1
|
Nakamura M, Hyakutake R, Morisako S, Sasamori T, Mizuhata Y, Tokitoh N, Nakashima K, Fukumoto H, Agou T. Boron complexes of π-extended nitroxide ligands exhibiting three-state redox processes and near-infrared-II (NIR-II) absorption properties. Dalton Trans 2022; 51:13675-13680. [PMID: 36040417 DOI: 10.1039/d2dt02545k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Persistent radicals have attracted increasing attention owing to their fascinating properties, including multi-step redox and long-wavelength absorption characteristics. In this study, boron complexes with π-extended nitroxide ligands were synthesised via Buchwald-Hartwig amination reactions of the corresponding boron-nitroxide complex and diarylamines. These nitroxide complexes exhibited two-step and reversible one-electron oxidation processes, suggesting stable redox triads involving anionic aminoxide, neutral nitroxide-radical, and cationic oxoammonium ligands. Cationic boron complexes of the nitroxide radical ligands were obtained via chemical oxidation of the aminoxide complexes and structurally characterised. The cationic nitroxide-radical complexes exhibited strong absorptions at approximately 1100 nm, demonstrating their potential as near-infrared (NIR)-II-active functional dyes.
Collapse
Affiliation(s)
- Marika Nakamura
- Department of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Naka-narusawa, Hitachi, Ibaraki 316-8511, Japan.
| | - Risa Hyakutake
- Department of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Naka-narusawa, Hitachi, Ibaraki 316-8511, Japan.
| | - Shogo Morisako
- Division of Chemistry, Faculty of Pure and Applied Sciences, and Tsukuba Research Center for Energy Materials Sciences (TREMS), University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
| | - Takahiro Sasamori
- Division of Chemistry, Faculty of Pure and Applied Sciences, and Tsukuba Research Center for Energy Materials Sciences (TREMS), University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
| | - Yoshiyuki Mizuhata
- Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
| | - Norihiro Tokitoh
- Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
| | - Kouichi Nakashima
- Department of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Naka-narusawa, Hitachi, Ibaraki 316-8511, Japan.
| | - Hiroki Fukumoto
- Department of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Naka-narusawa, Hitachi, Ibaraki 316-8511, Japan.
| | - Tomohiro Agou
- Department of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Naka-narusawa, Hitachi, Ibaraki 316-8511, Japan.
| |
Collapse
|
2
|
Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds. INORGANICS 2021. [DOI: 10.3390/inorganics9020010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Heterospin systems have a great advantage in frontier orbital engineering since they utilize a wide diversity of paramagnetic chromophores and almost infinite combinations and mutual geometries. Strong exchange couplings are expected in 3d–2p heterospin compounds, where the nitroxide (aminoxyl) oxygen atom has a direct coordination bond with a nickel(II) ion. Complex formation of nickel(II) salts and tert-butyl 2-pyridyl nitroxides afforded a discrete 2p–3d–2p triad. Ferromagnetic coupling is favored when the magnetic orbitals, nickel(II) dσ and radical π*, are arranged in a strictly orthogonal fashion, namely, a planar coordination structure is characterized. In contrast, a severe twist around the coordination bond gives an orbital overlap, resulting in antiferromagnetic coupling. Non-chelatable nitroxide ligands are available for highly twisted and practically diamagnetic complexes. Here, the Ni–O–N–Csp2 torsion (dihedral) angle is supposed to be a useful metric to describe the nickel ion dislocated out of the radical π* nodal plane. Spin-transition complexes exhibited a planar coordination structure in a high-temperature phase and a nonplanar structure in a low-temperature phase. The gradual spin transition is described as a spin equilibrium obeying the van’t Hoff law. Density functional theory calculation indicates that the energy level crossing of the high- and low-spin states. The optimized structures of diamagnetic and high-spin states well agreed with the experimental large and small torsions, respectively. The novel mechanism of the present spin transition lies in the ferro-/antiferromagnetic coupling switch. The entropy-driven mechanism is plausible after combining the results of the related copper(II)-nitroxide compounds. Attention must be paid to the coupling parameter J as a variable of temperature in the magnetic analysis of such spin-transition materials. For future work, the exchange coupling may be tuned by chemical modification and external stimulus, because it has been clarified that the parameter is sensitive to the coordination structure and actually varies from 2J/kB = +400 K to −1400 K.
Collapse
|
3
|
Deng SP, Yang YL, Cheng XX, Li WR, Cai JY. Synthesis, Spectroscopic Study and Radical Scavenging Activity of Kaempferol Derivatives: Enhanced Water Solubility and Antioxidant Activity. Int J Mol Sci 2019; 20:E975. [PMID: 30813425 PMCID: PMC6412309 DOI: 10.3390/ijms20040975] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2018] [Revised: 02/13/2019] [Accepted: 02/19/2019] [Indexed: 12/19/2022] Open
Abstract
Kaempferol (Kae) is a natural flavonoid with potent antioxidant activity, but its therapeutic use is limited by its low aqueous solubility. Here, a series of Kae derivatives were synthesized to improve Kae dissolution property in water and antioxidant activity. These compounds included sulfonated Kae (Kae-SO₃), gallium (Ga) complexes with Kae (Kae-Ga) and Kae-SO₃ (Kae-SO₃-Ga). The compound structures were characterized by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and thermal methods (TG/DSC). The results showed that a sulfonic group (-SO₃) was successfully tethered on the C3' of Kae to form Kae-SO₃. And in the metal complexation, 4-CO and 3-OH of the ligand participated in the coordination with Ga(III). The metal-to-ligand ratio 1:2 was suggested for both complexes. Interestingly, Kae-SO₃-Ga was obviously superior to other compounds in terms of overcoming the poor water-solubility of free Kae, and the solubility of Kae-SO₃-Ga was about 300-fold higher than that of Kae-Ga. Furthermore, the evaluation of antioxidant activities in vitro was carried out for Kae derivatives by using α,α-diphenyl-β-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) free radical scavenging. The results showed that Kae-SO₃-Ga was also optimal for scavenging free radicals in a dose-dependent manner. These data demonstrate that sulfonate kaempferol-gallium complex has a promising future as a potential antioxidant and as a potential therapeutic agent for further biomedical studies.
Collapse
Affiliation(s)
- Sui-Ping Deng
- Department of Chemistry, Jinan University, Guangzhou 510632, China.
| | - Yi-Li Yang
- Department of Chemistry, Jinan University, Guangzhou 510632, China.
| | - Xing-Xing Cheng
- Department of Chemistry, Jinan University, Guangzhou 510632, China.
| | - Wen-Rong Li
- Department of Chemistry, Jinan University, Guangzhou 510632, China.
| | - Ji-Ye Cai
- Department of Chemistry, Jinan University, Guangzhou 510632, China.
- State Key Laboratory of Quality Research in Chinese Medicines, Macau University of Science and Technology, Macau 000853, China.
| |
Collapse
|