胶原纤维内吸附水熔融热的差示扫描量热法的研究

用DSC法研究了天然与变性牛蹄跟腱胶原蛋白内吸附水的熔融热.在含水量(R)为0.33克(水)/克(蛋白)时观察到冰的熔融峰.在0.57克/克以下,水的积分熔融热(Q_f)与水含量呈非线性关系,由此得到出现熔融峰的临界水含量为0.26克/克.在0.57—1.05克/克范围内Q_f同R接近线性关系,其表观微分熔融热dQ/dR=69.5卡/克(水).R>1.05克/克时,dQ/dR=79.2卡/克.     

Specific heat studies of various wool–water systems

Measurements of specific heat of wool-water systems were made at approximately 5°C intervals over the temperature range ?70 to 100°C. Ten different, samples were used, each with a different amount of absorbed water in the range from dry ness to saturation at 0°C. The graph of specific heat against temperature for dry wool is precisely linear over the complete temperature range, suggesting that thermal motion is entirely vibrational. When absorbed water is present the data can be conveniently discussed in terms of behavior below and above an amount of absorbed water of 22.7 g in 100 g of wool (22.7% of absorbed water). Below 22.7% there is only one temperature range in which the results indicate an appreciable transition in heat absorbing properties. The temperature of transition depends on water content but is higher than 0°C. Above 22.7% a second transition appears in the range ?30 to 0°C and grows rapidly larger with increase of water content. The first transition is tentatively ascribed to a slightly cooperative breakdown of polar bonds in wool, and the second to a process analogous to melting in the absorbed water. The results are discussed in these terms as well as with reference to specific heat theories, the heat absorption of the wool component and the water component, and enthalpy differences between the various samples.     

Calorimetric studies of the state of water in seed tissues

To understand the physical state of water in hydrating biological tissues, thermodynamic properties of water in cotyledons of pea and soybean with moisture contents ranging from 0.01 g H₂O/g dw to 1.0 g H₂O/g dw were studied using differential scanning calorimetry. The heat capacity of the tissues increased abruptly at moisture contents above 0.08 and 0.12 g H₂O/g dw for soybean and pea cotyledons, respectively. Melting transitions of water were observed at moisture contents >0.23 and 0.26 g H₂O/g dw for soybean and pea. However, freezing of water was not observed unless moisture contents exceeded 0.33-0.35 g H₂O/g dw. In both seed tissues, the temperatures of the freezing and melting varied with moisture content and showed hysterisis. The energy of the transition also varied with moisture content and was similar to the heats of fusion and crystallization of pure water only at moisture contents >0.54 and 0.58 gH₂O/g dw for soybean and pea seeds, respectively. The thermal properties of water change distinctly as seed moisture content changes: at least five states or water can be identified.     

Calorimetry of rat tail tendon collagen before and after denaturation: the heat of fusion of its absorbed water

The specific heat, of rat tail tendon at various water contents was measured as a function of temperature. The resulting graphs showed peaks arising from the melting, near 50°C, of helical material in the collagen, and from the melting of absorbed water in the range -40°C to 0°C. The heat of melting of helical material was 11.7 cal per gram of dry tendon. Determination of the heat and temperature of fusion of the absorbed water allowed resolution of the water into four states in the case of tendon before denaturation, and three states after denaturation. The four states are (1) water not freezable on cooling to - 70°C, (2) freezable water with-both heat and temperature of fusion different from the values for ordinary water, (3) freezable water with the heat of fusion of ordinary water, but a different temperature of fusion, and (4) water not distinguished from ordinary water. The fourth state was absent in denatured tendon. The results are discussed in terms of increasing size of clusters of absorbed water molecules.     

Hydration and thermal denaturation of beta-lactoglobulin. A calorimetric study.

The thermal properties of the beta-lactoglobulin-water system were investigated by differential scanning calorimetry in the temperature range from -50 to 130 degrees C. Determination of the heat and temperature of fusion of the absorbed water allowed resolution of the water into four different states. The amounts of water in these states were different for samples before and after heat denaturation. In the case of denatured beta-lactoglobulin, a smaller amount of water with thermal properties different from ordinary water was observed and its total water binding capacity was lower. The thermal stability of beta-lactoglobulin in the water content range from 0 to 0.75 g/g showed a strong dependence on the degree of hydration. A correlation was observed between the changes in the thermal stability of the protein and the changes in the state of the absorbed water. The results are compared with those obtained from similar measurements of other globular proteins and of fibrillar proteins.     

The physical state of water at low temperatures in plasma with different water contents as studied by differential thermal analysis and differential scanning calorimetry

Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) have been used for a study of the physical state of water at low temperatures in freeze-dried blood plasma rehydrated to different water contents. Measurement of the amplitude of the specific heat change accompanying the glass transition, the quantity of ice formed during rewarming, and the total ice content in the sample provided a determination of the extent of crystallization in water at low temperatures. Even after slow cooling or annealing, a fraction of water remained incorporated in an amorphous phase. It is suggested that the unfreezable water (0.47 g per g of dry substance) could be divided into two more or less distinct species: 0.25 g per g is the minimum water content above which the system can gain enough mobility to give rise to a detectable glass transition.     

Studies on Rapidly Frozen Suspensions of Yeast Cells by Differential Thermal Analysis and Conductometry

Few, if any, yeast cells survived rapid cooling to -196°C and subsequent slow warming. After rapid freezing, the suspensions absorbed latent heat of fusion between -15° and 0°C during warming, and the relation between the amount of heat absorbed and the concentration of cells was the same as that in equivalent KCl solutions, indicating that frozen suspensions behave thermally like frozen solutions. The amount of heat absorbed was such that more than 80 per cent of the intracellular solution had to be frozen. The conductometric behavior of frozen suspensions showed that cell solutes were still inside the cells and surrounded by an intact cell membrane at the time heat was being absorbed. Two models are consistent with these findings. The first assumes that intracellular freezing has taken place; the second that all freezable water has left the cells and frozen externally. The latter model is ruled out because rapidly cooled cells do not shrink by an amount equal to the volume of water that would have to be withdrawn to prevent internal freezing.     

Protein--water interactions. Heat capacity of the lysozyme--water system.

Calorimetric measurements of the heat capacity of the lysozyme-water system have been carried out over the full range of system composition at 25 degrees C. The partial specific heat capacity of the protein in dilute solution is 1.483 +/- 0.009 J K-1 g-1. The heat capacity of the dry protein is 1.26 +/- 0.01 J K-1 g-1. The system heat capacity responds linearly to change in composition from dilute solution to 0.38 g of water per g of protein (h) and is an irregular function at lower water content. The break in the heat capacity function at 0.38 h defines the amount of water needed to develop the equilibrium solution properties of lysozyme as being 300 molecules of water/protein molecule, just sufficient for monolayer coverage. The heat capacity behavior at low water content describes three hydration regions. The most tightly bound water (0-0.07 h), probably principally bound to charged groups, is characterized by a partial specific heat capacity of 2.3 J K-1 g-1, a value close to that for ice. A heat of reaction associated with proton redistribution is reflected in the heat capacity function for the low-hydration region. Between 0.07 and 0.25 h the heat capacity increases strongly, which is understood to reflect the growth of patches of water covering polar and adjacent nonpolar portions of the protein surface. The hydration shell is completed by condensation of solvent over the weak-interacting portions of the surface, in a process displaying a transition heat.     

热变性前后水合醛缩酶中水状态的热力学研究

 用差示扫描量热计,测定了不同水合态(水含量h从0.08g/g至2.50g /g)冻结的水合醛缩酶样品中冰的熔化温度和熔化焓,并计算出熔化熵。实验结果表明,变性前,水合醛缩酶中的水转化成四种状状:(1)不冻结水,(2)熔化焓和熔化温度均低了普通水的可冻结水,(3)熔化焓与普通水相同而熔化温度低于普通水的可冻结水,(4)熔化焓和熔化温度均与普通水相同的容积水。变性后,水合醛缩酶中的水可处于五种状态,即不冻结水,熔化焓低于普通水而熔化温度与普通水相同的可冻结水,以及熔化温度均低于普通水且彼此不相同的三种状态的可冻结水。实验还观察到,水合醛缩酶在热变性前后,水在这些态中的量是不同的。     

海南尖峰岭热带山地雨林近冠层CO2及通量特征研究

采用梯度法及CI-301PS CO2系统,实现了海南尖峰岭热带山地雨林近冠层CO 2、微气象因子梯度观测研究,结果表明雨季晴、晴间少云及多云天气,900～1800CO 2浓度平均值分别在349～350ml/m3(冠上2.8m)、346～348ml/m3(冠上0.8m)、345～349ml/m3(林内16m)、352～357ml/m3(林内5m),较旱季相应天气分别小14～17.5、10.1～23.7、1 6.4～35.7和18.1～36.1ml/m3;100～800,则雨季CO2浓度大于旱季;梯度浓度廓变量和实时动力计算反映出,800～1800CO2通量由大气向林冠层,旱、雨季平均CO2通量分别为(0.61×10-6kg/(m2·s)和0.71×10-6kg/(m 2·s),1900通量甚微,2000～700CO2通量则由林冠向大气,平均CO2通量分别为0.36×10-6kg/(m2·s)和0.32×10-6kg/(m2·s);雨季昼夜大气流向冠层的净CO2通量是相应旱季的1.56倍.总辐射、冠顶净辐射通量以1300～1 500为最大时域,相对林内21m,80%的辐射热能被冠层吸收,与CO2通量正相关;晴天冠上潜热、感热最高值分别在1300～1400和900,反映热带山地雨林近冠层的汇、源即白昼光合固定CO2大于夜间呼吸排放CO2效应,且雨季高于旱季.     

Role of relative humidity, temperature, and water status in dormancy alleviation of sunflower seeds during dry after-ripening

The effect of various combinations of temperature and relative humidity on dormancy alleviation of sunflower seeds during dry after-ripening was investigated. The rate of dormancy alleviation depended on both temperature and embryo moisture content (MC). Below an embryo MC of 0.1 g H(2)O g(-1) dw, dormancy release was faster at 15 °C than at higher temperatures. This suggests that dormancy release at low MC was associated with negative activation energy, supported by Arrhenius plots, and low Q(10) values. At higher MC, the rate of dormancy alleviation increased with temperature, correlating well with the temperature dependence of biochemical processes. These findings suggests the involvement of two distinct cellular mechanisms in dormancy release; non-enzymatic below 0.1 g H(2)O g(-1) dw and associated with active metabolism above this value. The effects of temperature on seed dormancy release above the threshold MC were analysed using a population-based thermal time approach and a model predicting the rate of dormancy alleviation is provided. Sunflower embryo dormancy release was effective at temperatures above 8 °C (the base temperature for after-ripening, Tb(AR), was 8.17 °C), and the higher the after-ripening temperature above this threshold value, the higher was the rate of dormancy loss. Thermodynamic analyses of water sorption isotherms revealed that dormancy release was associated with less bound water and increased molecular mobility within the embryonic axes but not the cotyledons. It is proposed that the changes in water binding properties result from oxidative processes and can, in turn, allow metabolic activities.     

几种作物的生理指标对土壤水分变动的阈值反应

 在生长盛期,谷子、高梁、冬小麦的气孔导度、叶水势和光合速率在一定土壤含水量范围内并不随着土壤含水量的降低而发生明显变化,只有当土壤含水量低于一定程度时,才随着土壤湿度的降低而减少,表现为对土壤水分有明显的阈值反应。不同作物此阈值下限存在差异,高粱在大于田间持水量42％～45％的根层土壤湿度条件下,气孔阻力和叶水势基本维持恒定;谷子的这个指标在50％左右,冬小麦在60％左右。而夏玉米在所试土壤湿度范围内(20％～30％土壤体积含水量),气孔阻力和叶水势基本维持不变,而光合作用随着土壤含水量的增高而出现增加趋势。表明在这4种作物中,只有玉米需要充足的水分供应才能维持其良好的生长发育,而高粱具有比其它3种作物更强的适应土壤水分变动能力,从而比其它作物更抗旱和耐旱。     

Ribonuclease activity as an index of hidden hunger of zinc in crops

Summary The activity of RN-ase at zero zinc level was found to be 2, 173-1 and 2 times higher in all the varieties of rice (Jaya and HM484) and Maize (Ganga 5 and Vijay) than that of 5 ppm zinc at 15/20 days, 30/40 days and 45/60 days growth stages respectively, but the difference in the zinc content of leaves between two treatments was not found to be significant except that of 30/40 days growth stage. Similarly the potash content in both the treatments did not vary, but the dry matter production of whole plant and protein content of leaves except 15/20 days growth stage varied significantly. The data suggest thirty ppm P released per 100 g protein per hour (RN-ase activity) could be taken as threshold value above which hidden deficiency at an early growth stage is detected. Also an average concentration of 27 and 25 ppm zinc in rice and maize leaves respectively could be taken as critical limit for zinc deficiency at their 15/20 days of growth respectively. On the basis of RN-ase activity the hidden hunger of zinc in crop can be predicted at an early growth stage (15/20 days) where the zinc content in plant tissue fail to reveal the true picture of zinc deficiency.     

Heat capacities of transfer of some amino acids and peptides from water to aqueous urea solution

Integral enthalpies of solution at low concentrations of several amino acids and peptides in 2 and 6M urea solutions have been determined at 25 and 35°C. These data have been used to derive the enthalpies of transfer (at 25 and 35°C) and heat capacities of transfer (at 30°C) of these amino acids and peptides from water to aqueous urea solutions. Furthermore, the enthalpies of transfer and heat capacities of transfer per CH₂ group and per peptide group ? CONH? have also been estimated. These results show that while the enthalpies and heat capacities of transfer per CH₂ group are positive and negative, respectively, the reverse is true for ? CONH? group. The implications of these results in the mechanism of the denaturation of proteins by urea are discussed.     

A quantitative analysis on latent heat of an aqueous binary mixture

The latent heat during phase change of water-NaCl binary mixture was measured using a differential scanning calorimeter, and the magnitude for two distinct phase change events, water/ice and eutectic phase change, were analyzed considering the phase change characteristics of a binary mixture. During the analysis, the latent heat associated with each event was calculated by normalizing the amount of each endothermic peak with only the amount of sample participating in each event estimated from the lever rule for the phase diagram. The resulting latent heat of each phase change measured is 303.7 +/- 2.5 J/g for water/ice phase change, and 233.0 +/- 1.6 J/g for eutectic phase change, respectively regardless of the initial concentration of mixture. Although the latent heats of water/ice phase change in water-NaCl mixtures are closely correlated, further study is warranted to investigate the reason for smaller latent heat of water/ice phase change than that in pure water (335 J/g). The analysis using the lever rule was extended to estimate the latent heat of dihydrate as 115 J/g with the measured eutectic and water/ice latent heat values. This new analysis based on the lever rule will be useful to estimate the latent heat of water-NaCl mixtures at various concentrations, and may become a framework for more general analysis of latent heat of various biological solutions.     

Sea snake skin: Permeable to water but not to sodium

Summary Fasting yellow-bellied sea snakes (Pelamis) have a very low rate of exchange of Na with sea water. Influx and efflux are balanced at a value near 8 moles/100 g h. This is only a fraction of the rate of exchange found in marine fish. Na influx is due to uptake in the head region; dermal and cloacal influx are minimal. The impermeability of the skin to Na has been confirmed in isolated preparations. The outer keratin layer seems to be the primary barrier, since the shed skin alone is also impermeable. Na efflux can be increased to 140 m/100 g h by salt injections, and secretion by the sublingual salt gland can account for all of this loss. Fasting snakes are not in water balance in sea water. There is a net loss of water amounting to about 0.4% body wt/day that probably occurs mainly through the skin. The major osmotic problem ofPelamis in sea water seems to be water balance, not salt balance. Differences in salt gland size among sea snakes might be related to differences in skin permeability to water associated with dermal respiration. The importance of the skin as a permeability barrier suggests that the frequent skin shedding of sea snakes may be related to maintenance of low water permeability as well as to prevention of growth by marine fouling organisms.     

Heats of carbon monoxide binding by hemoglobin M Iwate.

The heat of reaction of CO gas with the alpha2Mmetbeta2 and alpha2Mbeta2 species of the alpha-chain mutant hemoglobin M Iwate has been studied in buffers with different heats of ionization of 25degrees and in the absence of organic phosphates. For the alpha2Mmetbeta2deoxy species we find a small Bohr effect (0.12 mol of H+/mol of CO) which is in correspondence with that found in equilibrium studies. The heat of reaction, when corrected for proton reaction with buffer, is -18.4 +/- 0.3 kcal/mol of CO at pH 7.4 At pH 9 the same value is observed within experimental error. This value compares closely with heats of reaction of CO with myoglobin and with van't Hoff determinations of the heat of oxygen binding to isolated hemoglobin alpha and beta chains after correction for the heat of replacement of O2 by CO. Furthermore, an analysis of the differential heat of ligand binding as a function of the extent of reaction indicated that, within experimental error, the heat of reaction with the first beta-chain heme in alpha2Mmetbeta2deoxy is the same as the second. Since the quaternary Tleads to R transition is blocked in this mutant hemoglobin, we compared it with Hb A to estimate the enthalpic component of the allosteric T leads to R transition in Hb A. The heats of reaction with CO(g) and Hb A are -15.7 +/- 0.5 and -20.9 +/- 0.5 kcal/mol at pH 7.4 and 9.0, respectively. In going from the T to the R state we find an enthalpy of transition of 9 +/- 2.5 kcal at pH 7.4 and -12 +/- 2.5 kcal at pH 9.0. From published free energies of transsition we conclude the T leads to R transition is enthalpically controlled at p/ 7.4 but entropically controlled at pH 9.0 A near normal Bohr effect is estimated from heats of reaction of CO with alpha2Mdeoxybeta2deoxy in various buffers. A large than normal heat of reaction (-21.6 +/- 0.5 kcal/mol of CO) is attributed to the abnormal alpha chains in Hb M Iwate.     

Water in keratin. Piezoelectric, dielectric, and elastic experiments.

To investigate actions of water in keratin, the piezoelectric, dielectric, and elastic constants are measured at 10 Hz, at temperatures between -160 and 150 degrees C, and at various hydration levels. From changes in the piezoelectric, dielectric, and dynamic mechanical parameters with moisture content (m.c.), we have identified three regimes (I, II, and III) in the hydration of water for keratin. At high hydration (21% m.c.) around 0 degree C, the piezoelectric constants for keratin steeply decrease with increasing temperature. This may be attributed to interfacial polarization which is strongly related to self-associated water molecules (particularly regime III water) just around crystalline helical regions which can exhibit the stress-induced, i.e., piezoelectric, polarization and may be attributed to electrode polarization induced by the increase of mobile ions in the amorphous matrix region, some of which would be released from their trapped states just around the piezoelectric phase by the regime III water. With increasing hydration, the elastic constants for keratin are found to increase below -70 degrees C and decrease above -70 degrees C. This suggests a viscoelastic transition of the keratin structure due to bound water (regime II water). The piezoelectric, dielectric, and elastic loss peaks are found at around -120 degrees C for hydrated keratin, believed to be due to tightly bound water (regime I water), which acts only to stiffen the keratin structure. The adsorption regions of water in keratin are discussed by a piezoelectric two-phase model, which consists of piezoelectric and nonpiezoelectric phases. It is proposed that water molecule would at least adsorb in the nonpiezoelectric phase.     

Study of absorption and retention of nitrogen in fast growing rats--II. Influence of IMAO (nialamide)

A study was made in fast growing rats (65 g) of the nutritive effects of protein and the effect on different organs when influenced by nialamide (IMAO), administered at a dosage of 10 mg/100 g diet, with food intake controlled (pair fed). The administration of nialamide reduces the protein absorbed and retained to a significant degree, both in males and females. No difference was observed between the sexes caused by the effect of the drug, due to the absence of the hormonal anabolizant situation caused by testosterone in adult rats. The administration of nialamide does not significantly modify nitrogen content per 100 g of body weight in any of the organs studied, with the exception of the longissimus dorsi.     

Synthesis and characterization of biodegradable cationic poly(propylene fumarate-co-ethylene glycol) copolymer hydrogels modified with agmatine for enhanced cell adhesion

We synthesized positively charged biodegradable hydrogels by cross-linking of agmatine-modified poly(ethylene glycol)-tethered fumarate (Agm-PEGF) and poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) to investigate the effect of the guanidino groups of the agmatine on hydrogel swelling behavior and smooth muscle cell adhesion to the hydrogels. The weight swelling ratio of these hydrogels at pH 7.0 increased from 279 +/- 4 to 306 +/- 7% as the initial Agm-PEGF content increased from 0 to 200 mg/g of P(PF-co-EG), respectively. The diffusional exponents, n, during the initial phase of water uptake were independent of the initial Agm-PEGF content and were determined to be 0.66 +/- 0.08, 0.71 +/- 0.07, and 0.60 +/- 0.05 for respective initial Agm-PEGF contents of 0, 100, and 200 mg/g. The heat of fusion of water present in the hydrogels increased from 214 +/- 11 to 254 +/- 4 J/g as the initial Agm-PEGF content increased from 0 to 200 mg/g. The number of adherent smooth muscle cells increased dose-dependently from 15 +/- 6 to 75 +/- 7% of the initial seeding density as the initial Agm-PEGF content increased from 0 to 200 mg/g. These results suggest that the incorporation of the guanidino groups of agmatine into P(PF-co-EG) hydrogels increases the hydrogel free water content and the total water content of the hydrogels and also enhances cell adhesion to the hydrogels.