Interfacial and intrafacial linkage isomerizations of rhenium complexes with aromatic molecules

The mechanisms for the interconversion of facial diastereomers of a variety of TpRe(CO)(L)(eta(2)-L(Ar)) complexes [L = (t)BuNC, pyridine (py), PMe(3), or 1-methylimidazole (MeIm); L(Ar) = benzene, anisole, naphthalene, 1-methylpyrrole, furan, or thiophene; Tp = hydridotris(pyrazolyl)borate] have been investigated by (1)H NMR spin saturation experiments. In addition, the rates and free energies of activation for these processes were calculated from spin saturation experiments and T(1) measurements. The operative mechanisms for interconversion of the pi diastereomers were found to be nondissociative, undergoing either an interfacial or intrafacial linkage isomerization. A comparison of the kinetic parameters for isomerization of related eta(2)-olefin complexes of the [TpRe(CO)(PMe(3))] and [CpRe(NO)(PPh(3))](+) fragments is also presented.     

Effect of total percent polyacrylamide in capillary gel electrophoresis for DNA sequencing of short fragments. A phenomenological model.

Polyacrylamide capillary gels were prepared with constant (5% C) cross-linker concentration and with total acrylamide concentration ranging from 2.5 to 6% T. At each acrylamide concentration, peak spacing was constant for DNA sequencing fragments ranging from 25 to 250 nucleotides in length. Peak spacing increased linearly with the total acrylamide concentration. The intercept of the retention time vs. fragment length plot was independent of % T. Ferguson plots were constructed for short DNA fragments; the polyacrylamide pore size falls in the 2.5 to 3.5 nm range for the gels studied. Theoretical plate count is independent of total acrylamide concentration; longitudinal diffusion, and not thermal gradients, limit the plate count. A phenomenological model is presented that predicts retention time, plate count, and resolution for sequencing fragments ranging in size from 25 to 250 bases and gels that range from 2.5 to 6% total acrylamide.     

Effects of various triamines on cell-free polypeptide synthesis of Escherichia coli and on growth of its polyamine auxotrophs

The effects of various synthetic triamines having a general structure, H2N(CH2)xNH(CH2)yNH2, where x = 2-5 and y = 2-8 (abbreviated, x-y; with 3-4 being spermidine itself), on poly(U)-directed polypeptide synthesis of Escherichia coli and on growth of its polyamine-requiring mutants were examined in comparison with those of spermidine. Except for 2-2 and 2-3, all of the triamines stimulated more or less polypeptide synthesis at suboptimal Mg2+ concentrations, but the Mg2+ concentration required for the maximal stimulatory effect was different for each triamine. The degree of maximal stimulation caused by 3-3 (norspermidine), 4-4 (homospermidine), or 4-5 was nearly comparable with that by spermidine. The acetylspermidines were inactive, however, they inhibited the spermidine-stimulated polyphenylalanine synthesis. Many of the triamines examined reduced the ratio of leucine to phenylalanine incorporation into polypeptides during poly(U)-directed translation, and the degree of this effect did not necessarily correspond with that of the stimulatory effect. Moreover, 2-4, 2-5, 3-3 and 4-4 could stimulate the growth of a polyamine auxotroph of E. coli, MA 261, as effectively as did spermidine. However, 3-3 was the only triamine which could fully replaced spermidine in promoting growth of a mutant strain, KK 101, which is more dependent on polyamines than MA 261. Thus, these results demonstrated that some synthetic triamines were as active as spermidine in eliciting these effects, and also that there were some differences among these effects in the structural requirement for triamine.     

On the calculation of the exciton ZFS hamiltonian for organic molecular crystals

The method of calculating exciton ZFS constants and ZFS tensor principla axes in the theoretical framework of Sternlicht and McConnell is presented. The molecular ZFS hamiltonians are transformed into a common coordinate system and averaged, and the ZFS tensor is then diagonalized. Results are presented for benzene, naphthalene, anthracene, tetracene, phenanthrene, fluorene, and coronene, and compared with experimental values where available.     

A high-resolution micro-gel system for analyzing small amounts of protein with a wide diversity of molecular weights

We have used a micro-gel system to analyze the proteins in extracts of amphibian neurulae. Maximum band separation and resolution was achieved by using a dissociating discontinuous buffer with gels made of a discontinuous gradient of acrylamide.     

On the thin cell method in time domain spectroscopy

A simple physical picture is given of Fellner-Feldegg's thin cell method in time domain spectroscopy. From this picture an accurate analytical relation is derived for the total reflection coefficient.     

Reaktionen von π-Organokomplexen des Nickels mit tertiären Phosphanen

Reactions of π-Organonickel Complexes with Tertiary Phosphanes In a hexane solution Ni(C₅H₅)₂ reacts with PBu₃ or Ph₂PBu forming the nickel(O) complexes Ni(PBu3)₄ or Ni(Ph₂PBu)₄ (A). Under the same conditions only one cyclopentadienyl ligand is substituted by PhPBu₂ and the nickel(I) compound (C₅H₅)Ni (PhPBu₂)₂ (B) is obtained. Products of the reactions between B and α,α′-dipyridyl, hydrogen chlorid in ether, or Ni(PhPBu₂),Cl₂ are Ni(dipy)₂, [PhPHBu₂]₂[NiCl₄], or (C₅H₅) Ni(PhPBu₂)₂Cl. By the reaction with HgCl₂ a cyclopentadienyl compound of an unknown structur is formed. The compound Ni(PhPBu₂)₄ which is analogous to A is synthesized by the reduction of bis(acety1acetonato)-nickel with Et₂AlOEt in the presence of PhPBu₂ or by the reaction of bis (cyclooctadiene-1,5)-nickel with PhPBu₂.     

Potential acting on the trapped electron

If the absorption of a trapped electron can be shown to correspond to bound—free transitions, it should be possible to calculate the potential acting on the trapped electron inversely from its absorption spectrum. In this paper we present the method of calculating the potential acting on a trapped electron from the observed absorption spectrum.     

Low temperature absorption spectra of TcO 4 − and ReO 4 − in KClO4

The low temperature spectra of TcO ₄ ^– and ReO ₄ ^– both show two band systems with pronounced vibrational structures. The bands are identified as¹ A ₁¹ T ₂ transitions. No other bands are observed with certainty. It seems likely that the KClO₄ crystals contain KReO₄ crystallites. They are therefore not pure mixed crystals. It is concluded that the virtual orbital (2e) used in the construction of the low lying states resembles an atomic nd orbital more and more when going from n=3, Mn to n=5, Re.

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Zusammenfassung Die Tieftemperaturspektren von TcO ₄ ^– und ReO ₄ ^– zeigen beide zwei Bandensysteme mit ausgeprägten Schwingungsstrukturen. Die Banden werden als ¹ A ₁¹ T ₂-Übergänge identifiziert. Keine anderen Banden werden mit Sicherheit beobachtet. Es scheint wahrscheinlich, daß die KClO₄-Kristalle KReO₄-Kristallite enthalten und deswegen keine reinen Mischkristalle sind. Es wird geschlossen, daß das virtuelle Orbital (2e), welches zur Konstruktion der tiefliegenden Zustände gebraucht wird, in der Reihe n=3, Mn bis n=5, Re immer weitgehender einem nd-Atomorbital ähnelt.

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Nachwuchsstipendiat, Schweizerischer Nationalfonds.     

Synthesis of 8,9-dialkoxy-substituted tetrahydrobenz[h] isoquinolines

6,7-Dimethoxy-2-naphthylethylamine, prepared by the diborane reduction of 6,7-dimethoxy-2-naphtlialeneacetamide, underwent a Pictet-Spengler cyclization to form 8,9-dimethoxy-1,2,3,4-tetrahydrobenz[h]isoquinoline. This compound is identical with that obtained by reduction of the corresponding dihydrobenzisoquinoline prepared from formamide cyclization. 6,7-Dialkoxy-2-naphthaleneacetic acids, the key intermediates for the preparation of these amides, were obtained from 6,7-dialkoxy-2-acetonaphthones by a modified Willgerodt reaction.