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Understanding the dissociation of molecules is the basis to modulate interactions of biomedical interest. Optimizing drugs for dissociation rates is found to be important for their efficacy, selectivity, and safety. Here, we show an application of the high-power relaxation dispersion (RD) method to the determination of the dissociation rates of weak binding ligands from receptors. The experiment probes proton RD on the ligand and, therefore, avoids the need for any isotopic labeling. The large ligand excess eases the detection significantly. Importantly, the use of large spin-lock fields allows the detection of faster dissociation rates than other relaxation approaches. Moreover, this experimental approach allows to access directly the off-rate of the binding process without the need for analyzing a series of samples with increasing ligand saturation. The validity of the method is shown with small molecule interactions using two macromolecules, bovine serum albumin and tubulin heterodimers.

We used Fourier-transform nuclear magnetic resonance (NMR) spectroscopy to investigate the temperature dependences of the chemical shift and resonance frequency observed with magic-angle spinning NMR and static NMR, respectively, to confirm a high-temperature behavior of NH4H2PO4. The hydrogen bonds in both O–H–O between two PO4 groups and N–H–O between NH4 and PO4 were distinguished, and the changes occurring in the chemical shift and resonance frequency near the characteristic temperature TP are related to changes in the atomic positions. The experimental results of thermogravimetric analysis conducted to interpret the high-temperature phenomena without the critical change around TP are consistent with a phase-transition-like phenomenon at TP.

Fast magic-angle spinning and partial sample deuteration allows direct detection of 1H in solid-state NMR, yielding significant gains in mass sensitivity. In order to further analyze the spectra, 1H detection requires assignment of the 1H resonances. In this work, resonance assignments of backbone HN and Hα are presented for HET-s(218–289) fibrils, based on the existing assignment of Cα, Cβ, C’, and N resonances. The samples used are partially deuterated for higher spectral resolution, and the shifts in resonance frequencies of Cα and Cβ due to the deuterium isotope effect are investigated. It is shown that the deuterium isotope effect can be estimated and used for assigning resonances of deuterated samples in solid-state NMR, based on known resonances of the protonated protein.

A method of hydrogen/deuterium (H/D) exchange with an unfolding-refolding process has been applied to hen egg-white lysozyme (HWL), and accurate evaluation of its deuteration was carried out by time-of-flight mass spectroscopy. Neutron crystallography requires a suitable crystal with enough deuterium exchanged in the protein to decrease incoherent scattering from hydrogens. It is very expensive to prepare a fully deuterated protein, and therefore a simple H/D exchange technique is desirable for this purpose. Acid or base addition to protein solutions with heating effectively increased the number of deuterium up to more than 20 % of that of all hydrogen atoms, and refolded structures were determined by X-ray structure analysis at 1.8 Å resolution. Refolded HWL had increased deuterium content in its protein core and its native structure, determined at atomic resolution, was fully preserved.

New pyridoxine derivative with multiple chemical exchanges was studied by 13C (at 298 K, 188 K) and 2D NMR (1H-13C HSQC, 1H-13C HMBC) spectroscopy in acetone-d6 solution. Complete 13C NMR data (table with chemical shifts at different temperatures) is presented. Intramolecular mobility of the molecule was analyzed based on the results of 13C NMR experiments in combination with the data obtained from previous study of this compound by dynamic 1H NMR spectroscopy.

A method is developed for measuring the content of hydrogen (2Н) and oxygen (17O) isotopes in liquid media based on quantitative nuclear magnetic resonance. It has been established that the shifting europium trifluoromethanesulfonate (III) reagent is the most appropriate chemical compound for a reference sample to study the isotopic composition of aqueous solutions. A dependence of the paramagnetic chemical shift of 2Н and 17O nuclei on the concentration of Eu3+ ions in a solution is studied.

Overuse and misuse of antibiotics have led bacteria to acquire several mechanisms of resistance. In response to this, researchers have identified natural antimicrobial peptides as promising candidates to fight against multiresistant bacteria. However, their mode of action is still unclear, and a better understanding of the mode of action of these peptides is of primary importance to develop new peptides displaying high antibacterial activity and low hemolytic activity. One of the main features that defines the mechanism of action is the membrane topology of the peptide. Among the spectroscopic techniques, solid-state NMR is the technique of choice for determining the location of the peptide within the membrane. It can be achieved by performing experiments with oriented samples. In the literature, the two most common types of oriented samples are bicelles and phospholipids mechanically oriented between glass plates. The mode of perturbation of the membrane-active peptide can be studied by phosphorus-31 and deuterium NMR. On the other hand, several experiments such as nitrogen-15 and fluorine solid-state NMR, that require labeled peptides, can give valuable information on the membrane topology of the peptide. The combination of the latter techniques allows the determination of a precise topology, thus a better knowledge of the molecular determinants involved in the membrane interactions of antimicrobial peptides.

T1 values in pure D2O and D2O solutions of human serum albumin (HSA) were measured versus temperature. A formula was derived based on H–H interactions between the surface HDO and non-exchangeable protein protons. The formula was used to evaluate the average distance of the interactions (rav). The effective correlation times were then derived by replacing the experimental data in the formula. Short correlation times obtained for the solution with low HSA (0.02 g albumin for one ml of D2O) decreased from 53 to 29 ps, while longer times increased from 1.19 to 2.22 ns. They are of the order of a fraction of a nanosecond for the solution with high HSA (0.08 g albumin per one ml of D2O). The perfect consistency between the derived theory and experimental data indicates that the high-field 1/T1 in D2O solutions of albumin is caused by dipolar interactions between the surface HDO and non-exchangeable protein protons. It also suggests that the effective correlation time of the surface HDO is of the order of the mean lifetime of short-lived surface water.

To clarify the nature of microscopic structural changes of N(CH3)4CdCl3 at high temperatures, the nuclear magnetic resonance (NMR) spectra of the protons and carbons in N(CH3)4CdCl3 were measured. NMR studies of the 1H and 13C spin–lattice relaxation time, T 1ρ, in the rotating frame were also performed. No changes in the T 1ρ of 1H and 13C associated with the N(CH3)4 groups were observed at the high-temperature transition from phase I to phase I′. However, the 14N NMR spectra reflected changes in the structural geometry during the transition to phase I′, indicating that this transition is driven by N(CH3)4.

Hydrogen is one of the two reagents of Fischer–Tropsch (FT) synthesis. In order to have the information about the role of hydrogen, which is the key to understand the mechanism of the reaction, deuterium tracer experiments are useful. One of the obstacles in conducting deuterium tracer experiments during FT reactions is to accurately determine the amounts of isotopomers of a hydrocarbon in the FT products. Because of an inverse isotope effect for isotopomers on a GC column, the isotopomer with more deuterium atoms will be eluted first. If the difference in deuterium atoms is >3, the quantitative analysis of a mixture of isotopomers can be conducted using GC–FID. However, if the difference in deuterium atoms is

400 MHz NMR T 2 in D2O solutions of albumin and pure D2O were measured at different temperatures. A relation, based on the chemical exchange between bound HDO and non-exchangeable protein protons, was derived theoretically for the contributions of bound HDO [P b(1/T 2b)]. A second relation was also derived theoretically by considering spin-rotation interactions between bound HDO and surrounding protein protons. The P b(1/T 2b) values in albumin solutions were then determined by replacing experimental data into the first relation. The values of the 1/T 2 and P b(1/T 2b) in albumin solutions increase linearly with temperature(T), whereas the 1/T 2 in D2O decreases with T. In addition, the spin-rotation correlation times were calculated from the second relation. The dipolar correlation time of albumin was then reproduced from the spin-rotation correlation times for confirmative purposes. In conclusion, the 1/T 2 in albumin solutions with D2O is caused by spin-rotation interactions.

An approach towards accurate NMR measurements of deuterium isotope effects on the chemical shifts of all backbone nuclei in proteins (15N, 13Cα, 13CO, 1Hα) and 13Cβ nuclei arising from 1H-to-D substitutions at amide nitrogen positions is described. Isolation of molecular species with a defined protonation/deuteration pattern at successive backbone nitrogen positions in the polypeptide chain allows quantifying all deuterium isotope shifts of these nuclei from the first to the fourth order. Some of the deuterium isotope shifts measured in the proteins ubiquitin and GB1 can be interpreted in terms of backbone geometry via empirical relationships describing their dependence on (φ; ψ) backbone dihedral angles. Because of their relatively large variability and notable dependence on the protein secondary structure, the two- and three-bond 13Cα isotope shifts, 2ΔCα(NiD) and 3ΔCα(Ni+1D), and three-bond 13Cβ isotope shifts, 3ΔCβ(NiD), are useful reporters of the local geometry of the protein backbone.

Hydrogen dynamics in one-dimensional hydrogen bonded organic antiferroelectric, co-crystal of 5,5’-dimethyl-2,2’-bipyridine (55DMBP) and chloranilic acid (H2ca), was investigated by use of 2H high resolution solid-state NMR. The two types of hydrogen bonds O-H …N and N+-H …O − in the antiferroelectric phase were clearly observed as the splitting of the side band of the 2H MAS NMR spectra of the acid-proton deuterated compound 55DMBP-D 2ca. The temperature dependence of the spin-lattice relaxation time was measured of the N+-H and O-H deuterons, respectively. It was suggested that the motion of the O-H deuteron is already in the antiferroelectric phase in the fast-motion regime in the NMR time scale, while that of the N+-H deuteron is a slow motion. In the high-temperature paraelectric phase, the both deuterons become equivalent and the fast motion of the deuterons in the NMR time scale is taking place with the activation energy of 7.9 kJ mol−1.

The hydrophobic lung surfactant protein, SP-B, is essential for survival. Cycling of lung volume during respiration requires a surface-active lipid-protein layer at the alveolar air-water interface. SP-B may contribute to surfactant layer maintenance and renewal by facilitating contact and transfer between the surface layer and bilayer reservoirs of surfactant material. However, only small effects of SP-B on phospholipid orientational order in model systems have been reported. In this study, N-terminal (SP-B(8-25)) and C-terminal (SP-B(63-78)) helices of SP-B, either linked as Mini-B or unlinked but present in equal amounts, were incorporated into either model phospholipid mixtures or into bovine lipid extract surfactant in the form of vesicle dispersions or mechanically oriented bilayer samples. Deuterium and phosphorus nuclear magnetic resonance (NMR) were used to characterize effects of these peptides on phospholipid chain orientational order, headgroup orientation, and the response of lipid-peptide mixtures to mechanical orientation by mica plates. Only small effects on chain orientational order or headgroup orientation, in either vesicle or mechanically oriented samples, were seen. In mechanically constrained samples, however, Mini-B and its component helices did have specific effects on the propensity of lipid-peptide mixtures to form unoriented bilayer populations which do not exchange with the oriented fraction on the timescale of the NMR experiment. Modification of local bilayer orientation, even in the presence of mechanical constraint, may be relevant to the transfer of material from bilayer reservoirs to a flat surface-active layer, a process that likely requires contact facilitated by the formation of highly curved protrusions.

The proton and carbon NMR resonances have been assigned for 3A-amino-3A-deoxy(2AS,3AS)-α-, β- and γ-CyDs (3α, 3β and 3γ). In these CyDs, a glucose residue has been replaced by an altro-pyranose unit with an axial hydroxyl group. Assignments were made with one-dimensional NMR and COSY, TOCSY, ROESY and CHSHF (heteronuclear shift correlation) spectra. Titration by NMR shift changes gave amino-group pKa values of 7.73 and 8.84 for 3β (left) and 6A-amino-6A-deoxy-β-CyD (6β, right), respectively.

An original method was developed for the synthesis of THF labeled selectively with the 13C isotope at the α-carbon atom. The effective reduction of symmetry brought about by the insertion of the isotopic label removes the excess degeneracy of the spin systems describing the multiplet structure of the 1H and 13C NMR spectra, making it possible to undertake a detailed analysis. Exact values for the 1H–1H spin-spin coupling constants through four bonds and also the 13C–1H and 13C–13C spin-spin coupling constants involving the α-carbon atom were determined for the first time. The isotopic chemical shifts of the protons and 13C nuclei caused by replacement of the 12C nucleus by 13C were determined. These data can be used to construct a quantitative model of the conformational behavior of THF as a molecular system in which pseudorotation in terms of vibrations with large amplitude is realized.

H/D isotope effects onto 79Br NQR frequencies of piperidinium p-bromobenzoate were studied by deuterium substitution of hydrogen atoms which form two kinds of N–H⋯O type hydrogen bonds, and the isotope shift of ca. 100 kHz were detected for a whole observed temperature range. In addition, 1H MAS NMR spectra measurements of piperidinium and pyrrolidinium p-bromobenzoate were carried out and little isotope changes of NMR line shape were detected. In order to reveal effects of molecular arrangements into the obtained isotope shift of NQR frequencies, single-crystal X-ray measurement of piperidinium p-bromobenzoate-d2 and density-functional-theory calculation were carried out. Our estimation showed the dihedral-angle change between piperidine and benzene ring contributes to isotope shift rather than those of N–H lengths by deuterium substitution.

HNCO/HNCACO type correlation experiments are an alternative for assignment of backbone resonances in extensively deuterated proteins in the solid-state, given the fact that line widths on the order of 14–17 Hz are achieved in the carbonyl dimension without the need of high power decoupling. The achieved resolution demonstrates that MAS solid-state NMR on extensively deuterated proteins is able to compete with solution-state NMR spectroscopy if proteins are investigated with correlation times τ c that exceed 25 ns.

The essential role played by local and collective motions in RNA function has led to a growing interest in the characterization of RNA dynamics. Recent investigations have revealed that even relatively simple RNAs experience complex motions over multiple time scales covering the entire ms-ps motional range. In this work, we use deuterium solid-state NMR to systematically investigate motions in HIV-1 TAR RNA as a function of hydration. We probe dynamics at three uridine residues in different structural environments ranging from helical to completely unrestrained. We observe distinct and substantial changes in (2)H solid-state relaxation times and lineshapes at each site as hydration levels increase. By comparing solid-state and solution state (13)C relaxation measurements, we establish that ns-micros motions that may be indicative of collective dynamics suddenly arise in the RNA as hydration reaches a critical point coincident with the onset of bulk hydration. Beyond that point, we observe smaller changes in relaxation rates and lineshapes in these highly hydrated solid samples, compared to the dramatic activation of motion occurring at moderate hydration.

1H NMR spectroscopy was used to establish that 7-alkoxyalkyl-3-thia-7-azabicyclo[3.3.1]nonan-9-ones and their decarbonylated derivatives in deuterochloroform solution exist in the double chair conformation. The predominantly formed secondary alcohols isomers have preferred double chair conformation with the hydroxyl group equatorial relative to the plane of the piperidine ring. On the other hand, the epimeric alcohols have predominant boat-chair conformation; the piperidine ring takes the boat form due to intramolecular hydrogen bonding between the unshared electron pair of the nitrogen atom and hydroxyl group proton.

The selectivity of deuterium distribution between the nonequivalent positions in 3-carene (1), 4-α-acetyl-2-carene (2), and 4-(1-hydroxyethyl)-2-carene (3) has been measured by 2H-{1H} NMR spectroscopy at the natural abundance of deuterium. These “H/D-isotope portraits” were shown to be typical of terpenes and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six-membered ring in compound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2) atom from the anti position with respect to the three-membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group.

A computational investigation using density-functional-theory methods has been performed concerning the structure and nuclear magnetic resonance (NMR) chemical shifts of bilirubin with a special emphasis on the hydrogen bonds. Solid-state effects on the NMR spectra are investigated by considering a trimeric model derived from the available X-ray structure. Satisfactory agreement between theory and experiment is found with ring-current effects playing only a minor role for the interpretation of the solid-state NMR spectra.

Resonances in PMR and 13C NMR spectra of anhydrolycoctonine were fully assigned based on a series of 1D and 2D NMR experiments. The conformation of ring A was concluded to be a distorted boat with H-1β from a comprehensive analysis of chemical shifts, SSCC, and the NOE for two possible conformations.

The phase behaviours of chain-perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62) and chain-perdeuterated dipalmitoylphosphatidylglycerol (DPPG-d62) bilayers were compared using 2H nuclear magnetic resonance spectroscopy and quadrupole echo decay measurements over pressures ranging from ambient to 196 MPa and temperatures ranging from 60 to -25 degrees C. At ambient pressure, the phase behaviours of DPPC-d62 and DPPG-d62 were nearly identical. At 196 MPa, their behaviours were also very similar and both lipids appeared to pass from an interdigitated gel phase at high temperature, through a non-interdigitated gel phase at intermediate temperature, to a chain-immobilized ordered phase at low temperature. At 85 MPa, the behaviour of DPPC-d62 was similar to its ambient pressure behaviour with no evidence of interdigitation. For DPPG-d62, however, the behaviour at 85 MPa was similar to its higher pressure behaviour and spectra characteristic of an interdigitated gel phase were observed. Pressure-temperature phase diagrams for both lipids were compared. While the minimum pressure for DPPC-d62 interdigitation is about 150 MPa, DPPG-d62 was observed to interdigitate at pressures as low as 60 MPa. Given the similarity of their phase behaviours at both higher and lower pressures, this difference reflects the extent to which bilayer phase behaviour depends on the balance between interactions in the headgroup and hydrocarbon regions of the bilayer.

We present an 27Al NMR study of the metal cluster compound Al50Cp*12 which is composed of (identical) Al50 clusters, each surrounded by a Cp* ligand shell, and arranged in a crystalline 3D array (here Cp* = pentamethylcyclopentadienyl = C5(CH3)5). The compound is found to be non-conducting, the nuclear spin-lattice relaxation in the temperature range 100–300 K being predominantly due to reorientational motions of the Cp* rings. These lead to a pronounced maximum in the relaxation rate at T ∼ 170 K, corresponding to an activation energy of about 850 K. Data for the related compound Al4Cp*4, containing very much smaller Al4 clusters are also presented. A comparison is drawn with the quadrupolar relaxation recently observed for the non-conducting fraction of Ga84 molecules in the metal cluster compound Ga84[N(SiMe3)2]20-Li6Br2(thf)20·2toluene.

In this paper we report measurements of the nuclear magnetic resonance (NMR) spectrum of 129Xe adsorbed on silica gel and Grafoil® substrates in a 15 tesla magnetic field and temperatures in the range 10 mK to 1 K. Liquid 3He is used to shorten the spin lattice relaxation time of the 129Xe spins and obtain a high degree of spin polarization of over 40% in around a day. The 129Xe NMR spectrum generally exhibits two lines. We show that one line corresponds to the monolayer of surface xenon atoms and the other line to the monolayers of bulk solid xenon between the substrate and the surface monolayer. By comparing the spectra and relaxation rates for xenon of different 129Xe concentrations and by adding 4He we were able to investigate the 129Xe interlayer coupling. The work has important implications in the study of porous materials using hyperpolarized gases, the study of surface atoms by NMR and the production of hyperpolarized species by the brute force technique.

Several skeletal and oxidative transformations of 11-deoxyglycyrrhetic acid were carried out to produce A-nor-derivatives. Signals for protons and C atoms in the PMR and 13C NMR spectra of the A-nor-derivatives were assigned using high-resolution 1H (400 MHz) and 13C (125 MHz) NMR spectroscopy.

Hydrogen/deuterium exchange (HDX) coupled to mass spectrometry permits analysis of structure, dynamics, and molecular interactions of proteins. HDX mass spectrometry is confounded by deuterium exchange-associated peaks overlapping with peaks of heavy, natural abundance isotopes, such as carbon-13. Recent studies demonstrated that high-performance mass spectrometers could resolve isotopic fine structure and eliminate this peak overlap, allowing direct detection and quantification of deuterium incorporation. Here, we present a graphical tool that allows for a rapid and automated estimation of deuterium incorporation from a spectrum with isotopic fine structure. Given a peptide sequence (or elemental formula) and charge state, the mass-to-charge ratios of deuterium-associated peaks of the specified ion is determined. Intensities of peaks in an experimental mass spectrum within bins corresponding to these values are used to determine the distribution of deuterium incorporated. A theoretical spectrum can then be calculated based on the estimated distribution of deuterium exchange to confirm interpretation of the spectrum. Deuterium incorporation can also be detected for ion signals without a priori specification of an elemental formula, permitting detection of exchange in complex samples of unidentified material such as natural organic matter. A tool is also incorporated into QUDeX-MS to help in assigning ion signals from peptides arising from enzymatic digestion of proteins. MATLAB-deployable and standalone versions are available for academic use at qudex-ms.sourceforge.net and agarlabs.com . Isotopic fine structure HDX-MS offers the potential to increase sequence coverage of proteins being analyzed through mass accuracy and deconvolution of overlapping ion signals. As previously demonstrated, however, the data analysis workflow for HDX-MS data with resolved isotopic fine structure is distinct. QUDeX-MS we hope will aid in the adoption of isotopic fine structure HDX-MS by providing an intuitive workflow and interface for data analysis.

The high-resolution 1H and 13C NMR spectra of 1-vinylimidazole complexes with iron group metals were recorded. The contact coupling in these systems was established in the 1H and 13C NMR spectra. The applicability of the NMR spectra transformed by long-range hyperfine coupling for elucidating the molecular structure of the ligand was shown.

It has been shown that a feature of the 1H NMR spectra of 5-R-3-aryl-2,1-benzisoxazoles is the large difference in chemical shift values for the H(4), H(6), and H(7) protons of the 2,1-benzisoxazole system in each of the compounds but with retention of the overall pattern for the series discussed. It was found that the effect of the heterocycle on the aryl residue in position 3 is equivalent to the effect of a moderately electron accepting group.

The 13C-{1H} and 119Sn-{1H} NMR spectra of hexaethyldistannane were measured and analyzed using an iteration program for the calculation of the complete line shape with correction of a residual inhomogeneity of the magnetic field and phase distortions. Signals of 22 isotopomers containing magnetic isotopes of tin and carbon in different pairwise and triple combinations were identified, and their spectral parameters were determined. The content of isotopes 119Sn, 117Sn, and 115Sn in the molecule was determined with a high accuracy sufficient for the study of isotope effects in chemical reactions.

Intermolecular interactions modify nuclear magnetic resonance (NMR) chemical shifts and spin-spin coupling constants. The intermolecular effects can be determined if the NMR parameters for an isolated molecule are known. Gas-phase NMR spectroscopy offers such methods which allow one to measure the shielding and spin-spin coupling constants at the zero-density limit where the NMR parameters are free from intermolecular contributions. It is also shown that at present the multinuclear NMR spectra can easily be obtained for gaseous samples containing several micrograms of a solute compound.

Deuterium NMR and modulated differential scanning calorimetry (MDSC) were used to probe the behavior of ultrathin adsorbed poly(methyl acrylate) (PMA). The spectra for the bulk methyl-labeled PMA-d 3 were consistent with the motions of the polymer segments being spatially homogeneous. For the polymers adsorbed on silica, multicomponent line shapes were observed. The segmental mobility of the surface polymers increased with increased adsorbed amounts. In contrast to the behavior of the polymers in bulk, the adsorbed lower-molecular-mass PMA-d 3 was less mobile than the adsorbed high-molecular-mass polymer. The presence of a polymer overlayer was sufficient to suppress the enhanced mobility of the more-mobile segments of the adsorbed (inner) polymer. MDSC studies on adsorbed poly(methyl methacrylate) showed that the glass-transition temperature of the thin polymer films increased and broadened compared to the behavior of the polymer in bulk. The presence of a motional gradient with the less-mobile segments near the solid--polymer interface and the more-mobile segments near the polymer-air interface was consistent with the experimental observations.

A new method for quantification of the relative distribution of deuterium in molecules is proposed. The technique is based on the lineshape analysis in the 2H NMR spectra obtained at the natural abundance level of deuterium with allowance for inhomogeneity of the magnetic field. The equilibrium thermodynamic H/D isotope effects for hindered rotation about the C—N bond in the N,N-dimethylformamide molecule and for prototropic exchange in the cyclopentadiene molecule were determined. The results obtained agree with those of DFT calculations of the vibrational energies.

Data on the NMR spectroscopy of C, N, O, Si, P, and Sn donor atoms of platinum metal complexes in solutions are surveyed. The chemical shift of a donor atom mainly depends on the ligand in the trans-position (due to the trans-effect). The chemical shift of a donor atom on a particular coordinate of the complex (coordinate shift, CSh) is an attribute of this coordinate and can be used to identify such a coordinate in platinum metal complexes and to determine the structures of complexes. Based on the known data, CSh diagrams were composed for 1H, 13C, 14N, 17O, 19F, 31P, and 119Sn. Examples of using the CShs for determining the structures of platinum metal complexes in solutions are presented.

Deuterium isotope effects and fractionation factors of N1.H3-N3 hydrogen bonded Watson-Crick A:T base pairs of two DNA dodecamers are presented here. Specifically, two-bond deuterium isotope effects on the chemical shifts of (13)C2 and (13)C4, (2)delta(13)C2 and (2)delta(13)C4, and equilibrium deuterium/protium fractionation factors of H3, Phi, were measured and seen to correlate with the chemical shift of the corresponding imino proton, delta(H3). Downfield-shifted imino protons associated with larger values of (2)delta(13)C2 and (2)delta(13)C4 and smaller Phi values, which together suggested that the effective H3-N3 vibrational potentials were more anharmonic in the stronger hydrogen bonds of these DNA molecules. We anticipate that (2)delta(13)C2, (2)delta(13)C4 and Phi values can be useful gauges of hydrogen bond strength of A:T base pairs.

A combined study of2H nuclear magnetic resonance lineshape and spin-lattice and spin-spin relaxation times as functions of temperature and the amount of hydration water in a cross-linked copolymer of sucrose and 1,4-butadienol diglycidyl ether in the hydrogel phase is reported. The results show strong evidence that the onset of the relaxation mechanisms is driven by anomalous water molecule diffusion depending on both temperature and the hydration degree of the hydrogel. In addition, these results are correlated with the transitions observed by differential thermal analysis.

For two isoanalogs of B,19-bisnortestosterone was carried out a complete assignment of signals in the 1H and 13C NMR spectra with the help of homonuclear and heteronuclear correlation NMR spectroscopy. The predominant conformations of the substances in solutions were derived from the values of coupling constants and nuclear Overhauser effect data.

Human serum albumin (HSA) binds numerous molecules, among which are suitably designed MRI contrast agents. The rotational tumbling of the protein is thus one of the parameters likely to affect the in vivo relaxivity of these agents. Literature unveils discrepancies about the value of the rotational correlation time (tau(R)) of HSA. In the present work, the tau(R) of this protein has been determined by studying the deuterium relaxation rate of small molecules known for their strong binding to HSA (warfarin and 4-hydroxycoumarin). Values of approx. 20-22 ns are obtained at 310 K in a 4% HSA solution and are in good agreement with the theoretical predictions.

MP-2269, the Gd(III) complex of 4-pentylbicyclo[2.2.2]octane-1-carboxyl-di-L-aspartyl-lysine-derived-DTPA, is a small Gd-agent that binds non-covalently to serum albumin in vivo to assume the enhanced relaxivities associated with macromolecular agents, (due in part to increased rotational correlation time, tau(R)). To further explore the fundamental parameters that govern the dynamics of water proton relaxation enhancement by this prototypical albumin-binding agent, the rotational correlation time (tau(R)) for the deuterated La(III) analog of MP-2269 has been independently measured in the presence and absence of 4% albumin using 2H-NMR approaches. The diamagnetic La(III) analog of MP-2269 was deuterated at the alpha-position of the carbonyl groups. 2H-NMR studies were conducted at 7.05T (46 MHz) and 310 degrees K on a Bruker NMR spectrometer. Spectral deconvolution permitted calculation of transverse relaxation rates, 1/T(2), from the NMR linewidths and subsequently, tau(R). The results yielded a tau(R) of the albumin bound complex of approximately 8 ns. This value is intermediate between those earlier estimated by 17O-NMR ( approximately 1 ns) and 1H-NMRD ( approximately 20-50 ns) and significantly shorter than that of albumin. The 2H-NMR study results also indicate that the exchange between free and albumin-bound forms of the La(III) analog is slow (exchange lifetimes1 ms). This slow exchange does not affect the water residence lifetimes (tau(M) 140-280 ns).

13 C NMR spectra were studied and signals of C atoms were assigned for 6-keto- and 6-hydroximinosteroids 1-10.

Substituted dihydropyrroles were characterized by13C and1H NMR spectra. The spectral patterns of these compounds and reversible hydrogen—deuterium exchange are discussed.

A review of studies on the ortho Mannich bases containing various substituents in the phenyl ring on the basis of1H,13C and15N nuclear magnetic resonance (NMR) spectra in various solvents over the temperature range 110–298 K is presented. Some new results are also included. The data gathered so far show that there is some critical (inversion) range of ΔpK a (= pK a(NH+) − pK a(OH)) in which the proton transfer equilibrium appears. This inversion range is well reflected in the behaviour of secondary deuterium isotope effect in13C NMR spectra. A strong temperature effect on the strength of hydrogen bonding should be emphasized. The1H chemical shift for trichloroderivative increases from 13.5 at room temperature up to 17 ppm at 130 K when the proton is equally shared between the bridging atoms (1 J(1H,15N) = 30–40 Hz). The potential for the proton motion in such bridges is discussed taking into account the behaviour in the ultraviolet and infrared spectra. The role of dimerization in proton transfer equilibria is shown. In addition the rotation of OH groups involved in hydrogen bond formation and nitrogen pyramidal inversion was studied by the1H dynamical NMR spectra.

Deuterium nmr has been employed to determine the average orientation of chain segment in poly(butadiene) networks. The nmr spectrum lineshape reveals the orientation distribution of network vectors due to the crosslinks, whereas the observed splitting gives information about the orientation due to segmental interactions. Both the lineshape and the splitting have been fitted simultaneously for a range of deformed poly(butadiene) networks varied in crosslink density and precursor chain length. From the fitting parameters the separate contribution to the average orientation arising from network constraints and interaction are calculated. These are used to estimate the effective molecular weight between topological constraints and the size of the segmental interaction. It could be shown that the latter remains constant as the crosslink density is varied. This is a strong evidence of the recently published theoretical framework.

Recent improvements in NMR methodology have significantly increased the scope of hydrogen bond related problems that can be now addressed by solution NMR methods. A growing number of applications are exploiting these NMR techniques to study complex molecular systems and elicit otherwise inaccessible information on hydrogen bonding in aqueous solution.

2H NMR (nuclear magnetic resonance) spectroscopy, in conjunction with X-ray diffraction experiments, was used to characterize the guest motions of 1,6-dibromohexane in its urea inclusion compound. These motions are characterized by alkyl chain jumps between two conformations, each approximately gauche to the terminal bromines, which remain stationary. In this distorted urea channel, one conformer is heavily preferred, but thermally activated population of the unfavorable conformer leads to reversible, temperature-dependent changes in the unit cell parameters. Although rapid motions of the guest chain give rise to ambiguities in the interpretation of the2H NMR spectra, fortuitous temperature-independent spectral features of guests containing deuterium at the α, β and γ positions indicate that the guest motion resembles a two-site jump with unequal probabilities. Analytical lineshape calculations on the three sets of2H NMR spectra indicate a single jump mechanism in which the range of jump angles is narrowly prescribed. This NMR model provided a starting point for successful solution and refinement of the crystal structures at 213 and 298 K, which had been complicated by motional disorder.

One- and two-dimensional 13C and 29Si solid-state NMR experiments at variable temperature demonstrate that crystalline (Ph3Si)Si(SiMe3)3 lacks all molecular symmetry and that internal 2π/3 reorientation of all three crystallographically inequivalent SiMe3 groups in the molecule occurs. Quantitative analysis of one-dimensional MAS NMR spectra and of two-dimensional NMR exchange experiments by spectral lineshape simulations yields exchange rate constants for internal SiMe3 reorientation as a function of temperature. The activation energies determined from these kinetic data are E a = 21±4, 22±4, and 30±5kJ−1 for internal reorientation of the three inequivalent SiMe3 groups in solid (Ph3Si)Si(SiMe3)3.

The complete assignment of the signals in the13C NMR spectra of 2,3,4,5-tetraphenyl-1-R1,R2-1-silacyclopenta-2,4-dienes (R1=R2=H, Me) and of the dianion of lithium salt [(PhC)4Si]2−·2Li+ was carried out by 2D NMR spectroscopy.

The intermolecular forces between occluded organic molecules and the atoms that bound the pores of zeolite structures determine the catalytic activity and diffusivity of the guest molecules. These organic-inorganic forces are also a crucial aspect of the process of structure-direction in zeolite synthesis. A molecular understanding of guest-host interactions can often be deduced by using NMR spectroscopy to study the rotational motion of the occluded molecules. This contribution is an overview of systems where NMR, particularly deuterium NMR, has been used to quantify the forces which exist between occluded organic molecules and the zeolite structure. Systems that are relevant to synthesis, separations, and catalysis are discussed. The works presented show that NMR is a powerful tool for studying guest-host interactions in zeolitic materials. A molecular level understanding of the nature and relative importance of the various forces discussed should lead to a more rational basis for the selection and development of zeolitic materials used in catalytic and adsorption applications.

Triple-resonance solid-state NMR spectroscopy is demonstrated to sequentially assign the 13C′ and 15N amide backbone resonances of adjacent residues in an oriented protein sample. The observed 13C′ chemical shift frequency provides an orientational constraint complementary to those measured from the 1H and 15N amide resonances in double-resonance experiments.