International Journal of Scientific & Engineering Research, Volume 5, Issue 9, September-2014 305 ISSN 2229-5518 Medicinal Industrial & Environmental Relevance of Metal Nitrosyl Complexes: A Review R. C. Maurya, J. M. Mir Abstract—This review sums up the necessary research upsurges that occurred since nitric oxide (NO) was declared as the signaling molecule in the cardio-vascular system and some recent trends in its study. Metal nitrosyl complexes are the mimicking biological models that exhibit the properties of nitric-oxide-synthase. Their roles in medicine, industry and environmental equilibrium are of immense importance. Besides these, their role in plant pathogenicity is recent research tool in botany. Cancer studies also reveal the nitric oxide, the median line to cancer disease. Index Terms— Metal nitrosyls, Nitric-oxide, Signaling molecule, Cancer, Plant pathogen, Water pollution, Air Pollution —————————— —————————— 1 INTRODUCTION etals play a vital role in an immense number of exten- first-row transition metal ions, with typically single occupa- Msively differing biological processes. Some of these pro- tion of at least some of their d-orbitals. For these elements, cesses are quite specific in their metal ion requirements, in that tuning the ligand field by the use of different ligands provides only certain metal ions in specified oxidation states can ac- a useful way of influencing structure, spin state and bond- complish the necessary catalytic structural requirement. Metal order. In essence, local structure about the metal plays an es- ion dependent processes are found throughout the life science sential role for catalytic mechanisms. and vary tremendously in their function and complexity. Res- One of the principal themes of bioinorganic chemistry piration, nitrogen fixation, photosynthesis, nerve transmission is the synthesis of metal complexes that have the ability to and muscle contraction are life-critical processes requiring mimic the functional properties of natural metalloproteins [2], metal ions [1]. IJSER[3]. Proteins, some vitamins and enzymes contain metal ions The role of a metal as structural component and as in their structure involving macromolecular ligands. The catalyst is broadly known. It is now appreciated that metal chemistry of metal complexes with multidentate ligands hav- ions control a vast range of processes in biology. Many new ing delocalized π-orbitals, such as Schiff bases or porphyrins and exciting developments in the field of biochemistry create has recently gained more attention because of their use as interest among inorganic chemists to court in the new area models in biological systems. From several studies of bioinor- called “Bioinorganic Chemistry”. Due to close-lying energy ganic systems, synthetic, structural, spectroscopic or computa- bands made up of partly filled d-orbitals, transition metal ions tional, principles have emerged that tie together seemingly have a rich chemistry and thus serve as unique agents in a unrelated facts. In this article, search for such facts is the pri- variety of biological processes. mary aim. The general interest in Molybdenum and Rutheni- ———————————————— um nitrosyl complexes stems partly from the fact that identical • Dr. R. C. Maurya is currently Prof & Head Department of Chemistry & or similar compounds have significant roles in biological med- Pharmacy R. D. University, Jabalpur M.P, India, PH-+917612600484. E- mail: [email protected] • J. M. Mir is currently pursuing Ph. D degree in Department of Chemistry & icine, industry and are environmentally relevant. The field of Pharmacy R. D. University, Jabalpur M.P, India. E-mail: [email protected] transition metal nitrosyls, referring to structural and bonding aspects, was termed a provocative subject by Enemark and In particular, this is the case for the middle and late Feltham [4] in their ground-breaking work from early 70ties. IJSER © 2014 http://www.ijser.org International Journal of Scientific & Engineering Research, Volume 5, Issue 9, September-2014 306 ISSN 2229-5518 Possibly less provocative today, the field is still of significant of blood pressure and vascular tone, inhibition of platelet ag- interest. gregation and leukocyte adhesion, and prevention of smooth Compounds containing the NO grouping(s) are usual- muscle cell proliferation. Reduced bioavailability of NO is ly referred to as nitrosyl compounds [5] when addendum is thought to be one of the central factors common to cardiovas- inorganic in nature and as nitroso compounds when adden- cular disease, although it is unclear whether this is a cause of, dum is organic in nature. Recently, there has been considera- or result of, endothelial dysfunction. Any disturbance in the ble upsurge in the study of coordination compounds contain- bioavailability of NO leads to a loss of cardio protective ac- ing coordinated NO grouping and the reactions of the nitrosyl tions and in some cases may even increase disease progression ligand. An impressive number of works have been published [23]. dealing with properties and applications of NO containing 1.1 NO Reactivity inside a Living System transition metal complexes [6-22, 57].This is due to potential NO is composed of an atom each of nitrogen and applicability of these compounds to be used in biomedical oxygen such that seven electrons from nitrogen and eight elec- science, in chemical industry as catalysts and as pollution con- trons from oxygen are involved to form an uncharged mole- trolling agents. Theoretical studies of metal-nitrosyl complexes cule (N:O). The high reactivity of NO is not due to the fact that has also been an immense aim of study to deal with the vari- it contains an unpaired electron having a half life of 2–30 s. If ous energy criteria along the suitable future studies of their this were the case, how would tissues survive in presence of existence and clarification of concepts related to NO. molecular oxygen with two unpaired electrons at a concentra- The initial studies of the nitric oxide (NO) molecule tion of 20–200 l M [24]. Nitric oxide only reacts with those dates back to 1772, when Joseph Priestly called it ‘‘nitrous air,’’ biological molecules that have unpaired orbital electrons e.g., and was first discovered as a colorless, toxic gas. Unfortunate- other free radicals or transition metal ions. Since most of the ly, the tag of toxic gas and IJSERair pollutant continued until 1987, biological molecules have completely filled orbitals, it renders when it was shown to actually be produced naturally in the nitric oxide non-reactive towards them [25]. The reactivity of body. By 1987, nitric oxide’s role in regulating blood pressure NO depends upon its physical properties, such as its small and relieving various heart ailments became well-established. size, high diffusion rate, and lipophilicity. Moreover, the reac- Two years later, research revealed that nitric oxide is used by tion products of nitric oxide, i.e. the related species, also react macrophages to kill tumor cells and bacteria. In 1992, nitric with biological molecules and may have toxic effect as well oxide was voted ‘‘Molecule of the Year’’. The importance of [26]. At low levels, NO can protect cells; however, at higher the molecule became front page news in 1998 when Louis J. levels, it is a known cytotoxin, having been implicated in tu- Ignarro, Robert F. Furchgott and Ferid Murad were awarded mor angiogenesis and progression [27]. the Nobel Prize for Medicine and Physiology for identifying 1.2 NO in Electron Transport System nitric oxide as a signaling molecule. The discovery opened up Mitochondrial diseases arise as a result of dysfunction newer ways of treatment for millions of patients. of the respiratory chain, leading to inadequate ATP produc- Nitric oxide (NO) plays an important role in the pro- tion required to meet the energy needs of various organs. On tection against the onset and progression of cardiovascular the other hand, nitric oxide (NO) deficiency can occur in mito- diseases. The cardioprotective roles of NO include regulation chondrial diseases and potentially play major roles in the IJSER © 2014 http://www.ijser.org International Journal of Scientific & Engineering Research, Volume 5, Issue 9, September-2014 307 ISSN 2229-5518 pathogenesis of several complications including stroke-like mentalizing NO synthesis and channeling citrulline efficiently episodes, myopathy, diabetes, and lactic acidosis. NO defi- to NO synthesis. Clinical research evaluating the effect of ar- ciency in mitochondrial disorders can result from multiple ginine and citrulline in mitochondrial diseases is limited to factors including decreased NO production due to endothelial uncontrolled open label studies demonstrating that arginine dysfunction, NO sequestration by cytochrome c oxidase, NO administration to subjects with MELAS (Mitochondrial shunting into reactive nitrogen species formation, and de- Encephalopathy, Lactic acidosis, and Stroke-like episodes) creased availability of the NO precursors arginine and citrul- syndrome results in improvement in the clinical symptoms line (Fig. 1 and 2). associated with stroke-like episodes and a decrease in the fre- quency and severity of these episodes. Therefore, controlled clinical studies of the effects of arginine or citrulline supple- mentation on different aspects of mitochondrial diseases are needed to explore the potential therapeutic effects of these NO donors [30], [31], [32]. 1.3 Promotion and Demotion of Cell Growth Thus Nitric oxide (NO),