Efficient tuning of potential parameters for liquid–solid interactions

Spherical and cylindrical water droplets on silicon surface are studied to tune the silicon–oxygen interaction. We use molecular dynamics simulations to estimate the contact angle of two different shaped droplets. We found that the cylindrical droplets are independent of the line tension as their three phases curvature is equal zero. Additionally, we compare an analytical model, taking into account or not the Tolman length and we show that for spherical small size droplets, this length is important to be included, in contrast to cylindrical droplets in which the influence of the Tolman length is negligible. We demonstrate that the usual convenient way to exclude linear tension in the general case can give wrong results. Here, we consider cylindrical droplets, since their contact angle does not depend on the droplet size in the range of few to 10ths of nanometres. The droplets are stabilised due to the periodic boundary conditions. This allows us to propose a new parameterisation for nanoscale droplets, which is independent the size of the droplets or its shape, minimising at the same time the calculation procedure. With the proposed methodology, we can extract the epsilon parameter of the interaction potential between a liquid and a solid from the nanoscaled molecular simulation with only as input the macrosized experimental wetting angle for a given temperature.     

On the evaluation of edgeless diode detectors for patient-specific QA in high-dose stereotactic radiosurgery

PurposeIn this work, the potential of an innovative “edgeless” silicon diode was evaluated as a response to the still unmet need of a reliable tool for plan dosimetry verification of very high dose, non-coplanar, patient-specific radiosurgery treatments. In order to prove the effectiveness of the proposed technology, we focused on radiosurgical treatments for functional disease like tremor or pain.MethodsThe edgeless diodes response has been validated with respect to clinical practice standard detectors by reproducing the reference dosimetry data adopted for the Treatment Planning System. In order to evaluate the potential for radiosurgery patient-specific treatment plan verification, the anthropomorphic phantom Alderson RANDO has been adopted along with three edgeless sensors, one placed in the centre of the Planning Target Volume, one superiorly and one inferiorly.ResultsThe reference dosimetry data obtained from the edgeless detectors are within 2.6% for output factor, off-axis ratio and well within 2% for tissue phantom ratio when compared to PTW 60,018 diode. The edgeless detectors measure a dose discrepancy of approximately 3.6% from the mean value calculated by the TPS. Larger discrepancies are obtained in very steep gradient dose regions when the sensors are placed outside the PTV.ConclusionsThe angular independent edgeless diode is proposed as an innovative dosimeter for patient quality assurance of brain functional disorders and other radiosurgery treatments. The comparison of the diode measurements with TPS calculations confirms that edgeless diodes are suitable candidates for patient-specific dosimetric verification in very high dose ranges delivered by non-isocentric stereotactic radiosurgery modalities.     

Development of a silicon carbide disruption method enables efficient extraction of proteins from cyanobacterium Synechocystis sp. PCC 6803

The oxygenic photosynthetic prokaryotes cyanobacteria have recently attracted worldwide interest in production of biofuels and bioactive natural compounds. Disruption of cells is a prerequisite for extraction of intracellular compounds. However, cyanobacterial cells are difficult to be disrupted because of the multiple-layered cell walls covered with a mucilaginous sheath. Here, we report a new disruption method for cyanobacteria, where an abrasive material, silicon carbide, is ground with cell pellet in situ. A cell disruption efficiency of 93.3 ± 2.3% was achieved in 6 min, an efficiency comparable to that obtained after 30 min of sonication. The new method yielded crude cell extracts with high concentrations of protein and high activity of the target enzyme, d-lactate dehydrogenase. This method has potential to be used for disruption of cells of photosynthetic microorganisms on a larger scale.     

闽江河口湿地不同植被带土壤全硅的含量及分布特征

硅是湿地系统元素循环所关注的重要内容之一,土壤全硅的分布特征与湿地土壤-植物系统活跃程度密切相关。于2016年1-12月,以闽江河口鳝鱼滩湿地为研究对象,通过野外原位采样及室内实验分析,对短叶茳芏、短叶茳芏与互花米草交错带、互花米草3种植物类型湿地的土壤全硅含量和储量的变化特征进行观测。结果表明：短叶茳芏、短叶茳芏与互花米草交错带、互花米草湿地土壤全硅的年平均含量依次为197.67、201.21、210.33 mg/g,表现为由陆向海方向逐渐增加的趋势;季节上均呈现秋冬高于春夏的趋势;土壤全硅含量和储量均表现为上部土层（0-30cm）高于下部土层（30-60cm）。经统计分析发现,湿地土壤全硅含量与有机质显著负相关（P < 0.05）,与含水率和pH有极显著正相关关系（P < 0.01）。除短叶茳芏湿地外,其余2种湿地土壤全硅含量与有效硅含量显著负相关（P < 0.05）。研究闽江河口湿地不同植被带土壤全硅含量和储量及其分布特征,旨在揭示湿地土壤全硅水平在不同类型湿地植被生长影响下的变化过程,为本研究区的硅素研究补充关键数据。     

Concentration of Disease-Associated Prion Protein with Silicon Dioxide

Reagents that can precipitate the disease-associated prion protein (PrP^Sc) are vital for the development of high sensitivity tests to detect low levels of this disease marker in biological material. Here, a range of minerals are shown to precipitate both ovine cellular prion protein (PrP^C) and ovine scrapie PrP^Sc. The precipitation of prion protein with silicon dioxide is unaffected by PrP^Sc strain or host species and the method can be used to precipitate bovine BSE. This method can reliably concentrate protease-resistant ovine PrP^Sc (PrP^res) derived from 1.69 μg of brain protein from a clinically infected animal diluted into either 50 ml of buffer or 15 ml of plasma. The introduction of a SiO₂ precipitation step into the immunological detection of PrP^res increased detection sensitivity by over 1,500-fold. Minerals such as SiO₂ are readily available, low cost reagents with generic application to the concentration of diseases-associated prion proteins.     

Preparation of polymers containing Fe(0)-coordinated 2,5-diethynylsilole units

UV irradiation of poly(organosilanylene-2,5-diethynylenesiloles) in benzene with an excess of Fe(CO)₅ led to the formation of Fe(CO)₃-coordinated silole units in the polymer backbone. The Fe(CO)₃-coordinated polymers exhibited suppressed π-conjugation, relative to the parent non-coordinated polymers. Hole-transporting properties of poly(organosilanylene-2,5-diethynylenesiloles) were examined by the performance of EL devices containing the polymer layer as the hole-transport and Alq3 layer as the electron-transporting emitter.     

Surface modification via wet chemical etching of single-crystalline silicon for photovoltaic application

The potential of solar cells have not been fully tapped due to the lack of energy conversion efficiency. There are three important mechanisms in producing high efficiency cells to harvest solar energy; reduction of light reflectance, enhancement of light trapping in the cell and increment of light absorption. The current work represent studies conducted in surface modification of single-crystalline silicon solar cells using wet chemical etching techniques. Two etching types are applied; alkaline etching (KOH:IPA:DI) and acidic etching (HF:HNO₃:DI). The alkaline solution resulted in anisotropic profile that leads to the formation of inverted pyramids. While acidic solution formed circular craters along the front surface of silicon wafer. This surface modification will leads to the reduction of light reflectance via texturizing the surface and thereby increases the short circuit current and conversion rate of the solar cells.     

Assessment of cytotoxicity and DNA damage exhibited by siloranes and oxiranes in cultured mammalian cells

The potential reactivity and structural properties of oxiranes (epoxides) are advantageous when considering polymers for medical devices. However, epoxy compounds are widely known to have genotoxic properties. The objective of the study was to evaluate the cytotoxicity and primary DNA damage effects induced by oxiranes and siloranes, silicon containing oxiranes. The siloranes, Ph-Sil, Tet-Sil, and Sil-Mix and the oxiranes Cyracure™ UVR-6105 and 1,3-bis[2-(2-oxiranylmethyl) phenoxy]pentane (OMP-5) were dissolved in organic solvents and dilutions containing less than 0.5% solvent were used in biological assays. The concentration that reduced the viability of 50% (TC₅₀) of L929 cells was measured using the MTT assay and guided the selection of subtoxic doses for evaluation of DNA damage. Ph-Sil was more cytotoxic than OMP-5, Cyracure™ UVR-6105 and Sil-Mix. However, the TC₅₀ value of Tet-Sil could not be determined due to its poor solubility. DNA damage was evaluated in the sister chromatid exchange (SCE) assay with CHO cells, and the alkaline comet assay with L929 cells. In contrast to the siloranes, the oxiranes exhibited significant increases (p > 0.05) in SCE frequencies and DNA migration relative to their solvent controls. Our findings support previous reports that siloranes have low genotoxic potential and can be suitable components for development of biomaterials.     

Silicon in rat liver organelles: Electron probe microanalysis

Summary Electron probe microanalysis of unfixed freeze-substituted rat liver tissue embedded in Spurr's low viscosity epoxy resin demonstrated the occurrence of Si as well as P, S, and Cl in the nucleus, nucleolus, mitochondria, and rough endoplasmic reticulum. Chemical analysis confirmed that the Si in the organelles did not originate from instrumental contaminants. This suggests that Si may be involved in the biochemistry of these subcellular organelles.Supported by Grant GM-08229-12-13 from the National Institutes of Health, USPHS.We are grateful to the Kevex Corporation and Mr. Glenn W. Meyer, Sales Engineer, for the use of the Kevex X-ray spectrometer; we wish to thank as well the Perkin-Elmer Corporation and their Western Branch Manager, Mr. Michael E. Mullen and Senior Microscopist, Mr. Minoru Shinorhara, for use of and assistance with the Hitachi HU 12 A transmission electron microscope. We also wish to acknowledge Mary Louise Chiappino for her technical assistance in preparing the thin sections, the final micrographs and the X-ray photographs, and Darlene Lum for technical assistance in the laboratory.     

Aquaglyceroporins: Generalized metalloid channels

Background

Aquaporins (AQPs), members of a superfamily of transmembrane channel proteins, are ubiquitous in all domains of life. They fall into a number of branches that can be functionally categorized into two major sub-groups: i) orthodox aquaporins, which are water-specific channels, and ii) aquaglyceroporins, which allow the transport of water, non-polar solutes, such as urea or glycerol, the reactive oxygen species hydrogen peroxide, and gases such as ammonia, carbon dioxide and nitric oxide and, as described in this review, metalloids.

Scope of review

This review summarizes the key findings that AQP channels conduct bidirectional movement of metalloids into and out of cells.

Major conclusions

As(OH)₃ and Sb(OH)₃ behave as inorganic molecular mimics of glycerol, a property that allows their passage through AQP channels. Plant AQPs also allow the passage of boron and silicon as their hydroxyacids, boric acid (B(OH)₃) and orthosilicic acid (Si(OH)₄), respectively. Genetic analysis suggests that germanic acid (GeO₂) is also a substrate. While As(III), Sb(III) and Ge(IV) are toxic metalloids, borate (B(III)) and silicate (Si(IV)) are essential elements in higher plants.

General significance

The uptake of environmental metalloids by aquaporins provides an understanding of (i) how toxic elements such as arsenic enter the food chain; (ii) the delivery of arsenic and antimony containing drugs in the treatment of certain forms of leukemia and chemotherapy of diseases caused by pathogenic protozoa; and (iii) the possibility that food plants such as rice could be made safer by genetically modifying them to exclude arsenic while still accumulating boron and silicon. This article is part of a Special Issue entitled Aquaporins.