嗜酸氧化亚铁硫杆菌生长动力学方程的应用

基于Monod模型推导出了A．f的生长动力学方程模型,采用Gauss-Newton算法确定了在不同初始条件下细菌生长的动力学参数,即最大比生长速率‰、Monod常数K及R0。通过在不同初始条件下细菌生长特性的研究,得到了相应初始生长条件下以限制性底物亚铁离子浓度为表征的生长动力学方程,理论上揭示了动力学参数变化对细菌生长的影响规律,其中生长动力学方程的数值模拟与实验数据相吻合。     

化香树果序总黄酮提取动力学研究

以化香树果序为原料,60%的乙醇水溶液为溶剂提取黄酮类化合物,在不同温度下对总黄酮的传质动力学进行了研究。采用平板模型,以Fick第二定律为基础,建立了化香树果序总黄酮提取的动力学方程,求得了速率常数、活化能、相对萃余率等一系列动力学参数。研究结果可为化香树果序总黄酮提取工程放大和深入理论研究提供一定的依据。     

杂质对蛋白质晶体影响研究进展

综述了杂质对蛋白质晶体生长影响研究领域的进展情况. 对可能的杂质来源以及杂质对结晶过程的影响进行了介绍.重点介绍了和结晶蛋白质分子结构相似的杂质分子的影响, 包括晶体成核、生长形态、表面形貌、生长动力学、质量等,以及杂质在晶体中的重新分配.     

槲皮素的热降解机理及其分解动力学研究

利用TG-DTG技术测得槲皮素在氮气气氛中不同升温速率β下的热分解曲线,协同使用Achar法、Coats-Redfern法、Kissinger法和Ozawa法等4种方法同时进行动力学处理,根据热分解的表观活化能Eα和指前因子A计算推断槲皮素的贮存期.随着升温速率的提高,槲皮素的热分解温度逐渐升高;槲皮素热二步分解的机理依次是随机成核与随后生长控制和化学反应控制,对应的函数名称是Avrami-Erofeev方程和反应级数方程;经Gaussian模拟和热重数据结合分析,槲皮素在第一步分解时,失去两个O原子;第二步分解时失去一个苯环;根据第一步热分解的表观活化能Eα和指前因子A推断,在室温25℃下,槲皮素的贮存期为1.5 ～2年.     

基因型×环境互作效应对水稻穗部性状杂种优势的影响

采用包括基因型×环境互作效应的加性显性加性×加性上位性遗传模型,分析了籼粳杂交穗部性状杂种优势的两年资料。结果表明,7个穗部性状的杂种优势既由基因型控制也受环境(年份)互作效应影响。主穗粒数、主穗长、一次和二次枝梗总长和着粒密度表现较强的正向群体平均优势,而一次和二次枝梗数则表现显着的负向优势。基因型×环境互作预测结果表明,主穗粒数、主穗长、一次枝梗总长在两年中的环境互作表现正效应,一次和二次枝梗数则为负效应,着粒密度和二次枝梗总长表现不同方向的效应。利用IR66158-37(P₁)、IR65600-85(P₂)、明恢63(P₄)和R669(P₆)进行杂交配组,其杂种后代易获得重穗型的穗部结构,可在超高产育种中加以利用。     

嗜酸氧化亚铁硫杆菌生长动力学

在确定二价铁离子为A.f生长过程中惟一限制性底物条件下,通过考察初始亚铁离子浓度、初始pH值两种影响亚铁离子氧化代谢的主要因素来研究细菌的生长特性,得到以限制性底物亚铁离子浓度为表征的细菌生长曲线。利用基于Monod方程建立的细菌生长动力学方程模型,采用Matlab软件中的Gauss-Newton算法确定了在不同条件下细菌生长动力学参数,包括最大比生长速率μm、Monod常数K及Ro,推导出了不同条件下A.f对数期以底物Fe(Ⅱ)浓度为表征的生长动力学方程。     

超声辅助深共晶溶剂高效提取枳实辛弗林的工艺优化及提取动力学分析

为了研究超声辅助深共晶溶剂提取枳实辛弗林的最佳工艺条件及该提取过程的传质动力学模型,本研究采用Plackett-Burman试验、最陡爬坡试验结合Box-Behnken响应面法对超声辅助深共晶溶剂提取枳实辛弗林的关键工艺参数进行优化,基于Fick第二定律建立超声辅助深共晶溶剂提取枳实辛弗林的提取动力学模型,通过测定在不同功率、不同提取时间下提取液中的辛弗林的质量浓度,对模型进行拟合验证,求解相应的动力学参数。结果表明,最优提取溶媒为一水甜菜碱-乳酸组成的深共晶溶剂(摩尔比1∶3,含水量50%),最佳工艺为：液料比39 mL/g,超声功率220 W,超声时间20 min,在此条件下,辛弗林得率为0.4284%,与模型预测值接近,且优于传统水回流提取法、85%乙醇回流提取法、超声辅助14%乙醇提取法、超声辅助70%甲醇提取法和超声辅助水提法。对动力学实验数据拟合得到的动力学一般方程和指数方程与动力学模型相关性良好,推算出了相应的速率常数、相对萃余率等动力学相关参数,拟合得到了半衰期和有效扩散系数回归方程,为枳实辛弗林的提取工艺优化和深入理论研究提供数据参考。     

描述神经元相互作用的非线性动力学方程的解析解

神经系统是由大量神经元构成的非线性动力系统,动力学行为十分复杂ＦＨＮ模型提供了在该系统中观察时间周期振荡这种非线性现象的实验证据．本文利用扰动法从理论上求出了ＦＨＮ模型所给出的非线性动力学方程的解析解,为进一步深入研究神经系统的动力学行为提供了理论依据     

长白山低山区森林土壤有机碳及养分空间异质性

以吉林延边汪清林业局金仓林场境内森林土壤为对象,采用多元线性回归方法和地统计学回归克里格方法,研究了土壤有机碳及养分的垂直分布规律,预测了其空间分布,并对预测结果进行插值.结果表明: 0～60 cm深度土壤有机碳密度为(16.14±4.58) kg·m^-2.随土壤深度增加,土壤有机碳含量、有机碳密度以及土壤全N、全P、全K、有效P及速效K含量都呈减小趋势,其中不同土层间土壤有机碳含量、有机碳密度差异显著(P<0.01).0～60 cm土层土壤有机碳含量和碳密度的拟合方程中,地形因子中高程和坡向余弦值是最优的拟合因子,方程的决定系数分别为0.34和0.39(P<0.01).0～20和0～60 cm土层的半方差函数模型分别为高斯模型和指数模型,利用回归克里格插值方法得到土壤有机碳的空间分布图.与普通克里格法相比,回归克里格法的空间预测精度改进了18%～58%.利用回归克里格插值方法预测了土壤全N的空间分布特征.     

三七的提取动力学研究

研究三七的提取动力学。以Fick第一扩散定律为基础建立三七中三七皂苷R1、人参皂苷Rg1、人参皂苷Rb1三种成分的提取动力学模型,根据方程计算获得提取速率常数、表观活化能、相对萃余率等一系列动力学参数。结果表明,温度升高,三种成分提取速率加快,提取浓度升高,且温度降低各成分浓度达平衡所需时间延长。本研究所建立的三七中三种成分的提取动力学模型均符合一级动力学方程特征,该模型较好的描述了三七药材各成分的动态溶出过程,以期为三七及复方丹参提取工艺的设计和优化提供理论依据。     

Modeling of Sugar Crystallization through Knowledge Integration

This paper reports on the comparison of three modeling approaches that were applied to a fed batch evaporative sugar crystallization process. They are termed white box, black box, and grey box modeling strategies, which reflects the level of physical transparency and understanding of the model. White box models represent the traditional modeling approach, based on modeling by first principles. Black box models rely on recorded process data and knowledge collected during the normal process operation. Among various tools in this group an artificial neural networks (ANN) approach is adopted in this paper. The grey box model is obtained from a combination of first principles modeling, based on mass, energy and population balances, with an ANN to approximate three kinetic parameters ‐‐ crystal growth rate, nucleation rate and the agglomeration kernel. The results have shown that the hybrid modeling approach outperformed the other aforementioned modeling strategies.     

Nucleation and Crystal Growth in a Vitrification Solution Tested for Organ Cryopreservation by Vitrification

Nucleation and crystal growth are investigated for vitrification solution VS41A (dimethyl sulfoxide, formamide, and 1,2-propanediol) in an aqueous carrier solution giving, when added to these three cryoprotectants, a concentration of other solutes in the whole solution the same as that in Euro-Collins, with a 55% (w/v) cryoprotectant concentration. This concentration is assumed to achieve physical properties under 1 atmosphere similar to those of solution VS4 used under 1000 atmospheres. The thermal range and the kinetics of nucleation and crystal growth are investigated by DSC through different thermal treatments. It is found that the nucleation thermal range is below -90 degrees C and that of crystal growth is above -85 degrees C for a relatively long experimental time. The nucleation density is also studied through direct observations by cryomicroscopy and is related to the amount of crystallization calorimetrically recorded. The effect of storage below the glass transition shows the possibility of a slow increase in nucleation below the glass transition, as already observed by other authors for different aqueous solutions. Isothermal crystallization is analyzed within the Johnson-Mehl-Avrami model for temperatures above -75 degrees C. The corresponding samples have been cooled and warmed at the same rate of 40 degrees C/min and calculations give, at constant nuclei numbers, an activation energy of 9.3 +/- 0.3 kcal/mol and the Avrami exponent n = 2.2 +/- 0.05. This shows a two-dimensional crystal growth as observed by cryomicroscopy. The estimated critical warming rate relevant to the preservation of rabbit kidneys by vitrification is 270 degrees C/min with or without an increase in the nucleus density during storage. The present results support the possibility of using VS4 solution for vitrification of rabbit kidneys if pressure is not a limiting factor. Copyright 1993, 1999 Academic Press.     

Protein purification by bulk crystallization: the recovery of ovalbumin

Crystallization is used industrially for the recovery and purification of many inorganic and organic materials. However, very little is reported on the application of bulk crystallization for proteins. In this work, ovalbumin was selected as a model protein to investigate the feasibility of using bulk crystallization for the recovery and purification of proteins. A stirred 1-L seeded batch crystallizer was used to obtain the crystal growth kinetics of ovalbumin in ammonium sulfate solutions at 30 degrees C. The width of the metastable region, in which crystal growth can occur without any nucleation, is equivalent to a relative supersaturation of about 20. The bulk crystallizations were undertaken within this range (using initial relative supersaturations less than 10) and nucleation was not observed. The ovalbumin concentration in solution was measured by UV absorbance and checked by crystal content measurement. Crystal size distributions were measured both by using a Malvern Mastersizer and by counting crystals through a microscope. The crystal growth rate was found to have a second-order dependence upon the ovalbumin supersaturation. While there is no discernible effect of ammonium sulfate concentration at pH 4.90, there is a slight effect at higher pH values. Overall the effect of ammonium sulfate concentration is small compared to the effect of pH, for which there is a 10-fold increase in the growth rate constant, k(Gsigma) over the range pH 4.6-5.4. To demonstrate the degree of purification which can be achieved by bulk crystallization, ovalbumin was crystallized from a solution containing conalbumin (80,000 Da) and lysozyme (14, 600 Da). After one crystallization and a crystal wash, ovalbumin crystals were produced with a protein purity greater than 99%. No contamination by the other proteins was observed when using overloaded sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) stained with Coomassie blue stain and only trace amounts of lysozyme were observed using a silver stain. The presence of these other proteins in solution did not effect the crystal growth rate constant, k(Gsigma). The study demonstrates the feasibility of using bulk crystallization for the recovery and purification of ovalbumin. It should be readily applicable to other protein systems. (c) 1995 John Wiley & Sons, Inc.     

Parameters for crystal growth of ribosomal subunits

A systematic analysis of the parameters that control the crystal growth of the large subunit of ribosomes from B stearothermophilus has been carried out. Several parameters have been identified and classified according to their significance. It was found that only biologically active particles can crystallize and that the critical period for the crystallization process is the first few days, during which changes in the volume and content of the crystallization drop are of importance for both nucleation and crystal growth. Consequently, an experimental procedure for fine control of these variables has been developed. As a result of these studies, the reproducibility of crystal formation was increased, and larger and more stable crystals have been obtained.     

Kinetics and template nucleation of self-assembled hydroxyapatite nanocrystallites by chondroitin sulfate

Biomineralization is an important process, which is often assisted by biomolecules. In this paper, the effect of chondroitin sulfate on the crystallization of hydroxyapatite was examined quantitatively based on a generic heterogeneous nucleation model. It is found that chondroitin sulfate can suppress the supersaturation-driven interfacial structure mismatch between the hydroxyapatite crystal and the substrate and promote the formation of ordered hydroxyapatite nanocrystallite assemblies. The nucleation mechanism of self-aligned hydroxyapatite nanocrystallites was examined from the viewpoints of kinetics and interfacial structure and properties, which contributes to an understanding of the fundamentals of biomineralization of self-assembled structures. The results obtained from this study will provide a basic principle to design and fabricate highly orderly organic-inorganic hybrid materials.     

Ice nucleation inhibition: mechanism of antifreeze by antifreeze protein

The effect of antifreeze protein type III (one type of fish antifreeze protein) on ice crystallization was examined quantitatively based on a "micro-sized ice nucleation" technique. It was found for the first time that antifreeze proteins can inhibit the ice nucleation process by adsorbing onto both the surfaces of ice nuclei and dust particles. This leads to an increase of the ice nucleation barrier and the desolvation kink kinetics barrier, respectively. Based on the latest nucleation model, the increases in the ice nucleation barrier and the kink kinetics barrier were measured. This enables us to quantitatively examine the antifreeze mechanism of antifreeze proteins for the first time.     

水/乙醇溶剂中阿奇霉素的热力学及多晶型研究

在278.2~308.2 K温度范围内,测定阿奇霉素在水/乙醇混合溶剂中的溶解度,根据固液平衡理论建立了该体系的溶解度修正模型。采用X线粉末衍射法和差示扫描量热法,对阿奇霉素在不同温度、不同体积比的水/乙醇混合溶剂中得到的晶体进行鉴别。同时利用溶解度数据估算了阿奇霉素在水/乙醇体系中的溶解热(-25.26~-16.11 k J/mol)、混合热(-9.94~-3.25 k J/mol)。通过溶液化学理论推导了阿奇霉素溶剂化平衡常数K与活度系数γ2的方程:γ2=1/(1+K),建立了溶剂化焓与温度、水/乙醇两者体积比(φ)之间的关系式,为ΔH=RTln(17.86exp(3.4φ)-1)。采用溶析结晶方法得到的6种阿奇霉素晶体,均属单斜晶系,但具有不同的晶胞参数且其密度和熔点也不同。同时发现温度越高,水/乙醇体积比越大,得到的晶体稳定性越差(晶体的熔点和密度降低)。在水/乙醇混合溶剂的溶析结晶体系中,产生阿齐霉素多晶型的现象与溶剂化作用的强弱有关。     

In Situ Probing the Crystallization Kinetics in Gas-Quenching-Assisted Coating of Perovskite Films

The pursuit of commercializing perovskite photovoltaics is driving the development of various scalable perovskite crystallization techniques. Among them, gas quenching is a promising crystallization approach for high-throughput deposition of perovskite films. However, the perovskite films prepared by gas-quenching assisted blade coating are susceptible to the formation of pinholes and frequently show inferior crystallinity if the interplay between film coating, film drying, and crystallization kinetics is not fully optimized. That arguably requires a thorough understanding of how single processing steps influence the crystallization kinetics of printed perovskite films. Here, in situ optical spectroscopies are integrated into a doctor-blading setup that allows to real-time monitor film formation during the gas-quenching process. It is found that the essential role of gas quenching treatment is in achieving a smooth and compact perovskite film by controlling the nucleation rate. Moreover, with the assistance of phase-field simulations, the role of excessive methylammonium iodide is revealed to increase grain size by accelerating the crystal growth rate. These results show a tailored control of crystal growth rate is critical to achieving optimal film quality, leading to fully printed solar cells with a champion power conversion efficiency of 19.50% and mini solar modules with 15.28% efficiency are achieved.     

Biliary cholesterol crystallization characterized by single-crystal cryogenic electron diffraction

Cholesterol crystals are the building blocks of cholesterol gallstones. The exact structure of early-forming crystals is still controversial. We combined cryogenic-temperature transmission electron microscopy with cryogenic-temperature electron diffraction to sequentially study crystal development and structure in nucleating model and native gallbladder biles. The growth and long-term stability of classic cholesterol monohydrate (ChM) crystals in native and model biles was determined. In solutions of model bile with low phospholipid-to-cholesterol ratio, electron diffraction provided direct proof of a novel transient polymorph that had an elongated habit and unit cell parameters differing from those of classic triclinic ChM. This crystal is exactly the monoclinic ChM phase described by Solomonov and coworkers (Biophysical J., In press) in cholesterol monolayers compressed on the air-water interface. We observed no evidence of anhydrous cholesterol crystallization in any of the biles studied. In conclusion, classic ChM is the predominant and stable form in native and model biles. However, under certain (low phospholipid) conditions, transient intermediate polymorphs may form. These findings, documenting single-crystal analysis in bulk solution, provide an experimental approach to investigating factors influencing biliary cholesterol crystal nucleation and growth as well as other processes of nucleation and crystallization in liquid systems.     

A Method to Evaluate the Effect of Contact with Excipients on the Surface Crystallization of Amorphous Drugs

Amorphous drugs are used to improve the solubility, dissolution, and bioavailability of drugs. However, these metastable forms of drugs can transform into more stable, less soluble, crystalline counterparts. This study reports a method for evaluating the effect of commonly used excipients on the surface crystallization of amorphous drugs and its application to two model amorphous compounds, nifedipine and indomethacin. In this method, amorphous samples of the drugs were covered by excipients and stored in controlled environments. An inverted light microscope was used to measure in real time the rates of surface crystal nucleation and growth. For nifedipine, vacuum-dried microcrystalline cellulose and lactose monohydrate increased the nucleation rate of the β polymorph from two to five times when samples were stored in a desiccator, while d-mannitol and magnesium stearate increased the nucleation rate 50 times. At 50% relative humidity, the nucleation rates were further increased, suggesting that moisture played an important role in the crystallization caused by the excipients. The effect of excipients on the crystal growth rate was not significant, suggesting that contact with excipients influences the physical stability of amorphous nifedipine mainly through the effect on crystal nucleation. This effect seems to be drug specific because for two polymorphs of indomethacin, no significant change in the nucleation rate was observed under the excipients.KEY WORDS: amorphous, drugs, growth rate, nucleation rate, tablet excipients