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Spectroscopic study of the Schiff bases of dodecylamine with pyridoxal 5'-phosphate and 5'-deoxypyridoxal. A model for the Schiff bases of pyridoxal 5'-phosphate in biological systems.

ABSTRACT: We recorded the absorption spectra of the Schiff bases of pyridoxal 5'-phosphate (PLP) and 5'-deoxypyridoxal (DPL) with dodecylamine (DOD) at different pH values. By applying deconvolution techniques to the spectra and analysing their different components we found that the above-mentioned Schiff bases in aqueous solutions of pH 7 adopted a conformation in which the pyridine ring is embedded in a very hydrophobic medium from which water is virtually completely excluded. This conformation in the same as that adopted by PLP when it acts as coenzyme for some enzymes such as glycogen phosphorylase. The experimental results obtained also show such a conformation to be highly favoured but sensitive to the protonation of the pyridine nitrogen, which makes the aromatic ring more readily accessible to the solvent.

SUBMITTER: Vazquez MA

PROVIDER: S-EPMC1151511 | biostudies-other | 1991 Nov

REPOSITORIES: biostudies-other

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Project description:In this contribution, five Ni(II) complexes have been synthesized from sulfonamide-based Schiff bases (SB1-SB5) that comprise bromo or iodo substituents in the salicylidene moiety. The chemical structures of these compounds were extensively elucidated by different analytical and physicochemical studies. All ligands act as bidentate chelators with ON binding mode yielding octahedral, square planar, or tetrahedral geometries. The phenolic OH at δ 12.80 ppm in the free Schiff base SB2 vanishes in the 1H NMRspectrum of diamagnetic complex [Ni(SB2-H)2] favoring the OH deprotonation prior to the chelation with Ni(II) ion. The appearance of twin molecular ion peaks ([M - 1]+ and [M + 1]+) is due to the presence of bromine isotopes (79Br and 81Br) in the mass spectra of most cases. Also, the thermal decomposition stages of all complexes confirmed their high thermal stability and ended with the formation of NiO residue of mass 6.42% to 14.18%. Besides, antimicrobial activity and cytotoxicity of the ligands and some selected complexes were evaluated. Among the ligands, SB4 showed superior antimicrobial efficacy with MIC values of 0.46, 7.54, and 0.95 µM against B. subtilis, E. coli, and A. fumigatus strains, respectively. The consortium of different substituents as two bromine atoms either at positions 3 and/or 5 on the phenyl ring and a thiazole ring is one of the reasons behind the recorded optimal activity. Moreover, there is a good correlation between the cytotoxicity screening (IC50) and molecular docking simulation outcomes that predicted a strong binding of SB2 (16.0 μM), SB4 (18.8 μM), and SB5 (6.32 μM) to the breast cancer protein (3s7s). Additionally, [Ni(SB4-H)2] (4.33 µM) has nearly fourfold potency in comparison with cisplatin (19.0 μM) against breast carcinoma cells (MCF-7) and is highly recommended as a promising, potent, as well as low-cost non-platinum antiproliferative agent after further drug authorization processes.