Continuous wave THz spectroscopy has been used to obtain spectra for four isostructural dipeptide nanotubes at 4.2K
from 2 cm-1 to 100 cm-1 (0.05 to 3 THz).
Line-narrowing of spectral features by a factor of 2 to 4 is observed for the crystalline dipeptide films investigated by absorption spectroscopy using a plane parallel waveguide, compared to
spectra from pressed disks of polyethylene-diluted samples. The
x-ray determined crystal structures of these peptides
formed the basis for a parallel computational investigation. Spectral predictions from the ab initio level computational
package DMOL3 and the empirical force field model CHARMM22 are compared to the experimentally obtained THz
absorption spectra. The THz waveguide spectroscopy technique can provide information on the orientation-dependent
dipole coupling of the vibrational modes, which can aid in validating computational models.
We create long polymer nanotubes by directly pulling on the membrane of polymersomes using either optical tweezers or a micropipette. The polymersomes are composed of amphiphilic diblock copolymers and the nanotubes formed have an aqueous core connected to the aqueous interior of the polymersome. We stabilize the pulled nanotubes by subsequent chemical cross-linking. The cross-linked nanotubes are extremely robust and can be moved to another medium for use elsewhere. We demonstrate the ability to form networks of polymer nanotubes and polymersomes by optical manipulation. The aqueous core of the polymer nanotubes together with their robust character makes them interesting candidates for nanofluidics and other applications in biotechnology.
Using optical tweezers and microfluidics, we stretch either the lipid or polymer membranes of liposomes or polymersomes, respectively, into long nanotubes. The membranes can be grabbed directly with the optical tweezers to produce sub-micron diameter tubes that are several hundred microns in length. We can stretch tubes up to a centimeter in length, limited only by the travel of our microscope stage. We also demonstrate the cross linking of a pulled polymer nanotube.
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