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At least 217 records · Page 12Linked to original sources
PubMed2004

Direct characterization of bitter acids in a crude hop extract by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

The applicability of on-line coupling of reversed-phase high-performance liquid chromatography to atmospheric pressure ionization tandem mass spectrometry for the separation and characterization of hop acids mixture from the crude extract of Humulus lupulus was investigated. The solvent system consisting of acetonitrile-aqueous formic acid was used to give proper separation of the six main hop bitter acids within 30 min. Further structural information about the components was acquired by collision-induced dissociation (CID). On the basis of analyses of the fragmentation patterns of the major alpha- and beta-bitter acids respectively, identification of the minor ones was performed using selected reaction monitoring (SRM) with a group of qualitatively relevant selected precursor-product ion transitions for each bitter acid in a single high performance liquid chromatography (HPLC) run. Using this technique, six minor hop acids, including "adprelupulone" observed for the first time in natural resources, were detected along with the six major acids. This hyphenated techniques provides potency for rapid qualitative determination of analogs and homologs in mixtures.

Acids↗
PubMed2006

Sensitive electrochemical detection method for alpha-acids, beta-acids and xanthohumol in hops (Humulus lupulus L.).

A new HPLC method with coulometric detection for the quantification of xanthohumol, alpha-acids and beta-acids in hops was developed. The separation of compounds was accomplished with a C18 column and isocratic elution with methanol: 50 mM potassium phosphate: ortho-phosphoric acid=80:20:0.25 (v/v/v). The method was validated and UV and electrochemical detectors (ECD) were compared. The HPLC method with ECD was precise, accurate and very sensitive for detection of xanthohumol and alpha- and beta-acids. The detection limits of analytes were at least 8.8 to 24 times lower with ECD than those of the UV detector. The ECD method was successfully applied for quantification of studied compounds in hop pellets. The concentrations of all compounds obtained with ECD and UV were found to be equivalent. This is the first study demonstrating a very sensitive and validated method for the quantification of xanthohumol, alpha- or beta-acids in hop samples with the use of the electrochemical detector.

Acids↗
PubMed2005

Rabbit knee joint biomechanics: motion analysis and modeling of forces during hopping.

Although the rabbit hindlimb has been commonly used as an experimental animal model for studies of osteoarthritis, bone growth and fracture healing, the in vivo biomechanics of the rabbit knee joint have not been quantified. The purpose of this study was to investigate the kinematic and kinetic patterns during hopping of the adult rabbit, and to develop a model to estimate the joint contact force distribution between the tibial plateaus. Force platform data and three-dimensional motion analysis using infrared markers mounted on intracortical bone pins were combined to calculate the knee and ankle joint intersegmental forces and moments. A statically determinate model was developed to predict muscle, ligament and tibiofemoral joint contact forces during the stance phase of hopping. Variations in hindlimb kinematics permitted the identification of two landing patterns, that could be distinguished by variations in the magnitude of the external knee abduction moment. During hopping, the prevalence of an external abduction moment led to the prediction of higher joint contact forces passing through the lateral compartment as compared to the medial compartment of the knee joint. These results represent critical data on the in vivo biomechanics of the rabbit knee joint, which allow for comparisons to both other experimental animal models and the human knee, and may provide further insight into the relationships between mechanical loading, osteoarthritis, bone growth, and fracture healing.

Animals↗
PubMed2004

In vitro binding experiments with a Valerian, hops and their fixed combination extract (Ze91019) to selected central nervous system receptors.

The fixed valerian-hops extract combination Ze91019 is used as a sleep aid. Although its exact mechanism of action is not well understood, earlier studies indicate that the CNS effect of valerian might occur through interaction with the GABA, melatonin and/or the adenosine systems in the brain. The use of hops in sleep remedies, however, is mainly based on traditional use and scarce scientific information. In this report, the binding of Ze91019, and the component valerian and hops extracts within, was tested on 14 subtypes of five classes of central receptors (dopamine, serotonin, melatonin, MCH and neuropeptide-Y). Binding affinities could be demonstrated at some of the screened melatonin (ML1 and ML2) and serotonin (5-HT4e, 5-HT6 and 5-HT7) receptor subtypes.

Animals↗
PubMed2001

Phase-dependent modulation of cutaneous reflexes of tibialis anterior muscle during hopping.

During human gait, the amplitude of cutaneous reflexes in the leg is modulated as a function of the phase of the step cycle. In tibialis anterior (TA) the responses to sural nerve stimulation are facilitatory at end stance while they are suppressive at end swing. To investigate in how far this modulation is specifically related to alternating locomotion, the modulation of such reflexes was studied during a symmetric rhythmic movement, namely hopping (as equivalent of galloping). The end-stance facilitation was present during hopping while the end-swing suppression was absent. It is concluded that the end-stance facilitation is not specific for alternating gait. The absence of the end-swing suppressive reflexes may be related to the absence of heel strike in hopping.

Adult↗
PubMed1999

Quantitative analysis of xanthohumol and related prenylflavonoids in hops and beer by liquid chromatography-tandem mass spectrometry.

A method for quantitation of six prenylflavonoids (xanthohumol, isoxanthohumol, desmethylxanthohumol, 6- and 8-prenylnaringenins and 6-geranylnaringenin) in hops and beer by HPLC-tandem mass spectrometry has been developed. The method allows direct analysis of beer and crude methanolic extracts of hops. After HPLC separation, prenylflavonoids were detected by positive ion multiple-reaction monitoring using a triple-quadrupole mass spectrometer equipped with a heated nebulizer--atmospheric pressure chemical ionization interface. The accuracy and precision were evaluated by replicate analyses of (spiked) samples. Thirteen commercial beers were analysed with the method. Isoxanthohumol, formed by isomerization of xanthohumol during the brewing process, was the most abundant flavonoid in hopped beers, ranging from 0.04 to 3.44 mg/l.

Beer↗
PubMed2003

Coordination and stability of one-legged hopping patterns in patients with anterior cruciate ligament reconstruction: preliminary results.

OBJECTIVES: To investigate whether the intralimb coordination of the lower extremity during one-legged hopping in patients with anterior cruciate ligament reconstruction is different and less stable compared to control subjects. DESIGN: Measures of coordination dynamics are applied to study the coordination and stability of movement patterns of the knee and ankle in patients and control subjects. BACKGROUND: Due to several factors, such as loss of proprioceptive function and muscle weakness, the intralimb coordination of the lower extremity might be altered. METHODS: Seven patients and 13 healthy control subjects were instructed to hop in place on one leg for 10 seconds at a comfortable frequency for each leg separately. RESULTS AND CONCLUSIONS: The one-legged hopping movement pattern of patients with anterior cruciate ligament reconstruction one-year post-operative is different and less stable compared to healthy subjects, and thus is still impaired. RELEVANCE: This paper shows that patients, one year after reconstruction of the anterior cruciate ligament, have a different coordination pattern of the lower limb compared to a matched control group. Intersegmental coordination and stability, features that are often observed by eye during a rehabilitation process, are objectified in this study.

Adolescent↗
PubMed2000

Hyperactivation of the Drosophila Hop jak kinase causes the preferential overexpression of eIF1A transcripts in larval blood cells.

Jak kinase-Stat protein pathways play a critical role in the response of blood cells to a range of cytokines and growth factors. We are using the fruit fly, Drosophila melanogaster, as a model system to elucidate additional components of Jak-Stat pathways, and to determine how abnormalities in this pathway lead to hematopoietic leukemia-like defects. To identify downstream targets, we conducted a molecular screen for genes whose transcripts are overexpressed in response to activation of the Drosophila Hop Jak kinase. We identified a Drosophila homolog of eIF1A, a eukaryotic initiation factor found in humans and other eukaryotes. D-eIF1A is highly overexpressed in the hemocytes and lymph glands of third instar larvae carrying the dominant, gain-of-function mutation hop(Tum-l). A quantitative comparison of poly(A)(+) RNA levels between D-eIF1A and other known Drosophila translation initiation factors indicates that D-eIF1A transcripts preferentially overaccumulate in response to the hyperactive Hop pathway. Our results support the model that D-eIF1A is one of the target genes through which the Drosophila Jak kinase pathway regulates hemocyte development.

Amino Acid Sequence↗
PubMed2003

Biotransformation of hop aroma terpenoids by ale and lager yeasts.

Terpenoids are important natural flavour compounds, which are introduced to beer via hopping. It has been shown recently that yeasts are able to biotransform some monoterpene alcohols. As a first step towards examining whether yeasts are capable of altering hop terpenoids during the brewing of beer, we investigated whether they were transformed when an ale and lager yeast were cultured in the presence of a commercially available syrup. Both yeasts transformed the monoterpene alcohols geraniol and linalool. The lager yeast also produced acetate esters of geraniol and citronellol. The major terpenoids of hop oil, however, were not biotransformed. Oxygenated terpenoids persisted much longer than the alkenes.

Acyclic Monoterpenes↗
PubMed2006

Coupled ion/electron hopping in Li(x)NiO2: a 7Li NMR study.

Deintercalated "Li(x)NiO2" materials (x = 0.25, 0.33, 0.50, 0.58, and 0.65) were obtained using the electrochemical route from the Li0.985Ni1.015O2 and Li0.993Ni1.007O2 compounds. Refinements of X-ray diffraction data using the Rietveld method show a good agreement with the phase diagram of the Li(x)NiO2 system studied earlier in this laboratory. Electronic conductivity measurements show a thermally activated electron-hopping process for the deintercalated Li0.5NiO2 phase. In the Li(x)NiO2 materials investigated (x = 0.25, 0.33, 0.50, and 0.58), 7Li NMR shows mobility effects leading to an exchanged signal at room temperature. A clear tendency for Li to be surrounded mainly by Ni3+ ions with the 180 degree configuration is observed, particularly, for strongly deintercalated materials with smaller Li+ and Ni3+ contents, even upon heating, when this mobility becomes very fast in the NMR time scale. This suggests that Li/vacancy hopping does occur on the NMR time scale but that Ni3+/Ni4+ hopping does not occur independently. The position of Li seems to govern the oxidation state of the Ni around it at any time; the electrons follow the Li ions to satisfy local electroneutrality and minimal energy configuration. The observed NMR shifts are compatible with the Li/vacancy and Ni3+/Ni4+ ordering patterns calculated by Arroyo y de Dompablo et al. for x = 0.25 and x = 0.50, but not for x = 0.33 and x = 0.58.

Electrons↗
PubMed2005

Directly meso-meso linked porphyrin rings: synthesis, characterization, and efficient excitation energy hopping.

Directly meso-meso linked porphyrin rings CZ4, CZ6, and CZ8 that respectively comprise four, six, and eight porphyrins have been synthesized in a stepwise manner from a 5,10-diaryl zinc(II) porphyrin building block. Symmetric cyclic structures have been indicated by their very simple (1)H NMR spectra that exhibit only a single set of porphyrin and their absorption spectra that display a characteristic broad nonsplit Soret band around 460 nm. Energy minimized structures calculated at the B3LYP/6-31G* level indicate that a dihedral angle between neighboring porphyrins decreases in order of CZ6 > CZ8 > CZ4, which is consistent with the (1)H NMR data. Photophysical properties of these molecules have been examined by the steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related with the excitation energy migration processes within the porphyrin rings, where the exciton-exciton annihilation time and the polarization anisotropy rise time are well described in terms of the Forster-type incoherent energy hopping model. Consequently, the excitation energy hopping rates have been estimated for CZ4 (119 +/- 2 fs)(-)(1), CZ6 (342 +/- 59 fs)(-)(1), and CZ8 (236 +/- 31 fs)(-)(1), which reflect the magnitude of the electronic coupling between the neighboring porphyrins. Overall, these porphyrin rings serve as a well-defined wheel-shaped light harvesting antenna model in light of very efficient excitation energy hopping along the ring.

Journal Article↗
PubMed2001

Development of a gas chromatographic method for fungicide cymoxanil analysis in dried hops.

An analytical method for detecting cymoxanil [2-cyano-N-[(ethylamino)carbonyl]-2-(methoxyimino)acetamide] residues in dried hops was developed utilizing liquid-liquid partitioning, automated gel permeation chromatography (GPC), solid phase extraction (SPE) cleanup, and gas chromatography (GC). Method validation recoveries from dried hops were 96 +/- 12, 108 +/- 11, and 136 +/- 8% over three levels of fortification (0.05, 0.5, and 1.0 ppm, respectively). The hop samples from three field sites, which were treated with cymoxanil, had residue levels ranging from 0.146 to 0.646 ppm. The detection limit and the quantitation limit of the method developed in the present study were 0.022 and 0.050 ppm, respectively.

Acetamides↗
PubMed2000

Gas chromatographic-mass spectrometric method for the analysis of dimethomorph fungicide in dried hops.

An analytical method for the determination of dimethomorph [(E,Z)-4-[3-(4-chlorophenyl)-3-(3,4-dimethoxyphenyl)acryloyl]morpholine] residues in dried hops was developed utilizing liquid-liquid partitioning, automated gel permeation chromatography (GPC), Florisil and aminopropyl solid phase extraction (SPE) column cleanups, and gas chromatography (GC) with mass selective detection (MSD). Method validation recoveries from dried hops ranged from 79 to 103% over four levels of fortification (0.1, 1.0, 5.0, and 20 ppm). Control and dimethomorph-treated hop samples collected from three field sites had residue levels of <0.10 and 4.06-17.32 ppm, respectively. The method was validated to the limit of quantitation at 0.10 ppm. The limit of detection for this method was 0.045 ppm.

Fungicides, Industrial↗
PubMed2006

Analysis of hop acids and their oxidized derivatives and iso-alpha-acids in beer by capillary electrophoresis-electrospray ionization mass spectrometry.

This study investigates the applicability of on-line coupling of capillary electrophoresis with electrospray ionization tandem mass spectrometry (CZE-ESI-MS) for the separation and characterization of alpha- and beta-acids and oxidized hop acids from crude extracts of different hop varieties. CZE-ESI-MS with negative-ion electrospray ionization proved to be a suitable technique for the determination of these types of natural compounds and their oxidized derivatives. The CZE parameters (pH, concentration, and buffer type) and ESI-MS parameters (nature and flow rate of the sheath liquid, nebulizer pressure, drying gas flow rate, temperature, and compound stability) were optimized. The optimized method provides the potential for a fast qualitative determination of hop acids and their oxidation compounds. The method was also applied to the determination of iso-alpha-acids in beer.

Beer↗
PubMed2007

Relevance of organic farming and effect of climatological conditions on the formation of alpha-acids, beta-acids, desmethylxanthohumol, and xanthohumol in hop (Humulus lupulus L.).

The concentrations of alpha-acids, beta-acids, desmethylxanthohumol, and xanthohumol were monitored in the hop varieties Admiral (A), Wye Challenger (WC), and First Gold (FG) during the harvest seasons of 2003 through 2005. Hops grown under an organic regimen were compared to plants grown conventionally in hop fields in close vicinity. The concentrations of the key compounds depended very much on climatological conditions showing, in general, highest levels in poorest weather conditions (2004). Of the three varieties studied, FG was the only one showing a clear trend for higher concentrations of secondary metabolites under organic growing conditions than under conventional farming conditions. Cultivation of A and WC seems to be very sensitive to climatic conditions and environmental stresses caused by pests and diseases, thereby leading to various results. WC proved to be a rich source of bioactive chalcones, particularly desmethylxanthohumol.

Agriculture↗
PubMed2004

"Lead hopping". Validation of topomer similarity as a superior predictor of similar biological activities.

Two extensive studies quantifying the ability of topomer shape similarity to forecast a variety of biological similarities are described. In a prospective trial of "lead hopping", using topomer similarity for virtual screening and queries from the patent literature, biological assays of 308 selected compounds (representing 0.03% of those available, per assay type) yielded 11 successful "lead hops" in the 13 assays attempted. The hit rate averaged over all assays was 39% ("activity"defined as inhibition > or =20% at 10 microM), significantly greater than an unexpectedly high negative control hit rate of 15%. The average "Tanimoto 2D fingerprint similarity" between query and "lead hop" structures (0.36) was little more than the Tanimoto similarity between random drug-like structures. Topomer shape and Tanimoto 2D fingerprint similarities were also compared retrospectively, in their tendencies to concentrate together potential and actual drugs reported to belong to the same "activity class", for twenty classes. Among the most similar 3% of structures (corresponding to "> or =0.85 Tanimoto" for these structures), an average of 62% of the topomer similar selection possessed a near neighbor belonging to the same activity class, roughly a one-third superiority over the "Tanimoto > or = 0.85" selection containing 48% actives in avoiding false positives. Conversely, the least similar 75% of structures contained 0.3% actives for topomer similarity vs 1.0% actives for Tanimoto 2D fingerprint similarity, a 3-fold superiority for topomers in avoiding false negatives.

Computing Methodologies↗
PubMed2004

A 3D similarity method for scaffold hopping from known drugs or natural ligands to new chemotypes.

A primary goal of 3D similarity searching is to find compounds with similar bioactivity to a reference ligand but with different chemotypes, i.e., "scaffold hopping". However, an adequate description of chemical structures in 3D conformational space is difficult due to the high-dimensionality of the problem. We present an automated method that simplifies flexible 3D chemical descriptions in which clustering techniques traditionally used in data mining are exploited to create "fuzzy" molecular representations called FEPOPS (feature point pharmacophores). The representations can be used for flexible 3D similarity searching given one or more active compounds without a priori knowledge of bioactive conformations or pharmacophores. We demonstrate that similarity searching with FEPOPS significantly enriches for actives taken from in-house high-throughput screening datasets and from MDDR activity classes COX-2, 5-HT3A, and HIV-RT, while also scaffold or ring-system hopping to new chemical frameworks. Further, inhibitors of target proteins (dopamine 2 and retinoic acid receptor) are recalled by FEPOPS by scaffold hopping from their associated endogenous ligands (dopamine and retinoic acid). Importantly, the method excels in comparison to commonly used 2D similarity methods (DAYLIGHT, MACCS, Pipeline Pilot fingerprints) and a commercial 3D method (Pharmacophore Distance Triplets) at finding novel scaffold classes given a single query molecule.

Cyclooxygenase 2↗
PubMed2006

Fewest switches adiabatic surface hopping as applied to vibrational energy relaxation.

In this contribution quantum/classical surface hopping methodology is applied to vibrational energy relaxation of a quantum oscillator in a classical heat bath. The model of a linearly damped (harmonic) oscillator is chosen which can be mapped onto the Brownian motion (Caldeira-Leggett) Hamiltonian. In the simulations Tully's fewest switches surface hopping scheme is adopted with inclusion of dephasing in the adiabatic basis using a simple decoherence algorithm. The results are compared to the predictions of a Redfield-type quantum master equation modeling using the classical heat bath force correlation function as input. Thereby a link is established between both types of quantum/classical approaches. Viewed from the latter perspective, surface hopping with dephasing may be interpreted as "on-the-fly" stochastic realization of a quantum/classical Pauli master equation.

Half-Life↗