高温核磁共振探头

本文设计研制了一种用于动态核磁共振研究的高温探头,它适用于磁铁极间距离为30mm的核磁共振波谱仪,探头中样品处的温度从室温至1300K连续可变,探头既可用于质子(¹H)也可用于其它核(如¹¹B,³¹P,²³Na等),并给出了高温探头的结构、指标及实际应用于测量的例子。     

HR/MAS高分辨魔角微量探头用于天然橡胶固体1H、13C NMR测试及其与液体BBO探头、固体CP/MAS探头测试的比较

采用BRUKER高分辨魔角微量探头（HR/MAS），液相宽带BBO探头和固体CP/MAS探头，对天然橡胶固体、乳液以及天然橡胶溶于氘代苯的溶液进行了¹H、¹³C 1D和2D NMR谱的测试和比较. 发现HR/MAS探头用于天然橡胶固体和乳液时可以得到高分辨的¹H、¹³C谱，克服了CP/MAS探头测试固体¹³C NMR谱或者是固体¹H NMR谱时，谱图存在S/N值可能较小、谱峰可能宽化的弱点.     

Estimation and measurement of flat or solenoidal coil inductance for radiofrequency NMR coil design

The inductance of a radiofrequency coil determines its compatibility with a given NMR probe circuit. However, calculation (or estimation) of inductance for radiofrequency coils of dimensions suitable for use in an NMR probe is not trivial, particularly for flat-coils. A comparison of a number of formulae for calculation of inductance is presented through the use of a straightforward inductance measurement circuit. This technique relies upon instrumentation available in many NMR laboratories rather than upon more expensive and specialized instrumentation often utilized in the literature. Inductance estimation methods are suggested and validated for both flat-coils and solenoids. These have proven very useful for fabrication of a number of new coils in our laboratory for use in static solid-state NMR probes operating at (1)H frequencies of 300 and 600MHz. Solenoidal coils with very similar measured and estimated inductances having inner diameters from 1 to 5mm are directly compared as an example of the practical application of inductance estimation for interchange of coils within an existing solid-state NMR probe.     

Low-cost high-temperature NMR probe head

The design of a simple high-temperature nuclear magnetic resonance (NMR) probe head for narrow-bore magnets is presented. It covers the temperature range from 20 to 1300°C, necessitating a heating power of below 100 W. Several probe heads of this design, manufactured for NMR solenoids with bores from 30 to 54 mm have shown good stability and long life times.     

NMR probe for the simultaneous acquisition of multiple samples.

A dual channel probe for the simultaneous acquisition of NMR data from multiple samples has been developed. This multiplex probe consists of two noninteracting sample coils that are each capable of detecting NMR signals at the same resonant frequency with good sensitivity and resolution. 13C free induction decays for the two samples, methanol (13C, 99%) and carbon tetrachloride (13C, 99%), were acquired simultaneously at 75.44 MHz using a single transmitter pulse and separate NMR receivers. S/N measurements are comparable to those observed using single coils. No evidence of cross talk is evident in the spectra even after considerable signal averaging. The probe demonstrates the feasibility of significant parallelism in NMR, which will be of interest in situations where high throughput analysis is desired.     

Small crystals and small coils in variable-temperature single-crystal NMR

Time savings by a factor of between 20 and 30 in the acquisition of multinuclear single-crystal (SC) NMR spectra have been obtained for submillimeter-size (0.01 to 0.03 mm(3)) single crystals when compared to recent results for (31)P and (87)Rb SC NMR. This gain in sensitivity is achieved by optimizing the filling factor using the smallest possible rf coil (2.0 mm inner diameter) for the specific SC probe design. Furthermore, this small coil is particularly useful for variable-temperature SC NMR studies. A probe design for such studies is presented and demonstrated experimentally.     

High-pressure,high-resolution NMR probe working at 400 MHZ

Abstract

A probe for obtaining high-resolution multinuclear NMR spectra at elevated pressures with a Bruker AM-400 spectrometer is described. The probe is designed for pressures up to 200 MPa and has been used between -40 to 150°C. We obtain routinely a resolution of about 1 Hz for proton (400 MHz) spectra using deuterium as an internal field lock. This probe is easily interchangeable with a commercial probe. We also describe a simple sample tube made of a 5 mm commercial NMR tube and a machinable glass cap with a total volume of about 1 cm³.     

Parallel-plate RF resonator imaging of chemical shift resolved capillary flow

Magnetic resonance imaging has been introduced to study flow in microchannels using pure phase spatial encoding with a microfabricated parallel-plate nuclear magnetic resonance (NMR) probe. The NMR probe and pure phase spatial encoding enhance the sensitivity and resolution of the measurement. In this paper, ¹H NMR spectra and images were acquired at 100 MHz. The B₁ magnetic field is homogeneous and the signal-to-noise ratio of 30 μl doped water for a single scan is 8×10⁴. The high sensitivity of the probe enables velocity mapping of the fluids in the micro-channel with a spatial resolution of 13×13 μm. The parallel-plate probe with pure phase encoding permits the acquisition of NMR spectra; therefore, chemical shift resolved velocity mapping was also undertaken. Results are presented which show separate velocity maps for water and methanol flowing through a straight circular micro-channel. Finally, future performance of these techniques for the study of microfluidics is extrapolated and discussed.     

On-line coupling of high temperature GPC and 1H NMR for the analysis of polymers

The on-line coupling of gel permeation chromatography (GPC) and 1H NMR operating at temperatures up to 130 degrees C is presented. A NMR flow probe with a cell volume of 120 microL and a stop-flow valve are developed for on-flow and stop-flow NMR measurements at high temperatures. To maintain high and constant temperatures through the whole probe, the flow probe contains two separate heating circuits. A modified stop-flow valve is developed as a control device for enabling on-flow and stop-flow experiments at high temperature conditions. Heated transfer lines connect the flow probe with the high temperature GPC system. Due to their semicrystalline nature, polyolefins can be studied by liquid chromatography only at temperatures above 100 degrees C. The novel high temperature GPC-NMR system is used for the separation of complex polyolefins regarding their molar mass and for the analysis of different chemical structures. Blends of polyethylene, poly(methyl methacrylate), and ethylene-methyl methacrylate copolymers are separated according to the molar masses of the components. The compositions of the components are directly studied by on-line NMR. Moreover, the chemical composition distribution of an ethylene-methyl methacrylate copolymer sample is analysed. Differences between results of on-flow and stop-flow measurements are discussed.     

A 4-mm probe for (13)C CP/MAS NMR of solids at 21.15 T

The design of a broadband 4-mm magic-angle spinning (MAS) X-(1)H/(19)F double resonance probe for cross-polarization (CP)/MAS NMR studies at 21.15 T ((1)H at 900 MHz) is described. The high-frequency (1)H/(19)F channel employs a new and efficient transmission line tuning design. The first (13)C CP/MAS NMR spectra recorded at 21.15 T have been obtained with this probe and exhibit the best S/N per milligram sample of hexamethylbenzene achieved so far for a 4-mm rotor.     

低温NMR探头的应用

在过去10年中研发新核磁共振探头一直是制造者争夺的活跃领域. 最近，因其灵敏度的巨大提高，低温冷却探头得到人们格外的关注. 利用这一技术可大量节省谱仪机时. 对于低γ核可直接测定天然丰度样品而不必标记，这远比节省机时更为重要. 本文评述了针对5～10 Hz优化2 mg天然丰度噁唑烷酮抗菌素eperezolid的 CIGAR-HMBC-¹H-¹⁵N谱的比较，一个是采自美国瓦里安公司的5 mm低温探头，另一个是采自瓦里安公司传统室温3 mm 梯度三共振探头. 利用低温探头大约10 min就可记录到大部份¹H-¹⁵N远 程相关，26 min可观察到几乎所有的远程共振. 而在同样条件下使用3 mm传统梯度反式三共振探头无法得到有用的谱图，要想取得相同的结果须累加约18 h.     

微量OVARC肽的1H NMR谱线归属

Serpin家族中的卵清蛋白,其反应中心肽段(OVARC,23肽)对应于卵清蛋白序列中343 位至366位残基. 建立在魔角旋转基础之上的Nano探头是一种全新的超微量探头. 本文运用魔角旋转微量检测新技术进行了有关2D NMR实验,完成了卵清蛋白反应中心肽段的¹H NMR 谱线归属.     

1H NMR characterization of the product from single solid-phase resin beads using capillary NMR flow probes.

A capillary NMR flow probe was designed to generate high-resolution (1)H NMR spectra at 600 MHz from the cleaved product of individual 160-microm Tentagel combinatorial chemistry beads. By injecting a dissolved sample sandwiched between an immiscible, perfluorinated organic liquid directly into the probe, NMR spectra of the product cleaved from single beads were acquired in just 1 h of spectrometer time without diffusional dilution. Sample handling efficiency on the single bead scale was comparable to that obtained with a bulk sample. Using the relative intensity of the DMSO-d(5)H versus the analyte signals in a fully relaxed CPMG spectrum, the amount of product cleaved from a single bead was determined to be 540+/-170 pmol in one of the samples. Following the NMR data collection, the samples were examined with electrospray ionization mass spectrometry to provide additional structural information. By coupling with microliter-volume fluidic capabilities, the capillary flow probe described here will enable multidimensional characterization of single solid-phase resin products in an online manner.     

Radiation damping in microcoil NMR probes

Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-microL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.     

Application of a portable nuclear magnetic resonance surface probe to porous media

A portable nuclear magnetic resonance (NMR) surface probe was used to determine the time-dependent self-diffusion coefficient D(t) of water molecules in two fluid-filled porous media. The measuring equipment and the inhomogeneous magnetic fields in the sensitive volume of the probe are described. It is discussed how to evaluate D(t) using a surface probe from the primary and stimulated echoes generated in three-pulse experiments. Furthermore, the evaluation of D(t) allows one to determine the geometrical structure of porous materials.     

Using NMR to study full intact wine bottles

A nuclear magnetic resonance (NMR) probe and spectrometer capable of investigating full intact wine bottles is described and used to study a series of Cabernet Sauvignons with high resolution 1H NMR spectroscopy. Selected examples of full bottle 13C NMR spectra are also provided. The application of this full bottle NMR method to the measurement of acetic acid content, the detection of complex sugars, phenols, and trace elements in wine is discussed.     

Auxiliary probe design adaptable to existing probes for remote detection NMR, MRI, and time-of-flight tracing

A versatile, detection-only probe design is presented that can be adapted to any existing NMR or MRI probe with the purpose of making the remote detection concept generally applicable. Remote detection suggests freeing the NMR experiment from the confinement of using the same radio frequency (RF) coil and magnetic field for both information encoding and signal detection. Information is stored during the encoding step onto a fluid sensor medium whose magnetization is later measured in a different location. The choice of an RF probe and magnetic field for encoding can be made based solely on the size and characteristics of the sample and the desired information quality without considering detection sensitivity, as this aspect is dealt with by a separate detector. While early experiments required building probes that included two resonant circuits, one for encoding and one for detection, a modular approach with a detection-only probe as presented here can be used along with any existing NMR probe of choice for encoding. The design of two different detection-only probes is presented, one with a saddle coil for milliliter-sized detection volumes, and the other one with a microsolenoid coil for sub-microliter fluid quantities. As example applications, we present time-of-flight (TOF) tracing of hyperpolarized (129)Xe spins in a gas mixture through coiled tubing using the microsolenoid coil detector and TOF flow imaging through a nested glass container where the gas flow changes its direction twice between inlet and outlet using the saddle coil detector.     

C NMR of polyolefins with a new high temperature 10 mm cryoprobe

Recently, a high temperature 10 mm cryoprobe was developed. This probe provides a significant sensitivity enhancement for ¹³C NMR of polyolefins at a sample temperature of 120–135 °C, as compared to conventional probes. This greatly increases the speed of NMR studies of comonomer content, sequence distribution, stereo- and regioerrors, saturated chain end, unsaturation, and diffusion of polymers. In this contribution, we first compare the ¹³C NMR sensitivity of this probe with conventional probes. Then, we demonstrate one of the advantages of this probe in its ability to perform 2D Incredible Natural Abundance Double Quantum Transfer Experiment (2D INADEQUATE) in a relatively short period of time. The 2D INADEQUATE has been rarely used for polymer studies because of its inherently very low sensitivity. It becomes even more challenging for studying infrequent polyolefin microstructures, as low probability microstructures represent a small fraction of carbons in the sample. Here, the 2D INADEQUATE experiment was used to assign the ¹³C NMR peaks of 2,1-insertion regioerrors in a poly(propylene-co-1-octene) copolymer.     

Effective Detection of Phenylalanine Using Pyridine Based Sensor

Journal of Fluorescence - Pyridine based organic molecule as probe has been synthesized for the detection of phenylalanine (PA) biomarker. The synthesized probe is characterized by 1H and 13C NMR...