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The worldwide interest in coral concrete stems from its use in reef engineering, where it is a composite material made by combining saltwater and coral. This analysis examines the components, mechanical characteristics, and durability of coral concrete. The micro hardness of the interfacial transition zone in coral concrete is significantly greater than that of normal concrete. However, it is found that the coral concrete has less compressive strength than standard concrete hence, the durability of standard concrete is also longer than this concrete. However, the addition of fibres to coral concrete improves the splitting tensile strength and flexural strength significantly. Inadequate cementation of the components hinders the performance of coral concrete because of the porous and brittle nature of coral aggregates. Further investigations can be carried out for underwater engineering applications and sea constructions by selecting appropriate coral aggregate type and developing mix design procedure to produce the high-strength coral concrete.

The tailoring of the coordination environment around a central metal ion by changing ligands in macrocyclic complexes is one of the key approaches to monitoring their functions in various applications. Herein, two macrocyclic complexes of Co(II) transition metal ion, tetra-aza and penta-aza, were synthesized using a condensation reaction between different diamine and dicarboxylic precursors. The prepared complexes were analyzed using various characterization techniques. Further, the electrochemical behavior of both the tetra-aza and penta-aza complexes was investigated using cyclic voltammetry. The Co(II)-penta-aza-complex exhibited a quasi-reversible redox couple for Co(III)/Co(II) transition in the more anodic region as compared to Co(II)-tetra-aza-complex. According to theoretical calculations, the fifth N-coordination transferred a high electron density in the eg-orbital of Co-atom of penta-aza-complex, resulting in an anodic shift in the Co(III)/Co(II) redox potential when compared to the Co(II)-tetra-aza-complex. Furthermore, both complexes were tested for antimicrobial activity against P. aeruginosa, E. coli, S. aureus, and B. subtilis, with the results indicating that Co(II)-penta-aza-complex had higher antimicrobial activity against these bacteria than Co(II)-tetra-aza-complex. This study offers new insight into tailoring the electrochemical and biological features of macrocyclic complexes by tuning the coordination environment around the central metal ion.

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