Spin-orbit ab initio investigation of the ultraviolet photolysis of diiodomethane.

The UV photodissociation (<5 eV) of diiodomethane (CH(2)I(2)) is investigated by spin-orbit ab initio calculations. The experimentally observed photodissociation channels in the gas and condensed phases are clearly assigned by multi-state second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space-state interaction potential energy curves. The calculated results indicate that the fast dissociations of the first two singlet states of CH(2)I(2) and CH(2)I--I lead to geminate-radical products, CH(2)I (.)+I((2)P(3/2)) or CH(2)I (.)+ I*((2)P(1/2)). The recombination process from CH(2)I--I to CH(2)I(2) is explained by an isomerization process and a secondary photodissociation reaction of CH(2)I--I. Finally, the study reveals that spin-orbits effects are significant in the quantitative analysis of the electronic spectrum of the CH(2)I--I species.     

Side-on bridging coordination of N2: spectroscopic characterization of the planar Zr2N2 core and theoretical investigation of its butterfly distortion

The vibrational and electronic structure of the side-on N(2)-bridged Zr complex [((P(2)N(2))Zr)(2)(mu-eta(2):eta(2)-N(2))] (P(2)N(2)=PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh) were analyzed. The vibrational characterization of the planar Zr(2)N(2) core was based on resonance Raman and infrared spectroscopy. In the Raman spectrum, the Nbond;N stretching band is found at 775 cm(-1) with an isotope shift of 22 cm(-1). Due to its appearance in many overtones and combination modes, the metal-metal stretch is assigned to the peak at 295 cm(-1). The two ungerade modes of the Zr(2)N(2) core were identified in the infrared spectrum. Based on these four vibrations of the Zr(2)N(2) unit, a quantum chemical assisted normal coordinate analysis (QCA-NCA) was performed. The force constants for the N--N and Zr--N bonds were calculated to be 1.53 and 2.58 mdyn A(-1), respectively. The butterfly distortion of the Zr(2)N(2) unit obtained in DFT geometry optimizations of planar side-on N(2)-bridged Zr complexes was analyzed in more detail. It was found that on bending of the Zr(2)N(2) core, the lone pairs of the axial amide ligands are rotated by 90 degrees. The bent Zr(2)N(2) unit is 11 kcal mol(-1) lower in energy than the planar core due to a more uniform distribution of electron density between the metal atoms and N(2) and delocalization of electron density from the amide ligands to the Zr(2)N(2) unit. The spectroscopic implications of this distortion are analyzed.     

HG-AFS测定垃圾焚烧炉烟道气中锑的形态

以某垃圾焚烧厂焚烧炉产生的烟道气为研究对象,采用酒石酸提取,对烟道气中sb形态进行了分析,用HG-AFS分别测出样品中Sb（Ⅲ）和总Sb的量,差减法得到Sb（V）的量。结果表明,sb（Ⅲ）和总sb检出限分别为0．13μg／L和0．11μg/L,相对标准偏差（RSD,n=11）分别为5．8％和6．3％,加标回收率在84．8％-113％。     

甲基丙烯醛氧化酯化制甲基丙烯酸甲酯催化剂的制备与应用

甲基丙烯醛氧化酯化制甲基丙烯酸甲酯催化剂的制备与应用;催化剂; 甲基丙烯酸甲酯; 甲基丙烯醛; 氧化-酯化反应     

温度与碱浓度对FeO_4~(2-)/FeO_2~-体系电化学行为的影响

研究了影响Fe(OH)3进行酸式电离反应的因素,在多种浓度和温度条件下的NaOH浓溶液中采用SnO2-Sb2O3/Ti电极,研究FeO42-/FeO2-体系的电化学氧化还原反应参数及其变化趋势,结果证实该体系发生电化学氧化还原反应的最佳碱溶液浓度范围为12~14 mol/L,最佳温度范围为295~315 K.阐明了在实验条件下FeO42-/FeO2-氧化还原体系中存在由FeO43-/FeO2-构成的氧化还原电对,而FeO42-不直接与FeO2-构成氧化还原电对;并给出了FeO42-/FeO2-氧化还原体系的Latim er图.     

A 1H NMR and theoretical investigation of the conformations of some monosubstituted cyclobutanes

The complete analysis of the complex (1)H NMR spectra of some monosubstituted cyclobutanes was achieved to give all the (1)H chemical shifts and (n)J(HH) (n = 2, 3 and 4) coupling constants in these molecules. The substituent chemical shifts of the substituents in the cyclobutane ring differ significantly from those in acyclic systems. For example, the OH and the NH(2) groups in cyclobutanol and cyclobutylamine produce a large shielding of the hydrogens of the opposite CH(2) group of the ring compared with little effect on the comparable methylene protons of butane. These effects and the other (1)H shifts in the cyclobutanes were modelled successfully in the CHARGE program. The RMS error (calculated vs observed shifts) for the 34 (1)H shifts recorded was 0.053 ppm. The conformational equilibrium in these compounds between the axial and the equatorial conformers was obtained by comparing the observed and the calculated (4)J(HH) couplings. These couplings in cyclobutanes, in contrast to the corresponding (3)J(HH) couplings, show a pronounced orientation dependence; (4)J(eq-eq) is ca 5 Hz and (4)J(ax-ax) ca 0 Hz. The couplings in the individual conformers were calculated at the B3LYP/EPR-III level. The conformer energy differences ΔG(ax-eq) vary from 1.1 kcal mol(-1) for OH to 0.2 kcal mol(-1) for the CH(2)OH substituent. The values of the conformer energy differences are compared with the previous IR data and the corresponding theoretical values from molecular mechanics (MM) and DFT theory. Generally, good agreement is observed although both the MM and the DFT calculations deviate significantly from the observed values for some substituents.     

Density-functional-theory studies of the infrared spectra of titanium carbide nanocrystals

The infrared (IR) spectra of cuboidic titanium carbide (TiC) nanocrystals have been studied at the density-functional-theory (DFT) level using the Becke-Perdew (BP) functional and triple-zeta quality basis sets augmented by one set of polarization functions (TZVP). The accuracy of the calculations was checked by DFT calculations using the Perdew-Burke-Ernzerhof hybrid functional (PBE0) and up to quadruple-zeta quality basis sets augmented by one set of polarization functions (QZVP). The calculated IR spectrum for Ti(14)C(13) (3 x 3 x 3) is found to be in fair agreement with the experimental IR spectrum obtained by infrared resonance-enhanced multiphoton ionization (IR-REMPI) measurements, whereas, for Ti(18)C(18) (4 x 3 x 3) and Ti(32)C(32) (4 x 4 x 4), the calculated IR spectra differ significantly from the experimental ones. The smallest TiC cluster (Ti(4)C(4), 2 x 2 x 2) considered has not been reported in any mass-spectrometer studies. The present DFT calculations show that the vibrational modes related to the in-plane vibrations of solid TiC are not observed in the IR-REMPI spectra of nanocrystals larger than Ti(14)C(13). Contrary to solid TiC, the studied TiC nanocrystals are nonmetallic with optical gaps of 0.62 eV (0.55 eV) and 0.028 eV (0.027 eV) for Ti(32)C(32) and Ti(108)C(108) (6 x 6 x 6), calculated at the time-dependent density-functional-theory (TDDFT) level using the BP functional. The HOMO-LUMO gaps obtained in the BP DFT calculations are given within parentheses. At the PBE0 DFT level, the HOMO-LUMO gaps for Ti(32)C(32) and Ti(108)C(108) are 1.74 and 0.32 eV, respectively.     

Photochemistry of peroxoborates: borate inhibition of the photodecomposition of hydrogen peroxide

The UV absorbance and photochemical decomposition kinetics of hydrogen peroxide in borate/boric acid buffers were investigated as a function of pH, total peroxide concentration, and total boron concentration. At higher pH borate/boric acid inhibits the photodecomposition of hydrogen peroxide (molar absorptivity and quantum yield of H(2)O(2) and HO(2) (-), (19.0+/-0.3) M(-1) cm(-1) and 1, and (237+/-7) M(-1) cm(-1) and 0.8+/-0.1, respectively). The results are consistent with the equilibrium formation of the anions monoperoxoborate, K(BOOH)=[H(+)][HOOB(OH)(3) (-)]/([B(OH)(3)][H(2)O(2)]), 2.0 x 10(-8), R. Pizer, C. Tihal, Inorg. Chem. 1987, 26, 3639-3642, and monoperoxodiborate, K(BOOB)=[BOOB(2-)]/([B(OH)(4) (-)][HOOB(OH)(3) (-)]), 1.0+/-0.3 or 4.3+/-0.9, depending upon the conditions, with molar absorptivity, (19+/-1) M(-1) cm(-1) and (86+/-15) M(-1) cm(-1), respectively, and respective quantum yields, 1.1+/-0.1 and 0.04+/-0.04. The low quantum yield of monoperoxodiborate is discussed in terms of the slower diffusion apart of incipient (.)OB(OH)(3) (-) radicals than may be possible for (.)OH radicals, or a possible oxygen-bridged cyclic structure of the monoperoxodiborate.     

钴(II)卟啉与咪唑类配体配位反应热力学、动力学

钴（Ⅱ）卟啉能可逆地结合氧而作为血红蛋白的模拟化合物．此外,维生素B12的某些辅酶反应是通过Co（Ⅱ）自由基中间物进行的,而Co（Ⅱ）卟啉的d7Co（Ⅱ）离子在dz2轨道的单个未配对电子使其具有自由基性质,所以人们对钴（Ⅱ）卟啉表示了极大的兴趣[1-5].Walker的早期工作[1]     

麒麟菜提取物中的8种无机元素分析

应用原子吸收光谱法分析了麒麟菜提取物中的8种无机元素含量。结果显示,麒麟菜提取物中含有丰富的人体必需无机元素,宏量元素以Na的含量最高,微量元素以Fe的含量最高,8种无机元素中的含量由大到小顺序是:Na,K,Mg,Ca,Fe,Zn,Cu,Mn。     

Synthesis and Characterization of Sterically Encumbered Derivatives of Aluminum Hydrides and Halides: Assessment of Steric Properties of Bulky Terphenyl Ligands

The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects.     

Self-aggregation of binary mixtures of alkyltriphenylphosphonium bromides: a critical assessment in favor of more than one kind of micelle formation

The micellization behavior of binary combinations of alkyltriphenylphosphonium bromides (ATPBs) with alkyl chain carbons 10, 12, 14, and 16 has been studied by conductometry and calorimetry. The combinations C(10)-C(12), C(10)-C(14), C(10)-C(16), C(12)-C(14), C(12)-C(16), and C(14)-C(16) were found to form two cmc's by both the methods, with good agreement, except C(14)-C(16)TPB, which has evidenced only a single cmc by calorimetry for all combinations. The combinations C(10)-C(12) (for both cmc(1) and cmc(2)) and C(10)-C(14)TPB (for cmc(2)) formed ideal mixtures, whereas the rest were nonideal. In the nonideal binary mixtures, the ATPB components showed antagonistic interaction with each other. The cmc, interaction parameter (beta), mixed micellar composition, extent of counterion binding, and thermodynamic parameters for the micellization process have been reported and discussed. The enthalpy of mixed micelle formation has been found to have a fair correlation with a Clint-type relation applicable to ideal binary mixtures of surfactants.     

六次甲基四胺与溴代丙烯加合物的晶体结构

我们对六次甲基四胺(HMT)加合物的研究早感兴趣。为探讨Sommelet反应机理,我们证实氯化苄与HMT加合物为季胺盐阳离子[(CH_2)_6N_4·CH_2C_6H_5]~ 与Cl~-交错堆积组成的离子晶体。晶体中与四配位N联结的C-N键长有明显的增长效应。本文为其平行的工作。实验HMT与溴代丙烯加合物晶体的制备0.8g HMT溶于30 mL 1∶1三氯甲烷-丙酮,滴入0.7mL溴丙烯,待有细小晶体析     

螯形主体分子的设计、包结性能及其在细辛挥发油 有效成分选择分离中的应用

设计了两种新的具有螯形骨架的主体分子反式-1,2-二苯基-1,2-苊二醇(1)和顺式-1,2-二(1'-萘基)-1,2-苊二醇(2),主体(1),(2)可与许多有机小分子化合物形成配位包合物。用IR和粉末XRD表征了主体分子(1)和(2)的包结物,用^1NMR测定了包结物的主客体分子摩尔比：(1)·DMF(1:2),(1)·DMSO(1:2),(1)·THF(1:2),(1)·二氧六环(1:1),(1)·吡啶(1:1),(2)·DMF(1:1)和(2)·DMSO(1:1)。单晶X射线衍射分析了包结物的晶体结构,(1)·DMF：空间群Pnaa,a=0.9377(1)nm,b=1.4351(1)nm,c=4.0463(3)nm;(1)·DMSO：空间群Pbcn,a=1.6278(1)nm,b=1.0751(1)nm,c=1.4980(1)nm;(2)·DMF：P2~1/n,a=0.9796(1)nm,b=1.2377(1)nm,c=2.2344(3)nm,β=93.02(1)°;游离主体(1)：空间群P1,a=1.0461(1)nm,b=1.1213(1)nm,c=1.5496(1)nm,α=81.74(1)°,β=75.71(1)°,γ=89.00(1)°;分析了主体分子的刚性和柔韧性对包结性能的影响。并研究了主体分子(1)选择分离细辛挥发油,将顺甲基异丁香酚从挥发油中分离出来。     

The nature of the chemical bond revisited: an energy-partitioning analysis of nonpolar bonds

The nature of the chemical bond in nonpolar molecules has been investigated by energy-partitioning analysis (EPA) of the ADF program using DFT calculations. The EPA divides the bonding interactions into three major components, that is, the repulsive Pauli term, quasiclassical electrostatic interactions, and orbital interactions. The electrostatic and orbital terms are used to define the nature of the chemical bond. It is shown that nonpolar bonds between main-group elements of the first and higher octal rows of the periodic system, which are prototypical covalent bonds, have large attractive contributions from classical electrostatic interactions, which may even be stronger than the attractive orbital interactions. Fragments of molecules with totally symmetrical electron-density distributions, like the nitrogen atoms in N(2), may strongly attract each other through classical electrostatic forces, which constitute 30.0 % of the total attractive interactions. The electrostatic attraction can be enhanced by anisotropic charge distribution of the valence electrons of the atoms that have local areas of (negative) charge concentration. It is shown that the use of atomic partial charges in the analysis of the nature of the interatomic interactions may be misleading because they do not reveal the topography of the electronic charge distribution. Besides dinitrogen, four groups of molecules have been studied. The attractive binding interactions in H(n)E-EH(n) (E=Li to F; n=0-3) have between 20.7 (E=F) and 58.4 % (E=Be) electrostatic character. The substitution of hydrogen by fluorine does not lead to significant changes in the nature of the binding interactions in F(n)E-EF(n) (E=Be to O). The electrostatic contributions to the attractive interactions in F(n)E-EF(n) are between 29.8 (E=O) and 55.3 % (E=Be). The fluorine substituents have a significant effect on the Pauli repulsion in the nitrogen and oxygen compounds. This explains why F(2)N-NF(2) has a much weaker bond than H(2)N-NH(2), whereas the interaction energy in FO-OF is much stronger than in HO-OH. The orbital interactions make larger contributions to the double bonds in HB=BH, H(2)C=CH(2), and HN=NH (between 59.9 % in B(2)H(2) and 65.4 % in N(2)H(2)) than to the corresponding single bonds in H(n)E-EH(n). The orbital term Delta E(orb) (72.4 %) makes an even greater contribution to the HC triple bond CH triple bond. The contribution of Delta E(orb) to the H(n)E=EH(n) bond increases and the relative contribution of the pi bonding decreases as E becomes more electronegative. The pi-bonding interactions in HC triple bond CH amount to 44.4 % of the total orbital interactions. The interaction energy in H(3)E-EH(3) (E=C to Pb) decreases monotonically as the element E becomes heavier. The electrostatic contributions to the E-E bond increases from E=C (41.4 %) to E=Sn (55.1 %) but then decreases when E=Pb (51.7 %). A true understanding of the strength and trends of the chemical bonds can only be achieved when the Pauli repulsion is considered. In an absolute sense the repulsive Delta E(Pauli) term is in most cases the largest term in the EPA.     

Kinetics of thermal dehydration of some bis-(4-aminosalicylato)-diaquo complexes of transition metal ions

The kinetics of thermal dehydration of bis-(4-aminosalicylato)-diaquo complexes of VO(II), Cu(II), Ni(II), Co(II), Fe(II) and Mn(II), were studied. The activation energies and other kinetic parameters have been evaluated. The observed kinetic parameters indicate a first-order reaction. The activation energy of the thermal dehydration decreases in the order: VO(II) > Cu(II) > Co(II) > Ni(II) > Fe(II) > Mn(II), which is also the order for the covalency in the MO bonds.     

Characterization of self-assembled monolayers of porphyrins bearing multiple thiol-derivatized rigid-rod tethers

A series of multithiol-functionalized zinc porphyrins has been prepared and characterized as self-assembled monolayers (SAMs) on Au. The molecules, designated ZnPS(n) (n = 1-4), contain from one to four [(S-acetylthio)methyl]phenylethynylphenyl groups appended to the meso-position of the porphyrin; the other meso-substituents are phenyl groups. For the dithiol-functionalized molecules, both the cis- and the trans-appended structures were examined. The ZnPS(n) SAMs were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and various electrochemical methods. The studies reveal the following characteristics of the ZnPS(n) SAMs. (1) The ZnPS(n) molecules bind to the Au surface via a single thiol regardless of the number of thiol appendages that are available per molecular unit. (2) The porphyrins in the ZnPS(3) and ZnPS(4) SAMs bind to the surface in a more upright orientation than the porphyrins in the ZnPS(1), cis-ZnPS(2), and trans-ZnPS(2) SAMs. The porphyrins in the ZnPS(3) and ZnPS(4) SAMs are also more densely packed than those in the cis-ZnPS(2) and trans-ZnPS(2) SAMs. The packing density of the ZnPS(3) and ZnPS(4) SAMs is similar to that of the ZnPS(1) SAMs, despite the larger size of the molecules in the former SAMs. (3) The thermodynamics and kinetics of electron transfer are generally similar for all of the ZnPS(n) SAMs. The general similarities in the electron-transfer characteristics for all of the SAMs are attributed to the similar binding motif.     

The possibility of the decomposition of 2'-deoxyribose moiety of thymidine induced by the low energy electron attachment

To evaluate the possibility of the decomposition of 2-deoxyribose moiety of thymidine induced by low energy electrons (LEE) attachment, the transition states and the energy barriers of the bond breaking processes of the ribose of the nucleoside have been studied theoretically by applying the density functional theory with the double zeta basis sets (DZP++). The energy barriers for the breakage of the C-C bonds (C(1')-C(2'), C(2')-C(3'), C(3')-C(4'), and C(4')-C(5')) of the ribose group of the radical anion of thymidine are found to be high (ca. 42-57 kcal/mol). The total energies of the C-C bond-broken products are significantly higher than that of the radical anion dT(*-). The decomposition of dT(*-) through the C-C bond rupture is unlikely to take place. The rupture of the C(1')-O(4') bond of dT(*-) needs an activation energy as low as 10.4 kcal/mol. However, the reversed reaction (C(1')-O(4') bond formation) needs the activation energy low as 0.3 kcal/mol. Therefore, the intermediate product LM1(C1')-(O4') is unlikely to be stable and the C(1')-O(4') bond-broken is not favored. The activation energy of the C(4')-O(4') bond rupture process amounts to 20.5 kcal/mol. The total energy of the C(4')-O(4') bond broken product is about 6.5 kcal/mol lower than that of the reactant dT(*-). The subsequent N1-glycosidic bond breaking process is found to have a very low energy barrier. Therefore, the LEE-induced base release through the C(4')-O(4') bond rupture might be a possible pathway.     

Kinetic study of the reaction of OH with CH2I2

Flash photolysis (FP) coupled to resonance fluorescence (RF) was used to measure the absolute rate coefficients (k(1)) for the reaction of OH(X(2)Π) radicals with diiodomethane (CH(2)I(2)) over the temperature range 295-374 K. The experiments involved time-resolved RF detection of the OH (A(2)Σ(+)→X(2)Π transition at λ = 308 nm) following FP of the H(2)O/CH(2)I(2)/He mixtures. The OH(X(2)Π) radicals were produced by FP of H(2)O in the vacuum-UV at wavelengths λ > 120 nm. Decays of OH radicals in the presence of CH(2)I(2) are observed to be exponential, and the decay rates are found to be linearly dependent on the CH(2)I(2) concentration. The results are described by the Arrhenius expression k(1)(T) = (4.2 ± 0.5) × 10(-11) exp[-(670 ± 20)K/T] cm(3) molecule(-1) s(-1). The implications of the reported kinetic results for understanding the atmospheric chemistry of CH(2)I(2) are discussed.     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlled-potential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k_obs) for the reaction of o-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.