Proton NMR Signals Research Articles

1H and 13C NMR spectroscopic study of oxidation of D,L‐cystine and 3,3′‐dithiobis(propionic acid) with hydrogen peroxide in aqueous solution

AbstractThe oxidation of symmetrical disulfides [D,L‐cystine (1) and 3,3′‐dithiobis(propionic acid) (2)] with hydrogen peroxide in D2O–NaOH solution (pH 10–11) was studied by NMR spectroscopy. Assignments of the proton and carbon NMR signals of starting materials (1 and 2) and products of oxidation are based on conventional 1D NMR methods (DEPT, selective spin decoupling). Formation of C—S bond cleavage products or, in case of 2, partially oxidized intermediates was not detected. The accelerating effect of Cu2+ cations, but not Fe3+ cations, on the oxidation rate of 1 in basic medium was demonstrated. Copyright © 2002 John Wiley & Sons, Ltd.

Micellar Aggregation and Structure of Dodecyl Heptaethoxylates (C12E7) with Different Oxyethylene Distributions in Aqueous Media

The micellar aggregation and structure, including aggregation number, hydrophobicity, micelle size, and micelle shape, were studied for four dodecyl heptaethoxylates with different oxyethylene distributions (Pure-7, NRE-7, BRE-7, and xBRE-7) using fluorescence, NMR, dynamic light scattering (DLS), and small angle neutron scattering (SANS). The aggregation number, measured from a steady state fluorescence quenching method, increased with the polydispersity of oxyethylene chain and with concentration. It was shown from the line half-width of proton NMR signals that the intermediate layer becomes wider as the polydispersity of the chain is increased. Changes in the hydrodynamic radius and radius of gyration show that micelles take different shapes with changing oxyethylene distributions and there is a transition, probably from rodlike to spherical, at a specific concentration. At very low concentrations, the fitted core and shell radii of monodisperse C12E7 from SANS experiments showed a marked change with concentration. The aggregation number estimated from a polydisperse core−shell sphere model showed fairly good agreement with that from steady state fluorescence quenching. However, the fitted results for broad ethoxylates using sphere, prolate, and oblate models were physically meaningless. Two possible explanations are suggested: first, a rough surface of micelles, and second, polydispersity of micelles in shape and size.

Structure-function relationship in type II cytochrome c(3) from Desulfovibrio africanus: a novel function in a familiar heme core.

NMR and visible spectroscopy were used to characterize the type II tetraheme cytochrome c(3) isolated from the periplasmic space of Desulfovibrio africanus, a sulfate-reducing bacterium. Although structurally similar to other cytochromes c(3), this protein displays distinct functional properties. Proton NMR signals from the four hemes were assigned to the structure in the ferri- and ferrocytochromes using two-dimensional NMR experiments. The thermodynamic parameters of the hemes and of an acid-base center in the type II cytochrome c(3) were determined using NMR and visible spectroscopies. The thermodynamic features indicate that electrostatic effects dominate all of the interactions between the centers and no positive cooperativity between hemes is observed. The redox-Bohr effect in this protein is associated with the acid-base equilibrium of a propionate of heme II instead of propionate 13 of heme I as is the case for all of the type I cytochromes c(3). These novel functional properties are analyzed together with the redox-linked structural differences reported in the literature and reveal a mechanistic basis for type II cytochromes c(3) having a physiological function that is different from that of type I cytochromes c(3).

3L1045 収縮に伴う骨格筋内水プロトンのNMR横緩和経過の変化(10.筋肉(筋蛋白・収縮),一般講演,日本生物物理学会第40回年会)

3L1045 収縮に伴う骨格筋内水プロトンのNMR横緩和経過の変化(10.筋肉(筋蛋白・収縮),一般講演,日本生物物理学会第40回年会)

An 1H and 13C NMR conformational study of 2-(benzotriazol-1-yl)-substituted tetrahydropyrans

Proton and carbon NMR signals for 2-(benzotriazol-1-yl)tetrahydropyrans are assigned on the basis of spin decoupling, H,H-COSY, HETCOR, and nuclear Overhauser enhancement experiments. Conformational preferences are deduced. It was found that 2-(benzotriazol-1-yl) substituents: (i) prefer the equatorial orientation; and (ii) display a rotameric preference to minimize the electronic repulsion and (or) steric interaction.Key words: anomeric, NMR, tetrahydropyrans.

Proton magnetization enhancement of solvents with hyperpolarized xenon in very low-magnetic fields

The polarization transfer between hyperpolarized xenon (Xe) and the protons (H) of different solutes at very low magnetic fields ranging from 0.001 to 0.014 T is reported. Due to Xe–H cross-relaxation (Spin Polarized Induced Nuclear Overhauser Effect (SPINOE)) the observed proton NMR signal of liquid ethanol, butanol and toluene is enhanced at room temperature by a factor of 1000 in a field of B=0.001 T. Smaller proton enhancement factors between 10 and 100 are measured for ethanol/water mixtures and for sunflower oil. Using high-field Xe NMR, the phase transitions of melting hyperpolarized Xe ice frozen onto the surface of ethanol ice is investigated.

Interaction of potassium fluoride with α- d-glucose

Addition of KF to solutions of α- d-glucose (α dG) in DMSO-d 6 and D 2O alters the 1H NMR spectra, which is attributed to an interaction of the hydrogen atoms of the OH groups with the basic F − anions of the salt. It is shown that K + cations do not interact with the oxygen atoms of the OH groups of the α dG. Mutarotation rates of α dG in D 2O in the presence of potassium halides and alkaline chlorides were measured from the integrated 13C NMR signal of the anomeric protons. The mutarotation rates were higher with KF than other potassium halides. In order to shed light on the interactions of KF with the α dG, the mutarotation of α dG in the presence of KF and KOH were also studied using polarimetric measurements. At similar pH values, the effect of KF on the mutarotation rate is about five times that observed for KOH, indicating a major affinity for the F − anion by the anomeric proton as compared with OH −. The acceleration of the mutarotation process of α dG is evidence for KF–α dG interactions, since NMR spectra of β conformer are also altered by the presence of KF.

Enantioselective Quenching of Luminescence: Molecular Recognition of Chiral Lanthanide Complexes by Biomolecules in Solution

Principles, experimental techniques, and applications of enantioselective quenching of lanthanide luminescence are addressed. Upon the addition of chiral, enantiomerically resolved quencher molecules to an aqueous, racemic solution of the tris (pyridine-2,6-dicarboxylate) chelate of Eu(III) or Tb(III), strong quenching of the lanthanide luminescence is observed, with a quenching rate that depends on the chirality of the lanthanide species. Quenching by c-type cytochromes and vitamin B12 derivatives is discussed in detail. For the latter quenchers, the energy transfer reaction held responsible for the quenching proceeds via formation of an encounter complex between donor and quencher in which the actual energy transfer takes place. A structural model for this transient pair has been constructed on the basis of data on complexation between B12 and ground-state lanthanide chelate obtained by measurements of lanthanide induced shifts and relaxation of the NMR signals of protons of B12 and from the induced cir...

Review: Strong hydrogen bonding in molecules and enzymatic complexes

The physicochemical properties of low barrier hydrogen bonds (LBHBs) and single well hydrogen bonds (SWHBs) are contrasted with the properties of conventional hydrogen bonds. The LBHBs are much more common than the rare, symmetrical SWHBs. LBHBs are characterized by shortened hydrogen bond lengths and correspondingly lengthened covalent bonding, shortened distances between participating heteroatoms, far downfield proton NMR signals, low deuterium fractionation factors and high values of the enthalpy of activation for exchange of the proton with solvent protons. For many years, it was thought that LBHBs could exist only in aprotic media or crystalline or vapor states. Recently, however, the downfield protons associated with hydrogen maleate, hydrogen cis-cyclohexane-1,2-dicarboxylate and hydrogen 2,2-dimethylmalonate have been observed in 0.32 mol fraction water in acetone-d6 at −50 °C. The activation enthalpy for exchange of the downfield proton in hydrogen maleate with solvent water has been found to be 7.2 kcal mol−1, consistent with strong hydrogen bonding. Two examples of LBHBs in enzymes are the downfield proton bridging His 57 and Asp 102 in transition state analog complexes of chymotrypsin, and the proton bridging Tyr 14 and the equilenin-OH group in its complex with 3-ketosteroid isomerase. These protons display the structural, spectroscopic and chemical properties of LBHBs. Their presence in transition state analogue complexes suggests their importance in the transition states of enzymatic reactions. Copyright © 2001 John Wiley & Sons, Ltd.

Spatial Structure of a DNA Duplex d(CGTTTATT)p-Net:d(AATAAACG) with an Unusual Localization of a Covalently Bound Netropsin (Net) Analog According to Two-Dimensional NMR Spectroscopy

Two-dimensional 1H NMR (NOESY, COSY) spectroscopy was used to study the spatial structure of a DNA complex CGTTTATTp-Net:AATAAACG with a netropsin analog bound at the terminal 3′-phosphate group in aqueous solution. The positions of the proton NMR signals of the duplex are compared with those for the unmodified duplex and the free ligand. A mean conformation of the duplex is constructed by the molecular mechanics technique using the obtained NMR limitations on the interproton distances. The data obtained indicate that the aromatic pyrrole rings of the netropsin analog are involved in a stacking interaction with the terminal AT base pair of the duplex; this is generally not typical of ordinary minor-groove netropsin type ligands.

The Deuterium Isotope Effect on the NMR Signal of the Low-Barrier Hydrogen Bond in a Transition- State Analog Complex of Chymotrypsin

The participation of a low-barrier hydrogen bond (LBHB) in the mechanism of action of chymotrypsin introduces a new role for Asp 102 and His 57 in catalysis [C. S. Cassidy, J. Lin, and P. A. Frey (1997) Biochemistry 36, 4576–4584]. It is postulated that the LBHB increases the basicity of His 57-Nϵ2 in the transition state, thereby facilitating the abstraction of a proton from Ser 195, and stabilizes the tetrahedral intermediate in the acylation step. Evidence for this mechanism includes the downfield chemical shift of the proton bridging His 57 and Asp 102 in transition-state analog complexes and the low deuterium fractionation factors for this proton in the same complexes. We present additional spectroscopic evidence supporting the assignment of an LBHB between His 57 and Asp 102. The tetrahedral addition complex between Ser 195 of chymotrypsin and N-acetyl-l-leucyl-l-phenylalanyl trifluoromethylketone is regarded as a close structural analog of a tetrahedral intermediate. The deuterium NMR signal for the downfield deuteron bridging His 57 and Asp 102 in D2O has now been observed as a broad band centered at 17.8 ± 0.5 ppm. The proton NMR signal in H2O is centered at 18.9 ± 0.05 ppm. The two signals are clearly separated corresponding to a deuterium isotope effect of Δ[δH − δD] = 1.1 ± 0.5 ppm. Deuterium isotope effects in this range are characteristic of LBHBs, and this observation provides further support for the assignment of the proton bridging His 57 and Asp 102 in transition-state analog complexes as an LBHB.

Effects of Anions on the NMR Relaxation of Pyridinium and Di-tert-Butylpyridinium Ions in Acid Solution. Implications for Chemisorption on Solid Acids

The line shape of the NMR signals of protons bonded to nitrogen shows that the longitudinal relaxation of 14N (T1N) is much faster for di-tert-butylpyridinium ions (DTBPH+) than for pyridinium (PyH+) in solution. The relaxation times for ring carbons (T1C) indicate that the difference comes from a different rate of tumbling in solution, rather than from a difference in the electric field gradient. Computer modeling gives ratios of relaxation times (T1N = 1/R1N) of 10−20. Ion pairing has an opposite effect upon the two ions: it accelerates the relaxation of PyH+ but slows down the relaxation of DTBPH+. In the absence of electrostatic interactions with the solvent, ion pairing should increase the correlation time τc (decrease T1) for the anion positioned in the plane of the ring and should have only a small effect on τc for the anion perpendicular to the ring (along the z axis). The anion in the ion pair of PyH+ is positioned on the x axis (the C2 axis of the ring) for maximum hydrogen bonding with the N−H group. The inability of DTBP to form hydrogen bonds at nitrogen was confirmed by the equality of its 15N chemical shifts in methyl tert-butyl ether, dry and containing water. B3LYP/6-31G* calculations indicate that the positioning of an anion along the z axis of DTBPH+ induces a charge redistribution that reduces the electrostatic interaction of the cation with the solvent dipoles in the xy plane, thus decreasing the tumbling correlation time, τc, and increasing the NMR relaxation time, T1. These data suggest that chemisorption of pyridine on acid sites on solid surfaces occurs with the nitrogen facing the surface but that DTBP is chemisorbed on the side (flatwise) with its degree of hydronation depending on the degree of curvature of the surface around the site.

Synthesis, X-ray structure, single-crystal EPR and 1H NMR studies of a distorted square planar Cu(salEen)2(ClO4)2 complex in a novel bilayered architecture: salEen = N,N-diethylethylenesalicylidenamine.

Single-crystal X-ray structure and spectroscopic characterizations of Cu(salEen)2(ClO4)2, are reported; salEen is a Schiff base condensation product of equimolar amounts of salicylaldehyde and N,N-diethylethylenediamine. The complex crystallizes in a triclinic space group P1 with a = 12.055(4) A, b = 10.652(3) A, c = 12.701(3) A, alpha = 90.54(2) degrees, beta = 94.39(2) degrees, gamma = 91.35(3) degrees, and Z = 2. The coordination geometry around Cu(II) ion is tetrahedrally distorted square planar with salEen coordinating as a neutral bidentate ligand through N and O donor atoms (average Cu-N and Cu-O distances are 2.004 and 1.880 A, respectively). The counterion ClO4- makes H-bonding contacts with the neighboring cation moieties and forms a one-dimensional layered arrangement of the molecules. The pendent, N,N-diethylethylenediamine groups of salEen (from the centrosymmetrically related molecules) in adjacent layers interpenetrate, forming novel bilayered architectures, which are further held together by pi-pi stacking interactions. EPR studies on single crystals, in three mutually orthogonal planes, yield a rhombic g tensor (gx = 2.041(1), gy = 2.073(1), and gz = 2.220(1)) consistent with the distorted square planar geometry of the CuN2O2 moiety. The peak-to-peak line width of the EPR signal exhibits a |3 cos2 theta - 1|4/3 variation, attributable to one-dimensional magnetic exchange behavior of the complex. The analysis suggests that both the dipole-dipole and exchange interactions contribute to the line width. Interestingly, the complex is amenable for both EPR and NMR studies at ambient temperatures. The proton NMR signals are narrow in CD3CN solutions and the HOMO correlation spectroscopy (COSY) studies reveal the 1H connectivities. Nuclear spin lattice relaxation time (T1) measurements, using inversion recovery method, indicate that T1 values for all the protons are remarkably long compared to those of other mononuclear Cu(II) complexes.

Characterization of signals in the solution1H NMR spectrum of poly(isobutylene-co-p-methylstyrene) and their utility

Poly(isobutylene-co-p-methylstyrene) is an important precursor to Exxpro™ elastomers. A previous report detailed the characterization of both the proton and the carbon NMR spectra of the copolymer.1 However, several resonances in the proton NMR spectrum of the copolymer were not assigned. Specifically, the proton methine resonance of the BSB triad sequence is now identified and used to calculate BSB triad contribution to the copolymer microstructure. This report describes the assignment of this resonance and other resonances associated with microstructural sequence distribution around p-methylstyrene. The proton NMR signals of interest resonate at 2.8 ppm and 2.5 ppm in a typical spectrum for poly(isobutylene-co-p-methylstyrene). The nature of these resonances were determined by preparation and characterization of specifically deuterated poly(isobutylene-co-p-methylstyrene)s employing both one and two dimensional NMR techniques. The 2.8 ppm signal is assigned as the methine proton of a p-methylstyrene incorporated between two isobutylene units (the BSB triad). The signal at 2.5 ppm is assigned to the meso-BSS triad. Determination of these resonances allows for rapid evaluation of isolated p-methylstyrene units (BSB triads) present in the copolymer using only 1H NMR. The utility of this technique is demonstrated by comparing BSB triad values determined by 1H and 13C NMR analysis. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1680–1686, 2000

Measurement of the relaxation rate of the magnetization in Mn12O12-acetate using proton NMR echo

We present a novel method to measure the relaxation rate W of the magnetization of Mn 12O (12)-acetate (Mn12) magnetic molecular cluster in its S = 10 ground state at low T. It is based on the observation of an exponential growth in time of the proton NMR signal during the thermal equilibration of the magnetization of the molecules. We can explain the novel effect with a simple model which relates the intensity of the proton echo signal to the microscopic reversal of the magnetization of each individual Mn12 molecule during the equilibration process. The method should find wide application in the study of magnetic molecular clusters in off-equilibrium conditions.

Interface Polymerization in a Polymer Micelle: An NMR Study of the Radical Polymerization of Methyl Methacrylate at the Core−Shell Interface of Polystyrene-block-poly(methacrylic acid) Micelles

Systems containing poly(styrene)-block-poly(methacrylic acid) micelles (1.67 g/L), methyl methacrylate (1.88−3.76 g/L), and initiator (polymerization) or inhibitor (pure solubilization) in D2O buffer solution were studied by 1H NMR. The proton NMR signals of MMA dissolved in the micellar system have the same chemical shifts as those in the corresponding D2O buffer solution but exhibit a characteristically broadened and asymmetric shape. Separate signals with different chemical shifts and signal shapes were observed for MMA absorbed into the poly(styrene) core. From the shape analysis of the signals of the water-dissolved MMA in the micellar system, it can be deduced that the monomer is almost exclusively accumulated near the core−shell interface. Its radial distribution can be approximated by a Gaussian function with the maximum at the core radius R and half-width b of 1.65R and 1.93R for the MMA concentrations 2 and 4 g/L, respectively. An increase in temperature from 295 to 330 K leads to a faster self-...

Effect of blood oxygenation on proton NMR signal shape

1. The NMR signal width of blood protons is determined by symmetric broadening caused by dipoledipole interaction of blood plasma protons and asymmetric broadening caused by erythrocytes.

Intramolecular Quadruplex Formation of the G-Rich Strand of the Mouse Hypervariable Minisatellite Pc-1

The minisatellite Pc-1, isolated from the mouse genome consisting of a tandem repeat of d(GGCAG), is hypervariable with a mutation rate of 0.15/generation. Here we describe a structural characterization of the G-rich strand of Pc-1 by biochemical and physicochemical methods. It was found to be comparatively resistant to both single-stranded DNA-binding protein binding and digestion by single-stranded DNA-specific nuclease and to cause arrest of DNA synthesis. The guanine imino proton NMR signals observed on the Pc-1 G-rich strand and their slow 1H/2H exchange profiles pointed to a quadruplex structure with guanine quartets. The melting temperature of the quadruplex determined by CD was not dependent on DNA concentration. These results indicate that the G-rich strand of Pc-1 forms an intramolecular folded-back quadruplex structure under physiological conditions. Possible mechanisms of the Pc-1 mutations implicated with the formation of the quadruplex structure are discussed.

Exploring zero-point energies and hydrogen bond geometries along proton transfer pathways by low-temperature NMR

We have followed by NMR the zero-point energy changes of the hydrogen bond proton in 1:1 acid-base complexes AHB triple bond {A—H···B <-–> Aδ-···H···Bδ+ <-–> A-···H—B+} as a function of the proton position between A and B. For this purpose, the isotopic fractionation factors K between the acid-base complexes AHB + Ph3COD···B –><- ADB + Ph3COH···B, where AH represents a variety of acids and B represents pyridine-15N, were measured around 110 K, using a 2:1 mixture of liquefied CDClF2-CDF3 as solvent. As under these conditions the slow hydrogen bond exchange regime is reached, the values of K could be obtained directly by integration of appropriate proton NMR signals. Using the valence-bond order concept established previously by crystallography, the fractionation factors and corresponding zero-point energy changes (ΔZPE) are related in a quantitative way to the hydrogen bond geometries, the 1H chemical shift of the hydrogen bond proton, and the pyridine-15N chemical shift. The K values are related in a quasi-linear way to the chemical shifts of the hydrogen bond proton, where the slope depends on whether the proton is closer to oxygen or nitrogen. In the region of the strongly hydrogen-bonded quasi-symmetric complexes, which are characterized by a strong hydrogen bond contraction, the variation of K is very small in spite of substantial proton displacements.Key words: NMR, isotopic fractionation, hydrogen bonding, acid-base complexes, proton transfer, geometric isotope effects.

NMR Study Directly Determining Drug Delivery Sites in Phospholipid Bilayer Membranes

The drug delivery (DD) process of benzene derivatives, n-propylbenzene (PrBe) and benzyl alcohol (BzOH), from water to phospholipid vesicles is first monitored by noninvasive NMR technique. The bilayer interface and interior as delivery sites are unambiguously specified by taking advantage of the site selectivity of NMR. Chemical shift differences of the ring proton signals provide direct evidence for the penetration of the “drugs” into the bilayer within a few minutes. PrBe is deeply penetrated into the hydrophobic chain region of the bilayer core. In contrast, BzOH is preferentially trapped in the interfacial region near the carbonyl group of the phospholipid, with the methylene group oriented toward the inside of the bilayer. The delivery site of BzOH is characterized by the doublet of the ring proton NMR signal, which is ascribed to BzOH delivered into the outer and inner layers of the vesicle. This is also confirmed by 13C NMR, for the first time applied to specify the delivery site. UV absorption sp...