Capillary electrophoresis and inductively coupled plasma spectrometry: Status report

This report focuses on the status, requirements, and potentials of CE-ICP-MS. The ultimate goal of a viable CE-ICP-MS system is to obtain quantitative elemental speciation information and isotopic ratio data for practical biological and environmental metal containing compounds. To make use of the CE separation features, the CE analyte must be introduced efficiently into the ICP. For practical samples, pre- and post-separation enrichment techniques probably are required. The features of electrospray ion sources that can be incorporated in CE-ICP-MS and the potential for microfabricated CE are discussed.     

Plasma desorption mass spectrometry of transition metal complexes of thio- and selenosemicarbazones of 2-acetylpyridines

Summary Californium-252 plasma desorption mass spectra were recorded for complexes of the anions of various thio-and seleno-semicarbazones of 3-acetylpyridines(1–4) with the transition metal ions iron(III) and cobalt(II). Positive ion spectra gave clear evidence of the cation present and fragmentation with loss of ligands or parts of ligands was straightforward. Negative ion spectra likewise provided evidence of the intact anion except with tetracoordinate metal halide systems [MX₄]^– which lost one or more halide atoms. Evidence of fragmentation of the ligand and recombination of the fragments with the metal ion was also observed in the negative ion mode. Spectra were used to revise the structure of a complex previously reported as [FeLCl₂]⁽¹⁾ to [FeL₂]⁺[FeCl₄]^–.     

Study of metal complexes of a tripodal hydroxypyridinone ligand by electrospray tandem mass spectrometry

The tripodal ligand N,N,N-tris[(1,hydroxy-2-pyridinon-6-yl)amide]propylamine was synthesized. It is composed of an anchor (nitrogen atom), a functional group (hydroxamate), and also a spacer of variable length defined by the number of methylene groups linking the anchor and the functional group. The characterization of this ligand in the presence of several divalent metal cations (Fe(II), Mn(II), Co(II) and Cu(II)), performed by electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS), allowed elucidation of oxidation states and also of different fragmentation patterns. The importance of the spacer length was studied in the case of the iron binary complex by comparing this ligand with another with a shorter spacer. In this way the stabilizing conditions, in which hydrogen bonds are implicated, were clarified.     

Hybridization and Melting Behavior of Peptide Nucleic Acid (PNA) Oligonucleotide Chimeras Conjugated to Gold Nanoparticles

Peptide nucleic acids (PNA) and PNA–DNA chimeras carrying thiol groups were used for surface functionalization of Au nanoparticles. Conjugation of PNA to citrate‐stabilized Au nanoparticles destabilized the nanoparticles causing them to precipitate. Addition of a tail of glutamic acid to the PNA prevented destabilization of the nanoparticles but resulted in loss of interaction with complementary sequences. Importantly, PNA–DNA chimeras gave stable conjugates with Au nanoparticles. The hybridization and melting properties of complexes formed from chimera–nanoparticle conjugates and oligonucleotide–nanoparticle conjugates are described for the first time. Similar to oligonucleotide–nanoparticle conjugates, conjugates with PNA–DNA chimeras gave sharper and more‐defined melting profiles than those obtained with unmodified oligonucleotides. In addition, mismatch discrimination was found to be more efficient than with unmodified oligonucleotides.     

Quantum similarity matrices column set as holograms of DF molecular point clouds

A simple argument proves that quantum similarity measures, performed on any density function (DF) tag set of a given quantum object set, create a hologram of such DF tag set.     

Completely soft molecular electrostatic potentials (CoSMEP) and total density functions

Soft molecular electrostatic potentials (SMEP or SEMP) have been recently defined substituting the point-like proton by a Gaussian positive charge distribution. In the present paper an additional step is taken forward, transforming SMEP into a completely soft MEP (CoSMEP). Such transformation is carried out using a charge distributed proton as in SMEP and also a Gaussian positive nuclear charge distribution, instead of the classical point-like nuclear charges. The general form of MEP is roughly preserved, but new features can be noticed. Such new point of view is also associated to the possibility to redefine the molecular charge density. Definition of CoSMEP is thus connected to the definition of total molecular density functions (DF), where to the negative electronic DF is summed up the soft nuclear DF, made of linear combinations of Gaussian distributions of nuclear charges.     

On the nature of atomic shell approximation (ASA) electrostatic molecular potentials (EMP)

General properties of the electrostatic molecular potential (EMP) when obtained by means of the atomic shell approximation (ASA) density function (DF) are discussed. In the present study it is proved that in general and without exceptions promolecular ASA DF provide EMP which are everywhere repulsive. The polarized ASA DF version, providing an alternative enhanced kind of EMP, behaves in such a way that in the neighborhood of negative charged atoms, attractive regions appear resembling the ab initio results.     

The gas phase oxidation of HCOOH by Cl and NH2 radicals. Proton coupled electron transfer versus hydrogen atom transfer*

ABSTRACT

The reaction of formic acid (HCOOH) with chlorine atom and amidogen radical (NH₂) have been investigated using high level theoretical methods such BH&HLYP, MP2, QCISD, and CCSD(T) with the 6–311?+?G(2df,2p), aug-cc-pVTZ, aug-cc-pVQZ and extrapolation to CBS basis sets. The abstraction of the acidic and formyl hydrogen atoms of the acid by the two radicals has been considered, and the different reactions proceed either by a proton coupled electron transfer (pcet) and hydrogen atom transfer (hat) mechanisms. Our calculated rate constant at 298?K for the reaction with Cl is 1.14?×?10^?13?cm³?molecule^?1?s^?1 in good agreement with the experimental value 1.8?±?0.12/2.0?×?10^?13?cm³?molecule^?1?s^?1 and the reaction proceeds exclusively by abstraction of the formyl hydrogen atom, via hat mechanism, producing HOCO+ClH. The calculated rate constant, at 298?K, for the reaction with NH₂ is 1.71?×?10^?15?cm³?molecule^?1?s^?1, and the reaction goes through the abstraction of the acidic hydrogen atom, via a pcet mechanism, leading to the formation of HCOO+NH₃.     

Emulsion Copolymerization of Vinyl Acetate and Vinyl Silanes: Kinetics and Development of Microstructure

The batch emulsion copolymerization of vinyl acetate with different vinyl silane functional monomers (vinyl trimethoxysilane [VTMS], vinyl triethoxysilane [VTES], and vinyl silanetriol [VSTO]) is studied. The nature of the silane strongly affects the development of the microstructure and crosslinking ability of the latexes. A combination of techniques (Soxhlet extraction, centrifugation, assymetric‐flow field flow fractionation AF4/MALS/RI) shows that the factor controlling the molar mass and crosslinking density is the degree of hydrolysis of the alkoxysilane, producing higher molar masses and degrees of crosslinking when the degree of hydrolysis is high. Thus, the copolymer containing VSTO produced a very crosslinked latex, the one with VTMS produced a latex with a low degree of crosslinking in the wet state that can yield high degrees of crosslinking upon drying, and the latex with VTES do not produce significant amounts of crosslinking neither before nor after drying.