Hannes Y. Kuchelmeister

Nucleotide Recognition in Water by a Guanidinium‐Based Artificial Tweezer Receptor

The water-soluble tweezer receptor 1 with two symmetric peptidic arms, which are connected by an aromatic scaffold and contain lysine, phenylalanine, and a guanidinium-based anion-binding site as headgroup, has been synthesized. UV/Vis-derived Job plots show that the receptor forms 1:1 complexes with nucleotides and phosphate in buffered water at neutral pH. Binding constants have been determined by fluorescence and UV/Vis spectroscopy. All nucleotides tested were bound very efficiently, even in pure water, with binding constants between 10(4) and 10(5) M(-1) . Interestingly, all mononucleotides were bound much stronger than phosphate by a factor of at least 5 to 10. Furthermore 1 favors the binding of adenosine monophosphate (AMP) over adenosine diphosphate (ADP) and adenosine triphosphate (ATP), which is unprecedented for artificial nucleotide receptors reported so far. According to NMR spectroscopy and molecular modeling studies, the efficient binding is a result of strong electrostatic contacts supported by π-π interactions with the nucleobase within the cavity-shaped receptor.

Efficient gene delivery into cells by a surprisingly small three-armed peptide ligand

The development of new non-viral transfection vectors for gene transport into cells is of current interest. A small, three-armed peptide ligand 1 is derived from the cationic dipeptide Lys-Phe with an additional anion recognition site at its N-terminus, binds to DNA with high affinity (K ca. 107 M−1) and efficiently delivers a GFP plasmid into cells. Compared to the cationic polymer polyethyleneimine (PEI), routinely used as a standard vector for transfection, 1 is significantly more efficient and also less cytotoxic. As DLS and AFM studies show, ligand 1 condenses DNA into tightly packed cationic aggregates which are then taken up by the cells. In contrast, the analogous divalent peptide ligand 2 of identical amino acid sequence and the highly charged divalent DNA-binder 3 (Lys-Lys-Arg) do not enable gene delivery though they also bind with high affinity (2: K ca. 106 M−1; 3: K ca. 107 M−1). All three ligands are able to transfer genetic material into cells but only the trivalent gene carrier is able to escape from the endosome due to its superior buffering capacity.

Quantitative label-free monitoring of peptide recognition by artificial receptors: a comparative FT-IR and UV resonance Raman spectroscopic study

Vibrational spectroscopic investigations on molecular recognition processes are surprisingly rare, even at the qualitative level. In this first comparative study, we employ Fourier-transform infrared (FT-IR) and UV resonance Raman (UVRR) spectroscopy for quantitative label-free monitoring of molecular recognition processes. Specifically, the complexation of two different tetrapeptide ligands by an artificial receptor is investigated. The central advantage of UVRR is its capability to selectively probe the binding site of the receptor in the free/unbound and complexed form. In contrast, FT-IR probes the entire receptor–ligand complex without spectral selectivity, thereby providing complementary vibrational information. Multivariate analysis of the experimental IR/UVRR binding studies is required for determining association constants and the vibrational spectrum of the complex, which is not directly accessible. Both FT-IR and UVRR spectroscopy provide similar association constants for the two different tetrapeptide ligands. Complementary DFT calculations support the interpretation of the observed spectral changes upon complexation, which is a prerequisite for extracting structural information from vibrational binding studies.

Plasmonically active micron-sized beads for integrated solid-phase synthesis and label-free SERS analysis

Self-assembly of gold nanospheres with a very thin glass shell onto the surface of beads yields a plasmonically active micron-sized substrate for integrated solid-phase synthesis and label-free SERS analysis. The proof-of-principle of this approach is demonstrated by the vibrational spectroscopic discrimination of three distinct amino acids and a dipeptide.