Study of water vapor and surfactant absorption by lipid model systems using the quartz crystal microbalance

Skin is constantly exposed to surfactants which compromise the essential barrier function of normal healthy skin. To model the interactions of surfactants with the barrier lipids of the stratum corneum (SC), it is essential to develop in vitro and in vivo quantitative measurement methods to predict, evaluate, and demonstrate the effect of the different surfactant chemistries and technologies on skin. In the current work, in vitro water vapor uptake and surfactant absorption onto skin lipid model films were quantitatively studied using a technique based on the piezoelectric effect, the quartz crystal microbalance (QCM). This approach is straightforward and reliable in providing subtle surface/interface related mass change information with high resolution and sensitivity. The results show that barrier properties of the lipid model system may be damaged by surfactant absorption, as well as by long-term water exposure due to alterations to the lipid film structure. Surfactant absorption is found to be concentration dependent even beyond its critical micelle concentration (CMC). QCM results for different surfactant systems are consistent with reported clinical data in showing that clinically milder surfactants (SLES) do not perturb the film as much as clinically harsh surfactants (SDS).     

Effects of non-ionic surfactants on the interactions between cellulases and tannic acid: a model system for cellulase-poly-phenol interactions

Addition of non-ionic surfactants (NIS) is known to accelerate enzymatic lignocellulose hydrolysis. The mechanism behind this accelerating effect is still not elucidated but has been hypothesized to originate from favorable NIS-lignin interactions which alleviate non-productive adsorption of cellulases to lignin. In the current work we address this hypothesis using tannic acid (TAN) as a general poly-phenolic model compound (for lignin and soluble phenolics) and measure the mutual interactions of cellulases (CBHI, CBHII, EGI, EGII and BG), TAN and NIS (Triton X-100) using isothermal titration calorimetry (ITC). The experimental results suggest rather strong enzyme-specific interactions with TAN in reasonable agreement with enzyme specific lignin inhibition found in the literature. Enzyme-TAN interactions were disrupted by the presence of NIS by a mechanism of strong TAN-NIS interaction. The presence of NIS also alleviated the inhibitory effect of TAN on cellulase activity. All together the current work provides strong indications that favorable NIS-poly-phenol interactions alleviate non-productive cellulase-poly-phenol interactions and hence may provide a mechanism for the accelerating effect of NIS on lignocellulose hydrolysis.     

Overcoming hysteresis to attain reversible equilibrium folding for outer membrane phospholipase A in phospholipid bilayers

The free energy of unfolding of a membrane protein from lipids into water (ΔG^o_w,l) describes its equilibrium thermodynamic stability. Knowing this parameter gives insight into a membrane protein's sequence-structure-energy relationships. However, there are few measures of membrane protein stability because of the technical difficulties associated with unfolded and partially folded states. Here, we describe the experimental process that allowed us to measure the ΔG^o_w,l of the outer membrane phospholipase A into large unilamellar vesicles (LUVs) of 1,2-dilauroyl-sn-glycero-3-phosphocholine. To arrive at this reversible folding condition, we screened a large number of experimental variables: temperature, incubation time, salt concentration, pH, lipid composition and liposome morphology. The principal challenge we encountered under most conditions was hysteresis between folding and unfolding titrations. A second factor that compromised reversible folding was the observation that a fraction of the protein population tended to aggregate. We found that hysteresis could be completely eliminated on a feasible timescale by conducting experiments at acidic pH, by the slow dilution of the protein in the initial titration setup and by utilizing a low concentration of a detergent as a temporary “holdase” to solubilize the protein upon its initial dilution into folding conditions. We confirmed that the detergent did not disrupt the LUVs using fluorescence emission of lipid-sensitive dyes and light scattering. The results of our parameter search should be generally useful for efforts to measure ΔG^o_w,l for other membrane proteins.     

Amphiphilic peptides with arginines and valines for the delivery of plasmid DNA

A non-toxic and efficient gene carrier is one requirement for clinical gene therapy. In this study, amphiphilic peptides composed of arginines and valines were synthesized and characterized as plasmid DNA (pDNA) carriers. The peptides have a cationic region containing 1-4 arginines and a hydrophobic region containing 6 valines. The arginine-valine peptides (RV peptides) formed micelles in aqueous solution with a critical micelle concentration (CMC) of 1.35 mg/ml. In gel retardation assay, the RV peptides retarded all pDNA at weight ratios (pDNA:RV peptide) of 1:3 for R1V6, 1:2 for R2V6 and R3V6, and 1:1 for R4V6. A heparin competition assay showed that the R3V6 peptide formed tighter complexes with pDNA than poly-L-lysine (PLL). In vitro transfection assay into HEK293 cells showed that the R1V6 and R2V6 peptides had the highest transfection efficiencies at 1:30 weight ratios (pDNA:RV peptide), while the R3V6 and R4V6 peptides had the highest efficiencies at 1:20 weight ratios. Under optimal conditions, the R3V6 peptide had the highest transfection efficiency of all the RV peptides and PLL. MTT assay showed that the RV peptides did not have any detectable toxicity to cells. Therefore, the RV peptide may be useful for the development of non-toxic gene carriers.     

Computer simulation of polymer and biopolymer self-assembly for drug delivery

Molecular simulation is an emerging tool to bridge relevant time- and length-scales in self-assembly and interfacial processes in soft matter and biological systems. In this review, we highlight mesoscale and coarse-grained molecular dynamics simulation techniques as applied to poly(ethylene oxide)-based diblock copolymer self-assembly. Moreover, we review recent progress pertaining to diblock copolymer and biopolymer self-assembly, stability, and finally, interactions of hydrophobic drugs with polymer membranes. We expect that these computational investigations should provide a useful complement to experimental studies that address open questions in the field of polymeric drug delivery.     

Luminescent complexes of terbium ion for molecular recognition of ibuprofen

The complexation behavior and luminescent properties of terbium (Tb³⁺) complexes containing bi‐dental ligands were studied: nitrogen – 1,10‐phenanthroline, and oxygen – trifluoroacetylacetone as well as acetylacetone ligands with ibuprofen (Ibu; a non‐steroidal anti‐inflammatory drug). Aqueous and aqueous alcohol microheterogeneous solutions were used as media. The effects of solubilization by various micellar solutions, pH and ligand type on luminescent properties of Tb³⁺ complexes were investigated. Sensitized luminescence of mixed ligand complex Tb(1,10‐phenanthroline)‐Ibu and dynamic quenching effect in complex Tb(trifluoroacetylacetone)₃‐Ibu allow Ibu determination with the limit of detection 5.3 × 10^–8 mol/L and 1.26 × 10^–6 mol/L, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of the Effect of Surfactants on the Movement of Pesticides in Soils Using a Soil Thin-Layer Chromatography Technique

In this study, the effect of concentration (1/2 CMC, at CMC and 2 x CMC) of surfactants, cetyl trimethyl ammonium bromide (cationic), sodium dodecyl sulfate (anionic), and tween ‘20’ (non-ionic) on the movement of carbofuran, chlorpyrifos and en-dosulfan in soils was evaluated by using a soil thin-layer chromatographic technique. The movement of pesticides was detected by spray reagents and expressed in terms of Rf values. The penetrability K was found to increase by decreasing the plate angle and followed the order as: sandy loam > loam > silt loam soils. The penetrability K also decreases in surfactant-free and surfactant-amended soils when developed in distilled water and aqueous surfactant solutions of different CMCs, respectively. The higher movement of pesticides was observed in sandy loam soil followed by loam and silt loam soils. On the basis of Rf values, the movement of pesticides follows the order as: carbofuran > chlorpyrifos > endosulfan, both in surfactant-amended and surfactant-free soils when developed in distilled water and aqueous surfactant solutions of different CMCs. The movement is directly proportional to the aqueous solubilities, polarities, and carbon numbers and inversely related to the molecular weights of pesticides. A significant increase or decrease of pesticides movement in soils was discussed on the basis of adsorption of pesticides on soils, chemical nature of the surfactants, and its concentrations in terms of critical micelle concentrations (CMCs) in soils and eluents. Results obtained may provide insights pertaining to the use of surfactants for solving soil pollution problems posed by pesticides.     

Impact of the green tea ingredient epigallocatechin gallate and a short pentapeptide (Ile-Ile-Ala-Glu-Lys) on the structural organization of mixed micelles and the related uptake of cholesterol

Background

High levels of blood cholesterol are conventionally linked to an increased risk of developing cardiovascular disease (Grundy, 1986). Here we examine the molecular mode of action of natural products with known cholesterol-lowering activity, such as for example the green tea ingredient epigallocatechin gallate and a short pentapeptide, Ile-Ile-Ala-Glu-Lys.

Crystal and molecular structure of polymeric [MnCl2(bpy)]n

A crystal and molecular structure determination of MnCl₂(bpy) showed that it exists as polymeric octahedral [MnCl₂(bpy)]_n. [MnCl₂(bpy)_n crystallizes in the monoclinic space group I2/a with A = 7.007(1), B = 9.200(1), C = 16.495(1) Å, β = 91.313(5)° and Z = 4. On the basis of 979 unique observed reflections with I 2.5σ(I) the structure was refined to R = 0.032.