FLUORESCENCE OF 5-METHYLCYTOSINE

Abstract— 5-Methylcytosine and 5-methyldeoxycytidylic acid are fluorescent in aqueous solution at room temperature and neutral pH. 5-Methylcytosine, 10^-3M, pH 8.5, 25°C, has a quantum yield of 5 ×10^-4, 5-Methyldeoxycitydylic acid, 10^-4M, pH 7.5, 20°C, has a quantum yield of 8 × 10^-4. Emission maxima are 2.91 and 2.80μ^-1. At pH 14, the quantum yield of 5-methylcytosine is 1.6 × 10^-2; the emission maximum is 2.82μ^-1. At pH I, the quantum yield of both compounds is less than or equal to 10^-4. Both compounds were chromatographically homogeneous, had absorption spectra which agreed with published data, and excitation spectra which agreed closely with absorption spectra.     

EXCITED STATES OF FLAVINES – V. THE QUENCHING OF FLAVINE LUMINESCENCE BY INDOLES

Abstract— The quenching of the fluorescence of flavines by indoles in aqueous solution has been studied as a function of concentration, viscosity and temperature. The quenching shows a negative temperature dependence, and is in part diffusion controlled. Static and dynamic processes both contribute to quenching.
In the presence of alcohol or denaturants static quenching is inhibited and dynamic quenching supervenes. The effect of indoles on the flavine fluorescence lifetimes and phosphorescence characteristics is consistent with the quenching mechanism proposed.     

EXCITED STATE DYNAMICS OF RETINAL PROTEINS AS STUDIED BY FOURIER TRANSFORM OF OPTICAL ABSORPTION SPECTRUM—I. DEVELOPMENT OF ANALYTICAL METHOD

Abstract— We significantly improved the analytical method for the study of excited state dynamics of pigments, by means of the time correlation function (tcf) of the vibrational wavepacket which is produced by the Fourier transform of experimentally obtained optical absorption spectra (FTOA). Applying the tcf method to the spectra of rhodopsin at 0°C and -180°C, we observed specific peaks which are slightly different between 0°C and -180°C in the early time region (1–130 fs) of the absolute value of tcf, representing a characteristic propagation of the wavepacket along a reaction coordinate pertinent to the cis-trans photoisomerization of the chromophore accompanying the motion of protein moiety. From the analysis of phase angle propagation, we obtained a rather small relaxation energy, 6–7 kcal/mol. Based on these results, we can say that FTOA analysis is useful as one of the most powerful techniques for the study of very early procedures in the excited state dynamics of pigments.     

TRIPLET ESR IN l-TYROSINE

Abstract— Triplet state electron spin resonances have been observed from L-tyrosine in low temperature glasses at 77° K on irradiation by u.v. light in the band between 220 and 300 millimicrons. Two different resonances have been observed. and ESR spectra and optical absorption spectra as a function of degree of ionization show that the resonances are due to the ionized and un-ionized forms of tyrosine respectively. Solvent composition and temperature affect the ratio of the concentrations of the two forms but not their resonant fields. The resonances have half lives of from two to three seconds at 77° K.     

硅胶表面结构的热稳定性研究

本文研究了热处理(200-1100℃)对自制的一种硅胶的表面结构的影响;测定了BET比表面(低温氮气吸附法)、孔体积、乙醇的吸附-脱附等温线,计算了孔径分布,求得了最可几Kelvin半径。结果表明,杂质的存在明显地降低硅胶的热稳定性。在发生熔结以前,孔径分布基本不变,当发生熔结时,孔半径显著减小。红外光谱的测定表明,随着热处理温度的升高,硅胶表面缔合羟基(～3500cm^-1)迅速减少,在～800°时已去除殆尽,而自由羟基(～3720cm^-1)减少缓慢,在1100℃时才迅速消失。X-射线衍射图表明,发生熔结后的硅胶显示有β-鳞石英的衍射峰,说明出现了有序晶相。对上述实验结果,文中作了初步的解释。     

DISTRIBUTION OF PORPHYRINS IN THE VARIOUS COMPARTMENTS OF UNILAMELLAR LIPOSOMES OF DIPALMITOYL-PHOSPHATIDYLCHOLINE AS PROBED BY FLUORESCENCE SPECTROSCOPY

Abstract— The spectroscopic properties of hematoporphyrin, hematoporphyrin-dimethyl ester, uroporphyrin and uroporphyrinoctamethyl ester, incorporated into unilamellar liposomes of dipalmitoylphos-phatidylcholine, have been studied with the aim to assess the distribution of porphyrins within the various liposomal compartments.
The results obtained indicate that the highly hydrosoluble uroporphyrin is partitioned in the endoliposomal aqueous pool while its octamethylester is homogeneously distributed in the inner lipid monolayer. Hematoporphyrin and its dimethylester show an heterogeneous distribution within the phospholipid bilayer. At T = 25°C these porphyrins are preferentially located in the outer phospholipid monolayer.
Detailed studies on hematoporphyrin indicate that the distribution between the inner and outer phospholipid monolayer is a function of temperature and liposome dimensions. In particular, the increase of temperature above the critical temperature for the liquid-gel phase transition of the liposomes causes a partial shift of the porphyrin molecules toward the inner phospholipid monolayer. Moreover, the increase of liposome dimensions leads to a greater accessibility of porphyrin to the external medium.     

PHOTOREDUCTION OF CRYSTAL VIOLET IN SOLUTION AND IN POLY(VINYL ALCOHOL) FILMS

Abstract— The photolysis of crystal violet oxalate has been studied in aqueous and non-aqueous solutions and in films of poly(viny1 alcohol) at room temperature. Evidence has been obtained from electron-spin-resonance, absorption and fluorescence spectroscopy for the formation of the semireduced dye radical, tri-( p -dimethylaminophenyl)methyl, both in solution and in the solid state. Electron spin resonance and luminescence spectra of the radical produced by electrolytic reduction of the dye are also reported.     

乙醇对柠檬酸铁水解聚合的影响

向Fe(Ⅲ)—柠檬酸水溶液体系中加入无水乙醇,并经放置处理等,体系中(?)_(Fe)Ⅲ(Fe(Ⅲ)各种形式平均克磁化率)比水体系及未经放置的加醇体系有所增加,pH滴定曲线终点前移,紫外、可见光度揭示有新物种生成,我们认为体系中可能生成了含醇的多元配合物,机理有待进一步探讨。     

FLASH PHOTOLYSIS OF ROD PARTICLE SUSPENSIONS

Abstract. Flash photolytic experiments with suspensions of rod particles isolated from cattle eyes reveal that at low temperatures a transient is formed following irradiation which preceeds lumirhodopsin in the bleaching process. Kinetic studies, in the range -75°C to -50°C, suggest that the transient is composed of three intermediate species, having similar absorption spectra but changing to lumirhodopsin at different rates. The energies of activation of the decay reactions appear to be identical and equal 12.5°3 kcal/mole. Spectrophotometric experiments have demonstrated that the low temperature transient is stable at liquid nitrogen temperatures and suggest that it can be reversibly converted to a mixture of rhodopsin and isorhodopsin at -195°C.
A detailed comparison of light initiated reactions of rhodopsin in rod particle suspensions and in solutions reveals striking similarity in the two systems.     

POLARIZED FLUORESCENCE OF 5-METHYLCYTOSINE SPECIES IN SOLUTION AT ROOM TEMPERATURE

Fluorescence yields (π_f,'s) and polarizations ( P ) are measured for aqueous 5-methylcytosine (˜ 0.1 m M ) at 20°C as a function of pH over the range 2–14. Both properties change abruptly and in parallel at pH's corresponding to the known pK_a values. Polarizations were also obtained for the 5-methylcytosine cation, neutral and anion species in ethylene glycol water glass at ˜180K. The weak fluorescence of the neutral and cation species at 20°C was polarized almost as highly as at low temperature. When the fluorescence lifetimes are assumed to be correctly given by the product of calculated radiative lifetimes and quantum yields, the polarizations are found to be consistent with rotational diffusion rates ˜4 times faster than predicted from Stokes-Einstein models for the neutral and anion species. The cation seemed to rotate about two times more slowly than the neutral and anion species. It was also shown that the properties of the three species are such that a plot of 1/P vs apparent π_f in the pH range 2–11 is fortuitously linear.     

FLUORESCENCE OF 1-DIMETHYLAMINONAPHTHALENE-5-SULFONATE AND PYRENE-1-SULFONATE CONJUGATED TO BACTERIORHODOPSIN

Abstract— Two fluorescence probes, 1-dimethylaminonaphthalene-5-sulfonylchloride and pyrene-1-sulfonylchloride, were conjugated to the protein in purple membrane and fluorescence intensity and anisotropy were measured as a function of temperature. The anisotropy of the 1-dimethyl-aminonaphthalene-5-sulfonate conjugate showed a characteristic temperature dependence, in which, the anisotropy is constant at 0.22 ± 0.01 until 25-30°C and decreases above 30°C. The fluorescence intensity, however, varies linearly with temperature. These results imply that the transition is due to bacteriorhodopsin in the trimer.     

SPECTRAL CHARACTERISTICS OF THE EXCITED STATES OF THE PRODUCT OF THE CHEMILUMINESCENCE OF LUMINOL*

Abstract— In dimethylsulfoxide the emission spectrum of luminol chemiluminescence is red-shifted by 300 cm^-1 from the photoexcited fluorescence of the product 3-aminophthalate dianion, while in aqueous solvent the two spectra are identical. The spectral properties of the product dianion have been measured in aqueous solvent and in a number of aprotic solvents, both at room temperature and at 77°K. The ground states and the excited states from which emissions are observed are characterized. Two alternatives are presented to explain the aprotic emission spectra.     

Interactions in water-alcohol mixtures studied by NMR and infrared spectroscopy

By using low temperatures and largely deuterated solvents, the rate of OH proton exchange for aqueous solutions of alcohols is reduced sufficiently to give separate NMR signals from water and alcohol OH protons. The limiting shifts for dilute alcohols in water are down-field of both the water resonance and those of the pure alcohols. This contrasts with the limiting shift for water in the alcohols, which is to high field of the bulk water resonance. The resonance shifts initially to low fields as [ROH] increases, the rate of shift being greatest for t-butyl alcohol. For dilute aqueous solutions, all the alcohols reduce the total concentration of free OH groups, as judged by the overtone infrared spectra. Some of these results are interpreted in terms of a scavenging of free OH groups by the excess lone-pairs of the alcohol molecules. An extra, temperature dependent, down-field shift in the water proton resonance induced by t-butyl alcohol is assigned to a clathrate cage effect.     

LUMINESCENCE OF TAUTOMERIC FORMS OF THYMINE MONOANIONS

Abstract— The fluorescence and phosphorescence emission and excitation spectra of monoan-ions of thymine. I-methyl-thymine and 3-methylthymine (in alkaline solutions, 10^-2N NaOH) at 300° and 77°K were measured. It was shown, that at 300°K only 3-HT- tautomeric thymine monoanion fluoresces; at 77°K emissions of both monoanionic species contribute to the observed luminescence spectrum.     

THE FLUORESCENCE OF ADENINE. THE EFFECTS OF SOLVENT AND TEMPERATURE ON THE QUANTUM YIELD

Abstract— To investigate the mechanism of the solvent and thermal quenching of fluorescence, the absolute fluorescence quantum yield of adenine has been determined in several alcoholic glasses as a function of the concentration (10^-5-10^-4M) and temperature (77°-298°K). The yield is independent of the concentration but increases with decreasing temperature and increasing bulk cohesion and rigidity of the solvent.
The environmental effects on the yield are attributed to radiationless electronic relaxation processes caused by solute-solvent interaction. Increasing the temperature and decreasing the intra-solvent cohesion cause increases in the interaction and therefore accelerate the relaxation. The rate determining step behaves like a diffusion in the limit of low viscosity.     

STRUCTURAL STUDIES OF BROWN MEMBRANE BY X-RAY DIFFRACTION, CIRCULAR DICHROISM AND ABSORPTION SPECTRA

Abstract— Time course of formation and crystallization of bacteriorhodopsin upon the addition of retinal to brown apo-membrane has been studied by X-ray diffraction, circular dichroism (CD) spectra and absorption spectra. The rate of formation of bacteriorhodopsin decreases markedly at low pH (4.8) and low temperature (5°C). Furthermore, the formation of bacteriorhodopsin does not proceed in fully dried membranes. The half-time of the increase of exciton CD band is about 70s at 17°C and pH 7.0, and is comparable to that of the formation of bacteriorhodopsins (∼48s). The crystallization of bacteriorhodopsin proceeds to a large extent within 30 min at pH 7.0 and 5°C.
The bilobed CD band of the brown holo-membrane attributed to exciton coupling of bacteriorhodopsin molecules becomes negligibly small at pH 4.8, even though X-ray diffraction pattern indicates the lattice structure to be similar to that of the native purple membrane.     

TEMPERATURE-SENSITIVITY OF LIGHT-INDUCED PHASE SHIFTING OF THE CIRCADIAN CLOCK OF NEUROSPORA

Two new mutants of Neurospora craasa , designated hth-1 and hth-2 , have been isolated which allow clear expression of the circadian conidiation rhythm at high temperature (36°C). Both strains showed single-gene segregation and produced similar phenotypes but mapped to different genetic loci. These mutants allowed an analysis of the effect of temperature on (1) light-induced phase-shifting of the circadian rhythm, (2) period length of rhythm, and (3) growth rate. The amplitude of the phase response curve to light was drastically reduced as the temperature was increased from 25°C to 34°C. Phase advances were decreased more than phase delays. As previously reported (Sargent et al. , 1966), the period length of the rhythm is temperature-compensated below 30°C ( Q ₁₀˜ 1) but not well-compensated above 30°C ( Q ₁₀ 1.3–1.7). The decrease in amplitude of the light phase response curve occurred in both temperature ranges. Furthermore, the Q ₁₀ value was lowered by addition of yeast extract in the high temperature range but not in the low range. Q ₁₀ values for growth rate also differed in these strains both in the low temperature range (25–30°C) and the high temperature range (30–34°C).     

SPECTRAL PROPERTIES OF THE RHODOPSIN-SYSTEM OF THE CRAYFISH Astacus leptodactylus

Abstract— The absorption spectra of the membrane-bound and of the digitonin-solubilized visual pigment of crayfish Astacus leptodactylus were investigated by conventional spectrophotometry. A method was developed to isolate purified rhabdoms almost entirely free from screening pigments from a single retina. The quantity of isolated and purified rhabdoms from a single retina was sufficient to measure the absorption spectra of the visual pigment.
The absorption spectra of the chromoprotein system (R and M) show that both the membrane-bound and the digitonin-solubilized visual pigment isomers are stable at 0°C and pH 7.0. Rhodopsin and metarhodopsin are photoreversible under these conditions without any light-induced denaturation. The difference spectra for the chromoprotein isomers and those of different photostationary states yield maximal values for ΔE at 570 and 485 nm.
At neutral pH, 0°C, Λ_max of rhodopsin is 530 nm. Irradiation with light of Λ= 630 to 640 nm isomerizes rhodopsin nearly quantitatively to metarhodopsin with Λ_max, of 500 nm. The molar extinction coefficient of metarhodopsin is greater than that of rhodopsin by a factor of ˜ 1.41. each measured at its respective Λ_max Metarhodopsin can be isomerized to rhodopsin by irradiating at Λ > 630 nm. As the absorption spectra of the two chromoprotein isomers overlap, only part of the metarhodopsin can be reversed to rhodopsin. The maximal photoreversion can be achieved by irradiating at 460 nm. The stability of the digitonin-solubilized chromoprotein is remarkably dependent on temperature. Warming the digitonin extract of rhabdoms from 0 to 20 or 30°C caused a shift of the rhodopsin spectrum to shorter wavelengths (Λ_max= 485 nm) accompanied by a decrease of E_Λmax by about 30%.     

PHOTOPHYSICAL STUDY OF THE SCHIFF BASES OF 5'-DEOXYPYRIDOXAL AND n-HEXYLAMINE IN CATIONIC MICELLES

Abstract-The absorption and fluorescence spectra of the Schiff bases formed between 5'-deoxypyridoxal and n-hex-ylamine in aqueous media containing different concentrations of the cationic surfactant hexadecyltrimethylammonium bromide were recorded at 25°C. The quantum yields of fluorescence of the different zwitterionic and enol forms of the chemical species of the Schiff bases occumng in media of pH 4.5–8.5 were determined. Also, the fluorescence quenching resulting from the presence of the surfactant and that of iodide ion were analyzed. From the results obtained it follows that the zwitterionic forms do not interact with the cationic surfactant, whereas the enol forms do interact with it.     

LUMINESCENCE OF L-TRYPTOPHAN IN THE DRY STATE AND IN AQUEOUS SOLUTION INDUCED BY X-RAYS AND U.V.-LIGHT AT 77°K

Abstract— The luminescence from tryptophan in the dry state and in aqueous glass. induced by u.v.-light and X-rays at 77°K, has been studied. The spectra of the luminescence from the dry material, which were identical for the two types of irradiation, were attributed to the same excited singlet level as that giving rise to the fluorescence from the aqueous sample. The strong phosphorescence exhibited by the latter. could not be detected for the dry material with either type of irradiation. This was attributed to a strong quenching of the radiative triplet level occurring upon crystallization of the substance. The yield of X-ray induced fluorescence of tryptophan in aqueous glass was found to be similar to that observed in the dry state. It was concluded that there is no extensive transfer of energy between the solvent and the solute molecules contributing to the fluorescence yield of tryptophan in aqueous glass.