Magnetic property studies of manganese-phosphate complexes

Phosphoric acid forms two distinct coordination compounds with manganese salts in aqueous media, a two-dimensional layered structure, [Mn(HPO4).(H2O)3], 1, under ambient conditions, and a three-dimensional synthetic mineral, [Mn5(mu-OH2)2(HPO4)2(PO4)2(H2O)2], 2, under hydrothermal procedures, at 120 degrees C. In compound 1, the oxygen atom of the doubly deprotonated phosphoric acid interconnects the metal centers to form a layered structure. The neutral hydrophilic layers of 1 are separated by 5.5 A and may potentially intercalate hydrophilic organic guest molecules. The metal centers in 2 are octahedral and bridged by PO4(3-), HPO4(2-), and OH2 groups to form a complex three-dimensional network. XPS analysis on 1 and 2 confirms that manganese exists in the +2 oxidation state. Compound 2 is a poor ion exchanger, but some improvement is observed on partial dehydration. The magnetic properties of both 1 and 2 were studied in detail to examine the amplitude of the magnetic interactions through phosphate ligand bridges. While 1 reveals dominant antiferromagnetic interactions between the spin carriers, a complete investigation of the magnetic properties of 2 revealed its true nature to be a glassy magnet.     

A Zinc Oxide Carbon Nanotube Based Sensor for In Situ Monitoring of Hydrogen Peroxide in Swimming Pools

Zinc oxide nanoparticles were tethered to carbon nanotubes to form an electrochemical sensing composite, which was characterized using transmission electron microscopy, and X‐ray photoelectron and attenuated total reflectance infrared spectroscopies. The sensor′s electrocatalytic response for measuring hydrogen peroxide was investigated using cyclic voltammetry and chronoamperometry in a dynamic, well defined swimming pool environment. A wide, linear response in the concentration range of 0.025–7.0 mM at a potential of ?0.360 V was shown, with rapid response time (<5 s). The sensor had excellent reproducibility, exhibited stability and selectivity, and was able to measure concentrations in a dynamic environment as they varied.     

直接键连原子间的NMR偶合常数的自然杂化轨道研究V.~(13)C-~(13)C和~(13)C-~(31)P核自旋偶合常数~1J_(CC)和~1J_(CP)

在前文工作的基础上，结合ＭＮＤＯ／ＥＨＭＯ分子轨道方法和自然杂化轨道方法，具体计算了ＣＣ键和ＣＰ键的核自旋偶合常数．计算结果表明，１ＪＣＣ和１ＪＣＰ主要由成键原子的轨道杂化作用和键极性这两种结构因素所决定．为从简单价键理论角度解释和计算１ＪＣＣ和１ＪＣＰ值提供了简便直观的方法．     

Sonochemical oxidation of multiwalled carbon nanotubes

Functionalization of carbon nanotubes (CNTs) is important for enhancing deposition of metal nanoparticles in the fabrication of supported catalysts. A facile approach for oxidizing CNTs is presented using a sonochemical method to promote the density of surface functional groups. This was successfully employed in a previous study [J. Phys. Chem. B 2004, 108, 19255] to prepare highly dispersed, high-loading Pt nanoparticles on CNTs as fuel cell catalysts. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, cyclic voltammetry, and settling speeds were used to characterize the degree of surface functionalization and coverage. The sonochemical method effectively functionalized the CNTs. A mixture of -C-O-/-C=O and -COO- was observed along with evidence for weakly bound CO at longer treatment times. The integrated XPS C 1s core level peak area ratios of the oxidized-to-graphitic C oxidation states, as well as the atom % oxygen from the O 1s level, showed an increase in peak intensity (attributed to -CO(x)()) with increased sonication times from 1 to 8 h; the increase in C surface oxidation correlated well with the measured atom %. Most of the CNT surface oxidation occurred between 1 and 2 h. The sonochemically treated CNTs were also studied by cyclic voltammetry and settling experiments, and the results were consistent with the XPS observations.     

具有切向控制的局部四点插值曲线设计方法

Ｎｉｒａ Ｄｙｎ等提出的四点插值法是一种典型的自由曲线离散造型方法，但该方法不能控制插值点的切向。本文利用薄板样很可能 量的极小化原理给出了具有切向控制的四点分插值条件。用户可以方便地交互控制任一插值点的切向，使得四点插值法更为有效和实用。     

Characterizing N-acetylcysteine (NAC) and N-acetylcysteine amide (NACA) binding for lead poisoning treatment

Using antioxidants is an important means of treating lead poisoning. Prior in vivo studies showed marked differences between various chelator antioxidants in their ability to decrease both blood Pb(II) levels and oxidative stress resulting from lead poisoning. The comparative abilities of NAC and NACA to Pb(II) were studied in vitro, for the first time, to examine the role of the -OH/-NH(2) functional group in antioxidant binding behavior. To assay the antioxidant-divalent metal interaction, the antioxidants were probed as solid surfaces, adsorbing Pb(II) onto them. Surface characterization was carried out using X-ray photoelectron spectroscopy (XPS) analysis to quantify Pb(II) in the resulting adducts. XPS of the Pb 4f orbitals showed that more Pb(II) was chemically bound to NACA than NAC. In addition, the antioxidant surfaces probed via point-of-zero charge (PZC) measurements of NAC and NACA were obtained to gain further insight into the Pb-NAC and Pb-NACA binding, showing that Coulombic interactions played a partial role in facilitating complex formation. The data correlated well with solution analysis of metal-ligand complexation. UV-vis spectroscopy was used to probe complexation behavior. NACA was found to have the higher binding affinity as shown by free Pb(II) available in the solution after complexation from HPLC data. Electrospray ionization mass spectrometry (ESI-MS) was applied to delineate the structures of Pb-antioxidant complexes. Experimental results were further supported by density functional theory (DFT) calculations of supermolecular interaction energies (E(inter)) showing a greater interaction of Pb(II) with NACA than NAC.     

Adsorption of trimethylamine on zirconium silicate and polyethylene powder surfaces

Sorptive interactions of volatile organic compounds (VOCs) with indoor surfaces play a major role in inhalation exposure to these species. Using ZrSiO₄ and polyethylene (PE) to model mineral surfaces and carpeting, respectively, the adsorption behavior of gaseous trimethylamine (TMA) was examined under conditions of 80% relative humidity (RH) in N₂ and in the presence of 1000 ppm CO₂ or NH₃. TMA adsorption and desorption behavior were studied using attenuated total reflection infrared (ATR-IR) and X-ray photoelectron (XPS) spectroscopies. Spectral data revealed that TMA adsorbed on both surfaces in a protonated state. Stronger adsorption was observed to occur on ZrSiO₄. XPS scans indicate that the “dry” ZrSiO₄ surface maintains OH groups available for bonding, supporting earlier research showing that partition coefficients increase as RH decreases.     

Graphene Defects in Saccharide Carbon Dots Govern Electrochemical Sensitivity

Galactose (Gal), lactose (Lac), and glucose (Glu) derived carbon dots (CDs) were evaluated for their utility as electrochemical sensing composites using acetaminophen (APAP) as a probe molecule. The goal of this work is to ascertain the role of graphene defects on electrochemical activity. Higher sp²-to-sp³ hybridized carbon ratios (in parentheses) in the CDs correlated with higher sensitivity in the order according to measured Raman I_G/I_D intensities: GluCDs (6.53)<LacCDs (9.30)<GalCDs (10.18). A dynamic measurement in the 0–2.0 mmol dm⁻³ APAP range at pH=7.0 was achieved, suitable for practical APAP toxicity monitoring. Defect density within the GalCDs provided the highest sensitivity.     

Plasma surface modification and characterization of POSS-based nanocomposite polymeric thin films

The effect of a remote oxygen plasma on nanocomposite hybrid polymer thin films of poly[(propylmethacryl-heptaisobutyl-polyhedral oligomeric silsequioxane)-co-(methylmethacrylate)] (POSS-MA) has been examined by advancing contact angle, X-ray photoelectron spectroscopy (XPS), and variable-angle spectroscopic ellipsometry (VASE). Exposure to a 25 W remote oxygen-containing plasma was found to convert the surface of POSS-MA films from hydrophobic to hydrophilic within 20 s. The exposure time needed for this conversion to occur decreased as the O2/N2 ratio in the plasma environment increased, indicating a positive correlation between the hydrophilicity and the presence of oxygen in the plasma. Local bonding information inferred from high-resolution XPS data showed that the isobutyl bonding to the POSS moiety is replaced with oxygen as a result of plasma exposure. Finally, VASE data demonstrates that increasing the weight percent of POSS in the copolymer significantly impedes the oxygen plasma degradation of POSS-MA films. On the basis of these results, a model is presented in which the oxygen plasma removes isobutyl groups from the POSS cages and leaves a SiO2-like surface that is correspondingly more hydrophilic than the surface of the untreated samples and is more resistant to oxidation by the plasma. The ability to modify surfaces in this manner may impact the utility of this material for biomedical applications such as microfluidic devices in which the ability to control surface chemistry is critical.     

Porcine dentin sialoprotein glycosylation and glycosaminoglycan attachments

Background  

Dentin sialophosphoprotein (Dspp) is a multidomain, secreted protein that is critical for the formation of tooth dentin. Mutations in DSPP cause inherited dentin defects categorized as dentin dysplasia type II and dentinogenesis imperfecta type II and type III. Dentin sialoprotein (Dsp), the N-terminal domain of dentin sialophosphoprotein (Dspp), is a highly glycosylated proteoglycan, but little is known about the number, character, and attachment sites of its carbohydrate moieties.