Modifying the 5′‐Cap for Click Reactions of Eukaryotic mRNA and To Tune Translation Efficiency in Living Cells

The 5′‐cap is a hallmark of eukaryotic mRNAs and plays fundamental roles in RNA metabolism, ranging from quality control to export and translation. Modifying the 5′‐cap may thus enable modulation of the underlying processes and investigation or tuning of several biological functions. A straightforward approach is presented for the efficient production of a range of N7‐modified caps based on the highly promiscuous methyltransferase Ecm1. We show that these, as well as N²‐modified 5′‐caps, can be used to tune translation of the respective mRNAs both in vitro and in cells. Appropriate modifications allow subsequent bioorthogonal chemistry, as demonstrated by intracellular live‐cell labeling of a target mRNA. The efficient and versatile N7 manipulation of the mRNA cap makes mRNAs amenable to both modulation of their biological function and intracellular labeling, and represents a valuable addition to the chemical biology toolbox.     

A Minimal,Unstrained S‐Allyl Handle for Pre‐Targeting Diels–Alder Bioorthogonal Labeling in Live Cells

The unstrained S‐allyl cysteine amino acid was site‐specifically installed on apoptosis protein biomarkers and was further used as a chemical handle and ligation partner for 1,2,4,5‐tetrazines by means of an inverse‐electron‐demand Diels–Alder reaction. We demonstrate the utility of this minimal handle for the efficient labeling of apoptotic cells using a fluorogenic tetrazine dye in a pre‐targeting approach. The small size, easy chemical installation, and selective reactivity of the S‐allyl handle towards tetrazines should be readily extendable to other proteins and biomolecules, which could facilitate their labeling within live cells.     

Synthesis,Dynamic Combinatorial Chemistry,and PCR Amplification of 3′–5′ and 3′–6′ Disulfide‐linked Oligonucleotides

Disulfide dithymidines linked 3′–5′ or 3′–6′ were synthesized and incorporated into oligonucleotides through a combined phosphotriester and phosphoramidite solid‐phase oligonucleotide synthesis approach. The disulfide links are cleaved and formed reversibly in the presence of thiols and oligonucleotides. This link was shown to be sequence‐adaptive in response to given templates in the presence of mercaptoethanol. The artificial 3′–5′ and 3′–6′ disulfide link was tolerated by polymerases in the polymerase chain reaction (PCR). By using sequencing analysis, we show that single mutations frequently occurred randomly in the amplification products of the PCR.     

Long‐Term Live‐Cell STED Nanoscopy of Primary and Cultured Cells with the Plasma Membrane HIDE Probe DiI‐SiR

Super‐resolution imaging of live cells over extended time periods with high temporal resolution requires high‐density labeling and extraordinary fluorophore photostability. Herein, we achieve this goal by combining the attributes of the high‐density plasma membrane probe DiI‐TCO and the photostable STED dye SiR‐Tz. These components undergo rapid tetrazine ligation within the plasma membrane to generate the HIDE probe DiI‐SiR. Using DiI‐SiR, we visualized filopodia dynamics in HeLa cells over 25 min at 0.5 s temporal resolution, and visualized dynamic contact‐mediated repulsion events in primary mouse hippocampal neurons over 9 min at 2 s temporal resolution. HIDE probes such as DiI‐SiR are non‐toxic and do not require transfection, and their apparent photostability significantly improves the ability to monitor dynamic processes in live cells at super‐resolution over biologically relevant timescales.     

Induction of a Four‐Way Junction Structure in the DNA Palindromic Hexanucleotide 5′‐d(CGTACG)‐3′ by a Mononuclear Platinum Complex

Four‐way junctions (4WJs) are supramolecular DNA assemblies comprising four interacting DNA strands that in biology are involved in DNA‐damage repair. In this study, a new mononuclear platinum(II) complex 1 was prepared that is capable of driving the crystallization of the DNA oligomer 5′‐d(CGTACG)‐3′ specifically into a 4WJ‐like motif. In the crystal structure of the 1 –CGTACG adduct, the distorted‐square‐planar platinum complex binds to the core of the 4WJ‐like motif through π–π stacking and hydrogen bonding, without forming any platinum–nitrogen coordination bonds. Our observations suggest that the specific molecular properties of the metal complex are crucially responsible for triggering the selective assembly of this peculiar DNA superstructure.     

Super‐Chelators for Advanced Protein Labeling in Living Cells

Live‐cell labeling, super‐resolution microscopy, single‐molecule applications, protein localization, or chemically induced assembly are emerging approaches, which require specific and very small interaction pairs. The minimal disturbance of protein function is essential to derive unbiased insights into cellular processes. Herein, we define a new class of hexavalent N‐nitrilotriacetic acid (hexaNTA) chelators, displaying the highest affinity and stability of all NTA‐based small interaction pairs described so far. Coupled to bright organic fluorophores with fine‐tuned photophysical properties, the super‐chelator probes were delivered into human cells by chemically gated nanopores. These super‐chelators permit kinetic profiling, multiplexed labeling of His₆‐ and His₁₂‐tagged proteins as well as single‐molecule‐based super‐resolution imaging.     

Graphene Functionalized Graphite Electrode with Diphenylacetylene for Sensitive Electrochemical Determination of Adenosine‐5′‐triphosphate

In this paper a molecular wire modified carbon paste electrode (MW‐CPE) was firstly prepared by mixing graphite powder with diphenylacetylene (DPA). Then a graphene (GR) and chitosan (CTS) composite film was further modified on the surface of MW‐CPE to receive the graphene functionalized electrode (CTS‐GR/MW‐CPE), which was used for the sensitive electrochemical detection of adenosine‐5′‐triphosphate (ATP). The CTS‐GR/MW‐CPE exhibited excellent electrochemical performance and the electrochemical behavior of ATP on the CTS‐GR/MW‐CPE was carefully studied by cyclic voltammetry with an irreversible oxidation peak appearing at 1.369 V (vs. SCE). The electrochemical parameters such as charge transfer coefficient (α) and electrode reaction standard rate constant (k_s) were calculated with the results of 0.53 and 5.28×10^?6 s^?1, respectively. By using differential pulse voltammetry (DPV) as detection technique, the oxidation peak current showed good linear relationship with ATP concentration in the range from 1.0 nM to 700.0 µM with a detection limit of 0.342 nM (3σ). The common coexisting substances, such as uric acid, ascorbic acid and guanosine‐5′‐triphosphate (GTP), showed no interferences and the modified electrode was successfully applied to injection sample detection.     

Electrochemically Active Cross‐Linking Reaction for Fluorescent Labeling of Aliphatic Alkenes

Although cross‐linking reactions serve as a valuable tool for the integration of two or more functionalities or properties, the application of electrochemical synthesis to cross‐linking reactions is restricted due to the difficulty of mass transfer. Thus, the primary purpose of this research is to explore electrochemical cross‐linking systems to construct a fluorescent probe, triggered by the formation of a covalent linkage. The second purpose is to apply the probe to insoluble targets. Towards these goals, a combination of electrochemically active phenol derivatives and aliphatic alkenes were employed to form polycyclic compounds. Several of the dihydrobenzofuran derivatives formed through [3+2] cyclization reactions exhibited fluorescence. Furthermore, this approach allowed the effective modification of alkene‐modified silica gel with electrochemically active species, which enables the construction of fluorescent probes that are triggered by C? C bond formation.     

Azido‐Substituted BODIPY Dyes for the Production of Fluorescent Carbon Nanotubes

A series of azido‐dyes were synthesized through Knoevenagel reactions of an azido‐BODIPY with aromatic aldehydes. The nature of the substituents allowed the fine tuning of their spectroscopic properties. The dyes were used to decorate oxidized multiwalled carbon nanotubes (ox‐MWCNTs), bearing terminal triple bond groups, by CuAAC reactions, affording fluorescent materials. This decoration allowed the efficient determination of the internalization of the ox‐MWCNT derivatives by different model cancer cells, such as MCF7.