A quantitative assessment of chemical techniques for detecting traces of explosives at counter-terrorist portals

Previous reviews have discussed in a qualitative manner the various highly sensitive analytical techniques for detecting minute traces of explosive material. However, there is no review available which compares quantitatively the sensitivities of the different analytical methods for detecting explosives. In view of the importance of this area to the present day planning of counter-terrorist strategies, this review makes a comprehensive and quantitative comparison of the analytical chemical methods which can be used for the detection of trace explosives in the luggage and on the persons of travelers. Possible directions of future development in this area are also discussed.     

Observation of the Low‐Frequency Spectrum of the Water Dimer as a Sensitive Test of the Water Dimer Potential and Dipole Moment Surfaces

Using the helium nanodroplet isolation setup at the ultrabright free‐electron laser source FELIX in Nijmegen (BoHeNDI@FELIX), the intermolecular modes of water dimer in the frequency region from 70 to 550 cm^?1 were recorded. Observed bands were assigned to donor torsion, acceptor wag, acceptor twist, intermolecular stretch, donor torsion overtone, and in‐plane and out‐of‐plane librational modes. This experimental data set provides a sensitive test for state‐of‐the‐art water potentials and dipole moment surfaces. Theoretical calculations of the IR spectrum are presented using high‐level quantum and approximate quasiclassical molecular dynamics approaches. These calculations use the full‐dimensional ab initio WHHB potential and dipole moment surfaces. Based on the experimental data, a considerable increase of the acceptor switch and a bifurcation tunneling splitting in the librational mode is deduced, which is a consequence of the effective decrease in the tunneling barrier.     

Water structure and mobility in acrylamide copolymer glycohydrogels with galactose and siloxane pendant groups

Glycohydrogels containing 2′‐acrylamidoethyl‐β‐d ‐galactopyranoside and varying levels of N,N′ methylene bisacrylamide and 3‐acrylamidopropyltris(trimethylsiloxy)silane were synthesized to determine the effects of crosslinker and amphipathic balance on equilibrium water content (EWC), bound water population, and hydrogen bonding dynamics at the water–polymer interface. Analogous dimethylacrylamide hydrogels were synthesized for comparison with a system containing lower hydrogen bonding propensity. An approach combining experiment (proton nuclear magnetic resonance, thermogravimetric analysis, differential scanning calorimetry, and dynamic vapor sorption analysis) and molecular dynamics simulations was employed to examine the relationship between bulk hydrogel properties, molecular water mobility, and hydrogen bonding characteristics. It was found that copolymer composition (hydrophobic content) and crosslink concentration in high water content glycohydrogels affect EWC, and by extension, structural water population. The organization of water at the polymer interface is greatly impacted by the surrounding environment, where hindered molecular water mobility promotes water–polymer binding and decreases water–water clustering. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 584–597     

Calculation of the Density and Activity of Water in ATPS Systems for Separation of Biomolecules

In this study, the perturbed hard sphere chain equation of state is utilized to calculate the activity of water in binary and ternary solutions of polyethylene glycol (PEG), salt and water. The liquid density of the binary and ternary solutions is also predicted. To estimate the water activity in PEG–water binary systems, a linear correlation is obtained for the binary interaction parameter between water and PEG. Then, using this correlation and without introducing any additional binary parameters, the water activities are predicted in ternary solutions of water, salt and PEG with different molecular weights (MW). Our results show that the mean absolute average relative deviation (AARD %) of water activity for binary PEG–water solutions in 298 K is 0.73 %. In addition, the water activity in ternary solutions of water and two PEGs with different MW is predicted within 0.31 % AARD %. Furthermore, the AARD % for prediction of water activities in binary PEG–water solutions over the temperature range 308–338 K is 0.41 %. Also, the water activities of aqueous two-phase systems are predicted with AARD % = 0.64 %. In this regard, no adjustable parameters were correlated between salt and PEG. Finally, liquid densities were predicted in binary solutions of water–PEG and ternary solutions of water–PEG–salt.     

Microwave-assisted chemoselective synthesis of novel pyrazolo[3,4-b]thieno[3,4-e]pyridines: substitution induced axial chirality

A microwave-assisted chemoselective synthesis of novel pyrazolo[3,4-b]thieno[3,4-e]pyridines has been achieved via tandem Michael addition–cyclization–tautomerization–oxidative aromatization sequence of reactions. Compounds with ortho-substituted phenyl rings exhibited axial chirality due to restricted rotation around C–C single bond.     

Fabrication of Silver Nanoparticles Decorated on Activated Screen Printed Carbon Electrode and Its Application for Ultrasensitive Detection of Dopamine

In the present study, we report the fabrication of silver nanoparticles (AgNPs) decorated on activated screen printed carbon electrode (ASPCE). The AgNPs were prepared by using Justicia glauca leaf extract as a reducing and stabilizing agent and the ASPCE was prepared by a simple electrochemical activation of screen printed carbon electrode (SPCE). The ASPCE/AgNPs shows a reversible electrochemical behaviour with enhanced response for DA than that of other modified SPCEs. Under optimum conditions, the electrochemical oxidation current response of DA is linear over the concentration range from 0.05 to 45.35 µM. The limit of detection is found as 0.017 µM with a high sensitivity of 7.85 µA µM^?1 cm^?2.     

Simultaneous Chemo/Enantioseparation and Assay of R-(+)-Rabeprazole and Related Impurities in Pharmaceutical Formulations

Simultaneous chiral and chemoseparation of R-(+)-rabeprazole and related (enantio)impurities was achieved on a cellulose tris-(3,5-dichlorophenylcarbamate) stationary phase chemically bonded to silica gel (Chiralpak IC). A gradient elution was applied in the reverse-phase separation mode. The mobile phase consisted of a mixture of acetonitrile and aqueous phosphate buffer at pH 7. The other operational parameters were flow rate of 1 mL min⁻¹, column temperature of 35 °C and ultraviolet (UV) detection at 282 nm. Quantification limits for R-(+)-rabeprazole and the related impurities ranged in the interval of 0.02–0.03 %. Linear response intervals of 0.02–0.66 % were obtained with UV detection. Validation of the proposed method was achieved according to current regulations in force. For better understanding of the R-(+)-rabeprazole impurity profile, (+)-EMS/MS and MS/MS detection were also used.

     

Theoretical Simulation of Vibrational Sum‐Frequency Generation Spectra from Density Functional Theory: Application to p‐Nitrothiophenol and 2,4‐Dinitroaniline

The molecular orientation of adsorbed molecules forming self‐assembled monolayers can be determined by combining vibrational sum‐frequency generation (SFG) measurements with quantum chemical calculations. Herein, we present a theoretical methodology used to simulate the SFG spectra for different combinations of polarizations. These simulations are based on calculations of the IR vectors and Raman tensors, which are obtained from density functional theory computations. The dependency of the SFG vibrational signature with respect to the molecular orientation is presented for the molecules p‐nitrothiophenol and 2,4‐dinitroaniline. It is found that a suitable choice of basis set as well as of exchange‐correlation (XC) functional is mandatory to correctly simulate the SFG intensities and consequently provide an accurate estimation of the adsorbed molecule orientation. Comparison with experimental data shows that calculations performed at the B3LYP/6‐311++G(d,p) level of approximation provide good agreement with experimental frequencies, and with IR and Raman intensities. In particular, it is demonstrated that polarization and diffuse functions are compulsory for reproducing the IR and Raman spectra, and consequently vibrational SFG spectra, of systems such as p‐nitrothiophenol. Moreover, the investigated XC functionals reveal their influence on the relative intensities, which show rather systematic variations with the amount of Hartree–Fock exchange. Finally, further aspects of the modeling are revealed by considering the frequency dependence of the Raman tensors.     

Comparison of DNA‐Reactive Metabolites from Nitrosamine and Styrene Using Voltammetric DNA/Microsomes Sensors

Voltammetric sensors made with films of polyions, double‐stranded DNA and liver microsomes adsorbed layer‐by‐layer onto pyrolytic graphite electrodes were evaluated for reactive metabolite screening. This approach features simple, inexpensive screening without enzyme purification for applications in drug or environmental chemical development. Cytochrome P450 enzymes (CYPs) in the liver microsomes were activated by an NADPH regenerating system or by electrolysis to metabolize model carcinogenic compounds nitrosamine and styrene. Reactive metabolites formed in the films were trapped as adducts with nucleobases on DNA. The DNA damage was detected by square‐wave voltammetry (SWV) using Ru(bpy) as a DNA‐oxidation catalyst. These sensors showed a larger rate of increase in signal vs. reaction time for a highly toxic nitrosamine than for the moderately toxic styrene due to more rapid reactive metabolite‐DNA adduct formation. Results were consistent with reported in vivo TD₅₀ data for the formation of liver tumors in rats. Analogous polyion/ liver microsome films prepared on 500 nm silica nanoparticles (nanoreactors) and reacted with nitrosamine or styrene, provided LC‐MS or GC analyses of metabolite formation rates that correlated well with sensor response.     

Production,blood compatibility and cytotoxicity evaluation of a single stage non-woven multicomponent electrospun scaffold mixed with sesame oil,honey and propolis for skin tissue engineering

Scaffolds used in skin tissue engineering must mimic the native function of the extracellular matrix (ECM) and facilitate the fibroblast cell response for new tissue growth. In this study, a novel dressing scaffold based on polyurethane (PU) with sesame oil, honey, and propolis was fabricated by electrospinning. Scanning electron microscopy (SEM) images showed that the diameter of the electrospun scaffolds decreased by blending sesame oil (784?±?125.46?nm) and sesame oil/honey/propolis (576?±?133.72?nm) into the PU matrix (890?±?116.911?nm). Fourier infrared (FT-IR) and thermogravimetric (TGA) analysis demonstrated the formation of hydrogen bonds and interaction between PU and sesame oil, honey, and propolis. Contact-angle measurement indicated reduced wettability of PU/sesame oil scaffold (114?±?1.732) and improved wettability (54.33?±?1.528) in the PU/sesame oil/honey/propolis scaffold. Further, tensile tests and atomic force microscopy (AFM) analysis indicated that the fabricated composite membrane exhibited enhanced mechanical strength and reduced surface roughness compared to the pristine PU. The developed composite displayed less toxicity to the red blood cells (RBC’s) compared to the pristine PU. Cytotoxicity assay showed enhanced cell viability of HDF in electrospun scaffolds than pristine PU after 72?h culture. These enhanced properties of the developed scaffolds suggest the potential of utilizing them in skin tissue engineering.