Acidic and basic properties of the surface of gas-chromatographic sorbents with grafted metal chelate layers

The acidic and basic properties of the surface of gas-chromatographic sorbents based on silica gels with grafted layers of nickel acetylacetonate and nickel-malonic and acetoacetic esters were studied by pH measurements and the Hammett indicators adsorption method. The acidic and basic state of the surface was shown to depend on the ligand of the modifying addition, the structure of the complex, and the structural and sorption properties of the silica gels used.     

Synthesis and investigation of chemically modified silicas with the island structure of the grafted layer

Island structures on the chemically modified surface of silica are synthesized by the method of matrix prints. Dichlorosilicon phthalocyanine and copper naphthalocyanine were used as molecular templates. Two types of heterogeneous surfaces are prepared by this method: the islands of nonmodified silica on the trimethylsilylated silica (the first type) and the islands of aminopropyl silica on the esteric groups grafted on silica (the second type). The structure of the surfaces prepared is studied by ESR spectroscopy with the use of paramagnetic probes.     

Synthesis of tri- and tetracyclosiloxanes with functional groups attached to the silicon atoms

Russian Chemical Bulletin -     

A thermodynamic study on the interaction of nickel ion with myelin basic protein by isothermal titration calorimetry

The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent nickel ion was studied by isothermal titration calorimetry at 37 and 47 °C in Tris buffer solution at pH = 7. The new solvation model was used to reproduce the heats of MBP + Ni²⁺ interaction over the whole Ni²⁺ concentrations. It was found that MBP has three identical and independent binding sites for Ni²⁺ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 89.953 μM, −14.403 kJ mol⁻¹ and 106.978 μM, −14.026 kJ mol⁻¹ at 37 and 47 °C, respectively. The binding parameters recovered from the new solvation model were correlated to the structural changes of MBP due to its interaction with nickel ion interaction. It was found that in the low and high concentrations of the nickel ions, the MBP structure was destabilized.     

Reducing the bias and uncertainty of free energy estimates by using regression to fit thermodynamic integration data

This report presents the application of polynomial regression for estimating free energy differences using thermodynamic integration data, i.e., slope of free energy with respect to the switching variable λ. We employ linear regression to construct a polynomial that optimally fits the thermodynamic integration data, and thus reduces the bias and uncertainty of the resulting free energy estimate. Two test systems with analytical solutions were used to verify the accuracy and precision of the approach. Our results suggest that use of regression with high degree of polynomials provides the most accurate free energy difference estimates, but often with slightly larger uncertainty, compared to commonly used quadrature techniques. High degree polynomials possess the flexibility to closely fit the thermodynamic integration data but are often sensitive to small changes in the data points. Thus, we also used Chebyshev nodes to guide in the selection of nonequidistant λ values for use in thermodynamic integration. We conclude that polynomial regression with nonequidistant λ values delivers the most accurate and precise free energy estimates for thermodynamic integration data for the systems considered here. Software and documentation is available at http://www.phys.uidaho.edu/ytreberg/software . © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Spectrofluorimetric determination of surface-bound thiol groups and its application to the analysis of thiol-modified silicas

A sensitive spectofluorimetric method has been developed for the quantitative measurement of surface-bound thiol groups. The procedure is based on the quantitative esterification of the thiol group with Rhodamine B and its subsequent release from the solid by base hydrolysis for spectrofluorimetric determination. Application of the method to the analysis of thiol-modified nanoparticulate silicas yielded results that compared favourably against alternative approaches based on measurements of mercury capacity and iodometric titration of the thiol groups. Non-specific Rhodamine uptake, assessed using unmodified silica and C18-modified silica, did not significantly influence the analytical results. When applied to a typical 50 mg sample, the detection limit of the procedure was 1 nmole SH g(-1) silica.     

Path-dependency of the interaction between coaggregating and between non-coaggregating oral bacterial pairs--a thermodynamic approach

Coaggregation, i.e. specific recognition between bacteria from different species, is a well-described phenomenon in the human oral cavity but remains physically poorly understood. With our study we aimed at elucidating some aspects of the mechanism of the coaggregation between the oral bacteria Streptococcus oralis J22 and Actinomyces naeslundii 147, in particular with respect to the driving force for coaggregation and its pathway-dependency. To that end, the macroscopic turbidity of the bacterial suspension, the morphology of the coaggregates, binding isotherms and heats of interaction were compared between the above-mentioned coaggregating bacterial pair and a non-coaggregating pair, Streptococcus sanguis PK1889 and A. naeslundii 147. The coaggregating pair forms large aggregates, which rapidly sediment from the suspension while the non-coaggregating pair forms only very small coaggregates that remain homogeneously suspended. Coaggregation is further characterized by a high affinity between the partner cells that bind to each other in a strong cooperative mode. The interactions between both pairs occur under the release of heat and are thus enthalpically favorable. More heat is released for the coaggregating than for the non-coaggregating pair. Adding the coaggregating bacteria in steps to each other leads to saturation of enthalpically favorable binding sites. This is observed when the streptococcus is added to the actinomyces as well as when the addition is done the other way around. It is concluded that the cooperativity of the coaggregation process is based on an increase of entropy. It is furthermore shown that the density of the coaggregates as well as the heat effect of formation of these coaggregates depend on the number of steps in which the partner cells are added to each other. Adding S. oralis J22 in three steps to A. naeslundii 147 results in the formation of denser coaggregates under the release of less heat, as compared to that of addition in one step. These differences point to a larger entropy increase when in a step-wise mixing the coaggregating bacteria are allowed to form more densely-packed coaggregates.     

A data mining and ab initio study of the interaction between the aromatic and backbone amide groups in proteins

Interactions between aromatic groups and backbone amide groups in protein environments are characterized both through data mining analyses of X‐ray protein structures and through ab initio molecular orbital calculations on a model complex. The data mining analyses of 1029 X‐ray protein structures elucidate the configurational characteristics of the interaction as well as the positions of the interacting moieties involved. On a statistical average, more than seven such interactions occur in a typical protein structure. The configurations of these interactions are restricted with the face‐to‐face orientation as the preferred arrangement. The interaction occurs mainly within a single peptide chain. Both α‐helix and β‐strand secondary structures provide an almost equal number of backbone amides to participate within this interaction. The interaction energy was evaluated with the supermolecular ab initio method at the MP2 level. It is shown that aromatic–amide(backbone) interactions identified in proteins can achieve a stabilization energy of 3.3 kcal/mol. The interaction involves the entirety of the backbone amide rather than only its amine portion. This study concludes that the interaction between aromatic and backbone amide groups is of general significance to protein structure due to its strength and common occurrence. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 44–60, 2000     

Determination of thermodynamic parameters for the interaction of a lipid-binding peptide and insulin with a reversed-phase column

The effect of temperature was investigated on the reversed-phase chromatography of a synthetic lipid associating peptide (LAP), with the following sequence (LESFLKSWLSALEQALKA) and on insulin. The LAP was chromatographed on a muBondapak-alkylphenyl column with 1% aq. triethylammonium phosphate, pH 3.2-2-propanol (80:20) as the isocratic mobile phase. The insulin was separated on a Resolve-C18 column with a mobile phase that contained 0.1 M sodium phosphate, pH 2.0-acetonitrile (71.5:28.5). With the LAP the Van't Hoff plot (In k' vs. 1000/T) was linear and the value of enthalpy for association of the peptide with the reversed-phase column was large and negative. The phase ratio was estimated for the column used in the separation and then derivation of the corresponding entropic term demonstrated that the association was enthalpy and not entropy drive. By contrast the corresponding Van't Hoff plot derived or the insulin study was non-linear and with a positive slope. Further study indicated that the formation of the insulin-reversed phase complex could be attributed to a favorable entropy change. It is probable that the non-classical thermodynamics observed during the insulin chromatography could be related to conformational changes in the insulin structure during the chromatographic process.     

Rate and thermodynamic studies of the interaction between water and iso-butyl cellosolve by ultrasonic methods

Ultrasonic absorption and velocity measurements in aqueous solution of iso-butyl cellosolve (ethylene glycol iso-butyl ether) as a function of the concentration are reported. The two relaxational absorptions have been attributed to the perturbation of the equilibria expressed by AB?A+B and Aα(1/n)A_n where A is the solute, B is the solvent, AB is the complex and A _n is the solute aggregate. The rate constants for each step have been determined. From the concentration dependence of the maximum excess absorption per wave length, the enthalpy change and the volume change for the reaction between the solute and the solvent have been determined for aqueous solutions of butyl cellosolve (ethylene glycol n-butyl ether), iso-butyl cellosolve and propyl cellosolve (ethylene glycol n-propyl ether). The results are consistent with a hydrogen bonding reaction. The effect of the ethers on water structure are considered and it is clear that the fraction of water molecules which can hydrogen bond to the solute decreases with the increasing hydrophobicity of the solute.     

The mechanism of interaction between molybdogermanic acid and the basic dye Crystal Violet

On the basis of light-absorption studies on solutions of Crystal Violet (CV) molybdogermanate in acetone, the optimal pH conditions for quantitative formation of molybdogermanic acid (MGA) have been determined. Di, tri-, and tetra-salts of MGA have been formed and isolated. It has been shown that formation of the higher salts is favoured by lowering the acidity, but this increases also the amount of the solid co-product CV—isopolymolybdate. To overcome this inconvenience the surplus molybdate ions are masked by adding oxalate ions, thus allowing the separation of the corresponding solid tetra-salt up to pH = 6.5; the molar absorptivity of this compound in acetone solution is very high (4.2 × 10⁵ 1.mole⁻¹.cm⁻¹).     

Synthesis and photochromic properties of indolinospirochromenes with benzyl,ethyl, and acetonyl groups attached to the nitrogen atom

A number of photochromic indoline spirochromenes with benzyl, acetonyl, and ethyl substituents attached to the nitrogen atom in the indoline part of the molecule were synthesized. The introduction of a benzyl group at the nitrogen atom in place of a methyl group does not change the rate constants of the dark decolorization of the photomerocyanines, whereas an acetonyl group increases them, and an ethyl group decreases them. The introduction of the indicated substituents in the 1 position gives rise to a bathochromic shift (up to 18 nm) of the long-wave absorption band of the merocyanine form of the spirochromene.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1363–1366, October, 1982.     

Studies on the energy transfer system of terbium-norfloxacin chelate and its interaction with serum albumins

The energy absorbed by norfloxacin could be transferred to terbium(Ⅲ) through chela-tion of norfloxacin with terbium(Ⅲ),then the characteristic fluorescence emission could be observed.The interaction of serum albumins with norfloxacin have been investigated in this paper.The results showed that HSA could inhibit the energy transfer between norfloxacin and terbium(Ⅲ).But,BSA could not.It was shown that the binding properties of norfloxacin to HSA and BSA were totally different.     

Anionic polymerization of caprolactam—LII. Effect of reaction conditions on the content of acidic and basic groups in the polymer

The concentration of acidic groups in water-extracted polymers at rather short reaction times and temperatures of about 200° is predominantly determined by the initial concentration of activator; at higher temperatures and long reaction times, the concentration of acidic groups depends in the first place on the initial concentration of sodium caprolactam as initiator. The acidic groups are not composed of carboxylic groups only; some of the groups are due to the hydrolysis of labile structures during extraction of the polymer with boiling water. While the concentration of acidic groups in the polymer approximately attains the initial concentration of sodium caprolactam, the concentration of basic groups in the polymer may exceed this value several times. The rate of formation of basic groups is proportional to the instantaneous concentration of the strong base.     

Single-step preparation and catalytic activity of mesoporous MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups analogous to Nafion

Preparation of hybrid organic-inorganic MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups has been achieved in a single step by reacting the mesoporous silicas with 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethane sulfonic acid beta-sultone; the catalysts showed higher activity than commercial Nafion-silica composite for the esterification of long chain fatty acids with ethanol.