t1-Noise Eliminated Dipolar Heteronuclear Multiple-Quantum Coherence Solid-State NMR Spectroscopy

<p>Heteronuclear correlation (HETCOR) spectroscopy is one of the key tools in the arsenal of the solid-state NMR spectroscopist to probe spatial proximity between two different nuclei and enhance spectral resolution. Dipolar heteronuclear multiple-quantum coherence (D-HMQC) is a powerful technique that can be potentially utilized to obtain ¹H detected 2D HETCOR solid-state NMR spectra of any NMR active nucleus. A long-standing problem in ¹H detected D-HMQC solid-state NMR experiments is the presence of <i>t</i>₁-noise which reduces sensitivity and impedes spectral interpretation. In this contribution, we describe novel pulse sequences, termed <i>t</i>₁-noise eliminated (TONE) D-HMQC, that suppress <i>t</i>₁-noise and can provide higher sensitivity and resolution than conventional D-HMQC. Monte-Carlo and numerical simulations confirm that <i>t</i>₁-noise in conventional D-HMQC primarily occurs because random MAS frequency fluctuations cause variations in the NMR signal amplitude from scan to scan, leading to imperfect cancellation of uncorrelated signals by phase cycling. The TONE D-HMQC sequence uses ¹H p-pulses to refocus the evolution of ¹H CSA across each recoupling block, improving the stability of the pulse sequence to random MAS frequency fluctuations. The ¹H refocusing pulses also restore the orthogonality of in-phase and anti-phase magnetization for all crystallite orientations, enabling the use of 90° flip-back or LG spin-lock trim pulses to reduce the intensity of uncorrelated signals. We demonstrate the application of these methods to acquire detected 2D ¹H-³⁵Cl and ¹H-¹³C HETCOR spectra of histidine•HCl•H₂O with reduced <i>t</i>₁-noise. To show generality, we also apply these methods to obtain 2D ¹H-¹⁷O spectra of 20%-¹⁷O fmoc-alanine and for the first time at natural abundance, 2D ¹H-²⁵Mg HETCOR spectra of magnesium hydroxide. The TONE D-HMQC sequences are also used to probe ¹H-²⁵Mg and ¹H-²⁷Al proximities in Mg-Al layered double hydroxides and confirm the even mixing of Mg and Al in these materials.</p>

t1-Noise Eliminated Dipolar Heteronuclear Multiple-Quantum Coherence Solid-State NMR Spectroscopy

<p>Heteronuclear correlation (HETCOR) spectroscopy is one of the key tools in the arsenal of the solid-state NMR spectroscopist to probe spatial proximity between two different nuclei and enhance spectral resolution. Dipolar heteronuclear multiple-quantum coherence (D-HMQC) is a powerful technique that can be potentially utilized to obtain ¹H detected 2D HETCOR solid-state NMR spectra of any NMR active nucleus. A long-standing problem in ¹H detected D-HMQC solid-state NMR experiments is the presence of <i>t</i>₁-noise which reduces sensitivity and impedes spectral interpretation. In this contribution, we describe novel pulse sequences, termed <i>t</i>₁-noise eliminated (TONE) D-HMQC, that suppress <i>t</i>₁-noise and can provide higher sensitivity and resolution than conventional D-HMQC. Monte-Carlo and numerical simulations confirm that <i>t</i>₁-noise in conventional D-HMQC primarily occurs because random MAS frequency fluctuations cause variations in the NMR signal amplitude from scan to scan, leading to imperfect cancellation of uncorrelated signals by phase cycling. The TONE D-HMQC sequence uses ¹H p-pulses to refocus the evolution of ¹H CSA across each recoupling block, improving the stability of the pulse sequence to random MAS frequency fluctuations. The ¹H refocusing pulses also restore the orthogonality of in-phase and anti-phase magnetization for all crystallite orientations, enabling the use of 90° flip-back or LG spin-lock trim pulses to reduce the intensity of uncorrelated signals. We demonstrate the application of these methods to acquire detected 2D ¹H-³⁵Cl and ¹H-¹³C HETCOR spectra of histidine•HCl•H₂O with reduced <i>t</i>₁-noise. To show generality, we also apply these methods to obtain 2D ¹H-¹⁷O spectra of 20%-¹⁷O fmoc-alanine and for the first time at natural abundance, 2D ¹H-²⁵Mg HETCOR spectra of magnesium hydroxide. The TONE D-HMQC sequences are also used to probe ¹H-²⁵Mg and ¹H-²⁷Al proximities in Mg-Al layered double hydroxides and confirm the even mixing of Mg and Al in these materials.</p>

Solid State NMR: A Powerful Tool for the Characterization of Borophosphate Glasses

This review will show how solid state nuclear magnetic resonance (NMR) has contributed to a better understanding of the borophosphate glass structure. Over the last fifteen years, 1D and 2D magic angle spinning (MAS)-NMR has been used to produce key information about both local and medium range organization in this type of glass. After a brief presentation on borophosphate glasses, the paper will focus on the description of the local order of phosphate and borate species obtained by 1D 31P-and 11B-MAS-NMR experiments, with a special emphasis on the improvements obtained at high magnetic fields on the borate speciation description. The last part of this review will show how correlation NMR provided new insights into the intermediate length scale order. Special attention will be paid to the quantitative data retrieved from 11B/31P REDOR-based NMR sequences and to the qualitative connectivity schemes observed on the 2D 11B/31P maps edited with the heteronuclear multiple quantum coherence (HMQC) NMR techniques.

t1-Noise eliminated dipolar heteronuclear multiple-quantum coherence solid-state NMR spectroscopy

t1-Noise eliminated (TONE) heteronuclear multiple quantum correlation (HMQC) solid-state nuclear magnetic resonance pulse sequences improve the sensitivity of 2D 1H{X} heteronuclear correlation experiments with X = 17O, 25Mg, 27Al and 35Cl.

The Inescapable Effects of Ribosomes on In-Cell NMR Spectroscopy and the Implications for Regulation of Biological Activity

The effects of RNA on in-cell NMR spectroscopy and ribosomes on the kinetic activity of several metabolic enzymes are reviewed. Quinary interactions between labelled target proteins and RNA broaden in-cell NMR spectra yielding apparent megadalton molecular weights in-cell. The in-cell spectra can be resolved by using cross relaxation-induced polarization transfer (CRINEPT), heteronuclear multiple quantum coherence (HMQC), transverse relaxation-optimized, NMR spectroscopy (TROSY). The effect is reproduced in vitro by using reconstituted total cellular RNA and purified ribosome preparations. Furthermore, ribosomal binding antibiotics alter protein quinary structure through protein-ribosome and protein-mRNA-ribosome interactions. The quinary interactions of Adenylate kinase, Thymidylate synthase and Dihydrofolate reductase alter kinetic properties of the enzymes. The results demonstrate that ribosomes may specifically contribute to the regulation of biological activity.

Toxicities of Eucalyptus dives Oil, 3-Carvomenthenone, and Its Analogues against Stored-Product Insects

ABSTRACT The insecticidal toxicities of essential oils and other active components extracted from Eucalyptus dives leaves (as well as structural analogues) were studied against stored-product insects, Plodia interpunctella and Tribolium castaneum. 3-Carvomenthenone was purified from E. dives oil, and the structures were elucidated by electron ionization mass spectra, 1H-nuclear magnetic resonance (NMR), 13C-NMR, heteronuclear multiple quantum coherence, 1H-1H correlation spectroscopy, and distortionless enhancement by polarization transfer NMR. Using the fumigant method against P. interpunctella larvae and adults, cyclohexenone exhibited the strongest toxicity (50% lethal dose [LD50] against larvae and adults, 2.45 and 3.63 μg/cm3), followed by methylcyclohexenone (2.95 and 4.24 μg/cm3), seudenone (3.02 and 4.44 μg/cm3), and 3-carvomenthenone (52.4 and 68.7 μg/cm3). Using the contact method, cyclohexenone (LD50 against larvae and adults, 17.25 and 19.35 μg/cm2) exhibited the most potent toxicities against T. castaneum larvae and adults, followed by methylcyclohexenone, seudenone, and 3-carvomenthenone. No functional radical on the backbone (2-cyclohexen-1-one) was more toxic than other chemicals. Structure-activity relationships between 3-carvomenthenone analogues and toxicities indicated that the toxicity of 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone might be conferred through the dermal organs of T. castaneum and P. interpunctella. This study indicates that E. dives oil, 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone have potential as natural agents to control stored-product insects.

Anti-inflammatory activity of highly oxygenated terpenoids from Achillea biebersteinii Afan

In continuation of our chemical investigation on some medicinal plants of the genus Achillea, chromatographic investigation of the methylene chloride/methanol (1:1) extract of the air-dried aerial part of Achillea biebersteinii Afan. (family Asteraceae) afforded a new natural monoterpene (2), in addition to two known sesquiterpenes (3 and 4). Compound 1 was isolated as light needle crystals. Structures were established on the basis of MS and NMR spectroscopic (1H, 13C, 1H-1H correlation spectroscopy, heteronuclear multiple-quantum coherence and heteronuclear multiple-bond correlation) data and in case of compound 1 were confirmed by X-ray analysis. All isolated compounds were examined for their anti-inflammatory activity to inhibit lipopolysaccharide-induced NO production in RAW264.7 macrophage cells. Compounds 3 and 4 produced a promising anti-inflammatory effect (76% and 80% inhibition, respectively). However, compounds 1 and 2 produced moderate inhibition of NO release recording a 41% and 36% inhibition of NO production, respectively.

Structure, mechanism and application of vinyl alcohol oligomers grafted onto poly(3-hydroxybutyrate): a proposal

Oligomers of poly(vinyl alcohol) were grafted onto poly(3-hydroxybutyrate) (PHB) by radiation-induced polymerization. The aim of this study was to elucidate the structure of these copolymers using nuclear magnetic resonance (heteronuclear multiple quantum coherence) spectroscopy supported by dynamic light scattering (DLS) and atomic force microscopy (AFM). It was concluded that vinyl alcohol (VA) was grafted onto PHB for the methylenic and methynic sites. A mechanism for the grafting reaction was proposed based on the experimental evidence. AFM and DLS allowed the characterization of the particles obtained from P(HB-g-VA). The prepared materials showed suitable properties for use in drug delivery systems.

One New Royleanumoate fromTeucrium royleanumWall. ex Benth

One new royleanumoate, a benzene ester (1), has been isolated fromT. royleanumWall. ex Benth along with two known compounds, namely, 3,4-dihydroxymethyl benzoate (2) and oleanolic acid (3). The structure elucidation of the isolated compounds was established on two-dimensional (2D) NMR techniques including heteronuclear multiple bond correlation (HMBC), heteronuclear multiple quantum Coherence (HMQC), and correlation spectroscopy (COSY) experiment.