Dataset Information

Cesium Cation Complexation by a Flavin Receptor via Self-Assembly and Deprotonation.

ABSTRACT: This study focuses on the self-assembly of a new flavin compound and its scaffolding function for a Cs+ ion. 7,8-Dimethyl-10-[4'-(methoxycarbonyl)phenyl]-isoalloxazine (FlH-MB) displays self-assembly in a DMSO solution and has strong dependence on the solvent. In the DMSO solution, both the resulting scaffold and the deprotonation of FlH-MB were demonstrated to induce complex formation with a Cs+ ion, which was investigated by UV-vis, 1H NMR, and fluorescence titrations. This complex formation involves both Coulombic and cation-? interactions through the Fl- site in an Fl--MB dimer.

SUBMITTER: Oka Y

PROVIDER: S-EPMC7450633 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

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Cesium Cation Complexation by a Flavin Receptor via Self-Assembly and Deprotonation.

Oka Yoshimi Y

ACS omega 20200814 33

This study focuses on the self-assembly of a new flavin compound and its scaffolding function for a Cs+ ion. 7,8-Dimethyl-10-[4'-(methoxycarbonyl)phenyl]-isoalloxazine (FlH-MB) displays self-assembly in a DMSO solution and has strong dependence on the solvent. In the DMSO solution, both the resulting scaffold and the deprotonation of FlH-MB were demonstrated to induce complex formation with a Cs+ ion, which was investigated by UV-vis, 1H NMR, and fluorescence tit ...[more]

PMID: 32875259

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Project description:Enzymes that are capable of detoxifying halogenated phenols (HPs) and nitrophenols (NPs) are valuable for bioremediation and waste biorefining. HadA monooxygenase was found to perform dual functions of oxidative dehalogenation (hydroxylation plus halide elimination) and denitration (hydroxylation plus nitro elimination). Rate constants associated with individual steps of HadA reactions with phenol, halogenated phenols and nitrophenols were measured using combined transient kinetic approaches of stopped-flow absorbance/fluorescence and rapid-quench flow techniques. Density functional theory was used to calculate the thermodynamic and electronic parameters associated with hydroxylation and group elimination steps. These parameters were correlated with the rate constants of hydroxylation, group elimination, and overall product formation to identify factors controlling individual steps. The results indicated that the hydroxylation rate constant is higher when the pK a of the phenolic group is lower, i.e. it is more easily deprotonated, but not higher when the energy gap between the E LUMO of the C4a-hydroperoxy-FAD intermediate and the E HOMO of the phenolate substrate is lower. These data suggest that the substrate deprotonation has a higher energy barrier than the -OH transfer, and thus controls the hydroxylation step. For the group elimination, the process is controlled by the ability of the C-X bond to break. For the overall product formation (hydroxylation and group elimination combined), this analysis showed that the rate constant of product formation is dependent on the pK a value of the substrate, indicating that the overall reaction is controlled by substrate deprotonation. This step also likely has the highest energy barrier and thus controls the overall process of oxidative dehalogenation and denitration by HadA. This report is the first to identify a key mechanistic factor controlling the enzymatic processes of oxidative dehalogenation and denitration.

Project description:To study the formation and subsequent reactions of the 5-methyl-2'-deoxycytidine cation radical (5-Me-2'-dC•(+)) in nucleosides and DNA-oligomers and compare to one-electron oxidized thymidine.Employing electron spin resonance (ESR), cation radical formation and its reactions were investigated in 5-Me-2'-dC, thymidine (Thd) and their derivatives, in fully double-stranded (ds) d[GC*GC*GC*GC*](2) and in the 5-Me-C/A mismatched, d[GGAC*AAGC:CCTAATCG], where C* = 5-Me-C.We report 5-Me-2'-dC•(+) production by one-electron oxidation of 5-Me-2'-dC by Cl(2)•- via annealing in the dark at 155 K. Progressive annealing of 5-Me-2'-dC•(+) at 155 K produces the allylic radical (C-CH(2)•). However, photoexcitation of 5-Me-2'-dC•(+) by 405 nm laser or by photoflood lamp leads to only C3'• formation. Photoexcitation of N3-deprotonated thyminyl radical in Thd and its 5'-nucleotides leads to C3'• formation but not in 3'-TMP which resulted in the allylic radical (U-CH(2)•) and C5'• production. For excited 5-Me-2',3'-ddC•(+), absence of the 3'-OH group does not prevent C3'• formation. For d[GC*GC*GC*GC*](2) and d[GGAC*AAGC:CCTAATCG], intra-base paired proton transferred form of G cation radical (G(N1-H)•: C(+ H(+))) is found with no observable 5-Me-2'-dC•(+) formation. Photoexcitation of (G(N1-H)•:C(+ H(+))) in d[GC*GC*GC*GC*](2) produced only C1'• and not the expected photoproducts from 5-Me-2'-dC•(+). However, photoexcitation of (G(N1-H)•:C(+ H(+))) in d[GGAC*AAGC:CCTAATCG] led to C5'• and C1'• formation.C-CH(2)• formation from 5-Me-2'-dC•(+) occurs via ground state deprotonation from C5-methyl group on the base. In the excited 5-Me-2'-dC•(+) and 5-Me-2',3'-ddC•(+), spin and charge localization at C3' followed by deprotonation leads to C3'• formation. Thus, deprotonation from C3' in the excited cation radical is kinetically controlled and sugar C-H bond energies are not the only controlling factors in these deprotonations.

Dataset Information

Cesium Cation Complexation by a Flavin Receptor via Self-Assembly and Deprotonation.

Publications

Cesium Cation Complexation by a Flavin Receptor via Self-Assembly and Deprotonation.

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