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1.
硫代嘧啶碱基是光动力疗法潜在的重要光敏剂,其最低单重激发态的光物理研究已有广泛报道。然而,其较高激发态的跃迁性质和反应动力学研究较为稀少。因此,本文采用共振拉曼光谱和密度泛函理论计算方法研究2,4-二硫代尿嘧啶的紫外光谱和几个较高单重激发态的短时结构动力学。首先,基于共振拉曼光谱强度与电子吸收带振子强度f的关系,将紫外光谱去卷积成四个吸收带,分别为358 nm(f=0.0336)中等强度吸收带(A带),338 nm(f=0.1491)、301 nm(f=0.1795)和278 nm(f=0.3532)强而宽的吸收带(B、C和D带)。这一结果既吻合密度泛函理论计算结果,又符合共振拉曼光谱强度模式对紫外光谱带的预期。据此,去卷积得到的四个吸收带被分别指认为S0→S2跃迁、S0→S6跃迁、S0→S7跃迁和S_0→S_8跃迁。同时,分别对B,C和D带共振拉曼光谱进行了详细的指认,获得了短时动力学信息。结果表明,S_8态短时动力学的显著特征是在Franck-Condon区域或附近发生了S8(ππ~*)/S(nπ~*)势能面交叉引发的、伴随超快结构扭转的非绝热过程。S7和S6态短时动力学的主要特征是反应坐标的多维性,它们分别沿C_5C_6/C_2S_8/C_4S_(10)/N_2C_3+C_4N_3H_9/N_1C_2N_3/C_2N_1C_6/C_6N_1H_7/C_5C_6H_(12)和C_5C_6/N_3C_2/C_4S_(10)/C_2S_8+C_6N_1H_7/C_5C_6H_(12)/C_5C_6N_1/C_5C_6H_(12)/C_2N_1C_6/N_1C_2N_3/C_4N_3H_9/N_1C_2N_3等内坐标演化。 相似文献
2.
The structures of alkali halide clusters Na nF n, Li nF n and Na nCl n, and their metal-excess clusters Na nF n−1+, Li nF n−1+ and Na nCl n−1+ were investigated by the ab initio molecular orbital method for cluster sizes from 1 to 14. The magic numbers for the neutral clusters Na nF n, Li nF n and Na nCl n are 4, 6, and 8. The most stable structure for these cluster sizes is a perfect crystallite for Na nF n and Na nCl n, and a double ring for Li nF n. The magic numbers for the metal-excess clusters are 5 and 8, which are near ideal cuboids with (100) facets. 相似文献
3.
Abstract— The rate constant k 5/ > for physical quenching of singlet oxygen O 2(δ 1;) by the sensitizer in dye-sensitized photooxygenations is determined in the case of chlorophylls a and b (7.3 times 10 8, 4.2 times 10 8 M -1 s -1 respectively), pheophytins a and b (7.4 times 10 7, 3.0 times 10 7 M -1 s _1 respectively), tetraphenylporphyrin (4.4 times 10 7 M -1 s _1), magnesium tetraphenylporphyrin (5.0 times 10 8 M -1 s _1), zinc tetraphenylporphyrin (1.5 times 10 8 M -1 s _l) and protoporphyrin IX-dimethylester (9.1 times 10 7 M -1 s _1) in benzene. These sensitizers show a linear correlation between log k sO , and their half-wave oxidation potentials and the value of the slope is similar to that observed for various compounds such as phenols. It is concluded that (i) the interaction between chlorophylls and related compounds with singlet oxygen may involve an exciplex as for phenols, and (ii) physical quenching may be envisaged as a spin-orbit-induced intersystem crossing within the exciplex. 相似文献
4.
Closo-B nH n−2(CO) 2 ( n = 5–12), isolobal analogues of closo-C 2B n−2H n, have been investigated at the B3LYP/6-311+G **density functional level of theory. The most stable isomers of closo-B nH n−2(CO) 2 are similar to those of closo-C 2B n−2H n in geometric patterns apart from closo-B 6H 4(CO) 2, and closo-B nH n−2(CO) 2 is much less strained than closo-C 2B n−2H n. Energetic analysis identifies closo-B 6H 4(CO) 2, closo-B 12H 10(CO) 2 and closo-B 10H 8(CO) 2 to be most stable, of which the latter two cages have been prepared experimentally. On the basis of the negative and rather large nucleus independent chemical shifts (NICS), closo-B nH n−2(CO) 2 are aromatic. To aid further experimental study, the CO stretching frequencies have been computed. 相似文献
5.
复杂水盐体系存在稳态和介稳固液相平衡以及复杂的成盐规律。为了解固液平衡状态下液相的结构特征,本文采用拉曼光谱技术并结合高斯-洛伦兹去卷积分峰拟合程序对Na +, Mg 2+//SO 42-, Cl -, H 2O四元体系及其二元和三元子体系中 ν1-SO 42-的离子缔合结构特征进行了分析。研究结果表明:SO 42-在Na 2SO 4-H 2O体系存在自由态SO 42-和SO 42-离子簇两种结构,在MgSO 4-H 2O, MgSO 4-MgCl 2-H 2O及Na +, Mg 2+//SO 42-, Cl -, H 2O等含镁体系中,还有Mg 2+-H 2O-SO 42-和Mg 2+-OSO 32-两种缔合结构。在二元和三元体系中 ν1-SO 42-的离子缔合结构以自由态SO 42-为主,随着SO 42-离子总浓度的变化,上述四种结构所占比例会发生规律性变化。Na +, Mg 2+//SO 42-, Cl -, H 2O四元体系在NaCl减少及等温蒸发过程中,自由态SO 42-结构比例逐步降低, Mg 2+和SO 42-相结合形成Mg 2+-H 2O-SO 42-或Mg 2+-OSO 32-结构的机会增多,在复盐区还会形成SO 42-离子簇结构。由此判断溶液结构的适应性变化是导致介稳现象的重要原因。进一步的相关分析表明:SO 42-的浓度和耶涅克指数 J与 ν1-SO 42-峰的峰强度和峰面积存在正相关关系, Mg 2+浓度是影响 ν1-SO 42-峰中四种缔合结构的比例发生变化的主要因素。 相似文献
6.
Abstract— The spectra and molar absorbances of the HO 2 and O 2- free radicals have been redetermined in aqueous formate solutions by pulse and stopped-flow radiolysis as well as by 60Co gamma-ray studies. The extinction coefficients at the corresponding maxima and 23°C are 225= 1400 ± 80 M -1 cm -1 and 225= 2350 ± 120 M -1 cm -1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO 2 and O 2-: K Ho2+HO2= (8.60 ± 0.62) × 10 5 M -1 s -1; K Ho2+O2-= (1.02 ± 0.49) × 10 8 M -1 s -1; K Ho2+O2- < 0.35 M -1 s -1. For the equilibrium HO 2→ O 2-+ H + the dissociation constant is K Ho2= (2.05 ± 0.39) × 10 -5 M or p K HO2= 4.69 ± 0.08. G (O 2-) has been evaluated as a function of formate concentration. 相似文献
7.
采用酶动力学方法研究了5种钒取代的Dawson型磷钼酸H 7[P 2Mo 17VO 62]、H 8[P 2Mo 16V 2O 62]、H 9[P 2Mo 15V 3O 62]、H 8[P 2Mo 14V 4O 62H 2]和H 9[P 2Mo 13V 5O 62H 2](分别简写为P 2Mo 17V、P 2Mo 16V 2、P 2Mo 15V 3、P 2Mo 14V 4和P 2Mo 13V 5)对蘑菇酪氨酸酶二酚酶的抑制作用,结果表明,效应物P 2Mo 17V、P 2Mo 16V 2和P 2Mo 15V 3能够明显地抑制酪氨酸酶的活性,其半抑制浓度(IC 50)值分别为0.409、0.386和0.386 mmol/L,且均表现为可逆的竞争型抑制,效应物P 2Mo 17V、P 2Mo 16V 2和P 2Mo 15V 3对游离酶的抑制常数K I分别为0.234、0.391和0.249 mmol/L。 而效应物P 2Mo 14V 4在0~1.0 mmol/L浓度范围内,对酪氨酸酶二酚酶无明显抑制作用,效应物P 2Mo 13V 5对酪氨酸酶二酚酶表现为激活作用。 相似文献
8.
The syntheses of the 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane-supported imido complexes [M(NR)(R′ 3tach)Cl 2] (M = Ti or Zr (NMR only); R = Bu t or 2,6-C 6H 3Pr i2; R′ = Me or Bu t) are reported, along with that of the thermally robust dibenzyl derivative [Ti(NBu t)(Me 3tach)(CH 2Ph) 2]. The tert-butylimido ligand in [Ti(NBu t)(Me 3tach)Cl 2] undergoes exchange with ArNH 2 (Ar = 4-C 6H 4Me or 2,6-C 6H 4Me or 2,6-C 6H 3Pr i2) to form the corresponding arylimides [Ti(NAr)(Me 3tach)Cl 2]. The Me 3tach ring in [Ti(NR)(Me 3tach)Cl 2] undergoes slow exchange with Bu t3tach or Me 3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) to give the ring-exchanged products [Ti(NR)(Bu t3tach)Cl 2] and [Ti(NR)(Me 3tacn)Cl 2], respectively. The complexes [Ti(NR)(Me 3tach)X 2] (R = Bu t or 2,6-C 6H 3Pr i2; X = Cl or CH 2Ph) exhibit room-temperature dynamic NMR behaviour via an unusual trigonal twist of the facially coordinated Me 3tach ligand, and the activation parameters for these processes have been measured and are discussed. The X-ray structures of [Ti(NR)(Bu t3tach)Cl 2] (R = Bu t or 2,6-C 6H 3Pr i2) and [Ti(NBu t)(Me 3tach)(X) 2] [X= Cl or CH 2Ph) are reported. Me 3tach and Bu t3tach = 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane, respectively. 相似文献
9.
Two novel types of transition-metal-containing liquid crystals, bis( p-n-koxydithiobenzoato)nickel(II) (abbreviated as (C nO-DTB) 2Ni), and ( p-n-alkoxydithiobenzoato)( p-n-alkoxyperthiobenzoato)nickel(II) (abbreviated as (C nO-DTB)(C nO-PTB)Ni), were synthesized. It was found that the (C nO-DTB) 2Ni complex for n = 8 has smectic H and C mesophases, and that the (C nO-DTB) 2Ni complexes for n = 4 and 8 easily transform into the corresponding monoperthio complexes, nO-PTB)Ni, by heating at temperatures between 230°C and 285°C. It was confirmed that the transformation originates from an intermolecular reaction between the (C nO-DTB) 2Ni complexes at high temperatures, and that the origin of the extra sulphurs in the resulting (C nO-DTB)(C nO-PTB)Ni complexes is the neighbouring (C nO-DTB) 2Ni complexes. Interestingly, each of the (C nO-DTB)(C nO-PTB)Ni complexes ( n = 4 and 8), has nematic mesophase and exhibits a unique double melting behaviour via the nematic phase, which is the first example in liquid crystals. The reversible transformation between the blue smectic rod-like (C nO-DTB) 2Ni complex and the red nematic Λ-like (C nO-DTB)(C nO-PTB)Ni complex is possible. 相似文献
10.
Mössbauer spectra of /pheophytinato a/ iron/III/ chloride [Fe/Pheo-a/Cl] and /pheophytinato b/ iron/III/ chloride [Fe/Pheo-b/Cl] have revealed that the central iron/III/ ion is in a high-spin state and axially coordinated by chloride ions in solid phase. Temperature-dependent asymmetry observed for the quadrupole splitting doublet of iron/III/ pheophytins, i.e., Fe/Pheo-a/Cl and Fe/Pheo-b/Cl, is interpreted on the basis of the zero-field splitting. The structural difference between iron/III/ pheophytins and iron/III/ porphyrins is reflected in the quadrupole splitting more than in the isomer shift. Magnetic behaviour of iron/III/ pheophytins near 4.2 K is very similar to that of iron/III/ porphyrins. 相似文献
11.
Abstract— The rapid bimolecular reaction SO + O 3= SO 2+O 2+ 106 kcal/mole yields electronically excited SO 2 in the 3B 1 and 1B 2 states with some vibrational excitation, as well as SO 2 in its electronic ground state. It is shown that k 1 = 1.5 x 10 12 exp (-2100/ RT ) cm 2 mole -1 s- 1 and that the formation of electronically excited SO 2 involves higher activation energies. 相似文献
12.
The heat capacities of NaNO 3 and KNO 3 were determined from 350 to 800 K by differential scanning calorimetry. Solid-solid transitions and melting were observed at 550 and 583 K for NaNO 3 and 406 and 612 K for KNO 3, respectively. The entropies associated with the solid-solid transitions were measured to be (8.43± 0.25) J K −1 mole −1 for NaNO 3 and (13.8±0.4) J K −1 mole −1 for KNO 3. At 298.15 K the values of C0P S0P, { H0( T)- H0(0)}/ T and -{ G0( T)- H0(0)}/ T, respectively, are 91.94, 116.3, 57.73, and 58.55 J K −1 mole −1 for NaNO 3 and 95.39, 133.0, 62.93, and 70.02 J K −1 mole −1 for KNO 3. Values for S0T, { H0( T)- H0(0)}/ T, and -{ G0( T)- H0(0)}/ T were calculated and tabulated from 15 to 800 K for NaNO 3 and KNO 3. 相似文献
13.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
14.
Abstract— From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen ( 1Δ g and 1Σ g+) were calculated for a number of conditions. For the gas phase we estimate K eq( 1Δ g3Σ g-) = 1.67 exp(-94.31 KJ/RT) and K eq( 1Σ g+/ 3Σ g-) = 0.33 exp(-157.0 KJ/RT). The calculated rate constants for the 3Σ g+→ 1Δ g transition of O 2 at 25°C varied from 2.5 × 10 -11 s -1 in water to 4.8 × 10 -16 s -1 in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will result in a pro-oxidant effect. 相似文献
15.
采用浸渍提拉法制得TiO 2,ZnO,Fe 2O 3,ZnO/TiO 2,TiO 2/ZnO,Fe 2O 3/TiO 2和TiO 2/Fe 2O 3石英玻璃基底负载膜.光催化降解亚甲基蓝实验表明,TiO 2和ZnO具有良好的光催化活性,Fe 2O 3活性较差.但形成异质结后,TiO 2和Fe 2O 3的光催化降解能力发生明显的变化.用254nm紫外光光照后,TiO 2,ZnO和Fe 2O 3等3种氧化物膜与水的接触角均有不同程度的降低,TiO 2表现出超亲水性,ZnO/TiO 2和Fe 2O 3/TiO 2膜与水的接触角小于对应的单纯ZnO和Fe 2O 3膜与水的接触角,其中Fe 2O 3/TiO 2表面出现超亲水性.瞬态光电导谱的少数载流子寿命的测定表明,异质结势垒电场能有效地增强光生电子-空穴对的分离效率.根据能带理论建立的两组异质结能带模型可合理地解释实验结果. 相似文献
16.
The effect of Zn2+ ions codoped on the upconversion emission of Er3+ ions in Er:LiNbO3 crystal under different excitation wavelength was reported.The upconversion emission spectra of Zn/Er:LiNbO3 follo... 相似文献
17.
The phase behaviour of the binary systems 4'- n-tetradecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-14)- n-alkane ( n-tetradecane or n-hexadecane) was investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The phase behaviour was a function of temperature ( T) and the effective carbon number of the system ( n*), where n* involves carbon atoms both from the alkoxy group of ANBC-14 and from the n-alkane added. ANBC-14 shows no cubic phase, but the addition of n-alkane induced cubic phases when n*≧c. 15. An interesting point is that the type of cubic phase is Ia3 d for 15 ≦n*≦17, while an Im3 m type is formed for 18 ≦n*≦20. Furthermore, for n* = 22, two types of cubic phase, one with Im3 m symmetry in the low temperature region and the other with Ia3 d in the high temperature region, were observed both on heating and cooling. The phase diagram with respect to T and n* is very similar to that of pure one-component ANBC- n, which is a function of T and the number of carbon atoms in the alkoxy group n. 相似文献
18.
在光解水制氢研究中,光产氢量子收率是一个重要参数。太阳能的光化学储存效率主要取决于光敏催化体系的光波长吸收范围和效率以及所得预期产物的量子收率,即光反应生成产物的分子数与体系吸收的光子数的比值。 相似文献
19.
通过共沉淀法制得类球形锂离子电池正极材料LiNi 1/3Co 1/3Mn 1/3O 2,并用非水相共沉法对其进行CoAl 2O 4包覆得到LNCMO(x). 采用X射线衍射(XRD)、扫描电子显微术(SEM)和透射电子显微术(TEM)测试材料的结构和观察材料形貌. 结果表明,CoAl 2O 4在材料表面形成8 nm均匀包覆层,未改变主体材料的结构. 电化学性能测试表明,1%(by mass)CoAl 2O 4包覆量的LiNi1/3Co1/3Mn1/3O2材料(LNCMO(1))高充电电压(3.0 ~ 4.6 V,150 mA·g -1)100周期循环放电容量保持率为93.7%(无包覆LNCMO(0)保持率为74.4%);55 °C高温100周期循环容量保持率为77%(无包覆LNCMO(0)保持率17%). XRD和电感耦合等离子体原子发射光谱(ICP-AES)测试表明,CoAl 2O 4包覆的LNCMO(x)材料可有效地减缓材料中Mn离子在电解液的溶解,提高材料结构稳定性和热稳定性. 相似文献
20.
The enthalpy change for anabolism is needed to model the growth/respiration relation in plants. If all CO 2 production is assigned to catabolism, the anabolic reaction becomes C substrate→C products+ xO 2 with an enthalpy change, Δ Hb. Four methods are proposed for determining Δ Hb: (a) From the difference in the heats of combustion of substrate and anabolic products (i.e. newly grown tissue). (b) From the composition of newly grown tissue and application of Thornton’s rule. (c) From independently measured values of the specific growth rate, RSG, and of the product ( RSG Δ Hb). The product ( RSG Δ Hb) equals (−Δ HCO2RCO2− Rq) where RCO2 is the specific rate of CO 2 production by respiration, Δ HCO2 is the heat of combustion of respiratory substrate per mole of CO 2 and Rq is the specific metabolic heat rate. Δ Hb is then calculated as the ratio ( RSG Δ Hb)/ RSG. (d) From (Δ Hb=−( Rq/ RCO2+Δ HCO2) [(1−)/] where is the substrate carbon conversion efficiency obtained from a total carbon balance. The first three methods have been tested and compared on oat seedlings and the last on corn seedlings. Δ Hb values from all four methods are in reasonable agreement despite the different assumptions involved. 相似文献
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