Unleashing the Potential of 17O NMR Spectroscopy Using Mechanochemistry

¹⁷O NMR spectroscopy has been the subject of vivid interest in recent years, because there is increasing evidence that it can provide unique insight into the structure and reactivity of many molecules and materials. However, due to the very poor natural abundance of oxygen-17, ¹⁷O labeling is generally a prerequisite. This is a real obstacle for most research groups, because of the high costs and/or strong experimental constraints of the most frequently used ¹⁷O-labeling schemes. Here, we show for the first time that mechanosynthesis offers unique opportunities for enriching in ¹⁷O a variety of organic and inorganic precursors of synthetic interest. The protocols are fast, user-friendly, and low-cost, which makes them highly attractive for a broad research community, and their suitability for ¹⁷O solid-state NMR applications is demonstrated.     

NMR Spectroscopy and Atomic Force Microscopy Characterization of Hybrid Organic – Inorganic Coatings

Hybrid organic–inorganic (O-I) epoxide-based products made from functionalized organosilicon precursors, oligomeric di- and triamines and in some cases colloidal silica particles were characterized by NMR spectroscopy and atomic force microscopy (AFM). The kinetics and reaction mechanism of condensation reactions, structure and segmental dynamics of final films, as well as homogeneity and partial ordering were studied by solid-state NMR spectroscopy (2D CRAMPS, 2D ¹H-¹³C WISE, relaxation experiments); the surface morphology and other surface characteristics were determined by AFM.     

Characterization of Poly(ethyleneoxyethylene terephthalate‐co‐adipate) using NMR Spectroscopy

Comonomer sequence distribution and ¹H‐NMR chemical shifts were determined for poly(ethyleneoxyethylene terephthalate‐co‐adipate) (PEOETA) copolyester. The sequence distribution of terephthalate (T) and adipate (A) residues was found to be random, which is typical for copolyesters synthesized via bulk polycondensation. The inner methylene protons of EOE residues appeared as a pair of doublets due to chemical shift differences among the EOE‐centered dyad sequences TT, TA, AT, and AA. The four equivalent phenylene protons of T residues appeared as a triplet due to chemical shift differences among the T‐centered triad sequences TTT, TTA (?ATA), and ATA. Higher‐order tetrad and pentad sensitivity were also observed for the inner methylene and phenylene protons, respectively, especially for TT‐ and TTT‐centered sequences. The sequence sensitivity of the phenylene protons was attributed to unique spatial interactions between themselves and protons within adjacent adipate and EOE units. These spatial interactions were confirmed using Nuclear Overhauser Enhancement Spectroscopy (NOESY).     

Investigation of RNA-Ligand Interactions by (19) F NMR Spectroscopy Using Fluorinated Probes

Spy swap: The interaction between an unlabeled RNA and unlabeled ligands (red hexagon) can be monitored by (19) F?NMR spectroscopy using small fluorinated diamines (green star) as spy reporters. This technique also enables the visualization of the conformational capture of a riboswitch by its ligand.     

Real-Time Analysis of Folding upon Binding of a Disordered Protein by Using Dissolution DNP NMR Spectroscopy

The kinase inhibitory domain of the cell cycle regulatory protein p27^Kip1 (p27) was nuclear spin hyperpolarized using dissolution dynamic nuclear polarization (D-DNP). While intrinsically disordered in isolation, p27 adopts secondary structural motifs, including an α-helical structure, upon binding to cyclin-dependent kinase 2 (Cdk2)/cyclin A. The sensitivity gains obtained with hyperpolarization enable the real-time observation of ¹³C NMR signals during p27 folding upon binding to Cdk2/cyclin A on a time scale of several seconds. Time-dependent intensity changes are dependent on the extent of folding and binding, as manifested in differential spin relaxation. The analysis of signal decay rates suggests the existence of a partially folded p27 intermediate during the timescale of the D-DNP NMR experiment.     

Mapping the Binding Site of P53 on UBC9 by NMR Spectroscopy

Human UBCP9 is a member of the E2 family of proteins.However,instead of conjugating to ubiquitin,it conjugates to a ubiquitin bomologue SUMO-1(also known as UBL1,GMP1,SMTP3,PICT-1 and sentrin).The SUMO-1 conjugation pathway is very similar to that of ubiquin with regard to the primary sequences of the ubiquitin activating enzymes(E1),the three-dimensional structures of the ubiquitin conjugating enzymes(E2),and the chemistry of the overall conjugation pathway.The interactiov of p53 and UBC9,the E2 of the SUMO-1 pathway,has heen studied by nuclear magnetic resonance spectroscopy.A peptide corresponding to the nuclear localization domain of p53 specifically interacts with UBC9 and this interaction is likely to be important for conjugation of p53 with SUMO-1.The largest chemical shift changes on UBC9 occur at residues94 and 129-135.This region is adjacent to the active site and has slgniflcant dynamic behavior on the μs-ms and ps-ns timescales.Correlation of chemical shift changes and mobility of these residues further suggest the importance of these residues in substrate recognition.     

Preparation and Characterization of Heparin‐Stabilized Gold Nanoparticles

A simple method for preparing gold nanoparticles in aqueous solution has been developed by using glycosaminoglycan‐heparin as reducing and stabilizing agent and HAuCl₄ as precursor. The obtained gold nanoparticles were characterized by UV‐vis spectroscopy, resonance light scattering spectroscopy (RLS), transmission electron microscopy (TEM) and electrophoresis technology. The influence of reactant concentration for the preparation of gold nanoparticles was investigated. The results indicated that the gold nanoparticles carried negative charges in the aqueous solution and the size and shape of the gold nanoparticles could be controlled by changing the concentration of the heparin. Moreover, the gold nanoparticles obtained with relatively high concentration of heparin were very stable and had relative narrow size distribution.     

A (31) P NMR Investigation of the CoPi Water-Oxidation Catalyst

Beneath the sheets: (31) P?NMR data suggests that phosphates are liberated freely in the interlayer of a cobalt-hydroxide water-oxidation catalyst. The cobalt-hydroxide sheets are separated by an interlayer region with water, counterions and phosphate, which help to shuttle protons as the layer develops charge.     

15N, 31P,and 13C NMR Spectroscopy of N-Arylsulfonyl-and N-Arylcarbonyl-P,P,P-triphenylphospha-λ-Azenes. Substituent Effects and Electronic Structure

Abstract

The ¹⁵N, ³¹P and ³¹C NMR spectra of several series of phospha-λ⁵-azenes are reported. For the N-arylsulfonyl-P,P,P-triphenylphospha-δ⁵-azene series (R-C₆H₄N-SO₂-PPh₃), the ³¹P chemical shifts, various ¹³C chemical shifts and ¹J_PN were observed to correlate linearly with the Hammett σ constants. Interestingly, the ¹⁵N chemical shifts did not correlate acceptably with any σ or with the Taft dual substituent parameter equation, and 1J_PC was invariant with substituent. For the N-arylcarbonyl-P,P,P-triphenylphospha-λ⁵-azene series (R-C₆H₄-CO-N=PPh₃), δ_31P and various δ_13C's were observed to linearly correlate with the δ constants, while δ_15N, ¹J_PN and ¹J_PC correlated with both the σ and σ constants. For the N-phenyl-P,P,P-triarylphospha-λ⁵-azene series [Ph-N=P(C₆H₄-R)₃] the best correlations were observed between ³¹P, ¹⁵N and several ¹³C chemical shifts and the σ constants.     

用31P NMR研究硫代磷酸酯水解反应历程

磷酸酯的水解反应是一类较为重要的反应,了解这类反应历程及机理对研究农药的毒性、环境保护、及指导农药的生产与合成具有十分重要的意义。~(31)PNMR灵敏度高,化学位移范围宽,偶合常数大.~(31)P NMR的化学位移对于分子中磷原子的价态、与磷原子直接相连的原子或基团的类型、数量、性质及构型的变化十分敏感.是研究有关含磷化合物结构问题的有效手段之一,因此本文采用~(31)P NMR方法研究了疏代磷酸酯的水解反应历程。本文所研究的化合物是一种新合成的含七元环的二硫代磷酸酯。其结构式如下:     

The Characterization of Comblike Polymer Electrolyte by Means of NMR

Polymer solid electrolytes are a class of solid materials whose properties lie betweenthose of solids and liquids, and they have been widely used in energy resources,. metallurgy, environmental protection, electro-chemistry device and so on' '2.Inoue had pointed out that polystyrene derivative with many poly (ethylene oxide)PEO side chain could make conductivity reach 10-' S/cm. They think that the flexibilityo f the backbone is not necessarily the impoFtant factor to achieve a high conducti…     

“True” Concentration Determination Using a Concentration and Composition Sensitive Infrared Detector for Molecular Weight Characterization of Polyolefins

Summary: The infrared detector with a composition channel provides the ability to construct “true” concentration of the polyethylene-polypropylene copolymer and polymer blends to compensate the different infrared responses to each component. Using this “true” concentration constructed by the infrared detector, triple detector gel permeation chromatography (GPC) could generate conventional (by column calibration) and absolute (by laser light scattering) molecular weight and molecular weight distribution data comparable to data obtained by using the concentration obtained by a differential reflex index concentration detector. In addition to its unique feature of in-situ composition detection, the infrared detector in its mass detection mode possesses the advantages of faster equilibrium time, more stable baseline, less effect from temperature variation, and low sensitivity to moisture or air in the solvent.     

Labeling and Probing the Silica Surface Using Mechanochemistry and 17O NMR Spectroscopy**

In recent years, there has been increasing interest in developing cost-efficient, fast, and user-friendly ¹⁷O enrichment protocols to help to understand the structure and reactivity of materials by using ¹⁷O NMR spectroscopy. Here, we show for the first time how ball milling (BM) can be used to selectively and efficiently enrich the surface of fumed silica, which is widely used at industrial scale. Short milling times (up to 15 min) allowed modulation of the enrichment level (up to ca. 5 %) without significantly changing the nature of the material. High-precision ¹⁷O compositions were measured at different milling times by using large-geometry secondary-ion mass spectrometry (LG-SIMS). High-resolution ¹⁷O NMR analyses (including at 35.2 T) allowed clear identification of the signals from siloxane (Si−O−Si) and silanols (Si−OH), while DNP analyses, performed by using direct ¹⁷O polarization and indirect ¹⁷O{¹H} CP excitation, agreed with selective labeling of the surface. Information on the distribution of Si−OH environments at the surface was obtained from 2D ¹H−¹⁷O D-HMQC correlations. Finally, the surface-labeled silica was reacted with titania and using ¹⁷O DNP, their common interface was probed and Si−O−Ti bonds identified.     

^31P NMR Studies on the Ligand Dissociation of Trinuclear Molybde-num Cluster Compounds

A series of carboxylate-substituted trinudear molybdenum dus-ter compounds formulated as Mo3S4(DTP)3(RCO2)(L), where RffiH, CH3, C2H5, CH2Cl, CCl3, R^1C6H4(R^1 is the group on the benzene ring of aromatic carboxylate ), L=pyridine,CH3CN, DMF, have been synthesized by the ligand substitu-tion reaction. The dissociation of the loosely-coordinated ligand L from the cluster core was studied by ^31p NMR. The dissocia-tion process of L is related to the solvent, temperature, and acidity of carboxylate groups, so as to affect the solution struc-ture and reactive properties of the duster. The long-distance in-teraction between ligands RCO2 and L is transported by Mo3S4 core.     

31P NMR and π bond in solid phosphorus compounds

The anisotropy of the ³¹P chemical shift in solid phosphorus compounds with C_3v symmetry and the PO bond length along the threefold axis are compared. The observed correlation is discussed.     

Enzymatic Resolution of α-Amino Phosphonous Acids -A Kinetic Comparison with Other α-Amino Acids Using 19F and 31P NMR Analysis

Abstract

We have previously reported (1,) the synthesis of a range of α-aminophosphonous acids and found them to be mimics of the naturally occurring amino acids. They inhibit the protein synthesis of E.Coli B (2) and other synthetases (3). We have now found that such compounds can be conveniently resolved via their N-acyl derivatives by enzymatic methods. Using penicillin-G-amidase from E.Coli (EC 3.5.1.11) the R-enantiomer is cleanly hydrolysed leaving the S-enantiomer intact.     

Structure of a Protein–RNA Complex by Solid-State NMR Spectroscopy

Solid-state NMR (ssNMR) is applicable to high molecular-weight (MW) protein assemblies in a non-amorphous precipitate. The technique yields atomic resolution structural information on both soluble and insoluble particles without limitations of MW or requirement of crystals. Herein, we propose and demonstrate an approach that yields the structure of protein–RNA complexes (RNP) solely from ssNMR data. Instead of using low-sensitivity magnetization transfer steps between heteronuclei of the protein and the RNA, we measure paramagnetic relaxation enhancement effects elicited on the RNA by a paramagnetic tag coupled to the protein. We demonstrate that this data, together with chemical-shift-perturbation data, yields an accurate structure of an RNP complex, starting from the bound structures of its components. The possibility of characterizing protein–RNA interactions by ssNMR may enable applications to large RNP complexes, whose structures are not accessible by other methods.     

Investigation of Bis(α-Phenylethylamido)Methylphosphonates by NMR Spectroscopy

Abstract

The influence of the relative location of chiral carbon and phosphorus atoms and the position of the aryl-group on diastereomeric anisochronity in non-racemic mixtures of enantiomers has been examined. The optical isomers of methanephosphonic acid bis(α-phenylethylamide) (I), which contain pro-chiral phosphorus atom, were synthesized by the reaction of methanephosphonic acid dichloride(II) with (+)- or (-) -α-phenylethylamine (III). The extent of chemical shift nonequivalence in ³¹P and ¹H NMR spectra of non-racemic mixtures of RR- and SS-I was negligible. It can be explained by the absence of aryl-amino group, favouring intermolecular association, effect of SCADA¹, and the long distance between the chiral center and pro-chiral phosphorus. Phosphonylation of non-racemic mixtures of (+)- and (-)-III by II proceeds stereospecifically giving mixture of RR-, SS-I, and two meso-compounds analyzed by ³¹P ¹H NMR.     

π-Conjugated Copper Phthalocyanine Nanoparticles as Highly Sensitive Sensor for Colorimetric Detection of Biomarkers

Though numerous nanomaterials with enzyme-like activities have been utilized as probes and sensors for detecting biological molecules, it is still challenging to construct highly sensitive detectors for biomarkers using polymeric materials. Benefiting from the π-d delocalization effect of electrons, excellent metal-chelating property, high electron transferability, and good chemical stability of π-conjugated phthalocyanine, the design of the copper phthalocyanine-based conjugated polymer nanoparticles (Cu-PcCP NPs) as a colorimetric sensor for a variety of biomarkers is reported. The Cu-PcCP NPs are synthesized through a simple microwave-assisted polymerization, and their chemical structures are thoroughly characterized. The colorimetric results of Cu-PcCP NPs demonstrate excellent peroxidase-like detecting activity and also great substrate selectivity than most of the reported Cu-based nanomaterials. The Cu-PcCP NPs can achieve a detection limit of 4.88 μM for the H₂O₂, 4.27 μM for the L-cysteine, and 21.10 μM for the glucose via a cascade catalytic system, which shows comparable detecting sensitivity as that of many earlier reported enzyme-like nanomaterials. Moreover, Cu-PcCP NPs present remarkable resistance to harsh conditions, including high temperature, low pH, and excessive salts. These highly specific π-conjugated copper-phthalocyanine nanoparticles not only overcome the current limitation of polymeric material-based sensors but also provide a new direction for designing next-generation enzyme-like nanomaterial-based colorimetric biosensors.     

(α-Phosphoryl Carbanions. Searching of Course of Wittig-Horner Reaction by 31P Low Temperature NMR

Abstract

Continuing our studies on utilization of the Wittig-Horner reaction in organic synthesis, we have examined reactivity of α-lithium derivatives of several phosphonates towards carbonyl compounds, by ³¹P NMR at low temperature (from -100°C to r.t.). The chemical shifts δ [ppm] of a few representative phosphonates (1), carbanions (2) and betains (3) will be given.