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51.
Ronald C. Crouch Ann O. Davis Timothy D. Spitzer Gary E. Martin Maged M. H. Sharaf Paul L. Schiff Charles H. Phoebe Albert N. Tackie 《Journal of heterocyclic chemistry》1995,32(3):1077-1080
Elucidation of minor natural product structures has been significantly augmented by inverse-detection; further improvement has been afforded by the development of micro inverse-detection probes. We report here the elucidation of the structure of a new alkaloid, quindolinone (5H, 10H-indolo[3,2-b]quinolin-11-one), from the West African plant Cryptolepis sanguinolenta. All nmr data for this minor, preparative hplc-isolated alkaloid, including 1H-15N one? bond heteronuclear shift correlation (HMQC) data, were recorded on an 800 μg sample of the alkaloid dissolved in 140 μl of 100% d6-DMSO using a 400 MHz spectrometer. 相似文献
52.
Yossef A. Elabd Marco Giacinti Baschetti Timothy A. Barbari 《Journal of Polymer Science.Polymer Physics》2003,41(22):2794-2807
Over the past 2 decades, the use of time‐resolved Fourier transform infrared/attenuated total reflection (ATR) spectroscopy for the measurement of diffusion in polymers has grown. ATR is a powerful technique for the measurement of diffusion in polymers because it is an in situ technique that is relatively inexpensive, provides reliable short‐time data, and provides a wealth of information at the molecular level. This article highlights the technique and its application to numerous studies, ranging from the diffusion of drugs in human skin to chemical warfare agents in barrier materials. In addition to these topics, recent studies with ATR to quantify and model molecular interactions during the diffusion process are reviewed. In the future, the ATR technique may have an impact on a variety of emerging fields in which diffusion in polymers plays an important role, such as fuel cells, membrane separation, sensors, and drug delivery. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2794–2807, 2003 相似文献
53.
Timothy B. Hutson Ming J. W. Chang Joseph T. Keller David J. Long 《Mikrochimica acta》1988,94(1-6):339-341
Fourier transform infrared techniques were used to monitor mammalian cell growth plated on attenuated total reflection (ATR) crystals. Consistently, the growth kinetics plots generated from the obtained spectra demonstrated a sigmoidal curve representing a sequence of slow, rapid, then tapering cell growth which correlated well with non-spectral cell growth determinations. Significant advantages over traditional methods of measuring cell growth kinetics are demonstrated. The technique has promising potential to be used to study events in areas such as toxicology and cell biology. 相似文献
54.
Proshlyakov DA Henshaw TF Monterosso GR Ryle MJ Hausinger RP 《Journal of the American Chemical Society》2004,126(4):1022-1023
The reaction of substrate-bound taurine/alpha-ketoglutarate dioxygenase with O2 has been studied using cryogenic continuous-flow spectroscopy. Transient absorption spectra acquired at -38 degrees C show an exponential decay of a 318-nm chromophore with an apparent rate of 1.3 s-1. The observed optical changes and their kinetics are consistent with the profile of an Fe(IV) species detected recently by M?ssbauer spectroscopy (Price et al., Biochemistry 2003, 42, 7497-7508). Resonance Raman measurement upon excitation at 363.7 nm reveal at least two oxygen isotope-sensitive vibrations at 821/787 cm-1 and 583/555 cm-1 for 16O and 18O derivatives, respectively. An additional mode is likely to be obscured by an ethylene glycol vibration at 865 cm-1 and/or 1089 cm-1. The 821 cm-1 vibration is assigned to the stretching mode of Fe(IV)=O species on the basis of its frequency and isotopic shift amplitude. The 583 cm-1 band is likely to originate from an Fe-O2 precursor of the Fe(IV)=O species, although its structural details are unclear at present. 相似文献
55.
The ultraviolet absorption spectrum of the neopentyl peroxy radical (CH3)3CCH2O2, and the kinetics and products of its self reaction have been studied in the gas phase at 298 K. Absorption cross sections were quantified over the wavelength range 230–290 nm. The measured cross section at 250 nm was; Errors represent statistical (2σ) together with our estimate of potential systematic errors(15%). The kinetics of the decay of the UV absorption following the generation of the neopentyl peroxy radicals was complicated by the rapid decomposition of the (CH3)3CCH2O radicals formed in channel (4a). By measuring the yield of t-butyl peroxy radicals, the branching ratio k4a/(k4a + k4b) was determined to be 0.39 ± 0.03. The rate constant for the self reaction of neopentyl peroxy radicals was k4 = (1.07 ± 0.22) × 10?12 cm3 molecule?1 s?1. Quoted errors represent 2σ. These results are discussed with respect to the available literature data. © John Wiley & Sons, Inc. 相似文献
56.
57.
Kimball DB Haley MM Mitchell RH Ward TR Bandyopadhyay S Williams RV Armantrout JR 《The Journal of organic chemistry》2002,67(25):8798-8811
The synthesis and study of dehydrobenzoannulene (DBA)-dimethyldihydropyrene (DDP) hybrids as models for the investigation of aromaticity in weakly diatropic systems is reported. Three new monofused DBA-DDP hybrids have been synthesized, and their NMR spectra are discussed with regard to quantifying the aromaticity remaining in multibenzene-fused DBAs. Nucleus-independent chemical shifts, determined at a series of locations for each compound, bond lengths, and (1)H and (13)C NMR chemical shifts were calculated and used to probe the aromaticity of these hybrids. Systems where more than one annulene/DBA is fused to the DDP core have also been obtained, and their potential use in photoinduced isomerization applications is discussed. 相似文献
58.
Swelling and network parameters of crosslinked thermoreversible hydrogels of poly(N-ethylacrylamide)
Samples of Poly(N-ethylacrylamide) (PEA) have been synthesized by free radical polymerization in water using N,N′-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels obtained by swelling them in water, 15 wt% KCl and 1 wt% sodium dodecyl sulphate (SDS) were examined by gravimetric, dimensional and compression-strain measurements to afford values of swelling ratio, polymer-solvent interaction parameters, elastic moduli and effective crosslinking density νe. Crosslinking inefficiency is evidenced by the low value (0.23) of νe relative to the theoretical crosslinking density νt based on the content of BIS in the synthesis. A small but finite extrapolated value of νe at νt = 0 is indicative of hydrophobic physical interactions. In water at 298 K increasing the content of BIS leads to a decrease in swelling and increases in values of elastic moduli and polymer-water interaction parameter. At a fixed content of BIS the values of νe and the elastic moduli exhibit an unusual increase with temperature, the crosslinking thus being thermally reversible. It is proposed that this results from a balance between hydrophobic interaction and breakage of hydrophilic hydrogen bonding. Although KCl in the medium decreases the swelling compared with that in water, the opposite effect occurs on incorporation of SDS, which is assumed to confer some polyelectrolyte character to the PEA chains. The finding, that these two swelling media reduce the values of νe and elastic moduli cf the value in water, has not been resolved satisfactorily. 相似文献
59.
The effect of ultrasonic irradiation (45KHz at 25°C) on the solvolysis of -butyl chloride in aqueous ethanol, -propanol and -butanol is (1) to increase the rate constants in the more alcoholic media and (2) to reduce the m values of these reactions. 相似文献
60.
Small clusters of toluene(n) (n = 1-8) were created in a supersonic expansion of toluene with argon as a carrier gas. Mass-selected resonance enhanced multiphoton ionization spectra of these clusters were recorded for each n. For the dimer, the appearance of the spectrum under warm and very cold conditions was studied. We discuss previous results in the light of the present spectra. For n>2, the spectra resemble very closely that of the dimer. 相似文献