Intramolecular donor-stabilized tetra-coordinated germanium(iv) di-cations and their Lewis acidic properties.

We report the first examples of intramolecular phosphine-stabilized tetra-coordinated germanium(iv) di-cationic compounds: [LiPr2Ge][CF3SO3]23iPr and [LPh2Ge][CF3SO3]23Ph (LiPr = 6-(diisopropylphosphanyl)-1,2-dihydroacenaphthylene-5-ide; LPh = 6-(diphenylphosphanyl)-1,2-dihydroacenaphthylene-5-ide). The step wise synthetic strategy involves the isolation of neutral and mono-cationic Ge(iv) precursors: [LiPr2GeCl][X] (X = GeCl31iPr, OTf 2iPr), [LPh2GeCl2] 1Ph and [LPh2GeCl][OTf] 2Ph. Both 3iPr and 3Ph exhibit constrained spiro-geometry. DFT studies reveal the dispersion of di-cationic charges over P-Ge-P sites. Anion or Lewis base binding occurs at the Ge site resulting in relaxed distorted trigonal bipyramidal/tetrahedral geometry. 3iPr and 3Ph activate the Si-H bond initially at the P-site. The hydride ultimately migrates to the Ge-site rapidly giving [LPh2GeH][CF3SO3] 3PhH, while sluggishly forming [LiPr2GeH][CF3SO3] 3iPrH. Compounds 3iPr and 3Ph were tested as catalysts for the hydrosilylation of aromatic aldehydes. While catalytic hydrosilylation proceeded via the initial Et3Si-H bond activation in the case of 3iPr, compound 3Ph as a catalyst showed a masked Frustrated Lewis Pair (FLP) type reactivity in the catalytic cycle.

Coordination Chemistry of the Antimony(III) and Bismuth(III) Cations using Bis(α-iminopyridine) as Ligand.

Bis(alpha-iminopyridine) L has been employed as the redox non-innocent Schiff-base ligand to coordinate with cationic antimony(III) and bismuth(III) centers. Mono- and di- cationic compounds: [LSbCl2 ][CF3 SO3 ] 1, [LBiCl2 ][CF3 SO3 ] 2, [LSbCl2 ]2 [Sb2 Cl8 ] 3, [LBiCl2 ]2 [Bi2 Cl8 ] 4, [LSbCl][CF3 SO3 ]2 5, [LBiCl][CF3 SO3 ]2 6 have been isolated and characterized using single crystal X-ray crystallography in the solid-state and solution-state NMR studies. These compounds have been prepared from PnCl3 (Pn=Sb, Bi) and chloride abstracting agent such as Me3 SiCF3 SO3 or AgCF3 SO3 in the presence of L. The Bi tri-cationic species forms heteroleptic compound 7, being coordinated by two types of Schiff-base donors L and L'. The latter has been in situ generated by the cleavage of one of the two imines present in L.

Chemistry of the Bis(imine)-Based Tetradentate Ligand Stabilized Group 14 E(II) Cations (E=Ge and Sn).

The ambiphilic Ge(II) and Sn(II) cationic species have been reported to be isolated through kinetic or thermodynamic stabilizations. Nonetheless, steric congestion or excessive coordination of donor atoms to the cationic center concurrently disfavors its prompt reactivity. Our research in this field revolves around the utilization of structurally non-rigid bis(imine) based tetradentate supporting ligands for the stabilization of Ge(II) and Sn(II) cationic species. Such E(II) cationic systems have been advantaged due to inherent flexibility present at the ligand backbone allowing disposal of E(II) orbitals through geometric rearrangements for further reactivity. The bifunctionality present in the ligand enables the first examples of Ge(II) bis-monocations. Furthermore, the redox-active nature of the ligand encourages participation in chemical transformations. In this personal account we have provided a detailed discussion of our published work in this direction in the last five years.

In silico studies on structural inhibition of SARS-CoV-2 main protease Mpro by major secondary metabolites of Andrographis paniculata and Cinchona officinalis.

The COVID-19 infection by Novel Corona Virus (SARS-CoV-2) has become one of the largest pandemic diseases, with cumulative confirmed infections of 275,233,892 and 5,364,996 deaths to date according to World Health Organization. Due to the absence of any approved antiviral drug to treat COVID-19, its lethality is getting severe with time. The main protease of SARS-CoV-2, Mpro is considered one of the potential drug targets because of its role in processing proteins translated from viral RNA. In the present study, four of the plant metabolites, 14-deoxy-11,12-didehydroandrographolide, andrograpanin, quinine, cinchonine from two eminent medicinal plants Andrographis paniculata and Cinchona officinalis, have been evaluated against the main protease of SARS-CoV-2 through in-silico molecular docking and molecular dynamics simulation study. From the result interpretations, it is found that andrograpanin has strong binding affinities with the target protein in its active site with potential negative energies. Molecular Dynamic simulation and MMGBSA studies suggest that earlier reported N3 inhibitor and andrograpanin exhibit effective binding interactions involving identical amino acid residues with the same binding pockets of the main protease of SARS-CoV-2. Therefore, the theoretical experiment suggests that andrograpanin, could be considered the promising inhibitor against SARS-CoV-2 Mpro. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11756-022-01012-y.

Reversible Redox Chemistry of Anionic Imidazole-2-thione-Fused 1,4-Dihydro-1,4-diphosphinines.

Anionic 1,4-dihydro-1,4-diphosphinines were synthesized from tricyclic 1,4-diphosphinines and isolated as blue powdery salts M[2a-2c]. Reaction of solutions of these monoanions with iodomethane led to P-methylated compounds 3a-3c. An oxidation/reduction cycle was examined, starting from solutions of K[2a] via P-P coupled product 4a and back to K[2a], and the recyclability and redox chemistry of this cycle were confirmed by experimental and simulated cyclic voltammetry analysis, which is proposed as a potential 2-electron cathode for rechargeable cells. TD-DFT studies were used to examine species that might be involved in the process.

Recent Developments in the Chemistry of Pn(I) (Pn=N, P, As, Sb, Bi) Cations.

The Group 15 Pn(I) cations (Pn=N, P, As, Sb and Bi), which are isoelectronic with the donor-stabilized carbones, have emerged recently. Despite the presence of two lone pair of electrons, the Pn(I) cations are weakly nucleophilic due to their inherent positive charge. Strongly electron-donating supporting ligands including zwitterionic forms have been used to enhance their Lewis basicity. Furthermore, the chelating effect of cyclic ligand systems proved effective in increasing their nucleophilicity. The strategies involved in successfully isolating the fleeting Sb(I) and Bi(I) cations as the recent most achievements in this field have been discussed. The syntheses, structure, bonding situations and reactivity of the Pn(I) cations are discussed. An outlook on the periodic trends and future applications of these electronically unique electron-rich cationic moieties have been provided.

Reductively disilylated N-heterocycles as versatile organosilicon reagents.

The reductively disilylated N-heterocyclic systems 1,4-bis(trimethylsilyl)-1-aza-2,5-cyclohexadiene (1Si), 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (2Si) and its methyl derivatives (3Si and 4Si), and 1,1'-bis(trimethylsilyl)-4,4'-bipyridinylidene (5Si) are proficient organosilicon reagents owing to their low first vertical ionization potentials and the heterophilicity of the polarized N-Si bonds. These have prompted their reactivity as two-electron reductants or reductive silylations. These reactions benefit from the concomitant rearomatization of the N-heterocycles and liberation of trimethylsilyl halides or (Me3Si)2O, which are mostly volatile or easily removable byproducts. In this perspective, we have discussed the utilization of these reductively disilylated N-heterocyclic systems as versatile reagents in the salt-free reduction of transition metals (A) and main-group halides (B), in organic transformations (C) and in materials syntheses (D).

Stabilization of the Elusive Antimony(I) Cation and Its Coordination Complexes with Transition Metals.

Upon stabilization by 5,6-bis(diisopropylphosphino)acenaphthene to form compound 1, the fugitive antimony (I) cation exhibited nucleophilic behavior towards coinage metals. Compound 1 was strategically synthesized at room temperature from SbCl3 , the bis(phosphine), and trimethylsilyl trifluoromethanesulfonate taken in a 1:2:3 ratio, whereby the bis(phosphine) plays the dual role of a reductant and a supporting ligand. The generation of 1 involves two-electron oxidation of the ligand to form a P-P bonded diphosphonium dication. Compound 1 was separated from this dication to give both products in pure form in moderate yields. Despite the overall positive charge, the SbI site in 1 was found to bind to metal centers, forming complexes with AuI , AgI and CuI . Compound 1 reduced CuII to CuI and formed a coordination complex with the resulting CuI species. The effects of the electron-rich bis(phosphine) and the constrained peri geometry in stabilizing and enhancing the nucleophilicity of 1 have been rationalized through computational studies.

Intramolecularly Double-Donor-Stabilized Stannylene and Its Coordination towards Ag(I) and Au(I) Centers.

The intramolecularly double-donor-stabilized stannylene 1 has been synthesized from the salt-metathesis reaction between two equivalents of lithium pyridine ene-amide L1 and SnCl2 . Compound 1 exhibits dipolar behavior when reacted with B(C6 F5 )3 leading to the zwitterionic compound 2. The reaction of 1 with one equivalent and 0.5 equivalent of AgOTf (OTf=trifluoromethane sulfonate) result in the formation of a stannylene-AgOTf complex 3 and a homoleptic distannylene-silver ionic complex 4, respectively. Analogous to complex 4, the gold(I) complex 5 has been synthesized from the reaction between two equivalents of 1 and 0.5 equivalent of AuCl.SMe2 /Me3 SiOTf. Complex 5 is the first example of homoleptic stannylene-Au(I) ionic complex among the very scarce reports on stannylene-gold(I) coordination complexes. All compounds have been structurally characterized using single crystal X-ray crystallography. Solution-state characterization have been performed using multinuclear NMR techniques. Detailed DFT calculations on the optimized geometries 1 o, 3 o-5 o reveal the change in sp- hybridization on the pyramidal Sn(II) center upon metal coordination and their bonding overlaps.

Air exposed 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine: an avant-garde carbonization precursor for multi-functionalized carbon material.

1,4-Bis(trimethysilyl)-1,4-dihydropyrazine 1 has been utilized as a small molecule precursor for carbonization to N,O-containing few-layered carbon sheets 3via the formation of a polymeric material 2 upon simple air exposure at room temperature. Without any further purification, this multi-functionalized carbon material 3 exhibited excellent anode performance in a lithium ion battery.

In vitro and in silico studies on the structural and biochemical insight of anti-biofilm activity of andrograpanin from Andrographis paniculata against Pseudomonas aeruginosa.

Microbial infections have become a global threat to drug-tolerant phenomena due to their biofilm formatting capacity. In many cases, conventional antimicrobial drugs fail to combat the infection, thus necessitating the discovery of some alternative medicine. Over several decades, plant metabolites have played a critical role in treating a broad spectrum of microbial infections due to its low cytotoxicity. Andrograpanin, a secondary metabolite, is a diterpenoid present in the leaf of Andrographis paniculata. In this study, andrograpanin (0.15 mM) exhibited significant inhibition on biofilm production by Pseudomonas aeruginosa in the presence of gentamicin (0.0084 mM). The impaired production of extracellular polymeric substances and several virulence factors of Pseudomonas aeruginosa were investigated to understand the mechanism of action mediated by andrograpanin. The structural alteration of biofilm was evaluated by using fluorescence microscopy, atomic force microscopy and field emission scanning electron microscopy. The in silico molecular simulation studies predicted interaction of andrograpanin with quorum sensing proteins such as RhlI, LasI, LasR, and swarming motility protein BswR of Pseudomonas aeruginosa. Overall the studies indicate that andrograpanin could be used as a therapeutic molecule against biofilm development by Pseudomonas aeruginosa.

Development of dual-tool nanosensor for cysteine based on N-(1-naphthyl)ethylenediamine cation functionalized silver nanoparticles.

In an accomplishment of development of silver nanoparticles (AgNPs) based nanosensor for cysteine in its anionic and neutral forms, we have preferred N-(1-naphthyl)ethylenediamine cation (NEDA+) stabilized AgNPs (NEDA-AgNPs), because NEDA+ is a fluorescent active ion and it imparts excellent stability to AgNPs. Surface Plasmon resonance (SPR) of AgNPs and fluorescence property of NEDA+ are thus useful for presenting NEDA-AgNPs as a dual-tool nanosensor for cysteine molecules. The surface adsorbed NEDA+ cations interact selectively with cysteine as a consequence, the particles get aggregated, which was monitored using spectrophotometric method. The fluorescence property of NEDA+ is heavily quenched in NEDA-AgNPs, which could be reversed in presence of cysteine. The spectrofluorimetric method was thus used for quantification of cysteine as well. The detection limits (LOD to LOL) of anionic cysteine are 0.1784-1.598 µM and 0.0842-2.0 µM, respectively in spectrophotometric and spectrofluorimetric methods. From a real sample matrix, the recovery results are excellent, >95%. For neutral cysteine, the sensitivity is a bit low; 0.308-2.8 µM for spectrophotometric and 0.131-2.8 µM for spectrofluorimetric methods. It is found that the anionic cysteine (Kasso = 2.24 × 105 M-1/4.02 × 105 M-1) binds surface adsorbed NEDA+ cations strongly than that of neutral cysteine (Kasso = 3.69 × 104 M-1/1.24 × 105 M-1). Thus, NEDA-AgNPs show its potentials for being a dual-tool nanosensor as well as dual-form nanosensor for quantification of cysteine in a sample which may be the attractive system to an analyst.

The effective adsorption of tetracycline onto zirconia nanoparticles synthesized by novel microbial green technology.

Pseudomonas aeruginosa bacteria have been used in this study for zirconia nanoparticles synthesis through green technology for adsorption driven bioremediation of tetracycline from wastewater. The characterization of synthesized nano zirconia has been performed by employing dynamic light scattering, field emission-transmission electron microscopy, energy dispersive X-ray, X-ray diffraction, fourier transform infrared spectroscopy, and point of zero charge analysis. The zirconia nanoparticles have shown average particle size ~15 nm, monoclinic and tetragonal crystal structure with 6.41 nm of crystallite size, the presence of elemental zirconium and oxygen, and the occurrence of functional groups like O-Zr-OH, Zr-O-Zr and Zr-O bonds. The zirconia nanoparticles mediated adsorption of tetracycline has been found to be effective at solution pH 6.0 and in a very less contact time 15 min. Strong electrostatic interaction between zwitterionic form of tetracycline and protonated surface of zirconia nanoparticles is the governing adsorption mechanism in this study. The kinetic study has been performed on the basis of the tetracycline adsorption process revealing that the adsorption phenomenon follows pseudo-second order kinetic, further suggesting chemisorption of tetracycline over zirconia nanoparticles. The Langmuir isotherm model has been found to be the best fitted model among the all isotherm models indicating the involvement of monolayer uptake of tetracycline on the surface of zirconia nanoparticles. Moreover, the maximum tetracycline adsorption capacity of zirconia nanoparticles calculated by the Langmuir isotherm model is close to 526.32 mg/g. This finding is quite reasonable to accept that zirconia nanoparticle may be used as an alternative adsorbent to mitigate the tetracycline contamination in wastewater.

Coherent Solution-phase Synthesis of a Germanium-Graphitic Nanocomposite and Its Evaluation for Lithium-Ion Battery Anodes: Non-innocent Role of the Mashima Reagent.

The organosilicon reagent 1,4-bis-(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene 2 plays the binary role of the simultaneous reduction of GeCl2 .dioxane 1 dissolved in oleylamine to Ge nanocrystals and the formation of graphitic sheets under hot-injection conditions. This colloidal synthetic route to germanium nanocrystals embedded on N-doped graphitic nanosheets Ge/NG is free of any template or catalyst and involves easy purification techniques. The Ge/NG/C obtained after carbonization has been explored for anode performance in lithium-ion batteries. Both Ge/NG and Ge/NG/C can be obtained on a gram scale and are bottleable under argon for months.

In vitro anti-biofilm activity of 14-deoxy-11,12-didehydroandrographolide from Andrographis paniculata against Pseudomonas aeruginosa.

14-Deoxy-11,12-didehydroandrographolide is a biologically active molecule present in the extract of Andrographis paniculata (Kalmegh), a classic ethnic herbal formula, which has been used for over thousand years as therapeutics to treat numerous infectious diseases like upper respiratory tract infection, urinary tract infection, and many more health issues. The present study is designed to ascertain an inhibitor against biofilm formation from the major metabolites of Andrographis paniculata, because the extract of this herb shows inhibition of bacterial quorum sensing (QS) communication and biofilm development against microorganisms. 14-Deoxy-11,12-didehydroandrographolide at 0.1 mM (sub-MIC dose) with azithromycin (6 µg/mL, sub-MIC) or gentamicin (4 µg/mL, sub-MIC) synergistically inhibits 92% biofilm production by a 48-h treatment against Pseudomonas aeruginosa. Further investigation carried out by atomic force microscopy shows promising reduction in roughness and height of biofilm in the presence of 14-deoxy-11,12-didehydroandrographolide compared with the control group. The content of extracellular polymeric substances, level of pyocyanin production, and synthesis of extracellular protease by P. aeruginosa have also been reduced significantly at around 90% in 14-deoxy-11,12-didehydroandrographolide-treated group. In conclusion, 14-deoxy-11,12-didehydroandrographolide could be used as a drug molecule against biofilm development by inhibiting QS pathway in Pseudomonas aeruginosa.

Versatile coordinating abilities of acyclic N4 and N2P2 ligand frameworks in conjunction with Sn[N(SiMe3)2]2.

The adaptability of three acyclic tetradentate ligands with the -CHR-CHR- (R = H or alkyl substituent) linker in the backbone: bis(α-iminopyridine) L1 and the reduced form L2 and diaminodiphosphine L3 to stabilize various stannylenes has been explored. The reaction of L1 with two equivalents of Sn[N(SiMe3)2]2 led to the stabilization of a bisstannylene 1 through the ene-amide transformation of L1. The reaction of bisstannylene 1 with B(C6F5)3 and silver trifluoromethane sulfonate led to the formation of ligand stabilized Sn(ii) dications 2 and 3 respectively. A mixture of Sn(ii) dication 3 and a Sn(ii) monocation 4 has been obtained from the reaction between 1 and trimethylsilyl trifluoromethane sulfonate. A 1 : 1 stoichiometric reaction between L3 and Sn[N(SiMe3)2]2 led to the isolation of a dimeric monostannylene 5 having a step-like structure with a Sn2N2 central ring. The reaction of L2 with Sn[N(SiMe3)2]2 underwent an electron transfer reaction ultimately leading to bis(α-iminopyridine) isolation.

Stabilization of bis(chlorogermyliumylidene)s within bifunctional PNNP ligand frameworks and their reactivity studies.

The diiminodiphosphine (Lim) and diaminodiphosphines (l-NH and l-NMe) with a bifunctional PNNP ligand framework have been employed to host two [GeCl]+ units leading to the formation of bis(chlorogermyliumylidene) 1-3, respectively. The synthetic route involves a 1 : 2 stoichiometric reaction between the PNNP ligand and GeCl2·dioxane and the subsequent addition of two equivalents of chloride abstracting agent. Compound 1 is unstable towards coordinating solvents and Lewis bases, resulting in the displacement of the GeCl unit and the formation of rearranged products 4 and 5. However, the diaminodiphosphine coordinated Ge(ii) bis(monocation)s 2 and 3 proved to be stable and revealed their electrophilic behaviour towards the Lewis bases studied.

Bis(chlorogermyliumylidene) and its significant role in elusive reductive cyclization.

Bis(chlorogermyliumylidene) 2 has been strategically obtained within redox-active bis(α-iminopyridine). Metal-free reduction of 2 followed by protonation led to elusive 2,3-di(pyridin-2-yl)piperazine with meso-stereoselectivity. Formation of persistent triplet diradicals upon reduction and isolation of piperazine stabilized Ge(ii) dication intermediates provide convincing evidence for the crucial role of [GeCl]+ units in reductive cyclization.

Phenylene-bridged cross-conjugated 1,2,3-trisilacyclopentadienes.

1,2,3-Trisilacyclopentadienes are obtained from the reactions of cyclotrisilene c-Si3R4 (R = iPr3C6H2) with phenyl and diphenyl acetylene, respectively. With 1,4-diethynyl benzene the cross-conjugated bridging of two of the Si3C2 cycles by a para-phenylene linker is achieved. UV/vis spectroscopy indicates a small but significant effect of cross-conjugation, which is confirmed by TD-DFT calculations. The formation mechanism of the 1,2,3-trisilacyclopentadienes is elucidated by VT NMR.