Study On Synthesis Of Ferrocene Boronic Acid-based Derivatives And Polymers And Their Redox Responsive And Saccharide Sensing Properties

The interest in saccharide (glucose, fructose, galactose, mannose, etc.) biosensors persisted over many years and persistent efforts have been made to develop long-term stable saccharide biosensors with precision, smart analytical performance, good linearity and resistance to common interferences. In this regard, ferrocene-based polymers and derivatives (FBPDs) as redox mediators have acquired utmost attention of the scientists, especially in the second-generation biosensors. Most of FBPDs are considered as active components in the development of glucose biosensors (GBs), due to their ease of modification, biocompatibility, stability, large surface area, good electrical conductivity and especially excellent redox properties.Due to easy availability of commercial devices, enzymatic amperometric glucose biosensors have been extensively studied in the past five decades, in which amperometric sensors (AS) work by the exchange of electrons between biological systems and electrode. The glucose-responsive systems can be discussed into two dimensions:glucose-responsive or glucose sensing mechanism and their application. Based on mechanism studies, glucose-responsive systems can further classified into three types:Lectin, glucose oxidase (GOx) and phenylboronic acid (PBA) derived systems. PBA is a chemically binding agent, which is used for sensing of glucose and other saccharides/diols. It represents one of the advanced, cost effective and most reliable method for glucose sensing.Boronic acids (BAs) are the main constituents of PBA-based systems for saccharide sensing. For constructing a continuous sensor, PBA is the better choice to assist as a glucose-sensitive part. During the past few decades, ferrocene boronic acid-based sensors have been extensively reported. The sensing principle covers a variety of techniques like fluorescence, UV-vis absorption, and circular dichroism. The majority of these sensors based on optically active derivatives along with their electrochemical properties was also studied and attained much more attention towards researchers in recent years. Among different methods discussed above for the detection of glucose, electrochemical sensing is rather new and promising field to explore, as very brief contribution has been done so far in the said field. Using PBA with ferrocene is a fantastic approach to develop electrochemical sensors and to develop novel derivatives and polymers for the detection of biological analytes, especially glucose. However, electrochemically responsive systems acquired very little attention, even though some of them exhibit very interesting potential to distinguish between free and bound forms of BA in a homogeneous assay. The sensing ability is assessed by the alteration of redox potential upon binding of an analyte (applicable for active BAs generally). Keeping in view the above crucial findings, we focused our research to explore ferrocene boron chemistry and designed following research plans.In second chapter, ferrocene boronic acid (FBA)-based derivatives, namely FcMAPBA and FcDAPBA were synthesized by the reaction of 3-APBA with ferrocenemonocarbonyl chloride and ferrocenedicarbonyl chloride, respectively. Both ferrocene derivatives were characterized by 1H NMR and FTIR spectroscopy. Their saccharides (glucose, fructose, galactose and mannose) sensing properties and binding affinities of FcAPBAs with saccharides were investigated by CV,1H NMR and UV-vis spectroscopy, (using sorbitol as a model compound). Thermal properties of derivatives were examined by DSC and TGA.It was found that in 1H NMR spectra, the disappearance of boronic acid hydroxyls signal clearly depicted the free and bound forms of derivatives. In agreement with 1H NMR results, two discrete peaks appeared in the CV curves after binding with cis-diol are evident. Moreover, a change in absorption intensities in UV was also evident as binding interaction of FcMAPBA with saccharides. Due to lack of redox active moiety in their structures, no such distinctive CV curves were observed for BMAPBA and BDAPBA. Hence, it was proposed that the potential shift can be employed for detection the of the glycated molecules. It was also found that, our proposed method for saccharide sensing can be successfully employed for simple and easy evaluation of interactions between the boronic acid and cis-diol. More importantly, ferrocene electrochemical response to the binding actions appears very fascinating as it signifies a substantial step towards robust and effective artificial bioelectronics/biosensors affinity receptors.Continuing of our interest in ferrocene-boron chemistry, third chapter focused the synthesis of ferrocene-containing methacrylate homopolymer, poly(2-(meth acrylolyoxy) ethyl ferrocenecarboxylate) (PMAEFc) was synthesized by RAFT polymerization. Using PMAEFc as a macroinitiator, three novel diblock copolymers (PMAEFc-b-PVAPBA, PMAEFc-b-PMVAPBA and PMAEFc-b-PSBA) were prepared through chain extension. The synthesized block copolymers were characterized by FT-IR,1H NMR and GPC. Thermal properties of homopolymers and block copolymers were investigated by DSC and TGA. Detailed micellization behaviour of PMAEFc-b-PMVAPBA (in binary organic solvents mixture and in aqueous solution) was also studied. The saccharide binding/sensing properties of PMAEFc-b-PVAPBA was explored by 11B NMR and 1H NMR spectroscopy.It was found that on binding with diols, the disappearance of hydroxyls signal of boronic acid in 1H NMR spectrum, and peak shifting of boron in 11B NMR spectrum of PMAEFc-b-PVAPBA, clearly depicted the free and bound forms of block copolymers. Comparative studies of micellization in binary organic solvents systems and in aqueous medium, showed that the larger aggregates (Rh=179-264 nm) were obtained in binary organic solvents system than during dialysis in aqueous medium (Rh=110-140 nm). PMAEFc-b-PMVAPBA block copolymer contains both boronic acid (BA) moiety and ferrocenyl (redox-active) groups in which BA can bind with glucose, while ferrocene moiety can undergo a reversible redox-triggered change in micelles size. It was also found that the increase in polarity and swelling of PMAEFc-b-PMVAPB A micelles was due to the redox behaviour of ferrocene and binding of glucose with boronic acids hydroxyls led to unimers or smaller aggregates. Block copolymers exhibited higher thermal stability than homopolymers.In fourth chapter, we have synthesized ferrocene-based block copolymer (PMAEFc-b-PMVAPBA) by using 2-(dodecylthio carbono thioyl thio)-2-methyl propanoic acid (DDMAT) as RAFT agent. PMAEFc-b-PMVAPBA linked to hydrophobic blocks of methyl vinylaminophenylboronic acid and ferrocene (redox-active). PMAEFc-b-PMVAPBA was characterized by FT-IR,1H NMR and GPC. The thermal properties of PMAEFc and PMAEFc-b-PMVAPBA were studied by using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The hydrophobic and hydrophilic blocks of copolymer self-assembled into spherical micelles in aqueous solution. The redox behaviour of ferrocene was studied by using water-soluble (NH4)Ce(NO3)6 and (NaHSO3) as oxidizing and reducing agents, respectively.’H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to investigate the redox-controlled behaviour of micelles.It was observed that the change in polarity and swelling of micelles increased the hydrodynamic diameter due to the oxidation of ferrocene, while glucose binding with boronic acid hydroxyls led to less aggregates or unimers. The redox-responsive behaviour provides a criterion for detection/binding of biological analytes study and redox-controlled release of encapsulants. Overall, the synthesis and the binding of glucose with boronic acids, both can demonstrate an example of saccharide sensing, which can be utilized to construct redox responsive saccharide detection methods.