Adhesion contact dynamics of fibroblasts on biomacromolecular surfaces

Biomacromolecules like gelatin and chitosan have emerged as highly versatile biomimetic coatings for applications in tissue engineering. The elucidation of the interfacial kinetics of cell adhesion on biomacromolecular surfaces will pave the way for the rational design of chitosan/gelatin-based systems for cell regeneration. Biomacromolecular ultra-thin films, chemically immobilized on fused silica are ideal experimental models for determining the effect of surface properties on the biophysical cascades following cell seeding. In this study, confocal reflectance interference contrast microscopy (C-RICM), in conjunction with phase contrast microscopy and fluorescence confocal microscopy, was applied to detect the adhesion contact dynamics of 3T3 fibroblasts on chitosan and gelatin ultrathin films. X-ray photoelectron spectroscopy (XPS) confirmed the immobilization of chitosan or gelatin on the silanized glass surface. Both the initial cell deformation rate and the change of two-dimensional spread area of the 3T3 fibroblasts are higher on gelatin-modified surfaces than on chitosan surfaces. The steady-state adhesion energy of 3T3 fibroblasts on gelatin film is three times higher than that on chitosan film. Immuno-staining of actin further demonstrates the different organization of cytoskeleton, likely induced by the change in cell signaling mechanism on the two biomacromolecular surfaces. The better attachment of 3T3 fibroblast to gelatin is postulated to be caused by the presence of adhesive domains on gelatin.     

The GROMOS software for biomolecular simulation: GROMOS05

We present the latest version of the Groningen Molecular Simulation program package, GROMOS05. It has been developed for the dynamical modelling of (bio)molecules using the methods of molecular dynamics, stochastic dynamics, and energy minimization. An overview of GROMOS05 is given, highlighting features not present in the last major release, GROMOS96. The organization of the program package is outlined and the included analysis package GROMOS++ is described. Finally, some applications illustrating the various available functionalities are presented.     

Luminescent gold(I) and silver(I) complexes of 2-(diphenylphosphino)-1-methylimidazole (dpim): characterization of a three-coordinate Au(I)-Ag(I) dimer with a short metal-metal separation

The Au(I) and Ag(I) closed-shell metal dimers of 2-(diphenylphosphino)-1-methylimidazole, dpim, were investigated. dpim formed the discreet binuclear species [Ag2(dpim)2(CH3CN)2](2+) (1) when reacted with appropriate Ag(I) salts. Likewise, [Au2(dpim)2](2+) (3) and [AuAg(dpim)3](2+) (4) were produced via reactions with (tht)AuCl, tht is tetrahydrothiophene, and Ag(I). Compound 3 exhibits an intense blue luminescence (lambdamax=483 nm) in the solid state. However, upon initial formation of 3, a small impurity of Cl- was present giving rise to an orange emission (lambdamax=548 nm). Attempts to form [Au2(dpim)2]Cl2 yielded only (dpim)AuCl (2), which is not visibly emissive. The rare three-coordinate heterobimetallic complex [AuAg(dpim)3](2+) (4) exhibits intense luminescence in the solid-state resembling that of 3. The crystal structures of 1-4 were determined, revealing strong intramolecular aurophilic and argentophilic interactions in the dimeric compounds. Compound 1 has an Ag(I)-Ag(I) separation of 2.9932(9) A, while compound 3 has a Au(I)-Au(I) separation of 2.8174(10) A. Compound 4 represents the first example of a three-coordinate Au(I)-Ag(I) dimer and has a metal-metal separation of 2.8635(15) A. The linear Au(I) monomer, 2, has no intermolecular Au(I)-Au(I) interactions, with the closest separation greater than 6.8 A.     

Low-frequency Raman-active vibrations of triclinic n-paraffins

The low-frequency Raman spectra of triclinic n-paraffins, n-C₈H₁₈ through n-C₂₄H₅₀, were observed. The normal-coordinate treatments of crystal vibrations of n-C₈H₁₈ through n-C₁₈H₃₈ were carried out. Six characteristic series of the observed Raman lines were assigned to rotatory lattice vibrations and intramolecular skeletal vibrations.     

Wide-line H NMR: a new application for the study of Brönsted acidity strength of solids with HY zeolite as example

The fitting of 4 K ¹H wide-line NMR spectra of Brönsted-acidic solid samples loaded with known amounts of water allows the determination of the concentration of the following species: H₃O⁺, H₂O…HO; and of the remaining initial species: OH and H₂O.     

A local approach to delocalized electronic systems: semilocal evaluation of the cohesive energies of tight-binding Hamiltonians

Starting from strongly localized N-electron functions built from either pure atomic orbitals or fully localized bond molecular orbitals, it is possible to evaluate the ground state energy of a periodic lattice ruled by a tight-binding Hamiltonian without explicitly introducing the monoelectronic crystal orbitals. The method consists of a self-consistent perturbation of the zeroth-order wave function which incorporates high order effects and offers reasonable convergence properties. Along this framework, a single variable per bond type is introduced, namely the amplitude of the charge transfer. The method leads to a set of coupled equations which can be numerically solved, if not analytically. Short-range delocalization effects under periodic conditions are explicitly taken into account and relatively accurate cohesive energies are estimated for regular homoatomic and heteroatomic one-dimensional chains as well as for honeycomb lattices. In addition, good agreement with experiment for the distortion amplitude in polyacetylene is obtained. This exploratory tool may be easily extended to more sophisticated Hamiltonians, for which the solutions are not accessible. Since our approach only introduces short-range delocalization effects, its performance questions the importance of the specifically collective delocalization effects.     

Isomerization dynamics in homo- and heterochiral atropoisomer copper(I) diimine complexes: a 2D EXSY NMR study

Two-dimensional exchange NMR spectroscopy has been employed to study the isomerization process of copper(I) complexes formed upon complexation of Cu+ with a racemic mixture of the atropoisomer diimine benzimidazole-pyridine ligands 1-3 and evaluate the configurational stability of the pseudotetrahedral complexes [Cu(1-3)2]PF6. Racemization of the heterochiral isomers RSLambda/RSDelta proceeds through an intramolecular ligand rearrangement on a time scale of about 1.9 s(-1) for 1, 4.4 s(-1) for 2, and 0.3 s(-1) for 3 in CD2Cl2 at room temperature. The intramolecular Lambda/Delta isomerizations in the homochiral diastereoisomers RRDelta/SSLambda and RRLambda/SSDelta of [Cu(1)2]PF6 proceed at room temperature on a time scale of about 0.6 s(-1) for the conversion of RRDelta/SSLambda into RRLambda/SSDelta and 13 s(-1) for the conversion of RRLambda/SSDelta into RRDelta/SSLambda. The kinetics of these intramolecular exchange processes were found to be sensitive to the stabilizing interligand pi-stacking interactions that develop within the [Cu(1-3)2]+ structure and to the bulkiness of the benzimidazole aryl substituents. The kinetics of racemization in the heterochiral RSLambda/RSDelta isomers of [Cu(3)2]PF6 with the bulky cumyl-derived ligand were 1 order of magnitude lower than in [Cu(2)2]PF6 with the tolyl-based ligand. Slower intermolecular ligand exchanges between all the isomers have also been shown to occur at ambient temperature in CD2Cl2 through complete ligand dissociation. Free energies at 298 K varying between 66.7 and 74.4 kJ.mol(-1) and entropies varying between -26.4 and 28.3 J.K(-1).mol(-1) were determined for the intramolecular Lambda/Delta isomerizations. For the intermolecular ligand exchanges free energies at 298 K varying between 55.6 and 62.5 kJ.mol(-1) and entropies varying between -97.9 and -74.5 J.K(-1).mol(-1) were measured.     

Influence of master fabrication techniques on the characteristics of embossed microfluidic channels

We describe protocols for the fabrication of microfluidic devices in plastics using a number of different embossing masters. Masters were fabricated by deep reactive ion etching (DRIE) of silicon (100), wet etching of silicon (100) and (110), and SU-8 processing. Structures embossed into a cyclo-olefin polymer were characterized in terms of the quality of pattern transfer as well as of the surface roughness. High quality pattern transfer was achieved with masters containing structures with angled sidewalls. Pattern distortions occurring during de-embossing were minimized by using masters consisting of SU-8 (which has a thermal expansion coefficient close to that of the substrates). Structures embossed with SU-8 masters also exhibited the lowest surface roughness. However, due to structural deformation, the reusability of the masters prepared for this study extended to only five embossing experiments. Masters fabricated on silicon, on the other hand, were more robust, but were subject to breakage during the de-embossing phase of the experiment. The results of this study will guide researchers in choosing master fabrication methods that will provide profile and surface characteristics of embossed microfluidic channels that are advantageous to their specific application.