Search results for "Reagent"

Determination of 5-nitrofurylacrylic acid in wines by high-performance liquid chromatography

1988

Scopolamine analysis in beverages: Bicolorimetric device vs portable nano liquid chromatography

2021

Abstract Scopolamine (SCP) is often involved in sexual assaults and robberies, particularly in recreational environments. Therefore, analytical tools are required for the analysis of this compound amenable for the field. In this work, a sensor for SCP is described based on the entrapment of KMnO4 into polydimethylsiloxane (PDMS). The possibility of using KMnO4 in combination with the reagent 1,2-naphtoquinone-4-sulfonate (NQS) giving a double sensor acting as a bicolorimetric device is also demonstrated. In contact with the sample, the PDMS composite delivers MnO4−, which reacts rapidly with SCP under basic conditions causing a change of the color of the solution that can be related to the …

Peak dispersion in gradient elution: An insight based on the plate model.

2020

Gradient elution in liquid chromatography reduces the analysis time, improves the efficiency and increases the peak capacity. The study of this chromatographic mode has been based mainly on kinetic dispersion models. The plate model has been applied to a lesser extent, despite being the basis for the concepts of plate height and chromatographic efficiency. In this work, a general equation describing peak dispersion in HPLC gradient elution is derived from the plate model. This equation is studied and validated for three types of gradients: (i) a reference gradient without ramp in which the retention factor varies with time identically throughout the column, (ii) a gradient of stationary pha…

Modulation of retention and selectivity in oil-in-water microemulsion liquid chromatography: A review

2019

Microemulsions (MEs) are stable, isotropically clear solutions consisting of an oil and water stabilized by a surfactant and a co-surfactant. Oil-in-water microemuslion liquid chromatography (MELC) is a relatively new chromatographic mode, which uses an O/W ME as mobile phase. Retention, selectivity and efficiency can be modified by changing the concentration of the ME components and the ratio between the aqueous and oil phases. This work makes a critical survey on the information found in the literature about the mobile phase compositions that lead to the creation of successful O/W ME mobile phases, as well as the effect of pH for ionizable compounds and temperature. The viability of perfo…

Preparation of ferulic acid derivatives and evaluation of their xanthine oxidase inhibition activity.

2007

Several ferulic acid ethyl esters (3a-h) were synthesized under the Knoevengel reaction condition and they were further reduced to afford the respective allylic alcohol derivatives (4a-g). Some of them were evaluated for the xanthine oxidase (XO) inhibitory activity. Among them, 3h exhibited a significant inhibitory activity with an IC50 value of 1.35 x 10(-5) M, while the IC50 value of allopurinol used as the positive control was 1.49 x 10(-5) M. The study suggested that the higher acidity of the phenolic OH group in the ferulic acid derivatives might result in improved XO inhibitory activity.

Perfluoroketene dithioacetals and perfluorodithiocarboxylic acid derivatives: Versatile tools for organofluorine synthesis

2007

Perfluoroketene dithioacetals are simple and versatile compounds that can be transformed into a large variety of trifluoromethyl derivatives, in particular aza- and thiaheterocycles, perhalodithiocrotonic esters, and fluorinated dithiol thiones. These unsaturated perfluorodithioesters and analogs give interesting polar cycloaddition reactions whose mechanism is strongly influenced by the fluorine substitution. This substitution plays an important role in the reactivity of saturated perfluorodithiocarboxylic acids as well. Except for the carbophilic addition of allyl Grignard reagents to perfluorocarboxamides, a domino thiophilic addition-fluoride elimination was the main reaction process. I…

Tuning the Basicity of Synergic Bimetallic Reagents: Switching the Regioselectivity of the Direct Dimetalation of Toluene from 2,5‐ to 3,5‐Positions

2008

Meta-meta metalation: Remarkably, toluene can be directly dimanganated or dimagnesiated at the 3,5-positions using bimetallic bases with active Me3SiCH2 ligands (see scheme, blue). In contrast, n-butyl ligands lead to 2,5-metalation (red). tmp=2,2,6,6-tetramethylpiperidide.

Fast blue B functionalized silica-polymer composite to evaluate 3,5-dihy-droxyhydrocinnamic acid as biomarker of gluten intake

2021

Celiac disease is an immune-mediated systemic disorder elicited by gluten and related prolamines in genetically susceptible individuals. The current treatment is a strict and lifelong gluten-free diet. However, compliance with the gluten-free diet is not always adequate and many food products contain low concentrations of gluten. The determination of dietary transgressions is a challenge for patients, physicians and dietitians. Alkylresorcinols (AR) have been proposed as sensitive and specific biomarkers of gluten consumption. In this work silica-polymer composites doped with fast blue B reagent (FB) have been used to estimate alkylresorcinols in biological samples. The proposed colorimetri…

Photocrosslinking of dextran and polyaspartamide derivatives: a combination suitable for colon-specific drug delivery.

2007

Abstract The aim of this study was to prepare and characterize novel hydrogels with polysaccharide–polyaminoacid structure, able to undergo an enzymatic hydrolysis in the colon and potentially useful for treating inflammatory bowel diseases (IBD). Starting materials were methacrylated dextran (DEX-MA) and methacrylated α,β-poly(N-2-hydroxyethyl)- dl -aspartamide (PHM). These polymers were photocrosslinked by exposure of their aqueous solutions at 313 nm without photoinitiators. Different samples, shaped as microparticles, were obtained as a function of polymer concentration and irradiation time. FT-IR analysis confirmed the occurrence of a co-crosslinking between DEX-MA and PHM in all exper…

Selektivit�tsstudien: OH-, NH- und SH-gruppenspezifische Reagentien - ihre Anwendung in der organischen Analytik und als Schutzgruppen in der Synthese

1992

Selectivity: OH-, NH- and SH-Groupspecific Reagents. The Application in Organic Analysis and as Protective Groups Phosphylhalides and -pseudohalides R1R2P(O)X (X = Cl, F, CN, N3, OC6H4NO2(p)) reactdepending on X- with a different selectivity with OHNH- and SH-groups. Vinylsulfones ArSO2CH = CH2 are SH-selective. Silanes R3SiH are OH-selective. By exchange of one ligand bound on P, SO2 or Si by the 5-dimethylamino resp. the 5-methoxynaphthalinogroup reagents are formed, which combine group selectivity with fluorescence. The fluorescence is quenched if a ligand or the leaving group is substituted by a NO2-group. The fluorescence appears again if after the group selective fixation the ligand w…