Temperature-dependent Kinetics on Laser Induced Photolysis of Aqueous CS2-HONO Solutions

Considerable quantities of wastewater effluents containing CS2are produced by industries engaged in the manufacture of artificial leather,viscose,and other synthetic fibers.In addition,CS2also naturally occurs in the condensation of water vapor and its precipitation from the atmosphere in the form of rain,snow or hail.The oxidation of CS2is the subject of a number of studies1-4.Nitrous acid is another pollutant which has been the subject of intensive investigation in recent years.The review…     

Dielectric Relaxation of Methyl Methacrylate and Ethyl Methacrylate on Complexation with Phenols

Dielectric absorption studies of H-bonded complexes of methyl methacrylate (MMA) and ethyl methacrylate (EMA) with p-cresol, p-chlorophenol, 2,4-dichlorophenol, and p-bromophenol were studied at microwave frequency 9.37 GHz in dilute solution of carbon tetrachloride at 308 K. Different dielectric parameters like dielectric constantε′ and dielectric loss ε″ at microwave frequency, static dielectric constant ε_0 and dielectric constant ε_∞ at optical frequency were determined. The validity of the single frequency equation of Higasi et al. for multiple relaxation time τ_(1) was found to be a function of the hydrogen bonding strength of phenolic hydrogen, whereas the group rotation relaxation time τ_(2) was a function of the steric interaction of proton donor. The relaxation time was the maximum at 50∶50 (molar ratio) of methacrylates with phenols.     

Study on Thermosensitive Micellization of Dextran-g-PNIPAAm in Aqueous Solutions

Poly(N-isopropylacrylamide) (PNIPAAm) is a well-known thermosensitive polymer. It shows the lower critical solution temperature (LCST) of about 32℃ in aqueous solution. Many PNIPAAm containing amphiphilic copolymers have been reported. The most frequentl…     

Conversion of Heterocycles of The Dihydrothiazine–Thiazoline Series in Aqueous Solutions

When heterocycles of the dihydrothiazine–thiazoline series are treated with an aqueous solution of base, they undergo ring opening, leading to formation of ureidoalkanethiols. Study of solvolysis of the heterocycles when treated with ammonia permitted us to observe a novel heterocyclic ring opening reaction, occurring with formation of 2(3)-guanidinoalkanethiols. We have developed a novel preparative method for obtaining 2(3)-guanidinoalkanethiols.     

Inclusion Behavior of α-Cyclodextrin with 2-Methylnaphthalene in Aqueous Solutions

By means of absorption and fluorescence spectroscopy, 2-methylnaphthalene (2MN) was found to be incorporated into the cavity of -cyclodextrin (-CD) to form a 1 : 1 inclusion complex. The 1 : 1 inclusion complex further associated with another -CD molecule, resulting in the formation of a 2 : 1 -CD-2MN inclusion complex. The equilibrium constants for the formation of the 1 : 1 and 2 : 1 inclusion complexes were estimated to be 44.6 and 376 mol-1 dm3, respectively, on the basis of a simulation of the observed 2MN fluorescence intensities. The induced circular dichroism spectra suggested that 2MN, buried within the -CD inclusion complexes, resided in a different orientation relative to the CD symmetry axis, as compared to 2MN within a -CD inclusion complex.     

Protonation Constants of Uridine 5′-Monophosphate in Different Aqueous Solutions of Methanol

The protonation equilibria of uridine 5′-monophosphate disodium salt (UMP) was determined in binary solvent mixtures of water–methanol containing 0, 10, 15, 20, 25, 30, 35, 40, 45, and 50 % (v/v) methanol, using a combination of spectrophotometric and potentiometric methods at 25 °C and constant ionic strength (0.1 mol·dm^?3 NaClO₄). The protonation constants were analyzed using Kamlet, Abboud, and Taft parameters. A good linear correlation of the protonation constants (on the logarithmic scale) was obtained. Dual-parameter correlation of log₁₀ K versus π* (dipolarity/polarizability) and α (hydrogen-bond donor acidity), as well as π* and β (hydrogen-bond acceptor basicity), gave good results in various aqueous solutions of methanol. Finally, the results are compared with CMP, a homolog of UMP, and are discussed in terms of the effect of the solvent on the protonation constants.     

Micellization Thermodynamics of Some Imidazolium Ionic Liquids in Aqueous Solutions—Conductometric Study

Conductances of the aqueous solutions of the ionic liquids, ILs, [1-alkyl-3-methylimidazolium chloride [C _n Mim]Cl and [1-alkyl-3-methylimidazolium bromide [C _n Mim]Br (n = 9 and 10) have been measured at 288.15, 293.15, 298.15, 303.15, 308.15 and 313.15 K. Critical micelle concentrations (CMCs) were determined from the conductance data. Concentration dependence of the specific conductance is discussed and the limiting equivalent conductance of the ionic liquids was determined and discussed. To define which temperature range should be investigated for the thermodynamic parameters, the Krafft temperature of each IL was investigated. The ionization degree and the thermodynamic parameters (?G _m ⁰ , ?H _m ⁰ , ?S _m ⁰ ) of the micelle formation were also estimated and discussed. The dependency of the CMC on the length of the alkyl chain of the investigated 1-alkyl-3-methylimidazolium ILs was also studied. It is shown that the CMC is directly related to the lipophilicity of the cation.     

Volumetric Properties of Amino Acids in Aqueous N-methylacetamide Solutions at 298.15 K

The apparent molar volumes (V _φ ) of glycine, L-alanine and L-serine in aqueous 0 to 4 mol⋅kg⁻¹ N-methylacetamide (NMA) solutions have been obtained by density measurement at 298.15 K. The standard partial molar volumes (V_f⁰)V_{\phi}^{0}) and standard partial molar volumes of transfer (D_trV_f⁰)\Delta_{\mathrm{tr}}V_{\phi}^{0}) have been determined for these amino acids. It has been show that hydrophilic-hydrophilic interactions between the charged groups of the amino acids and the –CONH– group of NMA predominate for glycine and L-serine, but for L-alanine the interactions between its side group (–CH₃) and NMA predominate. The –CH₃ group of L-alanine has much more influence on the value of D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0} than that of the –OH group of L-serine. The results have been interpreted in terms of a co-sphere overlap model.     

Enthalpies of Dilution of Cobalt–Amine-Type Salts in Aqueous Solutions at 25°C

The enthalpies of dilution for aqueous solutions of [Co(en)₃]Br₃, [Co(pn)₃]Cl₃, and [Co(tn)₃]Cl₃ (where en = 1,2-diaminoethane, pn = 1,2-diaminopropane, and tn = 1,3-diaminopropane) have been measured at 25°C, and up to m = 1 mol-kg^–1, using an isoperibol calorimeter by the long-jump method. Relative apparent molar enthalpies L have been extracted as an empirical equation relating L and m. Previously reported experimental data and theoretical predictions in the restricted primitive model (RPM) for 3:1 and 1:3 aqueous electrolytes are shown together with the new experimental material.     

Volumetric Properties of Aqueous Solutions of Acetamide in the 274.15–333.15 K Range of Temperatures

Russian Journal of Physical Chemistry A - The densities of aqueous solutions of acetamide up to a mole fraction of x2 = 0.3875 are measured over a wide range of temperatures (274.15–333.15) K...     

Chromato–Mass Spectrometric Identification of Unusual Products of 4-Isopropylphenol Oxidation in Aqueous Solutions

4-Isopropylphenol has been chosen as the simplest object to model the processes of oxidation of organic compounds with air oxygen in aqueous media, since it contains a hydrogen atom at the tertiary carbon atom in the α-position with benzene ring and a hydroxyl group enabling mass-spectrometric detection of the products in the negative ions mode. It has been stated that oxidation of 4-isopropylphenol with air oxygen in aqueous media becomes noticeable as the solution pH approaches the рK_а value of the substrate (10.25). The major product [4-isopropyl-2-(4-isopropylphenoxy)phenol] is formed via nucleophilic addition of the starting 4-isopropylphenol at the intermediate product of its oxidation, quinone methide. Intensity of electrochemical oxidation can be tubed by changing the electrode potential. The highest conversion of 4-isopropylphenol has been observed at potential 1.5–3.0 V, the formed compounds being the products of transformation of the same quinone methide intermediate. The obtained data have explained the formation and diversity of dimeric and oligomeric products of oxidation of natural flavonoids.     

Thermodynamic Studies of Amino Acid–Denaturant Interactions in Aqueous Solutions at 298.15 K

As proteins and other biomolecules consisting of amino acid residues require external additives for their dissolution and recrystallization, it is important to have information about how such additives interact with amino acids. Therefore we have studied the interactions of simple model amino acids with the additives urea and guanidine hydrochloride in aqueous solutions at 298.15 K, using vapor pressure osmometry. During the measurements, the concentration of urea was fixed as ∼2 mol⋅kg⁻¹ and that of guanidine hydrochloride was fixed as ∼1 mol⋅kg⁻¹ whereas the concentrations of amino acids were varied. The experimental water activity data were processed to get the individual activity coefficients of all the three components in the ternary mixture. Further, the activity coefficients were used to get the excess Gibbs energies of solutions and Gibbs energies for transfer of either amino acids from water to aqueous denaturant solutions or denaturant from water to aqueous amino acid solutions. An application of the McMillan-Mayer theory of solutions through virial expansion of transfer Gibbs energies was made to get pair and triplet interaction parameter whose sign and magnitude yielded information about amino acid–denaturant interactions, relative to their interactions with water. The pair interaction parameters have been further used to obtain salting constants and in turn the thermodynamic equilibrium constant values for the amino acid–denaturant mixing process in aqueous solutions at 298.15 K. The results have been explained in terms of hydrophobic hydration, hydrophobic interactions and amino acid–denaturant binding.     

Fluorometric and NMR Studies of the Naproxen–Cyclodextrin Inclusion Complexes in Aqueous Solutions

Inclusion complexation processesinvolving four cyclodextrins and naproxen have beenstudied for the protonated and unprotonated forms ofthe guest molecule. The association constants havebeen evaluated from changes in the fluorescenceintensity of naproxen following addition of acyclodextrin to an aqueous naproxen solution. ¹HNMR NOESY and ROESY spectra have shown that twoorientations of the guest molecule relative to-cyclodextrin are possible.     

Ion–Water Cooperative Interactions in Aqueous Solutions of MgCl2 by Dielectric Spectroscopy

The dielectric constant of aqueous MgCl₂ solution has been determined in the frequency range 0.2 MHz to 20 GHz at 298 K using the dielectric relaxation spectroscopy method. The behavior is well described according to four Cole-Cole terms whose evolution with composition is analyzed. The static dielectric constant and relaxation times decreases with the increasing aqueous MgCl₂ solution concentrations. Only one H-bonded water cluster with the aqueous MgCl₂ solution relaxes is reported during the cutoff relaxation time. A distinct ion–water cooperative interaction is observed, and water molecules perturbed by ion contribution on dielectric constant beyond the first hydration shell are obtained.     

Nonlinear Impedance of Liquid In–Ga Electrode in Aqueous Solutions of a Symmetrical Surface-Inactive Electrolyte

Experimental data related to the potential dependence of nonlinear characteristics of the electrical double layer at a liquid In–Ga electrode in aqueous solutions of a symmetrical surface-inactive electrolyte are obtained for the first time. It is shown that, as opposed to polycrystalline Cd and Pb electrodes, on a liquid (atomically smooth) In–Ga electrode, as on Hg, there is a clear intersection of the potential dependences of a nonlinear signal for different concentrations of a 1–1-valence surface-inactive electrolyte at one point. The intersection point exactly corresponds to the potential of zero charge of an electrode undistorted by specific adsorption of ions. It is established that, when estimating hydrophilicity of metals by a nonlinear impedance method, most information is provided by the region of average negative charges, rather than by the region near zero charge. It is shown that, as opposed to a linear impedance method, the nonlinear impedance method makes it possible to determine, directly from experiment, quantities that directly characterize the metal–solvent chemisorption interaction in a pure form; at the same time, these quantities are criteria of lyophilic nature of metals. Quantities that characterize the metal–solvent chemisorption interaction, obtained by the linear and nonlinear impedance methods are in good agreement, which confirms the validity of the approach we proposed earlier for separating the difference between reciprocal capacitances of the inner part of the electrical double layer on Hg and metal M, ^Hg _M C ^-1 _i= 1/C ^Hg _i– 1/C ^M _iinto physical (^Hg _M C ^–1)_physand chemical constituents. This coincidence also confirms correctness of numerical values obtained earlier for quantities (^Hg _M C ^–1)_phys.     

Thermodynamic Analysis of Homologous α-Amino Acids in Aqueous Potassium Fluoride Solutions at Different Temperatures

Partial molal volumes ( $V_{\phi} ^{0}$ ) and partial molal compressibilities ( $K_{\phi} ^{0}$ ) for glycine, L-alanine, L-valine and L-leucine in aqueous potassium fluoride solutions (0.1 to 0.5?mol?kg^?1) have been measured at T=(303.15,308.15,313.15 and 318.15) K from precise density and ultrasonic speed measurements. Using these data, Hepler coefficients ( $\partial^{2}V_{\phi} ^{0}/\partial T^{2}$ ), transfer volumes ( $\Delta V_{\phi} ^{0}$ ), transfer compressibilities ( $\Delta K_{\phi} ^{0}$ ) and hydration number (n _H) have been calculated. Pair and triplet interaction coefficients have been obtained from the transfer parameters. The values of $V_{\phi} ^{0}$ and $K_{\phi} ^{0}$ vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. The contributions of charged end groups ( $\mathrm{NH}_{3}^{+}$ , COO^?), CH₂ group and other alkyl chains of the amino acids have also been estimated. The results are discussed in terms of the solute?Ccosolute interactions and the dehydration effect of potassium fluoride on the amino acids.     

SEM Morphologies of a Water-Soluble Terpolymer with Vinyl Biphenyl in Aqueous and Brine Solutions

A terpolymer PAAP, synthesized from acrylamide (AM), vinyl biphenyl (VP), and sodium 2-acrylamido-2-methylpropane sulfonate (NaAMPS), exhibits intermolecular hydrophobically associating behavior in water and aqueous brine solutions. A scanning electron microscope (SEM) was used to observe the conformations of polymer chains and morphologies of their associating microstructures in pure water and in brine solutions. This was done to reveal the relevant relationships between solution properties and associated microstructures for the PAAP polymer in pure water and brine solutions, and the mechanisms for the previously reported viscoelastic behavior of PAAP solutions. Continuous supermolecular associating network structures are formed via strong intermolecular hydrophobic association of biphenyl groups in an aqueous 0.1 g⋅dL⁻¹ PAAP solution, which leads to the excellent viscoelastic character of aqueous PAAP solutions. With increasing polymer concentration, the network structures of the polymer become much larger and more compact in aqueous solution, which results in the excellent thickening properties of their solutions. The SEM results reveal that the elongated conformations of molecular chains in aqueous PAAP solutions are favorable for intermolecular hydrophobic association. With the addition of NaCl, the associating network structures of PAAP are destroyed because of electrostatic shielding effects on the –SO₃^-\mathrm{SO}_{3}^{-} groups, and huge tree-like associated structures are formed. This results in a decrease in the solution viscosity and a loss of viscoelastic properties of PAAP solutions. However, with increasing NaCl concentration, the number and size of the aggregates increase, which results in the salt-thickening behavior of PAAP brine solutions.     

β-Strand mimetics: formation of bend-strands in oligomers of enantiomeric β-amino acids

Oligomers comprising of enantiomeric cis-oxo-β-norbornene amino acid [2R,3S] and [2S,3R] residues at alternate positions were synthesized and characterized by extensive NMR and MD studies, which showed robust bend-strand secondary structures.     

The Influence of Temperature on the Heat Effects of Acid—Base Interaction in Aqueous Solutions of Citric Acid

The heat effects of interaction of a solution of citric acid with solutions of HNO₃ and KOH at 288.15, 298.15, and 308.15 K and ionic strength values 0.5, 1.0, and 1.5 (KNO₃) were measured calorimetrically. The heat effects of acid dissociation were calculated using the HEAT program. The standard thermodynamic characteristics of step dissociation of citric acid were determined.