{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,21]],"date-time":"2025-10-21T00:37:35Z","timestamp":1761007055217,"version":"build-2065373602"},"reference-count":26,"publisher":"Wiley","issue":"8","license":[{"start":{"date-parts":[[2008,5,9]],"date-time":"2008-05-09T00:00:00Z","timestamp":1210291200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Magnetic Reson in Chemistry"],"published-print":{"date-parts":[[2008,8]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>Homogeneous hydrogenation of barbituric acid derivatives with parahydrogen yields a substantial increase of the <jats:sup>1<\/jats:sup>H NMR signals of the reaction products. These physiologically relevant compounds were hydrogenated at both ambient and elevated temperatures and pressures using a standard cationic rhodium catalyst. The resulting nonthermal nuclear spin polarization <jats:bold><jats:italic>(hyperpolarization)<\/jats:italic><\/jats:bold> is limited by the spin\u2013lattice relaxation time <jats:italic>T<\/jats:italic><jats:sub>1<\/jats:sub> of the corresponding nuclei in the products, being shorter than the time constant of the hydrogenation. The signal\u2010to\u2010noise ratio of the NMR spectra could be further increased upon signal averaging the antiphase PHIP signals of 25 successive scans following 30\u00b0 pulse experiments and a delay of 10 s. 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