9 research outputs found
Diastereomeric ratio determination by high sensitivity band-selective pure shift NMR spectroscopy
Pure shift NMR using band-selective decoupling allows simpler and more reliable determination of diastereomeric ratio.</p
Sugar-Functional Vinyl Addition Poly(norbornene)–Photopatternable Poly(norbornenyl gluconamide) Compositions Developed with Water
The norbornenyl gluconamide (NBGA)
monomer can be polymerized by
a number of palladium catalysts to give water-soluble, vinyl addition
poly(NBGA). Depending on the catalyst used, the reaction conditions,
and the chain-transfer additives employed, high-molecular-weight polymers
can be obtained. These polymers can be thermally cross-linked at ca.
190 °C or at ca. 150 °C when the difunctional glutaraldehyde
is added. A photopatternable composition is formed by the addition
of a water-soluble diazide when the poly(NBGA) molecular weight is
sufficiently high. After image-wise exposure, negative-tone patterns
are revealed by water development. A detailed analysis of NBGA monomer
structures by high-resolution nuclear magnetic resonance techniques
including pure shift is reported showing that two diastereomers of
each endo- and exo-isomer are formed from the reaction of norbornene
methylamine and δ-gluconolactone
Real-time pure shift N-15 HSQC of proteins: a real improvement in resolution and sensitivity
Spectral resolution in proton NMR spectroscopy is reduced by the splitting of resonances into multiplets due to the effect of homonuclear scalar couplings. Although these effects are often hidden in protein NMR spectroscopy by low digital resolution and routine apodization, behind the scenes homonuclear scalar couplings increase spectral overcrowding. The possibilities for biomolecular NMR offered by new pure shift NMR methods are illustrated here. Both resolution and sensitivity are improved, without any increase in experiment time. In these experiments, free induction decays are collected in short bursts of data acquisition, with durations short on the timescale of J-evolution, interspersed with suitable refocusing elements. The net effect is real-time (t 2) broadband homodecoupling, suppressing the multiplet structure caused by proton–proton interactions. The key feature of the refocusing elements is that they discriminate between the resonances of active (observed) and passive (coupling partner) spins. This can be achieved either by using band-selective refocusing or by the BIRD element, in both cases accompanied by a nonselective 180° proton pulse. The latter method selects the active spins based on their one-bond heteronuclear J-coupling to 15N, while the former selects a region of the 1H spectrum. Several novel pure shift experiments are presented, and the improvements in resolution and sensitivity they provide are evaluated for representative samples: the N-terminal domain of PGK; ubiquitin; and two mutants of the small antifungal protein PAF. These new experiments, delivering improved sensitivity and resolution, have the potential to replace the current standard HSQC experiments
Nonanthocyanin Secondary Metabolites of Black Raspberry (<i>Rubus occidentalis</i> L.) Fruits: Identification by HPLC-DAD, NMR, HPLC-ESI-MS, and ESI-MS/MS Analyses
Nonanthocyanin
secondary metabolites potentially contributing to
the antiproliferative bioactivity of black raspberry (Rubus occidentalis L.) fruits were extracted in ethyl
acetate and isolated by semipreparative and analytical HPLC and analyzed
by NMR, HPLC-ESI-MS, and ESI-MS/MS techniques. Here we present complete
and partial structures of a variety of the chemical entities such
as quercetin 3-glucoside, quercetin 3-rutinoside, myricetin glucoside,
dihydrokaempferol glucoside, benzoic acid β-d-glucopyranosyl
ester, 3,4-dihydroxybenzoic acid, epicatechin, caffeic acid, <i>p-</i>coumaric acid, <i>p-</i>coumaryl glucoside, <i>p-</i>coumaryl sugar ester, ellagic acid, methyl ellagic acid
acetylpentose, methyl ellagic acid valerylpentose, <i>trans</i>-piceid, phloretin glucoside (phloridzin), dihydrosinapic acid, salicylic
acid β-d-glucopyranosyl ester, a salicylic acid derivative
without attached sugar, <i>p-</i>alkylphenyl glucoside,
and a citric acid derivative. To our knowledge, 15 of these compounds
were not previously reported in black raspberry fruits
NMR-Based Metabolomic Investigation of Bioactivity of Chemical Constituents in Black Raspberry (Rubus occidentalis L.) Fruit Extracts
Black
raspberry (Rubus occidentalis L.) (BR)
fruit extracts with differing compound profiles have shown
variable antiproliferative activities against HT-29 colon cancer cell
lines. This study used partial least-squares (PLS) regression analysis
to develop a high-resolution <sup>1</sup>H NMR-based multivariate
statistical model for discerning the biological activity of BR constituents.
This model identified specific bioactive compounds and ascertained
their relative contribution against cancer cell proliferation. Cyanidin
3-rutinoside and cyanidin 3-xylosylrutinoside were the predominant
contributors to the extract bioactivity, but salicylic acid derivatives
(e.g., salicylic acid glucosyl ester), quercetin 3-glucoside, quercetin
3-rutinoside, <i>p</i>-coumaric acid, epicatechin, methyl
ellagic acid derivatives (e.g., methyl ellagic acetyl pentose), and
citric acid derivatives also contributed significantly to the antiproliferative
activity of the berry extracts. This approach enabled the identification
of new bioactive components in BR fruits and demonstrates the utility
of the method for assessing chemopreventive compounds in foods and
food products