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Research Highlights

DNA-tethered Membrane Formation From Giant Unilamellar Vesicles

boxer.jpg We have developed two strategies for preparing tethered lipid bilayer membrane patches on solid surfaces by DNA hybridization. In the first strategy, single-stranded DNA strands are immobilized by click chemistry to a silica surface, whose remaining surface is passivated to prevent direct assembly of a solid supported bilayer. Then giant unilamellar vesicles (GUVs) displaying the anti-sense strand based on a DNA-lipid conjugate are allowed to tether, spread, and rupture to form tethered bilayer patches. In the second strategy, a supported lipid bilayer displaying the DNA-lipid conjugate is first assembled on the surface. Then GUVs displaying the anti-sense strand are allowed to tether, spread and rupture to form tethered bilayer patches.

Green Chemistry of Poly(l-lactides)

As part of a series of studies on the green chemistry of poly(l-lactides), we have performed a theoretical study of the mechanism of ring-opening polymerization. We have investigated two alternative mechanisms for the ring-opening polymerization of l-lactide using a guanidine-based catalyst, the first involving acetyl transfer to the catalyst, and the second involving only hydrogen bonding to the catalyst. Using computational chemistry methods, we show that the hydrogen bonding pathway shown above is preferred over the acetyl transfer pathway and that this is consistent with experimental information.

Education Highlight

CPIMA SURE Student Highlight: Vivian Trang

Scanning electron micrograph Vivian Trang joined CPIMA scientists at Stanford and IBM working to develop novel synthesis methods to control the porosity of hydrogels. She used an organocatalytic living polymerization method to make the systems. Cyclic carbonate functional macromolecules were ring-opened using an alcoholic initiator in the presence of an organic catalyst. A model reaction for the cross-linking identified the critical monomer concentration dependent reaction regimes, and enhanced kinetic control was demonstrated by introducing a co-monomer which facilitated near quantitative conversion of monomer to polymer (>96%).

Facility Highlight

Quartz Crystal Microbalance Sensor

The quartz crystal microbalance (QCM) sensor has recently been put into place in the Stanford CPIMA Shared Facilities and is experiencing a surge of use. This sensor is extraordinarily sensitive to mass changes associated with the deposition of material onto the surface of a quartz crystal. These changes are sensed as changes in the natural resonant frequency of the QCM.

The QCM is also sensitive to the mechanical losses in the film, which give rise to increasing resonance widths. This increasing width or decreasing quality factor (Q) is measured as an increase in the equivalent circuit resistance.