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Ekholm V, Caleman C, Hub JS, Wohlert M. Propensity, free energy contributions and conformation of primary n-alcohols at a water surface. Phys Chem Chem Phys 2021; 23:18823-18829. [PMID: 34612420 DOI: 10.1039/d1cp02818a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Atmospheric aerosols contain organic molecules that serve as cloud condensation nucleation sites and affect the climate. Several experimental and simulation studies have been dedicated to investigate their surface propensity, but the mechanisms that drive them to the water surface are still not fully understood. In this molecular dynamics (MD) simulation study, primary alcohols are considered as a model system representing polar organic molecules. We find that the surface affinity of n-alcohols increases linearly with the length of the hydrophobic tail. By decomposing the adsorption free energy into enthalpy and entropy contributions, we find that the transition from bulk to surface is entropically driven, compatible with the fact that the hydrophobic effect of small solutes is of entropic origin. The enthalpy of surface adsorption is nearly invariant among different n-alcohols because the loss of solvent-alcohol interactions is balanced by a gain in solvent-solvent interactions. Structural analysis shows that, at the surface, the linear alcohols prefer an orientation with the hydrophobic tail pointing out from the surface, whereas the hydroxyl group remains buried in the water. This general behaviour is likely transferable to other small molecules with similar structures but other functional groups that are present in the atmosphere. Therefore, the present study is a step forward toward a general description of organic molecules in aerosols.
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2
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Herboth R, Gopakumar G, Caleman C, Wohlert M. Charge State Dependence of Amino Acid Propensity at Water Surface: Mechanisms Elucidated by Molecular Dynamics Simulations. J Phys Chem A 2021; 125:4705-4714. [PMID: 34042438 PMCID: PMC8279654 DOI: 10.1021/acs.jpca.0c10963] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Revised: 04/19/2021] [Indexed: 11/28/2022]
Abstract
Atmospheric aerosols contain a variety of compounds, among them free amino acids and salt ions. The pH of the aerosol droplets depends on their origin and environment. Consequently, compounds like free amino acids found in the droplets will be at different charge states, since these states to a great extent depend on the surrounding pH condition. In droplets of marine origin, amino acids are believed to drive salt ions to the water surface and a pH-dependent amino acid surface propensity will, therefore, indirectly affect many processes in atmospheric chemistry and physics such as for instance cloud condensation. To understand the surface propensity of glycine, valine, and phenylalanine at acidic, neutral, and basic pH, we used molecular dynamics (MD) simulations to investigate them at three different charge states in water. Their respective surface propensities were obtained by the means of a potential of mean force (PMF) in an umbrella sampling approach. Glycine was found to have no preference for the surface, while both valine and phenylalanine showed high propensities. Among the charge states of the surface-enriched ones, the cation, representing the amino acids at low pH, was found to have the highest affinity. Free energy decomposition revealed that the driving forces depend strongly on the nature of the amino acid and its charge state. In phenylalanine, the main factor was found to be a substantial entropy gain, likely related to the side chain, whereas in valine, hydrogen bonding to the functional groups leads to favorable energies and, in turn, affects the surface propensity. A significant gain in water-water enthalpy was seen for both valine and phenylalanine.
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Affiliation(s)
- Radost Herboth
- Department
of Materials Science and Engineering, Uppsala
University, Box 35, 751 03 Uppsala, Sweden
| | - Geethanjali Gopakumar
- Department
of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Carl Caleman
- Department
of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
- Center
for Free-Electron Laser Science, DESY, Notkestraße 85, 226 07 Hamburg, Germany
| | - Malin Wohlert
- Department
of Materials Science and Engineering, Uppsala
University, Box 35, 751 03 Uppsala, Sweden
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3
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Dupuy R, Richter C, Winter B, Meijer G, Schlögl R, Bluhm H. Core level photoelectron spectroscopy of heterogeneous reactions at liquid-vapor interfaces: Current status, challenges, and prospects. J Chem Phys 2021; 154:060901. [PMID: 33588531 DOI: 10.1063/5.0036178] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Liquid-vapor interfaces, particularly those between aqueous solutions and air, drive numerous important chemical and physical processes in the atmosphere and in the environment. X-ray photoelectron spectroscopy is an excellent method for the investigation of these interfaces due to its surface sensitivity, elemental and chemical specificity, and the possibility to obtain information on the depth distribution of solute and solvent species in the interfacial region. In this Perspective, we review the progress that was made in this field over the past decades and discuss the challenges that need to be overcome for investigations of heterogeneous reactions at liquid-vapor interfaces under close-to-realistic environmental conditions. We close with an outlook on where some of the most exciting and promising developments might lie in this field.
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Affiliation(s)
- Rémi Dupuy
- Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Clemens Richter
- Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Bernd Winter
- Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Gerard Meijer
- Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Robert Schlögl
- Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Hendrik Bluhm
- Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
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Li J, Janoušková O, Fernandez-Alvarez R, Mesíková S, Tošner Z, Kereïche S, Uchman M, Matějíček P. Designed Boron-Rich Polymeric Nanoparticles Based on Nano-ion Pairing for Boron Delivery. Chemistry 2020; 26:14283-14289. [PMID: 32492217 DOI: 10.1002/chem.202001699] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Indexed: 12/13/2022]
Abstract
Boron-rich particles with the boron fraction ca.10-20 wt % of controllable shape and size that can be easily prepared via simple ion co-assembly are promising material for tumor treatment by boron neutron capture therapy. Electroneutral, dynamic core-shell polymeric nanoparticles were prepared by co-assembly of cationic PEO-block-PGEA diblock copolymer with sodium closo-dodecaborate, Na2 [B12 H12 ]. This is the first example of polymer nanoparticles based on [B12 H12 ]2- nano-ion pairing. The high [B12 H12 ]2- loading is proven by calorimetry at physiological salt concentration. As a result of rational design, rod-, worm- and sphere-like particles were produced and further tested using human glioblastoma and cervical carcinoma cell lines. Rod-like particles yielded the highest internalization capability in all tested cell lines.
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Affiliation(s)
- Jianwei Li
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43, Prague 2, Czech Republic
| | - Olga Janoušková
- Institute of Macromolecular Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 16206, Prague 6, Czech Republic
| | - Roberto Fernandez-Alvarez
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43, Prague 2, Czech Republic
| | - Soňa Mesíková
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43, Prague 2, Czech Republic
| | - Zdeněk Tošner
- NMR laboratory, Faculty of Science, Charles University in Prague, Hlavova 2030, 128 43, Prague 2, Czech Republic
| | - Sami Kereïche
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43, Prague 2, Czech Republic.,Institute of Biology and Medical Genetics, First Faculty of Medicine, Charles University and General University Hospital in Prague, Purkynie Ustav, Albertov 4, 12 801, Prague, Czech Republic
| | - Mariusz Uchman
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43, Prague 2, Czech Republic
| | - Pavel Matějíček
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43, Prague 2, Czech Republic
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5
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Persson I, Werner J, Björneholm O, Blanco YS, Topel Ö, Bajnóczi ÉG. Solution chemistry in the surface region of aqueous solutions. PURE APPL CHEM 2020. [DOI: 10.1515/pac-2019-1106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Solution chemistry is commonly regarded as the physical chemistry of reactions and chemical equilibria taking place in the bulk of a solvent, and between solutes in solution, and solids or gases in contact with the solution. Our knowledge about such reactions and equilibria in aqueous solution is very detailed such as their physico–chemical constants at varying temperature, pressure, ionic medium and strength. In this paper the solution chemistry in the surface region of aqueous solutions, down to ca. 10 Å below the water–air interface, will be discussed. In this region, the density and relative permittivity are significantly smaller than in the aqueous bulk strongly affecting the chemical behaviour of solutes. Surface sensitive X-ray spectroscopic methods have recently been applicable on liquids and solutions by use of liquid jets. This allows the investigation of the speciation of compounds present in the water–air interface and the surface region, a region hardly studied before. Speciation studies show overwhelmingly that neutral molecules are accumulated in the surface region, while charged species are depleted from it. It has been shown that the equilibria between aqueous bulk, surface region, solids and/or air are very fast allowing effective transport of chemicals over the aqueous surface region.
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Affiliation(s)
- Ingmar Persson
- Department of Molecular Sciences , Swedish University of Agricultural Sciences , P.O. Box 7015 , SE-750 07 , Uppsala , Sweden
| | - Josephina Werner
- Department of Molecular Sciences , Swedish University of Agricultural Sciences , P.O. Box 7015 , SE-750 07 , Uppsala , Sweden
- Department of Physics and Astronomy , Uppsala University , P.O. Box 516 , SE-751 20 , Uppsala , Sweden
| | - Olle Björneholm
- Department of Physics and Astronomy , Uppsala University , P.O. Box 516 , SE-751 20 , Uppsala , Sweden
| | - Yina Salamanca Blanco
- Department of Molecular Sciences , Swedish University of Agricultural Sciences , P.O. Box 7015 , SE-750 07 , Uppsala , Sweden
| | - Önder Topel
- Department of Molecular Sciences , Swedish University of Agricultural Sciences , P.O. Box 7015 , SE-750 07 , Uppsala , Sweden
| | - Éva G. Bajnóczi
- Department of Molecular Sciences , Swedish University of Agricultural Sciences , P.O. Box 7015 , SE-750 07 , Uppsala , Sweden
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6
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Palanisamy K, Prakash M, Rajapandian V. Combined DFT and MD simulation studies of protein stability on imidazolium–water (ImH+Wn) clusters with aromatic amino acids. NEW J CHEM 2020. [DOI: 10.1039/d0nj03085f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The hydrated clusters of protonated imidazole (ImH+) can induce protein denaturation through various kinds of monovalent interactions such as cation···π (stacking), N–H⋯π (T-shaped) and water-mediated O–H⋯O H-bonds.
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Affiliation(s)
- Kandhan Palanisamy
- Department of Chemistry, Faculty of Engineering and Technology, SRM Institute of Science and Technology, SRM Nagar
- Kattankulathur-603203
- India
| | - Muthuramalingam Prakash
- Department of Chemistry, Faculty of Engineering and Technology, SRM Institute of Science and Technology, SRM Nagar
- Kattankulathur-603203
- India
| | - Varatharaj Rajapandian
- Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science
- Coimbatore-641020
- India
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Blanco YS, Topel Ö, Bajnóczi ÉG, Werner J, Björneholm O, Persson I. Chemical equilibria of aqueous ammonium-carboxylate systems in aqueous bulk, close to and at the water-air interface. Phys Chem Chem Phys 2019; 21:12434-12445. [PMID: 31143906 DOI: 10.1039/c9cp02449b] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Previous studies have shown that the water-air interface and a number of water molecule layers just below it, the surface region, have significantly different physico-chemical properties, such as lower relative permittivity and density, than bulk water. The properties in the surface region of water favor weakly hydrated species as neutral molecules, while ions requiring strong hydration and shielding of their charge are disfavored. In this study the equilibria NH4+(aq) + RCOO-(aq) ⇌ NH3(aq) + RCOOH(aq) are investigated for R = CnH2n+1, n = 0-8, as open systems, where ammonia and small carboxylic acids in the gas phase above the water surface are removed from the system by a gentle controlled flow of nitrogen to mimic the transport of volatile compounds from water droplets into air. It is shown that this non-equilibrium transport of chemicals can be sufficiently large to cause a change of the chemical content of the aqueous bulk. Furthermore, X-ray photoelectron spectroscopy (XPS) has been used to determine the relative concentration of alkyl carboxylic acids and their conjugated alkyl carboxylates in aqueous surfaces using a micro-jet. These studies confirm that neutral alkyl carboxylic acids are accumulated in the surface region, while charged species, as alkyl carboxylates, are depleted. The XPS studies show also that the hydrophobic alkyl chains are oriented upwards into regions with lower relative permittivity and density, thus perpendicular to the aqueous surface. These combined results show that there are several chemical equilibria between the aqueous bulk and the surface region. The analytical studies show that the release of mainly ammonia is dependent on its concentration in the surface region, as long as the solubility of the carboxylic acid in the surface region is sufficiently high to avoid a precipitation in/on the water-air interface. However, for n-octyl- and n-nonylcarboxylic acid the solubility is sufficiently low to cause precipitation. The combined analytical and surface speciation studies in this work show that the equilibria involving the surface region are fast. The results from this study increase the knowledge about the distribution of chemical species in the surface region at and close to the water-air interface, and the transport of chemicals from water to air in open systems.
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Affiliation(s)
- Yina Salamanca Blanco
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden.
| | - Önder Topel
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden.
| | - Éva G Bajnóczi
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden.
| | - Josephina Werner
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden. and Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala, Sweden
| | - Olle Björneholm
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala, Sweden
| | - Ingmar Persson
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden.
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8
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Balamurugan K, Prakash M, Subramanian V. Theoretical Insights into the Role of Water Molecules in the Guanidinium-Based Protein Denaturation Process in Specific to Aromatic Amino Acids. J Phys Chem B 2019; 123:2191-2202. [PMID: 30672268 DOI: 10.1021/acs.jpcb.8b08968] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Noncovalent interactions between the guanidinium cation (Gdm+) and aromatic amino acids (AAs) in the water molecules have been studied using quantum chemical calculation and molecular dynamics (MD) simulations. Our studies show that there are two different modes of interactions between Gdm+ and AAs with and without water molecules. It is observed that nonhydrated Gdm+ interacts with AAs through N-H···π interactions, whereas hydrated clusters of Gdm+ are stabilized by stacking interactions with the help of the water-mediated hydrogen bond. Thus, different hydration patterns have significant effects on the predominant cation···π interactions in AAs-Gdm+ complexes. Findings from MD simulation elicit that the interaction pattern of Gdm+ with AAs varies as Phe < Tyr < Trp. Both the QM and MD calculations show a similar trend in the interaction of AAs with Gdm+. Moreover, the interaction of AAs with Gdm+ depends on the spatial orientation of AAs in the protein and the concomitant local structure, that is, the AAs present in the unstructured region of protein such as coils and bends exhibit higher binding for Gdm+ when compared to the AAs present in the structured region of the protein such as the α-helix and the β-sheet. Our study clearly reveals that H-bonded water molecules and the hydration pattern of Gdm+ as well as the positional presence of these AAs in the protein structure context play determining roles in the denaturation of protein by the Gdm+ cation.
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Affiliation(s)
- Kanagasabai Balamurugan
- Chemical Laboratory , CSIR-Central Leather Research Institute , Adyar, Chennai 600 020 , India
| | - Muthuramalingam Prakash
- Chemical Laboratory , CSIR-Central Leather Research Institute , Adyar, Chennai 600 020 , India
| | - Venkatesan Subramanian
- Chemical Laboratory , CSIR-Central Leather Research Institute , Adyar, Chennai 600 020 , India.,Academy of Scientific and Innovative Research (AcSIR) , CSIR-CLRI Campus , Chennai 600 020 , India
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9
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Ekholm V, Caleman C, Bjärnhall Prytz N, Walz MM, Werner J, Öhrwall G, Rubensson JE, Björneholm O. Strong enrichment of atmospherically relevant organic ions at the aqueous interface: the role of ion pairing and cooperative effects. Phys Chem Chem Phys 2018; 20:27185-27191. [PMID: 30339167 DOI: 10.1039/c8cp04525a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Surface affinity, orientation and ion pairing are investigated in mixed and single solute systems of aqueous sodium hexanoate and hexylammonium chloride. The surface sensitive X-ray photoelectron spectroscopy technique has been used to acquire the experimental results, while the computational data have been calculated using molecular dynamics simulations. By comparing the single solute solutions with the mixed one, we observe a non-linear surface enrichment and reorientation of the organic ions with their alkyl chains pointing out of the aqueous surface. We ascribe this effect to ion paring between the charged functional groups on the respective organic ion and hydrophobic expulsion of the alkyl chains from the surface in combination with van der Waals interactions between the alkyl chains. These cooperative effects lead to a substantial surface enrichment of organic ions, with consequences for aerosol surface properties.
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Affiliation(s)
- Victor Ekholm
- Dep. of Phys. & Astron., Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
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Werner J, Persson I, Björneholm O, Kawecki D, Saak CM, Walz MM, Ekholm V, Unger I, Valtl C, Caleman C, Öhrwall G, Prisle NL. Shifted equilibria of organic acids and bases in the aqueous surface region. Phys Chem Chem Phys 2018; 20:23281-23293. [PMID: 30191936 PMCID: PMC6146375 DOI: 10.1039/c8cp01898g] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Acid-base equilibria of carboxylic acids and alkyl amines in the aqueous surface region were studied using surface-sensitive X-ray photoelectron spectroscopy and molecular dynamics simulations. Solutions of these organic compounds were examined as a function of pH, concentration and chain length to investigate the distribution of acid and base form in the surface region as compared to the aqueous bulk. Results from these experiments show that the neutral forms of the studied acid-base pairs are strongly enriched in the aqueous surface region. Moreover, we show that for species with at least four carbon atoms in their alkyl-chain, their charged forms are also found to be abundant in the surface region. Using a combination of XPS and MD results, a model is proposed that effectively describes the surface composition. Resulting absolute surface concentration estimations show clearly that the total organic mole fractions in the surface region change drastically as a function of solution pH. The origin of the observed surface phenomena, hydronium/hydroxide concentrations in the aqueous surface region and why standard chemical equations, used to describe equilibria in dilute bulk solution are not valid in the aqueous surface region, are discussed in detail. The reported results are of considerable importance especially for the detailed understanding of properties of small aqueous droplets that can be found in the atmosphere.
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Affiliation(s)
- Josephina Werner
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
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