Femtosecond Fluorescence Spectra of NADH in Solution: Ultrafast Solvation Dynamics

Abstract

The ultrafast solvation dynamics of reduced nicotinamide adenine dinucleotide (NADH) free in solution has been investigated, using both a femtosecond upconversion spectrophotofluorometer and a picosecond time-correlated single-photon counting (TCSPC) apparatus. The familiar time constant of solvent relaxation originating in “bulk water” was found to be ∼1.4 ps, revealing ultrafast solvent reorientation upon excitation. We also found a slower spectral relaxation process with an apparent time of 27 ps, suggesting there could either be dissociable “biological water” hydration sites on the surface of NADH or internal dielectric rearrangements of the flexible solvated molecule on that timescale. In contrast, the femtosecond fluorescence anisotropy measurement revealed that rotational diffusion happened on two different timescales (3.6 ps (local) and 141 ps (tumbling)); thus, any dielectric rearrangement scenario for the 27 ps relaxation must occur without significant chromophore oscillator rotation. The coexistence of quasi-static self quenching (QSSQ) with the slower relaxation is also discussed.

Nature of Linear Spectral Properties and Fast Electronic Relaxations in Green Fluorescent Pyrrolo[3,4-c]Pyridine Derivative

“…Time-resolved transient absorption spectra of HPPT ( Figure 5 ) were obtained from the experimental dependences and exhibit obvious bathochromic temporal spectral shift typically observed for different types of solute-solvent interactions [ 26 , 27 , 29 , 30 , 31 ].…”

Two-Photon Excited Fluorescence Dynamics in NADH in water-methanol solutions: the Role of Conformational States

“…26 The study of picosecond vibrational dynamics in NADH first excited state under excitation at 360 nm in waterethanol solutions has recently been reported in our recent publications 27,28 using a novel polarization-modulation pump-probe transient spectroscopy. Very recently the analysis of spontaneous emission signals from NADH in the sub-picosecond and picoseconds time-scales obtained by means of up-conversion detection scheme was reported by Cao et al 29,30 and Cadena-Caicedo et al 24 These studies clarified further details of the energy transfer process.…”

Ultrafast Fluorescence Spectroscopy via Upconversion and Its Applications in Biophysics

“…In our recent work, NADH spectral evolution was also found to show two distinct solvation dynamics terms on ps time scales [ 16 ]. Figure 7 gives the upconversion fluorescence decay transients at different emission wavelengths [ 17 ]. Similar to Trp, the fluorescence of NADH contains a fast decay at “bluer” emission wavelength and a fast rise at “redder” emission wavelengths in the earliest ~5 ps, which is typical for bulk water, reflecting the librational/rotational motions of water around the surface of NADH.…”

“…From conventional photodetector studies, it was known that NADH free in solution exhibited short (~0.4 ns) decay times, but order of magnitude (2–8 ns) greater lifetimes were seen when it bound to cognate sites on target proteins. Our recent work showed the free molecule also exhibited a “dark” population, which, depending on detector, could hide 20–40% of the molecules from view [ 16 , 17 ]. Enzymatic binding abolished the quench.…”