A systematic overview of melt cast explosives is given. The research on melt cast explosives over several decades can be divided into three broad areas: (i) aromatic compounds with CCH3, NCH3, OCH3 CNO2, NNO2 and ONO2 groups, (ii) improved synthesis of compounds, which are currently used in formulations or which have shown promise for such use and (iii) the preparation of melt cast formulations with various compositions. Exudation, high volume change from liquid to solid, super cooling, irreversible growth, fragility and unpredictable sensitivity are the disadvantages of existing melt cast formulations.

We have investigated the decomposition kinetics of imidazole, 2-nitroimidazole, and 4-nitroimidazole using TG-DTA technique under nitrogen atmosphere. Isoconversional methods were used for the evaluation of kinetic parameters from the kinetic data of different heating temperatures. The Friedman method provided comparably higher values of activation energy than the Flynn-Wall-Ozawa method. Imidazole, 2-nitroimidazole, and 4-nitroimidazole were decomposed by the multistep reaction mechanism evident from the nonlinear relationship of activation energy and the conversion rate. The NO2 elimination and nitro-nitrite isomerization are expected to be competitive reactions in the decomposition of 2-nitroimidazole and 4-nitroimidazole. The present study may be helpful in understanding how the position of NO2 group affects the decomposition kinetics of substituted imidazoles.

Despite the intrinsic elemental analysis capability and lack of sample preparation requirements, laser-induced breakdown spectroscopy (LIBS) has not been extensively used for real world applications, e.g. quality assurance and process monitoring. Specifically, variability in sample, system and experimental parameters in LIBS studies present a substantive hurdle for robust classification, even when standard multivariate chemometric techniques are used for analysis. Considering pharmaceutical sample investigation as an example, we propose the use of support vector machines (SVM) as a non-linear classification method over conventional linear techniques such as soft independent modeling of class analogy (SIMCA) and partial least-squares discriminant analysis (PLS-DA) for discrimination based on LIBS measurements. Using over-the-counter pharmaceutical samples, we demonstrate that application of SVM enables statistically significant improvements in prospective classification accuracy (sensitivity), due to its ability to address variability in LIBS sample ablation and plasma self-absorption behavior. Furthermore, our results reveal that SVM provides nearly 10% improvement in correct allocation rate and a concomitant reduction in misclassification rates of 75% (cf. PLS-DA) and 80% (cf. SIMCA)-when measurements from samples not included in the training set are incorporated in the test data – highlighting its robustness. While further studies on a wider matrix of sample types performed using different LIBS systems is needed to fully characterize the capability of SVM to provide superior predictions, we anticipate that the improved sensitivity and robustness observed here will facilitate application of the proposed LIBS-SVM toolbox for screening drugs and detecting counterfeit samples as well as in related areas of forensic and biological sample analysis.

We report the effectiveness of laser-induced breakdown spectroscopy (LIBS) in probing the content of pharmaceutical tablets and also investigate its feasibility for routine classification. This method is particularly beneficial in applications where its exquisite chemical specificity and suitability for remote and on site characterization significantly improves the speed and accuracy of quality control and assurance process. Our experiments reveal that in addition to the presence of carbon, hydrogen, nitrogen and oxygen, which can be primarily attributed to the active pharmaceutical ingredients, specific inorganic atoms were also present in all the tablets. Initial attempts at classification by a ratiometric approach using oxygen to nitrogen compositional values yielded an optimal value (at 746.83 nm) with the least relative standard deviation but nevertheless failed to provide an acceptable classification. To overcome this bottleneck in the detection process, two chemometric algorithms, i.e. principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA), were implemented to exploit the multivariate nature of the LIBS data demonstrating that LIBS has the potential to differentiate and discriminate among pharmaceutical tablets. We report excellent prospective classification accuracy using supervised classification via the SIMCA algorithm, demonstrating its potential for future applications in process analytical technology, especially for fast on-line process control monitoring applications in the pharmaceutical industry.

Ultrafast nonlinear optical (NLO) properties of four novel Corroles in the visible spectral range (660–800 nm) were evaluated using picosecond Z-scan technique. Ultrafast excited state dynamics have also been appraised with picosecond (ps) and femtosecond (fs) degenerate pump–probe techniques using excitation wavelengths of 800 and 600 nm, respectively. The excitation by 800 nm photons resulted in two-photon absorption at adequately high peak intensities, thereby facilitating the access to higher excited states (S n ). The nonradiative relaxation mechanisms from these states, reflected in the pump–probe data, consisted of double-exponential decay with a slow component in the range of 54–277 ps and faster component in the range of 2.0 to 2.5 ps. When excited with 600 nm photons (unfocused), photoinduced absorption was observed with the first excited state S1 being populated, and as a consequence single decay was observed in the data of all molecules studied. These retrieved lifetimes were analogous to those obtained with picosecond pump–probe data. The long lifetime is attributed to nonradiative decay from the S1 state with possible contribution from triplet states, whereas the shorter lifetime is attributed to the internal conversion (S2 to S1*), followed by vibrational relaxation (S1* to S1) processes. Time-resolved fluorescence lifetime measurements revealed the magnitude of radiative lifetimes to be in the nanosecond regime. NLO coefficients were evaluated from the Z-scan data at wavelengths of 660, 680, 700, 740, and 800 nm. Large two-photon absorption coefficients (β)/cross-sections (σ2) at 740 nm/680 nm were recorded for these molecules, making them apposite for applications such as two-photon induced photodynamic therapy and lithography. Figure of merit, T, was <1 for all molecules at 740 and 800 nm, suggesting that these molecules find use in photonic device applications.