Simultaneous binding of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin and 4',6-diamidino-2-phenylindole at the minor grooves of poly(dA).poly(dT) and poly[d(A-T)(2)]: fluorescence resonance energy transfer between DNA bound drugs

The spectral properties of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) bound to poly(dA).poly(dT) and poly[d(A-T)(2)] in the presence and in the absence of 4',6-diamidino-2-phenylindole (DAPI) have been studied. DAPI fits deeply into the minor groove of both poly(dA).poly(dT) and poly[d(A-T)(2)], and TMPyP is also situated at the minor groove. The nature of the absorption, circular dichroism (CD), and flow linear dichroism (LD) spectra of the TMPyP-poly(dA).poly(dT) and -poly[d(A-T)(2)] complexes in the Soret band is essentially unaffected whether the minor groove is blocked by DAPI or not, although small variations been noticed in the presence of DAPI. Furthermore, a close analysis of the reduced LD spectrum in the Soret band results in angles of approximately 80 degrees and 55 degrees between transition moments of the TMPyP and DNA helix axes in the absence of DAPI. All these observations indicate that the side of TMPyP whose structure resembles that of classical minor groove binding drugs does not fit deeply into the minor groove. This suggests that TMPyP binds across the minor groove: two positively charged pyridiniumyl rings interact electrostatically with negatively charged phosphate groups of DNA. When DAPI and TMPyP are simultaneously bound to poly(dA).poly(dT) or poly[d(A-T)(2)], the fluorescence intensity of DAPI decreases as TMPyP concentration increases, indicating that the excited energy of DAPI is transferred to TMPyP.     

An abstract approach to evaporation models in rarefied gas dynamics

An efficient algorithm is presented for determining the unique solvability of certain one-dimensional stationary transport problems. The non-existence of stationary evaporation states with supersonic drift velocities for one and three dimensional BGK model is recovered.

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Sommario È presentato un algoritmo efficiente per determinare la solubilità univoca di alcuni probiemi unidimensionali di trasporto stazionario. È ripresa la non esistenza di stati stazionari di evaporazione con velocità di deriva supersoniche per modelli BGK a una e tre dimensioni.

     

Synthesis of 2‐(1‐methyl‐1,2,5,6‐tetrahydropyridin‐3‐yl)benzimidazoles

A useful approach for the synthesis of pharmacologically active tetrahydropyridinylbenzimidazoles is described. 2‐Pyridin‐3‐ylbenzimidazoles 3a‐d have been synthesized by condensation of 3‐pyridinecarbox‐aldehyde 1 with substituted 1,2‐phenylenediamines 2a‐d following oxidative cyclization with iodobenzene diacetate. Methylation of 3a‐d with iodomethane and potassium hydroxide, subsequent formation of methylpyridinium salts 4a‐d and 7a‐d and reduction thereafter afforded tetrahydropyridinylbenzimidazoles 5a‐d and 8a‐d .     

(2S,3R,4S,5R)‐Diethyl 2‐(10,10‐dimethyl‐3,3‐dioxo‐3λ6‐thia‐4‐azatricyclo[5.2.1.01,5]decan‐4‐ylcarbonyl)‐5‐phenylpyrrolidine‐3,4‐dicarboxylate: a novel isomorphous‐by‐addition compound

The title compound, C₂₇H₃₆N₂O₇S, (I), is isomorphous by addition with the dimethyl ester analogue [Garner, Dogan, Youngs, Kennedy, Protasiewicz & Zaniewski (2001). Tetrahedron, 57 , 71–85], (II), by replacing two methyl ester H atoms with two methyl groups. With the exception of the conformation of one of the ester groups, the molecules are almost superimposable. Likewise, apart from a slightly larger c axis in (I), few differences in the cell packing of (I) and (II) are found, with both dominated by the same C—H...O hydrogen bonds. Full synthetic and spectroscopic details of (I) are given. The molecular synthesis is important as an example of chiral auxiliary‐assisted 1,3‐dipolar cycloaddition of an azomethine ylid.     

Thermoreversible covalent crosslinking of maleated ethylene/propylene copolymers with diols

The objective of this study is the thermoreversible crosslinking of maleated ethylene/propylene copolymer (MAn‐g‐EPM) using the equilibrium reaction with diols. Covalent hemi‐ester crosslinks are formed via the reaction of anhydrides with alcohols, while an equilibrium shift at elevated temperatures may result in their removal. High conversions to hemi‐ester are obtained at low temperatures in the presence of p‐toluenesulfonic acid, whereas conversions are low at high temperatures. The presence of microphase‐separated aggregates acting as physical crosslinks was demonstrated for MAn‐g‐EPM and all crosslinked materials. The covalent crosslinks were only formed within the aggregates, resulting in stronger aggregates that persisted to higher temperatures. The tensile strength and elasticity were significantly improved upon increasing level of crosslinking, whereas the type of diol has less influence. The covalently crosslinked MAn‐g‐EPM was reprocessable via compression molding at temperatures above 175 °C. Irreversible diester formation occurred for the longer diols, but did not prevent reprocessing, while short diols evaporated. Both effects lowered the level of crosslinking, resulting in significantly changed mechanical properties. The reprocessability does not originate from an equilibrium shift, but from a dynamic exchange between crosslinked and non‐crosslinked functional groups, which allows crosslinks to disconnect and the corresponding chain segments to diffuse between aggregates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1810–1825, 2008     

Homolgation of β-silyl-α,β-unsaturated esters

Treatment of β-trimethylsilyl-α,β-unsaturated esters with diazomethane results in a stereospecific homolgation to the corresponding γ-trimethylsilyl-α,β-unsaturated esters.