不同结构的DNA激活序列对Cas12a反式切割活性的影响

CRISPR－Cas12a系统的反式切割活性在其识别特定的DNA激活序列后被激活,这不仅能实现特定DNA靶标的直接定量分析,同时也为构建针对多种生物标志物的体外传感体系带来了新的思路。然而,已有文献中所采用的双链DNA（dsDNA）和单链DNA（ssDNA）激活序列结构多种多样,缺乏全面、系统的设计指导原则。针对该问题,该文系统研究了不同结构的DNA激活序列对LbaCas12a反式切割活性的影响。通过对比研究,得出以下结论：（1）前间区序列邻近基序（PAM）位点有助于LbaCas12a更高效地靶向结合dsDNA激活序列和ssDNA激活序列;（2）PAM近端区域缺少序列片段会降低Cas12a-crRNA定位激活序列的效率;（3）删除PAM远端序列片段有利于增强LbaCas12a的反式切割活性;（4）由于省略了dsDNA解链过程,ssDNA激活序列在激活LbaCas12a的反式切割活性方面普遍比dsDNA激活序列产生的效果更好。根据这些发现,该文提出了一种LbaCas12a所青睐的高效激活序列结构,其激活的LbaCas2a反式酶切活性较采用含PAM位点的标准dsDNA激活序列高出3.7倍。研究结果为构建基于CRISPR-Cas12a的高效体外生物传感系统提供了重要支撑。     

超高效液相色谱-四极杆静电场轨道阱高分辨质谱测定聚丙烯酰胺中丙烯酰胺单体的残留

通过Hypercarb色谱柱分离,建立了四极杆静电场轨道阱高分辨质谱平行反应监测(PRM)模式检测聚丙烯酰胺(PAM)中单体残留量的方法。PAM经水稀释,高速搅拌溶解均匀,过0.22μm水相滤膜后,直接用高分辨质谱Q Exactive采集数据。以Hypercarb色谱柱为分析柱,水和甲醇为流动相,柱温为20℃,采用PRM模式,提取目标化合物及其二级子离子的精确质量数,并对二级特征碎片进行同位素匹配,推测碎裂规律,以强化定性效果。结果表明:在2~50μg/L范围内线性关系良好(相关系数为0.999 8),方法检出限(LOD)可达到1.5μg/kg,满足食品级PAM的检测要求。通过加标验证,回收率为101.3%~107.1%,相对标准偏差为3.1%~4.1%。实际样品验证结果表明,PAM中丙烯酰胺(AM)单体的残留质量分数范围为0~0.43%,存在一定的安全风险。该方法简单、准确、高效,可作为快检和确证检测技术广泛使用。     

聚丙烯酰胺与混合表面活性剂的相互作用

通过粘度和紫外吸收光谱的测定，研究了ＰＡＭ与Ｒ１２ＳＯ３Ｎａ－Ｒ１１ＣＯＯＮａ混合表面活性剂之间的相互作用，结果表明，ＰＡＭ可与混合表面活性剂形成复合物，从而使体系表现出典型聚电解质的粘度行为。可能的机理是，以疏水力形成的Ｒ１２ＳＯ３＾－—Ｒ１１ＣＯＯＨ（Ｎａ）预胶束或二聚体通过ＰＡＭ－Ｒ１１ＣＯＯＨ间的氢键力相结合。进而使大分子链上带有大量负电荷，静电斥力引起大分子链伸展，因而产生电粘效应。     

纳米硫化锌的生物还原-化学沉淀耦合制备及其性能表征

生物还原-化学沉淀耦合反应法制备了纳米硫化锌,采用XRD、SEM、TEM、EDS、PL、FTIR等测试手段对产物进行了结构形貌性能表征。结果表明,在加入与Zn²⁺等物质的量浓度的EDTA后,Zn²⁺对硫酸盐还原菌(SRB)的毒性消除,SRB的较快生长和SO₄^2-的高效还原得以实现,EDTA修饰的生物转化-化学沉淀耦合系统可制备出高纯的纳米硫化锌晶体。制备的纳米ZnS实心微球体形状规则、分散均匀、大小一致,一次粒子直径10～15 nm,二次粒子直径400 nm左右。光致荧光光谱和红外光谱分析显示,ZnS纳米粒子在396 nm处出现荧光发射峰,在465 nm处出现缺陷发光峰,而且具有良好的红外透过性。分散剂聚丙烯酰胺(polyacrylamide)的加入导致产物ZnS的形貌和粒度改变,二次粒子的平均直径减至100 nm以下,其荧光发射峰强度增强,红外透过性提高。     

辐射合成聚丙烯酰胺、聚丙烯酸钠及其共聚物水凝胶微观结构的扫描电镜研究

用６０Ｃｏ－γ射线辐射合成了低交联度的聚丙烯酰胺、聚丙烯酸钠及丙烯酰胺－丙烯酸钠共聚物水凝胶，用扫描电子显微镜研究了水凝胶经过丙酮脱水的干态试样的微观结构特征。发现聚合物中丙烯酰胺与丙烯酸钠单体单元的比例对其微观结构影响很大，并且从聚合物链段之间存在氢键和静电排斥这两种对立作用力相对强度的角度，定性地阐述了各水凝胶微观结构之间的差异。     

Phonon frequency shift and effect of correlation on the electron-phonon interaction in heavy fermion systems

The electron-phonon interaction in the periodic Anderson model (PAM) is considered. The PAM incorporates the effect of onsite Coulomb interaction (U) between f-electrons. The influence of Coulomb correlation U on the phonon response of the system is studied by evaluating the phonon spectral function for various parameters of the model. The numerical evaluation of the spectral function is carried out in the long wavelength limit at finite temperatures keeping only linear terms in U. The observed behaviour is found to agree well with the general features obtained experimentally for some heavy fermion (HF) systems.     

Calorimetric Determination of Phosphorylated Serum Cholinesterase and Its Reactivation by an Antidote

Abstract

Serum cholinesterase, inhibited in vitro up to 92% by 0, 0 dimethyl-2, 2-dichlorovinyl phosphate (4.52 × 10^?9 mole/ml of 40% serum), was reactivated up to 35% with 2-pyridine aldoxime methiodide (3.5 × 10^?6 mole/ml of 40% serum). Evaluation was based on the reaction rate between cholinesterase and acetylcholine chloride (2.2 × 10^?6 mole) measured with a microcalorimeter. It was thus possible to approximate the “normal” or pre-exposure level of serum cholinesterase, while simultaneously determining the extent of poisoning.     

Estimating whale density from their whistling activity: Example with St. Lawrence beluga

A passive acoustic method is developed to estimate whale density from their calling activity in a monitored area. The algorithm is applied to a loquacious species, the white whale (Delphinapterus leucas), in Saguenay fjord mouth near Tadoussac, Canada, which is severely affected by shipping noise. Beluga calls were recorded from cabled coastal hydrophones deployed in the basin while the animal density was estimated visually from systematic observations from a fixed-point on the shore. Beluga calling activity was estimated from an algorithm extracting the call events in time-frequency space, while simultaneously tracking the masking intensity resulting from local shipping noise. The activity index was summarized in 15- and 30-min bins using four different metrics. For bins containing more than 40% of valid data, the metrics were compared to the corresponding visual observations. The estimated mean acoustic detection range generally exceeded the fjord width, and extended to the whole ∼3-km long monitored area under low-noise conditions. The significant linear relations of the visual estimates with the calling activity metrics allowed assessing expected number of visually detected belugas in the basin from a weighted regression model, with a mean standard error of 7.1%.     

梯度引发自由基聚合体系(Ⅰ)——基原法合成超高分子量聚合物

90年代在自由基聚合基础研究领域的一个重要成是“长 短终止”理论被进一步确认和接受[1 ,2 ] .按照该模型 ,聚合反应中的终止反应主要发生在长链自由基与短链自由基或初级自由基之间 ,即长链自由基之间很难进行终止反应 ,链终止常数随链长增加而急剧下降 .80年代初 ,Ｓｉｍｉｏｎｅｓｃｕ等[3] 曾报道了用等离子体照射封有单体的玻璃管 ,尔后放入暗处聚合的工作 ,发现不仅可得到分子量上千万的聚丙烯酸或聚丙烯酰胺 ,而且聚合活性可保持几十个小时 ;国内学者[4] 利用该法也得到了分子量接近千万的聚丙烯酰胺 .基于这种终止模型和实验结果 ,…     

Synergic effect of hydride and proton donors in the Pd(0)-mediated deprotection of N-Aloc proline derivatives

In this study, the challenging Pd(0)-catalyzed N^α-Aloc removal from a proline residue using Me₂NH·BH₃ or PhSiH₃ as allyl scavengers has been investigated. Standard conditions led to a large amount of an allylamine byproduct. A careful study of the reactions allowed us to design the optimal conditions for the quick and quantitative formation of the desired product, while taking advantage of a synergic effect between hydride and proton donors.