SPECTROSCOPY OF POLYENES—IV. ABSORPTION AND EMISSION SPECTRAL PROPERTIES OF POLYENE ALCOHOLS RELATED TO RETINOL AS HOMOLOGUES

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.     

ABSORPTION AND EMISSION SPECTRAL PROPERTIES OF SOME 2-PHENYLQUINOLINES AND RELATED FUSED SYSTEMS

Abstract— A series of modified 2-phenylquinolines were synthesized and their absorption and emission spectral properties measured in order to determine the effect of structural modifications on excited states. It was hoped that modifications would sufficiently change excited-state properties so that similar structural modifications in 2-phenylquinolinemethanols would negate the phototoxicity of these compounds. The excited states of 2-( o -hydroxyphenyl)quinoline, 11 H-indeno[1,2-b]quinoline, and l,4-dimethyl-5,6-dihydrobenz[c]acridine proved to have properties different from those of normal 2-phenylquinolines, and this effect was shown to be reflected in simple photochemistry of the dihydrobenzacridine. Absorption spectra provided information on conformational preferences for several of the derivatives.     

THE TRANS → CIS PHOTOISOMERIZATION OF PROTONATED RETINYL SCHIFF BASES

Schiff bases were prepared from all- trans -retinal (I) and pyrrolidine perchlorate (II) and from I and n-butyl amine, protonated with anhydrous hydrogen chloride gas, Ill. Initial quantum yields of trans → cis photoisomerization (Φ°PI) were determined and primary photoproducts and product ratios were measured in aerated methanol. Φ°PI of all- trans -III is independent of excitation energy. All analyses were made using high-pressure liquid chromatographic (LC) methods. It was necessary to hydrolize the Schiff bases to corresponding retinals prior to LC analysis.     

PICOSECOND AND NANOSECOND TSOMERIZATION KINETICS OF PROTONATED 11-CIS RETINYLIDENE SCHIFF BASES

Abstract— Picosecond and nonosecond spectroscopy has been used to study the isomerization mechanism of protonated 11- cis retinylidene Schiff bases. The formation and bleaching of absorption bands within 10 ps and corresponding decay and recovery within 11 ns indicate that the isomerization mechanism of the protonated Schiff bases is not identical to rhodopsin in which the primary photophysical event is probably due to electron transfer or partial isomerization of the chromophore to a nonplanar conformation.     

SPECTROSCOPIC EXAMINATION OF HYDROGEN BONDING and PROTON TRANSFER IN MODEL SCHIFF BASES RELATED TO THE VISUAL PIGMENT CHROMOPHORE

By means of a variable low temperature cell holder, double beam spectra were obtained to temperatures as low as 88 K. As the temperature was lowered for a 3McP solution containing N-2,4,6,8,10-dodecapentaenylidene-n-butylamine (2) and phenol, three separate species could be detected, (i) The first spectrum taken at room temperature exhibits sharp fine structure and is the unperturbed spectrum of 2. As the temperature is lowered, a completely new spectrum with fine structure develops at slightly longer wavelength while simultaneously the old fine structure disappears. (ii) The new spectrum belongs to the H-bonded species formed between 2 and phenol. As temperature is further lowered, the second spectrum disappears as a new band develops at about 440 nm. (iii) This is the proton transferred species. The same phenomenon is repeated when p-nitrophenol and acetic acid are substituted for phenol. The -ΔH and ΔS values for the H-bonding process between phenol and 2 in 3MeP are 3900 cal mol^-1 and 1.4 cal dgr^-1 mol^-1 respectively. Additional experiments firmly establish the process to be H-bonding with the phenolic hydroxyl group. Alcohol also H-bonds with 2 but does not proton transfer.     

ABSORPTION SPECTRAL SHIFTS OF CAROTENOIDS RELATED TO MEDIUM POLARIZABILITY

Abstract–Solvent induced absorption spectral shifts of the electronic transition from ground 1 A_g state to the excited 1B_u state in carotenoids have been studied. It is shown that the shift depends only on dispersion interactions in non-polar solvents. In polar media there is just a small extra contribution to the red-shift, due to other forms of interactions. The spectral shifts are well described by the theory, which expresses the shift relative to the gas phase value, as a function of solvent polarizability. The main conclusion is that the dominating mechanism behind the large red-shifted absorbance of carotenoids in the proteinacous environment, in vivo, is the mutual polarizability interactions between the carotenoids and the surrounding medium. The solution-phase values of the dipole moments of the lA_g to 1B_u transitions and the differences of isotropic polarizability between 1B_u and lA_g states of carotenoids in non-polar solvents are calculated and found to be around 13 D and 360 ų respectively. From the great overlap of absorption spectra between carotenoids in quinoline and carotenoids in vivo in purple bacterial antenna complexes, it can be expected that the carotenoids are surrounded by several aromatic amino acids in vivo. Comparisons have been done between the exicted states in carotenoids and in linear conjugated polyenes.     

INVESTIGATION OF CHROMOPEPTIDES FROM C-PHYCOCYANIN BY UV-VIS ABSORPTION, EMISSION AND CIRCULAR DICHROISM SPECTROSCOPY

Four different chromopeptides were isolated after digestion of C-phycocyanin with pepsin. Their UV-vis absorption and circular dichroism spectra were measured at two different pH values without and with urea present in the buffered solutions. For one chromopeptide, fluorescence spectra and the kinetics of fluorescence decay were studied in more detail. The results are discussed in comparison with quantum-mechanical model calculations. It is concluded that due to the interaction between the oligopeptide chain and the chromophore, the latter is present as a mixture of helical and semi-extended forms, respectively.     

INVESTIGATION INTO THE SPECTROSCOPY AND PHOTOISOMERIZATION OF A SERIES OF POLY (ETHYLENE GLYCOL) PEPTIDE SCHIFF BASES OF 11-cis RETINAL

Abstract— The 11-cis and all-trans isomers of a series of poly(ethylene glycol)-oligopeptide - Schiff bases as models for rhodopsin were synthesized and studied. Absorption data for certain of the PEG-peptide Schiff bases demonstrated that no intramolecular hydrogen-bonding (or protonation) occurs between the Schiff base and an acidic amino acid residue, as was previously thought. Photoisomerization of the 11-cis protonated and unprotonated Schiff bases were examined using both steady state and laser flash techniques. Also with 355 nm excitation (and additionally 532 nm in one case), an approximate 40% increase in quantum yield of isomerization (φ) occurred for all protonated PEG-peptide Schiff bases compared to the H⁺-n-butylamine counterparts (in methanol). In one case, a > 100% increase in φ was found in dichloromethane. These data show that PEG-oligopeptide Schiff bases are still further improved models for rhodopsin compared to their n-butylamine analogs.     

ABSORPTION MAXIMA OF CATIONS RELATED TO RETINAL AND THEIR IMPLICATION TO MECHANISMS FOR BATHOCHROMIC SHIFT IN VISUAL PIGMENT*

Abstract— The cations resulting from eleven retinal-related polyenes by placing the latter in n-butanol-sulfuric acid were examined spectroscopically in an effort to explain the batho-chromic effect observed in visual pigments. A comparison of the Λ_max values, intensities and 1/2-band widths of the model carbonium ions with those of the visual pigments does not seem to justify the representation of the chromophore in visual pigments as a pure carbonium ion.     

SYNTHESIS AND NMR SPECTROSCOPIC STUDY OF NEW 5-METHYLFURYL-CONTAINING SCHIFF BASES AND RELATED BIS(AMINOPHOSPHONATES)

The synthesis of three novel 5-methylfuryl-containing Schiff bases: N,N′-bis(5-methylfurfurylidene)-4,4′-diaminodiphenylmethane, N,N′-bis(5-methylfurfurylidene)-1,4-phenylenediamine, and N,N′-bis(5methylfurfurylidene)benzidine and the corresponding bis(aminophosphonates) derived from them, 4,4′-bis{N-methyl(diethoxyphosphonyl)-1-[(5-methyl)-2-furyl]} diaminodiphenylmethane, 1,4-bis { N-methyl(diethoxyphosphonyl)-1-[(5-methyl)-2-furyl]} diaminobenzene, and bis{N-methyl(diethoxyphosphonyl)-1-[(5-methyl)-2-furyl]}- benzidine, is reported. The compounds have been characterized by elemental analysis, TLC, IR, and NMR ( ¹ H, ¹³ C, and ³¹ P) spectra. For comparison, new ¹³ C and ³¹ P NMR data of three furyl-containing analogues of the above bis(aminophosphonates) are also regarded. The NMR studies of the two series of bis(aminophosphonates) reveal the presence of one diastereomer (meso or racemic form).     

光异构化反应的研究——水杨醛缩芳胺席夫碱的吸收光谱与分子结构的关系

<正> 具有光致变色现象的席夫碱在过去几十年里一直为人们所感兴趣。一般认为,水杨醛上的邻羟基是这类席夫碱发生光致变色的必要条件。光致变色的过程就是邻羟基的质子转移到亚氨基的氮原子上,随后发生分子内的几何异构,但对此机理仍存在争执。本文主要报道一些席夫碱的电子吸收光谱与分子结构的关系,以及溶剂对电子吸收光谱的影响。     

SYNTHETIC,SPECTRAL AND BIOLOGICAL STUDIES OF ORGANOSILICON (IV) COMPLEXES WITH SCHIFF BASES OF SULFA DRUGS

Abstract

In the present paper synthetic and structural studies of six-coordinated Me₂Si(NN)₂ type of organosilicon(IV) complexes of Schiff bases (NN) have been described. The complexes were characterized by elemental analyses, conductance measurements, molecular weight determinations and electronic, infrared, ¹H, ¹³C and ²⁹Si NMR spectral studies. A few representative complexes were also screened for antimicrobial activity and found to be quite active in this respect.     

COMPARISON OF THE PATHWAYS AND QUANTUM YIELDS OF DIRECT PHOTOISOMERIZATION OF UNPROTONATED AND PROTONATED N-BUTYLAMINE SCHIFF BASES OF ISOMERIC RETINYLIDENEACETALDEHYDE WITH THOSE OF SCHIFF BASES OF ISOMERIC RETINAL: RATIONALIZATION OF THE SELECTION OF THE RETINYLIDENE CHROMOPHORE BY RETINOCHROME

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 (B_u) state. The T_I potential of C22 SB and the S₁ potential of C22 PSB are discussed based on photostationary state compositions.     

VISUAL PIGMENTS—10. SPECTROSCOPY AND PHOTOPHYSICAL DYNAMICS OF RETINOL AND RETINYL ETHER

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 ¹A^-_g. Retinol forms a dimer in an alkane solvent when cooling from 298 to 77 K. A general structure for the dimer is proposed.     

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.     

INFRARED AND RAMAN STUDIES ON SOME IMINES AND THEIR PICRATES. RELATION TO THE PROBLEM OF PROTONATION IN VISUAL PIGMENTS

Abstract— Picrates of conjugated Schiff bases have C=N stretching frequencies similar to those of the respective free bases. This raises the question if the frequency of this vibration can provide proof for the protonation of the retinylidene Schiff base occurring in visual pigments.     

PHOTOBLEACHING DIFFERENCE ABSORPTION SPECTRA OF HUMAN CONE PIGMENTS: QUANTITATIVE ANALYSIS AND COMPARISON TO OTHER METHODS

Four human cone pigment apoproteins were expressed by transfection of human tissue culture cells with the corresponding complementary DNA clones. Following reconstitution of the cone pigments by incubation with 11-cis retinal, photobleaching difference absorption spectra were obtained for the blue pigment, the green pigment, and two polymorphic variants of the red pigment. These spectra were analyzed to determine the wavelengths of maximal absorbance and the bandwidths. The recombinant cone pigment spectra were compared to human cone spectral sensitivities and cone pigment absorption spectra determined by microspectrophotometry, single-cell electrophysiology, reflection densitometry, electroretinography, and psychophysical color and brightness matching.     

SPECTROSCOPIC BEHAVIOR OF ALL-TRANS RETINAL AND ITS SCHIFF BASES IN VARIOUS MEDIA. THE ROLE OF CONFORMATIONAL PERTURBATION

Se ha encontrado que la n-all-trans-retinilideno-n-butilamina tiene propiedades espectroscópicas, absorción y emisión similares a las de la meta rodopsina I que as un intermediario en la fotólisis del pigmento visual rodopsina. La sensibilidad se presenta solamente cuando el compuesto modelo es adsorbido en silica gel o cuando se lo disuelve en metanol a 77°K. Se describen evidencias espectroscópicas a baja temperature lo cual indica que prelumi o lumirodopsina son artefactos que probablemente no juegan un rol importante en la respuesta visual.     

ABSORPTION OF METHYLBACTERIOPHEOPHORBIDE a SINGLE CRYSTALS: SPECTRAL SHIFTS DUE TO π-π INTERACTIONS

Abstract— Polarized absorption spectra were obtained for a single crystal of methylbacteriophorbide a (MeBPhide a). The Q_y band is red-shifted ∽ 1660 cm^-1 (∽ 110 nm) relative to MeBPhide a in a CH₂Cl₂/benzene solution. This is equivalent to the largest red shifts observed for in vivo bacteriochlorophyll a. The Soret band exhibits a smaller red shift and a significant reduction in intensity, and the Q_x band is not observed. The crystal spectra are qualitatively similar to spectra reported for several other aggregated (bacterio)chlorophyll and bacteriopheophytin systems. Since crystalline MeBPhide a contains no Mg, water or hydrogen bonding (Barkigia etal. , 1981), these results demonstrate that the spectral changes associated with the aggregation of photosynthetic chromophores can arise solely from IT-IT interactions between macrocycles.     

2,6—二乙酰吡啶类双希夫碱配合物的合成和研究 Ⅱ.Cu(Ⅱ)配合物的合成和研究

合成了五个2,6-二乙酰吡啶缩肼基硫代甲酸酯双希夫碱合铜(Ⅱ)配合物,用元素分析、磁化率、红外光谱及紫外-可见光谱等对它们进行了表征,研究了配合物的电化学性质和Cu_3L_2~2X_2(X=Cl~-、SCN~-)的光电子能谱。结果表明:五个Cu(Ⅱ)配合物均为三核配合物,在Cu_3L_2~2(SCN)_2中存在Cu(Ⅱ)间的自旋—交换作用。