Water dynamics in deuterated gypsum, CaSO4⋠2D2O, investigated by solid state deuterium NMR.

NMR relaxation theory and NMR lineshape calculations were used to characterize the rates of C2 symmetry jumps of deuterium nuclei in partly deuterated gypsum powder. The experimental data consisted of variable temperature deuterium NMR powder line shapes and deuterium T1 relaxation times. All of the Mathematica© notebooks used to simulate the spectra and match the experimental T1 values are included as supplementary material, and are suitable templates for similar calculations on other systems. Our simulations show that the deuterium nuclei of D2O in Gypsum undergo a two-site C2 180° jump about the D-O-D bisector angle of 54.8°. The jump rate stays in the fast motion regime down to about 218 K. Below 193 K the powder lineshapes change, the spectral intensities drop significantly, and the motion slows into the intermediate motion regime. The best fit quadrupole coupling constants (QCC's) vary between 216 kHz at the highest temperatures to 235 kHz at the lowest temperatures. The asymmetry parameters (ɳ) vary between 0.11 at the highest temperatures to 0.15 at the lowest temperatures. Knowledge of the C2 jump rates allowed us to calculate activation parameters for the jumps, namely ΔH‡ = 22 kJ/mol, and ΔS‡ = -10 J/mol·K which indicate a non-spontaneous activation process, an activation energy of Ea = 23 kJ/mol, and a pre-exponential factor of A = 3.6 × 1012. As expected, there was no evidence of quantum tunneling.

Solute diffusion in ionic liquids, NMR measurements and comparisons to conventional solvents.

Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imides ([Prn1][Tf2N], n = 3, 4, 6, 8, and 10), trihexyltetracedecylphosphonium bis(trifluoromethanesulfonyl)imide [P14,666][Tf2N], and assorted imidazolium ionic liquids are measured using pulsed field gradient (1)H 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 = kBT/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(VU/VV)(-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.

Identification and characterization of a cellulose binding heptapeptide revealed by phage display.

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 ∼10(5) 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 (13)C 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.

A catalytically driven organometallic molecular motor.

We have observed by NMR spectroscopy that the diffusive movement of a ruthenium-based Grubbs' catalyst increases during ring-closing metathesis as a function of the substrate concentration. This is one of the smallest single molecule motors to exhibit catalytically driven motion.

Characterization of water in proton-conducting membranes by deuterium NMR T1 relaxation.

(2)H T(1) NMR relaxation was used to characterize the molecular motion of deuterated water ((2)H(2)O) 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 (2)H T(1) relaxation on the magnetic field of the spectrometer. By comparing the (2)H 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 (2)H(2)O 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 (2)H(2)O is affected by the phase separation of the hydrophilic/hydrophobic domains and the size of the hydrophilic domains.

Multivalent dendrimeric compounds containing carbohydrates expressed on immune cells inhibit infection by primary isolates of HIV-1.

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 IC(50)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.

Incorporating 1H chemical shift determination into 13C-direct detected spectroscopy of intrinsically disordered proteins in solution.

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.

Solid state water motions revealed by deuterium relaxation in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-zeolite A.

Deuterium NMR relaxation experiments, low temperature deuterium NMR lineshape analysis, and FTIR spectra are consistent with a new model for solid state jump dynamics of water in (2)H(2)O-synthesized kanemite and (2)H(2)O-hydrated Na(+)-Zeolite A. Exchange occurs between two populations of water: one in which water molecules are directly coordinated to sodium ions and experience C(2) symmetry jumps of their OH bonds, and a population of interstitial water molecules outside the sodium ion coordination sphere that experience tetrahedral jumps of their OH bonds. For both samples the C(2) jump rate is much faster than the tetrahedral jump rate. (2)H NMR relaxation experiments match well with the fast exchange regime of the model over a wide range of temperatures, including room temperature and above. For hydrated Zeolite A, the kinetic activation parameters for the tetrahedral and C(2) symmetry jumps are Delta H tet++=+17 kJ/mol, Delta S tet++=-109 J/(mol K), Delta H C2++=+19 kJ/mol, and Delta S C2++=-20 J/(mol K). For kanemite, Delta H tet++ =+23 kJ/mol, Delta S tet++=-69 J/(mol K), Delta H C2++ =+23 kJ/mol, and Delta S C2++ =-11 J/(mol K).

Physical properties of ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various anions and the bis(trifluoromethylsulfonyl)imide anion with various cations.

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.

Room-temperature icelike water in kanemite detected by 2H NMR T1 relaxation.

2H NMR was used to study the nature of deuterated water in kanemite. Evidence is presented that shows that the water changes state from liquid to solid at room temperature during the hydration reaction that forms kanemite. The deuterium nuclei in the water experience rapid tetrahedral jumps in a hydrogen-bonded lattice like those observed in 2H2O ice.

Synthesis of novel, multivalent glycodendrimers as ligands for HIV-1 gp120.

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-(beta-D-galactopyranosylthio)propionic acid. Synthesis of 3-sulfogalactopyranosyl-derivatized dendrimers was accomplished using the novel compound, 3-(beta-D-3-sulfogalactopyranosylthio)propionic acid. The fourth series was made by random sulfation of the 3-(beta-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.

Using 19F NMR spectroscopy to determine trifluralin binding to soil.

Trifluralin is a widely used herbicide for the control of broad leaf weeds in a variety of crops. Its binding to soil may result in significant losses in herbicidal activity and a delayed pollution problem. To investigate the nature of soil-bound trifluralin residues, 14C-labeled herbicide was incubated for 7 weeks with four soils under anoxic conditions. As determined by radiocounting, trifluralin binding ranged between 10 and 53% of the initial 14C depending on the soil tested. 19F NMR analyses of the methanol extracts and different fractions of the extracted soil suggested that bound residue formation largely involved reduced metabolites of the herbicide. A 2,6-diamino product of trifluralin reduction with zero-valent iron (Fe-TR), and the standard of a 1,2-diaminotrifluralin derivative (TR6) formed covalent bonds with fulvic acid (FA), as indicated by the 19F NMR spectra taken periodically over a 3-week contact time. At short contact times, TR6 and Fe-TR formed weak physical bonds with FA, as the respective spin-lattice relaxation times (T1) decreased from the range 1300-1831 ms for TR6 or Fe-TR analyzed in the absence of FA to the range 150-410 ms for TR6/FA or Fe-TR/FA mixtures. In general, the results indicated that trifluralin immobilization involved a variety of mechanisms (covalent binding, adsorption, sequestration), and with time it became increasingly stable.