Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “FIRS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources
PubMed2000

Far-infrared spectroscopy of CH3OD in highly excited torsional states and the atlas of the Fourier transform spectra in the range 200-350 cm(-1).

The high resolution Fourier transform far-infrared (FIR) spectrum of the torsion rotation band of CH3OD has been analyzed for the highly excited torsion states (n > or = 2) in the vibrational ground state. The spectrum shows splitting of the lines due to strong torsional-rotational-vibrational interactions in the molecule. Assignments were possible for rotational sub-bands in the torsional state as high as n = 4 and for K values up to 8 and J values of up to approximately 30 in most cases, for all the symmetry species. For the third excited torsional state n = 3 assignments were possible to K = 10. The data were analyzed with the help of the energy expansion model, which has been proven very successful in methanol. The state dependent expansion parameters are presented. These molecular parameters were able to reproduce the observed wavenumbers almost to within experimental accuracy of 0.0002 cm(-1) for clean unblended lines. These expansion coefficients should prove valuable in the calculation of precise energy values for excited torsional states up to n = 4, which is way above the torsional barrier. The detailed high-resolution spectral atlas of CH3OD has been presented in the range 200-350 cm(-1). This atlas is an extension of our earlier atlas in the range 20-205 cm(-1). The availability of this atlas in the journal will be very valuable for spectroscopists and astrophysicists seeking information in the infrared (IR) region in the laboratory and in outer space.

Deuterium↗
PubMed2003

[Electronic structures of organometallic complexes of f elements. Part 54. Electronic Raman and f-f transitions in the low temperature vibrational spectra of Cp3Ce(NCCH3)2].

A comparison of the low temperature Raman spectra of Cp(3)Ce(NCCH(3))(2) (1), Cp(3)La(NCCH(3))(2) (2), Cp(3)La(NCCH(3))(2):Pr(3+) (3), Cp(3)La x NCCH(3) (4), Cp(3)Ce x NCCH(3) (5) and Cp(3)Tb x NCCH(3) (6) shows that the former compound exhibits three additional bands at 320, 2129 and 2154 cm(-1), which we ascribe to electronic Raman transitions. The two latter signals also appear in the low temperature IR spectrum of complex 1, but not in those of compounds 2-6. By performing crystal field (CF) calculations, the terminal states of the observed electronic Raman transitions could be identified. On the basis of both experimental and calculated CF energies as well as calculated wave functions the observed temperature dependence of mu(2)(eff) of complex 1 could be simulated in a satisfactory manner. A comparison of the low temperature Raman spectrum of compound 1 with the low temperature FIR spectrum of complex 2 shows that the selection rules for trigonal-bipyramidal coordination do not hold strictly for the skeletal vibrations. If the additional criterion of allowed vibronic side bands is applied to the transitions Gamma(1)-->Gamma(1, 4, 5, 6) of compound 3, the observed vibrational energies may be partly classified according to their symmetry.

Cerium↗
PubMed2004

Post-transcriptional gene silencing induced by short interfering RNAs in cultured transgenic plant cells.

Short interfering RNA (siRNA) is widely used for studying post-transcriptional gene silencing and holds great promise as a tool for both identifying function of novel genes and validating drug targets. Two siRNA fragments (siRNA-a and -b), which were designed against different specific areas of coding region of the same target green fluorescent protein (GFP) gene, were used to silence GFP expression in cultured gfp transgenic cells of rice (Oryza sativa L.; OS), cotton (Gossypium hirsutum L.; GH), Fraser fir [Abies fraseri (Pursh) Poir; AF], and Virginia pine (Pinus virginiana Mill.; PV). Differential gene silencing was observed in the bombarded transgenic cells between two siRNAs, and these results were consistent with the inactivation of GFP confirmed by laser scanning microscopy, Northern blot, and siRNA analysis in tested transgenic cell cultures. These data suggest that siRNA-mediated gene inactivation can be the siRNA specific in different plant species. These results indicate that siRNA is a highly specific tool for targeted gene knockdown and for establishing siRNA-mediated gene silencing, which could be a reliable approach for large-scale screening of gene function and drug target validation.

Cells, Cultured↗
PubMed2003

Bifunctional abietadiene synthase: mutual structural dependence of the active sites for protonation-initiated and ionization-initiated cyclizations.

Abietadiene synthase from grand fir catalyzes two sequential, mechanistically distinct cyclizations, of geranylgeranyl diphosphate and of copalyl diphosphate, in the formation of a mixture of abietadiene isomers as the committed step of diterpenoid resin acid biosynthesis. Each reaction is independently conducted at a separate active site residing in what were considered to be structurally distinct domains typical of terpene cyclases. Despite the presence of an unusual 250-residue N-terminal insertional element, a tandem pair of charged residues distal to the insertion was shown to form a functional part of the C-terminal active site. Because abietadiene synthase resembles the ancestral plant terpene cyclase, this observation suggests an early evolutionary origin of catalytically important positively charged residues at the N-terminus of enzymes of this general class. A series of N- and C-terminal truncations of this enzyme were constructed and characterized, both alone and as mixtures of adjacent polypeptide pairs, to assess the proposed domain architecture, the function of the insertional element, and the role of presumptive interdomain contacts. These studies indicated a requirement for the insertional element in functional folding and allowed definition of the minimum primary structure of N- and C-terminal active site peptides. Most importantly, the results showed that, although the two active sites of abietadiene synthase are catalytically independent, substantial contact between the two regions is essential for the functional competence of this enzyme. Thus, the two cyclization sites of abietadiene synthase cannot be dissected into catalytically distinct domains, and, therefore, abietadiene synthase is unlikely to have arisen by fusion of two previously independent genes.

Abies↗
PubMedDate not supplied

Sugar recovery and fermentability of hemicellulose hydrolysates from steam-exploded softwoods containing bark.

The hemicellulose sugar recovery and ethanol production obtained from SO2-catalyzed steam explosion of a mixed white fir (70%) and ponderosa pine (30%) feedstock containing bark (9% dry weight/dry weight) was assessed. More than 90% of the available hemicellulose sugars could be recovered in the hydrolysate obtained after steam explosion at 195 degrees C, 2.38 min, and 3.91% SO2, with 59% of the original hemicellulose sugars detected in a monomeric form. Despite this high sugar recovery, this hydrolysate showed low ethanol yield (64% of theoretical yield) when fermented with a spent sulfite liquor-adapted strain of Saccharomyces cerevisiae. In contrast, most hydrolysates prepared at higher steam explosion severity showed comparable or higher ethanol yields. Furthermore, the hydrolysates prepared from bark-free feedstock showed better fermentability (87% of theoretical yield) despite containing higher concentration of known inhibitors. The ethanol yield from the hydrolysate prepared from a bark-containing wood sample could be improved to 81% by an extra stage acid hydrolysis (121 degrees C for 1 h in 3% sulfuric acid). This extra stage acid hydrolysis and steam explosion at higher severity conditions seem to improve the fermentability of the hydrolysates by transforming certain inhibitory compounds present in the hydrolysates prepared from the bark-containing feedstock and thus lowering their inhibitory effect on the yeast used for the ethanol fermentation.

Abies↗
PubMedDate not supplied

Do enzymatic hydrolyzability and Simons' stain reflect the changes in the accessibility of lignocellulosic substrates to cellulase enzymes?

In an attempt to elucidate the impact of substrate accessibility to cellulases on the susceptibility of lignocellulosic substrates to enzymatic hydrolysis, a hydrogen peroxide treated, Douglas fir kraft pulp was dried using several methods with varying levels of intensity. Oven-drying at 50 and 100 degrees C, air-drying, and freeze-drying methods were employed to remove the interfibrillar water from the pulp samples. Subsequently, the never-dried and variably dried pulps were hydrolyzed using a commercial cellulase preparation supplemented with additional beta-glucosidase. Drying reduced the susceptibility of the substrates to enzymatic hydrolysis, which can be attributed to the hornifying effect that drying has on fibers. This effect was more pronounced for the fibers that were oven-dried at 100 degrees C (23% reduction) and 50 degrees C (15% reduction), and there was a good correlation between the Simons's stain results and the enzymatic digestibility of the dried pulps. These observations indicated that drying significantly reduced the population of larger pores and that the partial closure of larger pores created a large number of smaller pores that were not accessible to the displacement dye molecules (orange dye). The inaccessibility of the cellulose to the enzymes, due to the collapse or closure of the large pores, appears to be the primary reason for the lower susceptibility of the dried pulps to enzymatic hydrolysis.

Algorithms↗
PubMed2003

Using stable and radioactive isotopes to trace atmospherically deposited Pb in montane forest soils.

Atmospheric deposition of lead (Pb) throughout the 1900s resulted in elevated amounts of this toxic metal even in remote forest soils of the northeastern United States. Soils can act as a net sink for metals and thus minimize groundwater and surface water contamination. Recent studies utilizing forest floor temporal data and models of total Pb in precipitation, surface soils, and streams have estimated the time scale of Pb release from soils. However, due to the limited availability and spatial variability of forest floor survey data, other methods for quantifying anthropogenic Pb movement are needed. This study uses the isotopic composition (206Pb/207Pb) of soil Pb and measurements of 210Pb and 226Ra to directly trace the transit of atmospherically deposited Pb in the soil profile. We also report on the recovery of an enriched 207Pb dose applied in 1984 to the surface of a soil plot in the coniferous forest at Camels Hump in Vermont. The isotopic composition of soil Pb in low elevation deciduous forests suggests that approximately 65% of the original atmospheric Pb load has migrated from the forest floor to the upper 10 cm of the mineral soil. Higher elevation sites with coniferous vegetation have thicker forest floors, which have prevented significant amounts of Pb from entering the mineral soil. After 17 years, the soil organic horizon in the coniferous zone prevented any penetration of the applied Pb into the mineral soil. Using 210Pb budgets in different soil compartments, we determine forest floor response times for atmospherically delivered Pb to be approximately 60 years in the low elevation deciduous forest zone and 150 years for the high elevation spruce-fir forest zone at Camels Hump. According to its distribution in the soil profile, we conclude that a dispersed release of anthropogenic Pb to groundwater and surface water is possible this century. Our results also offer independent confirmation of Pb deposition models previously generated for the region.

Air Pollutants↗
PubMed2001

Bifunctional abietadiene synthase: free diffusive transfer of the (+)-copalyl diphosphate intermediate between two distinct active sites.

Abietadiene synthase (AS) catalyzes two sequential, mechanistically distinct cyclizations in the conversion of geranylgeranyl diphosphate to a mixture of abietadiene double bond isomers as the initial step of resin acid biosynthesis in grand fir (Abies grandis). The first reaction converts geranylgeranyl diphosphate to the stable bicyclic intermediate (+)-copalyl diphosphate via protonation-initiated cyclization. In the second reaction, diphosphate ester ionization-initiated cyclization generates the tricyclic perhydrophenanthrene-type backbone, and is directly coupled to a 1,2-methyl migration that generates the C13 isopropyl group characteristic of the abietane family of diterpenes. Using the transition-state analogue inhibitor 14,15-dihydro-15-azageranylgeranyl diphosphate, it was demonstrated that each reaction of abietadiene synthase is carried out at a distinct active site. Mutations in two aspartate-rich motifs specifically delete one or the other activity and the location of these motifs suggests that the two active sites reside in separate domains. These mutants effectively complement each other, suggesting that the copalyl diphosphate intermediate diffuses between the two active sites in this monomeric enzyme. Free copalyl diphosphate was detected in steady-state kinetic reactions, thus conclusively demonstrating a free diffusion transfer mechanism. In addition, both mutant enzymes enhance the activity of wild-type abietadiene synthase with geranylgeranyl diphosphate as substrate. The implications of these results for the kinetic mechanism of abietadiene synthase are discussed.

Amino Acid Motifs↗
PubMed2002

Mechanism of abietadiene synthase catalysis: stereochemistry and stabilization of the cryptic pimarenyl carbocation intermediates.

Abietadiene synthase (AS) catalyzes the complex cyclization-rearrangement of (E,E,E)-geranylgeranyl diphosphate (8, GGPP) to a mixture of abietadiene (1a), double bond isomers 2a-4a and pimaradienes 5a-7a as a key step in the biosynthesis of the abietane resin acid constituents (1b-4b) of conifer oleoresin. The reaction proceeds at two active sites by way of the intermediate, copalyl diphosphate (9). In the second site, a putative tricyclic pimaradiene or pimarenyl(+) carbocation intermediate of undefined C13 stereochemistry and annular double bond position is formed. Three 8-oxy-17-nor analogues of 9 (17 and 19a,b) and three isomeric 15,16-bisnorpimarenyl-N-methylamines (26a-c) were synthesized and evaluated as alternative substrates and/or inhibitors for recombinant AS from grand fir. The stereospecific cyclization of 8 alpha-hydroxy-17-nor CPP (19a) to 17-normanoyl oxide (20a) and the higher inhibitory potency of the norpimarenylamine 26a (K(i) = 0.1 nM) both suggest pimarenyl intermediates having the 13 beta methyl configuration and 8,14-double bond corresponding to sandaracopimaradiene (5a). The 2000-fold stimulation of inhibition by 26a in the presence of inorganic pyrophosphate indicates an important role for carbocation/OPP anion stabilization of the secondary sandaracopimaren-15-yl(+) ion. The failure of 8 beta-hydroxy-17-nor CPP (19b) to undergo enzymatic cyclization was taken as evidence that 9 is bound with a "coplanar" side chain conformation and that the S(N)' cyclization occurs on the 17 alpha face. The routing of the sandarcopimara-15-en-8-yl carbocation toward various diterpenes in biogenetic schemes is attributed to differing conformations of ring C and/or orientations of the C13 vinyl group in the active sites of the corresponding diterpene cyclases.

Catalysis↗
PubMed2002

Use of differential scanning calorimetry (DSC) as a new technique for detection of adulteration in honeys. 1. Study of adulteration effect on honey thermal behavior.

Differential scanning calorimetry (DSC) was used to study the thermal behavior of authentic honeys (Lavandula, Robinia, and Fir honeys) and industrial sugar syrups. Thermal or thermochemical parameters such as the glass transition temperature (Tg), enthalpies of fusion (DeltaH(fus)), and heat capacity variation (DeltaC(p)) were measured. The syrups and honeys showed significant differences in thermal phenomena, as well as in their amplitude and position on the temperature scale. Results showed good reproducibility of the method for all samples studied. The effect of adulteration of honey with different amounts of syrup (5, 10, 20, 40, and 60%) was investigated. A linear relationship was found between the percentage of added syrup and the glass transition temperature. A similar relationship was obtained from the enthalpy of fusion results in the temperature range of 40-90 degrees C. Under applied conditions, the effects of adulteration of honeys by industrial syrups appeared to be detectable from a level as low as 5%.

Calorimetry, Differential Scanning↗
PubMed2002

Fate of spinosad in litter and soils of a mixed conifer stand in the Acadian forest region of New Brunswick.

Spinosad is a natural insecticide, produced via fermentation culture of the actinomycete Saccharopolyspora spinosa, with potential use against a number of forest pests including spruce budworm (Choristoneura fumiferana [Clem]). Persistence of spinosad was determined in terrestrial fate experiments conducted within a semimature stand of black spruce (Picea mariana [Mill.]) and balsam fir (Abies balsamea [L]) in the Acadian forest region of New Brunswick, Canada. Results of experiments established under full coniferous canopy and in a canopy opening indicated that spinosad dissipated rapidly following hyperbolic kinetics in both litter and soils and was not susceptible to leaching. Time to 50% dissipation estimates for spinosyn A ranged from 2.0 to 12.4 days depending upon matrix and experimental conditions. Spinosyn D dissipated to levels below quantitation limits (0.02 microg/g of dry mass) within 7 days in all cases. Sporadic low-level detection of the demethylated metabolites suggested that parent compounds were degraded in situ.

Anti-Bacterial Agents↗
PubMed2006

Authentication of the botanical and geographical origin of honey by front-face fluorescence spectroscopy.

Front-face fluorescence spectroscopy, directly applied on honey samples, was used for the authentication of 11 unifloral and polyfloral honey types (n = 371 samples) previously classified using traditional methods such as chemical, pollen, and sensory analysis. Excitation spectra (220-400 nm) were recorded with the emission measured at 420 nm. In addition, emission spectra were recorded between 290 and 500 nm (excitation at 270 nm) as well as between 330 and 550 nm (excitation at 310 nm). A total of four different spectral data sets were considered for data analysis. Chemometric evaluation of the spectra included principal component analysis and linear discriminant analysis; the error rates of the discriminant models were calculated by using Bayes' theorem. They ranged from <0.1% (polyfloral and chestnut honeys) to 9.9% (fir honeydew honey) by using single spectral data sets and from <0.1% (metcalfa honeydew, polyfloral, and chestnut honeys) to 7.5% (lime honey) by combining two data sets. This study indicates that front-face fluorescence spectroscopy is a promising technique for the authentication of the botanical origin of honey and may also be useful for the determination of the geographical origin within the same unifloral honey type.

Animals↗
PubMed2006

Authentication of the botanical origin of honey by near-infrared spectroscopy.

Fourier transform near-infrared spectroscopy (FT-NIR) was evaluated for the authentication of eight unifloral and polyfloral honey types (n = 364 samples) previously classified using traditional methods such as chemical, pollen, and sensory analysis. Chemometric evaluation of the spectra was carried out by applying principal component analysis and linear discriminant analysis. The corresponding error rates were calculated according to Bayes' theorem. NIR spectroscopy enabled a reliable discrimination of acacia, chestnut, and fir honeydew honey from the other unifloral and polyfloral honey types studied. The error rates ranged from <0.1 to 6.3% depending on the honey type. NIR proved also to be useful for the classification of blossom and honeydew honeys. The results demonstrate that near-infrared spectrometry is a valuable, rapid, and nondestructive tool for the authentication of the above-mentioned honeys, but not for all varieties studied.

Discriminant Analysis↗
PubMed2006

Basic molecular mechanisms underlying complex permittivity of water and ice.

Four dielectric-loss frequency dependences epsilon''j(nu), j = 1-4, which constitute a basis for underlying far-infrared (FIR) spectra of water and ice, are briefly analyzed. The relevant molecular mechanisms are (a) free-like libration of a permanent dipole in a hat potential, (b) elastic vibration of a nonrigid dipole along the H-bond (HB), (c) elastic reorientation of a permanent dipole around this bond, and (d) vibration of HB water molecules transverse to the HB direction. A semiphenomenological (SP) approach, based on analytical calculation of the spectrum of autocorrelation function, is applied. The total loss curve epsilon''(nu), accounting for these mechanisms and presented for liquid water at 27 and 81.4 degrees C, for supercooled water at -5.6 degrees C, and for ice at -7 degrees C, demonstrates a very good agreement with experimental spectra. A simple formula is proposed for an "association factor" zeta relating the dipole moments mu(perpendicular) and mu(q) of transversally and longitudinally (with respect to HB direction) vibrating molecules. The parametrization of the model yields for T < 300 K a sharp increase of this factor zeta with a decrease of temperature.

Journal Article↗
PubMed2005

Desmethylabietospiran, a naturally occurring self-gelation agent.

A new self-gelating triterpenoid natural product has been isolated from the bark of the silver fir, Abies alba. The structure is desmethylabietospiran (3) on the basis of chemical and spectroscopic evidence. Also reported is a more efficient isolation procedure of abietospiran (1) from A. alba.

Abies↗
PubMed2000

The relationship of hardiness, coping strategies, and perceived stress to symptoms of illness.

We proposed a conceptual model based on research supporting the relationship between symptoms of illness and the determinants of hardiness, coping strategies, and perceived stress. In this model, hardiness, avoidance coping, and approach coping have paths to perceived stress, perceived stress has a path to symptoms of illness, and hardiness also has a path to symptoms of illness. We examined the goodness of fit of this model using path analysis and tested its stability, as well as the presence of gender effects, in corporate (N = 110) and university (N = 271) samples. The proposed model was a good fit for the data in the corporate sample, and no gender effects were found. The proposed model was not a good fir for the data in the university sample, therefore we added two paths that have received some support in the research: from approach coping to symptoms of illness and from avoidance coping to symptoms of illness. This model was a good fit for the data in the university sample, however, the path from approach coping to symptoms of illness had a critical ratio < 2.0, thus we removed this path and ran the model again. The final model was a good fit for the data, and no gender effects were found. Implications for the relationship of hardiness, coping strategies, and perceived stress to health are discussed.

Adaptation, Psychological↗
PubMed2000

Effects of digital filtering on the parameters of impulse-like eye movements.

Influence of two filtering modes were researched with electro-oculographically recorded impulse-like eye movements. Linear finite impulse response (FIR) and non-linear hybrid median filters were explored by considering gain and latency parameters that yield the most important information in the case of these eye movements. It is stated that carefully selected lowpass filtering can securely be run without considerable changes in parameter values in order to discard noise stemming from physiological or other reasons.

Data Display↗
PubMed2001

Male-specific sesquiterpenes from Phyllotreta and Aphthona flea beetles.

It was previously reported that males of the crucifer flea beetle, Phyllotreta cruciferae, feeding on host foliage are attractive to both males and females in the field. Based on this evidence for an aggregation pheromone, volatiles were collected from male and female P. cruciferae feeding on cabbage (Brassica oleracea) and analyzed. For comparison, volatiles were also collected from males and females of three other flea beetle species, Aphthona flava, A. czwalinae, and A. cyparissiae, all feeding on their host, leafy spurge foliage (Euphorbia esula). Six male-specific compounds were isolated from P. cruciferae, and the same compounds plus two additional ones were isolated from males of Aphthona flava, A. czwalinae, and A. cyparissiae. The blends of compounds were relatively consistent within species, but there were characteristic differences between species. Compound structures were studied by mass spectrometry, NMR spectroscopy, UV spectroscopy, polarimetry, chiral and achiral gas chromatography, molecular modeling, and microchemical tests. Three of the compounds were identified as (+)-ar-himachalene; (+)-trans-alpha-himachalene; (+)-y-cadinene. Two others were new enantiomers of himachalene hydrocarbons that were previously identified from the fir trees, Abies alba and Abies nordmanniana. Finally, there were two himachalene alcohols and one norsesquiterpene ketone that is a himachalene analog. Only (+)-ar-himachalene and (+)-y-cadinene are previously known natural products. Electrophysiological activity was demonstrated for five of the compounds. The chemical and electrophysiological patterns are consistent with, but do not prove, a pheromonal function.

Animals↗