Adhesion models: from single to multiple asperity contacts

This review presents a summary of the current adhesion models available to date, between real rough surfaces, starting from single asperity models and expanding to multiple asperity contacts. The focus is made on multi-asperity contact interactions. Both van der Waals and contact mechanics approaches have been considered and relevant adhesion models are reviewed and discussed. The influence of the meniscus forces on adhesion has been considered, along with a summary of the various meniscus models. The effect of surface geometry, its topography and environmental conditions on meniscus action are also discussed along with its integration into multi-asperity adhesion models.     

Formation of orthoester-linked d-arabinofuranose oligosaccharides and their isomerization into the corresponding glycosides

Orthoester-linked d-arabinofuranose oligosaccharides were isolated in high yield for the first time via glycosylations with 2-O-chloroacetyl-substituded d-arabinofuranose thioglycosides promoted by NIS-AgOTf in the presence of 4 Å molecular sieves in CH₂Cl₂. These orthoesters can be rearranged into the isomeric glycosidically-linked oligosaccharides by treatment with TMSOTf in CH₂Cl₂, or in situ by extension of the reaction time.     

Success and failure of colloidal approaches in adhesion of microorganisms to surfaces

Biofilms are communities of cells attached to surfaces, their contributions to biological process may be either a benefit or a threat depending on the microorganism involved and on the type of substrate and environment. Biofilm formation is a complex series of steps; due to the size of microorganisms, the initial phase of biofilm formation, the bacterial adhesion to the surface, has been studied and modeled using theories developed in colloidal science. In this review the application of approaches such as Derjaguin, Landau, Verwey, Overbeek (DLVO) theory and its extended version (xDLVO), to bacterial adhesion is described along with the suitability and applicability of such approaches to the investigation of the interface phenomena regulating cells adhesion. A further refinement of the xDLVO theory encompassing the brush model is also discussed. Finally, the evidences of phenomena neglected in colloidal approaches, such as surface heterogeneity and fluid flow, likely to be the source of failure are defined.     

Density functional theory study of the reaction mechanism of the DNA repairing enzyme alkylguanine alkyltransferase

The reaction mechanism of human O⁶-alkylguanine-DNA alkyltransferase (AGT) is studied using density functional theory. AGT repairs alkylated DNA by directly removing the alkyl group from the O6 position of the guanine. A quantum chemical model of the active site was devised based on the recent crystal structure of the AGT–DNA complex. The potential energy curve is calculated and the stationary points are characterized. It is concluded that the previously proposed reaction mechanism is energetically plausible. In this mechanism, His146 first acts as a water-mediated general base to activate Cys145, which then performs a nucleophilic attack to dealkylate the guanine base.     

Varying molecular interactions by coverage in supramolecular surface chemistry

The possibility of modifying the intermolecular interactions of absorbed benzene-carboxylic acids from coordination to hydrogen bonding by changing their surface coverage is demonstrated through a combination of scanning tunnelling microscopy, X-ray photoemission spectroscopy and density functional theory calculations.     

Could X-Ray Analysis Explain for the Differing Antimicrobial and Antioxidant Activity of Two 2-Arylamino-3-Nitro-Coumarins?

Abstract  

X-Ray analyses of 4-(naphthalen-1-ylamino)-3-nitro-chromen-2-one and 3-nitro-4-phenylamino-chromen-2-one showed that the mentioned compounds crystallize in the space groups P1- (triclinic crystal system; unit cell parameters: a = 8.087(2) ?, b = 9.241(3) ?, c = 10.911(3) ?, α = 93.77(3)°, β = 102.51(3)°, γ = 106.44(2)°, V = 756.4(4) ?³ and Z = 2) and P2₁2₁2₁ (orthorhombic crystal system; unit cell parameters: a = 4.9274(9) ?, b = 14.725(3) ?, c = 17.866(4) ?, α = β = γ = 90°, V = 1296.3(5) ?³ and Z = 4), respectively. The analyses of crystal structures and gas phase conformations, inferred from single X-ray crystallographic and molecular modeling experiments, respectively, showed that the changes in π delocalization of the farmacoactive formal 3-amino-2-nitro-acrylic acid derivatives might explain the observed significant difference of the antimicrobial and antioxidant activities and spectral properties of two 4-arylamino-3-nitro-coumarin derivatives.     

Synthesis,Crystal Structure and Biological Activity of N′-tert-butyl-N-(3-methoxylbenzoyl)-N-(4-methyl-1,2,3-thiadiazole-5-formylhydrazine

Abstract  

The title compound, N′-tert-butyl-N-(3-methoxylbenzoyl)-N-(4-methyl-1,2,3-thiadiazole-5-formylhydrazine (C₁₆H₂₀N₄O₃S) was prepared from the reaction of 4-methyl-1,2,3-thiadiazole-5-carbonyl chloride with N′-tert-Butyl-3-methoxylbenzohydrazine, and its structure was characterized by ¹Hydrogen Nuclear Magnetic Resonance, High-Resolution Mass Spectrometry, IR spectra, and single crystal X-ray diffraction. The crystal of the title compound belongs to monoclinic system, space group P 21/c with cell parameters a = 17.986(2) ?, b = 8.0180(10) ?, c = 12.0190(14) ?, α = 90°, β = 91.160(5)°, γ = 90°, V = 1732.9(4) ?³, Z = 4, D _c  = 1.335 g/cm³, μ (Mo Ka) = 0.209 mm⁻¹, F (000) = 736, R = 0.0367 and wR = 0.0932. X-ray diffraction analysis indicates that all rings in the title compound are non-planar. The bioassay results indicated that, the title compound had good fungicide activity against Sclerotinia sclerotiorum, certain extent of insecticidal activity against Plutella xylostella L.     

Quantum chemical modeling of enzymatic reactions: The case of histone lysine methyltransferase

Quantum chemical cluster models of enzyme active sites are today an important and powerful tool in the study of various aspects of enzymatic reactivity. This methodology has been applied to a wide spectrum of reactions and many important mechanistic problems have been solved. Herein, we report a systematic study of the reaction mechanism of the histone lysine methyltransferase (HKMT) SET7/9 enzyme, which catalyzes the methylation of the N‐terminal histone tail of the chromatin structure. In this study, HKMT SET7/9 serves as a representative case to examine the modeling approach for the important class of methyl transfer enzymes. Active site models of different sizes are used to evaluate the methodology. In particular, the dependence of the calculated energies on the model size, the influence of the dielectric medium, and the particular choice of the dielectric constant are discussed. In addition, we examine the validity of some technical aspects, such as geometry optimization in solvent or with a large basis set, and the use of different density functional methods. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Convergence estimates of a projection-difference method for an operator-differential equation

This article investigates the projection-difference method for a Cauchy problem for a linear operator-differential equation with a leading self-adjoint operator A(t) and a subordinate linear operator K(t) in Hilbert space. This method leads to the solution of a system of linear algebraic equations on each time level; moreover, the projection subspaces are linear spans of eigenvectors of an operator similar to A(t). The convergence estimates are obtained. The application of the developed method for solving the initial boundary value problem is given.     

On a space of smooth functions on a convex unbounded set in ℝ<Superscript><Emphasis Type="Italic">n</Emphasis></Superscript> admitting holomorphic extension in ℂ<Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>

For some given logarithmically convex sequence M of positive numbers we construct a subspace of the space of rapidly decreasing infinitely differentiable functions on an unbounded closed convex set in ? ⁿ . Due to the conditions on M each function of this space admits a holomorphic extension in ? ⁿ . In the current article, the space of holomorphic extensions is considered and Paley-Wiener type theorems are established. To prove these theorems, some auxiliary results on extensions of holomorphic functions satisfying some weighted L ²-bounds in a domain of holomorphy in ? ⁿ are obtained with the aid of L. Hörmander’s method of L ²-bounds for the \(\bar \partial\) operator. Also, some new facts on the Fourier-Laplace transform of tempered distributions complementing some well-known results of V.S. Vladimirov are employed.