Characterization by fourier transform infrared spectroscopy (FT-IR) and 2D IR correlation spectroscopy of PAMAM dendrimer

FT-IR and 2D correlation spectroscopy were employed to study the microstructural changes occurring during phase transitions of a liquid crystal poly(amidoamine) codendrimer (PAMAM (L1)16(L2)16) generation 3, functionalized on the terminal groups by one-chain promesogenic calamitic units (4-(4'-decyloxybenzoyloxy)salicylaldehyde (L1)) and two-chain promesogenic calamitic units (4-(3',4'-didecyloxybenzoyloxy)salicylaldehyde (L2)). Spectral modifications associated with molecular conformation rearrangements allowing for molecular shape change on going from a liquid-crystalline organization to another were found. The transition temperatures were calculated, and they are in good agreement with the DSC data. Spectral analysis gives evidence of the LC phase transitions and to an additional transition associated with the existence of conformers. Various types of hydrogen bonding have been established.     

Protonation of carbonate in aqueous tetraalkylammonium salts at 25 degrees C

Protonation constants of carbonate were determined in tetramethylammonium chloride (Me₄NCl_aq 0.1 ≤ I/mol kg⁻¹ ≤ 4) and tetraethylammonium iodide (Et₄NI_aq 0.1 ≤ I/mol kg⁻¹ ≤ 1) by potentiometric ([H⁺]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaCl_aq (0.1 ≤ I/mol kg⁻¹ ≤ 6) were also critically analysed. Both protonation constants of carbonate follow the trend Et₄NI > Me₄NCl > NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated.     

Coordinated and reversible reduction of enzymes involved in terminal oxidative metabolism in skeletal muscle mitochondria from a riboflavin-responsive, multiple acyl-CoA dehydrogenase deficiency patient

In this case report we studied alterations in mitochondrial proteins in a patient suffering from recurrent profound muscle weakness, associated with ethylmalonic-adipic aciduria, who had benefited from high dose of riboflavin treatment. Morphological and biochemical alterations included muscle lipid accumulation, low muscle carnitine content, reduction in fatty acid beta-oxidation and reduced activity of complexes I and II of the respiratory chain. Riboflavin therapy partially or totally reversed these symptoms and increased the level of muscle flavin adenine dinucleotide, suggesting that aberrant flavin cofactor metabolism accounted for the disease. Proteomic investigation of muscle mitochondria revealed decrease or absence of several flavoenzymes, enzymes related to flavin cofactor-dependent mitochondrial pathways and mitochondrial or mitochondria-associated calcium-binding proteins. All these deficiencies were completely rescued after riboflavin treatment. This study indicates for the first time a profound involvement of riboflavin/flavin cofactors in modulating the level of a number of functionally coordinated polypeptides involved in fatty acyl-CoA and amino acid metabolism, extending the number of enzymatic pathways altered in riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency.     

Complexation of quaternary ammonium ions by tetraester derivatives of [3.1.3.1]homooxacalixarene in mobile and in fixed conformation

In the tetraalkylation of p-tert-butyl[3.1.3.1]homooxacalixarene with BrCH2CO2R and K2CO3 in acetone, the initially formed cone conformer is converted into the more stable 1,4-alternate conformer when R = Me or Et, but not when R = i-Pr or t-Bu. In the case of R = i-Pr, derivatives in fixed 1,4-alternate conformation and in partial cone conformation were also isolated. Compounds in fixed cone conformation are good ligands for tetramethylammonium, acetylcholine, and N-methylpyridinium salts in CDCl3, but the partial cone isomer proved to be somewhat better and even the 1,4-alternate conformer turned out to be active. The possible involvement of the ester functions as additional binding sites is discussed; moreover, an insight into the energetics of the complexation and conformational isomerization processes is given.     

High-throughput pharmacokinetic method: cassette dosing in mice associated with minuscule serial bleedings and LC/MS/MS analysis

A method for pharmacokinetic studies using cassette dosing associated with serial bleeding in mice is described. PK profiles of four soluble epoxide hydrolase inhibitors were determined following oral, subcutaneous or intraperitoneal administration individually or in cassette dosing. Parent analyses were performed on only 5 μL of whole blood from serial bleeds (up to 10 per animal), by LC/MS/MS. An accuracy (88-100%) and precision (<10% RSD) were observed, leading to reliable datum points for PK calculation. PK profiles, T_max, C_max and half-life values after cassette dosing were similar to the individual PK results. This method dramatically increases speed of data collection while dramatically reducing cost and animal usage. The results presented here clearly indicate that this proposed method could be applicable to high-throughput PK studies.     

A simple two-phase route to silver nanoparticles/polyaniline structures

Novel silver nanoparticles/polyaniline composites were obtained through a two-phase water/toluene interfacial reaction. We show that by rigorously controlling the reaction time, different structures of the nanocomposites can be obtained, such as a thin sheet of polyaniline around the silver nanoparticles or a polymer mass with nanoparticles homogeneously embedded within it. Samples were characterized by FT-IR, UV-vis-NIR and Raman spectroscopy, X-ray diffraction, cyclic voltammetry, TEM, and HRTEM. Conductivity and current-voltage characteristics of the nanocomposites were measured, and the results indicate that different properties result from the different structures in which the nanocomposites were formed.     

A study on photolinkers used for biomolecule attachment to polymer surfaces

The use of photolinkers (photoactivatable heterobifunctional crosslinkers) is a popular method to attach biomolecules to polymer surfaces. This study addresses the selection of photolinker and the adjustment of reaction conditions, such as the concentration of biomolecule applied, and irradiation time. The influence of these variables are investigated for four prominent photolinkers: ketyl-reactive benzophenone (BP) and anthraquinone (AQ), nitrene-reactive nitrophenyl azide (NPA), and carbene-reactive phenyl-(trifluoromethyl)diazirine (PTD). The influence of substrate material is discussed, and three different polymers served as representative substrates: poly(methyl methacrylate) (PMMA), polystyrene (PS), and a cycloolefin copolymer (COC). We compared the overall photolinking efficiency of all photolinkers with respect to the polymer substrate they are applied to, and we found considerable differences for certain photolinker/substrate combinations. Of all photolinkers and substrates tested, PTD as photolinker and COC as substrate showed the highest photolinking efficiencies and fastest reaction times. For this study DNA oligonucleotides were chosen as a model system of biomolecular probes, and fluorescence detection of DNA microarrays served as method of detection.