1
|
Understanding flavin electronic structure and spectra. WIRES COMPUTATIONAL MOLECULAR SCIENCE 2022. [DOI: 10.1002/wcms.1541] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
|
2
|
Ye S, Tan J, Tian K, Li C, Zhang J, Luo Y. Directly monitoring the active sites of charge transfer in heterocycles in situ and in real time. Chem Commun (Camb) 2019; 55:541-544. [PMID: 30556076 DOI: 10.1039/c8cc08452a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Coherent degenerate infrared-infrared-visible sum frequency generation vibrational spectroscopy provides a powerful label-free sensitive probe for charge transfer active sites in heterocyclic molecules in situ and in real time.
Collapse
Affiliation(s)
- Shuji Ye
- Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center for Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
| | | | | | | | | | | |
Collapse
|
3
|
Shchepin RV, Chekmenev EY. Toward hyperpolarized molecular imaging of HIV: synthesis and longitudinal relaxation properties of (15) N-Azidothymidine. J Labelled Comp Radiopharm 2014; 57:621-4. [PMID: 25156931 PMCID: PMC4287256 DOI: 10.1002/jlcr.3220] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Revised: 05/28/2014] [Accepted: 06/30/2014] [Indexed: 11/11/2022]
Abstract
Previously unreported (15) N labeled Azidothymidine (AZT) was prepared as an equimolar mixture of two isotopomers: 1-(15) N-AZT and 3-(15) N-AZT. Polarization decay of (15) N NMR signal was studied in high (9.4 T) and low (~50 mT) magnetic fields. (15) N T1 values were 45 ± 5 s (1-(15) N-AZT) and 37 ± 2 s (3-(15) N-AZT) at 9.4 T, and 140 ± 16 s (3-(15) N-AZT) at 50 mT. (15) N-AZT can be potentially (15) N hyperpolarized by several methods. These sufficiently long (15) N-AZT T1 values potentially enable hyperpolarized in vivo imaging of (15) N-AZT, because of the known favorable efficient (i.e., of the time scale shorter than the longest reported here (15) N T1 ) kinetics of uptake of injected AZT. Therefore, 3-(15) N-AZT can be potentially used for HIV molecular imaging using hyperpolarized magnetic resonance imaging.
Collapse
Affiliation(s)
- Roman V. Shchepin
- Department of Radiology, Vanderbilt University Institute of Imaging Science (VUIIS), Nashville, TN 37232, USA
| | - Eduard Y. Chekmenev
- Department of Radiology, Vanderbilt University Institute of Imaging Science (VUIIS), Nashville, TN 37232, USA
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 37235, USA
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37205, USA
| |
Collapse
|
4
|
Miller AF. Solid-state NMR of flavins and flavoproteins. Methods Mol Biol 2014; 1146:307-40. [PMID: 24764096 DOI: 10.1007/978-1-4939-0452-5_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Why apply solid-state NMR (SSNMR) to flavins and flavoproteins? NMR provides information on an atom-specific basis about chemical functionality, structure, proximity to other groups, and dynamics of the system. Thus, it has become indispensable to the study of chemicals, materials, catalysts, and biomolecules. It is no surprise then that NMR has a great deal to offer in the study of flavins and flavoenzymes. In general, their catalytic or electron-transfer activity resides essentially in the flavin, a molecule eminently accessible by NMR. However, the specific reactivity displayed depends on a host of subtle interactions whereby the protein biases and reshapes the flavin's propensities to activate it for one reaction while suppressing other aspects of this cofactor's prodigious repertoire (Massey et al., J Biol Chem 244:3999-4006, 1969; Müller, Z Naturforsch 27B:1023-1026, 1972; Joosten and van Berkel, Curr Opin Struct Biol 11:195-202, 2007). Thus, we are fascinated to learn about how the flavin cofactor of one enzyme is, and is not, like the flavin cofactor of another. In what follows, we describe how the capabilities of SSNMR can help and are beginning to bear fruit in this exciting endeavor.
Collapse
Affiliation(s)
- Anne-Frances Miller
- Department of Chemistry, University of Kentucky, 505 Rose St, Lexington, KY, 40506-0055, USA,
| |
Collapse
|
5
|
Altheimer BD, Mehta MA. Effects of structural differences on the NMR chemical shifts in isostructural dipeptides. J Phys Chem A 2014; 118:2618-28. [PMID: 24654604 DOI: 10.1021/jp411220y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Porous crystalline dipeptides have gained recent attention for their potential as gas-storage materials. Within this large class is a group of dipeptides containing alanine, valine, and isoleucine with very similar crystal structures. We report the (13)C (carbonyl and Cα) and (15)N (amine and amide) solid-state NMR isotropic chemical shifts in a series of seven such isostructural porous dipeptides as well as shift tensor data for the carbonyl and amide sites. Using their known crystal structures and aided by ab initio quantum chemical calculations for the resonance assignments, we elucidate trends relating local structure, hydrogen-bonding patterns, and chemical shift. We find good correlation between the backbone dihedral angles and the Cα1 and Cα2 shifts. For the C1 shift tensor, the δ11 value shifts downfield as the hydrogen-bond distance increases, δ22 shifts upfield, and δ33 shows little variation. The C2 shift tensor shows no appreciable correlation with structural parameters. For the N2 tensor, δ11 shows little dependence on the hydrogen-bond length, whereas δ22 and δ33 both show a decrease in shielding as the hydrogen bond shortens. Our analysis teases apart some, but not all, structural contributors to the observed differences the solid-state NMR chemical shifts.
Collapse
Affiliation(s)
- Benjamin D Altheimer
- Department of Chemistry and Biochemistry, Oberlin College , 119 Woodland Street, Oberlin, Ohio 44074, United States
| | | |
Collapse
|
6
|
Raju G, Singh S, Mutter AC, Everson BH, Cerda JF, Koder RL. An extended scope synthesis of an artificial safranine cofactor. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2014.03.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
7
|
Abstract
(1)H-, (11)B-, (13)C-, (15)N-, (17)O-, (19)F-, and (31)P-NMR chemical shifts of flavocoenzymes and derivatives of it, as well as of alloxazines and isoalloxazinium salts, from NMR experiments performed under various experimental conditions (e.g., dependence of the chemical shifts on temperature, concentration, solvent polarity, and pH) are reported. Also solid-state (13)C- and (15)N-NMR experiments are described revealing the anisotropic values of corresponding chemical shifts. These data, in combination with a number of coupling constants, led to a detailed description of the electronic structure of oxidized and reduced flavins. The data also demonstrate that the structure of oxidized flavin can assume a configuration deviating from coplanarity, depending on substitutions in the isoalloxazine ring, while that of reduced flavin exhibits several configurations, from almost planar to quite bended. The complexes formed between oxidized flavin and metal ions or organic molecules revealed three coordination sites with metal ions (depending on the chemical nature of the ion), and specific interactions between the pyrimidine moiety of flavin and organic molecules, mimicking specific interactions between apoflavoproteins and their coenzymes. Most NMR studies on flavoproteins were performed using (13)C- and (15)N-substituted coenzymes, either specifically enriched in the pterin moiety of flavin or uniformly labeled flavins. The chemical shifts of free flavins are used as a guide in the interpretation of the chemical shifts observed in flavoproteins. Although the hydrogen-bonding pattern in oxidized and reduced flavoproteins varies considerably, no correlation is obvious between these patterns and the corresponding redox potentials. In all reduced flavoproteins the N(1)H group of the flavocoenzyme is deprotonated, an exception is thioredoxin reductase. Three-dimensional structures of only a few flavoproteins, mostly belonging to the family of flavodoxins, have been solved. Also the kinetics of unfolding and refolding of flavodoxins has been investigated by NMR techniques. In addition, (31)P-NMR data of all so far studied flavoproteins and some (19)F-NMR spectra are discussed.
Collapse
Affiliation(s)
- Franz Müller
- , Wylstrasse 13, CH-6052, Hergiswil, Switzerland,
| |
Collapse
|
8
|
Raju G, Capo J, Lichtenstein BR, Cerda JF, Koder RL. Manipulating Reduction Potentials in an Artificial Safranin Cofactor. Tetrahedron Lett 2012; 53:1201-1203. [PMID: 23335821 DOI: 10.1016/j.tetlet.2011.12.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Safranines hold great promise as artificial flavin-like electron transfer cofactors with tunable properties. We report the design and chemical synthesis of the p-methoxy derivative of safranine O using a new synthetic route based on the Ulmann condensation. Spectroelectrochemical comparison of the purified parent safranine and this derivative demonstrates that the modification increases its two-electron reduction potential by 125 mV, or 5.75 kcal/mol. This modification also causes redshifts in the absorbance and fluorescence spectra of the cofactor, suggesting that it may find future utility in arrayed sensor applications.
Collapse
Affiliation(s)
- Gheevarghese Raju
- Department of Chemistry, The City College of New York, New York, NY 10031
| | | | | | | | | |
Collapse
|
9
|
|
10
|
Cui D, Koder RL, Dutton PL, Miller AF. 15N solid-state NMR as a probe of flavin H-bonding. J Phys Chem B 2011; 115:7788-98. [PMID: 21619002 DOI: 10.1021/jp202138d] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Flavins mediate a wide variety of chemical reactions in biology. To learn how one cofactor can be made to execute different reactions in different enzymes, we are developing solid-state NMR (SSNMR) to probe the flavin electronic structure, via the (15)N chemical shift tensor principal values (δ(ii)). We find that SSNMR has superior responsiveness to H-bonds, compared to solution NMR. H-bonding to a model of the flavodoxin active site produced an increase of 10 ppm in the δ(11) of N5, although none of the H-bonds directly engage N5, and solution NMR detected only a 4 ppm increase in the isotropic chemical shift (δ(iso)). Moreover SSNMR responded differently to different H-bonding environments, as H-bonding with water caused δ(11) to decrease by 6 ppm, whereas δ(iso) increased by less than 1 ppm. Our density functional theoretical (DFT) calculations reproduce the observations, validating the use of computed electronic structures to understand how H-bonds modulate the flavin's reactivity.
Collapse
Affiliation(s)
- Dongtao Cui
- Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, United States
| | | | | | | |
Collapse
|
11
|
Cerda JF, Koder RL, Lichtenstein BR, Moser CM, Miller AF, Dutton PL. Hydrogen bond-free flavin redox properties: managing flavins in extreme aprotic solvents. Org Biomol Chem 2008; 6:2204-12. [PMID: 18528583 DOI: 10.1039/b801952e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a simple, single step reaction that transforms riboflavin, which is insoluble in benzene, to tetraphenylacetyl riboflavin (TPARF), which is soluble in this solvent to over 250 mM. Electrochemical analysis of TPARF both alone and in complexes with two benzene-soluble flavin receptors: dibenzylamidopyridine (DBAP) and monobenzylamidopyridine (MBAP), prove that this model system behaves similarly to other previously studied flavin model systems which were soluble only in more polar solvents such as dichloromethane. Binding titrations in both benzene and dichloromethane show that the association constants of TPARF with its ligands are over an order of magnitude higher in benzene than dichloromethane, a consequence of the fact that benzene does not compete for H-bonds, but dichloromethane does. The alteration induced in the visible spectrum of TPARF in benzene upon the addition of DBAP is very similar to the difference produced by transfer to dichloromethane, further indicating that the flavin head group engages in a similar degree of hydrogen bonding with dichloromethane as with its ligands. This work underlines the importance of using a truly nonpolar solvent for the analysis of the effects of hydrogen bonding on the energetics of any biomimetic host-guest model system.
Collapse
Affiliation(s)
- Jose F Cerda
- The Johnson Research Foundation and Department of Biochemistry and Biophysics, The University of Pennsylvania, Philadelphia, PA 19104, USA
| | | | | | | | | | | |
Collapse
|
12
|
Koder RL, Lichtenstein BR, Cerda JF, Miller AF, Dutton PL. A Flavin Analogue with Improved Solubility in Organic Solvents. Tetrahedron Lett 2007; 48:5517-5520. [PMID: 19568318 PMCID: PMC2702786 DOI: 10.1016/j.tetlet.2007.05.165] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report the synthesis and initial electrochemical characterization of a benzene-soluble flavin analogue: N(10)-2,2-dibenzylethyl-7,8-dimethylisoalloxazine (DBF, 1). This analogue, which has an unmodified flavin headgroup, is intended for use in the spectroscopic examination of the electronic effects of flavin hydrogen bonding in simple model systems in aprotic, non-hydrogen bonding solvents. With future spectroscopic studies in mind, we have developed a synthetic route which allows the incorporation of isotopic labels using inexpensive starting materials.
Collapse
Affiliation(s)
- Ronald L. Koder
- The Johnson Research Foundation and Department of Biochemistry and Biophysics, the University of Pennsylvania, Philadelphia, PA, 19104
- Department of Physics, The City College of New York, New York, NY 10031
| | - Bruce R. Lichtenstein
- The Johnson Research Foundation and Department of Biochemistry and Biophysics, the University of Pennsylvania, Philadelphia, PA, 19104
| | - Jose F. Cerda
- The Johnson Research Foundation and Department of Biochemistry and Biophysics, the University of Pennsylvania, Philadelphia, PA, 19104
| | - Anne-Frances Miller
- The University of Kentucky Department of Chemistry, Lexington, KY 40506-0055
| | - P. Leslie Dutton
- The Johnson Research Foundation and Department of Biochemistry and Biophysics, the University of Pennsylvania, Philadelphia, PA, 19104
| |
Collapse
|