叠氮苯及偶氮甲基吡啶的低温光化学

本文用低温基质分离(Matrix isolation)技术研究了叠氮苯及偶氮甲基吡啶的低温光化学反应及其历程,并对反应过程的中间体及最终产物之间的相互转化关系进行了探讨。     

ON THE STATE OF CHROMOPHORE PROTONATION IN RHODOPSIN: IMPLICATION FOR PRIMARY PHOTOCHEMISTRY IN VISUAL PIGMENTS

Resonance Raman multicomponent spectra of bovine rhodopsin, isorhodopsin, and bathorhodopsin are obtained at low temperature. Application of the double beam, 'pump-probe' technique allows an extraction of the rhodopsin and bathorhodopsin spectra in both protonated and deuterated media. Our results show that the Schiff bases of both rhodopsin and bathorhodopsin are fully protonated and the degree of protonation is unaffected by the rhodopsin-bathorhodopsin transformation. Further, the data support the concept or cis-trans isomerization as occurring in this transition. The effect of these results on various models for the primary photochemical event in vision is discussed.     

ESR STUDIES OF THE LOW TEMPERATURE IRRADIATION OF KERATIN AND ITS COMPONENT AMINO ACIDS

Abstract— The photoejection of electrons from the aromatic amino acids at 77°K by 290–340 nm radiation was found to involve both monophotonic and biphotonic processes. However, only monophotonic processes are involved when electrons are photoejected from cystine or cysteine. These electrons prefer to attach themselves to adjacent sulphur groups rather than the dielectric traps in the matrix, so that both anionic and cationic radicals are formed.
In keratin at 77°K, the disulphide anion radicals are produced by both monophotonic and biphotonic mechanisms, indicating that the electrons captured by the disulphides are photo-ejected from the aromatic amino acids. At room temperature the thiyl and aromatic radicals are produced only by monophotonic reactions.     

THEORETICAL STUDIES OF BILIPROTEIN CHROMOPHORES AND RELATED BILE PIGMENTS BY MOLECULAR ORBITAL AND RAMACHANDRAN TYPE CALCULATIONS

Abstract Ramachandran calculations have been used to gain insight into steric hindrance in bile pigments related to biliprotein chromophores. The high optical activity of denatured phycocyanin, as compared to phycoerythrin, has been related to the asymmetric substitution at ring A, which shifts the equilibrium towards the P-helical form of the chromophore. Geometric effects on the electronic structures and transitions have then been studied by molecular orbital calculations for several conjugation systems including the chromophores of phycocyanin, phytochrome P_r, cations, cation radicals and tautomeric forms. For these different chromophores some general trends can be deduced. For instance, for a given change in the gross shape (e.g. either unfolding of the molecule from a cyclic-helical to a fully extended geometry, or upon out-of-plane twists of the pyrrole ring A) of the molecules under study, the predicted absorption spectra all change in a similar way. Nonetheless, there are characteristic distinctions between the different n -systems, both in the transition energies and the charge distribution, which can be related to their known differences in spectroscopic properties and their reactivity.     

LOW TEMPERATURE FTIR STUDIES OF THE PROTONATION OF A RETINYLIDENE SCHIFF BASE

Abstract— This note supplements the paper by Badilescu et al. (1989) [ Photochem. Photobiol. 49 , 313-318]. Low temperature solution spectra of 1: 2 and 2: 1 mixtures of trans -retinylidene-tertbutylamine and propanoic acid are presented. The results show that the degree of protonation is both temperature and concentration dependent.     

LOW TEMPERATURE SPECTROPHOTOMETRIC STUDY OF CATTLE BATHORHODOPSINS PRODUCED FROM RHODOPSIN AND ISORHODOPSIN IN TRANSPARENT MEDIUM WITHOUT CRACKS

Abstract— Cattle rhodopsin (11-cis-Rh) and isorhodopsin (9-cis-Rh) were prepared from the same extract of cattle opsin by incubation in the dark with 114– and 9-cis-retinals, respectively. The preparations obtained were mixed with glycerol (67% in the final concentration) and then cooled to 77 K by a rapid cooling method for freezing the samples as a clear glass, without any cracks. The spectral changes during their photochemical reactions were measured. A computer analysis of the spectra obtained verified that bathorhodopsin from 11-cis-Rh was identical in spectrum with that from 9-cⁱs-Rh not only in photosteady state but also under a short time irradiation.     

LUMINESCENCE PROPERTIES AND RELATED PHOTOCHEMISTRY OF 4-AMINO-2-METHOXYPYRIMIDINE

Abstract— The luminescence properties of 4-amino-2-methoxypyrimidine, I, have been studied in several solvents. These studies indicate that the photochemical reaction of I with dihydrogen phosphate buffer proceeds via an intermediate derived from the fluorescent singlet excited state of I.     

PICOSECOND LASER PHOTOLYSIS OF SQUID RHODOPSIN AT ROOM AND LOW TEMPERATURES

Abstract. Squid rhodopsin extracted with 2% digitonin (pH 10.5 or 7.0) was excited with a 347 nm light pulse from a mode-locked ruby laser at room temperature. Within 19 ps after the excitation, absorbance at 430 nm due to hypsorhodopsin increased and subsequently decreased with a decay time of 45 ± 10 ps. Absorbance at 550 nm due to bathorhodopsin increased with a rise time of 50 ± 10 ps. These results are the first observations of hypsorhodopsin at room temperature and clearly show that hypsorhodopsin is a precursor of bathorhodopsin which has been considered to be the earliest photoproduct in the photobleaching process of rhodopsin.
Hypsorhodopsin appeared with a rise time of 70 ± 10 ps at 421 nm at liquid nitrogen temperature without any bathorhodopsin being observed during the formation of hypsorhodopsin. An experiment using an N₂ laser showed that squid bathorhodopsin converted to lumirhodopsin with a decay time of about 300 ns at room temperature.     

ON THE ORIGIN OF LOW TEMPERATURE THERMOLUMINESCENCE IN NUCLEIC ACID BASES: EXCITATION AND EMISSION SPECTRAL STUDIES

Abstract. Thermoluminescence excitation spectra of adenine, guanine, thymine and 1,3-dimethyluracil were observed to be similar to their phosphorescence excitation spectra. Intensity dependence studies of thermoluminescence induced by ultraviolet light suggest that thermoluminescence could not be due to biphotonic ionisation of the molecule by UV. Evidence is presented which demonstrates that the fluorescence component observed in thermoluminescence of some compounds may not be due to triplet-triplet fusion. Further, phosphorescence and thermoluminescence measurements following excitation with monochromatic light at very low intensities and short durations have shown for both a linear dependence on excitation intensity. It thus appears that direct entry of the electrons from the traps into the singlet manifold is necessary for explaining the fluorescence component of thermoluminescence.     

INTERMEDIATES IN THE ROOM TEMPERATURE FLASH PHOTOLYSIS AND LOW TEMPERATURE PHOTOLYSIS OF PURINE SOLUTIONS

The flash photolysis of purine in acetonitrile and in water at different pH was studied. The transients produced on flash excitation of degassed aqueous solutions have been identified as the triplet excited state, the hydrated electron, a purine radical cation and radical anion on the basis of quenching experiments and comparison to transients observed in low temperature photolysis.     

STUDIES ON THE PROTECTIVE FUNCTION OF THE CAROTENOID PIGMENTS OF SARCINA LUTEA

Abstract— An investigation was made of both the composition of and mechanism of photo-protection by the carotenoid pigments of Sarcina lutea ATCC 9341a and three induced mutants.
The wild-type and mutants 2a and 4b were each found to contain three major pigment fractions, each fraction consisting of a single pigment having identical absorption maxima but differing from each other in chromatographic mobility. Although the mutants contain the same kinds of pigments as does the wild-type, the mutant cells contain less pigment per cell than does the wild-type. The third mutant, 93a, contains no colored carotenoids.
It was found that there were changes in both the absolute and relative amounts of the various pigment fractions when cultures of wild-type, mutants 2a and 4b, grown in nutrient broth in the dark, were examined during the logarithmic and stationary phases of the growth curve. In addition, changes were observed in the pigments when the cells were exposed to light in buffer. These changes were similar in the wild-type and in mutant 2a, but were quite different in mutant 4b. Studies of photokilling curves suggested that these changes in amounts of the various pigment fractions were not related to photoprotection, but that the important factor may be the total amount of pigment per cell.     

SIMULATION ANALYSIS OF THE PHOTOCONVERSION PROCESS OF SQUID RHODOPSIN AT LIQUID HELIUM TEMPERATURE

The photoconversion process among squid rhodopsin, bathorhodopsin isorhodopsin and hypsorhodopsin was studied at liquid helium temperature. We evaluated the relative quantum yields of the photoconversion among four pigments by analysing the time-dependent change of absorption spectra. The result suggests that hypsorhodopsin is the common intermediate of rhodopsin and isorhodopsin, and there is no direct conversion between rhodopsin and isorhodopsin. Furthermore, rhodopsin converts to hypsorhodopsin or bathorhodopsin much more efficiently than does isorhodopsin, and bathorhodopsin does not convert directly to hypsorhodopsin. It was also found that rhodopsin and isorhodopsin convert to bathorhodopsin more efficiently than to hypsorhodopsin. In particular, the quantum yield of conversion from rhodopsin to bathorhodopsin was found to be about twice as large as that from rhodopsin to hypsorhodopsin. This result is somewhat in disagreement with the result obtained from the laser flash experiments at room and liquid nitrogen temperatures. The reason for the difference between the two experimental results is discussed.     

MICROSPECTROPHOTOMETRIC STUDIES ON THE PIGMENTS IN VIVO OF SINGLE ALGAL CELLS-I. PIGMENTS OF CHLORELLA PYRENOIDOSA

Abstract— The pigments in vivo of single cells of Chlorella pyrenoidosa were studied by the microspectrophotometric technique. An accessory recording the first derivative of absorption was used to obtain fine resolution and enhanced accuracy. The results suggest that there are several long-wavelength components of Chl a in vivo. In addition, there seem to be four short-wave forms of Chl a. It is also likely that Chl b exists in vivo in two different forms. The existence of all these forms was demonstrated at room temperature.     

LASER FLASH PHOTOLYSIS OF RHODOPSIN AT ROOM TEMPERATURE

Abstract. Nanosecond flash photolysis of rhodopsin with 530 or 353 nm light produces an initial transient absorption spectrum with peaks at ˜57O and ˜420nm, and a subsequent transient species with a maximum absorption at 480 nm. These results are interpreted as the initial formation of prelumi-rhodopsin (570 nm) followed by its conversion to lumirhodopsin (470 nm). The peak at 420 nm in the first transient may be due to either hypsorhodopsin or isorhodopsin.     

偶氮化合物的光电导性能的研究

本文合成了五种双偶氮颜料,它们是以芴酮为桥基,以含有五种不同取代基的色酚为偶合剂的化合物.测定了这些化合物的吸收光谱和X射线衍射光谱;分别以这五种偶氮颜料为电荷产生材料制备了功能分离型双层光电导体,并对它们的光电导性能进行了研究.     

STUDIES ON THE LOCALIZATION, FUNCTION, AND FORMATION OF THE CAROTENOID PIGMENTS OF A STRAIN OF MYCOBACTBRIUM MARINUM

Abstract— Aninvestigation was made of the location, function and characteristics of production of carotenoid pigments of a strain of Mycobacterium marinum , an organism which produces its pigments only when exposed to light.
It was found that light-grown cells of this organism contain only one pigment. The intracellular location of this pigment was found to be the cell envelope. The pigment was found to be capable of protecting the cells against lethal photo-oxidations mediated by the dye, toluidine blue.
These studies also revealed that in dark-grown cells exposed to light, pigment production occurred after a short lag and then remained constant during logarithmic growth. Pigment was produced by starved cells, but to a lesser degree than son-starved cells; the addition of a carbon or nitrogen source to starved cells increased pigmentation to the level in non-starved cells. Pigmentation did not occur in the absence of oxygen. Cells exposed to light at 4°C were not pigmented immediately after exposure, but became so if incubated at 30°C. Production of pigment was found to obey the Bunsen-Roscoe reciprocity law. The determination of an action spectrum for the production of pigment indicates that maximum pigment productiion occurs in the vicinity of 410 and 439 mµ, with smaller maxima in the vicinity of 502 , 528 and 560 mµ.