the effect of UVB irradiation on the number and function of the epidermal antigen-presenting cells in volunteers identified as UVB-R and UVB-S. Single cell suspensions of epidermal cells from control skin and skin exposed to 3 minimal erythema doses (MED) of UVB 3 days previously were stained for Langerhans cells (CD1a+HLA-DR+) and epidermal macrophages (CD1a-HLA-DR+). The UVB exposure of the skin significantly decreased the percentage of Langerhans cells (UVB-R: n = 7, P < 0.02, UVB-S: n = 6, P < 0.03) and increased the percentage of epidermal macrophages (UVB-R: n = 7, P < 0.03, UVB-S: n = 6, P < 0.03) however to the same degree in both the UVBR and the UVB-S group. To study the effect on Langerhans cell alloreactivity, epidermal cells were harvested immediately after UVB irradiation. However, in both UVB-R and UVB-S subjects the Langerhans cell alloreactivity was blocked to the same degree immediately after UVB irradiation compared to nonirradiated epidermal cells. To determine the effect of UVB irradiation on epidermal macrophages, epidermal cells were harvested 3 days after UVB irradiation. Irradiated epidermal cells from both UVB-R and UVB-S subjects demonstrated a strong antigen-presenting capacity compared to epidermal cells from control skin leading to activation of T cells that mainly secrete interferon (1FN)-γ and not interleukin (IL)-4. In conclusion we found that UVB susceptibility was not correlated with the number of Langerhans cells or epidermal macrophages in the skin at the same time of sensitization. Neither was it correlated with the capacity of Langerhans cells nor UVB-induced epidermal macrophages to activate T cells in vitro.     

Darstellung und Kristallstruktur von Cs2Sb4S7

Preparation and Crystal Structure of Cs₂Sb₄S₇ The first thioantimonite of Cesium has been synthesized and its crystal structure determined. The substance crystallizes monoclinic with spacegroup P2₁/_c. The lattice constants are a = 1111.2(5) pm, b = 1227.1(5) pm, c = 1163.7(5) pm and ß = 97.60(5)°. There are four formula units in the unit cell. Sb–S chains are formed by trigonal SbS₃ pyramids and ψ-trigonal SbS₄ bipyramids.     

The vitamin D3 pathway in human skin and its role for regulation of biological processes

The skin is the only tissue yet known in which the complete ultraviolet-B (UV-B)-induced pathway from 7-dehydrocholesterol to hormonally active calcitriol (1alpha,25-dihydroxyvitamin D(3)) occurs under physiological conditions. Epidermal synthesis of calcitriol could be of fundamental relevance because calcitriol regulates important cellular functions in keratinocytes and immunocompetent cells. Because of their antiproliferative and prodifferentiating effects, calcitriol and other vitamin D analogs are highly efficient in the treatment of psoriasis vulgaris. The known antipsoriatic effect of UV-B light could, at least in part, be mediated via UV-B-induced synthesis of calcitriol. In addition, mounting evidence indicates that cutaneous vitamin D(3) synthesis is of high importance for the prevention of a broad variety of diseases, including various malignancies. New but controversially discussed sun-protection guidelines were established for the prevention of internal cancers. A better understanding of the metabolism of vitamin D in the skin opens new perspectives for therapeutic applications of vitamin D analogs.     

Two new 5-deoxyflavones from Albizia odoratissima

Two new 5-deoxyflavones, 7,8-dimethoxy-3',4'-methylenedioxyflavone (1) and 7,2',4'-trimethoxyflavone (2) together with a known flavone, 7,4'-dimethoxy-3'-hydroxyflavone (3) were isolated from the rootbark of Albizia odoratissima. The structures of these new compounds were elucidated by electrospray ionization mass spectrometry (ESI-MS) and 1D and 2D-NMR spectral studies including (1)H-(1)H correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and nuclear Overhauser enhancement spectroscopy (NOESY).     

Total synthesis of dictyodendrin B

A concise total synthesis of dictyodendrin B (1) is reported, a scarce marine alkaloid endowed with promising telomerase inhibitory activity. Key steps of the chosen route are a reductive cyclization of ketoamide 11 to indole 12 mediated by low-valent titanium (from TiCl3 and KC8) followed by a photochemical 6pi-electrocyclization, which was performed in the presence of Pd/C and nitrobenzene to effect concomitant dehydrogenation/aromatization of the product initially formed. Regioselective bromination of the resulting pyrrolocarbazole 13 followed by lithium/bromine exchange and quenching of the resulting organolithium species with p-methoxybenzaldehyde installed the side chain at C2. Oxidation of the benzylic alcohol 15 thus obtained to ketone 17 was best achieved with catalytic amounts of tetra-n-propylammonium perruthenate (TPAP) and N-methylmorpholine-N-oxide (NMO) in dilute CH2Cl2 solution to avoid the formation of undue amounts of the unsymmetrical dimer 16. Ketone 17 was elaborated into the natural product by selective cleavage of the isopropyl ether with BCl3, introduction of the sulfate moiety with the aid of trichloroethyl chlorosulfuric acid ester, deprotection of all lateral methyl ether groups, and final reductive cleavage of the trichloroethyl ester moiety. The spectroscopic data of synthetic dictyodendrin B thus formed matched those of an authentic sample in all regards. Moreover, it was shown that global deprotection of the peripheral -OH groups in pyrrolo[2,3-c]carbazole 13 is accompanied by spontaneous air-oxidation to form the quinone core of dictyodendrin C.