Mechanism of interaction of polyethylene polyamides with sulfuric acid in aqueous media

Conclusions Del Re's molecular orbital technique is used to show that in titrating diethylenetriamine against H₂SO₄ in aqueous media the primary amino groups are neturalized first and then the secondary amino groups. The observed amino group titration sequence is determined by the magnitude of the negative charge on the nitrogem atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2639–2640, November, 1968.     

Thermometric and other titrations of sparingly soluble compounds in aqueous micellar media

Several organic acids and bases that are very sparingly soluble in water have been determined by acid-base and redox titrimetry after solubilizing them in micellar suspensions of sodium dodecylsulfate or cetyltrimethylammonium bromide. Thermometric titrations are much more rapid, convenient, accurate, and precise than the corresponding potentiometric ones. Titrations in such media can effect some differentiations that cannot be made in water and are also much more economical than titrations in non-aqueous solvents.     

Studies of a soluble polyethylene glycol immobilized ruthenium catalyst in aqueous media

We have developed an air-stable soluble polyethylene glycol bound ruthenium catalyst which performs efficient ring-closing metathesis in organic solvents as well as in aqueous media.     

Synthesis and characterization of a new dyestuff polymer soluble in alkaline aqueous media

Novel dyestuff polymers were successfully obtained through oxidative polymerization technique. The synthesized Schiff base and its polymer were soluble in alkaline＇aqueous medium and they have various colors in different solutions. Also, it can be said that the synthesized compounds are suitable as coloring agent （dyestuff） for textile applications. Fluorescence properties of the compounds were determined in DMF with different concentrations （mg/L）. Poly-tris（4- aminophenyl）methanol （P-TAPM） has quite high emission and excitation intensity values. Optical and electrochemical band gaps of the polymers were lower than those of the monomers indicating the more conjugated structure of the polymers. The oxidized states of the novel dyestuff compounds were examined by cyclic voltammetry （CV） technique. The solid state conductivity measurements showed that the synthesized polymers were semiconductors when exposed to the iodine vapour their conductivities could be increased. P-TAPM had the highest undoped conductivity. Thermal characterizations of the synthesized compounds were carried out by TG-DTA and DSC methods.     

Enthalpy of dilution of aqueous systems containing S-trioxane and some amides. Analysis of the interaction of saccharides with amides in aqueous media

Enthalpies of dilution of aqueous systems of trioxane+formamide and trioxane+dimethylformamide have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle, and a first estimate of the pairwise group interaction enthalpy for-O-/CONH is presented. Systems of saccharides and amides are not amenable to the Savage-Wood treatment used in recent works. However, when treated in conjunction with all available data to yield a different set of group interaction parameters, saccharides behave more predictably. Implications of this state of affairs are considered.     

Theory of lone pairs. Successive protonations of multi-lone pair bases

While single protonation is always exothermic in the gas phase multiple protonations are shown to be endothermic. The relevance of these results to acid catalysed reactions is discussed.     

Oligosaccharide sensing with chromophore-modified curdlan in aqueous media

A newly synthesized chromophore-modified curdlan functions as a saccharide chemosensor in aqueous solution, enabling us to discriminate tetrasaccharide acarbose from 24 mono-, di-, tri-, and tetrasaccharides.     

Host-guest interactions with hydrophobic cyclophanes in aqueous media

Hydrophobic cyclophanes containing amide nitrogens in a rigid macrocyclic skeleton and flexible hydrocarbon chains, branched out at such nitrogen atoms, were prepared and their substrate-binding behavior was studied in aqueous media. the fluorescence spectroscopy was primarily adopted for the investigation of host-guest interactions by the aid of various hydrophobic probes. These host molecules provide cavities that are deep and hydrophobic enough to incorporate hydrophobic substrates of various bulkiness through an induced-fit mechanism originated from the flexible character of the alkyl branches. In addition to the hydrophobic interaction, the roles of electrostatic and charge-transfer interactions in molecular recognitions were clarified. Much hydrophobic, less polar, and highly viscous binding sites for hydrophobic guest molecules were provided by the octopus azaparacyclophane bearing eight hydrocarbon chains and the tetraazacyclotetradecane-capped azaparacyclophane having four flexible hydrocarbon chains connecting both macrocycles.     

Modification of the thermal unfolding pathways of myoglobin upon drug interaction in different aqueous media

In this work, we have analyzed the influence of two structurally related phenothiazine drugs, promazine and triflupromazine hydrochlorides, when bound to myoglobin, a model protein, and how the drug concentration and solution conditions may affect the denaturation process of this protein. In this manner, we derive the thermodynamic quantities of the unfolding process by using a spectroscopic technique such as UV-vis spectroscopy at different drugs concentrations and at pH 2.5, 5.5, and 9.0. To do this, a thermodynamic model was used which included experimental data corresponding to the pre- and post-transition into the observable transition. It has been found that both drugs play a destabilizing role for the protein, at least at low concentrations. In addition, at acidic pH and higher drug concentrations, a stabilizing effect can be observed, which may be related to the formation of some type of protein refolding, subsequent aggregation, or both. The reason for this behavior has been suggested to be the different protein conformations at acidic pH, the increase of solvent-exposed hydrophobic and hydrophilic residues after denaturation and/or binding, and the different strength of drug-protein interactions when changing the solution conditions. For this reason, thermodynamic quantities such as Gibbs energies, DeltaG, and entropies of unfolding, DeltaS(m), increase as the solution pH increases provided that additional solvent-exposed hydrophobic residues are present, which were previously buried at room temperature. Moreover, the larger binding affinity at pH 9.0 due to enhanced electrostatic interactions between protein and drug molecules (drug and protein differ in their net electrical charge) additionally collaborates to this residue exposition to solvent as a consequence of the alteration of protein conformation as due to drug binding. Comparison of thermodynamic data between promazine and triflupromazine hydrochlorides also shows that drug-protein affinity and hydrophobicity also affect the thermodynamic denaturation parameters.     

Structural, textural and adsorption characteristics of nanosilica mechanochemically activated in different media

The structural, textural, and adsorption characteristics of mechanochemically activated (MCA) fumed silica A-300 as dry or water, ethanol, or water/ethanol-wetted powders (0.5 g of a solvent per gram of silica) in a ball mill for 1-6 h were studied in comparison with those of the initial powder. The MCA treatment enhances bulk density (ρ(b)) of the powder (from 0.045 g/cm(3) for the initial silica to 0.4 g/cm(3) for 6 h-MCA-treated water-wetted silica) depending on medium type and MCA time (t(MCA)). Stronger effects are observed for the MCA treatment of water-wetted silica than of dry or ethanol- or water/ethanol-wetted samples. The MCA treatment weakly affects the specific surface area (S(BET)). However, void (pore) size distribution, porosity, particle aggregation and size distribution in aqueous suspension, behavior of interfacial water, properties of poly(vinyl alcohol)/silica composites and adsorption of gelatin depend more strongly on the t(MCA) and ρ(b) values. Some of the observed changes in the characteristics (e.g., gelatin adsorption) depend on the ρ(b) value but are independent of the medium type used on the MCA. Other characteristics are nonlinear functions of both t(MCA) and ρ(b) values.     

Interaction of cationic surfactants with carboxymethylcellulose in aqueous media

We have examined the polymer-surfactant interaction in mixed solutions of the cationic surfactants, i.e., dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltriphenylphosphonium bromide, and tetradecylpyridinium bromide and a semiflexible anionic polyelectrolyte carboxymethylcellulose in water and aqueous salt solutions by various techniques: tensiometry, viscosimetry or ion-selective electrode method, and dynamic light scattering. We have investigated the effect of varying surfactant chain length, head group size, counterion, and ionic strength on the critical aggregation concentration (CAC) of mixed polymer surfactant systems and the collapse of the polymer molecule under different solution conditions. The CAC decreases with increasing alkyl chain length. Above a certain surfactant concentration, mixed aggregates start growing until their macroscopic phase separation. The growth is more rapid with greater surfactant tail length and with increasing head group size. This is attributed in both cases to the increasing hydrophobic interaction between polymer and surfactant. Among surfactants with monovalent halide counterions, iodide induces the strongest binding, reflected by the onset of growth of the mixed aggregates at low surfactant concentration. This is perhaps related to the decreasing hydration of the counterion from chloride to iodide. The surfactant concentration at which the viscosity of the solution starts to decrease sharply is smaller than the CAC, and probably reflects polymer chain shrinkage due to noncooperative binding.     

Interaction of fibrinogen with nanosilica

Interaction of human plasma fibrinogen (HPF) with fumed nanosilica A-300 in a phosphate buffer solution (PBS) was studied using ¹H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial water in the temperature range of 210–273 K, TSDC (90 < T < 265 K), adsorption, FTIR, and UV spectroscopy methods. An increase in concentration of HPF in the PBS leads to a decrease in amounts of structured water (frozen at T < 273 K) because of coagulation of HPF molecules. Addition of nanosilica to the HPF solution strongly reduces the amounts of structured water because of adsorption interaction of HPF molecules with silica nanoparticles, self-association of HPF molecules, formation of denser packed hybrid agglomerates with HPF and silica, and lastly, because of conformational changes of HPF. A monolayer adsorption capacity of A-300 corresponds to 156 mg of HPF per gram of silica. The FTIR and UV spectra show that the HPF adsorption on silica leads to structural changes of the protein molecules. These changes and formation of hybrid HPF/A-300 aggregates can increase the rate of clotting that is of importance on nanosilica application as a component of tourniquet preparations.      

Synthesis of a self organizable curcumin derivative and investigation of its interaction with metals in 100% aqueous media

We report the synthesis of a self organizable and water dispersible bis PEGylated (bis polyethyleneglycolated) curcumin (1) using an efficient synthetic method. Compound 1 forms nanoparticles on the order of 90 nm in water. Even though it forms nanoparticles, compound 1 interacts strongly with metal ions, Al⁺³, Cu⁺², and Hg⁺². Fluorescence and absorption spectroscopic techniques were employed to investigate the metal interactions of these nanoparticles. Al⁺³ and Cu⁺² ions interact with compound 1 leading to enhancement and dramatic quenching in the fluorescence of the latter in 100% water, respectively. Addition of Hg⁺² ions to compound 1 in water produces a ratiometric change in the absorption spectra of the nanoparticles. Although PEGylated curcumin derivatives were reported in the past, there have been no reports on their self organization into nanoparticles and extensive studies on their metal interaction properties in 100% water using its fluorescence and absorption properties.     

Sulfonic acids as water‐soluble initiators for cationic polymerization in aqueous media with Yb(OTf)3

Aqueous sulfonic acids (HOSO₂R; R = CH₃, Ph‐p‐CH₃, and Ph‐p‐NO₂), coupled with a water‐tolerant Lewis acid, ytterbium triflate [Yb(OTf)₃; OTf =  OSO₂CF₃], initiate the cationic suspension polymerization of p‐methoxystyrene (pMOS) in heterogeneous aqueous media. They induce controlled polymerization of pMOS at 30 °C, and the molecular weights of the polymers (weight‐average molecular weight/number‐average molecular weight ∼ 1.7) increase with conversion. These suspension polymerizations are initiated by the entry of sulfonic acid from the aqueous phase into the organic phase and proceed via reversible activation of the sulfonyl terminus by the Lewis acid. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2728–2733, 2000     

Kinetics and mechanism of interaction of dipeptide (glycyl–glycine) with ninhydrin in aqueous micellar media

The rates of reaction between ninhydrin and dipeptide glycyl–glycine (Gly–Gly) have been determined by studying the reaction spectrophotometrically at 70°C and pH 5.0 in aqueous and in aqueous cationic micelles of cetyltrimethylammonium bromide (CTAB). The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Gly] and [ninhydrin]. The observed rate constant is affected by [CTAB] changes and the maximum rate enhancement is ca. three‐fold. As the k_ψ ? [CTAB] profile shape is characteristic of bimolecular reactions catalyzed by micelles, the catalysis is explained in terms of the pseudo‐phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton and Romsted). The presence of inorganic salts (NaCl, NaBr, Na₂SO₄) does not reveal any regular effect but the data with organic salts (NaBenz, NaSal) show an increase in the rate followed by a decrease. The kinetic data have been used to calculate the micellar binding constants K_S for Gly–Gly and K_N for ninhydrin and the respective values are 317 and 69 mol^?1 dm³. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 643–650, 2006     

Relative basicities of carboxylate lone pairs in aqueous solution

Relative basicities of the lone pairs of the acetate ion have been determined using ab initio calculations for the gas phase and Monte Carlo simulations for the aqueous phase. The syn lone pair is found to be more basic by only 1.25 pK_a units. This small difference is the result of a large intrinsic preference for the syn conformer of the conjugate acid in the gas phase, offset by an almost equally large preferential solvation of the anti conformer in the aqueous phase. The better solvation of the anti conformer is due to stronger solute–solvent interactions. © 1993 John Wiley & Sons, Inc.     

Nonionic latices in aqueous media

Nonionic latices in aqueous media prepared using methoxy polyethylene glycol methacrylate as a comonomer/stabiliser and ascorbic acid/hydrogen peroxide as the initiator have been examined for stability in the presence of the 21 electrolyte, barium chloride. These latices were found to be stable up to the concentrations of barium chloride examined, 0.75 mol dm^–3. Charge stabilised latices, on the other hand, were coagulated in 2.1×10^–2 mol dm^–3 barium chloride. The high stability of the nonionic latices was attributed to the grafting, during polymerisation, of methoxy polyethylene glycol chains to the surface of the core particle of polystyrene. The nonionic latices on concentration to high volume fraction gave highly ordered packing of the particles even in the presence of 0.1 mol dm^–3 sodium chloride.     

Nonionic latices in aqueous media

The rate of conversion of styrene into polystyrene by emulsion polymerisation has been investigated in the absence and in the presence of methoxy-polyethyleneglycol methacrylate, MeOPEGMA. The effect of adding MeOPEGMA at different stages of the polymerisation was also investigated. Additions at the beginning of the polymerisation and at the early stages gave a bimodal particle size distribution whereas late additions gave small particle size, monodisperse latices which were electrosterically stabilised. The latter materials were found to be colloidally stable to the addition of high concentrations of electrolyte and to freeze-thaw conditions.Part 3: Brit. Polymer J., 1987, 19:435