Design and performance of some microflow-cell potentiometric transducers

The paper presents and compares the design of three potentiometric transducers: ion-selective field effect transistor (ISFET), solid-state Ag/AgCl electrode and miniaturized classical Ag/AgCl electrode. The reported transducers were fabricated using different, less or more complicated and expensive, technologies. The transducers were constructed to be compatible with the sensor housing of the flow-cell, designed previously. Moreover, the back-side contact structures of the two planar devices, where electrical connectors and the sensing layer are on the opposite sides, facilitated their application in the flow analysis. Exemplary potassium-selective microsensors based on developed transducers were prepared, applying plasticized PVC and polysiloxane membranes containing valinomycine. The determined microsensor performances allowed comparison of their usefulness for multiparameter flow analysis.     

Crystal structure of Schiff base derivative of 2,2′-dihydroxybiphenyl-3-carbaldehyde with n-butylamine

Crystals of the Schiff base derivative of 2,2′-dihydroxybiphenyl-3-carbaldehyde with n-butylamine were examined using X-ray diffraction, FT-IR and CPMAS spectroscopy. Their space group is with a=8.377(2), b=12.214(2), c=14.774(3) Å, =76.62(3)°, β=81.34(3)°, γ=86.62(3)° and Z=4. The unit cell contains two symmetry-independent zwitterions. The hydrogen atom of the protonated N atom of the Schiff base is linked to the oxygen atom of the carbonyl group at position 2, which in turn is linked to the hydroxyl group by a short hydrogen bond [molecule A: NO=2.614(3), OO=2.520(3) Å; molecule B: NO=2.594(4), OO=2.526(3) Å]. The OHO⁻H⁺N bifurcated intramolecular hydrogen bonds are crystallographically asymmetric. The results of the FT-IR, ¹H, ¹³C, ¹⁵N NMR and CPMAS study of the crystals are in agreement with the X-ray data. Instead of a continuous absorption, only a broad band is found indicating relatively low proton polarizability in the two types of the cooperative relatively short intramolecular hydrogen bonds. The ¹⁵N NMR chemical shift indicates the protonation of the Schiff base.     

Tyrosine nitration affects thymidylate synthase properties

Highly purified preparations of thymidylate synthase, isolated from calf thymus, and L1210 parental and FdUrd-resistant cells, were found to be nitrated, as indicated by a specific reaction with anti-nitro-tyrosine antibodies, suggesting this modification to appear endogenously in normal and tumor tissues. Each human, mouse and Ceanorhabditis elegans recombinant TS preparation, incubated in vitro in the presence of NaHCO(3), NaNO(2) and H(2)O(2) at pH 7.5, underwent tyrosine nitration, leading to a V(max)(app) 2-fold lower following nitration of 1 (with human or C. elegans TS) or 2 (with mouse TS) tyrosine residues per monomer. Enzyme interactions with dUMP, meTHF or 5-fluoro-dUMP were not distinctly influenced. Nitration under the same conditions of model tripeptides of a general formula H(2)N-Gly-X-Gly-COOH (X = Phe, Tyr, Trp, Lys, Arg, His, Ser, Thr, Cys, Gly), monitored by NMR spectroscopy, showed formation of nitro-species only for H-Gly-Tyr-Gly-OH and H-Gly-Phe-Gly-OH peptides, the chemical shifts for nitrated H-Gly-Tyr-Gly-OH peptide being in a very good agreement with the strongest peak found in (15)N-(1)H HMBC spectrum of nitrated protein. MS analysis of nitrated human and C. elegans proteins revealed several thymidylate synthase-derived peptides containing nitro-tyrosine (at positions 33, 65, 135, 213, 230, 258 and 301 in the human enzyme) and oxidized cysteine (human protein Cys(210), with catalytically critical Cys(195) remaining apparently unmodified) residues.     

Tabu search algorithm for DNA sequencing by hybridization with isothermic libraries

In this paper, a problem of isothermic DNA sequencing by hybridization (SBH) is considered. In isothermic SBH a new type of oligonucleotide libraries is used. The library consists of oligonucleotides of different lengths depending on an oligonucleotide content. It is assumed that every oligonucleotide in such a library has an equal melting temperature. Each nucleotide adds its increment to the oligonucleotide temperature and it is assumed that A and T add 2 degrees C and C and G add 4 degrees C. The hybridization experiment using isothermic libraries should provide data with a lower number of errors due to an expected similarity of melting temperatures. From the computational point of view the problem of isothermic DNA sequencing with errors is hard, similarly like its classical counterpart. Hence, there is a need for developing heuristic algorithms that construct good suboptimal solutions. The aim of the paper is to propose a heuristic algorithm based on tabu search approach. The algorithm solves the problem with both positive and negative errors. Results of an extensive computational experiment are presented, which prove the high quality of the proposed method.     

Examination of distribution of trace elements in hair, fingernails and toenails as alternative biological materials. Application of chemometric methods

The aim of this study was to find correlations between several studied elements and analyzed materials as well as the application and validation of an analytical method to determine trace elements in hair, fingernails and toenails of healthy volunteers (normal concentration). The method developed covers washing, mineralization and ICP-MS determination of 10 elements (Ca, Cd, Co, Cr, Cu, Fe, Mg, Ni, Pb and Zn) in hair and nails. Concentrations of the selected elements in hair, fingernails and toenails were measured for 24 women and 18 men. Furthermore, a chemometric approach (Principal Component Analysis, PCA) was employed to evaluate the correlations between concentrations of the elements in hair and nails and between these materials. Until now PCA has not been frequently applied in handling and interpretation of the results of analysis of biological materials. However, the results of the present investigation show the high potential of PCA in extraction of valuable information from analytical measurements. Additionally, PCA has become a useful tool for visualization of the obtained results. Moreover, the cluster analysis (CA) was used to group the samples according to gender, taking into account two different groups of elements: essential and toxic.      

Synthesis,characteristics and photochemical studies of novel porphyrazines possessing peripheral 2,5-dimethylpyrrol-1-yl and dimethylamino groups

The synthesis and physicochemical properties of novel porphyrazines possessing an alternate system of two peripheral substituents, 2,5-dimethylpyrrol-1-yl and dimethylamino, are presented. All the macrocycles were subjected to HPLC purity studies. Spectroscopic studies of magnesium(II) porphyrazine encompassed steady state absorption, emission measurements, including fluorescence decays, transient absorption spectra, and thermoluminescence. Additionally, magnesium(II) porphyrazine was found to be a moderate photosensitizer with singlet oxygen generation values of 0.12 and 0.14 in DMF and DMSO, respectively. Comparison of the quantum yields of singlet oxygen generation before and after deoxygenation showed that the photodynamic effect of magnesium(II) porphyrazine is governed by the photosensitization mechanism II. Magnesium(II) and manganese(III) porphyrazines were characterized using X-ray crystallography.     

Synthetic utility of 3-(perfluoro-1,1-dimethylbutyl)prop-1-ene. Part VI. A free-radical addition of CCl4 and CBr4 and dehydrohalogenation of the adducts

Heating the title compound 1 in excess CCl₄ and in the presence of a free-radical initiator (t-butyl peroxide) at 120 °C afforded 1,1,1,3-tetrachloro-4-(perfluoro-1,1-dimethylbutyl)butane (2) as the main product together with considerable amounts of cyclic dimer, 1,4-bis(perfluoro-1,1-dimethylbutyl)cyclohexane (3). Reaction of 1 with CBr₄ at 120 °C gave 1,1,1,3-tetrabromo-4-(perfluoro-1,1-dimethylbutyl)butane (4) as the sole product while at 220 °C a mixture of 1,2-dibromo-3-(perfluoro-1,1-dimethylbutyl)propane (5) and 1,1-dibromo-4-(perfluoro-1,1-dimethylbutyl)buta-1,3-diene (6) was formed. Treatment of adducts 2 and 4 with methanolic potassium hydroxide at ambient temperature gave mixtures of 1,1,3-trihalo-4-(perfluoro-1,1-dimethylbutyl)but-1-enes (7) or (8) and 1,1-dihalo-4-(perfluoro-1,1-dimethylbutyl)buta-1,3-dienes (9) or (6) in ratios depending on the adduct to base ratio and on the reaction conditions. Using an excess of the base and reflux temperature, adduct 4 and diene 6 were converted into methyl 4-(perfluoro-1,1-dimethylbutyl)buten-3-oate (10).     

Chemical transformations of alcohols sampled with the use of adsorptive enrichment on the carbon adsorbent traps followed by thermal desorption

Graphitized carbons, Carbopack X, Carbograph 5TD and Carbotrap B, used to enrich samples of C(3)-C(4) alcohols determined in the atmospheric air produce experimental artefacts. After thermal desorption, recoveries for alcohols are much smaller than unity with a concomitant appearance of aldehydes and ketones on chromatograms. Obviously, the adsorbents studied cannot be recommended for analysis of alcohols, ketones and aldehydes in the atmosphere. Polymeric adsorbents, Tenax TA and Chromosorb 106, do not exhibit such oxidative properties.     

Synthesis of phosphorofluoridates and phosphorofluoridothioates via the phosphoramidite approach

We present a very efficient synthetic procedure leading to the phosphorofluoridates RO-P(O)(OH)F 1 or phosphorofluoridothioates RO-P(S)(OH)F 2, which is based on the intermediary of fluorophosphoramidites (RO)P(F)N(i)Pr2 5 [R = 9-(hydroxyethyloxymethyl)guaninyl), 3'azido-3'deoxythymidinyl, thymidinyl, anhydrothymidinyl, cholesteryl, N6-benzoyl-5'-O-(4,4'-dimethoxytrityl)-2'-deoxyadenosinyl]. The activation of the amino group was performed with trimethylchlorosilane (TMCS).     

Charge recombination via intercolumnar electron tunneling through the lipid-like mantle of discotic hexa-alkyl-hexa-peri-hexabenzocoronenes

The recombination of the mobile charge carriers formed in pulse-ionized hexa-alkyl-substituted hexa-peri-hexabenzocoronenes occurs mainly via intercolumnar electron tunneling through the intervening hydrocarbon mantle. This is evidenced as a dramatic increase in the time scale of the decay of the radiation-induced conductivity from a few hundred nanoseconds to close to a millisecond as the peripheral alkyl substituents increase in size from 8 to 24 carbon atoms with corresponding disk diameters, D, from 23.4 to 36.6 A. The decay kinetics are a function only of the total number of peripheral carbon atoms with no evidence for specific effects of chain branching. The 1/e decay time, tau(e), increases exponentially with D according to tau(e) = tau(e)(0) exp(betaD) with tau(e)(0) = 48 fs and beta = 0.63 A(-1). Taking into account the tilted columnar configuration of the molecules in the solid phase leads to a beta value of ca. 0.8 A(-1) for the distance dependence of intercolumnar electron tunneling. In contrast to the orders of magnitude changes in the time scale for intercolumnar charge recombination, the intracolumnar charge hopping times vary by only a factor of 4, between 40 and 160 fs, with no systematic dependence on the nature of the alkyl substituents. On the basis of the results, the time scale estimated for electron tunneling across a 40 A thick lipid membrane is estimated to be close to 1 ms.