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Topic: Chemical shift

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	Protein backbone angle restraints from searching a database for chemical shift and sequence homology
		Chemical shifts of backbone atoms in proteins are exquisitely sensitive to local conformation, and homologous proteins show quite similar patterns of secondary chemical shifts.
		N chemical shift deviations (weighted according to the number of residues used for each type of secondary structure) is larger than 1 ppm, a correction to the chemical shifts needs to be applied.
		N chemical shift is known to be influenced by hydrogen bonding (de Dios et al., 1993), it is also influenced by backbone geometry and therefore is included as an input parameter in the torsion angle prediction procedure.
	spin.niddk.nih.gov /bax/software/TALOS/info.html (6590 words)

	Biomolecular NMR Facility - Chemical Shift Referencing and Temperature Calibration.
		The chemical shift of the water resonance relative to the DSS standard is temperature dependent by about -0.01 degrees C, and should always be the same at at given temperature.
		The relative chemical shift constants are given in the Markley et al.
		Shifting towards higher ppm is said to be shifting "downfield".
	nmr.uthscsa.edu /temp.shtml (1546 words)

	Chemical shift?
		Chemical shift is defined as the relative difference in resonant frequency compared to a standard signal.
		Co where the chemical shift range is 20000 ppm (or 2%).
		This is because the chemical shift of TMS varies from sample to sample and that the resonant frequency of different samples is affected by the difference in their magnetic susceptibilities.
	chem.ch.huji.ac.il /nmr/whatisnmr/chemshift.html (773 words)

	CHAPTER-4
		The chemical shift of a nucleus is the difference between the resonance frequency of the nucleus and a standard, relative to the standard.
		The chemical shift is a very precise metric of the chemical environment around a nucleus.
		Nuclei experiencing the same chemical environment or chemical shift are called equivalent.
	www.cis.rit.edu /htbooks/nmr/chap-4/chap-4.htm (1300 words)

	Carbon Chemical Shift Restraints (Site not responding. Last check: )
		Carbon chemical shifts of the alpha and beta carbons of an amino acid have been found to correlate with the phi and psi backbone angles of that amino acid.
		This secondary shift is compared to the expected secondary shift of the grid point closest to the phi, psi angles of the residue.
		The energy term is calculated from the difference of the observed secondary chemical shift and the expected one.
	nmr.cit.nih.gov /xplor-nih/xplorMan/node383.html (141 words)

	Carbon Chemical Shifts
		The range of chemical shifts in which most carbon resonances appear is 0 to 200 ppm, which is about 10-20 times the range of proton chemical shifts.
		C chemical shifts for the carbons of 2-methylhexane and hexane shown in Figure 9.
		A gross exception to the rule that carbon chemical shifts are 10-20 times the corresponding proton chemical shifts appears with the substituent iodine, and to a lesser extent with the substituent bromine.
	orgchem.colorado.edu /hndbksupport/nmrtheory/carbonchemshift.html (455 words)

	What is NMR?
		The chemical shift, using this equation, is not dependent on the magnetic field and it is convenient to express it in ppm where (for
		The increased chemical shift is due to the delocalized ring current of the phenyl group.
		Chemical shifts are affected slightly by isotopic substitution, an effect that is known as an isotope shift.
	chem.ch.huji.ac.il /nmr/whatisnmr/whatisnmr.html (859 words)

	Dr Christian Hill - Third Year NMR Tutorial - Chemical Shift
		(or the absolute shift) that is used to report the position of lines in a spectrum, but the relative shift: the frequency of the resonance relative to a reference frequency of a known nucleus in the same spectrometer.
		TMS is a good choice because it is inert, soluble in most organic solvents, and its magnetic nuclei are strongly shielded (which means that the reference signal appears well-separated from the sample spectrum).
		One advantage of using chemical shift instead of frequency is that spectra from different spectrometers can be directly compared.
	physchem.ox.ac.uk /~hill/tutorials/nm3_tutorial/chem_shift/index.html (277 words)

	Chemical shift artifacts in MRI
		Due to the chemical shift, voxels containing fat will not have the expected resonance frequency and will be spatially misregistrered, causing a shift in the spatial location in the frequency-encode direction.
		The narrower is the receiver bandwidth, the narrower is the bandwidth per pixel is and the wider the chemical shift in number of pixels is.
		With a 1.5 T field strength, the frequency shift is 225 Hz, corresponding to a period of 4.4 ms.
	www.e-mri.org /quality-artifacts/chemical-shift.html (681 words)

	[No title]
		B NMR chemical shifts is a selected compilation of representative organoborane and boron compounds that we believe would be of interest to the organoborane community and to my research group at San Diego State University.
		The chemical shift is dependent on the strength of the coordination complex, with the stronger complexes shifted to higher field.
		The chemical shifts of the trivalent organoboranes having a B-H bond are more variable than that of the trialkylboranes, and are dependent on the structure of the organic groups present.
	www.chemistry.sdsu.edu /research/BNMR (1095 words)

	Chemical & Engineering News: Latest News - Fast Route To Structures
		The new technique predicts likely structures of protein fragments on the basis of chemical shift data and assembles the fragments into an overall protein structure, which is then refined with chemical shift data and molecular force fields.
		The technique "will enable the determination of a vast range of protein conformations for which chemical shifts are essentially the only NMR observables that are possible to obtain," Vendruscolo says.
		For example, he believes it could be used to study transient or excited states of proteins, for which chemical shifts are often the only type of NMR data available.
	pubs.acs.org /cen/news/85/i23/8523notw6.html (702 words)

	Gonzaga University Faculty: Dennis McMinn
		Chemical shifts can be tabulated for various kinds of protons (i.e.
		True/False: The greater the electronegativity of a substituent (E), the greater the chemical shift of a proton under consideration.
		b) Determine the chemical shift of the "3 proton singlet" (this is the peak closest to the TMS peak).
	www.gonzaga.edu /archimedes/Faculty/custom.cfm?FID=983108104557Mc&MID=08990849 (635 words)

	Chemical shift imaging with spectrum modeling - Patent 5994902
		Chemical shift imaging with spectrum modeling (CSISM) models the general chemical shift spectrum as a system with N distinct peaks with known resonant frequencies and unknown amplitudes.
		This is equivalent to saying that every voxel in the sample consists of several chemical components, and all the components have fixed chemical shift values and no line broadening.
		The optimal timing parameters to shift the 180° RF pulses for image acquisitions are chosen to achieve the best data quality with a maximized data acquisition efficiency.
	www.freepatentsonline.com /5994902.html (3930 words)

	SCIENCE/TECHNOLOGY
		The chemical shifts of small molecules could be approximated, but those of larger systems such as peptides, proteins, and catalysts were all but impossible to calculate with the computers of the 1970s and '80s.
		Theorists wanting to model the chemical shifts of nuclei under the influence of a heavy atom, or the nucleus of a heavy atom itself, must contend with relativistic effects generated by the ultrafast electrons.
		In exploring chemical shift anisotropies, Judith Herzfeld, a professor of biophysical chemistry at Brandeis University in Waltham, Mass., made the assumption that the electron current density induced by an applied magnetic field is always perpendicular to the field.
	pubs.acs.org /hotartcl/cenear/980928/nmr.html (3109 words)

	Probability-based protein secondary structure identification using combined NMR chemical-shift data -- Wang and ...
		Nakamura, A. and Jardetzky, O. Systematic analysis of chemical shifts in the nuclear magnetic resonance spectra of peptide chains.
		Pastore, A. and Saudek, V. The relationship between chemical shifts and secondary structure in proteins.
		The chemical shift index: A fast and simple method for the assignment of protein secondary structure through NMR spectroscopy Biochemistry 31: 1647–1651.
	www.proteinscience.org /cgi/content/full/11/4/852 (3060 words)

	SECTION SIX: Chemical shift restraints.
		Values of calculated shifts will be printed only if the absolute error between calculated and observed shifts is greater than this value.
		The pseudocontact shift depends on the magnetic susceptibility anisotropy of the metal ion and on the location of the resonating nucleus with respect to the axes of the magnetic susceptibility tensor.
		atom number of the i-th proton whose shift is to be used as constraint.
	www.nersc.gov /vendor_docs/amber/AMBER-sh-6.12.html (770 words)

	Chapter 13 - NMR Chemical Shift
		The frequency of a signal is known as its chemical shift.
		The chemical shift in absolute terms is defined by the frequency of the resonance expressed with reference to a standard compound which is defined to be at 0 ppm.
		What would be the chemical shift of a peak that occurs 655.2 Hz downfield of TMS on a spectrum recorded using a 90 MHz spectrometer
	www.mhhe.com /physsci/chemistry/carey5e/Ch13/ch13-nmr-2.html (261 words)

	Chemical Shift
		This results in the sigma electrons to be shifted toward the carbon atoms in the methyl groups and consequently, the protons will be heavily shielded causing the one signal to be generated at a very high magnetic field strength setting.
		C-13 signals have a chemical shift range of 0-200 ppm compared to the Proton NMR Chemical Shift range of 0-12 ppm.
		The Chemical Shift is the nmr signal shift that occurs because of the electronic chemical environment of the proton.
	members.aol.com /logan20/shift.html (1556 words)

	Chemical shift, spin-spin interaction and J-coupling
		Chemical shift corresponds to a change in the resonance frequency of the nuclei within the molecules, in function of their chemical bonds.
		For a given molecule, the chemical shift in ppm versus the reference molecule is defined by the relationship:
		In chemical shift, the difference in frequency compared to the reference molecule is proportional to the amplitude of the B0 magnetic field.
	www.e-mri.org /mr-spectroscopy/chemical-shift-j-coupling.html (267 words)

	NMR spectroscopy - Wikipedia, the free encyclopedia
		Si, TMS (tetramethylsilane) is commonly used as a reference.) This difference between the frequency of the signal and the frequency of the reference is divided by frequency of the magnetic field to give the chemical shift.
		The units of chemical shift are parts per million (ppm) because the difference in frequencies is usually in hertz while the frequency of the magnetic field is in megahertz.
		A typical CH group has a shift around 1 ppm, the CH attached to a OH has a shift of around 4 ppm and the OH has a shift around 2–3 ppm depending on the solvent used.
	en.wikipedia.org /wiki/NMR_spectroscopy (1964 words)

	Analysis of NMR chemical shift titration tutorial
		The chemical shift in both nitrogen and proton dimension is sensitive to the chemical environment of the two nuclei.
		The surface accessible shifted residues of both molecules are used in the docking process to position the two interfaces and bring the molecules together.
		from chemical shift perturbation) to be involved in the interaction between the two molecules and solvent accessible.
	www.nmr.chem.uu.nl /~abonvin/tutorials/Titration-Data/titration.html (1896 words)

	Access: Stay Flexible
		The amount of shielding, and thus the chemical shift, is related to the number and arrangement of the electrons surrounding the nuclei.
		In other words, the chemical shift is determined by the company that the nuclei keep.
		Using this data, the team created a series of empirical functions that established the relationship between the chemical shift of carbons within polysaccharides and their conformations as described by the molecules' bond torsions.
	www.ncsa.uiuc.edu /News/Access/Stories/polysaccharide/StayFl2.html (453 words)

	NMR Chemical Shift Prediction by Atomic Increment Based Algorithms
		C resulted when all of the atoms were divided into approximately 70 different classes according to their chemical nature, stereochemistry, and formal charge; and the information associated with atoms up to 5 bonds away was used to influence the prediction.
		C shifts, the most efficient calculations had mean errors of prediction of 1.8 and 1.6 ppm (an independent test dataset of 150,000 chemical shifts was used) for each of the techniques.
		Our conclusion is that the most important factor influencing the precision of the chemical shift prediction (and, probably, other structure-activity relationship studies) is the scheme used for encoding a chemical structure into a numerical input.
	www.acdlabs.com /publish/publ07/enc2007_chemshift.html (535 words)

	Chemical Shifts in NMR Spectra
		The magnitude of the shift depends upon the type of nucleus and the details of the electron motion in the nearby atoms and molecules.
		The precision of NMR spectroscopy allows this chemical shift to be measured, and the study of chemical shifts has produced a large store of information about the chemical bonds and the structure of molecules.
		The signal shift is very small, parts per million, but the great precision with which frequencies can be measured permits the determination of chemical shift to three or more significant figures.
	hyperphysics.phy-astr.gsu.edu /Hbase/Nuclear/nmrcsh.html (295 words)

	ACD/CNMR Predictor: Technical Information
		Also, CNMR Predictor uses many different subalgorithms for estimating chemical shifts for those fragments that are not in the internal database of experimental values.
		The obtained chemical shifts are used to compose the final CNMR spectrum of your structure.
		As you assign new chemical shifts to the carbon atoms, the program treats these data as an update to its internal database.
	www.acdlabs.com /products/spec_lab/predict_nmr/cnmr/tech.html (465 words)

	Ca to Cl
		Detectable chemical reactions normally involve sets of molecular entities, as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e.
		If the equilibrium mixture of a chemical reaction is disturbed by a sudden change, especially of some external parameter (such as temperature, pressure, or electrical field strength), the system will readjust itself to a new position of the chemical equilibrium or return to the original position, if the perturbation is temporary.
		For example, two conformational isomers may be interconverted sufficiently slowly to be detectable by separate NMR spectra and hence to be considered to be separate chemical species on a time scale governed by the radiofrequency of the spectrometer used.
	www.chem.qmul.ac.uk /iupac/gtpoc/CaCl.html (2316 words)

	ACERC Abstracts - 1996 Thrust Area 1
		These values are referenced to an external sample of nitromethane and yield and isotropic shift value of -274 ppm, which is close to the -271.5 ppm MAS (Magic Angle Spinning) value and the liquid values of -278.4 ppm in DMSO and -282 ppm in CDC13, from the literature.
		This has been observed before in a previous study of the N-15 chemical shifts tensors of uracil but it appears that the magnitude of the effect is greater for an amide nitrogen than for the aromatic nitrogens in uracil.
		The ortho steric effect on the isotropic C-13 chemical shifts was obtained from a low-temperature MAS spectrum, and the effect on both the isotropic and the tensor principal components was determined from a low-temperature 2D magic angle turning (MAT) experiment.
	www-acerc.byu.edu /Abstracts/1996/1996-1.html (5675 words)

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