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991.
Juan?Feng Qian?Wang Xujia?Zhang Youguo?Huang Xicheng?Ai Xingkang?Zhang Jianping?ZhangEmail author 《中国科学B辑(英文版)》2004,47(1):80-90
The LH2 complex from Rhodopsudomonas (Rps.) palustris is unique in the heterogeneous carotenoid compositions. The dynamics of triplet excited state Carotenoids (3Car* has been investigated by means of sub-microsecond time-resolved absorption spectroscopy both at physiological temperature
(295 K) and at cryogenic temperature (77K). Broad and asymmetric T
n
←T
1 transient absorption was observed at room temperature following the photo-excitation of Car at 532 nm, which suggests the
contribution from various carotenoid compositions having different numbers of conjugated C=C double bonds (Nc=c). The triplet absorption bands of different carotenoids, which superimposed at room temperature, could be clearly distinguished
upon decreasing the temperature down to 77 K. At room temperature the shorter-wavelength side of the main Tn04T1 absorption band decayed rapidly to reach a spectral equilibration with a characteristic time constant of ∽1 μs, the same
spectral dynamics, however, was not observed at 77 K. The aforementioned spectral dynamics can be explained in terms of the
triplet-excitation transfer among heterogeneous carotenoid compositions. Global spectral analysis was applied to the time-resolved
spectra at room temperature, which revealed two spectral components peaked at 545 and 565 nm, and assignable to the Tn04 T1 absorption of Cars with Nc=c=11 and Nc=c=13, respectively. Surprisingly, the decay time constant of a shorter-conjugated
Car, i.e. 0.72 ώs (aerobic) and 1.36 ώs (anaerobic), is smaller than that of a longer-conjugated Car, i.e. 2.12 us (aerobic)
and 3.75 ώs (anaerobic), which is contradictory to the general rule of carotenoids and relative polyenes. The results are
explained in terms of triplet-excitation transfer among different types of Cars. It is postulated that two Cars with different
conjugation lengths coexist in an α, β-subunit in the LH2 complex. 相似文献
992.
Zhu Hai-Liang Huang Pei Duan Chun-Ying Zheng Li-Min Liu Yong-Jiang Wu Mei-Fang Tang Wen-Xia 《Transition Metal Chemistry》1999,24(4):380-383
An azide-bridged polymeric cationic chain complex, [LCu2(N3)2]n(ClO4)2n
·n(H2O)**, where L=the dinucleating macrocyclic ligand bis-p-xylylBISDIEN, has been prepared and characterized by x-ray crystallography, u.v.-vis and i.r. spectra, and by magnetic measurements. The structure consists of cationic azide-bridged [LCu2(N3)2]2+ (unit) chains, non-coordinated perchlorate anions and crystallized water molecules. The azide anion is bound to two copper atoms in neighboring units with an end-to-end bridging mode. In each unit, the copper atoms have a different coordination geometry; Cu(1) is a four-coordinated, distorted square-planar geometry, whereas Cu(2) is a five-coordinated, distorted square-pyramid. The electronic spectra of the title complex differ in anhydrous and in aqueous MeCN solutions, indicating that dissociation and solvation occur in aqueous solutions. The characteristic i.r. absorptions of azides and perchlorates are described. Magnetic moments vary from 2.05 (B.M.) at 300K to2.01 (B.M.) at 80K, which suggests that very weak interactions exist between the metals. 相似文献
993.
The MnIV complex of tetra-deprotonated 1,8-bis(2-hydroxybenzamide)-3,6-diazaoctane (MnIVL) engrossed in phenolate-amido-amine coordination is reduced by HSO3− and SO32− in the pH range 3.15–7.3 displaying biphasic kinetics, the MnIIIL− being the reactive intermediate. The MnIIIL− species has been characterized by u.v.–vis. spectra {λ max, (ε, dm3 mol−1 cm−1): 285(15 570), 330 sh (7570), 469(6472), 520 sh (5665), pH=5.42}. SO42− was the major oxidation product of SIV; dithionate is also formed (18 ± 2% of [MnIV]T) which suggests that dimerisation of SO3−• is competitive with its fast oxidation by MnIV/III. The rates and activation parameters for MnIVL + HSO3− (SO32−) → MnIIIL−; MnIIIL− + HSO3− (SO32−) → MnIIL2− are reported at 28.5–45.0 °C (I=0.3 mol dm−3, 10% (v/v) MeOH + H2O). Reduction by SO32− is ca. eight times faster than by HSO3− both for MnIVL and MnIIIL−. There was no evidence of HSO3−/SO32− coordination to the Mn centre indicating an outer sphere (ET) mechanism which is further supported by an isokinetic relationship. The self exchange rate constant (k22) for the redox couple, MnIIIL−/MnIVL (1.5 × 106 dm3 mol−1 s−1 at 25 °C) is reported. 相似文献
994.
995.
本文研究了抗癌药物氮三乙酰肼(Nitrilotriacetic hydrizide,NTH)和生命必需元素以及Al~(3 ),Ga~(3 ),In~(3 )的配位能力并用pH电位法测定了它们在生理条件下(37℃,Ⅰ=150mM dm~(-3)NaCl)的配合物生成常数。电位滴定数据是用ZPLOT,MINIQUAD,ESTA等计算机程序处理的。实验结果表明NTH与它的非生理活性的母体化合物氮三乙酸相比较,对Zn~(2 ),Mn~(2 )等过渡元素的配位能力表现较大的差异性。这种情况在Revercan,ICRF-198,ICRF-236和5-烯去甲基斑蝥酸等其他抗肿瘤活性化合物中也曾观察到。 NTH与三价金属Fe~(3 ),Ga~(3 ),Al(3 )和In~(3 )等有较大的配位能力,这与它的烯醇式结构有关。由于这些配合物在广泛的pH范围内生成,以及它的高稳定性,因此有可能被用作为肿瘤定位试剂或生物体营养元素铁传输的有效载体。 相似文献
996.
本文介绍了一种以氟气和惰性气体为原料合成 Kr F2 和 Xe F2 的热催化合成方法并对合成机理和条件作了简单的讨论 ,利用合成的 Kr F2 作为氟化剂合成了含氟高能氧化剂 NF4BF4,纯度约为 93%,其红外光谱和拉曼光谱基本与文献值吻合。元素分析结果表明产品 NF4BF4中含 B5.8%(mass) ,自由氟原子含量为 9.95%(mass) ,与理论值基本一致 ,此结果也间接证明了 Kr F2 质量的可靠性。粉末状的 Xe F2 经升华 -再结晶纯化后可得纯净晶体产品。 相似文献
997.
998.
999.
为了探讨铒离子掺杂材料的激光制冷可能性, 依据测量样品的吸收光谱, 计算了Er3 掺杂的ZBLAN玻璃材料的Judd-Ofelt参数, 得到Ω2=3.01×10-20 cm2, Ω4=1.59×10-20 cm2, Ω6=1.03×10-20 cm2, 进而获得了2H11/2, 4S3/2及其以下各能级间跃迁的跃迁几率、分支比、寿命等数据. 测量了77 K到315 K温度范围内Er3 较强的两个绿色发射2H11/2, 4S3/2→4I15/2的发射谱及荧光寿命. 讨论了2H11/2, 4S3/2这样处于热平衡中的两个能级的量子效率的计算方法, 进而计算了它们的量子效率, 并与其它材料进行了比较. 相似文献
1000.
用TEM研究了(NR SBR)/PE共混体系经动、静态硫化后的形态结构及其与力学性能的关系。未硫化和静态硫化体系的形态结构与其组成有关,均以含量大的组份为连续相;对动态硫化体系,当(NR=SBR)/PE<70/30时,均以PE为连续相,其性能主要依赖于构成连续相组份的性质。 动态硫化体系的T_g值低于静态体系,随PE组份含量的增加变化不大,而静态硫化体系的T_g值则随PE含量增加向高温方向迁移。用DSC测得动态硫化体系的结晶度比静态体系的大。前者的应力-应变性能也低于后者。 相似文献