Fluctuations in a superconducting quantum critical point of multi-band metals

In multi-band metals quasi-particles arising from different atomic orbitals coexist at a common Fermi surface. Superconductivity in these materials may appear due to interactions within a band (intra-band) or among the distinct metallic bands (inter-band). Here we consider the suppression of superconductivity in the intra-band case due to hybridization. The fluctuations at the superconducting quantum critical point (SQCP) are obtained calculating the response of the system to a fictitious space and time dependent field, which couples to the superconducting order parameter. The appearance of superconductivity is related to the divergence of a generalized susceptibility. For a single band superconductor this coincides with the \textit{Thouless criterion}. For fixed chemical potential and large hybridization, the superconducting state has many features in common with breached pair superconductivity with unpaired electrons at the Fermi surface. The T=0 phase transition from the superconductor to the normal state is in the universality class of the density-driven Bose-Einstein condensation. For fixed number of particles and in the strong coupling limit, the system still has an instability to the normal sate with increasing hybridization.Comment: 10 pages, 8 figure

Determination of structure and conformation in solution of syringotoxin, a lipodepsipeptide fromPseudomonas syringae pv.syringae by 2D NMR and molecular dynamics

Strain B427 of Pseudomonas syringae pv. syringae, originally isolated from lemon, produces several bioactive lipodepsipeptides. The structure of Syringotoxin (ST) and Syringopeptins (SPs) has been investigated in these last years. This paper reports the 2D NMR data collected in the study of ST covalent structure. The study was performed in different solvents in order both to prevent aggregation and to completely characterize the side chains features. These include the presence of common and less common aminoacids, which compose the macrocyclic ring and fatty acid side-chain moieties of ST. The nature and position in the molecule of the residues involved in the lactonic ring closure of ST have been identified with certainty. The interpretation of NOE data obtained in acetonitrile/water solution was performed by molecular dynamics calculations in vacuo. This procedure has allowed determination of the nature and number of intramolecular hydrogen bonds and the predominant conformation of ST

The behaviour od deoxyhexose trihaloacetimidates in selected glycosylations

Armed deoxyhexose glycosyl donors are very reactive and sometimes too uncontrollably activated in glycosylation reactions; yields can be thereby reduced, especially when unreactive glycosyl acceptors are involved. In this paper, the behaviour of a range of deoxyhexose trihaloacetimidate (trichloro- and N-phenyl trifluoro-) donors is compared in some selected glycosylations towards biologically relevant targets. The selected N-phenyl trifluoroacetimidates often afforded best results in terms of both donor synthesis and glycosylation yield

An Extended X-ray Absorption Fine Structure study of aqueous solutions by employing Molecular Dynamics simulations

Bromine–oxygen radial distribution functions [g(r)] have been calculated by means of molecular dynamics simulations for aqueous solutions of rubidium bromide, 2‐bromopropane and bromoethane. X‐ray absorption spectra at the bromine K edge have been recorded for these solutions. The water contribution to the extended x‐ray absorption fine structure spectra has been calculated starting from the gBr,O(r) distribution function. Fits of the x‐ray absorption spectra have been performed directly on the raw experimental data, allowing the reliability of the g(r) distribution functions to be verified. The agreement between theoretical and experimental spectra is satisfactory. A procedure to improve model g(r) functions on the basis of the short‐range structural information provided by extended x‐ray absorption fine structure data is proposed