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141.
Coombs ND Stasch A Cowley A Thompson AL Aldridge S 《Dalton transactions (Cambridge, England : 2003)》2008,(3):332-337
Sterically encumbered amido ligands based on a 1,8-diarylcarbazol-9-yl backbone have been investigated as electronically distinct alternatives to the widely-used terphenyl ligand class in the stabilization of low-coordinate metal complexes, and structurally characterized for the first time. While 1,8-diphenylcarbazol-9-yl derivatives are readily available, facile rotation about the Cipso-Cipso bonds leads to structurally characterized main group derivatives {e.g., [(1,8-Ph,-3,6-Me2C12H4N)K]2} in which the coordination geometry at the metal centre is augmented by secondary metal arene interactions. By contrast, the extra bulk inherent in the corresponding 1,8-dimesityl ligand results in essentially perpendicular alignments of the arene and carbazole planes, and a substituent-enforced sterically protected pocket. Comparative structural studies of complexes containing the GaCl2 fragment imply that the 1,8-dimesitylcarbazol-9-yl framework offers greater steric protection at the metal centre than does the corresponding 2,6-dimesitylphenyl ligand. 相似文献
142.
Herath W Mikell JR Hale AL Ferreira D Khan IA 《Chemical & pharmaceutical bulletin》2008,56(4):418-422
5,7-Dihydroxyflavone (chrysin) (1) when fermented with fungal cultures, Aspergillus alliaceous (ATCC 10060), Beauveria bassiana (ATCC 13144) and Absidia glauco (ATCC 22752) gave mainly 4'-hydroxychrysin (4), chrysin 7-O-beta-D-4-O-methylglucopyranoside (5) and chrysin 7-sulfate (6), respectively. Mucore ramannianus (ATCC 9628), however, transformed chrysin into six metabolites: 4'-hydroxy-3'-methoxychrysin (chrysoeriol) (7), 4'-hydroxychrysin (apigenin) (4) 3',4'-dihydroxychrysin (luteolin) (8), 3'-methoxychrysin 4'-O-alpha-D-6-deoxyallopyranoside (9), chrysin 4'-O-alpha-D-6-deoxyallopyranoside (10), and luteolin 3'-sulfate (11). Cultures of A. alliaceous (ATCC 10060) and B. bassiana (ATCC 13144) metabolized 5-hydroxyflavone (2) into 5,4'-dihydroxyflavone (12) and 4'-hydroxyflavone 5-O-beta-D-4-O-methylglucopyranoside (13), respectively. 6-Hydroxyflavone (3) was transformed into 6-hydroxyflavanone (14), flavone 3-O-beta-D-4-O-methylglucopyranoside (15) and (+/-)-flavanone 6-O-beta-D-4-O-methylglucopyranoside (16) by cultures of Beauveria bassiana (ATCC 13144). The structures of the metabolic products were elucidated by means of spectroscopic data. The significance of the metabolites as antioxidants in relation to their structure is briefly discussed. 相似文献
143.
A simple non-aqueous reversed-phase separation HPLC-MS method has been developed to allow for the rapid screening and separation of fullerenes and substituted fullerenes. This procedure provides confirmation that the proposed substitution methodology for the fullerene is not only successful but that multiple substitution products are obtained. The methodology is being expanded to analyze other substituted fullerene product mixtures. 相似文献
144.
Warner DL Hibberd AM Kalman M Klapars A Vedejs E 《The Journal of organic chemistry》2007,72(22):8519-8522
Hindered N-silylamines were examined for their utility to serve as protecting groups for the labile aziridine nitrogen found within the highly sensitive aziridinomitosene framework. tert-Butyldiphenylsilyl and modified tert-butyldiphenylsilyl groups were the most resistant to nitrogen-silicon bond cleavage under various reaction conditions and were thus employed in transformations relevant to aziridinomitosene synthesis. The N-silylaziridines 7a, 21a, and 21b underwent azomethine ylide cycloaddition and afforded, upon deprotection, the N-H aziridine 24 in 18-32% overall yield for the three steps. 相似文献
145.
Song L Wellman AD Yao H Adcock J 《Rapid communications in mass spectrometry : RCM》2007,21(8):1343-1351
An electron capture (EC) ionization mechanism has been found to be highly efficient in negative-ion atmospheric pressure photoionization (APPI) for the analysis of compounds with positive electron affinity (EA). Using negative-ion APPI, we first report the sensitive detection of natural electrophores with limited polarity, such as fullerenes and perfluorinated compounds, by mass spectrometry (MS). Using direct infusion on a quadrupole time-of-flight (QTOF) mass spectrometer, the limits of detection (LODs) for C(60) and perfluoromethylcyclohexane were determined to be 0.15 pg (0.2 fmol) and 1 femtoliter (fL) ( approximately 1.5 pg or 4.3 fmol), respectively. As the EA of the analyte increases, the detection sensitivity is enhanced. Making use of the accurate mass measurement capability of the QTOF mass spectrometer, we were able to investigate the elemental composition of the ions in each spectrum and attribute the observed high sensitivity to an EC-initiated ionization process. The proposed EC ionization mechanism is further supported by the observation of a dissociative EC reaction of pentafluorobenzyl (PFB)-derivatized phenols. The analysis of phenols by EC-APPI of their PFB derivatives resulted in very high sensitivity, with the lowest reported LOD of approximately 0.17 pg (0.5 fmol) being for 2,4-dinitrophenol. For future LC/EC-APPI-MS applications, the effect of additives and solvents on sensitivity was also tested and reported. 相似文献
146.
Negative ion-atmospheric pressure photoionization: Electron capture,dissociative electron capture,proton transfer,and anion attachment 总被引:1,自引:1,他引:0
Song L Wellman AD Yao H Bartmess JE 《Journal of the American Society for Mass Spectrometry》2007,18(10):1789-1798
To better guide the development of liquid chromatography/electron capture-atmospheric pressure photoionization-mass spectrometry (LC/EC-APPI-MS) in analysis of low polarity compounds, the ionization mechanism of 19 compounds was studied using dopant assisted negative ion-APPI. Four ionization mechanisms, i.e., EC, dissociative EC, proton transfer, and anion attachment, were identified as being responsible for the ionization of the studied compounds. The mechanisms were found to sometimes compete with each other, resulting in multiple ionization products from the same molecule. However, dissociative EC and proton transfer could also combine to generate the same [M - H](-) ions. Experimental evidence suggests that O(2)(-*), which was directly observed in the APPI source, plays a key role in the formation of [M - H](-) ions by way of proton transfer. Introduction of anions more basic than O(2)(-*), i.e., C(6)H(5)CH(2)(-), into the APPI source, via addition of di-tert-butyl peroxide in the solvent and/or dopant, i.e., toluene, enhanced the deprotonation ability of negative ion-APPI. Although the use of halogenated solvents could hinder efficient EC, dissociative EC, and proton transfer of negative ion-APPI due to their EC ability, the subsequently generated halide anions promoted halide attachment to compounds that otherwise could not be efficiently ionized. With the four available ionization mechanisms, it becomes obvious that negative ion-APPI is capable of ionizing a wider range of compounds than negative ion chemical ionization (NICI), negative ion-atmospheric pressure chemical ionization (negative ion-APCI) or negative ion-electrospray ionization (negative ion-ESI). 相似文献
147.
Amber Khuram Pervez Akram Waseem Bashir Muhammad Anser Khan Muhammad Sajid Kousar Anila 《Journal of Thermal Analysis and Calorimetry》2021,143(3):2355-2366
Journal of Thermal Analysis and Calorimetry - At higher ambient temperatures during summer months, the cell temperature of a photovoltaic (PV) module increases to 50–60 °C and sometimes... 相似文献
148.
Amber L. Thompson Sarah F. Jenkinson George W.J. Fleet 《Tetrahedron: Asymmetry》2017,28(10):1330-1336
Students of single crystal X-ray diffraction are often give advice as to how best to collect their data when attempting absolute configuration determination. These ‘rules’ often have more grounding in gut-feeling than evidence. Thus, in an effort to provide advice and evidence that today’s crystallographers can pass onto to tomorrow’s young scientists, we present a systematic study of 1-deoxy-l-arabinitol, a straight chain sugar which crystalises well in the space group . 相似文献
149.
Carbonylation of heterocycles by homogeneous catalysts 总被引:1,自引:0,他引:1
Church TL Getzler YD Byrne CM Coates GW 《Chemical communications (Cambridge, England)》2007,(7):657-674
This article summarizes the recent developments (particularly the uses of homogeneous organometallic catalysts) in ring-opening carbonylations, ring-opening carbonylative polymerizations and ring-expansion carbonylations of heterocycles such as epoxides, aziridines, lactones and oxazolines. 相似文献
150.
Verdree VT Pakhomov S Su G Allen MW Countryman AC Hammer RP Soper SA 《Journal of fluorescence》2007,17(5):547-563
Strategies are reported that produce symmetrical metal-free and metallo-phthalocyanine dyes, Pc and MPc, respectively, containing
various numbers of water solubilizing carboxylic acid groups on their periphery that provide a dual role by also serving as
functional groups to covalently link primary amine-containing targets to these dyes. In order to induce water compatibility
and to minimize the degree of aggregation, the periphery of the macrocycle was decorated with various numbers of water-solubilizing
groups and/or altering the identity of the metal center. The influence of the number of solubilizing groups and metal center
on the spectral and photophysical properties were evaluated. MPc dyes containing 4, 8, or 16 carboxylic acid groups exhibited
similar absorption and emission maxima (677 and 686 nm, respectively) with the molar absorptivity of the Q-band ∼105 M−1 cm−1. Results indicated that the fluorescence lifetimes and quantum yields varied as a function of the metal center; the degree
of carboxylation did not significantly alter these properties in DMSO, but did mediate the solubility and aggregation states
when placed in aqueous solvents. The water solubilizing groups could also serve as labeling moieties for targets bearing primary
amines. Results showed that the conjugate, produced by covalently linking an MPc to streptavidin through one of its carboxylate
groups, generated a red-shift in the emission maximum with a fluorescence lifetime shorter than that of the native MPc dye. 相似文献