Structures of Hydrated Li⁺−Thymine and Li⁺−Uracil Complexes by IRMPD Spectroscopy in the N−H/O−H Stretching Region

Abstract

The interaction of lithium ions with two pyrimidine nucleobases, thymine and uracil, as well as the solvation of various complexes by one and two water molecules, has been studied in the gas phase. IRMPD spectra are reported for each of B-Li(+)-(H(2)O)(n) (n = 1-2) and B(2)-Li-(H(2)O)(m) (m = 0-1) for B = thymine, uracil over the 2500-4000 cm(-1) region. Calculations were performed using the B3LYP density functional in conjunction with the 6-31+G(d,p) basis set to model the vibrational spectra as well as MP2/6-311++G(2d,p) theory to model the thermochemistry of potential structures. Experimental and theoretical results were used in combination to determine structures of each complex, which are reported here. The lithium cation in all complexes was found to bond to the O4 oxygen in both thymine and uracil, and the first two water molecules of solvation were found to bond to Li(+). The experimental spectra obtained for BLi(+)(H(2)O)(n) (n = 1-2) and B(2)Li(+) for thymine and uracil clearly resemble one another, suggesting similar structural features in terms of bonding between the base and Li(+), as well as for solvation. This was confirmed through theoretical work. The addition of water to the lithium ion-bound DNA base dimers has been shown to induce a significant change in structure of the dimer to a hydrogen-bonded system similar to base pairing in the Watson-Crick model of DNA.

Structures and Fragmentation of [Cu(Uracil‐H)(Uracil)]+ in the Gas Phase

“…[31] We believe that the inability to hydrate [Cu(Ura-H)(Ura)] + could be due to the charge being delocalized over the entire complex, unlike in Li + (Ura) 2 [24] and M + (Ade) 2 complexes (M = Li, Na, K, Cs), [32] whose hydrated complexes have been studied previously by the same method. We decided to probe the structure of [Cu(Ura-H)(Ura)] + through fragmentation and computational studies.…”

“…+ we tried to do wavelength-dependent IRMPD (IR spectrosocopy) with an optical parametric oscillator (OPO) laser, [25] but the complex proved to be too strongly bound to dissociate with this low powered laser, in contrast to other metal cationized uracil complexes [24,25] including [Pb(Ura-H)(Ura)]…”

“…[17,18] The interaction of bases, such as uracil and thymine, with various metal cations including K + , Li + , Mg 2 + , Ca 2 + , Zn 2 + , and Pb 2 + have been studied using different techniques. [19][20][21][22][23] Gillis et al [24] used infrared multiple photon dissociation (IRMPD) spectroscopy in the 2500-4000 cm À1 region to study the structures of complexes of B m -Li + -(H 2 O) n (n = 0,1,2; m = 1,2), where B = thymine or uracil. In all complexes the lithium cation was determined to be bonded to the O4 oxygen atom in both thymine and uracil, and water bound directly to the lithium cation (see Scheme 1 for numbering convention of uracil and thymine).…”

Ultraviolet photodissociation spectroscopy of cold, isolated adenine complexes with a potassium cation

“…The alkali metal ion affinities of nucleobases were determined from dissociation of the metal ion-bound heterodimers using mass spectrometry [15][16][17][18]. The structures of alkali metal cation-nucleobase complexes and their hydrated clusters were investigated using a combination of infrared multiphoton dissociation (IRMPD) spectroscopy and quantum theoretical calculations [19][20][21]. For the structures of alkali metal ion-adenine complexes (M + A), Rodgers and Armentrout [16] insisted that the metal cations bind most strongly to N7 of A9 (M + A9).…”

Mg2+/Ca2+ binding to DNA bases: a quantum chemical method and ABEEMσπ/MM fluctuating charge model study

“…One illustrative case is the cisplatin molecule, which links two consecutive bases together and is used as an anticarcinogenic drug [14,15]. Many efforts have been devoted to investigate the fundamental nature of these interactions as well as to determine the cation affinity of nucleobases, both experimentally [16][17][18][19][20][21][22][23][24] and theoretically .…”