Latest Research on Metal Complexes : Feb 2022

New metal complexes as potential therapeutics

The many activities of metal ions in biology have stimulated the development of metal-based therapeutics. Cisplatin, as one of the leading metal-based drugs, is widely used in treatment of cancer, being especially effective against genitourinary tumors such as testicular. Significant side effects and drug resistance, however, have limited its clinical applications. Biological carriers conjugated to cisplatin analogs have improved specificity for tumor tissue, thereby reducing side effects and drug resistance. Platinum complexes with distinctively different DNA binding modes from that of cisplatin also exhibit promising pharmacological properties. Ruthenium and gold complexes with antitumor activity have also evolved. Other metal-based chemotherapeutic compounds have been investigated for potential medicinal applications, including superoxide dismutase mimics and metal-based NO donors/scavengers. These compounds have the potential to modulate the biological properties of superoxide anion and nitric oxide.[1]


Metal Complexes as DNA Intercalators

DNA has a strong affinity for many heterocyclic aromatic dyes, such as acridine and its derivatives. Lerman in 1961 first proposed intercalation as the source of this affinity, and this mode of DNA binding has since attracted considerable research scrutiny. Organic intercalators can inhibit nucleic acid synthesis in vivo, and they are now common anticancer drugs in clinical therapy.

The covalent attachment of organic intercalators to transition metal coordination complexes, yielding metallointercalators, can lead to novel DNA interactions that influence biological activity. Metal complexes with σ-bonded aromatic side arms can act as dual-function complexes: they bind to DNA both by metal coordination and through intercalation of the attached aromatic ligand. These aromatic side arms introduce new modes of DNA binding, involving mutual interactions of functional groups held in close proximity. The biological activity of both cis- and trans-diamine PtII complexes is dramatically enhanced by the addition of σ-bonded intercalators. .[2]


Borabenzene Metal Complexes

This chapter discusses borabenzene–metal complexes. This cation was the first compound derived from the hypothetical borabenzene 2 and the first complex of a classical boroncarbon ligand. The nomenclature of boron compounds involves some intricacies. International Union of Pure and Applied Chemistry (IUPAC) rules allow the terms borabenzene or borinine for 2; the older name borin has become obsolete with the recent revision of the extended. The early 1960s saw a broad and intense interest in the making of the heretofore unknown molecular compounds with a boron–metal bond. All borabenzene–metal complexes investigated structurally so far show very similar patterns for the ligand geometry and for the metal–ligand bonding; only the cobalt complex 6 deserves separate consideration. The bonding situation in borabenzene–metal complexes has been treated by several authors and with varying methods and intentions. Borabenzene complexes show ‘H-nuclear magnetic resonance (NMR) spectra of the ABB’CC’ type. Electrochemical methods have been used for studying the redox properties of (boratabenzene) metal complexes. Borabenzene-metal complexes, just as their cyclopentadienyl counterparts, are not readily amenable to breaking of the metal–ligand bond. In contrast to the highly reactive organoboranes, borabenzene-metal complexes are surprisingly inert toward nucleophiles. Substitution of a boron-bonded group in a sandwich-type complex has first been observed in 1971 for cobalt complexes. Organocobalt complexes catalyze the cyclocotrimerization of acetylenes and nitriles, which affords pyridine and benzene derivatives.[3]

Investigation of Novel Tetrahalometallate Complexes of Cetrimonium Bromide Surfactant against in vitro Human Tumour Cell Lines of Lung, Colon and Liver

The synthesis of the tetrahalo Cu(II) and tetrahalo Zn(II) metal complexes with two cetrimonium bromide (CTAB) ligands is reported. Potentiometric studies showed that these complexes in aqueous solution showed no metal release, thus accounting for their high in vitro toxicity against three human cancer cell lines: A-549 (non-small cell lung carcinoma), HCT-116 (colon carcinoma cells), and HepG-2 (Hepatocellular carcinoma cells). The tetrahalo Cu(II) and Zn(II) metal complexes were synthesized by solid state grinding. Metal complexes of chelating CTAB with metal ion were studied on the basis of FT-IR, 1H-NMR and atomic absorption spectroscopic data. The tetrahalo Cu(II) and Zn(II) metal complexes induced cancer cell apoptosis. The tetrahalo complex of Cu(II) or Zn(II) inhibited in vitro the growth of three tumor cell lines at low concentrations. The tetrahalo copper(II) complex displayed against A-549 (non-small cell lung carcinoma) human cancer cell lines, IC50 values in mM range was similar to that of the antitumor drug cis-platin and they are considered for further stages of in vitro screening as potential antitumor activity.[4]


Whole Cell-based Biosensors for Environmental Heavy Metals Detection

Biosensors have emerged as new alternatives in environmental toxicity assessment. In the development of biosensors for heavy metals detection in environment, whole cells are highly favored as these cells are able to reflect the real toxicity effects of heavy metals to living organisms. For heavy metals detection, the integration of several types of cells such as bacteria, cyanobacteria, and algae into biosensors development has been widely reported. The usage of other cells such as plant cell, protozoa, and yeast has been reported as well. Although these biosensors are highly sensitive to heavy metals, the detection is still limited to the heavy metals which are bioavailable to the cells. Besides, the response of whole cells to wide range of heavy metals makes them excellent tools for wide spectrum screening but lack of specificity in detection. Whole cells are living entities with complex biochemical processes, which make the optimization of whole cell-based biosensors a tedious process, while maintaining the stability and storability are still challenging tasks. Although naturally occurring cells are highly favored, some reports show that recombinant cells can be a choice with better performance. In this paper, the usage of whole cells in biosensors for heavy metals detection and some of the current issues which are tied to the development of these biosensors are reviewed.[5]Reference

[1] Zhang, C.X. and Lippard, S.J., 2003. New metal complexes as potential therapeutics. Current opinion in chemical biology, 7(4), pp.481-489.

[2] Liu, H.K. and Sadler, P.J., 2011. Metal complexes as DNA intercalators. Accounts of Chemical Research, 44(5), pp.349-359.

[3] Herberich, G.E. and Ohst, H., 1986. Borabenzene metal complexes. In Advances in organometallic chemistry (Vol. 25, pp. 199-236). Academic Press.

[4] Ahmed, H.E.S.A., Zuky, M.F. and Badawi, A.M., 2017. Investigation of Novel Tetrahalometallate Complexes of Cetrimonium Bromide Surfactant against in vitro Human Tumour Cell Lines of Lung, Colon and Liver. Annual Research & Review in Biology, pp.1-9.

[5] Teo, S.C. and Wong, L.S., 2014. Whole cell-based biosensors for environmental heavy metals detection. Annual Research & Review in Biology, pp.2663-2674.

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