Electronic spectra of nitroethylene

A systematic study of the electronic excited states of nitroethylene (C₂H₃NO₂) was carried out using the approximate coupled‐cluster singles‐and‐doubles approach with the resolution of the identity (RI‐CC2), the time dependent density functional theory with the CAMB3LYP functional (TDDFT/CAMB3LYP) and the DFT multireference configuration interaction (DFT/MRCI) method. Vertical transition energies and optical oscillator strengths were computed for a maximum of 20 singlet transitions. Semiclassical simulations of the ultraviolet (UV) spectra were performed at the RI‐CC2 and DFT/MRCI levels. The main features in the UV spectrum were assigned to a weak n‐π* transition, and two higher energy π_CC+O‐π* bands. These characteristics are common to molecules containing NO₂ groups. Simulated spectra are in good agreement with the experimental spectrum. The energy of the bands in the DFT/MRCI simulation agrees quite well with the experiment, although it overestimates the band intensities. RI‐CC2 produced intensities comparable to the experiment, but the bands were blue shifted. A strong π_CC+O‐π* band, not previously measured, was found in the 8–9 eV range. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Is the choice of a standard zeroth‐order hamiltonian in CASPT2 ansatz optimal in calculations of excitation energies in protonated and unprotonated schiff bases of retinal?

To account for systematic error of CASPT2 method empirical modification of the zeroth‐order Hamiltonian with Ionization Potential‐Electron Affinity (IPEA) shift was introduced. The optimized IPEA value (0.25 a.u.), called standard IPEA (S‐IPEA), was recommended but due to its unsatisfactory performance in multiple metallic and organic compounds it has been questioned lately as a general parameter working properly for all molecules under CASPT2 study. As we are interested in Schiff bases of retinal, an important question emerging from this conflict of choice, to use or not to use S‐IPEA, is whether the introduction of the modified zeroth‐order Hamiltonian into CASPT2 ansatz does really improve their energetics. To achieve this goal, we assessed an impact of the IPEA shift value, in a range of 0–0.35 a.u., on vertical excitation energies to low‐lying singlet states of two protonated (RPSBs) and two unprotonated (RSBs) Schiff bases of retinal for which experimental data in gas phase are available. In addition, an effect of geometry, basis set, and active space on computed VEEs is also reported. We find, that for these systems, the choice of S‐IPEA significantly overestimates both S₀→S₁ and S₀→S₂ energies and the best theoretical estimate, in reference to the experimental data, is provided with either unmodified zeroth‐order Hamiltonian or small value of the IPEA shift in a range of 0.05–0.15 a.u., depending on active space and basis set size, equilibrium geometry, and character of the excited state. © 2018 Wiley Periodicals, Inc.     

Synthesis of diverse phenylglycine derivatives via transformation of Ugi four-component condensation primary adducts

3-(N-Substituted)amino-4-arylamino-1H-isochromenones (isocoumarins) which can be regarded as the enediamine tautomers of the Ugi four-component condensation primary adducts between 2-formylbenzoic acids, arylamines, and isocyanides undergo a facile ring cleavage with amines to give a series of phenylglycine derivatives. Thus, a synthetically useful post-condensation transformation of Ugi four-component condensation primary adducts is described for the first time.     

Star‐shaped poly(L‐lactide)s with variable numbers of hydroxyl groups at polyester arms chain‐ends and directly attached to the star‐shaped core—Controlled synthesis and characterization

Star‐shaped poly(L ‐lactide)s (PLAs) bearing variable numbers of secondary hydroxyl groups at linear arms chain‐ends and primary hydroxyl groups directly attached to dipentaerithritol core (DPE) ((HO)_6?xDPE(PLA‐OH)_x, where x = 1–6) were prepared and then analyzed by means of size exclusion chromatography (SEC), ¹H NMR spectroscopy, MALDI‐TOF mass spectrometry, and eventually by Liquid Chromatography at Critical Conditions (LC‐CC). First, starting from DPE(OH)₆ a series of polyols with various number of hydroxyl groups has been obtained ((BnO)_6?xDPE(OH)_x, where Bn denotes benzyl moiety and x = 1–6). The living ring‐opening polymerization of L ‐lactide (LA) with (BnO)_6?xDPE(OH)_x/tin(II) octoate mixtures as initiating and catalytic system led to star‐shaped (BnO)_6?xDPE(PLA‐OH)_x polymers with molar masses (M_n) controlled by LA and DPE concentrations ratio in the feed. Finally, deprotection (via hydrogenation) gave a series of (HO)_6?xDPE(PLA‐OH)_x PLA's. SEC (with Multiangle Laser Light Scattering Detector (MALLS)), NMR, and MALDI‐TOF analyses confirmed the assumed structures and M_n's of the prepared (BnO)_6?xDPE(PLA‐OH)_x and (HO)_6?xDPE(PLA‐OH)_x PLA's. LC‐CC measurements revealed that for (BnO)_6?xDPE (PLA‐OH)_x series the elution volumes increase monotonically with the increasing number of –PLA‐OH arms in one macromolecule and are independent on the given PLA molar mass because of the critical conditions. Contrary to the polymers having the protected core hydroxyl groups, the elution volume for (HO)_6?xDPE(PLA‐OH)_x series decreases with the increasing number of ‐PLA‐OH arms reaching a minimum value for 4‐arm PLA and then slightly increases for 5‐ and 6‐arm PLA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6116–6133, 2005     

Enhancing proton conductivity of proton exchange membrane with SPES nanofibers containing porous organic cage

Effective proton conducting sites and establishing proton channels are two critical factors in developing high‐performance proton exchange membranes. This study first establishes a strategy in designing effective proton conducting channels for Nafion by using solution blowing of sulfonated polyethersulfone (SPES) nanofibers containing CC3, which is an emerging porous organic cage that possesses the advantages of dissolvable organic solvents and high proton conduction from its interconnected three‐dimensional pore structure. Our strategy results in SPES nanofiber networks with CC3 uniformly involved in and composite membranes with Nafion‐filled interfiber voids. Benefiting from such structural features, the composite membrane exhibits high proton conductivity (0.315 S cm^?1 at 80°C and 100% RH), low methanol permeability (0.69 × 10^?7 cm² S^?1), excellent water absorption, thermal and dimensional stability, and single‐cell performance. This study provides not only a valuable reference for the application of CC3 but also a new idea for establishment of proton transfer channels.     

Adsorption and sequential thermal release of F2, Cl2, and Br2 molecules by a porous organic cage material (CC3-R): Molecular dynamics and grand-canonical Monte Carlo simulations

The adsorption–desorption behavior of fluorine, chlorine, and bromine molecules onto a crystalline porous organic cage, namely CC3-R was calculated at different temperatures using molecular dynamics (MD) and grand-canonical Monte Carlo (GCMC) simulations. Self-diffusion coefficients, radial distribution functions (RDF), and adsorption isotherms were calculated for this purpose. The results show that CC3-R has varied capacities to capture these halogens at ambient and high temperatures, so that the thermal release of fluorine is completed with increasing temperature up to around 70°C and chlorine molecules remain at the CC3-R surface up to 100°C and all bromine molecules are removed from the CC3-R surface at 200°C. We found that bromine self-diffusion was almost independent of temperature between 0 and 100°C in contrast to fluorine and chlorine. Among different diffusion regimes, Knudsen diffusion appears to have an important role in the adsorption of heavy halogens at higher temperatures.     

Identification and quantification of carbamate pesticides in dried lime tree flowers by means of excitation-emission molecular fluorescence and parallel factor analysis when quenching effect exists

A non-separative, fast and inexpensive spectrofluorimetric method based on the second order calibration of excitation-emission fluorescence matrices (EEMs) was proposed for the determination of carbaryl, carbendazim and 1-naphthol in dried lime tree flowers. The trilinearity property of three-way data was used to handle the intrinsic fluorescence of lime flowers and the difference in the fluorescence intensity of each analyte. It also made possible to identify unequivocally each analyte. Trilinearity of the data tensor guarantees the uniqueness of the solution obtained through parallel factor analysis (PARAFAC), so the factors of the decomposition match up with the analytes. In addition, an experimental procedure was proposed to identify, with three-way data, the quenching effect produced by the fluorophores of the lime flowers. This procedure also enabled the selection of the adequate dilution of the lime flowers extract to minimize the quenching effect so the three analytes can be quantified. Finally, the analytes were determined using the standard addition method for a calibration whose standards were chosen with a D-optimal design.     

Paper-based solid-state electrochemiluminescence sensor using poly(sodium 4-styrenesulfonate) functionalized graphene/nafion composite film

Herein, highly efficient solid-state ECL sensor was introduced for the first time onto the screen printed electrodes of the paper-based chips (PCs) based on the composite film of poly(sodium 4-styrenesulfonate) functionalized graphene (PSSG) and Nafion. Attributed to the cooperative characteristics of both PSS and graphene, PSSG ensured both effective Ru(bpy)₃²⁺ immobilization and fast electron transfer of Ru(bpy)₃²⁺ in the composite film. The ECL behaviors at the developed sensor were investigated using tripropylamine as a representative analyte and low detection limit (S N⁻¹ = 3) of 5.0 nM was obtained. It also exhibited more excellent reproducibility (relative standard deviations of 0.63% for continuous 45 cycles) and long-term stability (∼80% of its initial ECL intensity could be retained over 3 months). More importantly, assisted by the developed ECL sensor, discrimination of 1.0 nM single-nucleotide mismatch in human urine matrix could be realized on the PCs for the first attempt. Thus, the developed sensor was confirmed with the advantages of highly sensitivity, long-term stability, simplicity, low cost, disposability, high efficiency and potential applicability.     

Parallel DNA Constrained by“CC~ Clamps”

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超快微光分子光谱探测技术研究

按照超快极微弱分子吸收光谱学,荧光光谱学,时间分辨光谱学以及偏振荧光光谱学探测特性,设计、集成组建了能够探测紫外－可见－红外快到飞秒时间分辨的单分子光学事件的激光瞬态光谱仪.其光源有从300 nm到3000 nm连续可调的飞秒激光器、纳秒氢灯及连续氙灯.光谱分辨率达0.05 nm,在泵浦探测差异吸收下有小于150 fs的时间分辨率.谱仪能够实时给出光谱曲线及生物分子组分寿命.利用该谱仪探测了PSⅡCC,PSⅡRC的能量传递动力学.在83 K温度下PSⅡCC中的β-Car分子接收507 nm光能,以单步跃迁和随机转移的方式通过Chl a641.5637/638分子传递光能到反应中心Chl a683.2680/681,平均传能时间为77 ps,有59.94％的组分用355 ps时间电荷重组.在PSⅡRC中的β-Car分子接收507 nm光能,由Chl a641.5637/638分子传递光能通过Chl a678.2675.5到反应中心,平均传能时间为88.5 ps.在83 K温度下,反应中心复合物离子对;P680+·pheo-］平均再复合寿命为19.35 ns.