The porin MspA from M. smegmatis as Building Element in Nanotechnology
The octameric porin MspA from Mycobacterium smegmatis is sufficiently stable to form a nonmembrane-supported stand-alone porin on mica surfaces. About 98% of all MspA octamers were found to stand upright on mica, with their periplasmic loop regions bound to the hydrophilic mica surface. Both, small (d=3.7 nm) and large (d=17 nm) gold nanoparticles bind to MspA, however, in different positions: small gold nanoparticles bind within the MspA pore, whereas the large gold nanoparticles bind to the upper region of MspA. These experiments demonstrate that gold nanoparticles can be positioned at different, well-defined distances from the underlying surface using the MspA pore as a template. These findings represent a significant step toward the use of electrically insulating stable proteins in combination with metal nanoparticles in supramolecular nanodevices.
Calculated heights of the complexes: small Au@MspAQ126C (left, height: 10 nm), small Au@MspAWT (middle, height: 12.5 nm), and large Au@MspAWT complexes (right, height: 26.5 nm) (with thanks to Dr. Paul Smith, KSU Chem)
Photochromic Systems for Optical Information Storage
We are synthesizing new photochromic styryl-quinolyl dihydroindolizine/betaine systems for optical information storage, in which both constitutional isomers show remarkably strong fluorescence. The DHI (1) undergoes a 1,5-electrocyclic reaction to betaine (2) upon irradiation with UVA light λ < 400 nm). When stabilized in a PMMA matrix, the blue betaine (2) is stable for hours at room temperature and indefinitely stable at 77K against the thermal back reaction to the DHI (1).
Irradiation of betaine (2) with λ = 532 nm permits the photo-induced back switching process to DHI (1). The betaine (2) permits its destruction-free read-out at λ = 645 nm when excited with λ = 580 nm. This system has enabled the realization of a prototype for an information recording and storage system.
Left: VIS-absorption spectrum of the “runner” (DHI (1) in PMMA after writing with a 355nm laser beam. Right: Fluorescence spectrum from the “runner”, excitation at 532nm.