Sunita Rani

Organosilatranes with thioester-anchored heterocyclic ring assembly: Cu2+ ion binding and fabrication of hybrid silica nanoparticles

This work presents the design, synthesis, UV-Vis absorption properties and Cu2+ ion binding of the organo-silicon complexes (3a–h) with different coordination abilities that are derived from mercaptopropylsilatrane (MPS) and respective heteroaromatic carboxylic acids (1a–h). The prepared thioester based organosilatranes (ThE-OS) have been meticulously characterized by a series of characterization techniques such as elemental analyses, FT-IR, NMR (1H, 13C), LC-MS, and structure of 3e was unambiguously determined by X-ray single crystal analyses. All the compounds have shown judicious absorption enhancement in the intensity as well as λmax values on binding with Cu2+ ions compared to other surveyed metal ions. In addition, it is for the first time that the hybrid silica nanoparticles (H-SiNPs) bearing a thioester linkage in the silica framework are reported. The synthesis was achieved conveniently by an in situ co-condensation reaction of tetraethyl orthosilicate (TEOS) with the corresponding ThE-OS. The derivatization of silica is confirmed by FT-IR, 13C and 29Si solid state CP-MAS NMR, UV-Vis, TEM, XRD, TGA and EDX techniques. Furthermore, the H-SiNPs have exhibited greater affinity towards Cu2+ ions than the parent ThE-OS.

Chalcomer assembly of optical chemosensors for selective Cu2+ and Ni2+ ion recognition

The o-, m- and p-isomeric units of chalconyl triazole-based, caged organosilicon complexes were efficiently synthesized and explored for their cationic chemosensing activities. The UV-vis spectral studies performed show considerable variations in absorption spectra and molar absorptivity constant. The recognition studies display efficient sensing for the o-isomer of chalcone-linked 1,2,3-triazole silatrane (CTSI) 1–3, which act as dual-ion fluorescent sensors towards Cu2+ and Ni2+ ions. This preference of o-isomers (CTSI 1–3) over m- and p-isomers (CTSI 4–9) in quenching is due to specific ‘fitting in’ of the coordination sphere available for ion binding. Further, the exceptional activity of CTSI 8 to exclusively sense Ni2+ ions differs from the other studied quenching response patterns, acting via a ‘turn-on’ fluorescence response. The variation of pH and temperature on the chemosensing behavior of CTSI 1–3 led us to optimize conditions for quenching studies. Moreover, competitive quenching studies confirm the feebly enhanced selectivity for Cu2+ over Ni2+ ions. Stern–Volmer constant (KSV) for all active isomers show comparative quenching response towards both cationic species. This is the first the time that organosilicon complexes are used to actively sense Cu2+ and Ni2+ ions using water as part of the solvent mixture.

Thioester-appended organosilatranes: synthetic investigations and application in the modification of magnetic silica surfaces

The present investigation discloses a series of new organosilicon derivatives (3a–k) tailored with substituted benzoic acid modules (1a–k) via thioesterification with 3-mercaptopropylsilatrane (MPS). Product formation was authenticated using elemental analyses and different spectroscopic methods comprising FT-IR, NMR [1H, 13C] and LC-MS (Q-TOF). Thereafter, complete structural elucidation of compounds 3c and 3f was achieved by the single crystal X-ray technique. Photo-electronic inspection of all compounds by UV-Vis spectroscopy revealed their sensitivity towards substitution patterns. In addition, this is the first time that the potential of a silatranyl moiety has been tested for the modification of a silica surface pre-decorated with a magnetite core. The synthesis was achieved through a facile methodology involving chemical bonding at each stage, which proceeded without any external surfactant or template. The course of the reaction was followed by FT-IR, UV-Vis, XRD, TEM, FESEM, EDX and TGA techniques. Furthermore, the hybrid nanomaterial possessed significant sensorial ability toward copper ions, which makes the present protocol favourable for the construction of a new class of chelating ligands with an in-built multifunctional nanodevice.

Heteroaryl chalcone allied triazole conjugated organosilatranes: synthesis, spectral analysis, antimicrobial screening, photophysical and theoretical investigations

A series of heteroaryl tethered triazole conjoined organosilatranes were synthesized following an archetypal click reaction. The reaction sequence follows the initial generation of acetylinic Schiff bases (3a–3c, 4a–4c) which undergo 3 + 2 cycloaddition with 3-azidopropyltriethoxysilane (3-AzPTES) to give organotriethoxysilanes (5a–5c, 6a–6c) which were ultimately amended into their five-membered organosilatrane descendants (7a–7c, 8a–8c). The synthesized compounds were fully characterized by IR, 1H, 13C, mass spectrometry techniques and elemental analysis. Also, the complete structure elucidation of 7a and 8a was achieved via X-ray crystallography. The photophysical studies of the entire sequence of organosilatranes were performed in solvents of varying polarity to gain an insight into their solvatochromic behaviour. The results reveal that the molecules display trivial positive solvatochromism suggesting a high dipole moment of the excited state that has also been concurrently supported by the results derived from the Lippert–Mataga equation. Further, the molecular structures and photophysical properties of the organosilatranes were also studied theoretically by applying the IEFPCM model that mimics the desired solvent in combination with the TDDFT approach. Theoretical results were found to be in absolute accord with the experimental values. Additionally, several DFT based reactivity descriptors are reported presenting a meticulous view into the relative stability and reactivity of the chalcone linked organosilatranes. Further, all the organosilatranes were screened for their physiochemical and pharmacokinetic delineation by computational analysis and then investigated for their antimicrobial activities against different strains of bacteria and fungi. Compounds 8b and 8c were found to be the most potent antibacterial and antifungal agents, respectively.

Adamantylated organosilatranes: design, synthesis, and potential appraisal in surface modification and anti-protozoal activity

The present investigation evaluates the design and facile synthesis of a series of organosilatranes (1–7) tethered with the privileged adamantane motif, labelled as a ‘lipophilic bullet’, via numerous biocompatible linkages i.e. amide, ester, thioester, urea, thiourea, and thiocarbamate groups. The assembled silatranes have been scrupulously characterized by elemental analysis, FT-IR and NMR (1H and 13C) spectroscopy, and mass spectrometry. The parasitic diseases caused by unicellular protozoa, Giardia lamblia (G. lamblia) and Trichomonas vaginalis (T. vaginalis), represent a major health burden, therefore the synthesized compounds were probed for in vitro giardicidal and trichomonacidal activities. With this aim, firstly the pharmacokinetic profiles of the compounds were scrutinized using absorption, distribution, metabolism, excretion, and toxicity (ADMET) tools and on the whole, all compounds showed good oral bioavailability. The anti-parasitic activity of the newly synthesized compounds was evaluated in comparison to a standard drug (metronidazole) by 3-(4,5-dimethylthiazol-yl)-diphenyl tetrazolium bromide (MTT) assay. All the compounds displayed significant activity against G. lamblia and T. vaginalis with IC50 values ranging from 10.9–127.4 μM and 6.2–128.9 μM, respectively. To improve the aqueous solubility of the synthesized compounds, the enticing feature of the adamantane moiety to undergo inclusion binding with the β-cyclodextrin cavity is explored. Furthermore, a simplistic methodology is proposed to covalently anchor adamantylated silatrane onto the surface of magnetic silica nanoparticles. This material promises to be a non-invasive and externally controlled drug delivery system with enormous anti-protozoal potential.

Synthesis, X-Ray Structure and Anti-Bacterial Studies of 1,3-Thiazolylpropylsilatranes

GRAPHICAL ABSTRACT Abstract Syntheses of 1,3-thiazolyl functionalized propylsilatranes were carried out by the transesterification reaction of S-(3-triethoxysilylpropyl)mercaptobenzothiazole with triethanolamine, tris(isopropanol)amine and tris(2-aminoethyl)amine. The structures of the synthesized compounds were established by elemental analysis, IR, (1H, 13C) NMR spectroscopy, mass spectrometry and explored for thermal stability by thermogravimetric analysis. The structure of S-(3-silatranylpropyl)mercaptobenzothiazole was confirmed by single crystal X-ray diffraction analysis. All the synthesized silatranes were effectively screened for antibacterial activity against Gram-negative (Escherichia coli and Vibrio cholerae) and Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus).