Chemistry IROPs

IROP 1 - Supported Bilayer Membranes Fabricated with Bicelles: Optimization of Binding Conditions

Objectives and Methodology

Spherical supported bilayer membranes (SSBMs) are increasingly important in biophysical modeling and biotechnology applications.  They consist of a single lipid bilayer completely coating an underlying spherical polymer bead.  Our laboratory has developed a new method for fabricating SSBMs starting from bicelles.  Bicelles are mixtures of short-chain and long-chain phospholipids which spontaneously assemble into small disks consisting of a planar lipid bilayer formed by the long-chain phospholipids, stabilized at their edges by the short-chain phospholipid.  The bicelles are “locked” onto the polymer bead’s surface via a “chemoselective” covalent reaction between oxyamine-bearing ligands present in the bicelle and aldehyde groups present at the polymer bead surface.

A key requirement for improving the process of fabricating the bicelle-based SBMs is to optimize bicelle binding conditions, and is the main goal of this ROP project.   Binding will be measured using fluorescence assays on bicelles containing a fluorescently-labelled lipid as reporter group. Two principal parameters will be varied in separate experimental series: 1) quantity of oxyamine ligand, 2) quantity of overall bicelle material.  The results of these optimization experiments will permit us to more efficiently and effectively produce bicelle-based SSBMs and move forward with other developments of interest in our laboratory.

Description of Student Participation

Under the direct supervision of a senior graduate student and the principal investigator, the student will prepare bicelles, perform binding experiments involving fluorescence spectroscopy, analyze the results and prepare reports.

Students will meet weekly with their supervisor to provide updates and summaries of their progress in the form of data presentations.  Feedback will be provided to the student along with discussions of solutions to problems encountered during the course of the experiments. In keeping with CPS ROP standards and guidelines, a final report will be prepared and a final oral presentation will be conducted as part of the evaluation scheme.

List of Skills Required / Instructor Preference & Student Experience

Any student undertaking this project should be comfortable with concepts from second-year analytical and physical chemistry, at a minimum, should be highly motivated, and should able to work well under supervision.  Some university-level mathematical skill would be useful.


IROP 2 - Supported Bilayer Membranes Fabricated with Bicelles: Can We Use “Fluid” Bicelles ?

Objectives and Methodology

Spherical supported bilayer membranes (SSBMs) are increasingly important in biophysical modeling and biotechnology applications.  They consist of a single lipid bilayer completely coating an underlying spherical polymer bead.  Our laboratory has developed a new method for fabricating SSBMs starting from bicelles.  Bicelles are mixtures of short-chain and long-chain phospholipids which spontaneously assemble into small disks consisting of a planar lipid bilayer formed by the long-chain phospholipids, stabilized at their edges by the short-chain phospholipid.  The bicelles are “locked” onto the polymer bead’s surface via a “chemoselective” covalent reaction between oxyamine-bearing ligands present in the bicelle and aldehyde groups present at the polymer bead surface.

A key requirement for improving the properties of bicelle-based SSBMs is to fabricate low Tm versions.  The Tm is the temperature at which the bilayer lipids convert from a gel-like, relatively immobile state, to a fluid-like, relatively mobile state, akin to that found in natural biological membranes.  The main goal of this ROP project will be to explore the use of bicelles composed of phospholipids that yield a Tm below room temperature as starting materials for producing SSBMs.  The project will proceed in two stages.  In the first, a variety of low Tm phospholipids will be examined for their ability to assemble into discoid bicelles.  In the second stage, the most suitable bicelle compositions will be employed to fabricate SSBMs and the resulting properties will be examined.  In particular, we are interested in their extent of binding to polymer bead surfaces, and their ability to fuse into a continuous bilayer coating.  Fluorescence spectroscopy of bicelles containing a fluorescently-labelled lipid as reporter group will be the principal tool used to assess these questions. The success of these experiments will provide SSBMs that much better mimic the properties of natural biological membranes.

Description of Student Participation

Under the direct supervision of a senior graduate student and the principal investigator, the student will prepare bicelles, perform binding experiments involving fluorescence spectroscopy, analyze the results and prepare reports.

Students will meet weekly with their supervisor to provide updates and summaries of their progress in the form of data presentations.  Feedback will be provided to the student along with discussions of solutions to problems encountered during the course of the experiments. In keeping with CPS ROP standards and guidelines, a final report will be prepared and a final oral presentation will be conducted as part of the evaluation scheme.

List of Skills Required / Instructor Preference & Student Experience

Any student undertaking this project should be comfortable with concepts from second-year analytical and physical chemistry, at a minimum, should be highly motivated, and should able to work well under supervision.  Some university-level mathematical skill would be useful.


IROP 3 - Supported Bilayer Membranes Fabricated with Bicelles: Optimizing the Chemoselective Linker

Objectives and Methodology

Spherical supported bilayer membranes (SSBMs) are increasingly important in biophysical modeling and biotechnology applications.  They consist of a single lipid bilayer completely coating an underlying spherical polymer bead.  Our laboratory has developed a new method for fabricating SSBMs starting from bicelles.  Bicelles are mixtures of short-chain and long-chain phospholipids which spontaneously assemble into small disks consisting of a planar lipid bilayer formed by the long-chain phospholipids, stabilized at their edges by the short-chain phospholipid.  The bicelles are “locked” onto the polymer bead’s surface via a “chemoselective” covalent reaction between oxyamine-bearing ligands present in the bicelle and aldehyde groups present at the polymer bead surface.

A key factor in dictating the properties of the bicelle-based SBMs is the chemical structure of the oxyamine-bearing ligand.  This consists of a cholesterol group, to insert strongly into the lipid bilayer of the bicelle, and an oxyamine group, to react with the polymer bead surface aldehydes, separated by a short oligo-ethylene oxide spacer group, to alleviate steric constraints, facilitate the desired chemical reaction, and provide an aqueous space between the polymer bead surface and the attached bilayer.

The goal of this ROP project is to optimize the length of the ethylene oxide spacer between the cholesterol and oxyamine groups.  If too short, steric obstruction will inhibit the desired chemoselective reaction and leave too narrow an aqueous space, thereby inhibiting mobility.  If too long, the poly-ethylene oxide “brush” will itself sterically obstruct the desired chemoselective reaction.  This ROP project will progress in two stages.  First, a series of oxyamine-bearing ligands will be synthesized having a range of lengths of the ethylene oxide spacer group.  Second, these will be tested for their ability to react with aldehydes on the surface of polymer beads and thereby form the desired SSBMs.  The success of these optimization experiments will permit us to produce bicelle-based SSBMs with enhanced mobility of molecules incorporated onto the SSBM surface.

Description of Student Participation

Under the direct supervision of a senior graduate student and the principal investigator, the student will synthesize, purify and characterize various length linkers groups, incorporate these into bicelles, and perform bicelle binding experiments involving fluorescence spectroscopy, analyze the results and prepare reports.

Students will meet weekly with their supervisor to provide updates and summaries of their progress in the form of data presentations.  Feedback will be provided to the student along with discussions of solutions to problems encountered during the course of the experiments. In keeping with CPS ROP standards and guidelines, a final report will be prepared and a final oral presentation will be conducted as part of the evaluation scheme.

List of Skills Required / Instructor Preference & Student Experience

Any student undertaking this project should be comfortable with concepts from second-year organic, analytical and physical chemistry, at a minimum, should be highly motivated, and should able to work well under supervision.  Some university-level mathematical skill would be useful.