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Karnaker Reddy.T R.No.08171S0403

Karnaker Reddy.T R.No.08171S0403. NUCLEAR MAGNATIC RESONANCE SPECTROSCOPY INTRODUCTION BASICS PRINCIPLE INSTRUMENTATION SHEILDING AND DESHIELDING &APPLICATIONS. INTRODUCTION.

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Karnaker Reddy.T R.No.08171S0403

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  1. KarnakerReddy.T R.No.08171S0403

  2. NUCLEAR MAGNATIC RESONANCE SPECTROSCOPYINTRODUCTIONBASICSPRINCIPLEINSTRUMENTATIONSHEILDING AND DESHIELDING&APPLICATIONS

  3. INTRODUCTION Nuclear magnetic resonance (NMR) is a physical phenomenon based upon the quantum mechanical magnetic properties of an atom's nucleus. NMR also commonly refers to a family of scientific methods that exploit nuclear magnetic resonance to study molecules ("NMR spectroscopy"). The method of NMR was first developed by E.M. Purcell and Felix bloch(1946) Major application of NMR spectroscopy lies in the area of synthetic organic chemistry, inorganic chemistry, bio-organic chemistry, bio-inorganic chemistry,

  4. NMR Historic Review

  5. 2002 Nobel prize in Chemistry was awarded to Kurt Wuthrich

  6. Edward M. Purcell 1912-1997 Kurt Wuthrich 1938- Richard R. Ernst 1933- CW NMR 40MHz 1960 Felix Bloch 1905-1983

  7. 800 MHz

  8. 1nm 102 103 104 105 106 107 10 NMR Spectroscopy Where is it? (thewave) X-ray UV/VIS Infrared Microwave Radio Frequency (the transition) electronic Vibration Rotation Nuclear (spectrometer) X-ray UV/VIS Infrared/Raman NMR Fluorescence

  9. Before using NMR What are N, M, and R ? Properties of the Nucleus Nuclear spin Nuclear magnetic moments The Nucleus in a Magnetic Field Precession and the Larmor frequency Nuclear Zeeman effect & Boltzmann distribution When the Nucleus Meet the right Magnet and radio wave Nuclear Magnetic Resonance

  10. Nuclear magnetic moments Magnetic moment  is another important parameter for a nuclei  = I (h/2) I: spin number; h: Plank constant; : gyromagnetic ratio (property of a nuclei) 1H:I=1/2 ,  = 267.512 *106 rad T-1S-1 13C:I=1/2 ,  = 67.264*106 15N:I=1/2 ,  = 27.107*106

  11. PRINCIPLE • Subatomic particles (electrons, protons and neutrons) can be imagined as spinning on their axes. • In many atoms (such as 12C) these spins are paired against each other, such that the nucleus of the atom has no overall spin. • However, in some atoms (such as 1H and 13C) the nucleus does possess an overall spin. The rules for determining the net spin of a nucleus are as follows;

  12. If the number of neutrons and the number of protons are both even, then the nucleus has NO spin. • 2 . If the number of neutrons plus the number of protons is odd, then the nucleus has a half-integer spin (i.e. 1/2, 3/2, 5/2) • 3.If the number of neutrons and the number of protons are both odd, then the nucleus has an integer spin (i.e. 1, 2, 3)

  13. In an Applied Magnetic Field • Nuclei with 2 allowed spin states can align either withor against the field, with slight excess of nuclei aligned with the field • The nuclei precess about an axis parallel to the applied magnetic field, with a frequency called the Larmor Frequency (w)

  14. Larmor Frequency is Proportional to the Applied Magnetic Field Faster precession in larger magnetic field Slow precession in small magnetic field

  15. Nuclear Zeeman effect • Zeeman effect: when an atom is placed in an external magnetic field, the energy levels of the atom are split into several states. • The energy of a give spin sate (Ei) is directly proportional to the value of mI and the magnetic field strength B0 • Spin State Energy EI=- . B0 =-mIB0 r(h/2p) • For a nucleus with I=1/2, the energy difference between two states is • ΔE=E-1/2-E+1/2 = B0 r(h/2p) • m=1/2 • m=-1/2 • The Zeeman splitting is proportional to the strength of the magnetic field

  16. Boltzmann distribution • Quantum mechanics tells us that, for net absorption of radiation to occur, there must be more particles in the lower-energy state than in the higher one. • If no net absorption is possible, a condition called saturation. • When it’s saturated, Boltzmann distribution comes to rescue: • Pm=-1/2 / Pm=+1/2 = e -DE/kT where P is the fraction of the particle population in each state, T is the absolute temperature, k is Boltzmann constant 1.381*10-28 JK-1 • Anything that increases the population difference will give rise to a more intense NMR signal.

  17. Nuclear Magnetic Resonance Spectrometer How to generate signals? B0: magnet B1: applied small energy

  18. Rf Energy Can Be Absorbed • Precessing nuclei generates an oscillating electric field of the same frequency • Rf energy with the same frequency as the Larmor frequency can be applied to the system and absorbed by the nuclei

  19.  The Nucleus in a Magnetic Field • Precession and the Larmor frequency • The magnetic moment of a spinning nucleus processes with a characteristic angular frequency called the Larmor frequency w, which is a function of r and B0 • Remember  =  I (h/2) ? • Angular momentum dJ/dt=  x B0 • Larmor frequency w=rB0 • Linear precession frequency v=w/2p= rB0/2p J

  20. DE =hvphoton  When the Nucleus Meet the Magnet Nuclear Magnetic Resonance • For a particle to absorb a photon of electromagnetic radiation, the particle must first be in some sort of uniform periodic motion • If the particle “uniformly periodic moves” (i.e. precession) • at precession, and absorb erengy. The energy is E=hvprecession • For I=1/2 nuclei in B0 field, the energy gap between two spin states: • DE=rhB0/2p • The radiation frequency must exactly match the precession frequency • Ephoton=hvprecession=hvphoton=DE=rhB0/2p • This is the so called “ Nuclear Magnetic RESONANCE”!!!!!!!!! v

  21.  Magnet B0 and irradiation energy B1 B0 ( the magnet of machine) (1) Provide energy for the nuclei to spin Ei=-miB0 (rh/2p) Larmor frequency w=rB0 (2) Induce energy level separation (Boltzmann distribution) The stronger the magnetic field B0, the greater separation between different nuclei in the spectra Dv =v1-v2=(r1-r2)B0/2p   (3) The nuclei in both spin states are randomly oriented around the z axis. M z=M, Mxy=0   ( where M is the net nuclear magnetization)

  22. What happen before irradiation • Before irradiation, the nuclei in both spin states are processing with characteristic frequency, but they are completely out of phase, i.e., randomly oriented around the z axis. The net nuclear magnetization M is aligned statically along the z axis (M=Mz, Mxy=0)

  23. z Mo x x Mxy B1 y a y wo What happen during irradiation When irradiation begins, all of the individual nuclear magnetic moments become phase coherent, and this phase coherence forces the net magnetization vector M to process around the z axis. As such, M has a component in the x, y plan, Mxy=Msina. a is the tip angle which is determined by the power and duration of the electromagnetic irradiation. a deg pulse 90 deg pulse

  24. B1(the irradiation magnet, current induced) (1) Induce energy for nuclei to absorb, but still spin at w or vprecession Ephoton=hvphoton=DE=rhB0/2p=hvprecession And now, the spin jump to the higher energy ( from m=1/2m= – 1/2) (2) All of the individual nuclear magnetic moments become phase coherent, and the net M process around the z axis at a angel M z=Mcosa Mxy=Msina. m= –1/2 m= 1/2

  25. What happen after irradiation ceases • After irradiation ceases, not only do the population of the states revert to a Boltzmann distribution, but also the individual nuclear magnetic moments begin to lose their phase coherence and return to a random arrangement around the z axis. • (NMR spectroscopy record this process!!) • This process is called “relaxation process” • There are two types of relaxation process : T1(spin-lattice relaxation) & T2(spin-spin relaxation)

  26. Relaxation processes • How do nuclei in the higher energy state return to the lower state? • Emission of radiation is insignificant because the probability of re- emission of photons varies with the cube of the frequency. At radio frequencies, re-emission is negligible. • Ideally, the NMR spectroscopist would like relaxation rates to be fast - but not too fast. • If the relaxation rate is fast, then saturation is reduced. If the relaxation rate is too fast, line-broadening in the resultant NMR spectrum is observed. • There are two major relaxation processes; • Spin - lattice (longitudinal) relaxation • Spin - spin (transverse) relaxation

  27. T1(the spin lattice relaxation) • How long after immersion in a external field does it take for a collection of nuclei to reach Boltzmann distribution is controlled by T1, the spin lattice relaxation time. • (major Boltzmann distribution effect) • Lost of energy in system to surrounding (lattice) as heat • ( release extra energy) • It’s a time dependence exponential decay process of Mz components • dMz/dt=-(Mz-Mz,eq)/T1

  28. dephasing • T2(the spin –spin relaxation) • This process for nuclei begin to lose their phase coherence and return to a random arrangement around the z axis is called spin-spin relaxation. • The decay of Mxy is at a rate controlled by the spin-spin relaxation time T2. • dMx/dt=-Mx/T2 • dMy/dt=-My/T2

  29. Alcohols, protons a to ketones Aromatics Amides Acids Aldehydes Olefins Aliphatic ppm 15 10 7 5 2 0 TMS NMR Parameters  Chemical Shift • The chemical shift of a nucleus is the difference between the resonance frequency of the nucleus and a standard, relative to the standard. This quantity is reported in ppm and given the symbol delta, • = (n - nREF) x106 / nREF • In NMR spectroscopy, this standard is often tetramethylsilane, Si(CH3)4, abbreviated TMS, or 2,2-dimethyl-2-silapentane-5-sulfonate, DSS, in biomolecular NMR. • The good thing is that since it is a relative scale, the d for a sample in a 100 MHz magnet (2.35 T) is the same as that obtained in a 600 MHz magnet (14.1 T). Deshielded(low field) Shielded (up field)

  30. The NMR scale (d, ppm) • We can use the frequency scale as it is. The problem is that • since Bloc is a lot smaller than Bo, the range is very small • (hundreds of Hz) and the absolute value is very big (MHz). • We use a relative scale, and refer all signals in the spectrum • to the signal of a particular compound. • The good thing is that since it is a relative scale, the din a • 100 MHz magnet (2.35 T) is the same as that obtained for • the same sample in a 600 MHz magnet (14.1 T). C H 3 H C i C H 3 3 C H 3 w - wref d = ppm (parts per million) wref S

  31. Tetramethyl silane (TMS) is used as reference because it is soluble in most organic solvents, inert, volatile, and has 12 equivalent 1Hs and 4 equivalent 13Cs: Other references can be used, such as the residual solvent peak, dioxane for 13C, etc. What reference we use is not critical, because the instrument (software/hardware) is calibrated internaly. Don’t use them if you don’t need to...

  32. HO-CH2-CH3 high field low field wo w0=rBeffect Notice that the intensity of peak is proportional to the number of H

  33. three-bond one-bond 1 H 1 3 C J (Hz) bb 1 1 H H I S ab ba S I I S aa  J-coupling • Nuclei which are close to one another could cause an influence on each other's effective magnetic field. If the distance between non-equivalent nuclei is less than or equal to three bond lengths, this effect is observable. This is called spin-spin coupling or J coupling. • Each spin now seems to has two energy ‘sub-levels’ depending on the state of the spin it is coupled to: • The magnitude of the separation is called coupling constant (J) and has units of Hz.

  34. N neighboring spins: split into N + 1 lines Single spin: One neighboring spins: - CH – CH - Two neighboring spins: - CH2 – CH - • From coupling constant (J) information, dihedral angles can be derived ( Karplus equation) Cγ χ2 Cβ χ1 Cα N ω ψ Ψ N C’

  35. bb W1I W1S W2IS ab ba W0IS W1I W1S aa  Nuclear Over Hauser Effect (NOE) • The NOE is one of the ways in which the system (a certain spin) can release energy. Therefore, it is profoundly related to relaxation processes. In particular, the NOE is related to exchange of energy between two spins that are not scalarly coupled (JIS = 0), but have dipolar coupling. • The NOE is evidenced by enhancement of certain signals in the spectrum when the equilibrium (or populations) of other nearby are altered. For a two spin system, the energy diagram is as following: • W represents a transition probability, or the rate at which certain transition can take place. For example, the system in equilibrium, there would be W1I and W1S transitions, which represents single quantum transitions.

  36. INSTRUMENTATION 1. MAGNET Permanent magnets Conventional electromagnets and Super conducting magnets 2. SAMPLE PROBE 3. FIELD SWEEP GENARETOR 4. THE RADIO FREQUENCY SOURCE 5. THE SIGNAL DETECTOR& RECORDER SYSTEM

  37. The spectrometer

  38. N S Preparation for NMR Experiment • Sample preparation • Which buffer to choose? Isotopic labeling? • Best temperature? • Sample Position ? 2. What’s the nucleus or prohead? Anucleus with an even mass A and even charge Z  nuclear spin I is zero Example: 12C, 16O, 32S  No NMR signal A nucleus with an even mass A and odd charge Z  integer value I Example: 2H, 10B, 14N  NMR detectable A nucleus with odd mass A  I=n/2, where n is an odd integer Example: 1H, 13C, 15N, 31P  NMR detectable

  39. Tune Match RCVR 0% Absorption 100% Frequency 3. The best condition for NMR Spectrometer?  Wobble : Tune & Match & Shimming 4. What’s the goal?  Which type of experiment you need? Different experiments will result in different useful information

  40. 5. NMR Data Processing • The FID (free induction decay) is then Fourier transform to frequency domain to obtain vpression ( chemical shift) for each different nuclei. Time (sec) frequency (Hz)

  41. roperties of Some Deuterated NMR Solvents

  42. Limitations of nmr spectroscopy 1.Its lack of sensitivity. fairly large numbers are requried.minimum sample size is about0.1ml having minimum concentrations of about on1% 2.Limited number of nuclei which may be usefully studied with this technique. 3.Inmost of the cases ,the technique is limited to liquid samples or to a liquid capable of solutions in a suitable solvents or of melting at a temperature below 260oc 4.In some compounds two different types of hydrogen atoms resonance at similar resonance frequencies .this results in an overlap of spectra .hence the interpretation of spectra becomes difficult.

  43. APPLICATIONS 1.determination of optical purity 2.study of molecular interactions 3.quantative analysis: assay components, surfactant chain length Determination, hydrogen analysis, iodine value, moisture analysis 4.elemental analysis 5.Multicomponentmixture analysis 6.magnetic resonance imaging 7. NMR has also been used in various special fields that includes industrial quality control, biology, engineering and medicine 8.Structure elucidation

  44. other applications • Molecular conformation in solution Quantitative analysis of mixtures containing known compounds Determining the content and purity of a sample Through space connectivity (over Hauser effect) Chemical dynamics (Line shapes, relaxation phenomena) Solid State NMR is widely popular for the characterization of polymers, rubbers, ceramics,  and molecular sieves.

  45. Thank you

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