Recent Developments in the Electron Transfer Reactions and Their Kinetic Studies

Abstract

Electron transfer (ET) occurs when an electron moves from one atom or molecule to another. It’s the basis of chemical kinetics, which deals with the rates of chemical reactions and their mechanisms. It investigates how various factors and experimental conditions impact reaction rates. Chemical kinetics plays a pivotal role in industrial and biological processes, particularly in organic synthesis and manufacturing. The central role of redox reactions in both natural and industrial contexts. It elucidates how redox reactions drive energy generation, corrosion, metabolism, and a wide array of chemical transformations involving electron transfers between substances. Furthermore, electron transfer reactions, emphasize their significance in chemical and biological systems. It distinguishes between inner-sphere and outer-sphere mechanisms, offering examples of their relevance in various chemical reactions. Understanding and controlling electron transfer processes holds profound implications across various fields, from solid-state electronics to molecular electronics. It highlights the importance of these reactions in unraveling reaction mechanisms and advancing various research disciplines. Chemical kinetics, redox reactions, and electron transfer processes are fundamental concepts with extensive applications in scientific disciplines and industries, propelling innovation and advancement in chemistry and beyond.

1. Introduction

Chemical kinetics, also known as reaction kinetics, is one of the branch of physical inorganic chemistry that studies the rates of chemical reactions and it processes [1, 2, 3]. It includes investigations of how different factors or experimental conditions can have effects on the rates of chemical reaction and gives information on the reaction’s mechanism and transition states, as well as the production of exact models that can describe the characteristics of a chemical reaction [4, 5]. Kinetics is subdivided into physical kinetics, dealing with physical phenomena, and chemical kinetics which deals with the rate of chemical reactions [1]. The reaction rate is simply a change in a measurable quantity separated by the change in time [6], and is of great importance in industrial and biological processes, especially in determining optimum reactions as in organic synthesis and chemical manufacturing [7]. Scientists apply kinetic studies to hypothesize theories that imitate natural occurrences, determine the speed the product will be formed, and estimate the equilibrium composition of reaction mixtures using thermodynamics parameters [8]. The economic viability of many industrial processes is largely affected by the rate at which the reaction can occur at a rate carefully controlled by the complex catalysts called enzymes. Life would have been impossible without the rates of countless, complicated chemical processes being controlled with exceptional precision by finely formed enzymes [9]. The kinetic processes in living and chemical industries are essentially redox reactions involving one or more electrons transfer between any two chemical entities [10]. In a chemical reaction, the various factors that affecting reaction rate, including temperature, concentration of reactants, surface area, catalysts, and the presence of inhibitors.

Chemical kinetics has several practical applications in various fields which include the uncover the step-by-step sequence of elementary reactions that constitute an overall chemical reaction. This information is crucial for understanding of how reactions occur at the molecular level and for designing strategies to control reaction pathways. It allows scientists to determine the rates at which reactions occur and to optimizing reaction conditions in various processes, such as combustion processes [11], and industrial manufacturing, to achieve the desired reaction rate. Through kinetics studies, one can understand the factors that affect reaction rates (temperature, concentration, catalysts, etc.). Chemical kinetics helps to optimize reaction conditions to achieve higher yields and reduced reaction times in industrial processes by the used of catalyst. Catalyst are substances that increase the rate of chemical reaction without been consumed. The kinetics provides insights into how catalysts work and how they affect reaction rates, enabling the design of more efficient catalysts for various applications, such as in petroleum refining, pharmaceuticals, and environmental protection. Chemical kinetics is crucial in pharmaceutical research to study the rates at which drugs react in the body. This information helps determine dosing regimens and predict how quickly a drug will be metabolized or eliminated. Understanding the kinetics of chemical reactions that occur in the environment, such as atmospheric reactions involving pollutants, helps in predicting their behavior, degradation rates, and impact on air and water quality. In nuclear chemistry, chemical kinetics is used to understand the rates of nuclear reactions, such as radioactive decay and fission, which have applications in energy production and medical imaging. The kinetic processes in living and chemical industries are essentially a redox reactions [10].

2. Redox reactions

Redox reaction, short for reduction-oxidation reaction, is a type of chemical reaction in which electrons are transferred between distinct chemical species. In these reactions, one reactant is reduced (gains electrons), while another reactant is oxidized (loses electrons) [5, 12]. The word oxidation has been defined in many ways. The most prominent definitions, however, refer to the addition of oxygen, removal of hydrogen, or transfer of electron(s), of which the last one is the most favored one at present time [13]. The species that donates electrons to another substance during a chemical reaction is referred to as the reducing agent because it causes the reduction of another species by giving up its electrons. On the other hand, the species that accepts or gains electrons from another substance during chemical reaction is called the oxidizing agent as it causes the oxidation of another species by accepting the electron. Many redox reactions have been drawing attention of chemists throughout the world. They have been widely acclaimed to be very important as they play a key role in several natural processes [14]. A wide range of experimental methods has also been used to study the redox reactions, these methods include continuous-flow, accelerated flow methods, stopped flow methods, relaxation methods and line broadening in (nuclear magnetic resonance) NMR and (electronic spin resonance) ESR spectra methods for the study of fast reactions [15].

The continuous-flow NMR/ESR involves the continuous flow of reactants through the spectrometer for real-time reaction monitoring, ideal for fast reactions and kinetic analysis. Accelerated flow methods rapidly mix reactants before injection into the spectrometer, enabling quick data acquisition, particularly beneficial for short-lived fast reactions. Stopped flow methods swiftly mix reactants and halt flow to capture NMR or ESR spectra at different time points, facilitating high-resolution kinetic data collection, especially in the early reaction stages. Relaxation methods measure the time taken for nuclear or electronic spins to return to their equilibrium state, offering insights into reaction rates and mechanisms for fast reactions. Line broadening, observed as signal broadening in NMR and ESR spectra, indicates rapid motion or exchange processes during fast reactions, aiding the analysis of reaction kinetics and molecular interactions. These techniques are crucial for gaining valuable insights into fast chemical reactions via NMR and ESR spectroscopy [11, 16, 17].

Redox reactions play pivotal roles in both natural and industrial processes. They are essential for energy production, corrosion, metabolism, and various chemical reactions involving electron transfer between substances. To balance redox reactions, half-reactions are employed, segregating reduction and oxidation processes. This approach ensures the preservation of mass and charge during reactions [18]. Notably, redox reactions form the foundation of batteries, powering energy production and storage. They facilitate electron transfers among materials, generating electrical energy in alkaline batteries, lead-acid batteries, and lithium-ion batteries. Fuel cells also leverage redox reactions to convert chemical energy into electricity. For instance, hydrogen fuel cells oxidize hydrogen and reduce oxygen to create electricity. In the context of metabolism, redox reactions are central to cellular respiration, where cells convert glucose and oxygen into energy (ATP), yielding carbon dioxide and water as byproducts. Furthermore, in photosynthesis, plants and photosynthetic organisms employ redox reactions to transform light energy into chemical energy stored in glucose and other carbohydrates. In the realm of organic chemistry, redox reactions drive chemical synthesis, introducing functional groups and altering molecule oxidation states. For instance, alcohols can be oxidized to aldehydes or ketones, aiding organic transformations such as alkene reduction via catalytic hydrogenation or alcohol oxidation to aldehydes and ketones using oxidizing agents like chromic acid [19, 20].

Corrosion and rust prevention involve redox reactions, particularly in metal corrosion where metals undergo oxidation in the presence of oxygen and moisture. Countermeasures like galvanization or sacrificial anodes are employed. In galvanization, a more reactive metal is intentionally oxidized to shield the primary metal from corrosion. In water treatment, redox reactions are pivotal for disinfection. Chlorine-based compounds introduce redox reactions to eliminate harmful microorganisms. Water treatment processes now incorporate redox filters containing materials that promote redox reactions to eliminate contaminants. Environmental protection benefits from redox reactions too, particularly in bioremediation, where microorganisms deploy these reactions to degrade pollutants [21]. Similarly, redox reactions are central to the nitrogen cycle in ecosystems, as bacteria convert nitrogen between various oxidation states. In industries, redox reactions drive processes like electroplating and metal extraction from ores, such as iron extraction from iron oxide (hematite).

Recent research into electron transfer focuses on unveiling intricate mechanisms governing rapid electron movement in diverse systems. Cutting-edge techniques like ultrafast spectroscopy and advanced computation reveal electron transfer pathways, intermediate states, and quantum coherence effects [22]. Enzyme-catalyzed electron transfers, crucial in biological processes, are being comprehended at atomic scales. Moreover, charge transfer kinetics are harnessed in organic electronics to boost device efficiency. Studies in nanomaterials explore electron transfer for energy conversion and storage, aiming to enhance solar cells and batteries. In the catalysis domain, complex electron transfer steps in synthetic pathways are tapped for sustainable and selective chemical transformations. This breadth of electron transfer research enhances fundamental understanding and inspires applications in biology, materials science, and energy technologies [23].

In a recent development [18], demonstrated that benchtop 1H NMR possesses ample spectral resolution, temporal resolution, and sensitivity for operando monitoring of redox flow batteries (RFBs) at frequencies as low as 43 MHz. Although the flow rate is capped at 4 ml/min due to the modest sampling volume of 628 L, this suffices for many flow electrochemistry systems. For situations requiring higher flow rates during operando reaction monitoring, the authors suggest employing a flow cell with a larger detection volume or adopting a split-flow system. Furthermore, [24] envisage a broad spectrum of applications for operando benchtop NMR techniques in flow electrochemistry. This extends beyond redox flow batteries to encompass realms like carbon dioxide capture and utilization, ammonia synthesis, water desalination, and organoelectrochemical synthesis.

2.1 Electron transfer reactions

Electron transfer (ET) is a fundamental process in chemical and biological systems that occurs within and between different types of molecular species as well as protein molecules that serve as scaffolding for various redox centres (such as metal ions, porphyrins, flavins, quinones, and so on) [24]. It is one of the simplest chemical processes, yet it has a significant impact on chemical reactivity by inverting normal electron densities in an electron donor-acceptor pair, thereby activating previously inaccessible reaction modes. Because photosynthesis is the source of most energy and all life on Earth, our basic survival is dependent on this fundamental process. It is scarcely remarkable, then, that evidence of electron transfer activation may be found in almost every branch of research. To understand the nature of a redox reaction’s process, it is important to determine whether an atom, group, or electron transfer occurred, which atoms or electrons were transferred, and what the transition states of all stages were. $A=\pi r^2$measurements can help you get this information [25]. An oxidant accepting one electron is comparable to accepting a hydrogen atom, while accepting two electrons is equivalent to accepting a hydride ion. Most redox reactions can be divided into two types: direct electron transfer reactions and atom, group, or ion transfer processes [26] scheme was followed. Depending on the number of electrons exchanged during oxidation, electron transfer processes can be classed as one or two equivalents. Oxidants such as Mn(III), Ce(IV), Fe(III), Cu(III), Ag(II), Co(III), Ni(III), and others are one-equivalent oxidants, whereas Pb(IV), Ru(III), Ag(III), IO₄⁻, Cl₂, N-halo compounds, hypohalous acids, peroxide-anions, and others are two-equivalent oxidants. Some oxidants, such as Mn(VII), Cr(VI), Pt(IV), Tl(III), V(V), and others, behave as both one and two equivalent oxidants depending on the environment. Cr(VI) and Mn(VII) behaved as three and four-electron oxidants in some circumstances based on the products that were created [18]. According to the following chemical mechanism, one-equivalent oxidants tend to convert sulfite to dithionate and hydrazine to ammonia and nitrogen (Eqs. (1)–(3)) [26].

$$M{n}^{+}+S{O}_3\to M{n}^{\left(n-1\right)}+S{O}_3$$E1

$$2S{O}_3\to S_3{O}_6\left(\text{dithionate}\right)$$E2

$$M{n}^{+}+N_2{H}_4\to M{n}^{\left(n-1\right)}+N_2{H}_{3}S+H^{+}$$E3

The two equivalent oxidants have been found to react in the following manner (Eqs. (4) and (5))

$$M{n}^{+}+S{O}_3\to M{n}^{\left(n-2\right)+}+S{O}_3$$E4

$$S{O}_3+H_{2}O\to {\mathit{SO}}_4+2H^{+}$$E5

Since the late 1940s, the field of ET processes has grown enormously, both in chemistry and biology. The development of the field, experimentally and theoretically, as well as its relation to the study of other kinds of chemical reactions, represents an intriguing history, one in which many parts have been brought together [27, 28], noted that early electron transfer investigations focused on ‘isotopic exchange reactions’ (self-exchange reactions) and later, ‘cross-reactions in aqueous solution. The usual self-exchange electron transfer reactions (so-called because other methods besides isotope exchange were later utilized to examine some of them) are simple in two ways [29].

1. The reaction products are identical to the reactants, one factor that normally influences the rate of a chemical reaction in a significant degree, namely the relative thermodynamic stability of the reactants and products, is eliminated, and

2. In simple ET reactions, no chemical bonds are destroyed or produced. Indeed, for these combined reasons, self-exchange reactions are the simplest class of reactions in chemistry. Observations arising directly from this simplicity were to have far-reaching implications, not just for the ET field, but also, to a lesser measure, for the study of other types of chemical reactions [30, 31, 32]. The development of new instruments, which allowed the investigation of the speeds of fast chemical processes, was a second element in the growing popularity of the electron transfer field [15]. Electron transfers are frequently very rapid when compared to many other reactions that involve the breaking of chemical bonds and the formation of new ones. As a result of the development of this equipment, the analysis of a huge body of rapid ET reactions became possible [33], pioneered the stopped-flow apparatus for inorganic electron transfer processes as an example of the former ones. It permitted the study of bimolecular reactions in solution in the millisecond time scale (a fast time scale at the time). Such studies led to the investigation of what has been termed electron transfer ‘cross reactions,’ i.e., ET reactions between two different redox systems (Eq. (6)) which supplemented the earlier studies of the self-exchange electron transfer reactions.

$${\mathit{Fe}}^{2+}+{\mathit{Ce}}^{4+}\to {\mathit{Fe}}^{4+}+{\mathit{Ce}}^{3+}$$E6

A comparative study of self-exchange and cross-reactions, prompted by theory, would subsequently have significant implications for the field and, indeed, for other areas. For more than 5 decades, researchers have been fascinated by the detailed mechanics of electron transfer between metal-ion complexes in solution [34, 35]. Systematic studies that emphasized the interaction of thermodynamics, electronic structure, stereochemistry, and kinetics of inorganic systems, particularly those involving transition metal complexes, did not appear in the literature until the early 1950s [36]. Electron transfer (ET) is one of the most vital chemical processes in nature and plays a key role in many living system, physical, and chemical (both organic and inorganic) systems [37]. Knowledge and control over electron transfer processes is one of the most diverse and active fields of physical research in chemistry today [38]. ET occurs in nature in the photosynthetic reaction centre, where electron transfer is used to produce adenosine triphosphate (ATP). In oxidative phosphorylation, the reduced form of nicotinamide adenine dinucleotide (NADH) releases electrons to dioxygen, forming water and a significant amount of excess energy which is used to produce ATP. ET at the metal surface by oxygen is responsible for corrosion in a chemical system [38]. The study and control of electron transfer in and between molecules is crucial in solid state electronics, which is based on the control of ET in semiconductors, and in the nascent field of molecular electronics [39].

2.2 Types of reactants in electron transfer reactions

Reactants in a chemical reaction can be described in terms of homonuclear and heteronuclear reaction. These types of reactants involved in a chemical reaction based on whether the atoms of the same elements or different elements are participating in the reaction.

2.3 Homonuclear or self-exchange electron transfers reactions

A homonuclear or self-exchange electron transfer reaction is a type of electron transfer reaction that takes place between two identical molecules or species. These reactions involve the transfer of electrons between chemical entities of the same type. Examples of self-exchange reactions are presented in Eqs. (7)-(10).

$$\mathrm{A}+A^{˟}\to A^{˟}+A$$E7

$$V^{2+}+V^{˟3+}\to V^{3+}+V{˟}^{2+}$$E8

$${\mathit{Fe}}^{2+}+{\mathit{Fe}}^{˟3+}\to {\mathit{Fe}}^{3+}+\mathit{Ve}{˟}^{2+}$$E9

$${\mathit{Ce}}^{3+}+{\mathit{Ce}}^{˟4+}\to {\mathit{Ce}}^{4+}+\mathit{Ce}{˟}^{3+}$$E10

2.4 Heteronuclear or cross-electron transfer reactions

Heteronuclear or cross-electron transfer reactions are chemical processes that involve the transfer of electrons within different kinds of atoms or elements. Examples of such electron transfer reactions are represented by Eqs. (11) and (12).

$${\left[\mathrm{Co}{\left(\mathrm{N}{H}_3\right)}_{5}X\right]}^{2+}+{\mathit{Cr}}^{2+}+H^{+}\to C{\mathit{rX}}^{2+}+5{{\mathit{NH}}_4}^{+}$$E11

$${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_3\right]}^{3+}+{\left[\mathrm{Ru}{\left(\mathrm{N}{H}_3\right)}_6\right]}^{2+}\to {\left[\mathrm{Co}{\left(\mathrm{en}\right)}_3\right]}^{2+}+{\left[\mathrm{Ru}{\left(\mathrm{N}{H}_3\right)}_6\right]}^{3+}$$E12

Over the years, the mechanisms of electron transfer reactions involving various organic or inorganic substrates have been generally grouped as either the inner sphere or the outer-sphere mechanism, although some other complex reactions operate by simultaneous inner and outer-sphere mechanisms [8]. In a simpler term, the redox reactions involving metal ions can also be classified based on whether the transfer of electrons involves an ionic sphere or coordination sphere of the metal ion as outer-sphere electron transfer and inner-sphere electron transfer reactions [13].

2.5 Inner-sphere electron transfer

An inner sphere reaction represents a distinct category within coordination reactions where coordination compounds or ligands play an active role in the reaction mechanism. In this type of reaction, the reductant and oxidant mutually share a ligand within their inner or primary coordination spheres (as illustrated in Eq. (13)). Coordination compounds are composed of central metal ions surrounded by coordinating ligands, forming molecules or ions. In the context of inner sphere, both the central metal ion and the ligands actively participate in the chemical transformation, often involving the exchange of atoms, electrons, or entire ligands. These reactions exhibit several notable characteristics, including the formation of a transition state, ligand substitution, electron transfer, and structural rearrangement (as discussed [40]). Taube has conducted comprehensive investigations into various theoretical aspects of electron transmission. His work has explored concepts such as electronic delocalization in mixed-valence molecules and the impact of organic ligands as bridging groups in electron transfer reactions (as described in Ref. [41]). Furthermore, Taube has presented empirical applications, including the direct utilization of the relationship between substitution rates and electronic structure for species like [Co(NH₃)₅Cl]²⁺ and [Cr(H₂O)₆]²⁺ (as represented in Eq. (13)), as well as providing detailed insights into the geometric aspects of oxidation-reduction mechanisms involving inner sphere electron transfer [42].

E13

From the formation of Cl⁻ in the inert Cr complex product, it was determined that when electron transfer occurs, both metal centres must have been linked simultaneously to Cl⁻ as the bridging ligand [43]. The structural impacts, function of the nuclear frequency factor, energetic and dynamic aspects of solvent reorganization in electron transfer reactions. Based on the preceding works, the following generalized mechanism for inner-sphere electron transfer reactions was developed:

1. Formation of the bridged (μ) complex-precursor complex formation

   $$M^{\mathit{II}}{L}_{5}X+{M^{\prime }}^{\mathit{II}}{L}_6^{\prime }\rightleftharpoons \underset{\text{Precusor complex}}{L_5{M}^{\mathit{II}}-X-{M^{\prime }}^{\mathit{II}}{L}_5+L}$$E14

2. Activation of precursor complex and electron transfer

   $$\underset{\text{Precursor complex}}{L_5{M}^{\mathit{II}}-X-{M^{\prime }}^{\mathit{III}}{L}_5^{\prime }}\rightleftharpoons \underset{\text{Successor complex}}{L_5{M}^{\mathit{III}}-X-{M^{\prime }}^{\mathit{III}}{L}_5^{\prime }}$$E15

3. Dissociation into separated products

   $$L_5{M}^{\mathit{III}}-X-{M^{\prime }}^{\mathit{II}}{L}_5^{\prime }\leftrightharpoons M^{\mathit{III}}{L}_5+{M^{\prime }}^{\mathit{II}}{L}_5^{\prime }X$$E16

2.6. Outer-sphere electron transfer

An outer sphere reaction refers to a specific type of chemical interaction in which two reactants engage without directly exchanging atoms, ions, or electrons. In simpler terms, during an outer sphere reaction, the reactants largely maintain their original structure throughout the process, and any electron transfer or chemical transformation takes place through an external pathway, devoid of direct interaction between the reactants [44, 45, 46, 47]. In contrast to inner sphere, where reactants directly interchange atoms, electrons, or ligands, outer sphere reactions involve reactants that do not establish chemical bonds with one another during the reaction. Instead, electron transfer occurs through a mediator, resulting in minimal changes in coordination [48]. Outer sphere reactions are frequently encountered in various chemical processes, notably in the realms of electrochemistry and redox reactions. In these scenarios, electron transfer can happen either through an external circuit or with the assistance of a mediator molecule. This enables the reactants to undergo oxidation and reduction processes without forming new chemical bonds with each other. Typical examples of this type is given in Eq. (17).

$${\left[\mathrm{Fe}{\left({\mathit{CN}}_3\right)}_6\right]}^{4-}+{\left[\mathit{Ir}{\left({\mathit{CN}}_3\right)}_6\right]}^{2-}\to {\left[\mathrm{Fe}{\left({\mathit{CN}}_3\right)}_6\right]}^{3-}+{\left[\mathit{Ir}{\left({\mathit{CN}}_3\right)}_6\right]}^{3-}$$E17

In outer-sphere electron transfer, one reactant becomes involved in the outer or second coordination sphere of the other reactant and an electron flows from the reductant to oxidant. Such a mechanism is established when rapid electron transfer occurs between two substitution-inert complexes.

Several transition-metal complexes have been used for studying outer-sphere electron transfer reactions [49]. Among them octahedral cobalt(III) complexes, substitutionaly inert, and are ideal for theoretical and experimental studies. Hammershøi et al. [50] studied the kinetics and mechanism of reduction of cobalt(III) complexes by FeCN64- through the outer-sphere electron transfer reaction. The oxidation of iron(II) and its substituted tris(1,10 phenanthroline) complexes also proceed through outer-sphere electron transfer reactions. Studied of the kinetics and mechanism of the reactions between the oxygen-bonded complexes 4-,3-, and 2-pyridinecarboxylatopentaamminecobalt(III) and aquopentacyanoferrate(II). Reduction reactions involving V(II), Cr(II) and electron-exchange reactions in ${\left[\mathrm{Fe}{\left({\mathit{CN}}_3\right)}_6\right]}^{4-}$/${\left[\mathrm{Fe}{\left({\mathit{CN}}_3\right)}_6\right]}^{3-}$ and${\left[\mathrm{Co}{\left(\mathrm{N}{H}_3\right)}_6\right]}^{2+}$/${\left[\mathrm{Co}{\left(\mathrm{N}{H}_3\right)}_6\right]}^{3+}$ systems were also shown to follow outer-sphere path [51, 52, 53]. The following general mechanism for such type of outer-sphere electron transfer reactions are presented (Eqs. (18)–(22)).

1. Collision of the donor with the acceptor to form the precursor complex

   $$D+A\to \left[D\parallel A\right]$$E18

2. Thermal activation of the precursor complex to reach non equilibrium optimized nuclear and electronic configuration for ET to occur.

   $$\left[D+A\right]\to {\left[D\parallel A\right]}^{‡}$$E19

3. Electron transfer

   $${\left[D\parallel A\right]}^{‡}\to {\left[D^{+}\parallel A^{-}\right]}^{‡}$$E20

4. Relaxation to the ground state of the successor complex

   $${\left[D^{+}\parallel A^{-}\right]}^{‡}\to \left[D^{+}{A}^{-}\right]$$E21

5. Dissociation to the free product ions

   $${\left[D^{+}\parallel A^{-}\right]}^{‡}\to D^{+}+A^{-}$$E22

where, ║denotes that no chemical bonds have been made or broken.

3. Applications/uses of chemical kinetics

Chemical kinetics, just as other field of study has various important applications in different fields by offering valuable insights into a range of processes. Firstly, it aids in comprehending reaction mechanisms by examining rate-determining steps and intermediates, enhancing our understanding of chemical reactions. In the realm of pharmaceuticals, it’s indispensable for analyzing drug reaction rates in the body, optimizing dosages, and improving drug delivery systems to minimize side effects.

Additionally, it finds applications in environmental studies, helping us grasp how pollutants degrade in the environment, vital for effective environmental management. In automotive and energy industries, it optimizes fuel combustion for enhanced efficiency and reduced emissions. In the chemical industry, it’s vital for designing efficient catalytic processes for chemical production.

In the food industry, it determines optimal conditions for preserving food quality while in materials science, it aids in studying polymerization, crystallization, and corrosion, contributing to the development of new materials.

Furthermore, in atmospheric chemistry, it elucidates atmospheric pollutant formation and degradation, as well as ozone depletion. In biology, it explores biochemical reactions, from enzyme kinetics to cellular processes, illuminating biological functions. Also, it underpins safety considerations by assessing substance stability and reactivity in industries dealing with hazardous materials.

4. Recent advances in chemical kinetics

There have been recent advancements in the field of kinetics across various domains. One notable area of progress is in ultrafast kinetics, which involves studying chemical reactions on extremely rapid timescales. Innovations in femtosecond spectroscopy and time-resolved X-ray scattering have enabled scientists to observe molecular processes at incredibly short intervals, offering fresh insights into reaction mechanisms [52, 53, 54]. These techniques allow for the observation and manipulation of molecular dynamics at the atomic level, providing access to reaction mechanisms and transition states that were previously inaccessible [55].

Furthermore, there have been significant developments in single-molecule kinetics. The ability to investigate individual molecules has revolutionized kinetics, with techniques such as single-molecule fluorescence spectroscopy and atomic force microscopy enabling real-time probing of individual molecule kinetics. This approach has provided a more detailed understanding of molecular processes and the heterogeneity within a system, shedding light on the diversity and randomness in chemical reactions [56].

In computational kinetics, the field has seen notable progress due to the increasing power of supercomputers and advancements in computational methods. Researchers can now model complex reaction networks and simulate reactions at the quantum level, aiding in the design of new catalysts and materials [57]. Computational methods like quantum mechanics/molecular mechanics (QM/MM) simulations and molecular dynamics (MD) simulations have expanded our understanding of reaction kinetics, allowing for predictions of reaction rates and mechanisms that complement experimental studies [58].

Additionally, there has been a growing interest in the study of non-equilibrium processes, particularly in living systems and extreme conditions. Researchers are exploring kinetics within the realm of non-equilibrium thermodynamics, which has implications in fields like biochemistry and materials [59].

Chemical kinetics has also advanced in the area of nanomaterials, with nanotechnology offering new possibilities for designing and controlling reaction kinetics at the nanoscale. The synthesis and examination of nanomaterials with customized properties have applications in catalysis, medicine, and electronics [60].

In the field of atmospheric chemistry, understanding the kinetics of atmospheric reactions is essential for assessing air quality and climate change. Advances in experimental techniques and atmospheric modeling have improved our comprehension of complex reaction networks in the atmosphere [61].

Enzyme engineering has made significant strides as well, with kinetics data being used to design more efficient and specific enzymes for industrial and biomedical purposes. Enhanced understanding of enzyme kinetics and catalytic mechanisms has facilitated the rational design of drugs targeting specific enzymes [62, 63, 64].

Moreover, in systems biology, researchers are employing mathematical models to describe and predict the dynamics of complex biological systems. By integrating experimental data with kinetic models, scientists can gain insights into cellular processes and simulate the behavior of biological networks.

Lastly, in the realm of green and sustainable kinetics, there have been efforts to promote environmentally friendly chemistry. Researchers are developing more efficient catalysts and reaction pathways to minimize waste, energy consumption, and environmental impact [65].

5. Conclusion

Chemical kinetics deals the speeds of chemical reactions and their underlying processes. This field delves into understanding how distinct factors or experimental conditions impact reaction rates, providing insights into reaction mechanisms, transition states, and precise models that characterize these reactions. The practical applications of chemical kinetics span various domains, notably revealing the stepwise sequence of elementary reactions comprising an overall chemical reaction. By furnishing essential insights into molecular-level reaction dynamics, kinetics aids in devising strategies to govern reaction pathways. This knowledge empowers scientists to ascertain reaction rates and optimize reaction conditions across diverse processes, encompassing combustion and industrial manufacturing, in order to achieve desired rates of reaction. The kinetic phenomena pervasive in biological and chemical industries are primarily redox reactions, which entail electron transfers between distinct chemical entities. These redox reactions are pivotal in natural phenomena and industrial processes, playing a foundational role in energy production, corrosion, metabolism, and various electron-transfer-involved chemical reactions. Recent research has extensively explored rapid electron movement within diverse systems, focusing on unraveling intricate mechanisms behind electron transfers. The integration of cutting-edge tools like Ultrafast spectroscopy and advanced computational techniques has unveiled electron transfer pathways, intermediate states, and quantum coherence effects. Even enzyme-catalyzed electron transfers, vital in biological processes, are now being comprehended at atomic scales. Moreover, operando benchtop nuclear magnetic resonance (NMR) methods find a broad spectrum of applications in flow electrochemistry, encompassing redox flow batteries and beyond. These applications extend to areas such as carbon dioxide capture and utilization, ammonia synthesis, water desalination, and organoelectrochemical synthesis. Other recent advances in chemical kinetics have are at the area of ultrafast reaction mechanisms at the molecular level which aided by advanced spectroscopy and computational tools. Redox reactions is crucial in energy storage and catalysis which have witnessed novel electrocatalysts and reaction pathways, enabling efficient energy conversion and environmental remediation. These developments hold promise for greener technologies and a deeper understanding of fundamental chemical processes.

Acknowledgments

I first of all thank Allah for granting me through this review study. I acknowledged with deep appreciation, the assistance and untiring effort of Mr. Ibrahim Wakil for his professional advice and guide during the work.

I wish to thank my father advisor Mr. Ali Alimu and my friend Sadiq Bello for their words of encouragement toward this work. My regards also goes to Mr. Babagana that guide me in one way or the other especially in the area of using of computer applications at the time of this review study.

Conflict of interest

There is no any conflict of interest.

Acronyms and abbreviations

ATP	adenosine triphosphate
ET	electron transfer
ESR	electron spin resonance
NMR	nuclear magnetic resonance
NADH	nicotinamide adenine dinucleotide
RFBs	redox flow batteries