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- 저자 : ( FRANCIS KIRBY B BURNEA ) (검색결과 5 건)
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Burnea, Francis Kirby B.,Ko, Kyoung Chul,Lee, Jin Yong The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.31
<P>Cross-conjugated molecules are an interesting class of conjugated systems possessing a spatially separated HOMO and LUMO. Most previous studies have taken advantage of this property by using it in organic semiconductor applications. Herein, we undertake a new investigation on the use of this type of molecule, in particular benzo[1,2-<I>d</I>;4,5-<I>d</I>′]bisoxazole (BBO), as a coupler for organic diradicals. BBO has two sites available for adding a substituent and a spin center (SC) which are along its 4,8- and 2,6-axes. Functionalizations using electron donating (ED) and electron withdrawing (EW) groups were imposed to tune its FMOs and it was found that the longer 2,6-axis is an ideal site with a broader LUMO range <I>via</I> substituent effects. Diradicalization of these BBOs using nitronyl nitroxide (NN) and nitroxide (NO) as SCs was done using the remaining available axis. The calculated <I>J</I> values are linearly dependent on the LUMO energy of the coupler, but with 4,8-NH2-2,6-SC as an outlier. This exceptional case is related to 4,8-NH2-2,6-SC having the lowest BBO-NN dihedral angle. Moreover, the diradicals 4,8-X-2,6-SC (with X = H, NH2, CH3) have higher <I>J</I> values than 2,6-X-4,8-SC (with X = H, NH2, CH3), which is counterintuitive because the latter have a shorter coupling path. These diradicals are positioned to the right of the intersection of their trend lines, which implies that diradicals with LUMO values to the right of this intersection have the tendency to attain <I>J</I> values that are higher than those diradicals with a shorter coupling path. 4,8-NH2-2,6-SC even surpasses the projected <I>J</I>Max values which we associate with the highest attainable <I>J</I> values due to LUMO tuning <I>via</I> substituent effects. These results provide useful insights, especially into the interplay between the LUMO and the dihedral angle and how these affect magnetism in diradicals. In conclusion, we found that BBO can be a good candidate as an effective coupler for diradicals with tunable <I>J</I> values <I>via</I> incorporation of ED and EW groups. This first approach to studying the application of cross-conjugated molecules as couplers also paves the way for new candidates for the development of more effective diradical systems.</P>
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Burnea, Francis Kirby Bokingo,Shi, Hu,Ko, Kyoung Chul,Lee, Jin Yong Pergamon Press 2017 Electrochimica Acta Vol. No.
<P><B>Abstract</B></P> <P>We systematically investigated the tuning of the reduction potentials (<I>E<SUP>0</SUP> </I>) for the first row transition metal (M=Cr, Mn, Fe, Co, Ni) complexes with the functionalized 1,4,7-Triazacyclononane-N,N',N”-triacetate (TCTA) ligands by means of DFT calculations. To predict reliable <I>E<SUP>0</SUP> </I>, the modified UB3LYP functional and equilibrium concept between high and low spin states were utilized. The functional groups NH<SUB>2</SUB>, CN, −F, and NO<SUB>2</SUB> were attached to the carbon atoms carefully selected by considering the LUMO and steric hindrance. Based on firmed accuracy of DFT calculations, finally we obtained the calculated <I>E<SUP>0</SUP> </I> for a series of complexes. It was found that electron donating group such as NH<SUB>2</SUB> will cause a negative shift of <I>E<SUP>0</SUP> </I> while electron withdrawing groups have the opposite effect. The overall trend of the calculated <I>E<SUP>0</SUP> </I>s according to ligand modifications were predicted to have the order as −NH<SUB>2</SUB> < Pristine <−F≈−CN <−NO<SUB>2</SUB>. In addition, optimized geometries, LUMO, vertical electron attachment and energy components constituting <I>E<SUP>0</SUP> </I> were discussed in detail to assist the further understanding for <I>E<SUP>0</SUP> </I>s. Consequently, we suggested that 16 complexes can play a role as an electrolyte in aqueous redox flow battery. They can be classified into 5 groups having similar <I>E<SUP>0</SUP> </I> ranges: Group I (- 0.6V∼− 0.7V), Group II (around 0.0V), Group III (around 0.3V), Group IV (0.6∼0.8V) and Group V (1.1∼1.2V). Especially, it is expected that <B>[MnL<SUB>F</SUB>]</B>, <B>[MnL<SUB>CN</SUB>]</B> and <B>[NiL<SUB>NH2</SUB>]</B> can be used as promising catholyte candidates possibly possessing high <I>E<SUP>0</SUP> </I>s which almost reach to the reduction potential limitation 1.25V in aqueous redox flow battery. Our systematic approach to tune <I>E<SUP>0</SUP> </I> can be applied to the design of other complexes via rational ligand modification.</P>
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Insight into the histidine tautomerism effect on heterodimers of Aβ40
Li Hao,Salimi Abbas,Burnea Francis Kirby B.,Shi Hu,Lee Jin Yong 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.11
The intrinsic origin of amyloid aggregation has been pursued as a new pathogenesis for Alzheimer’s disease (AD). The aggregation mechanisms influenced by histidine tautomerism were previously investigated in Aβ40 and Aβ42 monomers. In the present study, we focus on the structural properties of Aβ40 heterodimer under the influence of histidine. The results of molecular dynamics simulation detected different aggregation trends were detected in different heterodimers formed by the εεε isomer and other isomers. In the (εεε:δδδ) dimer, the highest β-sheet content was obtained in the δδδ chain, which is in agreement with our previous studies that δδδ monomer is the most easily formed β-sheet secondary structure in the monomer. Further analysis confirmed that (εεε:δδδ) dimers more easily aggregate into fibrils in comparison with other heterodimers. This research will help in understanding the tautomeric effect on Aβ heterodimers, thereby helping to figure out the pathogenesis of AD.
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Hiluf T. Fissaha,Grace M. Nisola,Francis Kirby Burnea,Jin Yong Lee,Sangho Koo,Soong-Peong Lee,Kim Hern,Wook-Jin Chung 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-
Selective recovery of silver ions Ag+ has been a big challenge due to its difficult separation from complexaqueous feed streams. Herein, four novel highly selective 13- to 19-membered thia-crown ethers (TCEs)were successfully developed by intermolecular cyclization of S- and O-containing intermediates. TheTCEs have reactive hydroxyl group(s) for coating on solid supports. To evaluate their ability to captureAg+, the TCEs were coated on polypropylene (PP) membrane (TCE@PP) at high loading ( 280 wt%) viawet-incipient technique with glutaraldehyde acetalization. Adsorption results of all TCE@PP reveal highAg+ capacities with qe 124–179 mg g 1, excellent Ag+ selectivities with Kd 291–778 L g 1 and rapiduptake rate within 1 h. But DH19-TCE4 or 19TCE@PP is the most effective as it achieved 96% Ag+complexation compared with others53–86% at feed Co = 1.5 mM. Density functional theory calculationsreveal that DH19-TCE4 had the closest cavity size (;c = 2.35 Å) with Ag+ (;Ag+ = 2.30 Å), the most negativebinding energy (BE =65.76 kcal mol 1), and the least cavity distortion during Ag+ complexation. Alladsorbents are reusable and stable with consistent performance even afterfive cycles of adsorption/desorption runs. Overall results demonstrate the effectiveness of the synthesis strategies for TCEs andtheir high potential as adsorbents, especially DH19-TCE4, for selective Ag+ recovery from aqueoussources.
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