Evaluation of a direct1H NMR method for determining logK and ΔH values for crown ether -alkylammonium cation complexation

A direct¹H NMR method for determining logK and H values for crown ether-ammonium cation complexation using milligrams of sample was tested and evaluated for accuracy and precision by comparing the results with those obtained using a titration calorimetric method. LogK values for the interactions of a non-chiral crown ether, diketopyridino-18-crown-6 (K₂P18C6), with -phenylethylammonium (PhEt⁺) perchlorate in 50%–50% and 90%–10% (v/v) mixtures of deuterated methanol (CD₃OD) and deuterated chloroform (CDCl₃) at four temperatures and, with -(1-naphthyl)ethylammonium (NapEt⁺) perchlorate in 50%CD₃OD-50%CDCl₃ (v/v) at 25°C were determined by a direct¹H NMR method. Values of H for the interactions of K₂P18C6 with PhEt⁺ in the two solvents were calculated from the temperature dependence of logK. LogK values for the interactions of a chiral crown ether, dimethyldiketopyridino-18-crown-6 (M₂K₂P18C6), with (R) and (S) enantiomers of NapEt⁺ in pure CD₃OD at 25.0°C were also determined by the NMR method. The results were compared with those determined by a calorimetric method at 25.0°C in 50%-50% and 90%–10% (v/v) mixtures of plain methanol and chloroform, in 100% plain methanol, and in a 50%-50% mixture of partially deuterated methanol (with deuterium substitution on the methanol OH group, CH₃OD) and deuterated chloroform. The log K values determined by both methods were found to be in good agreement, but the standard deviations associated with the NMR logK values were two to three times greater. The agreement of the H values determined by the two methods was poor, differing by approximately 10 kJ/mol with the NMR method giving more negative values. The standard deviations associated with the NMR H values were approximately ten times greater than those for the calorimetric values. Ion-pairing was observed for the interaction of perchlorate ion with both free and bound PhEt⁺ in 50%methanol-50%chloroform mixture. It is concluded that the NMR procedure is satisfactory for the determination of logK, but not H values.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

1H NMR spectroscopy as a probe of intermolecular interactions in β-cyclodextrin inclusion compounds

¹H NMR spectroscopy was used to probe the formation of inclusion compounds of permethylated and peracetylated ß-cyclodextrins as host molecules and a variety of electronically very different guest molecules. Complexation, obtained only in water, was estimated quantitatively by means of chemical shift/concentration curves of relevant protons, and the intermolecular forces involved are criticially discussed.     

纽约发现狗感染H1N1病例

纽约出现美国首例狗感染甲型H1N1流感病例,病毒源为狗主人。一些分析师认为,尚无证据表明新型流感病毒会由宠物传染给人。     

1α-Acetoxy-11β(H),13-dihydrodouglanin, a New Eudesmanolide from Artemisia lehmanniana

A new sesquiterpene lactone, 1-acetoxy-11(H),13-dihydrodouglanin, was isolated fromArtemisia lehmanniana.The structure was established by spectral data and an x-ray analysis.     

Vibrational relaxation rates for H on a Si(1 0 0):(2×1) surface: a two-dimensional model

The results of calculations based on perturbation theory of vibrational relaxation rates due to coupling to substrate phonons for hydrogen atoms adsorbed on a Si(1 0 0):(2×1) surface are presented. For this purpose a two-dimensional model is adopted in which both the H–Si stretching and bending motions are included. It is shown that within this model the multiphonon emission and absorption processes play a negligible role. The calculated lifetimes agree well with available experimental data.     

Precision studies in supramolecular chemistry: a 1H NMR study of hydroxymethoxyacetophenone/β-cyclodextrin complexes

The association constants for the interactions of 2-hydroxy-4-methoxyacetophenone, 2-hydroxy-5-methoxyacetophenone, 2-hydroxy-6-methoxyacetophenone, 3-hydroxy-4-methoxyacetophenone and 4-hydroxy-3-methoxyacetophenone with β-cyclodextrin in water were measured by (1)H NMR and by isothermal titration calorimetry. Very good agreement was obtained between the different methods. The errors associated with the NMR method for measuring mM binding affinities were estimated to be 10-30%, and by isothermal titration calorimetry, 10-20%. Rotating frame nuclear Overhauser effect spectroscopy studies show that the solution phase host-guest complexes formed by β-cyclodextrin with these hydroxymethoxyacetophenone derivatives are not structurally well defined but that the hydroxymethoxyacetophenone derivatives are mostly associated with the narrow primary hydroxyl rim.     

JP H1型脉冲极谱仪

脉冲极谱是目前所有极谱新技术中最灵敏的方法,并已得到日益广泛的应用。应化所极谱组和所内工厂及吉林省国营8270厂的工人,技术人员和领导干部“三结合”组成脉冲极谱仪研制组。遵照毛主席“独立自主,自力更生,艰苦奋斗,勤俭建国”的方针,破除迷信,解放思想,在党的领导下,通过批林批孔运动,焕发革命精神,经过辛勤劳动,反复试验,克服种种困难,从无到有,终于研制成功与A3100型(英国南方分析仪器公司出品)相仿的国产脉冲极谱仪JP-M1型,并已     

DMA水溶液的1H NMR研究

测量了N，N-二甲基乙酰胺(DMA)水溶液体系不同温度下全浓度范围的^1H NMR数据，对体系中的缔合情况进行了讨论。应用化学缔合模型求得了各缔合平衡常数K和缔合平衡的△H，结合N，N-二甲基甲酰胺(DMF)和N-甲基乙酰胺(NMA)水溶液的研究结果，发现酰胺自身结构和酰胺浓度是影响酰胺水溶液性质的主要因素。     

Synthesis and Antimicrobial Activity of 1‐[(Substituted Carbamoyl)Amino]‐1H,3H‐1λ5‐[1,3,2]oxazaphospholo[3,4‐a]benzimidazol‐1‐ones

1‐[(Substituted carbamoyl)amino]‐1H,3H‐1λ⁵‐[1,3,2]oxazaphospholo[3,4‐a]benzimidazol‐1‐ones were synthesized by reacting benzimidazole 2‐methanol (4) with different chlorides of carbamidophosphoric acids (3) in the presence of triethylamine at 40–45°C. Their ¹H, ¹³C, and ³¹P NMR spectral data were discussed. The title compounds were tested for their activity against the fungi Aspergillus niger and Fusarium solani and bacteria Staphylococcus aureus and Escherichia coli. These compounds showed moderate antibacterial activity when compared with antifungal activity.     

From a localized H3O radical to a delocalized H3O+···e- solvent-separated pair by sequential hydration

The impact of microhydration on the electronic structure and reactivity of the H(3)O moiety is investigated by ab initio calculations. In the gas phase, H(3)O is a radical with spin density localized on its hydrogen end, which is only kinetically stable and readily decomposes into a water molecule and a hydrogen atom. When solvated by a single water molecule, H(3)O preserves to a large extent its radical character, however, two water molecules are already capable to shift most of the spin density to the solvent. With three solvating water molecules this shift is practically completed and the system is best described as a solvent-separated pair of a hydronium cation and a hydrated electron. The electronic structure of this system and its proton transfer reactivity leading to formation of a hydrogen atom already resemble those of a proton-electron pair in bulk water.     

N−H Bond Formation at a Diiron Bridging Nitride

Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N−H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N−H bonds via proton-coupled electron transfer to generate a μ-amide product. The structurally analogous μ-silyl- and μ-borylamide complexes were shown to form from the net insertion of the nitride into the E−H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH₃ in high yield through a reaction that engages the redox-activity of the ligand during PCET.     

Inclusion of Enantiomeric Carvones in β-Cyclodextrin: a Variable Temperature 1H NMR Study in Aqueous Solution

In aqueous solution, the apparent association constant at room temperature for the 1 : 1 inclusion of S-(+)-carvone in - cyclodextrin is double of that for R-(-)-carvone, whereas, at 45 °C, both enantiomers have association constants two orders of magnitude smaller, with the S-(+) inclusion being then slightly weaker than the R-(-) encapsulation. Calculations carried out at the molecular mechanics, AM1 and STO-3G levels confirm the preferential inclusion of the S-enantiomer and provide important clues for understanding chiral discrimination by -cyclodextrin.     

^3H—^1H化学位移相关NMR谱介绍

氚标记对于代谢和受体结合研究是一个重要的工具。然而确定其氚标记在化合物中的位置和相对强度对此研究至关重要。由于~3H的化学位移与的~1H 化学位移几乎相等,可将文     

Carbonium ion stabilization by (η5-cyclopentadienyl)dicarbonylnitrosylchromium; a 1H and 13C NMR study

the ¹H and ¹³C NMR spectra of a series of (η⁵-cyclopentadienyl)dicarbonylnitrosylchromium-substituted carbonium ions have been determined. These data suggest that the same mechanism is responsible for the stabilization of carbonium ions by (η⁵-cyclopentadienyl)dicarbonylnitrosylchromium as is operational in the analogous ferrocene and cymantrene complexes.     

C?H Hydroxylation Using a Heterocyclic Catalyst and Aqueous H2O2

Substituted benzoxathiazines function as catalysts for the selective hydroxylation of tertiary C? H bonds. Mechanistic studies have revealed an unanticipated disparity between oxaziridine reactivity and catalyst performance and have given way to a new catalyst and an aqueous H₂O₂ reaction protocol that greatly facilitate such transformations (see scheme).

     

(±)-3,4,4a,5,6,7-Hexahydro-4a-Methyl-7,7-Diphenyl-1(2H)-Naphthtlenone

The title compound was prepared in 48% overall yield using a seven-step sequence. The synthesis involves stepwise construction of a 3-formyl-3,3-diphenypropyl side chain from the double bond of 3-ethenyl-3-methylcyclohexanone followed by aldol ring closure. The approach represents a general strategy for the synthesis of a number of (±)-7,7-diary1–3,4,4a,5,6,7-hexahydro-1(2H)-naphthalenones.     

Dynamics of lysine side-chain amino groups in a protein studied by heteronuclear 1H−15N NMR spectroscopy

Despite their importance in macromolecular interactions and functions, the dynamics of lysine side-chain amino groups in proteins are not well understood. In this study, we have developed the methodology for the investigations of the dynamics of lysine NH3(+) groups by NMR spectroscopy and computation. By using 1H?15N heteronuclear correlation experiments optimized for 15NH3(+) moieties, we have analyzed the dynamic behavior of individual lysine NH3(+) groups in human ubiquitin at 2 °C and pH 5. We modified the theoretical framework developed previously for CH3 groups and used it to analyze 15N relaxation data for the NH3(+) groups. For six lysine NH3(+) groups out of seven in ubiquitin, we have determined model-free order parameters, correlation times for bond rotation, and reorientation of the symmetry axis occurring on a pico- to nanosecond time scale. From CPMG relaxation dispersion experiment for lysine NH3(+) groups, slower dynamics occurring on a millisecond time scale have also been detected for Lys27. The NH3(+) groups of Lys48, which plays a key role as the linkage site in ubiquitination for proteasomal degradation, was found to be highly mobile with the lowest order parameter among the six NH3(+) groups analyzed by NMR. We compared the experimental order parameters for the lysine NH3(+) groups with those from a 1 μs molecular dynamics simulation in explicit solvent and found good agreement between the two. Furthermore, both the computer simulation and the experimental correlation times for the bond rotations of NH3(+) groups suggest that their hydrogen bonding is highly dynamic with a subnanosecond lifetime. This study demonstrates the utility of combining NMR experiment and simulation for an in-depth characterization of the dynamics of these functionally most important side-chains of ubiquitin.