Binding of cationic bis-porphyrins linked with p- or m-xylylenediamine and their zinc(II) complexes to duplex DNA

Mass Spectrometry of Nucleic Acid Noncovalent Complexes

Nucleic acids have been among the first targets for antitumor drugs and antibiotics. With the unveiling of new biological roles in regulation of gene expression, specific DNA and RNA structures have become very attractive targets, especially when the corresponding proteins are undruggable. Biophysical assays to assess target structure as well as ligand binding stoichiometry, affinity, specificity, and binding modes are part of the drug development process. Mass spectrometry offers unique advantages as a biophysical method owing to its ability to distinguish each stoichiometry present in a mixture. In addition, advanced mass spectrometry approaches (reactive probing, fragmentation techniques, ion mobility spectrometry, ion spectroscopy) provide more detailed information on the complexes. Here, we review the fundamentals of mass spectrometry and all its particularities when studying noncovalent nucleic acid structures, and then review what has been learned thanks to mass spectrometry on nucleic acid structures, self-assemblies (e.g., duplexes or G-quadruplexes), and their complexes with ligands.

Macrocyclic Receptors for Identification and Selective Binding of Substrates of Different Nature

Molecular recognition of host/guest molecules represents the basis of many biological processes and phenomena. Enzymatic catalysis and inhibition, immunological response, reproduction of genetic information, biological regulatory functions, the effects of drugs, and ion transfer-all these processes include the stage of structure recognition during complexation. The goal of this review is to solicit and publish the latest advances in the design and sensing and binding abilities of porphyrin-based heterotopic receptors with well-defined geometries, the recognition ability of which is realized due to ionic, H-bridge, charge transfer, hydrophobic, and hydrophilic interactions. The dissection of the considered low-energy processes at the molecular scale expands our capabilities in the development of effective systems for controlled recognition, selective delivery, and prolonged release of substrates of different natures (including drugs) to their sites of functioning.

Metal complex interactions with DNA

Increasing numbers of DNA structures are being revealed using a diverse range of transition metal complexes and biophysical spectroscopic techniques. Here we present a review of metal complex-DNA interactions in which several binding modes and DNA structural forms are explored.

Consecutive intercalation of a cationic porphyrin dimer between the GC base-pairs: a kinetic study

One of the porphyrin moieties of the porphyrin dimer intercalates rapidly between the DNA base-pairs, followed by the slow intercalation of the other. The slow intercalation of the second porphyrin moiety of porphyrin dimer to poly[d(G-C)2] was investigated by normal absorption and circular dichroism spectroscopy. The change in absorbance in the Soret band of porphyrin upon association with poly[d(G-C)2] can be best elucidated by the combination of the two single exponential curves, suggesting the intercalation occurred via two independent first order reactions. Activation energies of these two first order reactions were calculated to be 0.37 kcal/mol and 3.19 kcal/mol, respectively. The intercalation associated with lower activation energy can be assigned to the intercalation of second porphyrin moiety to 5′CG3′ site while that with higher activation energy to 5′GC3′ intercalation site. Increasing the flexibility of poly[d(G-C)2] by adding Na+ ion resulted in an enhancement of the reaction rate for both steps in an exponential manner.

Bis-intercalation of a cationic porphyrin dimer linked with trietylene glycol derivative to DNA from the major groove

The binding mode of a porphyrin dimer to double stranded native DNA was investigated in this study using normal electric absorption, circular dichroism (CD) and linear dichroism (LD) spectroscopies. At the time of mixing, the spectral properties of the porphyrin dimer upon its association with DNA were characterized by hypochromism and a red shift in the absorption spectrum and by complicated CD and negative LD in the Soret region. As time elapsed, the CD spectrum became a negative single band and the negative LD signal increased. These spectral changes suggested that the majority of both porphyrin moieties of the dimer intercalated between the DNA base-pairs. The changes in the spectral characteristics of the DNA bound porphyrin-dimer were similar when the minor groove of DNA was saturated by 4′,6-diamidino-2-phenylindole (DAPI), which is well-known minor groove binding molecule. The spectral properties of DAPI, which can be summarized by a large positive induced CD in the DAPI absorption region (300~400 nm) and wavelength-independent positive reduced LD, remained intact when the porphyrin dimer was present. These observations indicated that both DAPI and porphyrin bind to DNA simultaneously, and furthermore, the bis-intercalation of the porphyrin dimer occurs in the major groove.