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1.
The complex dielectric spectra of ascorbic acid solutions in pure dimethylsulfoxide (or diethylsulfoxide) and in dimethylsulfoxide (or diethylsulfoxide)/water mixtures have been measured at frequencies between 100 MHz and 20 GHz at 298.15 K.Two kinds of dielectric relaxation processes were observed in each solution. The low frequency relaxation (Debye term) is assigned to solute. The high frequency relaxation (Cole-Davidson term) is ascribed to practically unaffected solvent.From the results obtained it follows that relaxation time and relaxation strength in DESO containing solutions (i.e. binary AA/DESO and ternary AA/DESO/water systems) are greater than those in DMSO containing solutions. 相似文献
2.
An Electronic spectroscopic study of the self-association of Vitamin C in the nonaqueous phase is reported, pre-sumably for
the first time. The oxidation of ascorbic acid in 1,4-dioxane has been studied by UV spectroscopy. The dramatic role of the
environment in the stability and identification of the possible intermediates formed in the oxidation of ascorbic acid is
shown.
Published in Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 263–265, March–April, 2006. 相似文献
3.
A highly sensitive H-point standard addition method (HPSAM) was investigated for identification of dopamine and ascorbic acid in some synthetic and pharmaceutical samples in an aqueous medium at pH 9.2 using a universal buffer. The most suitable wavelengths for dopamine and ascorbic acid detection are 260:271 nm and 248:270 nm respectively. Recovery values are between 99.0–101 %. Also, the effect of most common interferents was studied. Detection ranges for dopamine and ascorbic acid are 2·10–6–5·10–5 M and 6·10–6–3·10–5 M respectively with an RSD range between 1.3 and 2.0 %. The method was used to determine both reagents in real and synthesized samples. 相似文献
4.
A simple, sensitive, and selective method for the determination of cerium(IV), based on the oxidative reaction between cerium(IV)
and ascorbic acid, has been described. The fluorescence comes from Ce(III) at λexcitation 298 nm and λemission 358 nm, which, in turn, is obtained from the oxidation of ascorbic acid by Ce(IV) in the presence of sulfuric acid. The optimum
conditions such as concentrations of ascorbic acid, sulfuric acid media and pH of the buffer solution were investigated. The
fluorescent intensity of the system is linear over the range 0.0531 μg/ml to 0.3322 mg/ml Ce(IV) and detection limit and correlation
coefficient are 0.0145 μg/ml and R=0.99987,respectively. 相似文献
5.
The processes of ascorbic acid total and dissociative ionization by 6 to 100 eV electrons in the temperature interval 360–460
K are studied with an MX-7304A monopole mass spectrometer. A scheme of ascorbic acid fragmentation due to electron-impact-induced
ionization is suggested, and possible channels of producing the most intense fragment ions in the mass spectrum are indicated.
The energy dependences and thresholds of fragment ion formation are determined for the first time in the incident electron
energy range 7–30 eV. 相似文献
6.
Two new ligands derived from phloroglucinol 2-{[(4-methoxy benzoyl ) oxy ] } methyl benzoic acid[L1] and 2-{[(4-methyl benzoyl
)oxy] methyl} benzoic acid[L2] were synthesized. The solid complex Eu(III)-L2 has been synthesised and characterized by elemental
analysis ,UV and IR spectra. The reaction of Eu(III) with the two synthesized ligands has been investigated in I = 0.1 mol dm-3 p-toluene sulfonate by cyclic voltammetry and square wave voltammetry. The reaction of Eu (III)–L1 and Eu (III)–L2 binary
complexes with nucleotide 5′-AMP , 5′-ADP ,5′-ATP , 5′- GMP , 5′-IMP , and 5′-CMP has been investigated using UV, fluorescence
and electrochemical methods. The experimental conditions were selected such that self-association of the nucleotides and their
complexes was negligibly small, that is, the monomeric complexes were studied. The interaction of the Eu(III)–L1 or L 2 solid
complexes with calf-thymus DNA has been investigated by fluorescence and electrochemical methods including cyclic voltammetery(CV)
,differential pulse polarography (DPP) and square wave voltammetry (SWV) on a glassy carbon electrode. The fluorescence intensity
of Eu(III)-L2 complex was enhanced with the addition of DNA. Under optimal conditions in phosphate buffer pH 7.0 at 25 °C
the linear range is 3–20 μM for calf thymus DNA (CT–DNA) and the corresponding determination limit is 1.8 μM. 相似文献
7.
Chemiluminescence of the system containing Tb(III) ions, histidine and bromate ions in acid solution was studied. The kinetic
curves and CL emission spectra of the system were discussed. The emission spectrum of the histidine–Tb(III)–KBrO3–H2SO4 system revealed two emission maxima at ∼490 and 550 nm, characteristic of Tb(III) ions. Values of lifetimes of the Eu(III)
excited states in Eu(III)–histidine system have shown that the histidine formed ML and ML2 complexes in neutral solution and did not make them in acidic environment. On the basis of the results, a possible mechanism
of reaction system: histidine–Tb(III)–KBrO3–H2SO4 is presented. 相似文献
8.
M. M. Seleim M. S. Abu-Bakr E. Y. Hashem A. M. El-Zohry 《Journal of Applied Spectroscopy》2009,76(4):554-563
A highly sensitive and selective first-derivative spectrophotometric method has been developed for the determination of aluminum
and iron in mixtures. The method is based on the formation of the binary complexes of aluminum and iron with Alizarin yellow
R (AYR) 5-[4-nitrophenylazo]salicylic acid at pH 2.0 with molar absorptivity of 1.1∙104 l⋅mol–1⋅cm–1. A zero-crossing technique is found suitable for the direct measurement of the first derivative value at the specified wavelength,
so aluminum and iron were thus determined in the ranges 1.3–5.4 μg/ml and 1.1–8.3 μg/ml, respectively, in the presence of
both components. The detection limits were found to be 1.4 ng/ml for aluminum and 2.8 ng/ml for iron. The relative standard
deviations were in all cases less than 1.5%. The proposed method was successfully applied for the simultaneous determination
of aluminum and iron in certified reference aluminum samples. 相似文献
9.
A. Nakajima Y. Masuda E. Matsuda Y. Ueda H. Sameshima T. Ikenoue 《Applied magnetic resonance》2011,40(4):535-544
The reaction between 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (PCAM), which is a blood–brain-barrier (BBB)
permeable stable cyclic nitroxide, and ascorbic acid was examined in a low dissolved oxygen-phosphate buffer (low DO-PB, 0.1 mM
DO) under 8% oxygen in a glove bag or in an ordinal dissolved oxygen-phosphate buffer (ordinal DO-PB, 0.3 mM DO) under 21%
oxygen in an open atmosphere with and without diethylenetriaminepentaacetic acid (DTPA). In PB with DTPA, no difference was
observed between the results in the low DO-PB and those in the ordinal DO-PB. In the ordinal DO-PB without DTPA, the rate
constant of the PCAM decrease was half that in the low DO-PB without DTPA. The present results indicate that high DO and coexisting
transition metal ions caused the oxidation of ascorbic acid, which degraded the PCAM reduction. The stable nitroxide-ascorbic
acid system without DTPA was found to be applicable to an in vitro model for the acute hypoxia ischemia. 相似文献
10.
S. F. Baranovsky P. A. Bolotin M. P. Evstigneev D. N. Chernyshev 《Journal of Applied Spectroscopy》2009,76(1):132-139
Two component (ethidium bromide–caffeine, ethidium bromide–DNA) and three component (ethidium bromide–caffeine–DNA) systems
in aqueous saline (0.01 M NaCl) phosphate buffer solutions (pH 6.86, T = 298 K) are studied spectrophotometrically. The equilibrium constants for dimerization of caffeine, K
D
= 1.22 ± 2 M−1, and for heteroassociation of ethidium bromide with caffeine, K = 71 ± 8 M−1, in ethidium bromide–caffeine systems are determined. When the concentration of caffeine is increased, the dynamic equilibrium
of the solution shifts toward formation of heterocomplexes which are, presumably, stabilized by dispersive and hydrophobic
interactions of chromophores. The equilibrium parameters for ethidium bromide complex formation with DNA are calculated: the
coupling constant for the dye with the biopolymer, K
1 = (232 ± 16)⋅103 M−1, and the number of base pairs of the biopolymer participating in bonding with the ligand, n
1 = 3.6 ± 0.2, are calculated. Given these values, it is suggested that under these experimental conditions there are two types
of bonding between ethidium bromide and the nucleic acid — intercalation and “external” bonds. A McGhee–von Hippel model for
a three component system and the numerical values of the parameters for molecular complex formation in two component systems
are used to calculate the bonding constant for caffeine with DNA, K
2 = 127 ± 30 M−1, and the number of base pairs of DNA which bond with caffeine, n
2 = 1.7 ± 0.2. The concentrations of ethidium bromide and caffeine in the composition of two and three component complexes
are calculated as functions of the nucleic acid content in the solution. An analysis of the concentration dependences shows
that heteroassociation of ligands has a significant effect on the reduction in the concentration of ethidium bromide–DNA complexes
in a three component system for low DNA concentrations, while at high DNA concentrations the bonding of caffeine with the
biopolymer has this effect.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 143–151, January–February 2009. 相似文献
11.
Haowen Huang Chunhui Li Caiting Qu Shaowen Huang Fang Liu Yunlong Zeng 《Journal of nanoparticle research》2012,14(3):754
In this article, a type of core–shell nanostructure, Au2S/AuAgS/Ag3AuS2-coated gold nanorods (GNRs) with unique optical properties was used as a sensing platform to detect fish sperm DNA (fsDNA).
The prepared core–shell nanorods are positively charged due to the adsorption of the positively charged cetyltrimethylammonium
bromide (CTAB) cations on their surface. fsDNA can form ternary fsDNA–CTAB–nanorod complexes together with CTAB and nanorod,
which provides a useful platform to detect fsDNA through absorption spectra and resonance light scattering (RLS) spectroscopy.
In this sensitive core–shell nanorod sensor, CTAB concentration and the nanoparticle dosage play important roles and have
been investigated. Moreover, the fsDNA–CTAB–nanorod complexes induce a great enhancement of RLS intensity of the core–shell
GNRs and directly proportional to the concentration of fsDNA, reaching a detection limit of about 10−9 mg/mL. This study will be significant for as-prepared core–shell GNRs for future application in biological systems. 相似文献
12.
By controlling the reflux time and the quantity of the shell materials, different sizes of thioglycollic acid (TGA) modified
CdTe/CdSe core/shell quantum dots were synthesized in aqueous solution. This type of QDs was used for sensitive and selective
determination of ascorbic acid in commercial tablets. Under optimal conditions, a good linearity was observed between the
relative fluorescence (FL) intensity and the concentration of ascorbic acid in the range of 4.0 to 64.0 μg/mL with a correlation
coefficient of 0.9968. The limit of detection was 2.4 μg/mL. This method was applied to the determination of the ascorbic
acid in Vitamin C tablets and Vitamin C Yinqiao pills, and satisfactory results were obtained. 相似文献
13.
Complex formation of β-cyclodextrin with para-aminosalicylic acid in buffer solutions is studied by UV spectroscopy. It is
found that the stoichiometric proportion of the components in the β-cyclodextrin–para-aminosalicylic acid inclusion complex
is 1:1. The Ketelar equation is used to calculate the stability constants of the inclusion complexes at different temperatures.
The thermodynamic parameters of the complex formation process (ΔG, ΔH, ΔS) are calculated using the van’t Hoff equation. The
1:1 β-cyclodextrin–para-aminosalicylic acid inclusion complex is prepared in solid form and its characteristics are determined
by IR spectroscopic and x-ray diffraction techniques. 相似文献
14.
Moamen S. Refat Mohamed M. Ibrahim Mohamed A. A. Moussa 《Journal of Applied Spectroscopy》2012,78(6):772-781
Charge-transfer complexes (CTC) resulting from interactions of 1,3-di[(E)-1-(2-hydroxyphenyl) methylideneamino]-2-propanol Schiff base with some acceptors such as iodine (I2), bromine (Br2), and picric acid (PiA) have been isolated in the solid state in a chloroform solvent at room temperature.
Based on elemental analysis, UV-Vis, infrared, and 1H NMR spectra, and thermogravimetric analysis (TG/DTG) of the solid CTC, [(Schiff)(I2)] (1), [(Schiff)(Br2)] complexes with a ratio of 1:1 and [(Schiff)(PiA)3] complexes with 1:3 have been prepared. In the picric acid complex, infrared and 1H NMR spectroscopic data indicate that the charge-transfer interaction is associated with a hydrogen bonding, whereas the
iodine and bromine complexes were interpreted in terms of the formation of dative ion pairs [Schiff+, I2∙−] and [Schiff+, Br2∙−], respectively. Kinetic parameters were obtained for each stage of thermal degradation of the CT complexes using Coats–Redfern
and Horowitz–Metzger methods. DC electrical properties as a function of temperature of these charge transfer complexes have
been studied. 相似文献
15.
Using a competitive nitric oxide (NO)-trapping method between Fe–dithiocarbamate (DTC) complexes and liposome-encapsulated
2-[4-trimethylammonio]-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide (TMAPTIO), NO-trapping rates of Fe–DTC complexes in
the presence of phosphatidylcholine liposomes were quantified for five kinds of Fe–DTC complexes. We investigated how the
DTC ligand structure influences the NO-trapping rates of Fe–DTC complexes. The negatively charged liposomes give a higher
NO-trapping rate of Fe–DTC complexes than do the positively charged ones, suggesting that the presence of a charge on the
liposome surface affects the NO-trapping rate processes of Fe–DTC complexes. In addition, on the basis of the pressure dependence
experiments for the competitive reaction, we evaluated the difference in activation volumes between the NO-trapping reactions
by Fe–DTC complexes and TMA-PTIO, which allowed us to consider possible reaction mechanisms for the NO-trapping processes. 相似文献
16.
A validated simple, rapid, and selective spectrofluorimetric method was developed for the determination of some antihistaminic
H1 receptor antagonist drugs namely ebastine (EBS), cetirizine dihydrochloride (CTZ), and fexofenadine hydrochloride (FXD).
The method is based on the reaction of the cited drugs with some Π acceptors namely p-chloranilic acid (CLA), tetracyanoethylene
(TCNE), and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) to give highly fluorescent derivatives. The fluorescence intensity—concentration plots were rectilinear
over the concentration ranges of 0.2–3.0, 0.2–2.5 and 0.15–2.0 μg/ml for EBS with CLA, DDQ, and TCNE respectively; 0.5–7.0,
0.5–6.0, and 0.2–4.0 μg/ml for CTZ with the previously mentioned reagents, and 0.2–3.5, 0.5–6.0, and 0.2–3.5 μg/ml for FXD.
The factors affecting the formation of the reaction products were carefully studied and optimized. The method was applied
for the determination of the studied drugs in their dosage forms. The results obtained were in good agreement with those obtained
by the comparison methods. Reactions Stoichiometries of the complexes formed between the studied drugs and Π acceptors were
defined by the Job’s method of the continuous variation and found in 1:1 in all cases. 相似文献
17.
Dillip K. Pradhan R. N. P. Choudhary B. K. Samantaray Awalendra K. Thakur R. S. Katiyar 《Ionics》2009,15(3):345-352
Polymer–clay nanocomposites consisting of polymer (polyethylene oxide) and NaI as salt with different concentration of organically
modified Na+-montmorillonite (DMMT) have been fabricated and characterized. X-ray diffraction analysis shows that the polymer–salt complexes
have been intercalated into the nanometric silicate layers of DMMT. Fourier transform infrared analysis shows that the polymer
structure in the clay interlayer is similar to that of the polymer–salt complexes, and there is a strong interaction between
the polymer–salt complexes and clay layers. A study of surface morphology using scanning electron microscopy reveals that
microstructure of composites is affected by clay addition. Complex impedance analysis was used to calculate the bulk resistance
of the composites. An enhancement in the conductivity of about one order of magnitude has been observed on 5% clay addition
compared to that of the polymer–salt complexes, and it decreases monotonically for higher clay concentration. The effect of
clay concentration on the structural and physical properties of polymer nanocomposites is well correlated. 相似文献
18.
O. S. Kulakovich N D. Strekal A. A. Lyutich S. A. Maskevich 《Journal of Applied Spectroscopy》2009,76(3):402-407
We obtained complexes between core/shell type CdSe/ZnS semiconductor nanoparticles (NP) and the synthetic polyelectrolyte
polyallylamine (PAA) as a result of ionic interactions in aqueous solutions and subsequent stretching on flat substrates using
the "molecular combing" technology. By varying the size of the nanoparticles and the stoichiometric ratios of the concentrations
of nanoparticles and PAA molecules in solution, we determined the factors ensuring formation of filamentary fluorescent nanoparticle–PAA
complexes.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 428–433, May–June, 2009. 相似文献
19.
Complex formation between benzene carboxylic acids and β-cyclodextrin in aqueous solutions at 290–300 K was studied using
UV spectroscopy. The formation of 1:1 supramolecular inclusion compounds β-cyclodextrin-benzene and β-cyclodextrin-salicylic
acid was found. Stability constants (Ks) of the complexes and thermodynamic parameters for formation of the inclusion compounds (ΔG, ΔH, and ΔS) were calculated.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 299–303, May–June, 2008. 相似文献
20.
Paramagnetic centers in 3,4-dihydroxyphenylalanine–melanin and its complexes with Fe(III) were examined by electron paramagnetic
resonance (EPR) spectroscopy. Paramagnetic centers of melanin play an important role in detoxification of environment and
they reveal high activity in binding of metal ions. Two different signals were observed in EPR spectra: lines of o-semiquinone free radicals and lines of paramagnetic Fe(III). Amplitudes of EPR lines of both free radicals and iron ions
decrease with increasing Fe(III) content in melanin–metal ion complexes. Free radical concentrations in the melanin samples,
g-factors, amplitudes and line widths of EPR spectra were determined. It was stated that fast spin–lattice relaxation processes
exist in both free radical system and paramagnetic iron ions in melanin complexes. 相似文献