Category Archives: ChemPlusChem

Silver and Gold Pillarplex Pseudorotaxanes from α,ω‐Dicarboxylic Acids

Posted on 19 July 2023 by

The encapsulation of α,ω-dicarboxylic acids into Ag(I) and Au(I) pillarplexes is discussed in this work, including the particularly interesting pore alignment of the pillarplex cations in the solid state dependent on the length of the guest, which paves the way to future mechanically interlocked molecules by the utilization of these functional acid groups.

Abstract

A series of pseudorotaxanes with supramolecular organometallic silver(I) and gold(I) pillarplexes acting as rings and different α,ω-dicarboxylic acids as axle components are reported. The successful formation of the host-guest complexes is shown by ¹H NMR spectroscopy and respective NMR titration. Additional evaluation with ITC titration experiments yielded dissociation constants (K_d) ranging from 10⁻⁵ to 10⁻⁷ M. Single-crystal X-Ray diffraction analysis reveals a particularly exciting pore alignment of different examples in the solid state depending on the length of the guest. The work highlights, that dicarboxylic acids can penetrate the tight tubular pillarplex pore, paving the way to future mechanically interlocked molecules and materials.

Monitoring Conformation and Protonation States of Glutathione by Raman Optical Activity and Molecular Dynamics

Posted on 28 June 2023 by

An analysis of Raman and Raman optical activity (ROA) spectra of glutathione based on computational modeling revealed that this peptide is flexible, but its conformation profile does not change significantly across a wide pH range. The adopted methodology could be appropriate for further structural studies of similar biomolecular systems.

Abstract

Glutathione (GSH) is a common antioxidant and its biological activity depends on the conformation and protonation state. We used molecular dynamics, Raman and Raman optical activity (ROA) spectroscopies to investigate GSH structural changes in a broad pH range. Factor analysis of the spectra provided protonation constants (2.05, 3.45, 8.62, 9.41) in good agreement with previously published values. Following the analysis, spectra of differently protonated forms were obtained by extrapolation. The complete deprotonation of the thiol group above pH 11 was clearly visible in the spectra; however, many spectral features did not change much with pH. Experimental spectra at various pH values were decomposed into the simulated ones, which allowed us to study the conformer populations and quality of molecular dynamics (MD). According to this combined ROA/MD analysis conformation of the GSH backbone is affected by the pH changes only in a limited way. The combination of ROA with the computations thus has the potential to improve the MD force field and obtain more accurate populations of the conformer species. The methodology can be used for any molecule, but for a more detailed insight better computational techniques are needed in the future.

A Calcination‐Free Sol‐Gel Method to Prepare TiO2‐Based Hybrid Semiconductors for Enhanced Visible Light‐Driven Hydrogen Production

Posted on 12 June 2023 by nKang Yang, nDan Wei, nChunman Jia, nJianwei Lin

The extensive π system in the naphthalene structure and the carboxylic acid group of 1,4-naphthalene dicarboxylic acid (NA) render it an exceptional organic semiconductor for doping TiO₂ using a calcination-free sol-gel method. The resulting catalyst exhibited a significantly improved hydrogen production rate by photolyzing water molecules under visible light, outperforming the efficiency of the calcined material.

Abstract

In recent years, the sol-gel method has been extensively utilized to develop efficient and stable organic semiconductor composite titanium dioxide (TiO₂) photocatalysts. However, the high-temperature calcination requirements of this method consume energy during preparation and degrade encapsulated organic semiconductor molecules, resulting in decreased photocatalytic hydrogen production efficiency. In this study, we found that by selecting an appropriate organic semiconductor molecule, 1,4-naphthalene dicarboxylic acid (NA), high-temperature calcination can be avoided in the sol-gel process, yielding an organic-inorganic hybrid material with stable and effective photocatalytic properties. The uncalcined material displayed a hydrogen production rate of 2920±15 μmol g⁻¹ h⁻¹, which was approximately twice the maximum production rate observed in the calcined material. Likewise, the specific surface area of the uncalcined material, at 252.84 m² g⁻¹, was significantly larger compared to the calcined material. Comprehensive analyses confirmed successful NA and TiO₂ doping, while UV-vis and Mott-Schottky tests revealed a reduced energy bandgap (2.1 eV) and expanded light absorption range. Furthermore, the material maintained robust photocatalytic activity after a 40-hour cycle test. Our findings demonstrate that by using NA doping without calcination, excellent hydrogen production performance can be achieved, offering a novel approach for environmentally friendly and energy-saving production of organic semiconductor composite TiO₂ materials.

5‐Nitrofuryl‐Containing Thiosemicarbazone Gold(I) Compounds: Synthesis, Stability Studies, and Anticancer Activity

Posted on 16 May 2023 by

The stability of new gold(I) containing chloro and biologically active thiosemicarbazones in coordinating and non-coordinating solvents is presented, allowing for a description of potential species formed. The most stable compound (2) results cytotoxic, apoptotic, antimetastatic, and antiangiogenic in a renal cancer cell line like Auranofin but with higher selectivity. 2 accumulates in the nuclei and shows interaction with CT DNA.

Abstract

This work describes the synthesis of four gold(I) [AuClL] compounds containing chloro and biologically active protonated thiosemicarbazones based on 5-nitrofuryl (L=HSTC). The stability of the compounds in dichloromethane, DMSO, and DMSO/culture media solutions was investigated by spectroscopy, cyclic voltammetry, and conductimetry, indicating the formation overtime of cationic monometallic [Au(HTSC)(DMSO)]^± or [Au(HTSC)₂]^±, and/or dimeric species. Neutral [{Au(TSC)}₂] species were obtained from one of the compounds in dichlomethane/n-hexane solution and characterized by X-ray crystallography revealing a Au−Au bond, and deprotonated thiosemicarbazone (TSC). The cytotoxicity of the gold compounds and thiosemicarbazone ligands was evaluated against selected cancer cell lines and compared to that of Auranofin. Studies of the most stable, cytotoxic, and selective compound on a renal cancer cell line (Caki-1) demonstrated its relevant antimigratory and anti-angiogenic properties, and preferential accumulation in the cell nuclei. Its mode of action seems to involve interaction with DNA, and subsequent cell death via apoptosis.