N-heterocyclic carbene-silver complexes: Potential conductive materials for silver pastes in electronic applications

New organosilver complexes, silver(I) tetraalkylbis(benzimidazolidene) halide [1a-3a] and silver(I) dimethyl-N,N′-hexyl(imidazolyl) bromide [4a], were synthesized and incorporated into electroconductive silver pastes. Complex 3a had a 15-fold higher conductivity than conventional silver salt pastes, specifically silver(I) hexanoate, and exhibited a smooth, homogeneous surface after reductive heat-treatment of the silver paste. While the conductivity of silver(I) hexanoate can be increased by up to 33% by the addition of a supporting silver source, such as Ag₂O, the conductivity of 3a was markedly decreased by Ag₂O treatment. Thus, 3a can be used in silver pastes with moderate conductivity and can reduce the amount of conventional silver supporting materials without loss of electroconductivity.     

Asymmetric synthesis of 1-deoxyazasugars from chiral aziridines

A general and facile synthesis of enantiopure 1-deoxyazasugars was achieved from stereoselective dihydroxylation of a common synthetic intermediate, piperidine ring fused oxazolidin-2-one, originating from a commercially available starting substrate, chiral aziridine-2-carboxylate, in high yields.     

Cationic nucleolipids as efficient siRNA carriers

We synthesized five novel uridine-based cationic nucleolipids, introducing basic amino acid residues at the 5' position of uridine, through 1,3-dipolar cycloaddition, and hydrophobic alkyl moieties at the 2' and 3' positions, through carbamate linkages. Their lipoplexes delivered siRNAs efficiently to cells, in vitro, without any severe toxicity.     

ThermoData Engine (TDE): software implementation of the dynamic data evaluation concept. 5. Experiment planning and product design

ThermoData Engine (TDE) is the first full-scale software implementation of the dynamic data evaluation concept, as reported recently in this journal. In the present paper, we describe development of an algorithmic approach to assist experiment planning through assessment of the existing body of knowledge, including availability of experimental thermophysical property data, variable ranges studied, associated uncertainties, state of prediction methods, and parameters for deployment of prediction methods and how these parameters can be obtained using targeted measurements, etc., and, indeed, how the intended measurement may address the underlying scientific or engineering problem under consideration. A second new feature described here is the application of the software capabilities for aid in the design of chemical products through identification of chemical systems possessing desired values of thermophysical properties within defined ranges of tolerance. The algorithms and their software implementation to achieve this are described. Finally, implementation of a new data validation and weighting system is described for vapor-liquid equilibrium (VLE) data, and directions for future enhancements are outlined.     

Passivity-based control for Hopfield neural networks using convex representation

This paper considers the problem of passivity-based controller design for Hopfield neural networks. By making use of a convex representation of nonlinearities, a feedback control scheme based on passivity and Lyapunov theory is presented. A criterion for existence of the controller is given in terms of linear matrix inequality (LMI), which can be easily solved by a convex optimization problem. An example and its numerical simulation are given to show the effectiveness of the proposed method.     

Examination of Template Structural Effects on CEC Chiral Separation Performance of Molecule Imprinted Polymers Made by a Generalized Preparation Protocol

Some acidic chiral templates were used to prepare open tubular (OT) molecule imprinted polymer (MIP) capillary columns to explore the effects of molecular structures of templates on chiral recognition capabilities and to verify the feasibility of the general MIP preparation protocol introduced in the previous study. The templates are phenyl carboxylic acids and their derivatives. Optimization was carried out for chiral separation of template enantiomers for each MIP column through varying pH and composition of eluent. It was found that the preparation protocol can be successfully applied for the appropriate templates with functional groups fulfilling the three-points interaction rule. The chiral separation performances were quite satisfactory for MIPs of such templates although they are yet inferior to the separation performances of the MIP columns fabricated with the templates of profen drugs (2-arylpropionic acids with a large substituent on the phenyl ring). Subtle variations of the template molecular structures have been found to be critical to enhance chiral recognition ability of the resultant MIP column.     

A New Germanium Complex Containing Chelating Pyridinecarboxylate Ligands: cis‐Dihydroxybis(pyridine‐2‐carboxylato‐κN1,κO2)germanium Hydrate (1 : 2) (cis‐[Ge(pyca)2(OH)2]⋅2 H2O)

A new germanium complex, cis‐[Ge(pyca)₂(OH)₂]?2 H₂O ( 1 ; pyca=pyridine‐2‐carboxylato), was synthesized by the reaction of [Ge(acac)₂Cl₂] (acac=acetylacetonato=pentane‐2,4‐dionato) with potassium pyridine‐2‐carboxylate (Kpyca) in H₂O/THF. According to the single‐crystal X‐ray diffraction analysis, each Ge‐atom of 1 is coordinated by two pyca ligands and two OH^? groups (Fig. 1). These molecules are bonded to each other via a system of H‐bonds resulting in a sheet‐like structure (Fig. 2). The complex is decomposed during heating with stepwise mass loss and formation of GeO₂ as final product (Fig. 3).     

A study of mass transfer kinetics of alanyl-alanine on a chiral crown ether stationary phase

The mass transfer kinetics of alanyl-alanine enantiomers in a column packed with a chiral stationary phase (CSP) ChiroSil RCA(+) was studied by means of the moment method. Methanol-water solutions acidified with sulphuric acid were used as the mobile phase. It was shown that the spreading of peaks in the column was strongly affected by abnormal eddy diffusion. This effect was well described within the framework of the Giddings coupling theory. The comprehensive four-term Giddings equation for eddy diffusion was applied, considering simultaneous contribution of the trans-column, trans-channel, short-range inter-channel, and long-range inter-channel dispersion factors. Through these calculations, a predominant importance of the trans-column flow velocity bias was revealed. Besides eddy diffusion, the adsorption kinetic resistance to mass transfer plays a noticeable role in band broadening, all the other contributions (from longitudinal molecular diffusion, external and intraparticle mass transfer) being of minor significance. A relative importance of the mass transfer kinetics increases correlatively with a growth of the retention factor. Both the retention and kinetics of the adsorption of alanyl-alanine on the CSP in study are enantioselective. The influence of the column pressure on retention as well as corrections required because of this influence are also discussed.     

Molecular dynamics simulation study of nonconcatenated ring polymers in a melt. II. Dynamics

Molecular dynamics simulations were conducted to investigate the dynamic properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N = 1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. The ring melts were found to diffuse faster than their linear counterparts, with both architectures approximately obeying a D ～ N(-2.4) scaling law for large N. The mean-square displacement of the center-of-mass of the rings follows a sub-diffusive behavior for times and distances beyond the ring extension [linear span]R(g)(2)[linear span], neither compatible with the Rouse nor the reptation model. The rings relax stress much faster than linear polymers, and the zero-shear viscosity was found to vary as η(0) ～ N(1.4 ± 0.2) which is much weaker than the N(3.4) behavior of linear chains, not matching any commonly known model for polymer dynamics when compared to the observed mean-square displacements. These findings are discussed in view of the conformational properties of the rings presented in the preceding paper [J. D. Halverson, W. Lee, G. S. Grest, A. Y. Grosberg, and K. Kremer, J. Chem. Phys. 134, 204904 (2011)].