Dimensional Nuclear Magnetic Resonance Research Articles

Chemical exchange and spectral coalescence in low-hydration MCM-41 studied by proton NMR

In Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, involving silica-based porous media, containing surface OH groups and water, it is generally observed that the water proton and OH group proton resonances tend to coalesce with increasing moisture content. It has been suggested that chemical exchange between protons of surface OH groups and water may not be the only mechanism producing the coalescence in the mesoporous material MCM-41. [Chem. Eur. J. 10 (2004) 5689] Here the importance of such exchange was investigated in MCM-41, hydrated to one water molecule per OH group, using low-field, static NMR relaxation techniques and high-field MAS NMR techniques. First the surface-water chemical exchange rate was estimated from two dimensional time domain NMR selective inversion recovery experiments. Second the exchange rate required to produce coalescence was estimated by modeling the exchange spectra using expected water proton NMR spectral positions and surface OH proton NMR spectral positions obtained from MAS experiments in dry MCM-41. The results suggest that the surface-water chemical exchange rate is too small to produce substantive proton NMR spectral coalescence in the MCM-41 material at this hydration level.

Radical scavenging activities of the leaf extracts and a flavonoid glycoside isolated from Cineraria abyssinica Sch. Bip. Exa. Rich

The aqueous decoction of the leaves of Cineraria abyssinica Sch. Bip. exA. Rich (Asteraceae) is used for treatments of myriads of diseases associated with oxidative stress. However, there appear to have been lack reports on its phytochemistry and pharmacological activities. The main purpose of this study was, therefore, to determine the radical scavenging activities of the leaf extracts of C. abyssinica. The aqueous and 80% methanolic crude extracts, chloroform, acetone and methanol fractions of the leaf extracts of C. abyssinica showed potent radical scavenging activities (IC50 = 5.27-12.41 µg/ml). Activity-guided fractionation of the most active, methanol fraction resulted in the isolation of a flavonoidal glycoside, rutin. The structure was assigned on the basis of spectroscopic methods including ultraviolet spectroscopy (UV), infra red (FT-IR), mass spectrometry (MS) and one and two dimensional nuclear magnetic resonance spectrometry (1D- and 2D-NMR). Rutin showed the most potent DPPH scavenging activity (IC50 = 3.53 µg/ml) slightly higher than ascorbic acid (IC50 = 3.57 µg/ml). Acute toxicity studies on the crude extracts showed the nontoxic nature of the plant up to 3 g/kg. Therefore, the present study revealed for the first time the presence of antioxidant phytochemical in the leaves of C. abyssinica that scientifically validated the traditional use and its great potential to be used as a source of antioxidant phytochemicals.

Three new triterpenoids from Salacia hainanensis Chun et How showed effective anti-α-glucosidase activity

To identify the chemical constituents with hypoglycemic activity in Salacia hainanensis Chun et How, this study was carried out on the roots of S. hainanensis. By means of a bioassay-guided method, three new triterpenoids (2β,3β-dihydroxylup-20(29)-ene [compound 1], 30-hydroxy-D:A-friedo-olean-1-en-3-one [compound 2], and 24,25,26-trihydroxytirucall-7-en-3-one [compound 3]) along with three known compounds (olibanumol J [compound 4], 21α-hydroxy-D:A-friedo-olean-3-one [compound 5], and 29-hydroxy-D:A-friedo-olean-3-one [compound 6]) were isolated from the EtOAc part and were shown to have effective α-glucosidase inhibitory activity. Their structures were established on the basis of spectral analysis, especially according to the data obtained by two dimensional nuclear magnetic resonance spectroscopic and high-resolution mass spectra experiments. All compounds with the exception of compound 2 showed much stronger inhibitory activity against α-glucosidase than did the positive control (acarbose, IC50 1.02μM).

Quantitative analysis and characterization of the products of the model reaction of n-butyllithium with excess 1,1-diphenylethylene: 1,1-Diphenylhexane and 1,1,3,3-tetraphenyloctane

The model reaction of n-butyllithium with excess (11 M equivalents) 1,1-diphenylethylene (DPE) was reinvestigated using modern characterization techniques including SEC, one dimensional and two dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopy and electrospray ionization mass spectrometry (ESI MS). The products were the monoadduct, 1,1-diphenylhexane (nBuDPEH), and the diadduct, 1,1,3,3-tetraphenyloctane [nBu(DPE)2H], formed in 62 mol% and 38 mol% yields, respectively, as determined by SEC and 1H NMR spectroscopy. The 1H NMR spectrum of 1,1,3,3-tetraphenyloctane exhibited a terminal methine triplet resonance at δ 3.71 ppm that was uniquely coupled to the adjacent methylene doublet resonance at δ 3.09 ppm, located between the two carbons, each bonded to two phenyl groups [–C(C6H5)2-CH2-CH(C6H5)2. All of the characteristic 1H and 13C NMR resonances for both adducts were assigned using 2D NMR spectroscopic methods. The diadduct, nBu(DPE)2H, exhibited unique 13C NMR resonances at δ 50.79 ppm for the quaternary carbon resonance [CH2-C(C6H5)2−CH2], and at δ 43.74 ppm for the methylene group isolated between the two carbons, each bonded to two phenyl groups [–C(C6H5)2-CH2-CH(C6H5)2].

Arabinose content of arabinoxylans contributes to flexibility of acetylated arabinoxylan films

AbstractArabinoxylans (AX) from rye were partly debranched by chemical hydrolysis methods, and AXs differing in arabinosyl substitution were acetylated using chemical methods. The resulting materials are film forming, and these films underwent molecular structural analysis and were tested for their material properties. The composition and structure of the modified polymers were determined using high performance anion exchange chromatography and two dimensional nuclear magnetic resonance; it was shown that all free hydroxyl groups (of both xylose and arabinose) were acetylated. Further characterizations were done by dynamic mechanical analysis and thermo‐gravimetric analysis to evaluate the thermal behavior of the material. The observed glass transition temperatures (Tg) increased with a decrease in arabinosyl substitutions. The thermal degradation temperatures were all close to 380°C. The mechanical properties were characterized with tensile tests of the films. Tensile tests showed that the strain at break, which reflects the flexibility of the material, was significantly higher at higher arabinosyl substitution levels. The elastic Young's modulus was not significantly affected, although a tendency was seen toward a less stiff material at higher arabinosyl substitution. The ultimate strength of the materials was remarkably high in all cases, around 60 MPa, with little difference between them. Considering these properties, a great potential is foreseen in the application of acetylated arabinoxylans as packaging films and as matrix for composites. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Conformational studies of immunodominant myelin basic protein 1–11 analogues using NMR and molecular modeling

Τwo dimensional nuclear magnetic resonance studies complimented by molecular dynamics simulations were conducted to investigate the conformation of the immunodominant epitope of acetylated myelin basic protein residues 1-11 (Ac-MBP(1-11)) and its altered peptide ligands, mutated at position 4 to an alanine (Ac-MBP(1-11)[4A]) or a tyrosine residue (Ac-MBP(1-11)[4Y]). Conformational analysis of the three analogues indicated that they adopt an extended conformation in DMSO solution as no long distance NOE connectivities were observed and seem to have a similar conformation when bound to the active site of the major histocompatibility complex (MHC II). The interaction of each peptide with MHC class II I-A(u) was further investigated in order to explore the molecular mechanism of experimental autoimmune encephalomyelitis induction/inhibition in mice. The present findings indicate that the Gln(3) residue, which serves as a T-cell receptor (TCR) contact site in the TCR/peptide/I-A(u) complex, has a different orientation in the mutated analogues especially in the Ac-MBP(1-11)[4A] peptide. In particular the side chain of Gln(3) is not solvent exposed as for the native Ac-MBP(1-11) and it is not available for interaction with the TCR.

Sedimentation and resuspendability evaluation of pharmaceutical suspensions by low-field one dimensional pulsed field gradient NMR profilometry

In order to study the sedimentation of pharmaceutical suspensions using low-field one dimensional pulsed field gradient nuclear magnetic resonance (1D pfg NMR) profilometry, the accuracy of signal acquisition as well as the spatial resolution of a commercial spectrometer operating at 23.4 MHz was investigated. The use of a solid Teflon spacer revealed that the accuracy of signal acquisition was independent of spatial position (height). The standard deviation of distance determinations was less than 150 µm, whereas the accuracy of water content determination was within 2% in the central part of the detection zone and deteriorated to 4% in the outer parts. The study of aqueous paramagnetic MnCl2 solutions indicated an exponential relationship between the relative signal intensity and the transverse relaxation decay constant. From this relationship, the relative water content of suspensions could be derived from their signal intensity relative to that of water. Using concentrated paliperidone palmitate dispersions as model suspensions, low-field 1D pfg NMR profilometry has been proven to be suitable for the evaluation of both the sedimentation and resuspendability behavior of viscous, opaque suspensions, for which visual detection of homogeneity may be difficult.

OPTIMED : optimisation itérative pour la résolution de problèmes inverses de grande taille

This paper deals with image reconstruction using iterative algorithms. The fra me- work under consideration involves large amount of data and/or large ob servation operator. We proposed here algorithms for which we were able to state convergence proofs. The relia- bility and accuracy of the proposed approaches are demonstrated via th ree applications: the positron emission tomography (PET), the parallel magnetic resonance im aging (MRI) and two- dimensional nuclear magnetic resonance (2D NMR).

In vitro cytotoxic activity of abietane diterpenes from Peltodon longipes as well as Salvia miltiorrhiza and Salvia sahendica

Phytochemical investigations of the n-hexane extract from the roots of Peltodon longipes (Lamiaceae) resulted in the isolation of 12 known abietane diterpenes (1–12). Structures were established on the basis of one and two dimensional nuclear magnetic resonance spectroscopic data (1H and 13C, COSY, HSQC and HMBC), electron ionization mass spectrometric analysis (EIMS) as well as comparison with data from literature. These compounds, as well as eight known diterpenes (13–19) from Salvia miltiorrhiza, and two from Salvia sahendica (20 and 21) were evaluated for their cytotoxic effects in human pancreatic (MIAPaCa-2) and melanoma (MV-3) tumor cell lines using the MTT assay. Tanshinone IIa (13), 7α-acetoxyroyleanone (1), 1,2-dihydrotanshinone (16) and cryptotanshinone (14) had the highest cytotoxic effects in MIAPaCa-2, displaying IC50 of 1.9, 4.7, 5.6, and 5.8μM, respectively. Structure–activity relationships of abietane diterpenoid quinones are discussed.

Intercalation of XR5944 with the estrogen response element is modulated by the tri-nucleotide spacer sequence between half-sites

DNA-intercalating molecules can impair DNA replication, DNA repair, and gene transcription. We previously demonstrated that XR5944, a DNA bis-intercalator, specifically blocks binding of estrogen receptor-α (ERα) to the consensus estrogen response element (ERE). The consensus ERE sequence is AGGTCAnnnTGACCT, where nnn is known as the tri-nucleotide spacer. Recent work has shown that the tri-nucleotide spacer can modulate ERα–ERE binding affinity and ligand-mediated transcriptional responses. To further understand the mechanism by which XR5944 inhibits ERα–ERE binding, we tested its ability to interact with consensus EREs with variable tri-nucleotide spacer sequences and with natural but non-consensus ERE sequences using one dimensional nuclear magnetic resonance (1D 1H NMR) titration studies. We found that the tri-nucleotide spacer sequence significantly modulates the binding of XR5944 to EREs. Of the sequences that were tested, EREs with CGG and AGG spacers showed the best binding specificity with XR5944, while those spaced with TTT demonstrated the least specific binding. The binding stoichiometry of XR5944 with EREs was 2:1, which can explain why the spacer influences the drug–DNA interaction; each XR5944 spans four nucleotides (including portions of the spacer) when intercalating with DNA. To validate our NMR results, we conducted functional studies using reporter constructs containing consensus EREs with tri-nucleotide spacers CGG, CTG, and TTT. Results of reporter assays in MCF-7 cells indicated that XR5944 was significantly more potent in inhibiting the activity of CGG- than TTT-spaced EREs, consistent with our NMR results. Taken together, these findings predict that the anti-estrogenic effects of XR5944 will depend not only on ERE half-site composition but also on the tri-nucleotide spacer sequence of EREs located in the promoters of estrogen-responsive genes.

A New Sesquiterpene from Trichilia casarettii (Meliaceae)

The dichloromethane extract of the air-dried stems of Trichilia casarettii afforded a new sesquiterpene (1), lupeol, stigmasterol, campesterol and sitosterol. The structure of 1 was elucidated by extensive one-and two- dimensional nuclear magnetic resonance and mass spectrometry.

A new friedelane type triterpene from Euonymus hederaceus.

Euonymus hederaceus is distributed widely in the south of China; its stems and leaves have been used as folk medicines to treat many diseases such as renal deficiency and chronic diarrhea, traumatic injury, and abnormal menstruation. Chemical investigation of the leaves and stems of Euonymus hederaceus resulted in the isolation for the first time and characterization of a new friedelane type triterpene with a molecular mass of 472 and molecular formula of C30H48O4 by high resolution mass spectrometry. The 1H-NMR 13C-NMR and DEPT1350 spectra matched the characteristic data of the proposed triterpene skeleton. The compound was finally identified as 28-hydroxyfriedelan-3-one-29-oic acid on the basis of spectroscopic evidence, including two dimensional nuclear magnetic resonance as well as its IR spectrum.

Characterization and biological studies of a new platinum(II) complex with the amino acid L-alliin

Synthesis and characterization of a new Pt(II) complex with the amino acid L-alliin (S-allyl-L-cysteine sulfoxide, C6H11NO3S) are described. Elemental and mass spectrometric analyses of the solid complex are consistent with [PtCl2(alliin)], or [PtCl2(C6H11NO3S)]. 13C nuclear magnetic resonance (NMR), [1H–15N] two dimensional (2D) NMR and infrared spectroscopy indicate coordination of the ligand to Pt(II) through the N and S atoms. The complex is very soluble in dimethyl sulfoxide. Biological analysis for evaluation of a potential cytotoxic effect of the complex was performed using HeLa cells derived from human cervical adenocarcinoma. The complex presented moderate cytotoxic activity, inducing about 40% cell death at a concentration of 400 μmol · L−1.

A Cytotoxic and Apoptosis-Inducing Sesquiterpenoid Isolated from the Aerial Parts of Artemisia princeps PAMPANINI (Sajabalssuk)

Repeated silica gel and octadecyl silica gel (ODS) column chromatography of the aerial parts of Artemisia princeps PAMPANINI (Sajabalssuk) led to the isolation of a new sesquiterpenoid, 3-((S)-2-methylbutyryloxy)-costu-1(10),4(5)-dien-12,6 alpha-olide (2), along with two previously reported sesquiterpenoids: 8 alpha-angeloyloxy-3beta,4 beta-epoxy-6 beta H,7 alpha H,8 beta H-guaia-1(10),11(13)-dien-12,6 alpha-olide (1, carlaolide B) and 3beta,4 beta-epoxy-8 alpha-isobutyryloxy-6 beta H,7 alpha H,8 beta H-guaia-1(10),11(13)-dien-12,6 alpha-olide (3, carlaolide A). The structure of compound 2 was elucidated by spectroscopic data analysis, including one dimensional (1D) and two dimensional (2D) nuclear magnetic resonance (NMR) experiments. Of the isolates, compound 2 exhibited potent cytotoxicity against human cervix adenocarcinoma cells and induced apoptosis.

2D NMR metabonomic analysis: a novel method for automated peak alignment

Comparative metabolic profiling by nuclear magnetic resonance (NMR) is showing increasing promise for identifying inter-individual differences to drug response. Two dimensional (2D) (1)H (13)C NMR can reduce spectral overlap, a common problem of 1D (1)H NMR. However, the peak alignment tools for 1D NMR spectra are not well suited for 2D NMR. An automated and statistically robust method for aligning 2D NMR peaks is required to enable comparative metabonomic analysis using 2D NMR. A novel statistical method was developed to align NMR peaks that represent the same chemical groups across multiple 2D NMR spectra. The degree of local pattern match among peaks in different spectra is assessed using a similarity measure, and a heuristic algorithm maximizes the similarity measure for peaks across the whole spectrum. This peak alignment method was used to align peaks in 2D NMR spectra of endogenous metabolites in liver extracts obtained from four inbred mouse strains in the study of acetaminophen-induced liver toxicity. This automated alignment method was validated by manual examination of the top 50 peaks as ranked by signal intensity. Manual inspection of 1872 peaks in 39 different spectra demonstrated that the automated algorithm correctly aligned 1810 (96.7%) peaks. Algorithm is available upon request.

Characterization of the fast dynamics of protein amino acid side chains using NMR relaxation in solution.

The physical basis of protein structure, dynamics and function has been intensely studied for several decades. Indeed since the new millennium there has been a tremendous expansion in the number of unique topological folds that have been characterized at high resolution by crystallographic and nuclear magnetic resonance (NMR) based methods. In the midst of this rush towards a grand scale structural genomics effort, a quieter effort dedicated to the experimental characterization of protein conformational heterogeneity has also emerged. The influence of atomic scale structure on molecular recognition and catalysis by proteins is often the focus of attention while the role of dynamics is largely unknown and frequently ignored. Nevertheless, it has long been recognized that proteins are indeed dynamic systems. Early insights into the time scale and character of protein internal motion largely employed local optical probes, unresolved hydrogen exchange, and one dimensional NMR techniques that, though limited, revealed a startling complexity and richness in the internal motion of proteins.1–5 These initial views contributed significantly to the development of current treatments of protein dynamics and thermodynamics.6 The connection to biological function rather than just biological form is more recent. Internal protein dynamics can potentially affect protein function through a variety of mechanisms, some of which are tautological or obvious in nature while others are subtle and remain to be fully explored and appreciated. There are now several examples of protein-protein and protein-ligand interactions that illustrate that dynamics may be fundamentally linked to function in several ways. Nuclear magnetic resonance (NMR) spectroscopy is very much at the center of current efforts to illuminate the nature of protein dynamics and their role in biological function. Here we will focus on the use of solution NMR methods to provide fast subnanosecond dynamics of protein side chains. The interested reader is referred to separate reviews in this issue by Goehlert and Stone,7 Tolman8 and Palmer and Massi9 discussing dynamics of the polypeptide backbone. The emerging success of NMR spectroscopy in the arena of protein dynamics rests on four general areas of development over the past two decades. First and perhaps foremost, triple resonance NMR spectroscopy now provides an efficient and robust set of tools for the comprehensive resonance assignment of proteins of significant size.10,11 These methods, in turn, derive much of their power from companion isotopic enrichment strategies,12,13 which have been subsequently refined to allow for isotopic labeling patterns that are optimized for NMR relaxation studies (vide infra). Two-dimensional sampling of relaxation has allowed for comprehensive studies to be efficiently undertaken, albeit with great instrumental cost.14–16 A variety of technical issues such as the effects of macromolecular tumbling and the influence of competing relaxation mechanisms have also been largely resolved (vide infra). These advances have positioned solution NMR spectroscopy to efficiently and comprehensively characterize the fast internal dynamics of proteins of significant size. This review seeks to provide a compact but reasonably complete description of the theoretical and technical foundation for solution NMR relaxation methods that are currently being brought to bear on fast sub-nanosecond protein side chain dynamics and to present a summary of current findings and their possible significance. A survey of basic observations about side chain dynamics derived from NMR-relaxation studies is presented along with several analyses meant to dispel commonly held but apparently inaccurate correlations between dynamics, structure and function. How dynamics can enter into fundamental thermodynamic and kinetic aspects of protein function is also reviewed and illustrated with intriguing results from several systems that point to a promising future for this area of inquiry.

Chymotrypsin Inhibitory Triterpenoids from Silybum marianum

Marianine, the new lanostane triterpene (1) and marianosides A (2) and B (3) have been isolated from the whole plant of Silybum marianum. Their structures were elucidated on the basis of extensive analysis of their one dimensional and two dimensional nuclear magnetic resonance (1D, 2D-NMR) spectral data. All inhibited chymotrypsin in a concentration-dependent manner.

Use of relaxation-edited one-dimensional and two dimensional nuclear magnetic resonance spectroscopy to improve detection of small metabolites in blood plasma

The 1H nuclear magnetic resonance (NMR) spectra of biological samples, such as blood plasma and tissues, are information rich but data complex owing to superposition of the resonances from a multitude of different chemical entities in multiple-phase compartments, hampering detection and subsequent resonance assignments. To overcome these problems, several spectral-editing NMR experiments are described here, combining spin-relaxation filters (based on T 1, T ρ, and T 2) with both one-dimensional and two-dimensional (2D) NMR spectroscopy. These techniques enable the separation of NMR resonances based on their relaxation times and allow simplification of the complex spectra. In this paper, the approach is exemplified using a control human blood plasma, which is a complex mixture of proteins, lipoproteins, and small-molecule metabolites. In the case of T 1ρ- and T 2-edited 2D NMR experiments, a “flip-back” pulse was introduced after the relaxation editing to make the phase cycling of the “relaxation filter” and the 2D NMR part independent, thus enabling easy implementation of the phase-sensitive 2D NMR experiments. These methods also permit much higher receiver gains to be used to reduce digitization error, in particular, for the small resonances, which are sometimes vitally important for metabonomics studies. Both pulse sequences and experimental results are discussed for T 1-, T 1ρ-, and T 2-filtered COSY, T 2-filtered phase-sensitive DQF-COSY, and T 1, T 1ρ-, and T 2-filtered TOCSY NMR.

Spectroscopic and molecular dynamics simulation studies of the interaction of insulin with glucose

The interaction between monomeric insulin and monosaccharides has been investigated through circular dichroism, fluorescence spectroscopy and two dimensional nuclear magnetic resonance. CD spectra indicate that d-glucose interacts with monomeric insulin whereas d-galactose, d-mannose and 2-deoxy- d-glucose have a lower effect. Fluorescence emission was quenched at sugar concentrations of 5–10 mM. Titration with the different sugars produces a quenching of the tyrosine spectrum from which a binding free energy value for the insulin–sugar complexes has been evaluated. Transfer nuclear Overhauser enhancement NMR experiments indicate the existence of dipolar interactions at short interatomic distances between C-1 proton of d-glucose in the β form and the monomeric insulin. Further, NMR total correlation spectra experiments revealed that the hormone is in the monomeric form and that upon addition of glucose no aggregation occurs. The interaction does not involve relevant changes in the secondary structure of insulin suggesting that the interaction occur at the side chain level. Molecular dynamics simulations and modeling studies, based on the dynamic fluctuations of potential binding moiety sidechains, argued from results of NMR spectroscopy, provide additional informations to locate the putative binding sites of d-glucose to insulin.

Microstructure and compositional assignments of acrylamide/vinylidene chloride copolymers using one and two dimensional nuclear magnetic resonance spectroscopy

Copolymers containing acrylamide (A) and vinylidene chloride (V) units of different composition were synthesized by free radical solution polymerization. The reactivity ratios were estimated by Kelen Tudos and nonlinear error in variable methods. The triad sequence distribution in terms of A- and V-centered triads have been obtained from 13 C 1 H nuclear magnetic resonance spectroscopy. The complete spectral assignment in terms of compositional sequences of the overlapping carbon and proton spectra of these copolymers were done with the help of Distortionless Enhancement by Polarization Transfer, two-dimensional proton detected heteronuclear correlation (inverse-HETCOR) and Total Correlated Spectroscopy experiments.