Paal–Knorr synthesis of pyrroles: from conventional to green synthesis

The pyrrole molecular framework is found in a large number of natural and synthetic compounds of great importance. Since functionalized pyrroles are essential for the progress of many branches of science, its synthesis by simple, efficient and eco-friendly routes are particularly attractive in modern organic and bio-organic chemistry. To this end, a number of synthetic methods have been developed, in which the Paal–Knorr pyrrole synthesis stands out to be the easiest route to synthesize pyrroles. In spite of the efficiency, Paal–Knorr synthesis of pyrroles is considered limited by harsh reaction conditions, such as prolonged heating in acid, which may degrade sensitive functionalities in many potential precursors. Through this route almost all dicarbonyls can be converted to their corresponding heterocycles and therefore it is a synthetically valued process. To address the adverse issues this reaction route has undergone numerous modifications recently and today it can be said that this reaction route is a prominent green route for the synthesis of pyrroles. This review is a tour from the evolution and application of this harsh synthetic route to the eco-friendly greener route developed for the synthesis of pyrroles.     

χ measurements and optical limiting studies of 2-chloro-5-nitro-N′-[(1E)-phenylmethylidene] benzohydrazide with substituents

The nonlinear optical properties of hydrazones substituted with different donor groups were studied using single beam Z-scan technique with nanosecond laser pulses at 532 nm. The nonlinear response in these molecules was found to increase with increase in the donor strength of the substituted group. The χ⁽³⁾ value of these molecules is found to be of the order of 10⁻¹³ esu. The nonlinear refractive index (n₂) of the samples is found to be negative and the largest value of n₂ obtained for the strong donor-substituted molecule is −8.83 × 10⁻¹¹ esu. All samples show good optical limiting behavior at 532 nm. The best optical limiting behavior was observed with the molecule substituted by a strong electron donor.     

A symmetric Galerkin multi-zone boundary element formulation

The recent development of the symmetric Galerkin approach to boundary element analysis (BEA) has been demonstrated to be superior to the collocation method for medium to large problems. This fact has been shown in both heat conduction and elasticity. Accounts of collocation multi-zone analysis techniques have also been prevalent in the literature, dealing with multiple boundary integral relations associated with portions of overall objects. This technique results in overall system matrices with a blocked, sparse, but unsymmetric character. It has been shown that multi-zone techniques can produce smaller solution times than a single zone analysis for large problems. These techniques are useful for multi-material problems as well. This paper presents an approach for combining the benefits of both techniques resulting in a Galerkin multi-zone method, that is overall unsymmetric but contains a significant amount of block symmetry. A condensation technique in the multi-zone solver is shown to exploit the symmetry of the Galerkin formulation as well as the blocked sparsity of the multi-zone technique. This method is compared to collocation multi-zone on two elasticity problems from the literature. It is concluded that an appropriate implementation of the symmetric Galerkin multi-zone BEA indeed has the potential to be superior to the collocation based multi-zone BEA, for medium to large-scale elasticity problems. © 1997 John Wiley & Sons, Ltd.     

Design and Synthesis of Imidazo[2,1‐b]thiazole–Chalcone Conjugates: Microtubule‐Destabilizing Agents

A series of chalcone conjugates featuring the imidazo[2,1‐b]thiazole scaffold was designed, synthesized, and evaluated for their cytotoxic activity against five human cancer cell lines (MCF‐7, A549, HeLa, DU‐145 and HT‐29). These new hybrid molecules have shown promising cytotoxic activity with IC₅₀ values ranging from 0.64 to 30.9 μM . Among them, (E)‐3‐(6‐(4‐fluorophenyl)‐2,3‐bis(4‐methoxyphenyl)imidazo[2,1‐b]thiazol‐5‐yl)‐1‐(pyridin‐2‐yl)prop‐2‐en‐1‐one ( 11 x ) showed potent antiproliferative activity with IC₅₀ values ranging from 0.64 to 1.44 μM in all tested cell lines. To investigate the mechanism of action, the detailed biological aspects of this promising conjugate ( 11 x ) were carried out on the A549 lung cancer cell line. The tubulin polymerization assay and immunofluoresence analysis results suggest that this conjugate effectively inhibits microtubule assembly in A549 cells. Flow cytometric analysis revealed that this conjugate induces cell‐cycle arrest in the G2/M phase and leads to apoptotic cell death. This was further confirmed by Hoechst staining, activation of caspase‐3, DNA fragmentation analysis, and Annexin V–FITC assay. Moreover, molecular docking studies indicated that this conjugate ( 11 x) interacts and binds efficiently with the tubulin protein.     

A comparative study of B10 biodiesel blends and its performance and combustion characteristics

The current work is to investigate the diesel engine performance and combustion characteristics fuelled with Banalities aegyptiaca (BA) biodiesel and compare those with the performance and combustion characteristics of palm biodiesel, sesame biodiesel,rapeseed biodiesel, soybean biodiesel and diesel fuel. In this study, only 10% of each biodiesel (BA10, PALM10, SESAME10, RAPESEED10 and SOYBEAN10) was tested in a diesel engine. The physical properties of all the fuel samples are mentioned and compared with ASTM standards. The test rig consists of a single cylinder, auxiliary water-cooled and computer-based variable compression ratio diesel engine, which was used to evaluate their performance at a measured torque. All biodiesel fuel samples reduce brake power and brake thermal efficiency and increase brake-specific fuel consumption rate than diesel fuel. Combustion characteristics results indicated that the blended fuel samples performed with a significant reduction in terms of cylinder pressure and heat release rate compared with diesel fuel apart from diesel pressure. Among the biodiesel-blended fuel samples, BA10 showed better performance in terms of brake power, brake-specific fuel consumption and brake thermal efficiency and cylinder pressure and heat release rate in terms of combustion characteristics compared with D100.     

The combined effect of multiwalled carbon nanotubes and exhaust gas recirculation on the performance and emission characteristics of a diesel engine

The present experimental investigation focuses on the combined effects of multiwalled carbon nanotubes (MWCNTs) and exhaust gas recirculation (EGR) of a diesel engine fuelled with Calophyllum inophyllum biodiesel blends. The C. inophyllum biodiesel-diesel blend was prepared in a proportion of 20% biodiesel and 80% diesel (B20) by a volumetric basis with a magnetic stirrer. The MWCNTs (in the mass fraction of 40?ppm) were dispersed into the B20 fuel with the help of an ultrasonicator. The results show that brake thermal efficiency increases by 7.6% with the addition of MWCNTs to the B20 fuel, decreases by 2.42% with the EGR to the B20 fuel, and increases by 2.26% with the addition of MWCNTs and EGR to the B20 fuel compared to the B20 fuel. The maximum cylinder pressure and heat release rate was occurred as 67.35 bar and 74.80?kJ/m³ deg for the B20MWCNT40 fuel at full load condition. The CO and HC emissions for the B20MWCNT40+20%EGR fuel sample were lower compared to the B20 fuel. The Smoke emissions were reduced for B20MWCNT40 fuel compared to the B20 fuel. The NO_x emissions were reduced by 25.6%, 29.7% for B20+20%EGR, B20MWCNT40+20%EGR fuel samples compared to the B20 fuel.     

Studies on the role of microstructure on performance of a high strength armour steel

This investigation describes and analyses the experimental results pertinent to the ballistic performance of two apparently identical low alloy high strength steel plates against deformable lead projectiles at a velocity about 840 m/s. All the tests are carried out at normal impact angle, i.e. zero obliquity. One plate stopped all projectiles fired at it. However, the other plate failed to stop the projectiles at some locations. Both the plates were subjected to detailed analysis using standard metallurgical techniques to identify the cause of failure in one plate. The experimental results presented include the variation in the microstructure, hardness and retained austenite of the two target plates. The study concludes that the failure is caused by the decrease in resistance of the plate possibly due to higher retained austenite and coarser martensitic structure.     

An experimental study on ballistic performance of boron carbide tiles

Boron carbide is an attractive candidate for use as armour material because of its lower density combined with high hardness. The ballistic performance of boron carbide tiles were evaluated using standard Depth of Penetration (DOP) test method against hard steel 7.62 mm armour piercing (AP) projectiles. The effect of variation in thickness of tile and the projectile velocity on the ballistic efficiency of the material was studied. It has been found that the differential efficiency factor (DEF) increases with increase in projectile velocity from 600 to 820 m/s. And an insignificant or marginal increase in efficiency was observed for increase in tile thickness from 5.2 mm up to 7.3 mm. The effect of the type of radial confinement on the residual DOP was also studied. It was found that the steel radial confinement produces lower residual DOP values compared to aluminium alloy and with no radial confinement. Results along with photographs have been presented.     

Inhomogeneous flow and the effective pressure concept in pressure sintering

Many of the models proposed to describe pressure sintering of solids with a randomly distributed porosity have implicit in them the effect of porosity and it is incorrect to incorporate any extra pressure intensification factor. However, usually, pores are segregated into zones which leads to inhomogeneous deformation. A consequence of this inhomogeneity is to enhance densification rates by dislocation creep and particle sliding resulting in an anomalous pressure intensification factor. Some observations on microstructural development during hot isostatic pressing are also made.     

Effect of heat treatment on mechanical and ballistic properties of a high strength armour steel

In the present study an ultra high strength armour steel was austenatised at 910°C followed by tempering at 200, 300, 400, 500 and 600°C. After heat treatment the properties of tensile strength, ductility, charpy impact strength, hardness and microstructure were evaluated from the mechanical tests and metallographic analysis respectively. The ballistic behavior of the heat-treated plates was evaluated impacting against non-deformable hard steel core projectiles at 840 ± 15 m/s at normal angle of attack. The changes in the microstructure and mechanical properties with heat treatment have been correlated with ballistic performance of the steel. Experimental results showed that 200°C tempering gives the best ballistic performance.