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1.
Enantiomeric Cyclic Peptides with Different Caco‐2 Permeability Suggest Carrier‐Mediated Transport 下载免费PDF全文
B. Sc. Eduard Puig Prof. Dr. Beat Ernst Prof. Dr. Horst Kessler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8023-8027
Recently, oral absorption of cyclic hexapeptides was improved by N‐methylation of their backbone amides. However, the number and position of N‐methylations or of solvent exposed NHs did not correlate to intestinal permeability, measured in a Caco‐2 model. In this study, we investigate enantiomeric pairs of three polar and two lipophilic peptides to demonstrate the participation of carrier‐mediated transporters. As expected, all the enantiomeric peptides exhibited identical lipophilicity (logD7.4) and passive transcellular permeability determined by the parallel artificial membrane permeability assay (PAMPA). However, the enantiomeric polar peptides exhibited different Caco‐2 permeability (Papp) in both directions a–b and b–a. The same trend was observed for one of the lipophilic peptide, whereas the second lipophilic enantiomer pair showed identical Caco‐2 permeability (within the errors). These findings provide the first evidence for the involvement of carrier‐mediated transport for peptides, especially for those of polar nature. 相似文献
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Various types of glycosaminoglycans (GAGs) including heparins, chondroitin sulfates, dermatan sulfate and hyaluronic acid were studied from their proton nuclear magnetic resonance (1H NMR) spectra using chemometric techniques. Despite the complexity of the 1H NMR signals, data analysis using principal component analysis enabled the different GAG classes to be distinguished and permitted their classification according to their chemical structure. The analysis of the composition of the major disaccharide unit and other relevant chemical structures in the heparin samples was performed using partial least squares regression. 相似文献
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Barberá J Puig L Romero P Serrano JL Sierra T 《Journal of the American Chemical Society》2005,127(1):458-464
The work described here concerns a challenge of general interest in supramolecular chemistry: the achievement of chiral helical organizations with controlled structures. This work provides a strategy to obtain supramolecular polymers in which a chiral helical conformation has been induced by a noncovalent association, that is, through hydrogen bonding. Polycatenar 2,4,6-triarylamino-1,3,5-triazines, which organize into columnar mesophases and are susceptible to H-bonding interactions, were chosen as a starting point to build up the chiral supramolecular structure. The stacking of these mesogens has been forced to wind in a helical way by means of H-bond association with (R)-3-methyladipic acid, within the mesophase. The optically active columnar organization has been studied in depth by optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction, and circular dichroism. Formation of stable complexes between the triazine units and (R)-3-methyladipic acid has also been investigated by means of NMR diffusion-ordered spectroscopy (DOSY) experiments in chloroform. 相似文献
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A flow injection analysis-flame atomic absorption spectrometric method for the determination of cadmium in seawater was developed with the aim of yielding a sensitive assay with a low detection limit. The method employs a field flow preconcentration technique involving a minicolumn containing Amberlite XAD-4 impregnated with the complexing agent 4-(2-pyridylazo) resorcinol. A Plackett-Burman 2(7)x3/32 design for seven factors (sample pH, sample flow rate, eluent volume, eluent concentration, eluent flow rate, ethanol percentage in the eluent and minicolumn diameter) was carried out in order to find the significant variables affecting the field continuous preconcentration system (FCPS) and the flow injection elution manifold for cadmium determination in seawater samples by flame atomic absorption spectrometry. Cadmium can be preconcentrated with an enrichment factor of 1053 for a sample volume of 200 mL and a preconcentration time of 57 min. In these experimental conditions, the method provides a linear relationship between absorbance and cadmium concentration in the range from 22-1900 ng L(-1), with a detection limit (3SD) of 6 ng L(-1). The precision (expressed as relative standard deviation) for eleven independent determinations reached values of 8.9-0.8% in cadmium solutions of 50-700 ng L(-1). Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater from Galicia (Spain). 相似文献
7.
J. Lub Corresponding author V. Recaj L. Puig P. Forcén C. Luengo 《Liquid crystals》2013,40(12):1627-1637
The synthesis and photopolymerization of various liquid crystalline dioxetanes is described. The effects of the spacer length, structure of the mesogenic group and oxetane group on the liquid crystalline properties, polymerization behaviour and optical properties (birefringence) of the oriented and crosslinked network formed in photo-polymerization are discussed. Thermally stable films with birefringence values up to 0.13 can be formed from these materials. The dioxetanes show significantly lower polymerization shrinkage than do structurally related diacrylates. 相似文献
8.
H. R. Acevedo-Parra M. R. Torres-Vitela M. M. Castillo-Ortega F. Bautista J. E. Puig S. M. Nuño-Donlucas 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):876-884
The synthesis by emulsion polymerization and the characterization by a battery of techniques of poly(butyl acrylate-co-silver acrylate) [poly(BuAc-co-AgAc)] ionomers are reported here. Reaction rates were fast and conversions around 90% were obtained in less than one hour, regardless of the initial ratio of butyl acrylate and silver acrylate employed (BuAc/AgAc = 90/10, 80/20, 70/30). Particle size was in the range of 176 to 200 nm, depending on the BuAc/AgAc ratio. Ionomers’ formation was corroborated by infrared spectroscopy and inferred by differential scanning calorimetry (DSC). DSC disclosed that the poly(BuAc-co-AgAc) has two glass transition temperatures: one at ca. ?49°C due to relaxation of the ionomer backbone domains rich in BuAc and another ca. 35°C due to the relaxation of the backbone domains where the AgAc-units content was higher. Young moduli increased as the copolymers became richer in AgAc. Antibacterial tests against Escherichia coli with the 90/10 (BuAc/AgAc) ionomer revealed that the bacteria population diminishes from 5 log CFU/mL to less than 0.3 MPN/mL after one hour of contact with the ionomers. Also, we demonstrated that the ionomers are excellent compatibilizers for making semiconductive films of n-dodecylbenzene sulfonic acid-doped polyaniline (PANIDBSA)-poly(BuAc-co-AgAc) and poly(n-butyl methacrylate) (PBMA) blends. The electrical conductivity of the blend films, which were homogeneous, rose as the AgAc content in the films increased. 相似文献
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We put forward the concept of resonant, Rabi-like oscillatons and adiabatic transitions between confined light modes in properly modulated multimode waveguides. The phenomenon is shown to take place in both the linear and the nonlinear regimes. In addition, we find that the mode transitions occur not only in simple geometries, but also in complex confining multimode structures. The phenomenon is analogous to the familiar stimulated state transitions that occur in multilevel quantum systems. 相似文献