CURCUMIN-DERIVED TRANSIENTS: A PULSED LASER AND PULSE RADIOLYSIS STUDY

Abstract In this paper we report a time-resolved investigation of transients derived from curcumin, which may be intimately involved in the processes leading to its biological activity. Fluorescence and triplet quantum yields are respectively 0.06 and 0.11. The high percentage of internal conversion is proposed to proceed via H-transfer within the thermodynamically favored enol structure of what is formally a 1,3-diketone. The triplet energy (191 ± 2 kJ mol⁻¹), natural lifetime (1.5 μs) and self-quenching rate constant (5.0 × 10⁸ L mol⁻¹ s⁻¹) have been determined. Oxygen quenching of the triplet leads to the production of singlet oxygen with unit efficiency. Curcumin quenches the latter species very inefficiently (2.5 × 10⁵ L mob⁻¹ s⁻¹). The curcumin radical has been produced via three mechanistically distinct methods. This species is unreactive toward oxygen but is repaired by vitamins C and E and anthralin.     

A LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS STUDY OF AMILORIDE IN AQUEOUS AND ALCOHOLIC SOLUTION

Abstract Laser flash photolysis and pulse radiolysis have been carried out on the diuretic drug amiloride. The primary photochemical processes in aqueous solution were found to be photoionisation and triplet formation. Photoionisation was found to occur by a biphotonic process for 265 nm excitation but by a monophotonic process for excitation at 353 nm. The spectral properties of the resulting cation radical of amiloride were determined by pulse radiolysis using one electron oxidation by the radical anion Br₂·^¯ Photoexcitation of amiloride in isopropanol did not result in photoionisation but instead a semireduced radical of amiloride was observed. The spectral properties of the semireduced radical of amiloride were determined using one electron reduction by the CO₂·^¯ radical.     

ONE-ELECTRON OXIDATION AND REDUCTION OF AZAPROPAZONE AND PHENYLBUTAZONE DERIVATIVES IN AQUEOUS SOLUTION: A PULSE RADIOLYSIS STUDY

Abstract— Using pulse radiolysis techniques, 3 azapropazone and 3 phenylbutazone derivatives all structurally related to the potentially photosensitive anti-inflammatory drug, azapropazone, have been reacted with the free radical oxidants N₃, Br₂^- and (SCN)₂^- as well as with e^-_aq a strong reductant. It is demonstrated that for 5 derivatives, azapropazone (Az), 2-[a-Carboxy-valeryll-3-dimethylamino-7-meth1-1,2-dihydro-1,2,4-benzotriazine (Mi307), phenylbutazone (PB), oxyphenylbutazone (OPB), and ketophenylbutazone (KPB), N₃^- and Br₂^- appear to react via a one-electron removal process. For the other derivative, 8-hydroxy azapropazone (8-OH-Az), Nj and (SCN); oxidise via a one-electron process, while Br₂^- probably fqrms a free radical adduct.
The absolute spectra of the one-electron oxidised and reduced transient species for all six derivatives are thus given in this work and are a basis to the understanding of the action of light on these drugs.     

A PULSE RADIOLYSIS and PULSED LASER STUDY OF THE VITAMIN D3 TRIPLET STATE: LIFETIME, RELAXATION and 'NONVERTICAL'EXCITATION

Abstract— The triplet state of vitamin D3 in benzene has been characterised in terms of its absorption spectrum, Λ_max 315 nm, its lifetime, 300 ns, its rate constant for reaction with oxygen, 4.2 times 10⁹mol⁻¹ s⁻¹ and the efficiency with which it sensitizes the formation of singlet oxygen, 25%. There is a large difference in the electronic excitation energies of the spectroscopic and relaxed triplets, ˜ 237 kJ mol⁻¹ and147–168 kJ mol⁻¹, respectively. It has been shown that, in the endothermic situation, the vitamin D3 molecule is a 'nonvertical'acceptor of triplet energy. This is in accord with the non-planar character of its acyclic conjugated Il-system.     

PRIMARY PROCESSES IN THE LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS OF l-EPHEDRINE

Abstract— Transient absorption spectra produced by laser flash-photolysis of an aqueous solution of ephedrine have been measured under a variety of conditions. Ephedrine was found to photoionise via a biphotonic process. The apparent yield of photoionisation increases with lowering of pH, a value of 8.8 being found for the p K _a associated with this change. The cation radical absorption spectrum has been determined using the techniques of both pulse radiolysis and laser flash photolysis. The extinction coefficient of the cation at 295 nm was determined to be 1.37 × 10⁴ dm³ mol^-1 cm^-1 and 1.2 × 10⁴ dm³ mol-¹cm-¹ by the two techniques, respectively, at pH 11. It is also shown that the rate constant for electron abstraction by the azide radical to form the ephedrine cation is controlled by protonation of the amine group in the side chain. The ephedrine anion radical spectrum and its extinction coefficient at 305 nm were also determined. The excited states responsible for photoionisation and photodegradation are discussed.     

PRIMARY PROCESSES IN THE PHOTOCHEMISTRY OF AQUEOUS SULPHACETAMIDE: A LASER FLASH PHOTOLYSIS and PULSE RADIOLYSIS STUDY

Abstract— The spectra have been measured of the transient species formed in the nanosecond flash photolysis of aqueous solutions of sulphacetamide under a variety of conditions. In addition to the excited triplet state, the cation radical and the solvated electron were observed. The ionisation of aqueous sulphacetamide was found to occur by a biphotonic process. The extinction coefficient of the cation radical of sulphacetamide was determined by both laser flash photolysis and pulse radiolysis techniques, a value of 1.9 times 10₃ dm₃mol_-1cm_-1 being obtained. The rate of electron reaction with sulphacetamide and the anion radical spectrum were also determined by the two techniques, good agreement being obtained. The spectrum of the product of the reaction of the superoxide anion radical and the corresponding rate constant have also been determined. A possible mechanism of photosensitized skin reaction due to sulphacetamide is discussed.     

A PULSE RADIOLYSIS STUDY OF THE ONE-ELECTRON OXIDATION AND REDUCTION OF 5, 10-METHENYLTETRAHYDROFOLATE

Abstract— The one-electron reduction and oxidation of 5,10-methenyltetrahydrofolate has been studied in aqueous solution in the acidity range H₀= -1 to pH = 7 using the reducing species CO^-₂ and (CH₃)₂-COH and oxidising species Br^-₂, and H₂SeO+₃. The spectral and other properties of the radicals so formed were found to be indcpendent of the reductant/oxidant used. Two protolytic forms of both the oxidised and reduced radicals were observed with approximate p K , values of 0.5 ± 0.3 being determined. Both the bridged form (5.10-methenyltetrahydrofolate) and the unbridged form (5- formyltetrahydrofolate) were found to be easily oxidised, whereas only the former could be reduced.     

TRANSIENT PHENOMENA IN THE PULSE RADIOLYSIS OF RETINYL POLYENES—7. RADICAL ANIONS OF VITAMIN A AND ITS DERIVATIVES

Abstract— Upon e^--pulse irradiation in nonprotic solvents, all- trans retinol (ROH) and retinylmethyl ether (ROMe) form transient species (τ= 0.5–7μs, λ_max=575–590 nm) identifiable as radical anions. Similar species are also formed upon laser pulse photoexcitation of these retinyl derivatives in the presence of N,N-dimethylaniline in acetonitrile. In contrast, electron transfer or attachment to all- trans retinyl acetate (ROAc) and palmitate (ROPa) results in 'instantaneous' loss of carboxylate anions from electron adducts giving the retinylmethyl radical (R-, λ_max= 395 nm, τ_k > 100 μ,s); the radical anions in these cases are too short-lived to be detected by nanosecond pulse radiolysis. The lifetimes of radical anions of ROH and ROMe are very sensitive to water and alcohols (e.g. k_q = 10⁷ M ^-1 s^-1 with methanol as quencher for ROH^- in tetrahydrofuran). Based on these findings, the spectral dissimilarity of the one-electron reduction products from ROH and ROAc in alcohols and aqueous micelles becomes explainable in terms of fast formation of protonated radical anions (RH(OH), τ_1/2, > 100 μs, λ_max=370–375 nm) in the case of ROH and of retinylmethyl radical via loss of AcO^- from radical anion in the case of ROAc. In tetrahydrofuran, the complexation of ROH^- with cations such as Na⁺ and Bu₄N⁺ affects the relative importance of its major decay modes, namely, protonation and dehydroxylation, the latter process being significantly enhanced by the presence of Na⁺.     

FLUORESCENCE AND LUMINESCENCE STUDIES OF IN VIVO CHLOROPHYLL WITH A LASER PHOSPHOROSCOPE*

Abstract— A simple apparatus using a He-Ne laser and a rotating sector gives repetitive light pulses with rise and fall times of a few μsec and intensities of up to 0.65 W/cm². Fluorescence during the actinic pulse and luminescence following it (after 20 μsec) may be recorded and compared. Sampling of the suspension of photosynthetic cells or chloroplasts by intermittent flow permits the averaging of 25 such measurements. With Chlorella, the fast (30 μsec) and the medium (30 msec) components of luminescence do not saturate at the same light intensity. The former saturates in the same range as the photochemical fluorescence rise, whereas the latter saturates at higher intensities. Under a variety of conditions, the decay of luminescence intensity is always strongly polyphasic. Analysis of the kinetics discloses a dependency with the log concentration of the hypothetical precursor, suggesting a connection of luminescence with electrochemical phenomena. The shape of the luminescence integral, as well as the light saturation pattern, suggests another kind of interpretation, in terms of several pools, possibly two of equal size. In the presence of hydroxylamine, only one pool is seen. The stimulating effect of preillumination is only observed for the medium component. However, a stimulation of short duration also exists for the fast component. The problems of number of pools, mechanism, and stimulation are briefly discussed.     

丙烯酰胺-苯乙烯双亲嵌段共聚物水溶液的表面活性及增溶性

在微乳液介质中制备了系列的丙烯酰胺 (AM)与苯乙烯 (St)的双亲嵌段共聚物 (PAM b PSt) ,用紫外分光光度法测定了共聚物的组成 ,用乌氏粘度计测定了共聚物的特性粘数 [η],并用其相对表征共聚物的分子量大小 .重点研究了双亲嵌段共聚物 (PAM b PSt)疏水链段在水溶液中的缔合行为、共聚物的表面活性及其对有机物的增溶性能 ,考察了共聚物分子组成 (疏水链段含量 )与分子量对其表面活性与增溶性能的影响规律 .研究结果表明 ,由于疏水链段的憎水性 ,PAM b PSt的分子链在水溶液表面会形成表面吸附 ,从而降低水溶液的表面张力 ;而在水溶液中 ,在疏水相互作用下 ,PAM b PSt分子链中的苯乙烯疏水链段会形成分子间或分子内的胶束 ,烃类有机物可增溶其中 ;疏水链段含量越大 ,分子量越小 ,PAM b PSt的表面活性与增溶性能越强     

A SINGLE PULSE PICOSECOND LASER STUDY OF EXCITON DYNAMICS IN CHLOROPLASTS

Abstract. Using single picosecond laser pulses at 610 nm, the fluorescence yield (φ) of spinach chloroplasts as a function of intensity ( I ) (10¹²-10¹⁶ photons/pulse/cm²) was studied in the range of 21–300 K. The quantum yield decreases with increasing intensity and the φ vs I curves are identical at the emission maxima of 685 and 735 nm. This result is interpreted in terms of singlet exciton-exciton annihilation on the level of the light-harvesting pigments which occurs before energy is transferred to the Photosystem I pigments which emit at 735 nm.
The yield φ is decreased by factors of 12 and 43 at 300 and 21 K, respectively. The shapes of the φ vs I curves are not well accounted for in terms of a model which is based on a Poisson distribution of photon hits in separate photosynthetic units, but can be satisfactorily described using a one-parameter fit and an exciton-exciton annihilation model. The bimolecular annihilation rate constant is found to be γ= (5–15) times 10^-9cm³s^-1 and to exhibit only a minor temperature dependence. Lower bound values of the singlet exciton diffusion coefficient (≥ 10^-3cm²s^-1), diffusion length (≥ 2 times 10^-6cm) and Förster energy transfer rates (≥ 3 ≥ 10¹⁰s^-1) are estimated from γ using the appropriate theoretical relationships.     

A PULSED LASER SYSTEM FOR THE STUDY OF MICRO-SECOND DELAYED FLUORESCENCE FROM PLANTS

Abstract—A new laser system is designed for the investigation of S delayed fluorescence. This is intended to overcome some undesirable features present in other current designs, such as low actinic light fluxes and long illumination times, or slow responses owing to long turn-off times of the stimulation source and the presence of fluorescence artifacts.
The system uses a pulsed argon-ion laser and bears little resemblance to either the modified Becquerel phosphoroscope used by Lavorel (1971) or to those systems requiring shutters. Cheapness of design together with the ability to adjust such parameters as pulse duration easily, make this design attractive to most laboratories in which short (10 μs) high intensity (10⁵ W m^-2) pulses with rapid (1.5 μs) turn-off times and high on-to-off contrast ratios (10⁶:1) are required.
Certain design criteria are strictly imposed in order to produce kinetic data that can be meaningfully analysed.     

甲醛、丙酮与三聚甲醛及其衍生物相互作用的理论研究

分子间相互作用的研究对于解释物质的性质,化学反应机理等具有重要意义。在理论上主要的研究方法有:一、将相互作用能分解成静电能、短程斥力、极化能、诱导能和色散能,分别计算这些能量,然后给出总的作用能;二、将相互作用的两个分子作为单个超分子,相互作用能为超分子能量和两个孤立分子能量之差,原则上,ab initio CI能够解决达一问题,但其应用因目前计算条件而受到限制。ab initio和CNDO等在计算作用能时须进行色散能校正。在实验上研究方法主要有分子束电共振谱(molecular beam electric resona-     

苯并呋喃并香豆素的合成及其钙拮抗活性初步研究

１引言香豆素是一类具有重要生理活性的天然产物,具抗凝血、抗肿瘤、抗病毒等多种活性,最近又发现某些香豆素化合物具有钙桔抗活性［‘,’］。目前对此类物质钙站抗活性的研究国内外还开展较少。我们设计合成了一系列苯并吠哺并香豆素化合物,选取其中三个（;、Ｄ。、Ｄ３）＄０一个简单二羟基香豆素（Ｃ。）经放射性‘’Ｃａ跨膜流动技术测定,表明其对电压依赖性钙离于通道（ＰＤＣ）均有较显著阻滞作用（见表１）。其中Ｄ。未见文献报道,其结构经ＮＭＲ、ＩＲ、ＭＳ确证。已知物Ｄ;、Ｄ。和Ｃ。的钙通道阻滞活性尚未见其它文献报道…     

DIRECT OBSERVATION OF ELECTRON TRANSFER ACROSS A LIPID BILAYER: PULSED LASER PHOTOLYSIS OF AN ASYMMETRIC VESICLE SYSTEM CONTAINING CHLOROPHYLL,METHYL VIOLOGEN AND EDTA*

Abstract— Suspensions of vesicles composed of chlorophyll a (Chi) and phospholipid that were asymmetric with respect to aqueous solutions of methyl viologen (MV₂₊), an electron acceptor, and EDTA, an electron donor, were investigated using both flash and steady-state photolysis techniques. It was shown that Chl-photosensitized electron transfer occurred across the walls of the vesicles from EDTA to MV₂₊. Flash photolysis indicated that MV₂₊ dissolved in the interior aqueous compartments of the vesicles oxidized only those triplet excited state Chi molecules that were dissolved in the inner monolayers of the vesicle walls. The resultant radical products, Chi₊ and MV₊, recombined with a halftime of the order of 10_-4s. EDTA, added externally to the vesicles, competed effectively with MV₊ as a reducing agent for Chl₊. This places a lower limit of 10₄ s_-1 on the rate constant for transmembrane electron transfer. Compartmentalization by the vesicle wall of the competing pathways for the reduction of Chi₊ resulted in a nonlinear dependence of the rate constant of Chl₊ decay on EDTA concentration. The magnitude of the rate constant of electron transfer through the membrane and the way that the kinetics of Chl₊ decay depended on the concentration of Chi in the membrane strongly suggest that the electron transfer occurred by electron exchange between Chi and Chl₊.     

A QUANTITATIVE COMPARISON OF CHLOROPHYLL BILAYERS FORMED WITH AND WITHOUT SOLVENT

Abstract Bimolecular lipid membranes are formed from solutions containing lecithin and chlorophyll- a (chl- a ) in various molar ratios. Both the Mueller-Ruding technique as well as the solvent free, Montal-Mueller technique are used to form bilayers. In both methods, increasing the chl concentration produces greater photosensitivity. The photocurrent/area is about an order of magnitude higher in bilayers formed with the solvent free method, under similar conditions. From the quantum yield calculations, it appears that the higher photocurrent/area obtained with the Montal-Mueller membranes cannot be explained solely due to the greater concentration of pigment molecules in the solvent free system. The possible role of chl—chl interactions are considered.     

RADICAL PROCESSES IN LIPIDS. A LASER PHOTOLYSIS STUDY OF t-BUTOXY RADICAL REACTIVITY TOWARD FATTY ACIDS

Laser photolysis techniques have been used to measure the reactivity of t-butoxy radical (t-BuO) toward various fatty acids. Eight compounds varying both in number and in the configuration of olefinic bonds were examined. It has been found that the rate constant for hydrogen abstraction from these compounds by t-BuO may be related to the number of secondary, allylic, and doubly allylic hydrogens in each molecule by the equation: k_r= [0.072[H_sec] + 0.518[H_allylic] + 2.716[H_{doubly allylic}] x 10⁶M^-1 s^-1.     

水溶性高支化多糖及硫酸酯衍生物抗癌活性研究

从虎奶菇菌核中提取出一种水溶性高支化葡聚糖,并用氯磺酸和吡啶在无水二甲亚砜中进行硫酸酯衍生化,制备出硫酸酯衍生物.用巴比赛小鼠动物实验研究该多糖及其硫酸酯衍生物的体内抗肉瘤S-180活性,以及用肝癌细胞株HepG2研究体外活性,同时讨论多糖分子尺寸与抗癌活性的关系.通过形态学、组织切片、以及酶联免疫法研究硫酸酯化对多糖抗肿瘤活性的影响.结果表明,支链多糖的均方根旋转半径在42.5~113 nm之间,显示出较高的体内和体外抗肿瘤活性,硫酸酯衍生物的均方根旋转半径在17.8~34.9 nm之间,抗癌活性随其分子尺寸的增大而逐渐提高.多糖及其硫酸酯衍生物能诱导人体肝癌HepG2细胞凋亡,且具有时间依赖性.它们对免疫反应的调节作用可通过肿瘤坏死因子TNF-α来介导.     

THE INTERACTION OF MELANIN WITH 8-METHOXYPSORALEN: EFFECT ON RADIATIVE AND NONRADIATTVE TRANSITIONS. A FLUORESCENCE AND PULSED PHOTOACOUSTIC STUDY

Abstract: The interaction of 8-methoxypsoralen (8-MOP) with synthetic eumelanin was investigated using static and time-resolved fluorescence and pulsed photoacoustic calorimetry. Due to the strong overlap of the absorption bands of melanin and 8-MOP, a method is presented to account for the systematic errors introduced by the optical filter effect exerted by each absorbing species in the fluorescence and the photoacoustic measurements. As a preliminary step to the understanding of the nonradiative behavior of the psoralen-melanin complexes, the photoacoustic parameters of 8-MOP in various solvents were determined. Spectroscopic data indicate the absence of interaction at the ground-state level, whereas the singlet excited state of 8-MOP is quenched by the pigment; the average fluorescence lifetimes are independent of the melanin concentration, thus indicating a static quenching mechanism. The photoacoustic data show that the quenching process involves an increased intersystem crossing probability, which is almost unaffected by the presence of oxygen, as expected for a molecule essentially acting as a type I photosensitizing agent.     

EVALUATION OF THE STRUCTURE AND CHARACTERISTICS OF CIRCUMTRINDENE DERIVATIVES: A DFT STUDY

Journal of Structural Chemistry - The structures and properties of Circumtrindene derivatives were studied at M062X/6-31+G(d,p) level of theory. The UV spectra of compounds were simulated by TD DFT...