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A set of arylazo sulfones, known to undergo N-S bond cleavage upon light exposure, has been synthesized, and their activity in the dark and upon irradiation towards DNA has been investigated. Their interaction with calf-thymus DNA has been examined, and the significant affinity observed (most probably due to DNA intercalation) was analyzed by means of molecular docking "in silico" calculations that pointed out polar contacts, mainly via the sulfonyl moiety. Incubation with plasmid pBluescript KS II revealed DNA cleavage that has been studied over time and concentration. UV-A irradiation considerably improved DNA damage for most of the compounds, whereas under visible light the effect was slightly lower. Moving to in vitro experiments, irradiation was found to slightly enhance the death of the cells in the majority of the compounds. Naphthylazosulfone 1 showed photo-disruptive effect under UV-A irradiation (IC50 ~13 µΜ) followed by derivatives 14 and 17 (IC50 ~100 µΜ). Those compounds were irradiated in the presence of two non-cancer cell lines and were found equally toxic only upon irradiation and not in the dark. The temporal and spatial control of light, therefore, might provide a chance for these novel scaffolds to be useful for the development of phototoxic pharmaceuticals.

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RESUMEN

Saddle-shaped hemes have been discovered in the structures of most peroxidases. How such a macrocycle deformation affects the reaction of FeIII hemes with hydrogen peroxide (H2 O2 ) to form high-valent Fe-oxo species remains uncertain. Through examination of the ESI-MS spectra, absorption changes and 1 H NMR chemical shifts, we investigated the reactions of two FeIII porphyrins with different degrees of saddling deformation, namely FeIII (OETPP)ClO4 (1OE ) and FeIII (OMTPP)ClO4 (1OM ), with tert-butyl hydroperoxide (tBuOOH) in CH2 Cl2 at -40 °C, which quickly resulted in O-O bond homolysis from a highly unstable FeIII -alkylperoxo intermediate, FeIII -O(H)OR (2) into FeIV -oxo porphyrins (3). Insight into the reaction mechanism was obtained from [tBuOOH]-dependent kinetics. At -40 °C, the reaction of 1OE with tBuOOH exhibited an equilibrium constant (Ka =362.3 M-1 ) and rate constant (k=1.87×10-2  sM->1 ) for the homolytic cleavage of the 2 O-O bond that were 2.1 and 1.4 times higher, respectively, than those exhibited by 1OM (Ka =171.8 M-1 and k=1.36×10-2 s-1 ). DFT calculations indicated that an FeIII porphyrin with greater saddling deformation can achieve a higher HOMO ([Fe(d z 2 ,d x 2 - y 2 )-porphyrin(a2u )]) to strengthen the orbital interaction with the LUMO (O-O bond σ*) to facilitate O-O cleavage.

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RESUMEN

Bond homolysis (BHo) is a fundamental concept in chemical-bonding phenomena. To date, research studies on the BHo concept have provided crucial information for understanding the nature of chemical bonding and reactions. Two potential-energy minima, a σ-bonding isomer and a singlet-diradical isomer, have been known to exist in carbon-carbon BHo. Herein, a third isomer, that is, a puckered singlet diradical exhibiting unstructured long-wavelength fluorescence beyond 460 nm, was first observed in the excited states of 1,4-diarylbicyclo[2.1.0]pentane derivatives. The careful selection of appropriate substituents in the bicyclic structures enabled direct spectral detection. State-of-the-art ab initio quantum chemical calculations quantitatively reproduced the experimental observations. This new finding provides new insight into carbon-carbon bond-breaking and -forming processes.

RESUMEN

OO bond homolysis in hydrogen peroxide (H2 O2 ) has been studied using theoretical methods of four conceptually different types: hybrid DFT (B3LYP, M06-2X), double-hybrid DFT (B2-PLYP), coupled-cluster (CCSD(T)), and multiconfigurational (CASPT2). In addition, the effects of basis set size have also been analyzed. For all of these methods, the OO bond homolysis in hydrogen peroxide has been found to proceed through hydrogen bonded radical pair complexes. Reaction barriers for collapse of the radical pairs to hydrogen peroxide are minute, leading to an overall very flat potential energy surface. However, hydrogen bonding energies in the radical pair complex expressed as the energy difference to two separate hydroxyl radicals are sizeable and exceed 10 kJ/mol for all theoretical methods considered in this study. © 2017 Wiley Periodicals, Inc.

RESUMEN

Bismuth diphenylphosphanides Bi(NONR )(PPh2 ) (NONR =[O(SiMe2 NR)2 ], R=tBu, 2,6-iPr2 C6 H3 , Aryl) undergo facile decomposition via single-electron processes to form reduced Bi and P species. The corresponding derivatives Bi(NONR )(PCy2 ) are stable. Reaction of the isolated BiII radical . Bi(NONAr ) with white phosphorus (P4 ) proceeds with the reversible and selective activation of a single P-P bond to afford the bimetallic µ,η1:1 -bicyclo[1.1.0]tetraphosphabutane compound.

RESUMEN

In recent work, a 15-fold increase in the C-ON bond homolysis rate constant kd of 4-pyridylethyl-SG1-based alkoxyamine was observed upon protonation of the pyridyl moiety in organic solvent. In this report, the pH dependence of kd (pKa = 4.7) is investigated in D2O/CD3OD (v/v 1:1). A 64-fold increase in kd is observed at acidic pH. Calculations show that the increase in kd upon protonation is due to both an increase in the stabilization of the protonated 4-pyridylethyl radical and an increase of the destabilization of the starting materials through an increase in the polarity of the alkyl fragment. This new alkoxyamine is applied to NMP of styrene and sodium styrene sulfonate.

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