Apurinic/apyrimidinic (AP) sites are constantly formed in cellular DNA due to instability of the glycosidic bond, particularly at purines and various oxidized, alkylated, or otherwise damaged nucleobases. AP sites are also generated by DNA glycosylases that initiate DNA base excision repair. These lesions represent a significant block to DNA replication and are extremely mutagenic. Some DNA glycosylases possess AP lyase activities that nick the DNA strand at the deoxyribose moiety via a β- or β,δ-elimination reaction. Various amines can incise AP sites via a similar mechanism, but this non-enzymatic cleavage typically requires high reagent concentrations. Herein, we describe a new class of small molecules that function at low micromolar concentrations as both β- and β,δ-elimination catalysts at AP sites. Structure-activity relationships have established several characteristics that appear to be necessary for the formation of an iminium ion intermediate that self-catalyzes the elimination at the deoxyribose ring.
RNase H1 cleaves the RNA strand of RNA:DNA hybrids. Replacement of RNA 2'-hydroxyls by fluorine (FRNA) is commonly used to stabilize aptamers and siRNAs. However, FRNA:DNA hybrids fail to elicit RNase H activity. The underlying reasons are unclear, as 2'-OH groups are not directly involved in cleavage. We determined the crystal structure of Bacillus halodurans RNase H bound to a FRNA:DNA hybrid. The structure points to dynamic (slippage of the FRNA:DNA hybrid relative to the enzyme), geometric (different curvatures of FRNA:DNA and RNA:DNA hybrids), and electronic reasons (Mg(2+) absent from the active site of the FRNA:DNA complex) for the loss of RNaseH activity.
This study provides insight into the mechanism of capturing low energy electrons by peptide nucleic acid (PNA) and the role of the oligonucleotide backbone in the capture of low energy electrons. We studied by photoemission self-assembled monolayers of two types of oligonucleotides, DNA and PNA. PNA is a synthetic analogue of DNA that has a pseudopeptide backbone and which may have important medical and biotechological applications. We found that in both PNA and DNA, the guanine nucleobases capture the electrons more efficiently than thymines. In PNA, once the electrons are captured, their state is at least partially localized on the nucleobases, and the PNA molecule undergoes structural changes that stabilize the electron. This situation is in contrast to DNA, in which the captured electrons are transferred very efficiently to the backbone, and the final state of captured electron is base independent. SECTION: Biophysical Chemistry and Biomolecules
Single-step nonadiabatic electron tunneling models are widely used to analyze electrochemical rates through self-assembled monolayer films (SAMs). For some systems, such as nucleic acids, long-range charge transfer can occur in a "hopping" regime that involves multiple charge transfer events and intermediate states. This report describes a three-step kinetic scheme to model charge transfer in this regime. Some of the features of the three-step model are probed experimentally by changing the chemical composition of the SAM. This work uses the three-step model and a temperature dependence of the charge transfer rate to extract the charge injection barrier for a SAM composed of a 10-mer peptide nucleic acid that operates in the hopping regime.
Substitution of a nucleobase pair with a pair of 1,2-hydroxypyridinone (1,2-HOPO) ligands in the center of a 10-base-pair peptide nucleic acid (PNA) duplex provides a strong binding site for Eu(III) as evidenced by UV thermal melting curves, UV titrations, and luminescence spectroscopy. Eu(III) excitation spectra and luminescence lifetime data are consistent with Eu(III) bound to both 1,2 HOPO ligands in a PNA-HOPO duplex as the major species present in solution.
A number of transition metal complexes have been investigated as potential electrocatalystsfor C02 reduction. Among these are rhenium monometallic complexes, which have shownunique activity towards C02 reduction. Further development of multimetallic systems,capable of storing multiple equivalents of electrons has shown some potential in increasingthe selectivity of the C02 conversion processes toward highly reduced products. This studyreports the synthesis and characterization of novel polynuclear rhenium(I) complexes whererhenium is incorporated to the bridging ligand tppq (2,3,7,8-tetra-2-pyridylpyrazino[2,3-g]quinoxaline), which is capable of attaching up to four metal centers. The resultingcomplexes were characterized using different spectroscopic techniques (infrared, UV-Vis,emission) and cyclic voltammetry. The results suggest that the synthetic procedure adoptedwas successful.
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