Molecular sensitised probe for amino acid recognition within peptide sequences

The combination of low-temperature scanning tunnelling microscopy with a mass-selective electro-spray ion-beam deposition established the investigation of large biomolecules at nanometer and sub-nanometer scale. Due to complex architecture and conformational freedom, however, the chemical identification of building blocks of these biopolymers often relies on the presence of markers, extensive simulations, or is not possible at all. Here, we present a molecular probe-sensitisation approach addressing the identification of a specific amino acid within different peptides. A selective intermolecular interaction between the sensitiser attached at the tip-apex and the target amino acid on the surface induces an enhanced tunnelling conductance of one specific spectral feature, which can be mapped in spectroscopic imaging. Density functional theory calculations suggest a mechanism that relies on conformational changes of the sensitiser that are accompanied by local charge redistributions in the tunnelling junction, which, in turn, lower the tunnelling barrier at that specific part of the peptide.

Revealing the Influences of Solvent Boiling Point and Alkyl Chains on the Adlayer Crystallinity of Furan-Diketopyrrolopyrrole-Thienylene Copolymer at Molecular Level

Crystallinity of the polymer poly(3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-altthieylenevinylene) (PDVF) adlayers casted from low-boiling-point (L-bp), medium-bp (M-bp), and high-bp (H-bp) solvents was investigated through scanning tunneling microscopy (STM) and analyzed by the assistance of Hansen solubility parameter (HSP) theory and molecular dynamics (MD) simulations. Crystallinity of the PDVF adlayers increases evidently from the L- to H-bp solvents. Also, the solvent with an alkyl chain such as ethylbenzene (EB) facilitates in improving the crystallinity than the one without an alkyl chain such as chlorobenzene (CB) if the solvent bp is present in the same group. The HSP space discloses that EB is a marginal solvent for PDVF in contrast to CB. Quasi-isolate PDVF in the EB solution revealed by MD simulations facilitates the formation of crystallized domains through surface assembling mechanism. However, in CB, interconnected PDVF molecules through intermolecular overlapping tend to generate amorphous structures through direct deposition of the preformed structures in solution.

Sequencing conjugated polymers by eye

The solid-state microstructure of a conjugated polymer is the most important parameter determining its properties and performance in (opto)-electronic devices. A huge amount of research has been dedicated to tuning and understanding how the sequence of monomers, the nature and frequency of defects, the exact backbone conformation, and the assembly and crystallinity of conjugated polymers affect their basic photophysics and charge transporting properties. However, because of the lack of reliable high-resolution analytical techniques, all the structure-property relations proposed in the literature are based either on molecular modeling or on indirect experimental data averaged on polydisperse samples. We show that a combination of electrospray vacuum deposition and high-resolution scanning tunneling microscopy allows the imaging of individual conjugated polymers with unprecedented detail, thereby unraveling structural and self-assembly characteristics that have so far been impossible to determine.