Thermodynamic analysis of lysozyme adsorbed to silica

The structural stability of hen egg white lysozyme in solution and adsorbed to small colloidal silica particles at various surface concentrations was investigated using hydrogen-deuterium (H/D) exchange in combination with mass spectrometry (HDX-MS) and differential scanning calorimetry (DSC). The combination of HDX-MS and DSC allows a full thermodynamic analysis of the lysozyme structure as both the enthalpy and the Gibbs free energy can be derived from the various measurements. Moreover, both HDX-MS and DSC provide information on the relative structural heterogeneity of lysozyme in the adsorbed state compared to that in solution. Results demonstrated that at high surface coverage, the structural stability of lysozyme was only marginally affected by adsorption to silica particles whereas the unfolding enthalpy decreased by more than 10%, meaning that the entropy of lysozyme increased with a similar value upon adsorption. Furthermore, the structural heterogeneity increased considerably. At lower surface concentrations, the structural heterogeneity increased further whereas the enthalpy of unfolding decreased. Further analyses of the HDX-MS experiments clearly indicated that folding/unfolding of lysozyme occurs through a two-domain process. These two domains had a similar amount of structural elements and a difference in stabilization energy of 8 kJ/mol, regardless if lysozyme was in solution or adsorbed to silica.     

Potentiometric stripping analysis for bismuth(III) in seawater

Total bismuth(III) in seawater can be determined either directly after acidification with 0.1 M hydrochloric acid or after co-precipitation with magnesium hydroxide by means of pre-electrolysis for 8 min at —0.90 V vs. SCE at a rotated glassy carbon/mercury film electrode prior to potentiometric stripping analysis. The limits of detection (2σ) are 0.6 and 0.003 nM, respectively. Three Kattegatt surface seawater samples were found to contain bismuth(III) concentrations of 5–12 pM (l–2.5 ng l^-1).     

Assessment of pharmacokinetic interaction between piracetam and l‐carnitine in healthy subjects

A rapid, sensitive and specific method for quantifying piracetam in human plasma using Piracetam d‐8 as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by one‐step precipitation of protein using an acetonitrile (100%). The extracts were analyzed by high‐performance liquid chromatography coupled with electrospray tandem mass spectrometry (HPLC‐MS/MS). The method had a chromatographic run time of 3.8 min and a linear calibration curve over the range 0.5–50 µg/mL (r > 0.99). This LC‐MS‐MS procedure was used to assess the bioavailability of two piracetam formulations: piracetam + l‐carnitine (Piracar®; 270/330 mg tablet) and piracetam (Nootropil®; 800 mg tablet) in healthy volunteers of both sexes. The geometric means with corresponding 90% confidence interval (CI) for test/reference percentage ratios were 88.49% (90% CI = 81.19 – 96.46) for peak concentration/dose and 102.55% (90% CI = 100.62 – 104.51) for AUC_inf/dose. The limit of quantitation of 0.5 µg/mL is well suited for pharmacokinetic studies in healthy volunteers. It was concluded that piracetam (Piracar®; 270/330 mg tablet) has a bioavailability equivalent to the piracetam (Nootropil®; 800 mg tablet) formulation with regard to both the rate and the extent of absorption. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of Crude Oils by Frequency Domain Spectroscopy—Effect of Composition and Physical Properties on Conductivity and Dielectric Response

The dielectric properties and the composition of fourteen light to heavy crude oils have been analyzed. Frequency domain spectroscopy (FDS) has been used in order to determine their dielectric response in the frequency range 0.01 to 1000 Hz. For all the crude oils, over the whole frequency range under study, dielectric loss, ?″, shows a linear dependence of frequency indicating a pure direct current (DC) conductivity. As temperature is gradually increased, the dielectric loss, ?″, increases as well, showing a strong temperature dependence. The storage modulus, ?′, shows an explicit behaviour at low frequency that could be due to adsorption of oil components onto the electrodes. We tried to correlate some physical and chemical properties (density, viscosity, SARA, TAN, water content) of the studied crude oils with their conductivity measured at various temperatures. No correlation was found and different hypothesis are suggested by the authors to explain this phenomenon.     

The slow dielectric Debye relaxation of monoalcohols in confined geometries

Broadband dielectric relaxation measurements have been performed on monoalcohols confined in the quasi-two-dimensional space between clay platelets and the quasi-one-dimensional pores of approximately 10 A? diameter in a molecular sieve. Interestingly, the results show that the slow Debye-like process is present even in these severe confinements, proving that structural models that are based on two-dimensional or three-dimensional cluster formations as the structural origin of the Debye-like process can be excluded. Rather, the insensitivity of its time-scale to confinements suggests that it is of local character and in some way related to the lifetime or breaking and reformation of hydrogen bonds.     

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Structure, stability, and orientation of BSA adsorbed to silica

In this investigation, the structure, stability, and orientation of bovine serum albumin (BSA) adsorbed onto silica particles were studied using differential scanning calorimetry (DSC) and limited proteolysis in combination with mass spectrometry (MS). DSC gave information on the overall structural stability of BSA while limited proteolysis was used to probe the accessibility of enzymatic cleavage sites, thereby yielding information on the orientation and structure of BSA adsorbed to silica surfaces. Thermal investigation of BSA in various buffers, both free in solution and in the adsorbed state, showed that solutes that surround the protein played an important role with respect to the overall structural stability and the structural heterogeneity of BSA. Limited proteolysis with trypsin and chymotrypsin indicated that BSA in the adsorbed state is oriented with domain 2 facing the silica surface. Also, upon adsorption, no additional cleavage sites were exposed. The combination of the results presented in this study implied that BSA molecules adsorbed onto silica particles were significantly reduced in their structural stability, but not to an extent that internal residues within the native structure became fully exposed to the solution.     

Synthesis of Mesoporous Alumina Using Carboxyl Functional,Hyperbranched Polyesters as Templates

A series of mesoporous aluminas have been synthesized using commercial hyperbranched polyesters of the second to fourth generation as porogens. To achieve a suitable interaction between the polymer and the aluminium source, aluminium sec‐butoxide, the terminal hydroxyl groups of the hyperbranched polymer were first reacted by succinic anhydride. The mesoporous aluminas were analyzed by nitrogen adsorption/desorption, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). No dependence of the generation of the hyperbranched template on pore size was found in this study. Instead the pore size appears to depend on the amount of water added to the reaction mixture as well as the concentration of the hyperbranched polymer.     

Relaxation processes in supercooled confined water and implications for protein dynamics

We show that the viscosity-related main (alpha) relaxation of confined water vanishes at a temperature where the volume required for the cooperative alpha relaxation becomes larger than the size of the geometrically confined water cluster. This occurs typically around 200 K, implying that above this temperature we observe a merged alpha-beta relaxation, whereas below it only a local (beta) relaxation remains. This also means that such confined supercooled water does not exhibit any true glass transition, in contrast to other liquids in similar confinements. Furthermore, it implies that deeply supercooled water in biological systems, such as membranes and proteins, generally shows only a local beta relaxation, a finding of importance for low temperature properties of biological materials.