Chemical oxidation and photoinduced electron transfer by nickel and copper complexes

The energy appetite of our global society is enormous with the need only expected to double by midcentury and triple by 2100. The global energy demand calls for diversifying our energy sources and relying more on sustainable energy resources. Transition metals are ubiquitous in nature and central to many organic and biochemical transformations. Activation and catalytic conversion by multielectron redox reactions are crucial for the production of fuels (e.g., hydrogen) or useful chemicals (e.g., organic compounds). In this dissertation we will present our efforts on finding catalysts that can do organic transformations under ambient conditions. We also investigated different multi-component systems to understand the mechanism of electron transfer pathways so that an efficient photosensitizer-catalyst assembly can be designed. The development of efficient and selective hydrocarbon oxidation processes with low environmental impact remains a challenge. Herein we report the synthesis of nickel complexes supported by nitrogen rich tetradentate ligands. The complexes have been characterized by optical spectroscopy, mass spectrometry and elemental analyses. Crystal structures of three complexes have been reported. Oxidative properties of the complexes were studied by their reactivity with two substrates 1,4-cyclohexadiene and 2,4,6-tri-tert-butylphenol in the presence of potassium superoxide. Both sets of reactions led to the oxidation of the substrates and the product yields were quantified. Based on isotope labeling experiments a reaction mechanism was proposed for the oxidation of the phenol by the nickel complexes in the presence of superoxide. Photocatalytic water splitting using solar energy for hydrogen production offers a promising alternative form of storable and clean energy. To develop the photocatalytic system, we need to couple a catalyst for proton reduction to a photosensitizer and understand the mechanism of photoinduced electron transfer from the photosensitizer to the catalyst. We focused on the study of light driven electron transfer kinetics from quantum dot systems made with inorganic chalcogenides in the presence of nickel and copper reduction catalysts. The lifetime of the quantum dots was investigated in the presence of the complexes and absorbance, emission, dynamic light scattering, and electrochemical measurements were performed to gain a deeper understanding of the photoinduced electron transfer process

Environmentally Benign Catalysts by Design: Functional Mimics of Meralloenzymes

https://louis.uah.edu/research-horizons/1167/thumbnail.jp

Exploring the Potential of Water-Soluble Cu(II) Complexes with MPA–CdTe Quantum Dots for Photoinduced Electron Transfer

Three water-soluble copper complexes based on the amine/pyridine functionalities were investigated, along with quantum dots, as a catalyst–photosensitizer assembly, respectively, for fundamental understanding of photoinduced electron transfer. Luminescence quenching and lifetime measurements were performed to try and establish the actual process that leads to the quenching, such as electron transfer, energy transfer, or complex formation (static quenching). Cyclic voltammetry and dynamic light scattering experiments were also performed. Irrespective of the similar reduction potentials of the three complexes, very different photoluminescence properties were observed

Ups and Downs of Water Photodecolorization by Nanocomposite Polymer Nanofibers

Given the exponentially expanding water pollution causing water scarcity, there is an urgent need for operative nanotechnological systems that can purify water, with insignificant energy consumption, and rapidly. Here, we introduce a nanocomposite system based on TiO 2 nanoparticles (NPs) and PES nanofibers (NFs) that can adsorb and then photodecompose organic water pollutants such as dye molecules. We evaluate pros and cons of this system with respect to its purification efficiency and structural properties that can be impacted by the photocatalytic activity of the nanofillers. While the material is superhydrophilic and able to remove 95% methylene blue (MB) from water via adsorption/photodecomposition, its thermomechanical properties decline upon UV irradiation. However, these properties still remain at the level of the neat NFs. The removal behavior is modeled by the first-and second-order kinetic models from the kinetic point of view. The nanocomposite NFs’ removal behavior complies much better with the second-order kinetic model. Overall, such feedbacks implied that the nanocomposite can be effectively applied for water treatment and the structural properties are still as reliable as those of the neat counterpart.Peer reviewe

Percutaneous ultrasound-guided plugged liver biopsy : a single-centre experience

Background: Liver biopsy is a widely used, safe diagnostic tool utilised by clinicians for the histopathological assessment of the liver. Our study aims to report our experience in patients who underwent ultrasound-guided plugged percutaneous liver biopsy in a tertiary care hospital in India. Material and methods: The Institutional Ethical Review Board approved this retrospective study, and informed consent was obtained from all the patients. A total of 830 liver biopsies were performed between January 2014 and December 2018, of which 782 were plugged percutaneous liver biopsies. The tract was plugged using Gelfoam slurry. Various observations related to the procedures were recorded. Results: Seven hundred and eighty-two were plugged percutaneous liver biopsies, which were performed during the study period. Of the 782 patients, 163 were male, and 619 were female (20.8 % and 79.2 %, respectively), with a mean age of 49.6 ± 2 years (1 month to 86 years). A 100% technical success rate was seen. No immediate major complications were documented in any of the patients who underwent plugged biopsies. No significant complications were seen in any patient. Conclusions: Percutaneous liver biopsy is an extensively performed diagnostic tool. We found that ultrasound-guided percutaneous plugged liver biopsy is an easy to perform procedure, which is associated with a lower risk of a bleeding complications

Iron(II) complexes of 4-sulfanyl-, 4-sulfinyl- and 4-sulfonyl-2,6-dipyrazolylpyridine ligands. A subtle interplay between spin-crossover and crystallographic phase changes.

Oxidation of 4-(methylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine (LSMe) with hydrogen peroxide or mCPBA yields 4-(methylsulfinyl)-2,6-di(pyrazol-1-yl)pyridine (LSOMe) and 4-(methylsulfonyl)-2,6-di(pyrazol-1-yl)-pyridine (LSO2Me), respectively. Solid [Fe(LSMe)2][ClO4]2 (1[ClO4]2) is high-spin at room temperature, and exhibits an abrupt spin-transition at T1/2 = 256 K. A shoulder on the cooling side of the χMT vs. T curve is associated with a hysteretic crystallographic phase change, occurring around T↓ = 245 K and T↑ = 258 K. The phase change involves a 180° rotation of around half the methylsulfanyl substituents in the crystal. This contrasts with the previously reported BF4 − salt of the same compound, which is isostructural to 1[ClO4]2 at room temperature but transforms to a different crystal phase in its low-spin state. Solid [Fe(LSOMe)2][BF4]2 (2[BF4]2) and [Fe(LSO2Me)2][BF4]2 (3[BF4]2) both exhibit gradual spin-crossover equilibria centred significantly above room temperature. Solution measurements show that the oxidised sulphur centers in 2[BF4]2 and 3[BF4]2 stabilise the low spin states of those complexes

Antibacterial and antifungal efficacy of Cajanus scarabaeoides seed extracts: A comparative study of solvent-based phytochemical extraction

This study investigates the antibacterial and antifungal activities of various solvent extracts (ethyl acetate, hexane, methanol and chloroform) from Cajanus scarabaeoides seeds against both bacterial and fungal strains. The antibacterial activities were tested against gram-positive (Bacillus subtilis, Staphylococcus aureus, Micrococcus luteus) and gram-negative bacteria (Vibrio cholerae, Salmonella paratyphi, Escherichia coli), while antifungal activities were examined against Candida albicans, Saccharomyces cerevisiae, and Aspergillus niger. The methanol extract exhibited the highest antimicrobial activity, particularly against S. aureus (12.67 mm inhibition), M. luteus (19.83 mm inhibition), S. paratyphi (12.33 mm inhibition), S. cerevisiae (12.50 mm) and A. niger (10.63 mm inhibition). Minimum inhibitory concentrations (MICs) demonstrated the potency of the methanol extract, especially with M. luteus (MIC of 27.83 µg/mL), S. paratyphi (28.50 µg/mL), and S. cerevisiae (28.80 µg/mL). Principal component analysis (PCA) revealed a strong correlation between phytochemicals like phenols, tannins, and flavonoids, and their antimicrobial effects, particularly against B. subtilis, S. paratyphi, and S. cerevisiae. The findings suggest that polar solvent methanol is more effective in extracting bioactive compounds responsible for antimicrobial and antifungal activities in C. scarabaeoides