49 research outputs found
Limits of the Classical Concept of Concentration
No full textSolutions of very low concentrations cannot be treated by the usual concept of concentration. Stochastic calculations are performed for the analysis of such solutions containing one or a few molecule(s). It is concluded that these systems escape the usual concentration parameters. Two “case histories” are also shown for demonstration of the practical consequences of the theoretical analysis
Molecular elements of ion permeation and selectivity within calcium channels
No full textVoltage-dependent calcium channels are located in the plasma membrane and form a highly selective conduit by which Ca2+ ions enter all excitable cells and some nonexcitable cells. Extensive characterization studies have revealed the existence of one low (T) and five high-voltage-activated calcium channel types (L, N, P, Q, and R). The high voltage-activated calcium channels have been found to exist as heteromultimers, consisting of an alpha(1), beta, alpha(2)/delta, and gamma subunit. Molecular cloning has revealed the existence of 10 channel transcripts, and expression of these cloned calcium channel genes has shown that basic voltage-activated calcium channel function is strictly carried by the corresponding a, subunits. In turn, the auxiliary subunits serve to modulate calcium channel function by altering the voltage dependence of channel gating, kinetics, and current amplitude, thereby creating a likelihood for calcium channels with multiple properties. Although for calcium channels to be effective, Ca2+ ions must enter selectively through the pore of the alpha(1)-subunit, bypassing competition with other extracellular ions. The structural determinants of this highly selective Ca2+ filter reside within the four glutamic acid residues located at homologous positions within each of the four pore-forming segments. Together, these residues form a single or multiple Ca2+ affinity site(s) that entrap calcium ions, which are then electrostatically repulsed through the intracellular opening of the pore. This mechanism of high-selectivity calcium filtration, the spatial arrangement of pore glutamic acid residues; and the coordination chemistry of calcium binding are discussed in this review
ChemInform Abstract: Dicobalt Hexacarbonyl Derivatives of Chiral Acetylenes.
No full text(mu(2)-RC(2)R')Co-2(CO)(6) complexes are prepared where R not equal R' and one of these substituents is a chiral organic group. The structures of the 11 complexes (10 new) range from the simplest possible chiral acetylenic hydrocarbon derivative (S-3-methyl-1-pentyne 1a) to ethynylsteroid (1f, 1g, 1h) and ethynylcodeine (1i, 1j, 1k) derivatives. The CD spectra are reported and the results are analysed in terms of a quadrant rule. The CD spectra show that in all complexes the Co-2(CO)(6) fragment of the molecule gets chirally perturbed. The reasons for the chiral perturbation include apolar repulsing (dominant for the hydrocarbon acetylenes) and polar attractive (''autosolvation''; dominant for acetylenes with polar hetero-atom containing substituents) forces
Ovde. Mnogoglasje Banata u dokumentarnoj prozi Tibora Varadija
No full textDokumentarna proza Tibora Varadija posvećena je slučajevima iz advokatske prakse Kancelarije Varadi, koja je delovala više od jednog stoleća – od 1893. do 2014. godine – u Zrenjaninu/Bečkereku i sačuvala bogatu advokatsku arhivu. Na početku ovog poglavlja se daju podazi iz biografije Tibora Varadija, a drugi deo čini razgovor s autorom o njegovim knjigama, uz kritičko preispitivanje društvenih pojmova, kao što su značaj arhiva, iskustvo života u graničnim oblastima, kulturno pamćenje, značaj prava i pravednosti, mešoviti brakovi, višejezičnost, značaj svakodnevice, odnos prema fašizmu i komunizmu, pitanje izvesnosti identiteta, i dr. Zasnovan na primerima iz Varadijeve proze, intervju pokušava da odgovori na pitanje u kojoj meri se uočava (dis)kontinuitet s praksama višejezičnosti iz prošlosti i kako su određeni istorijski događaji oblikovali živote manjina i upotrebu jezika u Vojvodini.Tibor Várady’s documentary prose is based on the court cases from the Várady Law Office, which worked for more than a century – from 1893 to 2014 – in Zrenjanin/Nagybecskerek and has preserved a rich archive. The first part of the chapter is dedicated to the biography of Tibor Várady, and the second part is an interview with the author about his books, with a critical review of social concepts, such as the importance of archives, the experience of life in border areas, cultural memory, the importance of law and justice, mixed marriages, multilingualism, everyday life, attitude towards fascism and communism refracted through court archives, certainty of identity, etc. Based on the Várady’s prose, the interview attempts to answer to what extent there is a (dis)continuity with the practices of multilingualism from the past and how certain historical events shaped the lives of minorities and language use in Vojvodina
On the reactivity of acetylenes coordinated to cobalt, 9. Effects of substitution and coordination on the 13C-NMR chemical shifts of the sp carbons of (R1C2R2)Co2(CO)6 complexes. Molecular structure of (mu2-PhC2SiPh3)Co2(CO)6
No full textThirty-four (mu(2)-R(1)C(2)R(2))Co-2(CO)(6) complexes (14 new) were prepared and characterized by their IR v(CO) and H-1- and C-13-NMR spectra. The C-13-NMR chemical shifts of the coordinated sp carbon atoms were correlated with those of the corresponding free acetylenes. This indicated that the interaction between the R(1) and R(2) groups and the C2Co2(CO)(6) moiety is very sensitive not only to the donor/acceptor character of R(1) and R(2) but also to the orbital symmetry of the atoms attached directly to the C(sp) atoms. The changes of the delta(C-13) values of the C(sp) atoms upon coordination were also analyzed in these terms. It is concluded that although the dinuclear mu(2)-coordination of the acetylene results in a high degree of excitation the stability of the C2Co2(CO)(6) moiety diminished the reactivity of the organic ligand. Differences in the reactivity of the (mu(2)-R(1)C(2)R(2))Co-2(CO)(6) complexes in carbonylation are also discussed. The crystal and molecular structure of (PhC(2)SiPh(3))Co-2(CO)(6) was determined by single crystal X-ray diffraction. This compound crystallizes in the orthorhombic Pbca space group with a = 28.790(2) Angstrom, b = 11.577(1) Angstrom, c = 17.833(2) Angstrom, Z = 8. The structure was determined with R = 0.039, R(w) = 0.036
FE Simulation Of A Cord-Rubber Composite Tube Subjected To Bending Due To Operational Loads On A Railroad Reverse Curve With Extremely Low Curve Radius At Sub-Zero Temperature
No full textFE Model Of A Cord-Rubber Railway Brake Tube Subjected To Extreme Operational Loads On A Reverse Curve Test Track
No full textAcceleration of activation and inactivation by the β subunit of the skeletal muscle calcium channel
No full textEfficient Transdermal Delivery of Benfotiamine in an Animal Model
No full textWe designed a transdermal system to serve as a delivery platform for benfotiamine utilizing the attributes of passive penetration enhancing molecules to penetrate through the outer layers of skin combined with the advance of incorporating various peripherally-acting vasodilators to enhance drug uptake. Benfotiamine, incorporated into this transdermal formulation, was applied to skin in an animal model in order to determine the ability to deliver this thiamine pro-drug effectively to the sub-epithelial layers. In this proof of concept study in guinea pigs, we found that a single topical application of either a solubilized form of benfotiamine (15 mg) or a microcrystalline suspension form (25 mg) resulted in considerable increases of the dephosphorylated benfotiamine (S-benzoylthiamine) in the skin tissue as well as in significant increases in the thiamine and thiamine phosphate pools compared to control animals. The presence of a ~8000x increase in thiamine and increases in its phosphorylated derivatives in the epidermis and dermis tissue of the test animals gives a strong indication that the topical treatment with benfotiamine works very well for the desired outcome of producing an intracellular increase of the activating cofactor pool for transketolase enzyme, which is implicated in the pathophysiology of diabetic neuropathy
Developmental regulation of expression of the α1 and α2 subunits mRNAs of the voltage-dependent calcium channel in a differentiating myogenic cell line
No full textAbstractThe voltage-dependent calcium channel (VDCC) in skeletal muscle probably plays a key role in transducing membrane charge movement to the calcium release channel. We report here that the expression of VDCC α1 and α2 mRNAs is developmentally regulated in differentiating C2Cl2 myogenic cells. The α1 mRNA is not detectable in the myoblast form of C2Cl2 cells while its expression is induced 20-fold in differentiated myotubes. In contrast, the α2 mRNA is weakly expressed in myoblasts but is also induced upon myogenic differentiation
