An overview of lipid membrane supported by colloidal particles

In recent years, original hybrid assemblies composed of a particle core surrounded by a lipid shell emerged as promising entities for various biotechnological applications. Their broadened bio-potentialities, ranging from model membrane systems or biomolecule screening supports, to substance delivery reservoirs or therapeutic vectors, are furthered by their versatility of composition due to the possible wide variation in the particle nature and size, as well as in the lipid formulation. The synthesis, the characteristics, and the uses of these Lipid/Particle assemblies encountered in the literature so far are reviewed, and classified according to the spherical core size in order to highlight general trends. Moreover, several criteria are particularly discussed: i) the interactions involved between the particles and the lipids, and implicitly the assembly elaboration mechanism, ii) the most suited techniques for an accurate characterization of the entities from structural and physicochemical points of view, and iii) the remarkable properties of the solid-supported lipid membrane obtained.     

Determining the orientation of uniaxially rotating membrane proteins using unoriented samples: a 2H, 13C, AND 15N solid-state NMR investigation of the dynamics and orientation of a transmembrane helical bundle

Membrane protein orientation has traditionally been determined by NMR using mechanically or magnetically aligned samples. Here we show a new NMR approach that abolishes the need for preparing macroscopically aligned membranes. When the protein undergoes fast uniaxial rotation around the bilayer normal, the 0 degrees -frequency of the motionally averaged powder spectrum is identical to the frequency of the aligned protein whose alignment axis is along the magnetic field. Thus, one can use unoriented membranes to determine the orientation of the protein relative to the bilayer normal. We demonstrate this approach on the M2 transmembrane peptide (M2TMP) of influenza A virus, which is known to assemble into a proton-conducting tetrameric helical bundle. The fast uniaxial rotational diffusion of the M2TMP helical bundle around the membrane normal is characterized via 2H quadrupolar couplings, C-H and N-H dipolar couplings, 13C chemical shift anisotropies, and 1H T1rho relaxation times. We then show that 15N chemical shift anisotropy and N-H dipolar coupling measured on these powder samples can be analyzed to yield precise tilt angles and rotation angles of the helices. The data show that the tilt angle of the M2TMP helices depends on the membrane thickness to reduce the hydrophobic mismatch. Moreover, the orientation of a longer M2 peptide containing both the transmembrane domain and cytoplasmic residues is similar to the orientation of the transmembrane domain alone, suggesting that the transmembrane domain regulates the orientation of this protein and that structural information obtained from M2TMP may be extrapolated to the longer peptide. This powder-NMR approach for orientation determination is generally applicable and can be extended to larger membrane proteins.     

Cation deficient layered Ruddlesden-Popper-related oxysulfides La2LnMS2O5 (Ln=La, Y; M=Nb, Ta)

The structures of the new oxysulfide Ruddlesden-Popper phases La2LnMS2O5 (Ln=La, Y; M=Nb, Ta) are reported together with an iodide-containing variant: La3-xNb1+xS2O5I2x (0相似文献   

Preparation and characterization of novel cationic pH-responsive poly(N,N'-dimethylamino ethyl methacrylate) microgels

Novel monodisperse cationic pH-responsive microgels were successfully prepared by dispersion polymerization in ethanol/water mixture using N,N'-dimethylamino ethyl methacrylate (DMAEMA) as the monomer, poly(vinyl pyrrolidone) (PVP) as the steric stabilizer and N,N'-methylenebisacrylamide (MBA) as the cross-linker. The effects of various polymerization parameters, such as medium polarity, concentration of cross-linker, concentration of monomer, and concentration and molecular weight of stabilizer on the final diameter and monodispersity of poly(N,N'-dimethylamino ethyl methacrylate) (PDMAEMA) microgels were systematically studied. The pH-responsive characteristics of PDMAEMA microgels were also investigated. The experimental results showed that these microgels exhibited excellent pH-responsivity and significantly swelled at low pH values. The maximum ratio of volume change of the prepared microgels in response to pH variation was more than 11 times. It was found that the prepared microgels completely aggregated at the isoelectric point (IEP) around pH 6. On the other hand, the microgels were stable in aqueous solution at both low and high pH values. The results can be used for effectively controlled separation of particles.     

Identification and relative quantification of fatty acids in Escherichia coli membranes by gas chromatography/mass spectrometry

The lipids that are essential to the functioning of the bacterial membrane exist in hundreds of different forms. The reasons for this diversity are far from clear but are presumably related to the roles of these lipids in both facilitating enzymic activities and generating proteolipid domains. A full understanding of bacterial physiology therefore requires characterization of lipids in different strains in a variety of environmental conditions. This characterization then becomes the basis for lipidomics, the lipid aspect of the growing field of metabolomics. To exploit the power of derivatization chemistry and of gas chromatography/mass spectrometry (GC/MS) and tandem mass spectrometry (MS/MS) for metabolomics studies, we report here the development of various GC/MS electron ionization (EI) and negative and positive chemical ionization (CI) methods for the identification and, for the first time, the relative quantification of fatty acids present in extracts from membranes of a laboratory strain of Escherichia coli. They consist of seven saturated fatty acids (C10:0, C12:0, C14:0, C15:0, C16:0, C17:0 and C18:0) and six unsaturated fatty acids (C16:1, cyC17:0 plus two isomers of C18:1, C18:2 and cyC19:0).     

Lipid composition of membranes of Escherichia coli by liquid chromatography/tandem mass spectrometry using negative electrospray ionization

A liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method using reversed-phase chromatography was developed for the analysis of phospholipids from bacterial extracts of a wild-type strain of Escherichia coli. Product ion mass spectra from [M--H](-) precursor ions allowed an identification of individual phospholipid species that includes both fatty acid composition and fatty acyl location on the glycerol backbone using diagnostic product ions. Thus, complete assignment, including sn-1/sn-2 fatty acyl position, was achieved for this strain of E. coli. In addition, the phospholipids were quantified relative to one another using an internal standard method.     

Characterization of Green Paints in Ming and Qianlong Dynasties’ Lin’xi Pavilion by Complimentary Techniques

During conservation of the painted ceiling decoration of Lin’xi Pavilion in the Forbidden City, two distinct paint campaigns were isolated as a unique case study into architectural paint materials during both the Ming and Qing dynasties. Paint samples and cross sections from both paint generations were analyzed with SEM-EDX, time of flight-secondary ion mass spectrometry (ToF-SIMS), XRD, FTIR, and Raman spectroscopies. Similar organic and inorganic materials characteristic of these time periods were identified. The pigments of interest found in both paint generations were botallackite and atacamite polymorphs. This suggests a shift from natural mineral sources to synthetic copper-based pigments for these larger architectural projects.     

High-Pressure Processing and Ultrasonication of Minimally Processed Potatoes: Effect on the Colour,Microbial Counts,and Bioactive Compounds

HPP at 600 MPa alone, and in combination with US at 20 kHz (200 W), was applied to minimally processed potatoes of two commonly grown cultivars in Ireland. Changes in colour and microbial load (Enterobacteriaceae, total aerobic count, Salmonella, yeasts, and moulds) were monitored in vacuum-packaged potatoes during 14 days of storage at 4 °C. HPP and HPP/US significantly (p < 0.05) affected the colour parameters a*, b*, L*, and ΔE of minimally processed potatoes compared to the controls. Microbial growth was delayed in most of the treated samples with respect to those untreated (controls), while HPP completely inactivated Enterobacteriaceae in both cultivars. Total phenolic content and antioxidant activities were not altered in the treated samples of both varieties when compared to the controls. The levels of chlorogenic acid, ferulic acid, and caffeic acid were decreased after both treatments, with a significant (p < 0.05) increase in quinic acid in the treated samples as opposed to those untreated. A significant (p < 0.05) decrease in the levels of glycoalkaloids, namely α-chaconine and α-solanine, in HPP- and HPP/US-treated potatoes was also observed. These findings suggest that HPP and US can extend the shelf-life of minimally processed potatoes with a negligible impact on their antioxidant activity and phenolic content.     

Isomers of Terpyridine as Ligands in Coordination Polymers and Networks Containing Zinc(II) and Cadmium(II)

The use of divergent 4,2′:6′,4″- and 3,2′:6′,3″-terpyridine ligands as linkers and/or nodes in extended coordination assemblies has gained in popularity over the last decade. However, there is also a range of coordination polymers which feature 2,2′:6′,2″-terpyridine metal-binding domains. Of the remaining 45 isomers of terpyridine, few have been utilized in extended coordination arrays. Here, we provide an overview of coordination polymers and networks containing isomers of terpyridine and either zinc(II) and cadmium(II). Although the motivation for investigations of many of these systems is their luminescent behavior, we have chosen to focus mainly on structural details, and we assess to what extent assemblies are reproducible. We also consider cases where there is structural evidence for competitive product formation. A point that emerges is the lack of systematic investigations.