Nitrogen-15 Nuclear Magnetic Resonance Study Research Articles

Colorimetric Sugar Sensing Using Boronic Acid-Substituted Azobenzenes.

In association with increasing diabetes prevalence, it is desirable to develop new glucose sensing systems with low cost, ease of use, high stability and good portability. Boronic acid is one of the potential candidates for a future alternative to enzyme-based glucose sensors. Boronic acid derivatives have been widely used for the sugar recognition motif, because boronic acids bind adjacent diols to form cyclic boronate esters. In order to develop colorimetric sugar sensors, boronic acid-conjugated azobenzenes have been synthesized. There are several types of boronic acid azobenzenes, and their characteristics tend to rely on the substitute position of the boronic acid moiety. For example, o-substitution of boronic acid to the azo group gives the advantage of a significant color change upon sugar addition. Nitrogen-15 Nuclear Magnetic Resonance (NMR) studies clearly show a signaling mechanism based on the formation and cleavage of the B–N dative bond between boronic acid and azo moieties in the dye. Some boronic acid-substituted azobenzenes were attached to a polymer or utilized for supramolecular chemistry to produce glucose-selective binding, in which two boronic acid moieties cooperatively bind one glucose molecule. In addition, boronic acid-substituted azobenzenes have been applied not only for glucose monitoring, but also for the sensing of glycated hemoglobin and dopamine.

Resolving the Regioregularity of Poly(N-n-hexyl-N'-phenylcarbodiimide) via Nitrogen-15 Labeling.

Nitrogen-15 nuclear magnetic resonance (NMR) spectroscopy and infrared spectroscopy (IR) were performed on an isotope-enriched poly(N-n-hexyl-N'-phenylcarbodiimide) to determine directly the connectivity and regioregularity of a polymer. Up to this point, the imine, C═N, IR stretch at 1660-1620 cm-1 was thought to be a sufficient handle to elucidate the presence or absence of a regioregular microstructure; however, recent findings cast some uncertainties when expanded to all polycarbodiimides. Therefore, an enriched 15N NMR study was undertaken to unambiguously resolve that a N-n-hexyl-N'-phenylcarbodiimide, when polymerized with a 2,2,2-trifluoroethoxide trichlorotitanium(IV) catalyst in chloroform, will produce a completely regioregular polymer. The only regioisomer present is the one in which the phenyl pendant group is positioned on the imino-nitrogen. The study was expanded to a chiral, (R)-BINOL-Ti(IV)-diisopropoxide catalyst which revealed no change in the regioisomer or the degree of regioregularity. In addition to 15N NMR spectra, the IR imine stretch exhibited isotope shifts for poly(N-n-hexyl-N'-phenylcarbodiimide) when labeled on both imino- and amino-nitrogen or solely the imino-nitrogen of ∼11 cm-1; however, no shift was manifested when labeling was restricted to the amino-nitrogen.

Urocanic Acid Photochemistry and Photobiology

Urocanic acid (2-propenoic acid, 3-[ lH-imidazol-4(5)-yl], UA)? is one of the smallest molecules to have stimulated global interest among biologists, environmentalists, photochemists, photobiologists, medicinal chemists and immunologists. Its history can be traced back more than a century to when it was first found in the urine of dogs (1). Interest in the molecule remained dormant until the middle of the century but rekindled in the late 1940s when it was detected in animal skin and sweat. This led to the proposal that UA acts as a natural sunscreen, possibly as a specific photoprotecting agent for DNA because of the overlap of the UA and DNA absorption spectra (2). Since 1983 there has been an explosive growth in UA research, primarily as a consequence of the proposal by De Fabo and Noonan (3) that the cis photoisomer (cUA) of trans-UA (tUA) could be responsible for the phenomenon of photoimmunosuppression. In a recent literature survey we found that about 25 research papers have appeared every year over the last decade involving UA. Several comprehensive reviews of the molecule's photobiology, photochemistry and photophysics have appeared (4-

A direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of lutetium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of lutetium(III)-isothiocyanate complex formation in aqueous solvent mixtures has been completed. At −100°C to −120°C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate1H,13C, and15N NMR signals for coordinated and free water and isothiocyanate ions. In the13C and15N spectra of NCS−, resonance signals for five complexes are observed over the range of concentrations studied. The13C chemical shifts of complexed NCS− varied from −0.5 ppm to −3 ppm from that of free anion. For the same complexes, the15N chemical shifts from free anion were about −11 ppm to −15 ppm. The magnitude and sign of the15N chemical shifts identified the nitrogen atom as the binding site in NCS−. The concentration dependence of the13C and15N signal areas, and estimates of the fraction of anion bound at each NCS−:Lu3+ mole ratio, were consistent with the formation of [(H2O)5Lu(NCS)]2+ through [(H2O)Lu(NCS)5]2−. Although proton and/or ligand exchange and the resulting bulk-coordinated signal overlap prevented accurate hydration number measurements, a good qualitative correlation of the water1H NMR spectral results with those of13C and15N was possible.

A nitrogen-15 nuclear magnetic resonance study of the tetracycline antibiotics

Natural abundance 15N NMR has been used to study several tetracycline antibiotics in the solid state and in solution. In the solid state, the 15N chemical shifts of the tetracycline free bases are sensitive to the site of protonation in the "A" ring. A high frequency shift of 14 ppm is observed for the keto form of oxytetracycline (N protonated) relative to the enol form of oxytetracycline (O protonated). Comparison of 15N chemical shifts in the solid and solution states indicates for the first time that the structural integrity (site of protonation and hence conformation) of the tetracyclines is maintained in (CD3)2SO solutions. In addition, the solid state 15N CP/MAS NMR spectra are sensitive to subtle conformational changes of the "A" ring amide substituent. Key words: antibiotics, tetracyclines, 15N NMR, molecular structure.

Lactoperoxidase-catalyzed oxidation of thiocyanate by hydrogen peroxide: nitrogen-15 nuclear magnetic resonance and optical spectral studies

To establish the agent(s) responsible for the activity of the lactoperoxidase (LPO)/SCN-/H2O2 system, the oxidation of thiocyanate with hydrogen peroxide, catalyzed by lactoperoxidase, has been studied by 15N NMR and optical spectroscopy at different concentrations of thiocyanate and hydrogen peroxide and at different pHs. The formation of hypothiocyanite ion (OSCN-) as one of the oxidation products correlated well with the activity of the LPO/SCN-/H2O2 system and was maximum when the concentrations of the H2O2 and SCN- were nearly the same and the pH was less than 6.0. At [H2O2]/[SCN-] = 1, OSCN- decomposed very slowly back to thiocyanate. When the ratio [H2O2]/[SCN-] was above 2, formation of CN- was observed, which was confirmed by 15N NMR and also by changes in the optical spectrum of LPO. The oxidation of thiocyanate by H2O2 in the presence of LPO does not take place at pH greater than 8.0. Since thiocyanate does not bind to LPO above this pH, the binding of thiocyanate to LPO is considered to be prerequisite for the oxidation of thiocyanate. Maximum inhibition of oxygen uptake by Streptococcus cremoris 972 bacteria was observed when hydrogen peroxide and thiocyanate were present in equimolar amounts and the pH was below 6.0.

Nitrogen-15 nuclear magnetic resonance studies on the tautomerism of 8-hydroxy-2'-deoxyguanosine, 8-hydroxyguanosine, and other C8-substituted guanine nucleosides

The favored tautomeric and ionic structures were examined for the oxidative DNA damage adduct 8-hydroxy-2'-deoxyguanosine and its RNA analogue 8-hydroxyguanosine by 15N NMR spectroscopy. In addition, 15N chemical shifts and coupling constants from 13 different guanine nucleosides, including a wide variety of C8 substitutions (OH, SH, Br, OCH2C6H5, OCH3, SCH3, and SO2CH3), have been analyzed with respect to their tautomeric structures. A -98.5-Hz proton-nitrogen coupling constant observed for the N7 resonance of 8-hydroxyguanosine in dimethyl sulfoxide was evidence for 8-keto substitution, which is contrary to the structure implied by the generally used nomenclature. The pH dependence of 15N NMR spectra of 8-hydroxyguanosine in aqueous solution showed downfield shifts of the N1 and N7 resonances that were greater than 50 ppm, which indicated the conversion from a neutral 6,8-diketo to a 6-enolate-8-keto (pKa1 = 8.6) and finally to a 6,8-dienolate structure (pKa2 = 11.7). There was no evidence of an 8-enol substituent in the absence of ionization. It is proposed that the syn conformation of these oxidized bases in duplex DNA and RNA can be further stabilized by abnormal hydrogen bonding or mispairing that involves N7-H. The combined data show that 15N NMR is a sensitive probe to examine tautomerism of the guanine ring system. The analysis indicates that the change from a single to a double bond for the C8 substituent, and the accompanying removal of the normal double bond between N7 and C8 on the imidazole ring system, has no detectable effect on the tautomerism at the N1-O6 site of the pyrimidine ring system for both the 8-keto and 8-thio substitutions. In addition, large differences in electronegativity of the C8 substituents do not alter the N1-O6 tautomerism.

Binding of thiocyanate to lactoperoxidase: proton and nitrogen-15 nuclear magnetic resonance studies

The binding of thiocyanate to lactoperoxidase (LPO) has been investigated by 1H and 15N NMR spectroscopy. 1H NMR of LPO shows that the major broad heme methyl proton resonance at about 61 ppm is shifted upfield by addition of the thiocyanate, indicating binding of the thiocyanate to the enzyme. The pH dependence of line width of 15N resonance of SC15N- in the presence of the enzyme has revealed that the binding of the thiocyanate to the enzyme is facilitated by protonation of an ionizable group (with pKa of 6.4), which is presumably distal histidine. Dissociation constants (KD) of SC15N-/LPO, SC15N-/LPO/I-, and SC15N-/LPO/CN- equilibria have been determined by 15N T1 measurements and found to be 90 +/- 5, 173 +/- 20, and 83 +/- 6 mM, respectively. On the basis of these values of KD, it is suggested that the iodide ion inhibits the binding of the thiocyanate but cyanide ion does not. The thiocyanate is shown to bind at the same site of LPO as iodide does, but the binding is considerably weaker and is away from the ferric ion. The distance of 15N of the bound thiocyanate ion from the iron is determined to be 7.2 +/- 0.2 A from the 15N T1 measurements.

Crystal Versus Solution Structures of Enzymes: NMR Spectroscopy of a Crystalline Serine Protease

The hydrogen-bonding status of His57 in the catalytic triad (Asp-His-Ser) of serine protease has important mechanistic implications for this class of enzymes. Recent nitrogen-15 nuclear magnetic resonance (NMR) studies of alpha-lytic protease find His57 and Ser195 to be strongly hydrogen-bonded, a result that conflicts with the corresponding crystallographic studies, thereby suggesting that the crystal and solution structures may differ. This discrepancy is addressed and resolved in a nitrogen-15 NMR study of the enzyme in the crystalline state. The results show that the His-Ser and Asp-His interactions are identical in crystals and solutions, but that in crystals His57 titrates with a pKa of 7.9, nearly one pKa unit higher than in solution. This elevated pKa accounts for the absence of the His-Ser hydrogen bond in previous x-ray studies.

Magnetic resonance spectral characterization of the heme active site of Coprinus cinereus peroxidase

Examination of the peroxidase isolated from the inkcap Basidiomycete Coprinus cinereus shows that the 42,000-dalton enzyme contains a protoheme IX prosthetic group. Reactivity assays and the electronic absorption spectra of native Coprinus peroxidase and several of its ligand complexes indicate that this enzyme has characteristics similar to those reported for horseradish peroxidase. In this paper, we characterize the H2O2-oxidized forms of Coprinus peroxidase compounds I, II, and III by electronic absorption and magnetic resonance spectroscopies. Electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) studies of this Coprinus peroxidase indicate the presence of high-spin Fe(III) in the native protein and a number of differences between the heme site of Coprinus peroxidase and horseradish peroxidase. Carbon-13 (of the ferrous CO adduct) and nitrogen-15 (of the cyanide complex) NMR studies together with proton NMR studies of the native and cyanide-complexed Coprinus peroxidase are consistent with coordination of a proximal histidine ligand. The EPR spectrum of the ferrous NO complex is also reported. Protein reconstitution with deuterated hemin has facilitated the assignment of the heme methyl resonances in the proton NMR spectrum.

ChemInform Abstract: HYDROGEN BONDING AND TAUTOMERIC EQUILIBRIA OF COMPLEXES OF PYRIDINE WITH VARIOUS PROTON DONORS. A NITROGEN‐15 NUCLEAR MAGNETIC RESONANCE STUDY

Chemischer InformationsdienstVolume 16, Issue 10 Article ChemInform Abstract: HYDROGEN BONDING AND TAUTOMERIC EQUILIBRIA OF COMPLEXES OF PYRIDINE WITH VARIOUS PROTON DONORS. A NITROGEN-15 NUCLEAR MAGNETIC RESONANCE STUDY E. HASLINGER, E. HASLINGERSearch for more papers by this authorM. SCHLEDERER, M. SCHLEDERERSearch for more papers by this authorW. ROBIEN, W. ROBIENSearch for more papers by this authorP. WOLSCHANN, P. WOLSCHANNSearch for more papers by this author E. HASLINGER, E. HASLINGERSearch for more papers by this authorM. SCHLEDERER, M. SCHLEDERERSearch for more papers by this authorW. ROBIEN, W. ROBIENSearch for more papers by this authorP. WOLSCHANN, P. WOLSCHANNSearch for more papers by this author First published: March 12, 1985 https://doi.org/10.1002/chin.198510091Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume16, Issue10March 12, 1985 RelatedInformation

Investigation of phase transitions in ammonium nitrate by nitrogen–15 nuclear magnetic resonance

Abstract Exploratory Nitrogen-15 nuclear magnetic resonance (NMR) studies of ammonium nitrate (AN) have been undertaken using both conventional and magic angle spinning (MAS) methods. The chemical shift anisotropy is measured by two different methods at room temperature, and a precise measurement of the difference in isotropic chemical shift occurring at the phase transition IV to III is reported. Finally, the activation energy for the motion of both ions in the room temperature phase are obtained. No evidence in discontinuity of nitrogen relaxation times across the phase boundary at 32°C was observed.

Wasserstoffbrückenbindung und Protonenübertragung in Komplexen zwischen Pyridin und verschiedenen Protonendonatoren. Eine Stickstoff-15-NMR-Untersuchung

Wasserstoffbrückenbindung und Protonenübertragung in Komplexen zwischen Pyridin und verschiedenen Protonendonatoren. Eine Stickstoff-15-NMR-Untersuchung

Carbon-13 and nitrogen-15 nuclear magnetic resonance study on the interacton between riboflavin and riboflavin-binding apoprotein

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGet e-AlertsCarbon-13 and nitrogen-15 nuclear magnetic resonance study on the interacton between riboflavin and riboflavin-binding apoproteinChrit T. W. Moonen, Willy A. M. Van den Berg, Marleen Boerjan, and Franz MuellerCite this: Biochemistry 1984, 23, 21, 4873–4878Publication Date (Print):October 9, 1984Publication History Published online1 May 2002Published inissue 9 October 1984https://doi.org/10.1021/bi00316a009© American Chemical SocietyRIGHTS & PERMISSIONSArticle Views86Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (809 KB) Get e-AlertsGet e-Alerts Biochemistry Get e-Alerts

ChemInform Abstract: CARBON‐13 AND NITROGEN‐15 NUCLEAR MAGNETIC RESONANCE STUDY OF 1H,3H‐PYRIMIDINE‐2,4,5,6‐TETRONE 5‐OXIMATO COMPLEXES AND THEIR 1,3‐DIMETHYL DERIVATIVES

Chemischer InformationsdienstVolume 15, Issue 8 Physical Organic Chemistry ChemInform Abstract: CARBON-13 AND NITROGEN-15 NUCLEAR MAGNETIC RESONANCE STUDY OF 1H,3H-PYRIMIDINE-2,4,5,6-TETRONE 5-OXIMATO COMPLEXES AND THEIR 1,3-DIMETHYL DERIVATIVES C. BREMARD, C. BREMARDSearch for more papers by this authorB. MOUCHEL, B. MOUCHELSearch for more papers by this authorS. SUEUR, S. SUEURSearch for more papers by this author C. BREMARD, C. BREMARDSearch for more papers by this authorB. MOUCHEL, B. MOUCHELSearch for more papers by this authorS. SUEUR, S. SUEURSearch for more papers by this author First published: February 21, 1984 https://doi.org/10.1002/chin.198408047AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue8February 21, 1984 RelatedInformation

ChemInform Abstract: NITROGEN‐15 AND BORON‐11 NUCLEAR MAGNETIC RESONANCE STUDIES OF TRIMETHYLAMINE ADDUCTS OF THE MIXED TRIHALIDES OF BORON

Chemischer InformationsdienstVolume 14, Issue 46 Physical Organic Chemistry ChemInform Abstract: NITROGEN-15 AND BORON-11 NUCLEAR MAGNETIC RESONANCE STUDIES OF TRIMETHYLAMINE ADDUCTS OF THE MIXED TRIHALIDES OF BORON J. M. MILLER, J. M. MILLERSearch for more papers by this author J. M. MILLER, J. M. MILLERSearch for more papers by this author First published: November 15, 1983 https://doi.org/10.1002/chin.198346051AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue46November 15, 1983 RelatedInformation

Carbon-13 and nitrogen-15 nuclear magnetic resonance study of 1H,3H-pyrimidine-2,4,5,6-tetrone 5-oximato complexes and their 1,3-dimethyl derivatives

Etude par spectrometrie RMN de 13 C et de 15 N de la 1H,3H-pyrimidine-tetrone-2,4,5,6 oxime-5, de ses derives anioniques et methyles, et de ses complexes avec Co(III), Fe(II) et Ru(II). Du 13 C enrichi et des molecules marquees a l'azote 15 sont utilises pour l'interpretation des spectres. L'influence de la protonation, et de la coordination au centre metallique, sur les parametres RMN, ainsi que les effets de l'isotope 15 N sont discutes

Nitrogen-15 and boron-11 nuclear magnetic resonance studies of trimethylamine adducts of the mixed trihalides of boron

Nitrogen-15 and boron-11 nuclear magnetic resonance studies of trimethylamine adducts of the mixed trihalides of boron

Nitrogen-15 nuclear magnetic resonance study of benzenesulfonamide and cyanate binding to carbonic anhydrase.

The binding of inhibitors, cyanate and benzenesulfonamide, to the active-site zinc of human carbonic anhydrase B was studied by ^(15)N nuclear magnetic resonance spectroscopy. The cyanate nitrogen resonance moved 34 ppm upfield on binding to the enzyme. The shielding is comparable to that reported for a zinc-isocyanate complex and strongly suggests complexation of cyanate to zinc through nitrogen. The proton-coupled ^(15)N resonance of the enzyme-bound benzenesulfonamide was a doublet. Hence, benzenesulfonamide is bound as C_6H_5SO_2NH-. The proton-decoupled ^(15)N resonance of the bound benzenesulfonamide was observed 17 ppm upfield of that of free enzenesulfonamide anion. A model ligand, 2-aminobenzenesulfonamide anion, undergoes binding of zinc through the sulfonamide nitrogen which results in an 11.8 ppm shielding of the ^(l5)N resonance. In contrast, N-( 2-aminophenyl)benzenesulfonamide, which is reported to bind zinc through an oxygen, has its sulfonamide nitrogen deshielded by 4.3 and 1.2 ppm on complexation of zinc to the neutral and anionic ligands, respectively. Thus, coordination to the nitrogen causes shielding and to the oxygen deshielding of the sulfonamide resonance. The observed shielding of the enzyme-bound sulfonamide resonance strongly suggests that benzenesulfonamide binds primarily to zinc through the sulfonamide nitrogen. The implications of these results for the high affinity of association of the inhibitor are discussed.

ChemInform Abstract: NATURAL ABUNDANCE NITROGEN‐15 NUCLEAR MAGNETIC RESONANCE STUDY OF AMINO ACIDS COORDINATED TO COBALT(III)

Chemischer InformationsdienstVolume 14, Issue 3 Physical Organic Chemistry ChemInform Abstract: NATURAL ABUNDANCE NITROGEN-15 NUCLEAR MAGNETIC RESONANCE STUDY OF AMINO ACIDS COORDINATED TO COBALT(III) N. JURANIC, N. JURANICSearch for more papers by this authorR. L. LICHTER, R. L. LICHTERSearch for more papers by this authorM. B. CELAP, M. B. CELAPSearch for more papers by this authorM. J. MALINAR, M. J. MALINARSearch for more papers by this authorP. N. RADIVOJSA, P. N. RADIVOJSASearch for more papers by this author N. JURANIC, N. JURANICSearch for more papers by this authorR. L. LICHTER, R. L. LICHTERSearch for more papers by this authorM. B. CELAP, M. B. CELAPSearch for more papers by this authorM. J. MALINAR, M. J. MALINARSearch for more papers by this authorP. N. RADIVOJSA, P. N. RADIVOJSASearch for more papers by this author First published: January 18, 1983 https://doi.org/10.1002/chin.198303071Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue3January 18, 1983 RelatedInformation