Structure and thermodynamics of lipid bilayers on polyethylene glycol cushions: fact and fiction of PEG cushioned membranes

In developing well hydrated polymer cushioned membranes, structural studies are often neglected. In this work, neutron and X-ray reflectivity studies reveal that hybrid bilayer/polyethylene glycol (PEG) systems created from mixtures of phospholipids and PEG conjugated lipopolymers do not yield a hydrated cushion beneath the bilayer unless the terminal ends of the lipopolymers are functionalized with reactive end groups and can covalently bind (tether) to the underlying support surface. While reactive PEG tethered systems yielded bilayers with near complete surface coverage, a bimodal distribution of heights with sub-micrometer lateral dimensions was observed consisting of cushioned membrane domains and uncushioned regions in close proximity to the support. The membrane fraction cushioned by the hydrated polymer could be controlled by adjusting the molar ratio of lipopolymer in the bilayer. A general phase diagram based on the free energy of the various configurations is derived that qualitatively predicts the observed behavior and the resulting structure of such systems a priori. As further evidenced by ellipsometry, atomic force and fluorescence microscopy, the tethered system provides a simple means for fabricating small cushioned domains within a membrane.     

Archaeal tetraether lipids

The extremely stable biomolecules manufactured by organisms from extreme environments are of great scientific and engineering interest in the development of robust and stable industrial biocatalysts. Identification of molecules that impart stability under extremes will also have a profound impact on our understanding of cellular survival. This review discusses isolation and characterization of archaeal tetraethers as well as target technologies for tetraether lipid application. The isolation and characterization of archaeal tetraether lipids has led to some interesting applications improving on ester lipid technologies. Potential applications include novel lubricants, gene-delivery systems, monolayer lipid matrices for sensor devices, and protein stabilization. Following this review, patent abstracts and additional literature pertaining to the isolation, characterization, and application of archaeal membrane lipids are listed.     

Towards Heteroleptic Dicoordinate CuII Complexes

In this work we detail our efforts to systematically generate stable dicoordinate Cu^II complexes. Initial experiments via metathesis reactions of a bulky potassium carbazolide (RK) with copper(II) salts indeed yielded a stable product, RCuOTf ( 1 ). However, subsequent attempts to grasp systematic synthetic access to complexes of the type RCuX (X=monoanionic ligand) proved difficult as many of the complexes rapidly decomposed in solution. By using triflate-related ligands such as ethyl sulfate and bistriflimide, the additional dicoordinate copper complexes RCuOSO₃Et ( 2 ), [RCu(THF)][Cu(NTf₂)₂] ( 3 ) and RCuNTf₂ ( 4 ) could be isolated. Spectroscopic indications corroborate more Cu^I than Cu^II character in all RCuX derivatives.     

Real-time electrical impedance-based measurement to distinguish oral cancer cells and non-cancer oral epithelial cells

In this study, electrical impedance-based measurements were used to distinguish oral cancer cells and non-cancer oral epithelial cells based on their cellular activities on the microelectrodes in a real-time and label-free manner. CAL 27 and Het-1A cell lines were used as the models of oral cancer cells and non-cancer oral epithelial cells, respectively. Various cellular activities, including cell adhesion, spreading, and proliferation were monitored. We found that both the kinetics of cell spreading and the static impedance-based cell index were feasible to distinguish the two cell types. At each given cell number, CAL 27 cell spreading produced a smaller cell index change rate that was 60–70% of those of Het-1A cells. When cells were fully spread, CAL 27 cells generated a cell index more than four times greater than that of Het-1A cells. Since cell spreading and attachment occurs in the first few hours when they were cultured on the microelectrodes, this impedance-based method could be a rapid label-free and non-invasive approach to distinguish oral cancer cells from non-cancer oral epithelial cells. Cell viability analysis was performed along with the impedance-based analysis. Confocal microscopic imaging analysis showed the difference in cell morphology and the thickness of cell monolayers between the two cell types.     

Synthesis and thermolytic behavior of tin(IV) formates: in search of recyclable metal-hydride systems

The synthesis and characterization of the series of organotin formates together with their thermolytic behavior are described. The diformate Bu(n)(2)Sn{OC(O)H}(2) (1) was synthesized by the reaction of Bu(n)(2)SnH(2) with formic acid. The triorganotin monoformate compounds R(3)SnOC(O)H (R = Cy (cyclohexyl)) 3, Mes, (mesityl, 2,4,6-trimethylphenyl) 4, and Dmp (2,6-dimethylphenyl 5) were obtained by the reaction of R(3)SnOH with formic acid. Their X-ray crystal structures along with that of the previously reported formate (PhCH(2))(3)SnOC(O)H (2) were determined. The diformate 1 exhibits an extended two-dimensional polymeric structure in which six-coordinate tin centers are linked by formate bridges. The tribenzyltin formate (2) possesses a chain structure in which the five-coordinate Sn(CH(2)Ph)(3) units are bridged by formate ions. The cyclohexyl derivative 3 was observed to have a similar structure. In contrast, the Mes and Dmp derivatives 4 and 5 support monomeric structures in which the four-coordinate tin atom is bound to an oxygen of the formate ligand. Heating the compounds in various high boiling solvents produced no decomposition up to 120 °C in the case of 1 and refluxing a solution of 2 or 3 in mesitylene or diglyme left the starting material mostly unchanged, although 3 decomposed to an insoluble orange solid in refluxing decalin. In contrast, the heating of 4 and 5 in refluxing mesitylene led to elimination of CO to give the tin hydroxides. The results are in contrast to the known thermolytic behavior of R(3)SnOC(O)H (R = Pr(n) or Bu(n)) complexes, which eliminate CO(2) to generate R(3)SnH. Compounds 3-5 are rare examples of structurally characterized tin formates.     

An LC-MS-MS method for quantitative determination of maraviroc (UK-427,857) in human plasma, urine and cerebrospinal fluid

Maraviroc is a first‐in‐class CCR5 antagonist that shows potent anti‐HIV‐1 activity in vitro and in vivo and is well tolerated in both healthy volunteers and HIV‐1‐infected patients. The method for determination of maraviroc (UK‐427,857) and its major metabolite (UK‐408,027) in human plasma consists of a protein‐precipitation procedure and analysis by liquid chromatography/tandem mass spectrometry using positive ion TurboIonSpray® ionization and multiple reaction monitoring. The assay has been validated over a concentration range of 0.500–500 ng/mL for both analytes. The determinations of maraviroc in human cerebrospinal fluid (0.500–500 ng/mL) and in urine (5.00–5000 ng/mL) have also been validated but do not include measurement of the metabolite. The validations included extraction recovery, intra‐assay and inter‐assay precision and accuracy, stability of stock and spiking solutions, freeze–thaw stability, matrix stability, processed‐extract stability, and evaluation of potential interferences from selected medications in plasma or urine. Copyright © 2010 John Wiley & Sons, Ltd.     

Insights into the Electronic Structure of a U(IV) Amido and U(V) Imido Complex

Reaction of the N-heterocylic carbene ligand ⁱPrIm (L¹) and lithium bis(trimethylsilyl)amide (TMSA) as a base with UCl₄ resulted in U(IV) and U(V) complexes. Uranium's +V oxidation state in (HL¹)₂[U(V)(TMSI)Cl₅] (TMSI=trimethylsilylimido) ( 2 ) was confirmed by HERFD-XANES measurements. Solid state characterization by SC-XRD and geometry optimisation of [U(IV)(L¹)₂(TMSA)Cl₃] ( 1 ) indicated a silylamido ligand mediated inverse trans influence (ITI). The ITI was examined regarding different metal oxidation states and was compared to transition metal analogues by theoretical calculations.     

Quantitative analysis of five tobacco‐specific N‐nitrosamines in urine by liquid chromatography–atmospheric pressure ionization tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination of five total tobacco‐specific N‐nitrosamines (TSNA), including free and conjugated forms in urine. The limits of detection for 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol, N′‐nitrosonornicotine, 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone, N′‐nitrosoanatabine and N′‐nitrosoanabasine were 0.6, 0.6, 10.0, 0.4 and 0.4 pg/mL, respectively, with a linear calibration range of up to 20,000 pg/mL. Intra‐ and inter‐day precision for TSNA measurements ranged from 0.82 to 3.67% and from 2.04 to 7.73% respectively. For total TSNAs, the β‐glucuronidase amount was optimized for hydrolysis time and yield. Different liquid chromatography columns and mobile phases with different pH conditions were evaluated. The validated method was then applied to 50 smoker and 30 nonsmoker urine samples. Our results suggest that this sensitive and relatively simple analytical method is suitable for application to epidemiological investigations of health risks associated with the exposure to tobacco smoke or secondhand smoke in both smokers and nonsmokers. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

The nanoscale description of acid penetration to the gold colloids encapsulated in silica sol–gel matrix

Various sizes of gold nano colloidal particles ranging from 5 nm to 100 nm of size were encapsulated in a silica based sol–gel, and these surfaces were exposed to a pH 1 acid solution. This enabled us to observe the process of solvent intrusion and interaction with gold colloids by the absorption spectrum as a function of time. The rate was analyzed by a single exponential analytical function, and the maximum rate was found for gold colloid of 15 nm size. The least acid interaction and colour change was observed for the size of 60 nm. It was speculated that the surface of these gold colloids were homogeneously covered by the sodium tetra-borate buffer which insulated silica gel layer, thus avoiding direct contact of the acid with the surface of the gold colloid. This study confirmed that the nano scale dopant size affects the rate of solvent penetration into a sol–gel cavity.