1H and 13C NMR Spectroscopy of Stereoisomeric 2′-deoxy-C-Nucleosides

Eleven furanosyl 2′-deoxy-C-nucleosides with β-D-erythro, α-D-erythro and β-D-threo configurations have Been studied by IH and ¹³C NMR spectroscopy recorded in CDC1₃ and/or DMSO-d ₆. Results obtained indicate that each of the three stereoisomeric configurations studied are identifiable by ¹H and ¹³C NMR spectroscopy using a combination of coupling constant and chemical shift criteria.     

1H, 13C and 29Si NMR study of α- and β-silylstyrenes and their adducts with dichlorocarbene

¹H, ¹³C and ²⁹Si NMR spectra for the α- and β-silylstyrenes (E)-PhCHCHSiR₃ (I) and PhC(SiR₃)CH₂ (II) (R = Cl, Me, Ph), and those for some dichlorocarbene adducts of I and II (R = Me, Ph), were examined. From the ¹³C NMR data, the phenyl substituent in the molecules I and II enhances the electronic effects of the organosilicon substituent at Cα, and weakens these effects on the C_α resonance. The degree to which polarization of the vinyl CC bond is polarized increases with increased electron-withdrawing properties of substituent R in the SiR₃ group in compounds I and II, and correlates with the reduced reactivity of the bond toward electrophilic dichlorocarbene. Several long-range coupling constants (CC) in the molecules I, II and in their adducts with :CCl₂ were measured. The estimated CC is a useful aid for the study of electronic effects in organosilicon compounds.     

Deuterium quantification through deuterium-induced remote 1H and 13C NMR shifts

Partial labeling by deuterium may be quantified through simple integrations of those (1)H (200 or 400?MHz) and (13)C (100.6?MHz) NMR resonances that are split into pairs by chemical shifts (n)Δ = δ(deuterated) - δ(nondeuterated) as induced by deuterium across n>2 chemical bonds. The relative intensities of the two components of a pair are shown to be influenced to practically equal degrees by relaxation effects, so that a deuterium fraction may be determined from (1)H and (13)C integral pairs at more remote molecular positions under the routine conditions of fast accumulative spectral acquisition.     

13C NMR of carbonyl compounds -4. Solution conformation of β-ionone and related dienones

The steric factors relevant for the conformations of β-ionone and structurally related compounds were studied by dynamic n.m.r. and ¹H,¹H-NOE measurements.     

Structural characterization and diffusional analysis of the inclusion complexes of fluoroadamantane with β-cyclodextrin and its derivatives studied via 1H, 13C and 19F NMR spectroscopy

This research conducts method development to study the diffusions of β-cyclodextrin and its derivatives (collectively called β-CDs) in biological systems. We proposed using fluoroadamantane (FA) β-CD inclusion complexes as a model system to study the diffusion of β-CDs by using ¹⁹F self-diffusion NMR technique. The use of ¹⁹F signal over ¹H signal arises from the advantage of being able to avoid the interference of ¹H signals from biological molecules and water. Another benefit of using FA is that the ¹⁹F relaxation times are not significantly influenced by viscous biological solutions due to the tumbling nature of FA in β-CD cavities. To synthesize the FA β-CD inclusion complexes, a FA THF (tetrahydrofuran) solution and a β-CD water solution were mixed together followed by lyophilization. The formation of the inclusion complexes in water were determined using HMQC and ROESY NMR experiments with the assistance of molecular modeling. To assess the method, both ¹H and ¹⁹F diffusion NMR were carried out to study the diffusions of four typical FA β-CD inclusion complexes. The results of this study illustrate that the diffusion coefficients obtained from the FA ¹⁹F signal truly measure those of the β-CDs’ diffusion coefficients in water. Thus, the proposed technique using our model system is valid to be used to study the diffusions of β-CDs in biological systems.     

Complexation of inorganic anions by β-cyclodextrin studied by polarography and 1H NMR

Abstract

Complexation of o-chloronitrobenzene with β-cyclodextrin has been studied in 0.1 M aqueous solutions containing PF₆ ^?, ClO₄ ^?, C₂O₄ ^2-, SCN^?, SO₄ ^2- and F^? anions by a polarographic method. Using an equation which takes account of the change in the cyclodextrin concentration due to the simultaneous complexation of the anion, both stability constants have been calculated. Interaction of the ClO₄ ^? anion with β-cyclodextrin has been confirmed by ¹H NMR techniques. It has been found that the ClO₄ ^? anion is trapped in the β-cyclodextrin cavity. The stability constant has been calculated. Results of polarographic and ¹H NMR studies have been compared.     

(1)H and (13)C NMR studies of asymmetrically substituted bis- and tris-Tröger's bases

The (1)H and (13)C NMR spectra of two stereoisomeric bis-Tr?ger's bases and four stereoisomeric tris-Tr?ger's bases asymmetrically substituted on the external aromatic rings were recorded and the corresponding signals assigned. The relative configuration of the stereogenic units has been unequivocally determined on the basis of homoallylic couplings and NOE experiments.     

Characterization of β-cyclodextrin inclusion complex with procaine hydrochloride by 1H NMR and ITC

The inclusion of local anesthetic drug procaine hydrochloride by β-cyclodextrin was investigated by 1D and 2D proton NMR spectroscopy and isothermal titration calorimetry (ITC) at 298 K. The stoichiometry of the complex was determinate by the method of continuous variation, using the chemical induced shift of both host and guest protons. The association constant K, of the obtained complex was calculated and found to be 293.17 M^?1. Rotating frame NOE spectroscopy, was used to ascertain the solution geometry of the host–guest complex. The result reveals that the procaine molecule penetrates into the β-cyclodextrin cavity with the aromatic ring. The energetics of complexation process is investigated by ITC technique. The analysis indicates that the complexation of procaine by β-CD is an exothermic process and show that both enthalpy and entropy contribute to the binding process. The obtained value for the association constant is in good agreement with that obtained from NMR.     

Trimethylsilylation - Aid in NMR Analysis of Oligosaccharides. Assigment of 29Si and 13C NMR Spectra of Trimethylsilylated Methyl β-D-Xylobiosides by 2D NMR

The ¹H, ¹³C and ²⁹Si NMR spectra of methyl β-D-xylopyranoside and three methyl β-D-xylopyranosyl-β-D-xylopyranosides have been measured and assigned by two-dimensional NMR spectroscopy. According to the determined proton-proton coupling constants, the ring conformer ratio is essential ly the same in the studied compounds. The assigned chemical shifts provide correct substituent chemical shifts for assignments in the spectra of higher trimethylsilylated xylooligosaccharides. Heteronuclear chemical shift correlated 2D NMR spectroscopy is proven to be a usable experimental method for ²⁹Si NMR line assignment in carbohydrates. The assigned silicon shifts identify the site of glycosidation.     

~1H and ~(13)C NMR studies of TTHA complexes with diamagnetic rare earth ions

TTHA complexes with diamagnetic rare earth ions (La3+, Y3+ and Lu3+) were studied by 1H and 13C NMR spectroscopy. A symmetric structural model was suggested for La(TTHA) complex and an asymmetric model for Y(TTHA) and Lu(TTHA) complexes. The complex formation was dependent on the pH value of the solution. The interactions of La(TTHA) with the additional metal ions (La3+, Y3+ and Ca2+) were relatively weak, but relatively strong for that of Lu(TTHA) with the additional Lu3+.     

13 NMR Spectra of Functionally Substituted 3β-Chloroderivatives of Cholesterol and β-Sitosterol

¹³ C NMR spectra were studied and signals were assigned for C atoms of steroids 1-7     

Calculations of 13C NMR chemical shifts and F–C coupling constants of ciprofloxacin

Ciprofloxacin is a widely used fluoroquinolone antibiotic. In this work, a comprehensive evaluation of MP2 and DFT with different functionals and basis sets was carried out to select the most suitable level of theory for the study of the NMR properties of ciprofloxacin. Their relative predictive capabilities were evaluated comparing the theoretically predicted and experimental spectral data. Our computational results indicated that in contrast to the solid state, the molecule of ciprofloxacin does not exist as a zwitterion in gaseous state. The results of the calculations of the chemical shifts most close to the experimental were obtained with B3LYP/aug-cc-pVDZ. The F–C coupling constants were calculated systematically with different DFT methods and several basis sets. In general, the calculations of the coupling constants with the BHandH computational method including the applied in this work 6-311++G**, EPRII, and EPRIII basis sets showed a good reproducibility of the experimental values of the coupling constants.     

Thermodynamic and 13C NMR Studies of the Inclusion Complexes of α- and β-Cyclodextrins with Cyano- and Nitrophenols in Aqueous Solution

Equilibrium constants for the formation of 1 : 1 inclusioncomplexes of -cyclodextrin (-CD) with neutral and anionic phenol derivatives (3- and 4-cyanophenols and 3- and 4-nitrophenols) have been evaluated at 5, 12, 25, and 35 °C by means of spectrophotometry. Similarly, the equilibrium constants have been determined for the inclusion complexes of-cyclodextrin (-CD) with the phenols. Enthalpy and entropy changes for the formationof the inclusion complexes have been estimated from the temperature dependences of theequilibrium constants. With -CD, the enthalpy andentropy changes for the anionic species have been found to be more negative than those for the neutral ones, except for 4-cyanophenol, suggesting that the inclusion complexes of the anionic species are more rigid than those of the neutral species. From analyses of chemical shift differences in ¹³C NMR spectra of 3- and 4-cyanophenolsand 3- and 4-nitrophenols in aqueous solutions with and without CDs, a nitro ora cyano group has been found to be first bound to the - and -CD cavities.     

1H NMR and UV spectroscopic study of inclusion complex formation between pyridoxine and β- and γ-cyclodextrins

Inclusion complex formation between pyridoxine and - and -cyclodextrins in aqueous solution has been investigated by¹H NMR and UV spectroscopy. Both complexes exhibited a 1:1 stoichiometry and the inclusion process has been shown to perturb the equilibrium between the lactim and the lactam tautomer of pyridoxine, with a preferential inclusion of the former, less polar tautomer.     

13C NMR Spectroscopy on the Complexation of α-Cyclodextrin with 1-Alkanols and 1-Alkanoate Ions

Binding constants for -cyclodextrin ( -CD) complexes with 1- alkanols and 1- alkanoate ions were determined by analyzing changes ( ) in chemical shifts of guest ¹³C NMR signals with -CD concentration. The guests gave well-separated ¹³C NMR signals. The curve-fitting analyses of for individual carbons upon assumption of a simple 1:1 complexation gave virtually the same binding constants (K₁) in the cases of guests with relatively short alkyl chains, such as 1-propanol, 1-butanol, 1- pentanol , 1- butanoate , 1- pentanoate , and 1-hexanoate. However, thus obtained individual K₁ values were significantly different from one another, when the guests had relatively long alkyl chains such as 1- hexanol , 1- heptanol , and 1-octanoate. In these guests, satisfactorily consistent K₁ values were obtained by the curve-fitting analyses of for individual carbons upon an assumption that not only 1:1 but also 2:1 (host:guest) complexation occurs.     

Determination of the geometry of acetoxyendiynes and acetoxyenynes by NMR heteronuclear 13C?1H scalar couplings and 13C NMR chemical shifts. Structural assignment of the oxylipin natural products peyssonenynes A and B

Solution NMR methods were used for the structural characterization of the acetoxyendiyne E/Z configuration of the marine natural products peyssonenynes A and B and their synthetic analogs derived from palmitic acid. The scarcity of protons in the proximity of the olefin precluded the determination of the double bond geometry using ¹H NMR methods that rely on proton–proton scalar couplings or experiments such as NOESY or ROESY. Long range ¹H? ¹³C heteronuclear scalar couplings, ⁿJ_CH, measured with the 2D excitation sculptured indirect detection experiment (EXSIDE) proved useful and highly reliable for the analysis of the enol acetate geometry. In addition, it was found that the chemical shift of some carbon atoms in the proximity of the olefin was also sensitive to the double bond configuration of these molecules providing an even simpler way to determine their geometry. This protocol showed its robustness by similar analysis of simpler silyl‐protected acetoxyenynes derived from fatty acids. These NMR experimental results and stereochemical predictions were rationalized by DFT calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural Features of the β-CD Complexes with Naringin and its Dihydrochalcone and Aglycon Derivatives by 1H NMR

The -CD inclusion complexes of naringin 1, naringin dihydrochalcone 2 and the aglycon of naringin dihydrochalcone 3 have been investigated by ¹H NMR spectroscopy. Continuous variation plots show the stoichiometry of all complexes to be 1 : 1. Thestructure of complexes was determined from 2D ROESY and 1D ROE experiments. For 1 and 2 the inclusion involves the aromatic rings leaving the disaccharide unit -L-Rha-(1-2)--D-Glc outside the -CD cavity. For naringin 1 the inclusion occurs preferentially from the wider rim of the -CD truncated cone with the terminal phenolic ring deeply inserted into the -CD cavity while for naringin dihydrochalcon 2 it occurs from the side of the -CD narrower rim. The -CD/aglycon 3 complex exists as an equilibrium of the two inclusion modes.     

Surface Tension and 1H NMR Studies on Inclusion Complexes of β-Cyclodextrin with Sodium Alkyl Sulfonate

The inclusion complexes of -CD with sodium octylsulfonate (C8As), sodium dodecyl sulfonate (C12As), andsodium hexadecyl sulfonate (C16As) in aqueous solutions havebeen studied by surface tension measurement at the air/water interfaceand 1H NMR spectroscopy at 323 K.At fixed concentrations of the surfactants, the surface tensions firstincrease with the increase of -CD concentrations,then they attain a maximum. The surface tension curves of the surfactantsin the presence of -CD are higher than those in the absence of-CD. The values increase with increasing -CD concentrations foreach surfactant. The apparent critical micelle concentrations (CMC) of thesurfactants vary linearly with -CD concentrations.A 1H NMR study shows that the signals of theinner H-3 and H-5 of -CDshift upfield upon addition of the surfactants.The magnitude of the chemicalshift changes (= CD obs)varies as a functionof the concentrations of the surfactants. From therelationships between the chemicalshift changes of H-3 or H-5 inside the -CD cavityand guest/host molar ratios, a 1:1 stoichiometry foreach inclusion complex is assumed. The associationconstants of the inclusion complexes have beendetermined by 1H NMR spectroscopy.