Complexes of Co, Ni and Cu with maleic acid as ligand were synthesized using reported procedure and

characterized using UV spectrometry. The purity of the complexes was monitored and analyzed using

solubility, melting point test and the complexes were evaluated for anti-oxidant activities against 1,1-diphenyl-

2-picrylhydraxyl(DPPH) free radicals. All the complexes are of good yield, they are of different colors,

partially soluble in organic solvent and soluble in DMF. The result was analyzed and presented as mean± SEM.

The complex of Co, Ni and Cu at the concentration of 100ug/ml, 50ug/ml, 25ug/ml and 12.5ug/ml respectively

shows less scavenging activity compared to the standard (vitamin C) at all concentration. The EC

shows that all the complexes have less activity compared to the standard (Vit C.) but still showing notable

antioxidant capacity. On the bases of the above studies, an octahedral has been proposed for the complexes.

diseases, and diabetes mellitus (Halliwell & Gutteridge, 2015; Valko et al., 2007). Antioxidants are agents

capable of neutralizing these free radicals, thereby preventing or reducing the damage they cause. The need for

effective and safe antioxidants has prompted the exploration of various chemical compounds, including metal-

based complexes.

Coordination compounds, especially those involving transition metals, have attracted attention in

pharmaceutical and medicinal chemistry due to their structural diversity, redox potential, and ability to interact

with biological targets (Beraldo & Gambino, 2004; Chitrapriya & Joseph, 2014). Metal complexation often

enhances the biological activity of organic ligands, including their antioxidant capacity, by altering electron

distribution and enabling redox cycling (Abu-Dief & Mohamed, 2015). Among first-row transition metals,

cobalt (Co), nickel (Ni), and copper (Cu) form stable complexes with diverse ligands and exhibit a range of

or antioxidant properties (Turan et al., 2016).

In this study, we synthesized and characterized Co(II), Ni(II), and Cu(II) complexes of maleic acid and

evaluated their antioxidant activity using the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assay.

The DPPH method is widely used for assessing antioxidant potential due to its simplicity, sensitivity, and

reproducibility (Noipa et al., 2011). We hypothesize that metal coordination will enhance the antioxidant

activity of maleic acid by stabilizing its radical form and facilitating hydrogen donation.

Electron impairment makes metal complexes magnetic. Unpaired electrons occur when considering only

nonmetal complexes, either because electron pairing is unstable or because the complex contains an odd

means of adjusting the ground state properties. Some methods verifying the presence of complex ions include

studying it chemical behavior. This can be achieved by observing the compound's color, solubility, melting

point, absorption spectrum, magnetic properties etc. The characteristics of individual atoms are distinct from

those of complex compounds. Coordination compounds change the characteristics of the metal and the ligand

(Martell & Calvin, 1952).

The term "ligand" refers to the ions or molecules that surround the center atom. Ligands are referred to as

coordinated to the atom when they are typically joined to it by a coordinate covalent connection, which

donates electrons from an ion pair into an empty metal orbital. There are also organic ligands such as alkenes

The coordination number, or the number of ligands attached to the metal (more precisely, the number of donor

atoms), is the first characteristic of a structure in coordination chemistry. Usually, the number of ligands

attached can be counted, but occasionally even this becomes unclear. Although a coordination number of two

to nine is typical, lanthanide and actinide compounds can have a considerable number of ligands. Metal ions

may have more than one coordinate number. Typically, the chemistry of transitional and metal complexes is

dominated by interaction between s and p molecular orbital of the ligands and the d-orbital of the ion. The s, p,

and d-orbital of the metal can accommodate 18 elections. The maximum coordination number for a certain

metal to the electron configuration of the metal ions and to the ratio of the size of ligand and the metal

ions .Large metals and small ligands lead to high coordination number, example [ Mo(CN)

small metal

Pentagonal bipyrimidal (seven-coordination), Octahedral (six-coordination), Tetrahedral (four-coordination),

Trigonal (three-coordination), and Linear (for two-coordination) (Khaled et al., 2014).

Almost every area of industrial chemistry uses fumaric acid (FA) and maleic acid (MA), two crucial chemical

intermediates. An essential raw material for the production of surface coatings, copolymers, lubricant additives,

unsaturated polyester resins, plasticizers, and agricultural chemicals is maleic acid (Klaus, 2008).

Maleic acid is a dicarboxylic acid that occurs in nature as L-malic acid. Another optically active isomer is D-

malic acid which can be synthesized as the racemic mixture of D L-malic acid. Malic acid is commonly

of malic acid include acerola (Malpighiae marginata), alfalfa (Medicago sativa), angelica (Angelica

archangelica), blackhaw (Viburnum prunifolium), blood root (Sanguinaria Canadensis), cherries and others

tone fruit (Prunus spp.), cranberries (Vacciniumma crocarpon), horsetail (Equisetu marvense), jujube (Ziziphus

Biological production of L-malic acid from bacteria, including Lactobacillus L-malic acid is produced by the

fermentation of fumaric acid. Fumaric acid can be produced by the fermentation from glucose. Yeast (Aureo

basidium pullulans) can also be used to produce L-malic acid by fermentation (Zou et al., 2013). DL-Malic

acid can be commercially produced by several different synthetic processes. Most involve either maleic

anhydride or fumaric acid hydrated at high temperatures (Felthouse et al., 2000). Maleic anhydride is

converted to maleic acid, which in turn is converted to malic acid. Another process involves the mixing of

maleic acid, fumaric acid, and sodium hydrogen maleate in an aqueous solution (Ramsey and Schultz, 1993).

Foods and drinks include malic acid as an ingredient. Because little children lack the ability to metabolize D-

form, the use of the less common D-recemic forms in infant meals is restricted. It functions as a chelating and

buffering agent (Merck, 2015).

free ligands. Furthermore, the complexes may have bioactivities that the free ligand does not. Binding to a

metal ion in vivo or using the metal complex as a carrier to activate the ligand as the cytotoxic agent are two

possible mechanisms of action. Additionally, coordination could result in a notable decrease in medication

resistance (Beraldo et al., 2004).

In biological fluids, the metal ions exist in non-exchangeable form as metalloproteins or loosely bound to some

biological ligands as in metal-activated proteins. The loosely bound metal ions are in equilibrium with similar

metal ions present in the bio-fluids. These simultaneous equilibria involving a variety of metal ions and ligands

are important in biological fluids (May et al., 1977). Hence, the chemical speciation of ligands with metal ions

has been studied in this laborator. (Ramanaiah et al 2013). Maleic acid is a dicarboxylic acid. It is the cis

isomer of butenedioic acid, whereas fumaric acid is the trans isomer. It is soluble in water and moderately

behavior of protein residues with the metal ions and helpful to understand the interaction with other ligands

commonly exist in biological fluids. Chemical specification of metals is important for the understanding of

their distribution, mobility, bioavailability, toxicity, and for setting environmental quality standards.

Bioavailability of a particular metal depends on its complex chemical reactions of dissolution, binding, and

complexation with the constituents of the environmental aquatic media. Studies have been done on the

consumption of these foods has been suggested as a crucial part of a balanced diet for lowering risks and

preventing diseases (Genkinger et al., 2004). This is also true of white button mushrooms (Agaricus

busporum), which are used as functional foods and medicines in addition to being used as food because of

their high protein and mineral content and low levels of starch and cholesterol. It is also thought to be a

significant source of a number of antioxidant compounds, including ascorbic acid, carotenoids, flavonoids,

tocopherols, and phenol (Wani et al., 2010). Although button mushroom is reported to possess considerably

higher levels of antioxidant properties, from the point of view of post-harvest physiology, mushroom is one of

the most sensitive agricultural crops after harvesting and these antioxidant properties of button mushroom tend

to decrease during post-harvest storage with the passage of time (Jahangir et al., 2011). In order to increase

metal solubilization, there has been a greater focus on the generation of organic acids by plant-associated

microorganisms, such as oxalic acid, maleic acid, tartaric acid, succinic acid, and formic acid (Mahmud et al.,

2017).

In Brassica juncea plants under Cr stress, maleic acid (MA) increased the amount of non-enzymatic

other transition metal ions. This is mainly due to the fact that, for the d

ion, ligand stabilization energies

disfavour the tetrahedral configuration relative to the octahedral one to a smaller extent than for any other

configuration. Magnetic moment values for the high spin octahedral complexes lie between 4.7 and 5.2 BM.

Because of the intrinsic orbital angular momentum in the octahedral ground state, there is considerable orbital

contribution to the magnetic moment (Karthikyan, 1992). Low spin cobalt (II) octahedral complexes are rare.

either trigonal bipyramidal or square pyramidal structures. The strength of the ligand field, which determines

the magnitude of the splitting, is important in determining the spin state (Lee, 2009).

Cobalt (II) has a d

configuration and the ground state configuration in an octahedral ligand field is t

weak field or t

g

eg

in strong field. Octahedral coordinated cobalt (II) should have three spin-allowed d-d

transitions. The visible absorption spectra of cobalt (III) complexes consist of transitions from A

g ground

state to other singlet states. It is possible to observe spin-allowed, d-d bands in the visible region of the spectra

of low-spin. Thus, the strong field ligands that do not cause the low-energy charge-transfer bands, often dictate

the spectra of low-spin complexes. Consequently, the two absorption bands found in the visible spectra of

regular octahedral cobalt (II) complexes represent transition to the upper states T

g and T

g i.e. A

A

g (Karthikyan, 1992).

higher concentrations are dangerous. In certain enzymes, cobalt plays a crucial biological role. One cobalt

Nickel has a silvery shine and is a bright white metal. It has a density of 8.91 g/cm3 and melts at 1455 oC.

Nickel has oxidation states of +2 and +3. Nickel (II) forms a large number of complexes encompassing

[Ni(CN)

]

is an example of 5-coordinate, and exists as a trigonal bipyramidal. Some of the 4-coordinates are