Hideo Konno

Quantitative Fluorescent Detection of Pyrophosphate with Quinoline-Ligated Dinuclear Zinc Complexes

Dinuclear zinc complex [Zn2(TQHPN)(AcO)](2+) exhibits characteristic fluorescence response (λex = 317 nm and λem = 455 nm) toward pyrophosphate (PPi) with maximum fluorescence upon 1:1 Zn2(TQHPN)-PPi complex formation. The crystallographic investigation utilizing P(1)P(2)-Ph2PPi revealed that the fluorescent response mechanism is due to intramolecular excimer formation of two quinoline rings.

Isoquinoline-derivatized tris(2-pyridylmethyl)amines as fluorescent zinc sensors with strict Zn2+/Cd2+ selectivity

Tris(2-pyridylmethyl)amine-based fluorescent ligands, N,N-bis(1-isoquinolylmethyl)-2-pyridylmethylamine (1-isoBQPA) and N,N-bis(7-methoxy-1-isoquinolylmethyl)-2-pyridylmethylamine (7-MeO-1-isoBQPA), have been prepared and the Zn(2+)-induced fluorescence enhancement has been investigated. Upon excitation at 324 nm, 1-isoBQPA exhibits a very weak emission (ϕ = ~0.010) in DMF-H2O (1 : 1). Upon Zn(2+) addition, the 1-isoBQPA fluorescence increases (ϕ(Zn) = 0.055) at 357 nm and 464 nm. The fluorescence enhancement at longer wavelengths is Zn(2+)-specific, whereas Cd(2+) induces a small emission increase at 464 nm (I(Cd)/I0 = 1.1, I(Cd)/I(Zn) = 14%). The Zn(2+)/Cd(2+) selectivity of the fluorescent response correlates with the Cd-N(isoquinoline) and Zn-N(isoquinoline) bond distances measured in the crystal structures. Introduction of methoxy groups into the 1-isoBQPA chromophore enhances the fluorescence significantly (ϕ(Zn) = 0.213), which affords 7-MeO-1-isoBQPA properties amenable for fluorescence microscopy in living cells.

8-TQEN (N,N,N′,N′-tetrakis(8-quinolylmethyl)ethylenediamine) analogs as fluorescent cadmium sensors: strategies to enhance Cd2+-induced fluorescence and Cd2+/Zn2+ selectivity

In order to exploit the untapped sensing potential of the TQEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine) family of fluorescent probes, 8-TQEN (N,N,N′,N′-tetrakis(8-quinolylmethyl)ethylenediamine) analogs were designed and characterized. Although 8-TQEN lacks practicality owing to poor solubility in both aqueous media and organic solvents, 6-MeO-8-TQEN (N,N,N′,N′-tetrakis(6-methoxy-8-quinolylmethyl)ethylenediamine, 1b) exhibits Cd2+-selective fluorescence enhancement at 395 nm in DMF–HEPES buffer (1 : 1), (ICd/I0 = 25, λex = 332 nm, ϕCd = 0.025). Zn2+ induces weaker fluorescence (IZn/I0 = 9, IZn/ICd = 0.35). In contrast, both the parent probes TQEN (IZn/I0 = 23, ICd/IZn = 0.64) and 6-MeOTQEN (IZn/I0 = 11, ICd/IZn = 1.29 exhibit higher sensitivity toward Zn2+. When the quinoline groups were replaced with 8-hydroxyquinoline different responses were observed. The propanediamine derivative, 8-TQOEPN (N,N,N′,N′-tetrakis(8-quinolyloxyethylene)propanediamine, 2c) exhibits significant fluorescence enhancement at 423 nm upon Cd2+ binding (λex = 325 nm, ICd/I0 = 19, ϕCd = 0.31). Fluorescence enhancement is Cd2+-specific as Zn2+ induces only more modest emission increases (IZn/I0 = 8.8, IZn/ICd = 0.45).

Quinoline‐Based, Glucose‐Pendant Fluorescent Zinc Probes

Quinoline‐based tetradentate ligands with glucose pendants, N,N′‐bis[2‐(β‐d‐glucopyranosyloxy)ethyl]‐N,N′‐bis[(6‐methoxyquinolin‐2‐yl)methyl]ethylenediamine (N,N′‐6‐MeOBQBGEN) and its N,N‐counterpart, N,N‐6‐MeOBQBGEN, have been prepared, and their fluorescence‐spectral changes upon Zn binding were investigated. Upon excitation at 336 nm, N,N′‐6‐MeOBQBGEN showed weak fluorescence (ϕ≈ 0.016) in HEPES buffer (HEPES 50 mM, KCl 100 mM, pH 7.5). In the presence of Zn, N,N′‐6‐MeOBQBGEN exhibited a significant increase in fluorescence (ϕ=0.096) at 414 nm. The fluorescence enhancement is specific for Zn and Cd (ICd/IZn of 50% at 414 nm). On the other hand, N,N‐6‐MeOBQBGEN exhibited a smaller fluorescence enhancement upon Zn complexation (ϕ=0.043, λex=334 nm, λem=407 nm) compared with N,N′‐6‐MeOBQBGEN. Fluorescence microscopic analysis using PC‐12 rat adrenal cells revealed that N,N′‐6‐MeOBQBGEN exhibits a 1.8‐fold higher fluorescence‐signal response to Zn ion concentration compared with sugar‐depleted compound 2 (N,N′‐bis[(6‐methoxyquinolin‐2‐yl)methyl]ethylenediamine), due to its enhanced uptake into cells due to the targeting ability of the attached carbohydrates.

Quantitative Photochemical Formation of [Ru(tpy)(bpy)H]+

Quantitative photochemical production of [Ru(tpy)(bpy)H](+) (Ru-H(+)) was achieved by irradiation of [Ru(tpy)(bpy)(DMF)](2+) (Ru-DMF(2+); DMF = N,N-dimethylformamide) in a tetrahydrofuran (THF) solution containing excess triethylamine (NEt(3)). The mechanism of the Ru-H(+) formation was investigated in detail. A photochemical ligand substitution reaction of Ru-DMF(2+) in THF proceeded to give [Ru(tpy)(bpy)(THF)](2+) (Ru-THF(2+)) with a quantum yield of (7.6 +/- 0.7) x 10(-2). In the presence of NEt(3), a similar photochemical ligand substitution reaction also proceeded quickly, but the products were an equilibrium mixture of Ru-THF(2+) and [Ru(tpy)(bpy)(NEt(3))](2+) (Ru-NEt(3)(2+)) with a considerable amount of Ru-H(+) even in the first stage of the photochemical reaction. The equilibrium constant between Ru-THF(2+) and Ru-NEt(3)(2+) was determined as 6.9 +/- 2.1. Irradiation to Ru-NEt(3)(2+) gave Ru-H(+) with a quantum yield of (9.1 +/- 0.5) x 10(-3). An important intermediate, Ru-NEt(3)(2+), was isolated, and its properties were investigated in detail.

CCDC 995639: Experimental Crystal Structure Determination

Related Article: Yuji Mikata, Keiko Kawata, Saaya Takeuchi, Kaori Nakanishi, Hideo Konno, Saori Itami, Keiko Yasuda, Satoshi Tamotsu, Shawn C. Burdette|2014|Dalton Trans.|43|10751|doi:10.1039/C4DT01054J