A series of tetrahomodioxacalix[4]biscrown-n. Syntheses, crystal structures, and metal binding abilities

A series of novel tetrahomodioxacalix[4]biscrowns with crown-2, crown-3, crown-4, crown-5, and crown-6 units were synthesized. Conformations of each product are dependent on the base used and their conformation stabilities. All conformations were proven by NMR spectra and/or X-ray crystal structures. The 1,3-alternate homodioxacalix[4]biscrown-4 (4b) shows the best selectivity for K+, whereas the 1,3-alternate homodioxacalix[4]crown-5 (5) does for Cs+. Those selectivities are attributable to electrostatic interaction between the metal ion and the crown ring, as well as a pi-metal complexation. However, the C-1,2-alternate conformation does not take the metal ions regardless of the crown species as a result of steric hindrance from the methylene bridge of an ArCH2Ar unit.     

Basicities of thiazole heterocyclic compounds and the reaction of 3-methyl-2-methylimino-Δ4-thiazolines with ethyl bromoacetate and 2-bromoacetophenone

The pK_a′s of several thiazole heterocyclic compounds have been determined and represent products with significantly high values. Because of their high basicities, sometimes these compounds were able to act as not only nucleophiles but also strong organic bases. 4-Substituted-3-methyl-2-methylimino-Δ⁴-thiazolines 5a-d reacted with ethyl bromoacetate in refluxing benzene, giving the corresponding N-alkylated salts 8a-d , while the products obtained from the reaction with 2-bromoacetophenone in the presence of base were pyrrolothiazines 10b-d.     

Reciprocal Self‐Assembly of Peptide–DNA Conjugates into a Programmable Sub‐10‐nm Supramolecular Deoxyribonucleoprotein

To overcome the limitations of molecular assemblies, the development of novel supramolecular building blocks and self‐assembly modes is essential to create more sophisticated, complex, and controllable aggregates. The self‐assembly of peptide–DNA conjugates (PDCs), in which two orthogonal self‐assembly modes, that is, β‐sheet formation and Watson–Crick base pairing, are covalently combined in one supramolecular system, is reported. Despite extensive research, most self‐assembly studies have focused on using only one type of building block, which restricts structural and functional diversity compared to multicomponent systems. Multicomponent systems, however, suffer from poor control of self‐assembly behaviors. Covalently conjugated PDC building blocks are shown to assemble into well‐defined and controllable nanostructures. This controllability likely results from the decrease in entropy associated with the restriction of the molecular degrees of freedom by the covalent constraints. Using this strategy, the possibility to thermodynamically program nano‐assemblies to exert gene regulation activity with low cytotoxicity is demonstrated.     

Anion Recognition by Urea Derivatives of Anthraquinone: Dihydrogen Phosphate Ion Selective Neutral Receptors

Three urea derivatives of anthraquinone were synthesized and they showed a high selectivity for dihydrogen phosphate ions.     

Comparison of elemental contents of Korean space foods using instrumental neutron activation analysis

The analysis of mineral contents in space foods is needed to obtain an information on a comprehensive elemental composition as well as the investigation on the effects of human nutrition and health based on the dietary intake of mineral elements. Recently, six items of new Korean space foods (KSFs) such as kimchi, bibimbap, bulgogi, a ramen, a mulberry beverage and a fruit punch which was developed by the KAERI, and the contents of more than 15 elements in the samples were examined by using instrumental neutron activation analysis (INAA). Five biological certified reference materials, NIST SRM were used for analytical quality control. The results were compared with those of common Korean foods reported, and these results will be applied toward the identification of irradiated foods.     

Practical synthesis of (S)‐7‐(2‐isopropylamino)ethylcamptothecin hydrochloride,potent topoisomerase I inhibitor

A practical semi‐synthetic method of (S)‐7‐(2‐isopropylamino)ethylcamptothecin hydrochloride has been developed. The Mannich reaction of (S)‐7‐methylcamptothecin with isopropylamine hydrochloride in dimethyl sulfoxide as a formaldehyde source gave the desired product in moderate yield.     

Hydrogen bonding nature between calix[6]arene and piperidine/triethylamine

We investigated the binding nature of the 1,2,3-alternate calix[6]arene with one piperidine, two piperidines, and two triethyl amines with a special emphasis on the hydrogen bonding networks by density functional theory calculations. The 1,2,3-alternate calix[6]arene strongly binds with piperidines and triethylamines at two different binding sites, exo and endo sites. In the two binding sites, the hydrogen bonding nature shows a characteristic difference. In the exo site, there formed only one hydrogen bond, while in the endo site, two hydrogen bonds except for the triethylamine. The proton transfer within the hydrogen bonding and the hydrogen bonding types, normal hydrogen bonding (NHB), short strong hydrogen bond (SSHB), and low barrier hydrogen bonding (LBHB), will be discussed in detail.     

F− Preference of Polyamide Cryptand to Cl−

The variations in geometry structure, IR spectra, as well as the molecular orbitals upon anion recognition for polyamide cryptand are explored with the hybrid density functional theory. The cavity generated by six amide NH groups shrinks upon F ^? recognition because of the strong hydrogen bonds between the amide protons and F ^? , while the cavity expands upon Cl ^? binding because of the strong electron repulsion between the p electron of Cl ^? and the lone pair electrons of the nitrogen atom of the pyridine moieties. The “electropositive field space” …Cl ^? coupling exists when Cl ^? is recognized. The strong anion binding energy with F ^? indicates that the polyamide cryptand prefers F ^? to Cl ^? .