Luminescent colloidal silicon suspensions from porous silicon

A procedure for generating colloidal suspensions of Si that exhibit luminescence, attributed to quantum confinement effects, is described. Samples of n- or p-type Si that have been electrochemically etched to form porous Si can be ultrasonically dispersed into methylene chloride, acetonitrile, methanol, toluene, or water solvents, forming a suspension of fine Si particles that luminesce. Transmission electron microscopy analyses show that the Si particles have irregular shapes, with diameters ranging from many micrometers to nanometers. Luminescent, composite polystyrene/Si films can be made by the addition of polystyrene to a toluene suspension of the Si nanoparticles and casting of the resulting solution onto a glass slide.     

Luminescent color image generation on porous silicon

Black and white images were projected onto n-type silicon (100) wafers during a photoelectrochemical etch to produce a color image that photoluminesces. The photoluminescence originates from a thin layer of luminescent porous silicon that is produced in the photoetch, and the colors that appear in the etched image arise from thin-film optical interference. A diffraction grating was also photoetched into the substrate, demonstrating simultaneous encoding of a gray-scale image into thin-film interference, luminescence, and diffraction phenomena.     

Chemiluminescence of anodized and etched silicon: evidence for a luminescent siloxene-like layer on porous silicon

Treatment of anodized or chemically etched silicon ("porous silicon") with dilute nitric acid or persulfate solution results in weak chemiluminescence in the visible region. Concentrated nitric acid reacts violently with porous Si produced by anodization with a bright flash of light. The fact that similar reactions occur with siloxene (Si(6)H(6)O(3)) prepared from CaSi(2) suggests that the visible emission seen with porous Si can be attributed to this substance.     

嗜热真菌耐热木聚糖酶的活性中心

应用NBS ,WRK ,DTNB ,PMSF ,Phenylgloxalhydrate,DEPC等化学修饰剂对嗜热真菌所产的耐热木聚糖酶进行了化学修饰。分别作用于色氨酸残基和谷氨酸 (或天冬氨酸 )残基的NBS和WRK可使耐热木聚糖酶活性显著降低 ,而其他几种修饰剂无明显作用。木聚糖对NBS的修饰有抑制作用 ,3 0mg·mL-1的桦木木聚糖底物可完全阻止NBS对耐热木聚糖酶的修饰作用 ,但木聚糖底物不能阻止WRK对耐热木聚糖酶的失活作用。实验结果表明 ,色氨酸残基和谷氨酸 (或天冬氨酸 )残基位于酶的活性中心 ,且色氨酸残基位于酶的底物结合中心 ,而谷氨酸(或天冬氨酸 )残基可能位于酶的催化中心。     

罗非鱼碱性磷酸酶的化学修饰

采用PMSF、PCMB、NBS、TNBS、SUAN、DTT、IAc、BrAc等化学修饰剂在一定的条件下选择性修饰罗非鱼ALP,研究罗非鱼ALP分子中氨基酸侧链基团与酶活性中心的关系.结果表明:PMSF、NBS等两种化学修饰剂能显著抑制酶的活力,而PCMB、TNBS、SUAN、DTT、IAc、BrAc等对酶的活力影响不大.说明对丝氨酸残基、色氨酸残基的化学修饰后对酶的活力影响很大,而酶分子中的其他功能基团不在酶的活性中心,修饰后对酶的活力影响不大.     

Chemical modification of carotid body chemoreception by sulfhydryls

Sulfhydryl reagents cause striking augmentation of the chemoreceptor responses of the carotid body to hypoxia. This indicates that a cellular plasma membrane protein with a reactive sulfhydryl group is a constituent part of the chemoreceptor architecture and provides a means of identification, localization, and isolation of the protein.     

Polymer replicas of photonic porous silicon for sensing and drug delivery applications

Elaborate one-dimensional photonic crystals are constructed from a variety of organic and biopolymers, which can be dissolved or melted, by templating the solution-cast or injection-molded materials in porous silicon or porous silicon dioxide multilayer (rugate dielectric mirror) structures. After the removal of the template by chemical dissolution, the polymer castings replicate the photonic features and the nanostructure of the master. We demonstrate that these castings can be used as vapor sensors, as deformable and tunable optical filters, and as self-reporting, bioresorbable materials.     

木质素三甲基季铵盐为模板剂制备多孔氧化硅材料

为了探索以小质素为模板剂制备无机多孔材料的方法,提高木质素产品附加值,以小质素三甲 铵盐为模板剂、正硅酸乙酯为硅源,采用溶胶凝胶法和焙烧脱模法制备多孔氧化硅材料。结果表明：小质素三甲基事铵盐行在于煅烧前的复合物中,煅烧后得到的多孔氧化硅材料中木质素三甲基季铵盐吸收峰消失,但具有SiO2特征吸收峰;多扎氧化硅材料孔隙发达...     

瘦肉型猪(PIC344)精液碱性磷酸酶功能基团的化学修饰

经正醇抽提、硫酸铵分级沉淀、DEAE-SepharoseFF和SephacrylS-200柱层系，从瘦肉型猪(PIC344)精液中提取出电泳纯碱性磷酸酶。用NBS，PMSF，TNBS，DTT及AcBr在一定条件下分别选择性的作用于PIC344AKP的Trp，Set，Lys，His及巯基，并对酶活力的变化和吸收光谱的变化作了测定，结果表明，NBS，TNBS，PMSF，DTT的修饰能显著的抑制AKP的活力，活力的降低与修饰剂的浓度呈正相关；AcBr的修饰对AKP的活力没有明显的影响。作者认为Trp，Ser，Lys及巯基可能是AKP活力的必须基团。     

耐热Taq DNA聚合酶的酸酐修饰及其在降低PCR非特异性扩增中的应用评价

酸酐能与聚合酶上的赖氨酸结合形成聚合物,试验通过选用合适的酸酐,修饰Taq DNA聚合酶。在常温下,酶活性被封闭,升温过程中不表现酶活,从而减少非特异性扩增和引物二聚体的形成;而在较高的温度下一段时间后,一般为94℃、15 min,酸酐脱落,聚合酶得以恢复正常的扩增活性,从而实现PCR反应的热启动。由此建立的热启动PCR体系灵敏度高,可以检测到10个拷贝的DNA分子,较普通PCR体系提高了2个数量级。此方法较其他方法操作简单成本低廉,且所得的热启动Taq DNA聚合酶稳定性好,便于保存,其灵敏性与特异性也更高。这种通过化学修饰形成的复合物达到热启动PCR目的的方法的建立,具有着重要的意义,是提高PCR灵敏度和特异性的重要方法之一。     

Reversible chemical modification of the scrapie agent

The scrapie agent causes a degenerative nervous system disease in sheep and goats. Studies with extensively purified preparations demonstrated that the agent contains a protein that is required for infectivity. Chemical modification of the scrapie agent by diethyl pyrocarbonate reduced the titer 1000-fold. Exposure of the inactivated agent to hydroxylamine, a strong nucleophile, resulted in complete restoration of infectivity. Presumably, nucleophilic residues within a scrapie agent protein undergo carbethoxylation on reaction with diethyl pyrocarbonate, and subsequent addition of hydroxylamine displaces these carbethoxy groups.     

不同生育期施用硅肥对水稻吸收积累镉硅的影响

为探明硅肥对镉污染稻田降低稻米镉的作用机理,完善稻米镉消减的硅肥施用技术,采用田间试验,研究水稻不同生育期(基肥、分蘖期和孕穗期)施用硅肥对水稻吸收积累镉、硅的影响。结果表明:施用硅肥能够提高土壤0.160~0.290个pH单位,降低镉生物有效性,同时,显著增加土壤有效硅含量,增幅为295.3%~399.2%(P0.05);不同生育期施用硅肥中,基施硅肥能够显著增加9.7%的水稻产量,高于其他处理,基施硅肥显著降低了水稻茎秆、叶片、稻壳和稻米中的镉含量,降幅分别为31.9%(P0.05)、65.8%(P0.05)、46.1%(P0.05)和25.3%(P0.05),施硅降低了镉由茎秆向叶片和稻壳的转运,从而降低了稻米镉的积累,同时显著增加茎秆、叶片和稻壳硅含量,增加幅度分别为44.1%(P0.05)、71.5%(P0.05)和28.8%(P0.05)。综上表明,镉污染稻田基施硅肥能够显著增加水稻产量,降低土壤镉生物有效性,阻止镉的迁移转运,减少稻米镉积累,是镉污染稻田修复中推荐的硅肥施用技术。     

Ultralong-range polaron-induced quenching of excitons in isolated conjugated polymers

In conjugated polymers, radiative recombination of excitons (electron-hole pairs) competes with nonradiative thermal relaxation pathways. We visualized exciton quenching induced by hole polarons in single-polymer chains in a device geometry. The distance-scale for quenching was measured by means of a new subdiffraction, single-molecule technique--bias-modulated intensity centroid spectroscopy--which allowed the extraction of a mean centroid shift of 14 nanometers for highly ordered, single-polymer nanodomains. This shift requires energy transfer over distances an order of magnitude greater than previously reported for bulk conjugated polymers and far greater than predicted by the standard mechanism for exciton quenching, the unbiased diffusion of free excitons to quenching sites. Instead, multistep "energy funneling" to trapped, localized polarons is the probable mechanism for polaron-induced exciton quenching.     

Demineralization of porous solids

When a porous ionic solid is placed in acid, the acid will dissolve surface material. When this dissolved material and the acid diffuse into the solid's pores, they can precipitate more solid. If the acid is buffered, the diffusing species can bring about precipitation in some regions and dissolution in others. When the porous solid contains several chemical species, the diffusion can precipitate one species and dissolve another. The results have implications for the demineralization of teeth.     

对化学反应速度和化学平衡实验改进的研究

1　目的多年的实验证明 ,教育改革的一个重要方面在于引进新的教育技术 ,而技术引进后的一个重要方面在于更新方法。化学是一门以实验为基础的科学。离开了实验就谈不上化学的存在和发展。而鲜明的实验现象不仅能给学生以深刻的直观表象 ,还能大大提高学生的学习兴趣 ,激发学生思考问题的积极性和主动性 ,也是学生由形象思维升华到抽象思维的基础。许多科学家正是由于这种奇异的化学现象而被引入科学的殿堂。为了实验准确无误 ,方便学生用量少、节省时间、误差小 ,能很时显地看出实验的结果 ,通过改进后 ,实验效果很好 ,得到教师和同学们的…     

Chemical anatomy of the brain

The development of sensitive histochemical-neuroanatomical techniques has made it possible to analyze the content of specific compounds in single nerve cells and their processes. In consequence, it has been possible to construct detailed maps of the distribution of various types of neurons on the basis of their transmitter substance. There are now many examples of neurons containing both a classical transmitter and a peptide. In some instances the peptides seem to support the action of the classical transmitters. This interaction may have applications in the prevention and treatment of nervous disease states.     

细菌群体通讯信号及其淬灭研究进展

群体感应(Quorum sensing, QS)是细菌通过信号分子的分泌、识别,从而调控细胞运动性、生物膜形成、毒素产生等致病行为的细胞交流机制,是病原菌致病过程的指挥系统,也是细菌病害防控的新靶标.群体感应淬灭(Quorum quenching, QQ)则是通过信号分子类似物、信号分子降解酶剂、信号受体激活剂/抑制剂等策略干扰、阻断病原菌的群体感应通讯系统.文章综述了3类重要的细菌群体通讯信号及其淬灭研究的进展,并对研究进行了总结与展望.     

蛋白环形序列重组技术在脂肪酶分子改造中的应用

脂肪酶的底物特异性与酶的催化效率是限制其规模化应用的瓶颈,传统的分子改造技术在对脂肪酶的空间结构改变及大分子底物的催化效率提升方面效果并不明显。在介绍现有的脂肪酶改造技术的基础上,重点介绍了新型蛋白分子改造手段-蛋白环形序列重组(CP)技术的原理及在脂肪酶基因工程改造方面的应用。     

螟纹杀克防治水稻三化螟药效试验

螟纹杀克对 2代三化螟防治效果良好。用量 1 0 50～1 350g/hm2 ,杀虫效果药后 7天在 95.3%以上 ;药后 2 0天的保苗效果在90 .5%～94.9%。