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.      

Effects of dissolved metal chlorides on the behavior of silica nanoparticles in aqueous media

Effects of chlorides of univalent (LiCl, NaCl, KCl), bivalent (MgCl₂, BaCl₂) and trivalent (AlCl₃) metals at different concentration (0.001–0.1 M) on the behavior of nanosilica A-200 (0.5–5 wt.%) in aqueous media are analyzed using photon correlation spectroscopy (particle size distribution, PSD), electrophoresis (zeta potential ζ), potentiometric titration (surface charge density), and estimation of screening length of primary particles and their aggregates. The zeta potential and the PSD are affected by silica content, pH, and concentration and type of dissolved salts. Smaller but more strongly hydrated Li⁺ cations caused stronger nonlinear dependences of the zeta potential on pH and salt content than Na⁺ or K⁺. This nonlinearity is much stronger at a lower content of silica (0.5–1 wt.%) than at C _A-200 = 2.5 or 5 wt.%. At a high concentration of nanosilica (5 wt.%) the effect of K⁺ ions causes stronger diminution of the negative value of the zeta potential due to better adsorption of larger cations. Therefore, the influence of K⁺ on increasing screening length is stronger than that of Na⁺ for both primary nanoparticles and their aggregates. A similar difference in the ζ values is observed for different in size cations Ba²⁺ and Mg²⁺.      

Application of solid-state NMR (13C and 29Si CP/MAS NMR) spectroscopy to the characterization of alkenyltrialkoxysilane and trialkoxysilyl-terminated polyisoprene grafting onto silica microparticles

The solid-state Nuclear Magnetic Resonance (NMR) was used to characterize surfaces of silica gels chemically modified by alkenyltrialkoxysilanes and trialkoxysilyl terminated 1,4-polyisoprenes. The formation of covalent bonds created between alkoxy functional groups from alkenyltrialkoxysilane or trialkoxysilyl-terminated 1,4-polyisoprene and silanol groups on silica was clearly demonstrated by means of ¹³C and ²⁹Si CP/MAS NMR spectroscopy. Quantitative data, including calculation of the grafting yields in relation with the initial silanol concentrations, were also obtained by using solid-state ²⁹Si-NMR leading to a final well-defined characterization of the silica surfaces. A relatively good agreement was noticed between the grafting yields calculated from ²⁹Si-NMR spectra and those determined from other analytical techniques such as Wijs titration or elementary analysis. The reactivity of the various silica silanols towards each coupling agent was clearly characterized and estimated, as were the proportions of the various grafted structures formed at the silica surface. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 437–453, 1998     

NMR measurement of the surface dynamics of poly(dimethylsiloxane) adsorbed on silica gel

CPMAS-DD ¹³C NMR spectroscopy was used to examine the mobility of poly(dimethylsiloxane) adsorbed on silica gel (PDMS/SiO₂) at submonolayer coverages. The spin-lattice relaxation time in the rotating frame (T_1ρH) decreased linearly with increasing loading. This is consistent with a decrease in the mobility of the polymer segments as the loading is increased. The decrease in mobility results from interpolymer interference. We propose a model that explains these results in terms of a surface intrinsic viscosity that incorporates the polymer-polymer interactions on the surface.     

Analysis of silica hydride and surface hydrosilation reactions by solid-state NMR in the preparation of<Emphasis Type="Italic"> p</Emphasis>-chlorobenzamide bonded silica phase

²⁹Si and ¹³C CP-MAS NMR spectroscopy was used to follow the conversion of native silica to a p-chlorobenzamide bonded silica material. The benzamide bonded phase was prepared via a hydrosilation reaction of a hydride silica intermediate with p-chloro-N-allylbenzamide. Solid-state NMR was used to show the disappearance of reactive surface hydride species (M_H) and to identify newly formed bonded chemical species on the silica surface. DRIFT spectroscopy, elemental analysis, and specific surface-area determinations (BET) of the prepared phases are also reported.     

Building block approach to organic/silica hybrid materials

The reaction of the cubic octameric silicate anion, Si₈O ₂₀ ^8– , with dimethyldichlorosilane in 2,2-dimethoxypropane yielded solid products. FT-IR and solid-state ²⁹Si NMR spectra of the products indicate that the silicate anion becomes cross-linked via the dimethylsilyl group without degradation of the cubic core, resulting in the formation of organic/silica hybrids consisting of the Si₈O ₂₀ ^8– structure as a building block. The hybrids are thermally stable up to ca. 380°C in air. The specific surface area of the hybrids is 31 m² g^–1, while the value increases to 339 m² g^–1 after calcination at 350°C in air. The process of increasing the surface area of the hybrids by the heat-treatment was investigated using solid-state ¹³C NMR spectroscopy.     

Thermodynamic properties affect the molecular motion of novolac type phenolic resin blended with polyamide

The effect of association reaction length on the substantial increase of molecular motion as well as entropy (−TΔS_m) of phenolic-polyamide blends is investigated with the ¹³C solid-state NMR and DSC. The H-bonding strength by forming the phenolic-polyamide interaction is great enough to overcome the breaking off the self-association of phenolic. With respect to decreasing the association reaction, the polyamide resonance intensity of ¹³C solid-state NMR spectra is weakened due to the reduction of the cross-polarization efficiency at a high mobile sample. The glass transition temperature of phenolic-polyamide blend as well as T^H_1ρ value from NMR experiments is also decreased. The decreasing strength of H-bonding resulting from blending causes higher entropy (−TΔS_m) and higher molecular mobility of the phenolic-polyamide blends. Accordingly, the polyamide-66 possesses higher H-bonding force and exhibits more mobile role in this phenolic/polyamide blends family. It can be concluded that the molecular segmental motion and entropy are progressively decreased while increasing the inter-association force of the polyamide within the miscible window.     

Interfacial phenomena in starch/fumed silica at varied hydration levels

Hydrated powders of non-gelatinised starch and hydrogels of gelatinised starch alone or with addition of modified nanosilica (with grafted aminopropylmethylsilyl groups substituting one-third of surface silanols) were studied using broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarisation current (TSDC) method and ¹H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial waters. The ¹H NMR and TSDC techniques with the use of Gibbs–Thomson relation for the freezing point depression allow us to calculate: (i) the thermodynamic parameters of interfacial water weakly and strongly bound to polymer molecules and nanoparticles; (ii) size distributions of pores filled by structured water; (iii) surface area and volume of micro-, meso- and macropores. The DRS and TSDC results for hydrogels and hydrated powders with starch/modified fumed silica show that the β- and γ-relaxations of starch are strongly affected by water and functionalised silica nanoparticles which slow down both low- and high-frequency and low- and high-temperature relaxations.     

Fast and Selective Aqueous-Phase Oxidation of Styrene to Acetophenone Using a Mesoporous Janus-Type Palladium Catalyst

A heterogeneous Janus-type palladium interphase catalyst was obtained by selective surface modification of a hollow mesoporous silica material. The catalyst comprises hydrophobic octyl groups on one side of the silica nanosheets and single-site bis-imidazoline dichlorido palladium(II) complexes on the other. The structure of this composite material has been analyzed by means of elemental analysis, atomic absorption spectroscopy, BET surface analysis, TGA, SEM and solid-state CP-MAS ¹³C and ²⁹Si NMR spectroscopy. The catalyst showed extraordinary activity for the aqueous-phase oxidation of styrene to acetophenone using 30% hydrogen peroxide as the oxidant. An 88% yield of acetophenone could be achieved after 60 min.     

Polysiloxane-Modified Mesoporous Materials

We report the preparation of polysiloxane-modified mesoporous silica gels derived from the acid catalysed hydrolysis of tetraethoxysilane (TEOS) and oligomeric silanol terminated polydimethylsiloxane (PDMS) in the presence of the non-ionic surfactant, octaethylene glycol monohexadecyl ether. The gels were characterised using thermal gravimetric analysis (TGA), infra-red (IR) spectroscopy, X-ray diffraction (XRD) and ²⁹Si solid state cross-polarisation (CP) magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. TGA and IR spectroscopy showed the loss of surfactant after calcination and a decrease in the Si–OH band at 950 cm^–1 indicated further condensation had occurred. This was confirmed by the increase in Q⁴ at –110 ppm, in ²⁹Si MAS NMR spectroscopy, which also showed that calcination had led to the redistribution of PDMS forming a T species. XRD data showed ordering within the structure, with an initial d-spacing of 45 Å, decreasing to 35 Å after calcination.     

Investigation on the effect of nanosilica towards corn starch–lithium perchlorate-based polymer electrolytes

Biodegradable corn starch–lithium perchlorate (LiClO₄)-based solid polymer electrolytes with addition of nano-sized fumed silica (SiO₂) were prepared by solution casting technique. Ionic conductivity at ambient temperature was measured by AC impedance spectroscopy. Upon addition of nano-sized SiO₂, the ionic conductivity at room temperature is increased. The optimum ionic conductivity value obtained was 1.23?×?10^?4?S?cm^?1 at 4?wt% SiO₂. This may be attributed to the low crystallinity of the polymer electrolytes resulting from the dispersed nanosilica particles. Fourier–transform infrared spectroscopy studies confirmed the complexation between corn starch, lithium perchlorate, and silica. The thermal properties of the prepared samples were investigated with differential scanning calorimetry and thermogravimetric analysis. The surface morphology of the polymer electrolytes confirmed the agglomeration of particles after excess dispersion of inorganic filler. This was proven in the scanning electron microscopy studies.     

Surface Energy of Silica-TEOS-PDMS Ormosils

Inverse gas chromatography (IGC) was applied to characterize the surface energy of organically modified silicates (ormosils) by measuring the interaction of molecular organic probes with the ormosil surface. Ormosils were prepared by the sol-gel method by the reaction of TEOS (tetraethoxysilane), PDMS (polydimethylsiloxane) and different types of silica (Aerosil 130, Aerosil 200 and Aerosil 380). The isosteric heat of adsorption, q _st, and the dispersive component of the surface energy, _s ^D, were estimated by using the retention volume of different nonpolar and polar probes at infinite dilution. The dispersive component shows an increase as the specific surface area of the silica is increased from 29.6 mJ/m² to 51.4 mJ/m² at 60°C. Such values are lower than that obtained for aerosil particles meaning that PDMS chains impede the interaction with silanol groups located on the silica surface. The specific interaction parameter, I^SP, and the enthalpy of specific adsorption, H _a ^SP, of polar probes on the ormosil surface were also measured in order to obtain the acid-base character of ormosil surface. The H _a ^SP, was correlated with the donor, DN, and the acceptor, AN, numbers of the probes to quantify the acidic, K _A, and the basic, K _B, parameters of the substrate surface. The obtained results suggest that the silica particles were covered by PDMS chains in a different way depending on the type of silica used. The values of K _A and K _B suggest that the ormosil surface is amphoteric, with predominantly acceptor electron sites.     

Pentacyanoferrates(II) on the surface of organomodified silica gel: The matrix effect

Pentacyanoferrate(II) absorbed on a silica gel surface previously modified with 3-aminopropyl and 3-imidazolylpropyl groups were characterized by¹³C MAS/NMR, FT-IR, Mössbauer spectroscopy, and cyclic voltammetry. FT-IR and¹³C MAS/NMR data indicated that the pentacyanoferrate(II) complex is bonded to the surface by the nitrogen atom of the functional group. The differences in the isomeric shifts, the quandrupole splittings and the midpoint potentials of the adsorbed complexes in comparison with the model complexes were attributed to the matrix polar effect—i.e., the interaction of the complex with polar groups on the silica surface.     

Effect of reaction conditions on surface properties of TEOS–TBOT–PDMS hybrid materials

Hybrid materials based on tetraethoxysilane (TEOS), tetrabutyl orthotitanate (TBOT), and hydroxyl terminated polydimethyl siloxane (PDMS) have been prepared and characterized. The effects of HCl concentration and PDMS molecular weight (M_W) have been analysed. The physical and chemical characteristics have been discussed based on the results obtained from the characterization by Raman spectroscopy, nitrogen adsorption, mercury intrusion porosimetry and inverse gas chromatography (IGC). Specific surface areas (SSA) and pore volumes increase with HCl concentration and are independent on the PDMS Mw. SSA values as high as 300 m² g⁻¹ have been obtained for hybrid materials prepared with HCl:(TEOS + TBOT) concentration of 0.3 and PDMS Mw of 550 g mol⁻¹. These materials present the higher pore volumes and lower pore sizes. However, for HCl:(TEOS + TBOT) concentration of 0.5, only macroporous materials are obtained with SSA values as low as 2–4 m² g⁻¹, and pore sizes close to 10 μm. In general the presence of Ti on the SSA and porosities give a little decrease in such values. Surface energies are consistent with those of organic–inorganic materials. Dispersive surface energies are higher for the Si–Ti hybrid materials and, for all of them, they decrease with both HCl concentration and PDMS Mw. This result can be assigned to the presence of a higher concentration of PDMS (or CH₃ groups) on the surface of the hybrid material as well as the presence of disordered anatase-like structures. On the other hand, the acid and base properties are dependent on both HCl concentration and PDMS Mw. It has been observed that the acid and base parameters of the Si–Ti hybrid materials are influenced by the disorder degree of the amorphous titanium oxide present in them. As the disorder decrease both acid and base parameters increase.     

Evaluation of microstructural features of a new polymeric organic stationary phase grafted on silica surface: A paradigm of characterization of HPLC-stationary phases by a combination of suspension-state H NMR and solid-state C-CP/MAS-NMR

Silica-supported poly(octadecylacrylate) (Sil-ODA_n), polymeric octadecylsilyl silica (polymeric ODS), and monomeric octadecylsilyl silica (monomeric ODS) were studied by a combination of suspension-state ¹H NMR and solid-state ¹³C CP/MAS-NMR to probe the mechanisms underlying their functions as stationary phases for RP-HPLC. Sil-ODA_n, with a strong temperature dependent separation behaviour showed correspondent temperature dependent manifestations in both suspension-state ¹H NMR and solid-state ¹³C CP/MAS-NMR experiments. With a gradual increase in temperature, intensity of proton signals (¹H NMR) of octadecyl moieties (mainly methylene groups) rose dramatically. This dramatic rise was at the same temperature of an endothermic peak detectable in its DSC thermogram indicating a relatively complete solid to liquid phase transition. In addition temperature dependencies of the ratio of trans to gauche conformed well to temperature dependencies of the separation factor between naphthacene and triphenylene (as a simple indicator of shape selectivity). Therefore NMR spectra of Sil-ODA_n were used as a reference for ascertaining percentage of octadecyl moieties of liquid type mobility in the two other stationary phases. Using this method we determined percentage of liquid phase in polymeric ODS and monomeric ODS at various temperatures. We suggest a combination of suspension-state ¹H NMR and solid-state ¹³C CP/MAS-NMR for structure-dynamic characterization of various kinds of hydrocarbon chains grafted onto the silica particles.     

Structural Insights into Peptides Bound to the Surface of Silica Nanopores

The structure and surface functionalization of biologically relevant silica-based hybrid materials was investigated by 2D solid-state NMR techniques combined with dynamic nuclear polarization (DNP). This approach was applied to a model system of mesoporous silica, which was modified through in-pore grafting of small peptides by solid-phase peptide synthesis (SPPS). To prove the covalent binding of the peptides on the surface, DNP-enhanced solid-state NMR was used for the detection of ¹⁵N NMR signals in natural abundance. DNP-enhanced heterocorrelation experiments with frequency switched Lee–Goldburg homonuclear proton decoupling (¹H–¹³C and ¹H–¹⁵N CP MAS FSLG HETCOR) were performed to verify the primary structure and configuration of the synthesized peptides. ¹H FSLG spectra and ¹H-²⁹Si FSLG HETCOR correlation spectra were recorded to investigate the orientation of the amino acid residues with respect to the silica surface. The combination of these NMR techniques provides detailed insights into the structure of amino acid functionalized hybrid compounds and allows for the understanding for each synthesis step during the in-pore SPPS.     

Thermal Destruction of Polydimethyl-Siloxane on a Phosphorus-containing Silica Surface

Thermogravimetry, differential thermal analysis, and IR spectroscopy were used to investigate the process of thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air. The disperse adsorbents were pristine fumed silica and modified fumed silica whose surface contained oxygen compounds of phosphorus. It was shown that under the given experimental conditions the thermal destruction of PDMS on the fumed silica surface was accompanied by the complete transformation of the adsorbed PDMS to SiO₂. In the case of phosphorus-containing silica, the thermal destruction proceeded in a different way. It was found that at 140–300°C depolymerization of the siloxane chains of a certain part of the adsorbed polymer took place with the concurrent removal of volatile products of the reaction. However, the remaining part of the adsorbed PDMS interacted with the modified silica surface to form chemisorbed dimethylsilyl structures. The thermal destruction of the chemisorbed fragments of PDMS in air was initiated at 400°C or above for both types of silica investigated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Contact-angle,ellipsometric, and spin-diffusion solid-state nuclear magnetic resonance spectroscopic investigations of copolymeric stationary phases immobilized on SiO<Subscript>2</Subscript> surfaces

SiO₂ surfaces—silica gel particles and silica wafers—were modified by covalently immobilizing three poly(ethylene-co-acrylic acid) copolymers, (–CH₂CH₂–)_x[CH₂CH/(CO₂H)–]_y, with different chain lengths and mass fractions of acrylic acid. ¹³C solid-state NMR spectroscopy on the modified silica gel particles revealed both mobile gauche and rigid trans aligned alkyl chains in the copolymers. For copolymers attached to silica wafers via a 3-aminopropyltriethoxysilane spacer molecule, ellipsometric measurements revealed a mean value of the layer thickness distribution of 6.5 and 4.3 nm, respectively, for the more acidic and the shorter copolymers with mobile alkyl chains mostly in the gauche conformation. For the longest and least acidic copolymer with more rigid trans ordered alkyl chains, however, a mean phase thickness of 10.6 nm was found. When this copolymer was immobilized via a 3-glycidoxypropyltrimethoxysilane spacer molecule we measured a mean layer thickness of 9.9 nm. A model of the surface morphology of this immobilization strategy was derived using spin-diffusion ¹³C NMR measurements on the corresponding modified silica. It was thereby proven that the trans and gauche-aligned alkyl chains occur in distinct domains of certain sizes on the silica surface. The surface polarity of all modified silica wafers was also investigated by measurement of contact-angle.     

Correlating the Morphological Properties and Structural Organization of Monodisperse Spherical Silica Nanoparticles Grown on a Commercial Silica Surface

A variety of nanosilicas have been widely used to fabricate rough surfaces with superhydrophobic and superhydrophilic properties. In this context, we prepared mixed silica and mixed nanosilica that were generated by the growth and self‐assembly of synthesized monodisperse silica nanospheres (11–30 nm, 363 m² g^?1) on the surface of Sylopol‐948 and Dispercoll S3030 by using a base‐catalyzed sol–gel route. Using this process, the interactions and hierarchical structure between the nano‐ and microsized synthesized silica particles were studied by changing the amount of tetraethoxysilane. The resulting materials were characterized by BET analysis, small‐angle X‐ray scattering (SAXS), dynamic light scattering, FTIR spectroscopy, and SEM. The mixed silica presented a higher specific surface area (326 m² g^?1), a six‐fold higher percentage of (SiO)₆ (44–68 %), and a higher amount of silanol groups (14.0–30.7 %) than Sylopol‐948 (271 m² g^?1, 42.6 %, and 12.5 %, respectively). The morphological and hierarchical structural differences in the silica nanoparticles synthesized on the surface of commercial silica (micrometric or nanometric) were identified by SAXS. Mixed micrometric silica exhibited a higher degree of structural organization between particles than mixed nanosilica.     

Micro phase separated epoxy/poly(ε-caprolactone)-block-poly(dimethyl siloxane)-block-poly(ε-caprolactone)/4,4′-diaminodiphenylsulfone systems: Morphology,viscoelasticity, thermo-mechanical properties and surface hydrophobicity

Epoxy resin/4,4′-diaminodiphenylsulfone (DDS) system was modified by the incorporation of poly(ε-caprolactone)-block-poly(dimethyl siloxane)-block-poly(ε-caprolactone) (PCL–PDMS–PCL) triblock copolymer (TBCP). Morphology, viscoelasticity, thermo-mechanical and surface properties of these blends were investigated. All the blends were opaque after curing. PCL blocks of the TBCP were miscible with epoxy resin while the PDMS fraction was immiscible. However in the cured state, both PCL and PDMS blocks were phase separated from epoxy/DDS matrix. The blends exhibited matrix-droplet morphology in which TBCP phase dispersed as spherical domains in epoxy matrix. Addition of TBCP had profound impact on the cure reaction kinetics. Storage modulus and glass transition temperature (T_g) decreased while impact strength significantly increased. Incorporation of 15 phr of TBCP resulted in 80% improvement in impact strength. Further, thermal stability was unaffected while surface hydrophobicity of the blends increased.