Influence of the apical ligand in the thermotropic mesomorphism of cationic copper-based surfactants

A new pyridine-based bidentate ligand L (PyC18) was used to develop copper-containing surfactants that exhibit mesomorphism. Complexes [(L (PyC18)) 2Cu (II)Y]Y were synthesized, where Y is an anionic ligand bromo ( 1), nitrato ( 2), or perchlorato ( 3). The nature of these apical ligands determines the mesogenic behavior of 1- 3: The smallest bromo-substituted species 1 shows a metastable liquid crystalline phase at 110 degrees C, the nitrato-substituted 2 increases the transition temperature to 136 degrees C, and the bulky perchlorato-substituted 3 shows reversible mesophases at 153 degrees C. The behavior of these complexes shows similarities and suggests that at low temperatures the crystals of these compounds are bilayered structures with interdigitated alkyl tails. At higher temperatures the tails undergo rapid conformational changes that force these layers to swell until the opposing alkyl chains are separated from each other, and the mesophase is a monolayer smectic A. Small changes in the geometry of cationic mesogens can be imposed by the presence of apically coordinated anions, allowing for tuning in the properties of the resulting mesophases.     

Density functional theory study of the binding capability of tris(pyrazol-1-yl)methane toward Cu(I) and Ag(I) cations

Density functional theory (DFT) has been used to look into the electronic structure of [M(tpm)]+ molecular ion conformers (M = Cu, Ag; tpm = tris(pyrazol-1-yl)methane) and to study the energetics of their interconversion. Theoretical data pertaining to the free tpm state the intrinsic instability of its kappa3-like conformation, thus indicating that, even though frequently observed, the kappa3-tripodal coordinative mode is unlikely to be directly achieved through the interaction of M(I) with the kappa3-like tpm conformer. It is also found that the energy barrier for the kappa2-[M(tpm)]+ --> kappa3-[M(tpm)]+ conversion is negligible. As far as the bonding scheme is concerned, the tpm --> M(I) donation, both sigma and pi in character, is the main source of the M(I)-tpm bonding, whereas back-donation from completely occupied M(I) d orbitals into tpm-based pi* levels plays a negligible role.     

Nonlinear acoustic scattering by a partially closed surface-breaking crack

A theoretical model describing the nonlinear scattering of acoustic waves by surface-breaking cracks with faces in partial contact is presented. The nonlinear properties of the crack are accounted for by suitable boundary conditions that are derived from micromechanical models of the dynamics of elastic rough surfaces in contact. Both linear and nonlinear responses of the crack are shown to be largest for a shear vertical wave incident on the surface containing the crack at an angle just above the critical angle for longitudinal waves. These findings question the fitness for the purpose of a conventional inspection method, which utilizes shear vertical waves at 45 degrees of incidence to search for surface-breaking cracks in many engineering components. For angles of incidence proximal to the critical angle of longitudinal waves, the efficiency of the second harmonic's generation appears to be the highest. Thanks to the increased sensitivity to surface-breaking cracks, this configuration seems to offer a solution to the localization problem, a task that has eluded nonlinear techniques operating under other circumstances. Finally, this model suggests a simple interpretation of the highly localized nonlinear response of delaminations in composite materials.     

Preparation and reactivity of sterically encumbered organocatalysts and their use in the preparation of (S)-Pregabalin precursors

Herein we describe the preparation of a new class of sterically demanding organocatalysts derived from d-fructose and their use, alongside hitherto unreported doubly quaternarised Cinchona ammonium salts, in the Michael reaction of nitromethane with 4-nitro-5-alkenyl-isoxazoles.     

19F NMR transverse and longitudinal relaxation filter experiments for screening: a theoretical and experimental analysis

Ligand‐based ¹⁹F NMR screening represents an efficient approach for performing binding assays. The high sensitivity of the methodology to receptor binding allows the detection of weak affinity ligands. The observable NMR parameters that are typically used are the ¹⁹F transverse relaxation rate and isotropic chemical shift. However, there are few cases where the ¹⁹F longitudinal relaxation rate should also be used. A theoretical and experimental analysis of the ¹⁹F NMR transverse and longitudinal relaxation rates at different magnetic fields is presented along with proposed methods for improving the sensitivity and dynamic range of these experiments applied to fragment‐based screening. Copyright © 2016 John Wiley & Sons, Ltd.     

Groundstatable fermionic wavefunctions and their associated many-body Hamiltonians

In the vast majority of many-body problems, it is the kinetic energy part of the Hamiltonian that is best known microscopically, and it is the detailed form of the interactions between the particles, the potential energy term, that is harder to determine from first principles. An example is the case of high temperature superconductors: while a tight-binding model captures the kinetic term, it is not clear that there is superconductivity with only an onsite repulsion and, thus, that the problem is accurately described by the Hubbard model alone. Here we pose the question of whether, once the kinetic energy is fixed, a candidate ground state is groundstatable or not. The easiness to answer this question is strongly related to the presence or the absence of a sign problem in the system. When groundstatability is satisfied, it is simple to obtain the potential energy that will lead to such a ground state. As a concrete case study, we apply these ideas to different fermionic wavefunctions with superconductive or spin-density wave correlations and we also study the influence of Jastrow factors. The kinetic energy considered is a simple nearest neighbor hopping term.     

Classical foundations of quantum logic

We construct a languageL for a classical first-order predicate calculus with monadic predicates only, extended by means of a family of statistical quantifiers. Then, a formal semantic model is put forward forL which is compatible with a physical interpretation and embodies a truth theory which provides the statistical quantifiers with properties that fit their interpretation; in this framework, the truth mode of physical laws is suitably characterized and a probability-frequency correlation principle is established. By making use ofL and , a set of basic physical laws is stated that hold both in classical physics (CP) and in quantum physics (QP), which allow the selection of suitable subsets of primitive predicates ofL (the set _P of pure states; the sets _o and _E of operational and exact effects, respectively) and the introduction on these subsets of binary relations (a preclusion relation # on _P , an order relation < on _E . By assuming further physical laws, ( _E , <) turns out to be a complete orthocomplemented lattice [mixtures and atomicity of ( _E , <) also can be introduced by means of suitable physical assumptions]. Two languagesL _E ^x andL _E ^S are constructed that can be mapped intoL; the mapping induces on them mathematical structures, some kind of truth function, an interpretation. The formulas ofL _E ^x can be interpreted as statements about properties of a physical object, and the truth function onL _E ^x is two valued. The formulas ofL _E ^S can be endowed with two different interpretations as statements about the frequency of some physical property in some class (state) of physical objects; consequently, a two-valued truth function and a multivalued fuzzy-truth function are defined onL _E ^S . In all cases the algebras of propositions of these logics are complete orthocomplemented lattices isomorphic to ( _E , <). These results hold both in CP and in QP; further physical assumptions endow the lattice ( _E , <), henceL _E ^x andL _E/S , with further properties, such as distributivity in CP and weak modularity and covering law in QP. In the latter case,L _E ^S andL _E ^S , together with their interpretations, can be considered different models of the same basic mathematical structure, and can be identified with standard (elementary) quantum logics. These are therefore founded on the classical extended languageL with semantic model .