Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Intercalation of Toluidines into α-Zirconium Hydrogenphosphate

Intercalates of o-, m-, and p-toluidine into α-Zr(HPO₄)₂ · H₂O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom.     

The free energy of a reaction coordinate at multiple constraints: a concise formulation

The free energy as a function of the reaction coordinate (rc) is the key quantity for the computation of equilibrium and kinetic quantities. When it is considered as the potential of mean force, the problem is the calculation of the mean force for given values of the rc. We reinvestigate the PMCF (potential of mean constraint force) method which applies a constraint to the rc to compute the mean force as the mean negative constraint force and a metric tensor correction. The latter allows for the constraint imposed to the rc and possible artefacts due to multiple constraints of other variables which for practical reasons are often used in numerical simulations. Two main results are obtained that are of theoretical and practical interest. First, the correction term is given a very concise and simple shape which facilitates its interpretation and evaluation. Secondly, a theorem describes various rcs and possible combinations with constraints that can be used without introducing any correction to the constraint force. The results facilitate the computation of free energy by molecular dynamics simulations.     

Nanostructures of functionalized gold nanoparticles prepared by particle lithography with organosilanes

Periodic arrays of organosilane nanostructures were prepared with particle lithography to define sites for selective adsorption of functionalized gold nanoparticles. Essentially, the approach for nanoparticle lithography consists of procedures with two masks. First, latex mesospheres were used as a surface mask for deposition of an organosilane vapor, to produce an array of holes within a covalently bonded, organic thin film. The latex particles were readily removed with solvent rinses to expose discrete patterns of nanosized holes of uncovered substrate. The nanostructured film of organosilanes was then used as a surface mask for a second patterning step, with immersion in a solution of functionalized nanoparticles. Patterned substrates were fully submerged in a solution of surface-active gold nanoparticles coated with 3-mercaptopropyltrimethoxysilane. Regularly shaped, nanoscopic areas of bare substrate produced by removal of the latex mask provided sites to bind silanol-terminated gold nanoparticles, and the methyl-terminated areas of the organosilane film served as an effective resist, preventing nonspecific adsorption on masked areas. Characterizations with atomic force microscopy demonstrate the steps for lithography with organosilanes and functionalized nanoparticles. Patterning was accomplished for both silicon and glass substrates, to generate nanostructures with periodicities of 200-300 nm that match the diameters of the latex mesospheres of the surface masks. Nanoparticles were shown to bind selectively to uncovered, exposed areas of the substrate and did not attach to the methyl-terminal groups of the organosilane mask. Billions of well-defined nanostructures of nanoparticles can be generated using this high-throughput approach of particle lithography, with exquisite control of surface density and periodicity at the nanoscale.     

Semiconducting polymer thin films by surface-confined stepwise click polymerization

Surface-confined stepwise click polymerization was used to prepare surface-attached thin films of semiconducting polymers. These highly uniform films showed extended UV/vis absorption characteristics and a remarkable degree of molecular organization with a unidirectional alignment of the polymer chains normal to the surface.