Recent advances in the synthetic chemistry of 1,5-benzothiazepines: A minireview

Benzothiazepine, a prominent “drug prejudice core”, is a heterocyclic moiety of immense importance due to its presence in a wide range of bioactive compounds. They act as a primary “biolinker” in diverse synthetic routes to obtain bioactive molecules and serve as important templates in synthetic and medicinal chemistry. They are known to possess a plethora of pharmacological activities, which include Ca²⁺ channel blockers, CNS acting agents, anti-HIV, ACE inhibitors, antimicrobial, antifungal, anticancer. Their promising behaviour as drug molecules led the scientific community to develop novel, mild, green, and highly efficient synthetic routes for their synthesis. The conventional synthesis generally involved the condensation of chalcones with 2-aminothiophenol in the presence of acid/base with high-temperature heating, mostly resulting in poor yields or mixtures. However, recent trends are replacing these conditions with mild and green conditions through organocatalysis or other methodologies. In this review, an attempt has been made by authors to summarize (a) Recent developments in the synthetic strategies of 1,5-benzoathiazepines and its derivatives (b) Conventional methods for the synthesis of 1,5-benzothiazepines including progress in the green chemistry routes (c) Applications of various metals and organocatalysts to achieve the enantioselective synthesis of title compounds.     

Theoretical studies of the tautomers of pyridinethiones

Pyridinethiones are important ligand precursors of coordination complexes of therapeutic value. In aqueous solution, pyridinethiones can dimerize and tautomerize to the corresponding thiols. However, the tautomerism of pyridinethiones, which can impact on therapeutic performance, is yet not fully understood. To resolve this important issue, we have carried out ab initio and DFT calculations to compute the geometries, energies, dipole moments, and NMR, IR, and UV-vis spectroscopic properties of all possible tautomers of pyridinethiones and compared our theoretical results with the existing experimental data. We found that the thione form of the tautomer is dominant for monomers of the pyridinethiones studied here. This work can serve as a reference for exploring other similar organosulfur compounds.     

Performance of active and passive night viewing systems under low ambient illumination levels

A comparison of the estimated field performance of some typical active and passive night viewing systems under low illumination levels is presented. In addition to the ‘range’, a generalized figure of merit, the minimum detectable object size (MIDOS), is suggested and used as a basis of comparison. The influence of the optics and other parameters is discussed and the usefulness of the results in the optimization of system design is illustrated. The results indicate that active systems perform better than similar passive systems under certain commonly encountered ambient conditions.     

A nomograph for the estimation of the field performance of active night viewing systems

A nomographic method for the estimation of the field performance of active night viewing systems is described. The nomograph is based on a set of relationships which relate the field performance with system parameters that can be measured in the laboratory. The usefulness of the method is illustrated with the help of a practical active night viewing system.     

Spectrally Efficient 3D Optical CDMA Using Coherent Spatial Phase–Time Coding/Decoding

We demonstrate a WDM compatible optical CDMA system incorporating 3D spectral phase–time encoding/decoding. We provide coding and decoding using binary [0, π] phase chips for six users at 6 Gb/s, with a single coded signal separated with an acceptable bit-error rate ≤10 ^?9. The coding and decoding method is based on 3D coding of tightly spaced phase-locked laser lines that is compatible with conventional WDM networking. In optical CDMA systems, we propose to provide encoding and decoding done by converting Hadamard codes (used for conventional CDMA system) to the phase codes. We report that duo-binary modulation format is the best with adequate bandwidth compression. We confirm that better simulation results are reached in terms of the Q factor and bit error rate.     

Sensitivity of the Multiple Functional Moieties of Amino Acids for the Self-Assembly of Au Nanoparticles on Different Physicochemical Properties

This paper investigates the extent of the self-assembly process of Au nanoparticles, depending on the nature of structural and functional moieties of various amino acids (l-cystine, glutathione, l-cysteine and N-acetyl cysteine) and their influence on the plasmon sensitivity and electrokinetic parameters in correlation with the catalysis of p-nitrophenol reduction. DLS particle size analysis revealed that the hydrodynamic size 10–20 nm of Au nanospheres was increased to 135–550 nm, 100–460 nm and 130–240 nm after the addition of l-cystine, l-cysteine and glutathione, respectively, in contrast to no significant change of particle size (15–60 nm) after N-acetyl cysteine addition. This difference in the extent of aggregation as a function of structures of amino acids is further evidenced by lengthy tubular arrays formation by glutathione as compared to branched chain like morphology obtained by l-cystine through TEM. FTIR studies further confirmed the binding of amino acids to Au nanospheres via –SH followed by linking of adjacent nanoparticles through H-bonding. Due to the conformational diversity of amino acids, the surface adsorbed –SH, –COO^? and –NH₃ ⁺ species over assembled Au nanoparticles led to the alteration of zeta potential and conductance, thus affected the catalysis for the reduction of p-nitrophenol as compared to unmodified Au nanoparticles.     

Lanthanide(III) and group 13 metal ion complexes of tripodal amino phosphinate ligands

The tripodal amino-phosphinate ligands, tris(4-(phenylphosphinato)-3-benzyl-3-azabutyl)amine (H(3)ppba.2HCl.H(2)O) and tris(4-(phenylphosphinato)-3-azabutyl)amine (H(3)ppa.HCl.H(2)O) were synthesized and reacted with Al(3+), Ga(3+), In(3+) and the lanthanides (Ln(3+)). At 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(3)ppba)(2)](3+)(M = Al(3+), Ga(3+), In(3+), Ho(3+)-Lu(3+)) were isolated. The bicapped [Ga(H(3)ppba)(2)](NO(3))(2)Cl.3CH(3)OH was structurally characterized and was shown indirectly by various techniques to be isostructural with the other [M(H(3)ppba)(2)](3+) complexes. Also, at 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)(2)](5+)(M = La(3+)-Tb(3+)) were characterized, and the X-ray structure of [Gd(H(4)ppba)(2)](NO(3))(4)Cl.3CH(3)OH was determined. At 1 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)](4+)(M = La(3+)-Er(3+)) were isolated and characterized. Elemental analysis and spectroscopic evidence supported the formation of a 1 : 1 monocapped complex. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+), complex of the type [Ga(ppa)].3H(2)O was obtained. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+) a neutral complex [Ga(ppa)].3H(2)O was obtained. The formation of an encapsulated 1 : 1 complex is supported by elemental analysis and spectroscopic evidence.     

Performance analysis and improvement of spectrally amplitude encoded/decoded OCDMA system

This paper describes a performance analysis of an incoherent optical code-division multiple-access scheme based on wavelength/time (W/T) codes. The system supports 16 users operating at 2.5Gb/s/user while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. It has been observed that there are two major problems giving rise to performance degradation of the system in terms of number of users and type of code.In this paper we have studied the optical simulator Encoding/Decoding for different lengths & gain in terms of Quality factor (Q) and Bit Error Rate (BER) performance. The system supports 16 users while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. Our aim is to design and simulate a Tree Network Topology Optical Code Division Multiple Access System for large number of users using wavelength–time code and to analyze the performance of the system based on BER and Eye Diagram under the influence of number of simultaneous users with different received powers.     

Optimization considerations in the design of active night viewing systems

The problems associated with the optimization of the design of active night viewing systems based on the infra-red image converter tube are discussed with special reference to its key components; namely the optics, the imaging device and the infra-red source. The role of spectral matching between the response of the imaging device and the distribution of the infra-red source is highlighted, and these factors pertaining to some practical sources in combination with the imaging device are computed. A procedure for the design of an infra-red source to achieve a specified field irradiance is presented, and the use of these concepts in the optimization of the design of practical systems is illustrated.