Two artificial peptides with pendant pyridine or bipyridine ligands have been synthesized and incorporated into oligomeric strands that are analogous to peptide nucleic acid. Spectrophotometric titrations with Cu(2+) and Fe(2+) show that the oligomers bind stoichiometric quantities of transition metals based on the number of pendant ligands. The identities of the titration products are confirmed by high resolution mass spectrometry. In the case of the bipyridine tripeptides, the titration stoichiometry and mass spectra indicate that the metal ions form interstrand cross-links between two oligopeptides, creating duplex structures linked exclusively by metal ions. Calculated molecular structures of the metalated oligopeptides and duplexes indicate that the peptide backbone acts as a scaffold for the directed assembly of metal ions. Electron paramagnetic resonance spectroscopy of the Cu-containing molecules have varying degrees of electronic interaction based on their charge and supramolecular structure. Cyclic voltammetry of the Fe(2+)- and Cu(2+)-linked bpy oligopeptide duplexes shows that they possess unique electrochemical signatures based on the redox reactivity of the metal complex.

This paper presents the synthesis and characterization of pyridine-substituted artificial oligopeptides with an aminoethylglycine backbone of varying length, which are designed to act as scaffolds for the self-assembly of multimetallic structures. The identities and purities of the oligopeptides are confirmed with mass spectrometry, (1)H NMR, HPLC, and pH titrations. The acid dissociation constants for the oligopeptides were determined and were found to decrease with increasing pyridine units. Titrations of the oligopeptides with Cu(II) and Pt(II) complexes containing the tridentate ligands 2,2':6',2''-terpyridine and pyridine 2,6-dicarboxylic acid were monitored using UV-visible absorption spectroscopy and showed stoichiometric binding based on the number of pyridines on the peptide strand. Metal titrations performed using an analogous oligopeptide with methyl substituents (in place of the pyridine ligands) showed very weak or no binding. In the case of the oligopeptides containing bound Pt(terpyridine)(2+) complexes, cyclic voltammetry reveals two sequential one-electron reductions at formal potentials that do not vary as a function of oligopeptide length. The measured diffusion coefficients were measured with chronoamperometry and were found to decrease with increasing oliopeptide length.

An artificial tripeptide containing pendant pyridine and bipyridine ligands has been synthesized using a solution-phase method analogous to divergent dendrimer synthesis, yielding a palindromic multifunctional peptide chain. When compared to conventional solid-phase peptide synthesis, this method rapidly yields the tripeptide in significantly greater quantities. The pendant pyridine ligands are coordinated with stoichiometric quantities of either [Pt(tpy)] 2+ or [Cu(pda)] metal complexes. By addition of a second transition-metal ion, supramolecular structures are formed by chelation of the bipyridine ligands to create cross-links between oligopeptide strands. The resulting heteromultimetallic materials have unique optical, electrochemical, and magnetic properties that can be tuned by the choice of transition-metal ions.

The complexes Ru(CO) 2 L 2 (PHAQ-2H) (PHAQ ) 1,2,4-trihydroxy-9,10-anthracenedione (PUR), 1,2,3-trihydroxy-9,10-anthracenedione (AG), and 1,2,5,8-tetrahydroxy-9,10-anthracenedione (QAL); L ) PPh 3 , PCy 3 , PBu 3 ), and Ru(CO)(dppe)(PBu 3 )(PHAQ-2H), containing catecholate-type ligands were prepared. The complex Ru(CO) 2 -(PBu 3 ) 2 (AG-2H) crystallizes in the space group P2 1 /n (No. 14 Var) with a ) 13.317(2), b ) 15.628(2), c ) 21.076(3) Å, β ) 101.660(10)°, Z ) 4; the crystal structure shows it to contain a 2,3-catecholate ligand. The electrochemistry of these complexes was examined, and the semi-quinone complexes [Ru(CO) 2 L 2 (PHAQ-2H)] 1+ and [Ru(CO)(dppe)(PBu 3 )(PHAQ-2H)] 1+ were generated by chemical oxidation. One example of an o-acylphenolate complex, HRu(CO)(PCy 3 ) 2 (PUR-H), is also reported. * To whom correspondence should be addressed.(1) Throughout this paper the following abbreviations are used: purpurin (1,2,4-trihydroxy-9, 10-anthracenedione), PUR; anthragallol (1,2,3trihydroxy-9, 10-anthracenedione), AG; quinalizarin (1,2,5,8-tetrahydroxy-9, 10-anthracenedione), QAL. The removal of one hydroxyl proton is indicated by "-H" and of two hydroxyl protons as "-2H"; removal of three hydroxyl protons and O-methylation is indicated by "-3H+Me". (2) For example, see: (a)

Directed self-assembly using inorganic coordination chemistry is an attractive approach for making functional supramolecular structures. In this article, the synthesis and characterization of Ru(bpy) 3 (2+) compounds derivatized with aminoethylglycine (aeg) substituents containing pendant bipyridine (bpy) ligands is presented. The free bpy ligands in these complexes are available for metal chelation to form coordinative cross-links; addition of Cu (2+) or Zn (2+) assembles heterometallic structures containing two or three transition-metal complexes. Control over relative placement of metal complexes is accomplished using two strategies: two bipyridine-containing aeg strands tethered to Ru(bpy) 3 (2+) allow intramolecular coordination and result in a dimetallic hairpin motif. Ru(bpy) 3 (2+) modified with a single strand forms intermolecular cross-links forming the trimetallic complex. Each of these is characterized by a range of methods, and their photophysical properties are compared. These data, and comparison to an acetyl aeg- modified Ru(bpy) 3 (2+) complex, confirm that the metal ions cross-link bpy-containing aeg strands. Heterometallic complexes containing bound Cu (2+) cause a dramatic reduction in the Ru(bpy) 3 (2+) quantum yields and lifetimes. In contrast, the Ru(bpy) 3 (2+) hairpin with coordinated Zn (2+) has only a slight decrease in quantum yield but no change in lifetime, which could be a result of steric impacts on structure in the dimetallic species. Analogous effects are not observed in the trimetallic Ru-Zn-Ru structures in which this constraint is absent. Each of these heterometallic structures represents a facile and reconfigurable means to construct multimetallic structures by metal-coordination-based self-assembly of modular artificial peptide units.

In this paper, we presented emission lifetime data for a series of aminoethylglycine-functionalized Ru(bpy) 3 2þ compounds with coordinated copper or zinc. However, we found that the calculations of the radiative and nonradiative relaxation rates (k r and k nr , respectively) were incorrect because the wrong equation was used. The correct values and equations are given in the corrected Table 2. Note that these corrected values do not change the interpretation of the results.