Making benzotrithiophene a stronger electron donor

A new member of the benzotrithiophene family, benzo[2,1-b:-3,4-b':5,6-c″]trithiophene (3a), and its alkyl substituted derivatives (3b-e) were synthesized and characterized. Their photophyscial, electrochemical, crystallographic, and self-assembly properties were described. Thin film structures varied widely with the exact nature of the alkyl substitution pattern, with decreasing self-assembly propensity with increasing alkyl chain length. The high HOMO levels and the coplanarity of these molecules show their potential as organic semiconductors and as donor components in donor-acceptor copolymers.     

Making sense of a pedagogic text

Foundations of Chemistry -     

Making progress in a practical discipline

The proposals to redefine four of the base units of the SI led to an intense exchange of views in the pages of ACQUAL. It should be kept in mind that metrology is a practical discipline.     

Making a new turn in matrix metalloprotease inhibition

The paradigm for matrix metalloprotease inhibition combines active site tailoring and catalytic zinc ligation. But, selectivity has been difficult. Now, Engel et al. present novel compounds, completely selective for MMP-13, with a unique binding mode.     

Determination of priority pollutant phenols by isocratic HPLC

Summary An isocratic high performance liquid chromatographic method, able to determine ng/l of Priority Pollutant Phenols (PPP) in water, is proposed. A Nucleosil 5 C 18 column and an 30 mM ammonium acetate (pH 5.0): acetonitrile: methanol (56:34:10) eluent are used. Linearity ranges from 5–50 ppm of phenols; variation coefficients are about 4% (n=7) at the 30 ppm level with a 5μl injection. Dual UV detection helps to identify different phenols. The use of an anionic exchanger column and of methanol: hydrochloric acid (9:1) as eluent allows selective preconcentration of priority phenols and recoveries in the range 79–105%.     

PVA固定化脲酶电极的制作及电极特性的研究

利用PVA低温下的物理交联固定酶,制成酶电极并在不同尿素浓度、pH值、温度等条件下进一步研究这种酶电极的响应特性.     

Simultaneous analysis of all five organic priority pollutant fractions

Acrolein, acrylonitrile, volatile organics, base/neutral extractables, acid extractables, and pesticide fraction organics are analyzed in a single chromatographic run. This is accomplished by injecting the extractable organics, then applying a cryogenic focus to the front of the column, and desorbing the volatile components. The column utilized for this procedure is a fused silica open tubular (FSOT) column coated with the liquid phase SE-54. Minimum detection limits of this procedure by electron impact GC/MS are shown to be? 1 μg/liter in tests conducted on actual water samples.     

Fast-GC/HRMS to quantify the EU priority PAH

For the analysis of the 15 polycyclic aromatic hydrocarbons (PAH) classified as priority from the Scientific Committee on Food (SCF) and benzo[c]fluorene (BcL) assessed to be relevant by the Joint FAO/WHO Experts Committee on Food Additives (JECFA) in food, a sensitive analytical method is necessary. In the past, many methods were established for only the analysis of the 16 priority PAH recommended by the US Environmental Protection Agency (16 EPA-PAH) but not for the 15 SCF-PAH and BcL. Therefore, at the Max-Rubner-Institut, Federal Research Institute of Nutrition and Food in Kulmbach, Germany, an analytical method with a runtime of 72 min was developed. To shorten this runtime without a loss of separation, a Fast-GC/high resolution MS (HRMS) method with a runtime of only 25 min using a TR-50ms column (10 m x 0.1 mm x 0.1 microm) was created. The repeatability (n = 3) of spiked PAH concentrations in test-matrix tea ranged from 0.1 to 11%. The analytical parameters LOD (0.01-0.02 microg/kg) and LOQ (0.03-0.06 microg/kg) also in the test-matrix tea were determined. A good linearity for all PAH (R(2) >0.99) and averaged recoveries from 75 to 117% in the concentration range of 1-20 microg/kg were achieved.     

Retention of eleven priority phenols using micellar electrokinetic chromatography

The use of micellar electrokinetic chromatography (MECC) for the separation of eleven substituted phenols listed by the United States Environmental Protection Agency as priority pollutants was investigated. Solutions of potassium and sodium dodecyl sulphate in phosphate-borate buffer of pH 6.6, 7.0 and 7.5 were used as the electrophoretic media. Satisfactory separation of the eleven phenols was obtained using a 180-microns capillary at 10 kV and pH 6.6 with a solution containing both sodium and potassium dodecyl sulphate. Observations on the retention behaviour of the phenols in MECC were related to their physico-chemical properties.     

Entangled coordination polymers with mixed N- and O-donor organic linkers: a case of module-matching priority

A series of four coordination polymers showing entangled architectures based on cobalt and mixed N-donor/O-donor ligands, namely [Co(4,4'-BPIPA)(TP)]·2DMF (1), [Co(4,4'-BPIPA)(2,6-NDC)(DMF)]·DMF (2), [Co(4,4'-BPIPA)(2,6-NDC)]·2DMF (3) and [Co(4,4'-BPIPA)(4,4'-BPDC)]·2DMF (4) (4,4'-BPIPA = N,N'-bis-4-pyridinyl-isophthalamide, TP = terephthalic acid, 2,6-NDC = 2,6-naphthalenedicarboxylic acid, 4,4'-BPDC = 4,4'-biphenyldicarboxylic acid), have been synthesized under solvothermal conditions. Complex 1, containing 4,4'-BPIPA and relatively short dicarboxylate ligands (TP), exhibits two-dimensional (2D) two-fold interpenetration of double wavy 4(4)-sql nets. Complex 2 displays interesting 2D→3D parallel polycatenation of undulated 2D 4(4)-sql layers built by 4,4'-BPIPA and moderate dicarboxylate ligands (2,6-NDC). Complexes 3 and 4, although constructed of dicarboxylate ligands with different lengths (moderate 2,6-NDC and long 4,4'-BPDC), possess similar 3-fold interpenetration of identical self-catenated single nets with 6(5)·8-mok topologies. It has been found that the length of the dicarboxylate ligands plays a key role of module-matching in the self-assemblies of complexes 1-4. Moreover, the effect of the conformations of 4,4'-BPIPA, which can be controlled by tuning reaction temperatures, is also discussed.     

An optimized gas chromatographic determination of priority pollutant phenols

Priority pollutant phenols are determined by gas chromatography on an SE-30 WCOT column using hydrogen carrier and flame ionization detection with dual internal standards. Linear responses over ranges ca. 12–125 ng per component are achieved and detection limits at or below 1 ng are obtained. Carrier flow and temperature program are optimized to maintain baseline resolution while affording an analysis time of less than 15 minutes.     

Improving on Nature: Making a Cyclic Heptapeptide Orally Bioavailable

The use of peptides in medicine is limited by low membrane permeability, metabolic instability, high clearance, and negligible oral bioavailability. The prediction of oral bioavailability of drugs relies on physicochemical properties that favor passive permeability and oxidative metabolic stability, but these may not be useful for peptides. Here we investigate effects of heterocyclic constraints, intramolecular hydrogen bonds, and side chains on the oral bioavailability of cyclic heptapeptides. NMR‐derived structures, amide H–D exchange rates, and temperature‐dependent chemical shifts showed that the combination of rigidification, stronger hydrogen bonds, and solvent shielding by branched side chains enhances the oral bioavailability of cyclic heptapeptides in rats without the need for N‐methylation.     

Trace priority pollutant phenols enrichment from water by ion chromatography

Summary The efficiency of ion chromatography columns packed with styrene-divinylbenzene copolymer containing quaternary ammonium groups to preconcentrate phenols at g l^–1 levels has been established. Retention is carried out in acidic medium based on non-polar interactions between the column and phenols. Pure acetonitrile was used for one step elution. Enrichment factors of at least 100 times are achieved. Regeneration of the column can easily be accomplished with a mixture of 60 mM nitric acid: methanol (199). Recoveries from a river water sample for nine priority pollutant phenols were in the range 92–105%. Other retained organic substances do not disturb liquid chromatographic determination of the phenols studied.     

Multivariate optimization of a GC-MS method for determination of sixteen priority polycyclic aromatic hydrocarbons in environmental samples

This paper describes the development and optimization, by using multivariate analysis, of a GC-MS-SIM method for evaluation of the 16 polyaromatic hydrocarbons considered as priority pollutants in atmospheric particulate material by the US EPA. In order to assure an adequate separation in the shortest analysis time, a multivariate design was used to set the conditions of the oven temperature program. The optimization process was carried out using factorial fractional design and Box-Behnken design. The following factors were evaluated: initial temperature, temperature rate #1, intermediary temperature, temperature rate #2, and final temperature. The optimized conditions were set at: 70 degrees C (2 min) --> 200 degrees C (30 degrees C/min, 5 min) --> 300 degrees C (5 degrees C/min, 1.67 min). Moreover, we have also optimized the injector temperature as 310 degrees C and sampling time as 0.8 min. The total analysis time was 33 min. Validation of GC-MS-SIM yielded satisfactory results for repetitivity of the detector response and retention times, and linearity of calibration curves. LOD were established as 0.13-0.34 ng/mL (peak area) and 0.18-0.72 ng/mL (peak height). The method has been shown to be appropriate for the analysis of samples of atmospheric particulate material and/or other environmental matrices.     

Potentiometric transducer based biomimetic sensors for priority envirotoxic markers--an overview

Most of the potentiometric sensing electrodes offer detection limits of the order of approximately 1 micromol L(-1) rarely stretching down to 0.1 micromol L(-1). Recent advances have made it possible to bring these levels down to 0.01-10 nmol L(-1) for some inorganic ions. Most of these electrodes (barring a few) have come up to expectations in terms of selectivity in spite of significant strides made in the design and synthesis of novel chemical receptors. Imprinted polymers or plastic antibodies which rely on lock and key mechanism can, in principle, selectively rebind and sense a particular analyte in a host of other analogous species of similar size, shape and geometry. Thus, the integration of imprinted polymers with potentiometric transducers has immense potentialities in the fabrication of commercial sensing devices. This review gives an overview of research efforts made so far in this direction, critically discusses the virtues and vices and presents the futuristic scenario on imprinted polymer based potentiometric sensors.     

Preconcentration and determination of priority pollutant phenols in waters at trace levels using a polymeric solid-phase extraction cartridge

A method to preconcentrate and analyse the EPA priority pollutant phenols from water samples is evaluated. Spe-ed Advanta cartridges, containing 100mg of a polymeric matrix modified with polar groups, are used in the extraction and enrichment step. Several parameters are studied in order to find the best experimental conditions to perform a solid-phase extraction process. Sample flow rate and pH appear as variables that could significantly affect the recoveries obtained. Water samples need a pH adjustment to values lower than 3 units and must be percolated through the cartridges with flow rates over 5 mL min(-1). The highest recoveries and preconcentrations are obtained using acetonitrile as the elution solvent. Sample volumes from 100 mL to 1 L with concentrations ranging from 50 to 0.5 microg L(-1) are analysed with quantitative recoveries and similar efficiencies being achieved. After establishing the best conditions, we applied the method to the analysis of spiked natural waters.