共查询到20条相似文献,搜索用时 484 毫秒
1.
Abstract— The absorption and emission spectra of quinizarin (1,4-dihydroxy-anthraquinone) have been investigated in hydrocarbon and alcoholic solvents. Fluorescence spectra in 3 different Shpolskii matrices were recorded at 14 K. Vibrational analyses of these spectra revealed the presence of 3, 8, and 9 sites in octane, heptane, and hexane matrices, respectively. The fluorescence lifetime was found to be 6.5 ns in hexane and EPA. Fluorescence photoselection measurements in EPA (77 K) showed that the first 4 electronic transitions of quinizarin are polarized parallel, parallel, perpendicular, and parallel to the long molecular axis and can be assigned, in order of increasing energy, to 1 B2 , 1 B2 , 1 A1 and 1 B2 (ππ*)→1 A1 (C2v ,) transitions, respectively. The fluorescent transition is assigned as 1 B1 (ππ*)→1 A1 . The absence of phosphorescence is attributed to the intramolecular hydrogen bonding present which displaces the parent anthraquinone n →* states above the ππ* states, thereby rendering the intersystem crossing (S1 -T1 ) radiationless pathway inefficient.
Photoselection measurements on daunorubicin, a substituted quinizarin and known anticancer drug, revealed an absorption band polarization pattern identical to that of quinizarin. These results are in part at variance with assumptions used in previous work on the intercalation specificity of daunorubicin with DNA. 相似文献
Photoselection measurements on daunorubicin, a substituted quinizarin and known anticancer drug, revealed an absorption band polarization pattern identical to that of quinizarin. These results are in part at variance with assumptions used in previous work on the intercalation specificity of daunorubicin with DNA. 相似文献
2.
Abstract —The triplet states of the n -butyl-amine Schiff bases of 11- cis , 9- cis , 13- cis and all- trans retinal are produced via triplet-triplet energy transfer. Their absorption spectra, peaking around 435 nm, and their decay kinetics are recorded using pulsed-laser photolysis. Direct-excitation (φD ISO ) and triplet-sensitized (φT ISO ) photoisomerization yields, determined using steady irradiation methods, are found to be: φT ISO (9- cis ) = 0.06, φT ISO (11- cis ) = 045, φT ISO (13- cis ) = 008, φT ISO (all- trans ) = 0.02-0.05, φD ISO (11- cis , = (4 ± 1) × 10-3 , φD ISO (all- trans ) = (2 ± 1) × 10-3 . The possible role of the triplet state in the isomerization of rhodospin is discussed. 相似文献
3.
Abstract— The pathways and quantum yields of direct photoisomerization of unprotonated and pro-tonated n-butylamine Schiff bases (SB and PSB) of isomeric retinylideneacetaldehyde (C22 aldehyde) were determined in n-hexane, acetonitrile and methanol for the former and in acetonitrile and methanol for the latter. The results are compared with those of the Schiff bases of isomeric retinal (C20 SB and C20 PSB) reported previously (Koyama et al., Photochem. Photobiol. 54 , 433–443, 1991). The isomerization pathways and quantum yields of C22 SB are more or less similar to those of C20 SB, but conspicuous differences in the isomerization pathways are found between C22 PSB and C20 PSB. The homogeneous (exclusive) isomerization of the retinylidene chromophore from all-trum to 11-cis in retinochrome is rationalized not by C22 PSB but by C20 PSB.
Almost complete one-way isomerization from cis to trans of C22 SB (in n-hexane) is ascribed to isomerization via the T1 state, while mutual isomeritation between cis and tram of C22 PSB is ascribed to isomerization via the S1 (Bu ) state. The TI potential of C22 SB and the S1 potential of C22 PSB are discussed based on photostationary state compositions. 相似文献
Almost complete one-way isomerization from cis to trans of C22 SB (in n-hexane) is ascribed to isomerization via the T
4.
Abstract— Low-temperature (and some room temperature) absorption and emission, fluorescence and phosphorescence, data including quantum yields and lifetimes have been obtained from the title pyrimidine bases as a function of the nature of the solvent environment. Modest vibrational resolution has been observed for the first time in the absorption spectra, particularly for thymine and uracil. The excitation spectra also show structure. The quantum yields of fluorescence (φF ) and phosphorescence are independent of the excitation wavelength. Thymine, thymidine and uracil have profoundly different photophysical properties in polar-aprotic vs polar-protic solvents. The N, N-dimethyl substitution of thymine and uracil produces photophysical changes comparable to the solvent change for the unsubsti-tuted bases. The species involved in the emission processes is the keto (lactam) form. It is probable that 1,3 (n,π*) state(s) has(have) changed order relative to a lowest 1 (π,π*) state as a consequence of both the solvent change and N, N-dimethyl substitution. The lowest triplet state is assigned as 3 (n π*). We propose that an important factor contributing to the previously reported excitation wavelength dependence of φF and φT1 (φisc ) for nucleic-acid components is the equilibrium coexistence of H-bonded and non-H-bonded forms each having different photophysical properties. Consideration is given of the impact of the significantly different photophysical properties of nucleic-acid bases as a function of the nature of the solvent upon the photochemical properties. 相似文献
5.
Kohji Chihara Takeshi Takemura Tsuguo Yamaoka N. Yamamoto Arnold Schaffer Ralph S. Becker 《Photochemistry and photobiology》1979,29(5):1001-1008
Abstract— The absorption and emission spectra, lifetimes and quantum yields of all-trans retinol have been examined as a function of solvent and temperature. In addition, the spectroscopy of retinyl ether and 2 other polyene alcohols have been determined. Based on the results obtained, we conclude that the singlet excited state of retinol and retinyl cther is of a forbidden character and of the type loosely called 1 A- g . Retinol forms a dimer in an alkane solvent when cooling from 298 to 77 K. A general structure for the dimer is proposed. 相似文献
6.
L. S. Lussier C. Sandorfy H. OA L E-Thanh D. Vocelle 《Photochemistry and photobiology》1987,45(S1):801-808
Abstract— The Fourier-transform infrared spectra of chloroform-d solutions of conjugated imines CH3 CH=CHCH=NCH(CH3 )2 and CH3 CH2 CH=CHCH=CHCH=NCH(CH3 )2 and the related protonated species with HCl, HBr, HI, trichloro, dichloro, monobromo and monochloroacetic acids or propionic acid are presented. The effects of conjugation and protonation are examined. The results show that conjugation slightly increases the basicity of the Schiff bases. HCl, HBr and HI protonate the Schiff bases completely. The carboxylic acids protonate partially depending on their p K a , values. When the Schiff base contains two (or more) C=C bonds conjugated with C=N, the main C=C stretching band undergoes a strong intensification showing that sizeable dipole moment variations occur along the conjugated chain. 相似文献
7.
MARIAN ELBANOWSKI MARIA PAETZ JANUSZ SIAWINSKI LESZEK CIELA 《Photochemistry and photobiology》1988,47(3):463-466
Abstract— Chemiluminescence of the Eu(II)/Eu(III)-adenine nucleotide-H2 O2 system and fluorescence of the Eu(III)-adenosine triphosphate system have been investigated. The spectral distribution of the chemiluminescence emission has shown an occurrence of three main bands (Λ=470–480,590–620 and ca. 700 nm). The energy transfer process from the adenosine triphosphate molecules to the Eu(III) ions has been observed in the fluorescence spectrum. The examined chemiluminescence and fluorescence spectra show that these both kinds of emission originate from the 5 D *** τ7 F*** ( n =1–4) transitions in the Eu(III) ions. 相似文献
8.
Abstract— The absorption spectra, lifetimes, extinction coefficients and intersystem crossing quantum yields of the lowest triplet T 1 of 4-thiouridine have been determined both in acetonitrile and in water. An ordering of 1,3 (n,π)* and 1,3 (π,π)* states is suggested. Triplet quenching rate constants with various pyrimidine bases or amino acids are reported. 相似文献
9.
CHARACTERIZATION OF SOME SCHIFF BASES OF HETEROCYCLIC COMPOUNDS AND THEIR TRANSITION METAL COMPLEXES
Some new Schiff bases were synthesized by the condensation ofequimolar quantities of salicylaldehyde and 2-amino-5-phenylazo-pyridine orits derivatives in dry benzene(1):Metal complexes of the type ML_2and M'L_3where M=Cu~(2+),Co~(2+),Ni~(2+),Mn~(2+)Pd~(2+),M'=Fe~(3+)and L=different newly synthesizedmonobasic Schiff bases were prepared in absolute ethanolic medium(2)andcharacterized by elementary analysis,conductance measurements,infraredspectra,electronic spectra,magnetic moments studies. 相似文献
10.
Abstract— Emission and absorption spectra of neutral, monocation and dication dibucaine were recorded in hydrocarbon and hydroxylic solvents. The spectral analysis indicates that the lowest electronic states of dibucaine originate from the quinoline analogue in the molecule. The fluorescence and phosphorescence emission of neutral dibucaine in all solvents at 77 K are best assigned as resulting from 1 n ,π* and 3 π,π*, respectively, whereas those of both monocation and dication dibucaines are found to have 1 π,π* and 3 π,π*. The monocation and neutral dibucaines in ethanol solutions were shown to give identical emission spectral properties, indicating that dibucaine-HCl in ethanol is H+ dissociative; this was confirmed by FT-IR studies. The possible explanations for the deprotonation of dibucaine-HCl in ethanol environments are discussed. 相似文献
11.
Abstract— The triplet absorption spectra, lifetimes, extinction coefficients, eTT , and intersystem crossing quantum yields to the lowest triplet T1 , øT1 , of thymidine, thymidine monophosphate, uridine and uridine monophosphate, have been determined in various solvents at 300 K.
The effect of H-bonding on øT1 , of these nucleosides and nucleotides and also of uracil has been determined and discussed. This effect allows, an ordering of l,3 n, π* and 1,3 π, π* states in protic and aprotic solvents. 相似文献
The effect of H-bonding on ø
12.
Abstract— Results concerning absorption-emission spectra and fluorescence quantum yields at 77 and 298K. triplet absorption spectra, and quantum yields of intersystem crossing and photoisomerization at 298 K, are presented for 11- cis β-apo-14'-carotenal (C22 -Ald), the immediate higher homologue of 11- cis retinal. The absorption spectra are characterized by two band-systems with maxima at 390–400 and 270–280 nm, respectively. Upon cooling from 298 to 77 K, the intensities of these two band-systems undergo changes in opposite directions indicating 12-s- cis: 12- s-trans conformational changes. No intermediate band-system analogous to the one located at 270–310 nm in cis retinals is observed for 11- cis C22 -Ald. In nonpolar hydrocarbon solvents (e. g. cyclohexane) at room temperature, quantum yields of fluorescence (0.01), intersystem crossing (0.6) and photoisomerization (0.4) are all quite pronounced. The photophysical and photochemical properties of 11- cis C22 -Ald are discussed in the light of similarities and dissimilarities with those of all- trans C22 -Ald and 11- cis retinal under comparable conditions. 相似文献
13.
Miguel A. Vazquez Segura Josefa Donoso Francisco Muntoz Francisco Garciaa Blanco M. Angeles Garciaa del Vado Gerardo Echevarriaa 《Photochemistry and photobiology》1994,60(5):399-404
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. 相似文献
14.
Abstract— In bidistilled water, 4-thiouridine (4TU) exhibits a weak unusual luminescence, the quantum yield of which is 3 × 10-4 at 25°C. The excitation spectrum corresponds well to the 4TU absorption spectrum. The emission lies at longer wavelengths (Λmax 550 nm) than the 4TU phosphorescence observed at 77 K (Λmax , 470–480 nm). From the emission signal obtained after an excitation flash of 3 ns half-width, an "apparent" rate constant for the radiative deactivation process, shorter than 5 × 106 s, can be inferred. The 300 K emission is efficiently quenched by halides and by oxygen: quenching involves a long-lived intermediate (⋍ 200 ns).
Clearly the emissive state X is populated through the S0 -S1 electronic transition π→π* of 4TU. The nature of X cannot be unambiguously determined: it cannot be an excimer but can be either the 4TU triplet state or another chemical state distinct from the 4TU excited singlet or triplet states.
An interesting finding is that the 300 K emission and the ability of 4TU to photoreact are related: they are quenched with the same efficiency by halide anions. This indicates that quenching occurs at the same long-lived intermediate species , which is either a precursor of the emitter or the emitter itself. 相似文献
Clearly the emissive state X is populated through the S
An interesting finding is that the 300 K emission and the ability of 4TU to photoreact are related: they are quenched with the same efficiency by halide anions. This indicates that quenching occurs at the same long-lived intermediate species , which is either a precursor of the emitter or the emitter itself. 相似文献
15.
G. Schermann R. Schmidt A. Völcker H.-D. Brauer H. Mertes B. Franck 《Photochemistry and photobiology》1990,52(4):741-744
Abstract— –Photophysical properties of [26] porphyrin (26 P) were investigated in chloroform. The quantum yields of fluorescence, of S1 → T1 intersystem crossing and singlet oxygen formation were measured. The purity, stability, the strong absorption in the red (δmax = 783 nm; εmax = 28 000 M 1 cm-1 ) and the ability of singlet oxygen formation recommend 26 P as potential photosensitizer for tumor therapy. 相似文献
16.
A number of polyene alcohols related to retinol as homologues have been examined for their spectral and photophysical properties. The absorption spectra of the polyene alcohols with short polyene chainlength show an intense band system with its maximum at 3000–4000 cm-1 above that of the main band system. The intensity of this higher-energy band system decreases sharply as the polyene chainlength is increased. All the polyene alcohols fluoresce strongly or moderately strongly at 77 K, the intrinsic fluorescence lifetimes being significantly longer than those expected from the oscillator strengths of the main, low-energy absorption band system. Fluorescence (relatively weak) is also observed at room temperature in the cases of polyene alcohols of long chainlength. A discussion is presented regarding the possible assignments of the various observed absorption band systems, state order and nature of the lowest excited singlet state, and aggregate formation (in 3-methylpentane at 77 K) and its effect on spectral and photodynamical behavior. 相似文献
17.
Abstract —The pulsed ruby laser (347 nm) flash photolysis technique has been used to measure the triplet-triplet absorption spectra and triplet lifetimes of trans -retinal, N-frans -retinylidene- n -butylamine (NRBA), and protonated NRBA (NRBAH+ ) at room temperature. In methylcyclohexane solution, the triplet lifetimes are in the range 10–20 μs and decrease in the order NRBAH+ > NRBA > trans -retinal. Intersy stem-crossing efficiencies (φISC ) were determined by a comparison technique using anthracene and 1,2-benzanthracene as reference compounds. For trans -retinal, φISC is 0–50 pM 0–05 in methylcyclohexane and 0–08 in methanol, which confirms that earlier values of 0–11 and 0–017 in these solvents are in error. For NRBA and NRBAH+ in methylcyclohexane, ΦISC values are 0008 and < 0–001, respectively. Evidence is presented for a significant solvent effect in the isomerization of retinal via the triplet state, and that cis φ trans isomerization occurs from the triplet state of NRBAH+ . The relation between the intersystem-crossing properties of model compounds and the photochemistry of rhodopsin is discussed. 相似文献
18.
Abstract— –Problems associated with the protolytic equilibria of thionine and related molecules in their lowest excited electronic states were investigated. The theoretical arguments are based on semi-empirical SCF MO (CI) calculations for the π-electronic system of these molecules; all singly excited configurations were included in the CI. The results indicate that the basic form of thionine in its ground, first excited singlet and lowest triplet state is protonated at the heterocyclic N atom. The difference of the p K values of these three states can be explained in terms of the calculated charge densities. The photochemical reactivity of the lowest triplet of the acidic form of thionine (3 TH2 2+ ) differs greatly from that of the lowest triplet of the basic form (3 TH+ ). Some arguments for the assignment of nπ* character to 3 TH2 2+ and ππ* character to 3 TH+ are advanced. 相似文献
19.
Abstract— When TCA-denatured rhodopsin was frozen in liquid nitrogen, Λmax was markedly shifted to longer wavelengths as the concentration of TCA increased. After TCA denaturation, species specific absorption disappeared and the absorption maxima of the squid pigments became identical with those of corresponding pigments of octopus.
In solutions at 5° the bathochromic shift of Λmax of TCA denatured rhodopsin was observed at higher concentrations of TCA than in the frozen state. Λmax of N-retinylidene-butylamine (NRB) was also displaced towards longer wavelengths with increasing concentrations of TCA. This bathochromic shift was enhanced by freezing. The mode of the bathochromic shift of Λmax provoked by TCA was very similar both in the cases of denatured rhodopsin and of NRB. The absorption spectrum of NRB was identical in shape with that of TCA-denatured rhodopsin, as the half-band widths of both materials were about 5500 cm-1 in the liquid state and 5000 cm-1 in the frozen state. Λmax of retinal and NRB were red shifted in polar and polarizable solvents.
It was concluded that the strong acidity and the relatively large polarizability of TCA are responsible for the bathochromic shift of Λmax of the Schiff base in TCA-denatured rhodopsin. 相似文献
In solutions at 5° the bathochromic shift of Λ
It was concluded that the strong acidity and the relatively large polarizability of TCA are responsible for the bathochromic shift of Λ
20.
S. A. Naman 《Photochemistry and photobiology》1990,52(4):649-654
Abstract— –Flash photolysis at 450 nm over the temperature range 0.8–60°C was used to determine Arrhenius parameters for the first and second order disappearance of triplet lumiflavin (1.66 µ .M ) at a flash energy of 2 kj in deaerated phosphate buffer at varying pH:
3 Lf → Lf0
3 Lf +3 Lf → Lf0 + Lf0
Arrhenius parameters were also determined for the pseudo first-order quenching of triplet lumiflavin by 10 µ M ferri- and ferrocyanide ions,
3 Lf + Fe3+ → Fe3+ → Lf0 + Fe3+ (energy transfer)
3 Lf + Fe2+ → Lf- + Fe3+ (electron transfer)
and for disappearance of the semireduced lumiflavin in the presence of ferrocyanide at pH 6.8, by the second-order reaction
Lf- +Lf - → Lf0 + Lf= . 相似文献
Arrhenius parameters were also determined for the pseudo first-order quenching of triplet lumiflavin by 10 µ M ferri- and ferrocyanide ions,
and for disappearance of the semireduced lumiflavin in the presence of ferrocyanide at pH 6.8, by the second-order reaction
Lf