Proton NMR Measurements Research Articles

Crystal and Molecular Structures of the Free Base and the Monohydrochloride Salt of the Antileukemic Agent Glyoxal bis(Amidinohydrazone) [`Glyoxal bis(Guanylhydrazone)’

The first study on the crystal and molecular structures of basic forms of bis(amidinohydrazones) is reported. The structures of the free base and the monohydrochloride salt of the antileukemic agent glyoxal bis(amidinohydrazone) (GBG) were determined by single crystal X-ray diffraction and were refined to R-values of 0.038 and 0.040, respectively. These structures are of special interest because recent results indicate that, in contrast to previous assumptions, the free base may be the actual antileukemic form of bis(amidinohydrazones) and that the monocation form is the predominant species of antileukemic bis(amidinohydrazones) at physiological conditions. In the crystals of the free base as well as in those of the monohydrochloride salt, GBG was found to exist solely in the all-trans configuration of the chain and to consist of one of the three possible geometrical isomers only. In the solid state, GBG free base consists solely of the endiamine tautomer instead of the 'classical’ carboximidamide tautomer, as does also the non-protonated part of GBG monocation in the monohydrochloride salt. Proton NMR measurements indicated that the free base consists of the endiamine tautomer also in dimethyl sulfoxide solution. In the solid state, both of the compounds studied consist of stacks of planes. In the case of the free base, the stacks are crisscross to each other. The distance between the mean planes of the molecules or the monocations is approximately 3.5 Å. The crystals of the monohydrochloride salt contain one molecule of water per each GBG monocation. In both compounds studied, the molecules in the crystals are held together by very extensive hydrogen bond networks and by the interaction of delocalized π-electrons. The crystal of C4H10N8 is monoclinic, space group C2/c with a = 15.874(6), b = 6.972(4), c = 7.8l3(5)Å, β = 90.34(4)° and Z = 4. The crystal of C4H13N8OC1 is monoclinic, space group P21/n with α = 7.010(3), b = 22.307(9), c = 7.028(3)Å, β = 66.33(3)° and Ζ = 4.

Effects of the electron-withdrawing power of substituents on the electronic structure and reactivity in oxoiron(IV) porphyrin .pi.-cation radical complexes

The effects of the electron-withdrawing power of the substituents bound to a porphyrin ring on the electronic structures and the reactivities of oxoiron(IV) porphyrin π-cation radical complexes were studied by using 2,7,12,17-tetramethyl-3,8,13,18-tetraarylporphyrins (aryl=(1) mesityl, (2) 2-chloro-6-methylphenyl, 2,6-dichlorophenyl, or 2,4,6-trichlorophenyl). The electronic structures of oxoiron(IV) porphyrin π-cation radicals were investigated by low-temperature UV-visible absorption spectroscopy and proton NMR measurements.

Proton NMR and Dielectric Measurements on Sucrose Filled Agar Gels and Starch Pastes

ABSTRACTLow‐field proton NMR and high‐frequency dielectric measurements were performed on sucrose‐filled agar gels of 0 to 1.2g sucrose/g water and starch pastes of concentrations between 0.2 and lg starch/ g water. The dielectric constant decreased linearly with increasing concentration for both. The dielectric loss of sucrose‐filled agar gels showed two regions, first increasing and then decreasing with concentration. The dielectric loss data for starch pastes showed a constant value close to that of pure water throughout the concentration range. Dielectric data were related to hydration models derived from proton NMR measurements.

NMR investigation of spin density wave motion and fluctuations in (TMTSF)2PF6.

We report low field proton NMR measurements in the spin density wave (SDW) state of (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$ that show a narrowing of the linewidth when the SDW is depinned by an electric field. The NMR absorption amplitude affirms that sample heating is negligible. A shortening of the spin-phase memory time corresponding to the line narrowing is also observed. Low field measurements of the spin-lattice relaxation rate show a fluctuation enhancement just below the spin density wave transition and a rapid drop below 3 K that lack a quantitative understanding.

Nuclear magnetic resonance relaxation, permittivity, viscosity and ultrasonic velocity measurements in binary mixtures of methanol and tetrahydrofuran

Proton NMR relaxation rates of CD3OH and proton and oxygen-17 NMR relaxation rates of CD317OH with 6, 11.7 and 26.8%17O enrichment have been measured in binary mixtures with deuteriated tetrahydrofuran ([2H]THF) containing 10, 20, 30, 50, 60, 75, 85 and 95 mol% methanol at 288, 298 and 308 K. Deuteron NMR relaxation rates of CH3OD have also been measured in tetrahydrofuran (THF) at the same compositions and temperatures. From the measured proton relaxation rates, the 17O-induced intramolecular proton relaxation rates have been extracted. Using these values, the rotational correlation time (τOH2) of the OH bond of methanol has been determined at various compositions. The variation of τOH2 with composition indicates that the hydrogen bonding (self-association) of methanol begins to break up after the addition of ca. 25 mol%[2H]THF and at >40 mol%[2H]THF the structure breaking of methanol becomes much more pronounced. Negative values of the excess isentropic compressibility (KEs), excess permittivity (IµE), excess viscosity (ηE) and excess volume (VE) of CH3OH–THF mixtures over the whole composition range also indicate strong structure breaking, especially in the range 30–60 mol% THF, where all these excess parameters pass through a minimum. Proton NMR measurements also confirm that structure breaking of CH3OH by THF is stronger at >40 mol% THF. The deuteron and 17O quadrupole coupling constants of methanol in various CH3OD–THF and CD317OH–[2H]THF mixtures have been evaluated and a strong variation of the deuteron quadrupole coupling constant with composition and temperature as compared to that of 17O is observed.

Determination of concentrations by time domain fitting of proton NMR echo signals using prior knowledge.

A fast and flexible time domain iterative fitting procedure that can be used to fit free induction decays as well as echo-like signals is described. Damping constants of the first and second part of the echo do not have to be identical. Prior knowledge can be used to diminish the number of parameters to be fitted, which results in an improved accuracy. It is shown how prior knowledge is mathematically incorporated in the Gauss-Newton method. From proton NMR measurements of model solutions actual prior knowledge is extracted. With this knowledge relative concentrations are determined from a mixture of metabolites. The fitted results agree with the true values within the margins of the noise. After some minor changes the same prior knowledge was successfully used to analyze a series of in vivo rat brain measurements.

Demonstration of bicontinuous structures in microemulsions using automatic‐mode NMR (self‐)diffusion measurements

AbstractThe specifications of an NMR instrument dedicated to frequency‐resolved automated Fourier transform pulsed‐field‐gradient proton NMR measurements are reported. In order to be able also to monitor accurately the slow diffusion of surfactant aggregates and polymers in automatic mode, an option for matching of the gradient pulses was developed and implemented. In a first application, the spectrometer was used to carry out NMR (self‐) diffusion measurements of microemulsions of the surfactant sodium p‐(7‐tetradecyl)benzenesulphonate in benzene and water. They indicate drastic changes in the morphology of the aggregates in the microemulsion on increasing the surfactant concentration. The aggregate morphology changes from a bicontinuous structure to hard, noninteracting spheres by increasing the surfactant concentration in the microemulsion. The bicontinuous structure, i.e. a solution which is continuous in both water and oil, is the result of a strong interaction between the microemulsion droplets (‘percolation phenomenon’). It appears that the water molecules inside the microemulsion droplets with the hard sphere character exchange rapidly, on the (NMR) time scale of 10–100 ms, with water which is dissolved in the benzene. The droplets have an apparent diameter of 56 Å.

Diffusion and spatially resolved NMR in Berea and Venezuelan oil reservoir rocks

Conventional and spatially resolved proton NMR and relaxation measurements are used in order to study the molecular motions and the equilibrium and nonequilibrium diffusion of oils in Berea sandstone and Venezuelan reservoir rocks. In the water-saturated Berea a single line with T 2 ∗ ⋍ 150 μ sec is observed, while the relaxation recovery is multiexponential. In an oil reservoir rock (Ful 13) a single narrow line is present while a distribution of relaxation rates is evidenced from the recovery plots. On the contrary, in the Ful 7 sample (extracted at a deeper depth in a different zone) two NMR components are present, with 3.5 and 30 KHz linewidths, and the recovery plot exhibits biexponential law. No echo signal could be reconstructed in the oil reservoir rocks. These findings can be related to the effects in the micropores, where motions at very low frequency can occur in a thin layer. From a comparison of the diffusion constant in water-saturated Berea, D ⋍ 5 × 10 −6 cm 2/sec , with the ones in model systems, the average size of the pores is estimated around 40 Å. The density profiles at the equilibrium show uniform distribution of oils or of water, and the relaxation rates appear independent from the selected slice. The nonequilibrium diffusion was studied as a function of time in a Berea cylinder with z axis along H 0, starting from a thin layer of oil at the base, and detecting the spin density profiles d( z, t) with slice-selection techniques. Simultaneously, the values of T 1's were measured locally, and the distribution of the relaxation rates was observed to be present in any slice. It turns out that water is diffusing at a fast rate, while oil diffuses three orders of magnitude slower. The continue source diffusion does not follow a simple Fickian law, while the finite source diffusion shows a pluglike propagation.

A lineshape fitting model for 1H NMR spectra of human blood plasma

A lineshape fitting model was constructed for classifying the overlapping information in the 1H NMR spectrum of human blood plasma. A reliable assignment of the overlapping fatty acid (-CH2-)n and -CH3 resonances of the various lipoproteins (VLDL, very low density lipoprotein; LDL, low density lipoprotein; HDL high density lipoprotein) is introduced, and for the first time detailed characteristics (chemical shifts, half linewidths, and relative intensities) of the individual lipoprotein components were obtained directly from the whole plasma spectrum. This was achieved by combining the constructed lineshape fitting model and the proper 400 MHz proton NMR measurements from blood plasma of a healthy donor, from fractions of the different lipoproteins, and from plasma samples in which the lipoprotein fractions were separately added. The results suggest fair promise of future applications of the rapid and easy NMR analysis of lipoprotein distribution in various research and clinical situations.

Interactions of sorbed water with starch studied using proton nuclear magnetic resonance spectroscopy

Proton NMR measurements, made on hydrated starch, indicate that when small amounts of water (ca. 10% by weight) are sorbed by the polysaccharide, the water is highly mobile and reorients anisotropically. This may be compared with the dynamics of water in small crystalline organic hydrates, such as α-cyclodextrin hexahydrate, where the water motion is generally more constrained. Analysis of the wideline proton spectra indicates that an increase in sample crystallinity on addition of water is accompanied by an increase in the starch chain mobility. Cross-relaxation is shown to occur between the starch and the water protons via the secular ‘flip-flop’ process, rather than by proton chemical exchange. This process influences the proton spin–lattice relaxation and results in relatively fast communication between the different proton populations.

Proton environments and hydrogen-bonding in hydrous silicate glasses from proton NMR

The dissolution of water in magmas has profound effects on their physical and chemical properties, and an understanding of this process continues to be of major importance in igneous petrology and geochemistry. Systematic studies of the physical properties of hydrous melts, and infrared1,2, Raman2,3 and 29Si NMR4 spectro-scopic studies of glasses quenched from melts, have provided valuable information, but many questions remain unanswered. Previous proton NMR studies of glasses have generally concentrated on lineshape, to distinguish between the proton environments in Si–OH groups and in molecular H2O (refs 5, 6). Here we present proton NMR results in glasses quenched from hydrous melts, which allow us to resolve different proton sites on the basis of chemical-shift differences. Four separate proton resonances are resolved in a silica glass containing 8.7 wt% H2O, and a strongly hydrogen-bonded Si–OH group is identified in hydrous alkali and alkaline-earth disilicate glasses. Quantitative estimates of water speciation in the silica glasses agree with those from 29Si NMR4. Future proton NMR measurements which resolve different chemical environments will play an important role in elucidating the structures of hydrogen-bearing disordered solids.

Characterization of NH 3 adsorbed on γ-Mo 2N by NMR spectroscopy

Nuclear magnetic resonance techniques were used to study the structure and dynamics of NH 3 adsorbed on high-surface-area (~100 m 2/g) γ-Mo 2N. Proton NMR measurements indicate that NH 3 adsorbs associatively at 298 K, but decomposes on the surface upon heating. The species created by this decomposition are strongly held NH 2, NH, and atomic N and H. Part of the NH 3 adsorbed at 298 K undergoes rapid rotation and translation on the surface, while the species remaining after high-temperature evacuation are locally immobile. Adsorbed NH 2 rotates rapidly about its twofold axis.

Characterization of CO adsorbed on ?-Mo2N by NMR spectroscopy

Abstract Nuclear magnetic resonance techniques were used to study the structure and dynamics of NH 3 adsorbed on high-surface-area (~100 m 2 /g) γ-Mo 2 N. Proton NMR measurements indicate that NH 3 adsorbs associatively at 298 K, but decomposes on the surface upon heating. The species created by this decomposition are strongly held NH 2 , NH, and atomic N and H. Part of the NH 3 adsorbed at 298 K undergoes rapid rotation and translation on the surface, while the species remaining after high-temperature evacuation are locally immobile. Adsorbed NH 2 rotates rapidly about its twofold axis.

Actinomycin D induced DNase I cleavage enhancement caused by sequence specific propagation of an altered DNA structure.

Two DNA hexadecamers containing one central 5'-GC-3' base step have been examined by footprinting methodology in the presence and absence of actinomycin D. The results of these studies, coupled with imino proton NMR measurements indicate that the antitumor drug causes a change in DNA conformation at a distance from the actinomycin intercalation site in a molecule of sequence d[ATATATAGCTATATAT] that does not occur in d[AAAAAAAGCTTTTTTT]. The experiments demonstrate that DNase I rate enhancements associated with actinomycin D binding are caused by ligand alteration of equilibrium DNA structure.

The synthesis of 6,6′‐cyclo‐6′‐deoxyhexofuranosyluracils via a diazomethane‐promoted ring‐enlargement reaction

AbstractThe protected 5′‐oxo‐6,5′‐cyclouridine 13 reacts with diazomethane to afford mostly the spiro‐epoxide 18 (79%), but it also undergoes ring‐expansion to give the corresponding 5′‐oxo‐6,6′‐cyclonucleoside 16. Under the conditions of the reaction, ketone 16 reacts further with diazomethane to give the enol ether 20 (12% overall), the isomeric 4‐methoxy nucleoside 15 (2%), and the spiro‐epoxide 19 (4.4%). Acid hydrolysis of the enol ether 20, followed by reduction of the resulting ketone with sodium borohydride, affords a separable mixture of the 5′S (L‐talo) and 5′R (D‐allo) methylene‐bridged cyclonucleosides 7 and 8, respectively. From proton nmr measurements, it appears that the 6′‐methylene groups of these cyclonucleosides project towards the 2′,3′‐edge of the furanose ring.

Proton NMR measurements of bacteriophage T4 lysozyme aided by 15N isotopic labeling: structural and dynamic studies of larger proteins.

A strategy for resolution and assignment of single proton resonances in proteins of molecular mass up to at least 40 kDa is presented. This approach is based on 15N (or 13C) labeling of selected residues in a protein. The resonances from protons directly bonded to labeled atoms are detected in a two-dimensional 1H-15N (or 13C) spectrum. The nuclear Overhauser effects from isotopically tagged protons are selectively observed in one-dimensional isotope-directed measurements. Using this approach, we have observed approximately 160 resonances from 15N-bonded protons in the backbone and sidechains of uniformly 15N-labeled T4 lysozyme (molecular mass = 18.7 kDa). Partial proton-deuterium exchange can be used to simplify the 1H-15N spectrum of this protein. These resonances are identified by amino acid class using selective incorporation of 15N-labeled amino acids and are assigned to specific residues by mutational substitution, multiple 15N and 13C labeling, and isotope-directed nuclear Overhauser effect measurements. For example, using a phenyl[15N]alanine-labeled lysozyme variant containing two consecutive phenylalanine residues in an alpha-helical region, we observe an isotope-directed nuclear Overhauser effect from the amide proton of Phe-66 to that of Phe-67.

Sorption equilibrium and hydration studies of lysozyme: water activity and 360-MHz proton NMR measurements

Sorption equilibrium and hydration studies of lysozyme: water activity and 360-MHz proton NMR measurements

The preparation and properties of vinyl cellulose

AbstractThe vinylation of cellulose by acetylene under alkaline conditions was optimized with respect to both DS and DP. Shortening the reaction time reduced the harmful alkaline depolymerization of cellulose during the reaction and gave products with higher DP values. Thus cellulose, activated by KOH, was vinylated for 180 min at 431K and 5.5 MPa to yield 72.1% of a product with DS 1.46 and DPw 175. Results of vinyl cellulose analysis by new and old methods were in good agreement with each other. Trimethylsilylated vinyl cellulose was prepared for proton NMR and GPC measurements. It was found that vinyl cellulose slowly loses its vinyl groups when stored in light and air.

Deuteron and proton magnetic resonance in amorphous silicon.

Deuteron and proton NMR measurements have been made on a series of plasma-deposited a-Si:D,H samples. DMR line shapes show three components: a resolved quadrupolar doublet associated with D bonded to Si well removed from microvoids, a wide quadrupole-broadened central line associated with D located near to and on the surfaces of microvoids, and a sharp temperature-dependent feature associated with molecular ${\mathrm{D}}_{2}$ in the larger voids. Dipolar ${T}_{2}$ decays show two components for both protons and deuterons. There is no strong correspondence between the dipolar broad and narrow lines and the two quadrupolar resonance components observed for bonded D. ${T}_{1}$(H) and ${T}_{1}$(D) show components associated with spin diffusion to effectively dilute ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ relaxation centers located in microvoids. ${\mathrm{SiD}}_{4}$ and ${\mathrm{SiH}}_{4}$ starting gases produce similar amounts of ${\mathrm{D}}_{2}$ and ${\mathrm{H}}_{2}$ under comparable deposition conditions. Two samples show a strong apparently electronic carrier-related nuclear-spin-lattice relaxation contribution near room temperature.

Evidence for the existence of hydrogen-bonded cyclic tetramers in aqueous solutions of tetramethylammonium guanosine 5′-monophosphate

Proton NMR and FTIR measurements have shown that the formation of stable, interbase hydrogen-bonded species of 5′-GMP in aqueous solutions of the tetramethylammonium salt can occr without the subsequent formation of ordered, slowly-exchanging structures or base stacking. Analysis of the NMR data is in agreement with an equilibrium mixture of monomers, dimers and cyclic tetramers. The association constants and amino proton chemical shifts are reported for these species. This is the first report that the cyclic tetramer structure exists as a discrete species in 5′-GMP solutions.