Sets Of NMR Signals Research Articles

A Rotation-Inversion Dual-Motion Molecular Switch: Race for NMR Signaling.

The interplay between the thermal helical inversion (THI) of the stiff-stilbene moiety and the rotation of the dimethylamino (DMA) group in 1 results in a dependence of the DMA NMR signals on the THI kinetics in (E)-1 but the rotation kinetics in (Z)-1, because the faster motion mode is responsible. Consequently, the photochemical switching from (E)-1 to (Z)-1 illustrates the phenomenon of "switchable motion detection" by the same set of NMR signals in a dual-motion molecular system.

One‐Pot Synthesis of Phosphanylbis(N‐arylglycines) and Spontaneous Diastereoselective Lactamization of P‐Alkyl Derivatives To Form Five‐Membered P,N‐Heterocyclic Amino Acids

The one‐pot, three‐component reaction of phenylphosphane with two equivalents each of 4‐acetylaniline and glyoxylic acid hydrate (GAH) in diethyl ether at room temperature furnished phosphanyl‐bis(glycine) 1 as a rac/meso mixture (molar ratio 7:3) whereas condensation of primary alkylphosphanes (cHexPH2, iBuPH2) with p‐toluidine and GAH was followed by additional spontaneous and highly diastereoselective lactamization to form five‐membered P,N‐heterocyclic racemic amino acids 2 and 3. Compound 2, with three centres of asymmetry, displayed only one set of NMR signals, whereas for compound 3 one set was strongly preferred. Crystal structure analysis of 2 confirmed the presence of a racemate, with the asymmetric unit consisting of the 2R,3R,4R isomer; the molecules are linked by hydrogen bonds. The trans(eq‐eq)‐position of the P‐cyclohexyl group towards the substituents at the adjacent C2 and C4 atoms is maintained in [D8]THF solution, as shown by small 2JPH coupling constants. Large 2JPH couplings in compound 3 hint at the opposite preference, i.e. cis orientation, of the less spatially demanding isobutyl group at phosphorus towards the C2 and C4 substituents. The trans isomers of 3 were detected only in trace amounts on the basis of characteristic PCH proton doublets with small 2JPH values. This facile route to novel trialkylphosphane‐type hybrid ligands 2 and 3 may pave the way for further studies of their properties and use as ligands in transition metal compounds and catalysis.

E2 Conjugating Enzyme Selectivity and Requirements for Function of the E3 Ubiquitin Ligase CHIP

The transfer of ubiquitin (Ub) to a substrate protein requires a cascade of E1 activating, E2 conjugating, and E3 ligating enzymes. E3 Ub ligases containing U-box and RING domains bind both E2∼Ub conjugates and substrates to facilitate transfer of the Ub molecule. Although the overall mode of action of E3 ligases is well established, many of the mechanistic details that determine the outcome of ubiquitination are poorly understood. CHIP (carboxyl terminus of Hsc70-interacting protein) is a U-box E3 ligase that serves as a co-chaperone to heat shock proteins and is critical for the regulation of unfolded proteins in the cytosol. We have performed a systematic analysis of the interactions of CHIP with E2 conjugating enzymes and found that only a subset bind and function. Moreover, some E2 enzymes function in pairs to create products that neither create individually. Characterization of the products of these reactions showed that different E2 enzymes produce different ubiquitination products, i.e. that E2 determines the outcome of Ub transfer. Site-directed mutagenesis on the E2 enzymes Ube2D1 and Ube2L3 (UbcH5a and UbcH7) established that an SPA motif in loop 7 of E2 is required for binding to CHIP but is not sufficient for activation of the E2∼Ub conjugate and consequent ubiquitination activity. These data support the proposal that the E2 SPA motif provides specificity for binding to CHIP, whereas activation of the E2∼Ub conjugate is derived from other molecular determinants.

The NMR study of derivatives of substituted inosine – The precursors of AICAr

In this article we describe how the simultaneous presence and interaction of the aromatic ring at position 1 of an inosine derivative with the acetyl group at positions 2, 3, 5 of the furanose ring convert conformation of the nucleoside into the major conformer in solution. During the synthesis of AICAr, we obtained products ( A and B ) of inosine protected with 2,4-dinitrochlorobenzene, with two sets of NMR signals, each with very similar chemical shifts. Analysis of experimental NMR spectra and theoretical GIAO – DFT calculations were performed to obtain information about the stereochemistry of the products.

Li+, Cu+, and Ag+ Oligonuclear Structures with the Sterically Demanding Bis(3,5-tertbutylpyrazol-1-yl)dithioacetate Heteroscorpionate Ligand

The heteroscorpionate N(2)S(2) donor ligand bis(3,5-tertbutylpyrazol-1-yl)dithioacetate (L) was prepared as a Li(+) trinuclear complex, which co-crystallizes with tetrahydrofuran (THF) solvent molecules: [Li(L)](3) x (2.25)THF. When [Li(L)](3) was reacted with AgBF(4) or [Cu(CH(3)CN)(4)]BF(4), the oligonuclear species [Ag(L)](3) and [Cu(5)(L)(4)]BF(4) were isolated and structurally characterized. The Ag(+) complex presents an irregular trinuclear structure in which three AgL moieties define a central trigonal site that may potentially host a fourth metal ion. The Cu(+) complex exhibits a highly symmetric pentanuclear structure in which four equivalent CuL moieties shape an internal tetrahedral site occupied by an additional Cu(+) ion. According to electrospray-mass spectrometry (ESI-MS) and (1)H diffusion NMR spectroscopy, the Ag(+) and Cu(+) complexes maintain oligonuclear structures in solution. In particular, the Cu(+) pentanuclear complex, once dissolved, rapidly equilibrates with the tetranuclear species [Cu(4)(L)(3)](+). This is confirmed by the presence of two sets of NMR signals, which demonstrated a change in ratio at different complex concentrations effected by a NMR dilution titration. Variable temperature NMR experiments (210-303 K) defined the activation parameters associated with the fluxional behavior of [Cu(5)(L)(4)]BF(4) and [Cu(4)(L)(3)](+), and these results are consistent with intramolecular rearrangements in both species (DeltaS(double dagger) < 0).

CO fixation to stable acyclic and cyclic alkyl amino carbenes: stable amino ketenes with a small HOMO-LUMO gap.

CO fixation to stable acyclic and cyclic alkyl amino carbenes: stable amino ketenes with a small HOMO-LUMO gap.

Hemilabile Thioether Ligands Based on Pyrimidine and/or Pyridine Derivatives that Interconvert between N,S‐ and N‐Coordination in Congested Ruthenium(II) Complexes

AbstractThe thioether ligands L [L = 2‐pyridylmethyl 2'‐pyridyl sulfide (L1), 2‐pyridylmethyl 2'‐pyrimidyl sulfide (L2) and 2‐pyridylmethyl 2'‐(4‐methylpyrimidyl) sulfide (L3)] react with cis‐[Ru(N,N‐diimine)2Cl2] {diimine = 2,2'‐bipyridine (bipy), di‐2‐pyrimidyl sulfide (dprs), 2,2'‐bis(5‐ethylpyrimidyl) sulfide (5edprs)} to give compounds [Ru(N,N‐diimine)2L][PF6]2 {diimine = bipy, L =L1 (1), L2 (2), L3 (3); diimine = dprs, L = L1 (4); diimine = 5edprs, L = L1 (5); diimine = dprs, L = L2 (6), L = L3 (7); diimine = 5edprs, L = L2 (8), L = L3 (9)}. NMR investigations show that these potentially tridentate ligands act as N,S‐bidentate species, to form a five‐membered RuSCCN(Ru–N) ring, and in certain cases, as N‐monodentate species coordinated to the ruthenium through the 2‐pyridylmethyl group. The N,S‐chelated species contain chiral sulfur and ruthenium atoms with (R) and (S), and Δ and Λ configurations, respectively. Two invertomers and two sets of NMR signals in the slow‐exchange region are expected. However, the low‐temperature 1H NMR spectra show that sulfur inversion is fast. The variable‐temperature 1H NMR spectra allow two species to be observed (6a + 6b, 7a + 7b, 8a + 8b and 9a + 9b), which exhibit different abundances. In the minor species (6b, 7b, 8b, and 9b), L2 or L3 exhibits an N‐monodentate coordination, while in the major species, the usual N,S‐coordination. At low temperatures, the population ratio is about 85:15, while when the temperature increases, the abundance of the minor species grows rapidly. The one‐dimensional band‐shape analysis of the exchanging methylene proton signals shows that the energy‐barrier for the interchange process (ΔG#298) for 6a + 6b, 7a + 7b, 8a + 8b, and 9a + 9b is practically the same (ca. 59.5 kJ·mol–1), while the ΔS# values are negative or near to zero. The possible mechanisms for the process are discussed. The NMR spectroscopic findings strongly support the formation of an N,N‐chelated labile intermediate. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

1H-NMR Studies of the Inclusion Complexes between ?-Cyclodextrin and Adamantane Derivatives Using Both Exchangeable Hydroxy Protons and Non-Exchangeable Aliphatic Protons

The inclusion complexes between α-cyclodextrin (α-CD) and adamantane, 1-adamantanol, 1-(hydroxymethyl)-adamantane, 2-adamantanol, and 1,3-adamantanediol in aqueous solution have been studied by 1H-NMR spectroscopy using both non-exchangeable and exchangeable protons. The complexation-induced 1H-NMR shifts (CIS) and NOEs of non-exchangeable protons, as well as the CIS, NOEs, temperature coefficients, and linewidth of signals from exchangeable hydroxy protons have been determined. The stoichiometry of the adamantane/α-CD complex could not be determined due to the low solubility of adamantane. However, for 0.11 equivalent of adamantane added, two sets of separate 1H signals for the free and bound α-CD were observed. The signal from O(3)H in the complexed form appeared narrow and upfield shifted with a low-temperature coefficient indicating reduced hydration inside the hydrophobic cavity of α-CD. Both 1-adamantanol, and 1-(hydroxymethyl)-adamantane formed 1:1 inclusion complexes with α-CD and only one set of NMR signals was observed. The CIS and NOEs suggested that both complexes had similar structures. The O(2)H signal of α-CD was broadened at low temperature and became narrower as the temperature raised. The broadening increased with higher concentration of guest suggesting interaction between O(2)H of α-CD and the guest molecules. The stoichiometry of the α-CD/2-adamantanol complex could not be determined with certainty, but the NMR data suggested equilibrium between 2:1 and 1:1 complex. As with adamantane, a sharp and upfield shifted O(3)H signal with a very low-temperature coefficient was observed. No inclusion complex was formed between 1,3-adamantanediol and α-CD. This study showed how the hydroxy protons of α-CD could be used to obtain complementary information on the geometry and stability of inclusion complexes of α-CD.

Use of (13)c MAS NMR to study domain structure and dynamics of polysaccharides in the native starch granules.

To investigate the domain structure and dynamics of polysaccharides in the native starch granules, a variety of high resolution, solid-state (13)C NMR techniques have been applied to all three (A-, B-, and C-) types of starch with different water content. Both single-pulse-excitation magic-angle-spinning (SPEMAS) and cross-polarization-magic-angle-spinning (CPMAS) methods have been employed together with the PRISE (proton relaxation induced spectral-editing) techniques to distinguish polysaccharide fractions in different domains and having distinct dynamics. It has been found that, for all three types of dry starch granules, there are two sets of NMR signals corresponding to two distinct ordered polysaccharides. Hydration leads to substantial mobilization of the polysaccharides in the amorphous regions, but no fundamental changes in the rigidity of the polysaccharides in the crystalline (double) helices. Full hydration also leads to limited mobility changes to the polysaccharides in the amorphous lamellae (branching zone) within the amylopectin clusters and in the gaps between the arrays of the amylopectin clusters. Under magic-angle spinning, proton relaxation-time measurements showed a single component for T(1), two components for T(1rho), and three components for T(2). PRISE experiments permitted the neat separation of the (13)C resonances of polysaccharides in the crystalline lamellae from those in the amorphous lamellae and the amylose in the gaps between amylopectin clusters. It has been found that the long (1)H T(1rho) component ( approximately 30 ms) is associated with polysaccharides in the crystalline lamellae in the form of double helices, whereas the short T(1rho) component (2-4 ms) is associated with amylose in the gaps between amylopectin clusters. The short (1)H T(2) component ( approximately 14 micros) is associated with polysaccharides in the crystalline lamellae; the intermediate component (300-400 micros) is associated with polysaccharides in the amorphous lamellae and amylose in the gaps between amylopectin clusters. The long T(2) component is associated with both mobile starch protons and the residue water protons.

ANOVA and factor analysis applied to time domain NMR signals

Time domain (or low resolution pulse) NMR can generate a range of relaxation curves (CPMG, I–R, P–S, HSE, FID, etc.) which may vary depending on the characteristic of the product being controlled—water content, hydration state, solid fat content, iodine number or even authenticity of origin. Very often, the NMR signal is decomposed into a sum of exponential relaxation curves and the calculated NMR parameters (e.g. R1, R2, M0) are correlated with the property under study. Chemometric techniques, such as analysis of variance (ANOVA) and factor analysis, were shown to be effective means of determining whether a given set of NMR signals contains any interesting information before proceeding to use fastidious and often uncertain signal decomposition procedures. These techniques were applied to NMR signals acquired for spreads and gelatines with different compositions, to mixtures of a cation (Cu2+) and a ligand (tetraphenylporphin) and to glycine solutions at different pH values. © 1997 John Wiley & Sons, Ltd.

1H NMR Spectra at 360 MHz of Diosmin and Hesperidin in DMSO Solution

Abstract A complete analysis of the 360 MHz 1H NMR spectra of diosmin and hesperidin in DMSO-d6 solution has been performed and the corresponding values for chemical shifts and coupling constants given. Two sets of NMR signals have been detected in aged hesperidin samples, and based on NMR parameters and HPLC data, the second set has been assigned to an hesperidin isomer with a change of the natural configuration at the C2 atom.

Nuclear magnetic resonance of 55Mn and 75As in MnAs

Four sets of NMR signals, two each, from 55Mn and 75As nuclei have been observed. The temperature dependences of 55Mn resonances have been studied from 77 to 311 K and that of 75As, from 77 K to about 250 K. The results show that there is a phase transition at T 1 ≈ 220 K. This transition may be due to introduction of a local spontaneous distortion in the region of the domain walls in the lattice, resulting in lowering of symmetry at low temperatures. Another possibility is the canting of spins which would lower the magnetic group symmetry. The observed resonances have been assigned to arise from the nuclei at the edge and the centre of the domain walls at temperatures T > T 1 and from two types of wall edges with inequivalent orientation of atomic spins at T < T 1. The isotropic hyperfine field at 0 K obtained by extrapolating the resonance frequencies are 227 and 285.1 kOe at 55As nuclei, respectively. The anisotropy in the hyperfine field is nearly zero at 55Mn nuclei and about 5.8 kOe at 75As nuclei at 0 K.