NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives

Substituted pyrazolopyridines are potent inhibitors of phosphodiesterases and cyclin-dependent kinases. In this study, NMR was used to investigate the potential N1-H and N2-H tautomerism of 5-substituted pyrazolo[3,4-c]pyridine derivatives. Six compounds were fully characterized by using (1)H, (13)C, and (15)N chemical shifts and indirect (1)H--(13)C and (1)H--(15)N coupling constants. The (1)H NMR spectra were measured over a broad range of temperatures. All of the compounds were shown to exist predominantly in the N1-H tautomeric form. Complementary quantum-chemical calculations of the chemical shieldings and indirect spin-spin couplings support the structural conclusions drawn.     

Microstructural characterization of CPPD and hydroxyapatite crystal depositions on human menisci

Meniscus is a fibrocartilaginous tissue composed mainly of water and a dense elaborate collagen network with a predominantly circumferential alignment. Crystal formation and accumulation on meniscal tissue is frequently observed especially in elderly. In this study, we used X‐ray diffraction (XRD), FTIR and FT‐Raman for the structural identification of the depositions and Optical microscopy, Scanning Electron microscopy (SEM/EDX) and Atomic Force microscopy (AFM), in order to investigate the structural relationship between the crystal deposits and the collagen fibers of human meniscal tissues. We are reporting on the formation of intercalary “colonies” of Calcium Pyrophosphate Dihydrate (CPPD) crystals with two distinct morphologies corresponding to the monoclinic and the triclinic phase, as well as the formation of micro‐aggregations composed of nano‐crystalline HAP aggregations which are developed along the longitudinal axis of collagen fibers without extensively disturbing the collagens arrangement.     

Sensitivity analysis and determination of free relaxation parameters for the weakly-compressible MRT–LBM schemes

Lattice Boltzmann methods (LBMs) are very efficient for computational fluid dynamics, and for capturing the dynamics of weak acoustic fluctuations. It is known that multi-relaxation-time lattice Boltzmann method (MRT–LBM) appears as a very robust scheme with high precision. There exist several free relaxation parameters in the MRT–LBM. Although these parameters have been tuned via linear analysis, the sensitivity analysis of these parameters and other related parameters is still not sufficient for describing the behavior of the dispersion and dissipation relations of the MRT–LBM. Previous researches have shown that the bulk dissipation in the MRT–LBM induces a significant over-damping of acoustic disturbances. This indicates that the classical MRT–LBM is not best suited to recover the correct behavior of pressure fluctuations. In wave-number space, the first/second-order sensitivity analyses of matrix eigenvalues are used to address the sensitivity of the wavenumber magnitudes to the dispersion-dissipation relations. By the first-order sensitivity analysis, the numerical behaviors of the group velocity of the MRT–LBM are first obtained. Afterwards, the distribution sensitivities of the matrix eigenvalues corresponding to the linearized form of the MRT–LBM are investigated in the complex plane. Based on the sensitivity analysis and an effective algorithm of recovering linearized Navier–Stokes equations (L-NSEs) from linearized MRT–LBM (L-MRT–LBM), we propose some simplified optimization strategies to determine the free relaxation parameters of the MRT–LBM. Meanwhile, the dispersion and dissipation relations of the optimal MRT–LBM are quantitatively compared with the exact dispersion and dissipation relations. At last, some numerical validations on classical acoustic benchmark problems are shown to assess the new optimal MRT–LBM.     

Full Connectivity: Corners,Edges and Faces

We develop a cluster expansion for the probability of full connectivity of high density random networks in confined geometries. In contrast to percolation phenomena at lower densities, boundary effects, which have previously been largely neglected, are not only relevant but dominant. We derive general analytical formulas that show a persistence of universality in a different form to percolation theory, and provide numerical confirmation. We also demonstrate the simplicity of our approach in three simple but instructive examples and discuss the practical benefits of its application to different models.     

An efficient Monte Carlo algorithm for the fast equilibration and atomistic simulation of alkanethiol self-assembled monolayers on a Au(111) substrate

A new Monte Carlo algorithm is presented for the simulation of atomistically detailed alkanethiol self-assembled monolayers (R-SH) on a Au(111) surface. Built on a set of simpler but also more complex (sometimes nonphysical) moves, the new algorithm is capable of efficiently driving all alkanethiol molecules to the Au(111) surface, thereby leading to full surface coverage, irrespective of the initial setup of the system. This circumvents a significant limitation of previous methods in which the simulations typically started from optimally packed structures on the substrate close to thermal equilibrium. Further, by considering an extended ensemble of configurations each one of which corresponds to a different value of the sulfur-sulfur repulsive core potential, sigmass, and by allowing for configurations to swap between systems characterized by different sigmass values, the new algorithm can adequately simulate model R-SH/Au(111) systems for values of sigmass ranging from 4.25 A corresponding to the Hautman-Klein molecular model (J. Chem. Phys. 1989, 91, 4994; 1990, 93, 7483) to 4.97 A corresponding to the Siepmann-McDonald model (Langmuir 1993, 9, 2351), and practically any chain length. Detailed results are presented quantifying the efficiency and robustness of the new method. Representative simulation data for the dependence of the structural and conformational properties of the formed monolayer on the details of the employed molecular model are reported and discussed; an investigation of the variation of molecular organization and ordering on the Au(111) substrate for three CH3-(CH2)n-SH/Au(111) systems with n=9, 15, and 21 is also included.     

A structural reconsideration: Linear aliphatic or alicyclic hard segments for biodegradable thermoplastic polyurethanes?

Thermoplastic polyurethane elastomers (TPUs) with a biodegradable chain extender and different nonaromatic diisocyanate hard segments were synthesized and tested concerning their thermal, mechanical, and degradation properties and for their processability regarding electrospinning. The design of the TPUs was based on the structural modification of the hard segment using linear aliphatic hexamethylene diisocyanate (HMDI), more rigid alicyclic 4,4′-methylene bis(cyclohexylisocyanate) (H12MDI), 1,3-bis(isocyanatomethyl)cyclohexane (BIMC), or isophorone diisocyanate (IPDI). The soft segment consisted of poly(tetrahydrofuran). Bis(2-hydroxyethyl) terephthalate (BET) was used as chain extender with cleavable ester bonds. Some of the polyurethanes based on alicyclic diisocyanate showed better mechanical performance than the less rigid HMDI-based TPU. The TPU in vitro degradability was tested for 25 days at elevated temperatures in PBS buffer and indicated a bulk erosion process. Electrospinning experiments were conducted and promising results with respect to further applicability of these materials in vascular tissue engineering were obtained. © 2018 The Authors Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2214–2224