The Use of Coordination Chemistry Principles to Control Aggregation Processes of Metal Ions

The research presented in this thesis is based on the use coordination chemistry principles to control aggregation process of metal ions. Two important areas, which are currently being intensely researched, were chosen. Firstly, controlled aggregation of paramagnetic metal ions to produce cooperatively coupled molecule-based magnets was studied. In Chapter 3, the potential ways of producing single-molecule magnets (SMMs) using polyols as ligands and manganese and iron ions as the paramagnetic centers were investigated. SMMs are molecules which can store magnetic information, which requires both uniaxial anisotropy and non-zero overall spin. In contrast to most Mn and Fe clusters reported in the literature, it was found that the polyols tend to favor the formation of regular polyhedral arrangements of the metal ions. In Chapter 4 one polyol was chosen in order to survey the properties of a family of lanthanide chain compounds. Here the aim was to discover whether single-chain magnets, SCMs, based on 4f metals could be produced. In order to produce the chains, benzoate was employed to provide bridges. The 4f metal ions were chosen because of their inherent spins and anisotropies. As is becoming increasingly clear from the literature, DyIII seems to be the most promising choice for attaining exotic magnetic properties. The second area of study chosen aimed to investigate the utility of using the sort of small ligand molecules usually employed in constructing coordination compounds to mimic biomineralization processes. Biominerals are minerals utilized by biological systems to fulfill a variety of functions, and thus can be described as functional materials. Their specific shapes, phases and functions result in the majority of cases through the interaction of complicated, templating biomolecules, such as polysaccharides or proteins, with the growing surfaces of the minerals. Most research aiming to reproduce the fascinating shapes and properties of such materials in vitro uses correspondingly complicated templating molecules and systems, such as block copolymers, Langmuir-Blodgett films and inverse micelles. Previous research in our group using a simple polycarboxylate demonstrated that highly complex calcium carbonate structure could be produced such as micro-trumpets constructed from bundles of high-aspect ratio nanocrystallites. In Chapter 5 the formation of these structures was investigated further as well as the influence of some rigid polycarboxylates on calcium carbonate structures. In all cases, these additives appear to stabilize an initial phase of amorphous calcium carbonate which then evolves into one of the three crystalline phases of calcium carbonate in a range of topologies

Metal-Organic Frameworks as Potential Agents for Extraction and Delivery of Pesticides and Agrochemicals

[Image: see text] Pesticide contamination is a global issue, affecting nearly 44% of the global farming population, and disproportionately affecting farmers and agricultural workers in developing countries. Despite this, global pesticide usage is on the rise, with the growing demand of global food production with increasing population. Different types of porous materials, such as carbon and zeolites, have been explored for the remediation of pesticides from the environment. However, there are some limitations with these materials, especially due to lack of functional groups and relatively modest surface areas. In this regard, metal–organic frameworks (MOFs) provide us with a better alternative to conventionally used porous materials due to their versatile and highly porous structure. Recently, a number of MOFs have been studied for the extraction of pesticides from the environment as well as for targeted and controlled release of agrochemicals. Different types of pesticides and conditions have been investigated, and MOFs have proved their potential in agricultural applications. In this review, the latest studies on delivery and extraction of pesticides using MOFs are systematically reviewed, along with some recent studies on greener ways of pest control through the slow release of chemical compounds from MOF composites. Finally, we present our insights into the key issues concerning the development and translational applications of using MOFs for targeted delivery and pesticide control

Metal-Organic Frameworks as Potential Agents for Extraction and Delivery of Pesticides and Agrochemicals

Pesticide contamination is a global issue, affecting nearly 44% of the global farming population, and disproportionately affecting farmers and agricultural workers in developing countries. Despite this, global pesticide usage is on the rise, with the growing demand of global food production with increasing population. Different types of porous materials, such as carbon and zeolites, have been explored for the remediation of pesticides from the environment. However, there are some limitations with these materials, especially due to lack of functional groups and relatively modest surface areas. In this regard, metal–organic frameworks (MOFs) provide us with a better alternative to conventionally used porous materials due to their versatile and highly porous structure. Recently, a number of MOFs have been studied for the extraction of pesticides from the environment as well as for targeted and controlled release of agrochemicals. Different types of pesticides and conditions have been investigated, and MOFs have proved their potential in agricultural applications. In this review, the latest studies on delivery and extraction of pesticides using MOFs are systematically reviewed, along with some recent studies on greener ways of pest control through the slow release of chemical compounds from MOF composites. Finally, we present our insights into the key issues concerning the development and translational applications of using MOFs for targeted delivery and pesticide control

COMPARISON OF THE EFFECT OF PTEROCARPUS MARSUPIUM WITH PIOGLITAZONE IN DEXAMETHASONE-INDUCED INSULIN RESISTANCE

ABSTRACTObjective: This study was undertaken to evaluate the preventive effect of heartwood of P. marsupium in dexamethasone-induced hyperinsulinemiaand hyperglycemia and compare it with that of pioglitazone.Methods: Male albino wistar rats were divided into five groups (n=6). Plain control group received gum acacia (2%) orally from d 1 to d 12. Dexacontrol group received gum acacia (2%) orally for d 1 to d 12 and Dexa (8 mg/kg) intraperitoneal (i.p.) from d 7 to d 12, during the study period.Two test groups received ethanolic extract of Pterocarpus marsupium heartwood (PME) (1 and 2 g/kg/) per oral (PO), and standard control groupreceived pioglitazone (60 mg/kg/PO) from d 1 to d 12. During the 12-d study period, the two test groups and standard control group received Dexa(8 mg/kg/i.p.) from d 7 to d 12. On last day of the study, the blood samples were collected by retro-orbital sinus punctureand used for estimation ofserum insulin and glucose levels. Homeostatic Model Assessment (HOMA) method was employed to calculate the degree of insulin resistance(IR).Results were analyzed by using one-way analysis of variance followed by Scheffe's multiple comparison test (p<0.05).Results: Treatment with ethanolic extract of P. marsupium and pioglitazone significantly (p<0.05) reduced the elevated insulin and glucose levels aswell as HOMA-IR and HOMA-IS values in dexa treated animals.Conclusion: Ethanolic extract of P. marsupium heartwood effectively countered dexamethasone-induced hyperinsulinemia and hyperglycemia.Insulin-sensitizing activity of P. marsupium heartwood was found to be more effective than pioglitazone.Keywords: Pterocarpus marsupium, Insulin resistance, Hyperinsulinemia, Hyperglycemia

Mixed-linker approach in designing porous zirconium-based metal–organic frameworks with high hydrogen storage capacity

YesThree highly porous Zr(IV)-based metal–organic frameworks, UBMOF-8, UBMOF-9, and UBMOF-31, were synthesized by using 2,2′-diamino-4,4′-stilbenedicarboxylic acid, 4,4′-stilbenedicarboxylic acid, and combination of both linkers, respectively. The mixed-linker UBMOF-31 showed excellent hydrogen uptake of 4.9 wt% and high selectivity for adsorption of CO2 over N2 with high thermal stability and moderate water stability with permanent porosity and surface area of 2552 m2 g−1.University of Bath; Royal Society of Chemistry; Engineering and Physical Sciences Research Counci

Controlled delivery of ciprofloxacin using zirconium-based MOFs and poly-caprolactone composites

YesWith antimicrobial resistance (AMR) increasing at an alarming rate, there is a need to develop better antibiotic delivery platforms at the point of need, to reduce over-exposure to antibiotics that are delivered systemically. Recent studies have suggested the use of metal-organic frameworks (MOFs) as potential vehicles for controlled and efficient delivery of various active pharmaceutical ingredients (APIs). Development of MOF-polymer composite materials can assist in the development of medical devices that can deliver APIs to local sites in a targeted approach. This study reports the encapsulation of a widely used antibiotic - ciprofloxacin (CIP) - into two Zr-based MOFs (UiO-66 and UiO-66-NH2) and their subsequent integration into a biodegradable polymer; polycaprolactone (PCL), via solvent casting, to obtain a PCL-MOF composite membrane. The MOFs and PCL-MOF composites were characterised by Fourier-transformed infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results demonstrated that the structural integrity of the pristine MOFs was maintained after drug loading and incorporation into the PCL membranes. The ciprofloxacin release was studied using ultraviolet–visible (UV–Vis) spectroscopy, and the results showed that the PCL-MOF composites had a more controlled drug release profile compared to the MOF alone, when monitored for seven days in phosphate buffered saline (PBS) and accelerated ageing (AA) release media. In addition, release studies showed pH-dependence with faster release of ciprofloxacin at both acidic and basic conditions. Antimicrobial assay showed excellent efficacy for both CIP-loaded MOFs and their PCL composites against S. aureus and E. coli, a Gram-negative and Gram-positive bacterium, respectively, with inhibition zone as high as >50 mm against E. coli for UiO-66-NH2-CIP, indicating their potential applications in purpose-specific medical devices.LAMM and SN acknowledge an Erasmus + exchange studentship. VPT and LRT acknowledge funding via an EPSRC Research Fellowship for VPT [EP/R01650×/1]

Zirconium-based MOFs and their biodegradable polymer composites for controlled and sustainable delivery of herbicides

YesAdsorption and controlled release of agrochemicals has been studied widely using different nanomaterials and a variety of formulations. However, the potential for application of high surface-area metal-organic frameworks (MOFs) for the controlled release of agrochemicals has not been thoroughly explored. Herein, we report controlled and sustainable release of a widely used herbicide (2-methyl-4-chlorophenoxyacetic acid, MCPA) via incorporation in a range of zirconium-based MOFs and their biodegradable polymer composites. Three Zr-based MOFs, viz., UiO-66, UiO-66-NH2, and UiO-67 were loaded with MCPA either postsynthetically or in situ during synthesis of the MOFs. The MCPA-loaded MOFs were then incorporated into a biodegradable polycaprolactone (PCL) composite membrane. All three MOFs and their PCL composites were thoroughly characterized using FT-IR, TGA, SEM, PXRD, BET, and mass spectrometry. Release of MCPA from each of these MOFs and their PCL composites was then studied in both distilled water and in ethanol for up to 72 h using HPLC. The best performance for MCPA release was observed for the postsynthetically loaded MOFs, with PS-MCPA@UiO-66-NH2 showing the highest MCPA concentrations in ethanol and water of 0.056 and 0.037 mg/mL, respectively. Enhanced release of MCPA was observed in distilled water when the MOFs were incorporated in PCL. The concentrations of herbicides in the release studies provide us with a range of inhibitory concentrations that can be utilized depending on the crop, making this class of composite materials a promising new route for future agricultural applications.L.A.M.M. and S.N. acknowledge funding for a studentship by the Erasmus+ KA107 Student Mobility programme. V.P.T and L.R.T. acknowledge funding from the EPSRC (EP/R01650X/1

Polynuclear complexes as precursor templates for hierarchical microporous graphitic carbon: An unusual approach

YesA highly porous carbon was synthesized using a coordination complex as an unusual precursor. During controlled pyrolysis, a trinuclear copper complex, [CuII3Cl4(H2L)2]·CH3OH, undergoes phase changes with melt and expulsion of different gases to produce a unique morphology of copper-doped carbon which, upon acid treatment, produces highly porous graphitic carbon with a surface area of 857 m2 g–1 and a gravimetric hydrogen uptake of 1.1 wt % at 0.5 bar pressure at 77 K.EPSRC (EP/R01650X/1 for VPT, and EP/E040071/1 for MT) and the University of Bristo

Transition metal complexes of a versatile polyalkoxy oxazolidine-based ligand derived from in situ cyclization

YesOne-pot reaction between 8-hydroxyquinoline-2-carboxaldehyde (HQC) and tris(hydroxymethyl)aminomethane (TRIS) followed by in situ cyclization yielded an oxazolidine based ligand which produced four mononuclear complexes of MnII(1), CoII(2), NiII(3), ZnII(4), a tetranuclear iron (FeIII4) complex (5) and a trinuclear cobalt (CoIICoIII2) complex (6). Magnetic studies show dominant antiferromagnetic interaction in tetranuclear iron (FeIII4) complex 5 and presence of the slow relaxation of magnetisation in 6. The compounds were also studied for their antibacterial properties. The oxazolidine ligand (H3L2) of this study showed good antimicrobial activity not only against Gram-positive bacteria but against Gram-negative bacteria too. The antimicrobial efficacy of the metal complexes (1–6) is also reported.The full-text of this article will be released for public view at the end of the publisher's embargo period on 11 Apr 2019