Revisiting Keteniminium Salts: More than the Nitrogen Analogs of Ketenes

Keteniminium salts are powerful electrophilic heterocumulene reagents well‐known for their selectivity and stereocontrol in [2+2] cycloadditions to olefins and carbonyl derivatives. Furthermore, they are readily accessible from stable and simple precursors under a variety of different conditions. Herein, we present the chemistry of keteniminium salts with the hindsight of time, describe preparation methods, recent [2+2] chemistry, mechanistic studies, and assorted applications that significantly extend the scope of utility of these unique electrophilic heterocumulenes.     

Structural identification of fatty acid methyl esters by collision spectra of their [M ? H]− species

Negative ion chemical ionization linked to collisionally activated decomposition (CAD) experiments has proved to be an efficient analytical tool in mass spectrometric characterization of fatty acids. The CAD mass-analysed ion kinetic energy spectra of [M ? H]^? species, obtained by OH^? reaction with a selection of six C₁₈ fatty acid methyl esters, reveal useful correlations with the original structure of the neutrals, giving evidence of both chain branching and double bond positions.     

Serum protein profiles of patients with pancreatic cancer and chronic pancreatitis: searching for a diagnostic protein pattern.

In this study, 13 sera from patients with pancreatic cancer, 9 from chronic pancreatitis and 10 from healthy subjects were analyzed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The MALDI mass spectra revealed the presence of several low molecular weight peptides, among which some were detected only in the sera from both pathological conditions. On the other hand many peptides were observed only in control sera, and were absent in the sera from the two diseases. Therefore, MALDI analysis of the low molecular weight fraction (<10 000 Da) of sera from patients with pancreatic diseases enabled us to identify the presence of some disease-related signals and also some signals characteristic of normal subjects.     

High Level Languages Implementation and Analysis of 3D Navier-Stokes Solvers

In this work we introduce PRIN-3D (PRoto-code for Internal flows modeled by Navier-Stokes equations in 3-Dimensions), a new high level algebraic language (Matlab$^®$) based code, by discussing some fundamental aspects regarding its basic solving kernel and by describing the design of an innovative advection scheme. The main focus was on designing a memory and computationally efficient code that, due to the typical conciseness of the Matlab coding language, could allow for fast and effective implementation of new models or algorithms. Innovative numerical methods are discussed in the paper. The pressure equation is derived with a quasi-segregation technique leading to an iterative scheme obtained within the framework of a global preconditioning procedure. Different levels of parallelization are obtainable by exploiting special pressure variable ordering patterns that lead to a block-structured Poisson-like matrix. Moreover, the new advection scheme has the potential of a controllable artificial diffusivity. Preliminary results are shown including a fully three-dimensional internal laminar flow evolving in a relatively complex geometry and a 3D methane-air flame simulated with the aid of libraries based on the Flamelet model.     

Self-assembly of noncyclic bis-D- and L-tripeptides into higher order tubular constructs: design, synthesis, and X-ray crystal superstructure

Trans (1R,2R)-diaminocyclohexane was used as a semirigid vicinal diamine to anchor two N-protected tripeptides consisting of L-D-L amino acids as carboxy terminal amides. The bis-tripeptide consisting of L-Ser (OBn)-D-Ser (OBn)-L-Ser (O-p-bromobenzyl) Boc afforded X-ray quality crystals containing benzene and chloroform solvent molecules. Analysis of the solid-state structure revealed a highly H-bonded helical open-ended tubular superstructure. The tripeptide strands intertwine like a pair of self-embracing arms, held together by a gamma-turn and a 14-membered antiparallel H-bonded macroring spanning the first and third amino acid residues within each strand. Whereas the tripeptide from the R,R anchor gave beautiful crystals from benzene and chloroform, the analogous construct from the S,S-anchored diamine gave a gel. Related bis-tripeptides with different amino acids showed extensive intramolecular H-bonding based on NMR titration and dilution experiments.     

New platinum(II) and palladium(II) quinoline-imine-pyridine, quinoline-imine-thiazole and quinoline-imine-imidazole complexes by metal-assisted condensation reactions

Pt(II) and Pd(II) methyl- and chloro-complexes with the tridentate N-donor ligands ((pyridin-2-yl)methylene)quinolin-8-amine (NNPy), ((pyridin-2-yl)ethylidene)quinolin-8-yl-amine (NNMePy), (phenyl(pyridin-2-yl)methylene)quinolin-8-yl-amine (NNPhPy), ((thiazol-2-yl)methylene)quinolin-8-amine (NNTh) and ((imidazol-4-yl)methylene)quinolin-8-amine (NNImH) were prepared by metal-assisted condensation of 8-aminoquinoline and an ortho-substituted aldehydo- or keto- N-heterocycle. Preliminary reactivity studies involving the coordinated tridentate N-donors, the chloro-ligand and the M-CH₃ bond were carried out, leading to the synthesis of several new complexes. During these studies, the formation of a novel five-coordinate Pt(II) carbonyl-complex was observed.     

The racemate cage. Influence of p(1),n(1) salt occurrence on enantiomer separation processes. The case of trans-chrysanthemic acid

The occurrence of p(1),n(1) salt when accompanied by substrate self-association can have profound effects on enantiomer separation processes of non-racemic mixtures, impeding the complete recovery of the major enantiomer through formation of an inescapable racemate cage.