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1.
The effects of temperature and common ions on binding of puerarin to bovine serum albumin (BSA) are investigated. The binding
constants (K
a) between puerarin and BSA are 1.13×104 L⋅mol−1 (20 °C) and 1.54×104 L⋅mol−1 (30 °C), and the number of binding sites (n) is (0.95±0.02). However, at a higher temperature (40 °C) the stability of the puerarin–BSA system decreases, which results
in a lower binding constant (1.58×103 L⋅mol−1) and number of binding sites (n=0.73) of the puerarin–BSA system. However, the presence of Cu2+ and Fe3+ ions increases the binding constants and the number of binding sites in the puerarin–BSA complex. 相似文献
2.
Yi He Nathaniel Webber James P. Reilly 《Journal of the American Society for Mass Spectrometry》2013,24(5):675-683
Twenty singly-charged dipeptide ions with C-terminal arginine were photodissociated with 157 nm light and their tandem mass spectra recorded. Many of the small product ions that were observed are standard peptide fragments that have been commonly seen in VUV photodissociation studies. However, the study of a library of dipeptides containing all 20 N-terminal amino acids enabled the recognition of trends associated with the occurrence of w-, v-, and immonium ions, the observation of competition between forming N- and C-terminal fragments in dipeptide RR, and the identification of some unusual fragment ions appearing at masses of 183, 187, 196, and 197 Da. A highly accurate internal calibration of the photodissociation TOF-TOF data enabled molecular formulae for these four product ions to be derived. Their proposed structures reflect the rather high-energy nature of this fragmentation phenomenon. 相似文献
3.
Ligand protonation and stepwise dissociation constants, formation constants and speciation of four pyridyl sulfonamide ligands
(Congreeve et al., New J. Chem. 27:98–106, 2003) were assessed, using potentiometric and UV/Visible spectrophotometric pH titrations (in 80% MeOH − 20% H2O). The suitability of these ligands as Cu(II) and Zn(II) sensors for physiological applications was assessed. Two ligands
L1 and L4 were p-toluenesulfonamide derivatives while L2 and L3 were triflurosulfonamide derivatives. Additionally L3 and L4 were appended with α-methyl groups. The most stable complex was formed by L1 with Cu(II) owing to the fact that this complex was square planar (log 10
K
1=12.15±0.004 and log 10
β
2=15.42±0.006). The rest of the complexes invariably formed distorted tetrahedron geometry and complexation was weaker. Speciation
diagrams show the effect of ligand to metal concentration, revealing that the L2 and L3 ligands are the most suitable for forming ML2 complexes at physiological pH. 相似文献
4.
M. Teresa Barros João Martins Rui M. Pinto Mónica S. Santos Helena M. V. M. Soares 《Journal of solution chemistry》2009,38(12):1504-1519
As part of a search for environmentally friendly metal chelating ligands, the stability constants of N, N′-ethylenedi-L-cysteine
(EC) complexes with Ca(II), Cu(II), Mg(II) and Mn(II) were determined by potentiometry with a glass electrode in aqueous solutions
containing 0.1 mol⋅L−1 KCl at 25 °C. Final models are proposed. For the Ca(II)–EC system, the overall stability constants are log 10
β
CaHL=14.53±0.03, log 10
β
CaL=4.79±0.01 and log 10
β
CaL2=8.38±0.04. For the M(II)–EC systems, where M=Cu(II) or Mg(II), the overall stability constants are log10
β
CuHL=31.19±0.02 and log 10
β
CuL=27.02±0.06 for Cu(II), and are log 10
β
MgHL=14.84±0.02 and log 10
β
MgL=6.164±0.008 for Mg(II). For the Mn(II)–EC system, the overall stability constant is log 10
β
MnL=10.12±0.01.
Metal–chelate speciations simulations showed that EC is an efficient chelating agent for Cd(II), Co(II), Cu(II), Ni(II), Pb(II)
and Zn(II) for pH≥7. 相似文献
5.
Complexes of copper(II) with a number of polyphosphate and polymetaphosphate anions have been studied in aqueous solutions
by potentiometric, spectroscopic and theoretical methods. Stability constants of the complexes have been determined as well
as their coordination modes. Results of the equilibrium studies provided evidence for the formation of ML, MHL and ML(OH)
x
type complexes with the ligands studied. The length of the polyphosphate chain was found to affect the oxygen atom charge
that is reflected in the stability constants of the ML type complexes. Moreover, the stability of the complex is also influenced
by the spatial arrangement of the phosphate groups in phosphates and metaphosphates. The spectral parameters observed for
certain complexes have permitted us to deduce the inner coordination sphere of the studied complexes. 相似文献
6.
D. A. Palmer M. L. Machesky P. Bénézeth D. J. Wesolowski L. M. Anovitz J. C. Deshon 《Journal of solution chemistry》2009,38(7):907-924
Surface titrations were carried out on suspensions of monoclinic ZrO2 from 25 to 290 °C slightly above saturation vapor pressure at ionic strengths of 0.03, 0.1 and 1.0 mol⋅kg−1(NaCl). A typical increase in surface charge was observed with increasing temperature. There was no correlation between the
radius of the cations, Li+, Na+, K+ and (CH3)4N+, and the magnitude of their association with the surface. The combined results were treated with a 1-pKa MUSIC model, which yielded association constants for the cations (and chloride ion at low pH) at each temperature. The pH
of zero-point-charge, pHzpc, decreased with increasing temperature as found for other metal oxides, reaching an apparent minimum value of 4.1 by 250 °C.
Batch experiments were performed to monitor the concentration of LiOH in solutions containing suspended ZrO2 particles from 200 to 360 °C. At 350 and 360 °C, Li+ and OH− ions were almost totally adsorbed when the pressure was lowered to near saturation vapor pressure. This reversible trend
has implications not only to pressure-water reactor, PWR, operations, but is also of general scientific and other applied
interest. Additional experiments probed the feasibility that boric acid/borate ions adsorb reversibly onto ZrO2 surfaces at near-neutral pH conditions as indicated in earlier publications.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
7.
The formation of α-ferrocenylcarbenium ions FcC+H2 (λmax 600 nm) and FcC+HCH3 (λmax 730 nm) and their redox isomerism at the protonation of ferrocenylmethanol and vinylferrocene was proved using the method of electronic spectroscopy. The effect on the process of the solvent and acid nature as well as of hydrogen peroxide additives is discussed. 相似文献
8.
Yonit Sembira-Nahum Alexander Apelblat Emanuel Manzurola 《Journal of solution chemistry》2008,37(3):391-401
Densities of aqueous solutions of L-glutamic acid and magnesium-L-glutamate were determined from T=288.15 to 333.15 K at 5 K temperature intervals. The measured densities were used to evaluate the apparent molar volumes,
V
2,φ
(m,T), the cubic expansion coefficients, α(m,T), and the changes of isobaric heat capacities with respect to pressure, (∂
C
p
/∂
p)
T,m
. They were qualitatively correlated with changes in the structure of water that occur when L-glutamic acid or magnesium-L-glutamate
are present. 相似文献
9.
Xiaolei Shi Xuwen Li Yantao Sun Wei Wei Ruijie Yang Hanqi Zhang Yongri Jin 《Journal of solution chemistry》2010,39(4):482-494
The interaction between taxifolin and bovine serum albumin (BSA), and the effects of some common ions on their interaction,
were investigated by fluorescence and UV-visible absorption spectroscopy. The results indicate that taxifolin has a strong
ability to quench the intrinsic fluorescence of BSA through a static quenching process. According to values of the thermodynamic
parameters, the hydrophobic force plays a major role in the interaction. Based on Főster’s non-radiation theory, the energy
transfer distances between BSA and taxifolin in the absence and presence of some common ions were obtained. The experimental
results indicate that the transfer distances are almost unaffected by these ions. The conformation of BSA undergoes significant
change from the formation of a taxifolin–BSA complex, which was studied by synchronous and three-dimensional fluorescence
spectroscopy. 相似文献
10.
Simultaneous measurements with magnesium ion-selective and pH glass electrodes have been used for determination of the stability
constants of magnesium ions with various biologically relevant ligands by alkalimetric titration under physiological conditions
(37 ○C, I=0.15 mol⋅dm−3). New systems were investigated: magnesium with pyroglutamate, pyridoxine and HEPES, along with citrate, lactate, glycinate,
aspartate and glutamate. For comparison, calcium stability constants with the same ligands were determined similarly, using
calcium ion-selective and pH glass electrodes. Ligand protonation constants, necessary for the calculation of the metal complex
formation constants, were also determined. 相似文献
11.
《中国化学快报》1993,(2)
The inclusion crystal formed by the hexamethylenamine with p-nitrophenol has a layer type structure,and is divided or-ganic layer and inorganic layer,the latter has a width of 1.0136nm.Metal ions can enter hydrated layer of the crystal,the con-tents of the cations and water in the crystal are determined.The XRD analysis of the layer type structure of the crystal is also giv-en. 相似文献
12.
The promoter effects of rare earth ions on the electrocatalytic oxidation of methanol at the Pt electrode were studied using the cyclinc voltammetry and stable polarization techniques. It was found or the first time that Eu、Ho、Dy ions could accelerate the electrocatalytic oxidation of methanol at the Pt electrode,while Lu、Pr、Yb、Sm ions showed inhibitor effects. 相似文献
13.
The study of the diffusion of ferric ions in agar gel containing transition metal sulfates was carried out. The effect of
gel concentration, electrolyte concentration and temperature on the diffusion of Fe3+ ions in various transition metal sulfates was studied with a view to verify Wang’s model of diffusion and the applicability
of transition state theory to diffusion in a gel medium. The diffusion coefficients were measured using the zone diffusion
technique. For a given concentration of electrolyte the activation energy (E) is found to decrease with an increase in the charge density of the cation of the supporting electrolyte and for a given
system it is found to decrease with increasing electrolyte concentration in agreement with Wang’s model. This observation
is explained on the basis of the distortion in the water structure caused by ions and agar molecules. At a given electrolyte
concentration the magnitude of the Arrhenius parameters, E and D
o, is found to decrease with increasing gel concentration in agreement with the transition state theory of diffusion. 相似文献
14.
TheacetoneselfCImassspectrumAcetoneselfCImassspectrumisgiveninTable1.Table1.MajorproductionsandtheirrelativeabundanceofacetoneselfCIMSTheformationofionatmlZ73AnotherproductionintheselfCIMSofacetoneistheionatm/z73.InselfCIMSofacetone-d6,thecounterpartistheionatInjz82.InselfCIMSofthemixtureofacetoneandacetone-d6inaratioofl:l,thecorrespondingionsaretheionsatInlz73,76,79and82.TheirCIDreactionresultsarelistedinTable2.Table2.TheCIDMSoftheionatIn/z73andanalogsOnthebasisofthedatainTab… 相似文献
15.
Simón-Manso Y Neta P Yang X Stein SE 《Journal of the American Society for Mass Spectrometry》2011,22(2):280-289
While analyzing tandem mass spectra of tryptic tripeptides, intense unassigned peaks were observed, corresponding to neutral
loss of 45 Da from a2 ions. This process was confirmed by MS3 experiments. Based on exact mass analysis, the loss was ascribed to (NH3 + CO) or formamide. The proposed mechanism involves a cyclic form of the a2 ions. The structure of the a2 − 45 ions was confirmed by their fragmentation in MS3 experiments. Loss of (NH3 + CO) from the a2 ions occurs in competition with other paths, such as the loss of H2O or the formation of immonium ions. However, if the a2 ion contains methionine, a neutral loss of 48 Da (ascribed to CH3SH) predominates, and is followed by the loss of (NH3 + CO). These processes were confirmed by MS3 experiments. The intensity of the a2 − 48 peak formed from XaaMet has a maximum value of 42% (of the total intensity of all ions) for Xaa=Gly, varies between
15% and 40% for most other Xaa residues, is lower for residues that can undergo loss of water or ammonia, and is very low
for Lys or Arg. When the order of the residues is reversed to MetXaa, the loss of 48 Da is much smaller. This effect can be
used to determine the sequence of b2 ions containing Met in proteomic studies. Considerable loss of CH3SH is observed from doubly protonated tryptic tripeptides with N-terminal Met, but the loss is much less when they are singly
protonated or when Met is in the center position. 相似文献
16.
17.
Raphael da C. Cruz Rosana J. Martins Márcio J. E. de M. Cardoso Oswaldo E. Barcia 《Journal of solution chemistry》2009,38(8):957-981
Density measurements were made for binary aqueous solutions of polyethylene glycol at seven temperatures: 283.15, 288.15,
293.15, 298.15, 303.15, 308.15, and 313.15 K. Polyethylene glycol samples with nominal average molar masses of 3000 g⋅mol−1 (PEG 3000), 6000 g⋅mol−1 (PEG 6000), 10000 g⋅mol−1 (PEG 10000) and 20000 g⋅mol−1 (PEG 20000) were used. These results were used to determine the specific volumes of solutions with solute-to-solvent mass
ratios (mass of the solute/mass of the solvent) in the range 0.0546 to 1.4932 for PEG 3000, from 0.0553 to 1.4986 for PEG
6000, from 0.0552 to 1.2241 for PEG 10000, and from 0.0530 to 1.2264 for PEG 20000. The differences between the specific volume
of a solution and the specific volume of the pure solvent, at a given temperature, were represented by a virial-type equation
in terms of solute concentration. The first-order coefficient of the expansion is the partial specific volume of the solute
at infinite dilution. The higher-order coefficients are related to the contribution of pairs, triplets, and higher-order solute
aggregates, according to the Constant-Pressure Solution Theory. The functional dependence of the virial coefficients upon
temperature is discussed in terms of solute-solute and solute-solvent interactions. The effect of the PEG molar mass on the
partial specific volume of solute at infinite dilution, as well as the contributions of pairs of solute molecules to the solution
volume, are also investigated. The apparent specific volume, apparent specific expansibility, apparent specific expansibility
at infinite dilution and virial coefficients of the apparent specific expansibility are also presented. 相似文献
18.
Density, speed of sound and refractive index of the imidazolium-based ionic liquids (ILs), 1-methyl-3-octylimidazolium chloride
[C8mim][Cl], 1-butyl-3-methylimidazolium methyl sulfate [C4mim][C1OSO3], and 1-butyl-3-methylimidazolium octyl sulfate [C4mim][C8OSO3], have been measured in the temperature range from 283.15 to 343.15 K. Experimental density and speed of sound have been
used to calculate the internal pressure p
i of the ILs. The p
i values were found to be higher than those of water and molecular organic liquids, but lower than those of classical molten
salts. We also calculated molar refraction R
M from the measured refractive index n
D in the temperature range from 288.15 to 343.15 K. Refractive indices of ILs were also higher than those of normal organic
liquids, but comparable to long-chain hydrocarbon organic solvents. The structure-property correlation of the ILs has been
discussed and the results have been compared to our earlier studies (Kumar in J. Solution Chem. 37:203–214, 2008). 相似文献
19.
Hong Tao GUO Fei XU Xiao Hai ZHOU Jin Feng DONG Gao Yong ZHANG Xin Lin HONG 《中国化学快报》2005,16(12):1667-1670
This paper proved that octodecyl propylenediamine could form vesicles in pure water and aqueous solution of CuCl2 or Cu(NO3)2. The structure and morphology of vesicles were different when the copper (Ⅱ) salt was added to the solution. The results showed that both the counterions and the ligands had strong influence on the configuration of coordinated structures and packing model in bilayer membrane of vesicles. 相似文献
20.
A homopolymer of methyl methacrylate (MMA) and its copolymer with styrene at different compositions were synthesized and characterized.
Viscosity measurements of the synthesized homopolymer and the copolymers in toluene solutions were performed at 313 K. Different
equations were used to calculate the intrinsic viscosity, viscometric constants values, and molecular weight of the synthesized
polymers. The values of intrinsic viscosity and viscosity average molecular weight obtained by the two methods (single point
determination and graphical extrapolation) were compared in order to verify the validity of the single point determination
for the polymers. Viscometric properties derived included the specific viscosity (it determines the contribution of the solute
to the viscosity of the solution), the reduced viscosity (that provides a measure of the polymer capacity for increasing the
solution viscosity), and the intrinsic viscosity. 相似文献