A nuclear magnetic double‐resonance method for the determination of chemical exchange rates has been developed. The method is applicable to systems in which a nuclear spin is reversibly transferred between two nonequivalent sites, A and B. The lifetime (τA) and spin—lattice relaxation time (T1A) in Site A are obtained through the study of the decay to a new equilibrium value of Signal A upon the sudden saturation of Signal B. The converse experiment permits the determination of τB and T1B. A number of data for cross checks are furthermore obtained through the study of the recovery of the signals upon the release of various combinations of saturating rf fields.A simple theory based on the Bloch equations as modified by McConnell to incorporate the effects of chemical exchange is given. Experimental results on the hydroxyl proton exchange in the system salicylaldehyde and 2‐hydroxyacetophenone are well described by this simple theory.The present method, which can readily be extended to systems with several ...

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Study of Moderately Rapid Chemical Exchange Reactions by Means of Nuclear Magnetic Double Resonance

Measurements of the nuclear relaxation in water are reported. The transverse relaxation rate (1/T2) of the proton resonance is pH dependent. The effect is shown to be due to a spin‐spin splitting of the proton resonance by O17 (spin 5/2), which is only partially averaged out by proton exchange. The increase of relaxation rate is observable in natural water (0.037% O17), and becomes very appreciable in water enriched in O17. Additional information can be obtained by measuring relaxation rates in the presence of an rf field H1, using a method due to Solomon. A study of the width of the O17 resonance as a function of pH is in quantitative agreement with the results of the proton resonance. The observations provide a direct determination of the rate constants of the exchange reactions: H2O+H3O+→ lim k1H3O++H2O and H2O+HO−→ lim k2HO−+H2O. It is found that k1=(10.6±4)×109 liter mole−1 sec−1 and k2=(3.8±1.5)×109 liter mole−1 sec−1. The spin‐spin interaction between H and O17 in water is determined as 92±15 cps. In the Appendices, theoretical equations for the exchange contribution to the relaxation rate are derived.

Nuclear magnetic resonance study of the proton transfer in water

It is shown that multiple quantum N.M.R. allows straightforward identification of networks of scalar coupled spins. The information obtained is particularly useful for the identification of magnetic equivalence when multiplet splittings are not fully resolved. The interpretation of multiple quantum spectra is based on a set of simple selection rules which restrict coherence transfer between multiple quantum and single quantum transitions.

Analysis of networks of coupled spins by multiple quantum N.M.R.

An image formation method, using nuclear magnetic resonance techniques, has been developed which provides direct and detailed information on the interior details of heterogeneous samples. Time‐dependent magnetic field gradients are used to limit and control the region of spatial sensitivity of a standard pulsed NMR spectrometer. A continuous string of intense phase‐alternated rf pulses is used to provide a continuous monitor of the nuclear magnetization. The image is produced by directly plotting the phase‐detected resonance signal on a xy plotter as the limited region of spectrometer sensitivity is scanned through the sample. An analysis of the method in terms of the phenomenological Bloch equations, a description of the experimental method, and a representative selection of images are presented. A spatial resolution of about 0.3 mm has been achieved.

Image formation by nuclear magnetic resonance: The sensitive‐point method

A theoretical treatment of nuclear‐magnetic double‐irradiation experiments is given which is applicable to two groups of nuclei of arbitrary spin, either of different nuclear species or in a situation where the chemical shift is large in comparison with the spin‐coupling constant. A convention is introduced whereby the group which experiences the ``strong'' rf field H2 is given the symbol X, while the group to be investigated is represented by A. Particular attention is given to groups of spin ½ nuclei in AnXm type molecules where m, n≤3, and their spin‐decoupling behavior is presented in graphical form. Good correlations are observed with the experimental proton double‐resonance spectra of acetaldehyde, diethyl succinate, and 1,1,2 trichloroethane. When a single X transition is irradiated with a very weak H2 a splitting of the A spin‐multiplet lines into submultiplets is observed; at the same time an Overhauser‐type redistribution of intensities may occur in certain molecules. Intermediate strengths of H...

Influence of a Second Radiofrequency Field on High‐Resolution Nuclear Magnetic Resonance Spectra

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Nuclear Magnetic Resonance Spectra of Some Hydrocarbons.

An object surrounded by media of differing acoustical impedances (e.g., an anatomical organ surrounded by other kinds of tissue within the human body) is acoustically imaged by an array of ultrasonic transducers affixed to the outer surface of an ultrasonic lens. In a preferred embodiment, the lens is homocentric, with the common center of curvature of the inner and outer surfaces of the lens being located at a relatively small acoustic aperture in the body so that object points distributed over a relatively large solid angle from the aperture can be imaged with minimum lens aberations. Where the object to be imaged is a human heart, the acoustic aperture is most conveniently located at an intercostal space between adjacent ribs.

Lens system for acoustical imaging

A resonant coil for nuclear magnetic spectroscopy and microscopy is provided, in which the coil is in the form of nested, interrupted loops of a conductive material forming a distributed inductive element and having a plurality of capacitive elements with capacitance distributed over the periphery of the loops. The coil is preferably formed as a thin film of a superconductive material on an electrically nonconductive substrate.

Nuclear magnetic resonance probe coil

810,596. Gyromagnetic resonance apparatus. VARIAN ASSOCIATES. June 15, 1955, No. 17310/55. Class 37. [Also in Groups XVIII and XL (b)] Gyromagnetic resonance apparatus for analysis of materials comprises the known arrangement of a permanent magnet &c. for subjecting the materials to a unidirectional field, a coil for subjecting the materials to a radio-frequency field at right angles to the unidirectional field and a pick-up coil (not shown) having its maximum response to a field perpendicular to the two other fields together with means for integrating the signals due to gyro-magnetic resonance picked up by this coil. The integrated signal may be measured directly or indirectly. The system may be applied to the analysis of a water-oil mixture and to the determination of the moisture-content of flowing grain &c. Integrating and measuring circuit (Fig. 3). Meter 25 responsive to the potential difference between the anodes of triode valves 23, 24 is initially set to zero by means of potentiometer 27. The pulses due to gyro-magnetic resonance after amplification at 14 and integration in circuit 19, 21 upset the balanced condition of the valves 23, 24. Balance is restored by a further adjustment of 27, the new setting of which indicates the E.M.F. due to the precessing nuclei. Measuring moisture content (Figs. 3, 4, 5 and 7). In Fig. 4 measurement of gyromagnetic resonance is performed on flour in a diamagnetic (e.g. glass) hopper 32. In Fig. 5 galvanometer 25 (Fig. 3) is set to zero by resistor 27 while gyromagnetic resonance signals are being received from a standard sample 44. A suitable volume of test substance is then placed on top of sample 44 which moves against spring 46 and allows the test substance to come into the measuring position. Any further adjustment of potentiometer 27 needed to zeroize galvanometer 25 indicates the deviation of moisture content from the standard. In Fig. 7 the measurement is corrected for changes in density of the fluent material measured by a gamma-ray detector 58. Signals from the detector modify the bias and hence the gain of valve 66 in the path of the gyromagnetic resonance signals. Compensating for leakage signals in pick-up coil (Figs. 8 and 9 and Figs. 10, 11 (not shown). Triangular waves from sweep generator 85 vary the polarizing field and square waves from generator 84 are synchronized with the triangular waves as shown in Fig. 9 so that resonance points Ho occur when the square waves are at high level. The square wave output of generator 84 is transmitted to a relay 92 with two pairs of make and break contacts. The D.C. signal from cathode follower 88 is applied to integrator 89/91 and during high level of the square wave is a composite signal which consists of a component due to leakage flux from transmitter coil to pick-up coil and a component due to precessing nuclei in the substance under test. During low level of the square wave the signal from cathode follower 88 consists only of the leakage voltage. Throughout high level of the square wave, condenser 91 is in one connected direction and during low level, relay 92 changes over to reverse condenser 91. Thus the leakage voltage is subtracted from the composite signal so that the integrated signal is only that due to the precessing nuclei. The output from this flip-flop integrator may be connected to the null balancing circuit as shown in Fig. 3. The square wave and triangular wave frequencies may be the same so that two resonance points occur during each high level of the square wave, Fig. 10 (not shown). According to Fig. 11 (not shown) two integrator circuits are associated with the cathode follower 88 alternately and act differentially on the records so as to produce a nett output due only to the precessing nuclei. Specification 810,597 is referred to.

Weston A. Anderson

Papers

Nuclear Magnetic Resonance Spectra of Some Hydrocarbons.

Lens system for acoustical imaging

Nuclear magnetic resonance probe coil

Gyromagnetic resonance method and apparatus

Nuclear Resonance Saturation Effects and Multiple-Quantum Transitions