1
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Feng RR, Wang M, Zhang W, Gai F. Unnatural Amino Acids for Biological Spectroscopy and Microscopy. Chem Rev 2024; 124:6501-6542. [PMID: 38722769 DOI: 10.1021/acs.chemrev.3c00944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/23/2024]
Abstract
Due to advances in methods for site-specific incorporation of unnatural amino acids (UAAs) into proteins, a large number of UAAs with tailored chemical and/or physical properties have been developed and used in a wide array of biological applications. In particular, UAAs with specific spectroscopic characteristics can be used as external reporters to produce additional signals, hence increasing the information content obtainable in protein spectroscopic and/or imaging measurements. In this Review, we summarize the progress in the past two decades in the development of such UAAs and their applications in biological spectroscopy and microscopy, with a focus on UAAs that can be used as site-specific vibrational, fluorescence, electron paramagnetic resonance (EPR), or nuclear magnetic resonance (NMR) probes. Wherever applicable, we also discuss future directions.
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Affiliation(s)
- Ran-Ran Feng
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Manxi Wang
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Wenkai Zhang
- Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China
| | - Feng Gai
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
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2
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Zhou L, Feng RR, Zhang W, Gai F. Triple-Bond Vibrations: Emerging Applications in Energy and Biological Sciences. J Phys Chem Lett 2024; 15:187-200. [PMID: 38156972 DOI: 10.1021/acs.jpclett.3c02619] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
Triple bonds, such as that formed between two carbon atoms (i.e., C≡C) or that formed between one carbon atom and one nitrogen atom (i.e., C≡N), afford unique chemical bonding and hence vibrational characteristics. As such, they are not only frequently used to construct molecules with tailored chemical and/or physical properties but also employed as vibrational probes to provide site-specific chemical and/or physical information at the molecular level. Herein, we offer our perspective on the emerging applications of various triple-bond vibrations in energy and biological sciences with a focus on C≡C and C≡N triple bonds.
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Affiliation(s)
- Liang Zhou
- Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China
| | - Ran-Ran Feng
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Wenkai Zhang
- Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China
| | - Feng Gai
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
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3
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Yuan Y, Liu J, Feng RR, Zhang W, Gai F. Photophysics of Two Indole-Based Cyan Fluorophores. J Phys Chem B 2023; 127:4508-4513. [PMID: 37171997 DOI: 10.1021/acs.jpcb.3c01739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
For the purpose of searching for new biological fluorophore, we assess the photophysical properties of two indole derivatives, 4-cyano-7-azaindole (4CN7AI) and 1-methyl-4-cyano-7-azaindole (1M4CN7AI), in a series of solvents. We find that (1) the absorption spectra of both derivatives are insensitive to solvents and are red-shifted from that of indole, having a maximum absorption wavelength of ca. 318 nm and a broad profile that extends beyond 370 nm; (2) both derivatives emit in the blue to green spectral range with a large Stokes shift, for example, in H2O, the maximum emission wavelength of 4CN7AI (1M4CN7AI) is at ca. 455 nm (470 nm); (3) 4CN7AI has a higher fluorescence quantum yield (QY) and a longer fluorescence lifetime (τF) in aprotic solvents than in protic solvents, for example, QY (τF) = 0.72 ± 0.04 (7.6 ± 0.8 ns) in tetrahydrofuran and QY (τF) = 0.29 ± 0.03 (6.2 ± 0.6 ns) in H2O; (4) in all of the solvents used except H2O, the fluorescence QY (τF) of 1M4CN7AI is equal to or higher (longer) than 0.69 ± 0.03 (11.2 ± 0.7 ns). Taken together, these results suggest that the corresponding non-natural amino acids, 4-cyano-7-azatryptophan and 1-methyl-4-cyano-7-azatryptophan, could be useful as biological fluorophores.
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Affiliation(s)
- Yu Yuan
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Jingsong Liu
- Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China
| | - Ran-Ran Feng
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Wenkai Zhang
- Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China
| | - Feng Gai
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
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4
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Jacob MH, D’Souza RN, Lazar AI, Nau WM. Diffusion-Enhanced Förster Resonance Energy Transfer in Flexible Peptides: From the Haas-Steinberg Partial Differential Equation to a Closed Analytical Expression. Polymers (Basel) 2023; 15:polym15030705. [PMID: 36772006 PMCID: PMC9919848 DOI: 10.3390/polym15030705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 01/31/2023] Open
Abstract
In the huge field of polymer structure and dynamics, including intrinsically disordered peptides, protein folding, and enzyme activity, many questions remain that cannot be answered by methodology based on artificial intelligence, X-ray, or NMR spectroscopy but maybe by fluorescence spectroscopy. The theory of Förster resonance energy transfer (FRET) describes how an optically excited fluorophore transfers its excitation energy through space to an acceptor moiety-with a rate that depends on the distance between donor and acceptor. When the donor and acceptor moiety are conjugated to different sites of a flexible peptide chain or any other linear polymer, the pair could in principle report on chain structure and dynamics, on the site-to-site distance distribution, and on the diffusion coefficient of mutual site-to-site motion of the peptide chain. However, the dependence of FRET on distance distribution and diffusion is not defined by a closed analytical expression but by a partial differential equation (PDE), by the Haas-Steinberg equation (HSE), which can only be solved by time-consuming numerical methods. As a second complication, time-resolved FRET measurements have thus far been deemed necessary. As a third complication, the evaluation requires a computationally demanding but indispensable global analysis of an extended experimental data set. These requirements have made the method accessible to only a few experts. Here, we show how the Haas-Steinberg equation leads to a closed analytical expression (CAE), the Haas-Steinberg-Jacob equation (HSJE), which relates a diffusion-diagnosing parameter, the effective donor-acceptor distance, to the augmented diffusion coefficient, J, composed of the diffusion coefficient, D, and the photophysical parameters that characterize the used FRET method. The effective donor-acceptor distance is easily retrieved either through time-resolved or steady-state fluorescence measurements. Any global fit can now be performed in seconds and minimizes the sum-of-square difference between the experimental values of the effective distance and the values obtained from the HSJE. In summary, the HSJE can give a decisive advantage in applying the speed and sensitivity of FRET spectroscopy to standing questions of polymer structure and dynamics.
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5
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Yang Y, Feng RR, Gai F. 4-Cyanotryptophan as a Sensitive Fluorescence Probe of Local Electric Field of Proteins. J Phys Chem B 2023; 127:514-519. [PMID: 36598839 DOI: 10.1021/acs.jpcb.2c07605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Electrostatic interactions are key determinants of protein structure, dynamics, and function. Since protein electrostatics are nonuniform, assessment of the internal electric fields (EFs) of proteins requires spatial resolution at the amino acid residue level. In this regard, vibrational Stark spectroscopy, in conjunction with various unnatural amino acid-based vibrational probes, has become a common method for site-specific interrogation of protein EFs. However, application of this method is often limited to proteins with relatively high solubility, due to the intrinsically low oscillator strength of vibrational transitions. Therefore, it would be useful to develop an alternative method that can overcome this limitation. To this end, we show that, using solvatochromic study and molecular dynamics simulations, the frequency of maximum emission intensity of the fluorophore of 4-cyanotryptophan (4CN-Trp), 3-methyl-1H-indole-4-carbonitrile, exhibits a linear dependence on the local EF. Since the absorption and emission spectra of 4CN-Trp are easily distinguishable from those of naturally occurring aromatic amino acids, we believe that this linear relationship provides an easier and more sensitive means to determine the local EF of proteins.
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Affiliation(s)
- Yuyao Yang
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Ran-Ran Feng
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Feng Gai
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
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6
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Micikas RJ, Acharyya A, Smith AB, Gai F. Synthesis and characterization of the fluorescence utility of two Visible-Light-Absorbing tryptophan derivatives. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2022.139553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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7
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Mohan B, Modi K, Parikh J, Ma S, Kumar S, Kumar Manar K, Sun F, You H, Ren P. Efficacy of 2-nitrobenzylidene-hydrazine-based selective and rapid sensor for Cu2+ ions, histidine, and tyrosine: Spectral and computational study. J Photochem Photobiol A Chem 2022. [DOI: 10.1016/j.jphotochem.2021.113557] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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8
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Wu Y, Bertran MT, Rowley J, Calder EDD, Joshi D, Walport LJ. Fluorescent Amino Acid Initiated de novo Cyclic Peptides for the Label-Free Assessment of Cell Permeability*. ChemMedChem 2021; 16:3185-3188. [PMID: 34236771 PMCID: PMC8597039 DOI: 10.1002/cmdc.202100315] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Indexed: 11/11/2022]
Abstract
The major obstacle in applying peptides to intracellular targets is their low inherent cell permeability. Standard approaches to attach a fluorophore (e. g. FITC, TAMRA) can change the physicochemical properties of the parent peptide and influence their ability to penetrate and localize in cells. We report a label-free strategy for evaluating the cell permeability of cyclic peptide leads. Fluorescent tryptophan analogues 4-cyanotryptophan (4CNW) and β-(1-azulenyl)-L-alanine (AzAla) were incorporated into in vitro translated macrocyclic peptides by initiator reprogramming. We then demonstrate these efficient blue fluorescent emitters are good tools for monitoring peptide penetration into cells.
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Affiliation(s)
- Yuteng Wu
- Protein-Protein Interaction LaboratoryThe Francis Crick InstituteLondonNW1 1ATUK
- Department of ChemistryMolecular Sciences Research HubImperial College LondonLondonW12 0BZUK
| | - M. Teresa Bertran
- Protein-Protein Interaction LaboratoryThe Francis Crick InstituteLondonNW1 1ATUK
| | - James Rowley
- Protein-Protein Interaction LaboratoryThe Francis Crick InstituteLondonNW1 1ATUK
- Department of ChemistryMolecular Sciences Research HubImperial College LondonLondonW12 0BZUK
| | - Ewen D. D. Calder
- Protein-Protein Interaction LaboratoryThe Francis Crick InstituteLondonNW1 1ATUK
- Department of ChemistryMolecular Sciences Research HubImperial College LondonLondonW12 0BZUK
| | - Dhira Joshi
- Peptide ChemistryThe Francis Crick InstituteLondonNW1 1ATUK
| | - Louise J. Walport
- Protein-Protein Interaction LaboratoryThe Francis Crick InstituteLondonNW1 1ATUK
- Department of ChemistryMolecular Sciences Research HubImperial College LondonLondonW12 0BZUK
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9
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Mayorga-Burrezo P, Muñoz J, Zaoralová D, Otyepka M, Pumera M. Multiresponsive 2D Ti 3C 2T x MXene via Implanting Molecular Properties. ACS NANO 2021; 15:10067-10075. [PMID: 34125533 DOI: 10.1021/acsnano.1c01742] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The design and fabrication of active nanomaterials exhibiting multifunctional properties is a must in the so-called global "Fourth Industrial Revolution". In this sense, molecular engineering is a powerful tool to implant original capabilities on a macroscopic scale. Herein, different bioinspired 2D-MXenes have been developed via a versatile and straightforward synthetic approach. As a proof of concept, Ti3C2Tx MXene has been exploited as a highly sensitive transducing platform for the covalent assembly of active biomolecular architectures (i.e., amino acids). All pivotal properties originated from the anchored targets were proved to be successfully transferred to the resulting bioinspired 2D-MXenes. Appealing applications have been devised for these 2D-MXene prototypes showing (i) chiroptical activity, (ii) fluorescence capabilities, (iii) supramolecular π-π interactions, and (iv) stimuli-responsive molecular switchability. Overall, this work demonstrates the fabrication of programmable 2D-MXenes, taking advantage of the inherent characteristics of the implanted (bio)molecular components. Thus, the current bottleneck in the field of 2D-MXenes can be overcome after the significant findings reported here.
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Affiliation(s)
- Paula Mayorga-Burrezo
- Future Energy and Innovation Laboratory, Central European Institute of Technology, Brno University of Technology (CEITEC-BUT), Purkyňova 123, 61200 Brno, Czech Republic
| | - Jose Muñoz
- Future Energy and Innovation Laboratory, Central European Institute of Technology, Brno University of Technology (CEITEC-BUT), Purkyňova 123, 61200 Brno, Czech Republic
| | - Dagmar Zaoralová
- Czech Advanced Technology and Research Institute (CATRIN), Regional Centre of Advanced Technologies and Materials (RCPTM), Palacký University Olomouc, Šlechtitelů 27, 779 00 Olomouc, Czech Republic
| | - Michal Otyepka
- Czech Advanced Technology and Research Institute (CATRIN), Regional Centre of Advanced Technologies and Materials (RCPTM), Palacký University Olomouc, Šlechtitelů 27, 779 00 Olomouc, Czech Republic
- IT4Innovations, VSB - Technical University of Ostrava, 17. listopadu 2172/15, 708 00 Ostrava-Poruba, Czech Republic
| | - Martin Pumera
- Future Energy and Innovation Laboratory, Central European Institute of Technology, Brno University of Technology (CEITEC-BUT), Purkyňova 123, 61200 Brno, Czech Republic
- Center for Nanorobotics and Machine Intelligence, Department of Food Technology, Mendel University in Brno, Zemedelska 1/1665, 613 00 Brno, Czech Republic
- Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-Gu, Seoul 03722, South Korea
- Department of Medical Research, China Medical University Hospital, China Medical University, No. 91 Hsueh-Shih Road, Taichung 40402, Taiwan
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10
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Fong KP, Ahmed IA, Mravic M, Jo H, Kim OV, Litvinov RI, Weisel JW, DeGrado WF, Gai F, Bennett JS. Visualization of Platelet Integrins via Two-Photon Microscopy Using Anti-transmembrane Domain Peptides Containing a Blue Fluorescent Amino Acid. Biochemistry 2021; 60:1722-1730. [PMID: 34010565 DOI: 10.1021/acs.biochem.1c00238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The fluorescent reporters commonly used to visualize proteins can perturb both protein structure and function. Recently, we found that 4-cyanotryptophan (4CN-Trp), a blue fluorescent amino acid, is suitable for one-photon imaging applications. Here, we demonstrate its utility in two-photon fluorescence microscopy by using it to image integrins on cell surfaces. Specifically, we used solid-phase peptide synthesis to generate CHAMP peptides labeled with 4-cyanoindole (4CNI) at their N-termini to image integrins on cell surfaces. CHAMP (computed helical anti-membrane protein) peptides spontaneously insert into membrane bilayers to target integrin transmembrane domains and cause integrin activation. We found that 4CNI labeling did not perturb the ability of CHAMP peptides to insert into membranes, bind to integrins, or cause integrin activation. We then used two-photon fluorescence microscopy to image 4CNI-containing integrins on the surface of platelets. Compared to a 4CNI-labeled scrambled peptide that uniformly decorated cell surfaces, 4CNI-labeled CHAMP peptides were present in discrete blue foci. To confirm that these foci represented CN peptide-containing integrins, we co-stained platelets with integrin-specific fluorescent monoclonal antibodies and found that CN peptide and antibody fluorescence coincided. Because 4CNI can readily be biosynthetically incorporated into proteins with little if any effect on protein structure and function, it provides a facile way to directly monitor protein behavior and protein-protein interactions in cellular environments. In addition, these results clearly demonstrate that the two-photon excitation cross section of 4CN-Trp is sufficiently large to make it a useful two-photon fluorescence reporter for biological applications.
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Affiliation(s)
- Karen P Fong
- Hematology-Oncology Division, Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Ismail A Ahmed
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Marco Mravic
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94158-2517, United States
| | - Hyunil Jo
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94158-2517, United States
| | - Oleg V Kim
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Rustem I Litvinov
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - John W Weisel
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94158-2517, United States
| | - Feng Gai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Joel S Bennett
- Hematology-Oncology Division, Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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11
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Acharyya A, Zhang W, Gai F. Tryptophan as a Template for Development of Visible Fluorescent Amino Acids. J Phys Chem B 2021; 125:5458-5465. [PMID: 34029101 DOI: 10.1021/acs.jpcb.1c02321] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Most biological systems, at both molecular and cellular levels, are intrinsically complex, diverse, and nonfluorescent. Therefore, studying their structures, dynamics, and interactions via fluorescence-based methods requires incorporation of one or multiple external fluorophores that would not significantly affect any native property of the system in question. This requirement necessitates the development of a diverse set of fluorescence reporters that differ in chemical, physical, and photophysical properties. Herein, we offer our perspective on the need for, recent progress in, and future directions of developing tryptophan-based fluorescent amino acids.
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Affiliation(s)
- Arusha Acharyya
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Wenkai Zhang
- Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China
| | - Feng Gai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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12
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Hebestreit ML, Lartian H, Henrichs C, Kühnemuth R, Meerts WL, Schmitt M. Excited state dipole moments and lifetimes of 2-cyanoindole from rotationally resolved electronic Stark spectroscopy. Phys Chem Chem Phys 2021; 23:10196-10204. [PMID: 33951126 DOI: 10.1039/d1cp00097g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The permanent dipole moments of 2-cyanoindole (cyanoindole = CNI) in its ground and lowest excited singlet states have been determined from rotationally resolved electronic Stark spectroscopy under jet-cooled conditions. From the orientation of the transition dipole moment and the geometry changes upon electronic excitation the lowest excited singlet state could be shown to be of Lb-symmetry. The general statement, that the La-state has the larger permanent dipole moment of the two lowest excited singlet states, will be challenged in this contribution. On the basis of the different electronic nature of the first excited singlet state the behavior of 2-, 3-, 4- and 5-CNI is discussed. The excited state lifetime of isolated 2-CNI in the gas phase has been determined to be 9.4 ns. This value is compared to the excited state lifetime in ethyl acetate solution of 2.6 ns, which was quantified with a Strickler-Berg analysis. Using water as solvent shortens the 2-CNI lifetime to <40 ps. The reason for this drastic shortening is discussed in detail. Additionally, the rotationally resolved electronic spectrum of 2-CNI(1-d1) has been measured and analyzed.
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Affiliation(s)
- Marie-Luise Hebestreit
- Heinrich-Heine-Universität, Institut für Physikalische Chemie I, D-40225 Düsseldorf, Germany.
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13
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Micikas RJ, Ahmed IA, Acharyya A, Smith AB, Gai F. Tuning the electronic transition energy of indole via substitution: application to identify tryptophan-based chromophores that absorb and emit visible light. Phys Chem Chem Phys 2021; 23:6433-6437. [PMID: 33710175 DOI: 10.1039/d0cp06710e] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Fluorescent amino acids (FAAs) offer significant advantages over fluorescent proteins in applications where the fluorophore size needs to be limited or minimized. A long-sought goal in biological spectroscopy/microcopy is to develop visible FAAs by modifying the indole ring of tryptophan. Herein, we examine the absorption spectra of a library of 4-substituted indoles and find that the frequency of the absorption maximum correlates linearly with the global electrophilicity index of the substituent. This finding permits us to identify two promising candidates, 4-formyltryptophan (4CHO-Trp) and 4-nitrotryptophan (4NO2-Trp), both of which can be excited by visible light. Further fluorescence measurements indicate that while 4CHO-indole (and 4CHO-Trp) emits cyan fluorescence with a reasonably large quantum yield (ca. 0.22 in ethanol), 4NO2-indole is essentially non-fluorescent, suggesting that 4CHO-Trp (4NO2-Trp) could be useful as a fluorescence reporter (quencher). In addition, we present a simple method for synthesizing 4CHO-Trp.
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Affiliation(s)
- Robert J Micikas
- Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104, USA.
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14
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Micikas R, Acharyya A, Gai F, Smith AB. A Scalable Synthesis of the Blue Fluorescent Amino Acid 4-Cyanotryptophan and the Fmoc Derivative: Utility Demonstrated with the Influenza M2 Peptide Tetramer. Org Lett 2021; 23:1247-1250. [DOI: 10.1021/acs.orglett.0c04055] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Robert Micikas
- Department of Chemistry, University of Pennsylvania, 231 South 34th St, Philadelphia, Pennsylvania 19104, United States
| | - Arusha Acharyya
- Department of Chemistry, University of Pennsylvania, 231 South 34th St, Philadelphia, Pennsylvania 19104, United States
| | - Feng Gai
- Department of Chemistry, University of Pennsylvania, 231 South 34th St, Philadelphia, Pennsylvania 19104, United States
| | - Amos B. Smith
- Department of Chemistry, University of Pennsylvania, 231 South 34th St, Philadelphia, Pennsylvania 19104, United States
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15
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Abstract
Most biological molecules are intrinsically non- or weakly-fluorescent, hence requiring labeling with an external fluorophore(s) to be studied via fluorescence-based techniques. However, such labeling could perturb the native property of the system in question. One effective strategy to minimize such undesirable perturbation is to use fluorophores that are simple analogs of natural amino acids. In this chapter, we describe the synthesis and spectroscopic utility of two indole-based fluorophores, 4-cynaotryprophan (4CN-Trp) and 4-cyanoindole-2'-deoxyribonucleoside (4CNI-NS), with a focus on 4CN-Trp. This unnatural amino acid, which is only slightly larger than its natural counterpart, tryptophan (Trp), exhibits unique photophysical properties, making it a versatile fluorophore in biological spectroscopic and imaging applications. Through several specific examples, we highlight its broad utility in the study of various biological problems and processes.
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