Supported lipid bilayer nanosystems: stabilization by undulatory-protrusion forces and destabilization by lipid bridging

Control of the stabilization/destabilization of supported lipid bilayers (SLBs) on nanoparticles is important for promotion of their organized assembly and for their use as delivery vehicles. At the same time, understanding the mechanism of these processes can yield insight into nanoparticle-cell interactions and nanoparticle toxicity. In this study, the suspension/precipitation process of zwitterionic lipid/SiO(2) nanosystems was analyzed as a function of ionic strength and as a function of the ratio of lipid/SiO(2) surface areas, at pH = 7.6. Salt is necessary to induce supported lipid bilayer (SLB) formation for zwitterionic lipids on silica (SiO(2)) (Seantier, B.; Kasemo, B., Influence of Mono- and Divalent Ions on the Formation of Supported Phospholipid Bilayers via Vesicle Adsorption. Langmuir 2009, 25 (10), 5767-5772). However, for zwitterionic SLBs on SiO(2) nanoparticles, addition of salt can cause precipitation of the SLBs, due to electrostatic shielding by both the lipid and the salt and to the suppression of thermal undulation/protrusion repulsive forces for lipids on solid surfaces. At ionic strengths that cause precipitation of SLBs, it was found that addition of excess SUVs, at ratios where there were equal populations of SUVs and SLBs, restored the undulation/protrusion repulsive forces and restabilized the suspensions. We suggest that SUVs separate SLBs in the suspension, as observed by TEM, and that SLB-SLB interactions are replaced by SLB-SUV interactions. Decreasing the relative amount of lipid, to the extent that there was less lipid available than the amount required for complete bilayer coverage of the SiO(2), resulted in precipitation of the nanosystem by a process of nanoparticle lipid bridging. For this case, we postulate a process in which lipid bilayer patches on one nanoparticle collide with bare silica patches on another SiO(2) nanoparticle, forming a single bilayer bridge between them. TEM data confirmed these findings, thus indicating that lipid bridges are composed of half bilayers on adjoining SiO(2) nanoparticles.     

Actinobacterial Peroxidases: an Unexplored Resource for Biocatalysis

Peroxidases are redox enzymes that can be found in all forms of life where they play diverse roles. It is therefore not surprising that they can also be applied in a wide range of industrial applications. Peroxidases have been extensively studied with particular emphasis on those isolated from fungi and plants. In general, peroxidases can be grouped into haem-containing and non-haem-containing peroxidases, each containing protein families that share sequence similarity. The order Actinomycetales comprises a large group of bacteria that are often exploited for their diverse metabolic capabilities, and with recent increases in the number of sequenced genomes, it has become clear that this metabolically diverse group of organisms also represents a large resource for redox enzymes. It is therefore surprising that, to date, no review article has been written on the wide range of peroxidases found within the actinobacteria. In this review article, we focus on the different types of peroxidases found in actinobacteria, their natural role in these organisms and how they compare with the more well-described peroxidases. Finally, we also focus on work remaining to be done in this research field in order for peroxidases from actinobacteria to be applied in industrial processes.     

Identification of a higher-order organozincate intermediate involved in Negishi cross-coupling reactions by mass spectrometry and NMR spectroscopy

Negishi cross-coupling reactions were analyzed in solution by mass spectrometry and NMR spectroscopy to identify both the effect of LiBr as an additive as well as the purpose of 3-dimethyl-2-imidazolidinone (DMI) as a co-solvent. The results suggest that the main role of DMI is to facilitate a higher order bromozincate formation during the addition of LiBr.     

Highly efficient visible-light driven photochromism: developments towards a solid-state molecular switch operating through a triplet-sensitised pathway

We introduce a new highly efficient photochromic organometallic dithienylethene (DTE) complex, the first instance of a DTE core symmetrically modified by two Pt(II) chromophores [Pt(PEt(3))(2)(C≡C)(DTE)(C≡C)Pt(PEt(3))(2)Ph] (1), which undergoes ring-closure when activated by visible light in solvents of different polarity, in thin films and even in the solid state. Complex 1 has been synthesised and fully photophysically characterised by (resonance) Raman and transient absorption spectroscopy complemented by calculations. The ring-closing photoconversion in a single crystal of 1 has been followed by X-ray crystallography. This process occurs with the extremely high yield of 80%--considerably outperforming the other DTE derivatives. Remarkably, the photocyclisation of 1 occurs even under visible light (>400 nm), which is not absorbed by the non-metallated DTE core HC≡C(DTE)C≡CH (2) itself. This unusual behaviour and the high photocyclisation yields in solution are attributed to the presence of a heavy atom in 1 that enables a triplet-sensitised photocyclisation pathway, elucidated by transient absorption spectroscopy and DFT calculations. The results of resonance Raman investigation confirm the involvement of the alkynyl unit in the frontier orbitals of both closed and open forms of 1 in the photocyclisation process. The changes in the Raman spectra upon cyclisation have permitted the identification of Raman marker bands, which include the acetylide stretching vibration. Importantly, these bands occur in the spectral region unobstructed by other vibrations and can be used for non-destructive monitoring of photocyclisation/photoreversion processes and for optical readout in this type of efficiently photochromic thermally stable systems. This study indicates a strategy for generating efficient solid-state photoswitches in which modification of the Pt(II) units has the potential to tune absorption properties and hence operational wavelength across the visible range.     

Addition of boranes to N-aryl-salicylaldimines: intramolecular hydrogenation of imines

Addition of boranes to N-aryl-salicylaldimines takes place initially at the reactive phenolic O-H bond to give an activated boron-containing imine and dihydrogen. In some cases a subsequent intramolecular hydrogenation step is observed and the C=N imine bond is reduced to the corresponding amine. Reactions with dimesitylborane in THF are unique in that the reduced amine product is the major product observed in solution.     

Asymmetric bioreduction of alkenes using ene-reductases YersER and KYE1 and effects of organic solvents

Asymmetric trans-bioreduction of activated alkenes by KYE1 from Kluyveromyces lactis and Yers-ER from Yersinia bercovieri, two ene-reductases from the Old Yellow Enzyme family, showed a broad substrate spectrum with a moderate to excellent degree of stereoselectivity. Both substrate- and enzyme-based stereocontrols were observed to furnish opposite stereoisomeric products. The effects of organic solvents on enzyme activity and stereoselectivity were outlined in this study, where two-phase systems hexane and toluene are shown to sustain bioreduction efficiency even at high organic solvent content.     

Best Proximity Points: Optimal Solutions

This article elicits a best proximity point theorem for non-self-proximal contractions. As a consequence, it ascertains the existence of an optimal approximate solution to some equations for which it is plausible that there is no solution. Moreover, an algorithm is exhibited to determine such an optimal approximate solution designated as a best proximity point. It is interesting to observe that the preceding best proximity point theorem includes the famous Banach contraction principle.     

Structure and dynamics of highly PEG-ylated sterically stabilized micelles in aqueous media

Molecular assemblies of highly PEG-ylated phospholipids are important in many biomedical applications. We have studied sterically stabilized micelles (SSMs) of self-assembled DSPE–PEG2000 in pure water and isotonic HEPES-buffered saline solution. The observed SSM sizes of 2–15 nm largely depend on the solvent and the lipid concentration used. The critical micelle concentration of DSPE–PEG2000 is 10 times higher in water than in buffer, and the viscosity of the dispersion dramatically increases with the lipid concentration. To explain the experimentally observed results, we performed atomistic molecular dynamics simulations of solvated SSMs. Our modeling revealed that the observed assemblies have very different aggregation numbers (N(agg) ≈ 90 in saline solution and N(agg) < 8 in water) because of very different screening of their charged PO4(–) groups. We also demonstrate that the micelle cores can inflate and their coronas can fluctuate strongly, thus allowing storage and delivery of molecules with different chemistries.     

Silver metallation of hen egg white lysozyme: X-ray crystal structure and NMR studies

The X-ray crystal structure, NMR binding studies, and enzyme activity of silver(I) metallated hen egg white lysozyme are presented. Primary bonding of silver is observed through His15 with secondary bonding interactions coming from nearby Arg14 and Asp87. A covalently bound nitrate completes a four coordinate binding pocket.     

Application of thermal analysis in preservation and restoration of historic masonry materials

Thermal analysis techniques have been used in characterizing building materials from significant historic properties in the Charleston, South Carolina area. Determining the chemical and physical effects of deterioration resulting from long periods of exposure is a first step in formulating preservation strategies. In this regard, simultaneous thermal analysis coupled with evolved gas analysis has been used to study reactions between air, seawater, and masonry materials. Further, the traditional petrographic identification of mortar composition is greatly facilitated through use of thermal analysis. Simultaneous thermal analysis allows for an exact determination of the calcium carbonate content in mortars as an alternative to the use of an inferred value based on chemical analysis data. The partial dissolution of calcium carbonate in the presence of sea salt is a major deterioration process. Further, natural cements manufactured in the United States are identified, in part, based on their thermogravimetric (TG) traces and their evolved gases. The data indicates that natural cements form some carbonate phases in addition to the major hydrate phases. Clay bricks are found to exhibit interaction with sea water, with uptake of bicarbonate suggested. Additionally, there is evidence of re-hydroxylation in the 160 year old bricks. The bricks made in coastal zones contain a considerable free silica fraction that is composed of a small percentage of cristobalite. The silica content of the clay bricks is seen to result in very high thermal expansion coefficients in the area of 10 × 10⁻⁶ to 12 × 10⁻⁶ K⁻¹. These studies provide guidance in restoration efforts where authenticity of cements is important. In the event that replacement bricks are required, matching the thermal expansion coefficient of the original bricks is a requirement for preservation of the masonry structure.