Constrained polymer layers to reduce noise: reality or fiction?—An experimental inquiry into their effectiveness

The frequency and temperature dependent noise radiation properties of constrained polymer layered oil pans are examined through mobility and intensity measurements. Four metal/polymer/metal sandwich composites of varied thermo-plastic elastomer systems of polystyrene–polybutadiene–polystyrene triblock copolymers are investigated within a wide frequency range covering 1000–5000 Hz, and over a wide temperature range covering 20–100 °C, with results compared to those of an ordinary steel oil pan. The mobility and intensity are found to be strongly frequency and temperature dependent, displaying a substantial mobility reduction as compared to that of the ordinary pan, while using the constrained layer damping configurations at their maximum loss factor temperatures. However, the reduction of noise radiation is smaller than that of the mobility at those temperatures, mainly due to the increased radiation efficiency while adding damping materials.     

Synthesis, characterization, and complexation of tetraarylborates with aromatic cations and their use in chemical sensors

Five aromatic borate anions, namely tetrakis(4-phenoxyphenyl)borate (1), tetrakis(biphenyl)borate (2), tetrakis(2-naphthyl)borate (3), tetrakis(4-phenylphenol)borate (4), and tetrakis(4-phenoxy)borate (5), have been prepared and tested as ion-recognition sites in chemical sensors for certain aromatic cations and metal ions. To gain further insight into the complexation of the cations, some complexes have been prepared and structurally characterized. The complexation behavior of 1 and 2 towards N-methylpyridinium (6), 1-ethyl-4-(methoxycarbonyl)pyridinium (7), tropylium (8), imidazolium (9), and 1-methylimidazolium (10) cations has been studied, and the stability constants of the complexes of 1 with cations 6 and 8 have been measured to compare them with the values for the previously studied complexes of tetraphenylborate. The structures of the borate anions and their complexes have been characterized by NMR and mass spectrometric methods. X-ray crystal structures have been determined for potassium tetrakis(4-phenoxyphenyl)borate (K(+)1), N-methylpyridinium tetrakis(4-phenoxyphenyl)borate (61), 1-ethyl-4-(methoxycarbonyl)pyridinium tetrakis(4-phenoxyphenyl)borate (71), tropylium tetrakis(4-phenoxyphenyl)borate (81), and imidazolium tetrakis(biphenyl)borate (92). The results show that borate derivatives are potential candidates for a completely new family of charged carriers for use in cation-selective electrodes.     

Stereoelectronic effects in ring-chain tautomerism of 1,3-diarylnaphth[1,2-e][1,3]oxazines and 3-alkyl-1-arylnaphth[1,2-e][1,3]oxazines

The disubstitution effects of X and Y in 1-(Y-phenyl)-3-(X-phenyl)-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines on the ring-chain tautomerism, the delocalization of the nitrogen lone pair (anomeric effect), and the (13)C NMR chemical shifts were analyzed by using multiple linear regression analysis. Study of the three-component equilibrium B<==>A<==>C revealed that the chain<==>trans (A<==>B) equilibrium constants are significantly influenced by the inductive effect (sigma(F)) of substituent Y on the 1-phenyl ring. In contrast, no significant substituent dependence on Y was observed for the chain<==>cis (A<==>C) equilibrium. There was an analogous dependence for the epimerization (C<==>B) constants of 1-(Y-phenyl)-3-alkyl-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines. With these model compounds, significant overlapping energies of the nitrogen lone pair was observed by NBO analysis in the trans forms B (to sigma*(C1-C1'), sigma*(C1-C10b), and sigma*(C3-O4)) and in the cis forms C (to sigma*(C1-H), sigma*(C1-C10b), and sigma*(C3-O4)). The effects of disubstitution revealed some characteristic differences between the cis and trans isomers. However, the results do not suggest that the anomeric effect predominates in the preponderance of the trans over the cis isomer. When the (13)C chemical shift changes induced by substituents X and Y (SCS) were subjected to multiple linear regression analysis, negative rho(F)(Y) and rho(F)(X) values were observed at C-1 and C-3 for both the cis and trans isomers. In contrast, the positive rho(R)(Y) values at C-1 and the negative rho(R)(X) values at C-3 observed indicated the contribution of resonance structures f (rho(R) > 0) and g (rho(R) < 0), respectively. The classical double bond-no-bond resonance structures proved useful in explaining the substituent sensitivities of the donation energies and the behavior of the SCS values.     

Platinum-Group Element Distribution in Some Ore Deposits: Results of EPMA and Micro-PIXE Analyses

The distribution of platinum-group elements (PGE) in the Main Sulfide Zone of the Great Dyke of Zimbabwe, in the arsenide ores of Vammala and Kylmäkoski mines in Finland, and in the chromite-Ni arsenide ores from the Ronda and Beni Bousera massifs (Spain and Morocco) has been studied by means of different optical and microanalytical techniques. The results show a bimodal distribution of PGE in the ores from the Great Dyke and the Vammala and Kylmäkoski mines where Pd, Pt and, to lesser extent, Rh occur both as discrete platinum-group minerals and in solid solution in sulfides, arsenides and sulfarsenides. In the ores from Ronda and Beni Bousera, platinum-group elements occur only in solid solution in arsenides and sulfarsenides.Trace electron probe (EPMA) and micro-PIXE analyses of Pd in sulfides, arsenides and sulfarsenides produce comparable results at concentration levels well above their limit of detection (LOD). These are 27–29ppm by EMPA and 2.5–7ppm by micro-PIXE. Whereas trace EPMA on arsenides and sulfarsenides measure Pt concentrations above 33–35ppm, the proximity of the Pt L lines and the As K line severely degrade de detection limit for Pt in micro-PIXE analyses, increasing the LOD up to 440ppm. The rest of PGE were randomly detected by both methods at concentrations close to their LOD.     

Analysis of PAH compounds in soil with on-line coupled pressurised hot water extraction–microporous membrane liquid–liquid extraction–gas chromatography

Pressurised hot water extraction (PHWE) was coupled on-line with microporous membrane liquid-liquid extraction (MMLLE) and gas chromatography (GC) in the analysis of polycyclic aromatic hydrocarbon (PAH) compounds in soil. The MMLLE serves as a trapping device after the PHWE. Water from PHWE is directed to the donor side of the membrane unit and the analytes are extracted to the acceptor solution on the other side of the membrane. The role of MMLLE is to clean and concentrate the extract, which is then transferred on-line to the GC via a sample loop and an on-column interface using partially concurrent solvent evaporation. Separate optimisation of MMLLE and simulations of the PHWE-MMLLE connection were carried out before the actual on-line coupling. After optimisation of the whole on-line system, the efficiencies of the PHWE-MMLLE-GC and PHWE-solid-phase trap extractions were compared. The PHWE-MMLLE-GC method allowed on-line analysis of soil samples. The method was linear, with limits of detection in the range 0.05-0.13 ng and limits of quantification 0.65-1.66 microg g(-1). Comparison of the results with those obtained by other techniques confirmed the good performance.     

Analysis of polycyclic aromatic hydrocarbons in soil and sediment with on-line coupled pressurised hot water extraction,hollow fibre microporous membrane liquid-liquid extraction and gas chromatography

Pressurised hot water extraction (PHWE) was coupled on-line via hollow fibre microporous membrane liquid-liquid extraction (HF-MMLLE) to gas chromatography (GC) and applied in the analysis of polycyclic aromatic hydrocarbons (PAHs) in soil and sediment. In this combination, the MMLLE unit serves as a trapping device for the extracted compounds. Simultaneously it cleans and concentrates the extract, which is then transferred on-line to the GC. No extra clean-up steps are required between the trapping and the transfer to GC. The on-line system gives excellent sensitivity while allowing small sample size. The method was linear, with limits of detection in the range 50-890 pg and limits of quantification 0.11-1.22 microg g(-1). The concentration enrichment factors obtained with the method ranged from 9 to 55. Comparison of the results with those obtained by other techniques confirmed the good performance.     

Effect of extraction vessel geometry and flow homogeneity on recoveries of polycyclic aromatic hydrocarbons in pressurised hot water extraction

Extraction vessels of different length, internal diameter and volume were tested to evaluate the effect of vessel geometry on the recovery of polycyclic aromatic hydrocarbons (PAHs) from certified sediment by pressurised hot water extraction (PHWE). Pressurised hot water extractions were performed at 300 °C with both liquid water (pressure 250 kg cm^–2) and steam (pressure 50 kg cm^–2). In addition, the effects on the recoveries of sediment packing and water flow direction were examined in two vessels. The geometry of the vessel, the packing of the sediment and the flow direction of the water had only minor effect on the recoveries.     

Modification of glass capillary gas chromatographic columns by alkylation of the glass surface with pentafluorobenzyl bromide

Summary Glass surface alkylation with pentafluorobenzyl (PFB) bromide yields glass capillary gas chromatographic columns with modified retention characteristics. Glass-alkylated OV-225 columns have been tested in the analysis of PFB fluoroacetate, and the substantial increase in retention time of this highly volatile compound was found to improve the precision of analysis. PFB-alkylated columns should prove generally useful in gas chromatographic analysis of small relative molecular mass compounds.     

Sterically and guest-controlled self-assembly of calix[4]arene derivatives

In solvents such as chloroform or benzene, tetraurea calix[4]arenes 1 form dimeric capsules in which one solvent molecule is usually included as guest. To explore the structural requirements for the formation of such hydrogen-bonded dimers we replaced one p-tolylurea residue by a simple acetamide function. The resulting calix[4]arene 2 a, substituted at its wide rim with one acetamide and three p-tolylurea functions, assumes a C(1)-symmetrical conformation in apolar solvents as shown by (1)H NMR, which is not compatible with the usual capsule. In the crystalline state, four molecules of 2 a, adopting a pinched cone conformation, assemble into a quasi S(4)-symmetrical tetramer stabilized by a cyclic array of 24 NH.O==C hydrogen bonds and four NH.pi interactions. Four acetamide groups are hydrogen-bonded to each other and pack tightly in the center of the assembly. All polar residues are buried inside the tetramer, the surface of which is lipophilic. Extensive NMR studies revealed similar structures in apolar solvents such as [D]chloroform or [D(6)]benzene for calixacetamides 2 a-c. The formation of these tetramers in solution is critically dependent on the size of the amide fragment, so that propionamide 2 d, butyramide 2 e, and p-tolylamide 2 f form only ill-defined aggregates. This is caused by steric crowding inside the tetrameric assembly. The tetramers persist during molecular dynamics simulations, and the optimized average structure of the MD run is similar to that found in the crystalline state. Theoretical studies revealed that cooperation of hydrogen bonds with multiple NH.pi, C--H.pi, and pi.pi attractions make the tetramer more stable than the capsular dimer with the solvent as guest. In the presence of tetraethylammonium salts, however, compounds 2 a-e form dimeric capsular assemblies, each incorporating a single ammonium cation. Only one of two possible regioisomeric dimers is formed, in which both acetamide groups are surrounded by two urea residues. These examples give striking evidence of how self-assembly in solution can be strongly dependent on subtle structural factors and of how the formation of dimeric capsules can be induced by the presence of an appropriate guest.     

Bis(6‐thioxo‐1,6‐dihydro­purinium) tetra­chloro­zincate(II)

The title salt, (C₅H₅N₄S)₂[ZnCl₄], consists of two 6‐thioxo‐1,6‐dihydro­purinium (6mpH₂⁺) cations (A and B) and a tetra­chloro­zincate anion, which are held together by N—H⋯Cl and C—H⋯Cl inter­actions. There is an anion–π inter­action between one Cl atom of the [ZnCl₄]⁻ anion and the pyrimidine ring of the 6mpH₂⁺(B) cation. Inter­molecular π–π stacking inter­actions allow 6mpH₂⁺(A) cations to form anti­parallel pairs. One inter­esting structural feature is the double N—H⋯N inter­molecular hydrogen bonds between two 6mpH₂⁺(A) cations. This kind of inter­action, mimicking that of natural nucleobases, can be very valuable in designing new therapeutic purine derivatives.