Numerical simulation on compressible turbulence by spectral method

The numerical and physical issues of simulations on compressible turbulence are reviewed in the present paper. An outline of the global spectral methods and the progress of recent local spectral methods are illustrated. Several typical subjects in this field are studied, including homogeneous isotropic turbulence, autoignition in premixed turbulence, interaction between flames and turbulence, and shock wave in turbulence. The results of the numerical simulations are discussed, enabling us to discover and to understand the physical phenomena which have not been solved by experiments.     

Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism

A newly synthesized one‐dimensional (1D) hydrogen‐bonded (H‐bonded) rhodium(II)–η⁵‐semiquinone complex, [Cp*Rh(η⁵‐p‐HSQ‐Me₄)]PF₆ ([ 1 ]PF₆; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric–antiferroelectric second‐order phase transition at 237.1 K. Neutron and X‐ray crystal structure analyses reveal that the H‐bonded proton is disordered over two sites in the room‐temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF₆^? ion. The relative permittivity ε_b′ along the H‐bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of ¹³C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low‐temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10^?4–10^?6 s in the temperature range of 240–270 K. DFT calculations predict that the protonation/deprotonation of [ 1 ]⁺ leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π‐bonded rhodium fragment, producing the stable η⁶‐hydroquinone complex, [Cp*Rh³⁺(η⁶‐p‐H₂Q‐Me₄)]²⁺ ([ 2 ]²⁺), and η⁴‐benzoquinone complex, [Cp*Rh⁺(η⁴‐p‐BQ‐Me₄)] ([ 3 ]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [ 2 ]²⁺ and [ 3 ], which would be generated in the H‐bonded chain.     

Simple and validated UHPLC method coupled to UV detection for determination of daptomycin in human plasma and urine

Daptomycin, a lipopeptide antibiotic with excellent activity against Gram‐positive bacteria, is excreted primarily by the kidneys. Development of effective chromatographic methodologies for the determination of daptomycin in human specimens is necessary for clinical use. This study developed a simple and validated ultra‐high‐performance liquid chromatography method coupled to ultraviolet detection for determination of daptomycin in human plasma and urine. After the pretreatments involving protein precipitation, the supernatants were separated using a 2.3 µm particle size octadecylsilyl column, and the run time was 1 min. The calibration curves were linear over the concentration ranges of 2–200 mg/L for plasma and 25–300 mg/L for urine. Intra‐ and inter‐assay precision and accuracy values of plasma were within 13.5 and 92–100% and within 10.7 and 100–107%, respectively. Those of urine were within 5.0 and 101–104% and within 3.7 and 100–101%, respectively. The validated method was applied to the determination of plasma and urine samples in patients receiving 4–6 mg/kg of intravenous daptomycin, resulting in sufficient sensitivity for evaluating the plasma exposure and urinary excretion. In conclusion, the present method with acceptable analytical performance can be helpful for evaluating the pharmacokinetic disposition of daptomycin in clinical settings. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and Properties of Polycarbosilanes Having Lactose‐Derived Structures

A polycarbosilane having lactose‐derived structures was synthesized, and its thermal property, cytotoxicity, chemical crosslinking, and protein adsorption properties were investigated. The polycarbosilane (PSB‐Lac) was prepared by a thiol‐ene reaction between precursor poly(1‐(3‐butenyl)‐1‐methylsilacyclubane) (PSB) and heptaacetyl lactose that carried a thiol group at the anomeric position, and the successive deprotection of the acetyl groups. The lactose introduction efficiency determined by ¹H NMR measurement was 75%. TGA and DSC revealed that the polymer had a 5 wt% decomposition temperature of 260 °C and glass transition temperature (T_g) of 84 °C, which indicated that PSB‐Lac was a thermally stable polymer. PSB‐Lac had no significant cytotoxicity, which was evaluated by human liver cancer cell line HepG2 cultivation on the polystyrene dishes coated with the polymer. Urethane‐crosslinked PSB‐Lac films were prepared by casting solutions of PSB‐Lac and hexamethylene diisocyanate and heating at 120 °C after evaporation of the solvent. The crosslinked PSB‐Lac showed higher adsorption of bovine serum albumin than the similarly crosslinked polycarbosilane that had a glucose structure (PSB‐Glc). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2420–2425     

Identification of conjugation positions of urinary glucuronidated vitamin D3 metabolites by LC/ESI–MS/MS after conversion to MS/MS‐fragmentable derivatives

A liquid chromatography/electrospray ionization–tandem mass spectrometry‐based method was developed for the identification of the conjugation positions of the monoglucuronides of 25‐hydroxyvitamin D₃ [25(OH)D₃] and 24,25‐dihydroxyvitamin D₃ [24,25(OH)₂D₃] in human urine. The method employed derivatization with 4‐(4‐dimethylaminophenyl)‐1,2,4‐triazoline‐3,5‐dione to convert the glucuronides into fragmentable derivatives, which provided useful product ions for identifying the conjugation positions during the MS/MS. The derivatization also enhanced the assay sensitivity and specificity for urine sample analysis. The positional isomeric monoglucuronides, 25(OH)D₃‐3‐ and ‐25‐glucuronides, or 24,25(OH)₂D₃‐3‐, ‐24‐ and ‐25‐glucuronides, were completely separated from each other under the optimized LC conditions. Using this method, the conjugation positions were successfully determined to be the C3 and C24 positions for the glucuronidated 25(OH)D₃ and 24,25(OH)₂D₃, respectively. The 3‐glucuronide was not present for 24,25(OH)₂D₃, unlike 25(OH)D₃, thus we found that selective glucuronidation occurs at the C24‐hydroxy group for 24,25(OH)₂D₃.     

Room-Temperature Phosphorescence from a Series of 3-Pyridylcarbazole Derivatives

Exploration of pure metal-free organic molecules that exhibit strong room-temperature phosphorescence (RTP) is an emerging research topic. In this regard, unveiling the design principles for an efficient RTP molecule is an essential, but challenging, task. A small molecule is an ideal platform to precisely understand the fundamental role of each functional component because the parent molecule can be easily derivatized. Here, the RTP behaviors of a series of 3-pyridylcarbazole derivatives are presented. Experimental studies in combination with theoretical calculations reveal the crucial role of the n orbital on the central pyridine ring in the dramatic enhancement of the intersystem crossing between the charge-transfer-excited singlet state and the locally excited triplet states. Single-crystal X-ray crystallographic studies apparently indicate that both the pyridine ring and fluorine atom contribute to the enhancement of the RTP because of the restricted motion owing to weak C−H⋅⋅⋅N and H⋅⋅⋅F hydrogen-bonding interactions. The single crystal of the fluorine-substituted derivative shows an ultra-long phosphorescent lifetime (τ_P) of 1.1 s and a phosphorescence quantum yield (Φ_P) of 1.2 %, whereas the bromine-substituted derivative exhibits τ_P of 0.15 s with a Φ_P of 7.9 %. We believe that this work provides a fundamental and universal guideline for the generation of pure organic molecules exhibiting strong RTP.