Structure and nature of active sites on the surface of pyrogenic titanosilica

The structure and nature of active sites on the surface of pyrogenic titanosilica (TS) have been studied. The new acidic centers on TS surface occur with formation of titanosiloxane bridges, their formation seemed to be a result of combination of basic structural units of SiO₂ (tetrahedron) and TiO₂ (octahedron).     

Mass spectrometric study of thermal desorption of water from surface of titanosilica

A study has been made of the thermal desorption of water from the surface of titanosilica (TS) obtained by high-temperature hydrolysis (HTH) and low-temperature hydrolysis (LTE), and containing up to 37% TiO₂ by weight. For the samples of TS obtained by either method, only one thermal desorption maximum is observed; the position of the maximum does not depend on the content of the titanium dioxide phase in the TS, but it does depend on the method of preparation: For the LTH, T_max = 480 K; and for the ETH, T_max = 400 K. The shift of the temperature corresponding to the maximum of the H₂O⁺ desorption peak for the TS obtained by HTH may be due to migration of adsorbed water molecules along the surface to sections of titanium-siloxane bonds Si-O-Ti, from which the water molecules are then desorbed.Institute of Surface Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 6, pp. 734–736, November–December, 1991. Original article submitted February 20, 1989.     

Structure and immunogenicity of synthetic antigens

Synthetic antigens are often valuable tools in immunological research. They are usually linear or branched polypeptides, prepared by polymerization of N-carboxy-α-amino acid anhydrides or by polymerization of defined oligopeptides. Owing to their great variability, these simple antigens allow a systematic study of the chemical and physical parameters involved in immunogenicity, i.e. the ability of a substance to initiate an immune response in higher animals. The study of very simple synthetic antigens made possible the first detailed analysis of genetic factors controlling the immunogenicity of a substance. The results have led to a better understanding of many immunological phenomena, and have helped to explain the complex processes initiated by antigens that lead to a specific immune response.     

Dimethyltitanocene-induced surface chemical degradation of synthetic biodegradable polyesters

The purpose of this research was to selectively alter the rate of surface degradation of linear aliphatic polyesters without adversely affecting their bulk properties by way of functional group transformation, where the surface ester linkages would be converted to vinyl ether functionalities with dimethyltitanocene. It has been observed that dimethyl titanocene causes surface degradation of poly (glycolic acid) without adversely affecting its bulk properties, such as M_v, bursting strength, and thermal properties The vinvl ether resulting from the conversion of the PGA ester groups was unstable under ambient conditions, and further reacted by polymer chain scissioning, as was observed from measurements of molecular weight. © 1994 John Wiley & Sons, Inc.     

Morphology and surface heterogeneities in synthetic goethites

In the framework on a study of the acido-basic and sorption properties of iron oxides, a thorough characterization of two types of goethite powders was performed in several laboratories joined in a common project. Chemical analysis by ICPAES; high-resolution SEM, TEM, and AFM observations; XRD with line width analysis; and argon and nitrogen sorption isotherms were used for that purpose. The main crystallographic faces of goethite particles could be identified as {001}, {101}, and {121}, and their abundance correlated with the distribution of low-pressure argon adsorption local isotherms. These results will be very useful for further studies on the relationship between surface reactivity in aqueous solution and orientation of solid surfaces.     

Colloid stability of synthetic titania and the influence of surface roughness

The colloid stability of synthetic titania particles was studied as a function of KCl concentration at pH values of 6.3, 6.7, and 8.4, using static light scattering to obtain stability ratios. Standard DLVO theory was then used to calculate the stability ratios as a function of salt concentration. Reasonable agreement between theory and experiment could only be obtained if an effective interaction radius, corresponding to surface asperities on the titania particles, was used in the calculation. High-resolution TEM images suggest that the effective interaction radius corresponds to the size of surface crystallites formed during synthesis.     

Structure and reaction based evaluation of synthetic accessibility

De novo design systems provide powerful methods to suggest a set of novel structures with high estimated binding affinity. One deficiency of these methods is that some of the suggested structures could be synthesized only with great difficulty. We devised a scoring method that rapidly evaluates synthetic accessibility of structures based on structural complexity, similarity to available starting materials and assessment of strategic bonds where a structure can be decomposed to obtain simpler fragments. These individual components were combined to an overall score of synthetic accessibility by an additive scheme. The weights of the scoring function components were calculated by linear regression analysis based on accessibility scores derived from medicinal chemists. The calculated values for synthetic accessibility agree with the values proposed by chemists to an extent that compares well with how chemists agree with each other.     

Structure of synthetic erionite (zeolite T)

Summary Zeolite T is a synthetic analog of the natural-occurring zeolite-erionite.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1116–1118, June, 1965     

Impact of molecular surface characteristics on the reversed-phase retention behaviour of synthetic dyes

The lipophilicity and specific hydrophobic surface area of 42 synthetic dyes were determined on reversed-phase alumina layers using water-methanol mixtures as eluents, and their relationship with the molecular surface characteristics was elucidated by principal component analysis followed by a two-dimensional nonlinear map and cluster analysis. Four dyes remained on the origin in each eluent system. Except for two dyes, the majority showed regular retention behaviour with their retention decreasing steadily with increasing concentration of methanol in the mobile phase. Calculations indicated that both hydrophobicity parameters decrease with increasing polar surface area of the molecules.     

Structure of association in surface films

Association complexes which from on the polar groups of surface-active compounds during the spreading process on surfaces are described. In the hydration complexes of the interface 1, 2, 4, 9, 16 etc. water molecules surround the hydrophilic group. With the compression of a monolayer spread on water, complexes of higher water contents, out of which the water is pressed, are in thermodynamic equilibrium with the complexes of lower content thus formed.The association equilibrium described apply both to monomear and to polymer compounds, as is shown using the example of polydimethylsiloxane. The principles of the surface structures are discussed with the aid of surface tension, film pressure, space requirement, contact angle and heats of association.     

Dynamic surface elasticity of the mixed solutions of bovine serum albumin and synthetic polyelectrolytes

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Structure and synthetic utility ofβ,β-disubstituted aminoethylenes

Department of Organic Chemistry, Faculty of Chemical Technology, Slovak Technical University, Radlinskeho 9, SK-812 37 Bratislava, Slovakia. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 14, pp. 1385–1387, October, 1995. Original article submitted August 24, 1995.     

Structure of synthetic calcium hydroxyapatite particles modified with pyrophosphoric acid

Synthetic colloidal calcium hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2): CaHap) was treated with pyrophosphoric acid (H(4)P(2)O(7): PP) in acetone and the materials were characterized by XRD, TEM, FTIR, and N(2) and H(2)O adsorption measurements. XRD patterns and morphology of CaHap particles were essentially not changed by the modification. The additional amount of PO(4) of CaHap was increased with an increase of PP concentration and the Ca/P molar ratio of the particles decreased from 1.62 to 0.81. IR results indicated that the isolated surface POH band developed with increasing the PP concentration up to 6.0 mmol dm(-3) by the reaction of isolated surface POH groups of CaHap and pyrophosphoric acids. Above 10.2 mmol dm(-3), a hydrogen-bonding surface POH band appeared at 2913 cm(-1) and enlarged with increasing the PP concentration, while the isolated surface POH band was weakened. The results of N(2) and H(2)O adsorption measurements revealed that the modified particles aggregated compared to the unmodified ones, which would be due to the formation of hydrogen-bonding surface POH groups among the particles.     

Structure of the adiabatic ground-state potential surface for the ozone molecule

Institute for Physical and Organic Chemistry, Rostov University. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 6, pp. 15–20, November–December, 1991.