Intramolecular Electron Transfer across Amino Acid Spacers in the Picosecond Time Regime. Charge-Transfer Interaction through Peptide Bonds

Abstract

For a series of alanine-based peptides having 1-3 amino acid residues as spacers, the chromophore, pyrenesulfonyl (Pyr), has been attached at the N-terminus and an electron donor, dimethyl-1,4-benzenediamine (DMPD), covalently bound at the C-terminus. Evidence for an intramolecular charge-transfer interaction involving the electron donor and acceptor groups has been obtained from absorption spectra. Intramolecular electron transfer involving the end groups, Pyr (electron acceptor) and DMPD (electron donor) has been confirmed by ultrafast pump-probe methods. The radical-ion pair states that are generated on Ti/sapphire laser excitation at 400 nm decay in the picosecond to nanosecond time domain and generally show multiexponential decay kinetics. These rates of charge recombination are among the fastest yet observed involving electron transfer between terminal groups for peptide oligomers. The falloff of rate constants for ion pair recombination is irregular in terms of the through-bond distance that separates Pyr and DMPD groups for the various peptide links; i.e., back electron transfer remains fast for the tripeptide, Pyr-Ala-Ala-Ala-DMPD, despite an average through-bond distance between photoactive groups that reaches 18 Å. Molecular modeling studies show that the peptides are free to adopt conformations in essentially random fashion, without showing evidence for long range ordering of the peptide chain.

Measurement of Submicrosecond Intramolecular Contact Formation in Peptides at the Single-Molecule Level

“…46,47 Furthermore, electron-transfer reactions do not require intimate molecular contact and may well occur over larger distances, e.g., through space or through bond by a superexchange mechanism. 48 Hence, the measured rate constants may not directly reflect intrachain contact formation. However, the bimolecular quenching constants point out that efficient quenching via electron transfer occurs only at van der Waals contact (∼0.4 nm).…”

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“…The key steps in this reaction are electron transfer from the donor (carboxylate) to the acceptor (sulfonamide) 839 , 840 , 846 and the subsequent formation of a charge-separated state. 845 , 846 In the case of 157 , the ability of carboxylates to transfer a single electron to the excited BODIPY is yet to be established, but a similar process was proposed for the closely related compounds 225a , b ( section 4.1.1 ). 847 The formation of a charge-separated state was supported by the need for the carboxylate and sulfonamide groups to be in close proximity.…”

Regulation of electronic behavior via confinement of PPV-based oligomers on peptide scaffolds

“…For example, peptides have been utilized in combination with conjugated molecules for a variety of studies; porphyrins have been conjugated to peptide scaffolds to create porphyrin arrays in order to optimize electron coupling and energy transfer, 15,16 as conformation-sensitive optical probes in thiophene-based polyelectrolytes, 17,18 for stimulating selfassembly with negatively charged polythiophene derivatives 19 and in most cases for fluorescence resonance energy transfer (FRET) studies. [20][21][22][23][24][25][26][27][28][29][30] In addition, chromophores conjugated to diamino acid-N a -substituted oligopeptides and to B-DNA have been previously used for holographic data storage 31 and as helical rulers, 32 respectively. Although these previous investigations have yielded materials with interesting electronic properties, limitations still remain.…”