Influence of Divalent Counterions on the Dynamics in DNA as Probed by Using a Minor‐Groove Binder

Abstract

DNA dynamics, to which water, counterions, and DNA motions contribute, is a topic of considerable interest because it is closely related to the efficiency of biological functions performed by it. Simulation studies and experiments suggest that the counterion dynamics in DNA probed by a minor-groove binder are similar for various monovalent counterions. To date, the influence on DNA dynamics of higher-valence counterions, which are also present around DNA and are known to bind more strongly to it than monovalent ions, has not been studied. Herein we investigated DNA dynamics in the presence of Mg and Ca , chosen for their relative abundance in cells, by using minor-groove binder 4',6-diamidino-2-phenylindole (DAPI) as a fluorescence probe. The dynamics, as measured from the time-resolved fluorescence Stokes shifts of DAPI bound to calf thymus DNA on a subpicosecond-to-nanosecond timescale, were found to be very similar in the presence of both the divalent ions and Na ions. The observation is explained by considering the screening of the electric field of the divalent ion by its hydration shell, preferential binding of the ions to the phosphate groups, and displacement of ions from the minor groove by DAPI due to the stronger binding interaction of the latter. Furthermore, the similarity of our results in the presence of Na to those reported for smaller oligonucleotides suggests that the chain length of DNA does not influence the DNA dynamics.

Hot Hole Transfer Dynamics from CsPbBr3 Perovskite Nanocrystals

“…Two short time components (16 ± 1.4 and 160 ± 10.2 ps) are observable in addition to the long decay component of >1.2 ns. It is to be noted here that accurate estimation of the longest time component is not possible using the femtosecond time-resolved TA and PL UC setup for nonavailability of a larger time window. ,, It is clear, however, that this long component arises from radiative recombination of the electron and hole.…”

“…47,48 The higher the energy content of the hot hole, the larger the spread of its wave function beyond the NCs surface and consequently the greater the coupling of the hot hole wave function of the NCs with the HOMO of the organic moiety. 47,48 We have examined the hot carrier transfer process also by the upconverted PL technique, 49 in which the hot carriers were generated by 400 nm (corresponding to ∼1.28E g ) excitation of the NCs using ∼200 fs pulses and monitoring time-dependent formation of the band-edge emission (∼512 nm), which represents the cooling dynamics of the carriers. 35 The HCC time of the CsPbBr 3 NCs obtained by this method is found to be 460 ± 40 fs, which is in agreement with the literature 35 and also with our pump−probe measured value (440 ± 15 fs) for 400 nm excitation.…”

“…It is to be noted here that accurate estimation of the longest time component is not possible using the femtosecond time-resolved TA and PL UC setup for nonavailability of a larger time window. 49,51,52 It is clear, however, that this long component arises from radiative recombination of the electron and hole. The short 14−16 ps component represents the hole transfer time (τ HT ) from the band-edge states of the NCs (corresponding to a rate of 6.2−7.6 × 10 10 s −1 ).…”

Complete Solvation Dynamics of Coumarin 153 in Tetraalkylammonium Bromide-Based Deep Eutectic Solvents

“…The sub-picosecond fluorescence intensity decays were measured using a UPC setup (FOG 100, CDP systems, Russia) . The center wavelength of the mode-locked Ti:sapphire laser (Mai Tai), set at 800 nm, was directed to a β-barium borate (BBO) crystal to generate the second harmonic signal (400 nm).…”

“…The sub-picosecond fluorescence intensity decays were measured using a UPC setup (FOG 100, CDP systems, Russia). 53 The center wavelength of the mode-locked Ti:sapphire laser (Mai Tai), set at 800 nm, was directed to a β-barium borate (BBO) crystal to generate the second harmonic signal (400 nm). The output was then directed to a dichroic mirror, which reflected the 400 nm light (used as excitation beam) and transmitted the residual 800 nm light (used as gate beam).…”