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Biomedical subjects

J Penfold

Publications and source records attributed to J Penfold.

At least 37 records · Page 2Linked to original sources
PubMed2003

The structure of mixed nonionic surfactant monolayers at the air-water interface: the effects of different alkyl chain lengths.

The structure of mixed nonionic surfactant monolayers of monodecyl hexaethylene glycol (C10E6) and monotetradecyl hexaethylene glycol (C14E6) adsorbed at the air-water interface has been determined by specular neutron reflectivity. Using partial isotopic labeling (deuterium for hydrogen) of the alkyl and ethylene oxide chains of each surfactant, the distribution and relative positions of the chains at the interface have been obtained. The packing of the two different alkyl chain lengths results in structural changes compared to the pure surfactant monolayers. This results in changes in the relative positions of the alkyl chains and of the ethylene oxide chains at the interface. The role of the alkyl chain length is contrasted with that of the ethylene oxide chain length, determined from results reported previously on the nonionic surfactant mixture of monododecyl triethylene glycol (C12E3) and monododecyl octaethylene glycol (C12E8).

Journal Article↗
PubMed2002

Comparison of the coadsorption of benzyl alcohol and phenyl ethanol with the cationic surfactant, hexadecyl trimethyl ammonium bromide, at the air-water interface.

A comparison of the coadsorption of benzyl alcohol and phenyl ethanol with the cationic surfactant, hexadecyl trimethyl ammonium bromide, C16TAB, at the air-water interface is made using the specular reflection of neutrons. The phenyl ethanol is more surface active than the benzyl alcohol, and competes more effectively with the C16TAB for the interface. The structure of the C16TAB component in the mixed monolayer is compared with the structure of the pure C16TAB monolayer at an equivalent area per molecule. The addition of the aromatic alcohol subtly alters the conformation of the C16TAB and draws it closer to the aqueous subphase. The center of the alcohol distribution is located in the interface adjacent to the C6 group of the C16TAB alkyl chain closest to the headgroup. Compared to the benzyl alcohol, the more hydrophobic phenyl ethanol is slightly farther away from the headgroup, and has a greater impact on the conformation of the alkyl chain of the C16TAB.

Journal Article↗
PubMed2002

Adsorption of nonionic mixtures at the air-water interface: effects of temperature and electrolyte.

Specular neutron reflection has been used to investigate the effects of temperature and added electrolyte on the adsorption of nonionic surfactants and nonionic surfactant mixtures at the air-water interface. For the alkyl poly-oxyethylene oxide nonionic surfactants, C(n)EO(m), the adsorption at the air-water interface is independent of temperature for surfactants with shorter ethylene oxide groups, whereas there is an increasing tendency for increased adsorption with temperature for surfactants with longer ethylene oxide groups. The addition of "salting in" (sodium thiocyanate, NaSCN) and "salting out" (sodium chloride, NaCl, sodium sulphate, Na2SO4) electrolyte results in reduced and enhanced adsorption, respectively, for C12EO8, whereas both types of electrolyte result in enhanced adsorption for C12EO12. The addition of electrolyte does not substantially alter the temperature dependence of the adsorption of the pure monolayers. For the nonionic mixtures of C12EO3/C12EO8 increasing temperature results in a surface richer in the least surface-active component, C12EO8. For the same nonionic mixture, the addition of "salting in" and "salting out" electrolyte results in an reduced and increased adsorption, respectively. The addition of "salting in" electrolyte results in a surface more rich in C12EO3, whereas for the addition of both "salting in" and "salting out" electrolyte the surface composition is essentially unaltered.

Journal Article↗
PubMed2000

Surfactant layers at the air/water interface: structure and composition.

The use of neutron reflectometry to study the structure and composition of surfactant layers adsorbed at the air/water interface is reviewed. A critical assessment of the results from this new technique is made by comparing them with the information available from all other techniques capable of investigating this interface.

Adsorption↗
PubMed1999

Structural and Thermodynamic Properties of Solutions of Butane in Aqueous Sodium Dodecyl Sulfate: A Study Using Neutron Scattering and Solubility Measurements.

The solubility of n-butane at a pressure of 1.013 bar in aqueous solutions of sodium dodecyl sulfate (SDS) has been measured over a range of concentration from below the critical micelle concentration (CMC) at about 8 mol kg(-1) to about 90 mol kg(-1) at three different temperatures. The free energy, enthalpy, and entropy of transfer of butane from water to the micelle were respectively -19.0 kJ mol(-1), 5.5 kJ mol(-1), and 80 J K(-1) mol(-1). At 68 mol kg(-1) a transition was found with a free energy of about -400 J mol(-1). Small-angle neutron experiments were used to study the effect of butane on the state of aggregation of the SDS. For each butane molecule incorporated into a micelle, the aggregation number of the SDS increased by an average of about 1.4 molecules. Thus, at 1.013 bar of butane and 50 mM SDS, where the solubility is about 1 butane to 10 SDS, the average micelle increases in size by about 20%, most of which comes from the additional SDS molecules. The aggregation behavior is qualitatively similar to that reported for hexane, heptane, and octane, but the effect seems to be larger for butane for a given volume of solute hydrocarbon. Small-angle scattering did not observe any substantial change in structure across the phase transition at 68 mol kg(-1). Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Neutron Reflectivity Study of the Adsorption of beta-Lactoglobulin at a Hydrophilic Solid/Liquid Interface.

Adsorption of a globular protein on a hydrophilic solid/liquid interface was investigated. Neutron reflectivity was used to determine structural information on an adsorbed beta-lactoglobulin layer at a hydrophilic silicon surface. The thickness of the protein film was found to be compatible with the diameter of the native protein, indicating that possible conformational changes of the protein during adsorption are not gross enough to alter the shape of the protein. The amount adsorbed is consistent with that derived by our ellipsometry measurements, obtained in similar experiments. Evidence for significant H-D exchange in the adsorbed protein was found. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Incidence and predictors of central venous catheter related infection in intensive care patients.

This study investigated the incidence of and risk factors for central venous catheter (CVC) infection in intensive care. CVCs were prospectively studied in patients who had lines inserted in general or neurosurgical intensive care and were expected to have the line in situ for at least 72 hours. Catheters (n = 119) were cultured for CVC-related infection (CRI; > 15 colony forming units) and blood cultures done when indicated. CRI was identified in 32 (26.9%) catheters, CVC related bacteraemia in five cases (4.2%) and CVC related sepsis in none. After adjustment for duration of catheterization, independent predictors of CVC related infection were catheter insertion site, with jugular sites having the highest risk, and primary diagnosis, with neurosurgical patients at least risk.

Adolescent↗
PubMed1998

The Adsorption of Lysozyme at the Silica-Water Interface: A Neutron Reflection Study.

The adsorption of lysozyme (chicken egg white) from aqueous solution on to the hydrophilic silica surface and the variation of interfacial structure with solution conditions have been studied by neutron reflection. The accurate determination of the adsorbed layer thicknesses in combination with the dimension of the globular structure of lysozyme allows us to postulate the mean structural conformation of the lysozyme molecules within the adsorbed layer. It was found that the adsorption was completely reproducible with respect to lysozyme concentration, but it was irreversible. The effect of ionic strength on the adsorption of lysozyme was examined at pH 7 and at a bulk lysozyme concentration of 0.03 g dm-3. The adsorbed layer was not affected by changes in ionic strength when the total ionic strength was below 0.05 M, but above this concentration addition of NaCl gradually reduced the amount of lysozyme adsorbed. Complete removal of adsorbed lysozyme was achieved when the total ionic strength was above 0.5 M. The effect of solution pH on the amount of lysozyme adsorbed was characterized by varying the pH in cycles at fixed lysozyme concentrations. Adsorption was found to be completely reversible with respect to pH over a wide protein concentration range. The level of surface excess was dominated by the electrostatic repulsion between lysozyme molecules within the adsorbed layers, rather than the attraction between the surface and lysozyme. The lysozyme layer structure along the surface normal was characterized by varying the isotopic composition of the water. At pH 7 a monolayer 30 +/- 2 Å thick was formed when the lysozyme concentration was below 0.03 g dm-3, indicating that the lysozyme was adsorbed with its long axis parallel to the surface (sideways-on). At higher concentrations the thickness of the layer changed to 60 +/- 2 Å, suggesting the formation of a bilayer of lysozyme molecules in the sideways-on configuration. When the lysozyme concentration is above 1 g dm-3 the surface excess within the inner layer is sufficiently high that repulsion within the adsorbed layer becomes significant and the molecules start to tilt towards longways-on adsorption. At pH 4, the electrostatic repulsion between the adsorbed molecules is stronger than at pH 7, resulting in a lower surface excess and a tilting away from the sideways-on configuration at lower surface concentration. Copyright 1998 Academic Press.

Journal Article↗
PubMed1997

Neutron and X-Ray Reflectivity Studies of the Adsorption of Aerosol-OT at the Air-Water Interface: The Structure of the Calcium Salt

We have used neutron and X-ray reflection to determine the structure of a layer of calcium bis-(2-ethyl 1-hexyl) sulphosuccinate (Aerosol-OT or AOT) adsorbed at the air/solution interface. The widths of the distributions of the chains and head groups of the molecule, and their positions in relation to the underlying water, have been measured at four concentrations varying from the solubility limit (CMC) at 4 x 10(-4) M to 1 x 10(-6) M. Over this concentration range the coverage changes from 68 ± 3 to 142 ± 8 Å2 per AOT unit. The structure of the layer both is quite different from that of NaAOT and varies quite differently with surface concentration. The Ca(AOT)2 layer is slightly (1 Å) further out from the water, but the chain region is thinner for the calcium surfactant. This is reflected most in the greatly reduced chain to head separation, which drops from about 6 Å in NaAOT to about 4 Å in Ca(AOT)2.

Journal Article↗
PubMed1997

The Structure of Nonionic Micelles in Less Polar Solvents

Small angle neutron scattering, SANS, has been used to investigate the structure and geometry of nonionic micelles of monododecyl octaethylene glycol C12EO8, monododecyl hexaethylene glycol C12EO6, and monohexadecyl octaethylene glycol C16EO8 in less polar solvents: mixed solvents of water and glycerol, sorbitol, and ethylene glycol. For C12EO8 in glycerol/water solvent mixtures the addition of glycerol results in an increase in the micelle aggregation number and a decrease in the ethylene oxide (EO) headgroup hydration. The increase in micelle size is associated with the dehydration of the ethylene oxide headgroup and the consequent closer proximity of the lower consolute boundary. This follows from the observation that the same trends are seen at fixed glycerol content and increasing temperature where the intermicellar interactions become attractive. For C12EO6 micelles in water/ethylene glycol mixtures similar trends are observed, and the same conclusions may be drawn despite an increase in the clouding temperature. This can be explained by a greater dehydration of the solvent ethylene glycols such that the rate of change of solvent quality for the micelles with temperature is suppressed. A combination of SANS and Couette shear flow alignment has been used to investigate the structure of C16EO8 micelles in water/sorbitol and water/glycerol mixtures. The addition of sorbitol or glycerol results in less anisotropically shaped micelles. The resulting micelles are more labile, and show evidence of flexibility and shear induced transformations or extreme polydispersity. The temperature dependence of the micelle rod length of C16EO8/water/glycerol is similar to that previously observed for C16EO6 and C16EO8 micelles in water and for the mixed micelles of C16EO6/C16TAB.

Journal Article↗
PubMed1996

The Influence of Sorbitol on the Adsorption of Surfactants at the Air-Liquid Interface

Neutron reflection and surface tension have been used to study the adsorption of the nonionic surfactant monododecyl hexaethylene glycol (C12E6) and the mixed nonionic-anionic surfactants n-dodecyl triethylene glycol (C12E3) and Sodium dodecyl sulfate (SDS) at the air-liquid interface. Water and a sorbitol (d-glucitol, CH2OH(HCOH)4CH2OH)/water mixture were selected as the solvents. The addition of 300 g/liter of sorbitol to an aqueous solution of C12E6 reduces the critical micellar concentration, cmc, from approximately 7 x 10(-5) to approximately 3 x 10(-5) M, and increases the surface pressure at the cmc; the effect on the C12E3/SDS mixture is less. Despite these changes, the pattern of adsorption at the air-liquid interface is essentially unaltered by the addition of sorbitol, and the surface tension and neutron reflectivity data are in good agreement. The consequences of the sorbitol addition are however seen directly in the structure of the C12E6 monolayer. The ethylene oxide (EO) chain is more extended than in water, and more displaced from the solvent, consistent with dehydration of the ethylene oxide group.

Journal Article↗
PubMed1995

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.

Adsorption↗
PubMed1995

Final adult height and its relationship to blood glucose control and microvascular complications in IDDM.

The effect of longitudinal blood glucose control on final adult height was evaluated in 181 subjects (94 women and 87 men) with IDDM. Diabetes onset was at a median age of 6.9 years with an interquartile range of 4.7 years. Longitudinal glycated haemoglobin values were determined over a mean period of 6.6 +/- 2.6 years during their growth phase. Serial eye and joint examinations and urinary albumin excretion rates were performed with final assessment being carried out at a mean age of 21.1 +/- 3.0 years. The mean adult height standard deviation score of the whole group was -0.22 +/- 1.15 and was reduced compared to the mean height of the general population and to the mean height of the subjects' parents and siblings. There was an inverse correlation with mean longitudinal glycated haemoglobin and final adult height (p < 0.01). There was also an inverse relationship between adult height and the severity of eye, kidney, and joint complications, but when controlled by glycated haemoglobin, this relationship only remained significant for eye complications. Final adult height is reduced in subjects with early onset IDDM who remain in poor blood glucose control during their growth period.

Adult↗
PubMed1992

Pain syndromes in HIV infection.

Pain causes considerable disability and discomfort in HIV (Human Immunodeficiency Virus) infected individuals. A large number of patients infected with HIV suffer from one or more pain-related syndromes. Pain is under-reported and suboptimally managed in these patients. An outline of the different pain syndromes, including headache, oral cavity pain, chest pain, abdominal pain, anorectal pain, musculoskeletal pain and peripheral neuropathic pain, and their aetiologies are discussed. Current pain management modalities, including non-narcotic and narcotic analgesics, tricyclic antidepressants, anticonvulsants, physical therapy and psychological techniques, are outlined. Treatment should be based on the same principles applied to the management of cancer-related pain. A multi-disciplinary, comprehensive approach to pain management will assist these individuals to achieve improved levels of comfort, function and quality of life in this ultimately terminal illness.

HIV Infections↗
PubMed1991

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.

Biophysical Phenomena↗