Analysis of low molecular weight organic acids in water with capillary zone electrophoresis employing indirect photometric detection

A capillary zone electrophoretic method for the analysis of low molecular weight carboxylic acids in water was developed. The application uses the chromophore trimellitic acid that allows for indirect photometric detection at 254 nm. Selectivity control by the addition of Ca2+ to the carrier electrolyte made possible a baseline resolved separation of 14 carboxylic acids. Good linearity and repeatability were obtained for both electrokinetic and hydrostatic injection modes. The usefulness of the method is demonstrated by the analysis of a snow sample.     

Novel synthesis modes and properties of [1,4]benzodioxinopyridazines

A simple synthesis involving fusion of catechol and derivatives with 3,4,5-trichloropyridazine has furnished 4-chloro[1,4]benzodioxino[2,3-c]pyridazines 5 for the first time. This new method complements the previously reported base promoted procedure for preparing 4-chloro[1,4]benzodioxino-[2,3-d]pyridazines 3 . Employing both methods, 4-(trifluoromethyl)catechol was converted to the four regio isomers 3b,c and 5c,d . Structure assignment of these four was aided by the remarkably consistent influence of the pyridazine 4-chlorine substituent and diazo-linkage in inducing ¹H nmr downfield shifts of their nearest neighbor phenyl ring protons. Finally, contrary to what might be expected from previously reported results, reaction of methoxide with either 3 or 5 , gave chlorine substitution with formation of methoxybenzodioxinopyridazines 6 and 7 respectively. However, these reactions both give what appears to be an unprecedented rearrangement, with conversion of [2,3-c]-pyridazine to [2,3-d]pyridazine, and vice versa.     

Synthesis and conformational studies of a beta-turn mimetic incorporated in Leu-enkephalin

A beta-turn mimetic in which the four amino acids of a beta-turn have been replaced by a 10-membered ring has been designed, synthesized, and subjected to conformational studies. In the mimetic, the intramolecular CO(i)-HN(i)(+3) hydrogen bond that is often found in beta-turns has been replaced by an ethylene bridge. In addition, the amide bond between residues i and i + 1 was exchanged for a methylene ether isoster. Such a beta-turn mimetic, based on the first four residues of Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu), was prepared in 15 steps. The synthesis relied on a beta-azido alcohol prepared in five steps from Cbz-Tyr(tBu)-OH as a key, i-position building block. tert-Butyl bromoacetate, glycine, and a Phe-Leu dipetide were then used as building blocks for positions i + 1, i + 2, and i + 3, respectively. Conformational studies based on (1)H NMR data showed that the beta-turn mimetic was flexible, but that it resembled a type-II beta-turn at low temperature. This low energy conformer closely resembled the structure determined for crystalline Leu-enkephalin.     

On the structure and desorption dynamics of DNA bases adsorbed on gold: a temperature-programmed study

The structure and desorption dynamics of mono- and multilayer samples of adenine, cytosine, guanine, and thymine on polycrystalline gold thin films are studied using temperature-programmed desorption-infrared reflection absorption spectroscopy (TPD-IRAS) and temperature-programmed desorption-mass spectroscopy (TPD-MS). It is shown that the pyrimidines, adenine and guanine, adsorb to gold in a complex manner and that both adhesive (adenine) and cohesive (guanine) interactions contribute the apparent binding energies to the substrate surface. Adenine displays at least two adsorption sites, including a high-energy site (210 degrees C, approximately 136 kJ/mol), wherein the molecule coordinates to the gold substrate via the NH2 group in an sp3-like, strongly perturbed, nonplanar configuration. The purines, cytosine and thymine, display a less complicated adsorption/desorption behavior. The desorption energy for cytosine (160 degrees C, approximately 122 kJ/mol) is similar to those obtained for adenine and guanine, but desorption occurs from a single site of dispersed, nonaggregated cytosine. Thymine desorbs also from a single site but at a significantly lower energy (100 degrees C, approximately 104 kJ/mol). Infrared data reveal that the monolayer architectures discussed herein are structurally very different from those observed for the bases in the bulk crystalline state. It is also evident that both pyrimidines and purines adsorb on gold with the plane of the molecule in a nonparallel orientation with respect to the substrate surface. The results of this work are discussed in the context of improving the understanding of the design of capturing oligonucleotides or DNA strands for bioanalytical applications, in particular, for gold nanoparticle-based assays.     

Atomic absorption spectrometric determination of phosphorus in biological materials

The phosphorus content in the National Bureau of Standards, Standard Reference Materials orchard and tomato leaves, bovine liver and oyster tissue is determined by three atomic absorption spectrometric techniques: measurements of solid and liquid samples against liquid standards, and measurements based on standard additions. All methods gave results which agreed well with the certificate values. Compared to methods involving decomposition and atomization from solution, solid sampling offers the advantages of being direct and fast, and of requiring only small amounts of sample.     

Poly(dimethylsiloxane) microchip: microchannel with integrated open electrospray tip

A polymer microchip with an open tip for electrospray mass spectrometry is presented. The tip consists of a groove with parallel walls where a droplet can form at the end surface. A lid covers the whole chip except at the microchannel tip, which is left open. Poly(dimethylsiloxane) (PDMS) microchips were cast using a nickel mould which in turn was replicated from a dry etched silicon wafer. Tips with microchannel widths of around 50 microm could easily be replicated. Since the tip had no cover, the assembly of microchip and cover was simplified. A total ion current variation of 5% during 300 s was achieved for a 1 microM myoglobin solution. The non-complex design of the cover makes it suitable for versatile tests of chip prototypes. The nickel mould was found to be useful for PDMS microstructure fabrication. Also, such a robust mould allows casting electrospray tips in more rigid thermoset materials.     

Synthesis and identifications of potential metabolites as biomarkers of the synthetic cannabinoid AKB-48

AKB-48 belongs to the family of synthetic cannabinoids. It has strong binding affinity to CB₁ receptor and is psychoactive. It is banned in many countries including USA, Japan, Germany, New Zealand, Singapore and China etc. But the difficulty in detecting the parent compound in urine samples highlights the importance of studies of its metabolites. Here we report the synthesis of 19 potential metabolites of AKB-48, among which, compounds 2, 9, 10, 30 and 31, together with the commercially available substance 5 were identified as metabolites of AKB-48 by comparison with one authentic human urine sample and human liver microsomal data. Compounds 10 and 30 could be of use as biomarkers in detecting AKB-48 in human urine samples.