Novel photosystem involving protonation and deprotonation processes modelled on a PYP photocycle

Matsuhira, Takashi; Tsuchihashi, Kazuki; Yamamoto, H.; Okamura, Taka‐aki; Ueyama, Norikazu

doi:10.1039/b807417h

Cited by 5 publications

(4 citation statements)

References 64 publications

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“…The corresponding alteration generally provides only modest changes of proton-exchange constants. [25][26][27] In contrast, from partition coefficient measurements, Haberfield derived promising orders of magnitude for the photoenhancement of the ionization constants of two 2-hydroxyazobenzenes. [28] The best observed factor of 600 was explained by environmental changes of the acidic proton upon illumination: in the trans stereoisomer, acidity is diminished by the hydrogen bond between the phenol and an azo nitrogen, whereas in the cis configuration, the hydrogen bond is lost and the intrinsic acidity of the substituted phenol is restored (see Scheme 2; see below).…”

Section: Introductionmentioning

confidence: 90%

2‐Hydroxyazobenzenes to Tailor pH Pulses and Oscillations with Light

Emond

Saux

Maurin

et al. 2010

Chemistry A European J

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This paper evaluates the 2-hydroxyazobenzene platform for tailoring proton concentration pulses and oscillations with monochromatic light. The easily prepared 2-hydroxyazobenzenes exhibit large absorptions in the near-UV range. Photoisomerization was investigated by UV/Vis absorption, (1)H NMR spectroscopy, and steady-state fluorescence emission. In the whole investigated series, the trans stereoisomer of the 2-hydroxyazobenzene motif provides the corresponding cis derivative with an action cross section in the 10(3) M(-1) cm(-1) range. At the same time, photoisomerization is accompanied by a significant pK drop of the phenol group. According to the phenyl-substituent pattern, cis-to-trans thermal back-isomerization can be tuned in the 10 ms-100 s range. Up to 2 units of reversible pH drops or pH oscillations on the 10 s timescale have been obtained by appropriately tailoring single-wavelength illumination of 2-hydroxyazobenzene solutions.

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Section: Introductionmentioning

confidence: 90%

2‐Hydroxyazobenzenes to Tailor pH Pulses and Oscillations with Light

Emond

Saux

Maurin

et al. 2010

Chemistry A European J

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“…The pK a value for the carboxylic acid is lowered because of E/Z photoisomerization [25]. ortho-Coumaric acid derivatives with an amide group linked to an olefin moiety also show photoinduced switching accompanied with intramolecular hydrogen bonding [26]. Another type of intramolecular OHÁ Á ÁO¼C hydrogen bond in the Z-phenol compound switches to an intramolecular NHÁ Á ÁO hydrogen bond in the Z-phenolate state by deprotonation ( Figure 27.7(c)).…”

Section: Proton-driven Conformational Switching In Asp-oligopeptide Amentioning

confidence: 98%

Conformational Switching Between Acids and their Anions by Hydrogen Bonding

Okamura

Yamamoto

Ueyama

2010

Hydrogen Bonding and Transfer in the Excited State

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In general, pK a shifts for acids, such as thiols, carboxylic acids, phenols and phosphoric acid monoanions, are considered to occur under homogeneous conditions and change with dielectric constant. Theoretical calculations have been performed for homogeneous environments [1][2][3][4], and some improved theoretical studies have considered anisotropic and heterogeneous environments [4][5][6][7][8] to deal with the particularly large shift for thiols, phenols and carboxylic acids located inside proteins. This paper discusses pK a shifts for acids having neighbouring amide NHs.A relationship between the pK a shift and the formation constant is observed for metal complexes in hydrophobic environments. The influence of intramolecular NHÁ Á ÁX hydrogen bonds on the metal-X bond character is also observed for metal complexes. The presence of NHÁ Á ÁS hydrogen bonds in iron-sulfur proteins observed by crystallographic studies has been suggested by Adman and coworkers [9]. Various synthetic metal-thiolate complexes having chelating Cys-containing oligopeptides and synthetic simple intramolecularly NHÁ Á ÁS hydrogen-bonded thiolate ligands exist. NHÁ Á ÁS hydrogen bonds in metal-thiolate complexes play an important role in the following functions.Intramolecular hydrogen bonds contribute to the following: increase in the stabilization constant, e.g. Fe(II), Zn(II), Cd(II), Hg(II) and Ca(II) complexes; positive shift of the redox potential, e.g. Fe(II), Fe(III), Mo(IV) and W(IV) complexes; and increase in air stabilization, e.g. Fe(II) and Fe(III) complexes. In addition, the NHÁ Á ÁS hydrogen bond increases the formation constant for metal-sulfur complexes formed by substitution reaction between non-hydrogen-bonded and hydrogen-bonded thiolates [10]. The large formation constant is due not only to the pK a -lowering shift of thiol but also to a pp-dp interaction by the NHÁ Á ÁS hydrogen bond.

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“…During the optimization study we found that when silver acetate was used instead of NiCl 2 •6H 2 O, as the catalyst in the presence of MSA in toluene at 50 °C, the desired product was obtained in 53% yield (entry 16). We then optimized the reaction conditions further by using silver-based catalysts, and competitive results were obtained with 10 mol% of Ag 2 CO 3 in the presence of 3.0 equivalent of MSA (entries [16][17][18][19][20][21][22][23][24][25][26][27]. Unfortunately, the reaction was not successful in water as the solvent (see the Supporting Information for details).…”

Section: Paper Synthesismentioning

confidence: 99%