Modifying the crystallization of amorphous magnesium-calcium phosphate nanoparticles with proteins from Moringa oleifera seeds.

HYPOTHESIS: Endogenous Amorphous Magnesium-Calcium Phosphates (AMCPs) form in the human body and, besides their biomedical implications, the development of effective stabilization strategies is an open challenge. An interesting approach consists of stabilizing amorphous phosphates with macromolecules that have beneficial effects from a nutritional/medical point of view, for a potential application of the hybrid particles in nutraceutics or drug delivery. EXPERIMENTAL: We investigated the effect of proteins extracted from Moringa oleifera seeds (MO) on the features of synthetic analogs of AMCPs and on their crystallization pathway. The stability of the amorphous phase was studied using infrared spectroscopy and X-ray diffraction. To unravel the effect of the protein on the nano-scale structure of the inorganic particles, we also studied how MO affects the features of the amorphous phase using thermal analysis, small angle X-ray scattering and confocal Raman microscopy. FINDINGS: We observed that MO markedly delays the transition from amorphous to crystalline phosphate in a concentration-dependent fashion. Interestingly, MO not only enhances the lifetime of the amorphous phase, but also influences the type and amount of crystalline material formed. The results are relevant from both a fundamental and an applied perspective, paving the way for the use of these hybrids in the field of nutraceutics and drug delivery.

Comparative study of flocculation and adsorption behaviour of water treatment proteins from Moringa peregrina and Moringa oleifera seeds.

Trees of Moringa oleifera are the most widely exploited species of Moringa and proteins extracted from its seeds have been identified as the most efficient natural coagulant for water purification. Largely for climatic reasons, other Moringa species are more accessible in some regions and this paper presents a comparative study of the adsorption to different materials of the proteins extracted from seeds of Moringa peregrina and Moringa oleifera to explore their use as flocculating agents in regions where each is more readily accessible. Results showed that Moringa peregrina seed proteins had higher adsorption to alumina compared to silica, in contrast to opposite behavior for Moringa oleifera. Both species provide cationic proteins that can act as effective coagulants for the various impurities with different surface potential. Despite the considerable similarity of the amino acid composition, the seed proteins have significantly different adsorption and this presents the opportunity to improve processes by choosing the optimal species or combination of species depending on the type of impurity or possible development of separation processes.

Sticking particles to solid surfaces using Moringa oleifera proteins as a glue.

Experimental studies have been made to test the idea that seed proteins from Moringa oleifera which are novel, natural flocculating agents for many particles could be used to promote adhesion at planar interfaces and hence provide routes to useful nanostructures. The proteins bind irreversibly to silica interfaces. Surfaces that had been exposed to protein solutions and rinsed were then exposed to dispersions of sulfonated polystyrene latex. Atomic force microscopy was used to count particle density and identified that the sticking probability was close to 1. Measurements with a quartz crystal microbalance confirmed the adhesion and indicated that repeated exposures to solutions of Moringa seed protein and particles increased the coverage. Neutron reflectivity and scattering experiments indicate that particles bind as a monolayer. The various results show that the 2S albumin seed protein can be used to fix particles at interfaces and suggest routes for future developments in making active filters or improved interfaces for photonic devices.

Salt induced polystyrene latex flocs investigated by neutron scattering.

Studies with a model system consisting of polystyrene latex particles showed that the protein from seeds of Moringa trees adsorbs to the surface and causes flocculation as unusually dense aggregates. In this study, electrolytes sodium chloride (NaCl), ferric chloride (FeCl3) and aluminium sulfate (Al2(SO4)3) have been used to aggregate model polystyrene particles. The study augments previous work using neutron scattering on the flocculation of polystyrene latex with protein from seeds of Moringa trees that had indicated higher floc dimension, df, values as the concentration of particles increased. The measurements were made using ultra small-angle neutron scattering. Generally the fractal dimension, and thus the floc density, increased with particle concentration and salt concentration. Flocculation was apparent at much lower concentrations of FeCl3 and Al2(SO4)3 than of NaCl. The values of df were found not to simply scale with ionic strength for the three electrolytes studied with FeCl3 being the most effective flocculating agent.

Interaction of Moringa oleifera seed protein with a mineral surface and the influence of surfactants.

The paper describes the adsorption of purified protein from seeds of Moringa oleifera to a sapphire interface and the effects of addition of the anionic surfactant sodium dodecylsulfate (SDS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB). Neutron reflection was used to determine the structure and composition of interfacial layers adsorbed at the solid/solution interface. The maximum surface excess of protein was found to be about 5.3 mg m(-2). The protein does not desorb from the solid/liquid interface when rinsed with water. Addition of SDS increases the reflectivity indicating co-adsorption. It was observed that CTAB is able to remove the protein from the interface. The distinct differences to the behavior observed previously for the protein at the silica/water interface are identified. The adsorption of the protein to alumina in addition to other surfaces has shown why it is an effective flocculating agent for the range of impurities found in water supplies. The ability to tailor different surface layers in combination with various surfactants also offers the potential for adsorbed protein to be used in separation technologies.

A study of the removal of heavy metals from aqueous solutions by Moringa oleifera seeds and amine-based ligand 1,4-bis[N,N-bis(2-picoyl)amino]butane.

Uptake for lead, copper, cadmium, nickel and manganese from aqueous solution using the Moringa oleifera seeds biomass (MOSB) and amine-based ligand (ABL) was investigated. Experiments on two synthetic multi-solute systems revealed that MOSB performed well in the biosorption and followed the decreasing orders Pb(II)>Cu(II)>Cd(II)>Ni(II)>Mn(II) and Zn(II)>Cu(II)>Ni(II). The general trend of the heavy metal ions uptake by the amine-based ligand followed decreased in the order Mn>Cd>Cu>Ni>Pb, which is the reverse trend for what was observed for MOSB. Comparing the single- and multi-metal solutions, there was no clear effect in the biosorption capacity of MOSB suggesting the presence of sufficient active binding sites for all metal ions studied. The MOSB performance is also not affected by pH in the range 3.5-8.

Interactions of surfactants with a water treatment protein from Moringa oleifera seeds in solution studied by zeta-potential and light scattering measurements.

Protein extracted from Moringa oleifera (MO) seeds has been advocated as a cheap and environmental friendly alternative to ionic flocculants for water purification. However, the nature and mechanism of its interaction with particles in water, as well as with dissolved surface-active molecules, are not well understood. In this article, we report studies of the protein and its interaction with four surfactants using dynamic light scattering (DLS), zeta-potential and turbidity measurements. Zeta-potential measurements identified points of charge reversal and the turbidity and DLS measurements were used to characterize the microstructure and size of protein-surfactant complexes. From the points of charge reversal, it was estimated that 7 anions are required to neutralize the positive charges of each protein molecule at pH 7. For protein mixtures with sodium dodecyl sulfate and dodecyl di-acid sodium salt, the peak in turbidity corresponds to concentrations with a large change in zeta-potential. No turbidity was observed for protein mixtures with either the nonionic surfactant Triton X-100 or the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate. Changes of pH in the range 4-10 have little effect on the zeta-potential, turbidity, and the hydrodynamic radius reflecting the high isoelectric point of the protein. Addition of small amounts of salt has little effect on the size of protein in solution. These results are discussed in the context of the use of the MO protein in water treatment.

Adsorption of a water treatment protein from Moringa oleifera seeds to a silicon oxide surface studied by neutron reflection.

An extract from the seeds of the Moringa oleifera tree that is principally a low molecular mass protein is known to be efficient as a coagulating agent for water treatment. The present paper investigates the adsorption of the purified protein to silica interfaces in order to elucidate the mechanism of its function as a flocculent. Neutron reflection permits the determination of the structure and composition of interfacial layers at the solid/solution interface. Dense layers of protein with about 5.5 mg m(-2) were found at concentrations above 0.025% wt. The overall thickness with a dense layer in excess of 60 A at 0.05 wt % suggests strong co-operative binding rather than single isolated molecules. An ionic surfactant, sodium dodecyl sulfate, was also seen to coadsorb. This strong adsorption of protein in combination with the tendency for the protein to associate suggests a mechanism for destabilizing particulate dispersions to provide filterable water. This can occur even for the protein that has previously been identified as being of low mass (about 7 kDaltons) and thus is unlikely to be efficient in bridging or depletion flocculation.