Simple Hamiltonians which exhibit drastic failures by variational determination of the two-particle reduced density matrix with some well known N-representability conditions

Calculations on small molecular systems indicate that the variational approach employing the two-particle reduced density matrix (2-RDM) as the basic unknown and applying the P, Q, G, T1, and T2 representability conditions provides an accuracy that is competitive with the best standard ab initio methods of quantum chemistry. However, in this paper we consider a simple class of Hamiltonians for which an exact ground state wave function can be written as a single Slater determinant and yet the same 2-RDM approach gives a drastically nonrepresentable result. This shows the need for stronger representability conditions than the mentioned ones.     

Increased adhesion of Enterococcus faecalis strains with bimodal electrophoretic mobility distributions

Initial adhesion is a determinant in the development of microbial biofilms. It is influenced, amongst others, by the surface hydrophobicity and the electrostatic characteristics of the substratum and adhering organisms. Enterococcus faecalis strains, grown in pure cultures, generally display subpopulations with different electrokinetic features, reflected in a bimodal electrophoretic mobility distribution. Here, the initial adhesion kinetics of five heterogeneous and five homogeneous E. faecalis strains were followed in a parallel-plate flow chamber. After 4h of flow, heterogeneous strains adhered in significantly higher numbers than homogeneous strains (7.3 x 10(6) and 1.9 x 10(6)cm(-2), respectively), but the initial deposition rates were not significantly influenced (740 and 600 cm(-2)s(-1), respectively). Apparently, initial deposition of bacteria is mainly governed by attractive Lifshitz-Van der Waals forces that overwhelm the electrostatic repulsion energy barrier, thus resulting in similar initial deposition rates for the various bacterial populations investigated. In contrast, during later stages of adhesion, bacteria in heterogeneous cultures likely experience a lower electrostatic repulsion from already adhering bacteria than bacteria in homogeneous cultures, thus allowing a closer proximity of the bacteria with respect to each other, which ultimately leads to increased adhesion after 4 h.     

Biomimetic screening of class-B G protein-coupled receptors

The 41-amino acid peptide corticotropin releasing factor (CRF) is a major modulator of the mammalian stress response. Upon stressful stimuli, it binds to the corticotropin releasing factor receptor 1 (CRF(1)R), a typical member of the class-B G-protein-coupled receptors (GPCRs) and a prime target in the treatment of mood disorders. To chemically probe the molecular interaction of CRF with the transmembrane domain of its cognate receptor, we developed a high-throughput conjugation approach that mimics the natural activation mechanism of class-B GPCRs. An acetylene-tagged peptide library was synthesized and conjugated to an azide-modified high-affinity carrier peptide derived from the CRF C-terminus using copper-catalyzed dipolar cycloaddition. The resulting conjugates reconstituted potent agonists and were tested in situ for activation of the CRF(1) receptor in a cell-based assay. By use of this approach we (i) defined the minimal sequence motif that is required for full receptor activation, (ii) identified the critical functional groups and structure-activity relationships, (iii) developed an optimized, highly modified peptide probe with high potency (EC(50) = 4 nM) that is specific for the activation domain of the receptor, and (iv) probed the behavioral role of CRF receptors in living mice. The membrane recruitment by a high-affinity carrier enhanced the potency of the tethered peptides by >4 orders of magnitude and thus allowed the testing of very weak initial fragments that otherwise would have been inactive on their own. As no chromatography purification of the test peptides was necessary, a substantial increase in screening throughput was achieved. Importantly, the peptide conjugates can be used to probe the endogenous receptor in its native environment in vivo.     

Global potential energy surfaces for O((3)P) + H2O((1)A1) collisions

Global analytic potential energy surfaces for O((3)P) + H(2)O((1)A(1)) collisions, including the OH + OH hydrogen abstraction and H + OOH hydrogen elimination channels, are presented. Ab initio electronic structure calculations were performed at the CASSCF + MP2 level with an O(4s3p2d1f)/H(3s2p) one electron basis set. Approximately 10(5) geometries were used to fit the three lowest triplet adiabatic states corresponding to the triply degenerate O((3)P) + H(2)O((1)A(1)) reactants. Transition state theory rate constant and total cross section calculations using classical trajectories to collision energies up to 120?kcal mol(-1) (～11?km s(-1) collision velocity) were performed and show good agreement with experimental data. Flux-velocity contour maps are presented at selected energies for H(2)O collisional excitation, OH + OH, and H + OOH channels to further investigate the dynamics, especially the competition and distinct dynamics of the two reactive channels. There are large differences in the contributions of each of the triplet surfaces to the reactive channels, especially at higher energies. The present surfaces should support quantitative modeling of O((3)P) + H(2)O((1)A(1)) collision processes up to ～150?kcal mol(-1).     

An ab initio potential surface describing abstraction and exchange for H+CH4

We report an ab initio-based global potential energy surface for H+CH4 that describes the abstraction and exchange reactions. The PES, which is invariant with respect to any permutation of five H atoms, is a fit to 20,728 electronic energies calculated using the partially spin-restricted coupled-cluster method (RCCSD(T)) with a moderately large basis (aug-cc-pVTZ). A first set of quasiclassical trajectory calculations using this PES are reported for the H+CD4-->HD+CD3 reaction at collision energies of 0.65 and 1.52 eV and are compared to experiment and recent direct dynamics calculations done with density functional theory.     

Olefin copolymerization via reversible addition-fragmentation chain transfer

Successful statistical copolymerization of an alpha-olefin (1-octene) with an acrylate (butyl acrylate, BA) and with a methacrylate (methyl methacrylate, MMA), employing reversible addition-fragmentation chain transfer (RAFT) mediated polymerization has been accomplished     

Single-Electron Transfer in Frustrated Lewis Pair Chemistry

Frustrated Lewis pairs (FLPs) are well known for their ability to activate small molecules. Recent reports of radical formation within such systems indicate single-electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride, or tetrachloro-1,4-benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single-electron transfer (SET) events; that is, being direct SET to B(C₆F₅)₃ or not. The reactions of H₂ and Ph₃SnH with archetypal P/B FLP systems do not proceed via a radical mechanism. In contrast, reaction with TCQ proceeds via SET, which is only feasible by Lewis acid coordination to the substrate. Furthermore, SET from the Lewis base to the Lewis acid–substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical main-group chemistry.     

Development of a multi-objective coagulation system for long-term fouling control in dead-end ultrafiltration

In this paper, a multi-objective control system has been developed and experimentally tested. The multi-objective control system can be effectively used to control short-term fouling as well as long-term fouling. In an earlier study it was found that coagulant dosing in ultrafiltration can be used effectively to control the short-term fouling resistance during several sequential filtration cycles. To control long-term resistance increase during sequential chemical cleaning cycles, usually, in open-loop setting of the cleaning frequency or variables which influence the cleaning efficiency, such as, the cleaning time and the chemical composition are adjusted. Additional introductory experiments showed that changes in the coagulant dosing have a more pronounced effect on long-term fouling than changes in the usual applied variables. For this reason, it was decided to develop a closed-loop multi-objective controller where the coagulant dosing is used as the manipulated variable to accomplish both control objectives namely the fouling resistance over multiple filtration cycles (the short-term objective), as well as the irreversible fouling resistance over multiple chemical cleaning cycles (long-term objective). However, the controller is too slow to deal with temperature changes influencing the effectiveness of the coagulant dosing. To handle these influences a kind of gain scheduler should be included in the control algorithm.