Calculation of equilibrium constants from multiwavelength spectroscopic data—II32, 95.

Gampp, Harald; Maeder, Marcel; Cj, Meyer; Ad, Zuberbühler

doi:10.1016/0039-9140(85)80077-1

Cited by 487 publications

(267 citation statements)

References 35 publications

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“…Global Analysis-The resulting spectral sets were analyzed using SPECFIT, a global analysis system with singular value decomposition and non-linear regression modeling by the Levenberg-Marquardt method (21). For this analysis, kinetic difference spectra were generated by subtracting the time-zero spectrum from all subsequent spectra, and the resulting spectra were corrected for any small absorbance drift by setting the absorbance at 660 nm (where no form of flavin absorbs) to 0.…”

Section: Methodsmentioning

confidence: 99%

Light-activated Cryptochrome Reacts with Molecular Oxygen to Form a Flavin–Superoxide Radical Pair Consistent with Magnetoreception

Müller

Ahmad

2011

Journal of Biological Chemistry

153

207

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Cryptochromes are flavin-based photoreceptors occurring throughout the biological kingdom, which regulate growth and development in plants and are involved in the entrainment of circadian rhythms of both plants and animals. A number of recent theoretical works suggest that cryptochromes might also be the receptors responsible for the sensing of the magnetic field of the earth (e.g. in insects, migratory birds, or migratory fish). Cryptochromes undergo forward light-induced reactions involving electron transfer to excited state flavin to generate radical intermediates, which correlate with biological activity. Here, we give evidence of a mechanism for the reverse reaction, namely dark reoxidation of protein-bound flavin in Arabidopsis thaliana cryptochrome (AtCRY1) by molecular oxygen that involves formation of a spin-correlated FADH ⅐ -superoxide radical pair. Formation of analogous radical pairs in animal cryptochromes might enable them to function as magnetoreceptors.Cryptochromes are blue light-absorbing photoreceptors found throughout the biological kingdom, ranging from microbes to plants, animals, and humans (1-3). They are evolutionarily derived from photolyases, DNA repair enzymes using violet/blue light to repair damage (cyclobutane pyrimidine dimers) caused by exposure of DNA to UV light. Cryptochromes and photolyases exhibit a high degree of structural homology and bind the same flavin adenine dinucleotide (FAD) and folate light-absorbing cofactors; however, they differ very much in their function in biological systems. Cryptochromes have lost the ability to repair DNA, but they play a key role in controlling the growth and development in plants and in the circadian clock in plants and animals (4). Furthermore, recent evidence suggests that cryptochromes are likely to function as light-dependent magnetic field sensors, used for example by insects or migratory birds and fish for directional responses (5-7).Although photolyases and the mechanism of their action have been subject to extensive studies in the last five decades (3, 9), the photochemistry and the signaling pathways of cryptochromes are just beginning to become known. Recent attention has focused primarily on the pathway of flavin photoreduction as a possible mechanism of photoreceptor activation (10 -14). In the case of both plant and insect cryptochromes, studies with isolated proteins have shown that these can be photoreduced from flavin in the oxidized state to the radical state by light in the presence of reducing agent. This is in marked contrast to photolyases, where photoreduction results in formation of the fully reduced (FADH Ϫ ) form, which is active in DNA repair (11). Photoreduction of flavin correlates with biological activity, as shown by action spectra that demonstrate typical 450-nm peak and shoulders indicative of oxidized flavin with almost no activity above 500 nm (13, 15). Furthermore, both plant and animal cryptochromes show reduced biological activity upon co-illumination with green light, which selectively depletes the...

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Section: Methodsmentioning

confidence: 99%

Light-activated Cryptochrome Reacts with Molecular Oxygen to Form a Flavin–Superoxide Radical Pair Consistent with Magnetoreception

Müller

Ahmad

2011

Journal of Biological Chemistry

153

207

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“…Mathematical treatment of the spectrophotometric titrations was performed with factor analysis [23] and with the SPECFIT program. [24] IR spectra were obtained from KBr pellets with a Perkin ± Elmer 883 spectrometer. 1 H NMR spectra were recorded at 25 8C on a Broadband Varian Gemini 300 spectrometer.…”

Section: Methodsmentioning

confidence: 99%

“…Factor analysis [23] points to the existence of four absorbing species (L7, [Ln 2 (L7) 3 ] 6 , [Ln 3 (L7) 3 ] 9 , and [Ln 3 (L7) 2 ] 9 ) in agreement with the ESI-MS results, and the spectrophotometric data can be fitted with nonlinear least-squares techniques [24] to the equilibria given in Equations (1) ± (3), which characterize the assembly process (the formation constants log(b Ln ij are collected in Table 1). 17.5 ± 20.0); [13] ring between the closely packed benzimidazole rings (vide infra, Figure 6) …”

Section: Introductionmentioning

confidence: 97%

The First Self‐Assembled Trimetallic Lanthanide Helicates Driven by Positive Cooperativity

Floquet

Ouali

Bocquet

et al. 2003

Chemistry A European J

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by paramagnetic NMR spectroscopy and linear correlations for Ln Ce ± Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second-rank crystal-field parameters, obtained by LIS analysis, for the LnN 6 O 3 and LnN 9 sites with respect to the parameters extracted for Eu III from luminescence data, suggests that the geometry of the central LnN 9 site is somewhat relaxed in solution.

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“…NMR spectra 3 of a 1.7 × 10 Ϫ4 M solution of B 6 bL 6 in dry and degassed spectrophotometric grade acetonitrile were titrated in the glovebox by increasing the amount of a 2.4 × 10 Ϫ4 M solution of lanthanum perchlorate delivered by a 1 cm 3 micropipette; 30 spectra were recorded for Ln : L ratios between 0 and 4 : 1 and fitted using the SPECFIT program. 36 Low resolution luminescence spectra and lifetimes (at least five determinations), were recorded on a Perkin-Elmer LS-50B spectrofluorimeter at 295 and 77 K. High resolution laser excited luminescence spectra and lifetimes have been measured at variable temperature using published procedures. 37 The quantum yields of the metal-centred luminescence were determined using published procedures in degassed and anhydrous CH 3 CN at room temperature with respect to complexes with a cyclen derivative, [EuL] 38 The refractive indexes were 1.344 for solutions in CH 3 CN and 1.333 for solutions in water, the excitation wavelengths 279 (Eu, absorbance 0.50) and 278 (Tb, absorbance 0.37) nm; a filter (430 nm) was inserted to eliminate the Raleigh diffusion band and second order spectra.…”

Section: Physicochemical Measurementsmentioning

confidence: 99%

A p-tert-butylcalix[6]arene bearing phosphinoyl pendant arms for the complexation and sensitisation of lanthanide ions

Ramı́rez

Varbanov

Cécile

et al. 2002

J. Chem. Soc., Dalton Trans.

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The new lower rim functionalised macrocycle 5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexakis(dimethylphosphinoylmethoxy) (2) kJ mol Ϫ1 and reveal a semi-flexible macrocycle with alternate in-out cone conformation, a fact confirmed by molecular mechanics and dynamics calculations. B 6 bL 6 crystallises as a dimer where the two calixarenes are linked through hydrogen bonding and surrounded by water and toluene molecules in the lattice. UV-Vis spectrophotometric titration of B 6 bL 6 with La() in acetonitrile yields stability constants log β 1 = 9.8 and log β 2 = 19.6 for the 1 : 1 and 1 : 2 (Ln : B 6 bL 6 ) species, respectively. The corresponding complexes with La, Eu, Gd and Tb have been isolated and characterised. Lifetime determinations of the Eu() and Tb() complexes in acetonitrile solution are consistent with no or little interaction of water molecules in the inner co-ordination sphere. The new ligand sensitises reasonably well the luminescence of the Tb() (Q abs = 4.8%, τ f = 2.1 ms, 1 : 1 complex) and Eu() (Q abs = 2.5%, τ = 2.0 ms, 1 : 2 complex) ions.

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Calculation of equilibrium constants from multiwavelength spectroscopic data—II32, 95.

Cited by 487 publications

References 35 publications

Light-activated Cryptochrome Reacts with Molecular Oxygen to Form a Flavin–Superoxide Radical Pair Consistent with Magnetoreception

Light-activated Cryptochrome Reacts with Molecular Oxygen to Form a Flavin–Superoxide Radical Pair Consistent with Magnetoreception

The First Self‐Assembled Trimetallic Lanthanide Helicates Driven by Positive Cooperativity

A p-tert-butylcalix[6]arene bearing phosphinoyl pendant arms for the complexation and sensitisation of lanthanide ions

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