Zur komplexchemie von 4-zentren-π-systemen : VIII. ESR-untersuchungen an heterobutadien-chelaten. I. Kalium-(diazabutadien-tetracarbonyl-metallate)

Glyoxal- and diacetyl-bis(imine)metal tetracarbonyls (RNCR′CR′NR)M(CO)₄ (M = Cr, Mo, W) are reduced with potassium in DME to give paramagnetic mono-anions. Their high-resolutior, ESR spectra show the hyperfine splittings of the magnetically active ligand atoms as well as the satellites of the metal isotopes ⁵³Cr,^95,97Mo and ¹⁸³W. The coupling constants are discussed with respect to π-bonding mechanisms.     

Characterisation of flavonols in broccoli (Brassica oleracea L. var. italica) by liquid chromatography-uV diode-array detection-electrospray ionisation mass spectrometry

The flavonoid composition of broccoli inflorescences has been studied by LC/UV-DAD/ESI-MSn. A large number of hydroxycinnamic acid esters of kaempferol and quercetin glucosides has been characterised. The structures of the flavonoid glycosides were analysed after alkaline hydrolysis, and were identified as 3-sophoroside/sophorotrioside-7-glucoside/sophoroside of kaempferol, quercetin and isorhamnetin (this last found in trace amount). These complex quercetin and isorhamnetin glucosides have not been previously characterised in nature. In addition, several less complex glucosides based on the same aglycones have been identified. The effect of sugar substitution and acylation on chromatographic mobility and ESI ionisation and fragmentation are discussed.     

Sensitive determination of diquat by a kinetic method using the stopped-flow mixing technique

A simple, sensitive, selective, fast and inexpensive assay for the determination of diquat is proposed. The method is based on the reduction of the herbicide to a strongly fluorescent monocation radical with sodium dithionite. The initial rate of this reaction is directly proportional to the diquat concentration. The stopped-flow mixing technique was used because the kinetic data can be obtained in only 7 s, meaning that the method can be automated. The calibration graph is linear over the range 5-500 ng ml-1 and the precision (RSD) is close to 1.2%. The applicability of the method was demonstrated by determining the herbicide in different kinds of samples.     

相转移催化元素硫的歧化反应

本工作将相转移催化(PTC)应用于元素硫歧化反应,大大降低了反应温度,提高了反应速度。该反应被证实与熔态硫在水溶液中的歧化相同,即4S+6OH~-=2S~(2-)+S_2O_3~(2-)+3H_2O。比较了四乙基铵、四丁基铵、十六烷基三甲基铵和三辛基甲基铵四种相转移催化剂及四氯乙烯、二甲苯和四氯乙烷三种溶剂的影响。讨论了本体系相转移催化的证据。为改进以元素硫歧化反应为基础的提取冶金过程提供了依据。     

Duality and intersection theory in complex manifolds. I

We introduce the concept of a twisting cochain and a twisted complex associated to a coherent sheaf. For sheaves of submanifolds these twisted complexes are used to construct on cochain level the Grothendieck theory of dual class and Gysin map. These explicit constructions give, for instance, a local formula for dual class of higher codimensional submanifolds. We prove a refined version of the Hirzebruch Riemann Roch using such local formulas. We also prove a theorem on when global analytic intersection classes can be computed from first order geometric data. This theory will be used to prove the Holomorphic Lefschetz formula (in Part II) and the Hirzebruch Riemann Roch for analytic coherent sheaves.The first author is supported in part by NSF grants GP-36418X1 and MCS 76-08478. The second by MCS 75-07986 and Sonderforschungsbereich Theoretische Mathematik at Bonn University     

Shockley surface states on three faces of bcc iron

Strictly localized or resonance Shockley surface states have been found on the (111), (010) and (110) faces of paramagnetic bcc iron for ,¯M and ¯N points in the corresponding surface Brillouin zones. Energy, character of wave function and its damping for these states are reported. Emphasis is laid on implications of surface states in photoemission, field-electron and -ion emission, electron energy-loss or disappearance potential spectroscopy, Auger electron spectroscopy, work function, magnetic properties, electric conductivity, as well as chemisorption and catalysis.     

EXCITATION ENERGY TRANSFER IN THE CRYPTOPHYTES. FLUORESCENCE EXCITATION SPECTRA AND PICOSECOND TIME-RESOLVED EMISSION SPECTRA OF INTACT ALGAE AT 77 K

Excitation spectra of chlorophyll- a (Chl- a ) fluorescence in intact cells of Cryptomonas ovata, Chroomonas pauciplastida and Chroomonas salina were determined at 77 K. For all species the excitation spectra for emission from Chl- a associated with photosystem II (PSII) showed increased contributions by a carotenoid (493 nm) and phycobiliproteins, and decreased contributions by carotenoid (417 nm, 505 nm) and Chl- a (445 nm) as compared to excitation spectra for emission from Chl- a associated with photosystem I (PSI). Excitation spectra of C. salina and C. ovata showed an increased contribution by Chl- c ² to PSII Chl- a fluorescence emission. In all three species the absorbance band positions of Chl- a , as determined from the excitation spectra, were similar to those previously described in green plants. green algae and phycobilisome-containing organisms. Time-resolved 77 K fluorescence emission spectra of C. ovata and C. salina showed successive emission from both phycoerythrin and Chl- c ², PSII Chl- a , and PSI Chl- a. C. pauciplastida showed successive emission from phycocyanin, PSII Chl- a , and PSI Chl- a. Spectral red-shifts with time were observed for the phycobiliprotein peaks in all three species. The fluorescence decay of phycoerythrin in C. ovata and C. salina was faster than that of phycocyanin in C. pauciplastida. The results are discussed in relation to the organization of the antenna pigments of PSII and PSI in the cryptophyte algae.     

Synthesis and characterization of Ru2(DMBA)4X2 (X = CN, N3, N(CN)2, I): controlling structural, redox, and magnetic properties with axial ligands

Metathesis reactions between Ru(2)(DMBA)(4)Cl(2) (DMBA = N,N'-dimethylbenzamidinate) and MX (M = Na and K) yielded bis-adduct derivatives Ru(2)(DMBA)(4)X(2) (X = CN (1), N(3) (2), N(CN)(2) (3)). Metathesis reactions between Ru(2)(DMBA)(4)(NO(3))(2) and KI resulted in Ru(2)(DMBA)(4)I(2) (4). Compound 1 is diamagnetic, while compounds 2-4 are paramagnetic (S = 1). Both compounds 1 and 2 undergo two reversible one-electron processes, an oxidation and a reduction, while compound 3 features a quasireversible reduction. Single-crystal X-ray diffraction studies revealed that the Ru-Ru bond lengths are 2.4508(9), 2.3166(7), 2.304[1], and 2.328(1) A for compounds 1-4, respectively. Structural and electrochemical data clearly indicate that the axial ligands impart a significant influence on the electronic structures of diruthenium species.     

ortho-metallation reactions involving some triphenyl phosphite complexes of osmium

Osmium triphenylphosphine complexes, OsH₄(PPh₃)₃, OsH₂ (CO)(PPh₃)₃ and OsHCl(CO)(PPh₃)₃ react with triphenyl phosphite in boiling organic solvents to yield triphenyl phosphite derivatives which subsequently undergo ortho-metallation reactions.     

The Emission in the Acetone Photochemical System

The emission in the acetone photochemical system has been measured as a function of irradiating time and pressure. The emission yield generally increases with increase in irradiating time at both 3130 and 2654A. The increase of emission yields is due to the sensitized phosphorescence of the product biacetyl. The higher emission yield and lower biacetyl quantum yields at 3130A than that at 2654A support for that most of the excited acetone molecules are in the triplet state at 3130A.