Top PDF Use of gadolinium in 13C NMR studies

Use of gadolinium in 13C NMR studies

Use of gadolinium in 13C NMR studies

ABSTRACT , The addition of the reagents paramagnetic gadolinium18- crown-6 nitrate, gadoliniumdicyclohexano-18-crown-6 nitrate, and gadolinium ethylbenzene, nitrate and thymidine has bee[r]

63 Read more

MR of intracranial tumors: combined use of gadolinium and magnetization transfer

MR of intracranial tumors: combined use of gadolinium and magnetization transfer

Our results indicate that magnetization transfer sequence demonstrates edema as hyperintense relative to normal brain with shorter TR than conventional sequences; the contrast between en[r]

10 Read more

High resolution 13C and 1H NMR studies of proteins and peptides

High resolution 13C and 1H NMR studies of proteins and peptides

¿Me4si = “ 67*4 ppm. The chemical shift values were measured digitally. For the protein solutions referencing of the chemical shifts was done by first assuming that the chemical shifts of many resonances should not change under different conditions (except under denaturing conditions). That is, it was easy to find a large number of resonances whose relative chemical shifts had not changed. This assumption is based on a firm foundation of experimental data obtained in the present study for the proteins under different conditions. Hence, the chemical shifts of the spectrum of a'reference sample1* were first measured as described above. The 'pattern recognition' method was then applied to the chemical shifts of the protein samples which were subjected to conditions different from the 'reference sample’ . The dual display mode in the DISNMR programme facilitated the use of the 'pattern recognition' method. Both the reference spectrum and the spectrum of interest can be examined together on the screen.
Show more

279 Read more

Evaluation of Exchange-Correlation Functionals for Calculating 1H and 13C NMR Chemical Shifts of a Series of Lactones and Lactams in Solution

Evaluation of Exchange-Correlation Functionals for Calculating 1H and 13C NMR Chemical Shifts of a Series of Lactones and Lactams in Solution

CAM-B3LYP exchange-correlation functionals give the smallest errors for lactams with 1.438 ppm for the mean absolute error (MAE) and 1.837 ppm for the root mean squared error (RMSE), ahead of B3PW91 and wB97XD (MAE values of 2.033 – 2.109 ppm, RMSE values 2.429 – 2.340 ppm respectively). The B3PW91 method for lactones gives the best results with MAE of 0,085 ppm. These values indicate that the XC functionals used in this work, perform satisfactorily when compared to the values presented in the literature from other studies. 17, 21

11 Read more

13C NMR spectroscopy characterization of particle-size fractionated soil organic carbon in subalpine forest and grassland ecosystems

13C NMR spectroscopy characterization of particle-size fractionated soil organic carbon in subalpine forest and grassland ecosystems

NMR spectroscopy to characterize the change in compo- sition and structure of SOC after fire disturbance. Faria et al. (2015) used the NMR spectroscopy technique and found that wildfire increased the aromaticity of the top- soil SOC in forest in Portugal. Similarly, Lopez-Martin et  al. (2016) measured the changes in SOC pools after wildfire burnt a mountain forest in Andalusia and found that fire-affected soils retained similar C and N content but showed higher aromaticity as compared with adja- cent unburnt forest soils. However, previous research on composition of SOC pools of fire-affected soils were mostly based on whole bulk soils, and the composition of SOC in particle-size fractions may be worth studying.
Show more

7 Read more

Design synthesis and NMR studies of hybrid peptides

Design synthesis and NMR studies of hybrid peptides

Chapter I deal with introduction to peptides, peptidomimetics and their conformations. These conformations are classified as helices, sheets and turns based on the CO-N-Cα-CO (ϕ) and N-Cα-CO-N (ψ) dihedral angles in Ramachandran plot, which provides allowed regions for various secondary structures available. A brief discussion on synthesis of peptides in solution state and various substituted β-amino acids has been discussed. Applications of NMR spectroscopy in conformational studies is briefly reviewed along with the NMR techniques, Molecular Dynamics (MD) studies and Circular Dichroism (CD) spectroscopy, which are useful to obtain the conformations of peptides have been discussed.
Show more

11 Read more

Kinetic and NMR studies of some nitrogen heterocycles

Kinetic and NMR studies of some nitrogen heterocycles

The solid state ^^N nmr spectra of 4-nitro- and 4-methoxybenzenediazonium tetrafluoroborate were compared with the solution state spectra reported previously^"*. The chemical shifts for both solution and solid state are shown in Table 3. Normally a straightforward comparison can be made between solution and solid state nmr and the CPMAS technique provides a bridge between X-ray crystal structures and those existing in solution. Two signals are observed in the solid state spectrum of 4-nitrobenzenediazonium ion (Figure 7). This is an unexpected result as the solution state nmr exhibits only one signal indicating the existence of only one l^N environment. From the solid state spectrum, it is possible that is present in two environments in crystalline 4-nitrobenzenediazonium tetrafluoroborate. Furthermore, the solid state spectrum of the dibenzyl 18-crown-6/4-nitrobenzenediazonium ion complex contains three signals at chemical shifts at least 5ppm removed from the 4-nitrobenzenediazonium ion shifts. This is an intriguing observation as it was expected that only one environment would exist in the dibenzyl 18-crown-6 complex with all the diazonium ion expected to be held within the crown cavity. Any diazonium ion remaining outside the crown would have a chemical shift the same as that observed for the 4-nitrobenzenediazonium ion sample with no crown added. An explanation for these unexpected nmr results was sought by solving the X-ray crystal structure of 4-nitrobenzenediazonium tetrafluoroborate. Solving this structure should help to clarify the solid state l^N nmr spectrum of this species and possibly also of the 4-methoxy species, for which three signals are observed in the solid state nmr spectrum (Figure 9).
Show more

181 Read more

NMR Studies of Platinum bisphosphine complexes of phenylphosphonamidodiselenoate

NMR Studies of Platinum bisphosphine complexes of phenylphosphonamidodiselenoate

does selenium have the lowest natural abundance of the NMR active nuclei discussed herein, it also appears that both selenium atoms and the two phosphine phosphorus atoms are magnetically inequivalent in some complexes when rotation within the molecule is restricted due to bulky groups on the nitrogen atom. As such, between two and four resonances appear in the 77 Se{ 1 H} NMR spectra, often overlaying each other, giving complicated splitting

21 Read more

1H and 13C solution  and solid state NMR investigation into wax products from the Fischer Tropsch process

1H and 13C solution and solid state NMR investigation into wax products from the Fischer Tropsch process

Solid state 13 C NMR spectra were obtained for docosane (Figs 2, 3), as well as solution spectra, including that of octacosane (Fig. 4). Similar combinations of solid and solution state 13 C NMR data is shown from the three wax samples – Co-wax (Fig. 5), ReCo-wax, Fig. 6(a) and CeCo-wax, Fig. 6(b). The spectra were fitted using DMFit 43 . All four spectra show peaks for the -carbon at 14-16 ppm, the -carbon at 24-26 ppm and the other carbon atoms ( , and ) in a complex peak or group of peaks at 28-38 ppm. These are in broad agreement with the results of Cookson and Smith 39 for their shorter-chain alkanes in solution-state 13 C NMR. However, the chemical shifts observed in this work are slightly higher than those analysed by Cookson and Smith by 2-5 ppm. This is likely to be a consequence of (1) a longer carbon chain length and (2) the packing of the alkane chains in the solid wax, giving an extra intermolecular van der Waals force which is not observed in the solution state. An additional peak is observed at 53 ppm in the spectrum of ReCo-wax. This is assigned as an oxygenated species, such as C-OH.
Show more

32 Read more

19F NMR studies on DnaB helicase

19F NMR studies on DnaB helicase

GstDnaGC and Dnal Expression Instead of full-length DnaG, only a construct of solubility tag with the C-terminal pl6 DnaB binding domain, referred as DnaGC, was used to study the interac[r]

131 Read more

Unraveling the complexity of protein backbone dynamics with combined 13C and 15N solid state NMR relaxation measurements

Unraveling the complexity of protein backbone dynamics with combined 13C and 15N solid state NMR relaxation measurements

The dominant contribution of fast picosecond motions to spectral densities in solution leads to the opposite effect to that observed in solids. Based on the analysis of synthetic data, even in the presence of small amplitude nanosecond motions, a good SMF fit can be obtained with motional parameters close to the amplitude and time scale of the fast picosecond motion (i.e. a single-time scale fast motion model can explain the two- time scale motion well when the slow motion has a small amplitude, because the spectral densities calculated by the EMF and SMF are similar). If the amplitude of the slow motion is much smaller than that of the fast motion then the use of EMF may not be statistically justifiable. It is likely that such a phenomenon is partially behind the fact that EMF seems to be required primarily only for modeling residues in loop regions of proteins, where the amplitudes of slow motions are suffi- ciently large to lead to a statistically valid improvement of an EMF fit over an SMF fit. Another consequence of this behavior is that, in solution, a large number of independent data points (e.g. data at several different magnetic fields) may be necessary to identify motions that are slow (but still faster than the correla- tion time for the overall rotational diffusion) but of relatively small amplitude. In line with these observations, recent relaxometry experiments show that nanosecond motions are likely to be significantly underestimated by the traditional EMF analysis based on solution relaxation data obtained at one or two magnetic field strengths. 47
Show more

13 Read more

Solid-State 13C-NMR Investigation of Di- and Tri-block Biodegradable Copolymers Isolated In Their Inclusion Compounds with Cyclodextrins

Solid-State 13C-NMR Investigation of Di- and Tri-block Biodegradable Copolymers Isolated In Their Inclusion Compounds with Cyclodextrins

Francis Ebikefe Porbeni was born on May 25, 1964 in Lagos, Nigeria. His early childhood was spent in Lagos where he completed both his primary and secondary school education. He graduated secondary school in June 1979 from Government College Ketu having passed the West African School Certificate in the Upper Division. He then proceeded to study Chemical and Petrochemical Engineering at the Rivers State University of Science and Technology where he graduated and obtained his diploma in June 1984. His industrial internship with Lever Brothers Nigeria Ltd in January to June 1983 in the research and development department stimulated his interest in research and advanced studies. After graduation, he worked briefly with Mobil Producing Nigeria as a Production Engineer between August 1984 and June 1985. Thereafter, he worked with the National Directorate of Employment as a Project Officer evaluating small-scale industrial projects.
Show more

148 Read more

Site directed labelling of proteins for NMR and EPR studies

Site directed labelling of proteins for NMR and EPR studies

Site-speci fi c protein modi fi cation is a fundamental tool for a myriad of applications in protein chemistry, including protein immobilization on surfaces, enhancement of protein solubility by PEGylation, production of therapeutic conjugates with drugs, mimicking of natural post-translational modi fi cations, and introduction of tags for structural studies by fl uorescence resonance energy transfer (FRET), electron paramagnetic resonance (EPR) spectroscopy, or nuclear magnetic resonance (NMR) spectroscopy. 1−8 Cysteine is the most convenient target for protein modi fi cation as it is the most nucleophilic and oxidation-sensitive among the 20 canonical amino acids. Thus, site-directed modi fi cations of proteins are often carried out on cysteine residues with the formation of disul fi de or thioether bonds. To be site-selective, however, this approach requires that only a single cysteine residue is amenable to the chemical reaction, which is di ffi cult when the protein of interest contains other cysteine residues that are essential for the structure or function of the protein. In principle, this problem can be solved by genetic encoding of photocaged cysteine (PCC) as an unnatural amino acid (UAA), 9 which enables a protocol involving the chemical protection of the native cysteine residues, decaging of the PCC residue, and chemical modi fi cation and deprotection of the native cysteine residues. 10 Charging of the cognate amber suppressor tRNA CUA with the
Show more

136 Read more

NMR SPECTROSCOPIC STRUCTURAL STUDIES OF WOOD AND PULP COMPONENTS

NMR SPECTROSCOPIC STRUCTURAL STUDIES OF WOOD AND PULP COMPONENTS

Various NMR spectroscopic techniques were applied to investigate the polymeric components of wood and pulp. The main aim of the work was to obtain new information on the structural- changes occurring in the morphology of cellulose and inthe lignin structure during various chemical pulping related processes in order to help optimise the conditions for efficient delignification and bleaching reactions without affecting pulp yield or strength properties. One of the main objectives of this research was to investigate, the residual lignin structure and the crystallinity of cellulose in ray cells and on the fibre surface compared to the corresponding structuresinside the fibre by isolating fines fractions before and after refining of kraft pulp .Mainly softwood components were considered throughout this research.
Show more

9 Read more

Studies of high molecular weight systems by NMR spectroscopy

Studies of high molecular weight systems by NMR spectroscopy

It may be possible to gain more decisive information on the ssDNA binding polarity on SSB by biochemical rather than NMR spectroscopic techniques. For example, it has been shown that ssDNA can be cleaved site-specifically by radicals formed in Cu 2+ - catalysed oxidation of ascorbate (Sergey et al., 1988). This could be exploited by introducing a Cu 2+ ion at two individual sites (Trp88 and Tyr97) on the OB domain by incorporating a metal chelating unnatural amino acid or a tag. In the presence of ascorbate, the Cu 2+ ion would result in ssDNA cleavage at those sites. Cleavage of an ssDNA oligomer with a fluorophore attached at the 5’-end could then be analysed following separation of the different fragments by urea polyacrylamide gel electrophoresis (PAGE) using a fluorescence scanner. The different length fragments produced by copper at either position 88 or 97 would give information about the ssDNA binding polarity on SSB. A potential difficulty associated with this experiment, however, would be the possibility of digesting already digested ssDNA fragments, which may be difficult to distinguish from ssDNA with single cuts.
Show more

144 Read more

Quantitative 13C MultiCP solid-state NMR as a tool for evaluation of cellulose crystallinity index measured directly inside sugarcane biomass

Quantitative 13C MultiCP solid-state NMR as a tool for evaluation of cellulose crystallinity index measured directly inside sugarcane biomass

After carrying out the spectral subtraction procedure, the spectral regions from 80 to 86 and 86 to 94 ppm were integrated to evaluate the intensity of the lines associated with ordered and disordered cellulose phases, respec- tively (12). To evaluate the influence of lignin removal in the cellulose CI obtained by NMR, the same procedure was also carried out using the spectra without subtrac- tion. The CI results are shown in Fig.  6b. The CI values obtained without using the spectral subtraction approach (stars in Fig. 6b) show a slight, but progressive increase upon alkaline pretreatment due to lignin removal. Nev- ertheless, the CI values obtained using the spectral sub- traction (circles in Fig.  6b) remained mostly constant upon pretreatment. Therefore, within the experimental uncertainties, both calculations point to a constancy of the cellulose CI inside the biomass. Thus, despite that the subtraction method would provide more precise evalu- ation of the CI, the 13 C-solid-state Multi-CP NMR also
Show more

11 Read more

NMR studies of ribonuclease A and interactions of some spore constituents

NMR studies of ribonuclease A and interactions of some spore constituents

V CONTENTS Page Vlll ABSTRACT lX ABBREVIATIONS CHAPTER 1 SOME GENERAL ASPECTS OF THE APPLICATION OF NMR 1 IN BIOCHEMISTRY CHAPTER 2 CHAPTER 3 MATERIALS AND METHODS 10 2.1 MATERIALS 10 2.[r]

202 Read more

1H and 13C MAS NMR Evidence for Pronounced Ligand-Protein Interactions Involving the Ionone Ring of the Retinylidene Chromophore in Rhodopsin

1H and 13C MAS NMR Evidence for Pronounced Ligand-Protein Interactions Involving the Ionone Ring of the Retinylidene Chromophore in Rhodopsin

in the conformation around the C14–C15 bond between the 11-cis-retinylidene chromophore and the pSB model compound or by an interaction with a nearby protein residue (3, 4, 33, 34). The absence of conformational shifts for C-7, C-8, and C-19 provides strong evidence for a highly similar electronic and spatial conformation of the rhodopsin chromophore and the pSB model. In particular, Fourier transform IR and resonance Ra- man spectroscopic studies have been interpreted in terms of a close contact between the C-19 methyl group and the surround- ing protein (47, 48). Although these studies indicate strong ligand–protein interactions for CH 3 -19, it is clear from the NMR
Show more

6 Read more

The development of experimental models for NMR studies of neuropathology

The development of experimental models for NMR studies of neuropathology

In most animals, global cerebral ischaemia cannot be brought about simply by occluding both common-carotid arteries as there exists a collateral system comprising arteries which shunt blood from the vertebral arteries, via the circle o f Willis. In the absence of other variables these collateral pathways can support the cerebral circulation above critical levels in the absence of carotid flow. Exceptions to this include the Mongolian gerbil which lacks posterior communicating arteries (incomplete circle of Willis); sheep and stroke prone spontaneously hypertensive rats also have compromised collateral supply systems which can be exploited to produce ischaemic lesions under specific conditions (Busto and Ginsberg, 1985). There are a number of reports of successful use of a rat 4-vessel occlusion whereby the common-carotids and vertebral arteries are occluded to induce bilateral hemispheric ischaemia (Pulsinelli and Brierley, 1979; Pulsinelli et al., 1982; Dougherty et al., 1982). In this model the vertebral arteries are electro-cauterised 24 hours before the ischaemia-reperfusion experiment. The common-carotid arteries are then occluded by compression clamps induce reversible ischaemia. The initial description of the model used animal restraint rather than anaesthesia during the occlusion of the common-carotid arteries. This approach allowed the observation of effects in the absence of anaesthetic effects and represents one of the few models which has been shown to be reliable without the use of surgical anaesthesia.
Show more

297 Read more

Show all 10000 documents...