1,3-Dialkylimidazolium-2-carboxylates as versatile N-heterocyclic carbene-CO2 adducts employed in the synthesis of carboxylates and α-alkylidene cyclic carbonates

1,3-Dialkylimidazolium-2-carboxylate compounds of formulas 1a, 2, and 4 have been synthesized and fully characterized by X-ray spectroscopy quite recently. Up today, these compounds have found some interesting applications as precursors of N-heterocyclic carbenes (NHCs) used as ligands for metal-complexes or in the synthesis of organic compounds and ionic liquids. We have recently reported the use of 1-butyl, 3-methylimidazolium-2-carboxylate and 1,3-dimethylimidazolium-2-carboxylate in a CO₂-transfer reaction to CH₃OH and acetophenone for the synthesis of methylcarbonate and benzoylacetate. The scope of this CO₂-transfer reaction has been expanded to several organic compounds with active hydrogen (acetone, cyclohexanone, and benzylcyanide) for the synthesis of carboxylates of pharmaceutical interest, and to propargyl alcohols for the synthesis of α-alkylidene cyclic carbonates.     

Fast analysis of complex metallic alloys by double-pulse time-integrated Laser-Induced Breakdown Spectroscopy

Results are reported on the application of double-pulse Laser-Induced Breakdown Spectroscopy (LIBS) for fast analysis of complex metallic alloys. The approach followed for the determination of the composition of the alloys is based on the time-integrated acquisition of LIBS spectra emitted by plasmas induced by collinear double-pulse laser excitation. The spectra are analysed using the Partial Least Squares method, which allows the determination of sample composition even in the presence of strong spectral interferences. The results shown indicate the possibility of measuring the composition of complex metallic alloys in very short times and using relatively cheap LIBS instrumentation.     

Poly(ε-caprolactone) modified by functional groups: Preparation and chemical–physical investigation

Functionalization of polymers is a particular relevant approach in the field of biodegradable polymers, where modifications are often required to allow these materials to replace more conventional, not biodegradable polymers in a wider range of applications. This article will report on functionalization of poly(ε-caprolactone) with unsaturated monomers bearing either anhydride groups (PCL-g-(MA-GMA)) or tertiary amines (PCL-g-DMAEA), obtained through radical grafting in a Brabender mixer. Crystallization kinetics parameters have been determined with several techniques (rheology, optical microscopy and differential scanning calorimetry) and the results obtained are in good agreement. It was observed that the crystallization rate significantly increases in the case of the modified polymers.     

Synthesis of 1,3-dialkylimidazolium-2-carboxylates by direct carboxylation of 1,3-dialkylimidazolium chlorides with CO2

1,3-Dialkylimidazolium-2-carboxylates 1a and 1b are obtained in good to excellent yield and selectivity by carboxylation of the corresponding 1,3-dialkylimidazolium chloride salts with a CO₂/Na₂CO₃ system at temperatures ranging from 80 to 135 °C. The effect of temperature and reaction time on the yield and the selectivity of the carboxylation products has been studied. Coupling the CO₂-based synthesis of 1,3-dialkylimidazolium-2-carboxylates with the transcarboxylation reaction described earlier [Tommasi, I.; Sorrentino, F.; Tetrahedron Lett., 2005, 46, 2141] allows us to set up a new synthetic procedure for the synthesis of organic carboxylates and alkylcarbonate anions avoiding the use of strong bases.     

Iterative retrieval of one-dimensional x ray wave field using a single intensity measurement

The problem of retrieving a complex function from the modulus of its Fourier transform has non-unique solutions in one dimension. Therefore iterative phase retrieval methods cannot in general be confidently applied to one-dimensional problems, due to the presence of ambiguities. We present a method for a posteriori reduction of the ambiguities based on the correlation analysis of the solution of a large number of runs of an iterative phase retrieval algorithm with different random starting phases. The method is applied to experimentally measured diffraction patterns from an x ray waveguide illuminated by hard x rays. We demonstrate the possibility of retrieving the complex wave field at the exit face of the waveguide and compare the result with theoretical prediction.     

New Chemotypes for the Inhibition of (p)ppGpp Synthesis in the Quest for New Antimicrobial Compounds

Antimicrobial resistance (AMR) poses a serious threat to our society from both the medical and economic point of view, while the antibiotic discovery pipeline has been dwindling over the last decades. Targeting non-essential bacterial pathways, such as those leading to antibiotic persistence, a bacterial bet-hedging strategy, will lead to new molecular entities displaying low selective pressure, thereby reducing the insurgence of AMR. Here, we describe a way to target (p)ppGpp (guanosine tetra- or penta-phosphate) signaling, a non-essential pathway involved in the formation of persisters, with a structure-based approach. A superfamily of enzymes called RSH (RelA/SpoT Homolog) regulates the intracellular levels of this alarmone. We virtually screened several fragment libraries against the (p)ppGpp synthetase domain of our RSH chosen model Rel_Seq, selected three main chemotypes, and measured their interaction with Rel_Seq by thermal shift assay and STD-NMR. Most of the tested fragments are selective for the synthetase domain, allowing us to select the aminobenzoic acid scaffold as a hit for lead development.     

An FD-BPM with adaptive mesh for longitudinally varying optical structures

A finite difference beam propagation method (FD-BPM) algorithm using an adaptive mesh is proposed for optimal use of computer memory and minimization of CPU times in three-dimensional longitudinally varying guiding structures. Preliminary results confirming its feasibility and the advantages of the new algorithm both in CPU and computer memory requirements are described in a 2D case using a Y-junction.     

A new analytical technique for vibration analysis of non-proportionally damped beams

Vibrating linear mechanical systems, in particular continuous systems, are often modelled considering proportional damping distributions only, although in many real situations this simplified approach does not describe the dynamics of the system with sufficient accuracy. In this paper an analytical method is given to take into account the effects of a more general viscous damping model, referred to as non-proportional damping, on a class of vibrating continuous systems. A state-form expansion applied in conjunction with a transfer matrix technique is adopted to extract the eigenvalues and to express the eigenfunctions in analytical form, i.e., complex modes corresponding to non-synchronous motions. Numerical examples are included in order to show the efficiency of the proposed method; non-proportional damping distributions of different type, such as internal and external lumped or distributed viscous damping, are tested on non-homogeneous Euler-Bernoulli beams in bending vibration with different boundary conditions. Finally, a discussion on root locus diagrams behaviour and on modal damping ratio significance for non-proportionally damped systems is presented.