Front Cover: Enhancement of Chiroptical Responses of trans‐Bis[(β‐iminomethyl)naphthoxy]platinum(II) Complexes with Distorted Square Planar Coordination Geometry (ChemistryOpen 4/2022)

The Front Cover shows the comparison of circularly polarized luminescence (CPL) properties of square planar platinum(II) complexes with different coordination geometries. Computational studies have revealed that the distortion of the coordination geometry is key to enhancement of the chiroptical responses of these compounds. More information can be found in the Research Article by Masahiro Ikeshita et al.     

Quantification of Noncovalent Interactions in Azide–Pnictogen, –Chalcogen,and –Halogen Contacts

The noncovalent interactions between azides and oxygen-containing moieties are investigated through a computational study based on experimental findings. The targeted synthesis of organic compounds with close intramolecular azide–oxygen contacts yielded six new representatives, for which X-ray structures were determined. Two of those compounds were investigated with respect to their potential conformations in the gas phase and a possible significantly shorter azide–oxygen contact. Furthermore, a set of 44 high-quality, gas-phase computational model systems with intermolecular azide–pnictogen (N, P, As, Sb), –chalcogen (O, S, Se, Te), and –halogen (F, Cl, Br, I) contacts are compiled and investigated through semiempirical quantum mechanical methods, density functional approximations, and wave function theory. A local energy decomposition (LED) analysis is applied to study the nature of the noncovalent interaction. The special role of electrostatic and London dispersion interactions is discussed in detail. London dispersion is identified as a dominant factor of the azide–donor interaction with mean London dispersion energy-interaction energy ratios of 1.3. Electrostatic contributions enhance the azide–donor coordination motif. The association energies range from −1.00 to −5.5 kcal mol⁻¹.     

Spectroscopic properties and amplified spontaneous emission of a new derivative of fluorescein

The new laser dye, 2-(6-acryloyloxy-3-oxo-3H-xanthen-9-yl)-benzoic acid ethyl ester [AOXBE] has been synthesized. Its chemical structure was confirmed by ¹HNMR, IR, MS and elemental analysis. This new dye was covalently bonded with methyl methacrylate (MMA) and 2-hydroxy ethyl-methacrylate (HEMA) copolymer backbone. Its optical properties were experimentally investigated. Amplified spontaneous emission (ASE) and photostability were studied by pumping the dye polymeric sample with a 355 nm (8 ns) pulsed Nd:YAG laser. PACS 42.55.Mv; 42.70.Hj; 42.70.Jk; 42.55.Px     

Interaction between sulfonephthalein dyes and chitosan in aqueous solution and its application to the determination of surfactants.

A spectrophotometric method for the determination of ionic surfactants with Bromophenol Blue (BPB) based on incorporation into a precipitated chitosan was studied. Cationic surfactants (CS+), such as a quaternary ammonium ion containing a long-chain alkyl group, associate with BPB2- buffered at about pH 9 to form the ion associate (CS+)2 x BPB2-. CS+ associates with anionic surfactants (AS-). In the presence of a definite amount of CS+, an increase in the amount of AS- leads to a decrease in the amount of excess CS+, and therefore to a decrease in the amount of the ion associate of CS+ with BPB2-. The addition of a chitosan dissolved in acetic acid to a solution containing these ion associates leads immediately to precipitation of the chitosan and the incorporation of the ion associates (CS+)2 x BPB2- or CS+ x AS- into the precipitated chitosan. After centrifuging, ionic surfactants can be determined by the following two methods: (1) the absorbance of the supernatant solution is measured at 590 nm. (2) After the supernatant solution is separated, the precipitate is dissolved in an acetic acid solution and the absorbance is measured at 625 nm. Because the color of the precipitate is judged by the naked eye, this can be applied to the visual method. This is a simple and rapid method for the determination of a 10(-6) M order of ionic surfactants.     

Sequence Analysis for Alternating Copolymers by MALDI‐TOF‐MS: Importance of Initiator Selectivity for Comonomer Pair

A special initiator for metal‐catalyzed living radical polymerization facilitates sequence analyses by matrix‐assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF‐MS) of alternating copolymers from styrene and maleimide derivatives. The initiator is a malonate‐based alkyl halide (DEMM‐Br), in which two ester groups are attached on the carbon neighboring to bromide, and poor electron density of the radical species allows determination of next unit to the initiator in resultant alternating copolymers due to the selective initiation to styrene derivative. Thanks to the well‐defined α‐end group, sequence of the oligomeric products via radical copolymerization of PMS and EMI with DEMM‐Br can be more simply analyzed by MALDI‐TOF‐MS, and indeed the following are clarified: the crossover propagation is almost perfectly controlled regardless of the injection ratio; a minor error event of the disordered alternating sequence containing St–St sequential unit could take place; the minor error can be suppressed with an excess amount of maleimide.

     

Effects of Temperature and Mobile Phase Condition on Chiral Recognition of Poly(l-phenylalanine) Chiral Stationary Phase

Characteristics of the chiral stationary phase with poly(l-phenylalanine) peptide selector, which was in ??-helical state, was reported. Since environmental factors affect peptide conformation, the changes in enantioselectivity were examined depending on column temperature and mobile phase conditions (ionic strength, pH, mobile phase composition). Column temperature and pH drastically affected the enantioselectivity. Based on these changes, the relation between chiral recognition and secondary structure of the peptide selector was discussed. The column stability during sequential analysis under different separation conditions was also evaluated.     

Iodocyclization of hydroxylamine derivatives based on the control of oxidative aromatization leading to 2,5-dihydroisoxazoles and isoxazoles

An efficient method for the synthesis of 2,5-dihydroisoxazoles and isoxazoles using iodocyclization of N-alkoxycarbonyl O-propargylic hydroxylamines has been developed. 2,5-Dihydro-4-iodoisoxazole underwent the cross-coupling reactions without aromatization to afford polyfunctionalized 2,5-dihydroisoxazoles. This process was applied to the preparation of valdecoxib and its 2,5-dihydro-derivative.     

Lithium acetylides as alkynylating reagents for the enantioselective alkynylation of ketones catalyzed by lithium binaphtholate

Chiral lithium binaphtholate effectively catalyzed the enantioselective alkynylation of ketones using lithium acetylide as an alkynylating agent. This is the first example of the catalytic enantioselective addition of lithium acetylide to carbonyl compounds without the aid of other metal sources.     

Viscoelastic properties of bis(phenyl)fluorene‐based cardo polymers with different chemical structure

Viscoelastic properties of urethane and ester conjugation cardo polymers that contain fluorene group, 9,9‐bis(4‐(2‐hydroxyethoxy)phenyl)fluorene (BPEF), were investigated. As for the urethane‐type cardo polymers containing BPEF in the main chain, it had a high glass‐transition temperature (T_g), which was observed as the α dispersion on viscoelastic measurement, and its temperature depended on the chemical structure of the spacing unit, such as toluene diisocyanate (TDI), 4,4′‐methylene diphenyl diisocyanate (MDI), methylene dicycloexyl diisocyanate (CMDI), and hexamethylene diisocyanate (HDI). Moreover, the T_g of urethane‐type cardo copolymers with various cardo contents increased with an increase of cardo content. Owing to the increase of T_g of cardo polymers, another molecular motion can be measured at the temperature between the α and β dispersion that was assigned to the molecular motion of urethane conjugation unit around 200 K, and it was referred to as the α_sub dispersion. The peak temperature of the α_sub dispersion was influenced by the chemical structure of the spacing unit, but it did not change for the cardo polymer containing the same spacing unit. Consequently, it was deduced that the α_sub dispersion was originated in the subsegmental molecular motions of the cardo polymers. Ester‐type cardo polymer had higher T_g in comparison with noncardo polymer that consisted of dimethyl groups (BPEP) instead of BPEF as well. The α_sub dispersion was also measured at the temperature between the α and β dispersion, which was assigned to the molecular motion of ester conjugation unit, around 220 K. For ester cardo polymer, the γ dispersion was measured in a low‐temperature region around 140 K, and it was due to a small unit motion in the ester‐type cardo polymers, such as ethoxyl unit, ? C₂H₄O? . Moreover, the intensity of the γ dispersion of noncardo polymer was higher than that of cardo polymer, which means the molecular motion was much restricted by the cardo structure of BPEF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2259–2268, 2005