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Leonhartsberger, J.G.; Falk, Heinz

doi:10.1007/s706-002-8246-x

Cited by 20 publications

(4 citation statements)

References 22 publications

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“…Application of the Förster cycle yields Δ pK a = p K a * − p K a = −2.3 for OxyBP and −2.2 dOxyBP, the 0−0 transition location being estimated by the average wavenumber position of the absorption and fluorescence maxima. Such values are similar to the Δp K a value of −2.7 reported for the perihydroxyl groups of Hyp by Eloy et al It may be argued that since the p K a of the OxyBP perihydroxyl groups is situated around 11 in solution (reported value for Hyp , and blepharismin), one would expect the corresponding excited-state p K a in the range of 8−9. In order to explain that some excited-state deprotonation of OBIP occurs at pH 7.4, one would therefore need to hypothesize that the effective perihydroxyl p K a of OxyBP is somewhat reduced to a lower value upon binding to the protein, as is for example the case for the phenol group of the chromophore covalently bound to the Photoactive Yellow Protein .…”

Section: Discussionsupporting

confidence: 86%

“…On the other hand, solutions of peri-deprotonated OxyBP (dpOxyBP) were prepared by setting the pH at 14.3 with a 2.1 mol L −1 NaOH solution, containing 50 mmol L −1 NaCh and 1% vol/vol EtOH (this aqueous solution will be referred to as WCE, water with cholate and ethanol). These conditions are in good agreement with previous studies on hypericin, a parent molecule (Hyp, see Scheme ), situating the p K a of the perihydroxyls of this very similar compound around 11. ,, Since the p K a of the bay hydroxyl of Hyp was reported around 2, pH 14.3 ensures that most of the oxyblepharismin molecules should be bay monodeprotonated and peri-dideprotonated. It may be noted that the hydroxyl function of the lateral phenol of OxyBP, linked to the phenanthroperylene ring by two ether oxide groups, is also expected to be deprotonated at such pH (typical p K a of a para-substituted phenol: 8−10).…”

Section: Methodssupporting

confidence: 91%

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Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

et al. 2008

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We present new femtosecond transient-absorption and picosecond fluorescence experiments performed on OBIP, the oxyblepharismin-binding protein believed to trigger the photophobic response of the ciliate Blepharisma japonicum. The formerly identified heterogeneity of the sample is confirmed and rationalized in terms of two independent populations, called rOBIP and nrOBIP. The rOBIP population undergoes a fast photocycle restoring the initial ground state in less than 500 ps. Intermolecular electron transfer followed by electron recombination is identified as the excited-state decay route. The experimental results support the coexistence of the oxyblepharismin (OxyBP) radical cation signature with a stimulated-emission signal at all times of the evolution of the transient-absorption spectra. This observation is interpreted by an equilibrium being reached between the locally excited state and a charge-transfer state on the ground of a theory developed by Mataga and co-workers to explain the fluorescence quenching of aromatic hydrogen-bonded donor-acceptor pairs in nonpolar solvents. OxyBP is supposed to bind to an as yet unknown electron acceptor by a hydrogen-bond (HB) and the coordinate along which forward and backward electron transfer proceed is assumed to be the shift of the HB proton. The observed kinetic isotope effect supports this interpretation. Protein relaxation is finally proposed to accompany the whole process and give rise to the highly multiexponential observed dynamics. As previously reported, the fast photocycle of rOBIP can be interpreted as an efficient sunscreen mechanism that protects Blepharisma japonicum from continuous irradiation. The nrOBIP population, the transient-absorption of which strongly reminds that of free OxyBP in solution, might be proposed to actually trigger the photophobic response of the organism through excited-state deprotonation of the chromophore occurring in the nanosecond regime. Additional femtosecond transient-absorption spectra of OxyBP and peri-deprotonated OxyBP are also reported and used as a comparison basis to interpret the results on OBIP.

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Section: Discussionsupporting

confidence: 86%

Section: Methodssupporting

confidence: 91%

Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

et al. 2008

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“…Furthermore, the yield of 4a increased and that of 5a decreased by employing organic bases weaker than NMM (pK a =7.41). [16][17][18][19] The best result was obtained with N,N-diethylaniline (DEA; pK a =6.56) giving 4a in 78% and 5a in 1% yields (Entry 4). Interestingly, the reaction was not improved by the use of an inorganic base, NaHCO 3 , despite having the lowest pK a value (6.37) among the bases examined (Entry 5).…”

Section: Resultsmentioning

confidence: 99%

One-Pot Preparation of Oxazol-5(4<i>H</i>)-ones from Amino Acids in Aqueous Solvents

Fujita

Kunishima

2012

CHEMICAL & PHARMACEUTICAL BULLETIN

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A method for one-pot synthesis of oxazol-5(4H)-ones has been developed using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM), which is available for the activation of carboxylic acids in an aqueous solvent. The oxazolones were prepared by the N-acylation of amino acids with carboxylic acids and the subsequent cyclodehydration of the resulting N-acylamino acids by the addition of N,N-diethylaniline. Since both these reactions proceed effectively with the same coupling reagent, DMT-MM, in aqueous solvents, the procedure is simplified and becomes easy to perform. In addition, 5-(triazinyloxy)oxazole derivatives have been synthesized by controlling the basicity of the reaction system. Key words oxazolone; oxazole; dehydrocondensation; cyclodehydration; aqueous solvent Oxazol-5(4H)-ones (henceforth referred to as oxazolones) are useful precursors for the synthesis of substituted heterocyclic compounds, 1) natural products, 2) and chiral amino acids. 3,4)In general, the preparation of oxazolones from amino acids is effected by two-step synthesis: N-acylation of the amino group followed by cyclodehydration involving the activation of the carboxy group. The N-acylation of amino acids can be carried out in an aqueous solvent, typically using Schotten-Baumann conditions, 5) while the cyclodehydration of the resulting N-acylamino acids to form oxazolones is performed under anhydrous conditions with dehydrating reagents, such as carbodiimides and acid anhydrides. Thus, these reactions must be performed in separate vessels. If the latter reaction occurs in an aqueous solvent, both reactions can be conducted in the same vessel using water-soluble amino acids as a starting compound. Therefore, the procedure for preparing oxazolones becomes simplified. In this study, we focused on 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) 6) as a dehydrocondensing reagent because the chemoselective activation of carboxy groups using DMT-MM efficiently proceeds even in an aqueous solvent. 7)We report here a one-pot method for the synthesis of oxazolones from amino acids. In this method, DMT-MM is utilized successfully for both the N-acylation of amino acids with carboxylic acids and the subsequent cyclodehydration of the resulting N-acylamino acids. 8,9) Results and DiscussionTo find the optimum reaction conditions for the one-pot method, we first examined each reaction separately using Lleucine (2a) as a model compound.10,11) After several attempts, we succeeded in finding the optimum reaction conditions for the first reaction. Benzoic acid (1) was treated with DMT-MM in the presence of N-methylmorpholine (NMM) in acetone-H 2 O (3 : 1) at room temperature for 15 min; then an aqueous solution of 2a and NaOH was added (Chart 1). As a result, N-benzoyl-L-leucine (3a) was obtained in a satisfactory yield (91%). The addition of NaOH as a base was found to be essential to complete the coupling reaction.The second reaction needs to follow the final conditions of the former reaction to achie...

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“…3,4 This characteristic is essentially due to the steric hindrance between the OH moieties in the bay region and between the two methyl groups in the peri site. From the determined pKa values 29,30 and from previous theoretical studies, [3][4][5] it was established that the first deprotonation takes place at the expense of an OH group in the bay region. The structure of the obtained anion (hyp À ) still presents structural distortions (ϕ 1 = 30.3 and ϕ 2 = 33.2 ) which are similar to those found in the corresponding neutral though the OH OH repulsion in the bay region is not present in the anionic form.…”

Section: Geometriesmentioning

confidence: 95%

On the origin of photodynamic activity of hypericin and its iodine‐containing derivatives

et al. 2022

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The main photophysical properties, useful for establishing whether hypericin in anionic form and some of its derivatives containing heavy atoms such as iodine, can be proposed for their use in photodynamic therapy, were determined using density functional based computations. The results showed that in the anionic form and in the iodinated derivatives, the absorption wavelength undergoes a bathochromic shift, the singlet-triplet energy gap assumes values that allow to excite the oxygen molecule from its ground to the excited singlet state, and that the spin-orbit couplings between singlet and triplet states significantly increase.

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Cited by 20 publications

References 22 publications

Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

One-Pot Preparation of Oxazol-5(4<i>H</i>)-ones from Amino Acids in Aqueous Solvents

On the origin of photodynamic activity of hypericin and its iodine‐containing derivatives

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