Probing water micro-solvation in proteins by water catalysed proton-transfer tautomerism

Shen, Jau-Ji; Chao, Wei-Chih; Li, Chun; Pan, Hsiao‐An; Yang, Meihua; Chen, Chi‐Lin; Lan, Yi-Kang; Lin, Li‐Hung; Wang, Jinn‐Shyan; Lu, Jyh-Feng; Chou, Steven Chun-Wei; Tang, Kuo‐Chun; Chou, Pi‐Tai

doi:10.1038/ncomms3611

Cited by 72 publications

(109 citation statements)

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“…Moreover, replacing C(2) by an electron-withdrawing N(2) nitrogen, we have reported a wellresolved proton-transfer emission in 500 nm for (2,7-aza)Trp in neutral water (vide supra). 18 The prohibition of protonation on the (2,7-aza)Trp tautomer in the excited state correlates well with a pK a * of 5.9 of its tautomer analogue 7M(2,7-aza)Trp (Figure 1 and Table 1) example, we then added a substituent CF 3 at C(2) of 7AI to form 2CF 3 AI (see Figure 1), which also gives a well-resolved tautomer emission at 500 nm ( Figure 6). The existence of tautomer and hence the prominent green emission implies the low pK a * (≪7) of its conjugate acid.…”

Section: ■ Results and Discussionmentioning

confidence: 97%

“…This prominent proton-transfer emission thus serves as a unique fingerprint and has been successfully exploited for direct sensing of a sitespecific water environment in the human thromboxane A2 synthase (hTXAS) without disrupting its native structure. 18 We also noticed that upon removing the α-amino acid part from (2,7-aza)Trp, forming 2,7-diazaindole, similar proton-transfer emission was also resolved, which is in stark contrast to the lack of tautomer emission for 7AI in water. From the fundamental point of view, a core issue is thus raised regarding factors that govern the water-catalyzed ESPT and hence the resolution of proton-transfer tautomer emission.…”

Section: ■ Introductionmentioning

confidence: 87%

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Water-Catalyzed Excited-State Proton-Transfer Reactions in 7-Azaindole and Its Analogues

Huang

Shen

et al. 2014

J. Phys. Chem. B

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The mechanism of the water-catalyzed excited-state proton-transfer (ESPT) reaction for 7-azaindole (7AI) has long been investigated, but there are some controversial viewpoints. Recently, owing to the superiority of sensing biowaters in proteins by a 7AI analogue, 2,7-diazatryptophan, it is timely to reinvestigate water-catalyzed ESPT in 7AI and its analogues in an attempt to unify the mechanism. Herein, a series of 7AI analogues and their methylated derivatives were synthesized to carry out a systematic study on pKa, pKa*, and the associated fluorescence spectroscopy and dynamics. The results conclude that all 7AI derivatives undergo water-catalyzed ESPT in neutral water. However, for those derivatives with -H (7AI) and a electron-donating substituent at C(3), they follow water-catalyzed ESPT to form an excited N(7)-H proton-transfer tautomer, T*. T* is rapidly protonated to generate an excited cationic (TC*) species. TC* then undergoes a fast deactivation to the N(1)-H normal species in the ground state. Conversely, protonation in T* is prohibited for those derivatives with an electron-withdrawing group at the C(2) or C(3) or with the C(2) atom replaced by an electron-withdrawing nitrogen atom (N(2) in, e.g., 2,7-diazatryptophan), giving a prominent green T* emission. Additional support is given by the synthesis of the corresponding N(7)-CH3 tautomer species, for which pKa* of the cationic form, that is, the N(7)-CH3N(1)-H(+) species, is measured to be much greater than 7.0 for those with electron-donating C(3) substituents, whereas it is lower than 7.0 upon anchoring electron-withdrawing groups. For 7AI, the previously missing T* emission is clearly resolved with a peak wavelength at 530 nm in the pH interval of 13.0-14.3 (H- 14.2).

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Section: ■ Results and Discussionmentioning

confidence: 97%

Section: ■ Introductionmentioning

confidence: 87%

Water-Catalyzed Excited-State Proton-Transfer Reactions in 7-Azaindole and Its Analogues

Huang

Shen

et al. 2014

J. Phys. Chem. B

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“…Essentially, sensing hydration water in proteins occurs without disrupting their native structures (Shen et al 2013). Using this property, it was found that RNase T1, a small protein composed of 104 amino acid residues, exhibits the structure fluctuating between the two loop-close and loop-open forms differing by exposure to water of a single residue Trp59 (Chao et al 2014), see Fig.…”

Section: Responsive Analogs Of Amino Acids and Nucleic Acid Basesmentioning

confidence: 98%

“…4.17) has been recently synthesized and suggested for probing the hydration of particular sites in proteins (Shen et al 2013). This artificial amino acid can be recognized by biosynthetic Whereas Trp emits fluorescence in the near-UV with polarity-dependent band maxima at ~330-350 nm, (2,7-aza)Trp has two additional fluorescence bands extending to the visible that appear due to water-catalyzed proton transfer reaction.…”

Section: Responsive Analogs Of Amino Acids and Nucleic Acid Basesmentioning

confidence: 99%

Molecular-Size Fluorescence Emitters

Demchenko

2015

Introduction to Fluorescence Sensing

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A variety of fluorescent and luminescent materials in the form of molecules, their complexes and nanoparticles are available for implementation as response units into sensing and imaging technologies and we discuss their general properties that are essential for these applications. Organic dyes were the first and remain to be the most popular emitters used with these purposes. Their labeling and responsive properties are overviewed. Natural fluorescent proteins and their engineered analogues incorporate organic fluorophores that are synthesized spontaneously from the polypeptide chain inside the living cells without the need of their intrusion, as the gene products. They resulted in revolutionary advancement in cell imaging and show good prospects in sensing and reporting on cellular processes. Organic heterocyclic compounds can incorporate metal ions generating long-living luminescence. Moreover, noble metal particles of a very small size exhibit unique light-absorbing and fluorescent emission properties. In this Chapter we focus on these types of fluorophores that possess subnanometer dimensions and display single type of absorption-emission cycle. The more complex nanostructures and nanocomposites will be overviewed in Chaps. 5 and 6 that follow. Fluorophores and Their Characteristics General Properties of Fluorescent DyesIn view of tremendous diversity of structures, chemical reactivities and spectroscopic properties, one needs certain practically useful criteria for the dye selection for the purpose of sensing and imaging. They can be formulated in the form of spectroscopic parameters that have to be optimized. It is the parameter describing the ability of molecule to absorb light at a particular wavelength. The absorbance E measured at any wavelength on spectrophotometer is proportional to the dye concentration c (in mol/l) and the light path length in a sample l (in cm). In this relation, ε plays the role of coefficient of proportionality, so that E = εcl. The value of molar absorbance is obtained by purifying and drying the dye, dissolving it at low concentration and measuring E on a spectrophotometer. The broadly used term extinction includes absorbance and light scattering. Absorbance is a unique characteristic of a molecule under certain environmental conditions. In general, the bigger the fluorophore size, the greater is the probability that the photon will be absorbed.The value of ε max at the maximum of absorption band is the common characteristic of the light-absorbing power of the dye. The dye 'brightness' that determines the absolute sensitivity of fluorescence detection (Wetzl et al. 2003) is the product of molar absorbance and quantum yield, Φ. The absorbance is related to optical cross-section and for organic dyes, ε max varies from ca. 10 3 l mol −1 cm −1 for small dyes, such as coumarins to ca. 10 5 l mol −1 cm −1 for larger fluorophores such as cyanines and phthalocyanines (Lavis and Raines 2008). It should be selected as high as possible, but the limiting factor is the fluorophore size. Us...

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“…4.3 , 2,7-azatryptophan is of value not only as noncanonical artifi cial fl uorescent Trp analog but also as amino acid that can be incorporated into proteins instead of Trp by normal protein synthetic machinery (Shen et al 2013 ). Moreover, in addition to emission spectrum at ~340 nm (which is common for indole derivatives) it exhibits additional band in the visible, at ~500 nm.…”

Section: Co-synthetic Incorporation Of Fluorescence Dyesmentioning

confidence: 98%

Sensing Inside the Living Cells

Demchenko

2015

Introduction to Fluorescence Sensing

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Probing water micro-solvation in proteins by water catalysed proton-transfer tautomerism

Cited by 72 publications

References 53 publications

Water-Catalyzed Excited-State Proton-Transfer Reactions in 7-Azaindole and Its Analogues

Water-Catalyzed Excited-State Proton-Transfer Reactions in 7-Azaindole and Its Analogues

Molecular-Size Fluorescence Emitters

Sensing Inside the Living Cells

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