Internal Chemical Shift Research Articles

Identification by HSQC and quantification by qHNMR innovate pharmaceutical amino acid analysis

This study introduces a new NMR-based methodology for identification (ID) and quantification (purity, strength) assays of widely used amino acids. A detailed analysis of four amino acids and their available salts was performed with both a high-field (600 MHz) and a benchtop (60 MHz) NMR instrument. To assess sensitivity constraints, samples for 1H NMR analysis were initially prepared using only 10 mg of analyte and 1 mg of maleic acid (MA) as an internal calibrant (IC) and secondary chemical shift reference. The characteristic dispersion of the peak patterns indicating the presence or absence of a counterion (mostly chloride) was conserved at both high and low-field strength instruments, showing that the underlying NMR spectroscopic parameters, i.e., chemical shifts and coupling constants, are independent of the magnetic field strength. However, as the verbal descriptions of 1H NMR spectra are challenging in the context of reference materials and pharmaceutical monographs, an alternative method for the identification (ID) of amino acids is proposed that uses 13C NMR patterns from multiplicity-edited HSQC (ed-HSQC), which are both compound-specific and straightforward to document. For ed-HSQC measurements, the sample amount was increased to 30 mg of the analyte and several acquisition parameters were tested, including t1 increments used in the pulse program, number of scans, and repetition time. Excellent congruence with deviations <0.1 ppm was achieved for the 13C chemical shifts from 1D 13C NMR spectra (150 MHz) vs. those extracted from ed-HSQC (15 MHz traces). Finally, all samples of amino acid candidate reference materials were quantified by 1H qNMR (abs-qHNMR) at both 600 and 60 MHz. At high field, both IC and relative quantitations were performed, however, with the low-field instrument, only the IC method was used. The results showed that the analyzed reference material candidates were generally highly pure compounds. To achieve adequately low levels of uncertainty for such high-purity materials, the sample amounts were increased to 100 mg of analytes and 10 mg of the IC and replicates were analyzed for selected amino acids.

Selenate—An internal chemical shift standard for aqueous 77Se NMR spectroscopy

The 77 Se NMR spectra of selenate were studied under various circumstances, such as concentration, pH, temperature, ionic strength, and D2 O:H2 O ratio, in order to examine its potential as a water-soluble internal chemical shift standard. The performance of selenate as a chemical shift reference and that of other attempted ones from the literature (dimethyl selenide, tetramethylsilane/TMS, and 3-(trimethylsilyl)propane-1-sulfonate/DSS) was also explored. The uncertainty in the resulting chemical shift relative to the effective spectral width is comparable to that of DSS. Compared to the currently prevalent water-soluble external chemical shift reference, selenic acid solution, the properties of internal selenate are much more favorable in terms of ease of use. We have also demonstrated that selenate can be used in reducing media, which is inevitable for the analysis of selenol compounds. Thus, it can be stated that sodium selenate is a robust internal chemical shift reference in aqueous media for 77 Se NMR measurements; the chemical shift of this reference in a solution containing 5V/V% D2 O at 25°C and 0.15 mol·dm-3 ionic strength is 1048.65 ppm relative to 60 V/V% dimethyl selenide in CDCl3 and 1046.40 ppm relative to the 1 H signal of 0.03 V/V% TMS in CDCl3 . In summary, a water-soluble, selenium-containing internal chemical shift reference compound was introduced for 77 Se NMR measurements for the first time in the literature, and with the aforementioned results all previous 77 Se measurements can be converted to a unified scale defined by the International Union of Pure and Applied Chemistry.

Preparation and Characterization of Photoactive Anatase TiO2 from Algae Bloomed Surface Water

The purpose of the study was to effectively treat algae bloomed water while using a Ti-based coagulant (TiCl4) and recover photoactive novel anatase TiO2 from the flocculated sludge. Conventional jar tests were conducted in order to evaluate the coagulation efficiency, and TiCl4 was found superior compared to commercially available poly aluminum chloride (PAC). At a dose of 0.3 g Ti/L, the removal rate of turbidity, chemical oxygen demand (COD), and total phosphorus (TP) were measured as 99.8%, 66.7%, and 96.9%, respectively. Besides, TiO2 nanoparticles (NPs) were recovered from the flocculated sludge and scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), and X-ray diffraction (XRD) analysis confirmed the presence of only anatase phase. The recovered TiO2 was found to be effective in removing gaseous CH3CHO and NOx under UV-A lamp at a light intensity of 10 W/m2. Additionally, the TiO2 mixed mortar blocks that were prepared in this study successfully removed atmospheric nitrogen oxide (NOx) under UV irradiance. This study is one of the first to prepare anatase TiO2 from flocculated algal sludge and it showed promising results. Further research on this novel TiO2 concerning internal chemical bonds and shift in the absorbance spectrum could explore several practical implications.

New Stretching Method for Aligning Gels: Its Application to the Measurement Residual Chemical Shift Anisotropies (RCSAs) without the Need for Isotropic Shift Correction.

An existing gel stretching device is modified, permitting the use of organic solvents for the study of small molecules. Different from the original device, gels are stretched into 4 mm open-ended NMR tubes and then inserted into regular 5 mm NMR tubes. No open-ended tubes are inserted in the NMR probe avoiding the risk of sample leaking. It is also shown that residual chemical shift anisotropies (RCSAs) measured with the device are free of isotropic shift interferences and corrections for them are not needed during the post-acquisition data analysis. Three internal references for chemical shift were evaluated (CCl4 , CBr4 and TMS), being CCl4 the most convenient one to measure RCSAs in CDCl3 . RCSAs measured with the modified stretching device using CCl4 as the internal chemical shift reference were enough to determine the relative configuration of three small molecules with an excellent degree of configuration discrimination.

SU‐F‐I‐65: Fatty Acid Quantification in High‐Fat‐Diet Induced Abnormal Intrahepatic Triglyceride Storage Using Internal Standard Method at 3.0 T

Purpose:The objective of this study was to determine the metabolic changes in a rat model of high‐fat‐diet‐induced non‐alcoholic fatty liver disease (NAFLD) by using single‐voxel 1H‐MRS with a 3.0 T MRI scanner.Methods:The examination were performed on a 3.0T scanner using a 4‐channel animal coil for higher resolution. This method used point‐resolved spectroscopy (PRESS) (repetition time (TR)/echo time (TE) = 6000/35 ms; number of signal averages (NSA) = 64). To measure the lipid content, we quantified total lipids ((‐CH2‐)n/noise), total saturated fatty acids (3(‐CH2‐)/2(‐CH3)), total unsaturated fatty acids (3(‐CH2‐C=C‐CH2‐)/4(‐CH3)), total unsaturated bonds index (3(‐CH=CH‐)/2(‐CH3)), and polyunsaturated bonds index (3(=C‐CH2‐C=)/2(‐CH3)) by separating each peak area of (CH2)n, CH2C=CCH, =CCH2C=, and CH=CH by CH3. The ‐CH3 (0.90 ppm) peak was used as an internal chemical shift reference.Results:Total lipids and total saturated fatty acids were substantially upregulated in high‐fat‐diet‐fed rats in comparison with baseline values (total lipids, 16.22±6.60×10−4; total saturated fatty acids, 10.26±1.91). The resulting data on lipid accumulation were statistically significant in terms of total lipids at 3 weeks (78.65±36.20, p = 0.002), 6 weeks (88.14±22.36, p &lt; 0.001), 9 weeks (78.55±31.29, P &lt; 0.001), and 15 weeks (107.87±39.95, p &lt; 0.001) after initiation of the high‐fat diet.Conclusion:Our results of noninvasive in vivo MRS are based on accurate monitoring of the changes in lipid content, which were verified using the data on saturated fatty acids and unsaturated fatty acids. We can conclude that localized MRS holds promise as an indicator of fatty liver diseases in humans and in animal models for monitoring treatment.

Conformational analysis from statistical treatment of 13C NMR chemical shifts

Statistical treatment of experimental 13C NMR chemical shifts of different compounds and calculated isotropic shielding constants of their respective conformers has been carried out in two different ways. The first method was a ridge linear regression between experimental chemical shifts and calculated shielding constants where the calculated coefficients represent the mole fraction of each conformer. Consequently, the sum of all coefficients has to be restricted to 1. The second method was a linear regression between experimental and calculated internal chemical shifts using the same restriction. In general, both methods gave similar results although the second one had a larger standard deviation. The results showed that, in nearly all cases, there is a significant correlation between experimental and calculated data for, at least, one conformer, being this the major one present in the conformational equilibrium. For planar aromatic compounds the conformational equilibrium has been fully characterized when other conformers have been found statistically significant. The statistical analysis on cyclic aliphatic molecules always yielded a conformational composition comparable with the published values. The advantages and drawbacks of the methodology are discussed.

A facile synthesis of Methyl-2-(N-ethyl-N-phenylamino)naphthyridine-3-carboxylates

Abstract Objective To develop an efficient method for the synthesis of Methyl-2-(N-ethyl-N-phenylamino)naphthyridine-3-carboxylates which is suitable for different naphthyridines. Methods All reagents used were commercial grade, 1 H NMR spectra were obtained on a varian 400 MHz instrument with TMS as internal standard and chemical shifts are expressed δ ppm solvent used in DMSO-d 6 & CDCl 3 and LC–MS spectrum on a Waters LC–MS spectrometer operating at 70 ev. TLC is performed with E-Merch precoated silica gel plates (60F-254) with iodine as a developing agent. Acme, India silica gel, 60–120 mesh for column chromatography is used. All compounds are purified by column chromatography by using Silica gel (60–120 mesh) eluted with (50:1) dichloromethane in methanol. Conclusions We have developed an efficient protocol for the synthesis of Methyl-2-(N-ethyl-N-phenylamino)naphthyridine-3-carboxylates.

Electrical and ionic conductivity effects on magic-angle spinning nuclear magnetic resonance parameters of CuI

We investigate experimentally and theoretically the effects of two different types of conductivity, electrical and ionic, upon magic-angle spinning NMR spectra. The experimental demonstration of these effects involves (63)Cu, (65)Cu, and (127)I variable temperature MAS-NMR experiments on samples of γ-CuI, a Cu(+)-ion conductor at elevated temperatures as well as a wide bandgap semiconductor. We extend previous observations that the chemical shifts depend very strongly upon the square of the spinning-speed as well as the particular sample studied and the magnetic field strength. By using the (207)Pb resonance of lead nitrate mixed with the γ-CuI as an internal chemical shift thermometer we show that frictional heating effects of the rotor do not account for the observations. Instead, we find that spinning bulk CuI, a p-type semiconductor due to Cu(+) vacancies in nonstoichiometric samples, in a magnetic field generates induced AC electric currents from the Lorentz force that can resistively heat the sample by over 200 °C. These induced currents oscillate along the rotor spinning axis at the spinning speed. Their associated heating effects are disrupted in samples containing inert filler material, indicating the existence of macroscopic current pathways between micron-sized crystallites. Accurate measurements of the temperature-dependence of the (63)Cu and (127)I chemical shifts in such diluted samples reveal that they are of similar magnitude (ca. 0.27 ppm/K) but opposite sign (being negative for (63)Cu), and appear to depend slightly upon the particular sample. This relationship is identical to the corresponding slopes of the chemical shifts versus square of the spinning speed, again consistent with sample heating as the source of the observed large shift changes. Higher drive-gas pressures are required to spin samples that have higher effective electrical conductivities, indicating the presence of a braking effect arising from the induced currents produced by rotating a conductor in a homogeneous magnetic field. We present a theoretical analysis and finite-element simulations that account for the magnitude and rapid time-scale of the resistive heating effects and the quadratic spinning speed dependence of the chemical shift observed experimentally. Known thermophysical properties are used as inputs to the model, the sole adjustable parameter being a scaling of the bulk thermal conductivity of CuI in order to account for the effective thermal conductivity of the rotating powdered sample. In addition to the dramatic consequences of electrical conductivity in the sample, ionic conductivity also influences the spectra. All three nuclei exhibit quadrupolar satellite transitions extending over several hundred kilohertz that reflect defects perturbing the cubic symmetry of the zincblende lattice. Broadening of these satellite transitions with increasing temperature arises from the onset of Cu(+) ion jumps to sites with different electric field gradients, a process that interferes with the formation of rotational echoes. This broadening has been quantitatively analyzed for the (63)Cu and (65)Cu nuclei using a simple model in the literature to yield an activation barrier of 0.64 eV (61.7 kJ/mole) for the Cu(+) ion jumping motion responsible for the ionic conductivity that agrees with earlier results based on (63)Cu NMR relaxation times of static samples.

Chemical shift calibration of 1H MAS NMR liver tissue spectra exemplified using a study of glycine protection of galactosamine toxicity

High-resolution (1)H magic angle spinning (MAS) NMR spectroscopy is a useful tool for analysing intact tissues as a component of metabonomic studies. The effect of referencing MAS NMR spectra to the chemical shifts of glucose or to that or trimethylsilylpropionic acid on the resultant multivariate statistical models have been investigated. It is shown that referencing to known chemical shifts of either alpha-glucose or beta-glucose in (1)H MAS NMR-based metabolic data of intact liver tissues is preferred. This has been exemplified in studies of galactosamine toxicity in the rat where co-administration of glycine ameliorates the toxic response. This approach leads to better aligned sets of spectra and reduces the inter-sample variability in multivariate statistical models. If glucose is not present in the tissue under study, then a number of alternative internal reference chemical shifts are presented. Finally, the chemical shift difference between that of the anomeric H1 proton of alpha-glucose and residual water is confirmed as a suitable internal temperature calibration method.

4,4-Dimethyl-4-silapentane-1-ammonium trifluoroacetate (DSA), a promising universal internal standard for NMR-based metabolic profiling studies of biofluids, including blood plasma and serum

Nuclear magnetic resonance (NMR)-based metabolic profiling of biofluids and tissues are of key interest to enhance biomarker discovery for disease, drug efficacy and toxicity studies. Urine and blood plasma/serum are the biofluids of most interest as they are the most accessible in both clinical and preclinical studies. However, proteinaceous fluids, such as blood serum or plasma, represent the greatest technical challenge since the chemical shift (δ) and line-width (ν1/2) of internal standards currently used for aqueous NMR samples are greatly affected by protein binding. We have therefore investigated the suitability of 4,4-dimethyl-4-silapentane-1-ammonium trifluoroacetate (DSA) as a universal internal standard for biofluids. Proton (1H) NMR spectroscopy was used to determine the effect of serum pH (3, 7.4 and 10) and DSA concentration on the overall lineshape and position of the trimethylsilyl resonance of DSA. The results were compared to that of 3-(trimethylsilyl)propionic acid sodium salt (TSP). Both the chemical shift and line-width of the DSA peak were not significantly affected by pH or DSA concentration, whereas these parameters for TSP showed large variations due to protein binding. Furthermore, the peak area of DSA correlated linearly with its concentration under all pH conditions, whilst no linear correlation was observed with TSP. Overall, in contrast to TSP, these results support the use of DSA as an accurate universal internal chemical shift reference and concentration/normalisation standard for biofluids. In the case of proteinaceous biofluids such as serum, where no current standard is available, this offers a considerable saving in both operator and spectrometer time.

An alternative NMR method to determine nuclear shielding anisotropies for molecules in liquid-crystalline solutions with 13C shielding anisotropy of methyl iodide as an example

An alternative NMR method for determining nuclear shielding anisotropies in molecules is proposed. The method is quite simple, linear and particularly applicable for heteronuclear spin systems. In the technique, molecules of interest are dissolved in a thermotropic liquid crystal (LC) which is confined in a mesoporous material, such as controlled pore glass (CPG) used in this study. CPG materials consist of roughly spherical particles with a randomly oriented and connected pore network inside. LC Merck Phase 4 was confined in the pores of average diameter from 81 to 375 A and LC Merck ZLI 1115 in the pores of average diameter 81 A. In order to demonstrate the functionality of the method, the (13)C shielding anisotropy of (13)C-enriched methyl iodide, (13)CH(3)I, was determined as a function of temperature using one dimensional (13)C NMR spectroscopy. Methane gas, (13)CH(4), was used as an internal chemical shift reference. It appeared that methyl iodide molecules experience on average an isotropic environment in LCs inside the smallest pores within the whole temperature range studied, ranging from bulk solid to isotropic phase. In contrast, in the spaces in between the particles, whose diameter is approximately 150 microm, LCs behave as in the bulk. Consequently, isotropic values of the shielding tensor can be determined from spectra arising from molecules inside the pores at exactly the same temperature as the anisotropic ones from molecules outside the pores. Thus, for the first time in the solution state, shielding anisotropies can easily be determined as a function of temperature. The effects of pore size as well as of different LC media on the shielding anisotropy are examined and discussed.

Structural Determinants That Target the Hepatitis C Virus Core Protein to Lipid Droplets

Hepatitis C virus core protein is targeted to lipid droplets, which serve as intracellular storage organelles, by its C-terminal domain, termed D2. From circular dichroism and nuclear magnetic resonance analyses, we demonstrate that the major structural elements within D2 consist of two amphipathic alpha-helices (Helix I and Helix II) separated by a hydrophobic loop. Both helices require a hydrophobic environment for folding, indicating that lipid interactions contribute to their structural integrity. Mutational studies revealed that a combination of Helix I, the hydrophobic loop, and Helix II is essential for efficient lipid droplet association and pointed to an in-plane membrane interaction of the two helices at the phospholipid layer interface. Aside from lipid droplet association, membrane interaction of D2 is necessary for folding and stability of core following maturation at the endoplasmic reticulum membrane by signal peptide peptidase. These studies identify critical determinants within a targeting domain that enable trafficking and attachment of a viral protein to lipid droplets. They also serve as a unique model for elucidating the specificity of protein-lipid interactions between two membrane-bound organelles.

The Solution Structure of Escherichia coli Wzb Reveals a Novel Substrate Recognition Mechanism of Prokaryotic Low Molecular Weight Protein-tyrosine Phosphatases

Low molecular weight protein-tyrosine phosphatases (LMW-PTPs) are small enzymes that ubiquitously exist in various organisms and play important roles in many biological processes. In Escherichia coli, the LMW-PTP Wzb dephosphorylates the autokinase Wzc, and the Wzc/Wzb pair regulates colanic acid production. However, the substrate recognition mechanism of Wzb is still poorly understood thus far. To elucidate the molecular basis of the catalytic mechanism, we have determined the solution structure of Wzb at high resolution by NMR spectroscopy. The Wzb structure highly resembles that of the typical LMW-PTP fold, suggesting that Wzb may adopt a similar catalytic mechanism with other LMW-PTPs. Nevertheless, in comparison with eukaryotic LMW-PTPs, the absence of an aromatic amino acid at the bottom of the active site significantly alters the molecular surface and implicates Wzb may adopt a novel substrate recognition mechanism. Furthermore, a structure-based multiple sequence alignment suggests that a class of the prokaryotic LMW-PTPs may share a similar substrate recognition mechanism with Wzb. The current studies provide the structural basis for rational drug design against the pathogenic bacteria.

NMR and Alanine Scan Studies of Glucose-dependent Insulinotropic Polypeptide in Water

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone that stimulates the secretion of insulin after ingestion of food. GIP also promotes the synthesis of fatty acids in adipose tissue. Therefore, it is not surprising that numerous literature reports have shown that GIP is linked to diabetes and obesity-related diseases. In this study, we present the solution structure of GIP in water determined by NMR spectroscopy. The calculated structure is characterized by the presence of an alpha-helical motif between residues Ser(11) and Gln(29). The helical conformation of GIP is further supported by CD spectroscopic studies. Six GIP-(1-42)Ala(1-7) analogues were synthesized by replacing individual N-terminal residues with alanine. Alanine scan studies of these N-terminal residues showed that the GIP-(1-42)Ala(6) was the only analogue to show insulin-secreting activity similar to that of the native GIP. However, when compared with glucose, its insulinotropic ability was reduced. For the first time, these NMR and modeling results contribute to the understanding of the structural requirements for the biological activity of GIP.

Function and Solution Structure of Huwentoxin-X, a Specific Blocker of N-type Calcium Channels, from the Chinese Bird Spider Ornithoctonus huwena

Huwentoxin-X (HWTX-X) is a novel peptide toxin, purified from the venom of the spider Ornithoctonus huwena. It comprises 28 amino acid residues including six cysteine residues as disulfide bridges linked in the pattern of I-IV, II-V, and III-VI. Its cDNA, determined by rapid amplification of 3' and 5' cDNA ends, encodes a 65-residue prepropeptide. HWTX-X shares low sequence homology with omega-conotoxins GVIA and MVIIA, two well known blockers of N-type Ca2+ channels. Nevertheless, whole cell studies indicate that it can block N-type Ca2+ channels in rat dorsal root ganglion cells (IC50 40 nm) and the blockage by HWTX-X is completely reversible. The rank order of specificity for N-type Ca2+ channels is GVIA approximately HWTX-X > MVIIA. In contrast to GVIA and MVIIA, HWTX-X had no detectable effect on the twitch response of rat vas deferens to low frequency electrical stimulation, indicating that HWTX-X has different selectivity for isoforms of N-type Ca2+ channels, compared with GVIA or MVIIA. A comparison of the structures of HWTX-X and GVIA reveals that they not only adopt a common structural motif (inhibitor cystine knot), but also have a similar functional motif, a binding surface formed by the critical residue Tyr, and several basic residues. However, the dissimilarities of their binding surfaces provide some insights into their different selectivities for isoforms of N-type Ca2+ channels.

Correlation of Three-dimensional Structures with the Antibacterial Activity of a Group of Peptides Designed Based on a Nontoxic Bacterial Membrane Anchor

To understand the functional differences between a nontoxic membrane anchor corresponding to the N-terminal sequence of the Escherichia coli enzyme IIA(Glc) and a toxic antimicrobial peptide aurein 1.2 of similar sequence, a series of peptides was designed to bridge the gap between them. An alteration of a single residue of the membrane anchor converted it into an antibacterial peptide. Circular dichroism spectra indicate that all peptides are disordered in water but helical in micelles. Structures of the peptides were determined in membrane-mimetic micelles by solution NMR spectroscopy. The quality of the distance-based structures was improved by including backbone angle restraints derived from a set of chemical shifts ((1)H(alpha), (15)N, (13)C(alpha), and (13)C(beta)) from natural abundance two-dimensional heteronuclear correlated spectroscopy. Different from the membrane anchor, antibacterial peptides possess a broader and longer hydrophobic surface, allowing a deeper penetration into the membrane, as supported by intermolecular nuclear Overhauser effect cross-peaks between the peptide and short chain dioctanoyl phosphatidylglycerol. An attempt was made to correlate the NMR structures of these peptides with their antibacterial activity. The activity of this group of peptides does not correlate exactly with helicity, amphipathicity, charge, the number of charges, the size of the hydrophobic surface, or hydrophobic transfer free energy. However, a correlation is established between the peptide activity and membrane perturbation potential, which is defined by interfacial hydrophobic patches and basic residues in the case of cationic peptides. Indeed, (31)P solid state NMR spectroscopy of lipid bilayers showed that the extent of lipid vesicle disruption by these peptides is proportional to their membrane perturbation potential.

Internuclear distance dependence of the spin–orbit coupling contributions to proton NMR chemical shifts

The internuclear distance dependence of the electronic spin–orbit coupling contribution to nuclear magnetic resonance shielding constants – which causes the internal heavy-atom chemical shift of the proton shielding – is investigated using quadratic response theory. Calculations using a complete active space self-consistent field wavefunction on hydrogen iodide at different internuclear distances show a strong dependence of the spin–orbit coupling correction to the 1 H shielding constant on internuclear separation. These results, combined with comparative calculations on HCl and HBr, indicate that the conformational dependence of the shielding constant is qualitatively changed when relativistic spin–orbit coupling corrections are important. This change is observed for HI and HBr, but not for HCl.

Development of novel 19F NMR pH indicators: synthesis and evaluation of a series of fluorinated vitamin B6 analogues

We have synthesized a series of novel fluorinated vitamin B6 analogues (6-fluoropyridoxol derivatives) as potential 19F NMR pH indicators for use in vivo. Modifications included addition of aldehyde, carboxyl or aminomethyl groups at the 4- or 5-ring position, and examination of a trifluoromethyl moiety as an internal chemical shift standard. The variation in chemical shift with respect to acid–base titration showed pKa values in the range 7.05–9.5 with a chemical shift sensitivity in the range 7.4–12ppm. Several of the molecules readily cross cell membranes providing estimates of both intra- and extra-cellular pH in whole blood. 6-Fluoropyridoxamine (6-FPAM) exhibits a pKa=7.05, which is closer to normal physiological pH than the parent molecule 6-fluoropyridoxol (6-FPOL) (pKa=8.2), and should thus, be useful for precise and accurate measurements of pH in vivo. Enhanced spectral resolution for 6-FPAM over 6-FPOL is demonstrated in whole blood and the perfused rat heart.

Tris(trimethylsilyl)methane as an internal13C NMR chemical shift thermometer

Tris(trimethylsilyl)methane has excellent properties for an internal chemical shift thermometer to measure temperatures in 13C DNMR spectroscopy [Δδ between the 13C signals of Si(CH3)3 and CH carbons]. It is chemically inert, soluble in most organic solvents and has an almost linear dependence of Δδ on temperature. The sensitivity (approximately 1°C Hz-1 at 90 MHz) allows the measurement of temperature to within 1°C. The chemical shift is solvent dependent, so each solvent mixture must be calibrated. Calibrations are presented for seven solvents. © 1998 John Wiley & Sons, Ltd.

Tris(trimethylsilyl)methane as an internal 13C NMR chemical shift thermometer

Tris(trimethylsilyl)methane has excellent properties for an internal chemical shift thermometer to measure temperatures in 13C DNMR spectroscopy [Δδ between the 13C signals of Si(CH3)3 and CH carbons]. It is chemically inert, soluble in most organic solvents and has an almost linear dependence of Δδ on temperature. The sensitivity (approximately 1°C Hz-1 at 90 MHz) allows the measurement of temperature to within 1°C. The chemical shift is solvent dependent, so each solvent mixture must be calibrated. Calibrations are presented for seven solvents. © 1998 John Wiley & Sons, Ltd.