Mriganka Das

Copper complexes with a flexible piperazinyl arm: nuclearity driven catecholase activity and interactions with biomolecules

Abstract Three new Cu(II) complexes, [Cu(HL1)(pyridine)(H2O)](ClO4)2·2MeOH (1), [Cu2(HL1)2(NO3)2](NO3)2·3H2O (2) and [Cu(HL2)(NO3)2]·MeCN (3), have been synthesized from two Schiff base ligands [HL1 = 1-phenyl-3-((2-(piperazin-4-yl)ethyl)imino)but-1-en-1-ol and HL2 = 4-((2-(piperazin-1-yl)ethyl)imino)pent-2-en-2-ol] using the chair conformer of a flexible piperazinyl moiety. Structural analysis reveals that 1 and 3 are monomeric Cu(II) complexes consisting of five- and six-coordinate Cu(II), respectively, whereas 2 is a dinuclear Cu(II) complex consisting of two different Cu(II) centers, one square planar with the other distorted octahedral. Screening tests were conducted to quantify the binding of 1–3 towards DNA and BSA as well as the DNA cleavage activity of these complexes using gel electrophoresis. Enzyme kinetic studies were also performed for the complexes mimicking catecholase-like activities. Antibacterial activities of these complexes were also examined towards Methicillin-Resistant Staphylococcus aureus bacteria. The results reflect that 2 is more active than the monomeric complexes, which is further corroborated by density functional theory study.

Nickel tetrazolato complexes synthesized by microwave irradiation: Catecholase like activity and interaction with biomolecules

Abstract 1,3-Dipolar cycloaddition between nickel-ligated azide in [NiL(N3)] [HL = 3-(2-diethylamino-ethylimino)-1-phenyl-butan-1-one] and two different organonitriles furnished two new square-planar complexes viz. [NiL(5-phenyltetrazolato)] and [NiL{5-(4-pyridyl)-tetrazolato}]. Both the complexes have been characterized by spectroscopic tools and single-crystal X-ray crystallography. Interaction with different biomolecules revealed that both complexes bind strongly to serum albumin proteins and show moderate catecholase-like activity by catalyzing the oxidation of 3,5-ditertbutylcatechol (3,5-DTBC). Identification of intermediates formed in catechol oxidation has been explored by ESI-MS spectrometry.

The effect of remote substitution on the formation of preferential isomers of cobalt(III)-tetrazolate complexes by microwave assisted cycloaddition

The 1,3-dipolar cycloaddition reaction of cis-[Co(N3)2(en)2]NO31 with different organonitriles (NCR) under focussed microwave irradiation produced bis-tetrazolate complexes [Co(N4CR)2(en)2](NO3). Interestingly, in the case of 3-cyano pyridine the reaction produced both cis- and trans-isomers (cis-2 and trans-2), whereas for 4-cyano pyridine the compound obtained was exclusively cis (cis-3) and for 4-bromobenzonitrile it was only the trans- (trans-4) compound which was isolated. This indicates a probable role of remote substitution of the phenyl ring in dictating the formation of the preferential isomer. When starting from the trans-isomer of the diazido complex (trans-[Co(N3)2(en)2]ClO4, 1a), upon reacting with different nitriles a mixture of cis- and trans-isomers of [Co(N4CR)2(en)2]ClO4 was produced in each case, with a greater preference towards cis-geometry [R = 4-NC5H4 (cis-5 and trans-5), 4-BrC6H4 (cis-6 and trans-6) and C6H5 (cis-7 and trans-7)]. The preferential formation of the cis-analogue of compound trans-4 when starting from the trans-precursor was quite curious. A theoretical investigation of compounds trans-4 and cis-6 reveals that the greater stability of the trans-complex 4 may arise from additional van der Waals interactions in the solid state because of the presence of an extra DMF molecule as solvent of crystallization. However, an interacting counter-anion and a probable halogen–halogen interaction may also contribute to the formation of preferential isomers for cycloaddition complexes, even in the solution state.

Targeted synthesis of cadmium(II) Schiff base complexes towards corrosion inhibition on mild steel

Three ligands L1 [N,N-dimethyl-N′-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine], L2 [2-morpholino-N-(1-(pyridin-2-yl)ethylidene)ethanamine] and L3 [(2-(piperidin-1-yl)-N-(1-(pyridin-2-yl)ethylidene)ethanamine)] were introduced to prepare five Cd(II) Schiff base complexes [Cd(L1)2](ClO4)2 (1), [Cd(L1)(Cyanoacetate)(OAc)] (2), [Cd2(L1)2(N3)4] (3), [Cd(L2)(N3)2]n (4), [Cd2 (L3)2(N3)4]n (5) and the corrosion inhibition properties of these complexes on mild steel upon treatment with 15% HCl have been examined where azide complexes have shown corrosion inhibition properties as revealed by electrochemical impedance spectroscopy and potentiodynamic polarization. Field emission scanning electron microscopy (FE-SEM) images show that the mild steel surface was protected by cadmium complexes. Among azido complexes polymeric complexes have higher inhibition activity which was further explained using density functional theory. So finally a new bridge between nuclearity driven coordination inorganic chemistry and materials as well as corrosion engineering was established by this observation.