Ultrafast Dynamics of a Triazene: Excited-State Pathways and the Impact of Binding to the Minor Groove of DNA and Further Biomolecular Systems

Abstract

Many synthetic DNA minor groove binders exhibit a strong increase in fluorescence when bound to DNA. The pharmaceutical-relevant berenil (diminazene aceturate) is an exception with an extremely low fluorescence quantum yield (on the order of 10). We investigate the ultrafast excited-state dynamics of this triazene by femtosecond time-resolved fluorescence experiments in water, ethylene glycol, and buffer and bound to the enzyme β-trypsin, the minor groove of AT-rich DNA, and G-quadruplex DNA. Ab initio calculations provide additional mechanistic insight. The complementing studies unveil that the excited-state motion initiated by ππ* excitation occurs in two phases: a subpicosecond phase associated with the lengthening of the central N═N double bond, followed by a bicycle-pedal-type motion of the triazene bridge, which is almost volume-conserving and can proceed efficiently within only a few picoseconds even under spatially confined conditions. Our results elucidate the excited-state relaxation mechanism of aromatic triazenes and explain the modest sensitivity of the fluorescence quantum yield of berenil even when it is bound to various biomolecules.

Relaxation Dynamics of the Triazene Compound Berenil in DNA-Minor-Groove Confinement after Photoexcitation

“…1. Also, the UV/Vis spectra of berenil in solution, in complexation to AT-rich DNA or when bound to trypsin 25 do not show any sign for the persistence of the E-azo,s-cis and Z-azo,s-trans conformers of berenil under thermodynamically equilibrated conditions. 24 Moreover, ADC(2) calculations and time-resolved spectroscopy indicate that berenil relaxes in vacuum after photoexcitation on the S 1 surface along a bicycle-pedal pathway.…”

“…These findings corroborate conclusions drawn from time-resolved fluorescence and transient absorption spectroscopy of berenil in solvents of different viscosity and bound to the DNA minor groove. [24][25][26] To get further insight into the interplay between the nuclear relaxation on the excited- 1 Berenil exhibits three molecular conformers with respect to the triazene NHN− −N functional group.…”

Ultrafast Dynamics of a Fluorescent Tetrazolium Compound in Solution

“…[39]) is based on aT i:sapphire oscillator (MIRA, Coherent) and aF luoMax (IB Photonics) instrument. The employed fluorescenceu pconversion setup (temporal resolution % 200 fs, for detailss ee Ref.…”

“…The employed fluorescenceu pconversion setup (temporal resolution % 200 fs, for detailss ee Ref. [39]) is based on aT i:sapphire oscillator (MIRA, Coherent) and aF luoMax (IB Photonics) instrument. The Ti :sapphirel aser is tuned to ac entral wavelength of either 764 nm or 800 nm, the molecules under study can be excited with the corresponding second or third harmonic, respectively.…”

Divalent NI Compounds: Identifying new Carbocyclic Carbenes to Design Nitreones using Quantum Chemical Methods

“…Benzamidine ( 1 ) is an important functional unit in chemistry, such a functional unit has been found in a few medicinally important species for example pentamidine XV (anti‐leishmanial agent), diminazine XVI (marketed veterinary drug Berenil), [ 19 ] various kinase inhibitors. [ 19–20 ]…”