TY - JOUR
T1 - Fluorescence and Ultrafast Fluorescence Unveil the Formation, Folding Molecularity, and Excitation Dynamics of Homo-Oligomeric and Human Telomeric i-Motifs at Acidic and Neutral pH
AU - Ma, Chensheng
AU - Chan, Ruth Chau Ting
AU - Chan, Chris Tsz Leung
AU - Wong, Allen Ka Wa
AU - Chung, Bowie Po Yee
AU - Kwok, Wai Ming
PY - 2018/12/4
Y1 - 2018/12/4
N2 -
i-Motifs are tetraplex DNAs known to be stable at acidic pH. The structure of i-motifs is important in DNA nanotechnology; i-motif-forming sequences with consecutive cytosine (C) molecules are abundant throughout the human genome. There is, however, little information on the structure of C-rich DNAs under physiologically relevant neutral conditions. The electron dynamics of i-motifs, crucial to both biology and materials applications, also remains largely unexplored. In this work, we report a combined femtosecond and nanosecond broadband time-resolved fluorescence (TRF) and steady-state fluorescence investigation on homo-oligomer dC
20
, a human telomeric sequence (HTS) 5′-dC
3
(TA
2
C
3
)
3
, and its analogue performed with different excitation at both acidic and neutral pH. Our study provides direct observation of intrinsic fluorescence and the first full probe of the real-time dynamics of the intrinsic fluorescence from i-motifs formed from varied sequences and pH conditions. The results obtained demonstrate concrete evidence for the existence at neutral pH of i-motifs from both dC
20
and the HTS. It also identifies that, under neutral conditions, the i-motif from dC
20
adopting the bimolecular folding structure is significantly more stable than the HTS i-motif featuring the unimolecular topology. Our femtosecond and nanosecond TRF study unveils excitation dynamics distinctive of the interdigitated architecture of i-motifs with the excited states involved exhibiting deactivation over a remarkably broad timescale through multiple channels involving proton-coupled electron transfer lasting tens of picoseconds, as signified by the solvent kinetic isotope effect, and structure-dependent charge recombination in the hundreds of picoseconds to tens of nanoseconds time regime.
AB -
i-Motifs are tetraplex DNAs known to be stable at acidic pH. The structure of i-motifs is important in DNA nanotechnology; i-motif-forming sequences with consecutive cytosine (C) molecules are abundant throughout the human genome. There is, however, little information on the structure of C-rich DNAs under physiologically relevant neutral conditions. The electron dynamics of i-motifs, crucial to both biology and materials applications, also remains largely unexplored. In this work, we report a combined femtosecond and nanosecond broadband time-resolved fluorescence (TRF) and steady-state fluorescence investigation on homo-oligomer dC
20
, a human telomeric sequence (HTS) 5′-dC
3
(TA
2
C
3
)
3
, and its analogue performed with different excitation at both acidic and neutral pH. Our study provides direct observation of intrinsic fluorescence and the first full probe of the real-time dynamics of the intrinsic fluorescence from i-motifs formed from varied sequences and pH conditions. The results obtained demonstrate concrete evidence for the existence at neutral pH of i-motifs from both dC
20
and the HTS. It also identifies that, under neutral conditions, the i-motif from dC
20
adopting the bimolecular folding structure is significantly more stable than the HTS i-motif featuring the unimolecular topology. Our femtosecond and nanosecond TRF study unveils excitation dynamics distinctive of the interdigitated architecture of i-motifs with the excited states involved exhibiting deactivation over a remarkably broad timescale through multiple channels involving proton-coupled electron transfer lasting tens of picoseconds, as signified by the solvent kinetic isotope effect, and structure-dependent charge recombination in the hundreds of picoseconds to tens of nanoseconds time regime.
KW - DNA structures
KW - energy transfer
KW - fluorescence
KW - photophysics
KW - proton coupled charge transfer
UR - http://www.scopus.com/inward/record.url?scp=85055752238&partnerID=8YFLogxK
U2 - 10.1002/asia.201801117
DO - 10.1002/asia.201801117
M3 - Journal article
C2 - 30230251
AN - SCOPUS:85055752238
SN - 1861-4728
VL - 13
SP - 3706
EP - 3717
JO - Chemistry - An Asian Journal
JF - Chemistry - An Asian Journal
IS - 23
ER -