Capillary isotachophoresis of some isoquinoline alkaloids

The isotachophoretic behavior of quaternary benzo/c/phenanthridine, protoberberine and aporphine alkaloids in different electrolyte systems is described. The concentration of the leading ion and the pH value of the leading electrolyte affect the relative effective mobilities of the alkaloids. The system of pH 4.7, containing the leading ion K⁺ (0.005 M) counter ion acetate, and the terminating ion β-alanine (0.02 M), has been selected for the quantitative determination of the studied alkaloids in model mixtures and plant extracts.     

On the expansion of hole in main chain polymers determined by positron annihilation

The temperature dependence of positron annihilation characteristics, ₃ andI ₃, has been studied on sample of poly(butadiene), poly(isobutylene) and poly(chloroprene). The temperature range was between 15 and 470 K. The rate of expansion of holes or free-volume in all samples was deduced belowT _g as well aboveT _g as appr. 3·10^–3 K^–1 and 2·10^–2 K^–1, respectively. These values are very close to the rate of the mean squared displacement of scatterer<r ²>observed in neutron scattering experiments. A possibility to use an inverse value of free-volume,V _f ^–1 for study of viscoelastic state of polymers is demonstrated.     

Magnetic moments and the high field susceptibilities of MnFe2O4

An extended version of the noncollinear spin model bySawatzky et al. is developed to derive a dependence of the differential high field susceptibility on the degree of inversion of the ferrite MnFe₂O₄. Using the available data on the main molecular field coefficients it is shown that the present model imposes restrictions on values of. Determination of from the measurements of the field dependence of the saturated moments at low temperatures on samples with varying degrees of inversion reveals good quantitative agreement with the present model.     

Excitation of adsorbed molecule vibrations in low energy electron scattering

We develop a theory of low energy electron loss spectroscopy of vibrational modes of molecules adsorbed on metal surfaces. Differential and total cross sections are calculated in the Distorted Wave Born Approximation, assuming i) strong elastic scattering on the metal surface, ii) direct electron-molecule interaction via the electric dipole field associated with the molecular vibration. The angular distributions are calculated and discussed for molecules adsorbed at various distances above the metal surface and for several electron energies and impact angles. The influence of electronic screening of dipolar oscillations is discussed and the consequences of the classical induced image dipoles are explored. It is shown that the metal surface selection rule known in IR spectroscopy is only approximately valid in electron scattering. Finally, we give numerical estimates of the inelastic scattering cross sections for the stretching vibrations of CO molecule adsorbed on transition metal surfaces, in reasonable agreement with experiments.     

Biosensors based on highly sensitive acetylcholinesterases for enhanced carbamate insecticides detection

This paper presents the construction of amperometric biosensors for the highly sensitive detection of carbamate insecticides based on the inhibition of acetylcholinesterase (AChE). This enzyme was immobilised by entrapment in an optimised sol-gel matrix on TCNQ-modified screen-printed electrodes. The enzyme activity was estimated by measuring the thiocholine produced by the enzymatic hydrolysis of the acetylthiocholine using TCNQ as mediator. Wild and genetically engineered AChEs from Drosophila melanogaster (Dm) were chosen for their high sensitivity towards insecticides, which substantially improves the LOD compared with cholinesterases from other sources. The wild type and three mutant enzymes were tested against three carbamate insecticides: carbaryl, carbofuran and pirimicard. The best LOD were obtained with the Y370A mutant for carbaryl (1 × 10⁻⁸ M), the E69W mutant for pirimicarb (2 × 10⁻⁸ M) and the I161V mutant for carbofuran (8 × 10⁻¹⁰ M). The biosensors were applied to the analysis of two potable water samples.     

Oxidatively truncated docosahexaenoate phospholipids: total synthesis,generation, and Peptide adduction chemistry

The recent immunological detection of extraordinarily high levels of carboxyethylpyrrole (CEP) modifications of proteins from the retinas of individuals with age-related macular degeneration provided presumptive evidence for the involvement of docosahexaenoate-derived oxidatively truncated phospholipids in retinal pathology. To facilitate the in vivo detection and characterization of the chemistry and biological activities of these postulated naturally occurring molecules, a family of oxidatively truncated phospholipids was prepared by total syntheses. Their formation in oxidation reactions of a docosahexaenoate ester of 2-lysophosphatidylcholine (DHA-PC) was also demonstrated. Free radical-induced oxidative cleavage of DHA-PC promoted by myeloperoxidase or copper ions generates similar mixtures of these phospholipids. The most abundant products were 1-palmitoyl-2-succinoyl-sn-glycero-3-phosphatidylcholine (4.7%) and 2-(6-carboxy-4-oxohex-5-enoyl)-1-palmitoyl-sn-glycero-3-phosphatidylcholine (1.7%). Both of these oxidatively truncated phospholipids are homologues of biologically active arachidonate-derived phospholipids. A minor product from DHA-PC, 2-(4-hydroxy-7-oxohept-5-enoyl)-1-palmitoyl-sn-glycero-3-phosphatidylcholine (0.4% yield), reacted with the epsilon-amino group of a peptide lysyl residue to produce a CEP derivative in 0.7% yield. These observations support the previous conclusion, based on immunological evidence, that CEPs are generated by the reaction of an oxidatively truncated phospholipid with proteins in the retina and further indicate that CEP protein modifications probably represent only a tiny fraction of the products generated upon oxidative damage of DHA-PC in photoreceptor disk membranes.     

{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20]36-: a molecular quantum spin icosidodecahedron

Self-assembly of aqueous solutions of molybdate and vanadate under reducing, mildly acidic conditions results in a polyoxomolybdate-based {Mo72V30} cluster compound Na8K16(VO)(H2O)5[K10 subset{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20].150H2O, 1, a quantum spin-based Keplerate structure.     

Thermal isomerization of cis,anti,cis-tricyclo[6.3.0.0(2,7)]undec-3-ene to endo-tricyclo[5.2.2.0(2,6)]undec-8-ene

[reaction: see text] The gas-phase thermal isomerization of cis,anti,cis-tricyclo[6.3.0.0(2,7)]undec-3-ene (1) to endo-tricyclo[5.2.2.0(2,6)]undec-8-ene (2) at 315 degrees C occurs cleanly through a symmetry-forbidden [1,3] suprafacial,retention (sr) pathway.     

IR-Spektren der Caesium-bis-sulfato-metallate(III)

Compounds of the type CsLn(SO₄)₂, (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were prepared at 300°C. IR spectra were recorded in the range 4,000-250cm^–1 and tentatively assigned. The number of observed bands exceeds the predicted number by site symmetry selection rules. Streching bands show bathochromic shifts whereas the deformations exibit hypsochromic shifts on going to heavier lanthanides. At the same time there is an increased splitting of these bands in the same direction. All these facts indicate an increased coupling in the layer structure which is in accordance with the lanthanide contraction.

N. Bukovec, P. Bukovec undJ. iftar, Vest. Slov. Kem. Drus.26, 103 (1979).     

Sequence-specific fluorescence detection of DNA by polyamide-thiazole orange conjugates

Fluorescent methods to detect specific double-stranded DNA sequences without the need for denaturation may be useful in the field of genetics. Three hairpin pyrrole-imidazole polyamides 2-4 that target their respective sequences 5'-WGGGWW-3', 5'-WGGCCW-3', and 5'-WGWWCW-3' (W = A or T) were conjugated to thiazole orange dye at the C-termini to examine their fluorescence properties in the presence and absence of match duplex DNA. The conjugates fluoresce weakly in the absence of DNA but showed significant enhancement (>1000-fold) upon the addition of 1 equiv of match DNA and only slight enhancement with the addition of mismatch DNA. The polyamide-dye conjugates bound specific DNA sequences with high affinity (Ka > 10(8) M(-1)) and unwound the DNA duplex through intercalation (unwinding angle, phi, approximately 8 degrees). This new class of polyamides provides a method to specifically detect DNA sequences without denaturation.