Small Molecule Directed Aggregation of a Heme Peptide on Gold:  An STM Study

Abstract

Microperoxidase 11 was adsorbed on Au(111) from basic aqueous solutions containing pure heme peptide and co-added stoichiometric amounts of exogenous neutral and ionic ligands. The addition of small molecules to MP11 produced different aggregate structures that were easily differentiated by STM. In the absence of a complexing agent, the MP-11 formed large clusters of metallopeptide molecules on the gold surface. With neutral imidazole in solution the MP11 aggregated into regular elongated structures (nano-épis) on the substrate. When S(2-) is used as coupling agent, single heme peptide molecules are isolated with identifiable porphyrin ring and substructure in the peptide chain.

Mechanisms of Electron Transfer in Two Decaheme Cytochromes from a Metal-Reducing Bacterium

“…[23][24][25][26][27][28][29] Additional proteins examined by such techniques include other blue copper proteins, 30 photosynthetic reaction centers, [31][32][33] iron-sulfur proteins, 34 and various small cytochromes or heme proteins/ peptides. [35][36][37][38][39][40] Tunneling spectroscopy of proteins in air has both advantages and disadvantages versus other environments such as in vacuum or aqueous solution. Protein conformation is extremely sensitive to the presence of water, requiring either an aqueous solution environment or at least humid air which provides several monolayers of adsorbed water on surfaces at ambient conditions.…”

“…Measurement and interpretation of STM-based tunneling conductance of redox-active proteins in solution and in air continues to become more frequent. Such studies have primarily focused on proteins with defined crystal structures such as azurin, a blue copper protein isolated from Pseudomonas aeruginosa , using STM or a similar configuration such as conducting atomic force microscopy (C-AFM). − Additional proteins examined by such techniques include other blue copper proteins, photosynthetic reaction centers, − iron−sulfur proteins, and various small cytochromes or heme proteins/peptides. − …”

Scanning Probe Microscopy of Bacterial Red Light Photoreceptors

“…First developed in 1981, [9] scanning tunneling microscopy (STM) has since been used to study biologically relevant materials such as DNA, [5] dendrimers, [10] peptides, [11,12] and proteins [13] on a variety of conducting platforms. A pair of Bphs, RpBphP2 (P2) and RpBphP3 (P3), [14][15][16] from the photosynthetic bacterium Rhodopseudomonas palustris has been examined by STM on a highly ordered pyrolytic graphite (HOPG) surface.…”