Inclusion complexes of 2-phenoxyethanol and alkoxyethanols in cyclodextrins: an 1H NMR study

The association in aqueous solutions of small amphiphilic molecules [2-phenoxyethanol, PhE₁, and some α-n-alkyl-ω-hydroxyoligo(oxiethylenes], C₄E₁, C₄E₂ and C₆E₂) with β-cyclodextrin (βCD), heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB) was investigated by ¹H NMR spectroscopy. The upfield shifts observed for the H3 and H5 NMR signals due to anisotropic shielding confirm that the host–guest associations are of inclusion type. The stoichiometries and the apparent inclusion constants, K _app, were determined by ¹H NMR spectroscopy using the H5 and H3 signals. The relative differences in the K _app values for βCD inclusion complexes seem to reflect the hydrophobic/hydrophilic balance of the guests. The K _app values for the PhE₁ inclusion complexes can be related to the degree of methylation and hydrophobicity variation within the considered hosts. In addition, a comparative study between βCD and TRIMEB inclusion complexes using 2D ROESY (Rotating-frame Overhauser Enhancement SpectroscopY) NMR spectra provides structural features for these complexes which are inaccessible by other experimental methods.     

Stereochemicai study of 7-aryl-1,7,8,8a-tetrahydro-3(2H)indolizinones by1H and13C NMR

Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by¹H and¹³C NMR. Complete assignment of¹H NMR signals and analysis of¹H-¹H coupling constants were performed using the iterative PANIC program. Values of³ J _6,7,³ J _7,8endo, and⁴ J _5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of¹³C NMR signals was performed on the basis of analysis of the¹³C-¹H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996.     

Application of HSQC in the delineation of NMR signals of E and Z isomers of octadecyl p‐coumarates

Octadecyl p‐coumarates undergo E–Z isomerization in daylight. Although ¹H NMR, ¹³C NMR and ¹H–¹H COSY gave indications about this isomerization, the overlapping of some signals in the ¹H NMR of aromatic region prevented the delineation of signals of the individual isomers. However, heteronuclear spin quantum coupling correlation (HSQC) with the unique feature of two sets of nearby δ_C–δ_H correlations gave conclusive evidence for this isomerization and helped in the delineation of ¹H NMR and ¹³C NMR signals of E‐octadecyl p‐coumarate and Z‐octadecyl p‐coumarate. Copyright © 2012 John Wiley & Sons, Ltd.     

Atom transfer radical copolymerizationof acrylonitrile/n‐butyl acrylate: Microstructure determination by two‐dimensional nuclearmagnetic resonance spectroscopy

Atom transfer radical polymerization conditions were optimized and standardized with different initiator and catalyst systems. Acrylonitrile/n‐butyl acrylate copolymers were synthesized with 2‐bromopropionitrile as the initiator and CuCl/Cu(0)/2,2′‐bipyridine as the catalyst system. Variations of the feed composition led to copolymers with different compositions. The number‐average molecular weight and the polydispersity index were determined by gel permeation chromatography. Quantitative ¹³C{¹H} NMR was employed to determine the copolymer composition. The reactivity ratios calculated with a methodology based on the Mao–Huglin terminal model were r_A = 1.30 and r_B = 0.68 for acrylonitrile and n‐butyl acrylate, respectively. The reactivity ratios determined by the modified Kelen–Tudos method were r_A = 1.29 ± 0.01 and r_B = 0.67 ± 0.01. ¹³C{¹H} NMR and distortionless enhancement by polarization transfer (DEPT‐45, 90, and 135) were used to distinguish methyl, methylene, methine, and quaternary carbon resonance signals. The overlapping and broad signals of the copolymers were assigned completely to various compositional and configurational sequences by the correlation of one‐dimensional (¹H, ¹³C{¹H}, and DEPT) and two‐dimensional (heteronuclear single quantum coherence, total correlation spectroscopy, and heteronuclear multibond correlation) NMR spectral data. The complete spectral assignments of carbonyl and nitrile carbons were performed with the help of heteronuclear multibond correlation spectra. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2810–2825, 2005     

Quadruple‐Resonance Magic‐Angle Spinning NMR Spectroscopy of Deuterated Solid Proteins

¹H‐detected magic‐angle spinning NMR experiments facilitate structural biology of solid proteins, which requires using deuterated proteins. However, often amide protons cannot be back‐exchanged sufficiently, because of a possible lack of solvent exposure. For such systems, using ²H excitation instead of ¹H excitation can be beneficial because of the larger abundance and shorter longitudinal relaxation time, T₁, of deuterium. A new structure determination approach, “quadruple‐resonance NMR spectroscopy”, is presented which relies on an efficient ²H‐excitation and ²H‐¹³C cross‐polarization (CP) step, combined with ¹H detection. We show that by using ²H‐excited experiments better sensitivity is possible on an SH3 sample recrystallized from 30 % H₂O. For a membrane protein, the ABC transporter ArtMP in native lipid bilayers, different sets of signals can be observed from different initial polarization pathways, which can be evaluated further to extract structural properties.     

Modified,pulse field gradient‐enhanced inverse‐detected HOESY pulse sequence for reduction of t1 spectral artifacts

A modified pulse field gradient (PFG)‐enhanced inverse (¹H)‐detected 2D heteronuclear Overhauser effect spectroscopy (HOESY) pulse sequence is demonstrated for the acquisition of ¹H–⁷Li heteronuclear correlations. In practice, t₁ noise artifacts were observed using the original PFG‐enhanced inverse‐detected HOESY pulse sequence, which degraded the ability to detect accurately weak heteronuclear Overhauser signals. Experimentally it is shown that a simple modification of the PFG‐enhanced inverse‐detected HOESY pulse sequence greatly reduces the t₁ noise that may result from variations in magnetic susceptibility, and allows improved detection of weak ¹H–⁷Li correlations. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis,spectroscopic and configurational study,and ab initio calculations of new diazaphospholanes

New 2-substituted diazaphospholane-2-oxides (I-III, V-VIII) and diazaphosphorinane-2-oxide (IV) were synthesised and characterised by ¹H, ¹³C, and ³¹P NMR, IR spectroscopy, and elemental analysis. The presence of chiral diamino groups in compounds II and V–VIII gives rise to various diastereomers so that the ³¹P{¹H} NMR spectra demonstrated three and two peaks with different ratios, respectively. Also, the ¹H and ¹³C{¹H} NMR spectra of compounds II and V–VIII revealed three and two sets of signals for the related conformers (diastereomers). Interestingly, the ³¹P NMR spectrum of V in D₂O indicated a great upfield shift (Δδ = 19.0) for ³¹P relative to the value obtained in DMSO-d₆ (solvent effect). The two signals in V split further to three signals in the presence of β-cyclodextrin. Moreover, conformational analysis of diazaphospholane V was studied by ab initio calculations at the HF and B3LYP levels of theory using the Gaussian 98 program. Results indicated that among four suggested diastereomers (C1–C4) of V, C1 and C3 containing methyl group in the equatorial position are the most stable forms.     

Synthesis and Stereochemistry of New N-Substituted Cytisine Derivatives

A series of new N-substituted cytisine derivatives was synthesized. The ¹ H and ¹³ C NMR spectra of certain compounds exhibit a doubled set of signals. This is explained by formation of diastereomeric pairs in compounds containing an asymmetric center in the substituents. The signal splitting in -COHC=CHCO ₂ H and HC=O (formyl) derivatives is explained by the existence of Z and E invertomers. Their stereochemical features are discussed. Amide conjugation is confirmed by temperature experiments.     

Sequencing of trans-4-methacryloyloxyazobenzene/vinylidene chloride copolymers by one- and two-dimensional NMR spectroscopy

Trans-4-methacryloyloxyazobenzene/Vinylidene Chloride (M/V) copolymers of different monomer concentrations were prepared by solution polymerization using benzoyl peroxide as an initiator. The copolymer composition was determined from the ¹³C{¹H}-NMR spectrum. The quaternary carbon of M- and V-centered resonances were used for determining the sequences in terms of the distribution of M- and V-centered triads. The sequence distribution of M- and V-centered triads determined from ¹³C{¹H}-NMR spectra of the copolymer is in good agreement with the triad concentration calculated from the statistical model. The comonomer reactivity ratios, determined by both the Kelen Tudos (KT) and the nonlinear error in variables (EVM) methods are r_M = 3.59 ± 0.19, r_V = 0.89 ± 0.07; r_M = 3.76, and r_V = 0.93, respectively. ¹³C Distortionless Enhancement by Polarization Transfer (DEPT) spectrum was used to differentiate between the resonance signals of M- and V-methylene and methyl carbon units. Assignments to the methylene resonance signals have been assigned up to the tetrad levels using 2D HSQC experiments. The geminal couplings in the methylene proton region is shown in the 2D DQF-COSY spectrum. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3179–3185, 1999     

Syntheses and Characterization of a Pair of Isomers of Heteroleptic Bis(Bidentate) Ruthenium(II) Complexes with Two Different Monodentate Ligands

Two isomers of heteroleptic bis(bidentate) ruthenium(II) complexes with dimethyl sulfoxide (dmso) and chloride ligands, trans(Cl,N_bpy)- and trans(Cl,N_Hdpa)-[Ru(bpy)Cl(dmso-S)(Hdpa)]⁺ (bpy: 2,2′-bipyridine; Hdpa: di-2-pyridylamine), are synthesized. This is the first report on the selective synthesis of a pair of isomers of cis-[Ru(L)(L′)XY]ⁿ⁺ (L≠L′: bidentate ligands; X≠Y: monodentate ligands). The structures of the ruthenium(II) complexes are clarified by means of X-ray crystallography, and the signals in the ¹H NMR spectra are assigned based on ¹H–¹H COSY spectra. The colors of the two isomers are clearly different in both the solid state and solution: the trans(Cl,N_bpy) isomer has a deep red color, whereas the trans(Cl,N_Hdpa) isomer is yellow. Although both complexes have intense absorption bands at λ≈440–450 nm, only the trans(Cl,N_bpy) isomer has a shoulder band at λ≈550 nm. DFT calculations indicate that the LUMOs of both isomers are the π* orbitals in the bpy ligand, and that the LUMO level of the trans(Cl,N_bpy) isomer is lower than that of the trans(Cl,N_Hdpa) isomer due to the trans effect of the Cl ligand; thus resulting in the appearance of the shoulder band. The HOMO levels are almost the same in both isomers. The energy levels are experimentally supported by cyclic voltammograms, in which these isomers have different reduction potentials and similar oxidation potentials.     

Reversible Hyperpolarization of Ketoisocaproate Using Sulfoxide-containing Polarization Transfer Catalysts

The substrate scope of sulfoxide-containing magnetisation transfer catalysts is extended to hyperpolarize α-ketoisocaproate and α-ketoisocaproate-1-[¹³C]. This is achieved by forming [Ir(H)₂(κ²-ketoisocaproate)(N-heterocyclic carbene)(sulfoxide)] which transfers latent magnetism from p-H₂ via the signal amplification by reversible exchange (SABRE) process. The effect of polarization transfer field on the formation of enhanced ¹³C magnetization is evaluated. Consequently, performing SABRE in a 0.5 μT field enabled most efficient magnetisation transfer. ¹³C NMR signals for α-ketoisocaproate-1-[¹³C] in methanol-d₄ are up to 985-fold more intense than their traditional Boltzmann derived signal intensity (0.8 % ¹³C polarisation). Single crystal X-ray diffraction reveals the formation of the novel catalyst decomposition products [Ir(μ-H)(H)₂(IMes)(SO(Ph)(Me)₂)]₂ and [(Ir(H)₂(IMes)(SO(Me)₂))₂(μ-S)] when the sulfoxides methylphenylsulfoxide and dimethylsulfoxide are used respectively.     

Intramolecular Hydrogen Bonding In N-(2-Amino-2-Deoxy-β-D-Glucopyranoside)-N'-Carbamoyl-L-Dipeptidylesters: An Infrared And 1H Nmr Study

ABSTRACT

Ten N-(2-amino-2-deoxy-β-D-glucopyranoside)-N'-carbamoyl-L-dipeptidylesters with different amino acid sequences in the dipeptide unit were studied by means of IR and ¹H NMR spectroscopy. In the IR spectra three bands at 3453, 3420 and 3390 cm^-1 were observed which could be assigned to the free NH, the intramolecularly hydrogen bonded NH species forming five-membered, C₅, and seven-membered, C₇, rings, respectively. Comparing the NH band positions which correspond to the C₇ rings of the Gly-Xaa and the Xaa-Gly dipeptidylesters, the signals of the Xaa-Gly sequence were shifted by 10 cm^-1 to lower wave numbers indicating stronger hydrogen bonds. The temperature effect dv/dT was an order of magnitude larger for the C₇ associates than for C₅ showing the highest enthalpy of the C₇ hydrogen bond. The ¹H NMR spectra give three separate signals for the NH groups. The temperature coefficient ?δ/?T was the largest for N-1-H indicating the formation of less stable hydrogen bonds (C₇). The solvent induced changes of the chemical shift of the NH signals was lowest for the N-3-H signal. Obviously the deshielding properties on this function do not vary in dependence of the solvent polarity. The hydrogen/deuterium exchange rate was lowest for the N-6-H proton indicating the lower accessibility of this proton. Combining the results of both spectroscopic methods it can be concluded that the N-1-H forms only C₇ rings whereas N-6-H can participate in C₅ and C₇ intramolecular hydrogen bonds. The strength of the formed C₇ associates depends on the amino acid sequence in the dipeptide residue.     

Synthesis and NMR Spectroscopic Characteristics of a Series of Hydrazide‐Hydrazones Containing Furoxan Ring Derived from Isoeugenoxyacetic Acid

A novel hydrazide, 2‐methoxy‐4‐(3‐methyfuroxan‐4‐yl)‐5‐nitrophenoxyacetylhydrazine, was prepared from isoeugenoxyacetic acid. The hydrazide was condensed with aromatic aldehydes to give a series of 20 hydrazide‐hydrazones incorporating the furoxan ring. The structure of obtained compounds was determined by analytical and spectral data. It was demonstrated that the two sets of resonance signals in the ¹H‐NMR and ¹³C‐NMR spectra of the examined hydrazide‐hydrazones are caused by E_N–C(O) and Z_N–C(O) conformers. The energy barriers for the conformation exchange were determined by ¹H‐NMR‐measurement at various temperatures. Among seven tested hydrazide‐hydrazones, four compounds exhibit inhibition activities in vitro on human epidermis carcinoma (KB‐cell) with IC₅₀ = 47, 68, 79, and 103 μg/mL.     

Naphthalene‐1,6‐diol: a three‐dimensional framework built from O—H...O,O—H...π and C—H...O hydrogen bonds

The asymmetric unit of the title compound, C₁₀H₈O₂, contains two practically planar symmetry‐independent molecules linked by one O—H...O hydrogen bond. Molecules are further linked into a three‐dimensional network, which is built from R₆⁶(36), R₆⁶(18), R₆⁶(30) and R₄⁴(26) rings formed by the combined effect of three O—H...O and one C—H...O hydrogen bond. This network is additionally stabilized by an O—H...π interaction.     

2H/1H Isotope Shifts for 6Li-NMR: First Experimental Detection and Applications to Structural Problems in the Field of Organolithium Compounds

Deuterium-induced isotope effects on ⁶Li chemical shifts, transmitted over two bonds, ²Δ(⁶Li)(²H/¹H), have been measured for the first time for methyllithium and the system methyllithium/lithium iodide. The observed shifts are to low field and range from 15 to 20 ppb per CD₃ group. The multiplicity and intensity distribution of the ⁶Li signals resulting for mixtures of CH₃- and CD₃-containing samples in the limit of slow inter- as well as intra-aggregate exchange yield information about the size of the various clusters present in diethylether solution. It is expected that these isotope shifts can facilitate structural investigations of organolithium compounds. In some cases, the results of such measurements are expected to be less ambiguous then the conclusions based on multiplets that arise from scalar ¹³C,⁶Li spin-spin coupling.     

Red to Blue High Electrochromic Contrast and Rapid Switching Poly(3,4‐ethylenedioxypyrrole)–Au/Ag Nanocomposite Devices for Smart Windows

Poly(3,4‐ethylenedioxypyrrole) (PEDOP)–Ag and PEDOP–Au nanocomposite films have been synthesized for the first time by electropolymerization of the conducting‐polymer precursor in a waterproof ionic liquid, 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, followed by Ag/Au nanoparticle incorporation. That the Ag/Au nanoparticles are not adventitious entities in the film is confirmed by a) X‐ray photoelectron spectroscopy, which provides evidence of Ag/Au–PEDOP interactions through chemical shifts of the Ag/Au core levels and new signals due to Ag–N(H) and Au–N(H) components, and b) electron microscopy, which reveals Au nanoparticles with a face‐centered‐cubic crystalline structure associated with the amorphous polymer. Spectroelectrochemistry of electrochromic devices based on PEDOP–Au show a large coloring efficiency (η_max=270 cm² C^?1, λ=458 nm) in the visible region, for an orange/red to blue reversible transition, followed by a second, remarkably high η_max of 490 cm² C^?1 (λ=1000 nm) in the near‐infrared region as compared to the much lower values achieved for the neat PEDOP analogue. Electrochemical impedance spectroscopy studies reveal that the metal nanoparticles lower charge‐transfer resistance and facilitate ion intercalation–deintercalation, which manifests in enhanced performance characteristics. In addition, significantly faster color–bleach kinetics (five times of that of neat PEDOP!) and a larger electrochemical ion insertion capacity unambiguously demonstrate the potential such conducting‐polymer nanocomposites have for smart window applications.     

Multinuclear two-dimensional NMR: Assignments of natural abundance polypeptide 13C, 1H and 15N chemical shifts and demonstration of isomer interconversion

The polypeptide carbobenzoxy-glycyl-L -prolyl-L -leucyl-L -alanyl-L -proline (0.2 M in DMSO-d₆) was investigated using ¹³C, ¹H and ¹⁵N NMR in natural abundance at 4.7 tesla. The existence of cis–trans-Gly-Pro and -Ala-Pro bonds permits up to four isomers, and all four were observed (in a 60:30:7:3 ratio). ¹³C shifts of the proline β-CH₂ resonances are consistent only with the 60% form being trans–trans. The 30% form is either trans–cis or cis–trans (order as above) and was tentatively assigned as cis-trans on the basis of relaxation behavior. Refocused INEPT studies aided the ¹³C assignments. The ¹⁵N data were obtained using both NOE and INEPT excitation, with signals evident for the three major isomers. The spectra were analysed by starting from the ¹³C data, which were assigned based on known regularities in peptide spectra. A ¹³C? ¹H heteronuclear two-dimensional chemical shift correlation experiment allowed direct assignment of proton shifts for major and minor isomers. The NH proton shifts were assigned by running a homonuclear two-dimensional chemical shift correlation experiment and noting the correlation with the previously assigned α-CH protons. The ¹⁵N resonances were then assigned from a ¹⁵N? ¹H heteronuclear two-dimensional chemical shift correlation experiment, relating the ¹⁵N signals directly to the NH proton resonances. Isomer interconversion between the two major isomers was demonstrated by performing a magnetization transfer homonuclear 2D experiment. Off-diagonal intensity was noted relating the major and minor isomer alanine NH proton, as well as for the major and minor isomer leucine NH protons.     

Complete 1H NMR spectral analysis of ten chemical markers of Ginkgo biloba

The complete and unambiguous ¹H NMR assignments of ten marker constituents of Ginkgo biloba are described. The comprehensive ¹H NMR profiles (fingerprints) of ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, bilobalide, quercetin, kaempferol, isorhamnetin, isoquercetin, and rutin in DMSO‐d₆ were obtained through the examination of 1D ¹H NMR and 2D ¹H,¹H‐COSY data, in combination with ¹H iterative full spin analysis (HiFSA). The computational analysis of discrete spin systems allowed a detailed characterization of all the ¹H NMR signals in terms of chemical shifts (δ_H) and spin‐spin coupling constants (J_HH), regardless of signal overlap and higher order coupling effects. The capability of the HiFSA‐generated ¹H fingerprints to reproduce experimental ¹H NMR spectra at different field strengths was also evaluated. As a result of this analysis, a revised set of ¹H NMR parameters for all ten phytoconstituents was assembled. Furthermore, precise ¹H NMR assignments of the sugar moieties of isoquercetin and rutin are reported for the first time. Copyright © 2012 John Wiley & Sons, Ltd.     

4‐(3‐Azaniumylpropyl)morpholin‐4‐ium chloride hydrogen oxalate: an unusual example of a dication with different counter‐anions

The mixed organic–inorganic title salt, C₇H₁₈N₂O²⁺·C₂HO₄⁻·Cl⁻, forms an assembly of ionic components which are stabilized through a series of hydrogen bonds and charge‐assisted intermolecular interactions. The title assembly crystallizes in the monoclinic C2/c space group with Z = 8. The asymmetric unit consists of a 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dication, a hydrogen oxalate counter‐anion and an inorganic chloride counter‐anion. The organic cations and anions are connected through a network of N—H...O, O—H...O and C—H...O hydrogen bonds, forming several intermolecular rings that can be described by the graph‐set notations R₃³(13), R₂¹(5), R₁²(5), R₂¹(6), R₂³(6), R₂²(8) and R₃³(9). The 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dications are interconnected through N—H...O hydrogen bonds, forming C(9) chains that run diagonally along the ab face. Furthermore, the hydrogen oxalate anions are interconnected via O—H...O hydrogen bonds, forming head‐to‐tail C(5) chains along the crystallographic b axis. The two types of chains are linked through additional N—H...O and O—H...O hydrogen bonds, and the hydrogen oxalate chains are sandwiched by the 4‐(3‐azaniumylpropyl)morpholin‐4‐ium chains, forming organic layers that are separated by the chloride anions. Finally, the layered three‐dimensional structure is stabilized via intermolecular N—H...Cl and C—H...Cl interactions.     

31P-NMR-Daten heterocyclischer phosphine. Diastereomerenzuordnung an 1,3-Oxa-, 1,3-Aza- und 1,3-thiaphospholanen

The diastereomers of 16 1,3-oxa-, 1,3-aza- and 1,3- thiaphospholanes were assigned by means of the coupling constants ²J(P? C? H) and ³J(P? C? CH₃) and the linewidths of the ³¹P signals and ¹H chemical shifts of CH₃ groups. It is shown that the change in the ³¹P chemical shifts allows the estimation of the relative configuration in these compounds.