Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
-
Contributed by Ahmed H. Zewail
Article Figures & SI
Figures
- Figure 1
Structures of 1 (A) and 2 (B) and schematic picture of the binding of 2 (Δ,Δ isomer) to DNA (C). Molecular model of 2 (Δ,Δ isomer) bound to a duplex decanucleotide (D), with the ruthenium centers situated in the minor groove (obtained by energy minimization in the hyperchem software package with the Amber force field).
- Figure 2
(A) Absorption spectra of the molecules studied. (B) Experimental layout of femtosecond transient absorption apparatus. OPA, optical parametric amplifier; F, optical filters; P, prism polarizers; λ/2, half-wave plate; L, lens; PD, photodiode; S, sample cell.
- Figure 3
Transient absorption (A and C) and anisotropy (R) (B and D) of 1 (Δ isomer) in water on two different time scales. The pump wavelength was 502 ± 2 nm, and the probe wavelength was 566 ± 2 nm. Time constants are indicated. Inclusion of a long lifetime decay (with an amplitude of 6–14% at all wavelengths) was required for a good fit of the relaxation to the ground state (see text).
- Figure 4
Transient absorption (A and C) and anisotropy (B and D) of 2 (Δ,Δ isomer) in water on two different time scales. Pump and probe wavelengths are as described for Fig. 3. Time constants are indicated.
- Figure 5
Long time scale transient absorption and anisotropy of 1 (A) and 2 (B) bound to DNA (mixed-sequence calf thymus DNA). Short time scale traces (up to t = 20 ps, not shown) were included in the global fitting of the time constants shown. The samples contained 75 μM Ru(phen)2dppz subunits and 1.5 mM DNA bases in 5 mM phosphate (pH 7) and 50 mM NaCl aqueous solution. The pump wavelength was 502 ± 2 nm. The probe wavelengths and time constants are indicated.
- Figure 6
Schematic for the proposed relaxation pathways of 1 and 2 in water solution. The pump pulse selects overlapping MLCT singlet transitions (dominated by the indicated A polarized transition), populating MLCT states in which either the dppz or one of the phen ligands is reduced. Solvent field reorientation facilitates the phen⋅ → dppz⋅ transfer of charge such that all initially excited states end up in the dppz-localized MLCT state (CTun-eq). This transfer occurs in 700 fs (τ1). The solvent equilibration process continues (with an associated time constant, τ2, of 4 ps) involving reinforcement of hydrogen bonds and, as a consequence, a further lowering of energy (CTeq). The final modified MLCT state has a fast radiationless deactivation in water: a lifetime (τ3) of 360 ps is observed for 1, and a lifetime of 2,000 ps is observed for 2. Overlapping excited state absorption bands of orthogonal polarizations schematically illustrate how relaxation may lead to changes in anisotropy and/or isotropic absorption.
Femtosecond linear dichroism of DNA-intercalating chromophores: Solvation and charge separation dynamics of [Ru(phen)2dppz]2+ systems
Sign up for Article Alerts
Jump to section
You May Also be Interested in
Did the Caribbean sweep into the western Amazon millions of years ago, shaping the region’s rich biodiversity?
Image credit: Tacio Cordeiro Bicudo (University of São Paulo, São Paulo, Brazil), Victor Sacek (University of São Paulo, São Paulo, Brazil), and Lucy Reading-Ikkanda (artist).
Settlements 4,200 years ago may have suffered from overpopulation before drought and lower temperatures ultimately made them unsustainable.
Image credit: Andrea Ricci.
Mara Reed and Michael Manga explore why Yellowstone's Steamboat Geyser resumed erupting in 2018.
Some songbird parents might improve their own fitness by manipulating their offspring into leaving the nest early, at the cost of fledgling survival, a study finds.
Image credit: Gil Eckrich (photographer).