Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imides (Pr n1Tf2N, n = 3, 4, 6, 8, and 10), ...trihexyltetracedecylphosphonium bis(trifluoromethanesulfonyl)imide P14,666Tf2N, and assorted imidazolium ionic liquids are measured using pulsed field gradient 1H NMR. These data, combined with available literature data, are used to try to uncover the solute and solvent characteristics most important in determining tracer diffusion rates. Discussion is framed in terms of departures from simple hydrodynamic predictions for translational friction using the ratio ζobs/ζSE, where ζobs is the observed friction, determined from the measured diffusion coefficient D via ζobs = k B T/D, and ζSE = 6πηR is the Stokes friction on a sphere of radius R (determined from the solute van der Waals volume) in a solvent with viscosity η. In the case of neutral solutes, the primary determinant of whether hydrodynamic predictions are accurate is the relative size of solute versus solvent molecules. A single correlation, albeit with considerable scatter, is found between ζobs/ζSE and the ratio of solute-to-solvent van der Waals volumes, ζobs/ζSE = {1 + a(V U/V V)−p }, with constants a = 1.93 and p = 1.88. In the case of small solutes, the observed friction is over 100-fold smaller than predictions of hydrodynamic models. The dipole moment of the solute has little effect on the friction, whereas solute charge has a marked effect. For monovalent solutes of size comparable to or smaller than the solvent ions, the observed friction is comparable to or even greater than what is predicted by hydrodynamics. These general trends are shown to be quite similar to what is observed for tracer diffusion in conventional solvents.
Physical properties of 4 room-temperature ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various perfluorinated anions and the bis(trifluoromethylsulfonyl)imide (Tf2N-) anion ...with 12 pyrrolidinium-, ammonium-, and hydroxyl-containing cations are reported. Electronic structure methods are used to calculate properties related to the size, shape, and dipole moment of individual ions. Experimental measurements of phase-transition temperatures, densities, refractive indices, surface tensions, solvatochromic polarities based on absorption of Nile Red, 19F chemical shifts of the Tf2N- anion, temperature-dependent viscosities, conductivities, and cation diffusion coefficients are reported. Correlations among the measured quantities as well as the use of surface tension and molar volume for estimating Hildebrand solubility parameters of ionic liquids are also discussed.
2H T 1 NMR relaxation was used to characterize the molecular motion of deuterated water (2H2O) in Aquivion E87-05, Nafion 117, and sulfonated-Radel proton-exchange membranes. The presence of bound ...water with solid character was confirmed by the dependence of the 2H T 1 relaxation on the magnetic field of the spectrometer. By comparing the 2H T 1 relaxation times of the different membranes that were equilibrated in varying humidities, the factors that influence the state of water in the membranes were identified. At low levels of hydration, the molecular motion of 2H2O is affected by the acidity and mobility of the sulfonic acid groups to which the water molecules are coordinated. At higher levels of hydration, the molecular motion of 2H2O is affected by the phase separation of the hydrophilic/hydrophobic domains and the size of the hydrophilic domains.
Exclusively heteronuclear
13C-detected NMR spectroscopy of proteins in solution has seen resurgence in the past several years. For disordered or unfolded proteins, which tend to have poor
1H-amide ...chemical shift dispersion, these experiments offer enhanced resolution and the possibility of complete heteronuclear resonance assignment at the cost of leaving the
1H resonances unassigned. Here we report two novel
13C-detected NMR experiments which incorporate a
1H chemical shift evolution period followed by
13C-TOCSY mixing for aliphatic
1H resonance assignment without reliance on
1H detection.
Exclusively heteronuclear (13)C-detected NMR spectroscopy of proteins in solution has seen resurgence in the past several years. For disordered or unfolded proteins, which tend to have poor ...(1)H-amide chemical shift dispersion, these experiments offer enhanced resolution and the possibility of complete heteronuclear resonance assignment at the cost of leaving the (1)H resonances unassigned. Here we report two novel (13)C-detected NMR experiments which incorporate a (1)H chemical shift evolution period followed by (13)C-TOCSY mixing for aliphatic (1)H resonance assignment without reliance on (1)H detection.
Abstract Specific glycosphingolipids (GSL), found on the surface of target immune cells, are recognized as alternate cell surface receptors by the human immunodeficiency virus type 1 (HIV-1) external ...envelope glycoprotein. In this study, the globotriose and 3'-sialyllactose carbohydrate head groups found on two GSL were covalently attached to a dendrimer core to produce two types of unique multivalent carbohydrates (MVC). These MVC inhibited HIV-1 infection of T cell lines and primary peripheral blood mononuclear cells (PBMC) by T cell line-adapted viruses or primary isolates, with IC50 s ranging from 0.1 to 7.4 μg/ml. Inhibition of Env-mediated membrane fusion by MVC was also observed using a dye-transfer assay. These carbohydrate compounds warrant further investigation as a potential new class of HIV-1 entry inhibitors. The data presented also shed light on the role of carbohydrate moieties in HIV-1 virus–host cell interactions.
Cellulose nanowhiskers (CNWs) were used in conjunction with phage display technology to identify polypeptides which bind the crystalline region of cellulose. A consensus peptide WHWTYYW was ...identified to efficiently bind the CNWs. The binding affinities of specific phage particles were assessed using biopanning assays and enzyme-linked immunosorbent assay (ELISA). The WHWTYYW peptide was synthesized and isothermal titration calorimetry (ITC) analysis showed that the peptide exhibited a binding constant of ∼105 M–1 toward the crystalline CNWs. In order to understand how the affinity of this peptide differs for noncrystalline cellulose, binding properties were characterized using cello-oligosaccharides as substrates. Binding analysis was performed using UV spectroscopy and fluorescence quenching experiments. The specific molecular interactions of the WHWTYYW peptide with cellohexaose were examined using nuclear magnetic resonance (NMR). Interactions of this peptide with crystalline cellulose were also investigated using classical molecular modeling and quantum mechanical calculations of 13C NMR chemical shifts. The NMR experiments and calculations indicate that the WHWTYYW peptide exhibits a bent structure when bound, allowing the Y5 amino acid to form a CH/π stacking interaction and H-bond with the glucose ring of cellulose.
Multivalent neoglycoconjugates are valuable tools for studying carbohydrate−protein interactions. To study the interaction of HIV-1 gp120 with its reported alternate glycolipid receptors, galactosyl ...ceramide (GalCer) and sulfatide, galactose- and sulfated galactose-derivatized dendrimers were synthesized, analyzed as ligands for rgp120 by surface plasmon resonance, and tested for their ability to inhibit HIV-1 infection of CXCR4- and CCR5-expressing indicator cells. Four different series of glycodendrimers were made by amine coupling spacer-arm derivatized galactose residues, either sulfated or nonsulfated, to poly(propylenimine) dendrimers, generations 1−5. One series of glycodendrimers was prepared from the ceramide saccharide derivative of purified natural GalCer, and another was from chemically synthesized 3-(β-d-galactopyranosylthio)propionic acid. Synthesis of 3-sulfogalactopyranosyl-derivatized dendrimers was accomplished using the novel compound, 3-(β-d-3-sulfogalactopyranosylthio)propionic acid. The fourth series was made by random sulfation of the 3-(β-d-galactopyranosylthio)propionic acid functionalized dendrimers. Structures of the carbohydrate moieties were confirmed by NMR, and the average molecular weights and polydispersities of the different glycodendrimers were determined using MALDI-TOF MS. Surface plasmon resonance studies found that rgp120 IIIB bound to the derivatized dendrimers tested with nanomolar affinity, and to dextran sulfate with picomolar affinity. In vitro studies of the effectiveness of these compounds at inhibiting infection of U373-MAGI−CCR5 cells by HIV-1 Ba-L indicated that the sulfated glycodendrimers were better inhibitors than the nonsulfated glycodendrimers, but not as effective as dextran sulfate.
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