Department of Chemistry

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The dinuclear diorganotin sulfide [R2Sn(µ-S)]2 (1) (R = 2-phenylazophenyl) was synthesized by the room temperature reaction of the N → Sn intramolecularly coordinated starting precursor R2SnCl2 and Na2S·9H2O in acetone/methanol (1:1). The molecular structure of 1 was primarily characterized by single crystal X-ray crystallography. Furthermore, 1 was also characterized by other experimental techniques, such as 1H, 13C and 119Sn NMR, ESI-MS, FTIR spectroscopy. Complex 1 crystallized in the monoclinic P21/n space group. Each tin center of complex 1 is pentacoordinated and acquires a distorted trigonal bipyramidal geometry. Time dependent density functional theory (TD-DFT) analysis revealed that the transitions observed in complex 1 are predominantly of the ligand-to-ligand type. Natural bond orbital (NBO) analysis showed that complex 1 consists of three ionic bonds (2Sn-C and Sn-S) and two ligand to metal coordinate bonds (S → Sn and N → Sn). HOMO-LUMO analysis suggested that the HOMO of complex 1 is mainly sulfur based. The complex 1 showed significant bactericidal activity against both gram positive and negative bacteria. © 2021 Elsevier Ltd

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Department of Electrical Engineering

Polyhedron

Hemi Labile Intramolecular N → Sn Coordination in a Diorganotin (IV) Sulfide [R2Sn(µ-S)]2 (R = 2-phenylazophenyl) Complex: Synthesis, Structure, DFT-NBO and Antibacterial Studies

Heterocycles play an essential role in medicinal as well as in organic synthetic chemistry. The synthesis of these valuable scaffolds is an emerging and challenging field of today‘s research in organic chemistry. In recent years, several heterocycles as new synthons have emerged as potential nucleophiles in asymmetric transformations. Among them, 5H-oxazol-4-one is one of the strategic synthons for synthesizing enantioenriched α-alkyl-α-hydroxycarboxylic acid derivatives, which are otherwise very challenging via direct installation of a hydroxy group at the α-position of carbonyls. Over the years, considerable progress has been made to establish new and efficient methodologies under mild reaction conditions exploiting metal- and organo-catalysis. This review presents a comprehensive summary of various catalytic development in asymmetric synthesis employing 5H-oxazol-4-ones as α-alkyl-α-hydroxycarboxylic acid surrogates. (Figure presented.). © 2021 Wiley-VCH GmbH

Advanced Synthesis and Catalysis

Review on Asymmetric Catalysis Employing 5H-Oxazol-4-Ones as α-Hydroxy Carboxylic Acid Surrogates

In this chapter we describe the use of fluorescent quantum dots (QDs) as labels for microbial mRNA transcripts using fluorescence in situ hybridization (FISH). Unlike organic dyes, which are the standard labels in modern FISH methods, QDs provide fluorescence signals that are much brighter and resistant to photobleaching, with an expanded spectral range for multiplexing. We describe the preparation of QDs with compact sizes necessary for accurate labeling, their application for analyzing lacZ transcripts in Escherichia coli cells using FISH, and an assessment of signal stability. We further discuss differences between methods for mammalian cells and bacteria, for which individual nucleic acids cannot be discretely counted due to the small cell size and the optical diffraction limit. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.

Methods in Molecular Biology

Fluorescence In Situ Hybridization with Quantum Dot Labels in E. coli Cells

This study comprises the design and development of calix{[}4] arene-amido-based ionophores by varying structural stringency and steric hindrance at the lower rim to probe the anion sensing properties. The ionophores are prepared, purified, and characterized using various analytical techniques. The molecular structure of the most active ionophore I is established by single-crystal X-ray characterisation. Out of various anions investigated, iodide and cyanide show the highest sensitivity towards the ionophores investigated. Both anions are sensitive enough to give a visibly distinct color change. The binding properties of the ionophores are established with H-1 \&amp; I-127 NMR, fluorescence, and UV-vis spectroscopy, revealing that three ionophores strongly interact with CN- and I-. The binding constants are calculated via Benesi-Hildebrand plots using absorption data. The time-dependent H-1 NMR revealed strong hydrogen bonding between the OH and NH groups of the ionophore and cyanide anion. The I-127 NMR shows the highest 27.6 ppm shift after 6 h for ionophore I. The crystal structure revealed hydrogen bonding of N-H protons of the amide pendulum and phenolic oxygen of the calix rim. The Job's plot depicted the possibility of a 1 : 1 complex of ionophores with both anions.

Fulltext

RSC ADVANCES

Calix{[}4]amido crown functionalized visible sensors for cyanide and iodide anions

Understanding the nature of interactions between the aromatic organic pollutants with dissolved humic acid (HA) is fundamental for the prediction of their environmental fate and subsequent development of efficient remediation methods. The present study employs solution-state 1H/19F NMR methods to investigate the non-covalent interaction between aqueous peat humic acid (Aldrich HA) and monoaromatic carboxylic acids (CA), viz., 2, 6 diflourobenzoic acid (DFBA) and its non-fluorinated analog, benzoic acid (BA). NMR self-diffusion measurement of HA protons confirmed micellar nature indicating possibility of encapsulation of small molecules through host-guest interaction. 19F−1H and 1H−1H saturation transfer difference (STD) experiments reveal the mode of insertion of CA into HA superstructure. The strength of interaction has been evaluated by analyzing T1/T2 relaxation times and self-diffusion coefficients of CA as a function of HA concentration. Association constants extracted for CA-HA complexes from NMR diffusion experiments reflected that the association between DFBA-HA (2.34 mM−1) is significantly higher than that of BA-HA (0.97 mM−1). The experimental outcome reiterated that substitution of -H with halogen atoms (-F in specific) to aromatic ring plays a dominant role in modulating the strength of association and mode of insertion of organic pollutants into HA superstructure. The present study emphasizes that AHA can be a potential remediating agent for organic contaminants due to its superior binding affinity compared to less humified extracted HA (EHA) from Karwar, Rajasthan, India. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.

Environmental Science and Pollution Research

Solution-state NMR evaluation of molecular interaction between monoaromatic carboxylic acids and dissolved humic acid

The present study aims to characterize the molecular interaction and photo-degradation behaviour of halogen (–F and –Cl) containing novel insecticide, flupyradifurone, (FPD) in the presence of humic acid (KHA), isolated from Karwar, western Rajasthan, India. Time-dependent photo-degradation kinetics of UV-exposed FPD is quantified in the absence and presence of KHA employing one dimensional 1H and 19F solution-state NMR. The pseudo first-order photo-degradation rate constant quantified for FPD showed a significant decrease in the presence of KHA. Interestingly, variable degradation rates are found from 1H and 19F NMR spectral changes indicating chemical moiety wise degradation of FPD. Further, NMR saturation transfer difference (STD), relaxation, and diffusion experiments have been employed for the complete evaluation of binding interactions of KHA with FPD and its major degradation product difluoroacetic acid (DFA). STD experiments revealed that FPD binds to KHA through the chlorinated pyridine ring while the –F containing moiety of FPD does not show any detectable interaction. Relevant kinetic parameters, namely association constants and Gibbs free energy of interaction are quantified at neutral pH conditions by diffusion experiments depicting a stronger and more spontaneous association of FPD with KHA (KA = 55.55 M−1) compared to that of DFA-KHA (KA = 10.90 M−1). Both FPD and DFA bind with KHA through weak non-covalent interaction indicating the encapsulation of these molecules within KHA hindering the photo-degradation process of FPD. Concomitantly, it is also envisaged that FPD will be more persistent in soil compared to DFA that may leach out to groundwater. © 2020

Journal of Photochemistry and Photobiology A: Chemistry

Aqueous photo-degradation of Flupyradifurone (FPD) in presence of a natural Humic Acid (HA): A quantitative solution state NMR analysis

First step of formose or Butlerov reaction involves C–C bond formation between two formaldehyde molecules resulting in glycolaldehyde. This reaction happens under basic conditions in solution. A tandem mass spectrometry investigation of dissociation of deprotonated glycolaldehyde in the gas phase, to study the formose reaction in a retro-synthetic point of view, has been reported. In the present work, we have carried out electronic structure theory calculations and quasi-classical direct chemical dynamics simulations to model the gas phase dissociation of the conjugate base of glycolaldehyde. The dynamics simulations were performed on-the-fly using the hybrid density functional B3LYP theory with the 6-31+G∗ basis set under collision induced dissociation (CID) conditions. Trajectories were launched with two different deprotonated forms of glycolaldehyde for a range of collision energies mimicking experiments. Reverse formose reaction was observed primarily from the slightly higher energy isomer via a non-statistical pathway. Intramolecular hydrogen transfer was ubiquitous in the trajectories. Simulation results were compared with experiments and detailed atomic level dissociation mechanisms are presented. © 2020 Elsevier B.V.

International Journal of Mass Spectrometry

Chemical dynamics simulations of collision induced dissociation of deprotonated glycolaldehyde

In the last decade, visible light photoredox catalysis promoting radical-based organic transformations has received enormous synthetic applicability, as they allow unfolding of site-selective reactivities under mild reaction conditions. Moreover, the photoredox transformations utilizing organic dyes as photocatalysts are attractive with regard to low cost, less toxicity, easy availability and high functional group tolerance. The organophotoredox-catalyzed reaction technologies enabling direct, efficient and selective late-stage functionalization of various heterocycles leading to the formation of various C−C and C−X (X=N, P, O, S, Se, Br) bonds have emerged at the forefront of synthetic methodologies available to synthetic chemists. This minireview summarizes the developments made in the last five years in the field of late-stage functionalization of heterocycles governed by various organophotocatalysts and intends to provide the readers a comprehensive overview of this research field with representative examples and mechanistic insights. © 2021 Wiley-VCH GmbH

Asian Journal of Organic Chemistry

Organophotoredox-Catalyzed Late-Stage Functionalization of Heterocycles

An organophotoredox-catalyzed reduction/addition/oxidation cascade of N-protected maleimides and N-(acyloxy)phthalimides is documented. The mild and efficient redox-neutral process involves the hitherto unknown Giese-type addition of aryloxy-alkyl radicals on N-protected maleimides and a successive oxidation allowing an overall Z-alkenylation of the N-substituted pyrrolidine-2,5-dione motif through a formal translocation of the maleimide double bond. © the Partner Organisations.

Organic Chemistry Frontiers

An organophotoredox-catalyzed redox-neutral cascade involving: N -(acyloxy)phthalimides and maleimides

The past decade has witnessed the emergence of N-(acyloxy)phthalimides (NHPI esters) and its derivatives at the forefront of synthetic methods facilitating the construction of diverse molecular frameworks from the readily available carboxylic acid feedstock. The NHPI esters are predisposed to undergo reductive fragmentation via a single electron transfer (SET) process under thermal, photochemical, or electrochemical conditions to generate the corresponding carbon- or nitrogen-centered radicals that participate in a multitude of synthetic transformations to forge carbon-carbon and carbon-heteroatom bonds. The chemistry involving NHPI esters has received broad applicability not only in well-designed cascade annulations but also in medicinal chemistry and natural product synthesis. This comprehensive Review, broadly categorized according to the nature of the bond formation, details the progress made in this field since the initial discovery by providing representative examples with mechanistic details, with an emphasis on challenges and future directions. ©