Research Articles (Chemistry)

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Inhibition of HIV-1 enzymes, antioxidant and anti-inflammatory activities of Plectranthus barbatus
(Elsevier, 213) Kapewangolo, Petrina; Hussein, Ahmed A.; Meyer, Debra
Ethnopharmacological relevance: Plectranthus barbatus is widely used in African countries as an herbal remedy to manage HIV/AIDS and related conditions. Aim of the study: To investigate the HIV-1 inhibitory, anti-inflammatory and antioxidant properties of P. barbatus and thereby provide empirical evidence for the apparent anecdotal success of the extracts. Materials and methods: Ethanolic extract of P. barbatus's leaves was screened against two HIV-1 enzymes: protease (PR) and reverse transcriptase (RT). Cytotoxicity of the extract was determined through measuring tetrazolium dye uptake of peripheral blood mononuclear cells (PBMCs) and the TZM-bl cell line. Confirmatory assays for cytotoxicity were performed using flow cytometry and real-time cell electronic sensing (RT-CES). The free radical scavenging activity of the extract was investigated with 2,2- diphenyl-1-picrylhydrazyl while the anti-inflammatory properties of the plant extract were investigated using a Th1/Th2/Th17 cytometric bead array technique.
Analyzing chemical data in more than two dimensions: A tutorial on factor and cluster analysis
(Journal of chemical education, 1990) Auf der Heyde, Thomas P. E
This tutorial is intended to introduce factor and cluster analysis at a level that will afford a senior student-and the practicing chemist, for that matter-some insights into the workings of the computer packages employing these methods, without overwhelming him or her with mathematical detail in the process.
Crystal structure of saposin B reveals a dimeric shell for lipid binding
(National Academy of Sciences, 2003) Ahn, Victoria E.; Faull, Kym F.; Whitelegge, Julian P.
Saposin B is a small, nonenzymatic glycosphingolipid activator protein required for the breakdown of cerebroside sulfates (sulfatides) within the lysosome. The protein can extract target lipids from membranes, forming soluble protein-lipid complexes that are recognized by arylsulfatase A. The crystal structure of human saposin B reveals an unusual shell-like dimer consisting of a monolayer of -helices enclosing a large hydrophobic cavity. Although the secondary structure of saposin B is similar to that of the known monomeric members of the saposin-like superfamily, the helices are repacked into a different tertiary arrangement to form the homodimer. A comparison of the two forms of the saposin B dimer suggests that extraction of target lipids from membranes involves a conformational change that facilitates access to the inner cavity.
Electrocatalytic sensor devices: (I) cyclopentadienylnickel(II) thiolato Schiff base monolayer self-assembled on gold
(Elsevier, 2004) Morrin, Aoife; Moutloali, Richard M.; Killard, Anthony J.
The fabrication of a self-assembled monolayer (SAM) of a cyclopentadienylnickel(II) thiolato Schiff base compound, [Ni(SC6H4NC(H)C6H4 OCH2CH2SMe)( 5-C5H5)]2 on a gold electrode is described. Effective electronic communication between the Ni(II) centres and the gold surface was established by electrochemically cycling the Schiff base-doped Au electrode in 0.1 M NaOH from −200 mV to +600 mV. The SAM-modified electrode exhibited quasi-reversible electrochemistry. The integrity of this electrocatalytic SAM, with respect to its ability to block and electro-catalyse certain Faradaic processes, was interrogated using cyclic voltammetric experiments. The formal potential, E◦ , varied with pH to give a slope of about −30 mV pH−1. The surface concentration, G, of the nickel redox centres was found to be 1.548 × 10−11 mol cm−2. By electrostatically doping the SAM using an applied potential of +700 mV versus Ag/AgCl, in the presence of horseradish peroxidase (HRP), it was fine-tuned for amperometric determination of H2O2. The electrocatalytic-type biosensor displayed typical Michaelis–Menten kinetics and the limit of detection was found to be 6.25 mM. © 2004 Elsevier B.V. All rights reserved.
An electrochemical DNA biosensor developed on a nanocomposite platform of gold and poly(propyleneimine) dendrimer
(MDPI, 2008) Arotiba, Omotayo A.; Owino, Joseph; Songa, Everlyne; Hendricks, Nicolette; Waryo, Tesfaye T.; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.
An electrochemical DNA nanobiosensor was prepared by immobilization of a 20mer thiolated probe DNA on electro-deposited generation 4 (G4) poly(propyleneimine) dendrimer (PPI) doped with gold nanoparticles (AuNP) as platform, on a glassy carbon electrode (GCE). Field emission scanning electron microscopy results confirmed the codeposition of PPI (which was linked to the carbon electrode surface by C-N covalent bonds) and AuNP ca 60 nm. Voltammetric interrogations showed that the platform (GCE/PPI-AuNP) was conducting and exhibited reversible electrochemistry (E°′ = 235 mV) in pH 7.2 phosphate buffer saline solution (PBS) due to the PPI component. The redox chemistry of PPI was pH dependent and involves a two electron, one proton process, as interpreted from a 28 mV/pH value obtained from pH studies. The charge transfer resistance (Rct) from the electrochemical impedance spectroscopy (EIS) profiles of GCE/PPI-AuNP monitored with ferro/ferricyanide (Fe(CN)6 3-/4-) redox probe, decreased by 81% compared to bare GCE. The conductivity (in PBS) and reduced Rct (in Fe(CN)6 3-/4-) values confirmed PPI-AuNP as a suitable electron transfer mediator platform for voltammetric and impedimetric DNA biosensor. The DNA probe was effectively wired onto the GCE/PPI-AuNP via Au-S linkage and electrostatic interactions. The nanobiosensor responses to target DNA which gave a dynamic linear range of 0.01 - 5 nM in PBS was based on the changes in Rct values using Fe(CN)6 3-/4- redox probe.
Electrochemical immunosensor based on polythionine/gold nanoparticles for the determination of Aflatoxin B1
(MDPI, 2008) Owino, Joseph H.O.; Arotiba, Omotayo A.; Hendricks, Nicolette; Songa, Everlyne; Jahed, Nazeem; Waryo, Tesfaye T.; Ngece, Rachel F.; Baker, Priscilla; Iwuoha, Emmanuel I.
An aflatoxin B1 (AFB1) electrochemical immunosensor was developed by the immobilisation of aflatoxin B1-bovine serum albumin (AFB1-BSA) conjugate on a polythionine (PTH)/gold nanoparticles (AuNP)-modified glassy carbon electrode (GCE). The surface of the AFB1-BSA conjugate was covered with horseradish peroxidase (HRP), in order to prevent non-specific binding of the immunosensors with ions in the test solution. The AFB1 immunosensor exhibited a quasi-reversible electrochemistry as indicated by a cyclic voltammetric (CV) peak separation (ΔEp) value of 62 mV. The experimental procedure for the detection of AFB1 involved the setting up of a competition between free AFB1 and the immobilised AFB1-BSA conjugate for the binding sites of free anti-aflatoxin B1 (anti-AFB1) antibody. The immunosensor’s differential pulse voltammetry (DPV) responses (peak currents) decreased as the concentration of free AFB1 increased within a dynamic linear range (DLR) of 0.6 - 2.4 ng/mL AFB1 and a limit of detection (LOD) of 0.07 ng/mL AFB1. This immunosensing procedure eliminates the need for enzyme-labeled secondary antibodies normally used in conventional ELISA–based immunosensors.
Polyester sulphonic acid interstitial nanocomposite platform for peroxide biosensor
(MDPI, 2009) Al-Ahmed, Amir; Ndangili, Peter M.; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.
A novel enzyme immobilization platform was prepared on a platinum disk working electrode by polymerizing aniline inside the interstitial pores of polyester sulphonic acid sodium salt (PESA). Scanning electron microscopy study showed the formation of homogeneous sulphonated polyaniline (PANI) nanotubes (~90 nm) and thermogravimetric analysis (TGA) confirmed that the nanotubes were stable up to 230 °C. The PANI:PESA nanocomposite showed a quasi-reversible redox behaviour in phosphate buffer saline. Horseradish peroxidase (HRP) was immobilized on to this modified electrode for hydrogen peroxide detection. The biosensor gave a sensitivity of 1.33 μA (μM)-1 and a detection limit of 0.185 μM for H2O2. Stability experiments showed that the biosensor retained more than 64% of its initial sensitivity over four days of storage at 4 °C.
Electrochemical aptasensor for endocrine disrupting 17β-estradiol based on a poly(3,4-ethylenedioxylthiopene)-gold nanocomposite platform
(MDPI, 2010) Olowu, Rasaq A.; Mailu, Stephen N.; Waryo, Tesfaye T.; Baker, Priscilla; Iwuoha, Emmanuel I.; Arotiba, Omotayo A.
A simple and highly sensitive electrochemical DNA aptasensor with high affinity for endocrine disrupting 17β-estradiol, was developed. Poly(3,4-ethylenedioxylthiophene) (PEDOT) doped with gold nanoparticles (AuNPs) was electrochemically synthesized and employed for the immobilization of biotinylated aptamer towards the detection of the target. The diffusion coefficient of the nanocomposite was 6.50 × 10−7 cm2 s−1, which showed that the nanocomposite was highly conducting. Electrochemical impedance investigation also revealed the catalytic properties of the nanocomposite with an exchange current value of 2.16 × 10−4 A, compared to 2.14 × 10−5 A obtained for the bare electrode. Streptavidin was covalently attached to the platform using carbodiimide chemistry and the aptamer immobilized via streptavidin—biotin interaction. The electrochemical signal generated from the aptamer–target molecule interaction was monitored electrochemically using cyclic voltammetry and square wave voltammetry in the presence of [Fe(CN)6]−3/−4 as a redox probe. The signal observed shows a current decrease due to interference of the bound 17β-estradiol. The current drop was proportional to the concentration of 17β-estradiol. The PEDOT/AuNP platform exhibited high electroactivity, with increased peak current. The platform was found suitable for the immobilization of the DNAaptamer. The aptasensor was able to distinguish 17β-estradiol from structurally similar endocrine disrupting chemicals denoting its specificity to 17β-estradiol. The detectable concentration range of the 17β-estradiol was 0.1 nM–100 nM, with a detection limit of 0.02 nM.
Role of the methoxy group in product formation via TiCl4 promoted 4-phenyldioxolane isomerizations
(ARKAT USA INC, 2010) Green, Ivan R.; October, Natasha
The product distribution obtained from the TiCl4 initiated intramolecular isomerizations of 4- methoxyphenyl- and trimethoxyphenyldioxolanes at -78 oC, -30 oC and 0 oC provided insights into the important regiochemical role played by these groups in such Mukaiyama- type rearrangements through their resonance effects on the aryl ring of the dioxolanes.Our interest in naphthopyranquinones as potential antimicrobial and antibiotic agents has extended over two decades1-6 as a result of their well documented importance.7,8 Additionally, the synthesis of benzopyrans as model systems has received attention by ourselves6,9-13 and others.14- 16 Of particular interest to us was our earlier discovery of a TiCl4 - induced intramolecular isomerization in which phenyl- and naphthyldioxolanes were stereoselectively transformed into their corresponding benzo- and naphthopyrans.17
Determination of anthracene on Ag-Au alloy nanoparticles/overoxidized-polypyrrole composite modified glassy carbon electrodes
(MDPI, 2010) Mailu, Stephen N.; Waryo, Tesfaye T.; Ndangili, Peter M.; Ngece, Fanelwa R.; Baleg, Abd A.; Baker, Priscilla; Iwuoha, Emmanuel I.
A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy carbon electrode (GCE) with over-oxidized polypyrrole (PPyox) and Ag-Au (1:3) bimetallic nanoparticles (Ag-AuNPs). The composite electrode (PPyox/Ag-AuNPs/GCE) was prepared by potentiodynamic polymerization of pyrrole on GCE followed by its overoxidation in 0.1 M NaOH. Ag-Au bimetallic nanoparticles were chemically prepared by the reduction of AgNO3 and HAuCl4 using C6H5O7Na3 as the reducing agent as well as the capping agent and then immobilized on the surface of the PPyox/GCE. The nanoparticles were characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the bimetallic alloy nanoparticles. Transmission electron microscopy showed that the synthesized bimetallic nanoparticles were in the range of 20–50 nm. The electrochemical behaviour of anthracene at the PPyox/Ag-AuNPs/GCE with Ag: Au atomic ratio 25:75 (1:3) exhibited a higher electrocatalytic effect compared to that observed when GCE was modified with each constituent of the composite (i.e., PPyox, Ag-AuNPs) and bare GCE. A linear relationship between anodic current and anthracene concentration was attained over the range of 3.0 × 10−6 to 3.56 × 10−4 M with a detection limit of 1.69 × 10−7 M. The proposed method was simple, less time consuming and showed a high sensitivity.
2-Arylnaphthoquinone analogues: Potential anti-TB and pro-apoptotic agents
(Green, I. R. et al. (2011). 2-Arylnaphthoquinone analogues: Potential anti-TB and pro-apoptotic agents. ARKIVOC, (x), 192-212. https://doi.org/10.3998/ark.5550190.0012.a16, 2011) Green, Ivan R; Sagar, Sunil; Swigelaar, Wendell
A useful library of substituted 2-arylnaphthoquinones prepared by reaction between the corresponding bromonaphthoquinones and arylboronic acids via Suzuki-Miyaura protocols has been established. Conversion of some of the products into new analogues was effected. The bisnaphthoquinone disospyrin 1 comprises two 7-methyljuglone units linked between C2 and C6. 1,2 Antimycobacterial activity studies performed on diospyrin 1 alerted the scientific community to the potential importance of this natural product3 which was soon followed by its first published synthesis by Yoshida and Mori in the same year.4 Subsequent studies, which included the synthesis and evaluation of related analogues of diospyrin 1 demonstrated the potential of this basic scaffold to be considered as an integral aspect for good antimycrobacterial activity.
Correction: Baker, P. et al. electrochemical aptasensor for endocrine disrupting 17β-estradiol based on a poly(3,4-ethylenedioxylthiopene)-gold nanocomposite platform. Sensors 2010, 10, 9872-9890
(MDPI, 2011) Olowu, Rasaq A.; Arotiba, Omotayo A.; Mailu, Stephen N.; Waryo, Tesfaye T.; Baker, Priscilla; Iwuoha, Emmanuel I.
Herewith please find corrected structures for Figure 8 in our paper published in Sensors in 2010.
Metallo-graphene nanocomposite electrocatalytic platform for the determination of toxic metal ions
(MDPI, 2011) Willemse, Chandre M.; Tlhomelang, Khotso; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.
A Nafion-Graphene (Nafion-G) nanocomposite solution in combination with an in situ plated mercury film electrode was used as a highly sensitive electrochemical platform for the determination of Zn2+, Cd2+, Pb2+ and Cu2+ in 0.1 M acetate buffer (pH 4.6) by square-wave anodic stripping voltammetry (SWASV). Various operational parameters such as deposition potential, deposition time and electrode rotation speed were optimized. The Nafion-G nanocomposite sensing platform exhibited improved sensitivity for metal ion detection, in addition to well defined, reproducible and sharp stripping signals. The linear calibration curves ranged from 1 µg L−1 to 7 µg L−1 for individual analysis. The detection limits (3σ blank/slope) obtained were 0.07 µg L−1 for Pb2+, Zn2+ and Cu2+ and 0.08 µg L−1 for Cd2+ at a deposition time of 120 s. For practical applications recovery studies was done by spiking test samples with known concentrations and comparing the results with inductively coupled plasma mass spectrometry (ICP-MS) analyses. This was followed by real sample analysis.
New phenylene bridged binuclear bis (imino-quinolyl) palladium(II) complexes: synthesis, characterization and Heck reactions
(Elsevier, 2012) Motswainyana, William M.; Onani, Martin O.
Two new phenylene bridged binuclear bis(imino-quinolyl) palladium (II) complexes were prepared from the reaction of the ligand 1,4-bis(imino-quinolyl)benzene, L1 with either Pd(cod)Cl2 or Pd(cod)ClMe. The molecular structure of L1 was confirmed by single crystal X-ray diffraction analysis. The structure shows two planar molecules (A and B) in the asymmetric unit. The complexes were evaluated as catalysts for Heck coupling reactions of methyl and butyl acrylate with iodobenzene, and showed high activity. The reactions proceeded at a faster initial rate and there was good selectivity for the formation of the trans- isomers.
New imino-pyridyl nickel (II) complexes: synthesis, molecular structures and application as Heck coupling catalysts
(Elsevier, 2012) Motswainyana, William M.; Onani, Martin O.; Ojwach, Stephen O.; Omondi, Bernard
Reactions of imino-pyridyl ligands, (2-pyridyl-2-thiophenemethyl)imine (L1) and (2-pyridyl-2-thiopheneethyl)imine (L2) with NiBr2(DME) gave the corresponding complexes [Ni(L1)Br2] (1) and [Ni(L2)Br2] (2) in good yields. Treatment of 1 and 2 with one equivalent of 2-hydroxythiophenol resulted in the displacement of the bromide ligands to form the nickel(II) thiolato complexes 3 and 4. Molecular structure of 3 confirmed that L1 and L2 bind to the nickel atom in a bidentate fashion. Complexes 1-4 catalyzed the Heck coupling reaction of iodobenzene and bromobenzene with methyl acrylate.
Dichlorido-[2-(2,6-diethylphenyl)iminomethylquinoline-N,N’]palladium(II) acetonitrile monosolvate
(International Union of Crystallography, 2012) Motswainyana, William M.; Onani, Martin O.; Jacobs, Jeroen; van Meervelt, Luc
The title complex, [PdCl2(C20H20N2)] CH3CN, was synthesized by the reaction of 2-[(2,6-diethylphenyl)iminomethyl]quinoline with dichlorido(cycloocta-1,5-diene)palladium(II) in dry CH2Cl2. The PdII ion is coordinated by two N atoms of the bidentate quinoline ligand and by two chloride anions, generating a distorted square-planar coordination geometry around the metal centre. There is a detectable trans influence for the chloride ligands. The crystal packing is characterized by – stacking between the quinoline rings. The use of acetonitrile as the crystallization solvent was essential for obtaining good-quality crystals.
Bis(ferrocenylimine)palladium(II) and platinum(II) complexes: synthesis, molecular structures and evaluation as antitumor agents
(Elsevier, 2012) Motswainyana, William M.; Onani, Martin O.; Madiehe, Abram M.
Compounds (ferrocenyl-2-furylmethyl)imine (L1), (ferrocenyl-2-thiophenemethyl)imine (L2) and (ferrocenyl-2-thiopheneethyl)imine (L3) were synthesized by condensation reactions and obtained in very good yields. Reactions of L1 – L3 with 0.5 equiv of either PdCl2(cod), PdClMe(cod) or K2[PtCl4] gave the new corresponding trans bis(ferrocenylimine)palladium(II) and platinum(II) complexes 1 – 9. The compounds were characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy. The molecular structures of 3 and 6 were determined by single crystal X-ray diffraction analysis. Both structures crystallize in monoclinic P21/n space system. The coordination geometry around the palladium atom in complexes 3 and 6 exhibits a square planar geometry at the palladium atom. Complexes 1, 7 and 9 were evaluated for their cytotoxic activities against human breast (MCF-7) and human ovarian (A2780) cancer cell lines, and they exhibited low cytotoxic activities but comparable to that of cisplatin.
Amorphous Pt@dCu/CNT catalyst for methanol elextrooxidation
(South African Chemical Institute (SACI), 2013) Wang, Hui; Ji, Shan; Wang, Wei; Wang, Rongfang
A multi-walled carbon nanotube-supported, Pt decorated nano-sized amorphous PdCu alloy cores (denoted as Pt@PdCu/CNT) catalyst with lower Pt loading is synthesized via a galvanic displacement reaction. The structure is examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical activity of the Pt@PdCu/CNT catalyst is tested by cyclic voltammogrametry (CV) and compared to that of PtRu/CNT catalysts. The results show that amorphous Pt@PdCu/CNT catalyst exhibits better electro-catalytic performances for methanol oxidation than its crystalline counterpart.
Salicylaldiminato chromium complex supported on chemically modified silica as highly active catalysts for the oxidation of cyclohexene
(Elsevier, 2013) Titinchi, Salam J.J.; Abbo, Hanna S.
Immobilization of chromium complexes on modified silica support was achieved via two different synthetic routes using 3-aminopropyl triethoxysilane (APTS) as a linking group. The FTIR spectra, elemental and solid-state NMR analyses demonstrated incorporation of amine functional groups on the surface of the APTS-functionalized silica support, which was further confirmed by 29 Si solid-state CP MAS NMR spectroscopy. Oxidation of cyclohexene was carried out over the chromium complex supported on organically modified silica using H2 O2 as an oxidant under various conditions and different atmospheres viz. oxygen, nitrogen and air. The supported catalysts exhibited excellent activity (>94%) after 6 h reaction time under O2 atmosphere using THF as solvent. The catalysts showed high chemoselectivity towards formation 2-cyclohexen-1-ol and 2-cyclohexen-1-one. Activity of the immobilized catalysts remains nearly the same after three consecutive cycles, suggesting the true heterogeneous nature of the catalyst.
Imino-phospine palladium (II) and platinum (II) complexes: Synthesis, molecular structures and evaluation as antitumor agents
(Elsevier, 2013) Motswainyana, William M.; Onani, Martin O.; Madiehe, Abram M.; Saibu, Morounke; Thovhogi, Ntevheleni; Lalancette, Roger A.
The imino-phosphine ligands L1 and L2 were prepared via condensation reaction of 2-(diphenylphosphino) benzaldehyde with substituted anilines and obtained in very good yields. An equimolar reaction of L1 and L2 with either PdCl2(cod) or PtCl2(cod) gave new palladium(II) and platinum(II) complexes 1–4. The compounds were characterized by elemental analysis, IR, 1H and 31P NMR spectroscopy. The molecular structures of 2, 3 and 4 were confirmed by X-ray crystallography. All the three molecular structures crystallized in monoclinic C2/c space system. The coordination geometry around the palladiumand platinumatoms in respective structures exhibited distorted square planar geometry at the metal centers. The complexes were evaluated in vitro for their cytotoxic activity against human breast (MCF-7) and human colon (HT-29) cancer cells, and they exhibited growth inhibitory activities and selectivity that were superior to the standard compound cisplatin.

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