Cholesteryl acetate and cholesteryl chloroformate compounds have been irradiated with 60Co-γ rays at room temperatures. The irradiated samples have been examined for paramagnetic resonance, and the observed spectra in several cases have been identified with specific radicals. The results in each case have been considered in relation to the present knowledge of the radiation chemistry of the compound. The single crystals have been investigated between 120 and 300?K. The spectra are found to be temperature independent and radiation damage centers are attributed to ?HCH2 radical for cholesteryl acetate and ?H3 and ?HCH2 CH2 CH2 radicals for cholesteryl chloroformate. 相似文献
Abstract The Infrared and Raman spectra of 4-Phenylpyridine are reported for the first time in the 4000-400cm?1 range. Vibrational assignments have been made for fundamental modes on the basis of frequency shifts of coordinated legend, infrared and Raman band contours and comparisons with the assignments for related molecules. The infrared spectra of M (4-Phenylpyridine) Ni(CN)4 complexes (M=Mn, Ni or Cd) are reported. Their structure consists of polymeric layers of [M-Ni(CN)4]∞ with the 4-phenylpyridine molecules bound to metal (M), similar to the structure found in Hoffmann type host complexes. 相似文献
We report strong near-field electromagnetic localization by using subwavelength apertures and metamaterials that operate at microwave frequencies. We designed split ring resonators with distinct configurations in order to obtain extraordinary transmission results. Furthermore, we analyzed the field localization and focusing characteristics of the transmitted evanescent waves. The employed metamaterial configurations yielded an improvement on the transmission efficiency on the order of 27 dB and 50 dB for the deep subwavelength apertures. The metamaterial loaded apertures are considered as a total system that offered spot size conversion ratios as high as 7.12 and 9.11 for the corresponding metamaterial configurations. The proposed system is shown to intensify the electric fields of the source located in the near-field. It also narrows down the electromagnetic waves such that a full width at half maximum value of λ/29 is obtained. 相似文献
Spatial and temporal control over chemical and biological processes, both in terms of “tuning” products and providing site‐specific control, is one of the most exciting and rapidly developing areas of modern science. For synthetic chemists, the challenge is to discover and develop selective and efficient reactions capable of generating useful molecules in a variety of matrices. In recent studies, light has been recognized as a valuable method for determining where, when, and to what extent a process is started or stopped. Accordingly, this Minireview will present the fundamental aspects of light‐induced click reactions, highlight the applications of these reactions to diverse fields of study, and discuss the potential for this methodology to be applied to the study of biomolecular systems. 相似文献
We propose a new model of permanent monogamous pair formation in zoological populations with multiple types of females and males. According to this model, animals randomly encounter members of the opposite sex at their so-called firing times to form temporary pairs which then become permanent if mating happens. Given the distributions of the firing times and the mating preferences upon encounter, we analyze the contingency table of permanent pair types in three cases: (i) definite mating upon encounter; (ii) Poisson firing times; and (iii) Bernoulli firing times. In the first case, the contingency table has a multiple hypergeometric distribution which implies panmixia. The other two cases generalize the encounter-mating models of Gimelfarb (Am. Nat. 131(6):865–884, 1988) who gives conditions that he conjectures to be sufficient for panmixia. We formulate adaptations of his conditions and prove that they not only characterize panmixia but also allow us to reduce the model to the first case by changing its underlying parameters. Finally, when there are only two types of females and males, we provide a full characterization of panmixia, homogamy and heterogamy. 相似文献
Ionics - Poly(vinylidene fluoride) (PVDF)/sodium hydrogen carbonate (NaHCO3)-based microporous polymer membranes were prepared by salt leaching. In this study, lithium-trifluoromethane sulfonate... 相似文献
A representative series of diphosphine monophosphonium salts [1‐Ph2P(C10H6)‐8‐PRPh2]+X– ( 2 b : R = H, X = CF3SO3; 4 : R = Me, X = CF3SO3; 5 : R = C6H5CH2 = Bn, X = Br) has been prepared by treatment of 1,8‐bis(diphenylphosphino)naphthalene (dppn, 1 ) with stoichiometric amounts of HSO3CF3 or CH3SO3CF3 in CH2Cl2 at +20 °C and with C6H5CH2Br in toluene at +80 °C. Their X‐ray crystal structures show that there is no evidence for dative P → P+ interactions. Instead, steric repulsion deflects the substituent groups to opposite faces of the naphthalene plane [splay angles: +11.4° ( 2 b ), +13.6° ( 4 ); +16.7° ( 5 )]. In solution 2 b , 4 , and 5 were dynamic according to 31P, 13C, and 1H NMR spectroscopy. The fluxionality of 2 b involves rapid intramolecular proton exchange between the two phosphorus atoms, which slows down at low temperature, whereas the dynamic behaviour of 4 and 5 is interpreted in terms of hindered rotation of the bulky RPh2P+ groups (R = Me or Bn) about the P–C(naphthyl) bond. Treatment of 1,8‐bis(diphenylphosphoryl)naphthalene (dppnO2, 6 ) with HSO3CF3 gave the protonated bis(phosphine oxide), as the triflate salt, dppnO2H+ CF3SO3– ( 7 ). The X‐ray structure analysis of 7 revealed a highly strained molecule (P1…P2 365.5 pm) in which the P=O bonds point to the same face of the naphthalene plane to accommodate the proton. All isolated compounds were characterised by a combination of 31P, 1H, and 13C NMR spectroscopy, IR spectroscopy ( 7 ), mass spectrometry and elemental analysis. 相似文献
Inclusion complexes of the poorly-soluble antiestrogen drug tamoxifen citrate (TMX) were prepared with β-cyclodextrin (β-CD)
and 2,3-di-O-hexanoyl-β-cyclodextrin (β-CDC6) being natural and amphiphilic cyclodextrins, respectively using the co-lyophilization technique.
Complexation occurred in aqueous medium for natural cyclodextrin β-CD and a medium of water:ethanol mixture for the amphiphilic
cyclodextrin β-CDC6. The complexes were characterized using analytical techniques including Differential Scanning Calorimetry
(DSC), Fourier Transform Infrared spectroscopy (FTIR) and proton Nuclear Magnetic Resonance Spectrometry (1H NMR). Anticancer efficacies of the complexes were determined against MCF-7 human breast carcinoma cell line with MTT assay.
It was found that tamoxifen citrate can be incorporated in the cavity for β-CD and both in the cavity and the aliphatic chains
for β-CDC6. The latter having two hydrophobic sites for inclusion of water-insoluble drug exhibited significantly higher anticancer
efficacy accordingly. 相似文献
A sensitive high performance liquid chromatographic method has been developed and validated for the determination of proparacaine in human aqueous humour. The procedure involved extraction of proparacaine from aqueous humour with cyclohexane. The separation was achieved using a Bondesil C8 (250 × 4.6 mm i.d., particle size 5 μm) analytical column with a mobile phase consisted of acetonitrile and sodium dihydrogen phosphate (pH 3.0, 20 mM) (30:70, v/v). Proparacaine and lidocaine (internal standard, IS) detection was performed by UV–Vis detector at 220 nm. The retention times for proparacaine and IS were 12.01 and 5.58 min, respectively. HPLC–UV–Vis method was linear in the range of 75–4,000 ng mL−1. The limit of detection (LOD) was 25 ng mL−1 and the limit of quantification (LOQ) of proparacaine was found to be 75 ng mL−1 (RSD ≤ 15%, n = 6). In intra- and inter-day precision and accuracy analysis, the relative standard deviation was found to be in the range of 0.96 and 7.98%, the bias values were 0.64 and 3.33%. Recovery of proparacaine from human aqueous humour was 99.98% at 500 ng mL−1. Proparacaine solutions were stable at least 6 months at +4 and −20 °C. Proparacaine levels of aqueous humour in fifteen volunteers’ were in the range of 80.21 and 459.00 ng mL−1. According to system suitability tests and Shewhart’s quality control charts the proparacaine responses were in the acceptance ranges. Developed method was providing a sufficient quality at least over 3 months for determination of proparacaine in human aqueous humour.