Synthesis, characterization, structural, redox and electrocatalytic proton reduction properties of cobalt polypyridyl complexes

A monoanionic amido pentadentate ligand bpaqH (2-(bis(pyridin-2-ylmethyl)amino)-N-(quinolin-8-yl)acetamide) and its corresponding cobalt(III) chloro complex [Co(bpaq)Cl]Cl: 1 and aqua derivative [Co(bpaq)(OH2)](ClO4)2: 2 were successfully synthesized and fully characterized by different analytical and spectroscopic techniques such as FT-IR, 1H NMR, UV–vis spectroscopy, ESI mass spectra. The structures of 1 and 2 have been determined by the single-crystal X-ray diffraction. Spectral and redox properties were investigated along with free ligand under electrochemical conditions. Both complexes performed proton reduction activity under soluble, diffusion-limited conditions in acetonitrile with acetic acid as an external proton source with overpotentials of 0.412 V for 1 and 0.394 V for 2. The stability of the catalysts was inspected by the time-dependent UV–vis spectroscopy; 1 and 2 were found to be highly stable in the absence and presence of acetic acid. There was no significant spectral change before and after the controlled potential electrolysis suggesting no change in molecular integrity during electrocatalysis

Design, Synthesis and Characterization of Pyridine based ligands towards CO2 Reduction

As we all know that global warming is directly affecting the ecosystem and human kind in the 21st century, solutions are continuously coming into mind to reduce the emissions of greenhouse gases. Of a particular interest is carbon dioxide (CO2) due to its increasing levels in the atmosphere and contribution to global warming. The identification and characterization of a relatively cheaper and simple electro catalyst for CO2 reduction was achieved with a certain degree of success, with the optimization and development in such a way that not only the electro catalytic species, but also the entire electrochemical system was systematically investigated, in order to determine the roles played by the various components. Electrochemical carbon dioxide reduction reaction is a process in which we can store energy from intermittent electricity sources and for the synthesis of carbon-based compounds that are currently derived from fossil fuels which are decreasing day by day. In this regards we have designed and successfully synthesized a series of pyridine based ligand moiety and also fully characterized by different spectroscopic techniques such as 1HNMR, 13CNMR, DEPT, FTIR, Mass etc. which will be tested for catalytic CO2 reduction. Efforts to grow suitable single crystal for our targeted ligands has also been done

Cobalt(II) and Copper(II) based Molecular Catalysts for Hydrogen Production

Hydrogen takes special attention as the most promising fuel for the future use in transportation and energy storing in terms of sustainability, C-Neutrality and energy conversion. Solar-driven water splitting for hydrogen production represents one fascinating pathway for clean energy conversion and energy storage from visible light irradiation into chemical bonds. The transition metal complexes especially first row transition (3d) metals like iron, manganese, cobalt, nickel and copper based molecular complexes are capable to catalyze the reduction of protons into molecular hydrogen at low over potential or using light energy sources. We are interested to develop robust cobalt and copper based catalyst that could preserve their molecular nature under photo and electrocatalytic conditions. This thesis describes the development of different ligands with different substituents which will help to compare the reactivity as well as redox potential of complexes for water reduction. Here, we successfully designed and synthesized four different types of tridentate ligands (L1, L2, L3, L4). We successfully synthesized Co(II) complexes M1 and M2 with ligands L3 and L4 respectively. The binuclear Cu(II) complex M3 synthesized by using L4. All the ligands and metal complexes were characterized by various spectroscopic tools. The molecular structure of the metal complexes confirmed by single crystal X-ray crystallography which would be robust catalysts for hydrogen evolution

Engineering Hydrogels for the Development of Three-Dimensional In Vitro Models

The superiority of in vitro 3D cultures over conventional 2D cell cultures is well recognized by the scientific community for its relevance in mimicking the native tissue architecture and functionality. The recent paradigm shift in the field of tissue engineering toward the development of 3D in vitro models can be realized with its myriad of applications, including drug screening, developing alternative diagnostics, and regenerative medicine. Hydrogels are considered the most suitable biomaterial for developing an in vitro model owing to their similarity in features to the extracellular microenvironment of native tissue. In this review article, recent progress in the use of hydrogel-based biomaterial for the development of 3D in vitro biomimetic tissue models is highlighted. Discussions of hydrogel sources and the latest hybrid system with different combinations of biopolymers are also presented. The hydrogel crosslinking mechanism and design consideration are summarized, followed by different types of available hydrogel module systems along with recent microfabrication technologies. We also present the latest developments in engineering hydrogel-based 3D in vitro models targeting specific tissues. Finally, we discuss the challenges surrounding current in vitro platforms and 3D models in the light of future perspectives for an improved biomimetic in vitro organ system

Design, Synthesis, Characterization and Spectral Properties of para-Substituted Diimine Based Ligands for Catalytic Water Oxidation

The increasing global energy demand requires alternative sources to fossil fuels. Artificial Photosynthesis is among the most promising alternative for generation of such kind of fuels. Although the process is different from the natural photosynthetic process, the basic principles are the same, i.e. to convert solar energy into chemical energy. By achieving this, energy can be stored in bonds, which at a later stage can be released upon combustion. The water oxidation is bottleneck of artificial photosynthesis. Therefore, the aim of this research to develop catalysts for water oxidation which are stable at the working condition and having a great TONs and TOF. The molecular catalysts are comprised of ligands which have a great influence on the catalyst structure and activity. These ligands are often based on diimine or other nitrogen-containing aromatic compounds. This thesis describes the development of diimine ligands with different substituents which will help to compare the reactivity as well as redox potential of complexes for water oxidation. According to recent literature report electron withdrawing groups assisting increase the redox potential while electron donating groups decrease the same. Therefore, in this thesis we prepared diimine ligands with substituents like Methoxy, Bromo, Chloro and Methyl which will help us to determine the efficiency and stability of the metal complexes associated with these ligand systems aiming for the purpose of water oxidation study in details

Cobalt based homogeneous molecular water oxidation catalysts

The consequential rise of energy demand after industrial revolution has led mankind to massive use of fossil fuels in the last two centuries. This has resulted into accumulation of carbondioxide in atmosphere which is the direct cause of global warming. A renewable, carbonneutral energy source is now the only way to combat energy crisis in near future and mitigate the environmental hazards. Mimicking natural phenomenon for carrying out artificial photosynthesis, i.e., splitting water into molecular oxygen and protons in addition with electrons is of great interest considering the demand of energy. Molecular catalysts made of noble metals have been in study for last four decades, but due to their scarcity and economic reasons, they cannot be produced for mass usage. So 1st row based transition metal could be an alternate for noble metal because of their high abundancy and less toxicity. Therefore, our main aim is to develop Cobalt-based molecular catalysts which will be oxidatively rugged and commercially sustainable and will have a great TON and TOF. Potent water-oxidation catalysts [Co(bmpp)(bpy)Cl]PF6 and [Co(bmpp)(phen)Cl]PF6 have also been synthesized after a thorough review on this field, where the ligand bmpp, is encompassed pyrazole derivative of pyridine

Design, Synthesis and Spectroscopic Characterization of Iron Based Molecular Catalysts for Water Oxidation

The continuous increase in global energy consumption leads to find an alternative source of carbon-based fuel. One of the promising solutions is the artificial photosynthesis which follows a different mechanistic pathway than that of the natural photosynthesis in the green plant, but the fundamental principles remain the same, i.e., to reserve the solar energy in the form of chemical energy. Water oxidation is the promising and sustainable solution for that purpose. But the splitting of water requires a molecular catalyst, and in this thesis, the synthesis of iron-based molecular catalysts as Water Oxidation Catalyst (WOC) will be discussed. Molecular catalysts for the water oxidation are generally comprised of a good ligand framework, i.e., polypyridyl system or nitrogen-containing aromatic or chelating compounds. After a thorough mechanistic studies of the literature, it has been observed that negatively charged ligand system in the WOCs are better choices as they can decrease the redox potential of metal complexes. Here a series of anionic ligands and their metal complexes have been synthesized and successfully characterized by different spectroscopic tools such as NMR, FTIR, and ESI-HRMS. The synthesized ligands are 2-Pyridinecarboxamide, N-(4-methylphenyl) (L1); 2-Pyridinecarboxamide, N-(4-bromophenyl) (L2); 2-Pyridinecarboxamide, N-8 quinolinyl (L3); N, N’-1, 4-Phenylenebis [2-pyridinecarboxamide] (L4); and the metal complex [Fe(pcq)(bpy)Cl]Cl (M1)which will be tested as potential water oxidation catalyst and mechanistic study will be also performed. Efforts to grow suitable single crystals for our synthesized ligands as well as metal complexes also attempted

Formation, Reactivity, Photorelease, and Scavenging of NO in Ruthenium Nitrosyl Complexes

The two newly designed nitrosyl complexes with Enemark–Feltham notation {RuNO}6 and {RuNO}7 configurations have been isolated as the perchlorate salts in the molecular framework [RuII(dmdptz)(phen)(NO)]n+ (dmdptz: N,N-dimethyl-4,6-di(pyridin-2-yl)-1,3,5-triazin-2-amine and phen: 1,10-phenanthroline) [RuII(dmdptz)(phen)(NO+)](ClO4)3 [4](ClO4)3 and [RuII(dmdptz)(phen)(NO•)](ClO4)2 [5](ClO4)2 respectively. The single crystal X-ray structures of complexes [RuII(dmdptz)(phen)Cl](ClO4) [1](ClO4), [RuII(dmdptz)(phen)(NO2)](ClO4) [3](ClO4) and [4](ClO4)3 have been determined. The π– acceptance of the NO+ moiety in [4](ClO4)3 is reflected from the triple bond characteristic bond length 1.131(5) Å with simultaneous trans angle of 175.3(4)° as a proof of true linear coordination mode. A sizable shift in ν (NO) frequency (Δν = 361cm−1) on moving from [4](ClO4)3 to [5](ClO4)2 are in good agreement for largely NO centered reduction with the changes in bonding {RuNO}6 [4](ClO4)3 to {RuNO}7 [5](ClO4)2. The redox properties of [4](ClO4)3 along with the precursor complexes, have been investigated. On exposure to visible light in the deoxygenated acetonitrile solution at room temperature both [4](ClO4)3 and [5](ClO4)2 spontaneously transform to their corresponding solvated derivative [RuII(dmdptz)(phen)(CH3CN)](ClO4)2 [2](ClO4)2 via the facile photocleavage of Ru–NO bond with KNO 9.26 x 10–3 min–1 (t1/2 = 74 min) and 4.03 x 10–2 min–1 (t1/2 = 17 min) respectively. The photoreleased “NO” can be scavenged by biologically relevant target molecule myoglobin as an Mb–NO adduct

PAMAM (generation 4) incorporated gelatin 3D matrix as an improved dermal substitute for skin tissue engineering

The study explored the prospects of PAMAM (generation 4) applicability in gelatin based scaffolds for skin tissue engineering. The effect of PAMAM on physico-chemical and biological characteristics of gelatin scaffolds was evaluated. Gelatin scaffolds (with/without PAMAM) were prepared by lyophilization, chemically crosslinked by glutaraldehyde and characterized for their morphology (pore size), chemical features (bond nature), water adsorption, biodegradation and biological compatibility. The study demonstrated that addition of PAMAM did not significantly alter the pore size distribution or porosity of the scaffolds. However, water adsorption potential and collagenase mediated degradation significantly enhanced over period of the study. Both the scaffolds (with/without PAMAM) were highly biocompatible and hemocompatible. PAMAM (G4) blended scaffolds showed relatively higher cellular adhesion and proliferation of both keratinocytes and fibroblasts with an improved gene expression profile of native collagen type I of fibroblasts. Moreover, expression of angiogenesis inducing genes, HIF1α and VEGF were also higher in PAMAM blended gelatin matrix. Also, PAMAM incorporated gelatin matrix showed a slower rate of drug release which confirms its suitability for therapeutic delivery during wound healing. These results clearly suggest that blending PAMAM (G4) into the matrix could provide an additional support to scaffold assisted wound healing