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951.
Dey A Hocking RK Larsen P Borovik AS Hodgson KO Hedman B Solomon EI 《Journal of the American Chemical Society》2006,128(30):9825-9833
Iron L-edge, iron K-edge, and sulfur K-edge X-ray absorption spectroscopy was performed on a series of compounds [Fe(III)H(3)buea(X)](n-) (X = S(2-), O(2-), OH(-)). The experimentally determined electronic structures were used to correlate to density functional theory calculations. Calculations supported by the data were then used to compare the metal-ligand bonding and to evaluate the effects of H-bonding in Fe(III)(-)O vs Fe(III)(-)S complexes. It was found that the Fe(III)(-)O bond, while less covalent, is stronger than the Fe(III)(-)S bond. This dominantly reflects the larger ionic contribution to the Fe(III)(-)O bond. The H-bonding energy (for three H-bonds) was estimated to be -25 kcal/mol for the oxo as compared to -12 kcal/mol for the sulfide ligand. This difference is attributed to the larger charge density on the oxo ligand resulting from the lower covalency of the Fe-O bond. These results were extended to consider an Fe(IV)(-)O complex with the same ligand environment. It was found that hydrogen bonding to Fe(IV)(-)O is less energetically favorable than that to Fe(III)(-)O, which reflects the highly covalent nature of the Fe(IV)(-)O bond. 相似文献
952.
Pure component selectivity analysis (PCSA) was successfully utilized to enhance the robustness of a partial least squares (PLS) model by examining the selectivity of a given component to other components. The samples used in this study were composed of NH4OH, H2O2 and H2O, a popular etchant solution in the electronic industry. Corresponding near-infrared (NIR) spectra (9000-7500 cm−1) were used to build PLS models. The selective determination of H2O2 without influences from NH4OH and H2O was a key issue since its molecular structure is similar to that of H2O and NH4OH also has a hydroxyl functional group. The best spectral ranges for the determination of NH4OH and H2O2 were found with the use of moving window PLS (MW-PLS) and corresponding selectivity was examined by pure component selectivity analysis. The PLS calibration for NH4OH was free from interferences from the other components due to the presence of its unique NH absorption bands. Since the spectral variation from H2O2 was broadly overlapping and much less distinct than that from NH4OH, the selectivity and prediction performance for the H2O2 calibration were sensitively varied depending on the spectral ranges and number of factors used. PCSA, based on the comparison between regression vectors from PLS and the net analyte signal (NAS), was an effective method to prevent over-fitting of the H2O2 calibration. A robust H2O2 calibration model with minimal interferences from other components was developed. PCSA should be included as a standard method in PLS calibrations where prediction error only is the usual measure of performance. 相似文献
953.
We report the synthesis and characterization of luminescent rhenium(I) amidodipyridoquinoxaline biotin complexes [Re(CO)3(dpqa)(L)](PF6) (dpqa = 2-(n-butylamido)dipyrido[3,2-f:2',3'-h]quinoxaline; L = 4-(biotinamidomethyl)pyridine (py-4-CH2-NH-biotin) (1), 3-(N-((2-biotinamido)ethyl)amido)pyridine (py-3-CO-NH-en-NH-biotin) (2), 4-(N-((6-biotinamido)hexanoyl)aminomethyl)pyridine (py-4-CH2-NH-cap-NH-biotin) (3)), and their biotin-free counterpart [Re(CO)3(dpqa)(py)](PF6) (py = pyridine (4)). Upon irradiation, these complexes exhibited intense triplet metal-to-ligand charge-transfer (3MLCT) (dpi(Re) --> pi(dpqa)) emission in fluid solutions at 298 K and in alcohol glass at 77 K. However, the emission became much weaker in aqueous buffer, probably due to the interactions of water molecules with the amide substituent of the dpqa ligand. These properties render the complexes good candidates as luminescent probes for hydrophobic media, such as the substrate-binding sites of proteins. The avidin-binding properties of the new biotin complexes have been studied by 4'-hydroxyazobenzene-2-carboxylic acid (HABA) assays, emission titrations, and competitive association and dissociation assays. Most importantly, the complexes showed a profound increase in emission intensities upon binding to avidin. Additionally, we found that the fluorescence of anthracene was quenched by these rhenium(I) complexes, and the 3MLCT emission of the complexes was also quenched by anthracene. On the basis of these findings, new homogeneous assays for biotin using these complexes, avidin, and anthracene-labeled avidin have been designed. 相似文献
954.
Lee Y Lee DH Sarjeant AA Zakharov LN Rheingold AL Karlin KD 《Inorganic chemistry》2006,45(25):10098-10107
To model thioether-copper coordination chemistry including oxidative reactivity, such as occurs in the copper monooxygenases peptidylglycine -hydroxylating monooxygenase (PHM) and dopamine beta-hydroxylase (DbetaH), we have synthesized new tridentate N2S ligands LSEP and LSBz [LSEP = methyl(2-phenethylsulfanylpropyl)(2-pyridin-2-ylethyl)amine; LSBz = (2-benzylsulfanylpropyl)methyl(2-pyridin-2-ylethyl)amine)]. Both copper(I) and copper(II) complexes have been prepared, and their respective O2 and H2O2 chemistry has been studied. Under mild conditions, oxygenation of [(LSEP)CuI]+ (1a) and [(LSBz)CuI]+ (2a) leads to ligand sulfoxidation, thus exhibiting copper monooxygenase activity. A copper(II) complex of this sulfoxide ligand product, [(LSOEP)CuII(CH3OH)(OClO3)2], has been structurally characterized, demonstrating Cu-Osulfoxide ligation. The X-ray structure of [(LSEP)CuII(H2O)(OClO3)]+ (1b) and its solution UV-visible spectral properties [S-CuII LMCT band at 365 nm (MeCN solvent); epsilon = 4285 M-1 cm-1] indicate the thioether sulfur atom is bound to the cupric ion in both the solid (CuII-S distance: 2.31 A) and solution states. Reaction of 1b with H2O2 leads to sulfonation via the sulfoxide; excess hydrogen peroxide gives mostly sulfone product. These results may provide some insight into recent reports concerning protein methionine oxidation, showing the potential importance of copper-mediated oxidation processes in certain biological settings. 相似文献
955.
Laphookhieo S Syers JK Kiattansakul R Chantrapromma K 《Chemical & pharmaceutical bulletin》2006,54(5):745-747
A new prenylated xanthone, 5-O-methylcelebixanthone (1), together with six known compounds; celebixanthone (2), 1,3,7-trihydroxy-2,4-di(3-methylbut-2-enyl)xanthone (3), cochinchinone A (4), alpha-mangostin (5), beta-mangostin (6) and cochinchinone C (7) were isolated from roots of Cratoxylum cochinchinense. Their structures were elucidated by spectroscopic methods. Compounds 2 and 4-7 showed cytotoxic activity against the human lung cancer cell line (NCI-H187) with IC(50) values ranging from 0.65 to 5.2 microg/ml. Compounds 1, 2, 6 and 7 also showed antimalarial activity against Plasmodium falciparum with IC(50) values of 3.2, 4.9, 7.2 and 2.6 microg/ml, respectively. 相似文献
956.
The essential oil of aerial parts of Salviamicrostegia Boiss. et Balansa (Lamiaceae) growing wild in Lebanon was obtained by hydrodistillation and was analysed by GC and GC-MS. 70 compounds, representing 94.0% of the oil, were identified. The major components were caryophyllene oxide (6.2%), pulegone (5.7%), 4-vinylguaiacole (5.3%), hexadecanoic acid (5.1%) and menthone (4.9%). 相似文献
957.
Schofield K 《The journal of physical chemistry. A》2006,110(21):6938-6947
Although the "Golden" years of spectroscopy and the major studies on ionization processes now are behind us, as with many branches of science, much yet remains to be gleaned from such topics that is both full of interest and of significance to present day research. Presented here is one such overlooked example, an observation that relates to both these fields. An analysis is presented for the periodic table concerning the gas-phase thermochemical nature of MO+ and MO2+ ions. Unexpectedly, a pattern of 18 elements has been identified that exhibit the potential for having long-lived MO+ ions. Normally such molecular ions are expected to decay extremely rapidly by dissociative recombination with electrons, but in particular, 12 of this group behave not like molecules but rather as atomic ions. These are the diatomic oxide ions of Sc, Y, La, Zr, Hf, Ce, Pr, Nd, Pm, Gd, Tb, and Th. In the gas phase, they decay by much slower three-body recombination channels. As may be noted, these elements are located in the first two columns of the transition elements, among the earlier rare earths and an actinide. From all the elements, UO2+ is the only dioxide ion that behaves similarly. These findings now elevate the potential importance of these ions and should facilitate their spectral characterization. Moreover, subsequent comparisons with spectra of well-known isoelectronic and isovalent neutral monoxides and other diatomics will help in the stimulation of further theoretical advances. In addition, once characterized, an ease of spectrally monitoring such ionic states will provide a useful analytical tool. 相似文献
958.
Huang H Hughes RP Landis CR Rheingold AL 《Journal of the American Chemical Society》2006,128(23):7454-7455
Cp*Mo(CO)3CF3 undergoes two-electron reduction using potassium graphite or magnesium graphite to give Cp*Mo(CO)2(CF), the first example of a transition metal complex containing a terminal fluoromethylidyne ligand, which has been characterized spectroscopically, crystallographically, and computationally. 相似文献
959.
Mirica LM Rudd DJ Vance MA Solomon EI Hodgson KO Hedman B Stack TD 《Journal of the American Chemical Society》2006,128(8):2654-2665
The activation of dioxygen (O(2)) by Cu(I) complexes is an important process in biological systems and industrial applications. In tyrosinase, a binuclear copper enzyme, a mu-eta(2):eta(2)-peroxodicopper(II) species is accepted generally to be the active oxidant. Reported here is the characterization and reactivity of a mu-eta(2):eta(2)-peroxodicopper(II) complex synthesized by reacting the Cu(I) complex of the secondary diamine ligand N,N'-di-tert-butyl-ethylenediamine (DBED), [(DBED)Cu(MeCN)](X) (1.X, X = CF(3)SO(3)(-), CH(3)SO(3)(-), SbF(6)(-), BF(4)(-)), with O(2) at 193 K to give [[Cu(DBED)](2)(O(2))](X)(2) (2.X(2)). The UV-vis and resonance Raman spectroscopic features of 2 vary with the counteranion employed yet are invariant with change of solvent. These results implicate an intimate interaction of the counteranions with the Cu(2)O(2) core. Such interactions are supported further by extended X-ray absorption fine structure (EXAFS) analyses of solutions that reveal weak copper-counteranion interactions. The accessibility of the Cu(2)O(2) core to exogenous ligands such as these counteranions is manifest further in the reactivity of 2 with externally added substrates. Most notable is the hydroxylation reactivity with phenolates to give catechol and quinone products. Thus the strategy of using simple bidentate ligands at low temperatures provides not only spectroscopic models of tyrosinase but also functional models. 相似文献
960.
Simpson GL Gordon AH Lindsay DM Promsawan N Crump MP Mulholland K Hayter BR Gallagher T 《Journal of the American Chemical Society》2006,128(33):10638-10639
The synthesis of a triglycosylated helical foldamer based on a combination of cyclopentyl- and pyrrolidinyl-based amino acids is described. This structure is stable in water, maintaining as it does a series of carbohydrate units in proximity to one another, and represents the basis of a new approach to the study of carbohydrate-carbohydrate interactions. 相似文献