title: Structural Studies on Porphyrin-PNA Conjugates in Parallel PNA:PNA Duplexes: Effect of Stacking Interactions on Helicity.
abstract: Parallel PNA:PNA duplexes were synthesized and conjugated with meso-tris(pyridyl)phenylporphyrin carboxylic acid at the N-terminus. The introduction of one porphyrin unit was shown to affect slightly the stability of the PNA:PNA parallel duplex, whereas the presence of two porphyrin units at the same end resulted in a dramatic increase of the melting temperature, accompanied by hysteresis between melting and cooling curves. The circular dichroism (CD) profile of the Soret band and fluorescence quenching strongly support the occurrence of a face-to-face interaction between the two porphyrin units. Introduction of a L-lysine residue at the C-terminal of one strand of the parallel duplex induced a left-handed helical structure in the PNA:PNA duplex if the latter contains only one or no porphyrin moiety. The left-handed helicity was revealed by nucleobase CD profile at 240-280 nm and by the induced-CD observed in the presence of the DiSC2 (5) cyanine dye at ~500-550 nm. Surprisingly, the presence of two porphyrin units led to the disappearance of the nucleobase CD signal and the absence of CD exciton coupling within the Soret band region. In addition, a dramatic decrease of induced CD of DiSC2 (5) was observed. These results are in agreement with a model where the porphyrin-porphyrin interactions cause partial loss of chirality of the PNA:PNA parallel duplex, forcing it to adopt a ladder-like conformation.
authors.affiliation: Department of Chemistry, University of Parma, Parma, Italy.|Department of Chemistry, Columbia University, New York, New York, USA.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Accetta
authors.affiliation: Department of Chemistry, Columbia University, New York, New York, USA.|Department of Life Sciences, New York Institute of Technology (NYIT), New York, New York, USA.
authors.forename: Ana G
authors.initials: AG
authors.lastname: Petrovic
authors.affiliation: Department of Chemistry, University of Parma, Parma, Italy.
authors.forename: Rosangela
authors.initials: R
authors.lastname: Marchelli
authors.affiliation: Department of Chemistry, Columbia University, New York, New York, USA.
authors.forename: Nina
authors.initials: N
authors.lastname: Berova
authors.affiliation: Department of Chemistry, University of Parma, Parma, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Corradini
mesh_terms: D002942:Circular Dichroism; D015394:Molecular Structure; D020135:Peptide Nucleic Acids / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D020135:Peptide Nucleic Acids; D011166:Porphyrins
keywords: S-DNA; chirality; circular dichroism; handedness; parallel PNA; porphyrin