壳聚糖超声可控降解及降解动力学研究

通过正交实验法考察了壳聚糖溶液浓度、反应温度、超声强度以及醋酸溶液浓度对超声降解反应的影响,确定了最佳反应条件,制备了一系列不同分子量的壳聚糖.研究了壳聚糖溶液浓度、反应温度以及壳聚糖原料分子参数与降解速率常数的关系.通过红外光谱、X-射线衍射和凝胶渗透色谱对降解产物进行了表征.结果表明,超声降解壳聚糖的最佳条件为10℃,壳聚糖溶液浓度2.5g/L.降解速率常数随壳聚糖溶液浓度和反应温度的降低而增大.高分子量和低脱乙酰度的壳聚糖原料有较高的降解速率和降解速率常数,壳聚糖原料的分子量对降解速率和降解速率常数的影响大于脱乙酰度对其的影响.超声波导致了壳聚糖分子量的降低和产物晶体结构的破坏,但没有改变产物的脱乙酰度和糖残基结构.     

双指示剂法测定壳聚糖的脱乙酰度

壳聚糖是甲壳质经浓碱脱乙酰基后得到的衍生物,具有良好的生物相容性和生物可降解性,广泛应用于医药、食品、化妆品、轻工、印染、环保和生物工程等领域[1-2]。壳聚糖脱乙酰度(简称DD%)是指壳聚糖多糖分子氨基上脱去乙酰基的百分比,其高低直接影响到壳聚糖的溶解度、絮凝能力、螯合金属离子能力和N-选择性酰化能力等物化特性,是鉴定壳聚糖产品质量的一个重要指标。目前测定壳聚糖脱乙酰度的方法有酸碱滴定     

壳聚糖/SiO2杂化材料膜制备的研究

由甲壳质制得不同脱乙酰度、粘度的壳聚糖;制成的壳聚糖盐酸溶液与正硅酸乙酯在不同的条件下混合,得到一种杂化材料;通过红外光谱检测和物理性质观测到部分产物有新键形成;反应温度、时间ｐＨ值对产物形成膜的物理和机械性质有影响;与壳聚糖膜相比,部分杂化膜不溶解于稀酸溶液。     

壳聚糖对Zn2+的吸附性能研究

本文用壳聚糖对Ｚｎ＾２＋的吸附条件进行了研究,探讨了脱乙酰度,分子量,粒度大小,溶液的ｐＨ值,温度,Ｚｎ＾２＋起始浓度和不同锌盐等方面对壳聚糖吸附性能的影响。结果表明：壳聚糖对Ｚｎ＾２＋的吸附具有Ｌａｎｇｍｕｉｒ吸附特征,其吸附最佳条件是壳聚糖脱乙酰度为１００％,锌盐为硫酸锌,Ｚｎ＾２＋溶液ｐＨ值为６．０,起始浓度４－５ｍｇ／ｍｌ。     

蘑菇中甲壳素的提取及结构研究

以蘑菇为原料提取甲壳素,并制备壳聚糖。通过滴定法测定由蘑菇制备的壳聚糖的脱乙酰度,用乌氏黏度计测定了比浓黏度,并研究了制备工艺中加热温度和碱处理时间对它们的影响,计算了其产率;对以蘑菇为原料制取的甲壳素、壳聚糖的结构通过红外光谱进行表征。结果表明,在碱处理时间为24h、加热温度为100℃的条件下有较高的脱乙酰度;比浓黏度随着碱处理时间的延长、加热温度的增加都呈下降的趋势;壳聚糖产率为1．69％。制取的甲壳素、壳聚糖的红外光谱图表明,甲壳素在蘑菇中主要是以α-构型存在,α-构型甲壳素在浓碱中经过脱乙酰后生成β-构型的壳聚糖。     

甲壳素类液晶高分子的研究Ⅳ.脱乙酰度对壳聚糖液晶性的影响

通过壳聚糖乙酰化法制备了不同脱乙酰度的壳聚糖 ,并研究了脱乙酰度这一结构因素对壳聚糖溶致液晶性的影响 .观察到脱乙酰度为 5 0 %左右时 ,壳聚糖在水中和二氯乙酸中的溶致液晶临界浓度最高 .壳聚糖在水中的溶致液晶临界浓度远低于在二氯乙酸中的临界浓度 .     

串联式压电传感技术用于壳聚糖脱乙酰度测定及其对铜(Ⅱ)离子吸附的研究

基于酸碱滴定过程和金属离子吸附过程中的溶液电导率变化,首次将串联式压电石英晶体传感器(SPQC)用于壳聚糖脱乙酰度测定和壳聚糖对Cu2+的吸附特性考察.实验发现由滴定频率响应曲线测得的脱乙酰度与电位滴定法的测定值相近.用SPQC实时监测壳聚糖对Cu2+的吸附过程,通过比较频移响应曲线,考察了Cu2+初始浓度、吸附剂用量及脱乙酰度对壳聚糖吸附Cu2+性能的影响.结果表明,适当增加Cu2+浓度和吸附剂用量更利于壳聚糖对Cu2+的吸附,随着脱乙酰度的增加,壳聚糖对Cu2+的配位能力增强.     

壳聚糖制备新工艺及生产废水处理

研究一种制备壳聚糖的新方法——“一步法”，即将虾、蟹壳酸浸、碱煮、脱乙酰后直接制得壳聚糖，分析了操作中各步骤的溶液组成、处理温度和处理时间等因索对壳聚糖脱乙酰度和粘均分子量的影响，并通过正交实验对工艺参数进行了优化。采用自然沉淀、两次中和及活性污泥法组合处理壳聚糖生产废水，不仅能使处理后的废水达标排放，而且可完全回用，实现零排放。废水处理过程中产生的废渣水洗后经压滤，可作饲科。     

片状壳聚糖的脱乙酰化反应

本文采用一种新方法制备 10 0 %脱乙酰度的壳聚糖。低脱乙酰度壳聚糖溶解在酸溶液中并通过溶剂蒸发制备得到片状壳聚糖。片状壳聚糖进行一步碱处理就可以得到高脱乙酰度壳聚糖。     

脱乙酰度测定方法

甲壳质,一种N-乙酰基-D-氨基葡萄糖,通过β-(1→4)甙键联结起来的直链多糖。它大量存在于甲壳动物,昆虫和细菌中,甲壳质由于其在自然界中具有丰富的资源及广阔的应用前景而日益受到重视。脱乙酰甲壳质是甲壳质衍生物中用途最广也是最为重要的一个,它已被广泛应用于医药、食品、印染、纺织、造纸、金属提取及回收、环保、生物工程等部门。脱乙酰度作为脱乙酰甲壳质     

Investigation of the sorption of water vapor on cation-substituted vermiculite. 2. Thermodynamic description of sorption equilibria

The changes in the thermodynamic functions of the sorbents were calculated for the first time from measurements of the deformations of vermiculite during the sorption of water vapor and adsorption-calorimetric data.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Colloid Chemistry and the Chemistry of Water, Academy of Sciences of the Ukraine, 252180 Kiev. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1270–1275, June, 1992.     

Thermodynamics of ionization of water over wide ranges of temperature and pressure

We have summarized results of many experimental investigations of the thermodynamics of ionization of H₂O(liq.) from 0–300°C and from 1.0 atm to nearly 8000 atm. Results of these investigations (equilibrium constants, enthalpies of ionization, heat capacities, partial molal volumes, and compressibilities) have been used for a number of thermodynamic calculations. It is particularly noteworthy that it is possible to use thermal data from 0–145°C with an equilibrium constant for 25°C in calculating reasonably accurate equilibrium constants for temperatures as high as 300°C. Similarly, it is possible to use volumetric data that refer to 1.0 atm in calculating useful equilibrium constants that apply for pressures as high as 2000 atm.Much of the work reported here was done while the author was on leave at the University of Lethbridge.     

Thermodynamics of lonization of aqueous lodic acid,an “almost-strong” electrolyte

We have made calorimetric measurements of enthalpies of dilution of aqueous iodic acid and have used these results for evaluation of the standard enthalpy of ionization of HIO₃(aq.). We have also made calorimetric measurements of enthalpies of addition of perchloric acid solution to aqueous solutions of KIO₃, KNO₃, NaIO₃, and NaNO₃ and have used these results to obtain further values for the standard enthalpy of ionization of HIO₃(aq.). On the basis of all these results, we have selected H^o=–660±125 cal-mole^–1 as the best available standard enthalpy of ionization of HIO₃(aq.) at 298.15°K, compared to the previously accepted –2400 cal-mole^–1. Using the best available K=0.157 for ionization, we also obtain G^o=1097 cal-mole^–1 and S^o=–5.9 cal-^oK^–1-mole^–1 for ionization of HIO₃(aq) at 298.15°K.On study leave from Department of Inorganic and Analytical Chemistry, LaTrobe University, Bundoora, Victoria, 3083, Australia, to University of Lethbridge.On study leave from Department of Chemistry, University of Wollongong, Wollongong, N.S.W. 2500, Australia, to University of Lethbridge.     

Thermochemical study of aliphatic and phenyl-substituted geminal diacetates

The standard enthalpies of combustion _c H ^o of aliphatic diacetates1 and aromatic diacetates2 were measured calorimetrically. The enthalpies of vaporization _vap H ^o or sublimation _sub H ^o of1 and2 were obtained from the temperature function of the vapor pressure measured in a flow system. From _f H ^o(g) of1 and2 new values of group increments for the estimation of standard enthalpies of formation of these classes of compounds were derived. The geminal interaction energy between the geminal acyloxy groups shows no anomeric stabilization.Geminal Substituent Effects, Part 12, for part 11 see Ref. 7.     

Relation between characteristic adsorption energy and internal pressure in the theory of volume filling of micropores

An equation for the internal pressure acting on an adsorbate in micropores was obtained on the basis of the assumption that the chemical potential of an adsorbate in micropores is equal to that in an equilibrium gas phase and using the Dubinin-Radushkevich equation. The empirical relation between the characteristic adsorption energy and the half width of pores was expressed in terms of internal pressure and diameter of adsorbate molecules. The two-dimensional pressure was calculated for micropores with plane-parallel walls, where the width of a micropore coincides with the diameter of an adsorbate molecule. The results obtained were compared with the two-dimensional pressure of a monolayer on a free planar surface for an adsorbate and adsorbent of the same nature.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1928–1930, October, 1995.     

Thermochemistry of aqueous solutions of alkylated nucleic acid bases. VIII. Enthalpies of hydration of 6-alkyluracils

Enthalpies of solution in water H _sol ^o and enthalpies of sublimation H _sub ^o were determined for a number of crystalline derivatives of uracil: 1,6-dimethyluracil (m ₂ ^1,6 Ura), 1,3,6-trimethyluracil (m ₃ ^1,3,6 Ura), 6-ethyl-1,3-dimethyluracil (e⁶m ₂ ^1,3 Ura), 6-propyl-1,3-dimethyluracil (pr⁶m ₂ ^1,3 Ura) and 6-butyl-1,3-dimethyluracil (but⁶m ₂ ^1,3 Ura). Standard enthalpies of hydration H _hydr ^o and standard enthalpies of interaction H _int ^o of the solutes with their hydration shells were calculated. The data obtained show that dependence of H _int ^o on the number of-CH₂- groups of n-alkyl chain added upon substitution of diketopyrimidine ring is nonlinear. This finding is discussed in connection with results of X-ray diffraction structure determinations for the crystalline compounds.     

STUDIES ON THE REACTIVITY PATTERNS OF HETEROCYCLICS IN AQUEOUS DMSO‐INTERACTION BETWEEN POSITIVE END OF SULFOXIDE DIPOLE AND LONE PAIR ON RING NITROGEN IN PYRIDINE DERIVATIVES

Abstract

The signals for the α, β, and γ protons of pyridine exhibit a downfield shift in DMSO-d₆, compared to CCl₄ as solvent, the order being γ > β > α. This is attributed to an interaction between the positive end of the DMSO dipole and the lone pair of electrons on the ring nitrogen. This effect is also reflected in the faster rate of alkaline hydrolysis of ethyl isonicotinate over ethyl nicotinate and ethyl picolinate in aqueous DMSO relative to aqueous ethanol. Similar solvent effects are also observed in the pmr spectrum of pyrazine.     

Protonation of leucoemeraldine in the solid state and in solution

The protonation of leucoemeraldine in power form and in N-methylpyrrolidinone (NMP) solution by HCIO₄ and HBF₄ has been studied by x-ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet (UV)-visible absorption spectroscopy. In powder form, less than 25% of the amine nitrogens can be protonated in the absence of oxygen. The effects of oxygen on the degree of protonation and the distribution of amine and imine units upon deprotonation of the salt are investigated. The degree of protonation in leuccemeraldine can be increased to about 50% with 3 M HCIO₄, similar to that achievable with emeraldine base in powder form. In NMP solution, leucoemeraldine is easily oxidized by dissolved oxygen. Protonation of both leucoemeraldine and emeraldine base in NMP solutions results in metastable species which gradually undergo deprotonation. The resulting products are affected by the O₂ content of the solutions. © 1993 John Wiley & Sons, Inc.     

钾明矾溶液水解度计算公式

根据盐类水解关系式和水的离子积计算公式,建立了计算盐类水解度和水解产物离解常数的完全方程式。计算值同实验值比较,钾明矾溶液水解度平均偏差为0.6％,离解常数pK_b=11.6±0.1,水的离子积pK_w平均偏差小于0.06,从而改进了苏联的计算公式。     

碳量子点上转换材料的制备及其应用研究进展

碳量子点(CQD)具有化学惰性,生物相容性和低毒性等优势,可能在能源、生物医药等领域得到广泛的应用. CQD可通过表面被聚合物(例如PEG)钝化而表现出很强的光致发光特性.在生物成像,疾病检测和药物输送中使用表面钝化后的功能化生物分子更为有效.并且碳材料由于其优异的电化学性能还展现出在催化、电子器件等许多领域广泛的应用前景.我们将对近年来碳量子点发光材料的研究进行总结,并讨论碳量子点在能源、环境和其他一些领域的应用.