Construction of multiporphyrin arrays using ruthenium and rhodium coordination to phosphines

The synthesis of linear multiporphyrin arrays with mono- and bisphosphine-substituted porphyrins as ligand donors and ruthenium(II) or rhodium(III) porphyrins as ligand acceptors is described. With appropriate amounts of the building blocks mixed, linear dimeric and trimeric arrays have been synthesized and analyzed by (1)H NMR and (31)P NMR spectroscopy. The Ru/Rh acceptor porphyrins can be located either at the periphery or in the center of the array. Likewise, the monophosphine porphyrins can be positioned at the periphery, thus allowing a high degree of freedom in the overall composition of the arrays. This way, both donor and acceptor porphyrins can act as chain extenders or terminators. One of the trimeric complexes with two nickel and one ruthenium porphyrin has also been analyzed by X-ray crystallography. Attempts have also been made to synthesize higher order arrays by mixing appropriate amounts of the porphyrins; however, from the NMR data it cannot be concluded if monodisperse five, seven, or nine porphyrin arrays are present or if the solutions are composed of a statistical mixture of smaller and larger arrays.     

Single-photon vacuum-ultraviolet laser-pulsed-field ionization-photoelectron studies of trans- and cis-1-bromopropenes

The vacuum-ultraviolet (VUV) pulsed-field ionization-photoelectron (VUV-PFI-PE) spectra of trans-1-bromopropene (trans-CH(3)CH[Double Bond]CHBr) and cis-1-bromopropene (cis-CH(3)CH[Double Bond]CHBr) have been measured in the energy region of 74 720-76 840 cm(-1). The simulation of fine structures observed in the origin VUV-PFI-PE vibrational bands of these molecules has provided the ionization energies (IEs) of trans-1-bromopropene and cis-1-bromopropene to be 74 779.3+/-2.0 cm(-1) (9.2715+/-0.0002 eV) and 75 140.2+/-2.0 cm(-1) (9.3162+/-0.0002 eV), respectively. The vibrational bands resolved in these VUV-PFI-PE spectra at energies 0-1700 cm(-1) above the IEs of trans-1-bromopropene and cis-1-bromopropene have been assigned based on theoretical vibrational frequencies and calculated Franck-Condon factors for the ionization transitions.     

Synthesis of gramicidin S and its analogues via an on-resin macrolactamization assisted by a predisposed conformation of the linear precursors

A simple and efficient preparation of gramicidin S and its analogues is described. It involves solid-phase peptide synthesis and on-resin macrolactamization without side chain protection, affording cyclic products in high yield and high purity. The high specificity of the cyclization reaction was shown to originate in the formation of a pre-organized conformation of the linear biosynthetic precursor of gramicidin S. This facile method will provide convenient access to the analogues of the natural product for functional optimization to counter microbial resistance.     

The kinetics of hydrogen peroxide initiated polymerisation of methacrylamide

A kinetic study of the aqueous polymerisation of methacrylamide initiated by hydrogen peroxide has shown that the polymerisation proceeds in two stages. The rate of polymerisation up to about 16% conversion is represented by the equation

Within this period, the hydrogen peroxide is completely consumed and a hydroperoxide of methacrylamide is formed. Subsequently this hydroperoxide initiates polymerisation.     

Systematic optimization of micellar electrokinetic chromatographic separation of flavonoids

Summary A simple and rapid systematic optimization scheme was described for the micellar electrokinetic chromatographic separation of a group of flavonoids. The scheme employed an interpretative optimization approach to predict the optimum conditions for the separation of a group of flavonoids by micellar electrokinetic chromatography. By performing a set of nine pre-planned experiments conducted over the maximum working range for the system, global optimum separation conditions could be determined. To validate the optimization procedure, additional experiments were performed using the optimum experimental conditions derived from the optimization scheme. The results showed that satisfactory separation of all the peaks could be obtained. In addition, the application of the method in micropreparative micellar electrokinetic chromatography of the flavonoids was demonstrated.     

Simple alkenes as substitutes for organometallic reagents: nickel-catalyzed, intermolecular coupling of aldehydes, silyl triflates, and alpha olefins

A nickel-catalyzed method for the three-component coupling of alkenes (ethylene and alpha olefins), aldehydes, and silyl triflates is described, and this process represents the first catalytic method for coupling aldehydes and alkenes to give allylic alcohol derivatives. Conceptually, the alkene functions as a replacement for an alkenylmetal reagent.     

In-situ derivatisation of degradation products of chemical warfare agents in water by solid-phase microextraction and gas chromatographic-mass spectrometric analysis

A new analytical procedure was developed for the extraction of degradation products of chemical warfare agents from water and for in-situ derivatisation prior to analysis by gas chromatography-mass spectrometry (GC-MS). With this new procedure, degradation products of the chemical warfare agents can be analysed and identified without going through laborious sample preparation. Parameters such as fiber selection, pH, salt content, derivatisation temperature, extraction and derivatisation periods, and sequence of adsorption/derivatisation were experimented with, to optimise the efficiency of this method. The detection limit is in the ppb to sub-ppb range with GC-MS in the full scan mode. Based on six injections of the devised procedure, a relative standard deviation from 10-35% can be achieved, depending on the compound. This method was demonstrated during the 4th International Interlaboratory Proficiency Test organised by the Organisation for the Prohibition of Chemical Weapons to be comparable to existing recommended operating procedures for verification of degradation products of chemical warfare agents.