Molecular QTAIM Topology Is Sensitive to Relativistic Corrections

The topology of the molecular electron density of benzene dithiol gold cluster complex Au₄−S−C₆H₄−S′−Au′₄ changed when relativistic corrections were made and the structure was close to a minimum of the Born–Oppenheimer energy surface. Specifically, new bond paths between hydrogen atoms on the benzene ring and gold atoms appeared, indicating that there is a favorable interaction between these atoms at the relativistic level. This is consistent with the observation that gold becomes a better electron acceptor when relativistic corrections are applied. In addition to relativistic effects, here, we establish the sensitivity of molecular topology to basis sets and convergence thresholds for geometry optimization.     

Pharmacokinetic analysis of plasma bicyclol by liquid chromatography–tandem mass spectrometry

Bicyclol is a synthetic drug widely used to treat chronic hepatitis B. This study aimed to develop a selective, sensitive and high‐throughput liquid chromatography–tandem mass spectrometric method for the detection of bicyclol in human plasma. Bicyclol was detected using a multiple reaction monitoring mode, with ammonium adduct ions (m/z 408.2) as the precursor ion and the [M‐CH₃]⁺ ion (m/z 373.1) subjected to demethylation as the product ion. Chromatographic separation was achieved using a Zobax Eclipse XDB‐C₁₈ column with a gradient elution and a mobile phase of 2 mm ammonium formate and acetonitrile. Bicyclol was extracted from plasma matrix by precipitation. A linear detection response was obtained for bicyclol ranging from 0.500 to 240 ng/mL, and the lower limit of quantification was 0.500 ng/mL. The intra‐ and inter‐day precisions were all ≤7.4%, and the accuracies were within ±6.0%. The extraction recovery was >95.9%, and the matrix effects were between 96.0% and 108%. Bicyclol was found to be unstable in human plasma at room temperature, but the degradation was minimized by conducting sample collection and preparation in an ice bath. The validated method was successfully applied to investigate the pharmacokinetics of bicyclol tablets in six healthy Chinese volunteers.     

Development and validation of a sensitive liquid‐chromatography tandem mass spectrometry assay for mycophenolic acid and metabolites in HepaRG cell culture: Characterization of metabolism interactions between p‐cresol and mycophenolic acid

Mycophenolic acid (MPA), a frequently used immunosuppressant, exhibits large inter‐patient pharmacokinetic variability. This study (a) developed and validated a sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) assay for MPA and metabolites [MPA glucuronide (MPAG) and acyl‐glucuronide (AcMPAG)] in the culture medium of HepaRG cells; and (b) characterized the metabolism interaction between MPA and p‐cresol (a common uremic toxin) in this in vitro model as a potential mechanism of pharmacokinetic variability. Chromatographic separation was achieved with a C₁₈ column (4.6 × 250 mm,5 μm) using a gradient elution with water and methanol (with 0.1% formic acid and 2 mm ammonium acetate). A dual ion source ionization mode with positive multiple reaction monitoring was utilized. Multiple reaction monitoring mass transitions (m/z) were: MPA (320.95 → 207.05), MPAG (514.10 → 303.20) and AcMPAG (514.10 → 207.05). MPA‐d₃ (323.95 → 210.15) and MPAG‐d₃ (517.00 → 306.10) were utilized as internal standards. The calibration curves were linear from 0.00467 to 3.2 μg/mL for MPA/MPAG and from 0.00467 to 0.1 μg/mL for AcMPAG. The assay was validated based on industry standards. p‐Cresol inhibited MPA glucuronidation (IC₅₀ ≈ 55 μm ) and increased MPA concentration (up to >2‐fold) at physiologically relevant substrate‐inhibitor concentrations (n = 3). Our findings suggested that fluctuations in p‐cresol concentrations might be in part responsible for the large pharmacokinetic variability observed for MPA in the clinic.     

New lower bounds on the radius of spatial analyticity for the KdV equation

The radius of spatial analyticity for solutions of the KdV equation is studied. It is shown that the analyticity radius does not decay faster than $t^{?1/4}$ as time t goes to infinity. This improves the works of Selberg and da Silva (2017) [30] and Tesfahun (2017) [34]. Our strategy mainly relies on a higher order almost conservation law in Gevrey spaces, which is inspired by the I-method.     

Synergistic Surface Passivation of CH3NH3PbBr3 Perovskite Quantum Dots with Phosphonic Acid and (3-Aminopropyl)triethoxysilane

CH₃NH₃PbBr₃ perovskite quantum dots (PQDs) are synthesized by using four different linear alkyl phosphonic acids (PAs) in conjunction with (3-aminopropyl)triethoxysilane (APTES) as capping ligands. The resultant PQDs are characterized by means of XRD, TEM, Raman spectroscopy, FTIR spectroscopy, UV/Vis, photoluminescence (PL), time-resolved PL, and X-ray photoelectron spectroscopy (XPS). PA chain length is shown to control the PQD size (ca. 2.9–4.2 nm) and excitonic absorption band positions (λ=488–525 nm), with shorter chain lengths corresponding to smaller sizes and bluer absorptions. All samples show a high PL quantum yield (ca. 46–83 %) and high PL stability; this is indicative of a low density of band gap trap states and effective surface passivation. Stability is higher for smaller PQDs; this is attributed to better passivation due to better solubility and less steric hindrance of the shorter PA ligands. Based on the FTIR, Raman, and XPS results, it is proposed that Pb²⁺ and CH₃NH₃⁺ surface defects are passivated by R−PO₃²⁻ or R−PO₂(OH)⁻, whereas Br⁻ surface defects are passivated by R−NH₃⁺ moieties. This study establishes the combination of PA and APTES ligands as a highly effective dual passivation system for the synergistic passivation of multiple surface defects of PQDs through primarily ionic bonding.     

Synthesis of Highly Functionalized N,N-Diarylamides by an Anodic C,N-Coupling Reaction

We report an innovative, sustainable and straightforward protocol for the synthesis of N,N-diarylamides equipped with nonprotected hydroxyl groups by using electrosynthesis. The concept allows the application of various substrates furnishing diarylamides with yields up to 57 % within a single and direct electrolytic protocol. The method is thereby easy to conduct in an undivided cell with constant current conditions offering a versatile and short-cut alternative to conventional pathways.     

Nitroxide‐Mediated Polymerization of Bio‐Based Farnesene with a Functionalized Methacrylate

Farnesene (Far) is a bio‐based terpene monomer that is similar in structure to commercially used dienes like butadiene and isoprene. Nitroxide‐mediated polymerization (NMP) is adept for the polymerization of dienes, but not particularly effective at controlling the polymerization of methacrylates using commercial nitroxides. In this study, Far is statistically copolymerized with a functional methacrylate, glycidyl methacrylate (GMA), by NMP using N‐succinimidyl modified commercial BlocBuilder (NHS‐BB) initiator. Reactivity ratios are determined to be r _Far = 0.54 ± 0.04 and r _GMA = 0.24 ± 0.02. The ability of the poly(Far‐stat‐GMA) chains to reinitiate for chain extension with styrene showed a clear shift in molecular weight and monomodal distribution. Copolymerizations using a new alkoxyamine, Dispolreg 007 (D7), is explored as it is shown to homopolymerize methacrylates, but not yet reported for statistical copolymerizations. Bimodal molecular weight distributions are observed when an equimolar ratio of Far and GMA is copolymerized with D7 due to slow decomposition of the initiator, but chain ends are active as shown by successful chain extension with styrene. Both NHS‐BB and D7 initiators are used to synthesize poly[Far‐b‐(GMA‐stat‐Far)] and poly(Far‐b‐GMA) diblock copolymers. While the NHS‐BB initiated polymer chains have lower dispersity, D7 exhibits more linear polymerization kinetics and maintains more active chain ends.     

Red shifting of absorption maxima of phenothiazine based dyes by incorporating electron-deficient thiadiazole derivatives as π-spacer

This study was carried out to design phenothiazine based dyes by incorporating electron-deficient thiadiazole derivatives as π-spacer. Density functional theory and time-dependent density functional theory calculations of the geometries, electronic structures and absorption spectra of the dyes before and after binding to titanium oxide were carried out. Effects of the electron-deficient units on the spectra and electrochemical properties have been investigated. Compared with the reference compound CS1A, Dyes 1–4 display remarkably enhanced spectral responses in the red portion of the solar spectrum. The newly designed dyes demonstrate desirable energetic and spectroscopic parameters, and may lead to efficient metal-free organic dye sensitizers for DSSCs.     

Kinetics and mechanism of trichloroisocyanuric acid/NaNO2-triggered nitration of aromatic compounds under acid-free and Vilsmeier-Haack conditions

Kinetics and mechanism of nitration of aromatic compounds using trichloroisocyanuric acid (TCCA)/NaNO₂, TCCA-N,N-dimethyl formamide (TCCA-DMF)/NaNO₂, and TCCA-N,N-dimethyl acetamide (TCCA-DMA)/NaNO₂ under acid-free and Vilsmeier-Haack conditions. Reactions followed second-order kinetics with a first-order dependence on [Phenol] and [Nitrating agent] ([TCCA], [(TCCA-DMF)], or [(TCCA-DMA)] >> [NaNO₂]). Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups, but did not fit well into the Hammett's theory of linear free energy relationship or its modified forms like Brown-Okamoto or Yukawa-Tsuno equations. Rate data were analyzed by Charton's multiple linear regression analysis. Isokinetic temperature (β) values, obtained from Exner's theory for different protocols, are 403.7 K (TCCA-NaNO₂), 365.8 K (TCCA-DMF)/NaNO₂, and 358 K (TCCA-DMA)/NaNO₂. These values are far above the experimental temperature range (303-323 K), indicating that the enthalpy factors are probably more important in controlling the reaction.     

Infrared spectroscopy of closed s-shell gas-phase M+(N2O)n (M = Li,Al) ion-molecule complexes*

ABSTRACT

We present the results of a combined experimental and computational study of the structures of gas-phase M⁺(N₂O)_n (M?=?Li, Al) complexes. Infrared spectra were recorded in the region of the N₂O asymmetric (N?=?N) stretch using photodissociation spectroscopy employing the inert messenger technique. Unlike in our previous studies on M⁺(N₂O)_n (M?=?Cu, Ag, Au and M?=?Co, Rh, Ir) complexes, N– and O–bound isomers in this case are near isoenergetic and are not distinguished spectroscopically at this resolution. In the case of Li⁺ complexes, there is, however, evidence for the presence of bound N₂ moieties, indicating the presence of inserted, OLi⁺N₂(N₂O)_n–type structures. The weak N₂ band lies to the blue of the signature of molecularly N– and O–bound ligands and is well–reproduced in the simulated spectra of energetically low-lying structures computed from density functional theory. No such inserted isomers are observed in the case of Al⁺(N₂O)_n complexes whose infrared spectra can be understood on the basis of molecularly-bound N₂O ligands. The differences in M⁺(N₂O)_n structures observed for these closed–shell, ns², metal centres relative to other metal cations are discussed in terms of the likely bonding motifs.