Cycloaddition profile of pentafulvenes with 3-oxidopyrylium betaine: experimental and theoretical investigations

A detailed investigation on the effect of solvent polarity, temperature, and microwave irradiation on periselectivity in cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaine is described. The base catalyzed generation of 3-oxidopyrylium betaine in CHCl₃ resulted in the exclusive formation of [6+3] adducts. With increase in solvent polarity and temperature, mixtures of [6+3] and [3+2] adducts were formed, where as under microwave irradiation, [3+2] adducts were formed exclusively. The experimental results have been rationalized on the basis of theoretical calculations.     

Analyses of carcinogenic aromatic amines released from harmful azo colorants by Streptomyces SP. SS07

Extracellular fluid protein (ECFP) of Streptomyces species SS07 has been used to reduce water soluble azo dyes and the carcinogenic amines released have been compared with that from chemical reduction. The effect of temperature, pH and contact time on the recovery of amines using ECFP was studied. The ECFP releases carcinogenic amines at a pH of 9.2 and a temperature of 37 degrees C for a contact period of 24 h. The reduction products were analyzed with HPLC and their structures confirmed by LC-MS and GC-MS. It was observed that both the ECFP and chemical reduction methods released similar type of amine products. In the case of dye samples, compared to chemical reduction, 5-20% increase in the release of carcinogenic amines by ECFP was observed. The percentage of amine products released by chemical reduction was higher for leather garment samples compared to ECFP treatment.     

Computational study on energetic properties of nitro derivatives of furan substituted azoles

Density functional theory has been used to investigate geometries, heats of formation (HOFs), C-NO₂ bond dissociation energies (BDEs), and relative energetic properties of nitro derivatives of azole substituted furan. HOFs for a series of molecules were calculated by using density functional theory (DFT) and Møller–Plesset (MP2) methods. The density is predicted using crystal packing calculations; all the designed compounds show density above 1.71 g/cm³. The calculated detonation velocities and detonation pressures indicate that the nitro group is very helpful for enhancing the detonation performance for the designed compounds. Thermal stabilities have been evaluated from the bond dissociation energies. Charge on the nitro group was used to assess the impact sensitivity in this study. According to the results of the calculations, tri- and tetra-nitro substituted derivatives reveal high performance with better thermal stability.     

Antibacterial Effectiveness of Rice Water (Starch)‐Capped Silver Nanoparticles Fabricated Rapidly in the Presence of Sunlight

Green synthesized silver nanoparticles (AgNPs) have enormous applications. Hence, there is an increasing demand to explore diverse bioresources for AgNP fabrication to make the process more cost‐effective and rapid as possible. Due to the abundantly present hydroxyl groups of rice starch, it provides ideal sites for metal ion complexation and thereby synthesis of nanoparticles with promising activity. So the study was designed to develop rapid, eco‐friendly and cost‐effective method for green AgNP synthesis using boiled rice water starch in the presence of sunlight irradiation. The starch‐capped nanoparticles (sAgNPs) formed in the study were found to have the surface plasmon absorbance at 439 nm. The study showed optimum yield of sAgNPs when 25% rice starch was treated with aqueous 1 mM AgNO₃ for 15 min in the presence of sunlight. Fourier transform infrared spectroscopy analysis provided mechanistic insight into the role of –OH groups of starch in the reduction of AgNO₃ to sAgNPs. On further characterization by X‐ray diffraction analysis, the sAgNPs were identified to have FCC crystal structure. At the same time, high‐resolution transmission electron microscopic analysis showed majority of sAgNPs to have spherical morphology, and dynamic light scattering study revealed the average particle size as 36.3 nm. Further confirmation on presence of AgNPs was carried out by energy‐dispersive X‐ray spectroscopy. Moreover, the sAgNPs exhibited promising antibacterial activity against foodborne pathogens, Salmonella Typhimurium and Staphylococcus aureus.     

Polyelectrolyte‐Assisted Formation of Molecular Nanoparticles Exhibiting Strongly Enhanced Fluorescence

A polyelectrolyte‐assisted reprecipitation method is developed to fabricate nanoparticles of highly soluble molecules. The approach is demonstrated by using a zwitterionic diaminodicyanoquinodimethane molecule bearing remote ammonium functionalities with high solubility in water as well as organic solvents. Nanoparticles are prepared by injecting aqueous solutions of this compound containing an optimum concentration of sodium poly(styrenesulfonate) into methanol. The strong fluorescence exhibited by the compound in the aggregated state is reflected in the enhanced fluorescence of the polyelectrolyte complex in water. The nanoparticles formed in the colloidal state manifest even stronger fluorescence, which leads to an overall enhancement by about 90 times relative to aqueous solutions of the pure compound. The conditions for achieving the emission enhancement are optimized and a model for the molecular‐level interactions and aggregation effects is developed through a range of spectroscopy, microscopy, and calorimetry investigations and control experiments.     

Colorimetric and fluorescence sensing of fluoride anions with potential salicylaldimine based schiff base receptors

Salicylaldimine based schiff base receptors with different substituents showing fluorescent enhancement in the presence of fluoride anion was visualized through naked eye as well as by change in spectral properties (UV–vis and fluorescent techniques). The reason for such fluorescence enhancement may be due to hydrogen bond interaction between receptor recognition site and fluoride anion. Such a hydrogen bond interaction creates a six-membered transition state, which avoids quenching processes. To support this, fluorescence enhancement factor (FEF) was calculated and it was found to be more (FEF = 652) for –NO₂ substituted receptor compared to other receptors.     

Thermogravimetric analysis of PVC/ELNR blends

The thermal behaviour of a series of solution-cast blends of polyvinyl chloride/epoxidised liquid natural rubber (ELNR) of different mole percentage of epoxidation has been examined using thermogravimetric analysis. Thermal degradation is found to occur through a two-step route in which the first step corresponds to the dehydrochlorination of PVC to form a polyene and the second step is attributed to the decomposition of the ELNR and the polyene. Introduction of 20 and 50 mol% of epoxy group into the liquid NR is found to enhance the thermal stability of PVC. Probable mechanisms of degradation have been suggested on the basis of the kinetic analysis of the degradation studies. It is found that the mechanism is influenced by the epoxy content of the blend system. Activation energy for the degradation and the entropy change have also been reported.     

Iodine assisted palladium catalyzed ring opening of bicyclic hydrazines with organoboronic acids: stereoselective synthesis of functionalized cyclopentenes and alkylidene cyclopentenes

A novel reactivity of organoboronic acids with bicyclic hydrazines leading to the stereoselective formation of trans-vicinal disubstituted cyclopentenes in good to excellent yield is discussed. The reaction of cyclopentadiene and fulvene derived azabicyclic alkenes with organoboronic acids afforded the trans-3,4-disubstituted cyclopentenes and alkylidene cyclopentenes in good to excellent yields. The products, having a broad range of substituents, are important intermediates in the synthesis of a number of pharmaceutically important molecules.     

Pyridine-based,microwave-assisted one-pot synthetic protocol for the synthesis of ethyl 3-substituted-4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylates

Pyridine has been used for one-pot, two-component synthesis of ethyl 3-substituted-4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate derivatives in moderate to good yields by condensing N-substituted thioureas with diethyl ethoxymalonate under microwave irradiation.     

Stereopositional Outcome in the Packing of Dissimilar Aromatics in Designed β‐Hairpins

A popular strategy in the de novo design of stable β‐sheet structures for various biomedical applications is the incorporation of aromatic pairs at the non‐hydrogen‐bonding (NHB) position. However, it is important to explicitly understand how aryl pair packing at the NHB region is coordinated with backbone structural rearrangements, and to delineate the benefits and drawbacks associated with stereopositional choice of dissimilar aromatic pairs. Here, we probe the consequences of flipped Trp/Tyr pairs by using engineered permutants at the NHB position of dodecapeptide β‐hairpins, proximal and distal to the turn. Extensive conformational analysis of these peptides using NMR and CD spectroscopy reveal that a classic Edge‐to‐Face and Face‐to‐Edge geometry at the proximal and distal aromatic pairs, respectively, in YW‐WY, is the most stabilizing. Such a preferred packing geometry in YW‐WY results in a highly twisted β‐sheet backbone, with Trp always providing a ‘Face’ orientation to its dissimilar aromatic partner Tyr. Flipping the proximal and/or distal aromatic pair distorts the ideal T‐shaped geometry, and results in alternate aryl arrangements that can adversely affect strand twist and β‐sheet stability. Our study reveals the existence of a strong stereopositional influence on the packing of dissimilar aromatic pairs. Our findings highlight the importance of modeling physical interaction forces while designing protein and peptide structures for functional applications.