Papers by Reinout Meijboom
Anti-Cancer Agents in Medicinal Chemistry
Background: A broad range of metal-coordinated complexes have been studied for their anticancer a... more Background: A broad range of metal-coordinated complexes have been studied for their anticancer activities. However, some of these complexes display high toxicity profiles to non-malignant cells, therefore limiting their use in cancer therapeutics. Aims/Method: Several silver(I) triphenylphosphine adducts were prepared as 1:1 to 1:4 ratios of silver nitrate to triphenylphosphine. They were further used to determine their anticancer activity in a malignant SNO esophageal cell line. The silver(I) phosphine adducts include: [Ag(PPh3)]NO3 (1); [Ag(PPh3)2]NO3 (2); [Ag(PPh3)3]NO3 (3) and [Ag(PPh3)4]NO3 (4). In addition, the activity of complexes 1-4 was compared to previously reported complexes [Ag(Ph2P(CH2)2PPh2)2]NO3 (5) and [Ag(Ph2P(CH2)3PPh2)2]NO3 (6). The cytotoxicity of complexes 1-6 was also evaluated in non-malignant human dermal fibroblast cells (HDF-a). Results: The majority of the complexes (specifically those containing PPh3) were found to be highly toxic to the SNO cells and ...
Benzyl alcohol oxidation to benzaldehyde was performed by tert-butyl hydroperoxide (TBHP) in the
... more Benzyl alcohol oxidation to benzaldehyde was performed by tert-butyl hydroperoxide (TBHP) in the
absence of any solvent using -Al2O3 supported copper and gold nanoparticles. Li2O and ionic liquids
were used as additive and stabilizers for the synthesis of the catalysts. The physico-chemical properties
of the catalysts were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction
spectroscopy (XRD), N2 absorption/desorption (BET), transmission electron microscopy (TEM), scanning
electron microscopy (SEM), thermogravimetric analysis (TGA) and temperature programmed reduction
(TPR), whereas, the oxidation reaction was followed by gas chromatography with a flame ionization
detector (GC-FID). The as prepared catalysts exhibited good catalytic performance in terms of conversion
and selectivity towards benzaldehyde. The performance of the Au-based catalysts is significantly
higher than that of the Cu-based catalysts. For both Cu and Au catalysts, the conversion of benzyl alcohol
increased as the reaction proceeds, while the selectivity for benzaldehyde decreased. Moreover, the catalysts
can be easily recycled and reused with neither significant loss of activity nor selectivity. A kinetic
study for the Cu and Au-catalyzed oxidation of benzyl alcohol to benzyldehyde is reported. The rate at
which the oxidation of benzyl alcohol is occurring as a function of catalyst and oxidant amounts was
investigated, with the apparent rate constant, kapp being proportional to the amount of nano catalyst and
oxygen present in the system.
Well-dispersed, random alloy, palladium-gold nanoparticles (2.66 ± 0.51 nm) were immobilized onto... more Well-dispersed, random alloy, palladium-gold nanoparticles (2.66 ± 0.51 nm) were immobilized onto several reducible mesoporous transition metal oxide materials. The composites (palladium-gold nanoparticles immobilized onto mesoporous transition metal oxide (PdAu–MTMO)) were characterized through several analytical methods such as UV–vis spectroscopy, BET, XRD, FT-IR, ICP-OES, TEM and TPR analyses. Catalytic oxidation of morin (quercetin) was performed as a model reaction in the presence of hydrogen peroxide to investigate the synergic catalytic activity of the composite. Silica was used as inert support to isolate the catalytic activity of the metal nanoparticles (32.69 ± 9.93 kJ mol −2). Synergistic interaction of PdAu–MTMO was mechanically described according to Langmuir-Hinshelwood and Mars-van Krevelen approaches. The TOF of PdAu–Co 3 O 4 (6073.23 ± 85.01 s −1 mol −1) was considerably larger than that of random alloy nanoparticles (PdAu–SiO 2 (25.71 ± 2.35 s −1 mol −1)). The Arrhenius-type plot was constructed to determine the synergistic activity of the composite, where PdAu–Co 3 O 4 described the best synergistic interaction.
The novel cationic [RuH{PPh 2 (2-OMeC 6 H 4)} 2 ]BPh 4 and neutral trans-[Ru(NH 3) 2 {PPh 2 (2-OC... more The novel cationic [RuH{PPh 2 (2-OMeC 6 H 4)} 2 ]BPh 4 and neutral trans-[Ru(NH 3) 2 {PPh 2 (2-OC 6 H 4)} 2 ] complexes were isolated from phosphine substitution reactions with [RuH(1,5-cod)(NH 2 NMe 2) 3 ]BPh 4 and [RuCl(1,5-cod)(NH 3) 2 (NH 2 NMe 2)]BPh 4 respectively. Ligand induced bisdemethylation of the pendent ether moieties of the phosphines occurred to give rise to the bis-phosphanylphenoxy moieties. Both complexes catalyzed the one-pot reductive amination of carbonyl compounds where excellent selectivity of aryl aldehydes over aryl ketones as precursors to the alcoholic species existed. Through substrate screening and 1 H NMR studies, both steric and electronic effects of the substrates were found to influence the hydrogenation/amination mechanistic pathway, as well as direct the alcohol:amine selectivity.
BioMetals, 2014
Esophageal cancer is one of the least studied cancers and is found to be prominent in black South... more Esophageal cancer is one of the least studied cancers and is found to be prominent in black South African males. It is mainly diagnosed in the late stages, and patients tend to have a low 5-year survival rate of only 10%. Silver is generally used as an antimicrobial agent, with limited reports on anticancer studies. In this study, dimeric silver(I) thiocyanate complexes were used containing a variation of 4-substitued triphenylphosphines, including [AgSCN(PPh(3))(2)](2) (1), [AgSCN{P(4-MeC(6)H(4))(3)}(2)](2) (2), [AgSCN{P(4-FC(6)H(4))(3)}(2)](2) (3) and [AgSCN{P(4-ClC(6)H(4))(3)}(2)](2) (4). All four complexes, with their respective phosphine ligands, PPh(3) (L1), P(4-MeC(6)H(4))(3) (L2), P(4-FC(6)H(4))(3) (L3) and P(4-ClC(6)H(4))(3) (L4), were subjected to in vitro toxicity studies in SNO-esophageal cancer cells, using an alamarBlue(®) assay. Morphological changes, including blebbing and apoptotic body formation, were observed. Phosphatidylserine externalization, a marker of apoptosis, was quantified by flow cytometry. The phosphine ligands L1-L4, on their own, had minimal effect on the malignant while complexes 1-4 resulted in significant cell death. A 10x decreased concentration of these complexes had similar effects than cisplatin, used as the positive control. These complexes show promise as anticancer agents.
The mechanisms involving the nanoparticle surfaces in catalytic reactions are more difficult to e... more The mechanisms involving the nanoparticle surfaces in catalytic reactions are more difficult to elucidate due to the nanoparticle surface unevenness, size distributions, and morphological irregularity. True surface area and particle sizes determination are key aspects of the activity of metal nanoparti-cle catalysts. Here we report on the organothiol adsorption-based technique for the determination of specific surface area of Cu nanoparticles, and their resultant sizes on-Al 2 O 3 supports. Quantification of ligand packing density on copper nanoparticles is also reported. The concentration of the probe lig-and, 2-mercaptobenzimidazole (2-MBI) before and after immersion of supported copper catalysts was determined by ultraviolet-visible spectrometry (UV–vis). The amount of ligand adsorbed was found to be proportional to the copper nanoparticles surface area. Atomic absorption spectrometry (AAS), N 2-physisorption (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used for the characterization of the catalysts. A fair agreement was found between particle sizes obtained from ligand adsorption and TEM methods. The catalytic activity of the copper nanoparticles related to their inherent surface area was evaluated using the model reaction of the oxidation of morin by hydrogen peroxide.
Nano-MgO was successfully deposited on titania using deposition-precipitation method. The catalys... more Nano-MgO was successfully deposited on titania using deposition-precipitation method. The catalyst produced was characterised using FTIR, XRD, BET and XRF and its activity was tested on the transesterification reaction of soybean oil to biodiesel. The catalyst activity improved when the reaction temperature was increasedfrom 150 and 225 O C. It was also observed that increasing the reaction time above 1h had no significant benefit on conversion. The stability fixed MgO on TiO 2 was investigated using XRF and ICP-OES. It was observed that MgO loss during the reaction was between 0.5-2.3 percent and that there was no correlation between the reaction temperature and the MgO loss.
Journal of Sol-Gel Science and Technology, 2013
Triblock copolymer, pluronic P123 (EO 20 PO 70 EO 20 ) was used as the structure directing agent ... more Triblock copolymer, pluronic P123 (EO 20 PO 70 EO 20 ) was used as the structure directing agent for the simple synthesis and characterization of mesoporous SBA-15 with various porosities. Extending the sample recrystallization time, after the initial synthesis and ageing, seems to have a significant effect on the pore size. It also leads to an increase in the surface area and a narrow pore size distribution. The prepared materials could find applications in areas where the diffusion of large molecules is important, and in catalysis, where greater pore accessibility would enhance the activity and selectivity of the catalyst. A possible mechanism has been proposed to describe the effect of extended recrystallization on pore sizes.
Acta Crystallographica Section E: Structure Reports Online, Mar 31, 2012
The title compound, trans-[RhCl (C18H14BrP) 2 (CO)], has a slightly disordered square-planar geom... more The title compound, trans-[RhCl (C18H14BrP) 2 (CO)], has a slightly disordered square-planar geometry with the Rh ionI situated on an inversion the centre and carbonyl-chloride disorder observed as a result of the crystallographic inversion symmetry. Selected geometric parameters include: Rh-P= 2.3430 (8) A, Rh-Cl= 2.434 (3) A, Rh-C= 1.722 (8) A, P-Rh-P= 180.00 (3) Degrees, P-Rh-Cl= 95.40 (7) Degrees, 84.60 (7) Degrees and Rh-CO= 177.9 (8) Degrees.
Acta Crystallographica Section E Structure Reports Online, 2012
Key indicators: single-crystal X-ray study; T = 100 K; mean (C-C) = 0.004 Å; disorder in main res... more Key indicators: single-crystal X-ray study; T = 100 K; mean (C-C) = 0.004 Å; disorder in main residue; R factor = 0.027; wR factor = 0.063; data-to-parameter ratio = 18.8. metal-organic compounds m510 Malan et al.
We report on the kinetic analysis of catalytic activity of γ-Al2O3 supported gold nanoparticles (... more We report on the kinetic analysis of catalytic activity of γ-Al2O3 supported gold nanoparticles (AuNPs) on the rate of oxidation of morin by hydrogen peroxide as model reaction. Gold-based catalysts were revealed to be very active in the oxidation of morin under mild conditions, especially when Li2O is used as additive, and cationic imidazolium ionic liquids are used as AuNPs stabilizer. All kinetic data could be modeled in terms of the Langmuir–Hinshelwood model; that is both reactants are assumed to be adsorbed on the surface of the nanoparticles. The apparent reaction rate could therefore be related to the surface of the nanoparticles, to the kinetics constant, related to the rate determining steps, and to the adsorption constant of the reactants. The organothiol adsorption-based technique for the determination of specific surface area and particle sizes of AuNPs on γ-Al2O3 supports is also reported. A fair agreement was found between particle sizes obtained from ligand adsorption and TEM methods. Atomic absorption spectrometry (AAS), X-ray diffraction spectrometry (XRD), N2-physisorption (BET), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) are used for the characterization of the catalysts, while the oxidation reaction and the ligand adsorption was followed by ultraviolet-visible spectrometry (UV–vis).
Dendrimer encapsulated ruthenium nanoparticles (RuDEN) were prepared and immobilized on silica 60... more Dendrimer encapsulated ruthenium nanoparticles (RuDEN) were prepared and immobilized on silica 60 and silica 100. The size of the supported RuDENs was investigated using HRTEM and the generation six G6-RuDEN was found to be the most stable RuDEN upon immobilization. The catalysts were evaluated in the liquid-phase hydrogenation of toluene at a hydrogen pressure of 30 bar and 110 • C. Several ionic liquids were used as coatings for the G5-RuSil100 catalysts to give various Solid Catalysts with Ionic Liquid Layer (SCILL). In each case the selectivity towards methylcyclohexenes was increased compared to the uncoated catalyst, accompanied by an expected decrease in activity with the highest methylcyclohexene selectivity being observed when using [EMIM][NTf 2 ] as a coating.
The catalytic oxidation of methylene blue was investigated in the presence of dendrimer generatio... more The catalytic oxidation of methylene blue was investigated in the presence of dendrimer generation five terminated NH 2 encapsulated silver (AgDENs), and gold (AuDENs) nanoparticles as catalyst. The synthesis process of encapsulated metal nanoparticles were monitored by UV/vis spectrophotometry and their average diameters determined by transmission electron microscopy analysis, respectively. The kinetics was monitored using UV/vis spectrophotometry, under pseudo-first order conditions, resulting in observed rate constants k obs. Langmuir–Hinshelwood approach was applied to model the kinetic process. The adsorption of methylene blue on the catalyst surface is related to the type of metal nanoparticle present, and presents the rate-determining step.
Generation 4 PAMAM-NH 2 dendrimers were used as template to synthesize Au 13-and Au 100-dendrimer... more Generation 4 PAMAM-NH 2 dendrimers were used as template to synthesize Au 13-and Au 100-dendrimer-encapsulated nanoparticles (Au-DENs) with an average diameter of 2.1 ± 0.3 and 3.1 ± 0.5 nm respectively. Au-DENs were characterized using various techniques. Catalytic recycling of Au-DENs using a dialysis membrane bag in the reduction of 4-NP is presented. The reduction process was primarily monitored by UV–vis spectroscopy at around λ 400 nm. The catalyst was found to exhibit a very good activity and stability even after more than 3 catalytic reaction cycles without any leaching, confirming that the reduction of 4-NP is purely a heterogeneous reaction.
Mesoporous cobalt oxides were synthesized using an inverse surfactant micelle method. The prepare... more Mesoporous cobalt oxides were synthesized using an inverse surfactant micelle method. The prepared materials are mono-dispersed nanoparticle aggregates with connected, well defined intra-particle voids. Powder X-ray diffraction, N 2 sorption, scanning electron microscopy and transmission electron microscopy revealed that both pore and nanoparticle sizes are enlarged with thermal treatment temperatures. Nitrogen sorption experiments revealed that the pore diameters increased from 12.1 to 31.9 nm with the final heat treatment increase from 150 to 550 • C. The reduction of 4-nitrophenol has been chosen as a well-controlled model reaction allowing us to determine the catalytic activity as a function of crystallite size and pore diameter. A comparison of the various cobalt oxide catalysts is made in terms of Langmuir-Hinshelwood kinetics.
Generation six hydroxyl terminated PAMAM dendrimer was used as template for the synthesis of seve... more Generation six hydroxyl terminated PAMAM dendrimer was used as template for the synthesis of several palladium-gold random alloy nanoparticles. The synthesis process was monitored using UV–spectroscopy. The microscopy image of the alloy nanoparticles was captured by transmission electron microscopy and their average size was compared to the theoretical value. Catalytic oxidation of morin by hydrogen peroxide was performed to investigate the activity of the alloy nanoparticles. The Langmuir–Hinshelwood approach was used to conduct a full kinetic evaluation of the catalytic process. The catalytic activity exhibited by the alloy nanoparticles demonstrates a proportional increase with the relative palladium amount. The encapsulated alloy and mono metal nanoparticles remained narrowly dispersed after the reaction.
Carbon and nitrogen coated Stöber silica spheres were prepared by a standard procedure using acet... more Carbon and nitrogen coated Stöber silica spheres were prepared by a standard procedure using acetoni-trile at different CVD temperatures (800–1000 • C) and as a function of time (1–4 h). HF treatment was used to remove the silica from the carbon coated silica to give monodispersed nitrogen doped hollow carbon spheres (N-HCSs; shell thickness = 50 nm). The surface areas of the N-CSs increased significantly after removal of the SiO 2 core (N-HCS = 47 m 2 /g). Platinum nanoparticles, prepared by a [Pt(COD)Cl 2 ] deposition method were dispersed (d = 2.8 ± 0.4 nm) on the N-HCS supports. Thermal treatment of the Pt/N-HCS900-4 (prepared at 900 • C for 4 h) in a 5% H 2 /Ar atmosphere at 120 • C (Pt/N-HCS900-4-120) and 300 • C (Pt/N-HCS900-4-300) gave metallic Pt (2.48%) which was confirmed by XRD and XPS studies. The XPS N1s spectra of Pt/N-HCS900-4-120 showed the presence of quaternary, pyridinic and pyrollic nitrogen atoms. These nitrogen doped carbon supported Pt nanoparticle catalysts were observed to reduce cinnamaldehyde to the unsaturated alcohol, cinnamyl alcohol (isopropanol/30 bar H 2 /80 • C) with >99% conversion and selectivity. The catalyst used in the reduction of cinnamaldehyde to cinnamyl alcohol could be recycled 12 times with minimal loss in conversion and this correlated with the small amount of Pt leaching or physical loss of catalyst (<2%). The corresponding Pt/catalyst made on undoped HCSs showed a much greater loss of activity with recycling. It is seen that N doping of carbon is an effective method to bind Pt to carbon.
Here, we employed colloidal Pd and Pt nanoparticles synthesized by dendrimer templates as well as... more Here, we employed colloidal Pd and Pt nanoparticles synthesized by dendrimer templates as well as reverse microemulsions in the selective oxidation of styrene using tert-butyl hydroperoxide (TBHP) as an oxidant. We investigate their catalytic behavior and the feasibility as oxidation catalysts. High selectiv-ity to styrene oxide, was achieved in the oxidation of styrene. The catalytic activities in terms of styrene conversion decreased in the order of dendrimer-templated Pd nanoparticles > thiol-capped Pd nanoparti-cles by reverse microemulsions > dendrimer-templated Pt nanoparticles > thiol-capped Pt nanoparticles by reverse microemulsions. This indicated that Pd-based catalysts were more efficient to catalyze the styrene oxidation reaction as compared to Pt-based catalysts. Furthermore, the dendrimer template synthetic method produced catalysts with higher activity as compared to those prepared by the reverse microemulsion template. The catalytic activities and selectivity profiles in various reaction conditions such as solvent type, styrene to TBHP ratio, type of catalysts, catalyst dosing, and temperature are discussed. The changes of average nanoparticle size after the reactions and the recyclability of Pd and Pt catalysts are examined. Overall results indicated that although higher catalytic activities were obtained with the use of dendrimer-templated nanoparticles, better recyclability as well as selectivity to styrene oxide was achieved with the use of thiol-capped Pd nanoparticles synthesized by reverse microemulsions.
We present a study on the synthesis of narrowly dispersed silver and gold nanoparticles using gen... more We present a study on the synthesis of narrowly dispersed silver and gold nanoparticles using generation five amino-terminated poly(amidoamine) dendrimers as a template. UV–vis spectrophotometry was performed to monitor the synthesis process and to characterize the metal nanoparticles. Infrared (IR) spectroscopy, and transmission electron microscopy (TEM) were also used to characterize the metal nanoparticles. A catalytic oxidation of morin (quercetin) in the presence of hydrogen peroxide was performed as a model reaction to evaluate the metal nanoparticle activities. Ultra high performance liquid chromatography analysis was performed to identify the reaction products. The kinetic data obtained were modeled to the Langmuir–Hinshelwood equation. The encapsulated silver and gold nanoparticles show high activity which confirm the passive interaction with the dendrimer.
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Papers by Reinout Meijboom
absence of any solvent using -Al2O3 supported copper and gold nanoparticles. Li2O and ionic liquids
were used as additive and stabilizers for the synthesis of the catalysts. The physico-chemical properties
of the catalysts were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction
spectroscopy (XRD), N2 absorption/desorption (BET), transmission electron microscopy (TEM), scanning
electron microscopy (SEM), thermogravimetric analysis (TGA) and temperature programmed reduction
(TPR), whereas, the oxidation reaction was followed by gas chromatography with a flame ionization
detector (GC-FID). The as prepared catalysts exhibited good catalytic performance in terms of conversion
and selectivity towards benzaldehyde. The performance of the Au-based catalysts is significantly
higher than that of the Cu-based catalysts. For both Cu and Au catalysts, the conversion of benzyl alcohol
increased as the reaction proceeds, while the selectivity for benzaldehyde decreased. Moreover, the catalysts
can be easily recycled and reused with neither significant loss of activity nor selectivity. A kinetic
study for the Cu and Au-catalyzed oxidation of benzyl alcohol to benzyldehyde is reported. The rate at
which the oxidation of benzyl alcohol is occurring as a function of catalyst and oxidant amounts was
investigated, with the apparent rate constant, kapp being proportional to the amount of nano catalyst and
oxygen present in the system.
absence of any solvent using -Al2O3 supported copper and gold nanoparticles. Li2O and ionic liquids
were used as additive and stabilizers for the synthesis of the catalysts. The physico-chemical properties
of the catalysts were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction
spectroscopy (XRD), N2 absorption/desorption (BET), transmission electron microscopy (TEM), scanning
electron microscopy (SEM), thermogravimetric analysis (TGA) and temperature programmed reduction
(TPR), whereas, the oxidation reaction was followed by gas chromatography with a flame ionization
detector (GC-FID). The as prepared catalysts exhibited good catalytic performance in terms of conversion
and selectivity towards benzaldehyde. The performance of the Au-based catalysts is significantly
higher than that of the Cu-based catalysts. For both Cu and Au catalysts, the conversion of benzyl alcohol
increased as the reaction proceeds, while the selectivity for benzaldehyde decreased. Moreover, the catalysts
can be easily recycled and reused with neither significant loss of activity nor selectivity. A kinetic
study for the Cu and Au-catalyzed oxidation of benzyl alcohol to benzyldehyde is reported. The rate at
which the oxidation of benzyl alcohol is occurring as a function of catalyst and oxidant amounts was
investigated, with the apparent rate constant, kapp being proportional to the amount of nano catalyst and
oxygen present in the system.