乙腈-水和乙二醇-水均相溶液中光诱导杜醌激发三重态与色氨酸、酪氨酸的氢原子转移反应

本文用激光闪光光解技术研究了光诱导生物醌杜醌激发三重态(³DQ^*)和色氨酸(Trp)与酪氨酸(Tyr)在乙腈-水(MeCN-H₂O)及乙二醇-水(EG-H₂O)均相溶液中的光化学反应,分析了反应的机理,并基于Stern-Volmer方法测量了反应速率常数. 光解DQ体系可以生成³DQ^*,³DQ^*与Trp、Tyr发生的氢原子转移反应占主导地位. 对于DQ/Trp/MeCN-H₂O和DQ/Trp/EG-H₂O溶液,³DQ^*与Trp反应生成杜醌中性自由基DQH^·、以碳为中心的色氨酸中性自由基Trp^·/NH和以氮为中心的色氨酸中性自由基Trp/N^·. 对于DQ/Tyr/MeCN-H₂O和DQ/Tyr/EG-H₂O溶液,³DQ^*与Tyr反应生成DQH^·和酪氨酸中性自由基Tyr/O^·. ³DQ^*与Trp、Tyr的氢原子转移反应速率常数都在10⁹ L·mol^-1·s^-1量级,反应近似受扩散控制. MeCN/H₂O均相溶液中³DQ^*与Trp、Tyr的反应速率常数要明显高于EG/H₂O均相溶液中的反应速率常数,这与Stokes-Einstein方程定性一致.     

氧化石墨烯负载的Pt单原子催化硼胺烷水解机理的理论研究

本文研究了氧化石墨烯负载Pt单原子(Pt₁/Gr-O)催化硼胺烷(NH₃BH₃)全水解反应机理,即一分子的NH₃BH₃生成三分子的氢气(H₂)的过程. 在水解路径中,首先吸附的硼胺烷连续断裂两个B-H键生成第一分子的H₂. 接着,一个H₂O分子与^*BHNH₃基团(^*表示吸附态)反应生成^*BH(H₂O)NH₃,其中伸长的O-H键断裂后形成^*BH(OH)NH₃. 然后,第二个H₂O与^*BH(OH)NH₃反应生成^*BH(OH)(H₂O)NH₃,在指向Pt₁/Gr-O表面的O-H断裂后,生成BH(OH)₂NH₃并脱附到水溶液中. 两个水分子脱氢产生的两个H原子脱附生成第二个H₂分子,且Pt₁/Gr-O催化剂恢复. 脱附后的BH(OH)₂NH₃在水溶液中水解生成第三个H₂分子. 纵观整个水解反应,H₂O分子和^*BHNH₃基团的结合是反应速控步,其反应能垒是16.1 kcal/mol. 因此,Pt₁/Gr-O有希望成为室温催化NH₃BH₃全水解催化剂.     

Cl(2P)+D2→DCl+D反应中波恩-奥本海默近似有效性的交叉分子束研究

本文利用高分辨的里德堡态氘原子标识-交叉分子束装置，研究了碰撞能为4.5∽6.5 kcal/mol范围内Cl(²P)[Cl(²P_3/2)和Cl^*(²P_1/2)]与D₂的反应. 虽然自旋轨道激发态反应Cl^*(²P_1/2)+D₂在波恩-奥本海默(B-O)近似下本应是禁阻的，但实验中观测到了该反应的贡献. 通过测量靠近后向的碰撞能相关的微分散射截面连线，发现低碰撞能下的产物主要来自于B-O近似禁阻的反应Cl^*+D₂. 随着碰撞能的提高，自旋轨道基态反应Cl+D₂的反应性增加明显要比自旋轨道激发态反应Cl^*+D₂更快，并且在高碰撞能下成为产物的主要来源. 实验结果表明：在低碰撞能下，Cl^*中自旋轨道激发态的额外能量，可以帮助B-O近似禁阻的反应Cl^*+D₂越过势垒；然而当碰撞能接近和高于反应势垒时，B-O近似允许的反应Cl+D₂占主导地位. Cl/Cl^*+D₂反应中B-O近似有效性的特征与其同位素反应Cl/Cl^*+H₂是一致的.     

密度泛函理论方法研究6H-SiC(0001)表面对氧分子和水分子的吸附

本文通过密度泛函方法计算6H-SiC(0001)表面对氧分子和水分子的吸附. 在6H-SiC(0001)表面上吸附的O₂分子自发地解离成O^*,并被吸收在C与Si原子之间的空位上. 吸附的H₂O自发地分解成OH^*和H^*,它们都被吸附在Si原子的顶部,OH^*进一步可逆地转化为O^*和H^*. H^*可以使Si悬键饱和并改变O^*的吸附类型,并进一步稳定6H-SiC(0001)表面并防止其转变为SiO₂.     

离子速度成像系统校准及1,4-氯溴丁烷的紫外光解动力学

大气臭氧层破坏越来越严重, 卤代烷烃在太阳紫外线辐射下解离生成破坏臭氧的游离态卤素原子, 是主要元凶之一. 本文选用碘甲烷作为校准分子, 利用离子速度成像技术和共振增强多光子电离技术测得碘甲烷在266 nm紫外光解离下产生的基态碘原子I(²P_3/2)在不同聚焦电压下的离子速度影像, 得到离子速度成像系统的放大系数N=1.13. 并利用该系统研究了1, 4-氯溴丁烷在～ 234 nm紫外辐射下的解离动力学, 分析讨论了解离产生的基态Br (²P_3/2)和激发态Br^* (²P_1/2)的速度和角度分布信息, 揭示了1, 4-氯溴丁烷在～ 234 nm紫外光解离产生基态Br原子和激发态Br^* 原子的通道都是源于C-Br键排斥势能面上的快速解离. 文中通过计算碎片影像角度分布的各项异性参数β值, 得到了生成基态Br(²P_3/2)和激发态Br^* (²P_1/2) 两个解离通道中的平行跃迁和垂直跃迁比例. 另外, 本文还对氯溴甲烷, 1, 2-氯溴乙烷, 1, 3-氯溴丙烷和1, 4-氯溴丁烷在～ 234 nm下的光解动力学进行比较, 分析得到双卤代烷烃分子解离机理对烷基支链长度的依赖关系.     

硫酸(氢)根吸附层对Pd(111)电极上甲酸氧化反应的影响研究

本文使用循环伏安法和电势阶跃法分别研究了添加和不添加Na₂SO₄的0.1 mol/LH₂SO₄+0.1 mol/LHCOOH溶液中Pd(111)电极上甲酸氧化反应(FAO)的动力学行为,并与同样条件下0.1 mol/LHClO₄中的动力学行为进行比较. 加入0.05 mol/L或者0.1 mol/LNa₂O₄后,在相同的电位下负向扫描的FAO电流比正向扫描的显著减小. 本文推测在(SO₄^*_ad)_m+[(H₂O)_n-H₃O⁺]或(SO₄^*_ad)_m+[Na⁺(H₂O)_n-H₃O⁺]吸附层相转变电势以正的电位, 这个吸附层的结构可能随着电位的增加或Na₂SO₄的加入变得更加致密和稳定. 因此,破坏或者脱附致密的硫酸(氢)根吸附层变得更加困难,使得FAO 动力学在较高电位和随后的负扫电位受到明显的抑制.     

噻吨酮光物理和光化学行为对溶剂的依赖性

本文利用纳秒瞬态吸收光谱技术,在不同溶剂中,研究了噻吨酮的光物理和光化学行为. TX的激发三重态(³TX^*)涉及2种电子态,³nπ^*和³ππ^*态. 随着溶剂极性的增强,³ππ^*态的贡献加大. 在CH₃CN,CH₃CN/CH₃OH(1:1)和CH₃CN/H₂O(1:1)溶剂中,³TX^*的自猝灭速率常数k_sq逐渐减小. 这可能由于通过氢键形成的激基复合物阻碍了³TX^*的碰撞猝灭. 二苯胺通过电子转移还原³TX^*,生成TX^·-阴离子和DPA^·+阳离子自由基. 溶剂对该转移过程的影响不明显,表明TX的³nπ^*和³ππ^*态夺取电子的能力相近. 然而,溶剂的依赖性在TX^·-的猝灭过程中表现明显. 在强酸性条件下(pH=3.0),质子化的TX和非质子化的TX之间存在着动态平衡. 在激发光作用下,生成³TXH^+*,光谱上呈现出520 nm处的吸收峰.     

高灵敏，高选择和可视化识别Hg2+的罗丹明turn-on型化学传感器

Two novel rhodamine-based fluorescence enhanced molecular probes (RA₁ and RA₂) were synthesized, which were both designed as comparative fluoroionophore and chromophore for the optical detection of Hg²⁺. The recognizing behaviors were investigated both experimentally and computationally. They exhibited high selectivity and sensitivity for Hg²⁺ over other commonly coexistent metal ions in CH₃CN/H₂O (1:1, V/V) solution. Test shows that hydroxy benzene of rich electron was beneficial to the chelate of Hg²⁺ with sensors. The detection limit was measured to be at least 0.14 μmol/L. After addition of Hg²⁺, the color changed from colourless to pink, which was easily detected by the naked eye in both solution and hydrogel sensor.     

硫酸催化乙二醛气体相水化反应机理和速率常数理论计算研究

采用M06-2X和CCSD(T)高阶量化计算和传统过渡态理论研究硫酸催化乙二醛气体相水化反应.对HCOCHO+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O...H₂SO₄和HCOCHO+H₂O+H₂SO₄五个路径的反应机理和速率常数进行了研究.计算结果表明硫酸具有较强的催化能力,能显著减小乙二醛水化反应的能垒,在CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)理论水平,当硫酸分子参与乙二醛水化反应时,反应能垒从37.15 kcal/mol减少至7.08 kcal/mol.在室温条件下,硫酸催化乙二醛水化反应的反应速率1.34×10^-11 cm³/(molecule.s),是等量水分子参与乙二醛水化反应的速率的10¹²倍,大于乙二醛与OH自由基反应的反应速率1.10×10^-11 cm³/(molecule.s).这表明大气条件下,硫酸催化乙二醛水化反应可以发生,同乙二醛与OH自由基反应相竞争.     

香蕉叶片Chla荧光动力学参量对激发光强的反应

在蓝色激发光(λ_m＝660nm)作用下,香蕉叶片的叶绿素a(Chla)发出波长为720～740nm的荧光信号,荧光强度随时间呈现有规律的变化.随着激发光强的增加,荧光动力学参量F₀和F_VI/F_V呈上升趋势,F_V/F₀与F_V/F_M逐渐达到饱和,而CA和T_1/2呈下降趋势.研究结果表明,保证香蕉叶片光合机构高速有序运转的适宜光强在20～60μmol·m^-2·s^-1之间,过量的光强将造成叶片光合机构的损伤.讨论了香蕉叶片诸荧光动力学参量的生物学意义及其随激发光强度增加而变化的原因.     

Switching of hydrogen bonds of water in ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate

We have investigated temperature‐induced Raman spectral changes of deuterated water in an ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF₄]), between room temperature and 77 K. The comparison of the OH and OD stretching vibrational spectra at 77 K shows that the strength of the hydrogen bonds in [bmim][BF₄]–water mixtures strongly depends on the type of water, i.e. H₂O and D₂O. In the [bmim][BF₄]–D₂O system, remarkably strong hydrogen bonds form at low temperatures, but they switch to nearly free hydrogen bonds on heating. Copyright © 2013 John Wiley & Sons, Ltd.     

High pressure Raman study on the local structure of 1-ethyl-3-methylimidazolium tetrafluoroborate

We have investigated the pressure-induced Raman spectral changes of 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF₄]). We found that [emim][BF₄] did not crystallize up to 1.2 GPa. The Raman CH stretching spectra arising from the CH₃ groups of the ethyl-chain and the CH₃ group adjacent to the imidazolium-ring in [emim]⁺ cation largely changed against pressure. Moreover, the Raman intensity of the CH₂ (N) bending band arising from the alkyl-chain drastically changes with increasing pressure, but that of the imidazolium-ring in-plane bending band arising from the imidazolium-ring is independent of pressure. Our results show that the environment around the alkyl-chain of [emim][BF₄] is largely perturbed rather than that around the imidazolium-ring upon compression.     

Measuring the solubility of benzoic acid in room temperature ionic liquids using chronoamperometric techniques

The electrochemical reduction of benzoic acid (BZA) has been studied at platinum micro‐electrodes (10 and 2 µm diameters) in acetonitrile (MeCN) and six room temperature ionic liquids (RTILs): [C₂mim][NTf₂], [C₄mim][NTf₂], [C₄mpyrr][NTf₂], [C₄mim][BF₄], [C₄mim][NO₃] and [C₄mim][PF₆] (where [C_nmim]⁺ = 1‐alkyl‐3‐methylimidazolium, [NTf₂]^? = bis(trifluoromethylsulphonyl)imide, [C₄mpyrr]⁺ = N‐butyl‐N‐methylpyrrolidinium, [BF₄]^? = tetrafluoroborate, [NO₃]^? = nitrate and [PF₆]^? = hexafluorophosphate). Based on the theoretical fitting to experimental chronoamperometric transients in [C₄mpyrr][NTf₂] and MeCN at several concentrations and on different size electrodes, it is suggested that a fast chemical step preceeds the electron transfer step in a CE mechanism (given below) in both RTILs and MeCN, leading to the appearance of a simple one‐electron transfer mechanism. The six RTIL solvents and MeCN were saturated with BZA, and potential‐step chronoamperometry revealed diffusion coefficients of 170, 4.6, 3.2, 2.7, 1.8, 0.26 and 0.96 × 10^?11 m² s^?1 and solubilities of 850, 75, 78, 74, 220, 2850 and 48 mM in MeCN and the six ionic liquids, respectively, at 298 K. The high solubility of BZA in [C₄mim][NO₃] may suggest a strong interaction of the dissolved proton with the nitrate anion. Although there are relatively few literature reports of solubilities of organic solutes in RTILs at present, these results suggest the need for further studies on the solubilities of organic species (particularly acids) in RTILs, because of the contrasting interaction of dissolved species with the RTIL ions. Chronoamperometry is suggested as a convenient methodology for this purpose. Copyright © 2008 John Wiley & Sons, Ltd.     

Bright electrophosphorescent devices based on sterically hindered spacer-containing Cu(I) complex

A Cu(I) complex, [Cu(Dppp)(DPEphos)]BF₄ (Dppp=2,3-diphenyl-pyrazino[2,3-f][1,10]phenanthroline, DPEphos=Bis[2-(diphenylphosphino)phenyl]ether), is synthesized and used as the dopant in bright electrophosphorescent devices with the general structure ITO/m-MTDATA (30 nm)/NPB (20 nm)/CBP: ×wt% [Cu(Dppp)(DPEphos)]BF₄ (30 nm)/Bphen (20 nm)/Alq₃ (20 nm)/LiF (0.8 nm)/ Al (200 nm). These devices exhibit a maximum brightness of 4483 cd/m² and a peak efficiency of 3.4 cd/A. Compared with previously reported similar devices based on Cu(I) complexes, the brightness of the devices presented in this article is the best. Meanwhile, 2% [Cu(Dppp)(DPEphos)]BF₄-based devices exhibit white light-emitting properties with CIE coordinates of (0.32. 0.35) at 10 V.     

Thermodynamic properties of some ionic liquids using a simple equation of state

In this work, we have used a simple equation of state (EoS) to predict the density and other thermodynamic properties such as isobaric expansion coefficient, α_P , isothermal compressibility, κ_T, and internal pressure, P_i, for nine ionic liquids including trihexyl (tetradecyl) phosphonium chloride ([(C₆H₁₃)₃P(C₁₄H₂₉)][Cl]), trihexyl (tetradecyl) phosphonium acetate ([(C₆H₁₃)₃P(C₁₄H₂₉)][Ac]), trihexyl (tetradecyl) phosphonium bis {(trifluoromethyl) sulfonyl} amide ([(C₆H₁₃)₃P(C₁₄H₂₉)][NTf₂]), 1-butyl-3-methylimidazolium bis {(trifluoromethyl) sulfonyl} amide ([bmim][NTf₂]), 1-hexyl-3-methylimidazolium bis {(trifluoromethyl) sulfonyl} amide ([hmim][NTf₂]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), 1-butyl-3-octylimidazolium tetrafluoroborate ([omim][BF₄]), 1-butyl-3-octylimidazolium hexafluorophosphate ([omim][PF₆]), and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) at different temperatures and pressures. A wide comparison with experimental and literature data has been made. The results show that this EoS can be used to reproduce and predict different thermodynamic properties of ionic liquids within experimental errors.     

Zur Isotopenanalyse des Bors an Bandenköpfen des BO-Moleküs

Es wurde ein emissionsspektroskopisches Verfahren zur Bestimmung des Borisotopenverhältnisses ¹⁰B/¹¹B im Bortrifluorid-Diāthylāther-Komplex [BF₃(C₂H₅)₂O] studiert. Dazu wurde das Bortifluoridätherat durch ein probenchemisches Umarbeitungsverfahren in BF₃-Gas umgewandlet und dieses mit einer Hochfrequenzentladung angeregt. Das emittierle Licht wurde mit Hilfe eines Spektrographen oder Monochromators spektral zerlegt und mit Fotoplatte oder Schreiber registriert. Es ergab sich ein ausgegrägtes Emissionsspektrum des α-Systems der BO-Banden, wobei für die Bestimmung des Borisotopenverhāltnisses die Isotopieverschiebung an der 2-0 Bande bei 384,7 nm und an der 2–0 Bande bei 382,99 nm in Frage kam.     

结合除谱,差谱,二阶差谱的二氯化铜水溶液中直接接触离子对的紫外可见吸收光谱研究

The microstructure of aqueous CuCl₂ has been studied through lots of technologies for many years; however, it remains a controversial subject. In this study, a new spectroscopic method has been proposed to analyze the UV-visible spectra of thin film of CuCl₂/H₂O solutions at different concentrations. This method is the combination of ratio spectra, difference spectra and second order difference spectra. By using this method, two new bands at ~230 and ~380 nm are obviously observed. The bands are assigned as the contacted ion pairs[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2-, which demonstrates that ion pairs exist in the CuCl₂/H₂O solution. Such finding agrees with the recent theoretical spectra obtained by time-dependent density functional theory. Furthermore, the populations of the contacted ion pairs are discussed. This study not only offers the direct spectroscopic evidence of[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2- in aqueous CuCl₂, but also suggests that the spectroscopic analysis method is powerful to extract the weak bands in a strong overlapping spectrum.     

Mössbauer study of Sn(Fe)O2 prepared by mechanosynthesis

This work deals with first-principles investigation of the electronic structure of the BF₃??H₂O complex which is important in catalysis of organic reactions and polymerization. The dissociation energy of the BF₃??H₂O complex and the nuclear quadrupole interaction parameters for the excited nuclear state ¹⁹F* (I = 5/2) of the fluorine nuclei have been studied. Our investigation shows that the complexation bond BO between the BF₃ and H₂O units is strongly influenced by the larger electronegativity of Oxygen as compared to Nitrogen in BF₃??NH_3. The quadrupole coupling constants of ¹⁹F* and the asymmetry parameter are however quite close to those for BF₃??NH₃. The likely reasons for these features of these two important catalytic systems are suggested.     

Ionic liquid structure: the conformational isomerism in 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate ([bmim][BF4])

As a probe of local structure, the vibrational properties of the 1‐butyl‐3‐methylimidazolium tetrafluoroborate [bmim][BF₄] ionic liquid were studied by infrared (IR), Raman spectroscopy, and ab initio calculations. The coexistence of at least four [bmim]⁺ conformers (GG, GA, TA, and AA) at room temperature was established through unique spectral responses. The Raman modes characteristic of the two most stable [bmim]⁺ conformers, GA and AA, according to the ab initio calculations, increase in intensity with decreasing temperature. To assess the total spectral behavior of the ionic liquid both the contributions of different [bmim]⁺ conformers and the [bmim]⁺− [BF₄]⁻ interactions to the vibrational spectra are discussed. Copyright © 2008 John Wiley & Sons, Ltd.