1
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Nikolaev D, Mironov VN, Metelkina EM, Shtyrov AA, Mereshchenko AS, Demidov NA, Vyazmin SY, Tennikova TB, Moskalenko SE, Bondarev SA, Zhouravleva GA, Vasin AV, Panov MS, Ryazantsev MN. Rational Design of Far-Red Archaerhodopsin-3-Based Fluorescent Genetically Encoded Voltage Indicators: from Elucidation of the Fluorescence Mechanism in Archers to Novel Red-Shifted Variants. ACS PHYSICAL CHEMISTRY AU 2024; 4:347-362. [PMID: 39069984 PMCID: PMC11274289 DOI: 10.1021/acsphyschemau.3c00073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/25/2023] [Revised: 04/07/2024] [Accepted: 04/08/2024] [Indexed: 07/30/2024]
Abstract
Genetically encoded voltage indicators (GEVIs) have found wide applications as molecular tools for visualization of changes in cell membrane potential. Among others, several classes of archaerhodopsin-3-based GEVIs have been developed and have proved themselves promising in various molecular imaging studies. To expand the application range for this type of GEVIs, new variants with absorption band maxima shifted toward the first biological window and enhanced fluorescence signal are required. Here, we integrate computational and experimental strategies to reveal structural factors that distinguish far-red bright archaerhodopsin-3-based GEVIs, Archers, obtained by directed evolution in a previous study (McIsaac et al., PNAS, 2014) and the wild-type archaerhodopsin-3 with an extremely dim fluorescence signal, aiming to use the obtained information in subsequent rational design. We found that the fluorescence can be enhanced by stabilization of a certain conformation of the protein, which, in turn, can be achieved by tuning the pK a value of two titratable residues. These findings were supported further by introducing mutations into wild-type archeorhodopsin-3 and detecting the enhancement of the fluorescence signal. Finally, we came up with a rational design and proposed previously unknown Archers variants with red-shifted absorption bands (λmax up to 640 nm) and potential-dependent bright fluorescence (quantum yield up to 0.97%).
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Affiliation(s)
- Dmitrii
M. Nikolaev
- Institute
of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, St. Petersburg 198504, Russia
- Institute
of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University, 29 Polytechnicheskaya Str., St. Petersburg 195251, Russia
| | - Vladimir N. Mironov
- Saint
Petersburg Academic University, 8/3 Khlopina Street, St.
Petersburg 194021, Russia
| | - Ekaterina M. Metelkina
- Institute
of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, St. Petersburg 198504, Russia
| | - Andrey A. Shtyrov
- Institute
of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, St. Petersburg 198504, Russia
| | - Andrey S. Mereshchenko
- Institute
of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, St. Petersburg 198504, Russia
| | - Nikita A. Demidov
- Saint
Petersburg Academic University, 8/3 Khlopina Street, St.
Petersburg 194021, Russia
| | - Sergey Yu. Vyazmin
- Saint
Petersburg Academic University, 8/3 Khlopina Street, St.
Petersburg 194021, Russia
| | - Tatiana B. Tennikova
- Institute
of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, St. Petersburg 198504, Russia
| | - Svetlana E. Moskalenko
- Department
of Genetics and Biotechnology, Saint Petersburg
State University, 7/9
Universitetskaya emb, St. Petersburg 199034, Russia
- Vavilov
Institute of General Genetics, St. Petersburg
Branch, Russian Academy of Sciences, St. Petersburg 199034, Russia
| | - Stanislav A. Bondarev
- Department
of Genetics and Biotechnology, Saint Petersburg
State University, 7/9
Universitetskaya emb, St. Petersburg 199034, Russia
- Laboratory
of Amyloid Biology, Saint Petersburg State
University, St. Petersburg 199034, Russia
| | - Galina A. Zhouravleva
- Department
of Genetics and Biotechnology, Saint Petersburg
State University, 7/9
Universitetskaya emb, St. Petersburg 199034, Russia
- Laboratory
of Amyloid Biology, Saint Petersburg State
University, St. Petersburg 199034, Russia
| | - Andrey V. Vasin
- Institute
of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University, 29 Polytechnicheskaya Str., St. Petersburg 195251, Russia
| | - Maxim S. Panov
- Institute
of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, St. Petersburg 198504, Russia
- St.
Petersburg State Chemical Pharmaceutical University, Professor Popov str., 14, lit. A, St. Petersburg 197022, Russia
| | - Mikhail N. Ryazantsev
- Institute
of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, St. Petersburg 198504, Russia
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2
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Santra S, Manna RN, Chakrabarty S, Ghosh D. Conformational Effects on the Absorption Spectra of Phytochromes. J Phys Chem B 2024; 128:3614-3620. [PMID: 38581077 DOI: 10.1021/acs.jpcb.4c00859] [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: 04/07/2024]
Abstract
Bacteriophytochrome is a photoreceptor protein that contains the biliverdin (BV) chromophore as its active component. The spectra of BV upon mutation remain remarkably unchanged, as far as spectral positions are concerned. This points toward the minimal effect of electrostatic effects on the electronic structure of the chromophore. However, the relative intensities of the Q and Soret bands of the chromophore change dramatically upon mutation. In this work, we delve into the molecular origin of this unusual intensity modulation. Using extensive classical MD and QM/MM calculations, we show that due to mutation, the conformational population of the chromophore changes significantly. The noncovalent interactions, especially the stacking interactions, lead to extra stabilization of the cyclic form in the D207H mutated species as opposed to the open form in the wild-type BV. Thus, unlike the commonly observed direct electrostatic effect on the spectral shift, in the case of BV the difference observed is in varying intensities, and this in turn is driven by a conformational shift due to enhanced stacking interaction.
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Affiliation(s)
- Supriyo Santra
- School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Rabindra Nath Manna
- Department of Chemical and Biological Sciences, S. N. Bose National Centre for Basic Sciences, Salt Lake, Kolkata 700106, India
| | - Suman Chakrabarty
- Department of Chemical and Biological Sciences, S. N. Bose National Centre for Basic Sciences, Salt Lake, Kolkata 700106, India
| | - Debashree Ghosh
- School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
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3
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Nikolaev DM, Shtyrov AA, Vyazmin SY, Vasin AV, Panov MS, Ryazantsev MN. Fluorescence of the Retinal Chromophore in Microbial and Animal Rhodopsins. Int J Mol Sci 2023; 24:17269. [PMID: 38139098 PMCID: PMC10743670 DOI: 10.3390/ijms242417269] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 11/30/2023] [Accepted: 12/06/2023] [Indexed: 12/24/2023] Open
Abstract
Fluorescence of the vast majority of natural opsin-based photoactive proteins is extremely low, in accordance with their functions that depend on efficient transduction of absorbed light energy. However, several recently proposed classes of engineered rhodopsins with enhanced fluorescence, along with the discovery of a new natural highly fluorescent rhodopsin, NeoR, opened a way to exploit these transmembrane proteins as fluorescent sensors and draw more attention to studies on this untypical rhodopsin property. Here, we review the available data on the fluorescence of the retinal chromophore in microbial and animal rhodopsins and their photocycle intermediates, as well as different isomers of the protonated retinal Schiff base in various solvents and the gas phase.
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Affiliation(s)
- Dmitrii M. Nikolaev
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 St. Petersburg, Russia
| | - Andrey A. Shtyrov
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 St. Petersburg, Russia
| | - Sergey Yu. Vyazmin
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina Street, 194021 St. Petersburg, Russia
| | - Andrey V. Vasin
- Institute of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University, 29 Polytechnicheskaya Str., 195251 St. Petersburg, Russia
| | - Maxim S. Panov
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 St. Petersburg, Russia
- Center for Biophysical Studies, St. Petersburg State Chemical Pharmaceutical University, Professor Popov str. 14, lit. A, 197022 St. Petersburg, Russia
| | - Mikhail N. Ryazantsev
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 St. Petersburg, Russia
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4
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Nikolaev DM, Mironov VN, Shtyrov AA, Kvashnin ID, Mereshchenko AS, Vasin AV, Panov MS, Ryazantsev MN. Fluorescence Imaging of Cell Membrane Potential: From Relative Changes to Absolute Values. Int J Mol Sci 2023; 24:ijms24032435. [PMID: 36768759 PMCID: PMC9916766 DOI: 10.3390/ijms24032435] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 01/28/2023] Open
Abstract
Membrane potential is a fundamental property of biological cells. Changes in membrane potential characterize a vast number of vital biological processes, such as the activity of neurons and cardiomyocytes, tumorogenesis, cell-cycle progression, etc. A common strategy to record membrane potential changes that occur in the process of interest is to utilize organic dyes or genetically-encoded voltage indicators with voltage-dependent fluorescence. Sensors are introduced into target cells, and alterations of fluorescence intensity are recorded with optical methods. Techniques that allow recording relative changes of membrane potential and do not take into account fluorescence alterations due to factors other than membrane voltage are already widely used in modern biological and biomedical studies. Such techniques have been reviewed previously in many works. However, in order to investigate a number of processes, especially long-term processes, the measured signal must be corrected to exclude the contribution from voltage-independent factors or even absolute values of cell membrane potential have to be evaluated. Techniques that enable such measurements are the subject of this review.
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Affiliation(s)
- Dmitrii M. Nikolaev
- Institute of Biomedical Systems and Biotechnologies, Peter the Great Saint Petersburg Polytechnic University, 29 Polytechnicheskaya str., 195251 Saint Petersburg, Russia
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Vladimir N. Mironov
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Andrey A. Shtyrov
- Institute of Biomedical Systems and Biotechnologies, Peter the Great Saint Petersburg Polytechnic University, 29 Polytechnicheskaya str., 195251 Saint Petersburg, Russia
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Iaroslav D. Kvashnin
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Andrey S. Mereshchenko
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 Saint Petersburg, Russia
| | - Andrey V. Vasin
- Institute of Biomedical Systems and Biotechnologies, Peter the Great Saint Petersburg Polytechnic University, 29 Polytechnicheskaya str., 195251 Saint Petersburg, Russia
| | - Maxim S. Panov
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 Saint Petersburg, Russia
- Center for Biophysical Studies, Saint Petersburg State Chemical Pharmaceutical University, 14 Professor Popov str., lit. A, 197022 Saint Petersburg, Russia
| | - Mikhail N. Ryazantsev
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 Saint Petersburg, Russia
- Correspondence:
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5
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de Grip WJ, Ganapathy S. Rhodopsins: An Excitingly Versatile Protein Species for Research, Development and Creative Engineering. Front Chem 2022; 10:879609. [PMID: 35815212 PMCID: PMC9257189 DOI: 10.3389/fchem.2022.879609] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2022] [Accepted: 05/16/2022] [Indexed: 01/17/2023] Open
Abstract
The first member and eponym of the rhodopsin family was identified in the 1930s as the visual pigment of the rod photoreceptor cell in the animal retina. It was found to be a membrane protein, owing its photosensitivity to the presence of a covalently bound chromophoric group. This group, derived from vitamin A, was appropriately dubbed retinal. In the 1970s a microbial counterpart of this species was discovered in an archaeon, being a membrane protein also harbouring retinal as a chromophore, and named bacteriorhodopsin. Since their discovery a photogenic panorama unfolded, where up to date new members and subspecies with a variety of light-driven functionality have been added to this family. The animal branch, meanwhile categorized as type-2 rhodopsins, turned out to form a large subclass in the superfamily of G protein-coupled receptors and are essential to multiple elements of light-dependent animal sensory physiology. The microbial branch, the type-1 rhodopsins, largely function as light-driven ion pumps or channels, but also contain sensory-active and enzyme-sustaining subspecies. In this review we will follow the development of this exciting membrane protein panorama in a representative number of highlights and will present a prospect of their extraordinary future potential.
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Affiliation(s)
- Willem J. de Grip
- Leiden Institute of Chemistry, Department of Biophysical Organic Chemistry, Leiden University, Leiden, Netherlands
- Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, Netherlands
| | - Srividya Ganapathy
- Department of Imaging Physics, Delft University of Technology, Netherlands
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6
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Mikhailov OV. The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years. Int J Mol Sci 2021; 23:241. [PMID: 35008667 PMCID: PMC8745423 DOI: 10.3390/ijms23010241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Accepted: 12/15/2021] [Indexed: 11/16/2022] Open
Abstract
The Physical Chemistry and Chemical Physics Section (PCCP Section) is one of the youngest among the sections of the International Journal of Molecular Sciences (IJMS)-the year 2021 will only mark three years since its inception [...].
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Affiliation(s)
- Oleg V Mikhailov
- Department of Analytical Chemistry, Certification and Quality Management, Kazan National Research Technological University, K. Marx Street 68, 420015 Kazan, Russia
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7
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Azobenzene/Tetraethyl Ammonium Photochromic Potassium Channel Blockers: Scope and Limitations for Design of Para-Substituted Derivatives with Specific Absorption Band Maxima and Thermal Isomerization Rate. Int J Mol Sci 2021; 22:ijms222313171. [PMID: 34884976 PMCID: PMC8658355 DOI: 10.3390/ijms222313171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 11/24/2021] [Accepted: 12/01/2021] [Indexed: 11/17/2022] Open
Abstract
Azobenzene/tetraethyl ammonium photochromic ligands (ATPLs) are photoactive compounds with a large variety of photopharmacological applications such as nociception control or vision restoration. Absorption band maximum and lifetime of the less stable isomer are important characteristics that determine the applicability of ATPLs. Substituents allow to adjust these characteristics in a range limited by the azobenzene/tetraethyl ammonium scaffold. The aim of the current study is to find the scope and limitations for the design of ATPLs with specific spectral and kinetic properties by introducing para substituents with different electronic effects. To perform this task we synthesized ATPLs with various electron acceptor and electron donor functional groups and studied their spectral and kinetic properties using flash photolysis and conventional spectroscopy techniques as well as quantum chemical modeling. As a result, we obtained diagrams that describe correlations between spectral and kinetic properties of ATPLs (absorption maxima of E and Z isomers of ATPLs, the thermal lifetime of their Z form) and both the electronic effect of substituents described by Hammett constants and structural parameters obtained from quantum chemical calculations. The provided results can be used for the design of ATPLs with properties that are optimal for photopharmacological applications.
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8
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Abstract
Rhodopsins are photoreceptive membrane proteins consisting of a common heptahelical transmembrane architecture that contains a retinal chromophore. Rhodopsin was first discovered in the animal retina in 1876, but a different type of rhodopsin, bacteriorhodopsin, was reported to be present in the cell membrane of an extreme halophilic archaeon, Halobacterium salinarum, 95 years later. Although these findings were made by physiological observation of pigmented tissue and cell bodies, recent progress in genomic and metagenomic analyses has revealed that there are more than 10,000 microbial rhodopsins and 9000 animal rhodopsins with large diversity and tremendous new functionality. In this Cell Science at a Glance article and accompanying poster, we provide an overview of the diversity of functions, structures, color discrimination mechanisms and optogenetic applications of these two rhodopsin families, and will also highlight the third distinctive rhodopsin family, heliorhodopsin.
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Affiliation(s)
- Takashi Nagata
- The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.,PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Keiichi Inoue
- The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
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9
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Fujimoto KJ. Electronic Couplings and Electrostatic Interactions Behind the Light Absorption of Retinal Proteins. Front Mol Biosci 2021; 8:752700. [PMID: 34604313 PMCID: PMC8480471 DOI: 10.3389/fmolb.2021.752700] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 09/02/2021] [Indexed: 11/13/2022] Open
Abstract
The photo-functional chromophore retinal exhibits a wide variety of optical absorption properties depending on its intermolecular interactions with surrounding proteins and other chromophores. By utilizing these properties, microbial and animal rhodopsins express biological functions such as ion-transport and signal transduction. In this review, we present the molecular mechanisms underlying light absorption in rhodopsins, as revealed by quantum chemical calculations. Here, symmetry-adapted cluster-configuration interaction (SAC-CI), combined quantum mechanical and molecular mechanical (QM/MM), and transition-density-fragment interaction (TDFI) methods are used to describe the electronic structure of the retinal, the surrounding protein environment, and the electronic coupling between chromophores, respectively. These computational approaches provide successful reproductions of experimentally observed absorption and circular dichroism (CD) spectra, as well as insights into the mechanisms of unique optical properties in terms of chromophore-protein electrostatic interactions and chromophore-chromophore electronic couplings. On the basis of the molecular mechanisms revealed in these studies, we also discuss strategies for artificial design of the optical absorption properties of rhodopsins.
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Affiliation(s)
- Kazuhiro J Fujimoto
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Japan.,Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan
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10
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Nikolaev DM, Manathunga M, Orozco-Gonzalez Y, Shtyrov AA, Guerrero Martínez YO, Gozem S, Ryazantsev MN, Coutinho K, Canuto S, Olivucci M. Free Energy Computation for an Isomerizing Chromophore in a Molecular Cavity via the Average Solvent Electrostatic Configuration Model: Applications in Rhodopsin and Rhodopsin-Mimicking Systems. J Chem Theory Comput 2021; 17:5885-5895. [PMID: 34379429 DOI: 10.1021/acs.jctc.1c00221] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a novel technique for computing the free energy differences between two chromophore "isomers" hosted in a molecular environment (a generalized solvent). Such an environment may range from a relatively rigid protein cavity to a flexible solvent environment. The technique is characterized by the application of the previously reported "average electrostatic solvent configuration" method, and it is based on the idea of using the free energy perturbation theory along with a chromophore annihilation procedure in thermodynamic cycle calculations. The method is benchmarked by computing the ground-state room-temperature relative stabilities between (i) the cis and trans isomers of prototypal animal and microbial rhodopsins and (ii) the analogue isomers of a rhodopsin-like light-driven molecular switch in methanol. Furthermore, we show that the same technology can be used to estimate the activation free energy for the thermal isomerization of systems i-ii by replacing one isomer with a transition state. The results show that the computed relative stability and isomerization barrier magnitudes for the selected systems are in line with the available experimental observation in spite of their widely diverse complexity.
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Affiliation(s)
- Dmitrii M Nikolaev
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina Street, St. Petersburg 194021, Russia
| | - Madushanka Manathunga
- Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States
| | - Yoelvis Orozco-Gonzalez
- Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.,Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Andrey A Shtyrov
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina Street, St. Petersburg 194021, Russia
| | | | - Samer Gozem
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Mikhail N Ryazantsev
- Saint Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.,Institute of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University, St. Petersburg 195251, Russia
| | - Kaline Coutinho
- Instituto de Física, Universidade de São Paulo, Cidade Universitária, São Paulo 05508-090, Brazil
| | - Sylvio Canuto
- Instituto de Física, Universidade de São Paulo, Cidade Universitária, São Paulo 05508-090, Brazil
| | - Massimo Olivucci
- Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.,Dipartimento di Biotecnologie, Chimica e Farmacia, Università di Siena, via A. Moro 2, I-53100 Siena, Italy.,Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg-CNRS, UMR 7504, F-67034 Strasbourg, France
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