Total synthesis of (+)-belactosin A

A concise first total synthesis of the antitumour antibiotic belactosin A is reported, involving coupling of beta-lactone carboxylic acid 3 with N-Ala-aminocyclopropyl alanine 11.     

Interfacial electron transfer in FeII(CN)6 4- -sensitized TiO2 nanoparticles: a study of direct charge injection by electroabsorption spectroscopy

Electroabsorption (Stark) spectroscopy has been used to study the dye sensitized interfacial electron transfer in an Fe(II)(CN)(6)(4)(-) donor complex bound to a TiO(2) nanoparticle. The average charge-transfer distance determined from the Stark spectra is 5.3 A. This value is similar to the estimated distance between the Fe(II) center of the complex and the Ti(IV) surface site coordinated to the nitrogen end of a bridging CN ligand in (CN)(5)Fe(II)-CN-Ti(IV)(particle). This finding suggests that the electron injection is to either an individual titanium surface site or a small number of Ti centers localized around the point of ferrocyanide coordination to the particle and not into a conduction band orbital delocalized over the nanoparticle. The polarizability change, Tr(Deltaalpha), between the ground and the excited states of the Fe(II)(CN)(6)(4)(-)-TiO(2)(particle) system is approximately 3 time larger than normally observed in mixed-valence dinuclear metal complexes. It is proposed that the large polarizability of the excited state increases the dipole-moment changes measured by Stark spectroscopy.     

Asymmetric hydrogenation of aromatic olefins catalyzed by iridium complexes of proline derived phosphine-oxazoline ligands

The synthesis of a series of phosphine-oxazoline ligands is reported. This ligands are synthesized by reaction of a phosphine chloride with the secondary nitrogen of proline. Upon coordination to iridium the resulting complexes can be used in the asymmetric hydrogenation of simple olefins. The effect of different counter ions and substitution at the oxazoline and the phosphine is reported.     

Qy-excitation resonance Raman spectra of chlorophyll a and bacteriochlorophyll c/d aggregates. Effects of peripheral substituents on the low-frequency vibrational characteristics

Low-frequency (80-700 cm-1) Qy-excitation resonance Raman (RR) spectra are reported for thin-solid-film aggregates of several chlorophyll (Chl) a and bacteriochlorophyll (BChl) c/d pigments. The pigments include Chl a, pyrochlorophyll a (PChl a), methylpyrochloropyllide a (MPChl a), methylbacteriochloropyllide d (MBChl d), [E,M] BChl cS, [E,E] BChl cF, and [P,E] BChl cF. The BChl c/d's are the principal constituents of the chlorosomal light-harvesting apparatus of green photosynthetic bacteria. Together, the various Chl a's and BChl c/d's represent a series in which the peripheral substituent groups on the chlorin macrocycle are varied in systematic fashion. All of the Chl a and BChl c/d aggregates exhibit rich low-frequency vibrational patterns. In the case of the BChl c/d's, certain modes in the very low-frequency region (100-200 cm-1) experience exceptionally strong Raman intensity enhancements. The frequencies of these modes are qualitatively similar to those of oscillations observed in femtosecond optical experiments on chlorosomes. The RR data indicate that the low-frequency vibrations are best characterized as intramolecular out-of-plane deformations of the chlorin macrocycle rather than intermolecular modes. The coupling of the out-of-plane modes in turn implies that the Qy electronic transition(s) of the aggregate have out-of-plane character. The RR spectra of the BChl c/d's also reveal that the nature of the alkyl substituents at the 8 and 12 positions of the macrocycle plays an important role in determining the detailed features of the low-frequency vibrational patterns. The frequencies of the modes are particularly sensitive to larger substituent groups whose conformations may be more easily perturbed in the tightly packed aggregates. These factors also make aggregates of pigments containing larger substituents more susceptible to structural, electronic, and vibrational inhomgeneities. Collectively, the RR studies of the various pigments delineate the factors which influence the low-frequency vibrational characteristics of chlorosomal aggregates.     

A photoplate calibration technique applied to the determination of hafnium in zirconium by SSMS

A photoplate calibration procedure is suggested for spark source mass spectrometry /SSMS/ with photoplate detection. The technique uses the Churchill two-line method applied to the two stable isotopes of copper. The calibration curve thus obtained is split into fragments and each fragment is approximated by a polynomial. The method was applied for the quantitative determination of Hf as impurity in zirconium sponge obtained from a pilot plant dedicated to the depletion of the hafnium content in zirconium by fractional crystallization.     

Koordinationsverbindungen von Aminoacridin-N-oxiden mit Metallthiocyanaten der 3d-Reihe

Coordination Compounds of Aminoacridine-N-oxides with Thiocyanates of the 3d Metals . Reactions of thiocyanates of the 3d metals with selected aminoacridine-N-oxides in homogeneous dilutions of N,N-dimethylformamide form compounds of the type [M(AAcNO)_a(DMF)_b(NCS)₂] · cDMF and [M′(AAcNO)_d(DMF)_e(NCS)₃] · fDMF, M = Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺; M′ = Cr³⁺, Fe³⁺; AAc^INO = 3,6-diamino-2,7-dimethylacridin-N-oxide, AAc^IINO = 3,6-bis(dimethylamino)acridin-N-oxide, AAc^IIINO = 2-ethoxy-6,9-diaminoacridin-N-oxide; a = 1, 2, 3, 4; b = 0, 1; c = 0, 1, 2, 3; d = 1, 2, 3; e = 0, 1, 2; f = 0, 1, 2, 3. The complexes are characterized by IR (4000–200 cm^?1) and UV-VIS spectra in solutions and solids and by EPR and conductivity investigations.     

THE KINETICS OF REDUCTION OF CYTOCHROME c BY SEMI-REDUCED FLAVIN

Abstract— Flavin mononucleotide radicals, FMNH', generated by laser flash photolysis of FMN in the presence of the electron donors, histidine, guanosine monophosphate or EDTA, were found to reduce cytochrome c with an apparent rate constant of 6 ± 10⁷ M ⁻¹ s⁻¹. These flash photolysis results were, however, complicated by the electron donor radicals formed simultaneously which, particularly with EDTA, also lead to reduction of cytochrome c. Pulse radiolysis of a nitrous oxide saturated aqueous solution of FMN containing a high concentration of HCOONa, leads to the exclusive formation of FMNH'. By adding small concentrations of cytochrome c to this solution, a rate constant of 4.0 ± 10⁻¹ M ⁻¹ s⁻¹ was obtained for the reduction of cytochrome c by FMNH'. Replacement of the HCOONa by EDTA in such solutions leads to further routes for reduction of cytochrome c on radiolysis. as in the photolytic situation. The relevance of these results to flavin-photosensitised reduction of cytochrome c and other components of the mitochondrial electron transport chain is discussed.     

Molecular orbital study of gas phase basicities of carbofunctional derivatives of group IVB elements; stereochemical control

The gas phase basicities of a series of carbofunctional derivatives H₃M(CH₂)_nX (M = C, Si, Ge; X = NH₂, OH, F; n = 1–3) were investigated by the semiempirical CNDO/2 method. The calculations indicate that the electronic effects of silyl- and germyl-substituents differ greatly from the effect of simple alkyls. Moreover, in contrast to simple carbon derivatives, the overall nature of the electronic effects of siliyl- and germyl-substituents is crucially influenced by the molecular conformation.     

2-arylfuro [2,3-b] quinoxalines

2-Arylfuro[2,3-b]quinoxalines were obtained by cyclization of 2-phenacyl-3-quinoxalones in the presence of polyphosphoric acid or a mixture of phosphorus oxychloride and phosphorus pentachloride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 259–260, February, 1973.