Metal Complexes: Environmental and Biomedical Applications

There are 90 elements on the earth’s crust. Among these, 81 are life supporting and the remaining 9 are radioactive in nature. The human body consists of nearly 3% of metals. Transition metals having partially filled d-subshell can easily accept and donate electrons and hence achieve variable oxidation state. These variable oxidation states enable the modulation of variable redox systems, which are available in biological systems. They can also interact with a wide range of negatively charged compounds. The aforementioned properties of transition metals have sparked the creation of metal-based drug development that holds great promise for medicinal use. Metal-based drugs (metallodrugs) are now used in theranostics, i.e., therapy and diagnosis. Metal-based drugs like oxaliplatin, carboplatin, and cisplatin are being used in the treatment of cancer. Moreover, transition metal-based drugs are also used to treat cardiovascular diseases, inflammation, rheumatoid arthritis, ulcer, diabetes etc. In this chapter, various oxidation states of transition metals of different series of the periodic table are briefly discussed, along with their application in the field of medical science.

The synthesis of transition metal complexes from N-heterocyclic carbene and Schiff base ligands is discussed in this chapter. A few basic characteristics of water-soluble, N-heterocyclic carbene-based complexes are also described. The increased hydrophilicity of these water-soluble metal complex-based catalysts improves their applicability. Though research based on carbon-carbon coupling reactions is dominating, recent studies demonstrate that water-soluble N-heterocyclic carbene-based complexes can be utilized in the hydrocyanation and metathesis reactions. Compounds formed by the condensation of active carbonyl compounds and primary amines are called Schiff bases. RR’C=NR” is the general structure of Schiff bases, where R”, R’ and R are hydroxyaryl, hydroxyalkyl, cyclohexyl, alkyl, etc. In this chapter, the synthesis of metal complexes from N-heterocyclic carbenes and the synthesis of Schiff base complexes by ligand exchange, metal exchange, amine exchange, coordinated secondary amine oxidation, in situ methods, and direct synthesis methods are described.

Many different applications for coordination compounds can be found in human life, as they possess numerous interesting properties. Metal complexes consist of a central metal atom or ion known as a coordination center and binding molecules or ions in the surrounding environment called ligands. Metal ions have special qualities that can be used in medicinal inorganic chemistry to create novel medications. Drugs containing metals are useful in many medical applications, such as diagnosis and treatment. Here, we have covered the uses of metal complexes, particularly those involving enclosed metal ions, or cage metal complexes, in the biochemical and medical industries.

The development of therapeutics based on metals has been accelerated owing to the advanced activities of metal ions and their effective role in the field of biology. Therapeutics refers to the branch of science that deals with the treatment of diseases and the action of remedial agents. Metals are vital cellular substances opted by surroundings for numerous activities in various fundamental biochemical functions in living beings. The application of metals and their derivatives for clinical purposes has been practiced for a long time. A well-known drug based on metal, cisplatin, is universally utilized for the treatment of cancer, which chiefly aims at the retardation of genitourinary tumors like testicular cancer. However, drug resistance and certain side effects have restricted the applications of this drug in the medical field. With growing developments in the sector of inorganic chemistry, transition metals play a crucial role as therapeutic agents. Inorganic chemists have enabled the development of numerous transition metal-based complexes linked with required organic ligands, which are applied as therapeutics. This chapter throws light on the drugs based on metal complexes and their applications as therapeutic agents.

This chapter summarizes some metal complexes that have been used in recent years to diagnose disease states. Gamma scintigraphy, positron emission tomography (PET), and magnetic resonance imaging (MRI) are discussed as diagnostic imaging modalities. With the three imaging modalities, metal complexes are used to image a variety of diseases, including heart disease, brain tumors, and cancer. It has been shown that many different radiometals can be used in the synthesis of coordination compounds for gamma scintigraphy and PET, and each of these will be discussed separately. Besides that, metal complex chemistry encompasses an extensive area of study that analyzes radiometals. The development of coordination compounds for MRI enhancement and radiopharmaceuticals, particularly those that have been used in vivo in the case of humans, are described. Essentially, this chapter aims to show that coordination chemistry has made significant progress toward the development of diagnostic imaging agents as a whole.

The globe is currently dealing with an energy crisis, which is very concerning. While energy accessibility and availability have a significant impact on human well-being, the world's dependence on alternative energy sources is growing as a result of the ongoing depletion of fossil fuels. Scientists are developing other sustainable energy sources so that we can meet future energy needs and live in a cleaner environment. In the natural environment, excitation energy transfer is the principal procedure for the light-harvesting procedure. In recent years, transition metal complexes have been used in many applications, such as electroluminescent materials, photoinduced energy transfer materials, energy storage materials, and organic photovoltaic materials. Additionally, these materials provide the potential to behave as carbon sinks, hence providing a chance for more storage materials that are sustainable. For years, the electrochemical behavior of transition metal complexes has been explored in devices that store energy, such as redox flow batteries, supercapacitor electrodes, sodium-ion batteries, and lithium-ion batteries. In this chapter, various transition metals and other metal complexes that are utilized as energy materials are highlighted.

Analytical chemistry is used to detect the analytes by using various analysis methods. Quantitative and qualitative analysis can be done using this approach. Coordination compounds play a key role in our environment. They are used in almost every branch of the biomedical field. An overview of the applications of metal complexes in analytical chemistry is provided. This topic covers different types of complexes and the ways they are used for analysis purposes. Some miscellaneous applications in analytical chemistry are also covered in this chapter. Moreover, different types of precipitants, volumetric reagents, indicators, and solvent extraction reagents are also included in this chapter.

For a long time, research based on versatile novel catalysis processes utilizing coordination compounds and transition metal ions has witnessed many significant discoveries and developments. This chapter presents new directions and themes for the development of coordination compound-based catalysts in the future. This fundamental field comprises both homogeneous and heterogeneous systems, including a variety of reactions. These types of catalysts exhibit the activation of saturated inert molecules like hydrogen and also involve a wide range of addition reactions like Ziegler-Natta type polymerization, acetylene hydration, carbonylation and annulation reaction, isomerization, hydrogen peroxide decomposition, hydrosilylation, allylic alkylation, hydrocyanation process, hydrogenation reaction, hydroformylation reaction, olefins catalytic oxidation, olefins hydrogenation, etc. The aim of this chapter is to discuss a few applications of catalysts based on transition metal compounds.

Metal ions have an extremely important role in preserving the longevity of living organisms. Humans can suffer from a variety of health issues when particular metal ions are deficient, including growth retardation from a zinc deficiency in the diet, pernicious anemia from an iron deficiency, and infantile heart disease from a copper deficiency. Antibiotic resistance is becoming more severe every day, posing a growing risk to public health. The creation of innovative medications with improved efficacy and new mechanisms of action is urgently needed in this situation. Inorganic compounds, specifically metal complexes, have a significant role in novel metal-based drug development. Owing to the inclination of the scientific community towards designing new metal complexes as diagnostic agents and drugs, a new branch of chemistry was developed, which is known as inorganic medicinal chemistry. In this chapter, metal complexes used as anti-fungal and anti-bacterial agents are discussed.

Luminescent molecular chemosensors are designed in a way that sensing arises due to the binding of the analytes to the receptors. Here, the analyte binds to the metal-based receptor as a ligand. Researchers all around the world have been working to build these chemosensors to detect various analytes. These are used in many different disciplines, including biology, physiology, chemistry, and environmental science.Following the receptor-analyte engagement, an intercomponent process such as energy transfer or electron transfer occurs, which specifically modifies luminophore release and signals the recognition event. Because of their low detection limit and ease of use, the fluorescence probes are recognized as performing unique detection methods. This chapter discusses metal complex sensors for cation and anion detection.