In vitro haemocompatibility and stability of two types of heparin-immobilized silicon surfaces

Heparin was covalently immobilized onto a silicon surface by two different methods, carbodiimide-based immobilization and photo-immobilization. In the former method, a (3-aminopropyl) trimethoxysilane (APTMS) self-assembled monolayer (SAM) or multilayer was first coated onto the silicon surface as the bridging layer, and heparin was then attached to the surface in the presence of water-soluble carbodiimide. In the latter method, an octadecyltrichlorosilane (OTS) SAM was coated on the silicon surface as the bridging layer, and heparin was modified by attaching photosensitive aryl azide groups. Upon UV illumination, the modified heparin was then covalently immobilized onto the surface. The hydrophilicity of the silicon surface changed after each coating step, and heparin aggregates on APTMS SAM and OTS SAM were observed by atomic force microscopy (AFM). In vitro haemocompatibility assays demonstrated that the deposition of APTMS SAM, APTMS multilayer and OTS SAM enhanced the silicon's haemocompatibility, which was further enhanced by the heparin immobilization. There is no evident distinction regarding the haemocompatibility between the heparin-immobilized surfaces by both methods. However, heparin on silicon with APTMS SAM and multilayer as the bridging layers is very unstable when tested in vitro with a saline solution at 37 °C, due to the instability of APTMS SAM and multilayer on silicon. Meanwhile, photo-immobilized heparin on silicon with OTS SAM as the bridging layer showed superb stability.     

基因芯片-玻璃表面两种不同DNA探针固定化方法的比较研究

研究了基因芯片相关的DNA探针在芯片表面最佳固定化方法。用两种不同的双功能试剂1,4-苯二异硫氰酸酯和戊二醛分别把5'-端氨基衍生的21-mer寡脱氧核苷酸探针直接共价固定到玻片表面,固定化的寡脱氧核苷酸探针与5'-端FITC标记的互补靶序列进行分子杂交,杂交后用配有CCD的IX70型荧光倒置显微镜成像检测。结果表明,两种固定化方法的效果都比较好,能检测到靶序列的最低终浓度为1.5×10^-9mol/L,优化了探针固定化时间、杂交时间、杂交温度等对DNA芯片分析性能的影响,为构建高灵敏度基因芯片打下良好基础。     

Mechanism of lateral interactions between molecules adsorbed on oxide surfaces

Comparison of the observed and calculated values for static and dynamic frequency shifts due to lateral interactions between CO molecules adsorbed on oxides indicates that these interactions are indirect and performed through a solid. Mechanism of static interaction includes relaxation, i.e. the displacement of surface atoms due to their adsorption.

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, CO, , . , .. .

     

Dynamic interactions between approaching surfaces of biological interest

The dynamic interactions arising when two interfaces approach each other are reviewed. Experimental methods are summarized and briefly discussed. The basic physical laws describing the dynamic behavior of interfaces and the liquid film between them are presented and the thin film approximation is used in order to simplify them. It was shown that interface deformability decreases the approach rate (increases interaction) while surface tangential mobility and membrane permeability increase it. Formulae are also presented for the dynamic interactions between solid particles of different shapes. The influence of the rheological properties of the liquid film between approaching surfaces is considered using viscoelastic, liquid-crystalline and non-linear models. The interactions between surface shape perturbations which are important for liquid film stability are considered with special attention to the case of membranes. A hydrodynamic theory of bilayer membrane formation and some similar phenomena is described which coincides semi-quantitatively with available experimental data. It is pointed out that viscous interactions can significantly decrease the rate of aggregation and fusion in multiparticle systems. The influence of external fields is also briefly discussed. The general conclusion is that in any case of very close approach of two interfaces the dynamic interactions can significantly increase leading to a decrease in the rate of adhesion and fusion.     

Energy transfer between dyes on glass surfaces and ions in glasses

A method for radiative and non-radiative energy transfer between flourescent organic dyes incorporated in a thin film deposited on a glass and inorganic ions in the bulk or surface of the glass is proposed.     

Influence of surface topography on the interactions between nanostructured hydrophobic surfaces

Nanostructured particle coated surfaces, with hydrophobized particles arranged in close to hexagonal order and of specific diameters ranging from 30 nm up to 800 nm, were prepared by Langmuir-Blodgett deposition followed by silanization. These surfaces have been used to study interactions between hydrophobic surfaces and a hydrophobic probe using the AFM colloidal probe technique. The different particle coated surfaces exhibit similar water contact angles, independent of particle size, which facilitates studies of how the roughness length scale affects capillary forces (previously often referred to as "hydrophobic interactions") in aqueous solutions. For surfaces with smaller particles (diameter < 200 nm), an increase in roughness length scale is accompanied by a decrease in adhesion force and bubble rupture distance. It is suggested that this is caused by energy barriers that prevent the motion of the three-phase (vapor/liquid/solid) line over the surface features, which counteracts capillary growth. Some of the measured force curves display extremely long-range interaction behavior with rupture distances of several micrometers and capillary growth with an increase in volume during retraction. This is thought to be a consequence of nanobubbles resting on top of the surface features and an influx of air from the crevices between the particles on the surface.     

Van der Waals interactions between surfaces of biological interest

Microscopic and macroscopic approaches to calculations of long-range Van der Waals interactions between bodies are reviewed. Expressions are presented for various geometries, including planar-layered structures, sheathed spheres and rods. Retardation effects are shown to reduce dispersion interactions in a similar fashion in both approaches. Pair summation procedure gives 10–25% greater values of dispersion interactions than the macroscopic approach. Orientation effects, previously neglected in microscopic approaches are strongly dependent on many-body effects. When orientation effects are included in a pair summation procedure, its calculated values are close to those calculated with the macroscopic approach.Experimentally determined force values are in agreement with calculated ones for distances of separation above 15 Å in vacuum. In general, the theory is insufficient for yielding forces at distances of separation below 20 Å in water.Determination of Van der Waals parameters from refractive indices of pure liquids and solutions is described. Within 5%, dispersion coefficients are independent of concentration of solution, and isotropic electronic polarizabilities agree with those obtained by the addition of bond polarizabilities. Van der Waals parameters of several major components of cellular surfaces and intercellular media are arranged according to an ascending sequence: water<alkanes<phospholipids<proteins and cholesterol<sugars.Variations in compositions, distances of separation, and layer thicknesses are considered in the calculation of the interactions between cellular surfaces, both in planar and spherical systems, including phospholipid vesicles. In planar-cellular systems, Hamaker coefficients vary between 4 x 10^-15 and 6 x 10^-14 erg; at 50 Å distance of separation the free energies and forces are 210 to 1600 kT/μm², and 4 x 10^-5 to 3 x 10^-4 dynes/μm² respectively. The total potential curve, including electrostatic interactions, is calculated and the questions of cellular adhesion and fusion of phospholipid vesicles are discussed.     

Molecular modeling of interactions between L-lysine and functionalized quartz surfaces

Molecular modeling techniques have been used to investigate the interaction of L-lysine in aqueous medium with silanol and methyl sites onto quartz substrates. The substrate effect has been studied for partially hydrophilic surfaces formed by silanol and methyl groups with a ratio of 1:5 and hydrophobic fully methylated surfaces. Molecular dynamics and static calculations indicate that L-lysine does not show any significant interaction with fully methylated surfaces, while its interaction with hydroxylated/methylated surfaces is dominated by electrostatic and H-bond terms. Accordingly, on fully methylated surfaces there is no preferential orientation of L-lysine with respect to the surface, while for hydroxylated/methylated surfaces the L-lysine-surface interaction mainly depends on the molecular orientation, with a preferred geometry involving the ammonium group pointing toward the silanol site. The structure of water shells around L-lysine molecules was shown to be strongly affected by the relative hydrophilic/hydrophobic character of the surfaces. In particular, the order is almost completely lost for partially hydrophilic surfaces, while well-defined hydration shells around L-lysine are obtained for hydrophobic surfaces.     

Use of the JKR model for calculating adhesion between rough surfaces

A simple method for using the JKR model to determine interfacial adhesion between two ideal rough surfaces is demonstrated for individual asperity-asperity and asperity-flat contacts both in air and in water. The model takes into account the effect of a modified contact area at separation due to viscoelastic effects. The equilibrium version of the model significantly underestimates the measured adhesion, whereas the viscoelastic version of the model is much closer to the measured data. The asperity-flat geometry used with the viscoelastic version of the model seems to fit the experimental results best. This was thought to be due to the unlikely occurrence of direct asperity-asperity contacts. Instead, it would seem that the asperities have a far higher chance of fitting between each other on opposing surfaces, leading to correspondingly higher pull-off forces measured on separation. Many possible extensions to the roughness model described here may be made, allowing a much-improved understanding of the contact mechanics between two rough surfaces.     

Deposition of patterned glycosaminoglycans on silanized glass surfaces

We report the robust attachment of glycosaminoglycans (GAGs) on silanized glass surfaces. Depositions were performed both by immersion and by application of a pattern by means of microcontact printing. Immunofluorescence assays were performed to verify the deposition and the quality of the patterns. In addition, AFM studies of the coated surfaces were performed in order to study some physical characteristics of the deposited GAGs layers. These results may prove useful for the characterization of the mechanical properties of GAGs in the glycocalyx and its relation with cellular migration.     

In vitro interactions of Peucedanum officinale essential oil with antibiotics

The chemical composition and antibacterial activity of Peucedanum officinale L. (Apiaceae) essential oil were examined, as well as the association between it and antibiotics: tetracycline, streptomycin and chloramphenicol. The interactions of the essential oil with antibiotics were evaluated using the microdilution checkerboard assay. Monoterpene hydrocarbons, with α-phellandrene as the dominant constituent, were the most abundant compound class of the essential oil of P. officinale. The researched essential oil exhibited slight antibacterial activity against the tested bacterial strains in vitro. On the contrary, essential oil of P. officinale possesses a great synergistic potential with chloramphenicol and tetracycline. Their combinations reduced the minimum effective dose of the antibiotic and, consequently, minimised its adverse side effects. In addition, investigated interactions are especially successful against Gram-negative bacteria, the pharmacological treatment of which is very difficult nowadays.     

UV cross-linking of unmodified DNA on glass surfaces

The performance of DNA microarrays strongly depends on their surface properties. Furthermore, the immobilization method of the capture molecules is of importance for the efficiency of the microarray in terms of sensitivity and specificity. This work describes the immobilization of single-stranded capture oligonucleotides by UV cross-linking on silanated (amino and epoxy) glass surfaces. Thereby we used amino (NH₂) and poly thymine/poly cytosine modifications of the capture sequences as well as unmodified capture molecules. The results were compared to UV cross-linking of the same DNA oligonucleotides on unmodified glass surfaces. Immobilization and hybridization efficiency was demonstrated by fluorescence and enzyme-induced deposition of silver nanoparticles. We found out that single-stranded DNA molecules do not require a special modification to immobilize them by UV cross-linking on epoxy- or amino-modified glass surfaces. However, higher binding rates can be achieved when using amino-modified oligonucleotides on an epoxy surface. The limit of detection for the used settings was 5 pM.     

Ligand-receptor interactions between surfaces: the role of binary polymer spacers

The interactions between a receptor-modified planar surface and a surface grafted with a bimodal polymer layer, where one of the polymer species is ligand functionalized, are studied using a molecular theory. The effects of changing the binding energy of the ligand-receptor pair, the polymer surface coverage, the composition, and molecular weight of both the unfunctionalized and ligand functionalized polymers on the interactions between the surfaces are investigated. Our findings show that bridging exists between the surfaces including when the molecular weight of the ligand-bearing polymer is smaller than that of the unfunctionalized polymer, even though the ligand is initially buried within the polymer layer. The distance at which the surfaces bind depends only on the molecular weight of the ligand-modified polymer, while the strength of the interaction at a given surface separation can be tuned by changing the molecular weight of the polymers, the total polymer surface coverage, and the fraction of ligated polymers. The composition of the bimodal layer alters the structure of the polymer layer, thereby influencing the strength of the steric repulsions between the surfaces. Our theoretical results show good agreement with experimental data. The present theoretical study can be used as guidelines for the design of surfaces with tailored abilities for tunning the binding strength and surface-ligand separation distances for polymer-grafted surfaces bearing specific targeting ligands.     

Molecular orbital studies of gas-phase interactions between complex molecules

Describing interactions among large molecules theoretically is a challenging task. As an example, we investigated gas-phase interactions between a linear nonionic oligomer and various model compounds (cofactors), which have been reported to associate experimentally, using PM3 semiempirical molecular orbital theory. As oligomer, we studied the hexamer of poly(ethylene oxide) (PEO), and as cofactors, we studied corilagin and related compounds containing phenolic groups (R-OH). These systems are of interest because they are models for PEO/cofactor flocculation systems, used in industrial applications. The PM3 delocalized molecular orbitals (DLMO) describe the bonding between (PEO)6 and cofactors, and some of them cover the complete complex. The DLMOs which cover the traditionally considered hydrogen bonds R-OH...O or R-CH...O show a distinct "pinch", a decrease of the electron density, between the H...O atoms. Calculations of Gibbs free energy, entropy, and enthalpy show that the PEO/cofactor complexes do not form at room temperature, because the loss of entropy exceeds the increase in enthalpy. The change in enthalpy is linearly related to the change in entropy for the different complexes. Even though bond lengths, bond angles, DLMOs, and electron densities for the PEO/cofactor complexes are consistent with the definition of hydrogen bonds, the number of intermolecular R-OH...O and R-CH...O bonds does not correlate with the enthalpy of association, indicating that the bonding mechanism for these systems is the sum of many small contributions of many delocalized orbitals.     

Isotopically discriminated NMR spectroscopy: a tool for investigating complex protein interactions in vitro

A new NMR approach is presented for observing in vitro multicomponent protein-protein-ligand(s) interactions, which should help to understand how cellular networks of protein interactions operate on a molecular level and how they can be controlled with drugs. The method uniquely allows at least two polypeptide components of the mixture to be simultaneously closely monitored in a single sample, without increased signal overlap, and can be used to study complex (e.g., sequential, competitive, cooperative, allosteric, induced, etc.) binding events, witnessed by two polypeptides independently. One polypeptide is uniformly labeled with 15N and another with 15N and 13C. The 1H-15N correlation spectra are recorded for each of these molecules separately, discriminated on the basis of the type of 13C'/12C' atom attached to the amide group nitrogen. Any changes to the state of the two differently isotopically labeled molecules will be reported individually by fingerprint signals from amide groups, e.g., as unlabeled ligands are added. To our knowledge, no other technique currently exists which can monitor complex binding events in similar detail. The proposed method can be combined easily with traditional protein NMR techniques and incorporated in a variety of applications.     

Non-bonded organo-mineral interactions and sorption of organic compounds on soil surfaces: a model approach

Molecular mechanics and molecular dynamics calculations have been performed on organo-mineral composites that model the sorption of high-molecular-weight humic polymers on mineral surfaces and the sorption of low-molecular-weight organic contaminants on both mineral and organic surfaces in soil. Muscovite mica was chosen as a mineral model; an oxidized topological lignin-carbohydrate complex was chosen as a humic model; benzene, sodium benzoate, atrazine, and DDT represent different classes of contaminants. Sorption energies were estimated based on molecular mechanics calculations. Flexible linear polymers undergo drastic conformational changes when approaching the mineral surface, to ensure a gain in the interaction energy that outweighs a loss in the conformational energy proper. Therefore, the gas-phase conformation composi tion of environmental organic polymers is not directly related to their spatial organization in soil composites. Molecular dynamics simulation suggests high stability of the organic polymer coatings of mineral surfaces in the environment. Low-molecular-weight organic molecules demonstrate much less affinity for the mineral surface, which implies unhindered exchanges between the surface and its near environment. Ionizable compounds, e.g. salts of organic acids, are different, because they can form strong associations with a mineral surface through cation bridges. Sorption energies are compound-specific and depend on the sorbate-sorbent orientation. The calculations suggest some preference for the edges of a model muscovite sheet in comparison with the basal oxygen surface as a sorption site. Coating of mineral surfaces with organic polymers does not hinder the sorption of organic molecules except in the special case of organic ions.     

Growth of anisotropic gold nanostructures on conducting glass surfaces

In this paper, we describe a method for the growth of gold nanowires and nanoplates starting from a bilayer array of gold seeds, anchored on electrically conducting indium tin oxide (ITO) substrates. This is based on a seed-mediated growth approach, where the nanoparticles attached on the substrate through molecular linkages are converted to nanowires and nanoplates at certain cetyltrimethylammonium bromide (CTAB) concentration. Our modified approach can be used to make nanowires of several tens of micrometers length at a lower CTAB concentration of 0.1 M. The length of the nanowires can be varied by adjusting the time of the reaction. As the concentration of CTAB was increased to 0.25 M, the nanoparticles got converted to nanoplates. These Au nanoplates are (111) oriented and are aligned parallel to the substrate.