Composition of supported model membranes determined by neutron reflection

We have investigated the formation of supported bilayers by coadsorption of dipalmitoyl phosphatidylcholine (DPPC) with the nonionic surfactant beta-D-dodecyl maltoside. The adsorption of mixed phospholipid-surfactant micelles on hydrophilic silica surfaces at 25 degrees C was followed as a function of bulk concentration by neutron reflection. Using chain-deuterated d(25)-beta-D-dodecyl maltoside and d(62)-DPPC, we demonstrate that it is possible to determine the composition of the bilayers at each stage of a sequential dilution process, which enriches the adsorbed layer in phospholipid and leads to complete elimination of the surfactant. The final supported bilayers have thicknesses of 51 +/- 3 A and are stable to heating to 37 degrees C once all surfactant has been removed, and the structures agree well with other published data on DPPC supported bilayers. The coadsorption of cholesterol in a DPPC-surfactant mixture was also achieved, and the location and volume fraction of cholesterol in the DPPC bilayer was determined. Cholesterol is located in a 18 +/- 1 A thick layer below the lipid headgroup region and leads to an increased bilayer thickness of 58 +/- 2 A at 26 mol % of cholesterol.     

Phosphoryl choline introduces dual activity in biomimetic ionomers

Dual activity of phosphoryl choline (PC) functional poly(trimethylene carbonate) (PTMC) was found which induces the zwitterionic biomimetic PC group to form physical cross-links with ionomers in the bulk, and at the same time enrich at the surface of cast films. The formation of zwitterionic domains from a bifunctional PC-PTMC-PC (ionomer) provided firm films with a low elastic modulus in contrast to the tacky PTMC starting material (Mn approximately 3900 g/mol) with poor mechanical performance. In addition, the ionomer possessed improved hemocompatible properties that was explained by the enrichment of PC at the surface, suggesting a way to tailor the mechanical performance of biodegradable PTMC-based ionomers while providing its bioactivity. Tailored elasticity while maintaining hemocompatibility of a biodegradable ionomer should be of particular interest for a variety of in vivo applications.     

Bivalent cholesterol-based coupling of oligonucletides to lipid membrane assemblies

By mimicking Nature's way of utilizing multivalent interactions, we introduce in the present work a novel method to improve the strength of cholesterol-based DNA coupling to lipid membranes. The bivalent coupling of DNA was accomplished by hybridization between a 15-mer DNA and a 30-mer DNA, being modified with cholesterol in the 3' and 5' end, respectively. Compared with DNA modified with one cholesterol moiety only, the binding strength to lipid membranes appears to be significantly stronger and even irreversible over the time scale investigated ( approximately 1 hr). First, this means that the bivalent coupling can be used to precisely control the number of DNA per lipid-membrane area. Second, the strong coupling is demonstrated to facilitate DNA-hybridization kinetics studies. Third, exchange of DNA between differently DNA-modified vesicles was demonstrated to be significantly reduced. The latter condition was verified via site-selective and sequence-specific sorting of differently DNA-modified lipid vesicles on a low-density cDNA array. This means of spatially control the location of different types of lipid vesicles is likely to find important applications in relation to the rapid progress currently made in the protein chip technology and the emerging need for efficient ways to develop membrane protein arrays.     

Enzyme thermistors for process monitoring and control

In today’s biotechnology there is an increasing demand for appropriate analytical systems for process control. At present the most widely used control systems are based on measurements of pH, pO₂, and pCO₂. Such systems do not allow the direct measurement of substrates and products. To overcome this drawback sensors such as enzyme thermistors and enzyme electrodes have been designed and their development into industrial useful sensors for monitoring and controlling is the subject of active research.     

Electrokinetic-driven microfluidic system in poly(dimethylsiloxane) for mass spectrometry detection integrating sample injection, capillary electrophoresis, and electrospray emitter on-chip

A novel microsystem device in poly(dimethylsiloxane) (PDMS) for MS detection is presented. The microchip integrates sample injection, capillary electrophoretic separation, and electrospray emitter in a single substrate, and all modules are fabricated in the PDMS bulk material. The injection and separation flow is driven electrokinetically and the total amount of external equipment needed consists of a three-channel high-voltage power supply. The instant switching between sample injection and separation is performed through a series of low-cost relays, limiting the separation field strength to a maximum of 270 V/cm. We show that this set-up is sufficient to accomplish electrospray MS analysis and, to a moderate extent, microchip separation of standard peptides. A new method of instant in-channel oxidation makes it possible to overcome the problem of irreversibly bonded PDMS channels that have recovered their hydrophobic properties over time. The fast method turns the channel surfaces hydrophilic and less prone to nonspecific analyte adsorption, yielding better separation efficiencies and higher apparent peptide mobilities.     

A total synthesis of hydroxylysine in protected form and investigations of the reductive opening of p-methoxybenzylidene acetals

A synthesis of (2S,5R)-5-hydoxylysine, based on (R)-malic acid and Williams glycine template as chiral precursors, has been developed. This afforded hydroxylysine, suitably protected for direct use in peptide synthesis, in 32% yield over the 13-step sequence. Regioselective reductive opening of a p-methoxybenzylidene acetal and alkylation of the Williams glycine template were key steps in the synthetic sequence. Surprisingly, the regioselectivity in opening of the p-methoxybenzylidene acetal was reversed as compared to what was expected. It was found that this was due to chelation of the trialkylsilyl choride, used as an electrophile in the reductive opening, to an adjacent azide functionality. It was also discovered that an equivalent amount of trialkylsilyl hydride was formed in the reaction, a finding that led to additional mechanistic insight into reductive openings of p-methoxybenzylidene acetals with sodium cyanoborohydride as reducing agent.     

Directed assembly of gold nanoparticles

As a complement to common “top–down” lithography techniques, “bottom–up” assembly techniques are emerging as promising tools to build nanoscale structures in a predictable way. Gold nanoparticles that are stable and relatively easy to synthesize are important building blocks in many such structures due to their useful optical and electronic properties. Programmed assembly of gold nanoparticles in one, two, and three dimensions is therefore of large interest. This review focuses on the progress from the last three years in the field of directed gold nanoparticle and nanorod assembly using, for example, DNA or specific chemical interactions as template.     

Highly Water‐Dispersible Surface‐Modified Gd2O3 Nanoparticles for Potential Dual‐Modal Bioimaging

Water‐dispersible and luminescent gadolinium oxide (GO) nanoparticles (NPs) were designed and synthesized for potential dual‐modal biological imaging. They were obtained by capping gadolinium oxide nanoparticles with a fluorescent glycol‐based conjugated carboxylate (H L ). The obtained nanoparticles (GO‐ L ) show long‐term colloidal stability and intense blue fluorescence. In addition, L can sensitize the luminescence of europium(III) through the so‐called antenna effect. Thus, to extend the spectral ranges of emission, europium was introduced into L‐ modified gadolinium oxide nanoparticles. The obtained Eu^III‐doped particles (Eu:GO‐ L ) can provide visible red emission, which is more intensive than that without L capping. The average diameter of the monodisperse modified oxide cores is about 4 nm. The average hydrodynamic diameter of the L ‐modified nanoparticles was estimated to be about 13 nm. The nanoparticles show effective longitudinal water proton relaxivity. The relaxivity values obtained for GO‐ L and Eu:GO‐ L were r₁=6.4 and 6.3 s^?1 mM ^?1 with r₂/r₁ ratios close to unity at 1.4 T. Longitudinal proton relaxivities of these nanoparticles are higher than those of positive contrast agents based on gadolinium complexes such as Gd‐DOTA, which are commonly used for clinical magnetic resonance imaging. Moreover, these particles are suitable for cellular imaging and show good biocompatibility.     

Monobenzofused 1,4‐Azaborines: Synthesis,Characterization, and Discovery of a Unique Coordination Mode

We report the first general synthesis of boron‐substituted monobenzofused 1,4‐azaborines using ring‐closing metathesis of an enamine‐containing diene as a key synthetic strategy. As part of our investigations, we discovered that the B‐C3 moiety in a 1,4‐azaborine can serve uniquely as a η²‐L‐type ligand. This functionality is exemplified by two κ²‐N‐η²‐BC Pt complexes of a boron‐pyridyl‐substituted monobenzofused‐1,4‐azaborine. Single‐crystal X‐ray diffraction analysis of the Pt complexes shows a strong structural contribution from the iminium resonance form of the monobenzofused‐1,4‐azaborine ligand. We also demonstrate that a palladium(0) complex supported by a 1,4‐azaborine‐based phosphine ligand can catalyze hydroboration of 1‐buten‐3‐yne with unique selectivity. In view of the importance of arene–metal π‐interactions in catalytic applications, this work should open new opportunities for ligand design involving the 1,4‐azaborine motif as an arene substitute.     

Interfacial behavior of cubic liquid crystalline nanoparticles at hydrophilic and hydrophobic surfaces

The adsorption behavior of self-assembled lipid liquid crystalline nanoparticles at different model surfaces was investigated in situ by use of ellipsometry. The technique allows time-resolved monitoring of the adsorbed amount and layer thickness under transient and steady-state conditions. The system under study was cubic-phase nanoparticle (CPNP) dispersions of glycerol monooleate stabilized by a nonionic block copolymer, Pluronic F-127. Depending on the surface properties and presence of electrolytes, different adsorption scenarios were discerned: At hydrophilic silica thick surface layers of CPNPs are generated by particle adsorption from dispersions containing added electrolyte, but no adsorption is observed in pure water. Adsorption at the hydrophobic surface involves extensive structural relaxation and formation, which is not electrolyte sensitive, of a classic monolayer structure. The different observations are rationalized in terms of differences in interactions among the CPNP aggregates, their unimer constituents, and the surface and show a strong influence of interfacial interactions on structure formation. Surface self-assembly structures with properties similar to those of the corresponding bulk aggregates appear exclusively in the weak interaction limit. This observation is in agreement with observations for surfactant self-assembly systems, and our findings indicate that this behavior is applicable also to complex self-assembly structures such as the CPNP structures discussed herein.