• SUMAN

Articles written in Journal of Chemical Sciences

• A triad of rhenium-mediated transformations

The title transformations are oxygen atom transfer, twin isomerization and regiospecific imine oxidation.Bispyridyldiazole ligands have furnished new oxygen atom transfer reagents of coordination type ReVOCl3(NN) which undergo a slower transfer to PPh3 than the corresponding azole reagents. The rate of twin isomerization (linkage and geometrical) of meridional azole complexes of coordination type ReIII(OPnP)Cl3(NN) to facial ReIII(PnPO)Cl3(NN) decreases rapidly asn increases in the interval 1–4 (PnP is Ph2P(CH2)nPPh2). An α-diimine chelate of type ReV(NPh)Cl3(NN) is shown to undergo facile oxidation to the corresponding iminoamide complex ReVI(NPh)Cl3(NN) upon treating with dilute nitric acid. The reaction proceeds via regiospecific nucleophilic addition of waterto the more polarized imine function.

• Ca2+ and Mg2+ binding induce conformational stability of Calfumirin-1 from Dictyostelium discoideum

The apo-Calfumirin-1 (CAF-1) binds to Ca2+ with high affinity and also to Mg2+ with high positive cooperativity. The thermal unfolding curves of wtCAF-1 monitored at neutral pH by CD spectroscopy are reversible and show different thermal stabilities in the absence or presence of Ca2+ and Mg2+ ions. Metalfree wtCAF-1 shows greater thermal stability than EF-IV mutant protein. We observed that GdnHCl-induced unfolding of apo-wtCAF-1 monitored by CD and fluorescence spectroscopies increases co-operative folding with approximately same C$_m$ values. Binding of Ca2+ and Mg2+ ions to CAF-1 dramatically altered the fluorescence and CD spectra, indicating metal ion-induced conformational changes both in the wild-type and mutant proteins. The hydrophobic probe, ANS is used to observe alteration in surface hydrophobicity of the protein in different ligation states. In apo-wtCAF-1, the exposed hydrophobic surfaces are able to bind ANS which is in contrast to the unfolded or the metal ions ligated conformations. Isothermal titration calorimetry (ITC) resultsshow two possible independent binding sites of comparable affinity for the metal ions. However, their binding to the EF-IV E helix-loop-F helix mutant apo-protein happens with different affinities. The present study demonstrates that Ca2+ or Mg2+ binding plays a possible role in the conformational stability of the protein.

• Network and guest dependent thermal stability and thermal expansion in a trigonal host

Thermal stability and thermal expansion of bromo trimer synthon mediated hexagonal inclusion compounds of 2,4,6-tris(4-bromophenoxy)-1,3,5-triazine (BrPOT) with dichloromethane (DCM), tetrahydrofuran (THF) and hexamethyl benzene (HMB) and also the guest-free form of BrPOT are reported. Each of these three guests produced two concomitant inclusion compounds with BrPOT. The thermal stability of the solvate lattice increases with decreasing cavity size. The channel network of the DCM inclusion compound is stable only for a few seconds at room temperature outside the mother liquor, whereas the cage network of the DCM solvate is stable for months under similar conditions. Thermal expansions of the lattices depend upon the network, guest content as well as the type of guest molecules. The guest-free form exhibits the least thermal expansion in this series of systems.

• Conformation driven complexation of two analogous benzimidazole based tripodal ligands with Ag(I) resulting in a trigonal prism and a coordination polymer

Two analogous tripodal ligands, namely, 1,3,5-tris(benzimidazol-1-ylmethyl)-2,4,6-triethylbenzene (1-Et) and 1,3,5-tris(benzimidazol-1-ylmethyl)-2,4,6-trimethoxybenzene (1-OMe) have been used for complexation with silver(I) tetrafluoroborate. A trinuclear Ag(I) salt, formulated as $\mathbf{[Ag_3(1-Et)_2]^{3+}(BF_4){}^{−}_{3}\bullet 7CH_3CN\bullet yH_2O}$ was formed in the complexation reaction of 1-Et with silver(I) tetrafluoroborate, which consists of a trigonal prismatic cation formed by three bicoordinated Ag(I) coordinated with two 1-Et ligands. In case of the 1-OMe ligand, however, a one dimensional ladder, formulated as $\mathbf{[(Ag(1-OMe)OH_2)^{+}(BF_4)^{−}\bullet MeOH]_{\infty}}$ was obtained which is constituted of a tetracoordinated Ag(I) center in a distorted tetrahedral environment. The crystal structures of the ligand hydrates namely $\mathbf{1-Et\bullet H_2O}$ and $\mathbf{1-OMe\bullet 3.6H_2O}$ have been discussed along with the structure of methanol solvate-hydrate of 1-Et. The imidazole rings of the Bim groups in 1-Et in the crystal structures of the ligand as well as in its coordination complex with the Ag(I) are pointed inward with respect to the central ring, whereas it is pointed outwards in the crystal structures of 1-OMe as well as its Ag(I) complex.

• A new class of efficient 4-[(nitro substituted-phenyl)-hydrazonomethyl]- 1-phenyl-1H-pyrazole-3-carboxylate derived colorimetric chemosensor for selective sensing of fluoride and other biologically important anions

A new class of efficient colorimetric chemosensors derived from 4-[(nitro substituted-phenyl)-hydrazonomethyl]-1-phenyl-1H-pyrazole-3-carboxylate have been synthesized and characterized. The synthesized receptors exhibit instant color change from yellow to dark purple along with significant bathochromicshifts when interacted with fluoride ions. The UV-Visible and ¹H NMR titration experiments revealed that 4-[(4-nitro-phenyl)-hydrazonomethyl]-1-phenyl-1H-pyrazole-3-carboxylate derivatives showed selective sensing of fluoride ions in preference to Cl⁻, Br⁻, I⁻, PF⁻⁻, HSO₄⁻, ClO₄⁻ , CH₃COO⁻ and H₂PO₄⁻ ions while 4-[2,4-dinitro-phenyl)-hydrazonomethyl]-1-phenyl-1H-pyrazole-3-carboxylate derivatives showed sensing of acetate, dihydrogen phosphate ion and fluoride ion in organic media.

• Microstructures and their lifetimes in acetamide/electrolyte deep eutectics: anion dependence

Extensive computer simulations with deep eutectics made of acetamide (CH₃CONH₂) and lithium salts (LiX) have been performed at 303 K and 350 K to identify the solution-phase microstructures in these media and investigate the anion dependence of the size and lifetime distributions of these microstructures. In addition, we explore how the added electrolyte interferes with the natural hydrogen bonded (H-bonded) network structure of liquid acetamide. For this purpose several radial distribution functions have been analysedand visualised. The results reveal that amide–amide H-bond interaction decreases significantly upon the addition of electrolyte, and the interactions of Li⁺ and X⁻ (X⁻ being NO⁻3 , Br⁻ and ClO⁻4 ) with CH₃CONH₂ lead to heterogeneous solution structures. Furthermore, we have obtained the cluster size and lifetime distributions in order to estimate the size of local microstructures and their stability. Both these distributions are analysed by separating the contributions arising from (a)CH₃CONH₂−CH₃CONH₂, (b)Li⁺−CH₃CONH₂ and (c) Li⁺−X⁻ interactions. The size distribution of Li⁺−X⁻ clusters is found to be different from those for the other two. Also, the lifetime distributions show a pronounced anion dependence and suggest cluster stability time up to a fewnanoseconds.

• Chaotropes trigger conformational rearrangements differently in Concanavalin A

Concanavalin A (ConA) is a plant lectin having industrial and biological applications. Concanavalin A changes conformation upon exposure to different stress conditions, like exposure to sodium dodecyl sulphate, guanidine hydrochloride, varying hydronium ion potential, etc. The conformational changes were studied using circular dichroism spectroscopy and the structural rigidity of ConA was explored using fluorescence spectroscopy, taking tryptophan as an intrinsic and 8-anilino-1-naphthalenesulfonic acid as an extrinsic fluorescence probes, in different stress conditions. ConA loses the quaternary structure in all the studied stress conditions, which further leads to denaturation of the protein. However, the mechanism of denaturation varied with the studied conditions, like different SDS concentrations and hydronium ion potentials, wherein the proteinundergoes a conformational rearrangement from β-sheet to α-helix. Moreover, GdnHCl triggered complete denaturation of ConA into a predominantly random coil conformation. The results suggested that denaturation of ConA follows different pathways depending on the chemical properties and concentrations of the denaturants used.

• Solvent-assisted monomeric molecular structure of the phosphate diester and the synthesis of menthol-based phosphate diesters

Phosphate diesters are well known to form intermolecular H-bonded dimeric structures in their solid-state. Recently, we reported 2,6-(CHPh)2-4-iPr-phenyl substituted phosphate diester exists as H-bonded monomeric molecular structure along with water dimer in the solid-state. Herein we report 2,6-(CHPh)2-4-iPr-phenyl substituted phosphate diester forms a monomeric molecular structure in the solid-state upon cocrystallization with dimethylformamide, DMF(Me2NCHO). The -CHO group of DMF simultaneously acts as an H-bond acceptor to P-OH and an H-bond donor to P=O moieties. We also used the alcohols, ROH (R = Me, Et, iPr, and tBu), for crystallisation of 2,6-(CHPh)2-4-iPr-phenyl substituted phosphate diester. In these instances, solvent-incorporated dimeric structures are found in the solid-state. We also report the syntheses and molecular structures of anionic phosphate diesters of 2,6-(CHPh)2-4-iPr-phenyl substitutedphosphate diester possessing various counter cations. Moreover, we also report the syntheses and molecular structures of phosphate diesters based on (-)-menthol, (?)-menthol and (?)/(-)-menthol. These exist as H-bonded dimers in the solid-state.

• Poly (ethylene glycol)-400 crowned silver nanoparticles: a rapid, efficient, selective, colorimetric nano-sensor for fluoride sensing in an aqueous medium

Development of rapid and effective analytical sensing strategy for fluoride ion in aqueousmedium is an utmost need in view of naturally widely spread fluoride contaminated groundwater or drinkingwater which causes numerous adverse effects on human health. In prospect of the need, we have developed asimple synthetic route for poly(ethylene glycol)-400 crowned silver nanoparticles for sensitive sensing offluoride ions in aqueous medium. The silver nanoparticles embedded with polyethylene glycol-400 (PEG-400) were synthesized as colloids by heating an aqueous solution of silver nitrate and PEG-400 with trisodiumcitrate. The effects of temperature, the concentration of silver nitrate and trisodium citrate werethoroughly investigated and optimized. The structure and morphology of prepared poly(ethylene glycol)-400crowned silver nanoparticles as colloids was thoroughly examined by UV–visible spectroscopy, Fouriertransform infrared (FTIR) and field emission scanning electron microscopy (FESEM). The prepared poly(-ethylene glycol)-400 crowned Ag Nps selectively detects fluoride ion in an aqueous medium at low concentration(0.098 mg/L) via the change in optical properties. The change in optical properties of Ag Nps wasinvestigated with UV-visible and morphological changes were examined with field emission scanningelectron microscope. The FESEM and UV-Visible analysis demonstrate that synthesized Ag nanoparticles areagglomerates with fluoride ions with immediate visual color change from yellow to colorless.

* Polyethylene glycol crowned silver nanoparticles have designed and synthesized for selective fluoride sensing in aqueous medium. * Sensing occurrences explained with FSEM and UV-Visible spectroscopic techniques *NPs exhibits good limit of detection 0.0016 mg/L that is less than desirable limit 0.05 mg/L

• # Journal of Chemical Sciences

Volume 135, 2023
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Posted on July 25, 2019

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