化学计量学研究及其应用

本文介绍了化学计量学的产生、发展、研究内容及主要应用,对有关工作进行了评述。     

Physicochemical aspects of microbial adhesion — Influence of antibody adsorption on the deposition ofStreptococcus sobrinus in a parallel-plate flow chamber

Deposition of the oral bacteriumStreptococcus sobrinus HG977 onto glass (water contact angle 0°) and onto FEP-Teflon (fluoroethylenepropylene; water contact angle 110°) was studied in a parallel-plate flow chamber in the presence and absence of polyclonal antibodies (pAb) and monoclonal antibodies (mAbs) adsorbed onto the cells. The zeta potentials of the bacteria ranged from −7.1 to −8.5 mV at pH 6.8 and were not affected by the presence of pAb or mAbs. Hydrophobicity (by water contact angles) increased from 30° (no antibodies) to 88° in the presence of pAb adsorbed onto the bacterial cell surface. The untreatedS. sobrinus had a greater tendency to adhere to glass (44.5 × 10⁶ cm⁻²) than to FEP-Teflon (18.3 × 10⁶ cm⁻²), in accordance with thermodynamic modelling. After preincubation ofS. sobrinus with pAb, its clear preference for adhesion to glass disappeared as expected from its increased hydrophobicity. Although forS. sobrinus preincubated with OMVU10 no difference was found in hydrophobicity in comparison to the untreated bacteria, the number of bacteria adhering to glass decreased to 10.2 ¢ 10⁶ cm⁻². Formation of bacterial aggregates was found whenS. sobrinus, preincubated with pAb or OMVU10, adhered to glass and FEP. This was also observed when untreated bacteria adhered to glass coated with OMVU10, or to FEP coaled with OMVU10 or pAb. Adhesion in these experiments is therefore thought to occur via near-neighbour collection induced by the presence of pAb or mAbs. Low numbers of bacteria were removed from glass after draining the flow cell, whereas high numbers of untreated bacteria and bacteria preincubated with OMVU10 were removed from FEP.S. sobrinus cells preincubated with pAb were not removed but piled up. It was concluded that the adhesion of untreatedS. sobrinus andS. sobrinus preincubated with pAb is in accordance with thermodynamic modelling, based on the overall wettability of the cell surfaces, whereas the adhesion ofS. sobrinus preincubated with OMVU10 may be through localized interactions, not expressed in overall surface properties.     

Development of a mild mercaptoethanol extraction method for determination of mercury species in biological samples by HPLC–ICP-MS

A mild, efficient and convenient extraction method of using 2-mercaptoethanol contained extractant solution combined with an incubator shaker for determination of mercury species in biological samples by HPLC–ICP-MS has been developed. The effects of the concentration of 2-mercaptoethanol, the composition of the extractant solution and the shaking time on the efficiency of mercury extraction were evaluated. The optimization experiments indicated that the quantitative extraction of mercury species from biological samples could be achieved by using 0.1% (v/v) HCl, 0.1% (v/v) 2-mercapoethanol and 0.15% (m/v) KCl extractant solution in an incubator shaker for shaking overnight (about 12 h) at room temperature. The established method was validated by analysis of various biological certified reference materials, including NRCC DOLT-3 (dogfish liver), IAEA 436 (tuna fish), IAEA MA-B-3/TM (garfish filet), IAEA MA-M-2/TM (mussel tissue), GBW 08193 (bovine liver) and GBW 08572 (prawn). The analytical results of the reference materials were in good agreement with the certified or reference values of both methyl and total mercury, indicating that no distinguishable transformation between mercury species had occurred during the extraction and determination procedures. The limit of detection (LOD) for methyl (CH₃Hg⁺) and inorganic mercury (Hg²⁺) by the method are both as 0.2 μg L⁻¹. The relative standard deviation (R.S.D.s) for CH₃Hg⁺ and Hg²⁺ are 3.0% and 5.8%, respectively. The advantages of the developed extraction method are that (1) it is easy to operate in HPLC–ICP-MS for mercury species determination since the extracted solution can be directly injected into the HPLC column without pH adjustment and (2) the memory effect of mercury in the ICP-MS measurement system can be reduced.     

二(2,4,4-三甲基戊基)膦酸萃取分离稀土元素(Ⅲ)的研究

本文研究了二(2,4,4-三甲基戊基)磷酸(Cyanex 272)的煤油溶液在不同介质(HCI,HNO_3)中对三价混合稀土的萃取分离性能.观测了平衡水相酸度对萃取平衡的影响,由酸度曲线求出相邻元素的平均分离系数,并考察了酸度对反萃取平衡的影响.比较了HCI和HNO_3介质中,Cyanex 272对混合稀土(Ⅲ)的萃取性能.     

模式识别—人工神经网络在化学中的若干新应用

本文通过我们应用模式识别－人工神经网络方法预报新化合物、熔盐相图以及复杂化学反应体系的研究，展示应用模式识别－人工神经网络方法与物理化学理论相结合，研究化学现象的可能性和应用价值。     

新的不对称双Schiff碱镍配合物

乙二胺中2个氨基具有相同的反应活性,易同时反应形成对称的双Schiff碱,随着不对称配合物的设计和金属酶模型化合物的不断开发,业已发现严格控制反应条件和改变反应物摩尔比,可以有效地实现单个氨基的选择性反应,例如,在低温、稀的反应液中,乙酰丙     

On the Randić Index of Acyclic Conjugated Molecules

The Randić index of an organic molecule whose molecular graph is G is the sum of the weights (d(u)d(v))^−1/2 of all edges uv of G, where d(u) and d(v) are the degrees of the vertices u and v in G. We give a sharp lower bound on the Randić index of conjugated trees (trees with a perfect matching) in terms of the number of vertices. A sharp lower bound on the Randić index of trees with a given size of matching is also given Mei Lu: Partially supported by NNSFC (No. 60172005) Lian-zhu Zhang: Partially supported by NNSFC (No. 10271105) Feng Tian: Partially supported by NNSFC (No. 10431020)     

手性配体的空间结构与产物对映选择性的关系

首次采用4－烷氧羰基噻唑烷、E唑烷作为手性配体，诱导烷基锌对醛类的亲核加成反应，获得产物是烷基化的醛，最高达90％ee，产率98％的（S）－二级醇。系统地考察了该类手性配体三维空间结构变化与产物对映选择性的关系，当配体4－位烷氧羰基上的R、2－位R′基和环体上原子X发生变化时都会引起产物（S）－二 级醇的对映选择性发生规律性变化。对五种不同结构的底物醛在同一手性配体催化下，诱导烷基锌对醛类的亲核加成反应，底物结构变化也会引起（S）－二级醇对映选择性变化。     

载体γ-Al2O3和钐对非晶态NiB合金热稳定性的影响

用化学还原法制备了NiB、NiB/Al2O3和NiBSm/Al2O3三种催化剂，它们都呈非晶结构.用等离子耦合发射光谱仪(ICP)对催化剂组分进行了分析，采用差示扫描量热法（DSC）对三种催化剂进行了热稳定性分析.结果表明，载体的引入使非晶态NiB合金的体相组成中B的含量降低.将非晶态NiB合金负载到γ-Al2O3上,可以明显改善非晶态合金的热稳定性，少量Sm可以进一步提高晶化温度.晶化激活能数据亦表明了载体和Sm对非晶结构具有良好的稳定作用.载体和Sm可能通过不同的作用提高了非晶态合金的热稳定性.