Theoretical study of the substituent effect of hydroxy group on tandem Cope rearrangement and [2 + 2] cycloaddition in cis-1,2-diethynylcyclopropane and its mono-hetero analogues

The tandem Cope rearrangement and [2?+?2] cycloaddition of cis-1,2-diethynyl-1,2-dihydroxycyclopropane and its mono-hetero analogues have been investigated at the B3LYP/6-31+G* level. The presence of the hydroxy group lowers the activation enthalpies for the Cope rearrangement, whereas activation enthalpies for the [2?+?2] cycloaddition are raised as compared to those for their non-hydroxy derivatives. The NBO analysis indicates that in the transition structure involved in the Cope rearrangement, lone pairs of the oxygen atoms of the hydroxy groups are transferred into the σ* C–C bond undergoing migration, as a result of which it is weakened. On the other hand, the lone pairs of the oxygen atoms interact with the π* C=C orbitals of the bis-allenic systems in the intermediate thereby stabilizing it and, thus, suppressing its driving ability for the [2?+?2] cycloaddition. In the products so formed, 6π electrons are delocalized conferring stability on them, which is further augmented by extended conjugation with the hydroxy groups. Due to high stability of these products, activation barrier for the change of enol into ketone is very high.

     

A facile direct conversion of aldehydes to esters and amides using acetone cyanohydrin

Aromatic aldehydes with electron-withdrawing groups undergo rapid reactions with a variety of alcohols and secondary amines to afford the corresponding esters and amides, respectively, in high yields, when treated with NaCN or acetone cyanohydrin and base under ambient reaction conditions. In case of α,β-unsaturated aldehydes, simultaneous reduction of the CC bond along with esterification occurred to produce the saturated esters in high yields.     

Investigation on growth of 4-N,N-dimethylamino-N′-methylstilbazolium p-chlorobenzenesulfonate: An efficient organic NLO crystal with potential THz properties

The growth of an efficient organic nonlinear optical material 4-N, N-dimethylamino-N′-methylstilbazolium p-chlorobenzenesulfonate (DASC), a derivative of the stilbazolium tosylate family has been reported by employing the slope nucleation method coupled with slow solvent evaporation. The crystal system and lattice parameters are estimated by single crystal X-ray diffraction. The second harmonic conversion efficiency of DASC was determined using the Kurtz and Perry powder technique. The thermal stability of the compound is determined by thermo gravimetric/differential thermo gravimetric (TG/DTG) and differential scanning calorimetric (DSC) techniques. The hardness profile of the sample is investigated by Vickers microhardness test. The dielectric constant and dielectric loss of the crystal were studied as function of frequency. The surface properties of DASC are reported by undertaking scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies.     

3-Naphthylindoles as new promising candidate antioxidant,antibacterial, and antibiofilm agents

Research on Chemical Intermediates - Indole derivatives have attracted significant attention in organic synthesis and bioactivity research owing to their substantial biological activity. In the...     

Non-aqueous synthesis of nano-sized aluminium(III) isopropoxide derivatives with 8-hydroxyquinoline and their sol–gel transformation to nano-sized δ-alumina

Non-aqueous reactions of aluminum isopropoxide with 8-hydroxyquinoline (Hq = HONH₆C₉) in 1:1, 1:2 and 1:3 molar ratios in anhydrous benzene yield complexes of the type [q_nAl(OPrⁱ)_3?n] {where n = 1 (1), n = 2 (2), n = 3 (3)}. Progress of the reactions were monitored by estimating liberated 2-propanol in benzene-2-propanol azeotrope by oxidimetric method. All the products were fluorescent green powders, sparingly soluble in CHCl₃. They were characterized by elemental analysis, FT-IR and (¹H, ¹³C and ²⁷Al) NMR studies. The ESI mass spectral studies indicate dimeric nature for (1) and (2) and monomeric nature for the compound (3). The XRD spectra of (1–3) showed crystalline nature with the average particle size of 45, 32 and 27 nm respectively, as evaluated from Debye–Scherrer equation. The XRD spectrum of (3) also suggests the formation of β-crystalline polymorphs of Alq₃. The SEM images appear to indicate granular morphology for (1) and formation of cylindrical shaped rods for (2) and (3). Sol–gel hydrolysis of (1), (2) or (3) in presence of a strong acid as well as of the precursor, Al(OPrⁱ)₃,without acid or base catalyst, followed by sintering at 950 °C yielded tetragonal primitive phase of nano-sized δ-alumina in all the cases, as reflected by their powder X-ray diffraction pattern. The IR, SEM and EDX studies also support the formation of transition alumina.     

Cycloaddition Reactions of N-Sulphdvylanilines and N-(αCyano-α-aryl)-Methylanilines

Through the cycloaddition of N-(α-cyano-α-aryl)-methylanilines (II) on to N-sulphinylanilines (III) are synthesized 2,3,5-triaryl-4-imino-2H, 3H, 5H-[1.2.5]thiadiazoIidin-l-oxides (TV) in aood vields.     

Two dansyl fluorophores bearing amino acid for monitoring Hg in aqueous solution and live cells

A series of compounds (1-4) bearing one or two dansyl fluorophore(s) based on a Lys amino acid were synthesized in solid phase synthesis. Among them, two dansyl labeled Lys amino acid 3 detected Hg²⁺ in a 100% aqueous solution with high sensitivity (K_d=4.3 nM) via a turn-on response. Compound 3 was applied for monitoring Hg²⁺ in environmental and biological fields. 3 showed a hypersensitive response to Hg²⁺ without interferences from other metal ions and satisfied the requirements for monitoring the maximum allowable level (2 ppb) of mercury ions in drinking water demanded by EPA. In addition, 3 penetrated living HeLa cells and detected intracellular Hg²⁺. The organic spectroscopic data revealed the two sulfonamide and amide groups of 3 played a key role in stabilizing the 3-Hg²⁺ complex.     

AFLP marking and polymorphism among progenies of Gymnema sylvestre: an important medicinal plant of India

The level of polymorphism among twelve selected progenies of Gymnema sylvestre was investigated through AFLP markers by multiplexing PCR reactions using 64 (8x8) primer combinations. Fourteen primer combinations were selected as the most suitable combination for G. sylvestre. Analysis of the 12 progenies with these 14 primer pairs produced 1689 fragments of which 972 (57.5%) were polymorphic and 485 (28.7%) were unique to a particular genotype. The number of fragments produced by individual primer pairs was in the range of 55 to 225. Out of these, polymorphic fragments were in the range of 34 (E-ACC/M-CAC) to 157 (E-AGG/M-CAG) and unique bands observed were 8 (E-ACC / M-CAC) to 69 (E-AGG/M-CAC). Different primer combinations detected different levels of polymorphism, ranging from 33% (E-AGG/ M-CAC) to 69.8% (E-AGG/ M-CAC). From the observations, it appears that the primer combinations E-AGG/M-CAC, E-AGG/CTG, E-AGG/CAG and E-ACA/CAT were the most informative for the detection of polymorphism among the progenies compared with others, since they produced a high number of unique fragments. The similarity coefficient ranged from 0.212 to 0.731. High similarity was observed between progeny S8 and S9 (73%) and high divergence between progenies S3 and S11. Among the selected progeny, S9 was found to be the most similar to the parent (63%), while genotype S11 was the most distant (36.9%).     

Method for measuring the self-assembly of alkanethiols on gold at femtomolar concentrations

We describe a cantilever-based method for measuring the self-assembly of alkanethiols on a gold surface in a flow system that permits easy step changes in concentration and acquire a continuous in situ measure of the resulting chemisorption through the change in resonance frequency. A gold-coated (2.2 mm2), piezoelectric-excited, millimeter-sized cantilever (PEMC) sensor was exposed to 1-hexadecanethiol (HDT) in ethanol at concentrations ranging from 1 fM to 1 mM, sequentially and separately. A high-order flexural mode at approximately 850 kHz was monitored during the self-assembly. The resonance frequency decreases as a result of increased mass as chemisorption occurs on the surface. We show for the first time that the chemisorption of HDT at 1 fM is readily measurable and gave a response of 220 +/- 13 Hz (n = 4). At higher concentrations (10 and 100 fM; 1, 10, and 100 pM; 1, 10, and 100 nM; 1 microM; and 1 mM), the responses were proportionately, but nonlinearly, higher. At high concentrations (1 mM), the responses to C4, C8, C11, C16, and C18 alkanethiols were linearly proportional and were complete in approximately 25 min. We report for the first time that, once the Au surface is equilibrated at 1 pM, further chemisorption at a lower HDT concentration does not take place, even though over 99% of surface adsorption sites are available. At 1 fM, the overall chemisorption rate did not increase with a 2-fold increase in the HDT flow rate, suggesting that chemisorption at 1 fM is not transport-limited. The measured overall chemisorption rate constant at 1 fM was more rapid than 0.1 min-1.     

In Vitro and In Silico Studies for the Identification of Potent Metabolites of Some High-Altitude Medicinal Plants from Nepal Inhibiting SARS-CoV-2 Spike Protein

Despite ongoing vaccination programs against COVID-19 around the world, cases of infection are still rising with new variants. This infers that an effective antiviral drug against COVID-19 is crucial along with vaccinations to decrease cases. A potential target of such antivirals could be the membrane components of the causative pathogen, SARS-CoV-2, for instance spike (S) protein. In our research, we have deployed in vitro screening of crude extracts of seven ethnomedicinal plants against the spike receptor-binding domain (S1-RBD) of SARS-CoV-2 using an enzyme-linked immunosorbent assay (ELISA). Following encouraging in vitro results for Tinospora cordifolia, in silico studies were conducted for the 14 reported antiviral secondary metabolites isolated from T. cordifolia—a species widely cultivated and used as an antiviral drug in the Himalayan country of Nepal—using Genetic Optimization for Ligand Docking (GOLD), Molecular Operating Environment (MOE), and BIOVIA Discovery Studio. The molecular docking and binding energy study revealed that cordifolioside-A had a higher binding affinity and was the most effective in binding to the competitive site of the spike protein. Molecular dynamics (MD) simulation studies using GROMACS 5.4.1 further assayed the interaction between the potent compound and binding sites of the spike protein. It revealed that cordifolioside-A demonstrated better binding affinity and stability, and resulted in a conformational change in S1-RBD, hence hindering the activities of the protein. In addition, ADMET analysis of the secondary metabolites from T. cordifolia revealed promising pharmacokinetic properties. Our study thus recommends that certain secondary metabolites of T. cordifolia are possible medicinal candidates against SARS-CoV-2.