Stimuli‐Responsive Frustrated Lewis‐Pair‐Type Reactivity of a Tungsten Iminoazaphosphiridine Complex

Reactions of 3‐imino‐azaphosphiridine complexes 1 a,b with carbodiimides 2 a,b , isocyanates 3 a,b , and carbon dioxide are described. Whereas exchange of the carbodiimide unit occurs in the first case, an overall ring expansion takes place with phenyl isocyanate ( 3 a ) and carbon dioxide to yield complexes 4 and 5 bearing novel 1,3,5‐oxazaphospholane ligands; the isopropyl derivative 3 b did not react under these conditions. DFT calculations provide insight into the pathway of the reaction with carbon dioxide with model complex 1 c , revealing effects of initial non‐covalent interactions with the substrate onto the ring bonding, thus triggering an initially masked frustrated Lewis‐pair‐type behavior.     

Three new classes of optimal frequency-hopping sequence sets

The study of frequency-hopping sequences (FHSs) has been focused on the establishment of theoretical bounds for the parameters of FHSs as well as on the construction of optimal FHSs with respect to the bounds. Peng and Fan (IEEE Trans Inf Theory 50(9):2149–2154, 2004) derived two lower bounds on the maximum nontrivial Hamming correlation of an FHS set, which is an important indicator in measuring the performance of an FHS set employed in practice. In this paper, we obtain two main results. We study the construction of new optimal frequency-hopping sequence sets by using cyclic codes over finite fields. Let \(\mathcal {C}\) be a cyclic code of length n over a finite field \(\mathbb {F}_q\) such that \(\mathcal {C}\) contains the one-dimensional subcode \( \mathcal {C}_0=\{(\alpha ,\alpha ,\ldots ,\alpha )\in \mathbb {F}_q^n\,|\,\alpha \in \mathbb {F}_q\}. \) Two codewords of \(\mathcal {C}\) are said to be equivalent if one can be obtained from the other through applying the cyclic shift a certain number of times. We present a necessary and sufficient condition under which the equivalence class of any codeword in \(\mathcal {C}\setminus \mathcal {C}_0\) has size n. This result addresses an open question raised by Ding et al. (IEEE Trans Inf Theory 55(7):3297–3304, 2009). As a consequence, three new classes of optimal FHS sets with respect to the Singleton bound are obtained, some of which are also optimal with respect to the Peng–Fan bound at the same time. We also show that the two Peng–Fan bounds are, in fact, identical.     

ANCUT2, a Thermo-alkaline Cutinase from <Emphasis Type="Italic">Aspergillus nidulans</Emphasis> and Its Potential Applications

Biochemical characterization of purified ANCUT2 cutinase from Aspergillus nidulans is described. The identified amino acid sequence differs from that predicted in Aspergillus genomic databases in amino acids not relevant for catalysis. The enzyme is thermo-alkaline, showing its maximum activity at pH 9 and 60 °C, and it retains more than 60% of its initial activity after incubation for 1 h at 60 °C for pH values between 6 and 10. ANCUT2 is more active towards long-chain esters and it hydrolyzes cutin; however, it also hydrolyzes short-chain esters. Cutinase is inhibited by metal ions, PMSF, SDS, and EDTA (10 mM). It retains 50% of its activity in most of the solvents tested, although it is more stable in hydrophobic solvents. According to its found biochemical properties, preliminary assays demonstrate its ability to synthesize methyl esters from sesame oil and the most likely application of this enzyme remains in detergent formulations.     

DATINK pilot study: An effective methodology for ballpoint pen ink dating in questioned documents

Establishing the approximate age of an ink entry from a questioned document is often a complicated task and a controversial issue in forensic sciences. Among the existing approaches, the analysis of solvents in ballpoint inks may be a useful parameter for determining the age of ink on paper. In recent years, several ink dating methods have been proposed. These methods have been based on the analysis of common ink solvents using gas chromatography/mass spectrometry (GC/MS) as the analytical platform. Despite these recent methods, several questions remain. The aim of this work was to develop an ink dating methodology (DATINK) for documents written by ballpoint pens based on the disappearance of volatile solvents from the ink entry. Multiple solid-phase microextraction (MHS-SPME) coupled to GC/MS was used to measure the solvents from ink entries made with four BIC^® ballpoint pens. The β parameter, the remaining fraction of the analyte in the system after one equilibration, corresponding to the successive extractions was considered for modelling a mathematical equation for later ink age dating. Preliminary tests of DATINK method showed that it was possible to detect the presence of ink solvents on documents up to the studied five years. The analyses of different real samples of known age were analyzed in terms of β values, which provided a mean relative error of 21%. The proposed use of β parameter for estimating the absolute age of ballpoint ink entries has shown promising results with a standard deviation of β ranging from 0.002 to 0.004.     

Luminescent Quadrupolar Borazine Oligomers: Synthesis,Photophysics, and Two‐Photon Absorption Properties

A set of monodisperse bent donor–acceptor–donor‐type conjugated borazine oligomers, BnNn+1 (n=1–4), incorporating electron‐rich triarylamine donor and electron‐deficient triarylborane acceptor units has been prepared through an iterative synthetic approach that takes advantage of highly selective silicon–boron and tin–boron exchange reactions. The effect of chain elongation on the electrochemical, one‐ and two‐photon properties and excited‐state photodynamics has been investigated. Strong intramolecular charge transfer (ICT) from the arylamine donors to boryl‐centered acceptor sites results in emissions with high quantum yields (Φ_fl>0.5) in the range of 400–500 nm. Solvatochromic effects lead to solvent shifts as large as ～70 nm for the shortest member (n=1) and gradually decrease with chain elongation. The oligomers exhibit strong two‐photon absorption (2PA) in the visible spectral region with 2PA cross sections as large as 1410 GM (n=4), and broadband excited‐state absorption (ESA) attributed to long‐lived singlet–singlet and radical cation/anion absorption. The excited‐state dynamics also show sensitivity to the solvent environment. Electrochemical observations and DFT calculations (B3LYP/6‐31G*) reveal spatially separated HOMO and LUMO levels resulting in highly fluorescent oligomers with strong ICT character. The BnNn+1 oligomers have been used to demonstrate the detection of cyanide anions with association constants of log K>7.     

由微孔棒状羟基磷灰石为模板合成的新型层次孔炭材料的电化学电容性能

电化学电容器已经成为极具潜力的可满足高功率需求的储能系统器件. 多孔炭具有大比表面积、高导电性、化学惰性、廉价及可调孔结构等优势, 因此成为电化学电容器最为常用的电极材料. 本文报道由微孔棒状羟基磷灰石为模板及蔗糖为碳源合成的新型具有层次孔道结构的孔炭材料的电化学电容器的性能. 采用X射线衍射分析仪、扫描电子显微镜、透射电子显微镜、X射线光电子能谱及BET表面分析仪表征了合成的多孔炭的形貌及表面特性. 采用循环伏安法、交流阻抗图谱分析及恒流充放电评价多孔炭材料在1 mol·L^-1硫酸中的电化学电容性能. 多孔炭具有高的比表面积(719.7 m²·g^-1)和大的孔容(1.32 cm³·g^-1), 其无序的孔道由任意分布的微孔、坍塌的中孔及类模板形状的相互交织的棒状中孔组成. 随着炭化温度的增加, 微孔及棒状中孔的密度随之降低, 在炭化温度高达900℃时, 孔径分布图上出现了三个峰. 正是由于这些特殊的结构特征, 由900℃炭化得到的多孔炭制成的电极展示出很好的电化学电容性能.     

Mercury determination in sediments by CVAAS after on line preconcentration by solid phase extraction with a sol-gel sorbent containing CYANEX 471X®

The development of a preconcentration method for the measurement of trace levels of mercury in digested sediments is described. Solid phase extraction (SPE) was used for the preconcentration of mercury coupled on-line by means of a flow injection (FI) system followed by cold vapour atomic absorption spectrometry (CVAAS) detection. The SPE was carried out through a column packed with a sorbent material containing triisobutylphosphine sulfide (CYANEX 471X®) as mercury extractant and prepared by the sol-gel process. The effects of FI variables (argon, eluent, and reductant flow rates, loading and elution times) as well as the eluent concentration on the analytical performance of the method were evaluated. The proposed method was validated under the optimum conditions. The calibration graph was linear from 0.05?µg?L^?1 to 3.0 µg?L^?1 of Hg. The detection limit (DL), based on three times the standard deviation of the blank measurement criterion, was 24?ng^?L^?1. The repeatability was 1.5% and 1.8% RSD (n?=?10) at concentrations of 0.5 and 1 µg?L^?1 of Hg, respectively. Method enrichment factors of 16 with a productivity of 30 samples h^?1 or 32 with a productivity of 17 samples h^?1 were achieved under selected conditions. Certified reference materials, inductively coupled plasma mass spectroscopy (ICP-MS) and cold vapour atomic fluorescence spectrometry (CVAFS), were used to evaluate the accuracy of the proposed method.     

A Convenient Synthesis of 4,6-Dichloro-5-benzylthiopyrimidine

A practical and convenient two-step synthesis of the title compound 4,6-dichloro-5-benzylthiopyrimidine (3) from 4,6-dihydroxypyrimidine (1) is described.