Dynamic Properties of Molecular Tweezers with a Bis(2‐hydroxyphenyl)pyrimidine Backbone

4,6‐Bis(2‐hydroxyphenyl)‐2‐alkylpyrimidines with two anthryl or 9‐ethylnylanthryl substituents at the positions para to the OH groups prefer a U‐shaped conformation supported by two intramolecular OH ??? N hydrogen bonds in the solid state and in CDCl₃ solution. The compound with a hexyl substituent on the pyrimidine group and two 9‐ethynylanthryl arms at the hydroxyphenyl groups forms a 1:1 complex with 2,4,7‐trinitrofluorenone. Its association constant K_a was estimated to be 2100 M ^?1 at 298 K, which is larger than those of other molecular tweezers (K_a<1000 M ^?1). DFT calculations suggested that the complex adopts a stable conformation supported by intramolecular hydrogen bonds among the OH groups and the pyrimidine ring as well as by intermolecular π–π interaction between the anthryl groups and 2,4,7‐trinitrofluorenone. Addition of nBu₄NF to a solution of the molecular tweezers or their complexes causes the cleavage of one or two OH ??? N hydrogen bonds, formation of new O ??? HF hydrogen bonds, and changes in the molecular conformation. The resulting structure of the molecular tweezers contains nonparallel anthryl groups, which do not bind the guest molecule. Photochemical measurements on 4,6‐bis(2‐hydroxyphenyl)‐2‐methylpyrimidine with two anthryl substituents showed negligible luminescence (quantum yield ?<0.01), owing to photoinduced electron transfer of the molecule with a U‐shaped structure. However, the O‐hexylated compound exhibits emission from the anthryl groups with ?=0.39.     

Self‐Assembly of Bis(merocyanine) Tweezers into Discrete Bimolecular π‐Stacks

Dipolar aggregation : Examples of a novel class of tweezer molecules have been constructed through the tethering of two dipolar merocyanine chromophores. The electrostatic‐interaction‐directed self‐assembly of these tweezers affords centrosymmetric bimolecular complexes with a unique aggregate geometry of four π‐stacked chromophores (see picture) with an alternating arrangement of their dipole moments and very high dimerization constants, even in the good solvating solvent chloroform.

     

Adaptation and Optical Signal Generation in a Constitutional Dynamic Network

Self‐sorting dynamic library : The effector‐induced modulation of the shape and constitution of the members of a constitutional dynamic network (see scheme) allows for the regulation of the interconnected constituents and for the control of an emergent function, here the generation of an optical output which originates from a charge‐transfer interaction.

     

拉曼镊子在生物单细胞中的应用与进展

拉曼镊子(Raman tweezers)是将激光光镊(Optical tweezers)与显微拉曼光谱(Raman spectroscopy)结合的光学技术,可以在接近自然状态下研究单个生物细胞或细胞器.因其有无直接接触、无损伤、快速识别、实时追踪等特点,广泛用于生物细胞的识别、探测、筛选等.研究显示,拉曼镊子在微观生物研究的应用中,可提高拉曼光谱的信噪比,也能实现生化动力学过程的实时跟踪,从而能深刻了解细胞内生物大分子的活动规律.本文着重介绍了拉曼镊子的起源、原理及其在单细胞中的应用以及展望.     

Joule heating monitoring in a microfluidic channel by observing the Brownian motion of an optically trapped microsphere

Electric fields offer a variety of functionalities to Lab‐on‐a‐Chip devices. The use of these fields often results in significant Joule heating, affecting the overall performance of the system. Precise knowledge of the temperature profile inside a microfluidic device is necessary to evaluate the implications of heat dissipation. This article demonstrates how an optically trapped microsphere can be used as a temperature probe to monitor Joule heating in these devices. The Brownian motion of the bead at room temperature is compared with the motion when power is dissipated in the system. This gives an estimate of the temperature increase at a specific location in a microfluidic channel. We demonstrate this method with solutions of different ionic strengths, and establish a precision of 0.9 K and an accuracy of 15%. Furthermore, it is demonstrated that transient heating processes can be monitored with this technique, albeit with a limited time resolution.     

Non‐B DNA Structures Show Diverse Conformations and Complex Transition Kinetics Comparable to RNA or Proteins—A Perspective from Mechanical Unfolding and Refolding Experiments

With the firm demonstration of the in vivo presence and biological functions of many non‐B DNA structures, it is of great significance to understand their physiological roles from the perspective of structural conformation, stability, and transition kinetics. Although relatively simple in primary sequences compared to proteins, non‐B DNA species show rather versatile conformations and dynamic transitions. As the most‐studied non‐B DNA species, the G‐quadruplex displays a myriad of conformations that can interconvert between each other in different solutions. These features impose challenges for ensemble‐average techniques, such as X‐ray crystallography, NMR spectroscopy, and circular dichroism (CD), but leave room for single‐molecular approaches to illustrate the structure, stability, and transition kinetics of individual non‐B DNA species in a solution mixture. Deconvolution of the mixture can be further facilitated by statistical data treatment, such as iPoDNano (i ntegrated po pulation d econvolution with nano meter resolution), which resolves populations with subnanometer size differences. This Personal Account summarizes current mechanical unfolding and refolding methods to interrogate single non‐B DNA species, with an emphasis on DNA G‐quadruplexes and i‐motifs. These single‐molecule studies start to demonstrate that structures and transitions in non‐B DNA species can approach the complexity of those in RNA or proteins, which provides solid justification for the biological functions carried out by non‐B DNA species.     

Crystal structure of 25,27-bis[(2-cyanophenyl)methoxy] calix[4]arene

The crystal structure of 25,27-bis[(2-cyanophenyl)methoxy] calix[4]arene (C₄₄H₃₄N₂O₄) was determined by X-ray crystallographic analysis. It possesses space group R , with a = b = 35.993(8) Å, c = 13.842(3) Å, = = 90°, = 120°, and D _calc = 1.260 mg/cm³ for Z = 18. Crystal data indicate that Compound 1 exists in a pinched-cone conformation with intramolecular hydrogen bonds.     

碳酸钙微粒光致旋转的实验和理论研究

理论分析了由于光束轨道角动量和自旋角动量传递以及微粒的特殊形状导致微粒旋转的机理.实验建立了单光束激光光镊装置,不仅可以捕获并移动直径为微米量级的微小粒子,而且利用圆偏振光与微粒之间角动量的传递,实现了对具有双折射特性的碳酸钙微粒的光致旋转.实验中发现微粒的旋转不仅取决于光束的偏振态,还与微粒本身的形状有关,解释了实验中观察到的几种旋转现象.碳酸钙微粒旋转的最高转速达到12转/秒,转速与激光功率成正比.     

A Conformationally Flexible Dinuclear PtII Complex with Differential Behavior of its Two States toward Quadruplex DNA

The reaction of tetrakis(pyridine‐2‐yl)pyrazine (tppz) with 2 equiv of (2,2′‐bpy)Pt^II in water yields two isomeric dinuclear cations, [{Pt(2,2′‐bpy)}₂(tppz)]⁴⁺, in which Pt coordination exclusively takes place through the two pairs of pyridine‐2‐yl nitrogen atoms. The two conformational isomers differ in their overall shape, with the formation of “Z” and “U” shapes, which are formed at 40 °C (Z isomer, 1 ) and under reflux conditions (U isomer, 2 ), respectively. X‐ray crystal‐structure analyses of the Z isomer, [{Pt(2,2′‐bpy)}₂(tppz)](PF₆)₄ ? 3 CHCl₃ ? 4 H₂O ( 1 a ), and of the U isomer, [{Pt(2,2′‐bpy)}₂](PF₆)₄ ? 2 CH₃CN ? 1.5 H₂O ( 2 a ), were carried out. Co‐crystallization of compound 2 with PtCl₂(2,2′‐bpy) yielded [{Pt(2,2′‐bpy)}₂(tppz)](BF₄)₄?[PtCl₂(2,2′‐bpy)] ? 4.5 H₂O ( 3 ), in which the PtCl₂(2,2′‐bpy) entity was sandwiched between the two 2,2′‐bpy faces of the U‐shaped cation ( 2 ). Quantum chemical calculations revealed that the U isomer was more stable than the Z isomer, both in the gas phase and in an aqueous environment. These two isomers display different affinities toward duplex DNA and human telomeric quadruplex DNA (Htelo), as concluded from CD spectroscopy and FID assays. Thus, the U isomer binds significantly more strongly to quadruplex DNA (DC₅₀=0.38 μM ) than the Z isomer (DC₅₀=8.50 μM ).