摘要:

Abstract—Recent studies of the effects of molecular structure and reaction environment on the mechanism of primary photochemical processes involving transfer and conversion of electronic energy in relatively ‘simple’ organic molecules are presented and discussed. A quantitative i.r. spectroscopic method for studying intramolecular and intermolecular photoprocesses of u.v. irradiated substrates dispersed in solid alkali halide matrices at room temperature is described. Current data for the substratesortho‐nitrobenzaldehyde, anthracene and benzophenonebenzhydrol are presented.A series of ‘model’ ketones containing cyclopropyl groups have been synthesized and while their absorption spectra are similar, the efficiency of vapor‐phase photodissociation into radicals is shown to be strongly dependent on molecular structure.Butyrophenone and a series of ring substituted derivatives have been photolyzed in the liquid phase using the quantum yield of the photoelimination of ethylene (Type II split) as a “probe” to determine the effect of substituents on the internal H atom abstracting power of the excited carbonyl chromophore. Φc2H4is very sensitive to ring substitution, dropping from 0.24 in butyrophenone to 0.20, 0.058 and 0.00 in thep‐CH3,p‐OCH3andp‐NH2derivatives respectively, and to 0.00 in bothorthoandparahydroxy derivatives. This effect is correlated with their absorption spectra in terms of the lowest states of these alkyl aryl ketones being3(π, π*) rather than3(π, π*) in character.While several ‘classic’ photochemical reactions, unimolecular and bimolecular, proceed efficiently in solid KBr matrices giving the same product as in liquid systems, the ‘model’ cyclopropyl compounds and the alkyl aryl ketones did not undergo their usual intramolecular processes. Implications of this molecula

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09745.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—By applying the modifier ‘Space’ to the terms ‘Photochemistry’ and ‘Spectroscopy’ one implies a concern with electromagnetic radiation of wavelengths less than that found at the earth's surface (i.e., Λ≤23000Å) and with energetic particles, particularly electrons.It has been observed that for certain classes of organic compounds useful empirical correlations exist between reactions induced by electron impact, non‐ionizing ultraviolet radiation and ionizing radiation. These correlations allow qualitative or semi‐quantitative predictions of specific reactions and/or reaction mechanisms which will occur during photolysis or radiolysis, based on known optical or mass spectra.As an example of the above approach, we have shown that, in accord with recent spectroscopic evidence, benzene and toluene do not significantly react photochemically in their first absorption band (at ˜ 2500Å); however, they react with a quantum yield approaching unity in their second and third absorption bands (at ‐20008Å and 1850Å respectively). The products of this decomposition are primarily carbon and/or polymer which deposit on the cell windows, however, small yields of stable products have been isolated (i, e., φc2h2=0.01 for benzene; φ, C6H6=0.05 for irradiation of toluene).Another example of this extrapolation from one technique to another deals with the correlation of cyclic elimination reactions observed in the mass spectra, photochemistry and radiation chemistry of various classes of organic compounds. Classic examples of this type of reaction are the photolytic and radiolytic elimination of olefins from esters and ketones having a hydrogen γ to the carbonyl group (i.e., the elimination of ethylene from ethyl acetate and of propylene form methyln‐butyl ketone). Based on mass spectral correlations with the above reactions, the same type of elimination should be expected from a great number of compounds which contain hydrogens γ to unsaturated groups (i.e., C=O, C≡N, C=C, etc.). In those cases where the photochemistry or radiation chemistry of these compounds have been studied, an intramolecular cycloelimination of olefin has been observed to be an important process. It is suggested that mass spectra are a useful diagnostic tool for at least gross predictions in ‘space photochemistry’ and ‘space photobiology’, as well as in considering reactions of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09746.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—The photochemistry of Dhphenylakinine in dilute aqueous solutions has been investigated in detail by means of quantitative paper chromatography using C14‐labelled material. Solutions were irradiated at the exit slit of a grating monochromator using a high pressure xenon arc as light source. The illuminating beam contained wavelengths from 2475Å to 2675 Å at the half‐power points with maximum intensity at 2575 ÅBy using six different chromatographic solvent systems, the following photoproducts have been identified: tyrosine, 3, 4‐dihydroxyphenylalanine (DOPA), aspartic acid, benzoic acid, phenyllactic acid and a high molecular weight melanic polymer. An additonal photo‐product derived from two of the side chain carbons of phenylalanine and having anRfvalue of 0.13 inn‐butanol: acetic acid: water, 4:1:5 (v/v/v), has been detected in both oxygen saturated and oxygen free solutions, but has not yet been identified. All of these substances are stable solids at room temperature. Volatile or gaseous products could not be detected directly by the methods used in this investigation. Indirect evidence has been obtained that decarboxy‐lation is the dominant photochemical process in phenylalanine solutions irradiated both in the presence and absence of oxygen. The occurrence of phenyllactic acid in irradiated phenylalanine solutions shows indirectly that ammonia is liberated, but the quantum yield is about an order of magnitude smaller than that for carbon dioxide liberation.The kinetics of photoproduct accumulation and of phenylalanine loss have been determined under well‐defined conditions of incident light intensity, temperature, pH, dissolved oxygen, and phenylalanine concentration. These data were used to estimate quantum yields for the photoproducts and for phenylalanine loss after a specified dose of radiation at 2575Å under the given conditions. The results show that dissolved molecular oxygen greatly enhances the yields of tyrosine, DOPA, and the melanic polymer. Dissolved oxygen is not required for the synthesis of aspartic acid or phenyllactic acid. In the case of phenyllactic acid, water provides the necessary oxygen.Evidence is presented which suggests that the optical absorbance changes occurring during ultraviolet irradiation of phenylalanine are due in part to the formation of intermediates in melanin synthesis which cannot be detected by paper chromatography because they are too oxygen labile and occur in very

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09747.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—The photoelectric responseS(photoconduction and the photovoltaic effect) of a β‐carotene cell are shown to replicate in detail the photoelectric color responses of animal retina — the chromaticSpotentials, In both, short‐wavelength light generates a negative current flow with relatively fast time constants; long‐wavelength light generates a positive current flow with longer time constants; intermediate wavelength lights generate currents which are superpositions of these two currents and exhibit on/off peaks. A slight modification of the ‘primitive theory of the electroretinogram’ previously suggested, incorporates these color responses in the theory. The correlation between the physical detector and the retinal receptor unit suggested by this theory can explain the facts that agents which enhance the glial membrane potential increase the red response and decrease the blue response of the chromatic 5 potentials. The response changes due to adaptation can also be explained

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09748.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—The structural stability of chloroplasts was characterized by the proportion of leaf pigments present in the lipoprotein complex.Free or loosely protein‐bound pigments were separated by means of petroleum ether extraction of leaves. In normal barley seedlings equilibrium constants of 0.66 were found for carotenoid and 005 for chlorophyll‐protein complexes.In the pigment‐protein complex two types of bonding were distinguished which are based most probably on different number and/or energy of hydrogen bonds. The weaker bonding could be disrupted by heat denaturation (50–70°C), the stronger one could by polar solvents. Heat denaturation affects about 40 per cent of the carotenoid, 52 per cent of the chlorophyll‐a and 34 per cent of the chlorophyll‐bcomplexes.Chloroplast mutant leaves with abnormal carotenoid synthesis show characteristic differences in the stability of their pigment‐protein complex.It is concluded that the chlorophyll and carotenoid molecules are present in the chloroplasts in different physical states which may represent different

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09749.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—Studies of the luminescence and excitation spectra of proteins showed that in proteins, in contrast with mixed crystals of the amino acids, the migration of energy from tyrosine to tryptophan takes place in low yield. The migration of energy between nucleotides and from nucleotides to acridine orange in DNA proceeded with an average yield of 66%.The luminescence of more than ten proteins studied, at pH 1.0–13.0, temperatures from — 196 to + 100°C and monochromatic excitation from 240 to 303 mp was established as due to the luminescence of tyrosine and tryptophan. The amounts of energy stored by the molecules of these compounds in singlet and triplet excited states were 80 and 60 Kcal./ mole respectively. A sudden difference in the structure of the phosphorescence and fluorescence spectra suggests that the transition to the triplet state is connected with changes in the vibrational configurations of the molecules, which prepare conditions for a photochemical event. The enhanced probability of an S →T transition during a change in pH or the addition of KI always led to an increase in the rate of ‘fading’ of luminescence under irradiation by the exciting light.A comparison of the kinetics of bleaching of the luminescence of samples with low‐temperature thermoluminescence showed that two photo‐products had been formed under U.V. irradiation at 77°K. ProductRt, responsible for the thermoluminescence, recombined through the triplet state with the emission of a quantum on warming to 80–100°K or on supplementary irradiation by visible light. ProductRb, accumulating on fading of the original, was stable to light and was transformed to the original amino acid without emitting a quantum at a temperature of 150–200° K. At room temperature aromatic amino acid groups entered into two photo‐chemical reactions: (1) photo‐oxidation by atmospheric oxygen and (2) reaction with adjoining groups of the protein, not requiring the presence of oxygen. Reaction (2), probably the main one for peptides and proteins, may lead to the formation of cross links between peptide chain

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09750.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09751.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—A theory of photo‐adsorption onto semiconductors is developed using the kinetic expressions and the relations for steady state carrier concentrations in terms of the quasien Fermi levels. Expressions are derived which emphasize the importance of the surface potential. In particular it is shown that a significant quantity is the ratio of the surface potential to a critical quantity,Ysc. An expression for the latter is given and it is shown that photoadsorption occurs if the ratio is greater than unity while desorption occurs if the ratio is less than unity. The theory also suggests a useful graphical representation of the effects of impurities and surface potential on adsorpt

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09752.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—Oxygen evolution fromPorphyridium cruentumexposed to monochromatic light flashes with background light of different wavelengths and intensities was measured. Two different manifestations of the enhancement effect were found: (1) Type I (also referred asEH):an increase in the rate of O2evolution and (2) Type II (also referred asEt):a prolongation of O2evolution in time. Exposure of algae to red flashes with green background light revealed both types of enhancement whereas green flashes with red background light revealed only the first type of enhancement. Similar results were observed under both aerobic and anaerobic conditions except that in the latter, complications arise due to S‐shape of the curve of rate of photosynthesis versus light intensitity in a nitrogen atmosphere.The results presented in this paper and those presented in the earlier papers of French have been interpreted in terms of the ‘spill‐over’ and the ‘separate package’ model for the distribution of light energy into the two pigment systems. In both the models, we incorporate the idea that the product of light reaction I is long‐lived (half‐life of the order of seconds). No assumption is needed about the life time of the photoproduct of reaction II in the spillover model; in the separate package model, however, we have to incorporate an additional assumption that photoproduct II is short‐lived (half‐life less than 4 msec) to ex

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09753.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—The Kubelka‐Munk theory for diffuse reflectance has been applied to a quantitative study of photochromism in the crystalline state. For three systems investigated it was found possible to assign first order rate constants to the thermal relaxation process and estimate the pre‐exponential factorAand the activation energyEain Arrhenius equation. For the fading of the red photocolored form, Λmax=490 mμ, of benzaldehyde phenylhydrazone A = 1.4×108min‐1andEa=15.7 kcal mole‐1. For the fading of the blue photocolored form, Λmax=590 mμ, of 2–(2,4‐dinitrobenzyl)pyridineA=5×1014min‐1Ea=23.3 kcal mole‐1, Cinnamaldehyde semicarbazone showing ‘reversed phototropy’ has a photoactivated state, Λmax=400 mμ, which in dark is transformed into a strongly absorbing yellow species, Λmax= 430 mμ withA =14 ×

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb09754.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY