Determination of added sulfites in dried garlic with a modified version of the optimized Monier-Williams method

The optimized Monier-Williams method is slightly modified so that it could be applied for determining sulfite content in dried garlic. Dried garlic sample is directly acidified in a reactor at a pH below 3. At this pH level, the alliinase enzyme activity is irreversibly blocked, and the sulfur-containing amino acids such as alliin (the most abundant) present in dried garlic cannot be transformed into corresponding thiosulfinates such as allicin, which is absent in dried garlic. This prevents allicin from reacting with added sulfites and being probably converted to S-allyl thiosulfate, which is not volatile and has no taste. It is found that at a pH below 2.4 and at boiling water temperature, allicin produces sulfur dioxide in adequate quantity to explain the false-positive results when utilizing the optimized Monier-Williams method with allicin suppression for unsulfited dried garlic samples. Finally, when garlic samples are stabilized in a phosphoric acid buffer at a final pH around 2.4, no sulfite is produced during the Monier-Williams distillation, which is further proof there are no naturally occurring sulfites in unsulfited dried garlic under these mild conditions.     

同轴结构中压力波法测量空间电荷分布的物理模型研究

从压力波法测量平板样本中空间电荷分布的理论分析出发,提出了对于同轴结构的固体电介质中空间电荷分布的压力波法测量的物理模型,并得出了测量电流的解析的数学表达式.依据泊松方程,考虑样品内的电场强度、介电常数和空间电荷密度随外界声波扰动而发生变化,将圆柱试样受到的压力波的影响分解成样品形变和质点位移两部分,进而得到了以同轴结构中空间电荷分布的压力波法测量的电压与电流表达式.测量电流的数学表达式表明,对于同轴结构,压力波法的测量电流信号不像平板结构中那样基本正比于空间电荷分布,而是应该做进一步的修正处理.     

Improvement of the mechanical and barrier properties of methylcellulose-based films by treatment with HEMA and silane monomers under gamma radiation

Methylcellulose (MC)-based films were prepared by casting from its 1% aqueous solution containing 0.5% vegetable oil, 0.25% glycerol and 0.025% Tween^®-80. Puncture strength (PS), puncture deformation (PD) and water vapor permeability (WVP) of the films were found to be 147 N/mm, 3.46 mm, and 6.34 g mm/m² day kPa, respectively. The monomer, 2-hydroxyethyl methacrylate (HEMA) (0.1–1%, w/w) was incorporated into the MC-based solution and films were prepared by casting. Films were then exposed to gamma radiation (5–25 kGy) and it revealed that 1% HEMA containing films showed the highest PS values (282 N/mm at 10 kGy). Silane monomer (3-aminopropyl tri-ethoxy silane) (0.1–1%, w/w) was also added into the MC-based films and were found to improve the strength of the films significantly. In comparison between HEMA and silane treatment onto MC-based films, it was observed that silane performed better strength and barrier properties. Surface morphology of the monomer treated films was examined by scanning electron microscopy and suggested better appearance than MC-based film.     

Interactive quantum chemistry: a divide-and-conquer ASED-MO method

We present interactive quantum chemistry simulation at the atom superposition and electron delocalization molecular orbital (ASED-MO) level of theory. Our method is based on the divide-and-conquer (D&C) approach, which we show is accurate and efficient for this non-self-consistent semiempirical theory. The method has a linear complexity in the number of atoms, scales well with the number of cores, and has a small prefactor. The time cost is completely controllable, as all steps are performed with direct algorithms, i.e., no iterative schemes are used. We discuss the errors induced by the D&C approach, first empirically on a few examples, and then via a theoretical study of two toy models that can be analytically solved for any number of atoms. Thanks to the precision and speed of the D&C approach, we are able to demonstrate interactive quantum chemistry simulations for systems up to a few hundred atoms on a current multicore desktop computer. When drawing and editing molecular systems, interactive simulations provide immediate, intuitive feedback on chemical structures. As the number of cores on personal computers increases, and larger and larger systems can be dealt with, we believe such interactive simulations-even at lower levels of theory-should thus prove most useful to effectively understand, design and prototype molecules, devices and materials.     

When a Red–NIR-Emissive Cs2[Mo6Br14] Interacts with an Active Diureasil–PEO Matrix: Design of Tunable and White-Light-Emitting Hybrid Material

Hybrid materials that combine diureasil matrices and octahedral molybdenum clusters have been synthesized to design lead-, cadmium- and rare-earth-free emitters for lighting or optoelectronic applications. This association leads to homogeneous and stable hybrids, for which the emission color can be tailored in the entire visible range, including white light; this is thanks to effective energy transfers from the host to the nanocluster.