A review of legislation on industrial noise

This paper commences by reviewing the 1961 Factories Act, which placed a duty on the employer to provide a safe place of work. This duty is reiterated in the 1974 Health and Safety at Work Bill (given the Royal Assent on 31 July 1974 and now an Act), and the Secretary of State for Employment is given power to make regulations which will make perfectly clear what the liability of the employer is. Legal requirements concerning the design and manufacture of articles for use at work are also made in the new Bill. They must be designed so as to be safe and without risk to health. Furthermore, it is the duty of the manufacturer to carry out any necessary research with a view to the discovery, and the elimination or minimisation, of any risks to health or safety which the article may afford.     

Systematic studies of early actinide complexes: uranium(IV) fluoroketimides

The reaction of (C5Me5)2U(CH3)2 with 2 equiv of N[triple bond]C-ArF gives the fluorinated uranium(IV) bis(ketimide) complexes (C5Me5)2U[-N=C(CH3)(ArF)]2 [where ArF=2-F-C6H4 (4), 3-F-C6H4 (5), 4-F-C6H4 (6), 2,6-F2-C6H3 (7), 3,5-F2-C6H3 (8), 2,4,6-F3-C6H2 (9), 3,4,5-F3-C6H2 (10), and C6F5 (11)]. These have been characterized by single-crystal X-ray diffraction, 1H and 19F NMR, cyclic voltammetry, UV-visible-near-IR absorption spectroscopy, and variable-temperature magnetic susceptibility. Density functional theory (DFT) results are reported for complexes 6 and 11 for comparison with experimental data. The most significant structural perturbation imparted by the F substitution in these complexes is a rotation of the fluorinated aryl (ArF) group out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 7, 9, and 11 when the ArF group possesses two o-fluorine atoms. Excellent agreement is obtained between the DFT-calculated and experimental crystal structures for 11, which displays the distortion, as well as for 6, which does not. In 7, 9, and 11, the out-of-plane rotation results in large angles (phi=53.7-89.4 degrees) between the planes formed by ketimide atoms N=C(CMe)(Cipso) and the ketimide aryl groups. Complexes 6 and 10 do not contain o-fluorine atoms and display interplanar angles in the range of phi=7-26.8 degrees. Complex 4 with a single o-fluorine substituent has intermediate values of phi=20.4 and 49.5 degrees. The distortions in 7, 9, and 11 result from an unfavorable steric interaction between one of the two o-fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. All complexes exhibit UV/UIV and UIV/UIII redox couples, although the distortion in 7, 9, and 11 appears to be a factor in rendering the UIV/UIII couple irreversible. The potential separation between these couples remains constant at 2.15+/-0.03 V. The electronic spectra are dominated by unusually intense f-f transitions in the near-IR that retain nearly identical band energies but vary in intensity as a function of the fluorinated ketimide ligand, and visible and near-UV bands assigned to metal (5f)-to-ligand (pi*) charge-transfer and interconfiguration (5f2-->5f16d1) transitions, respectively. Variable-temperature magnetic susceptibility data for these complexes indicate a temperature-independent paramagnetism (TIP) below approximately 50 K that results from admixing of low-lying crystal-field excited states derived from the symmetry-split 3H4 5f2 manifold into the ground state. The magnitude of the TIP is smaller for the complexes possessing two o-fluorine atoms (7, 9, and 11), indicating that the energy separation between ground and TIP-admixed excited states is larger as a consequence of the greater basicity of these ligands.     

Shapes of sulfur, oxygen, and nitrogen mustards

Thorough conformational analyses have been performed on representative sulfur, oxygen, and nitrogen mustards. A total of 23, 18, and 38 unique conformers have been located for SM, OM, and NM, respectively, at the MP2/aug-cc-pVDZ level of theory. Despite the fact that these molecules differ only in the identity of the central heteroatom, comparison of their low energy conformations reveals that the shapes they adopt are distinctive to each molecule. Potential energy surfaces for CH(2)-X (X = S, O, and N-CH(3)) and CH(2)-CH(2) bond rotations are presented and, where possible, compared with dihedral angle distributions observed in crystal structure data. These results were used to benchmark and improve the performance of the MM3 and MMFF94 force fields.     

Stepwise Encapsulation of Sulfate Ions by Ferrocenyl‐Functionalized Tripodal Hexaurea Receptors

Three ferrocenyl‐functionalized tripodal hexaurea anion receptors with ortho‐ ( L² ), meta‐ ( L³ ), and para‐phenylene ( L⁴ ) bridges, which showed strong binding affinities toward sulfate ions, have been designed and synthesized. In particular, meta‐phenylene‐bridged ligand L³ , owing to its trigonal bipyramidal structure, can encapsulate two SO₄^2? ions in its “inner” and “outer” tripodal clefts, respectively, as supported by their clearly distinct NMR resonances and by molecular modeling. The sulfate complex of ortho‐ligand L² , (TBA)₂[SO₄? L² ] ? 2 H₂O ( 1 ), displays a caged tetrahedral structure with an encapsulated sulfate ion that is hydrogen bonded by the six urea groups of ligand L² . CV studies showed two types of electrochemical response of the ferrocene/ferrocenium redox couple upon anion binding, that is, a shift of the wave and the appearance of a new peak. Quantitative binding data were obtained from the NMR and CV titrations.     

Poly(Aryl Ether Ketone)s Containing the 2-Naphthalenyl Moiety

Abstract

Amorphous, thermally stable poly(aryl ether ketone)s (PAKs) were prepared by the condensation polymerization of the novel dihalide 1,2-bis(4-fluorobenzoyl)-3,6-diphenyl-4,5-bis(2-naphthalenyl)-benzene and biphenols in dipolar aprotic solvents in the presence of potassium carbonate. The presence of pendant 2-naphthalenyl moieties was found to have no deleterious effects on the thermal stabilities or solubilities of the PAKs. The properties of these polymers are compared to those of PAKs prepared previously in this laboratory. Evidence of a single electron transfer reaction between hydroquinone and the novel dihalide involving the pendant 2-naphthalenyl moieties was found and was investigated through model reactions.     

Polycarbazole Copolymers from 3-(4-Fluorobenzoyl)carbazole and 4,4′-Biphenol via Combined C-N and C-O Coupling Reactions with Activated Difluorides

3-(4-Fluorobenzoyl)carbazole was synthesized by a Friedel-Crafts reaction of carbazole with 4-fluorobenzoylchloride. ¹H-NMR and MALDI-TOF MS confirmed the structure and the purity. Copolymers of these NH/OH-containing monomers were prepared with 4, 4′-biphenol and bis(4-fluorophenyl)sulfone as comonomers by combined C-O and C-N coupling reactions with activated difluorides. These copolymers were soluble in N-methylpyrrolidinone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylacetamide (DMAc) and dimethylformamide (DMF). The inherent viscosities of the copolymers in NMP solutions at 30°C were all around 0.8 dL/g. They could be easily cast into tough films from NMP solutions. The copolymers exhibited T_gs ranging from 238°C to 282°C. Thermal stabilities by TGA showed no weight loss below 400°C and the temperatures of 5% weight loss ranged from 535°C to 558°C. The homopolymer of 3-(4-fluorobenzoyl)carbazole was insoluble in common solvents and had a T_g of 332°C, and temperature of 5% weight loss of 560°C. UV-VIS absorption and fluorescence of the polymers are also presented.     

Poly(Aryl Ether)s from a Novel Biphenol Monomer Containing a Dicyanoarylene Group

Abstract

The preparation of a novel biphenol, 1,4-bis(4-hydroxyphenyl)-2,3-dicyanonaphthalene, from phenolphthalein is described. This biphenol was prepared in high yield in a four-step reaction sequence. The biphenol can be polymerized with activated dihalides such as 1,2-bis-(4-fluorobenzoyl)-3,4,5,6-tetraphenylbenzene, bis(4-fluorophenyl) sulfone, and 4,4′-dichlorobenzophenone to give high molecular weight amorphous poly(aryl ether)s. The polymers have glass transition temperatures ranging from 284 to 319°C and are easily cast into flexible, colorless, and transparent films. The 5% weight loss temperatures of these polymers, by thermogravimetric analysis in air and nitrogen, are all above 500°C.     

Structure elucidation and NMR assignments of two new triterpenoids from the stems of Paragonia pyramidata (Bignoniaceae)

Phytochemical investigation of dichloromethane (DCM) extract from the stems of Paragonia pyramidata var. pyramidata L. Rich. (Bur.) resulted in the isolation and characterization of two new triterpenoids 3β,19β-dihydroxylup-12, 20(29)-diene-28-oic acid (1) and 3β,19β-dihydroxylup-12-en-28-oic acid (2), three known triterpenoids lupeol (3), spinosic acid A (4) and oleanolic acid (5), together with four known steroids (20R)-22E-24-ethylcholesta-4,22-dien-3-one (6), (20R)-24-ethylcholest-4-en-3-one (7), stigmasterol (8) and β-sitosterol (9). HREIMS, GC-MS and NMR experiments including HSQC, HMBC, COSY and NOESY were used for the determination of the structures and NMR spectral assignments. This is the first report about the chemical constituents for this plant.     

Enthalpic relaxation and the glass transition in polymer blends

The kinetics of enthalpic relaxation are reviewed and applied to the ageing of a range of blends made from polyether imide and polyether ether ketone. DSC has been used to follow the development of enthalpic relaxation and a Williams-Watt stretched exponential equation relating the extent of relaxation, ϕ(t), to the ageing time t and an average relaxation time, t́_a', has been used to quantify the ageing process. where β' is inversely related to the breadth of the relaxation spectrum such that 0<β>1.0. The relationship was modified to incorporate non-linearity in the relaxation behaviour. ϕ(t) was measured directly from the enthalpy change observed in the endotherms on heating aged specimens through the glass transition in the DSC. The PEI/PEEK blends were compatible over the full composition range in that they exhibited a single glass transition with a temperature that varied almost linearly with composition between those of the homopolymers. Enthalpic relaxation was found to be a useful technique for probing the molecular relaxations of polymer blends and confirming the degree of compatibility of the system. The β' values changed systematically with the blend composition between those of the homopolymers suggesting that the breadth of the relaxation spectra were similar in the blends to that in the homopolymers. Physical ageing was observed to embrittle the blends, and there was a close correlation between the extent of enthalpic ageing and the change in mechanical and impact behaviour. The yield stress increased and the elongation to break decreased progressively with ϕ(t) in addition to a reduction in impact strength. The model of enthalpic relaxation and the kinetic relationships, outlined above, have been used to determine the onset of the glass transition temperature and subsequent progress of enthalpic relaxation at fixed ageing temperatures, for direct comparison with the change in specific heat observed in DSC experiments. Good agreement was observed between experiment and calculated glass transitions and the effect of variables, such as activation enthalpies, pre-exponential factors, non-linear factors such as X and β' and fictive temperature on the observed glass transition temperatures and the temperature range over which the glass transition occurred determined. Modifications to the model for the enthalpic relaxation have been suggested.