On the interaction of bovine serum albumin with ionic surfactants: Temperature induced EPR changes of a maleimide nitroxide reflect local protein dynamics and probe solvent accessibility

The interaction of bovine serum albumin (BSA) with the ionic surfactants sodium dodecylsulfate (SDS, anionic), cetyltrimethylammonium chloride (CTAC, cationic) and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS, zwitterionic) was studied by electron paramagnetic resonance (EPR) spectroscopy of spin label covalently bound to the single free thiol group of the protein. EPR spectra simulation allows to monitor the protein dynamics at the labeling site and to estimate the changes in standard Gibbs free energy, enthalpy and entropy for transferring the nitroxide side chain from the more motionally restricted to the less restricted component. Whereas SDS and CTAC showed similar increases in the dynamics of the protein backbone for all measured concentrations. HPS presented a smaller effect at concentrations above 1.5 mM. At 10 mM of surfactants and 0.15 mM BSA, the standard Gibbs free energy change was consistent with protein backbone conformations more expanded and exposed to the solvent as compared to the native protein, but with a less pronounced effect for HPS. In the presence of the surfactants, the enthalpy change, related to the energy required to dissociate the nitroxide side chain from the protein, was greater, suggesting a lower water activity. The nitroxide side chain also detected a higher viscosity environment in the vicinity of the paramagnetic probe induced by the addition of the surfactants. The results suggest that the surfactant-BSA interaction, at higher surfactant concentration, is affected by the affinities of the surfactant to its own micelles and micelle-like aggregates. Complementary DLS data suggests that the temperature induced changes monitored by the nitroxide probe reflects local changes in the vicinity of the single thiol group of Cys-34 BSA residue. (C) 2011 Elsevier B.V. All rights reserved.

Interaction of bovine serum albumin (BSA) with ionic surfactants evaluated by electron paramagnetic resonance (EPR) spectroscopy

EPR spectra of 5- and 16-doxyl stearic acid nitroxide probes (5-DSA and 16-DSA, respectively) bound to bovine serum albumin (BSA) revealed that in the presence of ionic surfactants, at least, two label populations coexist in equilibrium. The rotational correlation times (tau) indicated that component I displays a more restricted mobility state, associated to the spin labels bound to the protein; the less immobilized component 2 is due to label localization in the surfactant aggregates. For both probes, the increase of surfactant concentration leads to higher motional levels of component 1 followed by a simultaneous decrease of this fraction of nitroxides and its conversion into component 2. For 10 mM cethyltrimethylammonium chloride (CTAC), the nitroxides are 100% bound to the protein, whereas at 10mM N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and sodium dodecyl sulfate (SDS) the fractions of bound nitroxides are reduced to 18% and 86%, respectively. No significant polarity changes were observed in the whole surfactant concentration range for component 1. Moreover, at higher surfactant concentration, component 2 exhibited a similar polarity as in the pure surfactant micelles. For 16-DSA the surfactant effect is different: at 10mM of HPS and CTAC the fractions of bound nitroxides are 76% and 49%, respectively, while at 10 mM SDS they are present exclusively in a micellar environment, consistent with 100% of component 2. Overall, both SDS and HPS are able to effectively displace the nitroxide probes from the protein binding sites. while CTAC seems to affect the nitroxide binding to a significantly smaller extent. (C) 2008 Elsevier B.V. All rights reserved.

Application of bending under tension test to determine the effect of tool radius and the contact pressure on the coefficient of friction in sheet metal forming

To quantify the frictional behaviour in sheet forming operations, several laboratory experiments which simulate the real forming conditions are performed. The Bending Under Tension Test is one such experiment which is often used to represent the frictional flow of sheet material around a die or a punch radius. Different mathematical representations are used to determine the coefficient of friction in the Bending Under Tension Test. In general the change in the strip thickness in passing over the die radius is neglected and the radius of curvature to thickness ratio is assumed to be constant in these equations. However, the effect of roller radius, sheet thickness and the surface pressure are also omitted in some of these equations. This work quantitatively determined the effect of roller radius and the tooling pressure on the coefficient of friction. The Bending Under Tension Test was performed using rollers with different radii and also lubricants with different properties. The tool radii were found to have a direct influence in the contact pressure. The effect of roller radius on friction was considerable and it was observed that there is a clear relationship between the contact pressure and the coefficient of friction.

Alternative methods for the MnO2 oxidation of codeine methyl ether to thebaine utilizing ionic liquids

The MnO2 oxidation of codeine methyl ether, CME, to thebaine has been accomplished via the use of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4. The ionic liquid has been used to remove or extract excess MnO2 and associated impurities from the reaction mixture to afford thebaine in 36 to >95% yield. © 2001 Elsevier Science Ltd. All rights reserved.

Manganese dioxide allylic and benzylic oxidation reactions in ionic liquids

Ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate [bmIm][BF₄] and 1-butyl-3-methylimidazolium hexafluorophosphate [bmIm][PF₆] were evaluated as reaction media for allylic and benzylic oxidation reactions using manganese dioxide. The use of ionic liquids as an extractant in the reaction work-up was also investigated. Procedures for recycling of the [bmIm][PF₆] ionic liquids used in these MnO₂ oxidation reactions were also developed.

Ice and pulsed electromagnetic field to reduce pain and swelling after distal radius fractures

Objective: To examine the relative effectiveness of ice therapy and/or pulsed electromagnetic field in reducing pain and swelling after the immobilization period following a distal radius fracture.Methods: A total of 83 subjects were randomly allocated to receive 30 minutes of either ice plus pulsed electromagnetic field (group A); ice plus sham pulsed electromagnetic field (group B); pulsed electromagnetic field alone (group C), or sham pulsed electromagnetic field treatment for 5 consecutive days (group D). All subjects received a standard home exercise programme. A visual analogue scale was used for recording pain; volumetric displacement for measuring the swelling of the forearm; and a hand-held goniometer for measuring the range of wrist motions before treatment on days 1, 3 and 5.Results: At day 5, a significantly greater cumulative reduction in the visual analogue scores as well as ulnar deviation range of motion was found in group A than the other 3 groups. For volumetric measurement and pronation, participants in group A performed better than subjects in group D but not those in group B.Conclusion: The addition of pulsed electromagnetic field to ice therapy produces better overall treatment outcomes than ice alone, or pulsed electromagnetic field alone in pain reduction and range of joint motion in ulnar deviation and flexion for a distal radius fracture after an immobilization period of 6 weeks.

Short-term and long-term site-specific effects of tennis playing on trabecular and cortical bone at the distal radius

Mechanical loading during growth magnifies the normal increase in bone diameter occurring in long bone shafts, but the response to loading in long bone ends remains unclear. The aim of the study was to investigate the effects of tennis playing during growth at the distal radius, comparing the bone response at trabecular and cortical skeletal sites. The influence of training duration was examined by studying bone response in short-term (children) and long-term (young adults) perspectives. Bone area, bone mineral content (BMC), and bone mineral density (BMD) of the radius were measured by DXA in 28 young (11.6 ± 1.4 years old) and 47 adult tennis players (22.3 ± 2.7 years old), and 70 age-matched controls (12 children, 58 adults) at three sites: the ultradistal region (trabecular), the mid-distal region, and the third-distal region (cortical). At the ultradistal radius, young and adult tennis players displayed similar side-to-side differences, the asymmetry in BMC reaching 16.3% and 13.8%, respectively (P < 0.0001). At the mid- and third-distal radius, the asymmetry was much greater in adults than in children (P < 0.0001) for all the bone parameters (mid-distal radius, +6.6% versus +15.6%; third-distal radius, +6.9% versus +13.3%, for BMC). Epiphyseal bone enduring longitudinal growth showed a great capacity to respond to mechanical loading in children. Prolonging tennis playing into adulthood was associated with further increase in bone mineralization at diaphyseal skeletal sites. These findings illustrate the benefits of practicing impact-loading sports during growth and maintaining physical activity into adulthood to enhance bone mass accrual and prevent fractures later in life.

Contact pressure evolution at the die radius in sheet metal stamping

The contact conditions at the die radius are of primary importance to the wear response for many sheet metal forming processes. In particular, a detailed understanding of the contact pressure at the wearing interface is essential for the application of representative wear tests, the use of wear resistant materials and coatings, the development of suitable wear models, and for the ultimate goal of predicting tool life. However, there is a lack of information concerning the time-dependant nature of the contact pressure response in sheet metal stamping. This work provides a qualitative description of the evolution and distribution of contact pressure at the die radius for a typical channel forming process. Through an analysis of the deformation conditions, contact phenomena and underlying mechanics, it was identified that three distinct phases exist. Significantly, the initial and intermediate stages resulted in severe and localised contact conditions, with contact pressures significantly greater than the blank material yield strength. The final phase corresponds to a larger contact area, with steady and smaller contact pressures. The proposed contact pressure behaviour was compared to other results available in the literature and also discussed with respect to tool wear.

Tunable wettability of polyimide films based on electrostatic self-assembly of ionic liquids

We have demonstrated that the surface wettability of negatively charged polyimide films could be turned by electrostatic self-assembly of ionic liquids. The water contact angles of the polyimide films varied in the range 27-80 degrees for 13 different ionic liquids based on imidazolium and ammonium salts. The surface morphology of the resulting surfaces was characterized using atomic force microscopy. The results revealed that the assembly of longer-substituent cations was characterized by the formation of spherical nanoparticles that were formed due to sequent aggregation of cations on those electrostatically assembled ones via hydrophobic interaction. In this case, the counteranions are present in the assembled layers and the wettability is accordingly affected. Whereas for shorter-substituent cations, no aggregates were formed due to the less hydrophobic interaction than the electrostatic repulsive interaction between the cations, and the counteranions were absent from the assembled layers. This method can also be utilized to quantify the hydrophobicity of various ionic liquids.

Bronsted acidic ionic liquids derived from alkylamines as catalysts and mediums for Fischer esterification : study of structure–activity relationship

Esterification of acetic acid with 1-octanol was studied using a series of alkylammonium salts as Brønsted acidic ionic liquids. The following
ionic liquids were prepared and used as catalysts and mediums in the esterification reaction; [Et₃NH][HSO₄], [Et₃NH][H₂PO₄], [Et₃NH][BF₄],
[Et₃NH][p-CH₃C₆H₄SO₃], [Et₂(PhCH₂)NH][HSO₄], [n-Bu₃NH][HSO₄], [n-Oct₃NH][HSO₄], [Et₂NH₂][HSO₄], [Et₂NH₂][H₂PO₄], [Et₂NH₂]
[BF₄], [i-Pr₂NH₂][HSO₄], [EtNH₃][HSO₄], [EtNH₃][H₂PO₄], and [EtNH₃][BF₄]. Higher acidity of the anion in the ionic liquid resulted in high yield of the ester. Yield of the ester decreased with increase in the size of the cation. There was no phase separation in the reactions where size of anion and/or cation was bigger

Dispersion of boron nitride nanotubes in aqueous solution with the help of ionic surfactants

We report that ammonium oleate surfactants can help the dispersion of multiwalled boron nitride nanotubes (BNNTs) in water to form a BNNT solution stable for several months, which was due to the non-covalent functionalization of nanotube surfaces. Fourier Transform Infrared Spectroscopy (FTIR) and Photoluminescence (PL) analysis with synchrotron radiation source revealed that this BNNT aqueous solution preserves the intrinsic optical properties of BNNTs. © 2009 Elsevier Ltd. All rights reserved.