Phthalide as an activating group for the synthesis of poly(aryl ether phthalide)s by nucleophilic aromatic substitution

The phthalide ring was examined as an activating group for nucleophilic aromatic substitution. The proposed mechanism by which activation occurs is through a ring opening of the phthalide ring to form a Meisenheimer‐like σ complex. 3,3‐Bis(4‐fluorophenyl)phthalide was synthesized and examined under different reaction conditions to determine its suitability for polymer formation. Semiempirical calculations at the PM3 level suggested that 3,3‐bis(4‐fluorophenyl)phthalide is only moderately activated, whereas ¹H, ¹³C, and ¹⁹F NMR spectroscopy suggested that the monomer was not sufficiently activated for nucleophilic aromatic substitution. However, low‐molecular‐weight polymers (number‐average molecular weight < 7000 g/mol) were produced from bisphenol A, hydroquinone, and phenolphthalein. The polymers were characterized by gel permeation chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, NMR spectroscopy, and differential scanning calorimetry. The polymers displayed relatively high glass‐transition temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3046–3054, 2002     

Novel thiazole‐piperazine derivatives as potential cholinesterase inhibitors

Dementia is a cognitive disorder mostly associated with Alzheimer's disease (AD) in addition to being seen in many other diseases of the central nervous system (CNS). The limited number of drugs is not sufficient to provide adequate improvement to increase the quality of life of patients suffering from this symptom; therefore, all treatment options should be evaluated in detail. In this study, new molecules, [2‐(4‐(2/3/4‐substituted phenyl)piperazin‐1‐yl)‐4‐phenylthiazol‐5‐yl][3/4‐substituted phenyl]methanone derivatives ( 1‐44 ), were obtained and analyzed in terms of their anticholinesterase activities. Kinetic mode and molecular interactions were also evaluated. An enzyme inhibition study was undertaken on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) using the Ellman method. Maestro program was used in molecular modeling studies. Forty‐four compounds were evaluated on AChE and BChE enzymes at 10^?3 and 10^?4 concentrations. The inhibition concentrations were calculated as 0.268μM to 2.104μM for six compounds ( 4 , 5 , 16 , 27 , 37 , and 38 ) on AChE. Compound 5 including the 4‐methoxy substituent (IC₅₀: 0.268μM) and compound 38 containing the 4‐methoxy and 3‐methyl substituents (IC₅₀: 0.286μM) showed the highest AChE inhibitory activity. They were further examined in terms of hydrogen bonding with Arg296 and Ar‐Ar interaction with Trp286. The activity of compound 5 was also assessed in mixed‐type kinetic mode.     

Using alpha-helical coiled-coils to design nanostructured metalloporphyrin arrays

We have developed a computational design strategy based on the alpha-helical coiled-coil to generate modular peptide motifs capable of assembling into metalloporphyrin arrays of varying lengths. The current study highlights the extension of a two-metalloporphyrin array to a four-metalloporphyrin array through the incorporation of a coiled-coil repeat unit. Molecular dynamics simulations demonstrate that the initial design evolves rapidly to a stable structure with a small rmsd compared to the original model. Biophysical characterization reveals elongated proteins of the desired length, correct cofactor stoichiometry, and cofactor specificity. The successful extension of the two-porphyrin array demonstrates how this methodology serves as a foundation to create linear assemblies of organized electrically and optically responsive cofactors.     

Poly l-lactide-layered double hydroxide nanocomposites via in situ polymerization of l-lactide

The use of clay nanofillers offers a potential route to improved barrier properties in polylactide films. Magnesium-aluminium layered double hydroxides (LDHs) are interesting in this respect and we therefore explored synthesis of PLA-LDH nanocomposites by ring-opening polymerization. This method is attractive because it should ensure good dispersion of LDH in the polymer. The effect of adding either LDH carbonate (LDH-CO₃) or laurate-modified LDH (LDH-C₁₂) was investigated. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy revealed that exfoliated nanocomposites were obtained when using LDH-C₁₂ but that LDH-CO₃ gave a partly phase-separated morphology. Thermogravimetric analysis showed that PLA-LDH combinations exhibited higher degradation onset temperatures and differential scanning calorimetry confirmed that LDHs can act as nucleating agents. However, PLA molecular weight was significantly reduced when in-situ polymerization was conducted in the presence of the LDHs and we suggest that chain termination via LDH surface hydroxyl groups and/or metal-catalyzed degradation could be responsible.     

ChemInform Abstract: Crystal Structures of New Alkali Metal-Rich Oxometallates: Rubidium Aluminate Tetrahydroxide,Rb9(AlO4)(OH)4, Rubidium Orthogallate,Rb5GaO4, Cesium bis-Chromate(IV) Oxide,Cs10(CrO4)2O,and Cesium Diindate,Cs8In2O7.

The crystal structures of several new alkali metal oxometallates are determined by single crystal XRD.     

Heats of formation of organic molecules by ab initio methods: Thiaalkanes

The bond energy scheme for calculating heats of formation of organic molecules from ab initio data (6–31G*) has been extended to include 24 compounds containing sulfur in the sulfide oxidation state. The rms deviation from the experimental values for these compounds is 0.54 kcal/mol, which is approximately experimental error.     

Application of electric fields in NMR

Anisotropic orientation states in materials such as liquid crystals, liquid crystalline polymers or polymeric electrets can be induced by the application of electric fields. This behaviour is exploited extensively in displays or sensors. Anisotropic optical properties induced by relatively high electric field strengths are used in the well known displays made from liquid crystalline materials. The anisotropy of electric properties in polymeric materials gives rise to properties such as the high piezoelectricity of fluorine containing electrets. Attempts have been made to investigate the orientational state induced by electric fields after poling using NMR techniques. However, there is only access to the irreversible part of the electrically induced orientation. In-situ application of (high) voltages during NMR experiments enables the investigation of the influence of the electric field on molecular orientational states or electrically-induced morphological changes. The NMR methods have been modified to investigate the dynamics of reorientation processes in electric fields and to extend the possible time range towards below1ms. The application of high voltages in NMR experiments requires experimental specifications. Some of our experiences are outlined in this paper.     

Metal complexes with polymeric ligands: modular synthesis of multifunctional materials for applications in biomedicine and nanotechnology

Polymeric metal complexes exhibiting useful properties were prepared by chelating macroligands to labile and inert metal ions. The specific structures elucidated through this method, as well as potential applications for these complexes are described. By carefully selecting the appropriate metal ion and polymer, these materials can be tuned for a host of applications in fields ranging from biomedicine to nanotechnology.