Study of an organically modified clay: selective adsorption of heavy metal ions and voltammetric determination of mercury(II)

In this work, a hydrophilic clay, Na-montmorillonite from Wyoming, USA, was rendered organophilic by exchanging the inorganic interlayer cations for hexadecyltrimethylammonium ions (HDTA), with the formulae of [(CH₃)₃N(C₁₆H₃₃)]⁺ ion. Based on fact that organo-clay has high affinities for non-ionic organic molecules, 1,3,4-thiadiazole-2,5-dithiol was loaded on the HDTA-montmorillonite surface, resulting in the 1,3,4-thiadiazole-2,5-dithiol-HDTA-montmorillonite complex (TDD-organo-clay).The following properties of TDD-organo-clay are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II).The main point of this paper is the construction of a selective sensor, a carbon paste electrode modified with TDD-organo-clay, its properties and its application to the determination of mercury(II) ions, as this element belongs to the most toxic metals. The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination.     

Evaluation of surface sediment contamination by polycyclic aromatic hydrocarbons in colony Z3—(Patos Lagoon, Brazil)

This paper describes the extraction and analysis of Polyaromatic Hydrocarbons (PAHs) in five points of the Patos Lagoon Estuary. These points were in the area named “colony Z3”, which is a craft fishermen community in Pelotas City (southern Brazil). Samples were collected in July of 2007, and the concentrations of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography coupled to a mass spectrometry detector (GC/MS). The PAH concentrations ranged from 4.7 to 112.5 µg kg^− 1 dry weight. Sediment samples with the highest PAH concentrations appeared at point 2, which is a pier. The correlation between the total organic material (TOM) and the total PAH concentration suggests that TOM plays an important role in controlling the PAH levels in sediments. According to the observed ratios of individual PAHs, the contamination in the studied areas originated both from high-temperature pyrolytic processes and petrogenic sources. The levels of PAHs at the studied sites in the Z3 colony (Patos Lagoon) were low enough that they should not exert adverse biological effects.     

Production of Lactic Acid from Sucrose: Strain Selection, Fermentation, and Kinetic Modeling

Lactic acid is an important product arising from the anaerobic fermentation of sugars. It is used in the pharmaceutical, cosmetic, chemical, and food industries as well as for biodegradable polymer and green solvent production. In this work, several bacterial strains were isolated from industrial ethanol fermentation, and the most efficient strain for lactic acid production was selected. The fermentation was conducted in a batch system under anaerobic conditions for 50 h at a temperature of 34 °C, a pH value of 5.0, and an initial sucrose concentration of 12 g/L using diluted sugarcane molasses. Throughout the process, pulses of molasses were added in order to avoid the cell growth inhibition due to high sugar concentration as well as increased lactic acid concentrations. At the end of the fermentation, about 90% of sucrose was consumed to produce lactic acid and cells. A kinetic model has been developed to simulate the batch lactic acid fermentation results. The data obtained from the fermentation were used for determining the kinetic parameters of the model. The developed model for lactic acid production, growth cell, and sugar consumption simulates the experimental data well.     

Lower Bounds for Measurable Chromatic Numbers

The Lovász theta function provides a lower bound for the chromatic number of finite graphs based on the solution of a semidefinite program. In this paper we generalize it so that it gives a lower bound for the measurable chromatic number of distance graphs on compact metric spaces. In particular we consider distance graphs on the unit sphere. There we transform the original infinite semidefinite program into an infinite linear program which then turns out to be an extremal question about Jacobi polynomials which we solve explicitly in the limit. As an application we derive new lower bounds for the measurable chromatic number of the Euclidean space in dimensions 10, . . . , 24 and we give a new proof that it grows exponentially with the dimension.     

Determination of the chemical oxygen demand (COD) using a copper electrode: a clean alternative method

A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater. The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l⁻¹ COD with detection limit of 20.3 mg l⁻¹ COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate) COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end products do not contain toxic metals.     

A kinetic study of the thermal decomposition of mesoionic compounds within scope of its application in nonlinear optical devices

The mesoionic compounds are pentagonal heterocyclic betaines with their potential use mainly in the pharmacology field due to the diversity of their biological activities. Their exceptional electric properties lead the compounds to be investigated in the field such as the nonlinear optical devices. In this study, five mesoionic compounds of the 1,3-thiazole-5-thiolate system had been synthesized from amino acids derived from glycine through 1,3-dipolar cycloaddition/cycloreversion reaction. The compounds were characterized by the use of infrared spectrometry, thermogravimetry and differential scanning calorimetry techniques. Thermal stability of each structure was determined and characterized by the kinetic study of the thermal decomposition by non-isothermal thermogravimetry. The DSC curves for MI-1, MI-2, MI-3, MI-4, and MI-5 demonstrated their fusion and subsequent decomposition with the exception of MI-3, which presented only decomposition stages. The kinetic models that better described the thermal decomposition mechanism of the mesoionic compounds achieved by the non-isothermal methods were R1, R2 and R3 (based on the geometric models).     

Synthesis of Unprecedented Scaffold Diversity

Building a better library : The synthesis of a library of natural‐product‐like small molecules with unprecedented scaffold diversity has been reported (see scheme; Ns=nosylate). The library represents a significant advancement in the capability of synthetic chemists to generate structurally diverse and complex small molecules in a rapid manner.

     

Thermo-oxidative stability and cold flow properties of babassu biodiesel by PDSC and TMDSC techniques

The babassu (Orbignya Phalerata Mart.) biodiesel has lauric esters as main constituents, resulting in high oxidative stability and low cloud and freezing points. In order to reduce these side effects, the saturated ethyl esters content was reduced by means of winterization process. The TMDSC and PDSC techniques were used to verify the thermal and oxidative stabilities of the ethyl babassu biodiesel. During the heating stage, the winterized solid phase of ethyl esters presented an endothermic transition associated to the solidification process. This behavior was not observed for the liquid winterized FAEE, confirming the efficiency of the winterization process.     

Influence of Intermolecular Vibrations on the Electronic Coupling in Organic Semiconductors: The Case of Anthracene and Perfluoropentacene

We have performed classical molecular dynamics simulations and quantum‐chemical calculations on molecular crystals of anthracene and perfluoropentacene. Our goal is to characterize the amplitudes of the room‐temperature molecular displacements and the corresponding thermal fluctuations in electronic transfer integrals, which constitute a key parameter for charge transport in organic semiconductors. Our calculations show that the thermal fluctuations lead to Gaussian‐like distributions of the transfer integrals centered around the values obtained for the equilibrium crystal geometry. The calculated distributions have been plugged into Monte‐Carlo simulations of hopping transport, which show that lattice vibrations impact charge transport properties to various degrees depending on the actual crystal structure.