Effects of acyl donor type, catalyst type, and reaction conditions on the activity and selectivity of Friedel-Crafts acylation

Acylation of anisole and 3-methylanisole was performed with several acylating reagents (acetylation by AcCl and Ac₂O and bromoacetylation by BrAcCl and (BrAc)₂O) over different solid acid catalysts. The reaction conditions were optimized with respect to the acylation reagent, overall yield, solid acid catalyst, and the products selectivities. While acylation of anisole with acetyl chloride or acetic anhydride resulted in its full conversion to para-substituted acetophenone, the use of bromoacetyl bromide or bromoacetic anhydride yielded also the ortho-substituted product. Acylation of 3-methylanisole also yielded both para- and ortho-substitutions, and the products distribution was affected by the reaction conditions and catalyst type. It was found that while more acidic catalysts (caesium salt of heteropolyacid and zeolites) were the most active towards anisole acylation, the most active catalysts for the acylation of 3-methylanisole were ion-exchange catalysts. Employing HY-740 zeolite resulted in the highest ortho-selectivity in the acylation of anisole with bromoacetyl bromide and bromoacetic anhydride and in the acylation of 3-methylanisole with acetic anhydride.     

Multiple vesicular morphologies from block copolymers in solution

It has been found that asymmetric, amphiphilic diblock copolymers can form a wide range of vesicle architectures in solution. These include small uniform vesicles, large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, onions, and vesicles with hollow tubes in the walls. The experimental conditions required for preparation and the proposed mechanisms for the formation of each type of structure are discussed.     

Effect of spatial heterogeneity on level of rejuvenation in Ni80P20 metallic glass

Understanding the relation between spatial heterogeneity and structural rejuvenation is one of the hottest topics in the field of metallic glasses (MGs). In this work, molecular dynamics (MD) simulation is implemented to discover the effects of initial spatial heterogeneity on the level of rejuvenation in the Ni$_{80}$P$_{20 }$MGs. For this purpose, the samples are prepared with cooling rates of $10^{10}$ K/s-$10^{12}$ K/s to make glassy alloys with different atomic configurations. Firstly, it is found that the increase in the cooling rate leads the Gaussian-type shear modulus distribution to widen, indicating the aggregations in both elastically soft and hard regions. After the primary evaluations, the elastostatic loading is also used to transform structural rejuvenation into the atomic configurations. The results indicate that the sample with intermediate structural heterogeneity prepared with 10$^{11}$ K/s exhibits the maximum structural rejuvenation which is due to the fact that the atomic configuration in an intermediate structure contains more potential sites for generating the maximum atomic rearrangement and loosely packed regions under an external excitation. The features of atomic rearrangement and structural changes under the rejuvenation process are discussed in detail.     

Miscibility enhancement in polymers via ionic interactions: Dynamic mechanical and NMR studies

The presence of ionic interactions can be used to control the degree of miscibility of otherwise immiscible polymer systems. This control, in turn, allows one to prepare blends with a very wide range of “tailor-made” properties. Several examples are cited. In some of these, the interactions are based on proton transfer from a donor site on one polymer to an aceptor site on another leading to ion-ion interactions. In others, the transfer of a metal cation from an ionomer to a polar polymer, as a result of ion-dipole interactions, is involved. Systems studied to date include, among others, mixtures of polystyrene with poly(ethyl acrylate), polyisoprene, segmented poly urethanes, poly(ethyleneimine), and poly(ethylene oxide). The polyurethane blends with polystyrene are discussed in some detail, focussing especially on the mechanism of miscibility enhancement as determined by NMR. This technique has also been utilised to study the dynamics of the coil overlap process in solution as well as the proximity of the polymer coils to each other. Two particularly noteworthy applications involve mixtures of poly (tetrafluoroethylene) (PTFE) or of phenylated poly(phenylene oxide) with poly (ethyl acrylate), which are also discussed in some detail. Blends of this type may be of special interest in membrane applications.     

A Lyapounov function approach to the theory of stability in a laser using the Scully-Lamb theory

The stability of a quantum model of a c.w. laser is demonstrated using Lyapounov's second method.     

Specular reflectance studies of bromide adsorption on gold

Specular reflectance changes have been used to examine the specific adsorption of bromide on gold in the presence of a large excess of supporting electrolyte (NaF) which is not specifically adsorbed. A linear relation has been demonstrated between the reflectance changes and the surface excess of bromide through the examination of the time dependence of the reflectance under conditions where the rate of adsorption of the bromide is diffusion controlled and hence known. The adsorption isotherms have been found to follow Temkin behavior. The electrosorption valency has been evaluated from the charge and surface excess at constant potential and found to be ?0.49 to ?0.59, depending on the potential. Various mechanisms for the subtantial changes in reflectance attending the specific adsorption of anions are discussed. The observed effects cannot be explained on the basis of changes in the charge on the electrode and corresponding changes in the contribution of the conduction band to the surface optical properties. The principal mechanism is proposed to be modifications in the surface electronic states of the metal electrode through direct orbital interactions between the adsorbed anions and the metal.     

Scanning white-light interferometry as a novel technique to quantify the surface roughness of micron-sized particles for inhalation

A novel approach of measuring the surface roughness of spherical and flat micron-sized drug particles using scanning white-light interferometry was applied to investigate the surface morphology of micron-sized active pharmaceutical ingredients (APIs) and excipient particles used for inhalation aerosols. Bovine serum albumin (BSA) and alpha-lactose monohydrate particles were chosen as model API and excipient particles, respectively. Both BSA and lactose particles were prepared with different degrees of surface corrugation using either controlled spray drying (four samples of BSA) or decantation (two samples of lactose). Particle size distributions were characterized by laser diffraction, and particles were imaged by scanning electron microscopy (SEM). Surface roughness of the BSA and lactose particles was quantified by white-light optical profilometry using vertical scanning interferometry (VSI) at full resolution using a 50x objective lens with 2.0x and 0.5x fields of view for BSA and lactose, respectively. Data were analyzed using Vision software (version 32, WYKO), and surface roughness values are expressed as root-mean-square roughness ( Rrms). Furthermore, data were compared to topographical measurements made using conventional atomic force microscopy. Analysis of the optical profilometry data showed significant variation in BSA roughness ranging from 18.58 +/- 3.80 nm to 110.90 +/- 13.16 nm for the smoothest and roughest BSA particles, respectively, and from 81.20 +/- 15.90 nm to 229.20 +/- 68.20 nm for decanted and normal lactose, respectively. The Rrms values were in good agreement with the AFM-derived values. The particle morphology was similar to SEM and AFM images. In conclusion, scanning white-light interferometry provides a useful complementary tool for rapid evaluation of surface morphology and roughness in particles used for dry powder inhalation formulation.     

A Cramer rule for least-norm solutions of consistent linear equations

The least (Euclidean-) norm solution of a consistent linear equation Ax = b is given a determinantal form, which reduces to Cramer's rule if A is nonsingular.     

Ionomeric blends. V. FTIR studies of ionic interactions in polyurethane-styrene blends

FTIR spectra of blends of lightly sulfonated polystyrene (PS-SSA) with polyurethanes (PU) containing a tertiary nitrogen in the chain extender were recorded. These blends exhibit a two-phase behavior, but the individual components are not phase separated. Earlier dynamic mechanical studies suggested the occurrence of proton transfer from the sulfonic acid to the tertiary nitrogen, which enhanced the miscibility via ionic interactions and resulted in the formation of a miscible blend between the PS-SSA and the hard segment of the PU, the soft segment being excluded. FTIR studies of these blends now confirm the proton transfer mechanism. A new absorption band at 3428 cm^?1 corresponds to a stretching vibration of an N⁺?H bond. The 1012 cm^?1 band of the SO₃H group, which strongly depends on the degree of protonation, shifts to lower frequency. The symmetric stretching vibration of the SO group, which occurred at 1043 cm^?1, shifts to lower frequency as well, suggesting a lower polarization of the S? O dipole due to the removal of H⁺.     

Analog computer simulation of a duffing oscillator and comparison with statistical linearization

We present the results of an analog computer simulation of a Duffing oscillator, i.e. of a damped anharmonic oscillator with a cubic non-linearity driven by Gaussian white noise. The simulations were performed for wide ranges of parameter values. The experimentally obtained spectral densities are compared with those obtained analytically using the method of statistical linearization.