Search results for "HP"
showing 10 items of 1505 documents
Peptide mapping by reversed-phase high-performance liquid chromatography employing silica rod monoliths.
2003
In this paper, a general procedure is described for the generation of peptide maps of proteins with monolithic silica-based columns. The peptide fragments were obtained by tryptic digestion of various cytochrome c species with purification of the tryptic fragments achieved by reversed-phase high-performance liquid chromatographic methods. Peak assignment of the various peptides was based on evaluation of the biophysical properties of the individual peptides and via mass spectrometric identification. The performance of several different monolithic sorbents prepared as columns of identical cross-sectional dimensions were investigated as part of these peptide mapping studies and the data evalu…
Interactions between 2-Aminobenzothiazole and Natural Organic Matter as Evidenced by CPMAS Nitrogen-15 NMR Spectroscopy
2009
Cross-polarization magic angle spinning (CPMAS) 15N nuclear magnetic resonance (NMR) spectroscopy was used to study the interactions between 2-aminobenzothiazole (ABT) and natural organic matter in the presence of the natural enzyme laccase and synthetic air. Through the use of synthesized model compounds, we were able to confirm previous findings by CPMAS 13C NMR spectroscopy that showed the formation of covalent amide bonds. We also provide evidence of the presence of two additional H bonds between ABT and the natural organic matter. Both H bonds involved the amino and thiazole groups of ABT.
A simplified description of viscoelastic behavior of polymers as illustrated with biaxially-oriented poly(ethylene terephthalate)
1978
A rheological model of solid polymers is proposed. Its mechanical analog is a parallel of a linear spring and a Maxwell element with variable viscosity. The viscosity of the dashpot is allowed to change with stress both directly, by an Eyring-type mechanism, and through free volume changes according to the Doolittle equation. Predictions of the model reproduce many of the features shown, especially after yielding, by constant velocity stress-strain, stress-relaxation and creep data taken at room temperature on biaxially-oriented poly(ethylene terephthalate) over a wide range of loading rates.
Synthesis, Characterization and Preliminary Biological Evaluation of P(HPMA)-b-P(LLA) Copolymers: A New Type of Functional Biocompatible Block Copoly…
2010
We describe a synthetic pathway to functional P(HPMA)-b-P(LLA) block copolymers. The synthesis relies on a combination of ring-opening polymerization of L-lactide, conversion into a chain transfer agent (CTA) for the RAFT polymerization of pentafluorophenyl methacrylate. A series of block copolymers was prepared that exhibited molecular weights $\overline M _{\rm n}$ ranging from 7 600 to 34 300 g · mol(-1) , with moderate PDI between 1.3 and 1.45. These reactive precursor polymers have been transformed into biocompatible P(HPMA)-b-P(LLA) copolymers and their fluorescently labeled derivatives by facile replacement of the pentafluorophenyl groups. The fluorescence label attached to this new …
Herbicidally Active Derivatives of Aminomethylenebis-Phosphonic Acid-Mode of Action and Structure - Activity Relationship
1996
Abstract: (N-pyridylamino)methylenebisphosphonates exhibit strong herbicidal activity which may be reversed by supplementation of the growth media with aromatic amino acids. They appeare to be the inhibitors of aromatic amino acids biosynthesis acting as inhibitors of DAHP synthase the first enzyme of shikimate pathway. Over 40 analogues of these acids were synthesized in order to determine the structure-activity relationship.
Concentration of amino acids using supported liquid membranes with di-2-ethylhexyl phosphoric acid as a carrier
1997
Abstract Basic studies of a procedure for extraction of amino acids using a supported liquid membrane containing di-2-ethylhexyl phosphoric acid are presented. The extractions are made from an aqueous donor phase with pH 3 to a more acidic acceptor phase and the mass transfer is driven by the proton gradient between these phases. For 0.01 mM tryptophan and with 1 M HCl as acceptor phase, an extraction efficiency of 60% is obtained, constant up to at least 12 h. This permits concentration enrichment factors linearly increasing with time up to values of at least 150. For higher amino acid concentrations, the extraction efficiency is constant only over shorter time intervals.
Effective conjugation in conjugated polymers with strongly twisted backbones: A case study on fluorinated MEHPPV
2016
Conjugated polymers with strongly twisted backbones, such as MEHPPV with fluorinated vinylene units (F-MEHPPV), demand a redefinition of the all-important ‘effective conjugation length’ ECL, which we extract here by a facile graphical method. In MEHPPV (being essentially planar), the ECL coincides with the ‘maximum conducive chain length’ MCC and extends over about n ≈ 9 repetition units (RU). In F-MEHPPV, the MCC is similarly long with n ≈ 8, but the ECL localizes on just one RU. The strong twist in F-MEHPPV persists in the excited state, broadening the emission spectrum and quenching the fluorescence with reduced radiative and enhanced non-radiative rates.
Reliable and simple analytical methods for determination of citrulline and metabolically related amino acids by liquid chromatography after derivatiz…
2014
We describe the development of a high-performance liquid chromatography (HPLC) method for the determination of citrulline and other amino acids relevant to intestinal diseases. The amino acids were derivatized with 9-fluorenylmethylchloroformate (FMOC-Cl) and their derivatives were separated on two different columns, a core-shell column (Halo C18) and a silica-based monolith (Chromolith Performance RP-18). The derivatization reaction was optimized with respect to pH, buffer concentration and reproducibility. The optimal derivatization conditions were achieved with 0.4 M borate buffer at pH 9.20, a constant ratio of FMOC-Cl/total amino acids (10 : 1) and 75 mM tyramine after 1 min (quenching…
Identification and quantification of valuable phenolic compounds from red wines from western part of Romania
2019
The aim of this paper is to identify and quantify different phenolic compounds known and appreciated for their antioxidant action from five red wines from the west side of Romania. For the determinations HPLC methods were used, the samples were done in cycles of three for better results. Phenolic acids that drew the attention have different values that ranging from 1.3007 mg/L (elagic acid) to 19.3315 (t-cafftaric acid), some various flavonoids (flavone, flavonoli și flavanoli) the values of which were recorded between 0.9997 mg/L (apigenin) and 56.1617 mg/L (catechin) and the stilbens namely the resveratrol has reached the maximum value of 8.1427 mg/L. The phenolic compounds that were det…
Methacrylate ester-based monolithic columns for nano-LC separation of tocopherols in vegetable oils
2010
The separation and determination of tocopherols (Ts) in vegetable oils by nano-LC chromatography with UV-vis detection using lauryl methacrylate ester-based monolithic columns has been developed. The separation of Ts was optimized in terms of mobile phase composition on the basis of the best compromise among efficiency, resolution and analysis time. Using a mobile phase composed of ACN/methanol/water, an excellent resolution between Ts was achieved within 18 min. The LODs were lower than 0.26 μg/mL, being repeatability values of retention time and peak area below 0.15 and 3.1%, respectively. The method was applied to the quantification of Ts and tocotrienols present in several vegetable oil…