Direct Observation of the Release of Phenylalanine from Diphenylalanine Nanotubes

Abstract

The core recognition motif of the amyloidogenic beta-amyloid polypeptide is a dipeptide of phenylalanine. This dipeptide readily self-assembles to form discrete, hollow nanotubes with high persistence lengths. The simplicity of the nanotube formation, combined with ideal physical properties, make these nanotubes highly desirable for a range of applications in bionanotechnology. To fully realize the potential of such structures, it is first necessary to gain a comprehensive understanding of their chemical and physical properties. Previously, the thermal stability of these nanotubes has been investigated by electron microscopy. Here, we further our understanding of the structural stability of the nanotubes upon dry-heating using the atomic force microscope (AFM), and for the first time identify their degradation product utilizing time-of-flight secondary-ion mass spectrometry. We show that the nanotubes are stable at temperatures up to 100 degrees C, but on heating to higher temperatures begin to lose their structural integrity with an apparent collapse in tubular structure. With further increases in temperature up to and above 150 degrees C, there is a degradation of the structure of the nanotubes through the release of phenylalanine building blocks. The breakdown of structure is observed in samples that are either imaged at elevated temperatures or imaged following cooling, suggesting that once phenylalanine is lost from the nanotubes they are susceptible to mechanical deformation by the imaging AFM probe. This temperature-induced plasticity may provide novel properties for these peptide nanotubes, including possible applications as scaffolds and drug delivery devices.

Role of Water in Directing Diphenylalanine Assembly into Nanotubes and Nanowires

“…S3a, Supporting Information), attributed to the heat-induced loss of the diphenylalanine moiety from the ordered hexagonal array that constitutes the NTs. [17] In the case of NWs, this temperature is reduced to 594 K (Fig. S3b, Supporting Information), indicating that NWs are thermodynamically less stable than NTs in the absence of solvent.…”

Liquid Crystalline Peptide Nanowires

“…[10,[26][27][28][29] We discovered that it forms individually-dispersed rigid nanowires in an organic solvent. Due to the rigidity and high aspect ratio of the nanowires, they formed colloidal liquid crystalline phase for a broad concentration range.…”

Piezoelectricity and ferroelectricity in biomaterials: Molecular modeling and piezoresponse force microscopy measurements

“…The structure of di-phenylalanine was studied in detail by Gorbitz [77][78][79] and by the group of Gazit. 75,76,[80][81][82] They are made from amino acids molecules, self-assembled as uniquely stable tubes with hydrophilic hollows, and possess high Young's modulus and chemical stability. 82 It was shown 41 that FF PNTs are also strongly piezoelectric, with the orientation of polarization along the tube axis.…”