Effect of β-Cyclodextrin on the Micellization of Cetyltrimethylammonium in Aqueous Solution at High Temperature

Molar volume and conductivity measurements have been carried out at 338.2 K for cetyltrimethylammonium chloride (CTAC) + H₂O and CTAC + β-cyclodextrin (β-CD) + H₂O systems. The apparent critical micelle concentrations, the dissociation degree of the micelle, the transfer free energy for the hydrocarbon chain of CTAC, the standard partial molar volumes of CTAC in aqueous β-CD solution and the stoichoimetry for the inclusion complex of CTAC with β-CD have been determined. The influence of β-CD and its complex on the micellization processes of CTAC are analyzed under this temperature. It is shown that β-CD partly screened the hydrophobic hydrocarbon chain of CTAC molecules from contact with the surrounding medium, and retarded the formation of CTAC micelles in a certain extent. The thermodynamic activity of CTAC is decreased. The β-CD and its complexes do not participate the formation of micelles of CTAC, and the complex have no effect on the micelle properties once the micelles are formed. Based on a simple model, the number of CH₂ groups entered the cavity of β-CD was calculated. The result suggests that β-CD forms strong complex with CTAC, and the stoichoimetry is found to be 2:1. This supports our conductivity results.     

Study on the Fluorescence System of Oxolinic Acid‐Tb(III) and the Determination of Oxolinic Acid

Abstract

In Tris‐HCl buffer (pH=7.43), Tb³⁺ can react with oxolinic acid (OA) and form a 1:2 complex, which emits the intrinsic fluorescence of Tb³⁺. Based on this, a new fluorimetric method of determination of OA is developed. Under the optimum conditions, the enhanced fluorescence intensity of the system is proportional to the concentration of OA in the range of 1.5×10^?7～2.5×10^?5mol/L, and the detection limit is 5.5×10^?9 mol/L. Recovery test was also satisfactory. The experiments indicated that the luminescence mechanism was attributed to the M*–M luminescence.     

Determination of the Glass Electrode Parameters by Means of Potentiometric Titration of Acetic Acid in Aqueous Sodium or Potassium Chloride Solutions at 25°C

Single-ion activity coefficient equations are presented for the calculation of stoichiometric (molality scale) dissociation constants K _m for acetic acid in aqueous NaCl or KCl solutions at 25°C. These equations are of the Pitzer or Hückel type and apply to the case where the inert electrolyte alone determines the ionic strength of the acetic acid solution considered. K _m for a certain ionic strength can be calculated from the thermodynamic dissociation constant K _a by means of the equations for ionic activity coefficients. The data used in the estimation of the parameters for the activity coefficient equations were taken from the literature. In these data were included results of measurements on galvanic cells without a liquid junction (i.e., on cells of the Harned type). Despite the theoretical difficulties associated with the single-ion activity coefficients, K _m can be calculated for acetic acid in NaCl or KCl solutions by the Pitzer or Hückel method (the two methods give practically identical K _m values) almost within experimental error at least up to ionic strengths of about 1 mol-kg^–1. Potentiometric acetic acid titrations with base solutions (NaOH or KOH) were performed in a glass electrode cell at constant ionic strengths adjusted by NaCl or KCl. These titrations were analyzed by equation E = E _o + k(RT/F) ln[m(H⁺)], where m(H⁺) is the molality of protons, and E is the electromotive force measured. m(H⁺) was calculated for each titration point from the volume of the base solution added by using the stoichiometric dissociation constant K _m obtained by the Pitzer or Hückel method. During each base titration at a constant ionic strength, E _o and k in this equation were observed to be constants and were determined by linear regression analysis. The use of this equation in the analysis of potentiometric glass electrode data represents an improvement when compared to the common methods in use for two reasons. No activity coefficients are needed and problems associated with liquid junction potentials have been eliminated.     

Determination of Stoichiometric Dissociation Constants of Benzoic Acid in Aqueous Sodium or Potassium Chloride Solutions at 25°C

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant K_m of benzoic acid in dilute aqueous NaCl and KCl solutions at 25°C from the thermodynamic dissociation constant K_a of this acid and from the ionic strength I_m of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study and the equations for K_m were based on the single-ion activity coefficient equations of the Hückel type. The existing literature data obtained by conductance measurements and by electromotive force (EMF) measurements on Harned cells were first used to revise the thermodynamic value of the dissociation constant of benzoic acid. A value of K_a = (6.326 ± 0.005) × 10^-5 was obtained from the most precise conductivity set [Brockman and Kilpatrick] and this value is supported within their precisions by the less precise conductivity set of Dippy and Williams and by the EMF data set measured by Jones and Parton with quinhydrone electrodes. The new data measured by potentiometric titrations in a glass electrode cell were then used for the estimation of the parameters of the Hückel equations of benzoate ions. The resulting parameters were also tested with the existing literature data measured by cells with and without a liquid junction. The Hückel parameters suggested here are close to those determined previously for anions resulting from aromatic and aliphatic carboxylic acids. By means of the calculation method based on the Hückel equations, K_m can be obtained almost within experimental error at least up to I_m of about 0.5 mol-kg_-1 for benzoic acid in NaCl and KCl solutions.     

Study on the Enhancement of Proton Affinity by N-Diisopropyloxy Phosphorylation of Amino Acid in Mass Spectrometry

With introduction of a diisopropyloxy phosphoryl group into the N terminal of amino acids,it was found that proton affinity(PA) of amino acid was enhanced in mass spectrometry.Density functional theory calculations showed that the energy for protonation of DIPP-amino acid is lower than that of amino acid,which means PA of DIPP-AA ishigher than that of corresponding amino acid.These results.Coincident with our empirical results.offer a useful interpretation of experimental observations.     

Effect of pressure on the solubility of naphthalene in water at 25°C

Solubility of naphthalene in water was measured at 25°C and pressures up to 200 MPa. The solubility decreased with increasing pressure. From the pressure coefficient of the solubility, the volume change V accompanying the dissolution was estimated as 13.8±0.4 cm ³ -mol ^–1 . Further we estimated the volume change V _CH accompanying hydrophobic hydration as –0.1±0.6 cm ³ -mol ^–1 using the V value, the molar volume of crystalline naphthalene, and the partial molar volume of naphthalene in n-heptane. This V _CH is much larger (i.e., less negative) than that for hydrophobic hydration of alkyl-chain compounds and suggests that the hydration structure of naphthalene differs from that of alkyl-chain compounds.     

The Effect of pH Difference Between Two Phases on the Partition of Lysozyme in Aqueous Two-Phase System

Aqueoustwo-phasesystems(ATPS)areformedwhentwoaqueoussolutionsofhydrophilicpolymersorapolymerandasaltaremixedathighconcentration.Forthechargedproteins,AlbertssonhasdevelopedtheclassicalmodelfortheelectrochemicalpartitioninginATPSfInK,=lnK, (Z,F/RT)Arp(l)HereK,denotesthepartitioncoefficientofproteins,InK,includesalltheotherfactorsaffectingproteinpartitioning,and(Z,F/RT)A(PistheelectrostatictermasaproductofproteinsurfacechargeZPandAam,theelectrostaticpotentialdifferencebetweenthetwopha…     

Aqueous Uranyl Complexes 1. Raman Spectroscopic Study of the Hydrolysis of Uranyl(VI) in Solutions of Trifluoromethanesulfonic Acid and/or Tetramethylammonium Hydroxide at 25°C and 0.1 MPa

Raman spectra have been used to identify and characterize aqueous hydroxouranyl(VI) complexes from 0.0038 to 0.647M at pH from 0.24 to 14.96 adjusted witheither HCF₃SO₃ and/or (CH₃)₄NOH under ambient conditions. In acidic media(0.24 pH 5.63), the existence of four species UO²⁺ ₂,(UO₂)₂(OH)³⁺,(UO₂)₂(OH)²⁺ ₂, and (UO₂)₃(OH)⁺ ₅ was confirmed. At high uranium concentrations(U 0.1M) and in strongly acidic solutions (pH 1.94), one additional weakband was observed at 883±1 cm^–1. This band was assumed torepresent thespecies UO²⁺ ₂ with a reduced hydration number.In neutral and basic solutions(5.63 pH 14.96), five complexes were postulated: (UO₂)₃(OH)^– ₇,(UO₂)₃(OH)^2– ₈,(UO₂)₃(OH)^4– ₁₀,(UO₂)₃(OH)^5– ₁₁, andUO₂(OH)^2– ₄, based on theassigned symmetrical stretching frequencies of the UO₂ group in each complex.(UO₂)₃(OH)^– ₇ is the dominant species over mostof the pH range (4.53–12.78).The stability ranges of the other trinuclear species are:(UO₂)₃(OH)^2– ₈ (10.97 pH 13.83), (UO₂)₃(OH)^4– ₁₀ (10.97 pH 13.85) and (UO₂)₃(OH)^5– ₁₁(12.53 pH 14.10), which were identified for the first time. Finally, the monomericuranate anion OU₂(OH)^2– ₄ dominates in highly basic solution (12.48 pH 14.96). The linear correlation between the symmetrical vibrational frequency v ₁of the linear O = U = O entity and the average number of hydroxide ligandscoordinated to each uranium atom in a given species has been reaffirmed andexpanded: The v ₁ correlation was also used to predict the vibration frequencies of theundetected monomers UO₂(OH)⁺, UO₂(OH)^o ₂,UO₂(OH)^– ₃ at 848±2, 826±2, and804±2 cm^±1, respectively. Characteristic band areas for eachuranyl hydrolyzedspecies were determined by Raman spectra decomposition and their hydrolysisquotients log Q, were calculated. Structures of the four triuranylspecies are proposed.     

The Effects of Cosolvents on the Complexation of α-Cyclodextrin with Alkylated Substances. Calorimetric Studies at 25 °C

The formation of complexes of -cyclodextrin with 1,2-alkanediols, ,-alkanediols and some cycloalkanols has been studied calorimetrically at 25 °C in water, in 7 mol kg^-1 aqueous urea and in 3 mol kg^-1 aqueous glucose. When a complex is formed, calorimetry enables the calculation of both the enthalpy and the association constant, from which the free energy and the entropy of the process can be obtained. The forces involved in the association process are discussed in the light of the signs and values of the thermodynamic parameters obtained. The effect of the variation of the aqueous medium on the hydration of the interacting substances and the consequent changes in the association parameters have been investigated. As respect to water, complexes are less stable in urea and more stable in glucose. The analysis of the data shows that this is the result of a different enthalpy-entropy balance in the two solvent media. Deaquation of the interacting substances plays a major role in determining the stability of the inclusion complexes.     

Effect of Ammonium Salts on the Volumetric and Viscometric Behavior of D(+)-Glucose,D(−)-Fructose and Sucrose in Aqueous Solutions at 25°C

Apparent molar volumes, V _φ, and viscosity, η, of D(+)-glucose, D(−)-fructose and sucrose in water and in 0.02, 0.05, 0.5, 1.0 and 2.0 mol·kg⁻¹ aqueous solutions of ammonium bromide, tetraethylammonium bromide and tetra-n-butylammonium bromide have been determined at 25 °C from density and efflux time measurements by using a vibrating-tube digital densimeter and a capillary viscometer, respectively. Partial molar volumes, , at infinite dilution that were extrapolated from the V _φ data were used to obtain the corresponding transfer volumes, , for saccharides from water to different aqueous solutions of co-solutes. The Jones-Dole equation viscosity B-coefficients were obtained from the viscosity data. Positive values of were obtained for the saccharides in the presence of ammonium bromide, whereas both positive and negative values were obtained in the presence of tetraethylammonium and tetra-n-butylammonium bromides. The negative values at very low concentrations have small magnitudes. Volumetric interaction coefficients have been calculated by using the McMillan-Mayer theory and Gibbs energies of activation of viscous flow have been calculated by using Feakin’s transition-state theory equation. The parameters obtained from the volumetric and viscometric studies were used to understand various mixing effects due to the interactions between saccharides and ammonium salts in aqueous solutions.     

A Gold Electrode QCM Study on the Self-Assembling Process of Thioglycollic Acid in Aqueous Solution

Quartzcrystalmicrobalance(QCM)iswellknownasanexcellenttoolforthestudyofchemicaland/orphysicalprocessesonthesolidsurfaceaccompaniedbymasschangedowntoananogramlevell.Inaddition,itiswellestablishedthatathiol-containingcompoundisabletoadsorbonsomesubstrates(e.g.,An,Cu,andCd)toformaself-assembledmonolayerbythewell-knownchemicalreactionofthethiolgroupwiththesubstrate2.Tothebestofourknowledge,therearenoreportsontheself-assemblingprocessesofalkanethiolcompoundsinaqueoussolutionswithQCMteclmique.In…     

A Spectrophotometric Study on the Host-Guest Complexation of β-Cyclodextrin with 3-Indolyl Acetate in Dilute Aqueous Solution by Determining Solubility of Guest Substance

Interestincyclodextrinshasincreasedsteadily,becausetheirinclusioncompoundshaveprovedmoreandmoreusefulinbothresearcllandindustry'.Furthermore,theyareofgreatilllportanceforsupramolecularchemistry,sincetheyaremembersofahomologousseriesofW'ater-solubleandchiralhostmoleculeswhichcanbeusedasmodelsforstudyingweakinteractionsl-'.Ontheotherhand.indolylgroupexistsinsomeimportantbiogentcsubstancessuchastryptophan.Soinvestigationontheinteractionsbetweenindolylderivativesandsuchbiologicmodelsubstancesascyc…     

Hygrometric Determination of the Water Activities of the Aqueous Solutions of the Mixed Electrolyte NaCl–CaCl2–H2O at 25°C

The mixture {yNaCl + (1 – y)CaCl₂}(aq) has been studied with the hygrometric method at the temperature 25°C. The water activities were measured at total molalities from 0.25 mol-kg^–1 to near saturation for different ionic-strength fractions y of NaCl with y = 0.33, 0.50, and 0.67. The obtained data allow the calculation of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LS II), Reilly–Wood–Robinson (RWR), and Pitzer models. From the measured osmotic coefficients, the Pitzer ionic mixing parameters _{Na Ca} and _{Na Ca} Cl are determined and are used to predict the solute activity coefficients in the mixtures. The excess Gibbs energy is also determined. These results are compared with those given in the literature.     

A Study on the Inclusion of α-Cyclodextrin with Mono-and 1,4-Disubstituted Benzenes by Neural Networks

Itiswellknownthatthecycledextrin(CD)isonekind0ftheidealenzyrnemedels.ThestudiesofcycboextrininmoIecularrmpition,mimeticenzyTneandseParationscienceandtechnolOgyhavebenexPeriencedanenormousinterestintherecentyears.l-5Inspite0fafewdrivingforceshavebenprohof0rtheinclusionofCDwithavarietyofgUestco~nds,therestillrernainsnoclearagreeInent0nthemechanisrnf0rCDinclusioncomPlexation.Daviesetal"'estabIishedamedelfortheinclusionofQ-CDwithl,4-disubstitutedbenzenesbased0naregress1onanalysis.According…     

A Study on the Driving Force for Binding of Benzene Derivatives by α-and β-Cyclodextrin

WehavedemonstTatedthattheassociationconstantsfortheinclusioncomplexationofa-and6-cyclodextrin(a-and9-CD)withsubstitutedbenzene(PhX)arecorrelatedwithpropertiessuchasmolarrefraction(R.),hydrophobicity(n.)andeIectroniceffect(a.)ofsubstitUentsintheguestcompounds.Uponapplicationofanariificialneuralnetwork(ANN),theassociationconstants(Ka)fortheinclusionofa-CDand6-CDwithsubstitutedbenzenewerepredictedfromR.,rrxandG.withsatisfactoryresultSl'2.Furthermore,theeffectsofsubstituentsinbenzenederivat…     

Effect of temperature on the organized self-assembly of SDS/β-Cyclodextrin aqueous solution by dielectric relaxation behavior

The temperature dependence of microstructures of SDS/β-cyclodextrin aqueous solution was investigated by impedance analyzer at the temperature range of 15°C to 55°C. The dielectric relaxation behaviors were observed from 15°C to 35°C, which was attributed to the Maxwell-Wagner interfacial polarization. The microstructure transition of the SDS/β-cyclodextrin aqueous solution from micro-tube to vesicle and then to monomer with increasing temperature was confirmed by conjointly analyzing dielectric parameters, confocal laser scanning microscopy, and infrared spectra. Furthermore, the dielectric analysis was proved to be useful to study surfactant-based organized self-assembly.     

Inclusion Complexation of the Sunscreen 2-Hydroxy-4-Methoxy Benzophenone (Oxybenzone) with Hydroxypropyl-β-Cyclodextrin: Effect on Membrane Diffusion

It is desirable to minimize skin penetration of some drugs, such as sunscreens and insect repellents. Available in vivo and in vitro data suggest appreciable absorption of some sunscreen agents. The purpose of this study was to investigate the effect of hydroxypropyl--cyclodextrin (HPCD) on the release and permeation of the sunscreen agent 2-hydroxy-4-methoxy benzophenone (oxybenzone). The interaction between oxybenzone and HPCD was studied in water by phase solubility analysis. The inclusion complex was characterized by thermal analysis and nuclear magnetic resonance spectroscopy. UV transmittance and percent UVA transmittance, as a preliminary measure of sun protection factor (SPF), were determined. In vitro permeation experiments were conducted in Franz-type diffusion cells at 37 °C, using the model membrane poly(dimethyl siloxane) (PDMS) and 4% bovine serum albumin in phosphate buffer solution (pH 7.4) as the receptor phase. HPCD caused a marked increase in the aqueous solubility of oxybenzone. Data from the phase solubility experiment indicated the formation of 1:1 oxybenzone-cyclodextrin complex. UV transmittance studies indicated that the presence of HPCD did not suppress the UV absorbing properties of oxybenzone. The release and membrane permeation of oxybenzone was significantly reduced in the presence of equimolar, 2 times molar and 1, 2 and 4% of HPCD. It is concluded that HPCD can reduce the release/membrane diffusion of oxybenzone whilst retaining its efficacy as a sunscreen agent. This formulation strategy may be useful in controlling skin penetration of topically applied sunscreens and other chemicals.     

Effect of pH on the Rheology of A1-Mg M iteed Meta1 Hydroxide——Montmorillonite Aqueous Suspension

The effects of the pHs of Mtsuspension(pH_Mt),AMH sol(pH_A)and mixedsuspension(pH_mix)on the rheology of mixed su sp en sion w ere studied.The mixed suspension consisted of the alum in ium magnesium mixed metal hydroxide(AM H) colloidal prt icles which possessed permanent positive charges and the Na-montmorillon ite(M t)particles which po ssessed permanent nega tive charges.The results showed that the pHs did not affect the Bingham yield poin t(YP)of the mixed suspen sionsin the various pHs(i.e.,pH_Mt,pH_A and pH_mix)range of 8—10 almost. When the pH values were above 10 the YPs increased ma rked ly w ith increa sing pH_Mt and pH_mix,but decreased sharply with increasing pH_A.The mechanisms of the effect of pH on the rheology of mixed suspensions were also investigated.     

New Physico-chemical Properties of Water Induced by Mechanical Treatments. A calorimetric study at 25°C

An extensive thermodynamic study has been carried out on aqueous solutions, obtained through the iteration of two processes: a dilution 1:100 in mass and a succussion. The iteration is repeated until extreme dilutions are reached (less than 1⋅10^–5 mol kg^–1 ) to the point that we may call the resulting solution an 'extremely diluted solution'. We conducted a calorimetric study, at 25°C, of the interaction of those solutions with acids or bases. Namely, we measured the heats of mixing of acid or basic solutions with bidistilled water and compared them with the analogous heats of mixing obtained using the 'extremely diluted solutions'. Despite the extreme dilution of the latter solutions, we found a relevant exothermic excess heat of mixing, excess with respects to the corresponding heat of mixing with the untreated solvent. Such an excess has been found in about the totality of measurements, and of a magnitude being well beyond one that could arise any issue of sensibility of the instrumental apparatus. Here we thus show that successive dilutions and succussions can permanently alter the physico-chemical properties of the solvent water. The nature of the phenomena here described still remains unexplained, nevertheless some significant experimental results were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Potentiometric Study of the Association of Copper(II) and Sulfate Ions in Aqueous Solution at 25 °C

A study of the association between copper(II) and sulfate ions in aqueous solution has been made using copper ion-selective electrode potentiometry at constant ionic strengths (I) of 0.05, 0.1, 0.25, 0.5, 1.0, 3.0 and 5.0 mol·L^?1 in NaClO₄ media at 25 °C. Only one complex was detected, corresponding to the equilibrium: \( {\text{Cu}}^{ 2+ } ({\text{aq}}) + {\text{SO}}_{4}^{2 - } ({\text{aq}}) \rightleftarrows {\text{CuSO}}_{4}^{0} ({\text{aq}}). \) No higher order complexes were detected even at sulfate/copper(II) concentration ratios of up to 1,000. The present potentiometric values of log₁₀ K ₁(I) are shown to be consistently higher than those obtained by UV–Vis spectrophotometry because of the failure of the latter technique to detect all of the solvent-separated ion pairs present. Extrapolation of log₁₀ K ₁(I) to infinite dilution using an extended Guggenheim equation yielded a standard state value of log₁₀ \( K_{1} \{ {\text{CuSO}}_{4}^{0} ({\text{aq}})\} = 2.32 \pm 0.09 \) , which is in excellent agreement with a recent IUPAC-recommended value.