The 2D {P} Spin-Echo-Difference Constant-Time [C, H]-HMQC Experiment for Simultaneous Determination of JH3′P and JC4′P in C-Labeled Nucleic Acids and Their Protein Complexes

A two-dimensional {³¹P} spin-echo-difference constant-time [¹³C, ¹H]-HMQC experiment (2D {³¹P}-sedct-[¹³C, ¹H]-HMQC) is introduced for measurements of ³J_C4′P and ³J_H3′P scalar couplings in large ¹³C-labeled nucleic acids and in DNA–protein complexes. This experiment makes use of the fact that ¹H–¹³C multiple-quantum coherences in macromolecules relax more slowly than the corresponding ¹³C single-quantum coherences. ³J_C4′P and ³J_H3′P are related via Karplus-type functions with the phosphodiester torsion angles β and ε, respectively, and their experimental assessment therefore contributes to further improved quality of NMR solution structures. Data are presented for a uniformly ¹³C, ¹⁵N-labeled 14-base-pair DNA duplex, both free in solution and in a 17-kDa protein–DNA complex.     

More line narrowing in TROSY by decoupling of long-range couplings: shift correlation and JNC′ coupling constant measurements

Since the introduction of RDCs in high-resolution NMR studies of macromolecules, there is a growing interest in the development of accurate, and sensitive methods for determining coupling constants. Most methods for extracting these couplings are based on the measurement of the splitting between multiplet components in J-coupled spectra. However, these methods are often unreliable since undesired multiple-bond couplings can considerably broaden the multiplet components and consequently make accurate determination of their position difficult. To demonstrate one approach to this problem, G-BIRD^(r) decoupled TROSY sequences are proposed for the measurement of ¹J_NH and ¹J_NC′ coupling constants. Resolved or unresolved splittings due to remote protons are removed by a G-BIRD^(r) module employed during t₁ and as a result, spectra with narrow, well-resolved peaks are obtained from which heteronuclear one-bond couplings can be accurately measured. Moreover, introduction of a spin-state-selective α/β-filter in the TROSY sequence allows the separation of the ¹J_NC′ doublet components into two subspectra which contain the same number of peaks as the regular TROSY spectrum. The ¹J_NC′ couplings are obtained from the displacement between the corresponding peaks in the subspectra.     

Global Entanglement Measures and Quantum Phase Transitions in the 1D J 1? J 2 Model

We have analyzed the behavior of multipartite global entanglement and average bipartite concurrence for the sign of quantum phase transitions in the frustrated J ₁−J ₂ model by using exact diagonalization technique for a chain of 12 qubits. It is found that although the magnitude of two classes of the measures show opposite trends the absolute value of their derivatives show similar structure near critical points.     

J Coupling between C and H across Hydrogen Bonds in Proteins

Two new two- or three-dimensional NMR methods for measuring ^3hJ_C′N and ^2hJ_C′H coupling constants across hydrogen bonds in proteins are presented. They are tailored to suit the size of the TROSY effect, i.e., the degree of interference between dipolar and chemical shift anisotropy relaxation mechanisms. The methods edit 2D or 3D spectra into two separate subspectra corresponding to the two possible spin states of the ¹H^N spin during evolution of ¹³CO coherences. This allows ^2hJ_C′H to be measured in an E.COSY-type way while ^3hJ_C′N can be measured in the so-called quantitative way provided a reference spectrum is also recorded. A demonstration of the new methods is shown for the ¹⁵N,¹³C-labeled protein chymotrypsin inhibitor 2.     

Simultaneous measurement of neuronal and glial metabolism in rat brain in vivo using co-infusion of [1,6-C2]glucose and [1,2-C2]acetate

In this work the feasibility of measuring neuronal-glial metabolism in rat brain in vivo using co-infusion of [1,6-¹³C₂]glucose and [1,2-¹³C₂]acetate was investigated. Time courses of ¹³C spectra were measured in vivo while infusing both ¹³C-labeled substrates simultaneously. Individual ¹³C isotopomers (singlets and multiplets observed in ¹³C spectra) were quantified automatically using LCModel. The distinct ¹³C spectral pattern observed in glutamate and glutamine directly reflected the fact that glucose was metabolized primarily in the neuronal compartment and acetate in the glial compartment. Time courses of concentration of singly and multiply-labeled isotopomers of glutamate and glutamine were obtained with a temporal resolution of 11 min. Although dynamic metabolic modeling of these ¹³C isotopomer data will require further work and is not reported here, we expect that these new data will allow more precise determination of metabolic rates as is currently possible when using either glucose or acetate as the sole ¹³C-labeled substrate.     

Proton Dynamics in Letovicite, (NH4)3H(SO4)2: A H and N NMR Spectroscopic Study

The improper ferroelastic phase letovicite (NH₄)₃H(SO₄)₂ has been studied by ¹H MAS NMR as well as by static ¹⁴N NMR experiments in the temperature range of 296–425 K. The ¹H MAS NMR resonance from ammonium protons can be well distinguished from that of acidic protons. A third resonance appears just below the phase transition temperature which is due to the acidic protons in the paraelastic phase. The lowering of the second moment M₂ for the ammonium protons takes place in the same temperature range as the formation of domain boundaries, while the signals of the acidic protons suffer a line narrowing in the area of T_c. The static ¹⁴N NMR spectra confirm the temperature of the motional changes of the ammonium tetrahedra. Two-dimensional ¹H NOESY spectra indicate a chemical exchange between ammonium protons and the acidic protons of the paraphase.     

Analysis of 1H and 13C{1H} NMR Spectral Parameters and Geometries of Three Isomeric Diphenylbicyclo[2.2.1]Hept-5-Ene-2,3-Dicarboxylic Anhydrides

Diels-Alder adducts of 1,4-diphenyl-1,3-cyclopentadiene and maleic anhydride were investigated by recording the ¹H and ¹³C{¹H} NMR spectra of three isomeric diphenylbicyclo[2.2.1]hept-5-ene endo and exo 2,3-dianhydrides. the spectra were recorded in CD₂Cl₂ and analysed completely. the effect of the endo and exo configuration of the anhydride ring on the chemical shifts of the bridgehead phenyl protons is discussed. the ortho protons of the exo isomers resonate at higher field than those of the endo isomer, and the resonance pattern of the aromatic protons is narrower in the exo than the endo anhydride. the aromatic regions of the spectra are compared with the same regions of the ¹H NMR spectra of the earlier investigated addition products of 1,4-di-p-tolyl-1,3-cyclopentadiene and 1-phenyl-4-p-tolyl-1,3-cyclopentadiene with maleic anhydride. Chemical shifts of the bridge protons are explained on the basis of X-ray data of the compounds and MacroModel calculations on the minimum energy conformations.     

13C NMR and 2D (H,H and H,C COSY) Spectra of Triazolo-triazino-indole Derivatives and the Conformational Analysis of the Respective C-Nucleoside Analogues

¹³C NMR and 2D (H,H and H,C COSY) spectra of selected examples of sugar (5H-1,2,4-triazino[5,6-b]-indol-3-yl) hydrazones, peracetylated sugar-1-acetyl -1- (5-acetyl-1,2,4-triazino[5,6-b]indol-3-yl)hydrazones, and 10-acetyl-3-(per-0-acetylalditol-1-yl)-1,2,4-triazolo[4′, 3′:2,3][1,2,4]triazino[5,6-b]indole have been reported. The conformation of the latter C-nucleoside analogues have been determined by analysis of their ¹H NMR spectra. The D-galacto, D-manno and L-arabino isomers are preponderantly existing in the planar zigzag arrangement of carbon atoms.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]3Sb2Br9

The crystal structure of [C(NH₂)₃]₃Sb₂Br₉ was determined at 143 K: monoclinic, space group C2/c, Z = 4, a = 15.695 (3), b = 9.039(2), c = 18.364(3) Å, β = 96.94(1)°. The structure consists of two crystallographically independent guanidinium ions and two-dimensional corrugated sheets of (Sb₂Br₉ ^3?) _n , in which SbBr₆ octahedra are connected through three bridging Br atoms each other. One of the cations situates in a cavity of the (Sb₂Br₉ ^3?) _n layer with statistical disorder, while the other situates between the layers without disorder. Three ⁸¹Br NQR resonance lines were assignable to terminal Br atoms, while only one line was found for two inequivalent bridging Br atoms. All the ⁸¹Br NQR resonance lines were subjected to fade-out at low temperatures. The temperature dependence curve of ¹H NMR T ₁ showed well defined two minima, which were explained by postulating the C₃ reorientations of two types of cations with very different activation energies. The DTA (DSC) measurement revealed a phase transition of a first-order type at 444 K.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

A new detection scheme for ultrafast 2D J-resolved spectroscopy

Recent ultrafast techniques enable 2D NMR spectra to be obtained in a single scan. A modification of the detection scheme involved in this technique is proposed, permitting the achievement of 2D 1H J-resolved spectra in 500 ms. The detection gradient echoes are substituted by spin echoes to obtain spectra where the coupling constants are encoded along the direct nu2 domain. The use of this new J-resolved detection block after continuous phase-encoding excitation schemes is discussed in terms of resolution and sensitivity. J-resolved spectra obtained on cinnamic acid and 3-ethyl bromopropionate are presented, revealing the expected 2D J-patterns with coupling constants as small as 2 Hz.     

Magnitudes and Orientations of the N Chemical Shift Tensor of [1-N]-2′-Deoxyguanosine Determined on a Polycrystalline Sample by Two-Dimensional Solid-State NMR Spectroscopy

The magnitudes and orientations of the ¹⁵N chemical shift tensor of [1-¹⁵N]-2′-deoxyguanosine were determined from a polycrystalline sample using the two-dimensional PISEMA experiment. The magnitudes of the principal values of the ¹⁵N chemical shift tensor of the N1 nitrogen of [1-¹⁵N]-2′-deoxyguanosine were found to be ς₁₁ = 54 ppm, ς₂₂ = 148 ppm, and ς₃₃ = 201 ppm with respect to (¹⁵NH₄)₂SO₄ in aqueous solution. Comparisons of experimental and simulated two-dimensional powder pattern spectra show that ς_33N is approximately collinear with the N–H bond. The tensor orientation of ς_33N for N1 of [1-¹⁵N]-2′-deoxyguanosine is similar to the values obtained for the side chain residues of ¹⁵N_ε1-tryptophan and ¹⁵N_π-histidine even though the magnitudes differ significantly.     

1H NMR Studies on the Methylation,Protonation, and Hydration Sites in Some Benzo[b]Naphthyridines (Azaacridines)

Abstract

The 300.13 MHz ¹H NMR spectra of the methylated and protonated 6(9)-methylbenzo[b][1,x] naphthyridines (x=5, 6, 7, 8) (5-methylazaacridines) were collected at 298 K in deuterated dimethyl sulfoxide and chloroform, respectively. The methylation and protonation sites were assigned by comparisons of these data with those of the free bases. The results were compared with similar data for related heterocycles and showed that both methylation and protonation occur at the nitrogen in the outer pyrido ring in all four series.

The hydration site in some 2-and 3-azaacridines was determined by specific line broadening in their ¹H NMR spectra to be the same nitrogen as that involved in methylation and protonation. Variable temperature ¹H NMR demonstrated that the specific line broadening results from some changes of ¹⁴N quadrupolar relaxation produced by the slow chemical exchange between unhydrated and hydrated species. Deuterium exchange experiments indicated that the direct spin-spin interaction of a water proton and the protons alpha to the hydrated nitrogen may also have some contribution.     

1H and 13C NMR Spectra of Alditolyl Derivatives of 3-Hydrazino-5-Methyl[1,2,4]triazino[5,6-b]indole and Their Cyclized Products.

The ¹H and ¹³C NMR spectra of sugar (5-methyl [1, 2, 4]-triazino [5, 6-b] indol-3-yl) hydrazones (1), per-0-acetyl aldehydo sugar 1-acetyl-1-(5-methyl [1, 2, 4] triazino [5, 6-b]-indol-3-yl) hydrazones (2), l- (penta-0-acetyl-pentitol-1-yl)-10-methyl [l, 2, 4] triazolo [3′, 4′:3, 4] [l, 2, 4] triazino [5, 6-b]-indoles (3) have been investigated. The 2 D NMR (H, C COSY) spectrum of 2a has been studied.     

Al2O3X(X=H,D, T)的电子振动近似理论方法研究

用密度泛函理论(DFT)方法在6-311++G(d,p)水平上对Al₂O₃X(X=H, D, T)分子较低能量的几何构型进行了优化. 计算结果表明该分子有两个可能基态, 即Al₂O₃X(X=H,D,T)(²A′)C_s和Al₂O₃X 关键词： 2O₃X(X=H;D;T)分子团簇')" href="#">Al₂O₃X(X=H;D;T)分子团簇 热力学函数 氢同位素效应 吉布斯自由能改变     

Theoretical investigation of EPR and optical spectra of Mo(V) in [Mo6O19][N(C4H9)4]3 salt

The electron paramagnetic resonance (EPR) spectral data (the g factors and hyperfine structure constants) and d–d transition spectra for the tetragonal Mo⁵⁺ centre in [Mo₆O₁₉][N(C₄H₉)₄]₃ salt are theoretically investigated from the complete diagonalization method (CDM) for a 4d¹ ion in tetragonally compressed octahedron. The theoretical results are in good agreement with the experimental data. The dependency of the g factors of the ground state on the R_∥(MoO bond length) has been studied. It is shown that the g factors varied with the R_∥ approximately in a linear way.     

Dietary fibre-rich resistant starches promote ammonia detoxification in the human colon as measured by lactose-[15N2]ureide

Three resistant starches (RSs), namely fibre of potatoes (FP), wrinkle pea starch (WPS), and high amylose maize starch (HAMS) with different dietary fibre contents, were supplemented in adults to evaluate their effects on urinary nitrogen and ammonia excretion as well as on faecal nitrogen excretion by means of lactose-[¹⁵N₂]ureide (¹⁵N-LU) degradation. Twenty subjects received a regular diet either without or with the supplementation of FP, WPS, and HAMS in a randomized order. After administration of ¹⁵N-LU, urine and faeces were collected over 48 and 72 h, respectively, whereas blood was collected after 6 h. The ¹⁵N-abundances were measured by isotope ratio mass spectrometry. In comparison to the dry run, supplementation with RS significantly lowered renal ¹⁵N-excretion (dry run: 43.2?%, FP: 34.6?%, WPS: 37.9?%, HAMS: 36.4?%) as well as the corresponding ¹⁵NH₃-excretion (dry run: 0.08?%, FP: 0.06?%, HAMS: 0.05?%), clearly indicating a reduced colonic nitrogen generation at high dietary fibre intake.     

1H NMR study of [N(CH3)4]2ZnCI4 at high pressures and low temperatures

Wide-line proton NMR studies on polycrystalline tetramethylammonium tetrachlorozincate have been carried out at high hydrostatic pressures up to 15 kbar in the temperature range 77-300 K and at ambient pressure down to 4.2 K. A second-moment transition is observed to occur starting around 161 K, the temperature for the V-VI phase transition. This transition temperature is seen to have a negative pressure coefficient up to 2 kbar, beyond which it changes sign. At 77 K the second moment decreases to 4 kbar and then increases again as a function of pressure. The results are explained in terms of the dynamics of the N(CH₃)₄ groups.     

Structure Elucidation and Assignment of 1H and 13C Spectra of the New Fused Cyclobutane-Naphthofuran Derivative by Two-Dimensional NMR in Different Solvents

One of the major product from the photodimerization of 2-[2-(2-methyl-phenyl)ethenyl)]naphtho[2. 1-b]furan (1) is a new fused cyclobutane-naphthofuran derivative, 6-(2-methylphenyl)-1-[2-(2-methylphenyl)ethenyl]-7-(2-naphtho-[2,1-b]furyl)-3-[2,1]naphtho-2-oxabicyclo[3.2.0]hept-3-ene (2). Its ¹H and ¹³C NMR spectra were fully assigned by the application of COSY, LR COSY, NOESY, APT and HETCOR experiments in deuterated chloroform, acetone and benzene solutions.