Ionic Liquids as Working Fluids for Heat Storage Applications: Decomposition Behavior of N-Butyl-N-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate.

Ionic liquids (ILs) represent promising working fluids to be used in thermal energy storage (TES) technologies thanks to their peculiar properties, such as low volatility, high chemical stability, and high heat capacity. Here, we studied the thermal stability of the IL N-butyl-N-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([BmPyrr]FAP), a potential working fluid for TES applications. The IL was heated at 200 °C for up to 168 h either in the absence or in contact with steel, copper, and brass plates to simulate the conditions used in TES plants. High-resolution magic angle spinning nuclear magnetic resonance spectroscopy was found to be useful for the identification of the degradation products of both the cation and the anion, thanks to the acquisition of 1H, 13C, 31P, and 19F-based experiments. In addition, elemental analysis was performed on the thermally degraded samples by inductively coupled plasma optical emission spectroscopy and energy dispersive X-ray spectroscopy. Our analysis shows a significant degradation of the FAP anion upon heating for more than 4 h, even in the absence of the metal/alloy plates; on the other hand, the [BmPyrr] cation displays a remarkable stability also when heated in contact with steel and brass.

Peptides Derived from Angiogenin Regulate Cellular Copper Uptake.

The angiogenin protein (ANG) is one of the most potent endogenous angiogenic factors. In this work we characterized by means of potentiometric, spectroscopic and voltammetric techniques, the copper complex species formed with peptide fragments derived from the N-terminal domain of the protein, encompassing the sequence 1-17 and having free amino, Ang1-17, or acetylated N-terminus group, AcAng1-17, so to explore the role of amino group in metal binding and cellular copper uptake. The obtained data show that amino group is the main copper anchoring site for Ang1-17. The affinity constant values, metal coordination geometry and complexes redox-potentials strongly depend, for both peptides, on the number of copper equivalents added. Confocal laser scanning microscope analysis on neuroblastoma cells showed that in the presence of one equivalent of copper ion, the free amino Ang1-17 increases cellular copper uptake while the acetylated AcAng1-17 strongly decreases the intracellular metal level. The activity of peptides was also compared to that of the protein normally present in the plasma (wtANG) as well as to the recombinant form (rANG) most commonly used in literature experiments. The two protein isoforms bind copper ions but with a different coordination environment. Confocal laser scanning microscope data showed that the wtANG induces a strong increase in intracellular copper compared to control while the rANG decreases the copper signal inside cells. These data demonstrate the relevance of copper complexes' geometry to modulate peptides' activity and show that wtANG, normally present in the plasma, can affect cellular copper uptake.

Unravelling Main- and Side-Chain Motions in Polymers with NMR Spectroscopy and Relaxometry: The Case of Polyvinyl Butyral.

Polyvinyl butyral (PVB) is an amorphous polymer employed in many technological applications. In order to highlight the relationships between macroscopic properties and dynamics at a microscopic level, motions of the main-chain and of the propyl side-chains were investigated between Tg - 288 °C and Tg + 55 °C, with Tg indicating the glass transition temperature. To this aim, a combination of solid state Nuclear Magnetic Resonance (NMR) methods was applied to two purposely synthesized PVB isotopomers: one fully protonated and the other perdeuterated on the side-chains. 1H time domain NMR and 1H field cycling NMR relaxometry experiments, performed across and above Tg, revealed that the dynamics of the main-chain corresponds to the α-relaxation associated to the glass transition, which was previously characterized by dielectric spectroscopy. A faster secondary relaxation was observed for the first time and ascribed to side-chains. The geometry and rate of motions of the different groups in the side-chains were characterized below Tg by 2H NMR spectroscopy.

Probing the Structure of Toxic Amyloid-ß Oligomers with Electron Spin Resonance and Molecular Modeling.

Structural models of the toxic species involved in the development of Alzheimer's disease are of utmost importance to understand the molecular mechanism and to describe early biomarkers of the disease. Among toxic species, soluble oligomers of amyloid-ß (Aß) peptides are particularly important, because they are responsible for spreading cell damages over brain regions, thus rapidly impairing brain functions. In this work we obtain structural information on a carefully prepared Aß(1-42) sample, representing a toxic state for cell cultures, by combining electron spin resonance spectroscopy and computational models. We exploited the binding of Cu2+ to Aß(1-42) and used copper as a probe for estimating Cu-Cu distances in the oligomers by applying double electron-electron resonance (DEER) pulse sequence. The DEER trace of this sample displays a unique feature that fits well with structural models of oligomers formed by Cu-cross-linked peptide dimers. Because Cu is bound to the Aß(1-42) N-terminus, for the first time structural constraints that are missing in reported studies are provided at physiological conditions for the Aß N-termini. These constraints suggest the Aß(1-42) dimer as the building block of soluble oligomers, thus changing the scenario for any kinetic model of Aß(1-42) aggregation.

A close view of the organic linker in a MOF: structural insights from a combined 1H NMR relaxometry and computational investigation.

The organic linker in a metal organic framework (MOF) affects its adsorption behavior and performance, and its structure and dynamics play a role in the modulation of the adsorption properties. In this work, the combination of 1H nuclear magnetic resonance (NMR) longitudinal relaxometry and theoretical calculations allowed details of the structure and dynamics of the organic linker in the NH2-MIL-125 MOF to be obtained. In particular, fast field cycling (FFC) NMR, applied here for the first time on MOFs, was used to disclose the dynamics of the amino group and its electronic environment through the analysis of the 14N quadrupole relaxation peaks, observed in the frequency interval 0.5-5 MHz, at different temperatures from 25 to 110 °C. The line width of the peaks allowed a lower boundary on the rotational correlation time of the N-H bonds to be set, whereas relevant changes in the amplitudes were interpreted in terms of a change in the orientation of the 14N averaged electric field gradient tensor. The experimental findings were complemented by quantum chemistry calculations and classical molecular dynamics simulations.

Dynamics of poly(vinyl butyral) studied using dielectric spectroscopy and 1H NMR relaxometry.

Dielectric Spectroscopy (DS) and 1H Fast Field-Cycling (FFC) NMR relaxometry were applied for understanding the dynamic behavior of the amorphous ter-polymer poly(vinyl butyral) (PVB) across the glass transition temperature (Tg = 70 °C by Differential Scanning Calorimetry). Above Tg, main chain segmental motions (α relaxation) were detected and characterized using both DS and FFC NMR relaxometry. The correlation times extracted by the analysis of DS and FFC NMR relaxometry data agreed within a factor of three and showed a Vogel-Fulcher-Tammann temperature dependence, with an associated Tg of 69 °C and a fragility of 155 for PVB glass. Below Tg, a secondary process (ß relaxation) was revealed by DS, and was ascribed to reorientations of the vinyl alcohol dipoles due to local twisting motions with an associated activation barrier of 11 kcal mol-1. The ß process was also found to contribute to 1H NMR relaxation above Tg.

Copper(II) complexes with peptides based on the second cell binding site of fibronectin: metal coordination and ligand exchange kinetics.

Copper(ii) complexes with short peptides based on the second cell binding site of fibronectin, PHSFN and PHSEN, have been characterized by potentiometric, UV-vis, CD, EPR and NMR spectroscopic methods. The histidine imidazole nitrogen is the anchoring site for the metal ion binding. Thermodynamic and spectroscopic evidence is given that the side chain oxygen donor atom of glutamyl residue in Ac-PHSEN-NH2 is also involved in the binding up to physiological pH. To determine ligand exchange kinetic parameters after the imidazole nitrogen anchoring, proton relaxation enhancement NMR data have been collected for the two hydrogen atoms of the imidazole ring in the temperature range 293-315 K at pH 5.2 and globally treated within different kinetic models for ligand exchange. The best fitting model involves two steps. In the first one, which is slow, a water molecule disengages a carbonyl or a carboxylate group coordinated to the metal ion in the complex formed by PHSFN or PHSEN, respectively. This stage is one order of magnitude slower for PHSEN, due to entropic effects. In the second step, which is fast, the complex just formed exchanges with the ligand. In this step, no appreciable differences are found for the two cases examined.

Structure and Dynamics of Ferrocyanide and Ferricyanide Anions in Water and Heavy Water: An Insight by MD Simulations and 2D IR Spectroscopy.

Combined computational and experimental techniques were employed to investigate at the microscopic level the structural and dynamic properties of ferro- and ferricyanide ions in aqueous solution. The characterization of the structural patterns and multiscale dynamics taking place within the first solvation spheres in water and heavy water solvents was first achieved through extensive molecular dynamics simulations, performed with refined force fields, specifically parametrized for the cyanide ions under investigation. The information gained about the solute-solvent interactions is then validated through the successful comparison of computed and measured waiting-time-dependent 2D IR spectra. The vibrational patterns resulting from 2D IR measurements were rationalized in terms of the interaction between the ion and the neighboring water molecules described by simulation. It was found that, within the first solvation sphere, the stronger interactions of the solvent with the ferro species are responsible for a delay in the relaxation dynamics, which becomes more and more evident on longer time scales.

Conformations of phenylalanine in the tripeptides AFA and GFG probed by combining MD simulations with NMR, FTIR, polarized Raman, and VCD spectroscopy.

Conformational properties of small, flexible peptides are a matter of ongoing interest since they can be considered as models for unfolded proteins. However, the investigation of the conformations of small peptides is challenging as they are ensembles of rapidly interconverting conformers; moreover, the different methods used are prone to different approximations and errors. In order to obtain more reliable results, it is prudent to combine different techniques; here, molecular dynamics (MD) simulations together with nuclear magnetic resonance (NMR), Fourier transform IR (FTIR), polarized Raman, and vibrational circular dichroism (VCD) measurements were used to study the conformational propensity of phenylalanine in the tripeptides AFA and GFG, motivated by the relevance of phenylalanine for the self-aggregation of peptides. The results of this analysis indicate that the F residue predominantly populates the beta-strand (beta) and polyproline II (PPII) conformations in both AFA and GFG. However, while phenylalanine exhibits a propensity for beta-strand conformations in GFG (0.40 < or = beta population < or = 0.69 and 0.29 < or = PPII population < or = 0.42), the substitution of terminal glycines with alanine residues induces a higher population of PPII (0.31 < or = beta population < or = 0.50 and 0.37 < or = PPII population < or = 0.57).

Study of the interaction of GFG tripeptide with cesium perfluorooctanoate micelles by means of NMR spectroscopy and MD simulations.

The interaction of glycyl-phenylalanyl-glycine (GFG) with bilayers formed by cesium perfluorooctanoate (CsPFO) in water was investigated in the isotropic phase by means of 1H NMR and molecular dynamics (MD) simulations. Details on the preferential location of the different residues of GFG were obtained from selective variations of chemical shift with peptide concentration and of line width in the presence of the paramagnetic ion Mn2+. The analysis of 1H NMR spectra recorded at different concentrations and temperatures allowed the association constant and the enthalpy change upon binding to be evaluated. MD simulations highlighted the hydrogen bonds formed between the different GFG functional groups and the micelle. Both NMR and MD gave indications of high affinity of GFG with the micelle, with the N-terminal residue anchoring on the surface via hydrogen bonds with the micelle COO(-) groups.

Interaction of a tripeptide with cesium perfluorooctanoate micelles.

The interaction of alanyl-phenylalanyl-alanine (Ala-Phe-Ala) with the micelles formed by cesium perfluorooctanoate (CsPFO) in water was studied in the isotropic phase by means of 1H NMR and by molecular dynamics (MD) simulations. Information on the location of the peptide was experimentally obtained from selective variations in Ala-Phe-Ala chemical shifts and from differential line broadening in the presence of the paramagnetic ion Mn2+. The peptide-micelle association constant was estimated analyzing the chemical shift variations of the most sensitive Ala-Phe-Ala resonances with the peptide concentration. MD simulations of Ala-Phe-Ala in the micellar environment confirmed the experimental observations, identifying the hydrogen bonding interactions of the different peptide moieties with the micelle, yielding a binding constant close to the experimental one. NOESY experiments suggest that the peptide in the micellar environment does not adopt a preferred conformation but is mainly unstructured. Details on the conformational behavior of the peptide in the micellar solution observed through MD were consistent with a different conformational equilibrium in the proximity of the micelle. Information on Ala-Phe-Ala dynamics was obtained from 1H T1 data and compared to MD simulation results on the overall tumbling motion.

Conformations of alanine-based peptides in water probed by FTIR, Raman, vibrational circular dichroism, electronic circular dichroism, and NMR spectroscopy.

We have used a combination of FTIR, VCD, ECD, Raman, and NMR spectroscopies to probe the solution conformations sampled by H-(AAKA)-OH by utilizing an excitonic coupling model and constraints imposed by the 3JCalphaHNH coupling constants of the central residues to simulate the amide I' profile of the IR, isotropic Raman, anisotropic Raman, and VCD spectra in terms of a mixture of three conformations, i.e., polyproline II, beta-strand and right-handed helical. The representative coordinates of the three conformations were obtained from published coil libraries. Alanine was found to exhibit PPII fractions of 0.60 or greater, mixed with smaller fractions of helices and beta-strand conformations. Lysine showed no clear conformational propensity in that it samples polyproline II, beta-strand, and helical conformations with comparable probability. This is at variance with results obtained earlier for ionized polylysine, which suggest a high polyproline II propensity. We reanalyzed previously investigated tetra- and trialanine by combining published vibrational spectroscopy data with 3JCalphaHNH coupling constants and obtained again blends dominated by PPII with smaller admixtures of beta-strand and right-handed helical conformations. The polyproline II propensity of alanine was found to be higher in tetraalanine than in trialanine. For all peptides investigated, our results rule out a substantial population of turn-like conformations. Our results are in excellent agreement with MD simulations on short alanine peptides by Gnanakaran and Garcia [(2003) J. Phys. Chem. B 107, 12555-12557] but at variance with multiple MD simulations particularly for the alanine dipeptide.

Conformations of banana-shaped molecules studied by 2H NMR spectroscopy in liquid crystalline solvents.

ClPbis11BB and Pbis11BB, two banana-shaped mesogens differing by a chlorine substituent on the central phenyl ring, show a nematic and a B2 phase, respectively. To obtain information on the structural features responsible for their different mesomorphic behavior, a study of the preferred conformations of these mesogens has been performed by NMR spectroscopy in two nematic media (Phase IV and ZLI1167), which should mimic the environment of the molecules in their own mesophases, avoiding problems of sample alignment by a magnetic field. To this aim, 2H NMR experiments have been performed on selectively deuterated isotopomers of ClPbis11BB and Pbis11BB and of two parent molecules, ClPbisB and PbisB, assumed as models in previous theoretical and experimental conformational studies. We found that only a limited number of conformations is compatible with experimental data, often very different from those inferred from theoretical calculations in vacuo, indicating a strong influence of the liquid crystalline environment on molecular conformation. No significant differences between chlorinated and non-chlorinated molecules were found, this suggesting that chlorine does not change the molecular conformational equilibrium, as previously proposed.

CP MAS 13C spectral editing and relative quantitation of a soil sample.

A hydrofluoric acid (HF)-treated soil sample was studied by 13C NMR spectroscopy. Cross polarization (CP) Magic Angle Spinning (MAS) 13C spectral editing and relative CP peak quantitation, obtained through variable-contact-time experiments, were used to aid the interpretation of the spectrum. The combination of these two types of experiment allowed to obtain a higher degree of detail on the composition of the sample with respect to a standard CP MAS experiment.

NMR study of the adsorption-desorption kinetics of dissolved tetraalanine in MCM-41 mesoporous material.

In this study we show how deuterium magic-angle spinning NMR spectroscopy can be used to investigate the adsorption-desorption kinetics of molecules in solution at surface-liquid interfaces. An aqueous solution of deuterium-labeled tetraalanine is inserted in the pores of MCM-41 mesoporous material, and its 2H MAS NMR spectrum is measured as a function of temperature and fraction of filling of the pores. Prior to this study, the different types of water in MCM-41 are characterized as a function of water loading of the pores. Analysis of 2H MAS sideband line shapes enabled the determination of the adsorption and desorption rates and the activation energies of desorption.

Conformation and orientation of tetraalanine in a lyotropic liquid crystal studied by nuclear magnetic resonance.

The (1)H NMR spectra of two isotopomers of tetraalanine deuterated on the two external methyl groups and on the two internal ones, respectively, were recorded in the lyotropic solvent cesium pentadecafluorooctanoate (CsPFO)/water. Eight dipolar couplings could be estimated from the spectra. The set of dipolar couplings was fitted assuming that one rigid conformer is present. Of the four major conformers considered, selected on the basis of theoretical calculations, the one characterized by the two couples of internal dihedral angles in the Ramachandran region of PPII resulted to be the only one to fit the set of couplings within experimental error. The data indicate that the molecule is oriented with the long molecular axis tilted with respect to the surface of the micelles formed by CsPFO.