1
|
Voinov MA, Nunn N, Rana R, Davidsson A, Smirnov AI, Smirnova TI. Measuring local pH at interfaces from molecular tumbling: A concept for designing EPR-active pH-sensitive labels and probes. Org Biomol Chem 2024; 22:3652-3667. [PMID: 38647161 DOI: 10.1039/d4ob00167b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
Molecular probes and indicators are broadly employed for pH measurements in bulk media and at interfaces. The underlying physical principle of pH measurements of most of these probes is based on a change in the electronic structure that, for example, results in a shift of the emission peak of the fluorescence probes, changes in NMR chemical shifts due to the affected electronic shielding, or magnetic parameters of pH-sensitive nitroxides as measured by EPR. Here we explore another concept for measuring local protonation state of molecular tags based on changes in rotational dynamics of electron spin-bearing moieties that are readily detected by conventional continuous wave X-band EPR. Such changes are especially pronounced at biological interfaces, such as lipid bilayer membranes, due to the probe interactions with adjacent charges and polarizable dipoles. The concept was demonstrated by synthesizing a series of pH-sensitive nitroxides and spin-labelled phospholipids. EPR spectra of these newly synthesized nitroxides exhibit relatively small - about 0.5 G - changes in isotropic nitrogen hyperfine coupling constant upon reversible protonation. However, spin-labelled phospholipids incorporated into lipid bilayers demonstrated almost 6-fold change in rotational correlation time upon protonation, readily allowing for pKa determination from large changes in EPR spectra. The demonstrated concept of EPR-based pH measurements leads to a broader range of potential nitroxide structures that can serve as molecular pH sensors at the desired pH range and, thus, facilitates further development of spin-labelling EPR methods to study electrostatic phenomena at chemical and biological interfaces.
Collapse
Affiliation(s)
- Maxim A Voinov
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695, USA.
| | - Nicholas Nunn
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695, USA.
| | - Roshan Rana
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695, USA.
| | - Atli Davidsson
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695, USA.
| | - Alex I Smirnov
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695, USA.
| | - Tatyana I Smirnova
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695, USA.
| |
Collapse
|
2
|
Farafonov VS, Lebed AV, Nerukh DA, Mchedlov-Petrossyan NO. Estimation of Nanoparticle's Surface Electrostatic Potential in Solution Using Acid-Base Molecular Probes I: In Silico Implementation for Surfactant Micelles. J Phys Chem B 2023; 127:1022-1030. [PMID: 36655872 DOI: 10.1021/acs.jpcb.2c07012] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Surface electrostatic potential Ψ is a key characteristic of colloid particles. Since the surface of the particles adsorbs various compounds and facilitates chemical reactions between them, Ψ largely affects the properties of adsorbed reactants and governs the flow of chemical reactions occurring between them. One of the most popular methods for estimating Ψ in hydrophilic colloids, such as micellar surfactant solutions and related systems, is the application of molecular probes, predominantly acid-base indicator dyes. The Ψ value is calculated from the difference of the probe's indices of the apparent acidity constant between the examined colloid solution and, usually, some other colloid solution with noncharged particles. Here, we show how to implement this method in silico using alchemical free energy calculations within the framework of molecular dynamics simulations. The proposed implementation is tested on surfactant micelles and is shown to predict experimental Ψ values with quantitative accuracy depending on the kind of surfactant. The sources of errors in the method are discussed, and recommendations for its application are given.
Collapse
Affiliation(s)
- Vladimir S Farafonov
- Department of Physical Chemistry, V. N. Karazin National University, Kharkiv61022, Ukraine.,Department of Mathematics, Aston University, BirminghamB4 7ET, U.K
| | - Alexander V Lebed
- Department of Physical Chemistry, V. N. Karazin National University, Kharkiv61022, Ukraine
| | - Dmitry A Nerukh
- Department of Mathematics, Aston University, BirminghamB4 7ET, U.K
| | | |
Collapse
|
3
|
4-Dialkylamino-2,5-dihydroimidazol-1-oxyls with Functional Groups at the Position 2 and at the Exocyclic Nitrogen: The pH-Sensitive Spin Labels. Gels 2021; 8:gels8010011. [PMID: 35049546 PMCID: PMC8774874 DOI: 10.3390/gels8010011] [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: 12/02/2021] [Revised: 12/17/2021] [Accepted: 12/17/2021] [Indexed: 11/16/2022] Open
Abstract
Local acidity and electrostatic interactions are associated both with catalytic properties and the adsorption activity of various materials, and with the vital functions of biomolecules. The observation of acid–base equilibria in stable free radicals using EPR spectroscopy represents a convenient method for monitoring pH changes and the investigation of surface electrostatics, the advantages of which are especially evident in opaque and turbid samples and in porous materials such as xerogels. Imidazoline nitroxides are the most commonly used pH-sensitive spin probes and labels due to the high sensitivity of the parameters of the EPR spectra to pH changes, their small size, and their well-developed chemistry. In this work, several new derivatives of 4-(N,N-dialkylamino)-2,5-dihydrioimidazol-1-oxyl, with functional groups suitable for specific binding, were synthesized. The dependence of the parameters of their EPR spectra on pH was studied. Several showed a pKa close to 7.4, following the pH changes in a normal physiological range, and some demonstrated a monotonous change of the hyperfine coupling constant by 0.14 mT upon pH variation by four units.
Collapse
|
4
|
Dzikovski B, Khramtsov VV, Chandrasekaran S, Dunnam C, Shah M, Freed JH. Microsecond Exchange Processes Studied by Two-Dimensional ESR at 95 GHz. J Am Chem Soc 2020; 142:21368-21381. [PMID: 33305945 PMCID: PMC7810061 DOI: 10.1021/jacs.0c09469] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Exchange processes which include conformational change, protonation/deprotonation, and binding equilibria are routinely studied by 2D exchange NMR techniques, where information about the exchange of nuclei between environments with different NMR shifts is obtained from the development of cross-peaks. Whereas 2D NMR enables the real time study of millisecond and slower exchange processes, 2D ESR in the form of 2D-ELDOR (two-dimensional electron-electron double resonance) has the potential for such studies over the nanosecond to microsecond real time scales. Cross-peak development due to chemical exchange has been seen previously for semiquinones in ESR, but this is not possible for most common ESR probes, such as nitroxides, studied at typical ESR frequencies because, unlike NMR, the exchanging states yield ESR signals that are not resolved from each other within their respective line widths. But at 95 GHz, it becomes possible to resolve them in many cases because of the increased g-factor resolution. The 95 GHz instrumental developments occurring at ACERT now enable such studies. We demonstrate these new capabilities in two studies: (A) the protonation/deprotonation process for a pH-sensitive imidazoline spin label in aqueous solution where the exchange rate and the population ratio of the exchanging states are controlled by the concentration and pH of the buffer solution, respectively, and (B) a nitroxide radical partitioning between polar (aqueous) and nonpolar (phospholipid) environments in multilamellar lipid vesicles, where the cross-peak development arises from the exchange of the nitroxide between the two phases. This work represents the first example of the observation and analysis of cross-peaks arising from chemical exchange processes involving nitroxide spin labels.
Collapse
Affiliation(s)
- Boris Dzikovski
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Valery V Khramtsov
- In Vivo Multifunctional Magnetic Resonance Center, Robert C. Byrd Health Sciences Center, West Virginia University, and Department of Biochemistry, West Virginia University School of Medicine, Morgantown, West Virginia 26506, United States
| | - Siddarth Chandrasekaran
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Curt Dunnam
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Meera Shah
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Jack H Freed
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| |
Collapse
|
5
|
Exploring the pH-Induced Functional Phase Space of Human Serum Albumin by EPR Spectroscopy. MAGNETOCHEMISTRY 2018. [DOI: 10.3390/magnetochemistry4040047] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A systematic study on the self-assembled solution system of human serum albumin (HSA) and paramagnetic doxyl stearic acid (5-DSA and 16-DSA) ligands is reported covering the broad pH range 0.7–12.9, mainly using electron paramagnetic resonance (EPR) methods. It is tested to which extent the pH-induced conformational isomers of HSA reveal themselves in continuous wave (CW) EPR spectra from this spin probing approach in comparison to an established spin-labeling strategy utilizing 3-maleimido proxyl (5-MSL). Most analyses are conducted on empirical levels with robust strategies that allow for the detection of dynamic changes of ligand, as well as protein. Special emphasis has been placed on the EPR spectroscopic detection of a molten globule (MG) state of HSA that is typically found by the fluorescent probe 8-Anilino- naphthalene-1-sulfonic acid (ANS). Moreover, four-pulse double electron-electron resonance (DEER) experiments are conducted and substantiated with dynamic light scattering (DLS) data to determine changes in the solution shape of HSA with pH. All results are ultimately combined in a detailed scheme that describes the pH-induced functional phase space of HSA.
Collapse
|
6
|
Voinov MA, Scheid CT, Kirilyuk IA, Trofimov DG, Smirnov AI. IKMTSL-PTE, a Phospholipid-Based EPR Probe for Surface Electrostatic Potential of Biological Interfaces at Neutral pH: Effects of Temperature and Effective Dielectric Constant of the Solvent. J Phys Chem B 2017; 121:2443-2453. [DOI: 10.1021/acs.jpcb.7b00592] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Maxim A. Voinov
- Department
of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695-8204, United States
| | - Christina T. Scheid
- Department
of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695-8204, United States
| | - Igor A. Kirilyuk
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Lavrentiev Avenue 9, Novosibirsk 630090, Russia
- Novosibirsk State University, Pirogova
Street 2, Novosibirsk 630090, Russia
| | - Dmitrii G. Trofimov
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Lavrentiev Avenue 9, Novosibirsk 630090, Russia
| | - Alex I. Smirnov
- Department
of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695-8204, United States
| |
Collapse
|
7
|
Majumder R, Sarkar Y, Das S, Ray A, Parui PP. Interfacial pH and polarity detection of amphiphilic self-assemblies using a single Schiff-base molecule. NEW J CHEM 2017. [DOI: 10.1039/c7nj01222e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The interfacial pH and polarity for different amphiphilic self-assemblies are estimated at a similar interfacial depth utilizing a unique Schiff-base molecule containing two identical phenol-conjugated-imine moieties.
Collapse
Affiliation(s)
- Rini Majumder
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
| | - Yeasmin Sarkar
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
| | - Sanju Das
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
- Department of Chemistry
| | - Ambarish Ray
- Department of Chemistry
- Maulana Azad College
- Kolkata 700013
- India
| | | |
Collapse
|
8
|
Kovaleva EG, Molochnikov LS, Stepanova DP, Pestov AV, Trofimov DG, Kirilyuk IA, Smirnov AI. Interfacial Electrostatic Properties of Hydrated Mesoporous and Nanostructured Alumina Powders by Spin Labeling EPR. Cell Biochem Biophys 2016; 75:159-170. [PMID: 27815780 DOI: 10.1007/s12013-016-0767-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2016] [Accepted: 10/14/2016] [Indexed: 11/24/2022]
Abstract
Acid-base equilibria and interfacial electrostatic properties of hydrated mesoporous and nanostructured alumina powders are determining factors for the use of these materials in heterogeneous catalysis and as a sorption media for filtration and chromatographic applications including life sciences. Here spin probe electron paramagnetic resonance spectroscopy of pH-sensitive nitroxides was employed to evaluate the surface charge and interfacial acid-base equilibria at the pore surface of mesoporous powders of α-Al2O3, γ-Al2O3, Al2O3 × nH2O, and basic γ-Al2O3 and nanostructured Al2O3 in the form of pristine materials and modified with aluminum-tri-sec-butoxide, hydroxyaluminum glycerate, and several phospholipids. A new pH-sensitive nitroxide probe, 4-dimethylamino-5,5-dimethyl-2-(4-(chloromethyl)phenyl)-2-ethyl-2,5-dihydro-1H-imidazol-1-oxyl hydrochloride semihydrate (nitroxide R1), has been synthesized and characterized. It was found that conditions of preparation of alumina powders exert strikingly large effects on the apparent pK a of nitroxides measured from electron paramagnetic resonance titration curves. Specifically, while the electron paramagnetic resonance titrations curves for the nitroxide R1 in mesoporous powders prepared from basic γ-Al2O3 and Al2O3 × nH2O were shifted by ΔpK a≈ +0.6 and up to ≈ +1.2 pH units respectively, the shift for γ-Al2O3 was found to be much higher: ΔpK a = +3.5. Assuming approximately the same ∆pH = 0.5-1.0 arising from a difference in the hydrogen ion activity between the bulk solution phase and that in a confined pore volume, the samples were ranked in the following order of descending magnitude of the effective surface electrostatic potential Ψ: mesoporous γ-Al2O3 > Al2O3 × nH2O > basic γ-Al2O3 > α-Al2O3. Conditions of the Al2O3 synthesis as well as the surface modification procedures were found to have profound effects on the interfacial electrostatic properties of hydrated samples that are likely related to the nature and concentration of the active sites on the alumina surfaces.
Collapse
Affiliation(s)
- Elena G Kovaleva
- Institute of Chemical Engineering, Ural Federal University, 19 Mira St., Yekaterinburg, 620002, Russian Federation.
| | - Leonid S Molochnikov
- Department of Chemistry, Ural State Forest Engineering University, 37 Siberian Highway, Yekaterinburg, 620100, Russian Federation.
| | - Darya P Stepanova
- Institute of Chemical Engineering, Ural Federal University, 19 Mira St., Yekaterinburg, 620002, Russian Federation
| | - Alexander V Pestov
- Laboratory of Organic Materials, I.Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, Akademicheskaya / S. Kovalevskoi, 22/20, Ekaterinburg, 620990, Russian Federation
| | - Dmitrii G Trofimov
- Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Akad. Lavrent'ev Av. 9, Novosibirsk, 630090, Russian Federation
| | - Igor A Kirilyuk
- Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Akad. Lavrent'ev Av. 9, Novosibirsk, 630090, Russian Federation
- Novosibirsk State University, Pirogova Str. 2, Novosibirsk, 630090, Russian Federation
| | - Alex I Smirnov
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC, 27695-8204, USA.
| |
Collapse
|
9
|
Clear KJ, Virga K, Gray L, Smith BD. Using membrane composition to fine-tune the p Ka of an optical liposome pH sensor. JOURNAL OF MATERIALS CHEMISTRY. C 2016; 4:2925-2930. [PMID: 27087967 PMCID: PMC4830428 DOI: 10.1039/c5tc03480a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Liposomes containing membrane-anchored pH-sensitive optical probes are valuable sensors for monitoring pH in various biomedical samples. The dynamic range of the sensor is maximized when the probe pKa is close to the expected sample pH. While some biomedical samples are close to neutral pH there are several circumstances where the pH is 1 or 2 units lower. Thus, there is a need to fine-tune the probe pKa in a predictable way. This investigation examined two lipid-conjugated optical probes, each with appended deep-red cyanine dyes containing indoline nitrogen atoms that are protonated in acid. The presence of anionic phospholipids in the liposomes stabilized the protonated probes and increased the probe pKa values by < 1 unit. The results show that rational modification of the membrane composition is a general non-covalent way to fine-tune the pKa of an optical liposome sensor for optimal pH sensing performance.
Collapse
|
10
|
Sarkar Y, Das S, Ray A, Jewrajka SK, Hirota S, Parui PP. A simple interfacial pH detection method for cationic amphiphilic self-assemblies utilizing a Schiff-base molecule. Analyst 2016; 141:2030-9. [DOI: 10.1039/c5an02128f] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
A simple pH-sensing method to monitor interfacial pH deviation from the bulk pH for cationic micelle and vesicle is introduced by estimating the change in the Schiff-base molecule (AH) proton dissociation between interface and bulk.
Collapse
Affiliation(s)
- Yeasmin Sarkar
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
| | - Sanju Das
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
- Department of Chemistry
| | - Ambarish Ray
- Department of Chemistry
- Maulana Azad College
- Kolkata 700013
- India
| | - Suresh K. Jewrajka
- CSIR-Central Salt & Marine Chemicals Research Institute
- Gujarat-364002
- India
| | - Shun Hirota
- Graduate School of Materials Science
- Nara Institute of Science and Technology
- Nara 630-0192
- Japan
| | | |
Collapse
|
11
|
Voinov MA, Smirnov AI. Ionizable Nitroxides for Studying Local Electrostatic Properties of Lipid Bilayers and Protein Systems by EPR. Methods Enzymol 2015; 564:191-217. [PMID: 26477252 PMCID: PMC5008871 DOI: 10.1016/bs.mie.2015.08.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Electrostatic interactions are known to play a major role in the myriad of biochemical and biophysical processes. Here, we describe biophysical methods to probe local electrostatic potentials of proteins and lipid bilayer systems that are based on an observation of reversible protonation of nitroxides by electron paramagnetic resonance (EPR). Two types of probes are described: (1) methanethiosulfonate derivatives of protonatable nitroxides for highly specific covalent modification of the cysteine's sulfhydryl groups and (2) spin-labeled phospholipids with a protonatable nitroxide tethered to the polar head group. The probes of both types report on their ionization state through changes in magnetic parameters and degree of rotational averaging, thus, allowing the electrostatic contribution to the interfacial pKa of the nitroxide, and, therefore, the local electrostatic potential to be determined. Due to their small molecular volume, these probes cause a minimal perturbation to the protein or lipid system. Covalent attachment secures the position of the reporter nitroxides. Experimental procedures to characterize and calibrate these probes by EPR, and also the methods to analyze the EPR spectra by simulations are outlined. The ionizable nitroxide labels and the nitroxide-labeled phospholipids described so far cover an exceptionally wide range of ca. 2.5-7.0 pH units, making them suitable to study a broad range of biophysical phenomena, especially at the negatively charged lipid bilayer surfaces. The rationale for selecting proper electrostatically neutral interface for probe calibration, and examples of lipid bilayer surface potential studies, are also described.
Collapse
Affiliation(s)
- Maxim A Voinov
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina, USA
| | - Alex I Smirnov
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina, USA.
| |
Collapse
|
12
|
Bagryanskaya EG, Krumkacheva OA, Fedin MV, Marque SR. Development and Application of Spin Traps, Spin Probes, and Spin Labels. Methods Enzymol 2015; 563:365-96. [DOI: 10.1016/bs.mie.2015.06.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
|
13
|
Afri M, Alexenberg C, Aped P, Bodner E, Cohen S, Ejgenburg M, Eliyahu S, Gilinsky-Sharon P, Harel Y, Naqqash ME, Porat H, Ranz A, Frimer AA. NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer. Chem Phys Lipids 2014; 184:105-18. [DOI: 10.1016/j.chemphyslip.2014.07.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2014] [Revised: 07/10/2014] [Accepted: 07/21/2014] [Indexed: 01/20/2023]
|
14
|
Towards label-free and site-specific probing of the local pH in proteins: pH-dependent deep UV Raman spectra of histidine and tyrosine. J Mol Struct 2014. [DOI: 10.1016/j.molstruc.2014.03.053] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
|
15
|
Kovaleva EG, Molochnikov LS, Parshina EV, Shishmakov AB, Mikushina YV, Kirilyuk IA, Grigor’ev IA. Effect of the surface charge on the complexing and catalytic properties of Cu2+-containing composite materials based on zirconia and powdered cellulose. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY B 2014. [DOI: 10.1134/s199079311403021x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
|
16
|
Chipem FAS, Behera SK, Krishnamoorthy G. Enhancing Excited State Intramolecular Proton Transfer in 2-(2′-Hydroxyphenyl)benzimidazole and Its Nitrogen-Substituted Analogues by β-Cyclodextrin: The Effect of Nitrogen Substitution. J Phys Chem A 2013; 117:4084-95. [DOI: 10.1021/jp311438s] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Francis A. S. Chipem
- Department
of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
| | - Santosh Kumar Behera
- Department
of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
| | - G. Krishnamoorthy
- Department
of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
| |
Collapse
|
17
|
Voinov MA, Rivera-Rivera I, Smirnov AI. Surface electrostatics of lipid bilayers by EPR of a pH-sensitive spin-labeled lipid. Biophys J 2013; 104:106-16. [PMID: 23332063 DOI: 10.1016/j.bpj.2012.11.3806] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2012] [Revised: 10/02/2012] [Accepted: 11/13/2012] [Indexed: 01/21/2023] Open
Abstract
Many biophysical processes such as insertion of proteins into membranes and membrane fusion are governed by bilayer electrostatic potential. At the time of this writing, the arsenal of biophysical methods for such measurements is limited to a few techniques. Here we describe a, to our knowledge, new spin-probe electron paramagnetic resonance (EPR) approach for assessing the electrostatic surface potential of lipid bilayers that is based on a recently synthesized EPR probe (IMTSL-PTE) containing a reversibly ionizable nitroxide tag attached to the lipids' polar headgroup. EPR spectra of the probe directly report on its ionization state and, therefore, on electrostatic potential through changes in nitroxide magnetic parameters and the degree of rotational averaging. Further, the lipid nature of the probe provides its full integration into lipid bilayers. Tethering the nitroxide moiety directly to the lipid polar headgroup defines the location of the measured potential with respect to the lipid bilayer interface. Electrostatic surface potentials measured by EPR of IMTSL-PTE show a remarkable (within ±2%) agreement with the Gouy-Chapman theory for anionic DMPG bilayers in fluid (48°C) phase at low electrolyte concentration (50 mM) and in gel (17°C) phase at 150-mM electrolyte concentration. This agreement begins to diminish for DMPG vesicles in gel phase (17°C) upon varying electrolyte concentration and fluid phase bilayers formed from DMPG/DMPC and POPG/POPC mixtures. Possible reasons for such deviations, as well as the proper choice of an electrostatically neutral reference interface, have been discussed. Described EPR method is expected to be fully applicable to more-complex models of cellular membranes.
Collapse
Affiliation(s)
- Maxim A Voinov
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina, USA
| | | | | |
Collapse
|
18
|
Yeo SJ, Kang H, Kim YH, Han S, Yoo PJ. Layer-by-layer assembly of polyelectrolyte multilayers in three-dimensional inverse opal structured templates. ACS APPLIED MATERIALS & INTERFACES 2012; 4:2107-2115. [PMID: 22439630 DOI: 10.1021/am300072p] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A novel means of layer-by-layer deposition (LbL) of polyelectrolyte multilayers on three-dimensionally porous inverse opal (3D-IO) structures is presented. The 3D-IO structures comprising UV-curable polymer are highly flexible and can be readily demonstrated as free-standing films with double-sided open porosity over a large scale. A conflict between the intrinsically hydrophobic polymeric structures and waterborne characteristics of the LbL deposition process is overcome by employing a mixed solvent system of water and alcohol. The deposition pH of the LbL assembly can strongly affect the charge density and the degree of entanglement of polyelectrolyte chains, resulting in contrastingly different film deposition and growth behaviors. Since this method utilizes a three-dimensionally structured surface as a deposition substrate, 3D-IO films with a thickness of tens of micrometers can be uniformly and completely deposited with polyelectrolyte multilayers using only several tens of bilayer depositions, which can offer a new pathway of fabricating functionalized polymeric films. Finally, the LbL treated 3D-IO films are applied to nanofiltration membranes for removing multivalent metallic cations. Due to the enhanced Donnan exclusion effect as a result of multiple interfaces formed inside the 3D-IO structures and the relatively large volumetric ratio of water-permeable polyelectrolyte complexes, outstanding membrane performance was observed. Specifically, a good rejection rate of metal ions was achieved even under highly diluted feed conditions without sacrificing the high permeation flux.
Collapse
Affiliation(s)
- Seon Ju Yeo
- School of Chemical Engineering, Sungkyunkwan University, Suwon, Republic of Korea
| | | | | | | | | |
Collapse
|
19
|
Abstract
Stable nitroxyl radicals are important tools in chemistry, biophysics, biology, and materials science. Their stability and the sensitivity of their EPR spectra to the local environment make them valuable molecular probes. This review seeks to give an overview of the developments in the field of nitroxide spin probes and their various applications, with the main focus on the pH-sensitive imidazoline nitroxide family.
Collapse
Affiliation(s)
- Evelyn Zottler
- Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria
| | - Georg Gescheidt
- Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria
| |
Collapse
|
20
|
Lomize AL, Pogozheva ID, Mosberg HI. Anisotropic solvent model of the lipid bilayer. 2. Energetics of insertion of small molecules, peptides, and proteins in membranes. J Chem Inf Model 2011; 51:930-46. [PMID: 21438606 DOI: 10.1021/ci200020k] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
A new computational approach to calculating binding energies and spatial positions of small molecules, peptides, and proteins in the lipid bilayer has been developed. The method combines an anisotropic solvent representation of the lipid bilayer and universal solvation model, which predicts transfer energies of molecules from water to an arbitrary medium with defined polarity properties. The universal solvation model accounts for hydrophobic, van der Waals, hydrogen-bonding, and electrostatic solute-solvent interactions. The lipid bilayer is represented as a fluid anisotropic environment described by profiles of dielectric constant (ε), solvatochromic dipolarity parameter (π*), and hydrogen bonding acidity and basicity parameters (α and β). The polarity profiles were calculated using published distributions of quasi-molecular segments of lipids determined by neutron and X-ray scattering for DOPC bilayer and spin-labeling data that define concentration of water in the lipid acyl chain region. The model also accounts for the preferential solvation of charges and polar groups by water and includes the effect of the hydrophobic mismatch for transmembrane proteins. The method was tested on calculations of binding energies and preferential positions in membranes for small-molecules, peptides and peripheral membrane proteins that have been experimentally studied. The new theoretical approach was implemented in a new version (2.0) of our PPM program and applied for the large-scale calculations of spatial positions in membranes of more than 1000 peripheral and integral proteins. The results of calculations are deposited in the updated OPM database ( http://opm.phar.umich.edu ).
Collapse
Affiliation(s)
- Andrei L Lomize
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan , 428 Church St., Ann Arbor, Michigan 48109-1065, USA.
| | | | | |
Collapse
|
21
|
Parshina EV, Molochnikov LS, Kovaleva EG, Shishmakov AB, Mikushina YV, Kirilyuk IA, Grigor’ev IA. Medium acidity and catalytic properties of composite materials based on silica and titania and powder cellulose in the presence of Cu2+ ions. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2011. [DOI: 10.1134/s003602441103023x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
|
22
|
Dash N, Chipem FAS, Krishnamoorthy G. Encapsulation of 2-(4′-N,N-dimethylamino)phenylimidazo[4,5-b]pyridine in β-cyclodextrin: effect on H-bond-induced intramolecular charge transfer emission. Photochem Photobiol Sci 2009; 8:1708-15. [DOI: 10.1039/b9pp00023b] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|