Contact angle hysteresis in multiphase systems

Contact angle (CA) hysteresis is the difference between the maximum (advancing) and minimum (receding) water CA. Hysteresis is caused by adhesion hysteresis in the solid–water contact area (2D effect) and by pinning of the solid–water–air triple line due to the surface roughness (1D effect). In this work, we show that CA hysteresis is present also in more complex systems, such as an organic liquid (oil) in contact with a solid immersed in water. In order to decouple the 1D and 2D effects, we study CA hysteresis in solid–water–air (droplet), solid–air–water (bubble), solid–water–oil, and solid–water–air–oil systems involving rough and microstructured surfaces. The comparative analysis of these systems allows decoupling the 1D and 2D effects as well as hydrogen bonding and entropic forces (water–air tension) and dispersion forces (oil–air tension).     

Spectrophotometric Determination of Phenols and Cyanides After Distillation from Natural Waters

Abstract

Total phenols were determined by molecular spectrophotometry, after distillation, complexation with 4-aminoantipyrine and extraction into chloroform. Cyanides were also determined spectrophotometrically after distillation from the acidified samples, and complexation in moderate acidic solution with barbituric acid. The dynamic ranges were 0 – 100 μg L^?1 for total phenols and 0 – 30 μg L^?1 for cyanides. The above methods were applied in the analysis of river, lake and stream waters collected from Northern Greece. The seasonal and spatial variation of concentrations was evaluated by two-way ANOVA. Background levels (4 – 12 μg L^?1 for total phenols and 0.3 – 3 μg L^?1 for cyanides), were found in almost all surface waters, with some exceptions.     

Separation and Detection of Arsenic and Selenium Species in Environmental Samples by HPLC-ICP-MS

A method is presented for arsenic speciation analysis of an oyster sample using ion chromatography coupled with an inductively coupled plasma mass spectrometry (ICP-MS) instrument. A strong anion exchange resin was employed with a step gradient elution of 0.1 mM/0.1 M K 2 SO 4 at pH 10.2. Arsenobetaine and dimethylarsinic acid were determined following extraction based on trypsin enzymolysis with 95-100% extraction efficiency. Limits of detection in the range 0.1-0.3 mg kg m 1 of arsenic were obtained for organic arsenic species. No inorganic arsenic was detected. Validation was performed using TORT-2 as a certified reference material. Although high performance liquid chromatography (HPLC) coupled to ICP-MS is an effective method for speciation analysis it is not always necessary to obtain such a detailed picture. A simple liquid chromatographic separation technique based upon mini-column technology is presented. It was developed to obtain a fast, efficient and reliable separation of inorganic from organic, i.e. assumed toxic from non-toxic, arsenic and selenium species suitable for use as an initial screening method for environmental analysis. Two types of strong anion exchange resin were tested. Excellent separation was obtained for both min-column resins and analysis times were within 7 min. Limits of detection obtained for inorganic arsenic, organic arsenic, selenomethionine, Se IV and Se VI were 1.6, 1.8, 66, 32 and 22 µg kg m 1 , respectively.     

Anodic stripping voltammetry of antimony at unmodified carbon electrodes

Antimony is an element of significant environmental concern, yet has been neglected relative to other heavy metals in electroanalysis. As such very little research has been reported on the electroanalytical determination of antimony at unmodified carbon electrodes. In this paper we report the electrochemical determination of Sb(III) in HCl solutions using unmodified carbon substrates, with focus on non-classical carbon materials namely edge plane pyrolytic graphite (EPPG), boron doped diamond (BDD) and screen-printed electrodes (SPE). Using differential pulse anodic stripping voltammetry, EPPG was found to give a considerably greater response towards antimony than other unmodified carbon electrodes, allowing highly linear ranges in nanomolar concentrations and a detection limit of 3.9?nM in 0.25?M HCl. Furthermore, the sensitivity of the response from EPPG was 100 times greater than for glassy carbon (GC). Unmodified GC gave a comparable response to previous results using the bare substrate, and BDD gave an improved, yet still very high limit of detection of 320?nM compared to previous analysis using an iridium oxide modified BDD electrode. SPEs gave a very poor response to antimony, even at high concentrations, observing no linearity from standard additions, as well as a major interference from the ink intrinsic to the working electrode carbon material. Owing to its superior performance relative to other carbon electrodes, the EPPG electrode was subjected to further analytical testing with antimony. The response of the electrode for a 40?nM concentration of Sb(III) was reproducible with a mean peak current of 1.07?µA and variation of 8.4% (n?=?8). The effect of metals copper, bismuth and arsenic were investigated at the electrode, as they are common interferences for stripping analysis of antimony.     

Heptachlorepoxides: theoretical versus experimental study of the embedded samples in the matrixes of organic crystals

The analysis of heptachlorepoxides in gas- and condense phase of embedded in the organic matrixes analyte samples is highlighted. The electrospray ionization, matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS), nuclear magnetic resonance, Raman and CD spectroscopy as well as quantum chemical methods are used. The competitive formation of the variety of epoxides, strongly depending of the reaction conditions. Thus, the products of interaction of matrix-analyte matrixes under the UV–MALDI–MS experiment are comprehensively examinated. Nonetheless, that for heptachlor (HA) is known an epoxide, existing in two isomeric forms, i.e. A and B (exo- and endo-one), the study on the mechanism of the epoxidation of HA, showed formation of new epoxides C–F and an intermediate (I), characterizing with high stability, decreasing in the raw F > A > C > B > I > D > E. The epoxide D appeared enantiomer of the insecticide oxychlodran. The reported results on the pesticides, their metabolites and decomposition reactivity products contributed significantly to the field of analytical chemistry, providing possibility for elaboration of highly selective protocols for assessment of environmental contaminant issues.     

Preparation of Methyl 6‐O‐p‐Nitrobenzoyl‐β‐d‐Glucoside

Methyl 6‐O‐p‐nitrobenzoyl‐β‐d‐glucoside was synthesized by reacting methyl 4,6‐O‐p‐nitrobenzylidine‐β‐d‐glucoside with N‐bromosuccinimide (NBS). First, methyl β‐d‐glucoside was converted into methyl 4,6‐O‐p‐nitrobenzylidine‐β‐d‐glucoside with p‐nitrobenzaldehyde. Later, methyl 4,6‐O‐p‐nitrobenzylidine‐β‐d‐glucoside was opened oxidatively with NBS to give methyl 6‐O‐p‐nitrobenzoyl‐β‐d‐glucoside.     

Identifying ligand binding sites and poses using GPU-accelerated Hamiltonian replica exchange molecular dynamics

We present a method to identify small molecule ligand binding sites and poses within a given protein crystal structure using GPU-accelerated Hamiltonian replica exchange molecular dynamics simulations. The Hamiltonians used vary from the physical end state of protein interacting with the ligand to an unphysical end state where the ligand does not interact with the protein. As replicas explore the space of Hamiltonians interpolating between these states, the ligand can rapidly escape local minima and explore potential binding sites. Geometric restraints keep the ligands from leaving the vicinity of the protein and an alchemical pathway designed to increase phase space overlap between intermediates ensures good mixing. Because of the rigorous statistical mechanical nature of the Hamiltonian exchange framework, we can also extract binding free energy estimates for all putative binding sites. We present results of this methodology applied to the T4 lysozyme L99A model system for three known ligands and one non-binder as a control, using an implicit solvent. We find that our methodology identifies known crystallographic binding sites consistently and accurately for the small number of ligands considered here and gives free energies consistent with experiment. We are also able to analyze the contribution of individual binding sites to the overall binding affinity. Our methodology points to near term potential applications in early-stage structure-guided drug discovery.     

Synthesis and Characterization of the Naturally Occurring Monocyclic γ-Pyrone Glucosides

β-D-Glucosides of pyromeconic acid (3-hydroxy-4-oxo-4H-pyran), maltol (3-hydroxy-2-methyl-4-oxo-4H-pyran) and α-hydroxymaltol (3-hydroxy-2-hydroxymethyl-4-oxo-4H-pyran) were synthesized in one pot by reaction of stoichiometric amounts of acetobromoglucose and preformed hydroxypyrone anion followed by catalytic deacetylation with methanolic KOH. Products were identified and characterized by comparison of mp and molar rotation with literature, and by FAB-MS, negative ferric chloride test, and H-1 and C-13 NMR. All glycosides were levorotatory, beta and gave recognizable pseudo-molecular ions.     

High Charge Delocalization and Conjugation in Oligofuran Molecular Wires

The extent of charge delocalization and of conjugation in oligofurans and oligothiophenes was studied by using mixed valence systems comprising oligofurans and oligothiophenes capped at both ends by ferrocenyl redox units. Using electrochemical, spectral, and computational tools, we find strong charge delocalization in ferrocene‐capped oligofurans which was stronger than in the corresponding oligothiophene systems. Spectroscopic studies suggest that the electronic coupling integral (H_ab) is roughly 30–50 % greater for oligofuran‐bridged systems, indicating better energy matching between ferrocene units and oligofurans. The distance decay constant (damping factor), β, is similar for oligofurans (0.066 A^?1) and oligothiophenes (0.070 A^?1), which suggests a similar extent of delocalization in the bridge, despite the higher HOMO–LUMO gap in oligofurans. Computational studies indicate a slightly larger extent of delocalization in furan‐bridged systems compared with thiophene‐bridged systems, which is consistent with oligofurans being significantly more rigid and less aromatic than oligothiophenes. High charge delocalization in oligofurans, combined with the previously reported strong fluorescence, high mobility, and high rigidity of oligofuran‐based materials makes them attractive candidates for organic electronic applications.