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991.
Arslan M Duymus H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(3-4):573-577
Charge transfer complexes between colchicine as donor and pi acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL) have been studied spectrophotometrically in dichloromethane at 21 degrees C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515 nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi-Hildebrand and van't Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used. 相似文献
992.
Sekerci M Atalay Y Yakuphanoglu F Avci D Başoğlu A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(2):503-508
The molecular geometry and vibrational frequencies of 1-(thiophen-2-yl-methyl)-2-(thiophen-2-yl)-1H-benzimidazole (C(16)H(12)N(2)S(2)) in the ground state has been calculated using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT (B3LYP) show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of 1-(thiophen-2-yl-methyl)-2-(thiophen-2-yl)-1H-benzimidazole (C(16)H(12)N(2)S(2)) and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. 相似文献
993.
There is increased interest in accurately assessing the total dietary intake of vitamins from all sources, including foods
and dietary supplements. Consequently, a Dietary Supplement Ingredient Database (DSID), based upon analytical values, is being
established by USDA with support of the Office of Dietary Supplements (ODS), NIH. The DSID necessitated the development of
a new SRM, 3280 — Multivitamin/Multimineral Tablets, by the National Institute of Standards and Technology (NIST), with support
from the ODS. As a continuation of a long-term project to develop and validate new methods of determining water-soluble B
vitamins in foods and dietary supplements, and as part of a collaborative effort with NIST to characterize SRM 3280, values
for the vitamin contents of SRM 3280 have been generated by a liquid chromatographic isotope dilution mass spectrometric (LC/IDMS)
method. Isotope-labeled (13C and/or 2H) B vitamins (B1-thiamine, B6-pyridoxine, B3-nicotinamide, and B5-pantothenic acid) were obtained from commercial sources,
with the support of the ODS/NIH. Our LC/IDMS method uses a C18 reversed phase column, an Agilent 1100 HPLC system, and a Quattro
Micro triple-quad mass spectrometer (MS). B vitamin determination was achieved using a gradient LC profile combined with MS/MS
detection in multiple reaction monitoring mode. Stock solutions of the isotope-labeled vitamins were calibrated against USP
standard solutions. The SRM tablets, with added amounts of the four isotope-labeled B vitamins, were extracted and the vitamins
simultaneously determined in a single LC run, in contrast with the single-component determinations performed via IDMS. Unknown
vitamin concentrations were calculated by comparing the ratios of the integrated LC peaks at the different masses of the unlabeled
and labeled vitamins. 相似文献
994.
Suo Z Yang X Avci R Kellerman L Pascual DW Fries M Steele A 《Langmuir : the ACS journal of surfaces and colloids》2007,23(3):1365-1374
Most bacteria, planktonic and sessile, are encapsulated inside loosely bound extracellular polymeric substance (EPS) in their physiological environment. Imaging a bacterium with its capsule requires lengthy sample preparation to enhance the capsular contrast. In this study, Salmonella typhimurium was investigated using atomic force microscopy for a practical means of imaging an encapsulated bacterium in air. The investigation further aimed to determine the relation between the buffers used for preparing the bacterium and the preservation of the capsular material surrounding it. It was observed that rinsing bacteria with HEPES buffer could stabilize and promote capsule formation, while rinsing with PBS, Tris, or glycine removes most of the capsular EPS. For bacteria rinsed with HEPES and air-dried, the height images showed only the contour of the capsular material, while the phase and amplitude images presented the detailed structures of the bacterial surface, including the flagella encapsulated inside the capsular EPS. The encapsulation was attributed to the cross-linking of the acidic exopolysaccharides mediated by the piperazine moiety of HEPES through electrostatic attraction. This explanation is supported by encapsulated bacteria observed for samples rinsed with N,N'-bis(2-hydroxyethyl)-piperazine solution and by the presence of entrapped HEPES within the dry capsular EPS suggested by micro-Raman spectroscopy. 相似文献
995.
The conventional method of measurement in 14 MeV activation analysis is to employ gamma-ray spectrometry. The method has the
advantage of good selectivity but this is at the expense of sensitivity. In order to improve sensitivity the authors have
employed Cerenkov counting techniques and by the careful use of absorbers in a specially designed cell together with double
decay procedures have still retained a considerable degree of selectivity. The method has been applied to neutron flux measurement
and to the majority of the elements in the periodic table. 相似文献
996.
Elif Gungor Mustafa Burak Coban Hulya Kara Yasemin Acar 《Journal of Cluster Science》2018,29(6):967-974
A new cubane-based cobalt(II) cluster, [Co4L4] (1), where H2L?=?2-((E)-(2-hydroxyethylimino) methyl)-4-chlorophenol has been prepared using a solvothermal process and characterized by structural, optical and magnetism. The crystal structure of 1 consists of a tetranuclear Co4O4 core in an open-cubane framework. Each cobalt(II) ion is penta-coordinated in a distorted square pyramidal geometry (τCo1=Co1i?=?0.030, τCo2=Co2i?=?0.023). Furthermore, the photoluminescence analysis indicates that 1 has a strong blue emission which should be attributed to coordination of the metal to the ligand. The temperature dependence of the magnetic susceptibilities of 1 shows antiferromagnetic coupling (J?=???26.61?±?0.01) between cobalt(II) ions. 相似文献
997.
Sadin Özdemir M. Kadir Oduncu Ersin Kılınç Mustafa Soylak 《Journal of Radioanalytical and Nuclear Chemistry》2018,315(2):185-193
Bacillus vallismortis and Bacillus mojavensis were loaded onto Amberlite XAD-4 resin and used for solid phase extraction (SPE) of uranium(VI). A quick and simple UV–Vis spectrophotometric method was used to determine U(VI) ion. The best experimental conditions were determined as being a pH of 5.0; a sample flow rate of 2.0 mL min?1; 200.0 mg of biosorbent; 800 mg of Amberlite XAD-4, and 5.0 mL of 1 mol L?1 HCl as desorption solution for both immobilized bacteria. The preconcentration factors were achieved as 80 for both solid phase extractor. The developed methods were validated by applying to reference water and tea samples. 相似文献
998.
H. Dilara Kiliç Seda Deveci Koray B. Dönmez Ebru Çetinkaya Sevinç Karadağ Mustafa Doğu 《International journal of environmental analytical chemistry》2018,98(4):308-322
Determination of copper (Cu), zinc (Zn) and manganese (Mn) micronutrients in soil samples have been studied for an efficient fertiliser application. Plant-available micronutrients of soils were extracted with DTPA extraction procedure, then differential pulse stripping voltammetry (DPSV) and square wave stripping voltammetry (SWSV) methods were performed with inexpensive and disposable pencil graphite electrode for determination of Cu(II), Zn(II) and Mn(II). Parameters such as deposition potential, deposition time, pH and concentration of the supporting electrolyte were optimised for these ions. Under optimised conditions, the limits of detection were found as 0.01 mg L?1 for Cu(II) and 0.02 mg L?1 for Zn(II) and 0.25 mg L?1 for Mn(II). Relative standard deviation (%RSD) was 6.80, 8.86 and 3.29 for Cu(II), Zn(II) and Mn(II), respectively. The experimental study was conducted using a flame atomic absorption spectroscopy. The described stripping voltammetry methods were successfully applied for the determination of Mn(II), Cu(II) and Zn(II) in soil samples. 相似文献
999.
Mustafa Soylak Zeliha Erbas 《International journal of environmental analytical chemistry》2018,98(9):799-810
A novel vortex-assisted magnetic solid phase extraction method followed by flame atomic absorption spectrometry was improved to separate, preconcentrate and determine the lead, copper and cadmium ions by using 1-Nitro-2-naphthol-3, 6-disulfonic acid disodium salt (Nitroso-R salt) impregnated magnetic Ambersorb-563 resin. The adsorbent was characterised by Fourier transform infrared spectra, BET surface analyser and scanning electron microscopy. The influences of various analytical parameters, such as pH value, type and volume of the eluent, sample volume, were optimised and the effects of potentially interfering ions were investigated. The analyte ions were quantitatively recovered at pH 7.0 on magnetic adsorbent and desorbed with a 2.0 M HNO3 in 10% acetone as eluent. The detection limits were 1.4, 5.8 and 1.5 ng mL?1 for Cd(II), Cu(II) and Pb(II), respectively. The method has been validated with analytically by the analysis certified reference materials and standard additions prior to application to determine metal ions in water samples. 相似文献
1000.
Low-cost pistachio shells were used for the production of small pore carbon molecular sieves by the benzene deposition method. The prepared materials were characterized by the Brunauer–Emmett–Teller surface area and scanning electron microscopy. The deposition temperature and the deposition time parameters, which affect the formation of carbon molecular sieves, were examined. The effect of deposition temperature was examined in the range of 700–900°C, while deposition time was examined between 30 and 60?min. The optimum surface area of the carbon molecular sieve prepared by benzene deposition was 895?m2/g at 800°C. The average pore diameter of the carbon molecular sieve was 0.27?nm, principally denoted ultramicropore characteristics. The obtained values of the pore size distributions of the prepared carbon molecular sieves were in the range of 0.26–0.29?nm. 相似文献