Release of an Encapsulated Peptide from Carbon Nanotubes Driven by Electric Fields: A Molecular Dynamics Study

Targeted drug delivery into cells has been of tremendous scientific interest, and carbon nanotubes (CNTs) can be deemed as a promising material for the loading and unloading of drugs. One of the major challenges is the release of drugs from CNTs, which have a great potential well to trap molecules. By performing molecular dynamics simulations, this work attempts to study the releasing process of encapsulated protein/peptide molecules from CNTs in the presence of uniform electric fields. Zadaxin serves as a model for protein/peptide drugs. External electric fields can assist the peptide in overcoming the potential well during its release. It is found that successful release of the peptide depends on the pore width, the pore length, and the net charges on the peptide. The peptide is less likely to be released either from CNTs with a smaller pore diameter due to a deeper potential well of the tubes or from CNTs with a longer pore length due to a broader and deeper potential well. Peptides with more net charges are ideal for the releasing process driven by electric fields. This work can provide insights into the design of an optimal tube size for effective release of a given protein/peptide.

Separation of peptides and intact proteins by electrostatic repulsion reversed phase liquid chromatography

A new brand of BEH-C18 hybrid particles chemically bonded to a leash carrying an amine group permits the implementation of electrostatic repulsive interactions chromatography. Using columns packed with this material, the influence of the concentration of positive charges bonded to the BEH-C18 surface on the overloaded band profiles of a few positively charged peptides and proteins was investigated in the gradient elution mode. Three columns packed with endcapped BEH-C18 particles bonded with three different surface-charge densities (LOW, MEDIUM and HIGH) were used and compared with those provided by a column packed with non-doped, endcapped BEH-C18 particles. The surface concentrations of fixed charges in the LOW, MEDIUM and HIGH columns were estimated at 0.029, 0.050, and 0.064μmol/m(2), for example, about two orders of magnitude smaller than the surface density of bonded C18 chains (2.1μmol/m(2)). Three different mobile phase additives (0.1% v/v of trifluoro-acetic, phosphoric, and formic acid) were used to optimize the purification levels of proteins under different loading conditions. The weak ion-pairing ions (formate and phosphate) generate smaller retention but broader, more fronting band profiles than those eluted with a stronger ion-pairing ion (trifluoroactate). This effect is worse in the presence of fixed charges at the surface of the BEH-C18 particles. This was explained by an enhanced anti-Langmuirian adsorption behavior of the charged proteins in the presence of fixed surface charges. As the protein concentration increases in the bulk, so does the internal ionic strength, the electrostatic repulsive interactions weaken, and retention increases. Band fronting is mostly eliminated by replacing weak ion-pairing acids with TFA with which the adsorption isotherm remains weakly langmuirian. Faster but still complete gradient separation of insulin and myoglobin were achieved with the HIGH column than with the reference neutral column, despite a measurable loss in selectivity.

Conductive polymer nanotube patch for fast and controlled ex vivo transdermal drug delivery

Aim: To uptake and release hydrophilic model drugs and insulin in a novel conductive polymer (CP) nanotube transdermal patch. Materials & methods: The externally controlled transdermal delivery of model drugs and insulin were tested ex vivo and results were compared with CP films. The unique intrinsic properties of CPs provide electrostatic interaction between the model drugs and polymer backbone. Results & discussion: When a pulsed potential was applied, the drug delivery release profile mimics that of injection delivery. With a constant potential applied, the release rate constants of the patch system were up to three-times faster than the control (0 V) and released approximately 80% more drug molecules over 24 h. Conclusion: The CP nanotube transdermal patch represents a new and promising drug method, specifically for hydrophilic molecules, which have been a large obstacle for conventional transdermal drug delivery systems.

Original submitted: 7 March 2013; Revised submitted: 1 August 2013

Electrophoretic transport of biomolecules through carbon nanotube membranes

Electrophoretic transport of proteins across electrochemically oxidized multi-walled carbon nanotube (MWCNT) membranes has been investigated. A small charged protein, lysozyme, was successfully pumped across MWCNT membranes by an electric field while rejecting larger bovine serum albumin (BSA). Transport of lysozome was reduced by a factor of about 30 in comparison to bulk mobility and consistent with the prediction for hindered transport. Mobilities between 0.33 and 1.4 × 10(-9) m(2) V(-1) s(-1) were observed and are approximately 10-fold faster than comparable ordered nanoporous membranes and consistent with continuum models. For mixtures of BSA and lysozyme, complete rejection of BSA is seen with electrophoretic separations.