细胞色素b5突变体V45H NMR初步研究

通过分析在H2O和D2O中采集,DQF-COSY,TOCSY和NOESY等二维核磁共振波谱鉴定了细胞色素b5定点突变体V45H(残基Val^45突变为His^45)的大多数氨基酸残基的质子自旋系统,通过解析NOESY谱中的dNN(i,i+1),dαN(i,i+1),dαN(i,i+2),dαN(i,i+3),dαβ(i,i+3)和dβN(i,i+1)等NOE相关,完成了其序列特异性归属以及主链和侧链质子共振信号的全归属。突变体V45H的二级结构分析表明残基Val^45突变为His^45对分子的整体折叠影响不大。但是,与野生型细胞色素b5相比较,突变体V45H主链酰胺质子的化学位移指数提示突变使其血红素疏水腔的微环境受到扰动。以上实验结果为进一步测定V45H的溶液结构和分析残基Val^45在蛋白质中的作用提供了基础。     

Solid-state NMR and calorimetry of structural waters in helical peptides

The peptide hydrates Gly-Gly-Val x 2H(2)O (GGV) and Gly-Ala-Leu x 3H(2)O (GAL) are known to adopt alpha-helical configurations containing waters of hydration in which each water is H-bonded to three or four peptide groups. Herein we report a thermodynamic and solid-state NMR ((2)H and (17)O) study of these peptides. From TGA and DSC, the average enthalpy per H-bond is 15 kJ/mol. The dynamics and average orientation of the hydrate are studied by powder and single-crystal (2)H NMR. Whereas waters that are shown by the X-ray structure to be coordinated by four hydrogen bonds do not yield observable (2)H NMR signals at room temperature, two of the three triply coordinated waters yield residual (2)H quadrupole coupling tensors characteristic of rapid 180 degrees flip motions and the orientation of the residual tensor is that expected from the X-ray structure-derived H-bonding pattern. At -65 degrees C, the flip motions of triply coordinated water in GGV slow into the (2)H NMR intermediate exchange regime whereas the tetrahedrally coordinated water approaches the slow-exchange limit and yields an observable NMR signal. Extensive isotope exchange between water vapor and crystalline GGV establishes the presence of additional hydrate dynamics and solid-state proton transfer along a chain of water-bridged protonated alpha-amino groups.     

Solid-state NMR structural studies of peptides immobilized on gold nanoparticles

In this paper we describe solid-state NMR experiments that provide information on the structures of surface-immobilized peptides. The peptides are covalently bound to alkanethiolates that are self-assembled as monolayers on colloidal gold nanoparticles. The secondary structure of the immobilized peptides was characterized by quantifying the Ramachandran angles phi and psi. These angles were determined in turn from distances between backbone carbonyl 13C spins, measured with the double-quantum filtered dipolar recoupling with a windowless sequence experiment, and by determination of the mutual orientation of chemical shift anisotropy tensors of 13C carbonyl spins on adjacent peptide planes, obtained from the double-quantum cross-polarization magic-angle spinning spectrum. It was found that peptides composed of periodic sequences of leucines and lysines were bound along the length of the peptide sequence and displayed a tight alpha-helical secondary structure on the gold nanoparticles. These results are compared to similar studies of peptides immobilized on hydrophobic surfaces.     

Si-VPI-5分子筛的多核固体NMR研究

磷酸铝类分子筛是近年来继Y型和ZSM七分子筛之后的第三代合成分子筛材料，其骨架由A10。和P0。四面体均匀交替地组成问．由于带负电行的A10。和带正电荷的PO。四面体数目相等，整个骨架呈电中性，所以这类分子筛本身无离子交换能力和催化活性．当用硅或某些金属离子（如Mg、Fe、Co、Zn等）对磷酸铝分子筛进行同晶取代，就会在骨架上造成电行不平衡，从而使这类分子筛具有一定的离子交换能力和酸性【习．因而对硅或金属离子在磷酸错类分子筛中取代机理的研究一直是人们感兴趣的问题问．Vpl－5是最近才合成出来的具有18圆环一维孔结构的…     

Solid-state 17O NMR as a probe for structural studies of proteins in biomembranes

We report the first example of 17O NMR spectra from a selectively labeled transmembrane peptide, 17O-[Ala12]-WALP23, as a lyophilized powder and incorporated in hydrated phospholipid vesicles. It is shown that at high magnetic field it is feasible to apply 17O NMR to the study of membrane-incorporated peptides. Furthermore, we were able to estimate distances within the selectively labeled WALP peptide, which represents a consensus transmembrane protein sequence. This work opens up new applications of 17O solid-state NMR on biological systems.     

Glycerol revisited molecular dynamic simulations of structural,dynamical, and thermodynamic properties

We performed molecular dynamics simulations to investigate the properties of glycerol for a wide range of temperatures at standard pressure. We calculated structural (radial distribution functions and pair potential of mean force), dynamical (mean square displacement and transport properties), and thermodynamic (density, thermal expansion, and Hildebrand solubility parameter) properties of glycerol. The results of structural properties showed that the correlation between glycerol atoms weakens as temperature increases. The values of mean square displacement showed that changing temperature has a strong influence on mobility of glycerol atoms. The values of diffusion coefficient and viscosity are remarkably close to the experimental values over the whole range of temperatures studied. The simulation results provide a reasonable estimation of density with percent error of 0.40 %. The simulated values of Hildebrand solubility parameter of glycerol decrease with raising temperature because the cohesive forces weaken. To the best of our knowledge, this work for the first time calculates the potential of mean force, viscosity, and Hildebrand solubility parameter of glycerol by MD simulation.     

NMR and structural properties of CsAu and RbAu

NMR and X-ray diffraction studies of granular samples of the intermetallic compounds, CsAu and RbAu, are reported. Studies of X-ray line intensities indicate that the CsCl lattice structure is well ordered for both materials. For the semiconducting compound CsAu, excess Cs in the lattice is shown to be the primary source of conduction electrons. X-ray studies show an expansion of lattice constant with addition of excess Cs. Measurements of NMR line shapes, Knight shifts, and relaxation times for CsAu confirm that the excess Cs is atomically dispersed in the samples. NMR measurements show our RbAu samples to have a metallic nature. However, the metallic characteristics may well derive from excess Rb known to be present in the samples.     

Computational study of structural and dynamical properties of formamide-water mixtures

A molecular dynamics simulation study of structural and dynamical properties in liquid mixtures of formamide and water is presented. Site-site radial pair distribution functions, local mole fractions, pair energy distributions, and tetrahedral orientational order are the quantities analyzed to investigate the local structure in the simulated mixtures, along with a review of the intermolecular structure in terms of the distribution of hydrogen bonds. Our results indicate that there is a substitution of formamide molecules by water in the hydrogen bonds and a formation of a common hydrogen bond network. By analyzing the extent of tetrahedral order in the liquid as a function of composition, it is observed that whereas the tetrahedral network of liquid water is progressively lost by increasing the formamide concentration, the water structure within the first coordination shell is preserved and somewhat enhanced. The hydrogen-bond mean lifetimes were estimated by performing a time integration of the autocorrelation functions of bond occupation numbers. The lifetimes associated with hydrogen bonds between water, formamide, and interspecies pairs are found to increase with increasing formamide concentration. The lifetimes of the water hydrogen bonds show the largest variations, supporting the picture of an enhancement of the water structure among the nearest neighbors within the first coordination shell. We have used two different force field models for water, SPC/E [J. C. Berendsen et al., J. Phys. Chem. 91, 6269 (1987)] and TIP4P/2005 [J. L. F. Abascal and C. Vega, J. Chem. Phys. 123, 234505 (2005)]. Our results for structural and dynamical properties yield very small differences between those models, the TIP4P/2005 predicting a slightly more structured liquid and, consequently, exhibiting a slightly slower translational and librational dynamics.     

INS,IR, RAMAN, 1H NMR and DFT investigations on dynamical properties of l-asparagine

Results of inelastic neutron scattering (INS), infra-red (IR), Raman and ¹H NMR spectroscopy used for investigations on the l-asparagine dynamics are reported. The crystallographic structure and experimental vibrational spectra are compared with those calculated by the DFT methods applied to the solid state. Very good conformity of the experimental and theoretical structures has been found. The NH₃⁺ torsional vibration mode is observed in the INS spectra at 494 cm⁻¹, while the bands assigned to the vibrations of the strong NH⋯O hydrogen bonds are observed at 2849, 2650, and 2480 cm⁻¹ in the IR spectrum. A ¹H NMR investigation has been carried out at 26.75 MHz in the temperature range 150–300 K. For l-asparagine the activation energy needed for the NH₃⁺ group reorientation is equal 5.6 kcal/mol.     

Solid-state NMR spectroscopy reveals that water is nonessential to the core structure of alpha-synuclein fibrils

Protein aggregation is implicated in the etiology of numerous neurodegenerative diseases. An understanding of aggregation mechanisms is enhanced by atomic-resolution structural information, of which relatively little is currently available. Lewy bodies, the pathological hallmark of Parkinson's disease, contain large quantities of fibrillar alpha-synuclein (AS). Here we present solid-state NMR spectroscopy studies of dried AS fibrils. The spectra have high resolution and sensitivity, and the site-resolved chemical shifts agree very well with those previously observed for hydrated fibrils. The conserved chemical shifts indicate that bulk water is nonessential to the fibril core structure. Moreover, the sample preparation procedure yields major improvements in spectral sensitivity, without compromising spectral resolution. This advance will greatly assist the atomic-resolution structural analysis of AS fibrils.     

Solid-state NMR on a large multidomain integral membrane protein: the outer membrane protein assembly factor BamA

Multidomain proteins constitute a large part of prokaryotic and eukaryotic proteomes and play fundamental roles in various physiological processes. However, their structural characterization is challenging because of their large size and intrinsic flexibility. We show here that motional-filtered high-resolution solid-state NMR (ssNMR) experiments allow for the observation and structural analysis of very large multidomain membrane proteins that are characterized by different motional time scales. This approach was used to probe the folding of the 790-residue membrane protein BamA, which is the core component of the Escherichia coli outer membrane protein assembly machinery. A combination of dipolar- and scalar-based two-dimensional ssNMR experiments applied to two uniformly (13)C,(15)N-labeled BamA variants revealed characteristic secondary structure elements and distinct dynamics within the BamA transmembrane protein segment and the periplasmic POTRA domains. This approach hence provides a general strategy for collecting atomic-scale structural information on multidomain (membrane) proteins in a native-like environment.     

Ab initio calculation of structural,lattice dynamical,and thermal properties of cubic silicon carbide

We present first-principles calculations of the structural, lattice dynamical, and thermal properties as well as Raman results for cubic silicon carbide (3C SiC). The plane-wave pseudopotential approach to density functional theory (DFT ) in the local density approximation has been used to calculate the equilibrium properties of 3C SiC, i.e., the ground-state energy, the band structure, the valence electron density, the lattice constant, the bulk modulus, its pressure derivative, and the ionicity factor of the chemical bonds. The linear-response theory within DFT has been used to obtain the phonon frequencies, the eigenvectors, and the mean-square atomic displacements. Furthermore, we calculated the mode Grueisen parameters, the internal-strain parameter, the elastic constants, the Born effective charge, and the high-frequency dielectric constant. The specific heat at constant volume and at constant pressure, the thermal expansion coefficient, the temperature dependence of the lattice constant, and that of the isothermal and adiabatic bulk modulus have been derived within the quasi-harmonic approximation. Finally, the second-order Raman spectrum of 3C SiC has been calculated using phenomenological polarizability coefficients and ab initio frequencies and eigenvectors. © 1995 John Wiley & Sons, Inc.     

Solid-state 17O NMR study of α-d-glucose: exploring new frontiers in isotopic labeling,sensitivity enhancement,and NMR crystallography

We report synthesis and solid-state ¹⁷O NMR characterization of α-d-glucose for which all six oxygen atoms are site-specifically ¹⁷O-labeled. Solid-state ¹⁷O NMR spectra were recorded for α-d-glucose/NaCl/H₂O (2/1/1) cocrystals under static and magic-angle-spinning (MAS) conditions at five moderate, high, and ultrahigh magnetic fields: 14.1, 16.4, 18.8, 21.1, and 35.2 T. Complete ¹⁷O chemical shift (CS) and quadrupolar coupling (QC) tensors were determined for each of the six oxygen-containing functional groups in α-d-glucose. Paramagnetic Cu(ii) doping was found to significantly shorten the spin–lattice relaxation times for both ¹H and ¹⁷O nuclei in these compounds. A combination of the paramagnetic Cu(ii) doping, new CPMAS CryoProbe technology, and apodization weighted sampling led to a sensitivity boost for solid-state ¹⁷O NMR by a factor of 6–8, which made it possible to acquire high-quality 2D ¹⁷O multiple-quantum (MQ) MAS spectra for carbohydrate compounds. The unprecedented spectral resolution offered by 2D ¹⁷O MQMAS spectra permitted detection of a key structural difference for a single hydrogen bond between two types of crystallographically distinct α-d-glucose molecules. This work represents the first case where all oxygen-containing functional groups in a carbohydrate molecule are site-specifically ¹⁷O-labeled and fully characterized by solid-state ¹⁷O NMR. Gauge Including Projector Augmented Waves (GIPAW) DFT calculations were performed to aid ¹⁷O and ¹³C NMR signal assignments for a complex crystal structure where there are six crystallographically distinct α-d-glucose molecules in the asymmetric unit.

We report the first “total synthesis” of ¹⁷O-labeled d-glucose and its solid-state ¹⁷O NMR characterization with unprecedented sensitivity and resolution.     

Solid-state NMR of a paramagnetic DIAD-FeII catalyst: sensitivity, resolution enhancement, and structure-based assignments

A general protocol for the structural characterization of paramagnetic molecular solids using solid-state NMR is provided and illustrated by the characterization of a high-spin Fe(II) catalyst precursor. We show how good NMR performance can be obtained on a molecular powder sample at natural abundance by using very fast (>30 kHz) magic angle spinning (MAS), even though the individual NMR resonances have highly anisotropic shifts and very short relaxation times. The results include the optimization of broadband heteronuclear (proton-carbon) recoupling sequences for polarization transfer; the observation of single or multiple quantum correlation spectra between coupled spins as a tool for removing the inhomogeneous bulk magnetic susceptibility (BMS) broadening; and the combination of NMR experiments and density functional theory calculations, to yield assignments.     

Study of dynamical and structural properties of microemulsions by chemical physics methods

In an attempt to elucidate structural properties, high resolution NMR, NMR proton relaxation time, viscosity, and electron microscopy experiments have been run on microemulsions (water, toluene, sodium dodecyl sulfate, n-butanol). Results are in good agreement with water/oil, oil/water, and perhaps lamellar structures. They show a continuous evolution between all these structures; inversion zones have been pointed out. Over all the stability domain, the surfactant is responsible for the membrane-like structure, and fast molecular dynamics seems to be a fundamental parameter of the stability.     

Solid-state (14)N MAS NMR of ammonium ions as a spy to structural insights for ammonium salts

The high resolution offered by magic-angle spinning (MAS), when compared to the static condition in solid-state NMR of powders, has been used to full advantage in a (14)N MAS NMR study of some ammonium salts: CH(3)NH(3)Cl, (NH(4))(2)(COO)(2) x H(2)O, (CH(3))(3)(C(6)H(5)CH(2))NCl, (CH(3))(3)(C(6)H(5))NI, [(n-C(4)H(9))(4)N](2)Mo(2)O(7), (NH(4))(2)HPO(4), and NH(4)H(2)PO(4). It is shown that the high-quality (14)N MAS NMR spectra, which can be obtained for these salts, allow determination of the (14)N quadrupole coupling parameters, i.e. C(Q) (the quadrupole coupling constant) and eta(Q) (the asymmetry parameter), with very high precision. In particular, it is shown that precise C(Q), eta(Q) parameters can be determined for at least two different (14)N sites in case the individual spinning-sideband (ssb) intensities arise from a single manifold of ssbs, i.e. the ssbs for the two sites cannot be resolved. This feature of (14)N MAS NMR, which is the first demonstration for manifolds of ssb in MAS NMR without the potential information from a central transition, becomes especially useful at the slow spinning frequencies (nu(r) = 1000-1500 Hz) applied to some of the ammonium salts studied here. The detection of the number of sites has been confirmed by the corresponding crystal structures determined from single-crystal X-ray diffraction (XRD), either in this work for the unknown structure of benzyl trimethylammonium chloride or from reports in the literature. The magnitudes of the (14)N quadrupole coupling constants for the ammonium salts studied here are in the range from C(Q) approximately 20 kHz to 1 MHz while the asymmetry parameters span the full range 0 < or = eta(Q) < or = 1. Clearly, the (14)N quadrupole coupling parameters (C(Q), eta(Q)) for ammonium ions appear highly sensitive toward crystal structure and therefore appreciably more informative for the characterization of ammonium salts in comparison to the isotropic (14)N (or (15)N) chemical shifts.