A proton shelter inspired by the sugar coating of acidophilic archaea

<div id="first-paragraph" class="first-paragraph"><p>The acidophilic archaeons are a group of single-celled microorganisms that flourish in hot acid springs (usually pH &lt; 3) but maintain their internal pH near neutral. Although there is a lack of direct evidence, the abundance of sugar modifications on the cell surface has been suggested to provide the acidophiles with protection against proton invasion. In this study, a hydroxyl (OH)-rich polymer brush layer was prepared to mimic the OH-rich sugar coating. Using a novel pH-sensitive dithioacetal molecule as a probe, we studied the proton-resisting property and found that a 10-nm-thick polymer layer was able to raise the pH from 1.0 to &gt; 5.0, indicating that the densely packed OH-rich layer is a proton shelter. As strong evidence for the role of sugar coatings as proton barriers, this biomimetic study provides insight into evolutionary biology, and the results also could be expanded for the development of biocompatible anti-acid materials.</p></div

A quartz crystal microbalance-based molecular ruler for biopolymers

We developed a quartz crystal microbalance (QCM) based molecular ruler that measures the length of surface immobilized, hydrated biopolymers (DNA and proteins). These biopolymers acted as stakes that solidified surrounding liquid at high frequency vibration in QCM measurements, which led to a simple linear frequency-thickness relation

Swelling induced Au-S bond breakage is determined by the molecular composition of surface tethered copolymers-carboxylated poly(OEGMA-r-HEMA)

We developed a novel method to determine the molecular composition of surface tethered carboxylated poly(OEGMA-r-HEMA), which in turn determines the swelling induced Au-S bond breakage (CBB) event. More accurate control over CBB will eventually lead to many applications in mechanochemistry and controlled release

Predicting Au-S bond breakage from the swelling behavior of surface tethered polyelectrolytes

Surface tethered weak polyelectrolyte, carboxylated poly(OEGMA-r-HEMA), was prepared via surface initiated polymerization (SIP) from metal (Au, Pt and Ag) surfaces functionalized with initiators through metal-S bonds. The swelling behavior of carboxylated poly(OEGMA-r-HEMA) in phosphate buffered saline (PBS) was studied by quartz crystal microbalance (QCM) and was found to obey the following equation: T(eff) = (0.32ln([Na(+)]) + 2.53) x T(COOH,dry), where T(eff) and T(COOH, dry) are the thicknesses of carboxylated poly(OEGMA-r-HEMA) in PBS measured by QCM and in air measured by ellipsometry, respectively. We also confirmed that the event of covalent bond breaking (CBB) of Au-S bonds occurred at a certain critical T(eff), i.e. similar to 255 nm. Thus, one could predict the CBB of Au-S or other metal-S bonds from the swelling behavior of surface tethered carboxylated poly (OEGMA-r-HEMA)

Molecular Composition, Grafting Density and Film Area Affect the Swelling-Induced Au-S Bond Breakage

In previous studies, we reported the first observation of the Au-S bond breakage induced mechanically by the swelling of the saline (PBS), a phenomenon with broad applications in the fields of surface-tethered weak polyelectrolyte brushes in phosphate buffered biosensors and functional surfaces. In this study, three factors, namely the molecular composition, grafting density and film area of the weak polyelectrolyte, carboxylated poly(oligo(ethylene glycol) methacrylate-random-2-hydroxyethyl methacrylate) (poly(OEGMA-r-HEMA)), were studied systematically on how they affected the swelling-induced Au-S bond breakage (ABB). The results showed that, first, the swelling-induced ABB is applicable to a range of molecular compositions and grafting densities; but the critical thickness (T-critical,T-dry) varied with both of the two factors. An analysis on the swelling ratio further revealed that the difference in the T-critical,T-dry arose from the difference in the swelling ability. A film needed to swell to similar to 250 nm to induce ABB regardless of its composition or structure, thus a higher swelling ratio would lead to a lower T-critical,T-dry value. Then, the impact of the film area was studied in micrometer- and sub-micrometer-scale brush patterns, which showed that only partial, rather than complete ABB was induced in these microscopic films, resulting in buckling instead of film detaching. These results demonstrated that the ABB is suitable to be used in the design of biosensors, stimulus-responsive materials and mechanochemical devices. Although the &gt;160 mu m(2) required area for uniform ABB hinders the application of ABB in nanolithography, the irreversible buckling provides a facile method of generating rough surfaces

Surface Confined Retro Diels–Alder Reaction Driven by the Swelling of Weak Polyelectrolytes

Recently, the type of reactions driven by mechanical force has increased significantly; however, the number of methods for activating those mechanochemical reactions stays relatively limited. Furthermore, in situ characterization of a reaction is usually hampered by the inherent properties of conventional methods. In this study, we report a new platform that utilizes mechanical force generated by the swelling of surface tethered weak polyelectrolytes. An initiator with Diels–Alder (DA) adduct structure was applied to prepare the polyelectrolyte-carboxylated poly­(OEGMA-r-HEMA), so that the force could trigger the retro DA reaction. The reaction was monitored in real time by quartz crystal microbalance and confirmed with atomic force microscopy and X-ray photoelectron spectroscopy. Compared with the conventional heating method, the swelling-induced retro DA reaction proceeded rapidly with high conversion ratio and selectivity. A 23.61 kcal/mol theoretical energy barrier supported the practicability of this retro DA reaction being triggered mechanically at ambient temperature. During swelling, the tensile force was controllable and persistent. This unique feature imparts this mechanochemical platform the potential to “freeze” an intermediate state of a reaction for in situ spectroscopic observations, such as surface-enhanced Raman spectroscopy and frequency generation spectroscopy

黄花苜蓿地下芽库构成及其数量特征研究/Studies on Structures and Quantitative Properties of Underground Bud Banks of Wild Medicago falcata L.[J]

对来自我国新疆、内蒙古和俄罗斯的34份野生黄花苜蓿地下营养繁殖芽的类型、芽库数量特征及芽库组成结构进行了定株观测和分析.结果表明:黄花苜蓿营养繁殖芽在秋季生长旺盛并且已经形成了许多长度不等的短地下茎；二年生黄花苜蓿平均可产生45.13～48.55个芽/株,地下芽库由55.10％～62.86％的地下茎枝芽、36.78％～40.58％的根颈芽和0.26％～4.33％的根蘖芽组成.不同地理种群间芽库的数量没有显著差异,但种群内个体间芽库的数量存在较大差异