Electrochemical Determination of Neomycin and Norfloxacin at a Novel Polymer Nanocomposite Electrode in Aqueous Solution

Organic compounds such as antibiotics that are not effectively removed by modern-day treatment technology are a growing threat to water quality and health. The emergence of antibiotics in the aquatic environment is a matter of concern as they may induce bacterial resistance, a major threat to health-care management and an increasing economic crisis. The current methods that are used to detect antibiotics are expensive and time consuming due to the sample preparation necessary for the determination of low concentrations of antibiotics in water and the instruments used. Electrochemical sensors and biosensors are simple systems, with high selectivity and sensitivity for individual measurements and low cost. In this study, we present a novel polyamic acid/graphene oxide electrode that was prepared for electrochemical screening of selected antibiotic residues in aqueous solution. Polyamic acid and graphene oxide were synthesized independently and characterized using microscopic, spectroscopic, and voltammetric approaches. A polyamic acid/graphene oxide/screen-sprinted carbon electrode was prepared in situ by electrochemical deposition of polyamic acid/graphene (0.03?mg/mL 50:50 mass ratio) on screen-printed carbon electrodes using five cycles between ?1000 and 1000?mV at 50?mV/s. The polyamic acid/graphene oxide/screen-printed carbon electrode provided limits of detection of 0.034?µM for norfloxacin and 1.07?µM for neomycin. Recovery studies on synthetic urine showed good inter-day and intra-day coefficients of variation (n?=?3).     

On a generalization of the Selberg formula

In this paper, we prove a theorem related to the asymptotic formula for ψk(x;q,a) which is used to count numbers up to x with at most k distinct prime factors (or k-almost primes) in a given arithmetic progression . This theorem not only gives the asymptotic formula for ψk(x;q,a) (or Selberg formula), but has played an essential role, recently, in obtaining a lower bound for the variance of distribution of almost primes in arithmetic progressions.     

On the universality of the long-/short-range separation in multiconfigurational density-functional theory

In many cases, the dynamic correlation can be calculated quite accurately and at a fairly low computational cost in Kohn-Sham density-functional theory (KS-DFT), using current standard approximate functionals. However, in general, KS-DFT does not treat static correlation effects (near degeneracy) adequately which, on the other hand, can be described in wave-function theory (WFT), for example, with a multiconfigurational self-consistent field (MCSCF) model. It is therefore of high interest to develop a hybrid model which combines the best of both WFT and DFT approaches. The merge of WFT and DFT can be achieved by splitting the two-electron interaction into long-range and short-range parts. The long-range part is then treated by WFT and the short-range part by DFT. In this work the authors consider the so-called "erf" long-range interaction erf(micror12)/r12, which is based on the standard error function, and where mu is a free parameter which controls the range of the long-/short-range decomposition. In order to formulate a general method, they propose a recipe for the definition of an optimal microopt parameter, which is independent of the approximate short-range functional and the approximate wave function, and they discuss its universality. Calculations on a test set consisting of He, Be, Ne, Mg, H2, N2, and H2O yield microopt approximately 0.4 a.u.. A similar analysis on other types of test systems such as actinide compounds is currently in progress. Using the value of 0.4 a.u. for micro, encouraging results are obtained with the hybrid MCSCF-DFT method for the dissociation energies of H2, N2, and H2O, with both short-range local-density approximation and PBE-type functionals.     

Transport of wetting liquid plugs in bifurcating microfluidic channels

A plug of wetting liquid is driven at constant pressure through a bifurcation in a microchannel. For a plug advancing in a straight channel, we find that the viscous dissipation in the bulk may be estimated using Poiseuille's law while Bretherton and Tanner's laws model the additional dissipation occurring at the rear and front interfaces. At a second stage, we focus on the behavior of the plug flowing through a T-junction. Experiments show the existence of a threshold pressure, below which the plug remains blocked at the entrance of the junction. Above this required pressure, the plug enters the bifurcation and either ruptures or splits into two daughter plugs, depending on the applied pressure and on the initial length of the plug. By means of geometrical arguments and the previously cited laws, we propose a global model to predict the transitions between the three observed behaviors.     

Suzuki-miyaura cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN

We addressed an unexplored application of the Suzuki-Miyaura protocol to the cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN. The use of bisphosphine ligands with a large P-Pd-P bite angle allowed us to synthesize Z-chlorinated internal alkenes in good yields resulting from a selective monocoupling process, a recurrent challenge with 1,1-dichloro-1-alkenes. Moreover, these monochlorinated olefins could be further transformed providing stereospecifically trisubstituted olefins.     

Modified Julia fluoroolefination: selective preparation of fluoroalkenoates

The modified Julia olefination reaction has been applied to develop a stereoselective synthesis of fluoroalkenoate derivatives from a fluorobenzothiazolyl sulfone and aldehydes or a ketone. The olefination reaction can be achieved by using a variety of bases. DBU and DBU in the presence of MgBr2 were found to be the most efficient systems to prepare either (Z)- or (E)-alkenoates in moderate to excellent stereoselectivity.     

Stereocontrolled synthesis of enantiomeric imidazolopiperidinoses and imidazoloazepanoses using Wittig/dihydroxylation reactions

A new route for the synthesis of imidazolosugars—6-deoxyimidazolopiperidinoses 1 and 2 and 7-deoxyimidazoloazepanoses 3 and 4 in two enantiomerical forms—is reported. The new synthetic approach is based on two key reactions: (i) stereocontrolled Wittig Z-olefination of an imidazolecarbaldehyde with phosphoranes containing one chiral centre, obtained from (S)- and (R)-1,2,4-butantriol; (ii) diastereoselective cis-dihydroxylation of previously obtained olefins. All synthesised imidazolosugars were evaluated as potential inhibitors of glycosidases.     

First example of an Ugi type reaction on phenylsulfinimine-avermectin B1 derivatives

A short synthesis of 4″-(S)-4″-deoxy-4″-trifluoroacetylamino-4″-alkylcarbamoyl-avermectin B₁4 has been developed through the diastereoselective Ugi reaction to an phenylsulfinimide intermediate.     

Changing the oxothiomolybdate ring from an anionic to a cationic receptor

The ionic recognition properties of neutral oxothiomolybdenum wheels can be changed from anionic to cationic through ionization of the internal aquo ligands. In the solid state, [Mo8O8S8(OH)10(H2O)]2- (1) interacts with two Cs+ cations to give a close supramolecular host-guest arrangement. Such interactions appear to be maintained in solution as a labile association.