Engineering a Chemical Switch into the Light‐driven Proton Pump Proteorhodopsin by Cysteine Mutagenesis and Thiol Modification

For applications in synthetic biology, for example, the bottom‐up assembly of biomolecular nanofactories, modules of specific and controllable functionalities are essential. Of fundamental importance in such systems are energizing modules, which are able to establish an electrochemical gradient across a vesicular membrane as an energy source for powering other modules. Light‐driven proton pumps like proteorhodopsin (PR) are excellent candidates for efficient energy conversion. We have extended the versatility of PR by implementing an on/off switch based on reversible chemical modification of a site‐specifically introduced cysteine residue. The position of this cysteine residue in PR was identified by structure‐based cysteine mutagenesis combined with a proton‐pumping assay using E. coli cells overexpressing PR and PR proteoliposomes. The identified PR mutant represents the first light‐driven proton pump that can be chemically switched on/off depending on the requirements of the molecular system.     

Accurate Extraction of Nanometer Distances in Multimers by Pulse EPR

Pulse electron paramagnetic resonance (EPR) is gaining increasing importance in structural biology. The PELDOR (pulsed electron–electron double resonance) method allows extracting distance information on the nanometer scale. Here, we demonstrate the efficient extraction of distances from multimeric systems such as membrane‐embedded ion channels where data analysis is commonly hindered by multi‐spin effects.     

膜富集-紫外光谱法快速检测自来水中痕量2-萘酚

基于紫外光谱结合膜富集技术,提出了一种快速、灵敏检测自来水中2-萘酚的方法。以尼龙滤膜(孔径0.22μm)为富集材料,将富集到膜上的2-萘酚不经洗脱直接测定其漫反射紫外光谱,以实现定量分析目的。该方法方便快捷,大大提高了灵敏度。对p H值、样品体积和真空度等条件进行优化,并对方法的分析性能进行了评价。结果显示,2-萘酚的浓度与吸光度(波长为331 nm)在0.3~10 mg/L范围内用二次函数可得到良好的拟合关系,在0.3~1.0 mg/L和1.0~10 mg/L范围内呈分段的线性关系,相关系数(r2)分别为0.999 1和0.995 5。在最佳条件下,检出限达0.265 6 mg/L。该方法准确度和精密度较理想,适用于对自来水中2-萘酚的检测。     

Effects of Inorganic Nano-Additives on Properties and Performance of Polymeric Membranes in Water Treatment

Separation using selective polymeric membranes has been well-established as an energy-efficient and cost-effective technology in water treatment and many other applications involving aqueous solutions. However, limited chemical, thermal, and mechanical resistances besides their tendency to fouling and inadequate pure water flux may often restrict their applications. To this end, inorganic materials as additives have been demonstrated to be able to enhance chemical, thermal, and fouling membrane resistances, which demonstrate their great potential for developing novel membranes by using them as additives in polymer matrices. Considering the excellent characteristics of the nanosized particles, this study reviews the effects of inorganic nano-additives on properties and performance of polymer/nanoparticle composite membranes. It has been demonstrated that using nanomaterials in a polymer matrix could enhance the mechanical strength and stiffness, wettability, selectivity, water permeability, and antifouling characteristics of the host polymer.     

Study on poly(imide-ethylene glycol) and graphene oxide-based hybrid proton exchange membrane

In this study, novel poly(imide-ethylene glycol) (PIEG) was prepared via polycondensation of ethylenediaminetetraacetic dianhydride, 4-aminophenyl sulfone, and poly(ethylene glycol) bis(amine). Later, thermally stable and mechanically robust undoped and acid-doped proton exchange membranes were prepared using the graphene oxide (GO) nanofiller. Field emission scanning electron microscope revealed a unique hexagonal imprinted morphology of the fractured surface. Increasing the GO content from 1 to 5 wt% increased tensile strength (59.7–65.9 MPa) and the modulus (20.3–23.9 GPa) of the undoped PIEG/GO series. Thermal properties of the undoped PIEG/GO 1–5 membranes were also higher, i.e., T₁₀ = 438–487°C. However, dop-PIEG/GO 1–5 membranes have a higher ion exchange capacity (IEC) of 2.4–2.9 mmol/g and proton conductivity 1.8–2.7 S cm^?1 (94% RH).     

Highly Conductive Anion‐Exchange Membranes from Microporous Tröger's Base Polymers

The development of polymeric anion‐exchange membranes (AEMs) combining high ion conductivity and long‐term stability is a major challenge for materials chemistry. AEMs with regularly distributed fixed cationic groups, based on the formation of microporous polymers containing the V‐shape rigid Tröger's base units, are reported for the first time. Despite their simple preparation, which involves only two synthetic steps using commercially available precursors, the polymers provide AEMs with exceptional hydroxide conductivity at relatively low ion‐exchange capacity, as well as a high swelling resistance and chemical stability. An unprecedented hydroxide conductivity of 164.4 mS cm^?1 is obtained at a relatively a low ion‐exchange capacity of 0.82 mmol g^?1 under optimal operating conditions. The exceptional anion conductivity appears related to the intrinsic microporosity of the charged polymer matrix, which facilitates rapid anion transport.     

1H‐Detected Solid‐State NMR Studies of Water‐Inaccessible Proteins In Vitro and In Situ

¹H detection can significantly improve solid‐state NMR spectral sensitivity and thereby allows studying more complex proteins. However, the common prerequisite for ¹H detection is the introduction of exchangeable protons in otherwise deuterated proteins, which has thus far significantly hampered studies of partly water‐inaccessible proteins, such as membrane proteins. Herein, we present an approach that enables high‐resolution ¹H‐detected solid‐state NMR (ssNMR) studies of water‐inaccessible proteins, and that even works in highly complex environments such as cellular surfaces. In particular, the method was applied to study the K⁺ channel KcsA in liposomes and in situ in native bacterial cell membranes. We used our data for a dynamic analysis, and we show that the selectivity filter, which is responsible for ion conduction and highly conserved in K⁺ channels, undergoes pronounced molecular motion. We expect this approach to open new avenues for biomolecular ssNMR.     

聚间苯二甲酰间苯二胺中空纤维膜研究

以聚间苯二甲酰间苯二胺(PMIA)为成膜聚合物,N,N-二甲基乙酰胺(DMAc)为溶剂,氯化钙(Ca Cl2)、氯化锂(Li Cl)和聚乙二醇(PEG)为添加剂,调制铸膜液,采用干—湿法纺丝技术制备了PMIA中空纤维膜.研究表明,PEG的加入可显著提高PMIA中空纤维膜的纯水通量,而随PEG添加量增加,膜的纯水通量呈现先增加后减小趋势;膜对牛血清蛋白(BSA)有较好的截留性能,截留率可达92%;膜具有良好的亲水性能,膜对纯水接触角可低至44°;膜的断裂强度达5.8 MPa,具有较好的力学性能,以及良好的耐热水和耐碱性能,可用于高温和碱性水处理等领域.     

PVDF微孔滤膜负载金纳米粒子用于牛奶中三聚氰胺的SERS快速检测

本文报道了一种利用聚偏二氟乙烯(Polyviny Lidene Fluoride,PVDF)微孔滤膜为载体的三聚氰胺(Melamine,MAM)的简便快速痕量分析技术。通过柠檬酸钠还原法制得平均粒径为30nm的纳米金溶胶,加入不同浓度的三聚氰胺后金纳米粒子快速聚集,这种纳米金聚集体可以通过简便快捷的过滤技术截留在PVDF微孔滤膜表面,进而用于SERS检测,在水溶液中最低检测浓度为0.05mg/L。我们进一步在牛奶样品中进行检测,在牛奶中检测限可以达到1mg/L,满足大部分国家规定的婴儿配方食品中三聚氰胺的限量值为1mg/kg的参考标准。该分析方法制备过程简单、成本低廉、总分析时间短,易于实现现场快速灵敏检测,应用前景广阔。