Deuterium contains one neutron and one proton. The electron rest mass is replaced with that of the proton. The electron has a mass that is approximately 1/1836 that of the proton. One dalton is approximately the mass of one a single proton or neutron. The lightest baryons are the proton and the neutron. Another difficulty was the difference in masses of the electron and the proton. Neutrons are neutral particles having a mass slightly greater than that of the proton. The nucleus consists of a proton and four neutrons. Omeprazole is a selective and irreversible proton pump inhibitor. H consists of a proton and six neutrons. For example, the charges of a proton and antiproton must sum to exactly zero. Most use a combination of two antibiotics and a proton pump inhibitor. Stepwise dissociation constants are each defined for the loss of a single proton. Velocity-encoded MRI is based on the detection of changes in the phase of proton precession. The formyl proton itself does not readily undergo deprotonation.