分光光度法测定蒙药卷柏中总黄酮含量

采用分光光度法 ,测定了蒙药卷柏中总黄酮的含量 ,检测波长为 5 0 0 nm,校准曲线相关系数为 0 .9996 ,相对标准偏差为 1 .0 1 %,平均加样回收率为 1 0 1 .6 1 %。此法准确度较高 ,为卷柏中黄酮含量测定提供了一种切实可行的方法。     

Infrared spectra of ThH2, ThH4, and the hydride bridging ThH4(H2)x (x = 1-4) complexes in solid neon and hydrogen

Laser-ablated Th atoms react with molecular hydrogen to give thorium hydrides and their dihydrogen complexes during condensation in excess neon and hydrogen for characterization by matrix infrared spectroscopy. The ThH2, ThH4, and ThH4(H2)x (x = 1-4) product molecules have been identified through isotopic substitution (HD, D2) and comparison to frequencies calculated by density functional theory and the coupled-cluster, singles, doubles (CCSD) method and those observed previously in solid argon. Theoretical calculations show that the Th-H bond in ThH4 is the most polarized of group 4 and uranium metal tetrahydrides, and as a result, a strong attractive "dihydrogen" interaction was found between the oppositely charged hydride and H2 ligands ThH4(H2)x. This bridge-bonded dihydrogen complex structure is different from that recently computed for tungsten and uranium hydride super dihydrogen complexes but is similar to that recently called the "dihydrogen bond" (Crabtree, R. H. Science 1998, 282, 2000). Natural electron configurations show small charge flow from the Th center to the dihydrogen ligands.     

Methane activation by laser-ablated V, Nb, and Ta atoms: Formation of CH3-MH, CH2=MH2, CHMH3-, and (CH3)2MH2

Methane activation by group 5 transition-metal atoms in excess argon and the matrix infrared spectra of reaction products have been investigated. Vanadium forms only the monohydrido methyl complex (CH3-VH) in reaction with CH4 and upon irradiation. On the other hand, the heavier metals form methyl hydride and methylidene dihydride complexes (CH3-MH and CH2=MH2) along with the methylidyne trihydride anion complexes (CHMH3-). The neutral products, particularly the methylidene complex, increase markedly on irradiation whereas the anionic product depletes upon UV irradiation or addition of a trace of CCl4 or CBr4 to trap electrons. Other absorptions that emerge on irradiation and annealing increase markedly at higher precursor concentration and are attributed to a higher-order product ((CH3)2MH2)). Spectroscopic evidence suggests that the agostic Nb and Ta methylidene dihydride complexes have two identical metal-hydrogen bonds.     

Zinc and cadmium dihydroxide molecules: matrix infrared spectra and theoretical calculations

Laser-ablated zinc and cadmium atoms were mixed uniformly with H2 and O2 in excess argon or neon and with O2 in pure hydrogen or deuterium during deposition at 8 or 4 K. UV irradiation excites metal atoms to insert into O2 producing OMO molecules (M = Zn, Cd), which react further with H2 to give the metal hydroxides M(OH)2 and HMOH. The M(OH)2 molecules were identified through O-H and M-O stretching modes with appropriate HD, D2, (16,18)O2, and (18)O2 isotopic shifts. The HMOH molecules were characterized by O-H, M-H, and M-O stretching modes and an M-O-H bending mode, which were particularly strong in pure H2/D2. Analogous Zn and Cd atom reactions with H2O2 in excess argon produced the same M(OH)2 absorptions. Density functional theory and MP2 calculations reproduce the IR spectra of these molecules. The bonding of Group 12 metal dihydroxides and comparison to Group 2 dihydroxides are discussed. Although the Group 12 dihydroxide O-H stretching frequencies are lower, calculated charges show that the Group 2 dihydroxide molecules are more ionic.     

Thermal decomposition of pentacene oxyradicals

The energetics and kinetics of the thermal decomposition of pentacene oxyradicals were studied using a combination of ab initio electronic structure theory and energy-transfer master equation modeling. The rate coefficients of pentacene oxyradical decomposition were computed for the range of 1500-2500 K and 0.01-10 atm and found to be both temperature and pressure dependent. The computational results reveal that oxyradicals with oxygen attached to the inner rings are kinetically more stable than those with oxygen attached to the outer rings. The latter decompose to produce CO at rates comparable to those of phenoxy radical, while CO is unlikely to be produced from oxyradicals with oxygen bonded to the inner rings.     

Bonding of multiple noble-gas atoms to CUO in solid neon: CUO(Ng)n (Ng=Ar, Kr, Xe; n=1, 2, 3, 4) complexes and the singlet-triplet crossover point

Laser-ablated U atoms co-deposited with CO in excess neon produce the novel CUO molecule, which forms distinct Ng complexes (Ng=Ar, Kr, Xe) with the heavier noble gases. The CUO(Ng) complexes are identified through CO isotopic and Ng reagent substitution and comparison to results of DFT frequency calculations. The U[bond]C and U[bond]O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from neon matrix (1)Sigma(+) CUO values, which indicates a (1)A' ground state for the CUO(Ng) complexes. The CUO(Ng)(2) complexes in excess neon are likewise singlet molecules. However, the CUO(Ng)(3) and CUO(Ng)(4) complexes exhibit very different stretching frequencies and isotopic behaviors that are similar to those of CUO(Ar)(n) in a pure argon matrix, which has a (3)A" ground state based on DFT vibrational frequency calculations. This work suggests a coordination sphere model in which CUO in solid neon is initially solvated by four or more Ne atoms. Up to four heavier Ng atoms successively displace the Ne atoms leading ultimately to CUO(Ng)(4) complexes. The major changes in the CUO stretching frequencies from CUO(Ng)(2) to CUO(Ng)(3) provides evidence for the crossover from a singlet ground state to a triplet ground state.