Design rationale,synthesis, and characterization ofnon‐natural analogs of the cationic amino acids arginine and lysine

Abstract: A series of non‐natural isosteric analogs of the cationic, ion‐pairing, natural amino acids arginine and lysine have been synthesized, characterized with regard to relevant physical parameters, and protected for routine inclusion in Merrifield solid‐phase synthesis. The design of these molecules is based on the concept of steric inhibition of solvation, in that judicious placement of alkyl groups can destabilize aqueous ion solvation and favor ion‐pairing [see Beeson & Dix (1993) J. Am. Chem. Soc. 115, 10275]. When the residues are substituted for the natural amino acids in biologically active peptides, enhanced ion‐pairing of the peptides to their receptors to increase the peptides’ biological activities can result. The increased lipophilicity of the non‐natural residues can also improve pharmacokinetic parameters and agonist/antagonist behaviors of peptides. While the synthesis of the L‐series is described, theD‐isomers were also prepared using identical chemistry     

Evaluation of the characteristics of oral dosage forms with release controlled by erosion

This paper is concerned with oral dosage forms with controlled release based on the erosion of the polymer matrix. A numerical model taking all the facts into account, i.e., the kinetics of release and pharmacokinetic parameters of the drug, makes it possible to calculate the plasma drug level. Diagrams are built which connect the half life times obtained either through i.v. or with these dosage forms as a function of the full time of erosion of the polymer. Thus, it is possible to determine the right dosage form matrix associated with the desired therapy. Their interest stands for possible bioadhesion extending the gastrointestinal tract time.     

Influence of Deposition Method on the Structural and Optical Properties of Ge2Sb2Te5

Ge2Sb2Te5 (GST-225) is a chalcogenide material with applications in nonvolatile memories. However, chalcogenide material properties are dependent on the deposition technique. GST-225 thin films were prepared using three deposition methods: magnetron sputtering (MS), pulsed laser deposition (PLD) and a deposition technique that combines MS and PLD, namely MSPLD. In the MSPLD technique, the same bulk target is used for sputtering but also for PLD at the same time. The structural and optical properties of the as-deposited and annealed thin films were characterized by Rutherford backscattering spectrometry, X-ray reflectometry, X-ray diffraction, Raman spectroscopy and spectroscopic ellipsometry. MS has the advantage of easily leading to fully amorphous films and to a single crystalline phase after annealing. MS also produces the highest optical contrast between the as-deposited and annealed films. PLD leads to the best stoichiometric transfer, whereas the annealed MSPLD films have the highest mass density. All the as-deposited films obtained with the three methods have a similar optical bandgap of approximately 0.7 eV, which decreases after annealing, mostly in the case of the MS sample. This study reveals that the properties of GST-225 are significantly influenced by the deposition technique, and the proper method should be selected when targeting a specific application. In particular, for electrical and optical phase change memories, MS is the best suited deposition method.