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  • 1. Bialik, Erik
    et al.
    Stenqvist, Bjorn
    Fang, Yuan
    Ostlund, Asa
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Lindman, Björn
    Lund, Mikael
    Bernin, Diana
    Ionization of Cellobiose in Aqueous Alkali and the Mechanism of Cellulose Dissolution2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 24, p. 5044-5048Article in journal (Refereed)
    Abstract [en]

    Cellulose, one of the most abundant renewable resources, is insoluble in most common solvents but dissolves in aqueous alkali under a narrow range of conditions. To elucidate the solubilization mechanism, we performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5. Chemical shift differences between cellobiose in NaOH and NaCl were estimated using 2D NMR and compared to DFT shift differences upon deprotonation. The dissociation steps are the deprotonation of the hemiacetal OH group and the deprotonation of one of four OH groups on the nonreducing anhydroglucose unit. MD simulations reveal that aggregation is suppressed upon charging cellulose chains in solution. Our findings strongly suggest that cellulose is to a large extent charged in concentrated aqueous alkali, a seemingly crucial factor for solubilization. This insight, overlooked in the current literature, is important for understanding cellulose dissolution and for synthesis of new sustainable materials.

  • 2.
    Fang, Yuan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ions interacting with macromolecules: NMR studies in solution2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Specific ion effects, identified for more than hundred years, play an important role in a wide range of phenomena and applications. Several mechanisms such as direct ion interaction with molecules have been suggested to explain these effects, but quantitative experimental evidence remains scarce. Electrophoretic NMR (eNMR) has been emerging as a very powerful tool for studying molecular association and ionic transport in a variety of systems. Yet its potential in studying specific ion effect has been unexplored. In this thesis, eNMR was in part developed further as an analytical method and was in part used as one of the main techniques to study ions interacting with macromolecules in aqueous and non-aqueous solutions.

    The complexation of a large group of cations with poly ethylene oxide (PEO) in methanol was studied with eNMR. The binding of monovalent ions was demonstrated not to follow the Hofmeister order; multivalent cations except barium all showed negligible complexation. As a unifying feature, only cations with surface charge density below a threshold value were able to bind suggesting that ion solvation is critical. The binding mechanism was examined in greater detail for K+ and Ba2+ with oligomeric PEO of different chain lengths. Those two cations exhibited different binding mechanisms. K+ was found to bind to PEO by having at least 6 repeating units wrap around it while retaining the polymer flexibility. On the other hand, Ba2+ (and, to some extent, (BaAnion)+) needs a slightly shorter section to bind, but the molecular dynamics at the binding site slow considerably.

    The binding of anions with poly (N-isopropylacrylamide) in water was quantified at low salt concentration with eNMR and the binding affinity, though very weak, followed the Hofmeister order. This result indicates the non-electrostatic nature of this specific ion effects. The increase of binding strength with salt concentration is well described by a Langmuir isotherm.

    The specific ion binding to a protein, bovine serum albumin (BSA), was also studied at pH values where BSA has either net positive and negative charges. Our results show that anions have the same binding affinity irrespective of the surface charge while the binding strength of cations is reversed with the change in net surface charge. This indicates different binding mechanisms for cations and anions.

    The ionization of cellobiose in alkaline solutions was measured quantitatively by eNMR. The results show a two-step deprotonation process with increasing alkaline strength. Supported by results from 1H-13C HSQC NMR and MD simulation, ionization was proposed to be responsible for the improved solubility of cellulose in alkaline solution. eNMR was also used to characterize the effective charge of tetramethylammonium ions in a variety of solvents. In solvents of high polarity, the results agree well with predictions based on Onsager’s limiting law but for nonpolar solvents deviations were found that were attributed to ion pair formation. 

  • 3.
    Fang, Yuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Different Binding Mechanisms of Cations and Anions to Proteins: Electrophoretic NMR Studies in Bovine Serum AlbuminManuscript (preprint) (Other academic)
  • 4.
    Fang, Yuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Weak Anion Binding to Poly(N-isopropylacrylamide): A Quantitative Study by Electrophoretic NMRManuscript (preprint) (Other academic)
  • 5.
    Fang, Yuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Giesecke, Marianne
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Complexing Cations by Poly(ethylene oxide): Binding Site and Binding Mode2017In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 121, no 9, p. 2179-2188Article in journal (Refereed)
    Abstract [en]

    The binding of K+ and Ba2+ cations to short poly(ethylene oxide) (PEO) chains with ca. 4-25 monomeric units in methanol was studied by determining the effective charge of the polymer through a combination of electrophoretic NMR and diffusion NMR experiments. These cations were previously found to bind to long PEO chains in a similar strong manner. In addition, H-1 chemical shift and longitudinal spin relaxation rate changes upon binding were quantified. For both systems, binding was stronger for the short chains than that for the longer chains, which is attributed mainly to interactions between bound ions. For K+ ions, the equilibrium binding constant of a cation to a binding site was measured. For both cations, the binding site was estimated to consist of ca. six monomeric units that coordinated with the respective ions. For the systems with barium, a significant fraction of the bound ions are (BaAnion)(+) ion pairs. This leads to a strong anion effect in the effective charge of the oligomers acquired upon barium ion binding. For K+, the coordinating oligomer segment remains rather mobile and individual oligomers exchange rapidly (<<s) between their free and ion-complexing states. In contrast, segmental dynamics slows significantly for the oligomer section that coordinates with the barium species, and for individual oligomers, binding and nonbinding sections do not exchange on the time scale of seconds. Hence, oligomers also exchange slowly (>s) between their free and barium complexing states.

  • 6.
    Fang, Yuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Giesecke, Marianne
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Complexing Cations by Polyethylene Oxide. Binding Site and Binding Mode2017In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207Article in journal (Refereed)
  • 7.
    Fang, Yuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Yushmanov, Pavel V.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Assessing the potential of 2D electrophoretic mobility spectroscopy (2D MOSY) for analytical applications2017In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 55, no 6, p. 584-588Article in journal (Refereed)
    Abstract [en]

    Electrophoretic displacement of charged entity phase modulates the spectrum acquired in electrophoretic NMR experiments, and this modulation can be presented via 2D FT as 2D mobility spectroscopy (MOSY) spectra. We compare in various mixed solutions the chemical selectivity provided by 2D MOSY spectra with that provided by 2D diffusion-ordered spectroscopy (DOSY) spectra and demonstrate, under the conditions explored, a superior performance of the former method. 2D MOSY compares also favourably with closely related LC-NMR methods. The shape of 2D MOSY spectra in complex mixtures is strongly modulated by the pH of the sample, a feature that has potential for areas such as in drug discovery and metabolomics.

  • 8.
    Gao, Jiajia
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Yang, Wenxing
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 523, SE-75120 Uppsala, Sweden..
    El-Zohry, Ahmed M.
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 523, SE-75120 Uppsala, Sweden..
    Prajapati, Govind Kumar
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Fang, Yuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Dai, Jing
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Hao, Yan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Leandri, Valentina
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Svensson, Per H.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. RISE Surface Proc Formulat, Forskargatan 20j, SE-15136 Sodertalje, Sweden..
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Boschloo, Gerrit
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 523, SE-75120 Uppsala, Sweden..
    Lund, Torben
    Roskilde Univ, Dept Sci & Environm, DK-4000 Roskilde, Denmark..
    Kloo, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Light-induced electrolyte improvement in cobalt tris(bipyridine)-mediated dye-sensitized solar cells2019In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 33, p. 19495-19505Article in journal (Refereed)
    Abstract [en]

    Lithium-ion-free tris(2,2 '-bipyridine) Co(ii/iii)-mediated electrolytes have previously been proposed for long-term stable dye-sensitized solar cells (DSSCs). Such redox systems also offer an impressive DSSC performance improvement under light soaking exposure, manifested by an increase in photocurrent and fill factor without the expense of decreasing photovoltage. Kinetic studies show that charge transfer and ion diffusion at the electrode/electrolyte interface are improved due to the light exposure. Control experiments reveal that the light effect is unambiguously associated with electrolyte components, [Co(bpy)(3)](3+) and the Lewis-base additive tert-butylpyridine (TBP). Electrochemical and spectroscopic investigation of the [Co(bpy)(3)](3+)/TBP mixtures points out that the presence of TBP, which retards the electrolyte diffusion, however causes an irreversible redox reaction of [Co(bpy)(3)](3+) upon light exposure that improves the overall conductivity. This discovery not only provides a new strategy to mitigate the typical J(sc)-V-oc trade-off in Co(ii/iii)-mediated DSSCs but also highlights the importance of investigating the photochemistry of a photoelectrochemical system.

  • 9.
    Giesecke, Marianne
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Fang, Yuan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Binding modes of cations to polyethylene oxide: An NMR studyManuscript (preprint) (Other academic)
  • 10.
    Giesecke, Marianne
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Hallberg, Fredrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Fang, Yuan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Binding of monovalent and multivalent metal cations to polyethylene oxide in methanol probed by electrophoretic and diffusion NMR2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 39, p. 10358-10366Article in journal (Refereed)
    Abstract [en]

    Complex formation in methanol between monodisperse polyethylene oxide (PEO) and a large set of cations was studied by measuring the effective charge acquired by PEO upon complexation. Quantitative data were obtained at a low ionic strength of 2 mM (for some salts, also between 0.5 and 6 mM) by a combination of diffusion nuclear magnetic resonance (NMR) and electrophoretic NMR experiments. For strongly complexing cations, the magnitude of the acquired effective charge was on the order of 1 cation per 100 monomer units. For monovalent cations, the relative strength of binding varies as Na+ < K+ ≈ Rb+ ≈ Cs+, whereas Li+ exhibited no significant binding. All polyvalent cations bind very weakly, except for Ba2+ that exhibited strong binding. Anions do not bind, as is shown by the lack of response to the chemical nature of anionic species (perchlorate, iodide, or acetate). Diffusion experiments directly show that the acetate anion with monovalent cations does not associate with PEO. Considering all cations, we find that the observed binding does not follow any Hofmeister order. Instead, binding occurs below a critical surface charge density, which indicates that the degree of complexation is defined by the solvation shell. A large solvation shell prevents the binding of most multivalent ions.

  • 11.
    Giesecke, Marianne
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Meriguet, Guillaume
    Hallberg, Fredrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Fang, Yuan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ion association in aqueous and non-aqueous solutions probed by diffusion and electrophoretic NMR2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 5, p. 3402-3408Article in journal (Refereed)
    Abstract [en]

    The results of diffusion and electrophoretic NMR (eNMR) measurements are reported for a series of tetramethylammonium (TMA) electrolytes (with sulphate, fluoride, acetate, chloride, bromide, nitrate, iodide and perchlorate as anions) in deuterated solvents such as water, dimethylsulphoxide (DMSO), acetonitrile, methanol and ethanol. In addition, similar data are presented for aqueous solutions of tetraalkylammonium salts with increasing alkyl chain length. The combination of diffusion NMR and eNMR yields the effective charge for the TMA cation. Relative to the nominal charge of z(nom) = 1 of TMA, the effective charge in the different solvents is found to be progressively smaller in the order water > DMSO > methanol > acetonitrile > ethanol. A part of this observed trend is ascribed to regular ion-ion interactions incorporated in the Onsager limiting law. Indeed, in solvents with high dielectric constants such as water, DMSO and methanol, the Onsager limiting law describes well the observations for all tetraalkylammonium ions. For ethanol and acetonitrile, there is a significant difference between the experimental data and the expected limiting-law behavior that is attributed to ion association (ion pairing) not taken into consideration by the Onsager limiting law.

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