Values of the bending modulus KC are reviewed, and possible causes for the considerable differences are discussed. One possible cause is the use of glucose and sucrose in the classical micromechanical manipulation and shape analysis methods. New data, using the more recent low angle x-ray method, are presented that do not support an effect of glucose or sucrose on KC. Another possible cause is using an incomplete theory to interpret the data. Adding a tilt term to the theory clearly does not affect the value obtained from the shape analysis method. It is shown that a tilt term, using a value of the modulus Kθ indicated by simulations, theory, and estimated from order parameters obtained from NMR and from the wide angle x-ray method, should also not affect the value obtained using the micromechanical manipulation method, although it does require a small correction when determining the value of the area compressibility modulus KA. It is still being studied whether including a tilt term will significantly affect the values of KC obtained using low angle x-ray data. It remains unclear what causes the differences in the experimental values of KC for simple lipid bilayers.

Improving the efficiency of enzymatic hydrolysis of cellulose is one of the key technological hurdles to reduce the cost of producing ethanol and other transportation fuels from lignocellulosic material. A better understanding of how soluble enzymes interact with insoluble cellulose will aid in the design of more efficient enzyme systems. We report a study involving neutron reflectometry (NR) and quartz crystal microbalance with dissipation monitoring (QCM-D) of the interaction of a fungal enzyme extract ( T. viride ) and an endoglucanse from A. niger with amorphous cellulose films. The use of amorphous cellulose is motivated by that the fact that several biomass pretreatments currently under investigation disrupt the native crystalline structure of cellulose and increase the amorphous content. NR reveals the profile of water through the film at nanometer resolution and is highly sensitive to interfacial roughness, whereas QCM-D provides changes in mass and film stiffness. NR can be performed using either H(2)O- or D(2)O-based aqueous reservoirs. NR measurement of swelling of a cellulose film in D(2)O and in H(2)O revealed that D/H exchange on the cellulose chains must be taken into account when a D(2)O-based reservoir is used. The results also show that cellulose films swell slightly more in D(2)O than in H(2)O. Regarding enzymatic digestion, at 20 °C in H(2)O buffer the T. viride cocktail rapidly digested the entire film, initially roughening the surface, followed by penetration and activity throughout the bulk of the film. In contrast, over the same time period, the endoglucanase was active mainly at the surface of the film and did not increase the surface roughness.

Recent simulations have indicated that the traditional model for topographical fluctuations in biomembranes should be enriched to include molecular tilt. Here we report the first experimental data supporting this enrichment. Utilizing a previously posited tilt-dependent model, a height-height correlation function was derived. The x-ray scattering from a liquid crystalline stack of oriented fluid phase lipid bilayers was calculated and compared with experiment. By fitting the measured scattering intensity, both the bending modulus K(c)=8.3±0.6×10⁻²⁰ J and the tilt modulus K(θ)=95±7  mN/m were determined for DOPC lipid bilayers at 30 °C.

A hydrated, surface-tethered polymer network capable of fivefold change in thickness over a 25-37 degrees C temperature range has been demonstrated via neutron reflectivity and fluorescence microscopy to be a novel support for single lipid bilayers in a liquid environment. As the polymer swells from 170 to 900 A, it promotes both in- and out-of-plane fluctuations of the supported membrane. The cushioned bilayer proved to be very robust, remaining structurally intact for 16 days and many temperature cycles. The promotion of membrane fluctuations offers far-reaching applications for this system as a surrogate biomembrane.

We report the effect on lipid bilayers of the Tat peptide Y47GRKKRRQRRR57 from the HIV-1 virus transactivator of transcription (Tat) protein. Synergistic use of low-angle X-ray scattering (LAXS) and atomistic molecular dynamics simulations (MD) indicate Tat peptide binding to neutral dioleoylphosphocholine (DOPC) lipid headgroups. This binding induced the local lipid phosphate groups to move 3 Å closer to the center of the bilayer. Many of the positively charged guanidinium components of the arginines were as close to the center of the bilayer as the locally thinned lipid phosphate groups. LAXS data for DOPC, DOPC/dioleoylphosphoethanolamine (DOPE), DOPC/dioleoylphosphoserine (DOPS), and a mimic of the nuclear membrane gave similar results. Generally, the Tat peptide decreased the bilayer bending modulus KC and increased the area/lipid. Further indications that Tat softens a membrane, thereby facilitating translocation, were provided by wide-angle X-ray scattering (WAXS) and neutron scattering. CD spectroscopy was also applied to further characterize Tat/membrane interactions. Although a mechanism for translocation remains obscure, this study suggests that the peptide/lipid interaction makes the Tat peptide poised to translocate from the headgroup region.