From simple surface models to lipid membranes: Universal aspects of the hydration interaction from solvent-explicit simulations

A review of atomistic simulation approaches including explicit water for the study of hydration forces between polar surfaces is presented. In particular, we discuss different methods for keeping the chemical potential of water constant and compare advantages and limitations of each method. It turns out that modifications of hydration forces due to surface softness can be accounted for by a convolution over the surface shape profile. Universal aspects of the hydration interaction observed in simulations of different surface chemistries are highlighted, while special attention is given to hydration forces between self-assembled phospholipid membranes.     

Conformational and adsorptive characteristics of albumin affect interfacial protein boundary lubrication: From experimental to molecular dynamics simulation approaches

The lifetime of artificial joints is mainly determined by their biotribological properties. Synovial fluid which consists of various biological molecules acts as the lubricant. Among the compositions of synovial fluid, albumin is the most abundant protein. Under high load and low sliding speed articulation of artificial joint, it is believed the lubricants form protective layers on the sliding surfaces under the boundary lubrication mechanism. The protective molecular layer keeps two surfaces from direct collision and thus decreases the possibility of wear damage. However, the lubricating ability of the molecular layer may vary due to the conformational change of albumin in the process. In this study, we investigated the influence of albumin conformation on the adsorption behaviors on the articulating surfaces and discuss the relationship between adsorbed albumin and its tribological behaviors. We performed the friction tests to study the effects of albumin unfolding on the frictional behaviors. The novelty of this research is to further carry out molecular dynamics simulation, and protein adsorption experiments to investigate the mechanisms of the albumin-mediated boundary lubrication of arthroplastic materials. It was observed that the thermal processes induce the loss of secondary structure of albumin. The compactness of the unfolded structure leads to a higher adsorption rate onto the articulating material surface and results in the increase of friction coefficient.     

Polymers in living systems: from biological lubrication to tissue engineering and biomedical devices

The roles of macromolecules in living systems as information storage systems (as DNA) and in biochemical synthesis have been much studied and are relatively well understood. Far less is known about their physical behavior at biological surfaces and interfaces. This review considers in particular the roles of polymers in biological lubrication and its relation both to diseases such as osteoarthritis and to remedies such as tissue engineering. The lubricating behavior of common bio‐interfacial macromolecules including mucins, hyaluronan, lubricin, and aggrecan are described, and insights into the mechanism of biolubrication are examined in the light of the recently revealed role of hydration lubrication in water‐based (including living) systems. Copyright © 2012 John Wiley & Sons, Ltd.     

From precipitation to vesicles: a study on self-organized assemblies by alkylammonium and its mixtures in polar solvents

The formation of self-organized assemblies by C_nH_2n+1NH₂·HCl and C₁₂H₂₅SO₄ Na in polar solvents was studied. By adding 1-propanol or 2-propanol, the precipitation formed in aqueous solution was resolved and a bilayer structure was discovered. Furthermore, multilamellar vesicle formation could be observed by methods of adjusting the molar ratio of C_nH_2n+1NH₂·HCl to C₁₂H₂₅SO₄Na, changing the length of the hydrocarbon chain of C_nH_2n+1NH₂·HCl, or adding 1-octanol to the mixed surfactant systems. Received: 18 January 2001 Accepted: 15 March 2001     

Heat-induced changes to lipid molecular structure in Vimy flaxseed: spectral intensity and molecular clustering

Autoclaving was used to manipulate nutrient utilization and availability. The objectives of this study were to characterize any changes of the functional groups mainly associated with lipid structure in flaxseed (Linum usitatissimum, cv. Vimy), that occurred on a molecular level during the treatment process using infrared Fourier transform molecular spectroscopy. The parameters included lipid CH(3) asymmetric (ca. 2959 cm(-1)), CH(2) asymmetric (ca. 2928 cm(-1)), CH(3) symmetric (ca. 2871 cm(-1)) and CH(2) symmetric (ca. 2954 cm(-1)) functional groups, lipid carbonyl CO ester group (ca. 1745 cm(-1)), lipid unsaturation group (CH attached to CC) (ca. 3010 cm(-1)) as well as their ratios. Hierarchical cluster analysis (CLA) and principal components analysis (PCA) were conducted to identify molecular spectral differences. Flaxseed samples were kept raw for the control or autoclaved in batches at 120°C for 20, 40 or 60 min for treatments 1, 2 and 3, respectively. Molecular spectral analysis of lipid functional group ratios showed a significant decrease (P<0.05) in the CH(2) asymmetric to CH(3) asymmetric stretching band peak intensity ratios for the flaxseed. There were linear and quadratic effects (P<0.05) of the treatment time from 0, 20, 40 and 60 min on the ratios of the CH(2) asymmetric to CH(3) asymmetric stretching vibration intensity. Autoclaving had no significant effect (P>0.05) on lipid carbonyl CO ester group and lipid unsaturation group (CH attached to CC) (with average spectral peak area intensities of 138.3 and 68.8 IR intensity units, respectively). Multivariate molecular spectral analyses, CLA and PCA, were unable to make distinctions between the different treatment original spectra at the CH(3) and CH(2) asymmetric and symmetric region (ca. 2988-2790 cm(-1)). The results indicated that autoclaving had an impact to the mid-infrared molecular spectrum of flaxseed to identify heat-induced changes in lipid conformation. A future study is needed to quantify the relationship between lipid molecular structure changes and functionality/availability.     

Pyrolysis–GC–MS to trace terrigenous organic matter in marine sediments: a comparison between pyrolytic and lipid markers in the Adriatic Sea

The effectiveness of semiquantitative pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) as a rapid analytical technique for sourcing continental organic matter (OM) in marine sediments was examined by comparison with classical GC–MS analyses of solvent extractable lipid markers. Py–GC–MS was directly applied to HCl/HF de-ashed surface sediment samples collected in five stations located in north western Adriatic Sea. The resulting pyrolysates were characterised by compounds indicative of different biological precursors (e.g. proteins, carbohydrates, chlorophylls), including lignin methoxyphenols diagnostic for continental inputs. The relative abundance of pyrolytic markers was compared to the distribution of n-alkanes, n-alkanols and sterols extracted from the same sediments and determined by GC–MS analyses. For each class of molecular indicators, the terrigenous to aquatic ratio (TAR) was determined as follows: relative abundance of methoxyphenol/protein markers (TAR_PY), concentration ratios of (C27 + C29 + C31)/(C15 + C17 + C19) n-alkanes (TAR_HC), (C26 + C28+ C30)/(C14 + C16) n-alkanols (TAR_AL) and sitosterol/cholesterol (TAR_ST). A positive correlation was found between TAR_PY and both TAR_HC and TAR_AL indicating a decreasing contribution of land-plant-derived materials seaward in two investigated transects. TAR_ST values displayed a different trend suggesting a mixed origin for sitosterol. The distribution of TAR_PY values was also in good agreement with that of atomic C/N ratios. Considering the complexity of environmental systems (diagenetic alteration, different fractions of OM analysed) the obtained results indicate that the pyrolytic marker approach by Py–GC–MS is valuable for sourcing marine OM on a semiquantitative base, providing data consistent with GC–MS determinations of lipid markers and elemental bulk analyses.