Saliu Alao Amolegbe

Chitosan–cobalt(II) and nickel(II) chelates as antibacterial agents

Antibacterial behavior of chitosan-bivalent metal chelates (Co and Ni) was investigated in vitro against standard bacteria, Staphylococcus aureus ATCC 4533, S. faecalis ATCC 8043 and Escherichia coli ATCC 25923. The chitosan-metal chelates were prepared by varying the molar ratio of metal ions to a fixed amount of chitosan. The metal ion contents, structural properties and morphology of the chelates were respectively determined using ICP-OES, FT-IR and SEM. All the chitosan-metal chelates showed wide spectrum of effective antibacterial activities better than free chitosan and the individual metal ions. The results indicated that inhibitory effects of the chelates were dependent not only on the property of the coordinated metal ion, but also on the molar ratio of the metal ion. Consequently, the ideal inhibitory effects could be obtained with metal ion of high charge intensity and when the molar ratio of chitosan to metal was above 1:1. These chelates are promising materials for novel antibacterial agents.

Poly[β-(1→4)-2-amino-2-deoxy-D-ghicopyranose] based zero valent nickel nanocomposite for efficient reduction of nitrate in water

Chemical reduction of nitrate using metal nanoparticles has received increasing interest due to over-dependence on groundwater and consequence health hazard of the nitrate ion. One major drawback of this technique is the agglomeration of nanoparticles leading to the formation of large flocs. A low cost biopolymeric material, poly [beta-(1-->4)-2-amino-2-deoxy-D-glucopyranose] (beta-PADG) obtained from deacetylated chitin was used as stabilizer to synthesize zero valent nickel (ZVNi) nanoparticles. The beta-PADG-ZVNi nanocomposite was characterized using infra red (IR), UV-Vis spectrophotometric techniques and Scanning Electron Microscope (SEM). The morphology of the composite showed that beta-PADG stabilized-ZVNi nanoparticles were present as discrete particles. The mean particle size was estimated to be (7.76 +/- 2.98) nm and surface area of 87.10 m2/g. The stabilized-ZVNi nanoparticles exhibited markedly greater reactivity for reduction of nitrate in water with 100% conversion within-2 hr contact owing to less agglomeration. Varying the beta-PADG-to-ZVNi ratio and the ZVNi-to-nitrate molar ratio generally led to a faster nitrate reduction. About 3.4-fold difference in the specific reaction rate constant suggests that the application of the beta-PADG-stabilizer not only increased the specific surface area of the resultant nanoparticles, but also greatly enhanced the surface reactivity of the nanoparticles per unit area.

Synthesis, Spectroscopic, Surface and Catalytic Reactivity of Chitosan Supported Co(II) and Its Zerovalentcobalt Nanobiocomposite

Chitosan was used as a stabilizer to synthesize chitosan cobalt(II) [Chit–Co(II)] and its zerovalentcobalt nanobiocomposite via chemical reduction. The complex and Chit–ZVCo were used to polymerize vinylacetate in aqueous Na2SO3. The Chit–Co(II) and Chit–ZVCo were characterized by spectroscopic (FT-IR and UV–Visible), XRD and SEM techniques. Application of these biomaterials for the polymerization of VAc afforded polyvinylacetate with improved yield. Comparing the reactivity of Chit–Co(II) and Chit–ZVCo, it was evident that Chit–ZVCo performed as better heterogeneous catalyst based on the synergic effect of interaction of cobalt nanoparticles and chitosan at the nanometric scale.

Synthesis of mesoporous materials as nano-carriers for an antimalarial drug

An antimalarial drug artesunate (ATS) was encapsulated in both functionalized MCM-41 and ordinary MCM-41 with an excellent loading capacity and sustained release behavior for possible biomedical applications.

Reduction of Bromate in Water using Zerovalent Cobalt 2,6-Pyridine Dicarboxylic Acid Crosslinked Chitosan Nanocomposite

Zerovalent cobalt 2,6-Pyridinedicarboxylic acid crosslinked chitosan (ZVCo-PDCA-CHIT) nanocomposite, which was obtained by chemical reduction of cobalt (II) ion chelated nanocomposite with NaBH4, was tested for bromate reduction in water. 2,6-pyridinedicarboxylic acid (PDCA) was used for intramolecular crosslinking of the chitosan linear chains. The products were characterized by FT-IR, XRD and SEM. The FT-IR analyses revealed the presence of coordinating –NH2 and –OH functional groups in chitosan while crosslinked chitosan showed –COOH absorption peaks. The XRD spectrum revealed a typical fingerprint of semi-crystalline chitosan which disappeared in crosslinked chitosan due to disruption of the interpolymer bonds. SEM image revealed a smooth surface for the Chitosan while large pores were observed for the PDCAcrosslinked Chitosan (PDCA-CHIT). ZVCo-PDCA-CHIT nanocomposite showed significant morphological changes with the surface structure being smooth with the disappearance of the holes observed in the crosslinked chitosan structure, indicating a very strong binding of cobalt with most of the functional groups. The applied ZVCo-PDCA-CHIT nanocomposite reduced bromate ions to bromide with possible adsorption onto the nanocomposite. The result showed that bromate reduction in water was significantly higher and near completion under 1 h using ZVCo-PDCA-CHIT (99 ± 1.1%) as compared to PDCAcrosslinked Chitosan (65 ± 1.47%) and Chitosan (53 ± 0.25%).

Mesoporous silica nanocarriers encapsulated antimalarials with high therapeutic performance

The use of nanocarriers in drug delivery is a breakeven research and has received a clarion call in biomedicine globally. Herein, two newly nano-biomaterials: MCM-41 encapsulated quinine (MCM-41 ⊃ QN) (1) and 3-phenylpropyl silane functionalized MCM-41 loaded QN (pMCM-41 ⊃ QN) (2) were synthesized and well characterized. 1 and 2 along with our two already reported nano-antimalarial drugs (MCM-41 ⊃ ATS) (3) and 3-aminopropyl silane functionalized MCM-41 contained ATS (aMCM-41 ⊃ ATS) (4) were screened in vitro for their activity against P. falciparium W2 strain, cytotoxicity against BGM cells and in vivo for their activity against Plasmodium bergheiNK65. 1 has the highest antimalarial activity in vivo against P. berghei NK65, (ED50: < 0.0625 mg/kg body weight) and higher mean survival time compared to the other nano biomaterials or unencapsulated drugs at doses higher than 0.0625 mg/kg body weight. This encapsulation strategy of MCM-41 ⊃ QN (1) stands very useful and effective in delivering the drug to the target cells compared to other delivery systems and therefore, this encapsulated drug may be considered for rational drug design.

Photoswitching of the dielectric property of salicylideneaniline

Temperature dependent dielectric constant changes for salicylideneaniline (SA) were observed before and after light irradiation. The dielectric constant for a non-illuminated sample is higher than that for an illuminated one. It was considered that this fascinating observation might reflect dynamic chromophoric structural changes within the tautomers of SA.