Organophosphate hydrolase conjugated UiO-66-NH2 MOF based highly sensitive optical detection of methyl parathion.

The hexahistidine-tagged organophosphorus hydrolase (OPH6His) has been immobilized on a Zr-MOF, namely UiO-66-NH2. The resulting enzyme-MOF composite was used as a carrier to facilitate the hydrolysis of an organophosphate pesticide, i.e., methyl parathion in to p-nitrophenol (PNP). The formation of PNP took place in direct proportion to the added pesticide concentration. Coumarin1 (7-diethylamino-4-methylcoumarin) was then introduced in the reaction mixture as a reporter fluorescent molecule. As PNP acted to quench the fluorescence of coumarin1, it became possible to detect methyl parathion over a wide concentration range of 10-106 ng/mL with an achievable limit of quantification as 10 ng/mL. The immobilization of OPH6His on the surface of UiO-66-NH2 was found to endow an improvement in the enzymatic activity by about 37%. The OPH6His/UiO-66-NH2 conjugate was reusable for at least up to eight times and also found stable toward long-term storage (minimum 60 days). The potential practical utility of the above proposed sensing method has been demonstrated by employing it for an accurate analysis of pesticide-spiked food samples.

A study of DNA/BSA interaction and catalytic potential of oxidovanadium(v) complexes with ONO donor ligands.

The study of DNA/BSA interaction and the catalytic potential of four mononuclear oxidoalkoxido vanadium(v) [VVO(L1-4)OEt] (1-4) and one dinuclear oxidoalkoxido mixed-ligand vanadium(v) [{VO(L2)OEt}2(Q)]{Q = 4,4'-bipyridine}(5) complexes, with tridentate binegative aroylazine ligands are reported [where H2L1 = anthranylhydrazone of 2-hydroxy-1-napthaldehyde, H2L2 = salicylhydrazone of 2-hydroxy-1-napthaldehyde, H2L3 = benzoylhydrazone of 2-hydroxy-1-acetonaphthone, H2L4 = anthranylhydrazone of 2-hydroxy-1-acetonaphthone]. All the complexes are characterized by elemental analysis as well as various spectroscopic techniques. Single crystal X-ray diffraction crystallography of 2 reveals that the metal centre is in distorted square pyramidal geometry with O4N coordination spheres, whereas 5 exhibits a distorted octahedral geometry around the metal center. In addition, all the complexes (1-5) show moderate DNA binding propensity which is investigated using UV-vis absorption titration, circular dichroism, thermal denaturation and fluorescence spectral studies. The experimental results show that the complexes effectively interact with CT-DNA through both minor and major groove binding modes, with binding constants ranging from 104-105 M-1. Among 1-5, complexes 3 and 4 show higher binding affinity towards CT-DNA than others and at the same time also exhibit negative ΔTm values of about ∼1.5 and 1.0 °C which resembles the properties shown by cisplatin. All complexes show moderate photo-induced cleavage of pUC19 supercoiled plasmid DNA with complex 3 showing the highest photo induced DNA cleavage activity of ∼48%. In coherence with the DNA interaction studies, 3 and 4 also exhibit good binding affinity towards BSA in the range of 1010-1011 M-1, which is also supported by their ability to quench the tryptophan fluorescence emission spectra of BSA. All the complexes show remarkable photo-induced BSA cleavage activity (>90%) at a complex concentration of 50 µM. The catalytic potential of 1-5 is also tested for the oxidative bromination of styrene, salicylaldehyde and oxidation of methyl phenyl sulphide. All the reactions show a high percentage of conversion (>90%) with a high turnover frequency (TOF). Particularly, in the oxidative bromination of styrene the percentage of conversion and TOF vary from 96-98% and 8000-19 600 (h-1) respectively, which signifies the potential of these oxidovanadium(v) complexes to stimulate research for the synthesis of a better catalyst.