复合物Mg+-NCSCH3光诱导反应

观察了复合物Mg⁺-NCSCH₃在230~440 nm范围的光解离光谱. 在此波段内的复合物光诱导产物的质谱显示, 存在着非反应猝灭产物Mg⁺和反应产物Mg⁺NC、Mg⁺NCS. 反应产物来源于S－C化学键的断裂. 复合物的光解离光谱由两个对应于原子Mg⁺(3²P←3²S)跃迁的宽峰构成. 由量化计算中的CIS方法所获得的吸收谱理论值与实验值吻合较好.     

N-(末端三丁基锡取代基)酰亚胺的光诱导单电子转移成环反应

合成了两种新的分子内给受电子体系N-[2-(2-三丁基锡甲硫基)乙基]邻苯二甲酰亚胺(1a)和N-(3-三丁基锡丙基)马来酰亚胺(1b),并在甲醇、乙腈-30%水、乙腈中进行了光诱导单电子转移反应.化合物1a在光诱导下发生分子内单电子转移反应,以很高的产率和区域选择性生成环胺醇2.化合物1b在光诱导下发生分子内单电子转移反应生成环胺醇3,同时有[2+2]环加成副反应产物4生成.以上所有新化合物的结构经质谱和核磁共振谱验证.     

生物细胞内Mg2+的无损伤NMR研究

建立了无损伤性研究细胞内游离[Mg2+]i的31P-NMR方法,通过测量细胞的31P-NMR谱中ATP的α磷和β磷的化学位移差值,得出细胞内Mg2+与ATP结合的复合物MgATP和整个ATP量的比值,计算得到细胞内游离Mg2+浓度.与其它分析方法相比,31P-NMR测定细胞内游离Mg2+浓度具有对细胞样品无损伤的优点.     

碱式氯化镁5Mg(OH)2·MgCl2·3H2O的制备与表征

以氨水和盐湖盛产的水氯镁石为原料经过两步反应制备碱式氯化镁.第一步,水氯镁石和氨水反应制备氢氧化镁;第二步,利用氢氧化镁和水氯镁石,通过水热反应得到了具有纤维形貌、结晶较好的碱式氯化镁.应用化学分析、XRD、SEM和FIIR等手段对产物进行测试与表征.化学分析结果表明产物组成为5Mg(OH)2·MgCl2·3H2O.将得到的5Mg(OH)2·MgCl2·3H2O和碱式氯化镁系列标准XRD图对照,未有较好的匹配,且结合化学分析和已报道碱式硫酸镁具有5Mg(OH)2·MgSO4·3H2O物相,因而推测其为新物相;SEM图中5Mg(OH)2·MgCl2·3H2O纤维直径约为0.4μm,平均长度大于24 μm,长径比大于60;FTIR图谱中3419 cm-1附近出现了氢键的O-H伸缩振动吸收峰,1635 cm-1附近出现了游离水中H-O-H的弯曲振动吸收峰.水热合成的5Mg(OH)2·MgCl2·3H2O和常压下的产物相比直径较小,晶形更完整,强度更高.     

苝醌／富勒烯C60超分子与电子给体的电子转移作用

利用紫外-可见吸收光谱、瞬态吸收光谱及x射线衍射等方法研究了苝醌染料竹红菌素镁离子配合物(Mg2+-HA)与富勒烯C60的相互作用.结果表明,Mg2+-HA与C60在溶液和固体状态下都能够形成稳定的超分子.Mg2+-HA 存在条件下,C60 能够溶于多种极性溶剂,在二甲基亚砜(DMSO)中的溶解度能够达到1×10-4mol·L-1.作为超分子体系中的光捕获分子,Mg2+-HA 能显著地提高C60 与N,N.二甲基苯胺(DMA)的光诱导电子转移反应效率,生成的C60 负离子自由基的电子自旋共振光谱(ESR)信号强度比未加入Mg2+-HA 时增强了9倍左右.     

碳酸氢根与金属阳离子反应的理论推演和实验研究

通过热力学理论推演和实验验证碳酸氢根与金属阳离子反应的情况,得出Al3+、Fe3+、Cu2+、Ag+与CO32-、HCO3- 不能共存,Fe2+、Ca2+、Ba2+、Mg2+与CO32-不能共存,Fe2+、Ca2+、Ba2+、Mg2+与HCO3- 有条件(稀溶液中)能共存等结论。     

Ce3+对菠菜D1/D2/Cytb559复合物影响的光谱学研究

从Ce³⁺处理过的菠菜PSⅡ颗粒中纯化出了D1/D2/Cytb559复合物并研究了Ce³⁺对其光谱学性质的影响. 结果表明Ce³⁺处理过的菠菜生长发育改善, PSⅡ颗粒电子传递效率明显加快, D1/D2/Cytb559复合物UV-Vis 谱在Soret区和Q区分别蓝移3和2 nm; 荧光发射峰蓝移5 nm; EXAFS谱表明Ce³⁺已结合到D1/D2/Cytb559复合物上. 推测Ce³⁺已同时参与叶绿素卟啉环中N的配位和多肽氨基酸羧基氧的配位, Ce—N键长为0.253 nm, Ce—O键长为0.32 nm. CD谱表明Ce³⁺结合后其复合物二级结构未发生明显变化. 认为Ce³⁺加强了D1/D2/Cytb559复合物P680⁺原初电子供体的功能, 但对反应中心复合物的构象影响不大.     

苝醌/富勒烯C60超分子与电子给体的电子转移作用

利用紫外-可见吸收光谱、瞬态吸收光谱及X射线衍射等方法研究了苝醌染料竹红菌素镁离子配合物(Mg2+-HA)与富勒烯C60的相互作用. 结果表明, Mg2+-HA与C60在溶液和固体状态下都能够形成稳定的超分子. Mg2+-HA存在条件下, C60能够溶于多种极性溶剂, 在二甲基亚砜(DMSO)中的溶解度能够达到1×10^-4 mol·L^-1. 作为超分子体系中的光捕获分子, Mg2+-HA能显著地提高C60与N,N-二甲基苯胺(DMA)的光诱导电子转移反应效率, 生成的C60负离子自由基的电子自旋共振光谱(ESR)信号强度比未加入Mg2+-HA时增强了9倍左右.     

激光溅射-分子束法研究镁、铝离子与乙腈分子的气相化学反应

利用激光溅射-分子束技术研究了Mg+、 Al+与乙腈分子的气相团簇反应.根据反射式飞行时间质谱检测的结果发现, Mg+、 Al+与乙腈分子反应形成不同尺寸的团簇离子产物,其中Al+与(CHCN)n的结合数n=1～10,而Mg+与(CHCN)n的结合数n=1～5. Al+(CHCN)n、 Mg+(CHCN)n团簇离子产物的强度分布都存在明显的强度间隙现象. Al+与(CHCN)n进行缔合时,出现了两个强度间隙;而Mg+与(CHCN)n进行缔合时,则只存在一个强度间隙. Al+的第一强度间隙在n=4～5,第二强度间隙在n=6～7;而Mg+的强度间隙在n=2～3.     

气相CBr2 自由基的产生及激光诱导荧光色散谱研究

利用双层流动反应管作为束源,研究了F与CH2Br2反应生成的CBr2和Br2的气相激光诱导荧光色散谱,将得到的谱线分别指定为CBr2的(0,13,0)→(0,v2″,0)(v2″=1～6)跃迁和Br2的 3Π+u→ 1Σ+g跃迁,从光谱中首次得到气相CBr2自由基基态弯曲振动频率ν2″=215 cm-1,实验确认了CBr2自由基和Br2是F+CH2Br2过程多步反应的产物.     

芳氧功能化咪唑基五氯化铕[HO-4,6-di-tBu-C6H2-2-CH2{CH（NCHCHNiPr）}]2+[EuCl5（THF）]2-的合成与结构

芳氧功能化咪唑盐L+Cl-(L=HO-4,6-di-tBu-C6H2-2-CH2{CH[iPrNCHCHN]})与无水EuCl3分别按照摩尔比为1∶2和1∶3反应成功合成相同芳氧功能化咪唑基五氯化铕L+2[EuCl5(THF)]2-,产物通过元素分析、IR、X-ray射线衍射表征。晶体结构数据表明此配合物属于单斜晶体,空间群P21/c,晶胞参数a=0.96664(8)nm,b=1.63312(12)nm,c=3.6850(3)nm,β=97.600(2)°,V=5.7662(8)nm3,Mr=1060.30,Z=4,Dc=1.221 Mg/m3,μ(MoKα)=1.36 mm-1,F(000)=2200。目标化合物是由阴离子[EuCl5(THF)]2-和[HO-4,6-di-tBu-C6H2-2-CH2{CH(iPrNCHCHN)}]2+通过氢键作用而形成的空间网状结构的晶体,阴离子中中心金属(Eu)是由五个氯原子以及来自THF的氧原子形成扭曲八面体的构型。     

The first structural characterisation of a group 2 metal alkylperoxide complex: comments on the cleavage of dioxygen by magnesium alkyl complexes

A new high-yield synthesis of [(PhCH(2))(2)Mg(thf)(2)] and [[(PhCH(2))CH(3)Mg(thf)](2)] via benzylpotassium has allowed a simple entry into benzylmagnesium coordination chemistry. The syntheses and X-ray crystal structures of both [(eta(2)-Me(2)NCH(2)CH(2)NMe(2))Mg(CH(2)Ph)(2)] and [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] (Ar'=2,6-diisopropylphenyl) are reported. The latter beta-diketiminate complex reacts with dioxygen to provide a 1:2 mixture of dimeric benzylperoxo and benzyloxo complexes. The benzylperoxo complex [[eta(2)-HC[C(CH(3))NAr'](2)Mg(mu-eta(2):eta(1)-OOCH(2)Ph)](2)] is the first example of a structurally characterised Group 2 metal-alkylperoxo complex and contains the benzylperoxo ligands in an unusual mu-eta(2):eta(1)-coordination mode, linking the two five-coordinate magnesium centres. The O[bond]O separation in the benzylperoxo ligands is 1.44(2) A. Reaction of the benzylperoxo/benzyloxo complex mixture with further [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] results in complete conversion of the benzylperoxo species into the benzyloxo complex. This reaction, therefore, establishes the cleavage of dioxygen by this system as a two-step process that involves initial oxygen insertion into the Mg[bond]CH(2)Ph bond followed by O[bond]O/Mg[bond]C sigma-bond metathesis of the resulting benzylperoxo ligand with a second Mg[bond]CH(2)Ph bond. The formation of a 1:2 mixture of the benzylperoxo and benzyloxo species indicates that the rate of the insertion is faster than that of the metathesis, and this is shown to be consistent with a radical mechanism for the insertion process.     

Infrared laser spectroscopy of the CH3OO radical formed from the reaction of CH3 and O2 within a helium nanodroplet

Helium nanodroplet isolation and infrared laser spectroscopy are used to investigate the CH(3) + O(2) reaction. Helium nanodroplets are doped with methyl radicals that are generated in an effusive pyrolysis source. Downstream from the introduction of CH(3), the droplets are doped with O(2) from a gas pick-up cell. The CH(3) + O(2) reaction therefore occurs between sequentially picked-up and presumably cold CH(3) and O(2) reactants. The reaction is known to lead barrierlessly to the methyl peroxy radical, CH(3)OO. The ~30 kcal/mol bond energy is dissipated by helium atom evaporation, and the infrared spectrum in the CH stretch region reveals a large abundance of droplets containing the cold, helium solvated CH(3)OO radical. The CH(3)OO infrared spectrum is assigned on the basis of comparisons to high-level ab initio calculations and to the gas phase band origins and rotational constants.     

Magnesium monocationic complexes: a theoretical study of metal ion binding energies and gas-phase association kinetics

Bond dissociation energies (BDEs) for complexes of ground state Mg+ (2S) with several small oxygen- and nitrogen-containing ligands (H2O, CO, CO2, H2CO, CH3OH, HCOOH, H2CCO, CH3CHO, c-C2H4O, H2CCHOH, CH3CH2OH, CH3OCH3, NH3, HCN, H2CNH, CH3NH2, CH3CN, CH3CH2NH2, (CH3)2NH, H2NCN, and HCONH2) have been calculated at the CP-dG2thaw level of theory. These BDE values, as well as counterpoise-corrected MP2(thaw)/6-311+G(2df,p) calculations on the Mg+ complexes of several larger ligands, augment and complement existing experimental or theoretical determinations of gas-phase Mg+/ligand bond strengths. The reaction kinetics of complex formation are also investigated via variational transition state theory (VTST) calculations using the computed ligand and molecular ion parameters. Radiative association rate coefficients for most of these systems increase by approximately 1 order of magnitude with every 3-fold reduction in temperature from 300 to 10 K. Several of the largest molecules surveyed-notably, CH3COOH, (CH3)2CO, and CH3CH2CN-exhibit comparatively efficient radiative association with Mg+ (k(RA) > or = 1.0 x 10(-10) cm3 molecule(-1) s(-1)) at temperatures as high as 100 K, implying that these processes may have a considerable influence on the metal ion chemistry of warm molecular astrophysical environments known to contain these potential ligands. Our calculations also identify the infrared chromophoric brightness of various functional groups as a significant factor influencing the efficiency of the radiative association process.     

Theoretical mechanistic study on the radical-molecule reaction of CH2OH with NO2

The complex singlet potential energy surface for the reaction of CH2OH with NO2, including 14 minimum isomers and 28 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and Gaussian-3 (single-point) levels. The initial association between CH2OH and NO2 is found to be the carbon-to-nitrogen approach forming an adduct HOCH2NO2 (1) with no barrier, followed by C-N bond rupture along with a concerted H-shift leading to product P1 (CH2O + trans-HONO), which is the most abundant. Much less competitively, 1 can undergo the C-O bond formation along with C-N bond rupture to isomer HOCH2ONO (2), which will take subsequent cis-trans conversion and dissociation to P2 (HOCHO + HNO), P3 (CH2O + HNO2), and P4 (CH2O + cis-HONO) with comparable yields. The obtained species CH2O in primary product P1 is in good agreement with kinetic detection in experiment. Because the intermediate and transition state involved in the most favorable pathway all lie blow the reactants, the CH2OH + NO2 reaction is expected to be rapid, as is confirmed by experiment. These calculations indicate that the title reaction proceeds mostly through singlet pathways; less go through triplet pathways. In addition, a mechanistic comparison is made with the reactions CH3 + NO2 and CH3O + NO2. The present results can lead us to deeply understand the mechanism of the title reaction and may be helpful for understanding NO2-combustion chemistry.     

Secondary kinetics of methanol decomposition: theoretical rate coefficients for 3CH2 + OH, 3CH2 + 3CH2, and 3CH2 + CH3

Direct variable reaction coordinate transition state theory (VRC-TST) rate coefficients are reported for the (3)CH(2) + OH, (3)CH(2) + (3)CH(2), and (3)CH(2) + CH(3) barrierless association reactions. The predicted rate coefficient for the (3)CH(2) + OH reaction (approximately 1.2 x 10(-10) cm(3) molecule(-1) s(-1) for 300-2500 K) is 4-5 times larger than previous estimates, indicating that this reaction may be an important sink for OH in many combustion systems. The predicted rate coefficients for the (3)CH(2) + CH(3) and (3)CH(2) + (3)CH(2) reactions are found to be in good agreement with the range of available experimental measurements. Product branching in the self-reaction of methylene is discussed, and the C(2)H(2) + 2H and C(2)H(2) + H2 products are predicted in a ratio of 4:1. The effect of the present set of rate coefficients on modeling the secondary kinetics of methanol decomposition is briefly considered. Finally, the present set of rate coefficients, along with previous VRC-TST determinations of the rate coefficients for the self-reactions of CH(3) and OH and for the CH(3) + OH reaction, are used to test the geometric mean rule for the CH(3), (3)CH(2), and OH fragments. The geometric mean rule is found to predict the cross-combination rate coefficients for the (3)CH(2) + OH and (3)CH(2) + CH(3) reactions to better than 20%, with a larger (up to 50%) error for the CH(3) + OH reaction.     

Reactions of thioethers with Mn(2)(CO)(7)(mu-S(2)) proceed with CO displacement and insertion of the sulfur atom into the Mn-Mn bond

The reaction of Mn(2)(CO)(7)(mu-S(2)) (2) with SMe(2) yielded the new complexes Mn(2)(CO)(6)(mu-S(2))(mu-SMe(2)) (3) and Mn(4)(CO)(14)(SMe(2))(mu(3)-S(2))(mu(4)-S(2)) (4) in 18 and 41% yields, respectively. The reaction of 2 with the cyclic thioether thietane SCH(2)CH(2)CH(2) yielded the new complexes Mn(2)(CO)(6)(mu-S(2))(mu-SCH(2)CH(2)CH(2)) (5) and Mn(4)(CO)(14)(SCH(2)CH(2)CH(2))(mu(3)-S(2))(mu(4)-S(2)) (6) in 12 and 52% yields, respectively, and the reaction of 2 with 1,4,9-trithiacyclododecane (12S3) yielded Mn(2)(CO)(6)(mu-12S3)(mu-S(2)) (7) and Mn(4)(CO)(14)(12S3)(mu(3)-S(2))(mu(4)-S(2)) (8) in 8 and 24% yields, respectively. Compounds 3 and 5-7 were characterized crystallographically. Compounds 3, 5, and 7 have similar structures in which the thioether ligand has replaced the bridging carbonyl ligand of 2 and its sulfur atom has been inserted into the manganese-manganese bond. The two manganese atoms are not mutually bonded, and two Mn(CO)(3) groups are held together through the bridging disulfido ligand and the bridging sulfur atom of the thioether ligand. Compound 6 contains a Mn(4)(mu(3)-S(2))(mu(4)-S(2)) moiety without metal-metal bonds. On the basis of spectroscopic data, compounds 4 and 8 are believed to have similar structures.     

The effects of water vapor on the CH3O2 self-reaction and reaction with HO2

The gas phase reactions of CH3O2 + CH3O2, HO2 + HO2, and CH3O2 + HO2 in the presence of water vapor have been studied at temperatures between 263 and 303 K using laser flash photolysis coupled with UV time-resolved absorption detection at 220 and 260 nm. Water vapor concentrations were quantified using tunable diode laser spectroscopy operating in the mid-IR. The HO2 self-reaction rate constant is significantly enhanced by water vapor, consistent with what others have reported, whereas the CH3O2 self-reaction and the cross-reaction (CH3O2 + HO2) rate constants are nearly unaffected. The enhancement in the HO2 self-reaction rate coefficient occurs because of the formation of a strongly bound (6.9 kcal mol(-1)) HO2 x H2O complex during the reaction mechanism where the H2O acts as an energy chaperone. The nominal impact of water vapor on the CH3O2 self-reaction rate coefficient is consistent with recent high level ab initio calculations that predict a weakly bound CH3O2 x H2O complex (2.3 kcal mol(-1)). The smaller binding energy of the CH3O2 x H2O complex does not favor its formation and consequent participation in the methyl peroxy self-reaction mechanism.     

Formation of a Criegee intermediate in the low-temperature oxidation of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is the major sulfur-containing constituent of the Marine Boundary Layer. It is a significant source of H2SO4 aerosol/particles and methane sulfonic acid via atmospheric oxidation processes, where the mechanism is not established. In this study, several new, low-temperature pathways are revealed in the oxidation of DMSO using CBS-QB3 and G3MP2 multilevel and B3LYP hybrid density functional quantum chemical methods. Unlike analogous hydrocarbon peroxy radicals the chemically activated DMSO peroxy radical, [CH3S(=O)CH2OO*]*, predominantly undergoes simple dissociation to a methylsulfinyl radical CH3S*(=O) and a Criegee intermediate, CH2OO, with the barrier to dissociation 11.3 kcal mol(-1) below the energy of the CH3S(=O)CH2* + O2 reactants. The well depth for addition of O2 to the CH3S(=O)CH2 precursor radical is 29.6 kcal mol(-1) at the CBS-QB3 level of theory. We believe that this reaction may serve an important role in atmospheric photochemical and irradiated biological (oxygen-rich) media where formation of initial radicals is facilitated even at lower temperatures. The Criegee intermediate (carbonyl oxide, peroxymethylene) and sulfinyl radical can further decompose, resulting in additional chain branching. A second reaction channel important for oxidation processes includes formation (via intramolecular H atom transfer) and further decomposition of hydroperoxide methylsulfoxide radical, *CH2S(=O)CH2OOH over a low barrier of activation. The initial H-transfer reaction is similar and common in analogous hydrocarbon radical + O2 reactions; but the subsequent very low (3-6 kcal mol(-1)) barrier (14 kcal mol(-1) below the initial reagents) to beta-scission products is not common in HC systems. The low energy reaction of the hydroperoxide radical is a beta-scission elimination of *CH2S(=O)CH2OOH into the CH2=S=O + CH2O + *OH product set. This beta-scission barrier is low, because of the delocalization of the *CH2 radical center through the -S(=O) group, to the -CH2OOH fragment in the transition state structure. The hydroperoxide methylsulfoxide radical can also decompose via a second reaction channel of intramolecular OH migration, yielding formaldehyde and a sulfur-centered hydroxymethylsulfinyl radical HOCH2S*(=O). The barrier of activation relative to initial reagents is 4.2 kcal mol(-1). Heats of formation for DMSO, DMSO carbon-centered radical and Criegee intermediate are evaluated at 298 K as -35.97 +/- 0.05, 13.0 +/- 0.2 and 25.3 +/- 0.7 kcal mol(-1) respectively using isodesmic reaction analysis. The [CH3S*(=O) + CH2OO] product set is shown to form a van der Waals complex that results in O-atom transfer reaction and the formation of new products CH3SO2* radical and CH2O. Proper orientation of the Criegee intermediate and methylsulfinyl radical, as a pre-stabilized pre-reaction complex, assist the process. The DMSO radical reaction is also compared to that of acetonyl radical.