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This work presents an analysis of the lidocaine spatial structure in SC-CO2. Two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) and quantum chemical calculations (DFT) were used to identify the preferable conformers in an SC-CO2 solution (70°C, 20 MPa). The data obtained in this work can be used to calculate the optimal micronization parameters by the RESS method. [ABSTRACT FROM AUTHOR]

For interpreting the pressure induced shifts of resonance lines of folded as well as unfolded proteins the availability of data from well-defined model systems is indispensable. Here, we report the pressure dependence of 1H and 15N chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (Xxx is one of the 20 canonical amino acids) measured at 800 MHz proton frequency. As observed earlier for other nuclei the chemical shifts of the side chain nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The pressure response is described by a second degree polynomial with the pressure coefficients B1 and B2 that are dependent on the atom type and type of amino acid studied. A number of resonances could be assigned stereospecifically including the 1H and 15N resonances of the guanidine group of arginine. In addition, stereoselectively isotope labeled SAIL amino acids were used to support the stereochemical assignments. The random-coil pressure coefficients are also dependent on the neighbor in the sequence as an analysis of the data shows. For Hα and HN correction factors for different amino acids were derived. In addition, a simple correction of compression effects in thermodynamic analysis of structural transitions in proteins was derived on the basis of random-coil pressure coefficients. [ABSTRACT FROM AUTHOR]

Previous investigations of the sensitivity of the lac repressor to high-hydrostatic pressure have led to varying conclusions. Here high-pressure solution NMR spectroscopy is used to provide an atomic level view of the pressure induced structural transition of the lactose repressor regulatory domain (LacI* RD) bound to the ligand IPTG. As the pressure is raised from ambient to 3 kbar the native state of the protein is converted to a partially unfolded form. Estimates of rotational correlation times using transverse optimized relaxation indicates that a monomeric state is never reached and that the predominate form of the LacI* RD is dimeric throughout this pressure change. Spectral analysis suggests that the pressure-induced transition is localized and is associated with a volume change of approximately − 115 ml mol − 1 and an average pressure dependent change in compressibility of approximately 30 ml mol − 1 kbar − 1 . In addition, a subset of resonances emerge at high-pressures indicating the presence of a non-native but folded alternate state. [ABSTRACT FROM AUTHOR]

For evaluating the pressure responses of folded as well as intrinsically unfolded proteins detectable by NMR spectroscopy the availability of data from well-defined model systems is indispensable. In this work we report the pressure dependence of C chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH (Xxx, one of the 20 canonical amino acids). Contrary to expectation the chemical shifts of a number of nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The size of the polynomial pressure coefficients B and B is dependent on the type of atom and amino acid studied. For H, N and C the first order pressure coefficient B is also correlated to the chemical shift at atmospheric pressure. The first and second order pressure coefficients of a given type of carbon atom show significant linear correlations suggesting that the NMR observable pressure effects in the different amino acids have at least partly the same physical cause. In line with this observation the magnitude of the second order coefficients of nuclei being direct neighbors in the chemical structure also are weakly correlated. The downfield shifts of the methyl resonances suggest that gauche conformers of the side chains are not preferred with pressure. The valine and leucine methyl groups in the model peptides were assigned using stereospecifically C enriched amino acids with the pro-R carbons downfield shifted relative to the pro-S carbons. [ABSTRACT FROM AUTHOR]

[Display omitted] • An approach in conducting high-pressure 2D NOESY measurements at supercritical parameters of state is discussed. • The conformation state of lidocaine in supercritical CO 2 solution is studied by high-pressure 2D NOESY. • The conformational change of lidocaine in relations of pressure was observed. • This paper has potent application in the area of pharmaceutical and green chemistry. The work reports the results of an analysis of the lidocaine molecule conformational behavior in a supercritical carbon dioxide medium. Based on the nuclear Overhauser effect spectroscopy (2D NOESY) data, the authors determine the fractions of lidocaine molecule conformers in scCO 2 at temperatures and pressures exceeding the critical point (308.15 K; 10–20 MPa). The paper also shows the effect of conformational inversion for this system at 308.15 K and 22 MPa. Since lidocaine polymorphic transformations can be accompanied by changes in the molecule conformation in the crystal elemental unit cell, it is quite urgent to determine the conformer fractions of this compound. [ABSTRACT FROM AUTHOR]

The dynamism of life depends critically on the dynamism of bio-macromolecules themselves, notably proteins. The bio-macromolecular dynamism originates from weak non-bonding interactions, which inevitably fluctuate under physiological conditions. The fascination lies in the fact that, in proteins, the basically random “non-biological fluctuations” of atoms are often turned into specific “biological fluctuations” of larger amplitude, which would be directly coupled to protein function and consequently the dynamism of life such as growth, motility, sensing, adaptation and disease. The success of the combination of pressure perturbation with advanced nuclear magnetic resonance (NMR) spectroscopy by using the online cell method has provided a powerful means for investigating details of such “biological fluctuations”, which encompass, in general, a much wider conformational space of a protein than hitherto explored. Some representative strategies of high pressure NMR spectroscopy for characterizing protein dynamism will be discussed with actual examples. [ABSTRACT FROM PUBLISHER]

Abstract: The effects of temperature and pressure on physical properties of the ferroelectric inclusion compound bis-thiourea pyridinium bromide were studied by dielectric spectroscopy, neutron and X-ray diffractometry and nuclear magnetic resonance (NMR). The results permitted a construction of the p–T phase diagram for this compound. At ambient pressure bis-thiourea pyridinium bromide exists in three phases and the ferro-ferroelectric phase transition observed at T 2 =150K is discontinuous in contrast to the ferro-paraelectric phase transition observed at T 1 =180K. The application of pressure of about 800MPa at room temperature and then cooling of this compound to below T= 160K induces the appearance of a new phase (IV). [Copyright &y& Elsevier]

Abstract: The unique role of pressure in protein folding studies is emphasized. Variable-pressure NMR experiments carried out under equilibrium conditions give unique opportunities to explore the energy landscape for protein folding. Intermediate conformers that may appear transiently in the kinetic folding experiments may be stably trapped under pressure, allowing examination of their conformations in site-specific detail with modern NMR spectroscopy. The intimate relationship between the kinetic folding experiment and the equilibrium pressure experiment is described with examples from ubiquitin and hen lysozyme. [Copyright &y& Elsevier]

Abstract: High pressure measurements in most scientific fields rely on metal vessels given the superior tensile strength of metals. We introduce high pressure magnetic resonance imaging (MRI) measurements with metallic vessels. The developed MRI compatible metallic pressure vessel concept is very general in application. Macroscopic physical systems are now amenable to spatially resolved nuclear magnetic resonance (NMR) study at variable pressure and temperature. Metallic pressure vessels not only provide inherently high tensile strengths and efficient temperature control, they also permit optimization of the MRI RF probe sensitivity. An MRI compatible pressure vessel is demonstrated with a rock core holder fabricated using non-magnetic stainless steel. Water flooding through a porous rock under pressure is shown as an example of its applications. High pressure NMR spectroscopy plays an indispensable role in several science fields. This work will open new vistas of study for high pressure material science MRI and MR. [Copyright &y& Elsevier]

Abstract: The effect of temperature and pressure on physical properties of the ferroelectric bis-thiourea pyridinium nitrate inclusion compound has been studied by dielectric spectroscopy and nuclear magnetic resonance (NMR). At ambient pressure the ferroparaelectric phase transition observed at T 2 =216K is continuous in contrast to the nonferroelectric phase transition observed at T 1 =273K. Under small pressures, the temperatures of the phase transitions T 1 and T 2 increase with increasing pressure. Starting from about 250MPa, T 1 temperature decreases with increasing pressure, while T 2 temperature increases with increasing pressure. At 450MPa and 245K a triple point is observed. Bis-thiourea pyridinium nitrate undergoes a continuous phase transition from the ferroelectric to paraelectric phase under 450MPa, while above this pressure the phase transition from the ferroelectric to paraelectric phase is discontinuous. The change in the phase transition character is related to the crystallographic change in the group–subgroup relation between the ferro- and paraelectric phases taking place with increasing pressure. [Copyright &y& Elsevier]

Abstract: We have used low temperatures (down to −20°C) and high pressures (up to 2000bar) to populate low-lying excited state conformers of hen lysozyme, and have analyzed their structures site-specifically using 15N/1H two-dimensional HSQC NMR spectroscopy. The resonances of a number of residues were found to be selectively broadened, as the temperature was lowered at a pressure of 2000bar. The resulting disappearance of cross-peaks includes those of residues in the β-domain of the protein and the cleft between the β- and α-domains, both located close to water-containing cavities. The results indicate that low-lying excited state conformers of hen lysozyme are characterized by slowly fluctuating local conformations around these cavities, attributed to the opportunities for water molecules to penetrate into the cavities. Furthermore, we have found that these water-containing cavities are conserved in similar positions in lysozymes from a range of different biological species, indicating that they are a common evolutionary feature of this family of enzymes. [Copyright &y& Elsevier]

NMR experiments at variable pressure reveal a wide range of conformation of a globular protein spanning from within the folded ensemble to the fully unfolded ensemble, herewith collectively called 'high-energy conformers'. The observation of 'high-energy conformers' in a wide variety of globular proteins has led to the 'volume theorem': the partial molar volume of a protein decreases with the decrease in its conformational order. Since 'high-energy conformers' are intrinsically more reactive than the basic folded conformer, they could play decisive roles in all phenomena of proteins, namely function, environmental adaptation and misfolding. Based on the information on high-energy conformers and the rules on their partial volume in its monomeric state and amyloidosis, one may have a general view on what is happening on proteins under pressure. Moreover, one may even choose a high-energy conformer of a protein with pressure as variable for a particular purpose. Bridging 'high-energy conformers' to macroscopic pressure effects could be a key to success in pressure application to biology, medicine, food technology and industry in the near future. [ABSTRACT FROM AUTHOR]

The equilibrium unfolding of hen lysozyme at pH 2 was studied as a function of pressure (0.1~700MPa) and temperature (-10°C~50°C) using Trp fluorescence as monitor supplemented by variable pressure 1H NMR spectroscopy (0.1~400MPa). The unfolding profiles monitored by the two methods allowed the two-state equilibrium analysis between the folded (N) and unfolded (U) conformers. The free energy differences ΔG (=GU -GN) were evaluated from changes in the wavelength of maximum fluorescence intensity (λ max) as a function of pressure and temperature. The dependence of ΔG on temperature exhibits concave curvatures against temperature, showing positive heat capacity changes (ΔCp =CpU -CpN = 1.8-1.9 kJ mol-1 deg-1) at all pressures studied (250~400 MPa), while the temperature TS for maximal ΔG increased from about 10°C at 250MPa to about 40°C at 550MPa. The dependence of ΔG on pressure gave negative volume changes (ΔV=VU -VN) upon unfolding at all temperatures studied (-86~-17 mlmol-1 for -10°C~50°C), which increase significantly with increasing temperature, giving a positive expansivity change (Δα~1.07mlmol-1 deg-1). A phase-diagram between N and U (for ΔG=0) is drawn of hen lysozyme at pH 2 on the pressure-temperature plane. Finally, a three-dimensional free energy landscape (ΔG) is presented on the p-T plane. [ABSTRACT FROM AUTHOR]

Abstract: A recoverable, water soluble, hydrogenation catalyst was synthesized by reacting poly-N-isopropylacrylamide containing a terminal amino group (H2N–CH2CH2–S–pNIPAAm) with [Rh(CO)2Cl]2 in organic solvents to form the square planar rhodium complex (Rh(CO)2Cl(H2 N–CH2CH2–S–pNIPAAm)). The catalyst–ligand structure was characterized using in situ multinuclear NMR, XAFS and IR spectroscopic methods. Model complexes containing glycine (H2NCH2COOH), cysteamine (H2NCH2CH2SH) and methionine methyl ester (H2NCH(CH2CH2SCH3)COOCH3) ligands were studied to aid in the interpretation of the coordination sphere of the rhodium catalyst. The spectroscopic data revealed a switch in ligation from the amine bound (Rh–NH2–CH2CH2–S–pNIPAAm) to the thioether bound (Rh–S(–CH2CH2NH2)(–pNIPAAm)) rhodium when the complex was dissolved in water. The evolution of the structure of the rhodium complex dissolved in water was followed by XAFS. The structure changed from the expected monomeric complex to form a rhodium cluster of up to four rhodium atoms containing one SRR′ ligand and one CO ligand per rhodium center. No metallic rhodium was observed during this transformation. The rhodium–rhodium interactions were disrupted when an alkene (3-butenol) was added to the aqueous solution. The kinetics of the hydrogenation reaction were measured using a novel high-pressure flow-through NMR system and the catalyst was found to have a TOF of 3000/Rh/h at 25°C for the hydrogenation of 3-butenol in water. [Copyright &y& Elsevier]

High pressure nuclear magnetic resonance (HP-NMR) spectroscopy has become a useful tool for homogeneous catalysis research, both in industry and academia. It is a “window” on catalysis at variable temperatures and elevated pressures, and allows the researcher unprecented access to information on catalyst behaviour under process conditions. HP-NMR studies carried out on modified cobalt hydroformylation catalysts are presented from an industrial perspective. The ligands of interest are bridged bicyclic phosphines derived from phobane and (R)-(+)-limonene. Integration of HP-NMR with HP-IR, molecular modelling and bench experiments is also discussed. [Copyright &y& Elsevier]

Encapsulating a protein in a reverse micelle and dissolving it in a low-viscosity solvent can lower the rotational correlation time of a protein and thereby provides a novel strategy for studying proteins in a variety of contexts. The preparation of the sample is a key element in this approach and is guided by a number of competing parameters. Here we examine the applicability of several strategies for the preparation and characterization of encapsulated proteins dissolved in low viscosity fluids that are suitable for high performance NMR spectroscopy. Ubiquitin is used as a model system to explore various issues such as the homogeneity of the encapsulation, characterization of the hydrodynamic performance of reverse micelles containing protein molecules, and the effective pH of the water environment of the reverse micelle. [ABSTRACT FROM AUTHOR]

Application of triple-resonance and isotope-edited-NOE methods to the study of increasingly larger macromolecules and their complexes remains a central goal of solution NMR spectroscopy. The slow reorientational motion of larger molecules leads to rapid transverse relaxation and results in losses in both resolution and sensitivity of multidimensional-multinuclear solution NMR experiments. A recently described technique employs a physical approach to increase the tumbling rate of macromolecules in an attempt to preserve access to the full range of structural restraints available to studies of smaller systems. This technique involves encapsulation of a hydrated protein in a surfactant shell which is subsequently solubilized in a low viscosity solvent. A simple, efficient and cost effective NMR cell that accommodates the moderate liquefaction pressures required in the encapsulation method is described. Application of the method to the 56 kD triose phosphate isomerase homodimer is demonstrated. [ABSTRACT FROM AUTHOR]

In situ, high-pressure NMR was used to investigate the hydroformylation reaction of ethylene in liquid CO2 using Rh(CO)2acac as the catalyst precursor and (p-CF3C6H4)3P, tris(p-trifluoromethylphenyl)phosphine, as the ligand under different thermodynamic conditions (T=10–23 °C, PCO=PH2=10–15 bar, PC2H4=10–15 bar, PCO2=207 bar). 1H-NMR was used to monitor the reaction progress of the hydroformylation of ethylene with a rhodium catalyst under select conditions of temperature and CO2 solvent pressure. Potential resting states of the rhodium catalyst were investigated by 31P{1H}-NMR. This is the first description of a rhodium catalyzed hydroformylation reaction in liquid CO2 monitored in situ by high pressure NMR. [Copyright &y& Elsevier]

The majority of proteins are too large to be comprehensively examined by solution NMR methods, primarily because they tumble too slowly in solution. One potential approach to making the NMR relaxation properties of large proteins amenable to modern solution NMR techniques is to encapsulate them in a reverse micelle which is dissolved in a low viscosity fluid. Unfortunately, promising low viscosity fluids such as the short chain alkanes, supercritical carbon dioxide, and various halocarbon refrigerants all require the application of significant pressure to be kept liquefied at room temperature. Here we describe the design and use of a simple cost effective NMR tube suitable for the preparation of solutions of proteins encapsulated in reverse micelles dissolved in such fluids. [ABSTRACT FROM AUTHOR]

The effect of pressure on the structure of gurmarin, a globular, 35-residue protein from Gymnema sylvestre, was studied in aqueous environment (95% 1H2O/5% 2H2O, pH 2.0) with an on-line variable pressure NMR system operating at 750 MHz. Two-dimensional TOCSY and NOESY spectra were measured as functions of pressure between 1 and 2000 bar at 40 °C . Practically all the proton signals of gurmarin underwent some shifts with pressure, showing that the entire protein structure responds to, and is altered by, pressure. Most amide protons showed different degrees of low field shifts with pressure, namely 0–0.2 ppm with an average of 0.051 ppm at 2000 bar, showing that they are involved in hydrogen bonding and that these hydrogen bonds are shortened by pressure by different degrees. The tendency was also confirmed that the chemical shifts of the amide protons exposed to the solvent (water) are more sensitive to pressure than those internally hydrogen bonded with carbonyls. The pressure-induced shifts of the Hα signals of the residues in the β-sheet showed a negative correlation with the ‘folding’ shifts (difference between the shift at 1 bar and that of a random coil), suggesting that the main-chain torsion angles of the β-sheet are slightly altered by pressure. Significant pressure-induced shifts were also observed for the side-chain protons (but no larger than 10% of the ‘folding’ shifts), demonstrating that the tertiary structure of gurmarin is also affected by pressure. Finally, the linearity of the pressure-induced shifts suggests that the compressibility of gurmarin is invariant in the pressure range between 1 and 2000 bar. [ABSTRACT FROM AUTHOR]