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1.
The physico-chemical, morphological, thermal, pasting, textural, and retrogradation properties of the starches isolated from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro, Moemoe) of New Zealand were studied and compared with starch properties of a modern potato cultivar (Nadine). The relationships between the different starch characteristics were quantified using Pearson correlation and principal component analysis. Significant differences were observed among physico-chemical properties such as phosphorus content, amylose content, swelling power, solubility and light transmittance of starches from the different potato cultivars. The starch granule morphology (size and shape) for all the potato cultivars showed considerable variation when studied by scanning electron microscopy and particle size analysis. Starch granules from Nadine and Moemoe cultivars showed the presence of large and irregular or cuboid granules in fairly high number compared with the starches from the other cultivars. The transition temperatures ( To; Tp; Tc) and the enthalpies (Δ Hgel) associated with gelatinization suggested differences in the stability of the crystalline structures among these potato starches. The Moemoe starch showed the lowest To, while it was higher for Tutaekuri and Karuparera starches. Pasting properties such as peak, final and breakdown viscosity and texture profile analysis (TPA) parameters of starch gels such as hardness and fracturability were found to be higher for Nadine and Huakaroro starches. The Nadine and Huakaroro starch gels also had lower tendency towards retrogradation as evidenced by their lower syneresis (%) during storage at 4 °C. Principal component analysis showed that the Tutaekuri and Nadine cultivars differed to the greatest degree in terms of the properties of their starches. 相似文献
2.
The effects of starch/water ratio, amylose content, degree of phosphorylation, and added KI on water mobility in maize starch-water dispersions were studied by oxygen-17 spin-spin relaxation time measurements over a range of temperatures. The results demonstrate that: (i) the changes in spin-spin relaxation time (Δ T2) reflect the degree of starch-water interaction at different stages of the heating process; (ii) the amount of added water affects the initial T2 and Δ T2 during gelatinization; (iii) higher amylose contents result in lower water mobility in starch-water systems; (iv) higher degrees of phosphorylation lead to a decrease in water mobility, accompanied by a decrease in gelatinization temperature; and (v) added KI effectively decreases water mobility and gelatinization temperature in the starch-water systems studied. 相似文献
3.
Sol–gel and gel–sol phase transitions of κ-carrageenan in pure water and in KCl solution were studied using photon transmission technique. Photon transmission intensity, Itr, was monitored against temperature to determine the sol–gel and gel–sol temperatures ( Tsg and Tgs) and activation energies (Δ Hsg and Δ Hgs). It was observed that Tgs was notably higher than Tsg due to the hysteresis on the phase transition loops. Tgs and Δ Hgs values were also higher for gels containing KCl than for those without KCl. The increase in carrageenan content caused an increase in both critical temperatures and activation energies for the gels prepared in pure water and in KCl solution. Increases in the KCl/carrageenan ratio, raised both Tgs and Tsg. Similarly Δ Hsg was elevated by the increase in cation content of the gel. These results were interpreted as the formation of stronger gels in the presence of KCl in water. 相似文献
4.
1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C Thy (F40), local temperature coefficients (Δ/ΔT) and Q10. 2. 2.|Q10 and either F40 or ΔF/ΔT were little or not related. 3. 3.|A positive correlation between F40 and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q10 of <2 and >2. 4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships. 5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.
Author Keywords: Neuronal thermosensitivity; hypothalamic thermosensory function; Temperature and synaptic transmission; avian thermoregulation; mammalian thermoregulation 相似文献
5.
1. 1.|Circadian changes in heat production (M), heat loss (H), core temperature (Tc) and feeding activity (FA) of ad-lib fed rats were observed by direct and indirect calorimetry. 2. 2.|M, H and Tc showed a clear nocturnal increase associated with several discrete increases. 3. 3.|Whereas the slope of M vs Tc relation did not change appreciably within a day, the slope of H vs Tc or thermal conductance vs Tc relation tended to decrease at night, implying that the correlation between heat loss and body temperature is also a function of time of day in rats.
Author Keywords: Heat loss vs core temperature; thermal conductance; circadian rhythm; direct and indirect calorimetry 相似文献
6.
Knowing the ambient temperature ( Ta) limits of normothermia in laboratory rodents is important because their thermoregulatory responses are useful in studies of physiology, pharmacology and toxicology. The present study assessed the Ta limits of normothermia using radiotelemetry to monitor core temperature ( Tc), heart rate (HR), and motor activity (MA) in unrestrained, male and female Long-Evans rats over a 24 h period. Rats were housed individually in acrylic cages with wire-screen tops and bottoms and maintained at T' as ranging from 12 to 33.5°C for 24 h with food and water provided ad libitum on a 12:12 L:D photoperiod. The limits of normothermia (i.e. where there was no significant change in Tc) were <12–29.5°C for females and 14.5–29.5°C for males. Tc of males at T' as of 12, 32, and 33.5°C increased significantly above the baseline Tc. Female rats had a lower Tc than males at the warmest and coldest T' as. HR and MA were generally higher in females at all T' as. Males appeared to be poorly adapted to thermoregulate at T' as above 30°C as based on their excessively high T' cs, low MA, and marked weight loss compared to that of the females. Within the limits of normothermia the stability of Tc regulation (i.e. [(Δ Tc/Δ Ta) × 100]/2) was ±1.3 and ± 0.9% for males and females, respectively, over a 24 h period. These data on the stability of Tc in the male and female rat provide a valuable framework to study the acute and chronic effects of drugs, chemicals and other agents that affect temperature regulation. 相似文献
7.
Differential scanning calorimetry, circular dichroism, and visible absorption spectrophotometry were employed to elucidate the structural stability of thermophilic phycocyanin derived from Cyanidium caldarium, a eucaryotic organism which contains a nucleus, grown in acidic conditions (pH 3.4) at 54°C. The obtained results were compared with those previously reported for thermophilic phycocyanin derived from Synechococcus lividus, a procaryote containing no organized nucleus, grown in alkaline conditions (pH 8.5) at 52°C. The temperature of thermal unfolding ( td) was found to be comparable between C. caldarium (73°C) and S. lividus (74°C) phycocyanins. The apparent free energy of unfolding (Δ G[urea]=0) at zero denaturant (urea) concentration was also comparable: 9.1 and 8.7 kcal/mole for unfolding the chromophore part of the protein, and 5.0 and 4.3 kcal/mole for unfolding the apoprotein part of the protein, respectively. These values of td and Δ G[urea]=0 were significantly higher than those previously reported for mesophilic Phormidium luridum phycocyanin (grown at 25°C). These findings revealed that relatively higher values of td and Δ G[urea]=0 were characteristics of thermophilic proteins. In contrast, the enthalpies of completed unfolding (Δ Hd) and the half-completed unfolding (Δ Hd)1/2 for C. caldarium phycocyanin were much lower than those for S. lividus protein (89 versus 180 kcal/mole and 62 versus 115 kcal/mole, respectively). Factors contributing to a lower Δ Hd in C. caldarium protein and the role of charged groups in enhancing the stability of thermophilic proteins were discusse. 相似文献
8.
The electron-spin relaxation rates of the two species of cytochrome a3+3-azide found in the azide compound of bovine-heart cytochrome oxidase were measured by progressive microwave saturation at T = 10 K. It has been shown previously that Cyt a+33-azide gives rise to two distinct EPR resonances, depending upon the oxidation state of Cyt a. When Cyt a is ferrous, Cyt a3+3-azide has g = 2.88, 2.19 and 1.64; upon oxidation of Cyt a, the a3+3-azide g-values become g = 2.77, 2.18, and 1.74 (Goodman, G. (1984) J. Biol. Chem. 259, 15094–15099). The relaxation effect of Cyt a on Cyt a3 could be measured as the difference in microwave field saturation parameter H1/2 between the g = 2.77 and g = 2.88 species. For each signal the spin-lattice relaxation time T1 was determined from H1/2 using the transverse relaxation time T2. The value of T2 at 10 K was extrapolated from a plot of line-width vs. temperature at higher temperature. The dipolar contribution to T1 was related to the Cyt a-Cyt a3 spin-spin distance utilizing available information on the relative orientation of Cyt a3-azide and Cyt a (Erecinska, M., Wilson, D.F. and Blasie, J.K. (1979) Biochim. Biophys. Acta 545, 352–364). By taking into account the relaxation parameters for both gx and gz components of the Cyt a3-azide g-tensor, the angle between the gz components of the Cyt a and Cyt a3g-tensors was determined to be between 0 and 18°, and the Cyt a-Cyt a3 spin-spin distance was found to be 19 ± 8 Å. 相似文献
9.
Three fractions containing hemicellulosic material were obtained by sequential extraction of barley residue (left after removal of water-extractable polysaccharides) with saturated barium hydroxide [Ba(OH) 2 fraction], distilled water [ Ba( OH) 2/ H2O fraction], and 1 m sodium hydroxide [NaOH fraction]. The yields of the fractions were 1.6, 1.7, and 2.6% (w/w), respectively, of the dry barley grist. The Ba(OH) 2 fraction contained mainly arabinose and xylose, 35.8% and 60.9%, respectively. The Ba( OH) 2/ H2O fraction in addition to 26.7% Ara and 36.6% Xyl contained also 34.8% Glc. The NaOH fraction was composed of 14.2% Ara, 44.0% Xyl, and 40.9% Glc. The Ba( OH) 2/ H2O and NaOH extracts were further fractionated by stepwise (NH 4) 2SO 4 precipitation into several subfractions with varying amounts of β-glucans and arabinoxylans. β-Glucans in Ba( OH) 2/ H2O and NaOH fractions were characterized by high ratios of β-(1→4)/β-(1→3) linkages, large amounts of contiguously linked β-(1→4) segments, and high ratios of cellotriosyl/cellotetraosyl units. The alkali-extractable arabinoxylans, especially those NaOH-extractable, were characterized by a very low degree of substitution, high xylose/arabinose ratio, and a small content of doubly substituted xylose residues. Some populations of arabinoxylans displayed structural features that would enable them to self-associate or to interact with β-glucans. 相似文献
10.
This paper describes a 13C solid state NMR study of hydrated powders and gels of locust bean gum galactomannan-LBG and Konjac glucomannan-KGM. Changes in relative spectral intensities, cross-polarization dynamics ( TCH, T1ρH) and relaxation times ( T1C, T1H, T2H) show that hydration (0–90%) of LBG powders increases the 10 8 Hz frequency molecular motions, probably reflecting the enhanced motion of non-aggregating segments and chain ends. Slower motions (10 4–10 5 Hz) are enhanced only slightly at 90% hydration. LBG gel shows higher spatial distinction between aggregated and non-aggregated segments than the hydrated powder and relaxation times indicate higher mobility for galactose-ramified segments, compared to linear mannose segments. While the dynamics of KGM hydration is similar to that of LBG, i.e. mainly affecting fast 10 8 Hz motions, the gel is significantly more rigid. Both spectra and relaxation times show that glucose residues in KGM gel are particularly hindered, probably due to their preferential involvement in chain aggregation. 相似文献
11.
The reactions of various proton donors (phenol, hexafluoro-2-propanol, perfluoro-2-methyl-2-propanol, monochloroacetic acid, and tetrafluoroboric acid) with the rhenium (I) hydride complex [(triphos)Re(CO) 2H] (1) have been studied in dichloromethane solution by in situ IR and NMR spectroscopy. The proton donors from [(triphos)Re(CO) 2H…HOR] adducts exhibiting rather strong H…H interactions. The enthalpy variations associated with the formation of the H-bonds (−Δ H = 4.4–6.0 kcal mol −1) have been determined by IR spectroscopy, while the H…H distance in the adduct [(triphos)Re(CO) 2H…HOC(CF 3) 3] (1.83 Å) has been calculated by NMR spectroscopy through the determination of the T1min relaxation time of the Re---H proton. It has been shown that the [(triphos)Re(CO) 2H…HOR] adducts are in equilibrium with the dihydrogen complex [(triphos)Re(CO) 2(η 2-H 2)] +, which is thermodynamically more stable than any H-bond adduct. 相似文献
12.
The influence of lipophilic moieties attached to a 4-1 H-imidazole ring on the histamine H 3 receptor activity was systematically investigated. Series of 4-( n-alkyl)-1 H-imidazoles and 4-(ω-phenylalkyl)-1 H-imidazoles were prepared, with an alkyl chain varying from 2–9 methylene groups and from 1–9 methylene groups, respectively. The compounds were tested for their activity on the H 3 receptor under in vitro conditions. For the 4-( n-alkyl)-1 H-imidazoles the activity is proportional to chain length, ranging from a p A2 value of 6.3±0.2 for 4-( n-propyl)-1 H-imidazole to a p A2 value of 7.2±0.1 for 4-( n-decyl)-1 H-imidazole. For the series 4-(ω-phenylalkyl)-4 H-imidazoles an optimum in H 3 activity was found for the pentylene spacer: 4-(ω-phenylpentyl)-1 H-imidazole has a p A2 value of 7.8±0.1. 相似文献
13.
The reversible equilibrium conversion under H 2 of [RuCl(dppb) (μ-Cl)] 2 (1) to generate (η 2-H 2) (dppb) (μ-Cl) 3RuCl(dppb) in CH 2Cl 2 (dppb = Ph2P( CH2) 4PPh2) has been studied at 0–25 °C by UV-Vis and 31P{ 1H} NMR spectroscopy, and by stoppe kinetics; the equilibrium constant and corresponding thermodynamic parameters, and the forward and reverse rate constants at 25 °C have been determined. A measured Δ H° value of 0 kJ mol −1 allows for an estimation of an exothermicity of 60 kJ mol −1 for binding an η 2-H 2 at an Ru(II) centre; a Δ S° value of 60 J mol −1 K −1 indicates that in solution 1 contain s coordinated CH 2Cl 2. The kinetic and thermodynamic data are compared to those obtained from a previously studied hydrogenation of styrene catalyzed by 1. Preliminary findings on related systems containing Ph 2P(CH 2) 3PPh 2 and (C 6H 11) 2P(C 6H 11) 2 are also noted. 相似文献
14.
The level of γ-aminobutyric acid (GABA) in the posterior hypothalamus, the firing rate of the nerves innervating interscapular brown adipose tissue (IBAT), IBAT and colonic temperatures ( TIBAT and Tc) were monitored in urethane-anesthetized male Sprague–Dawley rats. These variables were measured before and after an intracerebroventricular injection of 500 ng prostaglandin E 1 (PGE 1). The same variables were monitored in other rats with saline injection. The results showed that PGE 1 caused an increase in GABA concentration, firing rate, TIBAT, Tc. These findings suggest that GABA-ergic tone in the posterior hypothalamus is important in the control of the sympathetic and thermogenic changes induced by PGE 1. 相似文献
15.
Carbonylation of the anionic iridium(III) methyl complex, [MeIr(CO) 2I 3] − (1) is an important step in the new iridium-based process for acetic acid manufacture. A model study of the migratory insertion reactions of 1 with P-donor ligands is reported. Complex 1 reacts with phosphites to give neutral acetyl complexes, [Ir(COMe)(CO)I 2L 2] (L = P(OPh) 3 (2), P(OMe) 3 (3)). Complex 2 has been isolated and fully characterised from the reaction of Ph 4As[MeIr(CO) 2I 3] with AgBF 4 and P(OPh) 3; comparison of spectroscopic properties suggests an analogous formulation for 3. IR and 31P NMR spectroscopy indicate initial formation of unstable isomers of 2 which isomerise to the thermodynamic product with trans phosphite ligands. Kinetic measurements for the reactions of 1 with phosphites in CH 2Cl 2 show first order dependence on [1], only when the reactions are carried out in the presence of excess iodide. The rates exhibit a saturation dependence on [L] and are inhibited by iodide. The reactions are accelerated by addition of alcohols (e.g. 18× enhancement for L = P (OMe) 3 in 1:3 MeOH-CH 2Cl 2). A reaction mechanism is proposed which involves substitution of an iodide ligand by phosphite, prior to migratory CO insertion. The observed rate constants fit well to a rate law derived from this mechanism. Analysis of the kinetic data shows that k1, the rate constant for iodide dissociation, is independent of L, but is increased by a factor of 18 on adding 25% MeOH to CH 2Cl 2. Activation parameters for the k1 step are Δ H≠ = 71 (±3) kJ mol −, Δ S≠ = −81 (±9) J mol −1 K −1 in CH 2Cl 2 and Δ H≠ = 60(±4) kJ mol −1, Δ S≠ = −93(± 12) J mol −1 K −1 in 1:3 MeOH-CH 2Cl 2. Solvent assistance of the iodide dissociation step gives the observed rate enhancement in protic solvents. The mechanism is similar to that proposed for the carbonylation of 1. 相似文献
16.
The effects of forskolin on electrical coupling among pancreatic β-cells were studied. Two microelectrodes were used to measure membrane potentials simultaneously in pairs of islet β-cells. Intracellular injection of a current pulse ( ΔI) elicited a membrane response ΔV1 in the injected cell and also a response ΔV2 in a nearby β-cell confirming the existence of cell-to-cell electrical coupling among islet β-cells. In the presence of glucose (7 mM), application of forskolin evoked a transient depolarization of the membrane and electrical activity suggesting that the drug induced a partial inhibition of the β-cell membrane K + conductance. Concomitant with this depolarization of the membrane there was a marked decrease in β-cell input resistance ( ΔV2/ ΔI) suggesting that exposure to forskolin enhanced intercellular coupling. Direct measurements of the coupling ratio ΔV2/ ΔV1 provided further support to the idea that forskolin enhances electrical coupling among islet cells. Indeed, application of forskolin reversibly increased the coupling ratio. These results suggest that cAMP might be involved in the modulation of electrical coupling among islet β-cells. 相似文献
17.
1H NMR line broadening is found to be an effective complimentary method to chemical trapping for determining the rates and activation parameters for organo-metal bond homolysis events that produce freely diffusing radicals. Application of this method is illustrated by measurement of bond homolysis activation parameters for a series of organo-cobalt porphyrin complexes ((TPP)Co-C(CH 3) 2CN (Δ H≠ = 19.5±0.9 kcal mol −1, Δ S≠ = 12±3 cal°K −1 mol −1), (TMP)Co-C(CH 3) 2CN (Δ H≠ = 20±1 kcal mol −1,Δ S≠ = 13±2 cal°K −1 mol −1), (TAP)Co-C(CH 3) 2CO 2CH 3 (Δ H≠ = 18.2±0.5 kcal mol −1, Δ S≠ = 12±2 cal °K −1 mol −1), (TAP)Co-CH(CH 3)C 6H 5 (Δ H≠ = 22.5±0.5, Δ S≠ = 17±2 cal °K −1 mol −1)). The line broadening method is particularly useful in determining activation parameters for dissociation of weakly bonded organometallics where the rate of homolysis can exceed the range measurable by conventional chemical trapping methods. 相似文献
18.
κ-Carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in pure water. Photon transmission measurements were performed using a UV-Vis (UVV) spectrometer during the swelling of κ-carrageenan gels. Transmitted photon intensity, Itr, increased exponentially as swelling time is increased for all gel samples. The behaviour of Itr was interpreted by Monte-Carlo Simulation. The increase in Itr was quantified by employing Li-Tanaka equation, from which time constants τ1 and collective diffusion coefficients, Do were determined for the gels in various carrageenan concentrations. Gravimetric and volumetric measurements were also carried out during swelling of gels. It is observed that gel with high carrageenan content possess more double helices and more lattice dislocations and swell slower than gels with low carrageenan content which may contain less double helices and less lattice imperfections. Increase in Itr was interpreted by the homogeneous distribution of double helices in the carrageenan gel system. 相似文献
19.
1. 1.|Colonic temperature (Tc) of mice rose about 2°C in 20 min when the mice were taken out of their home cages and the Tc measured every 5 min. 2. 2.|The maximal rise in Tc diminished if the procedure was repeated daily for 43 days and increased abruptly again when the Tc measurements were taken, in one session, in the presence of a rat. 3. 3.|Salicylate diminished the maximal Tc but not the difference between the maximal and the initial Tc, i.e. the magnitude of the Tc rise.
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20.
Deuterium magnetic resonance ( 2H-NMR) and Raman spectroscopy are used to investigate order and fluidity at the terminal methyl position in 16- d3, 16′- d3 dipalmitoylphosphatidylcholine (16- d6 DPPC) multibilayers. These methods reveal substantial motion and disorder in the gel phase, 5–10°C below the gel-liquid crystal phase transition temperature ( Tm). The phase transition is sensed in the 2H-NMR spectrum as a reduction in the quadrupole splitting from 14 kHz to 3 kHz. In contrast, the Raman parameter used to characterize the CD 3 vibrations is quite insensitive to the melting process, although an analogous parameter does sense disordering at Tm at the 10 and 10′ position in 10- d2, 10′- d2 DPPC. The difference in the response of the NMR and Raman parameters may arise because the vibrational spectrum of the CD 3 group is inhomogenously broadened and is therefore quite sensitive to alterations in the local environment around the methyl group. In contrast, the NMR quadrupole splitting is sensitive to both local motion of the methyl group and, near Tm, to motions of the CD 2 group induced by transgauche isomerizations further up the chain. The difficulties that arise when results from different spectroscopic techniques are compared are demonstrated. 相似文献
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