ABC and BAC triblock copolymers - morphological engineering by variation of the block sequence

Different morphologies and phase transitions of ternary triblock copolymers with different block sequences (ABC and BAC) are discussed qualitatively. The interplay between interfacial energies and elastic energies of the different blocks leads to various morphologies and enhances or prevents mixing of different blocks, depending on composition and topology.     

The effects of premenstrual syndrome (PMS) on the female singer

A review of the medical literature concerning the psychological, physical, and vocal effects of premenstrual syndrome reveals a wide range of significant effects for the female singer and a larger number of proposed treatments. A survey was conducted to evaluate the frequency and severity of 67 general physical and psychological symptoms and 20 vocal symptoms experienced by 104 female singers. The variables of age, menstrual history, voice type, and performing experience were examined. The average number of general symptoms was 33 and the average number of vocal symptoms three. The most frequently reported general symptom was abdominal bloating, while the most frequently reported vocal symptom was difficulty in singing high notes. The subjects reported that symptoms occurred with moderate regularity and severity. At age 35 symptoms decreased in number and severity.     

Triblock terpolymer micelles: A personal outlook<Superscript>a</Superscript>

This outlook paper focuses on micelles formed by ABC triblock copolymers (triblock terpolymers) and related systems resulting from mixtures of diblock copolymers. Micelles with different internal structure such as micelles with a heterogeneous core and a homogeneous corona or micelles with a homogeneous core and a mixed corona are presented. More complex nanoobjects such as vesicles and Janus particles are also reviewed. Finally, potential applications of these objects are discussed.     

Relaxation dynamics of selected polymer chain segments and comparison with theoretical models

Simultaneous measurement of infrared dichroism and birefringence is used to study selected polymer segment dynamics in isotopically labeled block copolymers. Two different polymers were studied: polybutadiene and poly (ethylene propylene). The first type consisted of a triblock with a short middle block labeled and a diblock with a short end block labeled, while the second type consisted of a triblock with three equal blocks and the end blocks labeled. Results of step strain experiments at –10°C for polybutadiene and at room temperature for poly(ethylene propylene) indicated that segments located at chain ends relax faster than segments located at chain centers. These experimental data were compared to the predictions of two molecular models: the bead-spring model of Rouse and the tube model of Doi and Edwards, and it was found that both models correctly predict the qualitative features of segmental relaxation. However, the tube-model predictions were closer to the experimental results. In addition, when the effects of orientational coupling interactions between segments in the melt were incorporated into this model, its predictions quantitatively agreed with the experimental results. The orientational coupling coefficient for poly(ethylene propylene) was 0.45 as measured from previous work, and for polybutadiene it was found to be 0.4.Delivered as a Keynote Lecture at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990.Dedicated to Prof. R.S. Stein, University of Massachussets at Amherst, USA, on the occasion of his 65th birthday.     

Synthesis of Fructooligosaccharides from Aspergillus niger Commercial Inulinase Immobilized in Montmorillonite Pretreated in Pressurized Propane and LPG

Commercial inulinase from Aspergillus niger was immobilized in montmorillonite and then treated in pressurized propane and liquefied petroleum gas (LPG). Firstly, the effects of system pressure, exposure time, and depressurization rate, using propane and LPG, on enzymatic activity were evaluated through central composite design 2³. Residual activities of 145.1 and 148.5 % were observed for LPG (30 bar, 6 h, and depressurization rate of 20 bar?min^?1) and propane (270 bar, 1 h, and depressurization rate of 100 bar?min^?1), respectively. The catalysts treated at these conditions in both fluids were then used for the production of fructooligosaccharides (FOS) using sucrose and inulin as substrates in aqueous and organic systems. The main objective of this step was to evaluate the yield and productivity in FOS, using alternatives for enhancing enzyme activity by means of pressurized fluids and also using low-cost supports for enzyme immobilization, aiming at obtaining a stable biocatalyst to be used for synthesis reactions. Yields of 18 % were achieved using sucrose as substrate in aqueous medium, showing the potential of this procedure, hence suggesting a further optimization step to increase the process yield.     

New strategies for the chemical characterization of multi-walled carbon nanotubes and their derivatives

Industrially relevant characterization of multi-walled carbon nanotubes (MWCNT) is still a challenging task. The aim of this work is to show novel and fast concepts for the chemical characterization of carbon nanotubes (CNT) by a combination of analytical techniques. Information obtained by individual tools like Fourier transform infrared spectroscopy (FTIR), attenuated total reflection infrared spectroscopy or Raman spectroscopy is not providing a full picture of the functionalization of MWCNTs. However, a combination of tools such as FTIR or mass spectrometry with thermogravimetric methods proved to be very useful. Sample preparation for FTIR and Raman spectroscopy is another focus of this contribution because of its strong effect on the results obtained. We also are suggesting methods for sample preparation that lead to highly reproducibility results. Measurements have been carried out on typical CNT samples such as commercially available pristine, carboxylated and amino-functionalized MWCNTs, and on polystyrenegrafted MWCNTs. The results may serve as a guidance for the qualitative and quantitative characterization of CNT.

Reactivity and Operational Stability of N‐Tailed TAMLs through Kinetic Studies of the Catalyzed Oxidation of Orange II by H2O2: Synthesis and X‐ray Structure of an N‐Phenyl TAML

The catalytic activity of the N‐tailed (“biuret”) TAML (tetraamido macrocyclic ligand) activators [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂NR}Cl]^2? ( 3 ; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me ( a ); NO₂, Me ( b ); H, Ph ( c )] in the oxidative bleaching of Orange II dye by H₂O₂ in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂CMe₂}OH₂]^? ( 1 ) and the more aggressive analogue [Fe(Me₂C{CON(1,2‐C₆H₃‐4‐X) N CO}₂)OH₂]^? ( 2 ). Catalysis by 3 of the reaction between H₂O₂ and Orange II (S) occurs according to the rate law found generally for TAML activators (v=k_Ik_II[Fe^III][S][H₂O₂]/(k_I[H₂O₂]+k_II[S]) and the rate constants k_I and k_II at pH 7 both decrease within the series 3 b > 3 a > 3 c . The pH dependency of k_I and k_II was investigated for 3 a . As with all TAML activators studied to‐date, bell‐shaped profiles were found for both rate constants. For k_I, the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a . For k_II, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition k_I?k_II holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants k_i for suicidal inactivation of the active forms of complexes 3 a – c were calculated using the general formula ln([S₀]/[S_∞])=(k_II/k_i)[Fe^III]; here [Fe^III], [S₀], and [S_∞] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X‐ray characterization of 3 c are also described.     

Effect of hydrostatic pressure on the fluorescence of indole derivatives

Effects of hydrostatic pressure on the fluorescence emission of L-tryptophan, N-acetyl-L-trytophanamide and indole were investigated. An increase in pressure ranging from 1 bar to 2.4 kbar results in reversible red-shifts of the emission of the three fluorophores. The pressure-induced redshift amounts to about 170 cm^–1 at 2.4 kbar, and appears related to changes in Stokes shift of the fluorophores caused by pressure effects on the dielectric constant and/or refractive index of the medium. As the pressure range investigated here is the range commonly used in studies of protein subunit association and/or folding, these observations raise the need for caution in interpreting pressure-induced spectral shifts. The significance of these observations to pressure studies of proteins is illustrated by investigation of pressure effects on human Cu,Zn Superoxide dismutase (SOD) and azurin fromPseudomonas aeruginosa. A reversible 170 cm^–1 red-shift of the emission of SOD was observed upon pressurization to 2.4 kbar. This might be interpreted as pressure-induced conformational changes of the protein. However, further studies using SOD that had been fully unfolded by guanidine hydrochloride, and fluorescence anisotropy measurements indicated that the observed red-shift was likely due to a direct effect of pressure on the fluorescence of the single tryptophan residue of SOD. Similar pressure-induced red-shifts were also observed for the buried tryptophan residue of azurin or for azurin that had been previously denatured by guanidine hydrochloride. These observations further suggest that the effective dielectric constant of the protein matrix is affected by pressure similarly to water.