Electrophoretic investigation of the boron cluster anion [7-(2'-pyridyl)-nido-7,8-dicarbaundecaborate]- and its protonated zwitterionic product

ACN is a better solvent than methanol for both [NMe(4)] [7-(2'-pyridyl)-nido-7,8-C(2)B(9)H(11)] and its protonated anion. The investigated laboratory preparations of the salt and of its protonated anion are electrophoretically pure solids stable for 2 months at 4 degrees C. At a longer storage, the solid salt is more stable than the solid protonated anion. In the 40:60 v/v water-methanol solvent, decomposition products of the salt anion are detectable after one-week storage of the salt solution at 4 degrees C. The protonated anion does not decompose for almost 1 year in water-organic solutions at 4 degrees C. The exchange of the proton between the protonated anion and the solution is reversible and fast at room temperature. The pH dependence of the mobility of the [7-(2(-pyridyl)-nido-7,8-C(2)B(9)H(11)](-) anion reveals that the basicity of the nitrogen atom in the pyridine ring is not significantly affected by the bonding of the pyridyl group to the nido-7,8-C(2)B(9)H(11) cluster in position 7 and that the proton from the solution is accepted by the nitrogen atom in the 2-pyridyl ring. The UV-spectra of the salt and of its protonated anion indicate that the accepted proton is probably slightly shifted to the open face of the nido-7,8-C(2)B(9)H(11) cluster. The [1](-) is chiral.     

Incorporation of a monolithic column into sequential injection system for drug-protein binding studies

A sequential injection analysis (SIA) manifold was incorporated with a monolithic strong anion-exchanger disk for on-line drug-protein interaction studies. The antibiotic ciprofloxacin (CF) was selected as a model drug compound. The separation principle was based on the strong retention of bovine serum albumin (BSA) on the monolithic strong anion-exchanger and the liberation/release of the free form of the drug. Elution of the retained BSA was easily achieved by delivering a different mobile phase via the SIA manifold. The type of functional group of the monolithic support, the breakthrough volume and the injected volumes of CF and BSA were studied and optimized. The influence of the variation of incubation time was studied in on-line binding assays. Scatchard plot was employed to obtain the number of binding sites and the equilibrium binding constants. For the off-line study of the CF-BSA binding, two binding classes were determined with constants of (3.16+/-0.21)x10(6)M(-1) and (1.27+/-0.48)x10(4)M(-1) and 6.1+/-1.3 and 17.8+/-3.9 binding sites per class, respectively. In non-equilibrium binding experiments the binding rate constant was k(1)=785 M(-1)min(-1). All measurements were monitored with fluorescence (lambda(ext)=300 nm, lambda(em)=460 nm) and spectrophotometric detection (lambda=280 nm). To evaluate the accuracy of the developed method the obtained results were compared versus ultrafiltration experiments and were found in good agreement.     

Investigation of multi-layered silicate ceramics using laser ablation optical emission spectrometry,laser ablation inductively coupled plasma mass spectrometry,and electron microprobe analysis

The applicability of laser ablation (LA) inductively coupled plasma (ICP) spectrometry for assessing elemental distributions in layered ceramics was investigated and compared with electron probe microanalysis (EPMA). Ordinary glazed wall tiles were employed as model specimens due to their defined structure and composition. They were used for calibration in the analysis of ancient pottery. A qualitative depth profile was acquired by single-spot laser drilling perpendicular to coatings with a Nd:YAG (1064 nm) laser coupled with an ICP optical emission spectrometer (OES). The lower lateral resolution associated with the laser spot diameter of 1.0 mm led to smoothing of the depth profile due to the averaging of local irregularities. In addition, transverse line scans by ablation across the tile section using an ArF* (193 nm) laser coupled with an ICP mass spectrometer (MS) were performed. LA-ICP-OES depth profiles and LA-ICP-MS transverse scans were validated by EPMA section scans and 2D back-scattered electrons images. The LA-ICP-OES acquisition was less dependent on sample surface and layer irregularities, whereas the transverse line scan over the tile section with the small-spot beam offered insight into the micromorphology of the individual layer. The combined approach revealed the occurrence of individual mineral grains, micro-heterogeneities and the character of interfaces between layers.     

Design and synthesis of novel N-benzylidenesulfonohydrazide inhibitors of MurC and MurD as potential antibacterial agents

A series of novel N-benzylidenesulfonohydrazide compounds were designed and synthesized as inhibitors of UDP-N-acetylmuramic acid: L-alanine ligase (MurC) and UDP-N-acetylmuramoyl-L-alanine: D-glutamate ligase (MurD) from E. coli, involved in the biosynthesis of bacterial cell-walls. Some compounds possessed inhibitory activity against both enzymes with IC(50) values as low as 30 microM. In addition, a new, one-pot synthesis of amidobenzaldehydes is reported.     

An experimental and theoretical study of stereoselectivity of furan-maleic anhydride and furan-maleimide diels-alder reactions

The stereoselectivity of the reaction of furan (1) with maleic anhydride (2) and maleimide (3) was studied experimentally and theoretically. Although the two reactions are highly similar with regard to their preference for endo and exo steroisomers, notable differences were experimentally observed and explained on the basis of calculated reaction-free energies and transition-state barriers. The experimental values of rate constants (k(1+2endo) = (1.75 +/- 0.48) x 10(-5); mol(-1) l s(-1); k(1+2exo) = (3.10 +/- 0.55) x 10(-5); mol(-1) l s(-1); k(1+3endo) = (1.93 +/- 0.082) x 10(-5); mol(-1) l s(-1), k(1+3exo) = (1.38 +/- 0.055) x 10(-5); mol(-1) l s(-1) all at 300 K) and the observed reaction course clearly confirm that neither of these reactions are prototypical examples of Diels-Alder [4 + 2] cycloadditions, whose dominant preference is for endo isomers. However, only by comparing their energetics-calculated at the CCSD(T) level of theory-with the analogous reactions involving cyclopentadiene (8) as a diene can these observations be understood. The low thermodynamic stability of furan [4 + 2] adducts opens retro-Diels-Alder reaction channels and overrules the very small kinetic preference (calculated and measured here) of initial formation for endo stereoisomers. On a macroscopic scale "an irregular"-thermodynamically more stable-exo stereoisomer was consequently observed as a dominant species.     

Optodynamic study of multiple pulses micro drilling

This paper describes an analysis of pulsed lasers micro-drilling of different metals. Study focuses to an optodynamic phenomenon which appears as thermal effects induced by laser light pulses and leads to dynamic process manifested as ultrasonic shock waves propagating into the sample material. The shock waves are detected by a non-contact optical method by using arm compensated Michelson. Monitoring of the main parameters of the micro drilling such as material ablation rate and efficiency was realized by analysis of the optodynamic signals. The process is characterized by decreasing ablation rate that leads to the finite hole depth. The experimental part of study comprehends a comparison between various metals. In order to describe decreasing ablation rate a theoretical model based on the energy balance is proposed. It considers the energy/heat transfer from the laser beam to the material and predicts a decreasing drilling rate with an increasing number of successive laser pulses. According to the proposed model, the finite depth of the hole appears as a consequence of the increasing surface area through which the energy of the laser beam is conducted away to the material around the processed area. Decreasing ablation rate and the finite hole depth predicted by model were in good agreement with the experimental results.     

Matrix-assisted laser desorption/ionization analysis of lipids and high molecular weight hydrocarbons with lithium 2,5-dihydroxybenzoate matrix

Lithium 2,5-dihydroxybenzoate (LiDHB) is shown to be a very effective matrix for matrix-assisted laser desorption/ionization (MALDI) analysis of nonpolar long-chain lipids, hydrocarbons and polymers. Under standard desorption and ionization conditions using a conventional nitrogen UV laser (337 nm), hydrocarbons (C(24)-C(40)), diverse lipids (triglycerides, diglycerides, wax esters from leaves) and saturated polymers are effectively lithiated providing [M+Li](+) ions. The formation of lithiated hydrocarbons is not accompanied by an elimination of hydrogen or other fragmentation reactions and, due to the relatively simple isotopic distribution of lithium, seems to be more useable for analysis of hydrocarbon mixtures than the previously used silver cationization agents. The mass calibration can be conveniently performed either externally or internally using poly(ethylene glycol) commercial standards.     

Implementation of proficiency testing schemes for a limited number of participants

A metrological background for the selection and use of proficiency testing (PT) schemes for a limited number N of laboratories-participants (less than 20–30) is discussed. The following basic scenarios are taken into account: (1) adequate matrix certified reference materials (CRM) or in-house reference materials (IHRM) with traceable property values are available for PT use as test items; (2) no appropriate matrix CRM is available, but a CRM or IHRM with traceable property values can be applied as a spike or similar; (3) only an IHRM with limited traceability is available. The discussion also considers the effect of a limited population of PT participants N _p on statistical assessment of the PT results for a given sample of N responses from this population. When N _p is finite and the sample fraction N/N _p is not negligible, a correction to the statistical parameters may be necessary. Scores suitable for laboratory performance assessment in such PT schemes are compared. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel.