摘要:

AbstractThe various primary processes in excited oxyanions are discussed. The most common processes appear to involve one‐unit change of oxidation number (one electron processes): the generation of e−aqand O−aq(or OHaq). The production of oxygen atoms (a two‐electron process) occurs only with central atoms having high electron‐affinities. There is no convincing evidence for one‐step evolution of O2. Some major secondary processes are als

ISSN:0021-2148    

DOI:10.1002/ijch.197000018

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractIt was attempted to recreate on molecules of biological interest including enzymes some of the photodynamic effects using the excited species of molecular oxygen. Such a species is produced by a chemical reaction in a separate vessel and is carried into the sample by a stream of gaseous nitrogen.

ISSN:0021-2148    

DOI:10.1002/ijch.197000019

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractFollowing an outline of the pioneering work of Haber's School, emphasis is placed on a critical review of the most important recent achievements. These embrace, in the area of thermal autoxidation: the concept of critical antioxidant concentration, the multiple effects of heavy metals (including catalyst‐inhibitor conversion), the development of new synergistic antioxidant combinations composed of free radical acceptor and peroxide decomposer and, finally, Denisov's direct experimental evidence for the reaction of heavy metals with molecular oxygen in organic media in support of Uri's trace metal hypothesis of the general mechanism of the initiation of autoxidation. The following recent advances in the field of photochemical autoxidation are described: photosensitized initiation by trace metals and its inhibition, the singlet oxygen hypothesis, the inadequacy of phenolic antioxidants and the reliance on UV absorbers, the importance of energy transfer in photochemical protection leading to new stabilizers. A very recent innovation which is relevant to both thermal and photochemical autoxidation is highlighted, i.e., the development of new α‐dithidiketone chelates, particularly bis (stilbenedithiolate) nickel (= NiS4C4Ph4or, abbreviated, NiSDT) as antioxidants which combine in a unique way the properties of free radical acceptors, peroxide decomposers and UV stabilizers. They were then found to be the most powerful antioxidants for polyethylene and polypropy

ISSN:0021-2148    

DOI:10.1002/ijch.197000020

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractPulsing cyclohexane or methanol‐water solutions of chlorobenzene and fluorobenzene with the Nd laser at 265 mμ (half‐height width 30 nsec) gives rise to intermediates, absorbing in the 290–300 mμ region, attributed to the corresponding triplet states. The decay of the triplet states is roughly first order with rate constants of (2.1 ± 0.1) × 106sec−1and (1.5 ± 0.1) × 106sec−1respectively. No transient absorption was observed with bromo‐ and iodobenzene under the same conditions. Solutions of the two latter compounds containing KI or KBr show the appearance of I−2or IBr−follo

ISSN:0021-2148    

DOI:10.1002/ijch.197000021

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractBy photolyzing hydrogenated molecules, H or D atoms with kinetic energies in the range of about 0.5 to 5 eV are produced. The special features of their chemical properties are reviewed and compared with recoil tritium atom reactions on the one hand and with systems in thermal equilibrium on the other. Although the mechanism of reactive and non‐reactive collisions are by no means well known, hot hydrogen atom chemistry is, in first approximation, rather similar to high temperature chemistry. However, energy losses by energy transfer to molecules and even to rare gases are much smaller than expected from classical hard‐sphere models. For the sake of clearness, this article is rather arbitrarily, divided into three parts: physical aspects, various modes of formation and chemical propert

ISSN:0021-2148    

DOI:10.1002/ijch.197000022

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractThe photochemistry of the 670 nm band in fluid sodium amine solutions is investigated by applying flash (optical detection) or steady state (ESR detection) irradiation techniques. The photoregeneration of faded alkali metal solutions induced by exciting the amide decomposition product, is also submitted to flash investigation. In both cases the primary act appears to be the generation of solvated electrons. The available photochemical data are examined in light of a recent spectroscopic study which attributes the 670 nm band to a sodium anion (Na−) and the 850, 920 and 1030 metal bands to K−. Rb−and Cs−, respectively. It is concluded that the photochemical observations provide new evidence for the model involving the alkali metals negative ions. Electron photoejection in a rigid amine glass at −196°C produces a (IR) band which is red shifted relative to that present in an equilibrium liquid solution, frozen to the same low temperature glass. The effect is attributed to two, physically distinguishable, solvated electrons in glasses or, alternatively, to an additional (unidentified) IR species present in the dark equilibrium

ISSN:0021-2148    

DOI:10.1002/ijch.197000023

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractPhotochemical effects occurring in rigid polar matrices are reviewed. Organic solutes in aqueous, alcoholic rigid solutions and in boric acid glasses are considered in some details. Electron photodetachment of solutes, sensitized photodetachment of solutes, solvent sensitized decomposition, solute sensitized decomposition and reaction with host are discussed.

ISSN:0021-2148    

DOI:10.1002/ijch.197000024

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractIrradiation of charge transfer absorption bands of coordination complexes can result in net oxidation reduction or ligand exchange reactions. The photoredox processes generally involve the formation of reactive radicals in the primary photochemical act. The identification of these primary radicals is essential to the specification of the primary photochemical act since radical reactions with substrate, other radicals, etc. can make the net products and yields appear vastly different from the nature of the primary act. For example, in a few documented cases, the metal ion fragment formed in a photoredox process has characteristics of a radical and can couple with ligand radicals giving rise to a net photochemical process which appears to be ligand exchange rather than photoredox. A variety of radicals, organic as well as inorganic, can be generated and studied in aqueous solution. Some information has also been obtained concerning the nature of the photochemical precursors to the radicals formed in photoredox processes.

ISSN:0021-2148    

DOI:10.1002/ijch.197000025

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractStudies of the X‐ray‐ and UV‐induced luminescence of tryptophan and tyrosine in solution between 77°K and 300°K are reviewed. The fluorescence and phosphorescence spectra observed during X‐irradiation are identical to those induced by UV light, but the phosphorescence to fluorescence ratios obtained with X‐rays are much larger than those found with UV light. The experiments seem to show that charge recombination is the dominating mode of the X‐ray‐induced excitation at low temperatures, giving rise to roughly 85% of the X‐ray‐induced luminescence at 77°K. The fraction of the X‐ray‐induced excitation which results from charge recombination decreases with increasing temperature and becomes negligible above 220°K. This causes the yield of X‐ray‐induced excitation of the radiative levels of tryptophan to decrease from G = 5 excited molecules/100 eV absorbed in solute, at 77°K, to G = 0.4 at room temperature. The mechanisms for quenching of char

ISSN:0021-2148    

DOI:10.1002/ijch.197000026

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY

摘要:

AbstractThe fluorescence quantum yields of tryptophan, 3‐methylindole and 3‐β‐hydroxyethylindole were investigated as a function of temperature in a variety of polar and non polar solvents. Similar quantum yields and “activation energies” were found for the different systems. It was concluded that the same collisional solvent deactivation is responsible for the decrease in quantum yield with temperature irrespective of solvent system used. A notable exception is water where a different mechanism is indicated. The quenching of the indole chromophore fluorescence by a variety of specific agents both attached to the ring by an ethylene bridge and in homogeneous solution was also studied. It was found that potential proton donating groups were good quenching agents, the effect being much greater for groups carrying a positive charge. Polarization by a neighboring group also enhanced the quenching ability of any specific group. It was concluded that an excited state charge transfer complex is probably involved as a first step in the quenchi

ISSN:0021-2148    

DOI:10.1002/ijch.197000027

出版商:WILEY‐VCH Verlag    

年代:1970

数据来源: WILEY