# Metal-Coordinated Polymer-Inorganic Hybrids: Synthesis, Properties, and Application
## 3 Polymer-Inorganic Coordinated Hybrids: Complexation-Induced Properties
### Pyridine-Based Polymers
#### 3.1.3 Catalytic Activity of Coordination Complexes of PVPs with Metal Ions
Adapted with permission from the Royal Society of Chemistry [111; 113] and Elsevier [112]. units (I2M) in other ruthenium-based catalysts. The P4 VP polymer matrix plays a crucial role by preventing the dimerization of the Ru centers due to its multi-charge properties and slow diffusion characteristics, which enforce electrostatic repulsion and maintain the mononuclear catalytic pathway. Schematic synthesis of P4 VP-Ru polymer-metal complex is shown in Figure 5b. Ru-PVP complexes can be further enhanced by immobilization on carbon nanotubes for biomass conversion [111]. The catalyst showed selective aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF). The functionalization process begins with the covalent grafting of PVP onto carbon nanotubes, which provides a robust matrix for immobilizing Ru(III) ions. The nitrogen atoms in the pyridine rings of PVP coordinate with Ru(III), creating a stable and active catalytic site. The coordination between Ru(III) and PVP allows the catalyst to operate effectively in an aqueous medium with molecular oxygen (O\({}_{2}\)) as the oxidant. This approach avoids the need for harsh chemicals or additional oxidants, making the process more environmentally friendly. The catalytic system demonstrated outstanding performance in the selective oxidation of HMF to DFF, achieving a yield of 94% under optimal conditions (at 100 \({}^{\circ}\)C and a reaction time of 6 h). The Ru-VVP/CNT catalyst (Figure 5c) demonstrates not only high catalytic efficiency but also selectivity toward DFF, minimizing side reactions and unwanted byproducts. Additionally, there are many reports highlighting copper-P4 VP metal complexes with applications for catalysis. [PERSON] and coworkers [112] explore the catalytic application of coordination complexes formed between dichlorcopper(II) and P4 VP in a divinylbenzene matrix. P4 VP-Cu complexes demonstrate catalytic activity in two significant reactions: the water-gas shift reaction (WGSR) and the reduction of nitrobenzene. In the WGSR, the Cu/P4 VP complex facilitates the conversion of carbon monoxide and water into hydrogen and carbon dioxide. The nitrogen functionalities in P4 VP enhance copper's stability and catalytic efficacy in this reaction, making it comparable to traditional copper catalysts. Furthermore, in the reduction of nitrobenzene, the Cu/P4 VP catalyst selectively converts nitrobenzene to aniline and, to a minor extent, azobenzene. Both reactions benefit from the coordination of copper with P4 VP, which supports the copper species' stability and catalytic performance under different conditions. Figure 5d presents two proposed structures for the fresh Cu(II)/P4 VP catalyst: one with two pyridine ligands coordinated to copper and another with three pyridine ligands. However, based on EPR and XPS results, the structure with three pyridine ligands coordinated to copper is more likely predominant. PVP-metal catalyst complexes have found applications in biomedical fields as well. [PERSON] et al. [113]. present a highly sensitive glucose sensor that utilizes an Electrolyte Metal-Oxide-Semiconductor Field-Effect Transistor (EMOSFET) to measure glucose concentrations through potentiometric methods (Figure 5e). The sensor's design includes a gate structure with glucose oxidase (GOD) immobilized within a bovine serum albumin (BSA) matrix using glutaraldehyde, layered on top of an electroactive osmium bipyridine poly(vinylpyridine) (Os-PVP) polymer that contains horseradish peroxidase (HRP). This innovative multi-layer system serves as the gate material for the FET, allowing it to detect glucose by measuring the work function changes of the electroactive gate material, which is influenced by the redox reaction involving hydrogen peroxide generated during the enzymatic reaction between glucose and glucose oxidase. The operating principle of the sensor is based on the detection of hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) as a byproduct of the glucose-glucose oxidase reaction.