Science Journals RSS Feeds
Sponsored Links
Recent Comments

    General Chemistry

    Camptothecin‐Grafted DNA Tetrahedron as Precise Nanomedicine to Inhibit the Tumor Growth

    Most chemotherapeutics are hydrophobic molecules and need to be converted into hydrophilic form before administration. Based on the excellent hydrophilicity and programmability of DNA, herein, we report a general strategy to construct a precise drug‐containing DNA framework for cancer treatment. In this novel drug delivery system, carbonethyl bromide‐modified camptothecin (CPT) is employed to directly react with phosphorothioate (PS) modified DNAs, resulting in the formation of chemotherapeutics‐grafted DNAs with a responsive disulfide linkage. By tuning the number and site of PS modifications on DNA strands, hydrophilicity of the obtained DNA‐drug conjugates (DDCs) can be regulated to retain their aqueous solubility and capability of molecular recognition. Subsequently, programmable DNA nanotechnology enables the self‐assembly of a precise drug‐containing tetrahedral framework with stimuli‐responsive feature and enhanced antitumor efficacy both in vitro and in vivo.

    …read more

    Source:: Angewandte Chemie Int. edition

          

    Basic [Au₂₅(SCH₂CH₂Py)₁₈]−·Na+ Clusters: Synthesis, Layered Crystallographic Arrangement, and Unique Surface Protonation

    We report the first synthesis of high‐purity and high‐yield Au₂₅ clusters protected by the basic pyridyl ethanethiol (HSCH2CH2Py, 4‐PyET and 2‐PyET). Single‐crystal X‐ray diffraction of the [Au₂₅(4‐PyET)₁₈]−·Na+ clusters has revealed a structure similar to that known for the phenyl ethanethiolate analog, but with pyridyl‐N coordination to Na+, a more relaxed ligand shell, and a profoundly layered arrangement in the solid state. Because of the pendant Py moiety, the [Au₂₅(4‐PyET)₁₈]− clusters are endowed with a unique (de)protonation equilibria, which has been characterized in detail by UV‐vis absorption and 1H‐NMR spectroscopy. [Au₂₅(4‐PyET)₁₈]− clusters showed an unexpectedly H+‐dependent solubility that is tunable in aqueous and organic solvents. The successful synthesis of the basic Py‐terminated thiolate‐protected Au₂₅ clusters paves the way to realize a new family of metalloid clusters possessing basic properties.

    …read more

    Source:: Angewandte Chemie Int. edition

          

    What Is XNA?

    X files: The term “xeno‐nucleic acids” (XNA) has grown in popularity to the point that it has become a catch‐all phrase for almost any unnatural nucleic acid, raising the question: what is XNA and how does it differ from chemically modified DNA?

    Abstract

    The term “xeno‐nucleic acids”, abbreviated XNA, has grown in popularity to the point that it has become a catch‐all phrase for almost any unnatural nucleic acid, raising the question: what is XNA and how does it differ from chemically modified DNA?

    …read more

    Source:: Angewandte Chemie Int. edition

          

    Late stage 18F‐difluoromethyl labeling of N‐heteroaromatics with high molar activity for PET imaging

    In spite of a growing interest in CHF2 in medicinal chemistry, there is a lack of efficient methods for the insertion of CHF18F on drug‐like compounds. We herein describe a photoredox flow reaction for 18F‐difluoromethylation of N‐heteroaromatics widely used in medicinal chemistry. Following the two‐step synthesis of a new 18F‐difluoromethylation reagent, the photoredox reaction is completed within 2 minutes and proceeds through C‐H activation circumventing the need for pre‐functionalization of the substrate. The method is operationally simple and affords a straightforward access to radiolabeled N‐heteroaromatics with high molar activity suitable for biological in vivo studies and clinical application.

    …read more

    Source:: Angewandte Chemie Int. edition

          

    Bowl Inversion in an Exo‐type Supramolecule in Solid State

    Bowl inversion is a unique property of buckybowls. The polarity and assembly configuration of buckybowls are reversed after bowl inversion. So far, this unique phenomenon has been studied in solution and on surface, but not in solid state due to spatial constraint. Here we present a series of exo‐type supermolecular assemblies of trithiasumanene and nanographene. Tuning the electron density of the nanogaphene component was found to directly affect the binding constant of the complex. Reversible bowl inversion in the solid state was then successfully achieved by subjecting the trithiasumanene‐nanographene assembly with the weakest binding strength to repeated heating‐cooling cycles, which is unambiguously observed by single crystal X‐ray diffraction.

    …read more

    Source:: Angewandte Chemie Int. edition

          

    Successful application of machine learning in the discovery of new polymers

    A joint research group including Ryo Yoshida (Professor and Director of the Data Science Center for Creative Design and Manufacturing at the Institute of Statistical Mathematics [ISM], Research Organization of Information and Systems), Junko Morikawa (Professor at the School of Materials and Chemical Technology, Tokyo Institute of Technology [Tokyo Tech]), and Yibin Xu (Group Leader of Thermal Management and Thermoelectric Materials Group, Center for Materials Research by Information Integration, Research and Services Division of Materials Data and Integrated System [MaDIS], NIMS) has demonstrated the promising application of machine learning (ML)—a form of AI that enables computers to “learn” from given data—for discovering innovative materials. …read more

    Source:: PhysOrg Chemistry

          

    An air-stable and waterproof lithium metal anode

    Lithium metal anode offers a promising pathway to upgrade the energy density of lithium ion batteries for its high specific capacity (3800 mAh g-1) and low voltage (-3.04 V vs. Li/Li+). But the safety issues caused by dendrite growth and instability in air caused by its high chemical activity limit its large-scale use as an electrode material. Lithium metal is highly sensitive to moisture and oxidative components in the air, leading to the generation of insulating products like lithium hydroxides on its surface and the resultant deterioration of the electrochemical performance. Moreover, when lithium contacts water, combustion and explosion can occur due to the production of hydrogen and heat. The sensitivity of lithium metal therefore necessitates demanding requirements for the transport, storage and process of lithium metal anode. It is hence highly desirable to develop an air-stable and waterproof lithium metal anode for potential use in the future. …read more

    Source:: PhysOrg Chemistry

          

    Periodic Melting of Oligonucleotides by Oscillating Salt Concentrations triggered by Microscale Water Cycles inside Heated Rock Pores

    To understand the emergence of life, a better understanding of the physical chemistry of primordial non‐equilibrium conditions is essential. Significant salt concentrations are required for the catalytic function of RNA. As a result, the separation of oligonucleotides into single strands becomes a difficult problem, especially since at elevated temperatures, the hydrolysis of RNA becomes a limiting factor. Salt concentrations strongly modulate the melting of DNA or RNA, and its periodic modulation would enable melting and annealing cycles at low temperatures. Such salt oscillations can be found at the microscale. They are driven by the local evaporation and condensation of water inside heated gas voids. In our experiments, a moderate temperature difference created a miniaturized water cycle. The microfluidic analog of rain diluted the solutes transiently and lead to melting of oligonucleotides at temperatures 20 °C below the melting temperature. The setting would enable the reshuffling of double stranded oligonucleotides, necessary for example for a ligation chain replication reaction. The findings suggest an autonomous route to overcome the strand separation problem of non‐enzymatic replication in early evolution.

    …read more

    Source:: Angewandte Chemie Int. edition

          

    Catalytic Desymmetric Cycloaddition of Diaziridines with Metalloenolcarbenes: the Special Role of Donor‐Acceptor Cyclopropenes

    Chiral copper(I) catalysed reactions of symmetrical diaziridines with enoldiazo compounds undergo novel N‐N bond ring opening with formal [3+3] cycloaddition to form four chiral centers with high stereocontrol. A broad spectrum of highly enantioenriched bridged bis‐nitrogen heterocyclic compounds were obtained in high yield and diastereoselectivity using γ‐substituted enoldiazoacetates, but their geometrical isomers gave different enantioselectivities. Donor‐acceptor cyclopropenes formed from the geometrical isomers of γ‐substituted enoldiazoacetates underwent catalytic ring opening to give only the more selective Z‐isomer of the metallo‐enolcarbene intermediate provided optimum yields and selectivities for the 1,5‐diazabicyclo[n.3.1]non‐2‐ene derivatives.

    …read more

    Source:: Angewandte Chemie Int. edition

          

    Triplet Fullerenes as Prospective Spin Labels for Nanoscale Distance Measurements by Pulsed Dipolar EPR

    Precise nanoscale distance measurements by pulsed Electron Paramagnetic Resonance (EPR) play crucial role in structural studies of biomolecules and their complexes. The properties of spin labels used in this approach are of paramount importance, since they determine the sensitivity limits, attainable distances and proximity to biological conditions, including physiological temperatures. Herewith, we propose and validate the use of photoexcited fullerenes as spin labels for pulsed dipolar (PD) EPR distance measurements. Hyperpolarization and narrower spectrum of fullerenes compared to other triplets (e.g., porphyrins) boost the sensitivity, and superior relaxation properties allow PD EPR measurements up to a near‐room temperature. The capabilities of new approach are demonstrated using fullerene‐nitroxide and fullerene‐triarylmethyl pairs, as well as supramolecular complex of fullerene with nitroxide‐labeled protein. Therefore, photoexcited triplet fullerenes can be considered as new spin labels with the outstanding spectroscopic properties for future structural studies of biomolecules.

    …read more

    Source:: Angewandte Chemie Int. edition

          

    Sponsored Links
    Archives

    Copyright © 2013. All Rights Reserved.