Antibiotic Detection in Urine Using Electrochemical Sensors Based on Vertically Aligned Carbon Nanotubes

A sensitive way to determine levofloxacin using a sensor based on vertical aligned carbon nanotubes is described. The morphology and the electrochemical performance of the electrodes were characterised by atomic force microscopy, cyclic voltammetry and square wave voltammetry. A scan‐rate study and electrochemical impedance spectroscopy showed that the levofloxacin oxidation product is adsorbed on the electrode surface. Differential pulse voltammetry in phosphate‐buffer solution allowed the development of a method to determine levofloxacin levels in the range of 1.0–10.0 µmol L^?1, with a detection limit of 75.2 nmol L^?1. The proposed sensor was successfully applied in the determination of levofloxacin in urine, and the obtained results were in full agreement with those from the HPLC procedure.     

Fluorine Substitution Effects on Flexibility and Tunneling Pathways: The Rotational Spectrum of 2‐Fluorobenzylamine

The effect of ring fluorination on the structural and dynamical properties of the flexible model molecule 2‐fluorobenzylamine has been studied by rotational spectroscopy in free‐jet expansion and quantum chemical methods. The complete potential energy surface originating from the flexibility of the aminic side chain has been calculated at the B3LYP/6‐311++G** level of theory and the stable geometries were also characterized with MP2/6‐311++G**. The rotational spectra show the presence of two of the predicted four stable conformers: the global minimum (I), in which the side chain’s dihedral angle with the phenyl plane is almost perpendicular, is stabilized by an intramolecular hydrogen bond between the fluorine atom and one hydrogen of the aminic group; and a second conformer II (E_II?E_I≈5 kJ mol^?1) in which the dihedral angle is smaller and the amino group points towards the aromatic ortho hydrogen atom. This conformation is characterized by a tunneling motion between two equivalent positions of the amino group with respect to the phenyl plane, which splits the rotational transition. The ortho fluorination increases, with respect to benzylamine, the tunneling splitting of this motion by four orders of magnitude. The motion is analyzed with a one‐dimensional flexible model, which allows estimation of the energy barrier for the transition state as approximately 8.0 kJ mol^?1.     

Pressurized-liquid extraction for determination of illicit drugs in hair by LC–MS–MS

An LC–MS–MS-based procedure for determination in hair of 14 different drugs of abuse belonging to the classes cocaine, amphetamine-like compounds, opiates, and hallucinogens has been developed. A pressurized-liquid extraction procedure was used and proved useful for quantitative recovery of all the analytes tested. This procedure, in conjunction with a simple decontamination step, performed to avoid false-positive samples, enabled the detection of all the analytes with LOQ ranging from 1.8 to 16 pg mg^?1 and accuracy varying from 85 to 111 %. The procedure was validated in accordance with the SOFT/AAFS guidelines and seems to be suitable for routine determination of the drugs tested in hair.     

Preferential Solvation of Ketoprofen in Some Co-solvent Binary Mixtures

The preferential solvation parameters of ketoprofen (KTP) in ethanol (EtOH) + water and propylene glycol (PG) + water binary solvent mixtures were obtained from their thermodynamic properties by means of the inverse Kirkwood–Buff integrals (IKBI) and quasi-lattice quasi-chemical methods. According to the IKBI method, it is found that KTP is very sensitive to specific solvation effects, so the preferential solvation parameter by co-solvents, δx _1,3, is negative in the water-rich mixtures of both binary systems but positive in the other compositions at temperatures of 293.15, 303.15 and 313.15 K. From this it can be assumed that, in water-rich mixtures, hydrophobic hydration around the aromatic rings and the methyl group, present in the drug, plays a relevant role in the solvation. The bigger amount of drug solvation by the co-solvent in mixtures of similar solvent proportions and in co-solvent-rich mixtures could be due mainly to polarity effects. Moreover, in these mixtures the solute will be acting as a Lewis acid with the co-solvent molecules, because they are more basic than water.     

Ab Initio MP2 and Density Functional Theory Computational Study of AcAlaNH2 Peptide Hydration: A Bottom‐Up Approach

AcAlaNH₂?n H₂O (n=1–13) complexes have been proposed as models to account for water solvent effects on the molecular properties of N‐acetyl‐L ‐alanine amide. Ab initio computations are planned to evaluate peptide–water interactions and to provide a means for approximating relative effects of the short‐range many‐body interactions arising in real solution without introducing any external parameters intended to quantify empirical or semiempirical potential‐energy functions. The present bottom‐up approach reveals the formation of compact ring clusters of water molecules strongly bonded to peptidic polar groups throughout hydrogen bonds. The explicit coordination of water molecules around the peptide renders the fully extended (FE) and polyproline II (PPII) conformers more stable with respect to the 3₁₀ helix or γ turn. The alternance of donor and acceptor groups on both sides of the FE and PPII conformers allows for synergy and extensive H‐bonding.     

Investigating the inclusion of the Ag(I)-nimesulide complex into β-cyclodextrin: studies in solution and in the solid state

The present work describes the preparation and characterization of inclusion systems involving β-CD and the silver(I) nimesulide coordination complex (Ag-NMS), prepared by kneading (K) and co-evaporation (CE) methods. Solid state characterization by DSC, XRD and IR vibrational spectroscopic measurements provided remarkable evidences of the formation of true inclusion systems. Solution measurements provided information about the inclusion mode. The UV–Vis spectroscopy was used to obtain the association constants by the Scatchard method, and the value obtained was 370 ± 2 L mol^?1. The ¹H NMR spectroscopic measurements indicate a total inclusion of the guest into the cavity. A 2D NOESY experiment was carried out for the inclusion complex. The spectrum shows that hydrogens 3–6 of the cyclodextrin clearly correlate with the protons of the phenoxy ring of nimesulide in the Ag-NMS coordination compound, which confirms the formation of the inclusion complex. The antibacterial activities of the Ag-NMS and CE-[(Ag-NMS)·β-CD] inclusion system were evaluated by the well diffusion method over Escherichia coli and Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive) pathogenic bacterial strains. The observed data shows the significant antibacterial activity of the Ag-NMS coordination complex, and no activity for the inclusion complex under the same considered conditions.     

Structural relaxation and anharmonicity in polymer electrolytes: Effect of the thermal history

Summary The effects of the storage at room temperature of PEO-KSCN polymer electrolytes have been studied by differential scanning calorimetry (DSC) and dynamical mechanical analysis. It has been revealed that, over the explored time interval, the annealing causes small variations in the anharmonic and relaxation properties of the samples, which are to be ascribed to changes in the relative amount of the phases building up the structure. The elastic and anelastic characteristics show a well-defined dependence on the degree of crystallinity of the polymer, which grows slightly with increasing annealing time. The application of a simplified version of a quasi-harmonic model and of the Kolrausch-Williams-Watts stretched exponential function permits to describe the temperature behaviour of the elastic modulusE′ and to obtain an anharmonicity parameter characterizing the polymeric system. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Perpendicular transport across (Al,Ga)As and the Γ to X transition

Tunneling (TU) and thermionic emission (TE) through GaAs/Al_xGa_1−xAs/GaAs structures was studied in the (001) direction, as a function of AlAs mole fraction x, from x=0.3 to x=0.8. Barrier heights deduced for TU and TE were the same, with a broad peak of 0.35eV for 0.4<x<0.5. Pre-factors for TU and TE were in reasonable agreement with theory for x<0.5 but dropped rapidly for larger x. The effective mass ratio for TU was Γ like for x<0.4 and increased to 0.2 for x > 0.5. These data suggest that TU transport is via the transverse X valleys for large x and the low pre-factors for both TU and TE indicate reflections at this boundary caused by wave-function mismatch. These data are also directly applicable to the design and optimization of heterojunction transistors.     

Integrated approach for modeling the emission fluorescence of 4-(N,N-dimethylamino)benzonitrile in polar environments

A stochastic model for the interpretation of the emission fluorescence of 4-( N, N-dimethylamino)benzonitrile (DMABN) is discussed. We proceed by reviewing the stochastic modeling approach ( Polimeno, A. ; Barbon, A. ; Nordio, P. L. ; Rettig, W. J. Phys. Chem. 1994, 98, 12158 ), in which internal degrees of freedom are coupled with an effective solvent relaxation variable. Potential energy surfaces are obtained using a reliable but computationally cost-effective quantum mechanical (QM) approach, and estimates of dissipative parameters are calculated on the basis of direct hydrodynamic arguments. Emission fluorescence is estimated by solving numerically a diffusion/sink/source equation for the stationary population of excited state and compared to emission fluorescence of DMABN measured experimentally.     

Assessment of hand-held Raman instrumentation for in situ screening for potentially counterfeit artesunate antimalarial tablets by FT-Raman spectroscopy and direct ionization mass spectrometry

Pharmaceutical counterfeiting has become a significant public health problem worldwide and new, rapid, user-friendly, reliable and inexpensive methods for drug quality screening are needed. This work illustrates the chemical characterization of genuine and fake artesunate antimalarial tablets by portable Raman spectroscopy and validation by FT-Raman spectroscopy and ambient mass spectrometry. The applicability of a compact and robust portable Raman spectrometer (TruScan™) for the in situ chemical identification of counterfeit tablets is reported.