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.     

不同脱乙酰度壳聚糖Mark-Houwink方程的订定

通过多步脱乙酰基反应和溶液超声波降解制备了脱乙酰度D.D在49—100％(wt),重均分子量在1.94—25.1×10~5的系列壳聚糖样品,在0.1mol/L CH_3COONa+0.2mol/L CH_3COOH溶剂中和30℃下,用光散射法首次订定出了不同D.D壳聚糖的M-H方程常数K和α值,结果如下:D.D(wt％) K×10~3(ml·g~(-)1) α69 0.104 1.1284 1.424 0.9691 6.589 0.88100 16.800 0.81导致K和α值差别的主要原因是由于壳聚糖大分子链上的胺基(—NH_2)被酸质子化后,失去了形成分子内氢键的能力,减弱了内旋转受阻程度,同时,质子化后形成的阳离子聚电解质分子链链段间以及链段与溶剂之间的相互作用增强,有效电荷密度的增加使得聚电解质溶液粘度增大。     

测定零切变速度下特性粘数的简便方法

引言高分子溶液的特性粘数是一个十分重要的物理量。它和大分子的化学结构、分子量和大分子在溶液中的形态、尺寸大小等重要特性有关。特性粘数和分子量之间的联系更被广泛地利用于测定分子量。因此,如何准确而又简便地测定特性粘数值一向被人们所重视。无数实验事实表明,高分子溶液并非牛顿流体。特性粘数随切变速度的增加而下降,其下降量的大小随分子链刚硬程度、溶剂性能良好程度和分子量的增     

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.     

羟丙基三甲基氯化铵壳聚糖制备的可控性研究

用壳聚糖与缩水甘油三甲基氯化铵反应制备羟丙基三甲基氯化铵壳聚糖,所得产物的结构受壳聚糖分子量和脱乙酰度、反应温度、反应时间、壳聚糖与缩水甘油三甲基氯化铵投料比的影响。实验结果表明：随着反应温度升高,羟丙基三甲基氯化铵壳聚糖的取代度增加,在70～80℃达最大;反应时间增加,取代度增加,产物分子量降低。缩水甘油三甲基氯化铵与壳聚糖比例达3：1前取代度随比例升高而增加。脱乙酰度和分子量越大的壳聚糖其季铵盐取代度越高。控制反应温度在30～90℃,反应时间3～10h,投抖比为1：1～4：1,可以得到取代度15％～909／6,分子量1万到100万的羟丙基三甲基氯化铵壳聚糖。     

壳聚糖在稀溶液中的分子构象及其影响因素

结合国内外对壳聚糖在溶液性质方面的研究进展,从壳聚糖的分子量、乙酰度和溶液的离子强度三个方面,探讨了它们对壳聚糖在稀溶液中的分子构象所产生的影响,并从分子间和分子内相互作用力(主要是范德华力、氢键、疏水作用和静电作用)的角度对这种构象转变进行了理论解释。     

不同脱乙酰度对壳聚糖表面物理及吸附性能的影响

壳聚糖是甲壳素部分脱乙酰化的产物,脱乙酰度的大小对壳聚糖的性能影响很大。利用碱液法,通过对反应时间的控制,制备了不同脱乙酰度的壳聚糖并对其性能进行了研究。结果表明,随着脱乙酰度的增大,壳聚糖膜的吸水率增加,而对其表面接触角的变化则没有影响。同时,壳聚糖海绵对Ca2+和牛血清蛋白(BSA)的吸附能力也随着脱乙酰度的增大而增加。     

碱量法测定壳聚糖脱乙酰度的研究

碱量法(包括酸碱滴定法和电位滴定法)是目前测定壳聚糖脱乙酰度较为常用的方法,其原理是用过量的稀酸与一定量的待测壳聚糖反应,然后用标准NaOH溶液滴定过量的酸来测量壳聚糖中自由氨基的量,从而计算壳聚糖的脱乙酰度(DD值)。计算脱乙酰度的公式多用:DD=(-NH2)%/0.094×100%(公式一)。而另外一个碱量法中未用过的脱乙酰度计算公式为:DD=[203n/(G 42n)]×100%(公式二),本文用计算公式一和公式二分别计算在酸碱滴定法和双突跃电位滴定法中壳聚糖的脱乙酰度,结果表明:在酸碱滴定法中,用公式一的计算的结果准确度更高,而在双突跃电位滴定法中用公式二计算的结果准确度更高。     

脱乙酰甲壳质和卡拉胶在溶液中的反应及其复合物性质研究

脱乙酰甲壳质(CTS)和卡拉胶(CGN)在溶液中反应生成不溶于水的沉淀,红外光谱分析及相反离子含量测定证明,CTS和CGN分子间的联结是以CTS分子中的-NH_3~+与CGN分子中的-SO_3~-通过静电相互作用来实现的。形成的聚电解质复合物N/S摩尔比在较宽的范围内依赖于反应混合溶液组成比、pH值及CTS的脱乙酰度。不同条件下形成的复合物具有不同的形态结构,当CTS分子与CGN分子上的电荷密度接近时,电镜观察到的复合物呈纤维状结构。复合物不溶于二甲基亚砜及CH_3COCH_3/KBr/H_2O(20∶20∶60wt)三元溶剂,在加热时溶于浓甲酸和稀盐酸,其溶解性随CTS脱乙酰度的增加而降低,CTS和CGN形成的聚电解质复合物具有一定的抗血凝性。     

光纤折射率传感用于壳聚糖脱乙酰度测定

建立了一种基于光纤折射率传感技术的壳聚糖脱乙酰度测定方法. 利用光纤折射率传感器监测酸碱滴定过程中溶液折射率的变化, 根据折射率变化转折点之间碱的用量来计算壳聚糖的脱乙酰度. 该方法测得的3种不同含量实际样品的脱乙酰度与氢核磁共振波谱(¹H NMR)方法测定结果相符, 验证了方法的可靠性. 该方法具有用量少、 结构简单、 准确、 重复性好和转折点明显等优点, 可应用于工业生产中壳聚糖脱乙酰度的测定.     

壳聚糖浓溶液流变性质研究──零剪切粘度的测定和外推

用落球法测定了不同溶剂体系和浓度的壳聚糖浓溶液的零剪切粘度η０，用ＲＰＸ－７０５多功能流变仪同轴圆筒方法测定了各浓溶液的粘度随剪切速率的变化关系，并用Ｐｅｒｒｒ、Ｃｒｏｓｓ和Ｂａｌｌａｕｆｆ方法进行了求η０的外推．将外推结果与落球法结果进行了比较，认为Ｃｒｏｓｓ方法的结果与实际测得结果更接近，可以代替落球法，这样可以简单地得到壳聚糖浓溶液η０的信息．     

C-C versus C-H bond activation of alkynes by early second-row transition metal atoms

The reactions of Y (a2D), Zr (a3F), Nb (a6D), Mo (a7S), and electronically excited-state Mo* (a5S) with propyne (methylacetylene) and 2-butyne (1,2-dimethylacetylene) were investigated using crossed molecular beams. For all of the metals studied, reactions with propyne led to H2 elimination, forming MC3H2. For Y + propyne, C-C bond cleavage forming YCCH + CH3 also was observed, with an energetic threshold in good agreement with an earlier determination of D0(Y-CCH). For Y + 2-butyne, three reactive channels were observed: YC4H4 + H2, YC3H3 + CH3, and YC3H2 + CH4. The C-C bond cleavage products accounted for 21 and 27% of the total products at Ecoll = 69 and 116 kJ/mol, respectively. For Zr and Nb reactions with 2-butyne, competition between H2 and CH4 elimination was observed, with C-C bond cleavage accounting for 12 and 4% of the total product signal at Ecoll = 71 kJ/mol, respectively. For reactions of Mo and Mo* with 2-butyne, only H2 elimination was observed. The similarity between reactions involving two isomeric species, propyne and allene, suggests that H atom migration is facile in these systems.     

氟丙烯在高温下的热稳定性

用单脉冲激波管研究了全氟丙烯C3F6的分解。使用H2作为清扫剂。产物包括 CH4、 C2F4、 CF3H和C2F3H,作为对断键反应过程的指示。C3F6的断键反应为 C3F6  CF3+C2F3 （1） 得到其速率常数表达式为 k（C3F6  CF3+C2F3)=10(17.4±0.2)exp-(355300±8360)/(RT) s-1 温度范围为1090 K相似文献   

氨和甲醇团簇中的质子转移反应

应用激光多光子电离质谱和分子束技术研究了氨和甲醇二元团簇,实验观测到两个系列质子化的团簇离子: (CH3OH)nH+和(CH3OH)nNH4+(1≤n≤14 ),其产生是经过二元团簇内的质子转移反应。同时也研究了氘代甲醇CH3OD和氨混合团簇,结果表明OD原子团中的D转移概率比CH3原子团中的质子转移概率大几倍。在HF/STO-3G和MP2/6-31G*　*水平上对氨和甲醇二元团簇进行了计算,结果表明与CH3相比OH中的质子转移更加容易,因为CH3中的质子转移过程要克服高度约120 kJ/mol的能垒。     

Enzyme sensor for L-lactate with a chitosan-mercury film electrode

Summary An amperometric enzyme sensor composed of a mercury film electrode and an enzyme-immobilized chitosan membrane is developed. This biosensor is based on both a mercury film electrode detecting the consumption of dissolved dioxygen following enzymatic reaction, and a chitosan membrane. The latter provides an excellent permselectivity and excludes electroactive interferents. The detection range of this biosensor was 1.0×10^–5–3.0×10^–4 mol/l and the relative standard deviation, R.S.D. at 5.0×10^–5 mol/l was 1.4% (n=3). This biosensor was applied to the direct determination of L-lactate in human serum without pretreatment.     

流动注射分光光度法研究壳聚糖树脂吸附阴离子染料

利用流动注射分光光度法技术，跟踪观察交联壳聚糖树脂吸附阴离子染料的行为，讨论了外加氯化钠或甲醇以及温度等因素对吸附的影响。利用固－液相互作用方程，求取了吸附剂－吸附质相互作用能。实验结果表明，交联壳聚糖树脂吸附 子染料，其表观吸附速率常数随体系中氯化钠浓度或甲醇含量的增大而减小，随温度的升高而增大；交联壳聚糖树脂吸附酸性铬蓝K染料的表观活化能力26.095kJ/mol。     

壳聚糖碳纳米管修饰电极测定痕量铜

建立了用自制的碳纳米管壳聚糖修饰电极测定Cu^2＋离子的电分析方法,在0．10mol／L的CH,COOH—CH3 COONa（pH4．2）缓冲溶液中,以此修饰电极作为工作电极,以-0．60V为富集电位,搅拌富集6min后,用差分脉冲伏安法测定-0．10V处的峰电流。结果发明,该电极对铜离子吸附的灵敏度较高,当铜离子浓度为1．0×10^-6～4．6×10^-5mol／L时,线性关系良好,相关系数为0．9997,对含铜血清样本进行测定,取得了满意的结果,加标回收率在98％～102％之间。     

193-nm photodissociation of acryloyl chloride to probe the unimolecular dissociation of CH2CHCO radicals and CH2CCO

The work presented here uses photofragment translational spectroscopy to investigate the primary and secondary dissociation channels of acryloyl chloride (CH2==CHCOCl) excited at 193 nm. Three primary channels were observed. Two C-Cl fission channels occur, one producing fragments with high kinetic recoil energies and the other producing fragments with low translational energies. These channels produced nascent CH2CHCO radicals with internal energies ranging from 23 to 66 kcal/mol for the high-translational-energy channel and from 50 to 68 kcal/mol for the low-translational-energy channel. We found that all nascent CH2CHCO radicals were unstable to CH2CH + CO formation, in agreement with the G3//B3LYP barrier height of 22.4 kcal/mol to within experimental and computational uncertainties. The third primary channel is HCl elimination. All of the nascent CH2CCO coproducts were found to have enough internal energy to dissociate, producing CH2C: + CO, in qualitative agreement with the G3//B3LYP barrier of 39.5 kcal/mol. We derive from the experimental results an upper limit of 23 +/- 3 kcal/mol for the zero-point-corrected barrier to the unimolecular dissociation of the CH2CHCO radical to form CH2CH + CO.     

Synthesis, structure, and reactivity of O-donor Ir(III) complexes: C-H activation studies with benzene

Various new thermally air- and water-stable alkyl and aryl analogues of (acac-O,O)2Ir(R)(L), R-Ir-L (acac-O,O = kappa2-O,O-acetylacetonate, -Ir- is the trans-(acac-O,O)2Ir(III) motif, R = CH3, C2H5, Ph, PhCH2CH2, L = Py) have been synthesized using the dinuclear complex [Ir(mu-acac-O,O,C3)-(acac-O,O)(acac-C3)]2, [acac-C-Ir]2, or acac-C-Ir-H2O. The dinuclear Ir (III) complexes, [Ir(mu-acac-O,O,C3)-(acac-O,O)(R)]2 (R = alkyl), show fluxional behavior with a five-coordinate, 16 electron complex by a dissociative pathway. The pyridine adducts, R-Ir-Py, undergo degenerate Py exchange via a dissociative mechanism with activation parameters for Ph-Ir-Py (deltaH++ = 22.8 +/- 0.5 kcal/mol; deltaS++ = 8.4 +/- 1.6 eu; deltaG++298 K) = 20.3 +/- 1.0 kcal/mol) and CH3-Ir-Py (deltaH++ = 19.9 +/- 1.4 kcal/mol; deltaS++ = 4.4 +/- 5.5 eu; deltaG++298 K) = 18.6 +/- 0.5 kcal/mol). The trans complex, Ph-Ir-Py, undergoes quantitatively trans-cis isomerization to generate cis-Ph-Ir-Py on heating. All the R-Ir-Py complexes undergo quantitative, intermolecular CH activation reactions with benzene to generate Ph-Ir-Py and RH. The activation parameters (deltaS++ =11.5 +/- 3.0 eu; deltaH++ = 41.1 +/- 1.1 kcal/mol; deltaG++298 K = 37.7 +/- 1.0 kcal/mol) for CH activation were obtained using CH3-Ir-Py as starting material at a constant ratio of [Py]/[C6D6] = 0.045. Overall the CH activation reaction with R-Ir-Py has been shown to proceed via four key steps: (A) pre-equilibrium loss of pyridine that generates a trans-five-coordinate, square pyramidal intermediate; (B) unimolecular, isomerization of the trans-five-coordinate to generate a cis-five-coordinate intermediate, cis-R-Ir- square; (C) rate-determining coordination of this species to benzene to generate a discrete benzene complex, cis-R-Ir-PhH; and (D) rapid C-H cleavage. Kinetic isotope effects on the CH activation with mixtures of C6H6/C6D6 (KIE = 1) and with 1,3,5-C6H3D3 (KIE approximately 3.2 at 110 degrees C) are consistent with this reaction mechanism.     

Magnitude of the CH/pi interaction in the gas phase: experimental and theoretical determination of the accurate interaction energy in benzene-methane

The accurate CH/pi interaction energy of the benzene-methane model system was experimentally and theoretically determined. In the experiment, mass analyzed threshold ionization spectroscopy was applied to the benzene-methane cluster in the gas phase, prepared in a supersonic molecular beam. The binding energy in the neutral ground state of the cluster, which is regarded as the CH/pi interaction energy for this model system, was evaluated from the dissociation threshold measurements of the cluster cation. The experimentally determined binding energy (D(0)) was 1.03-1.13 kcal/mol. The interaction energy of the model system was calculated by ab initio molecular orbital methods. The estimated CCSD(T) interaction energy at the basis set limit (D(e)) was -1.43 kcal/mol. The calculated binding energy (D(0)) after the vibrational zero-point energy correction (1.13 kcal/mol) agrees well with the experimental value. The effects of basis set and electron correlation correction procedure on the calculated CH/pi interaction energy were evaluated. Accuracy of the calculated interaction energies by DFT methods using BLYP, B3LYP, PW91 and PBE functionals was also discussed.