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A chiral cage is proposed as an effective chiroptical sensor for perrhenate (surrogate for 99TcO4-) in water, fruit juice and artificial urine medium. The key mechanism for the chiroptical sensing...

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Porous organic cages (POCs) are a new kind of porous molecular materials, which have gained widespread interest in many fields due to their intriguing properties, including excellent molecular solubility, inherent molecular cavity and rich host-guest chemistry. To date, many chiral POCs have been explored as chiral stationary phases (CSPs) for gas chromatographic (GC) separation of enantiomers. However, the applications of chiral POCs for high performance liquid chromatography (HPLC) enantiomeric separation is extremely rare. In this study, we report the construction of thiol-ene click reaction for the preparation of CSP for HPLC by using a [4+8]-type chiral POC NC4-R as chiral selector. The fabricated CSP showed good chiral resolution performance not only in normal-phase HPLC (NP-HPLC) but also in reversed-phase HPLC (RP-HPLC). Seventeen and ten racemates were well resolved in the two separation modes, respectively, including ketones, esters, alcohols, phenols, amines, ethers, organic acids, and amino acids. Moreover, the fabricated column also shows good chiral recognition complementarity to two popular chiral HPLC columns (Chiralpak AD-H and Chiralcel OD-H columns) and previously reported chiral POC NC1-R-based HPLC column, which can resolve some racemates that unable to be resolved by the two commercially available chiral HPLC columns and NC1-R-based column. The relative standard deviation (RSD) values (n = 4) of retention time and resolution (Rs) of analytes separated on the column were less than 0.3 % and 0.5 % after it was subjected to different injections, showing the good reproducibility and stability of the NC4-R-based column. This work demonstrated high potentials of chiral POCs for HPLC enantioseparation and the applicability of chiral POC-based HPLC columns can be broadened by developing more chiral POCs with diverse structures as chiral selector for HPLC.
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Cryptands were introduced by Jean-Marie Lehn in 1969 as cage-shaped selective ligands for alkali and alkaline-earth metal ions, which lie at the heart of supramolecular chemistry. This book reports on much of the research in the field since the '70s, and looks at, amongst other topics, metal coordination chemistry, anion coordination chemistry, the encapsulation and taming of reactive anions, the formation of cascade complexes and the design of fluorescent sensors for ionic analytes. Cryptands and Cryptates has been written as a coursebook, structured as a series of lectures for graduate students or advanced researchers in chemistry, materials science, chemical biology and nanotechnology. It is fully illustrated to show experiments and results, and is intended to stimulate further interest in this fertile field of supramolecular chemistry. © 2018 by World Scientific Publishing Europe Ltd. All rights reserved.
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Technetium decontamination factor as a function of the acidity, flow ratio, scrubbing stage number was investigated by counter-current cascade experiments or mixer-settler batch tests. Results showed that the acidity of the scrubbing acid has little influence on the decontamination factor of technetium when the acidity was kept in the range of 4.5–6 M. The most effective method to increase the decontamination factor is to lower the feed-to-acid flow ratio. Keeping other condition same the factor increased to 10.3 from 3.1 when feed-to-acid ratio changed to 4 from 5.6. The loss of uranium and plutonium can be recovered through a re-extraction technology.
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Too hot to handle: Unprecedented affinity and specificity for (99) TcO(4) (-) in aqueous solution was shown with the p-xylyl azacryptand in the hexaprotonated form. A crystal structure of the complex reveals how the anion fits within the cavity of the cage, and the formation of multiple H-bond interactions with protonated amino groups stabilize the adduct.
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MEANS of distinguishing between enantiomers of a chiral molecule are of critical importance in many areas of analytical chemistry and biotechnology, particularly in drug design and synthesis. In particular, solution-based sensor systems capable of chiral recognition would be of tremendous pharmaceutical value. Here we report the chiral discrimination of D- and L-monosaccharides using a designed receptor molecule that acts as a sensor by virtue of its fluorescent response to binding of the guest species. Our receptor contains boronic acid groups that bind saccharides by covalent interactions; such receptor systems have been much studied previously(1-6) for complexation of saccharides, and have an advantage over others based on hydrogen-bonding interactions(7-11), for which polar protic solvents such as water can compete with guest binding. Our molecular sensor also incorporates a fluorescent naphthyl moiety; binding of each enantiomer of the monosaccharides alters the fluorescence intensity to differing degrees, enabling them to be distinguished. These water-soluble molecular sensors might form the basis of a quantitative and selective analytical method for saccharides.
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(Figure Presented) The shining: Readily accessible BINOL amino alcohol (S)-I is a highly enantioselective fluorescent sensor for structurally diverse α-hydroxycarboxylic acids, and is the first highly enantioselective fluorescent sensor for the recognition of linear aliphatic α- hydroxycarboxylic acids and α-tertiary-hydroxycarboxylic acids.
Article
Site-specific radiopharmaceuticals that are labeled with particle-emitting radionuclides offer opportunities for selective in vivo cellular destruction. A limited number of radiolabeled drugs are being routinely used for treatment of cancers and other diseases in humans. The patient outcomes resulting from their utilization demonstrate the value of these types of agents for treatment of diffuse and otherwise untreatable conditions. One of the inherent problems associated with the design of novel radiolabled compounds relates to development of radiolabeled conjugates that have the capacity for achieving specific tissue targeting to meet therapeutic objectives with an acceptable degree of systemic toxicity. Critical to the success of using unsealed therapeutic radioactive agent for cancer therapy is the need for the development of compounds labeled with particle-emitting radionuclides that possess the following attributes, either alone or in combination: (1) demonstrated ability to in vivo target cancer cells selectively relative to normal cells, (2) capability to achieve sufficiently high radioactivity concentration and spacial distributions in the cellular matrixes of tumors to irradiate all cells in the tumor, (3) ability to achieve long-term residualization in the tumor for delivery of cytotoxic radiation doses to the tumor, and (4) capability to clear the radiolabeled drug or its radioactive metabolites efficiently from nontarget tissues (particular radiosensitive normal cells) in order to minimize radiation-induced side effects. To successfully design, synthesize, and evaluate effective therapeutic radiopharmaceuticals, there is a great need for involvement of synthetic, organic, analytical, inorganic, and radiochemists working in concert with scientists with expertise in the biochemical, pharmacological, physiological, and oncological sciences. Interdisciplinary efforts of this level will provide reasonable possibilities for the efficient development of radiopharmaceuticals capable of delivering cytotoxic doses of radiation in high specificity to cancerous tumors.
  • B Moosa
B. Moosa, et al., Angew. Chem., Int. Ed., 2020, 59, 21367-21371;
  • X Zhao
X. Zhao, et al., Angew. Chem., Int. Ed., 2021, 60, 17904-17909;
  • Y.-Y Xu
Y.-Y. Xu, et al., J. Org. Chem., 2021, 86, 3943-3951; (d) S. N. Berry, et al., Chem. Sci., 2020, 11, 7015-7022; (e) W. Liu, et al., J. Am. Chem. Soc., 2020, 142, 3165-3173.
  • T L Mako
  • J M Racicot
  • M Levine
T. L. Mako, J. M. Racicot and M. Levine, Chem. Rev., 2018, 119, 322-477.
  • Q Sun
Q. Sun, et al., Nat. Commun., 2019, 10, 1646.
  • S Khan
S. Khan and S. K. Mandal, ACS Appl. Mater. Interfaces, 2021, 13, 45465-45474.