CS+(B2Σ+ → A 2Πi) fluorescence from penning excitation of CS

The energy transfer reation of He(2³S) + CS was studied spectroscopically in a flowing afterglow apparatus. The CS⁺(B²Σ⁺ → A ²Π_i) transition is identified via three members of the Δν = 0 sequence (406–415 nm). The spin-orbit splitting of the (0, 0) band of CS⁺(A ²Π_i) is 301 ± 5 cm^?1. A weak emitting system (280–340 nm) is tentatively identified as CS⁺(B²Σ⁺→ X²Σ⁺).     

Cyclopentadienyl-ruthenium and -osmium chemistry: XXVIII. Reactions and isomerisation of 1,2-bis(methoxycarbonyl)ethenyl complexes: X-ray structures of Ru{Z)-C(CO2Me)CH(CO2Me)} -(CO)(PPh3)(η-C5H5) · 0.5EtOH,Ru{(E)-C(CO2Me)CH(CO2Me)}(dppe)(η-C5H5) and Ru{C(CO2Me)C(CO2Me)C(CO2Me)CH(CO2Me)} - (PPh3)(η-C5H5)

A reinvestigation of the reaction between C₂(CO₂Me)₂ and RuH(PPh₃)₂(η-C₅H₅) and some related complexes is reported. Initial cis addition is followed by conversion into the trans isomer. In the case of the bis-(PPh₃) complex, isomerisation is followed by chelation of the ester CO group with concomitant displacement of one PPh₃ligand. The resulting chelate complex reacts with CO or CNBu^t to give the (Z)-RuC(CO₂Me)CH(CO₂Me) complexes; the (E)-isomer of the carbonyl complex is obtained by addition of C₂(CO₂Me)₂to RuH(CO)(PPh₃)(η-C₅H₅). The ^1Hand ¹³C NMR spectra are not a reliable guide to assignment of the stereochemistry of the vinyl group. Other products isolated from the initial reaction are the bis-insertion product $\text{Ru{C(CO}{}_2\text{Me)C(CO}{}_2\text{Me)C(CO}{}_2\text{Me)}$CH(CO₂Me)} -(PPh₃)(η-C₅H₅) and the 1/2 PPh₃/C₂(CO₂Me)₂ adduct. The molecular structures of Ru{(Z)-C(CO₂Me)CH(CO₂Me)}(CO)(PPh₃(η-C₅H₅) · 0.5EtOH, Ru{(E)-C(C₂Me)CH(CO₂Me)}(dppe)(η-C₅H₅) and $\text{Ru{C(CO}{}_2\text{Me)C(CO}{}_2\text{Me)C(CO}{}_2\text{-Me)}$CH(CO₂Me)}(PPh₃)(η-C₅H₅) have been determined. The cis isomer is monoclinic, space group P2₁,with a 9.328(8), b 17.385(10), c 10.356(7) Å, β 101.78(3)° and Z = 2; 2107 data with I ≥ 2.5σ(I) were refined to R = 0.076 R_w = 0.085. The trans isomer is triclinic, space group P$\text{1}$, with a 10.404(7) b 11.221(6), c 13.230(9) Å, α 92.67(5), β 110.56(5), γ 106.21(5)° and Z = 2; 2520 data with I ≥ 2.5σ(I) were refined to R = 0.055 R_w = 0.068. The butadienyl complex is monoclinic, space group P2₁/a, with a 19.655(8), b 8.674(4), c 21.060(5) Å, β 116.22(3)° and Z = 4; 2724 data with I ≥ 2.5σ(I) were refined to R = 0.042, R_w = 0.047.     

Energy migration in novel pH-triggered self-assembled beta-sheet ribbons

Energy migration between tryptophan residues has been experimentally demonstrated in self-assembled peptide tapes. Each peptide contains 11 amino acids with a Trp at position 6. The peptide self-assembly is pH-sensitive and forms amphiphilic tapes, which further stack in ribbons (double tapes) and fibrils in water depending on the concentration. Fluorescence spectra, quenching, and anisotropy experiments showed that when the pH is lowered from 9 to 2, the peptide self-assembly buries the tryptophan in a hydrophobic and restricted environment in the interior of stable ribbons as expected on the basis of the peptide design. These fluorescence data support directly and for the first time the presence of such ribbons which are characterized by a highly packed and stable hydrophobic interior. In common with Trp in many proteins, fluorescence lifetimes are nonexponential, but the average lifetime is shorter at low pH, possibly due to quenching with neighboring Phe residues. Unexpectedly, time-resolved fluorescence anisotropy does not change significantly with self-assembly when in water. In highly viscous sucrose-water mixtures, the anisotropy decay at low pH was largely unchanged compared to that in water, whereas at high pH, the anisotropy decay increased significantly. We concluded that depolarization at low pH was not due to rotational diffusion but mainly due to energy migration between adjacent tryptophan residues. This was supported by a master equation kinetic model of Trp-Trp energy migration, which showed that the simulated and experimental results are in good agreement, although on average only three Trp residues were visited before emission.     

Synthesis of a homoleptic niobium(V) thiolate complex and the preparation of niobium sulfide via thio "sol-gel" and vapor phase thin-film experiments

Reaction of [Nb(NMe(2))(5)] with 10 equiv of 2,6-Me(2)C(6)H(3)SH in toluene results in the formation of red crystals of [Nb(SC(6)H(3)Me(2)-2,6)(5)]. Crystal structure analysis of [Nb(SC(6)H(3)Me(2)-2,6)(5)] showed that the niobium center adopts a distorted trigonal bipyramidal geometry. Niobium disulfide, NbS(2), has been successfully prepared via a thio "sol-gel" process using [Nb(SC(6)H(3)Me(2)-2,6)(5)] as the metal source. In contrast, vapor phase thin-film studies revealed that [Nb(SC(6)H(3)Me(2)-2,6)(5)] functions as a single-source precursor to NbS films.     

Structure and synthesis of physoperuvine: x-ray crystal and molecular structures of the n-benzoyl derivatives of (±)-3- and (+)-4-methylaminocycloheptanone

Single-crystal X-ray analyses have defined the structures and solid-state conformations of (±)-N-benzoyl-3-methylaminocycloheptanone [(±)-$\text{3}$]and (+)-N-benzoyl-4-methylaminocycloheptanone [(±)$\text{4}$]. Resolution of (±)-[4- methylaminocycloheptanone α 1-hydroxytropane]to yield the (+)-enantiomer. Identical in all respects with the free base from natural (+)-physoperuvine, was achieved via the di-p-toluoyl-(+)-tartrate salt.     

Bismuth-catalyzed benzylic oxidations with tert-butyl hydroperoxide

[reaction: see text] Oxidation of alkyl and cycloalkyl arenes with tert-butyl hydroperoxide catalyzed by bismuth and picolinic acid in pyridine and acetic acid gave the corresponding benzylic ketones (48-99%). Alternatively, oxidation of methyl arenes gave the corresponding substituted benzoic acids (50-95%). Preliminary mechanistic studies were consistent with a radical mechanism rather than a bismuth(III)-bismuth(V) cycle.     

Synthesis of a transition metal-dithionite complex, (η5-C5H5)(CO)2FeS(O)2S(O)2Fe(CO)2(η5-C5H5)

The reaction of Na[η⁵-C₅H₅Fe(CO)₂] with large excess of SO₂ in THF at ?78°C followed by warming to room temperature affords an iron—dithionite complex, (η⁵-C₅H₅)(CO)₂FeS(O)₂S(O)₂Fe(CO)₂(η⁵-C₅H₅).     

Synthesis of substituted 3-amino[6,5-b]triazinoindoles

4-[(9-Methyl-as-triazino[6,5-b]indol-3-yl)amino]-2-methyl-2-butanol ( 13 ) and the corresponding 2-methyl-3-imino derivative 12 were synthesized and tested in vitro against Rhino 2 virus. The two compounds were more active than the known triazino[5,6-b]indole 4 . 2,9-Dimethyl-3-methoxy-9H-as-triazino[6,5-b]indolium tosylate ( 21 ) and the related 3-methylthio compound 9 were prepared. Quaternary 21 formed a pseudo base, 22a , whereas quaternary 9 did not form a pseudo base.     

PROPERTIES OF THE ULTRAVIOLET-LIGHT-MEDIATED BINDING OF BOVINE SERUM ALBUMIN TO DNA*

Abstract— The binding of DNA to protein mediated by U V (254 nm) radiation has been investigated using binding of the complex to Millipore membrane filters as an assay technique. The reaction proceeds through an activated protein intermediate which then reacts with the DNA. The activated protein has a half-life of about 75 min at 0°C and about 18 min at 37°C. Short wavelengths are more efficient in forming the complex than wavelengths in the 250–280 nm range. N-ethyl maleimide treatment of protein before irradiation markedly inhibits the reaction.     

The [2 + 4] Diels-Alder cycloadditon product of a probable dialuminene,Ar'AlAlAr' (Ar' = C(6)H(3)- 2,6-dipp(2); dipp = C(6)H(3)-2,6-Pr(i)(2)), with toluene

Reduction of Ar'AlI2 (Ar' = Ar'= C6H3-2,6-Dipp2; Dipp = C6H3-2,6-Pri2) with KC8 in diethyl ether most probably affords the first "dialuminene", Ar'AlAlAr'; it was characterized by its reaction with toluene which yielded a [2 + 4] cycloaddition product incorporating the Ar'AlAlAr' unit.