Novel coumarin-chalcone derivatives: Synthesis, characterization, antioxidant, cyclic voltammetry, molecular modelling and biological evaluation studies as acetylcholinesterase, α-glycosidase, and carbonic anhydrase inhibitors.

In this study, a total of 12 coumarin-chalcone derivatives, 6 of which are original were synthesized. The structures of the newly synthesized compounds were elucidated by 1H NMR, 13C NMR, IR, and elemental analysis methods (7g-7l). The antioxidant potencies measured by using CUPRAC method (Trolox equivalent total antioxidant capacity) were as follows: 7j > 7i > 7c > 7d > 7k > 7l > 7f > 7h > 7e > 7g > 7a > 7b. Furthermore, the compounds were evaluated against human carbonic anhydrases I, II, acetylcholinesterase and α-glycosidase enzymes. Compounds 7c, 7e, 7g, 7i, 7j and 7l showed promising human carbonic anhydrase I inhibition compared to the standard Acetazolamide (Ki: 16.64 ± 4.72-49.82 ± 5.82 nM vs Ki: 57.64 ± 5.41 nM). In addition, all compounds exhibited strong inhibition against acetylcholinesterase and α-glycosidase. Ki values were between 2.39 ± 0.97-9.35 ± 3.95 nM (Tacrine Ki: 13.78 ± 4.36 nM) for acetylcholinesterase, and 14.49 ± 8.51-75.67 ± 26.38 nM (Acarbose Ki: 12600 ± 78.00 nM) for α-glycosidase. Binding of 7g was predicted using molecular docking and stability of the complex was confirmed with molecular dynamics simulations which shed a light on the observed activity against acetylcholinesterase. Finally, cyclic voltammetry was also used for the electrochemical characterization of the synthesized compounds.

Design and in silico study of the novel coumarin derivatives against SARS-CoV-2 main enzymes.

The novel coronavirus (SARS-CoV-2) causes severe acute respiratory syndrome and can be fatal. In particular, antiviral drugs that are currently available to treat infection in the respiratory tract have been experienced, but there is a need for new antiviral drugs that are targeted and inhibit coronavirus. The antiviral properties of organic compounds found in nature, especially coumarins, are known and widely studied. Coumarins, which are also metabolites in many medicinal drugs, should be investigated as inhibitors against coronavirus due to their pharmacophore properties (low toxicity and high pharmacokinetic properties). The easy addition of substituents to the chemical structures of coumarins makes these structures unique for the drug design. This study focuses on factors that increase the molecular binding and antiviral properties of coumarins. Molecular docking studies have been carried out to five different proteins (Spike S1-subunit, NSP5, NSP12, NSP15, and NSP16) of the SARS-CoV-2 and two proteins (ACE2 and VKORC1) of human. The best binding scores for 17 coumarins were determined for NSP12 (NonStructural Protein-12). The highest score (-10.01 kcal/mol) in the coumarin group is 2-morpholinoethan-1-amine substituted coumarin. Molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) analyses of selected ligand-protein complexes were performed. The binding energies in each 5 ns were calculated and it was found that the interaction between ligand and target protein were stable.Communicated by Ramaswamy H. Sarma.

Ultrasound phantom with solids mimicking cancerous tissue for needle breast biopsy.

This study aimed at synthesizing hydrogels to simulate opaque breast tissue (BT) and coloured cancerous tissues (CT) at different densities of the designed phantom to improve the biopsy-related skills along with ultrasonography. Both tissues are tear-resistant and therefore, the phantom can be trained multiple times in order to lower the price and improve the eye-hand coordination of users. For this purpose, self-healing (SH) polyacrylamide (PAAm) hydrogels (SH hydrogel) obtained by free-radical polymerization of AAm, in the presence of chemical cross-linker, BAAm, physical cross-linker stearyl methacrylate, C18, and ammonium persulfate APS as initiator were used in the design of phantoms. Psyllium was added to the BT to differentiate density and obtain human skin color and it could be distinguished from the CT which was also colored with methyl violet. BT and CTs were characterized with FTIR spectroscopy, mechanical, swelling, and refractive index measurements. Designing phantoms from BT and CT were characterized by ultrasonography, mechanical tests, observation of needle track after biopsy, and stabilization tests to follow the self-healing behaviours of tissues with time. As a result of this study, self-healing, low-cost, and suitable for multi-usage ultrasonographic phantom for needle breast biopsy was designed and cancerous tissue was successfully detected.

Synthesis and molecular docking study of novel COVID-19 inhibitors.

In 2020, the world tried to combat the corona virus (COVID-19) pandemic. A proven treatment method specific to Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is still not found. In this study, seven new antiviral compounds were designed for COVID-19 treatment. The ability of these compounds to inhibit COVID-19's RNA processing was calculated by the molecular docking study. It has been observed that the compounds can have high binding affinities especially against NSP12 (between -9.06 and -8.00 kcal/mol). The molecular dynamics simulation of NSP12-ZG 7 complex proved the stability of interaction. The synthesis of two most active molecules was performed by one-pot reaction and characterized by FT-IR, 1H-NMR, 13C-NMR, and mass spectroscopy. The compounds presented with their synthesis are inhibitory core structures against SARS-CoV-2 infection.

Development of a gold nanoparticles-based colorimetric sensor for the indirect determination of ammonium dinitramide and tetryl.

Ammonium dinitramide (ADN) is a strong, environmentally friendly oxidizer used in composite solid rocket propellants. As there is no reliable colorimetric sensor for ADN assay applicable to in-field screening, we developed a sensitive and practical sensing method to determine it in the presence of other explosives and possible interferents, based on the detection of nitrite formed from ADN degradation under UV light in a slightly alkaline (i.e. of lower alkalinity than needed to hydrolyze nitramines) solution by a nanoparticle-based colorimetric sensor. The ADN-derived nitrite formed a colored product via a Griess reaction using gold nanoparticles modified with 4-aminothiophenol (4-ATP-AuNPs) along with a coupling reagent N-(1-naphthyl)ethylene diamine (NED) for forming an azo dye. The method used for ADN detection could also be applied to tetryl samples at a different wavelength. The limit of detection (LOD) was 0.012 mg L-1 for ADN and 0.615 mg L-1 for tetryl. Interference effects of energetic materials like trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and pentaerythritol tetranitrate (PETN) to ADN determination could be overcome. In addition, common soil ions did not adversely affect the nanosensor performance. The developed method was statistically validated against reference voltammetric, UV, and HPLC methods using t- and F- tests.

Magnetite nanoparticles-based hydroxyl radical scavenging activity assay of antioxidants using N, N-dimethyl-p-phenylenediamine probe.

Excessive amounts of reactive oxygen species (ROS), unless counterbalanced by antioxidants, can cause cellular damage under oxidative stress conditions; therefore, antioxidative defenses against ROS must be measured. With the development of nanotechnology, nanoparticles have found numerous applications in science, health, and industries. Magnetite nanoparticles (Fe 3 O 4 :MNPs) have attracted attention because of their peroxidase-like activity. In this study, hydroxyl radicals (•OH) generated by MNPs-catalyzed degradation of H 2 O 2 converted the N,N-dimethyl-p-phenylenediamine (DMPD) probe into its colored DMPD•+ radical cation, which gave an absorbance maximum at λ = 553 nm. In the presence of antioxidants, •OH was partly scavenged by antioxidants and produced less DMPD• + , causing a decrease in the 553 nm-absorbance. Antioxidant concentrations were calculated with the aid of absorbance differences between the reference and sample solutions. The linear working ranges and trolox equivalent antioxidant capacity coefficients of different classes of antioxidants were determined by applying the developed method. In addition, binary and ternary mixtures of antioxidants were tested to observe the additivity of absorbances of mixture constituents. The method was applied to real samples such as orange juice and green tea. Student t-test, F tests, and the Spearman's rank correlation coefficient were used for statistical comparisons.

Titanium dioxide nanoparticles-based colorimetric sensors for determination of hydrogen peroxide and triacetone triperoxide (TATP).

Due to its relatively simple preparation and readily available precursors, determination of triacetone triperoxide (TATP) by portable devices has become important. In this work, two different titanium dioxide nanoparticles (TiO2NPs)-based colorimetric sensors based on complex formation on the solid surface were developed for determination of H2O2 and TATP. The first sensor, (3-aminopropyl)triethoxysilane (APTES) modified-TiO2NPs-based paper sensor (APTES@TiO2NPs), exploits peroxo-titanate binary complex formation between APTES@TiO2NPs and H2O2 on chromatographic paper. The second sensor, 4-(2-pyridylazo)-resorcinol-modified-TiO2NPs-based solid sensor (PAR@TiO2NPs), relies on the formation of a ternary complex between Ti(IV), PAR and H2O2. The developed sensors were also applied to TATP determination after acidic hydrolysis of samples to H2O2. The limits of detection (LODs) of APTES@TiO2NPs-based paper sensor were 3.14 × 10-4 and 5.13 × 10-4 mol L-1 for H2O2 and TATP, respectively, whereas the LODs of PAR@TiO2NPs solid sensor were 6.06 × 10-7 and 3.54 × 10-7 mol L-1 for H2O2 and TATP, respectively. Possible interferences of common soil ions, passenger belongings used as camouflage materials during public transport (e.g., detergent, sweetener, acetylsalicylic acid and paracetamol-caffeine based analgesic drugs) and of other explosives were examined. The developed methods were statistically validated using t- and F- tests against the titanyl sulfate (TiOSO4) colorimetric literature method.

Diaminocyclohexane-Functionalized/Thioglycolic Acid-Modified Gold Nanoparticle-Based Colorimetric Sensing of Trinitrotoluene and Tetryl.

Detection of explosive residues in soil and postblast debris is an important issue in sensor design for environmental and criminological purposes. An easy-to-use and low-cost gold nanoparticle (AuNP)-based colorimetric sensor was developed for the determination of nitroaromatic explosives, i.e., trinitrotoluene (TNT) and tetryl, capable of analyte detection at picomolar (pM) levels. The sensor nanoparticles were synthesized by functionalizing the negatively charged thioglycolic acid (TGA)-modified AuNPs with positively charged (±)- trans-1,2-diaminocyclohexane (DACH) at a carefully calculated pH. The working principle of the sensor is charge-transfer (CT) interaction between the electron-rich free amino (-NH2) group of DACH and the electron-deficient -NO2 groups of TNT/tetryl, added to possible nanoparticle agglomerization via electrostatic interaction of TNT-Meisenheimer anions with more than one cationic DACH-modified AuNP. The limit of detection (LOD) and limit of quantification (LOQ) of the sensor were 1.76 pM and 5.87 pM for TNT and 1.74 pM and 5.80 pM for tetryl, respectively. TNT, tetryl, and tetrytol, extracted from a nitroaromatic explosive-contaminated soil sample, were determined with the proposed sensor, yielding good recoveries. The sensor could be selectively applied to various mixtures of TNT with common energetic materials such as RDX, HMX, and PETN. Additionally, common soil ions (Cl-, NO3-, SO42-, K+, Mg2+, Ca2+, Cu2+, Fe2+, Fe3+, and Al3+) as well as detergents, sugar, sweeteners, acetylsalicylic acid (aspirin), caffeine, and paracetamol-based painkiller drugs, which may be used as camouflage materials for explosives, either had no adverse effects or removable interferences on the detection method. The developed method was statistically validated against a GC-MS literature method.

Colorimetric Determination of (Aminoalkyl)indole-containing Synthetic Cannabimimetics.

Cannabis is an important industrial plant, in addition to its illicit drug use. Compound Δ9-THC (Δ9-tetrahydrocannabinol) is mainly responsible for the hallucinogenic effect on humans. The aminoalkylindole group cannabimimetics targets at the same physiological receptors to mimic the analgesic effects of Δ9-THC. Since there is no reliable colorimetric test to detect these synthetic cannabimimetics on site, a simple colorimetric assay for (aminoalkyl)indole group-containing drugs was developed, based on the silica/sulfuric acid-catalyzed Ehrlich reaction of (aminoalkyl)indoles with p-dimethylaminobenzaldehyde. The electrophilic substitution reaction of indoles with carbonyl compounds resulting in the formation of bis(indolyl)alkanes in an acid-catalyzed reaction has been used for the first time for their spectrophotometric determination by color change from yellow to purple/blue. The method was statistically validated against liquid chromatography tandem mass spectrometry, and applied to certain (aminoalkyl)indole derivatives, with 0.5 - 2.5 µg mL-1 detection limits for AM-2201, JWH-081, MAM-2201, JWH-018, JWH-210, JWH-122, 5F-PB-22 and XLR-11.

Electrochemical Determination of TNT, DNT, RDX, and HMX with Gold Nanoparticles/Poly(Carbazole-Aniline) Film-Modified Glassy Carbon Sensor Electrodes Imprinted for Molecular Recognition of Nitroaromatics and Nitramines.

Since nitroaromatic- and nitramine-type energetic materials, mostly arising from military activities, are persistent pollutants in soil and groundwater, on-site sensing of these hazardous chemicals has gained importance. A novel electrochemical sensor was designed for detecting nitroaromatic- and nitramine-type energetic materials, relying on gold nanoparticles (Aunano), modified glassy carbon (GC) electrode coated with nitro-energetic memory-poly(carbazole-aniline) copolymer (Cz- co-ANI) film (e.g., TNT memory-GC/P(Cz- co-ANI)-Aunano modified electrode). Current was recorded against concentration to build the calibration curves that were found to be linear within the range of 100-1000 µg L-1 for 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT): 50-1000 µg L-1 for 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The corresponding limits of detection were 25 µg L-1 for TNT, 30 µg L-1 for DNT, and 10 µg L-1 for both RDX and HMX, using nitro-energetic memory-GC/P(Cz- co-ANI)-Aunano electrodes. These electrodes were used separately, and specific determinations were made in various mixtures of nitro-energetic materials. The developed method could be efficiently used in electroanalyzing nitroaromatics and nitramines in military explosives (i.e., comp B, octol, and comp A5). The sensor electrodes were specific for the tested nitro-energetic compounds and did not respond to paracetamol-caffeine-based analgesic drug, acetylsalicylic acid (aspirin), sweetener, and sugar that can be used as camouflage materials in passenger belongings. The developed method was statistically validated against the standard LC-MS reference method in contaminated clay soil samples containing TNT and RDX explosives.

Novel Spectroscopic and Electrochemical Sensors and Nanoprobes for the Characterization of Food and Biological Antioxidants.

Since an unbalanced excess of reactive oxygen/nitrogen species (ROS/RNS) causes various diseases, determination of antioxidants that can counter oxidative stress is important in food and biological analyses. Optical/electrochemical nanosensors have attracted attention in antioxidant activity (AOA) assessment because of their increased sensitivity and selectivity. Optical sensors offer advantages such as low cost, flexibility, remote control, speed, miniaturization and on-site/in situ analysis. Electrochemical sensors using noble metal nanoparticles on modified electrodes better catalyze bioelectrochemical reactions. We summarize the design principles of colorimetric sensors and nanoprobes for food antioxidants (including electron-transfer based and ROS/RNS scavenging assays) and important milestones contributed by our laboratory. We present novel sensors and nanoprobes together with their mechanisms and analytical performances. Our colorimetric sensors for AOA measurement made use of cupric-neocuproine and ferric-phenanthroline complexes immobilized on a Nafion membrane. We recently designed an optical oxidant/antioxidant sensor using N,N-dimethyl-p-phenylene diamine (DMPD) as probe, from which ROS produced colored DMPD-quinone cationic radicals electrostatically retained on a Nafion membrane. The attenuation of initial color by antioxidants enabled indirect AOA estimation. The surface plasmon resonance absorption of silver nanoparticles as a result of enlargement of citrate-reduced seed particles by antioxidant addition enabled a linear response of AOA. We determined biothiols with Ellman reagent-derivatized gold nanoparticles.

Indirect Determination of Pentaerythritol Tetranitrate (PETN) with a gold nanoparticles-based colorimetric sensor.

Pentaerythritol tetranitrate (PETN) is the nitrate ester of pentaerythritol, used as an energetic and filling material for military and civilian purposes and rarely for terrorist actions. As there is no reliable nano-colorimetric method for PETN assay, we developed an indirect method based on the determination of nitrite, obtained by reduction of nitrate derived from the alkaline hydrolysis of PETN with H2O2. We colorimetrically determined the final product, nitrite, by both conventional Griess reaction and a recently developed gold nanoparticle-4-aminothiophenol-N-(1-naphthyl)-ethylenediamine (AuNP-4-ATP+NED) method. Nitramines (RDX and HMX), if present, could be degraded by alkaline hydrolysis, without affecting PETN. The analytical performance characteristics of the developed assays as molar absorptivity (ε), limits of detection (LOD) and quantification (LOQ) were: ɛ=1.06×105 L mol-1 cm-1, LOD=0.03mgL-1 and LOQ=0.11mgL-1 for indirect Griess method; ɛ=1.9×104Lmol-1 cm-1; LOD=0.12mgL-1 and LOQ=0.4mgL-1 for AuNP-4-ATP+NED method. Both methods were applied to a 1:1 (w/w) mixture of PETN and TNT (corresponding to the composition of military explosive 'Pentolite'). In order to eliminate the interference from TNT, the Meisenheimer anion of TNT formed in alkaline medium was retained on a strongly basic anion exchange resin column. As PETN had a very low solubility in water, common soil ions could be eliminated by prewashing the sample with water, or in acetone-water mixtures, Ca2+, K+, Cl-, SO42-, and NO3- could be tolerated at equal (1:1) mass ratios. Soil nitrates and nitrites, at a mass ratio of 50:1, could be separated from PETN with the aid of their insolubilities in acetone and of their retention affinity toward a strongly basic anion-exchange resin. The developed method was statistically validated against a reference GC-MS method.

Electrochemical Determination of Food Preservative Nitrite with Gold Nanoparticles/p-Aminothiophenol-Modified Gold Electrode.

Due to the negative impact of nitrate and nitrite on human health, their presence exceeding acceptable levels is not desired in foodstuffs. Thus, nitrite determination at low concentrations is a major challenge in electroanalytical chemistry, which can be achieved by fast, cheap, and safe electrochemical sensors. In this work, the working electrode (Au) was functionalized with p-aminothiophenol (p-ATP) and modified with gold nanoparticles (Au-NPs) to manufacture the final (Au/p-ATP-Aunano) electrode in a two-step procedure. In the first step, p-ATP was electropolymerized on the electrode surface to obtain a polyaminothiophenol (PATP) coating. In the second step, Au/p-ATP-Aunano working electrode was prepared by coating the surface with the use of HAuCl4 solution and cyclic voltammetry. Determination of aqueous nitrite samples was performed with the proposed electrode (Au/p-ATP-Aunano) using square wave voltammetry (SWV) in pH 4 buffer medium. Characteristic peak potential of nitrite samples was 0.76 V, and linear calibration curves of current intensity versus concentration was linear in the range of 0.5-50 mg·L(-1) nitrite with a limit of detection (LOD) of 0.12 mg·L(-1). Alternatively, nitrite in sausage samples could be colorimetrically determined with high sensitivity by means of p-ATP‒modified gold nanoparticles (AuNPs) and naphthylethylene diamine as coupling agents for azo-dye formation due to enhanced charge-transfer interactions with the AuNPs surface. The slopes of the calibration lines in pure NO2(-) solution and in sausage sample solution, to which different concentrations of NO2(-) standards were added, were not significantly different from each other, confirming the robustness and interference tolerance of the method. The proposed voltammetric sensing method was validated against the colorimetric nanosensing method in sausage samples.

Determination of triacetone triperoxide with a N,N-dimethyl-p-phenylenediamine sensor on nafion using Fe3O4 magnetic nanoparticles.

The explosive triacetone triperoxide (TATP) can be easily manufactured from readily accessible reagents and is extremely difficult to detect, owing to the lack of UV absorbance, fluorescence, or facile ionization. The developed method is based on the acidic hydrolysis of TATP into H2O2, pH adjustment to 3.6, and the addition of magnetite nanoparticles (Fe3O4 MNPs) to the medium to produce hydroxyl radicals from H2O2, owing to the peroxidase-like activity of MNPs. The formed radicals converted the N,N-dimethyl-p-phenylenediamine (DMPD) probe to the colored DMPD(+) radical cation, the optical absorbance of which was measured at a wavelength of 554 nm. The molar absorptivity (ε) of the method for TATP was 21.06 × 10(3) L mol(-1) cm(-1). The colored DMPD(+) product in solution could be completely retained on a cation-exchanger Nafion membrane, constituting a colorimetric sensor for TATP and increasing the analytical sensitivity. The proposed method did not respond to a number of hand luggage items like detergent, sweetener, sugar, acetylsalicylic acid (aspirin), and paracetamol-caffeine-based analgesic drugs. On the other hand, TATP could be almost quantitatively recovered from a household detergent and sweetener that can be used as camouflage for the analyte. Neither common soil and groundwater ions (e.g., Ca(2+), Mg(2+), K(+), Cl(-), SO4(2-), and NO3(-)) at 100-fold ratios nor nitro-explosives of trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and pentaerythritol tetranitrate (PETN) at 10-fold amounts interfered with the proposed assay. The method was statistically validated against the standard GC/MS reference method.

Electrochemical sensor for nitroaromatic type energetic materials using gold nanoparticles/poly(o-phenylenediamine-aniline) film modified glassy carbon electrode.

In this work, a novel electrochemical sensor was developed for the detection of nitroaromatic explosive materials, based on a gold nanoparticle-modified glassy carbon (GC) electrode coated with poly(o-phenylenediamine-aniline film) (GC/P(o-PDA-co-ANI)-Aunano electrode). Nitroaromatic compounds were detected through their π-acceptor/donor interactions with o-phenylenediamine-aniline functionalities on the modified electrode surface. The enhanced sensitivities were achieved through π-π and charge-transfer (CT) interactions between the electron-deficient nitroaromatic compounds and σ-/π-donor amine/aniline groups linked to gold nanoparticles (Au-NPs), providing increased binding and preconcentration onto the modified GC-electrodes. Selective determination of nitroaromatic type explosives in the presence of nitramines was enabled by o-PDA and reusability of the electrode achieved by Au-NPs. Calibration curves of current intensity versus concentration were linear in the range of 2.5-40mgL(-1) for 2,4,6-trinitrotoluene (TNT) with a detection limit (LOD) of 2.1mgL(-1), 2-40mgL(-1) for 2,4-dinitrotoluene (DNT) (LOD=1.28mgL(-1)), 5-100mgL(-1) for tetryl (LOD=3.8mgL(-1)) with the use of the GC/P(o-PDA-co-ANI)-Aunano electrode. For sensor measurements, coefficients of variation of intra- and inter-assay measurements were 0.6% and 1.2%, respectively (N=5), confirming the high reproducibility of the proposed assay. Deconvolution of current contributions of synthetic (TNT+DNT) mixtures at peak potentials of constituents was performed by multiple linear regression analysis to provide high sensitivity for the determination of each constituent. Determination options for all possible mixture combinations of nitroaromatic explosives are presented in this work. The proposed methods were successfully applied to the analysis of nitroaromatics in military explosives, namely comp B, octol, and tetrytol. Method validation was performed against GC-MS on real post-blast residual samples containing both explosives.

4-Aminothiophenol functionalized gold nanoparticle-based colorimetric sensor for the determination of nitramine energetic materials.

The heterocyclic nitramine compounds, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), are two most important military-purpose high explosives. Differentiation of RDX and HMX with colorimetric methods of determination has not yet been made because of their similar chemical structures. In this study, a sensitive colorimetric method for the determination of RDX and HMX was proposed on the basis of differential kinetics in the hydrolysis of the two compounds (yielding nitrite as a product) followed by their colorimetric determination using 4-aminothiophenol (4-ATP) modified gold nanoparticles (AuNPs) and naphthylethylene diamine (NED) as coupling agent for azo-dye formation, abbreviated as "4-ATP-AuNP+NED" colorimetric method. After alkaline hydrolysis in a 1 M Na2CO3 + 0.04 M NaOH mixture solution at room temperature, only RDX (but not HMX) was hydrolyzed to give a sufficient colorimetric response in neutralized solution, the molar absorptivity (ε) at 565 nm and the limit of detection (LOD) for RDX being (17.6 ± 1.3) × 10(3) L mol(-1) cm(-1) and 0.55 µg mL(-1), respectively. On the other hand, hot water bath (at 60 °C) hydrolysis enabled both nitramines, RDX and HMX, to give substantial colorimetric responses; i.e., ε and LOD for RDX were (32.8 ± 0.5) × 10(3) L mol(-1)cm(-1) and 0.20 µg mL(-1) and for HMX were (37.1 ± 2.8) × 10(3) L mol(-1)cm(-1) and 0.24 µg mL(-1), respectively. Unlike other AuNP-based nitrite sensors in the literature showing absorbance quenching within a relatively narrow concentration range, the developed sensor operated with an absorbance increase over a wide range of nitrite. Synthetic mixtures of (RDX + HMX) gave additive responses, and the proposed method was statistically validated against HPLC using nitramine mixtures.

Determination of nitroaromatic and nitramine type energetic materials in synthetic and real mixtures by cyclic voltammetry.

Nitro-explosives contain reducible aromatic -NO2 groups or cyclic >N-NO2 bonds that may undergo reductive cleavage. This work reports the development of a cyclic voltammetric (CV) assay for nitro-aromatics (trinitrotoluene (TNT), dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) using a glassy carbon electrode. This determination was first used for these energetic materials by resolving current responses of reduction potentials primarily due to one constituent but partly contributed by other constituents. Calibration curves of current intensity versus concentration were linear in the range of 30-120 mg L(-1) for RDX with a limit of detection (LOD) of 10.2 mg L(-1), 40-120 mg L(-1) for HMX (LOD=11.7 mg L(-1)), 40-120 mg L(-1) for TNT (LOD=11.2 mg L(-1)), and 40-140 mg L(-1) for DNT (LOD=10.8 mg L(-1)). Results showed that the CV method could provide a sensitive approach for the simultaneous determination of RDX and TNT in synthetic and real mixtures. Deconvolution of current contributions of mixtures at peak potentials of constituents was performed by multiple linear regression. The proposed method was successfully applied to the analysis of military explosives comp A5 and octol, and method validation was performed both against HPLC on a comp B (TNT+RDX) sample and against GC-MS on real post-blast residual samples containing both explosives.

Spectrophotometric and chromatographic determination of insensitive energetic materials: HNS and NTO, in the presence of sensitive nitro-explosives.

As there are no molecular spectroscopic determination methods for the most widely used insensitive energetic materials, 2,2',4,4',6,6'-hexanitrostilbene (HNS) and 3-nitro-1,2,4-triazole-5-one (NTO), in the presence of sensitive nitro-explosives, two novel spectrophotometric methods were developed. For HNS and TNT mixtures, both analytes react with dicyclohexylamine (DCHA) forming different colored charge-transfer complexes, which can be resolved by derivative spectroscopy. The spectrophotometric method for NTO measures the 416-nm absorbance of its yellow-colored Na(+)NTO(-) salt formed with NaOH. TNT, if present, is pre-extracted into IBMK as its Meisenheimer anion forming an ion-pair with the cationic surfactant cetyl pyridinium (CP(+)) in alkaline medium, whereas the unextracted NTO is determined in the aqueous phase. The molar absorptivity (ε, L mol(-1)cm(-1)) and limit of quantification (LOQ, mg L(-1)) are as follows: for HNS, ε=2.75 × 10(4) and LOQ=0.48 (in admixture with TNT); for NTO, ε=6.83 × 10(3) and LOQ=0.73. These methods were not affected from nitramines and nitrate esters in synthetic mixtures or composite explosives. The developed methods were statistically validated against HPLC, and the existing chromatographic method was modified so as to enable NTO determination in the presence of TNT. These simple, low-cost, and versatile methods can be used in criminology, remediation/monitoring of contaminated sites, and kinetic stability modeling of munitions containing desensitized energetic materials.

Rapid detection of nitroaromatic and nitramine explosives on chromatographic paper and their reflectometric sensing on PVC tablets.

Rapid and inexpensive sensing of explosive traces in soil and post-blast debris for environmental and criminological purposes with optical sensors has recently gained importance. The developed sensing method for nitro-aromatic and nitramine-based explosives is based on dropping an acetone solution of the analyte to an adsorbent surface, letting the solvent to dry, spraying an analytical reagent to produce a persistent spot, and indirectly measuring its reflectance by means of a miniature spectrometer. This method proved to be useful for on-site determination of nitro-aromatics (trinitrotoluene (TNT), 2,4,6-trinitrophenylmethylnitramine (tetryl) and dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) pre-adsorbed on a poly vinyl chloride (PVC) surface, with the use of different spray reagents for each group of explosives producing different colors. The calibration equations of the tested compounds as reflectance vs. concentration showed excellent linearity (correlation coefficient: 0.998-0.999). The linear quantification interval in terms of absolute quantity of analyte was 0.1-0.5 µg. The developed method was successfully tested for the analysis of military explosives Comp B and Octol, and was validated against high performance liquid chromatography (HPLC). The reflectometric sensing method could also be used for qualitative identification of the nitrated explosives on a chromatographic paper. The reagent-impregnated paper could also serve as sensor, enabling semi-quantitative determinations of TNT and tetryl.