CPS LG 313 Phenylalkanol — adsorbates on silica as types of immobilized drugs 1. Chemiadsorption on activated silica surfaces

The chemiadsorption of phenylalkanols onto a porous silica support (d _pore 10 nm) viaSi-O-C bonds was studied. The silica support was activated prior to the alcohol adsorption by annealing or by the introduction ofSi-Cl groups. Different reaction conditions were applied, namely time, temperature, solvent and drug-support ratio. The yield of chemiadsorption was dependent on both the reaction conditions and the structure of the alcohols. Long alkyl chains, especially those with an alcohol OH-group positioned in the vicinity of bulky substituents, reduce the yield considerably. Using chlorinated silica, a reasonable yield of chemiadsorption can be obtained even at relatively low reaction temperatures.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occassion of his 60th birthday.     

A small-angle neutron scattering study on polydisperse silica spheres coated with polyisobutene

Neutron-scattering studies at small angles are performed on dilute dispersions of small, polydisperse silica spheres coated with polyisobutene in mixtures of h₁₂ and d₁₂-cyclohexane. The contrast variation method is applied to reveal the internal structure of the compound particles. For a detailed interpretation of the scattering curves, it is assumed that the particles consist of spherical silica cores with concentric PIB-layers into which solvent molecules can penetrate. Also the polydispersity of the particle cores is taken into account. Model calculations fit the experimental curves fairly well except for the curves near the matching point, and at higher wavevectors, where experimental errors are relatively large due to the smallness of the scattering of the particles compared to that of the background.     

Functionalization of colloidal silica and silica surfaces via silylation reactions

A series of trialkoxysilane compounds tipped with primary amine groups were used to functionalize the surfaces of glass and colloidal silica. Streaming potential and microelectrophoretic mobility measurements were used to monitor the stability of the functionalized surfaces.Hydrolytic breakdown of the surface-to-silane coupling was induced by either successively increasing and decreasing the pH of the solution in contact with the surface, or by aging the derivatised surfaces in aqueous solution over prolonged periods of time. The chemistry of the spacer units between the trialkoxysilane group and the primary amine tip had a major influence on the subsequent hydrolytic stability. Large hydrophobic spacer groups showed small changes in the electrokinetic properties on storage, but large changes when successively titrated with acid and base through the pH range. The behavior observed with small hydrophobic spacer groups was that large changes in electrokinetic properties were obtained on storage and with pH titration.     

Coagulation kinetics of amorphous colloidal silica suspensions with and without hydroxypropyl cellulose polymer

The coagulation rate constant of submicron silica has been measured as a function of solution pH, salt concentration and hydroxypropyl cellulose (HPC) polymer concentration. Results show that the colloidal stability of silica is dominated by the cation concentration in the presence of salt in the pH range 3–9.5. The stability increases as cation concentration decreases. At low salt concentration and a minimum colloid stability was found in the intermediate pH range 4–8. These results show that differences in the literature values of the critical coagulation constant by relative light-scattering experiments can be explained by the use of the coagulation rate constant analysis. When HPC polymer was present in the solution, the colloid stability of the silica increased. The adsorption of polymer stabilizes the silica suspensions, both at low pH near the isoelectric point and at high ionic strength where it coagulates without the polymer. A monolayer coverage was necessary to provide steric stabilization. At 10^–3 M KCl a smaller equilibrium concentration of HPC in solution is needed to give monolayer coverage and steric stabilization than at 1 M KCl and pH 4.2.     

Formation of the surface charge on silica in mixed solvents

At sufficiently high concentrations of methanol and of alkali salts in aqueous silica dispersions, the negative -potentials of the particles are decreased. This effect is more pronounced with lithium than with other alkali cations, and it is independent on the anion. The NMR spectra indicate lithium adsorption on silica from mixed solvents, but not in the absence of alcohol.Supported by a contract with the XMX Corporation, Burlington, Massachusetts, USA     

Monolayers of neutral and charged polyamino-acids spread on silicic acid substrates

Surface pressure-area isotherms (-A) of poly(L-alanine) (PA), poly(L-glutamic acid) (PG), and poly(L-arginine) (PArg) monolayers spread on substrates of varous pH values containing silicic acid were recorded and compared with those obtained on silica-free substrates. The compression curves of PA showed a pH-independent plateau region which was assumed to correspond to a monolayer to bilayer transition. The inflection observed in the -A curves of PG was attributed to the formation of loops made up of the terminal heads of the polymer and lying under the monolayer. Polysilicic acid interacted with the PArg films at pH 6; such films were more rigid and stable and had larger specific areas than those obtained in the absence of silica, which prompts the occurrence of an ionic interaction. The other two polyamino-acids did not interact with silicic acid at any pH value, so we may rule out the formation of hydrogen bonds between the silanol groups of polysilicic acid and the peptide or carboxyl groups of these amino acids.     

Gas adsorption by a crystalline silicic acid

Crystalline silicic acids are prepared from alkali layer silicates by exchanging protons for the alkali ions. The acid H₂Si₂₀O₄₁ · xH₂O (parent material K₂Si₂₀O₄₁ · xH₂O) exhibits some outstanding gas adsorption properties which are related to the layer structure and the interlamellar microporosity. The external surface, about 20 m² g^–1, is estimated from nitrogen adsorption data after blocking the micropores. Slit-shaped ultramicropores (with diameters similiar to that of the nitrogen molecule) between the layers are widened to supermicropores near the crystal edges. During an adsorption run the nitrogen molecules penetrate more deeply into the ultramicropores. Nitrogen molecules strongly adsorbed in the ultramicropores are not desorbed at 77 K. Additional amounts of nitrogen are adsorbed by widening of the slit-shaped micropores at the crystal edges when pressure increases. This process proceeds slowly and is reversible.     

Infrared and raman studies on the phase structure of barium ethyl(octyl)phosphate-water system

Barium ethyl(alkyl)phosphates, as new simple surfactants ((C₂H₅O)(RO)-PO ₂ ^– )₂Ba²⁺ with various chain length ofR, were synthesized. The infrared spectra in the CH stretching region were measured for these surfactants in the solid state and in aqueous solution, and assignments were made. In particular, the ordering and environment of octyl chains in the different phases of the barium ethyl(octyl)phosphate-water system were studied by the Fourier-transform-infrared and Raman spectra. The CH stretching bands in the infrared spectra reflected the ordering and environment of octyl chains in each phase. The Raman band connected to the PO ₂ ^– symmetric stretching mode was sensitively shifted. This was caused by the change of aggregation structures with different Ba²⁺...PO ₂ ^– interaction. The infrared band arising from the PO ₂ ^– antisymmetric stretching mode was insensitive to the phase structures. The C–C stretching region in the infrared spectra was used to discuss the ordering of each phase.     

Reversible flocculation of silica suspensions by water-soluble polymers

The possibility to concentrate, then redisperse colloidal suspensions is not only of great theoretical interest, but is also relevant to the industrial process of solid-liquid separation, which must often be followed by a redispersion stage. Up to now, these consecutive operations were unrealizable in the presence of polymers, since flocculation and adsorption were generally considered irreversible in this case. Previous studies have pointed out the occurrence of two main flocculation mechanisms: charge neutralization and interparticle bridging. The use of copolymers makes it possible to take into account these two different mechanisms together. Using this fact we prepared new copolymers of acrylamide with N-vinylimidazole via radical polymerization and characterized them by light scattering, viscometry, potentiometric titrations, and UV studies. One peculiarity of the chosen system is its dependence on pH: actually the degree of neutralization of such cationic polyelectrolytes does vary with pH, especially near the pK value. This paper shows that these copolymers may induce reversible flocculation of negatively charged suspensions, e.g., silica suspensions, by simple pH adjustment. Performances of the system were followed by various physico-chemical methods. The observed results are explained in terms of flocculation mechanisms as a function of pH.     

The structure of water and methanol adsorbed on silica gel by FT-NIR spectroscopy

The NIR adsorption spectra were analyzed quantitatively on the fundamental, combination and first overtone region of OH vibrations of silanol groups, water and methanol adsorbed on mesoporous silica gels. Adsorbed methanol constitutes first layer of about 3 molecules/um^–2 and second layer, the structure of which is similar to that of bulk methanol liquid. Adsorbed water consists of a first layer of about 3 molecules/nm^–2, the second layer of about 9 molecules/nm^–2 and the third layer has a structure similar to the that of bulk water. The molecular configuration at the interface is discussed.     

Cholesterol-dipalmitoyl cephalin and cholesterol-dilauroyl cephalin monolayers spread on silicic acid substrates

Mixed cholesterol-dipalmitoyl cephalin and cholesterol-dilauroyl cephalin monolayers are slightly more expanded on silicic acid substrates than on silica-free substrates. Plotting the mean molecular area of the mixed monolayers against the mole fraction of cephalin shows that cholesterol produces condensation of the cephalin monolayer whether or not the substrate contains silicic acid, and the more expanded the pure phospholipid film, the greater is the condensation produced. These phenomena have been tentatively interpreted in terms of hydrophobic interactions between hydrocarbon chains and electrostatic interactions between the horizontally oriented polar groups of the cephalin molecules.     

Spectrophotometric behavior of polyvinylpyrrolidone in aqueous and nonaqueous media (I)

Electronic spectral behavior of polyvinylpyrrolidone solutions in various media has been determined by UV-VIS spectrophotometry. A theoretical approach has been developed to explain the experimentally observed concentration dependent spectral behavior of polyvinyl pyrrolidone in aqueous and nonaqueous solvents. Increase in the concentration of the polymer or the addition of guanidine salts caused bathochromic shift. A similar concentration effect has been observed in nonaqueous media in the absence of guanidine salts.     

Binding of naproxen and 1-anilino-8-naphtalenesulphonic acid to albumin: Characterization of their binding sites in bovine serum albumin

The binding of naproxen (NP) and 1-anilino-8-naphtalenesulphonic acid (ANS) to bovine serum albumin (BSA) has been studied by equilibrium dialysis and spectrophotofluorometry, respectively. The drug protein (D/P) ratio is found to determine the nature of binding sites for NP but not for ANS. At low D/P ratio, NP possesses a specific site in BSA and one of the tryptophan residues is part of it. Fluorometric investigation reveals non-displacement of ANS from its sites by the binding of NP to its specific site. At high D/P ratio, NP instead causes localized conformational changes in BSA. Furthermore, it is possible to infer the location of NP's specific site as loop 4 of BSA. NP and ANS binding sites have also been examined by employing Bromocresol Green (BCG) as a spectrophotometric probe. Competition studies are also able to establish distinct binding pattern for the two ligands in BSA. The displacement pattern points out the presence of independent sites for NP (specific site) and ANS (initially occupied site) in BSA in spite of their amphipathically similar nature.     

Electrically conducting,thermally stable,and mechanically strong CuS-poly(parabanic acid) composite films and their shielding effect of electromagnetic wave

Poly(parabanic acid)-CuS composite film (wt-% of CuS=20–50) prepared by using organosol of CuS (=1500 Å) showed electrical conductivity of 0.1–70 S cm^–1, high thermal stability up to 250°C, high mechanical strength (breaking stress=7.0–12 × 10⁷ Pa), and good shielding effect of electromagnetic wave.     

Characterization of wood fibers modified by phenol-formaldehyde

Wood-fiber phenol-formaldehyde-resin (PFR) modified surfaces, obtained from the adsorption of a PFR/water solution, are investigated as a function of the nature and the amount of PFR adsorbed. Surface are measurements are performed by using krypton adsorption at 77 K. Chemical modification is monitored by the electron spectroscopy for chemical analysis (ESCA) technique and the surface energy by the inverse phase gas chromatography (IPGC) method at infinite dilution. The London dispersive componentγ _S ^L of the surface energy shows a relationship to the concentration of carbon and oxgen at the fiber surface.γ _S ^L increases from 27.5 mN·m⁻¹ for the untreated fiber to 42.5 mN·m⁻¹ for the fibers treated with 20% high molecular-weight-grade phenol-formaldehyde. The surface atomic ratio O/C determined using the ESCA technique exhibits a decrease from 44% for untreated to 31% for treated samples. Surface area also decreases from 2.09 m²/g to 1.50 m²/g. The PFR adsorbed by wood fibers is observed as the dispersive component of surface energy starts to increase, as the surface oxygen concentration decreases, and on the surface area of the wood fiber.     

The effect of carrier solution on the particle size distribution of inorganic colloids measured by steric field-flow fractionation

The number average and the weight average particle diameters for suspended inorganic colloids found by the new technique of steric field-flow fractionation may be successfully used provided that the most suitable carrier solution is selected, in order to minimize the coagulation and adhesion phenomena.In the present work polydisperse, irregular colloidal particles of FePO₄·2H₂O (strengite) were studied. The average particle diameters were found to vary with the electrolyte concentration in the suspending medium. A strong variation of the number and weight average particle diameters was also observed with the quantity of the surfactant added to aquatic medium in order to increase colloidal stability. The influence of the electrokinetic charge of the FePO₄·2H₂O particles in relation to the surface charge of the material of the column employed, on the particle size measured was investigated. The proper carrier solution for minimizing coagulation and adhesion phenomena in the FePO₄·2H₂O colloidal particles was found to contain either 1.5% (v/v) detergent FL-70 and 0.1 MKNO₃ or 0.5% (v/v) detergent FL-70 and 0.033 MNa₂SO₄.     

Determination of the structure factor for concentrated silica dispersions using small angle x-ray scattering. II. Experiment

The structure factor of a number of silica suspensions in cyclohexane, with concentrations ranging from 0.01 to 0.714 gcm^–3, has been determined with small angle x-ray scattering, using a Kratky camera. The experimental structure factor is compared with a theoretical one for which polydispersity effects on the particle scattering factor and on the structure are explicitly taken into account.Analysis of the scattered intensity at a scattering angle=0 shows that the particles in the suspension interact like hard spheres, with a specific hard sphere volume of 0.61 cm³g^–1. A comparison of the experimentally determined structure factor with the structure factor found by a model calculation for a polydisperse system, using the experimental particle size distribution, showed a general agreement. The height of the first maximum agreed well for all concentrations, however its position varied stronger with concentration in the experimental curves. A possible explanation of this effect is given.     

The rheological properties of concentrated cetyltrimethylammonium bromide-salicylic acid solutions in water

Data on the rheological properties of the hexadecyl-trimethylammonium salicylate system (CTAB-SA) in water are reported. Three concentrations were used (0.1, 0.01, and 0.001 M). For the highest concentration, the effect of temperature on the rheology was studied in detail.The rheology of the 0.1 M CTAB-SA solution indicates a very uniform micellar size. By contrast with concentrated polymethyl methycrylate dispersions studied by the author, there was a strong divergence between the viscosity-shear rate and viscosity-frequency data, although the plateau low shear rate and frequency values agreed over a wide range of temperature. This effect could be explained by a shear rate dependent diffusion constant. The large temperature variation of the plateau viscosity and elasticity modulus values could be explained by a combination of micellar number concentration and flexibility changes as the temperature varies.At lower concentrations, the rheological data shows evidence of polydispersity in micellar size. Strong shear thickening and extensional viscosity effects are also evident, probably due to micellar overlap and cluster formation in strong shear fields and the alignment of the very long micelles in elongational flow. The shear thickening effects take some 200 s to relax (0.01 M solution). Recovery of the elasticity after shearing the 0.1 M solution is rapid (a few hundred milliseconds).     

Preparation of composite fine particles by heterocoagulation

To prepare regular composite particles comprised of organic and inorganic compounds, based on heterocoagulation theory, the properties of the mixture of small amphoteric latices (2a=250 nm) and large spherical silica (2a=240–1590 nm) were investigated as a function of pH, particle number ratio, particle size ratio and electrolyte concentration in the medium. It is apparent that under suitable conditions, we may prepare a stable mixed suspension comprising uniform composite particles, which are made up of many latices regularly adsorbed on silica surfaces, and each composite particle is undergoing Brownian motion as an isolated unit. This new composite particle is very stable for electrolyte, base and acid medium, and its surface charges (sign and magnitude) can be controlled by changing the pH of the medium.     

Electrolytic conductivity of poly(1,3-propylene phosphate) solutions containing mono- and divalent-counterions

The results of conductivity measurements for aqueous solutions of poly(1,3-propylene phosphate) (PPP), which can be considered as a synthetic analogue of naturally occurring teichoic acids, are reported. Experiments were carried out with oligomeric fractions of a polymer in acidic, sodium, potassium, magnesium and calcium forms. The concentration and molecular weight dependence of the equivalent conductivity of PPP was analysed and the limiting equivalent conductivity determined. From the conductivity data, the polyion-counterion interaction parameter F and the equivalent conductivity of a polyion _p were calculated. It was shown that both F and _p depend on polyelectrolyte solution concentration and molecular weight of PPP. Conclusions concerning mono- and divalent metal ions binding to PPP are drawn.