Towards a molecular understanding of the water purification properties of Moringa seed proteins.

Seed extracts from Moringa oleifera are of wide interest for use in water purification where they can play an important role in flocculation; they also have potential as anti-microbial agents. Previous work has focused on the crude protein extract. Here we describe the detailed biophysical characterization of individual proteins from these seeds. The results provide new insights relating to the active compounds involved. One fraction, designated Mo-CBP3, has been characterized at a molecular level using a range of biochemical and biophysical techniques including liquid chromatography, X-ray diffraction, mass spectrometry, and neutron reflection. The interfacial behavior is of particular interest in considering water purification applications and interactions with both charged (e.g. silica) and uncharged (alumina) surfaces were studied. The reflection studies show that, in marked contrast to the crude extract, only a single layer of the purified Mo-CBP3 binds to a silica interface and that there is no binding to an alumina interface. These observations are consistent with the crystallographic structure of Mo-CBP3-4, which is one of the main isoforms of the Mo-CBP3 fraction. The results are put in context of previous studies of the properties of the crude extract. This work shows possible routes to development of separation processes that would be based on the specific properties of individual proteins.

Characterization of the flow of anisotropic colloidal particles using energy-dispersive X-ray diffraction.

The technique of energy-dispersive X-ray diffraction to study the orientation of microscopic crystalline particles dispersed in a liquid has been described recently. This complements previous neutron diffraction studies by permitting measurements at higher spatial resolution. Work with synchrotron radiation and high-energy X-rays has allowed studies on liquid dispersions flowing in pipes with a thickness of about 1 cm and a spatial resolution of 100 mum. Kaolinite is often found as a dispersion of monocrystalline, microscopic plates. The crystallographic layer structure is commensurate with the particle shape: the 00l direction is normal to the plane of the plates. Measurements of diffraction of the flowing liquid dispersion in a pipe oriented in various directions to the incident beam can be used to deduce the average orientation and order parameters of the particles. The competing effects of alignment with walls and in flow fields were observed. Further work has measured the orientation near a bend in a pipe.

Pumping of water with ac electric fields applied to asymmetric pairs of microelectrodes.

Bulk fluid flow induced by an ac electric potential with a peak voltage below the ionization potential of water is described. The potential is applied to an ionic solution with a planar array of electrodes arranged in pairs so that one edge of a large electrode is close to an opposing narrow electrode. During half the cycle, the double layer on the surface of the electrodes charges as current flows between the electrodes. The electrodes charge in a nonuniform manner producing a gradient in potential parallel to the surface of the electrodes. This gradient drives the ions in the double layer across the surface of the electrode and this in turn drags the fluid across the electrode surface. The anisotropic nature of the pairs of electrodes is used to produce a net flow of fluid. The flow produced is approximately uniform at a distance from the electrodes that is greater than the periodicity of the electrode array. The potential and frequency dependence of this flow is reported and compared to a simple model. This method of producing fluid flow differs from electrical and thermal traveling-wave techniques as only a low voltage is required and the electrode construction is much simpler.

Neutron reflection study of bovine beta-casein adsorbed on OTS self-assembled monolayers.

Specular neutron reflection has been used to determine the structure and composition of bovine beta-casein adsorbed on a solid surface from an aqueous phosphate-buffered solution at pH 7. The protein was adsorbed on a hydrophobic monolayer self-assembled from deuterated octadecyltrichlorosilane solution on a silicon (111) surface. A two-layer structure formed consisting of one dense layer of thickness 23 +/- 1 angstroms and a surface coverage of 1.9 milligrams per square meter adjacent to the surface and an external layer protruding into the solution of thickness 35 +/- 1 angstroms and 12 percent protein volume fraction. The structure of the (beta-casein) layer is explained in terms of the charge distribution in the protein.

Coupling of spectrin and polylysine to phospholipid monolayers studied by specular reflection of neutrons.

The technique of specular reflection of neutrons is applied for the first time to study the charge-dependent interaction of the protein spectrin and the polypeptide poly-L-lysine with model phospholipid monolayers in the condensed phase state. We first established the structure of a pure monolayer of dimyristolyphosphatidylcholine (DMPC) in both the expanded and condensed fluid phase states without protein in the subphase. The thickness of the hydrocarbon chains increases from 11.4 +/- 1.5 A in the expanded state to 15.8 +/- 1.5 A in the condensed state, whereas the head group region is approximately 10 A thick for both phase states. When spectrin is present in the subphase, the dimensions of DMPC in the condensed state are not significantly affected, but there is approximately 0.09 volume fraction spectrin in the head group region. Lipid-spectrin coupling is enhanced by electrostatic interaction, as the volume fraction of spectrin in the head group region increases to 0.22 in a mixed monolayer of DMPC and negatively charged dimyristolyphosphatidylglycerol in the condensed state. In contrast to spectrin, polylysine does not penetrate the head group region, but forms a layer electrostatically adsorbed to the charged head groups.

Structure of an adsorbed dimyristoylphosphatidylcholine bilayer measured with specular reflection of neutrons.

Using specular reflection of neutrons, we investigate for the first time the structure of a single dimyristoylphosphatidylcholine bilayer adsorbed to a planar quartz surface in an aqueous environment. We demonstrate that the bilayer is strongly adsorbed to the quartz surface and is stable to phase state changes as well as exchange of the bulk aqueous phase. Our results show that the main phase transition is between the L alpha phase and the metastable L beta'* phase, with formation of the P beta' ripple phase prevented by lateral stress on the adsorbed bilayer. By performing contrast variation experiments, we are able to elucidate substantial detail in the interfacial structure. We measure a bilayer thickness of 43.0 +/- 1.5 A in the L alpha phase (T = 31 degrees C) and 46.0 +/- 1.5 A in the L beta'* phase (T = 20 degrees C). The polar head group is 8.0 +/- 1.5 A thick in the L alpha phase. The water layer between the quartz and bilayer is 30 +/- 10 A for the lipid in both the L alpha and L'* phase. Our results agree well with those previously reported from experiments using lipid vesicles and monolayers, thus establishing the feasibility of our experimental methods.

Labour-intensive civil construction.

This paper presents the results of a literature review of the ergonomics of labour-intensive civil construction. The work capacity of Asian and European workers is compared. Metabolic rates and other factors limiting productivity presented in the literature are summarised. Comparison is made with the results of productivity measurements taken in India and Indonesia. The considerable scope and need for further work in this field is outlined.