Conductance of Selected Alkali Metal Salts in Aqueous Binary Mixtures of 2-Methoxyethanol at 25°C

Precise conductance measurements have been performed for lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, sodium perchlorate, and sodium tetraphenylborate in 2-methoxyethanol–water mixtures at four different mole fractions, i.e., 0.056, 0.136, 0.262, and 0.486 of 2-methoxyethanol (69.73 D 26.55) at 25°C in the concentration range 0.0004–0.0642 mol-dm^–3. The limiting molar conductivity °, the association constant K _A, and the association distance R for the solvent mixtures have been evaluated from the conductance concentration data using the 1978 Fuoss conductance equation. The single-ion conductances have been estimated using the reference electrolyte tetrabutylam-monium tetraphynylborate(Bu₄NBPh₄). The analysis of the data indicates that for most salts ion association is appreciable in the solvent mixtures with a mole fraction of the cosolvent of 0.262 or higher. The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvent media.     

高效毛细管电泳-电导检测对四环素衍生物分离测定的研究

运用毛细管电泳-电导检测方法对4种四环素衍生物——土霉素(OTC)、金霉素(CTC)、强力霉素(DOC)和四环素(TC)的分离进行了研究。在3．5mmol/L三羟基氨基甲烷(Tris)-7．5mmol/L柠檬酸(Cit)pH4．0的运行缓冲液中，4种四环素衍生物在15min内获得完全分离。四环素衍生物的线性范围分别为5．0-500μg/mL OTC，3．6-420μg/mL CTC，4.5-470μg/mL DOC和2.5-400μg/mL TC。检测限(S／N＝3)分别为OTC2．0μg/mL，CTC 1．8μg／mL，DOC2．5μg/mL和TC1．0μg/mL。采用本法对实际样品强力霉素片中强力霉素和土霉素片中土霉素进行测定，回收率分别为97．2％和96.4％。     

Ion-solvent interactions and ionic association in ethanol solutions

The electrical conductivities of potassium halides in ethanol have been measured at 25°C. The limiting molar conductances, ionic association constants and the closest approach parameter were calculated (Justice method) and compared with existing literature data. An inversion of the anion size dependence of ionic association constants for these solutions was observed. The results are explained by what has been called localized solvolysis, in which both the cation and the anion of the solvent separated ion pair are connected with different parts of the separating solvent molecule by donor-acceptor bonding. A correlation between K _A and protonic affinity of anions was found. Similar literature data for aqueous and non-aqueous solutions are also examined.     

Conductance of substituted amine perchlorates and picrates in N-methyl-2-pyrrolidinone at 25°C

Conductance measurements of 16 perchlorates and picrates of substituted ammonium cations have been made in N-methyl-2-pyrrolidinone (NM-2-Py) at 25°C. To aid in the estimation of ionic conductances, measurements of tetrabutyl-ammonium tetraphenylborate were also included. The data were analyzed by both the full Pitts equation and the expanded Pitts equation in order to obtain limiting molar conductances _o and the ion association constants K _A . The results showed that pyridinium perchlorate and piperidinium, 2,4-dimethyl-pyridinium, 2,4,6-trimethylpyridinium picrates and tetrabutylammonium tetraphenylborate appear to be completely dissociated in NM-2-Py. The values of K _A for the other salts range from 1 to 36 dm³-mol^–1. Limiting molar conductances for the cation were based on the Coplan-Fuoss assumption.On leave 1973–1975 from University of Gdask, Poland.     

Electrical conductance of aqueous solutions of KCl solutions at pressures up to 2000 atm

Electrical conductance measurements are reported for aqueous KCl solutions at 25°C as a function of concentration up to 0.02 M and pressure up to 2000 atm. The data from 103 runs were analyzed with the Fuoss-Hsia-Fernandez-Prini (FHFP) equation. The standard error of fit varies from 0.018 at 1 atm to 0.12 at 2000 atm. The increase of with pressure arises from increasing nonrandomness in the distribution of errors about the FHFP equation, suggesting that modifications in the theory are necessary. Departures from the Walden product for KCl as a function of pressure are compared with MgSO₄ and CaSO₄ in aqueous solutions.     

Ab initio study of the electronic and transport properties of waved graphene nanoribbons

We apply the nonequilibrium Green's function method based on density functional theory to investigate the electronic and transport properties of waved zigzag and armchair graphene nanoribbons. Our calculations show that out-of-plane mechanical deformations have a strong influence on the band structures and transport characteristics of graphene nanoribbons. The computed I-V curves demonstrate that the electrical conductance of graphene nanoribbons is significantly affected by deformations. The relationship between the conductance and the compression ratio is found to be sensitive to the type of the nanoribbon. The results of our study indicate the possibility of mechanical control of the electronic and transport properties of graphene nanoribbons.     

SnO2 nanograins Au-doped: A quantum mechanical evaluation of CO adsorption

In this study an analysis is made of the adsorption properties of nanocrystalline SnO₂ containing a metallic dopant. The analysis is based on semi-empirical Hartree–Fock and scattering theories and the structures considered are SnO₂ grains, with a rutile lattice, whose size and shape are comparable with the nanograins and nanowires produced in experiments. The grains contain rows of gold atoms located externally, on the grain surface, or in an endohedral position, in the grain interior, and the adsorbed system is generated by depositing CO molecules on the grain surface. The calculations illustrate the dependence of the binding energies and of the conductance on the grain size and on the location of the metallic additives in both the clean and in the CO-adsorbed grains. These results show that adsorption and current transport are determined by the intrinsic electronic structure of the adsorbing grains.     

Antiresonance of electron tunneling through a quantum dot array

Electronic transport through a one-dimensional quantum dot array is theoretically studied. In such a system both electron reservoirs of continuum states couple with the individual component quantum dots of the array arbitrarily. When there are some dangling quantum dots in the array outside the dot(s) contacting the leads, the electron tunneling through the quantum dot array is wholly forbidden if the electron energy is just equal to the molecular energy levels of the dangling quantum dots, which is called as antiresonance of electron tunneling. Accordingly, when the chemical potential of the reservoir electrons is aligned with the electron levels of all quantum dots, the linear conductance at zero temperature vanishes if there are odd number dangling quantum dots; Otherwise, it is equal to 2e²/h due to resonant tunneling if the total number of quantum dots in the array is odd. This odd–even parity is independent of the interdot and the lead–dot coupling strength.     

Slow mixing of Glauber dynamics for the hard‐core model on regular bipartite graphs

Let ∑ = (V,E) be a finite, d‐regular bipartite graph. For any λ > 0 let π_λ be the probability measure on the independent sets of ∑ in which the set I is chosen with probability proportional to λ^|I| (π_λ is the hard‐core measure with activity λ on ∑). We study the Glauber dynamics, or single‐site update Markov chain, whose stationary distribution is π_λ. We show that when λ is large enough (as a function of d and the expansion of subsets of single‐parity of V) then the convergence to stationarity is exponentially slow in |V(∑)|. In particular, if ∑ is the d‐dimensional hypercube {0,1}^d we show that for values of λ tending to 0 as d grows, the convergence to stationarity is exponentially slow in the volume of the cube. The proof combines a conductance argument with combinatorial enumeration methods. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2006     

Conductivity measurements and relative association constants of some 3:1 electrolytes

Conductance measurements are reported for dilute aqueous solutions at 25°C of potassium hexacyanoferrate(III) and of sodium, potassium, rubidium, and cesium octacyanotungstate(V). The results are interpreted in terms of ion-pair formation, and association constants for the formation of these ion pairs are calculated. For the ion pairs MW(CN) ₈ ^2– , the results are: M=Na, 12±8; K, 23±7; Rb, 37±10; and Cs, 51±4M ^–1, at 25°C and zero ionic strength.