Accurate determination of pyridine-poly(amidoamine) dendrimer absolute binding constants with the OPLS-AA force field and direct integration of radial distribution functions

OPLS-AA force field and direct integration of intermolecular radial distribution functions (RDF) were employed to calculate absolute binding constants of pyridine molecules to amino group (NH2) and amide group hydrogen atoms in and first generation poly(amidoamine) dendrimers in chloroform. The average errors in the absolute and relative association constants, as predicted with the calculations, are 14.1% and 10.8%, respectively, which translate into ca. 0.08 and 0.06 kcal/mol errors in the absolute and relative binding free energies. We believe that this level of accuracy proves the applicability of the OPLS-AA, force field, in combination with the direct RDF integration, to reproducing and predicting absolute intermolecular association constants of low magnitudes (ca. 0.2-2.0 range).     

Dimeric iron n-confused porphyrin complexes

A dimeric iron N-confused porphyrin, [Fe(NCTPP)]2 was obtained from the anaerobic reaction of Fe(NCTPP)Br with NaSePh while under aerobic conditions a hydroxo bridged iron dimer with Na bridging the outer-N atoms was obtained and oxygenation occurred on the inner core pyrrolic carbon to form a novel ONCTPP porphyrinic ring.     

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.     

洋葱状富勒烯的提纯研究

以石墨粉为碳源, Al为催化剂, 采用真空热处理法制备了平均粒径为15～35 nm的洋葱状富勒烯(OLFs).并用CS₂分离和空气氧化法对得到的OLFs初产品进行了提纯处理.高分辨透射电镜(HRTEM)、X射线衍射(XRD)、热重分析(TGA)对提纯前后样品的分析表明, CS₂分离处理可有效去除初产品中裸露的金属催化剂微粒,然后在空气中610 ℃焙烧200 min,可基本去除无定型碳,并大量去除了石墨状碎片等碳杂质, OLFs的纯度在50％(体积分数)以上.     

Cell-permeable GPNA with appropriate backbone stereochemistry and spacing binds sequence-specifically to RNA

Guanidine-based peptide nucleic acid (GPNA) with a d-backbone configuration and alternate spacing binds sequence-specifically to RNA and is readily taken up by both human somatic and embryonic stem (ES) cells.     

紫外分光光度法测定中草药中铁的含量

对白芍、党参、白术、茵陈、天冬、枸杞子、当归、菟丝子、金银花、桔梗中微量元素铁的含量进行了测定,为进一步研究其药理作用提供基础。中草药消化后配制成溶液,用邻二氮菲作显色剂,使用UV-1200型紫外分光光度计在510 nm处测定各样品的吸光度(A),求出样品中微量元素铁的含量。结果显示,当归和金银花中铁的含量较丰富,分别为(135.367 8±0.111 1)μg/g和(125.936 4±0.159 9)μg/g;桔梗含铁量最少,为(3.510 9±0.159 9)μg/g,10种中草药中铁含量有显著性差异(P<0.05)。结果为使用中草药治疗系统疾病提供了可靠数据,10种中草药在用量范围内Fe含量适合人体每天正常摄入量。     

双亲半柔性两嵌段共聚物在溶液中自组装形态的模拟退火研究

针对一系列疏溶剂嵌段与溶剂间的相互作用,用模拟退火方法研究了双亲半柔性两嵌段共聚物在溶液中的自组装形态.模拟结果显示共聚物在溶液中均形成核-壳聚集体,其中疏溶剂嵌段形成聚集体的核,亲溶剂嵌段形成聚集体的壳.当上述相互作用较小时,核呈球形,而壳如同长在核上的刺.随着上述相互作用的增大,核逐渐增大.在较大的相互作用时,核呈柱形;而随着相互作用的加大,长在核上的刺逐渐伏贴于核表面.在更大的相互作用时,核又呈球状,壳伏贴于核表面.     

工业废水中微量铜（Ⅱ）和氰化物的流动注射光度分析

采用ＦＩＡ技术，以光度比色法为基础，建立了工业废水中微量Ｃｕ＾２＋和ＣＮ＾－的顺序自动分析方法和装置。其对二种离子的测定频率为６０样／ｈ，相对标准偏差＜１．０％，工作曲线的ｒ值≥０．９９９，各项分析技术指标均优于手工法操作。     

Fragmentation of wastewater sludge floc by planar ice front

Floc size has substantial impact on sludge dewaterability, which might be increased or reduced after freezing and thawing. It is commonly assumed that floc size would be increased by low-speed freezing, with a planar ice front rejecting most flocs ahead of it to form large aggregates. We demonstrate in this work that an advancing planar ice front can not only engulf an activated sludge floc of size 3030 mum, but also fragment it. During floc freezing, when the ice engulfed a thin layer of floc, the latter would be pulled apart vertically by the action of the former. This particular portion of floc was then axially elongated and fixed in the frozen layer, with accumulated force pushing upward. In the present test the floc's vertical length was increased by over 92% and its width decreased by 37% over freezing. The force measurement and floc morphology tracking revealed that the force gradient that pulled apart the floc was 0.0027 N/m. The floc under investigation was fragmented at the point where the normal stress acting on the interior network exceeded 8 Pa.     

用质谱技术对钾、钙同位素体系特征参数测定的初探

报道了用FinniganMAT 2 62质谱技术和同位素稀释法测定了光谱纯CaO和国际二级标准Tahiti(CaCO3)的同位素40 Ca 42 Ca比值以及后者的40 Ca含量 ,RSD分别为 0 .0 2 %和 0 .1 %。对国家钾标样的测定表明 :39K、40 K和41 K同位素丰度分别为 0 .93 2 60± 0 .0 0 1 2、0 0 0 0 1 1 2 0± 0 .0 0 0 0 1 2 9和 0 .0 672 86± 0 .0 0 0 1 2 5。其中39K含量为 0 .1 2 1 72± 0 .0 0 0 2 9,与标准值在误差范围内一致。实验测定结果为在我国开展40 K 40 Ca同位素体系的定年和环境的示踪研究打下了基础