Facile Synthesis of Metal–Organic Framework (ZIF-11) and Ag NPs Encapsulated-ZIF-11 Composite as an Effective Heterogeneous Catalyst for Photodegradation of Methylene Blue

Facile synthesis of metal–organic framework based on zeolitic imidazolate (ZIF-11) has been optimized to get a material with rho topology. For the first time AgNPs in various dosing amounts (using 150, 300 and 500 μL of its suspension in methanol) have been successfully encapsulated within ZIF-11 matrix at room temperature using binary solvent (methanol and toluene) yielding novel multi-core-shell AgNPs@ZIF-11 (AZ1, AZ2 and AZ3) composites. Encapsulation of AgNPs (particle size: 11.76 ± 2.3 nm) has been confirmed by TEM and ultraviolet diffuse reflectance spectroscopic (UV-DRS) analysis. The lowering of band gap of ZIF-11 from 4.36 to 4.21 eV indicates the micro-environment of AgNPs within ZIF-11 framework, which has also been ensured by XPS analysis. ZIF-11 and AgNPs@ZIF-11 composites are highly stable up to 500 °C under air and N₂ atmosphere. It has been found that AZ1 composite exhibits excellent photocatalytic activity (almost 100% degradation) toward MB (1.6 mg/L) at pH ≥ 8. Further, various factors such as loading amount of AgNPs (150, 300 and 500 μL suspension in methanol), amount of catalysts (5 mg, 10 mg and 15 mg) and concentration (1.6 mg L⁻¹, 3.19 mg L⁻¹ and 6.38 mg L⁻¹) of methylene blue (MB) dye during photodegradation experiments have been investigated. The capacious achievement of AZ1 composite is its reusability and recyclability; it can be reutilized up to three cycles with the same efficiency (100%) while under fourth and fifth cycle, it can degrade off 92.12% and 72.75% MB, respectively. AgNPs may act as a mediator to promote the quick transfer of photo-induced electrons and electron–hole pairs separation in ZIF-11. This work opens a new type of easily fabricated core-shell composites utilizing ZIF-11 for wastewater remediation process.     

Interactions of a Low Molecular Weight Inhibitor from Streptomyces sp. MBR04 with Human Cathepsin D: Implications in Mechanism of Inactivation

Cathepsin D, a lysosomal aspartic protease, is of potential interest as a target for drug design due to its implication in breast and ovarian cancer. The article reports a low molecular weight cathepsin D inhibitor from Streptomyces sp. MBR04. The M_r of the inhibitor was 1,078 Da as determined by MALDI-TOF, and the amino acid analysis showed the presence of Asp, Asp, Gly, Ala, Lys, Leu, Tyr, Trp residues. The steady-state kinetic interactions revealed reversible, competitive, slow-tight-binding nature of the inhibitor with an IC₅₀ and K _i values of 3.2 and 2.5 nM, respectively. The binding of the inhibitor with the enzyme and the subsequent conformational changes were monitored by exploiting the intrinsic fluorescence of the surface exposed Trp-54 residue. Based on the fluorescence and circular dichroism studies, we demonstrate that the inhibitor binds to the active site of cathepsin D and causes inactivation. All these kinetic, thermodynamic, and quenching studies suggest that the newly isolated peptidic inhibitor could be a potential scaffold to study and can be used to develop new potent therapeutic lead molecule for the development of drugs. The inhibitor will be significant as a potential lead molecule to target cathepsin D.     

Synthesis,Structure–Activity Relationship of Some New Triorganotin(IV) Derivatives of Dipeptides as Anti-Inflammatory Agents

Abstract

New triorganotin(IV) derivatives of dipeptides with general formulae, R₃Sn(HL), where R = Me and Ph, and HL is the monoanion of histidinylalanine and histidinylleucine, have been synthesized and characterized on the basis of infrared (IR), multinuclear NMR (¹H, ¹³C, and ¹¹⁹Sn), and ¹¹⁹Sn Mössbauer spectroscopic studies. These derivatives exhibit distorted trigonal-bipyramidal geometry around tin in which dipeptide anion acts as bidentate ligand coordinating through carboxyl oxygen and amino nitrogen. Ph₃Sn(HHis-Ala),

Ph₃Sn(HHis-Leu), and previously reported Ph₂Sn(His-Ala), Me₂Sn(His-Ala), n-Oct₂Sn(His-Ala), Me₂Sn(His-Leu), n-Oct₂Sn(His-Leu), Ph₃Sn(HTyr-Phe), Ph₂Sn(Tyr-Phe), Bu₂Sn-(Tyr-Phe), and n-Oct₂Sn(Tyr-Phe) along with standard drugs, viz. phenyl butazone and indomethacin were screened for in vivo anti-inflammatory activity and acute toxicity (LD₅₀). Diorganotin(IV) derivatives are more active than triorganotin(IV) derivatives. Me₂Sn(His-Leu) shows the highest activity.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Finitely Generated Quasi-Proximities

In this paper we deal with the proximal properties of relators which are straightforward generalizations of Weil's uniformities. We prove that every finitely generated quasi-proximity is simple and show that a theorem in Kenyon [4] can be set in a more general form.     

Chemistry and applications of organotin(IV) complexes of Schiff bases

Schiff bases are the most widely used versatile ligands, able to coordinate many elements and to stabilize them in various oxidation states. Recently, this class of compounds has been employed as models for biological systems, and in control of stereochemistry in six-coordinate transition metal complexes. Recently, the chemistry of organotin(IV) complexes of Schiff bases has also stemmed from their antitumour, antimicrobial, antinematicidal, anti-insecticidal and anti-inflammatory activities. Furthermore, organotin(IV) complexes of Schiff bases present a wide variety of interesting structural possibilities. Both aliphatic and aromatic Schiff bases in their neutral and deprotonated forms have been used to yield adducts and chelates with variable stoichiometry and different modes of coordination. This critical review (>155 references) focuses upon the chemistry and biological applications of organotin(IV) complexes of Schiff bases reported in the past 15 years. Thermal behavior of these complexes is also discussed.     

Fluorescence study on Interactions of α–Crystallin with the Molten Globule State of 1, 4–β–D–Glucan Glucanohydrolase from Thermomonospora sp. induced by guanidine hydrochloride

In this paper, the interaction between α- crystallin and molten globule structure of 1,4–β–D–Glucan Glucohydrolase (TSC) from an alkalothermophilic Thermomonospora sp. was investigated mainly by fluorescence quenching spectra, circular dichroism and three dimensional fluorescence spectra under simulative physiological conditions. Denaturation studies using GdnCl indicated that TSC folds through a partially folded state that resembles molten globule at 1.8 M GdnCl. The chaperone activity of α- crystallin was employed to study refolding of TSC. Here we studied the refolding of GdnCl denatured TSC from its molten globule state (TSC-m complex) in the presence and absence of α-crystallin to elucidate the molecular mechanism of chaperone-mediated in vitro folding. Our results, based on intrinsic tryptophan fluorescence and ANS binding studies, suggest that α-crystallin formed a complex with a putative intermediate molten globule – like intermediate in the refolding pathway of TSC. Reconstitution of the active TSC was observed on cooling the α-crystallin • TSC -m complex to 4°C. Addition of α-crystallin to the molten globule – like intermediate of TSC (TSC-m complex) complex initiated the refolding of TSC with 69 % recovery of the biological activity of the enzyme.     

Symmetry and measurability

In the Hewitt–Savage 0-1 law, symmetric measurable sets are considered in a countable product of a σ-algebra Σ with itself. Therefore, it may be of interest to find simple generators for these sets in terms of the generators of Σ. We put the problem into a more general framework of action groups and as an application find simple generators for the finite product case. We also have a partial result in the countable product case.