Rapid solid-phase syntheses of a peptidic-aminoglycoside library

A library of mono- and di-amino acid peptidic-aminoglycosides (PAs), with kanamycin and neomycin as the model aminoglycosides, was systematically and rapidly synthesized via solid phase peptide synthesis. Aminoglycosides were first converted into N-Boc protected carboxylic acids and fifteen l-amino acids were then used in the diversification of the full library. The approach outlined describes a rapid synthetic procedure where >200?PA compounds can be synthesized in a few months with 85–95% purity. UV thermal denaturation assessed the binding stabilization by PAs to model human and bacterial A-site rRNA sequences. Significant differences were found in thermal melting profiles among PAs that were attributed to specific amino acid sequences. Neomycin PAs lead to a much larger variation in the stabilization of A-site rRNA sequences (ΔT_m?=?2.6–17.1?°C) as compared to kanamycin PAs (ΔTm?=?0.4–4.3?°C). Kanamycin PAs had little activity against Gram-negative and Gram-positive bacteria as compared with neomycin PAs that had significant antibacterial activity with MIC ranging from 2 to 16?μM.     

The element level time domain (ELTD) method for the analysis of nano-optical systems: II. Dispersive media

We study a 3-dimensional, dual-field, fully explicit method for the solution of dispersive Maxwell's equations in the time domain on unstructured, tetrahedral grids. In a previous paper, we investigated the element level time domain (ELTD) algorithm for solving electromagnetic problems with parameters independent of the excitation frequency content, i.e. nondispersive materials. The suitability of the ELTD method for the numerical analysis of nanometer structured systems in the optical frequencies was thoroughly studied. This paper introduces the generalization of the method and its implementation as a computer code for problems with dispersive material properties. We profit from the ELTD formulation in conjunction with the auxiliary differential equation (ADE) approach for modeling dispersion. Examples with analytical solutions are solved and verified in order to benchmark the method. Eventually, to demonstrate the potential of the method, we consider the structure of a single field emitter and solve for the electromagnetic fields when illuminated by a plane wave. We have obtained a flexible and versatile method of 2nd order accuracy that is applicable to both dispersive and nondispersive problems with a wide range of nano-optical configurations.     

Effect of mercaptopropionic acid as linker on structural,thermal, and optical properties of TiO<Subscript>2</Subscript>–CdSe nanocomposites

In this study, we have studied the stability of TiO₂–CdSe nanocomposites in which the individual moieties are linked using a bifunctional linker (mercaptopropionic acid). Nanoparticles of TiO₂ and CdSe are synthesized by sol–gel and one pot methods. The equimolar amount of the above particles is utilized to prepare nanocomposites with and without linker. These samples are characterized for their structural, thermal, and optical properties using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TG), Fourier transform infra-red spectroscopy (FTIR), and UV–Vis spectroscopy. The average particle size of TiO₂ and CdSe are 16 and 23 nm, respectively. The addition of a bifunctional linker shows remarkable effect on the properties of TiO₂–CdSe nanocomposites.     

Microwave-assisted rapid cyclization of lapachol, a main constituent of Heterophragma adenophyllum

Cyclization reactions of lapachol (1) isolated from Heterophragma adenophyllum have been studied under microwave irradiation under different conditions using alumina (acidic, basic and neutral)/silica gel/montmorillonite (KSF and K-10) as solid support along with neat reaction using 2-3 drops of DMF giving naturally occurring dehydro-alpha-lapachone (2), alpha-lapachone (3), beta-lapachone (4) depending upon the nature of support and irradiation time. A novel naphthoquinone derivative adenophyllone (5) can be synthesized from lapachol using DMF under microwaves.     

Nanoparticles of complex metal oxides synthesized using the reverse-micellar and polymeric precursor routes

Current interest in the properties of materials having grains in the nanometer regime has led to the investigation of the size-dependent properties of various dielectric and magnetic materials. We discuss two chemical methods, namely the reverse-micellar route and the polymeric citrate precursor route used to obtain homogeneous and monophasic nanoparticles of several dielectric oxides like BaTiO₃, Ba₂TiO₄, SrTiO₃, PbTiO₃, PbZrO₃ etc. In addition we also discuss the synthesis of some transition metal (Mn and Cu) oxalate nanorods using the reverse-micellar route. These nanorods on decomposition provide a facile route to the synthesis of transition metal oxide nanoparticles. We discuss the size dependence of the dielectric and magnetic properties in some of the above oxides     

Characterization of snake skin by thermoanalytical techniques

Snake skin is a viable and readily available material as a model for human skin. Pharmaceutical applications use shed snake skin to study the effects of sunscreens on exposure to UV radiation (e.g. benzophenone on Boa integument). In order to understand the effects of radiation or drug transport through this model skin, one must determine its basic physical properties. This preliminary study evaluated two types of snake skin, namely Cuban Boa a 'dark' skin (Epicrates angulifer) and Green tree python a 'light' skin (Morelia viridis). Previous studies by other investigators have used pig, rabbit and snake skin as a human skin substitute. The structure of both snake skins was comparable based on IR spectroscopy and were functionally amino acids and moisture. Photomicrography by light and scanning electron microscopy revealed strong anatomic similarities. Morphologically there were two structures visible, namely a cellular and hinge-fibrous area. The thermal techniques indicated a phase transition at 35-75°C, which is associated with lipid melting. There was an 8 and 12% mass loss for the light skin and dark skin, respectively, which is interpreted, in part, as moisture loss at <100°C. The physical and analytical properties establish a base line that will be used in the future to differentiate various sunscreen types, such as benzophenone and octyl salicylate. Study was also done to determine the effect of an application of a commercially available sunscreen using SEM.This revised version was published online in November 2005 with corrections to the Cover Date.     

2Inc/Chlorotrimethns Ilane: A Mild Reducing System for the Conversion of Epoxides into Alcohols

Reduction of epoxide into the corresponding saturated alcohol is an important synthetic transfornation. Various reagents t o bring about such a conversion have been reported in the literature¹. An important aspect of such a transformation is the regioselective opening in case of unsymmetrical epoxides. Numerous modifications of the existing reducing agents have also been reported¹ to meet with the regioselective requirements. Every reagent reported so far, to our knowledge, makes use of its hydride donating ability to effect the reduction.     

Zwitterionic Base‐Stabilized Digermadistannacyclobutadiene and Tetragermacyclobutadiene

The syntheses of a zwitterionic base‐stabilized digermadistannacyclobutadiene and tetragermacyclobutadiene supported by amidinates and low‐valent germanium amidinate substituents are described. The reaction of the amidinate Ge^I dimer, [LGe:]₂ ( 1 , L=PhC(NtBu)₂), with two equivalents of the amidinate tin(II) chloride, [LSnCl] ( 2 ), and KC₈ in tetrahydrofuran (THF) at room temperature afforded a mixture of the zwitterionic base‐stabilized digermadistannacyclobutadiene, [L₂Ge₂Sn₂L′₂] ( 3 ; L′=LGe:), and the bis(amidinate) tin(II) compound, [L₂Sn:] ( 4 ). Compound 3 can also be prepared by the reaction of 1 with [L^ArSnCl] ( 5 , L^Ar=tBuC(NAr)₂, Ar=2,6‐iPr₂C₆H₃) in THF at room temperature. Moreover, the reaction of 1 with the “onio‐substituent transfer” reagent [4‐NMe₂‐C₅H₄NSiMe₃]OTf ( 8 ) in THF and 4‐(N,N‐dimethylamino)pyridine (DMAP) at room temperature afforded a mixture of the zwitterionic base‐stabilized tetragermacyclobutadiene, [L₄Ge₆] ( 9 ), the amidinium triflate, [PhC(NHtBu)₂]OTf ( 10 ), and Me₃SiSiMe₃ ( 11 ). X‐ray structural data and theoretical studies show conclusively that compounds 3 and 9 have a planar and rhombic charge‐separated structure. They are also nonaromatic.     

Aqueous Polymerization of Methyl Methacrylate Initiated by Ce4+-Glycolic Acid Redox System

The aqueous heterogeneous polymerization of methyl methacrylate (MMA) initiated by the Ce⁴⁺-glycolic acid (GA) redox system was studied at 35 × 0.2°C under a nitrogen atmosphere. The rate of monomer disappearance was proportional to [MMA]¹[GA]¹[Ce⁴⁺]°, and the rate of eerie ion disappearance was found to be directly proportional to [Ce⁴⁺] and [GA] but independent of [MMA]. The activation energy was found to be 34 kJ/mol. The molecular weight of polymethyl methacrylate increased with increasing [MMA] and decreased with increasing [oxidant]. The effect of increasing [H₂SO₄] on polymerization was also studied. The results are compared with those obtained for the aqueous homogeneous polymerization of acrylamide with the same redox pair.