{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,14]],"date-time":"2026-05-14T03:32:18Z","timestamp":1778729538898,"version":"3.51.4"},"reference-count":32,"publisher":"Wiley","issue":"8","license":[{"start":{"date-parts":[[2004,2,1]],"date-time":"2004-02-01T00:00:00Z","timestamp":1075593600000},"content-version":"vor","delay-in-days":9680,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Biopolymers"],"published-print":{"date-parts":[[1977,8]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>We have monitored the helix\u2010coil transition of the self\u2010complementary <jats:italic>d<\/jats:italic>\u2010CpCpGpG and <jats:italic>d<\/jats:italic>\u2010GpGpCpC sequences (20m<jats:italic>M<\/jats:italic> strand concentration) at the base pairs, sugar rings, and backbone phosphates by 360\u2010MHz proton and 145.7\u2010MHz phosphorus nmr spectroscopy in 0.1<jats:italic>M<\/jats:italic> phosphate solution between 5 and 95\u00b0C. The guanine 1\u2010imino Watson\u2010Crick hydrogen\u2010bonded protons, characteristic of the duplex state, are observed below 10\u00b0C, with solvent exchange occurring by transient opening of the tetranucleotide duplexes. The cytosine 4\u2010amino Watson\u2010Crick hydrogen\u2010bonded protons resonate 1.5 ppm downfield from the exposed protons at the same position in the tetranucleotide duplexes, with slow exchange indicative of restricted rotation about the C\u2010N bond below 15\u00b0C. The guanine 2\u2010amino exchangeable protons in the tetranucleotide sequence exhibit very broad resonances at low temperatures and narrow average resonances above 20\u00b0C, corresponding to intermediate and fast rotation about the C\u2010N bond, respectively. Solvent exchange is slower at the amino protons compared to the imino protons since the latter broaden out above 10\u00b0C. The well\u2010resolved nonexchangeable base proton chemical shifts exhibit helix\u2010coil transition midpoints between 37 and 42\u00b0C. The transition midpoints and the temperature dependence of the chemical shifts at low temperatures were utilized to differentiate between resonances located at the terminal and internal base pairs while the H\u20105 and H\u20106 doublets of individual cytosines were related by spin decoupling studies. For each tetranucleotide duplex, the cytosine H\u20105 resonances exhibit the largest chemical shift change associated with the helix\u2010coil transition, a result predicted from calculations based on nearest\u2010neighbor atomic diamagnetic anisotropy and ring current contributions for a B\u2010DNA duplex. There is reasonable agreement between experimental and calculated chemical shift changes for the helix\u2010coil transition at the internal base pairs but the experimental shifts exceed the calculated values at the terminal base pairs due to end\u2010to\u2010end aggregation at low temperatures. Since the guanine H\u20108 resonances of the CpCpGpG and <jats:italic>d<\/jats:italic>\u2010CpCpGpG sequences exhibit upfield shifts of 0.6\u20130.8 and &lt;0.1 ppm, respectively, on duplex formation, these RNA and DNA tetranucleotides with the same sequence must adopt different base\u2010pair overlap geometries. The large chemical shift changes associated with duplex formation at the sugar H\u20101\u2032 triplets are not detected at the other sugar protons and emphasize the contribution of the attached base at the 1\u2032 position. The coupling sum between the H\u20101\u2032 and the H\u20102\u2032 and H\u20102\u2033 protons equals 15\u201317 Hz at all four sugar rings for the <jats:italic>d<\/jats:italic>\u2010CpCpGpG and <jats:italic>d<\/jats:italic>\u2010GpGpCpC duplexes (25\u00b0C), consistent with a C\u20103\u2032 exo sugar ring pucker for the deoxytetranucleotides in solution. The temperature dependent phosphate chemical shifts monitor changes in the \u03c9,\u03c9\u2032 angles about the O\u2010P backbone bonds, in contrast to the base\u2010pair proton chemical shifts, which monitor stacking interactions.<\/jats:p>","DOI":"10.1002\/bip.1977.360160804","type":"journal-article","created":{"date-parts":[[2005,5,27]],"date-time":"2005-05-27T16:22:00Z","timestamp":1117210920000},"page":"1635-1656","source":"Crossref","is-referenced-by-count":46,"title":["<i>d<\/i>\u2010CpCpGpG and <i>d<\/i>\u2010GpGpCpC self\u2010complementary duplexes: Nmr studies of the helix\u2010coil transition"],"prefix":"10.1002","volume":"16","author":[{"given":"Dinshaw J.","family":"Patel","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2004,2]]},"reference":[{"key":"e_1_2_1_2_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi00708a025"},{"key":"e_1_2_1_3_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi00693a012"},{"key":"e_1_2_1_4_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0006-291X(74)80395-5"},{"key":"e_1_2_1_5_2","doi-asserted-by":"publisher","DOI":"10.1002\/bip.1976.360150310"},{"key":"e_1_2_1_6_2","doi-asserted-by":"publisher","DOI":"10.1111\/j.1749-6632.1973.tb15259.x"},{"key":"e_1_2_1_7_2","volume-title":"High Resolution NMR of Macromolecules","author":"Bovey F. 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