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971.
Abstract— The rates of photosensitized oxidation of a number of sulphides were determined under standard conditions in 1, 1, 2,2-tetrachloroethane and in methanol. It was found that the ratio of the rates of reaction in the two solvents was not constant for different sulphides and that t -butyl sulphide does not react in methanol. It is inferred that the presence of an H atom in the α position is essential for reaction in polar solvents and an appropriate mechanism is suggested. The results indicate that reaction in chlorinated solvents may take place by a different mechanism which possibly involves H-abstraction by triplet sensitizer. 相似文献
972.
Analysis of tea components by high-performance liquid chromatography and high-performance capillary electrophoresis 总被引:3,自引:0,他引:3
Tea is one of the most popular beverages in the world. The number of reports on the analysis of tea components, especially for catechins, has recently been increasing. We review the recent reports on the analysis of tea components using the analytical methods of high-performance liquid chromatography and high-performance capillary electrophoresis. 相似文献
973.
D. Beese R. Steiner H. Scheer A. Angerhofer B. Robert M. Lutz 《Photochemistry and photobiology》1988,47(2):293-304
Abstract— Reaction centers from Rhodobacter sphaeroides have been modified by treatment with sodium borohydride similar to the original procedure [Ditson et al., Biochim. Biophys. Acta 766 , 623 (1984)], and investigated spectroscopically and by gel electrophoresis.
(1) Low temperature (1.2 K) absorption, fluorescence, absorption- and fluorescence-detected ODMR, and microwave-induced singlet-triplet absorption difference spectra (MIA) suggest that the treatment produces a spectroscopically homogeneous preparation with one of the 'additional' bacteriochlorophylls being removed. The modification does not alter the zero field splitting parameters of the primary donor triplet (T P870).
(2) From the circular dichroism and Raman resonance spectra in the1500–1800 cm-1 region, the removed pigment is assigned to BchlM , e.g. the "extra" Bchl on the "inactive" M-branch.
(3) A strong coupling among all pigment molecules is deduced from the circular dichroism spectra, because pronounced band-shifts and/or intensity changes occur in the spectral components assigned to all pigments. This is supported by distinct differences among the MIA spectra of untreated and modified reaction centers, as well as by Raman resonance.
(4) The modification is accompanied by partial proteolytic cleavage of the M-subunit. The preparation is thus spectroscopically homogeneous, but biochemically heterogenous. 相似文献
(1) Low temperature (1.2 K) absorption, fluorescence, absorption- and fluorescence-detected ODMR, and microwave-induced singlet-triplet absorption difference spectra (MIA) suggest that the treatment produces a spectroscopically homogeneous preparation with one of the 'additional' bacteriochlorophylls being removed. The modification does not alter the zero field splitting parameters of the primary donor triplet (
(2) From the circular dichroism and Raman resonance spectra in the1500–1800 cm
(3) A strong coupling among all pigment molecules is deduced from the circular dichroism spectra, because pronounced band-shifts and/or intensity changes occur in the spectral components assigned to all pigments. This is supported by distinct differences among the MIA spectra of untreated and modified reaction centers, as well as by Raman resonance.
(4) The modification is accompanied by partial proteolytic cleavage of the M-subunit. The preparation is thus spectroscopically homogeneous, but biochemically heterogenous. 相似文献
974.
Conclusions On the example of the homolytic reaction of methallyl chloride with CCl4 it was found that iron pentacarbonyl in catalytic amounts can selectively suppress the radical process involving chlorine atoms, and at the same time it catalyzes the chain reaction with trichloromethyl radicals, which act as carriers of the kinetic chain.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2320–2322, October, 1972. 相似文献
975.
P. J. Hauser A. F. Schreiner J. D. Gunter W. J. Mitchell M. K. Dearmond 《Theoretical chemistry accounts》1972,24(1):78-88
MCD, electronic absorption, external heavy atom, and crystal field data are presented for the low energy region (2
E
g, 2
T
1g, 4
T
2g) and high energy region (2
T
2g, 4
T
1g) of Cr(dtp)3, Cr(dtc)3, and Cr(exan)3. At low energy, MCD intensities of 2
E(2
E
g) and 2
E(2
T
g) are as large or larger than 4
T
2g, and the MCD technique is advantageous over electronic absorption in this respect. The MCD positions of 2
E
g and 2
T
1g are nearly the same for these molecules ( 13 kK and 13.6 kK) · 4
T
2g of this region appears trigonally split ( 500 cm–1) in the MCD of dtp but to a smaller extent than in the electronic crystal spectrum of Lebedda and Palmer ( 600 cm–1). MCD did not resolve such components for exan and dtc. The higher energy region includes 2
T
2g and 4
T
1g, and the combined MCD and electronic absorption data of the three compounds taken together lead us to conclude the ordering 2
A
1(2
T
2g)<2
E(2
T
2g)<4
E(4
T
1g). The potentially useful external heavy atom affect on the solution-observed electronic 2
E and 4
E bands of Cr(dtp)3 did not shed additional light on this order of E states. Finally, it is concluded that the order of 4
T
1g and 2
T
2g cannot be decided from O
h crystal field calculations because of experimental uncertainties about choosing centers of gravity. In addition, 4
T
1g and 2
T
2g are close together so that ordering 2
E<4
E does not guarantee 2
T
2g<4
T
1g. However, it can be concluded that the ratio C/B4 is not correct, whereas the larger 7<(C/B)<8 is consistent with the data of all three molecules because of small B parameters ( 0.4). Locating OO transitions may somewhat decrease C/B and Dq.
Presented in part at the 161st American Chemical Society National Meeting, Los Angeles, California, March–April, 1971.
NDEA Pre-Doctoral Fellow. 相似文献
Zusammenfassung In der vorliegenden Arbeit werden folgende Meßergebnisse mitgeteilt; MCD, elektronische Absorption, Einfluß eines äußeren schweren Atoms sowie Kristallfelddaten für den Bereich niedriger Energie (2 E g, 2 T 1g, 4 T 2g) und den Bereich hoher Energie (2 T 2g, 4 T 1g) von Cr(dtp)3, Cr(dtc)3 und Cr(exan). Bei niedriger Energie sind die MCD-Intensitäten von 2 E(2 E g) und 2 E(2 T 1g) genau so groß, oder größer als 4 T 2g, und die MCD-Technik bietet Vorteile gegenüber der elektronischen Absorptionsmethode. Die MCD-Werte von 2 E g und 2 T 1g sind für die genannten Moleküle etwa gleich ( 13 kK und 13,6 kK). 4 T 2g dieses Gebietes erscheint trigonal aufgespalten ( 500 cm–1) bei MCD von dtp, aber in einem geringeren Maß als im elektronischen Kristallspektrum von Lebedda und Palmer ( 600 cm–1) MCD löste solche Komponenten bei exan und dtc nicht auf. Der Bereich höherer Energie enthält 2 T 2g und 4 T 1g, und aus der Kombination von Daten der MCD-Methode sowie der elektronischen Absorption schlossen wir auf die Anordnung 2 A 1g(2 T 2g)<2 E(2 T 2g)<4 E(4 T 1g). Der möglicherweise nützliche Effekt eines äußeren schweren Atoms auf die in Lösung beobachteten elektronischen 2 E- und 4E-Banden von Cr(dtp)3 brachte bezüglich dieser Anordnung der E-Zustände nichts Neues. Weiterhin wird gefolgert, daß die Ordnung von 4 T 1g und 2 T 2g nicht aus O h-Kristallfeldberechnungen entschieden werden kann, da experimentelle Unsicherheiten bezüglich der Wahl von Schwerpunkten bestehen. Außerdem liegen 4 T 1g und 2 T 2g nahe zusammen, sodaß aus der Anordnung 2 E<4 E nicht notwendig 2 T 2g<4 T 1g folgt. Es kann jedoch gefolgert werden, daß das Verhältnis C/B4 nicht korrekt ist, während 7<(C/B)<8 konsistent mit den Daten aller drei Moleküle ist, da die B-parameter klein sind (0,4). Die Vokalisierung der OO-Übergänge könnten C/B und Dq etwas erniedrigen.
Presented in part at the 161st American Chemical Society National Meeting, Los Angeles, California, March–April, 1971.
NDEA Pre-Doctoral Fellow. 相似文献
976.
M. Yu. Lidak R. A. Paégle V. É. Straume D. É. Shnore Yu. P. Shvachkin 《Chemistry of Heterocyclic Compounds》1971,7(3):372-376
The synthesis of peptides which include a DL--(N1-uracilyl)--alanine (DL-willardiine) residue as an N-terminal or C-terminal group was investigated, dipeptides of DL-willardiine with glycine and L-tyrosine were obtained, and DL-willardiyl-DL-willardiine was synthesized; the latter is the simplest representative of the family of monotonic homopeptides which contain, as a repeating side substituent, a natural nucleic base capable of participation in intermolecular interactions of the complementary type.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 404–408, March, 1971. 相似文献
977.
A new mechanism is suggested for the anionic polymerization of isoprene. The key moment of this mechanism is thermal electron excitation of the complex of a living polymer with a monomer to the low lying S1 (T1) state involving a charge (electron) and (Li+) cation transfer from the terminal unit to the monomer molecule. It is stated that the probability of chemical bonding depends on the spin density on the radical centers of reactant molecules and on the geometry of the reaction complex. The semiempirical AM1 and ab initio 6-31G* quantum-chemical calculations revealed strong interaction for the ground electronic state of the complex (5-10 kcal/mole) and low energies of the excited triplet levels (<10 kcal/mole). 相似文献
978.
Odd/even effect in the chain length on the enthalpy of micellization of gemini surfactants in aqueous solution 总被引:1,自引:0,他引:1
Li Y Li P Wang J Wang Y Yan H Thomas RK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(15):6703-6706
The micellization properties of cationic symmetric gemini surfactants, [CmH(2m+1)(CH3)2N(CH2)6N(CH3)2CmH(2m+1)]Br2 (designated as CmC6CmBr2, with m = 7, 8, 9, 10, 11, 12, and 16), has been investigated by isothermal titration microcalorimetry. The critical micelle concentration (CMC) and enthalpy of micellization (DeltaHmic) were determined from calorimetric titration curves. The linear decreasing of log CMC with increasing the length of the hydrophobic chain is consistent with an increase in the hydrophobicity of the alkyl chain. Interestingly, with increasing the length of the alkyl chain, the DeltaHmic values of the surfactants with even numbered alkyl chains vary from endothermic to exothermic, whereas the DeltaHmic values of the surfactants with odd numbered alkyl chains are all endothermic and tend to become more endothermic. The pronounced even/odd effect in DeltaHmic is discussed with respect to the "donor-acceptor" interaction. 相似文献
979.
The use of 1,2-naphthoquinone-2-semicarbazone-4-sulphonic acid and 1,2-naphtho-quinone-2-thiosemicarbazone-4-sulphoic acid as indicators in the titrimetric estimation of phosphate, molybdate, tungstate and sulphate with lead has been examined. The precision, accuracy and applicability of the methods have been evaluated. 相似文献
980.
A R P?s? O A Forsander 《Acta chemica Scandinavica. Series B: Organic chemistry and biochemistry》1976,(9):801-806
The effect of the ethanol oxidation rate on the interaction between the phosphorylation state (the [ATP]/[ADP] X [HPO4]2- ratio) and the redox state (the free [NAD+]/[NADH] ratio) of the liver cytosol was studied in intact fed rats. The rate of ethanol oxidation was inhibited to different degrees with pyrazole. The ethanol oxidation rate had no influence on the liver lactate level but correlated significantly with the pyruvate level. Accordingly, a significant correlation was also found between the ethanol oxidation rate and the lactate/pyruvate ratio. The rate of ethanol oxidation correlated significantly with the liver 3-phosphoglycerate level. No change in the glyceraldehyde-3-phosphate level was found. No correlation was found between the ethanol oxidation rate and the glyceraldehyde-3-phosphate/3-phosphoglycerate redox couple. Ethanol administration slightly increased the liver ATP level, but the simultaneous administration of pyrazole eliminated this effect. Other adenine nucleotides and HPO4 2- were not changed. The changes in the rate of ethanol oxidation had no effect on the phosphorylation state in the fed liver. It is assumed that in the fed liver the phosphorylation state is so well stabilized that the redox level has no influence. 相似文献