Photophysical properties of a tetraphenoxy-substituted perylene bisimide derivative characterized by single-molecule spectroscopy.

We present a detailed study of the photophysical properties of a tetraphenoxy-substituted perylene bisimide derivative. The probe molecules were immobilized in a Shpol'skii matrix of hexadecane and investigated by single-molecule spectroscopy at cryogenic temperatures. By using single-molecule spectroscopic techniques we reveal the triplet substate kinetics and the fluorescence quantum yield, and we provide an estimate for the S1-S0 transition dipole moment.     

Machine learning dielectric screening for the simulation of excited state properties of molecules and materials

Accurate and efficient calculations of absorption spectra of molecules and materials are essential for the understanding and rational design of broad classes of systems. Solving the Bethe–Salpeter equation (BSE) for electron–hole pairs usually yields accurate predictions of absorption spectra, but it is computationally expensive, especially if thermal averages of spectra computed for multiple configurations are required. We present a method based on machine learning to evaluate a key quantity entering the definition of absorption spectra: the dielectric screening. We show that our approach yields a model for the screening that is transferable between multiple configurations sampled during first principles molecular dynamics simulations; hence it leads to a substantial improvement in the efficiency of calculations of finite temperature spectra. We obtained computational gains of one to two orders of magnitude for systems with 50 to 500 atoms, including liquids, solids, nanostructures, and solid/liquid interfaces. Importantly, the models of dielectric screening derived here may be used not only in the solution of the BSE but also in developing functionals for time-dependent density functional theory (TDDFT) calculations of homogeneous and heterogeneous systems. Overall, our work provides a strategy to combine machine learning with electronic structure calculations to accelerate first principles simulations of excited-state properties.

Machine learning can circumvent explicit calculation of dielectric response in first principles methods and accelerate simulations of optical properties of complex materials at finite temperature.     

Bis(dimethylamino)trifluoromethylsulfonium Salze: [CF3S(NMe2)2]+[Me3SiF2]‐, [CF3S(NMe2)2]+[HF2]‐ und [CF3S(NMe2)2]+[CF3S]‐

Bis(dimethylamino)trifluoro sulfonium Salts: [CF₃S(NMe₂)₂]⁺[Me₃SiF₂]^‐, [CF₃S(NMe₂)₂]⁺ [HF₂]^‐ and [CF₃S(NMe₂)₂]⁺[CF₃S]^‐ From the reaction of CF₃SF₃ with an excess of Me₂NSiMe₃ [CF₃(NMe₂)₂]⁺[Me₃SiF₂]^‐ (CF₃‐BAS‐fluoride) ( 5 ), from CF₃SF₃/CF₃SSCF₃ and Me₂NSiMe₃ [CF₃S(NMe₂)₂]⁺‐ [CF₃S]^‐ ( 7 ) are isolated. Thermal decomposition of 5 gives [CF₃S(NMe₂)₂]⁺ [HF₂]^‐ ( 6 ). Reaction pathways are discussed, the structures of 5 ‐ 7 are reported.     

Rapid speciation of Se(IV) and Se(VI) by flow injection–capillary electrophoresis system with contactless conductivity detection

A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM l-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 g L^–1 and 7.5 g L^–1 for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations.     

Size-related vaporisation and ionisation of laser-induced glass particles in the inductively coupled plasma

Ongoing discussions about the origin of elemental fractionation occurring during LA-ICP-MS analysis show that this problem is still far from being well understood. It is becoming accepted that all three possible sources (ablation, transport, excitation) contribute to elemental fractionation. However, experimental data about the vaporisation size limit of different particles in the ICP, as produced in laser ablation, have not been available until now. This information should allow one to determine the signal contributing mass within the ICP and would further clarify demands on suitable laser ablation systems and gas atmospheres in terms of their particle size distribution.The results presented here show a vaporisation size limit of laser induced particles, which was found at particle sizes between 90 nm and 150 nm using an Elan 6000 ICP-MS. Due to the fact that the ICP-MS response was used as evaluation parameter, vaporisation and ionisation limits are not distinguishable.The upper limit was determined by successively removing the larger particles from the aerosol, which was created by ablation of a NIST 610 glass standard at a wavelength of 266 nm, using a recently developed particle separation device. Various particle fractions were separated from the aerosol entering the ICP. The decrease in signal intensity is not proportional to the decrease in volume, indicating that particles above 150 nm in diameter are not completely ionised in the ICP. Due to the limited removal range of the particle separation device, which cannot remove particles smaller than 150 nm, single hole ablations were used to determine the lower vaporisation limit. This is based on measurements showing that larger particles occur dominantly during the first 100 laser pulses only. After this period, the ratio of ICP-MS counts and total particle volume was found to be constant while most of the particles are smaller than 90 nm, indicating complete vaporisation and ionisation of these particles.To describe the influence of different plasma forward powers on the vaporisation limit, the range 1000–1600 W was studied. Results indicate that optimum vaporisation and ionisation occurs at 1300 W. However, an increase of the particle ionisation limit towards larger particles was not observed within the accuracy of this study using the full range of parameters available for optimisation on commonly used ICP-MS instruments.     

Evaluation of polymeric flocculants for oily water systems using a photometric dispersion analyzer

During oil production and treatment, oil-in-water (O/W) emulsions are formed. These dispersions require treatment prior to disposal. In order to improve oil/water separation processes through any physical process (decanting, flotation, centrifuging etc), the particle size of the dispersed phase should be increased. This may be obtained by a flocculation process, which consists in the agglomeration of several particles or drops using as flocculating agent hydrophilic high molecular weight macromolecules. Poly (ethylene-b-propylene oxide) and poly (vinyl alcohol) polymers have been evaluated as flocculating agents for oily water systems. Their performance is related to the particle size increase of the dispersed phase. In this work, a photometric dispersion analyzer (PDA) has been used to accomplish the oil drop agglomeration. Synthetic as well as produced water was used. Data are in good agreement with previous tests. Qualitative information related to aggregates or particle size distribution of the oily water systems can be obtained using PDA.     

A theory of adsorption kinetics with time delay and its application to overshoot and oscillation in the surface tension of gelatin solution

A theory of adsorption kinetics with time delay [Ohshima et al. (1992) Colloid Polym. Sci. 270:707] is developed and applied to the surface tension of a polymer solution. It is found that the general appearance of the overshoot and oscillation in the time course of the surface tension of aqueous gelatin solution observed by Sato and Ueberreiter [(1979) Makromol. Chem. 180:829, 1107; (1979) Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 20:907) can be explained by the present theory.     

The effect of β-cyclodextrin on the properties of cetyltrimethylammonium bromide micelles

The effect of ß-cyclodextrin (ß-CD) on cetyltrimethylammonium bromide (CTAB) micellar properties was studied by the determination of the diffusion coefficient, D. When the CTAB micelles have a spherical structure, D firstly increased and then remained unchanged, while the micellar aggregation number, N, decreased with the addition of ß-CD. When the CTAB concentration was less than the first critical micellar concentration, CTAB molecules could be included into ß-CD cavities with the molar ratio of CTAB to ß-CD being about 1:1. However, when the CTAB concentration was higher than the first critical micellar concentration, mixed spherical micelles were formed with the molar ratio of CTAB to ß-CD being 9:1.     

A sensitive and specific HPLC-MS method for the determination of sophoridine,sophocarpine and matrine in rabbit plasma

A sensitive and specific method was developed for the determination of sophoridine (SRI), sophocarpine (SC) and matrine (MT) in rabbit plasma by HPLC-MS. After an administration of Kuhuang by injection, blood samples were collected and extracted with methanol. The extract solutions were analysed by HPLC-MS method. The separation was performed on a ZORBAX Extend-C18 column using methanol/water/diethylamine (50:50:0.07, v/v/v) as mobile phase. The quinolizidine alkaloids were detected by using mass spectrometry in the SIM mode. There was a good linear relationship between peak area and concentration of analytes over the concentration range of 13.2–995.0 ng mL^–1 for SRI, 7.0–530.0 ng mL^–1 for SC and 8.8–655.0 ng mL^–1 for MT, respectively. The absolute recovery of this method was more than 57% for SRI, 87% for SC and 91% for MT. The accuracy of assay was more than 90%. The limits of detection (LODs) were 6.8 ng mL^–1 for SRI, 3.5 ng mL^–1 for SC and 4.2 ng mL^–1 for MT, respectively. The limits of quantitation (LOQs) were 13.2 ng mL^–1 for SRI, 7.0 ng mL^–1 for SC and 8.8 ng mL^–1 for MT, respectively. The intra-day and inter-day coefficients of variation (RSDs) were less than 10.1, 6.3 and 5.8% for SRI, SC and MT, respectively. The developed method was applied to determine the concentration–time profiles of SRI, SC and MT in rabbit plasma after injection of Kuhuang.     

Synthesis,Characterization and DNA-binding Properties of Three 3d Transition Metal Complexes of the Schiff Base Derived from Diethenetriamine with PMBP

A new ligand H₂L, 1,7-di(1-phenyl-3-methyl-5-pyrazolone-4-benzylidene)diethenetriamine and its three transition metal complexes, ML · nH₂O [M=Cu(II), n=2; M=Zn(II), n=0.5; M=Ni(II) (1), n=3] have been synthesized in anhydrous EtOH and characterized on the basis of elemental analyses, molar conductivities, i.r. spectra, u.v. spectra and thermal analyses. In addition, the DNA-binding properties of the ligand and its complexes have been investigated by absorption, fluorescence and viscosity measurements. The experimental results indicated that the ligand and the complex (1) can bind to DNA , but the other two complexes can’t; the binding affinity of the complex (1) is higher than that of the ligand and the intrinsic binding constant k_b of the complex (1) is 7.893×10⁵ m⁻¹.