Two-Dimensional Proton Chemical Shift Correlated NMR Spectroscopy of Digitoxose1

Abstract

The hydroxyl proton coupled ¹H NMR spectra of solutions of β-d-digitoxopyranose and of an equilibrated mixture of the four ring forms of d-digitoxose in dimethylsulfoxide-d ₆ have been assigned completely by two-dimensional, proton chemical shift correlated NMR spectroscopy and spin decoupling at 400 MHz. Analysis of resolution enhanced, one-dimensional ¹H NMR spectra yielded an almost complete set of CH and OH proton-proton coupling constants for the four ring forms. The free aldehydo form of d-digitoxose in dimethylsulfoxide-d ₆ solution has been detected by means of its characteristic H-l quartet at 6 9.687. Quantitative analysis of the equilibrated mixture of the five forms of d-digitoxose gave the composition:- α-pyranose, β-pyranose, α-furanose, β-furanose, aldehydo form, 11.2, 67.3, 8.4, 13.0, and 0.1%, respectively. The ⁴ C ₁ chair conformations have been assigned to the α- and β-pyranose forms by analysis of the coupling constants and are discussed qualitatively in terms of their relative stabilities.     

1H AND 31P NMR Spectroscopy of Agrocinopine

The ¹H NMR data of agrocinopine in D₂O solution as extracted from standard 2D NMR experiments, along with 1D ³¹P and ¹³C NMR experiments allow to support the trisaccharide structure originally proposed on basis of comparative ¹³C NMR measurements.     

高聚合度聚磷酸铵中特征磷的31P核磁共振分析

采用一维³¹P核磁共振(³¹P NMR)、 二维J分解谱(J-resolved)和扩散核磁(³¹P DOSY)等方法, 研究了高聚合度聚磷酸铵(APP)和多聚磷酸盐的特征磷及其偶合常数. 研究表明, 多聚磷酸盐及其中所含的二聚磷酸盐端基磷分别呈双峰和单峰特征, 多聚磷酸盐自旋偶合裂分的端基磷共振峰的偶合常数为19.4 Hz. APP中含有小分子二聚磷酸铵和正磷酸铵, 用³¹P NMR定量表征APP聚合度时需排除二聚体端基磷峰的面积. 在100 ℃水中溶解APP制备的APP水溶液中, 部分高聚合度APP发生断链, 中间磷共振峰处出现短链APP的磷共振峰.     

Accurate Backbone 13C and 15N Chemical Shift Tensors in Galectin-3 Determined by MAS NMR and QM/MM: Details of Structure and Environment Matter

Chemical shift tensors obtained from solid-state NMR spectroscopy are very sensitive reporters of structure and dynamics in proteins. While accurate ¹³C and ¹⁵N chemical shift tensors are accessible by magic angle spinning (MAS) NMR, their quantum mechanical calculations remain challenging, particularly for ¹⁵N atoms. Here we compare experimentally determined backbone ¹³C^α and ¹⁵N^H chemical shift tensors by MAS NMR with hybrid quantum mechanics/molecular mechanics/molecular dynamics (MD-QM/MM) calculations for the carbohydrate-binding domain of galectin-3. Excellent agreement between experimental and computed ¹⁵N^H chemical shift anisotropy values was obtained using the Amber ff15ipq force field when solvent dynamics was taken into account in the calculation. Our results establish important benchmark conditions for improving the accuracy of chemical shift calculations in proteins and may aid in the validation of protein structure models derived by MAS NMR.     

Phosphorus dendrimers as viewed by 31P NMR spectroscopy; synthesis and characterization

This review emphasizes the role of phosphorus for the elaboration of dendrimers and of various highly sophisticated dendritic structures, and the invaluable role played by ³¹P NMR for their characterization and to ascertain their purity. A few properties, highlighting the importance of phosphorus are reported at the end of this review.     

~(31)P NMR Spectral Evidence for the Formation of Amino Acid Highcoordinated Phosphorus Intermediates

Ithasbeenknownthatmanyenzymes'activitiesareregulatedthroughthephosphorylationanddephosphorylationofserine,threonineorcysteineresiduesinprotein.However,therelationshipbetweenthephosphorylgroupandaminoacidresiduesintheproteinisstillnotwellunderstood.Recently,aseriesofreactionintermediatesofthepentacoordinatedphosphoriccarboxylicmixedanhydride("PN'MR5:-35-45ppm)wereobservedbythereactionofO,O-phenylenephosphorochloridate(O-PPC)withN,O,O--Tris(trimethyIsilyl)aminoacids.However,therewasnoevide…     

P,N-Bidentate Phosphorus Derivatives of (S)-Prolinol

Phosphorylation of (S)-prolinol with P(NEt₂)₃was used to synthesize aminophosphite (2R,5S)- , which was reacted with the corresponding amino alcohols to afford (2S,5R)- (Va) and (2S,5R)- (Vb). Reaction of Vawith [Rh(CO)₂Cl]₂(P/Rh = 1) yields the mononuclear chelate [Rh(CO)(P^N)Cl] (VIIa), while the analogous reaction with Vbresults in a mixture of products with cis- and trans-orientation of the coordinated phosphorus and nitrogen atoms. Spectral characteristics of the products of coordination of ligands Vaand Vbwere compared with those for the binuclear reference complex [Rh(CO)(L)Cl]₂(VIII), where L is P-monodentate ligand (2S,5R)- (VI). The ligands and complexes were studied by IR, NMR, ³¹P and ¹³C spectroscopy, mass spectrometry, and elemental analysis methods. X-ray diffraction analysis of crystals VIIIwas performed.     

CPCWS中水质子的核磁共振自旋晶格弛豫时间和化学位移

运用核磁共振手段，揭示了浆体中水的形态及其动态行为，并研究浆体性质与之的关联.实验测得神府煤-石油焦-水浆（CPCWS）中水质子的化学位移与煤焦中煤的百分含量的线性关系.并从NMR测得束缚水的化学位移δb ，导出计算浆体中束缚水百分含量的公式.从CPCWS中水质子的化学位移与浆体表观粘度的相关曲线可确定最佳配比的浆体.测得全焦浆中水质子自旋-晶格驰豫时间T1比全煤浆大42倍，讨论了CPCWS的T1随煤含量的变化趋势.实验表明,T1可作为CPCWS中碳质点的疏水或亲水性以及水分子形态和动态行为的定量表征.     

Monitoring of the insecticide trichlorfon by phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy

Trichlorfon is an organophosphorus insecticide, which is extensively being used for protection of fruit crops. Trichlorfon is a thermal labile compound, which cannot be easily determined by gas chromatography (GC) and has no suitable group for sensitive detection by high performance liquid chromatography (HPLC). In this study, a ³¹P nuclear magnetic resonance (³¹P NMR) has been described for monitoring of trichlorfon without any separation step. The quantitative works of ³¹P NMR spectroscopy has been performed in the presence of an internal standard (hexamethylphosphoramide). Limit of detection (LOD) for this method has been found to be 55 mg L⁻¹, without any sample preparation, and the linear working range was 150-5500 mg L⁻¹. Relative standard deviation (R.S.D.%) of the method for three replicates within and between days was obtained ≤9%. The average recovery efficiency was approximately 99-112%. This method was applied for monitoring trichlorfon in a commercial insecticide sample and tomato sample.     

Observation of (31)P-(31)P Indirect Spin-Spin Coupling in Copper-Bis(phosphine) Complexes by Two-Dimensional Solid-State NMR

The first observations of (31)P-(31)P indirect spin-spin (J) coupling in copper(I) phosphine complexes are reported for solid Cu(PPh(3))(2)X (X = NO(3)(-), BH(4)(-)). Values of (2)J((31)P,(31)P), 157 +/- 5 and 140 +/- 5 Hz for Cu(PPh(3))(2)NO(3) and Cu(PPh(3))(2)BH(4), respectively, have been obtained from two-dimensional (2D) J-resolved (31)P NMR spectra obtained under slow magic-angle spinning (MAS) conditions. In both complexes, the two phosphine ligands are crystallographically equivalent; thus, the two (31)P nuclei have identical isotropic chemical shifts. Under rapid sample spinning conditions, the (31)P MAS NMR spectra exhibit relatively sharp overlapping asymmetric quartets arising from (1)J((63/65)Cu,(31)P) and residual (63/65)Cu-(31)P dipolar interactions. No evidence of (2)J((31)P,(31)P) is apparent from the spectra obtained with rapid MAS; however, under slow MAS conditions there is evidence of homonuclear J-recoupling. Peak broadening due to heteronuclear dipolar interactions precludes measurement of (2)J((31)P,(31)P) from standard 1D (31)P MAS NMR spectra. It is shown that this source of broadening can be effectively eliminated by employing the 2D J-resolved experiment. For the two copper(I) phosphine complexes investigated in this study, the peak widths in the f(1) dimension of the 2D J-resolved (31)P MAS NMR spectra are about three times narrower than those found in the corresponding 1D (31)P MAS NMR spectra.     

DFT Calculations of 31P NMR Chemical Shifts in Palladium Complexes

In this study, comparative analysis of calculated (GIAO method, DFT level) and experimental ³¹P NMR shifts for a wide range of model palladium complexes showed that, on the whole, the theory reproduces the experimental data well. The exceptions are the complexes with the P=O phosphorus, for which there is a systematic underestimation of shielding, the value of which depends on the flexibility of the basis sets, especially at the geometry optimization stage. The use of triple-ζ quality basis sets and additional polarization functions at this stage reduces the underestimation of shielding for such phosphorus atoms. To summarize, in practice, for the rapid assessment of ³¹P NMR shifts, with the exception of the P=O type, a simple PBE0/{6-311G(2d,2p); Pd(SDD)}//PBE0/{6-31+G(d); Pd(SDD)} approximation is quite acceptable (RMSE = 8.9 ppm). Optimal, from the point of view of “price–quality” ratio, is the PBE0/{6-311G(2d,2p); Pd(SDD)}//PBE0/{6-311+G(2d); Pd(SDD)} (RMSE = 8.0 ppm) and the PBE0/{def2-TZVP; Pd(SDD)}//PBE0/{6-311+G(2d); Pd(SDD)} (RMSE = 6.9 ppm) approaches. In all cases, a linear scaling procedure is necessary to minimize systematic errors.     

Determination of absolute configuration by 31P NMR

The determination of absolute configuration is crucial for all chiral molecules; therefore many techniques have been developed to serve this purpose. It is especially important for the invention of new medicines, as in some cases only one enantiomer has a positive medical effect, while the other is inactive or even harmful. Herein we present the usefulness of the ³¹P NMR technique in the determination of the absolute configuration of chiral molecules, as an alternative to other methods. The models presented herein, often developed on the basis of ¹H NMR, describe conformations and configurations and following shielding effects in chiral molecules, that can be applied to determine the stereochemistry of a molecule by ³¹P NMR spectroscopy. Numerous examples of the use of some of the described models are presented as well.     

聚酯酰亚胺三元共聚物的核磁共振波谱法表征

用一维1H NMR、13C NMR方法研究了以N,N′-己二撑-1,6-双苯偏三酸酰亚胺二酸(IA6)、6-羟基-2-萘甲酸(HNA)和4,4′-二羟基二苯酮(DHBP)为单体的一种液晶聚酯酰亚胺三元共聚物的结构,并通过DEPT(无畸变极化转移增益法)、1H-1H COSY(氢-氢化学位移相关谱)、HMQC(异核多量子相关谱)、HMBC(异核多键相关谱)进一步确定了该类共聚物的1H谱和13C谱中各谱峰的归属,为研究热致性液晶聚酯酰亚胺共聚物的链结构和链序列提供了有价值的结构分析数据。     

Purity Determination of Phosphorus Compounds by Internat- Standard31 P Nmr Spectroscopy. an Experimental Study and Validation

Abstract

Due to the proportionality between the area of the NMR signal and the number of nuclei, internal standard³¹P NMR spectroscopy is in principle a rapid and simple method for determination of the purity of phosphorus compounds.nuclei, internal standard³¹P NMR spectroscopy is in principle a rapid and simple method for determination of the purity of phosphorus compounds.nuclei, internal standard³¹P NMR spectroscopy is in principle a rapid and simple method for determination of the purity of phosphorus compounds.nuclei, internal standard³¹P NMR spectroscopy is in principle a rapid and simple method for determination of the purity of phosphorus compounds.     

Study of ion exchange selectivity of organic ions by using (31)P NMR spectroscopy

Ion exchange distribution of the phenylphosphoric acid has been studied on various types of chloride form strong base resins as a function of pH at 25 °C, at 0.1 M ionic strength. Equilibrium measurements were supplemented by the study of pH dependence of the ³¹P NMR spectra of the resin-phase phenylphosphate species. Equations were derived to describe the pH dependence of the overall distribution coefficient and the chemical shift of the resin-phase solute species. Experimental data were evaluated by using these model equations and the values of the individual distribution coefficients, ion exchange selectivity coefficients and the resin-phase ³¹P chemical shifts of the mono- and divalent ions have been calculated. Comparison of distribution data of the individual species corroborated the significance of the role of hydrophobic interaction in the selectivity of organic ion exchange processes. A well-defined correlation between the ion exchange selectivity and the resin-phase ³¹P NMR chemical shift data has been pointed out.     

The Composition of Keto Aldoses in Aqueous Solution as Determined by NMR Spectroscopy

Keto aldoses usually form complex mixtures of equilibrating isomers in solution. This is due to the two different positions that may be used for ring closure in dicarbonyl sugars. The composition of various 2‐keto aldoses 1 – 5 and 8 , the 3‐keto aldose 2‐deoxy‐D ‐erythro‐hexos‐3‐ulose ( 9 ), and the ketose 1‐deoxy‐D ‐ribulose ( 10 ) in aqueous solution has been determined by NMR spectroscopy. The investigated keto aldoses form equilibria containing three to fifteen isomers. Among various furanose and pyranose ring structures stemming from 1,4‐, 1,5‐, 2,5‐, and 2,6‐cyclization, bicyclic forms were also found in several cases. The 2‐keto aldoses mainly exist as hydrated isomers in H₂O. Therefore, these forms and their proportions were compared to forms found in two homomorphous aldoses and one homomorphous ketose as model compounds. Besides the NMR data, also the composition of the 2‐keto aldoses agreed with the average of forms found in the model compounds, a finding that might eventually be useful for deducing the composition of other keto aldoses.     

Complex Chemical Synthesis of Unstable Sulfinyl- and Sulfonyl Derivatives of Phosphorus(III)

Abstract

The phosphorus(III) homologues of sulfonamides, R′₂P-S(O)₂R, are hitherto unknown. This is also in the case of phosphorus(V) derivatives: sulfinylphosphinates undergo symmetrization reactions to the homogeneous anhydrides. Sulfinylphosphinites, the O-isomers of sulfonylphosphanes, can only be built up as unstable ligands in the coordination sphere of transition metals, where the Br(CO)₄Mn-fragment seems to be more stable than the (CO)₅M-fragment (M=Cr, Mo, W). Thus, we now synthesized the iodo complexes I(CO)₄Mn[P(C₆H₅)₂X] (X=H, SiMe₃) as suitable starting material for the synthesis of SO-, SO₂-, RSO- and RSO₂-derivatives of coordinated phosphorus(III). Because of the surprising cis-position of the iodo and silyl group (x-ray structure analysis) the silyl-phosphane complex 2 is also of high interest to 1,2-elimination reactions to give metal-phosphorus double bonds.     

Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates

¹¹B and ³¹P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO₅ and BPO₄ represent nearly pure samples, SrBPO₅ contains β-Sr₂P₂O₇ as well as BPO₄ as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO₄ and PO₄ building units. Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996