Novel Mn2+, Fe3+, Co2+, Ni2+ and Cu2+complexes of potential OS donor thiosemicarbazide: Design, structural elucidation, anticorrosion potential study and antibacterial activity

Corrosion inhibition relevance of semicarbazides: electronic structure, reactivity and coordination chemistry

Semicarbazide (OC(NH2)(N2H3)) and thiosemicarbazide (SC(NH2)(N2H3)) are well-known for their coordination complex formation ability. They contain nonbonding electrons in the form of heteroatoms (N, O and S) and π-electrons in the form of >C=O and >C=S through they strongly coordinate with the metal atoms and ions. Because of their association with this property, the Semicarbazide (SC), thiosemicarbazide (TSC) and their derivatives are widely used for different applications. They serve as building blocks for synthesis of various industrially and biologically useful chemicals. The SC, TSC and they derivatives are also serve as strong aqueous phase corrosion inhibitors. In the present reports, the coordination ability and corrosion protection tendency of Semicarbazide (SC), thiosemicarbazide (TSC) and their derivatives is surveyed and described. These compounds are widely used as inhibitors for different metals and alloys. Through their electron rich sites they adsorb on the metal surface and build corrosion protective film. Their adsorption mostly followed the Langmuir adsorption isotherm. Through their adsorption they increase the value of charge transfer resistance and decrease the value of corrosion current density. Computational studies adopted in the literature indicate that SC, TSC and their derivatives adsorb flatly and spontaneously using charge transfer mechanism.

The inhibition effects of Cu and Ni alloying elements on corrosion of HSLA steel influenced by Halomonas titanicae

Halomonas titanicae accelerated steel corrosion by dissimilatory Fe(III) reduction under anaerobic environments, and their adhesion was the key to achieving extracellular electron transfer between cells and Fe(III). This work investigated the inhibition effects of Cu and Ni alloying elements on corrosion of high strength low alloy (HSLA) steel affected by H. titanicae. It was found that both the addition of Cu (1.3%) and high content of Ni (7.2%) brought better corrosion resistance than the steel containing 4.8% Ni via decreasing the amount of sessile bacterial cells. And the inhibition efficiency of Cu with the lower content was stronger than that of Ni with the higher content. Biofilm inhibition mechanisms varied from Cu to Ni alloying elements, and the former was achieved via bactericidal Cu ions released from steel. While for the HSLA steel with high Ni content, the formation of nickel oxides including NiFe₂O₄ and Ni(OH)₂ refined the grains of corrosion products and decreased the bacterial attachment.

Synthesis, Spectral, Thermal and Biological Studies of 4-Cyclohexyl-3-(4-nitrophenyl)methyl-1,2,4-triazolin-5-thione and Its Copper(II) Coordination Compound, [CuCl2(H2O)2L2]

One of the strategies for seeking new biologically active substances is to modify compounds with potential biological activity. In this paper, 1,2,4-triazolin-5-thione derivative (3) was obtained in the cyclization reaction of appropriate thiosemicarbazide (2) as an organic ligand. The copper(II) complex, [CuCl₂(H₂O)₂L₂] (L=4-cyclohexyl-3-(nitrophenyl)methyl-1,2,4-triazolin-5-thione) (Cu-3) was prepared in a reaction of free ligand (3) with a CuCl₂·2H₂O solution in MeOH/EtOH mixture at room temperature. TGA data show that Cu-3 and free ligand are stable at room temperature. Both compounds were screened in vitro for antibacterial and antifungal activities using the broth microdilution method. The obtained complex (Cu-3) showed higher antibacterial effect, especially towards Gram-positive bacteria (with moderate activity and Minimal Inhibitory Concentration MIC = 250–500 µg/mL) than the free ligand (3) (with mild or no bioactivity and MIC ≥ 1000 µg/mL). In turn, yeasts, belonging to Candida albicans, exhibited similar sensitivity to both the copper(II) complex (Cu-3) and the organic ligand (3). The anticandidal activity of these compounds was moderate (MIC = 500 µg/mL), or, in the case of other Candida spp., lower (MIC ≥ 1000 µg/mL).