Improved Livingness and Control over Branching in RAFT Polymerization of Acrylates: Could Microflow Synthesis Make the Difference?

The superior capabilities of structured microreactors over batch reactors are demonstrated for reversible addition–fragmentation chain transfer (RAFT) solution polymerization of n‐butyl acrylate with the aid of simulations, explicitly accounting for the chain length distribution of all macrospecies types. Since perfect isothermicity can be established in a microreactor, less side products due to backbiting and β‐scission are formed compared to the batch operation in which ineffective heat removal leads to an undesirable temperature spike. For a given RAFT chain transfer agent (CTA), additional microstructural control results under microflow conditions by optimizing the reaction temperature, lowering the dilution degree, or decreasing the initial molar ratio of monomer to RAFT CTA.

     

Effects of elevated temperature and mobile phase composition on a novel C18 silica column

A novel polydentate C18 silica column was evaluated at an elevated temperature under acidic, basic, and neutral mobile phase conditions using ACN and methanol as the mobile phase organic modifier. The temperature range was 40-200 degrees C. The mobile phase compositions were from 0 to 80% organic-aqueous v/v and the mobile phase pH levels were between 2 and 12. The maximum operating temperature of the column was affected by the amount and type of organic modifier used in the mobile phase. Under neutral conditions, the column showed good column thermal stability at temperatures ranging between 120 and 200 degrees C in methanol-water and ACN-water solvent systems. At pH 2 and 3, the column performed well up to about 160 degrees C at two fixed ACN-buffer compositions. Under basic conditions at elevated temperatures, the column material deteriorated more quickly, but still remained stable up to 100 degrees C at pH 9 and 60 degrees C at pH 10. The results of this study indicate that this novel C18 silica-based column represents a significant advancement in RPLC column technology with enhanced thermal and pH stability when compared to traditional bonded phase silica columns.     

Synthesis,characterization and antimicrobial activity of nalidixic acid derivatives with spirohydantoins

This article presents the synthesis of a series of amides, based on the interaction of several 3-aminospirohydantoins with nalidixic acid. The target compounds were characterized by physicochemical parameters, IR, ¹H and ¹³C NMR spectral data. The antimicrobial activity of the products obtained was determined against Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa and Salmonella abony, the yeasts Candida albicans and Saccharomyces cerevisiae and the molds Penicillium chrysogenum and Aspergillus niger. The relationship between structure and biological activity of the products obtained was discussed. It was found that the most effective compounds are tetralin (5f) and indane (5g) derivatives, which exhibit a pronounced antimicrobial activity against both tested Gram-positive and Gram-negative bacteria.

     

Dynamic scaling method and interface growth

The dynamic scaling approach is an important tool for describing the time evolution of rough interfaces. It computes dynamic scaling parameters alpha and beta, which characterize surface and time correlations. Applications of dynamic scaling to random deposition and ballistic deposition are discussed. A model of random adsorption on fractal substrates is presented. Then the influence of surface diffusion on adsorption is analyzed. The dependence of alpha and beta on the substrate fractal dimension, together with the dependence of the fractal dimension of the gas-solid interface on adsorption coverage are computed.     

KrF pulsed laser ablation of thin films made from fluorinated heterocyclic poly(naphthyl-imide)s

Among the many aspects of laser ablation, development of conical structures induced by excimer laser radiation on polyimide surfaces has been thoroughly investigated. Because the mechanisms that produce these surface textures are not fully understood, two theories, photochemical bond breaking and thermal reaction, have been introduced. Here we present the first study of ultraviolet laser ablation behavior of thin films made from fluorinated poly(naphthyl-imide)s containing oxadiazole rings and the investigation of the mechanism of cone-like structure formation at two laser fluences, 57 and 240 mJ/cm(2). The morphology of thin films before and after laser ablation was studied by using various spectroscopy techniques such as Fourier transform infrared spectroscopy, time-resolved emission and X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements. All of the data suggest impurities shielded at low fluence radiation (57 mJ/cm(2)) and a radiation hardening process at high value fluence (240 mJ/cm(2)), which are proposed as the main mechanisms for laser ablation of our polyimide films, and we bring evidence to support them.     

Localization effects in the charge density wave state [4]of the quasi-two-dimensional monophosphate tungsten bronzes {(P{O_2})_4}{(W{O_3})_{2m}}(m = 7,8,9)

The monophosphate tungsten bronzes (PO ₂ ) ₄ (WO ₃ ) _2m are quasi-two-dimensional conductors which show charge density wave type electronic instabilities. We report electrical resistivity and magnetoresistance measurements down to 0.30 K and in magnetic fields up to 16 T for the m = 7, 8 and 9 members of this family. We show that these compounds exhibit at low temperature an upturn of resistivity and field dependences of the magnetoresistance characteristic of localization effects. We discuss the dimensionality of the regime of localization as m is varied. We show that for m =7, the regime is quasi-two-dimensional and three-dimensional for m = 8, 9. Received 16 September 1999     

InclusiveK *'s and∑ *'s production in 360 GeV/cpp interactions using the European hybrid spectrometer

We have studied the inclusive production of strange meson and baryon resonances in 360 GeV/cpp interactions. Cross sections forK ^*+(892) andK ^*?(892) are estimated to be 4.42±0.62 mb and 2.54±0.47 mb respectively and those for∑ ⁺(1385) and∑ ^?(1385) are 0.67±0.11 mb and 0.26±0.07 mb respectively. Longitudinal and transverse momentum distributions forK ^*(892) and Σ(1385) are presented, as well as for their decay productsK ⁰ and Λ. An estimation is given on theK ^*(1430) and∑ ^*(1915) productions.     

New Hydrogels Based on Agarose/Phytagel and Peptides

Short aromatic peptide derivatives, i.e., peptides or amino acids modified with aromatic groups, such as 9-fluorenylmethoxycarbonyl (Fmoc), can self-assemble into extracellular matrix-like hydrogels due to their nanofibrillar architecture. Among different types of amino acids, lysine (Lys) and glycine (Gly) are involved in multiple physiological processes, being key factors in the proper growth of cells, carnitine production, and collagen formation. The authors have previously successfully presented the possibility of obtaining supramolecular gels based on Fmoc-Lys-Fmoc and short peptides such as Fmoc-Gly-Gly-Gly in order to use them as a substrate for cell cultures. This paper investigates how the introduction of a gelling polymer can influence the properties of the network as well as the compatibility of the resulting materials with different cell types. A series of hydrogel compositions consisting of combinations of Fmoc-Lys-Fmoc and Fmoc-Gly-Gly-Gly with Agarose and Phytagel are thus obtained. All compositions form structured gels as shown by rheological studies and scanning electron microscopy. Fourier transform infrared spectroscopy analysis evidences the formation of H-bonds between the polysaccharides and amino acids or short peptides. Moreover, all gels exhibit good cell viability on fibroblasts as demonstrated by a live-dead staining test and good in vivo biocompatibility, which highlights the great potential of these biomaterials for biomedical applications.     

Manufacturing and Assessing the New Orally Disintegrating Tablets,Containing Nimodipine-hydroxypropyl-β-cyclodextrin and Nimodipine-methyl-β-cyclodextrin Inclusion Complexes

The aim of the present study was to manufacture new orally disintegrating tablets containing nimodipine–hydroxypropyl-β-cyclodextrin and nimodipine–methyl-β-cyclodextrin inclusion complexes. For obtaining a better quality of the manufactured tablets, three methods of the preparation of inclusion complexes, in a 1:1 molar ratio, were used comparatively; namely, a solid-state kneading method and two liquid state coprecipitation and lyophilization techniques. The physical and chemical properties of the obtained inclusion complexes, as well as their physical mixtures, were investigated using Fourier transformed infrared spectroscopy, scanning electron microscopy, X-ray diffraction analyses, and differential scanning calorimetry. The results showed that the lyophilization method can be successfully used for a better complexation. Finally, the formulation and precompression studies for tablets for oral dispersion, containing Nim–HP-β-CD and Nim–Me-β-CD inclusion complexes, were successfully assessed.