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1.
Rabindra N. Roy Lakshmi N. Roy Michael S. Fuge Chandra N. Roy Curtis A. Himes Paul A. Bryant Kyle T. Robinson Daniel A. Kaufmann II Colby H. Grove Toshi Gosh Adonis Bwashi 《Journal of solution chemistry》2009,38(4):471-483
The values of the second dissociation constant, pK
2, and related thermodynamic quantities of [N-(2-acetamido)-2-aminoethanesulfonic acid] (ACES) have already been reported over
the temperature range 5 to 55 °C including 37 °C. This paper reports the pa
H values of four chloride ion free buffer solutions and eight buffer solutions with I=0.16 mol⋅kg−1, matching closely that of the physiological sample. Conventional pa
H values for all twelve buffer solutions from 5 to 55 °C are reported. The residual liquid-junction potential correction for
two widely used temperatures, 25 and 37 °C, has been made. The flowing-junction calomel cell method has been utilized to measure
E
j
, the liquid-junction potential. The operational pH values for four buffer solutions at 25 and 37 °C are calculated using
the physiological phosphate buffer standard based on the NBS/NIST convention. These solutions are recommended as pH standards
in the pH range of 6.8 to 7.2 for physiological fluids. 相似文献
2.
Rabindra N. Roy Lakshmi N. Roy Cole E. Denton Sean R. LeNoue Craig D. Dunseth Michael S. Fuge Shahaf Ashkenazi Jared L. Durden Chandra N. Roy Joshua T. Wollen Shawn M. Hayden 《Journal of solution chemistry》2009,38(11):1417-1431
The values of the thermodynamic second dissociation constant, pK 2, and related thermodynamic quantities of N-(2-hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic acid (HEPPSO) have already been reported from 5 to 55?°C, including 37?°C, by the emf method. This paper reports the results for the pH of one chloride-free buffer solution containing the composition: (a) HEPPSO (0.08 mol?kg?1)+NaHEPPSO (0.04 mol?kg?1). The remaining seventeen buffer solutions contain a saline medium of ionic strength I=0.16 mol?kg?1, matching closely that of physiological fluids. Conventional pH values, denoted as pa H, for all eighteen buffer solutions from 5 to 55?°C have been calculated. The operational pH values, designated as pH, with residual liquid-junction corrections for five buffer solutions, one without NaCl, and four with buffer solutions in saline media of I=0.16 mol?kg?1 are recommended as pH standards in the range of physiological application. These are based on the NBS/NIST standard scale for pH measurements. 相似文献
3.
Spectroscopic and spectrofluorimetric studies were made of the interaction between the drug atenolol and iodine. The interaction
was found to proceed through the initial formation of a charge transfer (CT) complex as an intermediate species. The product
of this interaction has been isolated and characterized using UV-Vis, FT-IR and Raman spectroscopic techniques. Formation
of the triodide
I3-\mathrm{I}_{3}^{-}
species was confirmed by its electronic and Raman spectra. Peaks appeared in Raman spectrum of the isolated product at 153,
102 and 85 cm−1 that are assigned to ν
as(I-I), ν
s(I-I) and
d(I3-)\delta(\mathrm{I}_{3}^{-})
respectively, which confirmed the presence of the
I3-\mathrm{I}_{3}^{-}
ion. The stoichiometry of the complex was found to be 1:2. The rate of their reaction has been measured as a function of time
and solvent. Pseudo-first-order rate constants for the reaction were measured at various temperatures and the thermodynamic
activation parameters (ΔG
#,ΔS
# and ΔH
#) were computed. Preliminary fluorescence quenching studies indicated that the interaction between atenolol and iodine is
spontaneous and proceeds through a CT complex, and the quenching of fluorescence of atenolol by iodine increases as the extent
of such complexation increases 相似文献
4.
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
5.
To understand the thermodynamic characteristics of cationic surfactants in binary mixtures, the aggregation behavior of hexadecyltrimethylammonium
chloride (CTAC) has been investigated in ethylene glycol (EG) + water solvent mixtures at different temperatures and EG to
water ratios. The critical micelle concentration (CMC) and degree of counter ion bonding (β) were calculated from electrical conductivity measurements. An equilibrium model for micelle formation was applied to obtain
the thermodynamic parameters for micellization, including the standard Gibbs energies of micellization (DGmico)\Delta G_{\mathrm{mic}}^{\mathrm{o}}), standard enthalpies of micelle formation (DHmico)\Delta H_{\mathrm{mic}}^{\mathrm{o}}) and standard entropies of micellization (DSmico)\Delta S_{\mathrm{mic}}^{\mathrm{o}}). Our results show that DGmico\Delta G_{\mathrm{mic}}^{\mathrm{o}} is always negative and slightly dependent on temperature. The process of micellization is entropy driven in pure water, whereas
in EG + water mixtures the micellization is enthalpy driven. 相似文献
6.
Leydi Erika Sarmiento Mildred Rodríguez Lorenzo Echevarria Vito Lubes 《Journal of solution chemistry》2010,39(10):1484-1491
The complex species formed between vanadium(III) and 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), and 8-hydroxyquinoline
(8hq) were studied in aqueous solution by means of electromotive forces measurements, emf(H), at 25 °C with 3.0 mol⋅dm−3 KCl as the ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, taking
into account the hydrolytic vanadium(III) species formed in solution. Analysis of the vanadium(III)–phen system data shows
the formation of [VHL]4+, [V(OH)L]2+, [V2OL2]4+ and [V2OL4]4+ complexes. In the vanadium(III)–bipy system the [VHL]4+, [V(OH)L]2+, [V2OL2]4+ and [V2OL4]4+ complexes were observed, and in the vanadium(III)–8hq system the complexes [V(OH)L]+, [V(OH)2L], [VL2]+ and [VL3] were detected. 相似文献
7.
Nikos G. Tsierkezos 《Journal of solution chemistry》2008,37(10):1437-1448
The cyclic voltametric technique utilizing a platinum working electrode was applied for the investigation of the electrochemical
oxidation of bis(benzene)chromium(0), (C6H6)2Cr to bis(benzene)chromium(I), (C6H6)2Cr+ in diethyl ketone (DEK), N,N-dimethylformamide (DMF), and DEK/DMF binary mixtures containing n-tetrabutylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte at T=298.15 K. The half-wave potentials (E
1/2) of the (C6H6)2Cr+/0 redox couple in DEK, DMF and DEK/DMF binary mixtures, were determined. The variation of E
1/2 with the solvent composition was found to be almost linear. The E
1/2 results were analyzed in terms of the electron-donating power of the solvent medium. The diffusion coefficients, D, were calculated using the Randles-Sevcik equation. The kinetics of the electrode reaction were investigated through the
determination of the heterogeneous electron-transfer rate constants, k
s, according to the electrochemical rate equation proposed by Nicholson. Furthermore, the activation Gibbs energies for the
electron-transfer process (ΔG
≠) were also calculated. The results indicate that the redox couple (C6H6)2Cr+/0 exhibits an electrochemically reversible and diffusion-controlled process in all the investigated solvent media. 相似文献
8.
Shekappa D. Lamani Praveen N. Naik Sharanappa T. Nandibewoor 《Journal of solution chemistry》2010,39(9):1291-1310
The kinetics of the osmium(VIII) (Os(VIII)) catalyzed oxidation of diclofenac sodium (DFS) by diperiodatocuprate(III) (DPC)
in aqueous alkaline medium has been studied spectrophotometrically at a constant ionic strength of 1.0 mol⋅dm−3. The reaction showed first order kinetics in [Os(VIII)] and [DPC] and less than unit order with respect to [DFS] and [alkali].
The rate decreased with increase in [periodate]. The reaction between DFS and DPC in alkaline medium exhibits 1:2 [DFS]:[DPC]
stoichiometry. However, the order in [DFS] and [OH−] changes from first order to zero order as their concentration increases. Changes in the ionic strength and dielectric constant
did not affect the rate of reaction. The oxidation products were identified by LC-ESI-MS, NMR, and IR spectroscopic studies.
A possible mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated.
The catalytic constant (K
C) was also calculated for Os(VIII) catalysis at the studied temperatures. From plots of log 10
K
C versus 1/T, values of activation parameters have been evaluated with respect to the catalytic reaction. The activation parameters with
respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined.
The active osmium(VIII) and copper(III) periodate species have been identified. 相似文献
9.
Nemanja Trišović Nebojša Banjac Nataša Valentić Gordana Ušćumlić 《Journal of solution chemistry》2009,38(2):199-208
The absorption spectra of nine compounds structurally related to phenytoin (5,5-diphenylhydantoin) were recorded in twelve
solvents over the range of 200 to 400 nm. The effects of solvent dipolarity/polarizability and solvent/solute hydrogen bonding
interactions were analyzed by means of the linear solvation energy relationship (LSER) concept proposed by Kamlet and Taft.
The lipophilic activity of the investigated hydantoins was estimated by calculation of their log 10
P values. The calculated values of log 10
P were correlated with the ratio of the contributions of specific and non-specific solute/solvent interactions. The correlation
equations were combined with the corresponding ED50 values to generate new equations that demonstrate exact relationship between solute/solvent interactions and the structure-activity
parameters. 相似文献
10.
The well-known adsorption integral equation (AIE) for calculating pore size and adsorption energy distributions from adsorption isotherms on porous solids is, from the mathematical point of view, a linear Fredholm integral equation of the first kind and therefore an ill-posed problem. What can we realistically expect from the solution of such an ill-posed problem by regularization? Does it make sense to restrict the number of possible solutions by the so-called ansatz method? In this paper, the two methods for solving ill-posed problems are from scratch explained and illuminated by concrete examples. Their relevance and fundamental limitations are discussed. 相似文献
11.
J. C. Alexandre de Oliveira R. H. López J. P. Toso Sebastião M. P. Lucena C. L. CavalcanteJr. D. C. S. Azevedo G. Zgrablich 《Adsorption》2011,17(5):845-851
We model carbon-based microporous materials, such as activated carbons, taking into account surface defects in the form of
geometrical rugosity in the inner surface of each graphitic slit pore. The used model is a simplified variation of the randomly
etched graphite (REG) pore model (Seaton et al., Langmuir 13:1199–1204, 1997). 相似文献
12.
Gas adsorption process in activated carbon over a wide temperature range above the critical point. Part 1: modified Dubinin-Astakhov model 总被引:1,自引:1,他引:0
Simulations of the thermal effects during adsorption cycles are valuable tools for the design of efficient adsorption-based
systems such as gas storage, gas separation and adsorption-based heat pumps. An analytical representation of the measured
adsorption data over the wide operating pressure and temperature swing of the system is necessary for the calculation of complete
mass and energy conservation equations. In Part 1, the Dubinin-Astakhov (D-A) model is adapted to model hydrogen, nitrogen,
and methane adsorption isotherms on activated carbon at high pressures and supercritical temperatures assuming a constant
microporous adsorption volume. The five parameter D-A type adsorption model is shown to fit the experimental data for hydrogen
(30 to 293 K, up to 6 MPa), nitrogen (93 to 298 K, up to 6 MPa), and for methane (243 to 333 K, up to 9 MPa). The quality
of the fit of the multiple experimental adsorption isotherms is excellent over the large temperature and pressure ranges involved.
The model’s parameters could be determined as well from only the 77 K and 298 K hydrogen isotherms without much reducing the
quality of the fit. 相似文献
13.
Solution densities over the temperature range 288.15 to 328.15 K have been measured for aqueous solutions of N-acetylarginamide monotrifluoroacetate and sodium trifluoroacetate, from which the partial molar volumes at infinite dilution,
V2oV_{2}^{\mathrm{o}}, were determined. The partial molar heat capacities at infinite dilution, Cp,2oC_{p,2}^{\mathrm{o}}, were also determined for these solutes over the same temperature range. These V2oV_{2}^{\mathrm{o}} and Cp,2oC_{p,2}^{\mathrm{o}} results, along with relevant data taken from the literature, have been used to calculate the contributions of the protonated
arginyl side-chain to the thermodynamic properties. These new side-chain values were critically compared with those obtained
previously using alternative side-chain model compounds. 相似文献
14.
The electrodes (anode and cathode) have an important role in the efficiency of a microbial fuel cell (MFC), as they can determine the rate of charge transfer in an electrochemical process. In this study, nanoporous gold electrode, prepared from commercially available gold-made compact disk, is utilized as the anode in a two-chamber MFC. The performance of nanoporous gold electrode in the MFC is compared with that of gold film, carbon felt and acid-heat-treated carbon felt electrodes which are usually employed as the anode in the MFCs. Electrochemical surface area of nanoporous gold electrode exhibits a 7.96-fold increase rather than gold film electrode. Scanning electron microscopy analysis also indicates the homogeneous biofilm is formed on the surface of nanoporous gold electrode, while the biofilm formed at the surface of acid-heat-treated carbon felt electrode shows rough structure. Electrochemical studies show although modifications applied on carbon felt electrodes improve its performance, nanoporous gold electrode, due to its structure and better electrochemical properties, acts more efficiently as the MFC’s anode. The maximum power density produced by nanoporous gold anode is 4.71 mW m?2 at current density of 16.00 mA m?2, while this value for acid-heat-treated carbon felt anode is 3.551 mW m?2 at current density of 9.58 mA m?2. 相似文献
15.
K. P. Singh Harshit Agarwal Vivek Kumar Shukla Isht Vibhu Manisha Gupta J. P. Shuka 《Journal of solution chemistry》2010,39(11):1749-1762
Measurements of the ultrasonic velocity (u), density (ρ) and refractive index (n) for binary mixtures of polyethylene glycol 250 dimethyl ether with 1-propanol and 1-butanol have been made at three temperatures
(T=293, 303 and 31 K) over the entire composition range in order to investigate the nature of intermolecular interactions between
the components of these liquid mixtures. Various excess thermodynamic properties such as the excess ultrasonic velocity (Δu), deviation in isentropic compressibility (Δk
S
), excess intermolecular free length (LfE)(L_{\mathrm{f}}^{\mathrm{E}}), excess acoustic impedance (Z
E), excess pseudo-Grüneisen parameter (Γ
E), and molar refraction deviation (ΔR
m) were calculated using experimental values of the ultrasonic velocity, density and refractive index and were then represented
with the Redlich-Kister polynomial equation. The observed excess deviation parameter values were explained on the basis of
the strength of intermolecular interactions between the components of the mixtures. Estimations of the refractive index and
ultrasonic velocity have also been made using various empirical relations and are discussed in terms of the average percentage
deviations (APD). 相似文献
16.
The structures and stability of the designed PNP pincer amido M(NO)2(PNP) and amino HM(NO)2(PNHP) complexes [M = V, Nb, and Ta, PNP = N(CH2CH2P(isopropyl)2)2, PNHP = HN(CH2CH2P(isopropyl)2)2] and their hydrogenation mechanisms for phenyl-substituted unsaturated functional groups have been explored at the B3PW91 level of density functional theory. Under H2 environment, these conjugated complexes can form equilibrium and fulfill the criteria of metal–ligand cooperated bifunctional hydrogenation catalysts. For the hydrogenation of Ph-CN, Ph-CHNH, Ph-CHNH-Ph, Ph-CHNCH2Ph, Ph-CCH, Ph-CHCH2, Ph-CHO, and Ph-COCH3, the reaction prefers either a two-step or one-step mechanism for the hydridic MH and protonic NH transfer. These results clearly show that the V, Nb, and Ta complexes are promising catalysts for the hydrogenation reactions, and these provide experimental challenges. 相似文献
17.
Alexandra Golikova Artemiy Samarov Maya Trofimova Sevastyan Rabdano Maria Toikka Oleg Pervukhin Alexander Toikka 《Journal of solution chemistry》2017,46(2):374-387
The chemical equilibrium (CE) for the quaternary reacting system ethanol–acetic acid–ethyl acetate–water was studied at 303.15, 313.15 and 323.15 K and atmospheric pressure. The CE compositions were determined by gas chromatography and nuclear magnetic resonance analytical methods. The thermodynamic constants of CE at 303.15, 313.15 and 323.15 K were calculated based on the obtained experimental data with the use of the NRTL model. 相似文献
18.
Multicomponent reactions for the synthesis of β-acetamido carbonyl compounds have been gained considerable attention in organic synthesis. In this articles, aromatic aldehydes have been employed in a one-pot reaction with enolizable ketones, acetonitrile, benzonitrile, and acetyl chloride in the presence of copper(II) sulfate petahydrate at ambient temperature to afford the corresponding β-acetamido ketones in very good yields. New compounds are reported. The use of readily available copper(II) sulfate petahydrate as a reusable and recyclable catalyst makes this process quite simple, convenient, and environmentally friendly. 相似文献
19.
Artemis P. Guimarães Andreas Möller Reiner Staudt Diana C. S. de Azevedo Sebastião M. P. Lucena Célio L. Cavalcante Jr. 《Adsorption》2010,16(1-2):29-36
The diffusion behavior of C4–C10 n-alkanes in silicalite-1 has been investigated by using the Zero Length Column method. The diffusivities derived from measurements at different purge rates with different purge gases confirming intracrystalline diffusion control. Data are compared with results reported in the literature for MFI zeolites. The diffusivities were found to be consistent and agree well with data previous obtained by ZLC. However, these data showed a remarkable disagreement with other reported techniques (PFG-NMR, QENS and Permeation). The eventual influence of carbon dioxide (CO2) adsorption on diffusion properties of n-alkanes in silicalite was also investigated. For this purpose, a series of experiments was performed involving hydrocarbons mixed with CO2. Data were obtained at 303 K and flow rates between 20 and 80 mL/min. The presence of CO2 does not seem to influence the intracrystalline transport rate of the investigated light hydrocarbons (n-C4 and n-C6). On the other hand, the situation for n-C8 and n-C10 is more complex. The diffusivity values are higher compared to the previously reported values. 相似文献
20.
Tame JR 《Journal of computer-aided molecular design》2005,19(6):445-451
The use of simple linear mathematical models to estimate chemical properties is not a new idea. Albert Einstein used very
simple ‘gravity-like' forces to explain the capillarity of different liquids in 1900–1901. Today such models are used in more
complicated situations, and a great many have been developed to analyse interactions between proteins and their ligands. This
is not surprising, since proteins are too complicated to model accurately without lengthy numerical analysis, and simple models
often do at least as good a job in predicting binding constants as much more computationally expensive methods. One hundred
years after Einstein’s ‘miraculous year’ in which he transformed physics, it is instructive to recall some of his even earlier
work. As approximations, ‘scoring functions’ are excellent, but it is dangerous to read too much into them. A few cautionary
tales are presented for the beginner to the field of ligand affinity prediction by linear models. 相似文献