Structures, Antioxidant Properties, and Antimicrobial Properties of Eu(III), Gd(III), and Dy(III) Caffeinates and p-Coumarates.

In this study, we investigated the structures of lanthanide (Eu(III), Dy(III), and Gd(III)) complexes with p-coumaric (p-CAH2) and caffeic (CFAH3) acids using the FTIRKBr, FTIRATR, and Raman spectroscopic methods. The compositions of the solid phase caffeinates and p-coumarates were obtained on the basis of the amounts of hydrogen and carbon determined using an elemental analysis. The degree of hydration and the thermal decomposition of each compound were examined via a thermal analysis of TG, DTG, and DSC. Antioxidant spectroscopic tests were performed using the DPPH (1,1-diphenyl-2-picrylhydrazyl radical), FRAP (ferric reducing antioxidant activity), and ABTS (2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (diammonium salt radical cation) methods. The antimicrobial activity of each compound against Escherichia coli, Bacillus subtilis, and Candida albicans was investigated. The electrical properties of the liposomes which mimicked the microbial surfaces formed in the electrolyte containing the tested compounds were also investigated. The above biological properties of the obtained complexes were compared with the activities of p-CAH2 and CFAH3. The obtained data suggest that lanthanide complexes are much more thermally stable and have higher antimicrobial and antioxidant properties than the ligands (with the exception of CFAH3 in the case of antioxidant activity tests). The Gd(III) complexes revealed the highest biological activity among the studied lanthanide complexes.

Biologically Active Compounds of Plants: Structure-Related Antioxidant, Microbiological and Cytotoxic Activity of Selected Carboxylic Acids.

Natural carboxylic acids are plant-derived compounds that are known to possess biological activity. The aim of this review was to compare the effect of structural differences of the selected carboxylic acids (benzoic acid (BA), cinnamic acid (CinA), p-coumaric acid (p-CA), caffeic acid (CFA), rosmarinic acid (RA), and chicoric acid (ChA)) on the antioxidant, antimicrobial, and cytotoxic activity. The studied compounds were arranged in a logic sequence of increasing number of hydroxyl groups and conjugated bonds in order to investigate the correlations between the structure and bioactivity. A review of the literature revealed that RA exhibited the highest antioxidant activity and this property decreased in the following order: RA > CFA ~ ChA > p-CA > CinA > BA. In the case of antimicrobial properties, structure-activity relationships were not easy to observe as they depended on the microbial strain and the experimental conditions. The highest antimicrobial activity was found for CFA and CinA, while the lowest for RA. Taking into account anti-cancer properties of studied NCA, it seems that the presence of hydroxyl groups had an influence on intermolecular interactions and the cytotoxic potential of the molecules, whereas the carboxyl group participated in the chelation of endogenous transition metal ions.

The Mineral Profile of Polish Beers by Fast Sequential Multielement HR CS FAAS Analysis and Its Correlation with Total Phenolic Content and Antioxidant Activity by Chemometric Methods.

Beer is the most common alcoholic beverage worldwide, and is an excellent source of macro- and microelements, as well as phenolic compounds. In this study, a fast method for the determination of Na, K, Mg, Ca, Fe, Mn, and Cu in beer was developed using flame atomic absorption spectrometry. The precision of this method was between 0.8 and 8.0% (as the relative standard deviation (RSD)), and limits of detections were in the range of 0.45 (Mn)-94 µg/L (Na). Among the macroelements tested in the beer samples, K was found at the highest concentration, whereas Na was found at the lowest concentration level. Beer also turned out to be a good source of Mg and K. The total phenolic content (TPC) was determined by the Folin-Ciocalteu method, while the antioxidant activity was estimated by the ABTS method. The results show remarkable variations in the mineral content, TPC, and antioxidant activity across the beer types and brands. Moreover, the relations between the type, color, refraction index, antioxidant activity, extract, alcohol, mineral, and the total phenolic contents were investigated using the factor analysis of mixed data (FAMD) combined with hierarchical clustering on principal components (HCPC).

Dispersive liquid-liquid microextraction coupled to liquid chromatography tandem mass spectrometry for the determination of phenolic compounds in human milk.

This work describes a novel approach for the analysis of 11 phenolic compounds (naringenin, hesperetin, kaempferol, quercetin, epicatechin, epicatechin gallate, epigallocatechin gallate, genistein, daidzein, caffeic acid, gallic acid) in human milk. Clean-up of the sample and extraction of 11 analytes from milk was performed by dispersive liquid-liquid microextraction (DLLME). Under the optimal conditions, the extraction recoveries of 11 analytes were in a range from 94.3% to 108%. For determination of phenolic compounds in extracts, LC-ESI-MS/MS method was used. The calibration curves showed linearity in the concentration ranges from 0.01 to 1500 ng mL-1 and the limits of detection were in a range from 0.18 ng L-1 to 74 ng mL-1. The repeatability and intermediate precision expressed as the relative standard deviations were below 7.6% and 9.9%, respectively. The DLLME-LC-ESI-MS/MS method was successfully applied to the determination of phenolic compounds present in breast milk.

Postcolumn determination of polyphenolic antioxidants in Cirsium vulgare (Savi) Ten. extracts.

Novel methods for the determination of polyphenolic antioxidants present in extracts from inflorescences of Cirsium vulgare (Savi) Ten. based on ultra-high performance liquid chromatography with photodiode array and chemiluminescence detection have been developed. Under the optimized conditions of chromatographic separation the analytical characteristic of the method was performed. The proposed method was successfully applied to the determination of ten polyphenols present in inflorescences of Cirsium vulgare. A comparison of the contents of analytes in extracts prepared by using various extraction media (methanol, ethanol, 70% methanol, 70% ethanol, and water) was carried out for the first time. For the postcolumn detection of scavenging activity of polyphenolic antioxidants against reactive oxygen species (H2 O2 , • OH, O2• - ) three systems based on chemiluminescence of luminol were used. A review of the current scientific literature shows that this is the first report on the application of luminol-based postcolumn detection for the on-line investigation of • OH scavenging activity. The main compound determined in extracts from inflorescences of Cirsium vulgare was apigenin 7-O-glucuronide, whereas the highest antioxidant activity was observed for chlorogenic acid, luteolin 7-O-glucoside, and apigenin.

S-adenosyl-L-homocysteine hydrolase from a hyperthermophile (Thermotoga maritima) is expressed in Escherichia coli in inactive form - Biochemical and structural studies.

Thermotoga maritima is a hyperthermophilic bacterium but its genome encodes a number of archaeal proteins including S-adenosyl-L-homocysteine hydrolase (SAHase), which regulates cellular methylation reactions. The question of proper folding and activity of proteins of extremophilic origin is an intriguing problem. When expressed in E.coli and purified (as a homotetramer) at room temperature, the hyperthermophilic SAHase from T.maritima was inactive. ITC study indicated that the protein undergoes heat-induced conformational changes, and enzymatic activity assays demonstrated that these changes are required to attain enzymatic activity. To explain the mechanism of thermal activation, two crystal structures of the inactive form of T. maritima SAHase (iTmSAHase) were determined for an incomplete binary complex with the reduced cofactor (NADH), and in a mixture of binary complexes with NADH and with adenosine. In contrast to active SAHases, in iTmSAHase only two of the four subunits contain a bound cofactor, predominantly in its non-reactive, reduced state. Moreover, the closed-like conformation of the cofactor-containing subunits precludes substrate delivery to the active site. The two other subunits cannot be involved in the enzymatic reaction either; although they have an open-like conformation, they do not contain the cofactor, whose binding site may be occupied by an adenosine molecule. The results suggest that this enzyme, when expressed in mesophilic cells, is arrested in the activity-incompatible conformation revealed by its crystal structures.

Ultra-high Performance Liquid Chromatography with Photodiode Array and Chemiluminescence Detection for the Determination of Polyphenolic Antioxidants in Erigeron acris L. Extracts.

INTRODUCTION: The quality of herbs is directly related to the presence of polyphenolic antioxidants. This is the first report on the quantification of individual polyphenolic constituents of Erigeron acris L. OBJECTIVE: To develop a new method using ultra-high performance liquid chromatography with photodiode array and chemiluminescence (UHPLC-PDA-CL) detection for the separation and determination of polyphenols in Erigeron acris extracts. METHODOLOGY: The methanolic extracts from leaves and inflorescences of Erigeron acris were prepared by ultrasound assisted extraction. The chromatographic separation was performed on C18 column packed with 1.7-µm particles. The post-column CL detection was based on the enhancing effect of polyphenols on the CL generated in manganese(IV)-hexametaphosphate-formaldehyde system. RESULTS: The UHPLC method allowed to separate polyphenols in a short running time (13 min), which was three times shorter compared with traditional HPLC. The CL detection was characterised by 6-48 times higher sensitivity and up to three times lower detection limits compared to PDA detection. Qualitative and quantitative differences were observed in polyphenolic composition of Erigeron acris extracts. The main components of leaves were scutellarin and chlorogenic acid, whereas in inflorescences quercetin 3-O-glucoside was predominant. CONCLUSION: Coupling of UHPLC with CL detection has been developed for the first time. This advanced chromatographic technique coupled with sensitive CL detection is a powerful approach for the investigation of polyphenolic profiles in natural products. The shorter analysis time and diminished waste generation makes the UHPLC method more environmentally friendly and more cost-effective in comparison with conventional HPLC. Copyright © 2016 John Wiley & Sons, Ltd.

Application of direct-injection detector integrated with the multi-pumping flow system to chemiluminescence determination of the total polyphenol index.

In this work, we present a novel chemiluminescence (CL) method based on direct-injection detector (DID) integrated with the multi-pumping flow system (MPFS) to chemiluminescence determination of the total polyphenol index. In this flow system, the sample and the reagents are injected directly into the cone-shaped detection cell placed in front of the photomultiplier window. Such construction of the detection chamber allows for fast measurement of the CL signal in stopped-flow conditions immediately after mixing the reagents. The proposed DID-CL-MPFS method is based on the chemiluminescence of nanocolloidal manganese(IV)-hexametaphosphate-ethanol system. The application of ethanol as a sensitizer, eliminated the use of carcinogenic formaldehyde. Under the optimized experimental conditions, the chemiluminescence intensities are proportional to the concentration of gallic acid in the range from 5 to 350 ng mL(-1). The DID-CL-MPFS method offers a number of advantages, including low limit of detection (0.80 ng mL(-1)), high precision (RSD = 3.3%) and high sample throughput (144 samples h(-1)) as well as low consumption of reagents, energy and low waste generation. The proposed method has been successfully applied to determine the total polyphenol index (expressed as gallic acid equivalent) in a variety of plant-derived food samples (wine, tea, coffee, fruit and vegetable juices, herbs, spices).

A study on the selection of chemiluminescence system for the flow injection determination of the total polyphenol index of plant-derived foods.

Different chemiluminescence systems based on luminol, permanganate, manganese(IV) and cerium(IV) reagents were compared regarding their sensitivity and selectivity to determine plant polyphenols. Among the seventeen systems tested, Mn(IV)-formaldehyde-hexametaphosphate was considered to be the most suitable for polyphenols detection. The developed flow injection method (FI-CL) based on enhancing effect of polyphenols on Mn(IV) chemiluminescence is characterised by low detection limit of gallic acid (0.02µgL(-1)) and high precision (RSD=1.7%). The calibration graph was linear from 0.1 to 100µgL(-1). The selectivity studies revealed that the FI-CL method ensures accurate determination of the total polyphenols content in food samples. The method was successfully applied to analysis of a variety of plant-derived foods (wine, tea, cereal coffee, fruit and vegetable juices, herbs and spices). The proposed method is superior to conventional spectrophotometric assays due to its higher sample throughput (195samplesh(-1)), simplicity, sensitivity and, above all, higher selectivity.

Determination of polyphenolic compounds in Cirsium palustre (L.) extracts by high performance liquid chromatography with chemiluminescence detection.

The first method for the simultaneous determination of polyphenolic antioxidants in extracts from leaves of Cirsium palustre based on high performance liquid chromatography combined with flow injection chemiluminescence detection (HPLC-FI-CL) has been developed. The extracts were prepared by using methanol as extraction medium and two types of extraction methods (reflux and ultrasound assisted extraction). The post-column CL determination of polyphenols was based on their enhancing effect on the chemiluminescence intensity generated in manganese(IV)-hexametaphosphate-formaldehyde system in a phosphoric acid medium. Main antioxidants determined in C. palustre leaves were eriodictyol-7-O-glucoside, luteolin-7-O-glucoside and 6-hydroxyluteolin-7-O-glucoside belonging to flavonoids, and chlorogenic acid belonging to phenolic acids. Chromatographic separation was carried out on a C18 column with gradient elution by using a mobile phase containing 0.25% (v/v) phosphoric acid in water (solvent A) and 100% methanol (solvent B). Under the optimized conditions of chromatographic separation and CL detection the validation of the method was performed. The calibration curves showed good linearity in the concentration range from 0.5 to 40 µg mL(-1). The HPLC-FI-CL method was successfully applied to the determination of four polyphenolic compounds in methanolic extracts from leaves of C. palustre. The accuracy of the developed method was confirmed by the comparison of the results with those obtained by an HPLC-PDA method. The relative error of determination does not exceed 6.1%. However, the HPLC-FI-CL method is characterized by 40-65 times higher sensitivity compared to the HPLC-PDA method.

Determination of the total polyphenolic content in Cirsium palustre (L.) leaves extracts with manganese(IV) chemiluminescence detection.

It was found that weak chemiluminescence of manganese(IV)-hexametaphosphate-formaldehyde system was greatly enhanced by plant polyphenolic compounds. Based on this finding, a new flow injection chemiluminescence method (FI-CL) was developed for the determination of the total content of polyphenols in plant extracts. The calibration graph obtained for standard solutions of 6-hydroxyluteolin 7-O-glucoside (6OHLG) was linear in the range 0.001-0.8 µg mL(-1). The method was simple, rapid (203 samples h(-1)) and sensitive with a detection limit of 0.25 ng mL(-1). The FI-CL method was successfully applied to the determination of the total polyphenols content (as 6OHLG equivalents) in methanolic, ethyl acetate and aqueous extracts from leaves of Cirsium palustre (L.). Two types of solvent extraction methods (reflux and ultrasound assisted extraction) were used and compared in terms of extraction efficiency. A positive, significant linear correlation between the results obtained by FI-CL method and spectrophotometric methods was observed.

Determination of the flavonoids/antioxidant levels in Cirsium oleraceum and Cirsium rivulare extracts with cerium(IV)-rhodamine 6G chemiluminescence detection.

The determination of the sum of flavonoid compounds in extracts from inflorescences (expressed as mgL(-1) of apigenin) and leaves (expressed as mgL(-1) of linarin) of Cirsium oleraceum and Cirsium rivulare species by flow injection system with chemiluminescence detection (FI-CL) has been carried out. The method is based on the strong enhancement by polyphenols occurring in both plants of the CL signal generated by the reaction of cerium(IV) with rhodamine 6G in a sulfuric acid medium. Under the optimized conditions, the linear working ranges of 0.1-10 and 2.5-50µmolL(-1) were obtained for apigenin and linarin, respectively. The developed method is simple, sensitive with the detection limits of 38nmolL(-1) (apigenin) and 840nmolL(-1) (linarin) and offers high sample throughput (up to 300 samples per hour). The relative standard deviation was 0.62% and 3.75% for 10 measurements of 5µmolL(-1) apigenin and linarin, respectively. The proposed method has been successfully applied to determine the flavonoids/antioxidant levels in aqueous and methanolic extracts from inflorescences and leaves of C. oleraceum and C. rivulare. A possible mechanism of the enhancement of cerium(IV)-rhodamine 6G CL system by polyphenols was briefly discussed. For comparative studies, the antioxidant activity of C. oleraceum and C. rivulare extracts was also evaluated by spectrophotometric 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging method.

Flow injection chemiluminescence determination of the total phenolics levels in plant-derived beverages using soluble manganese(IV).

This study established a flow injection (FI) methodology for the determination of the total phenolic content in plant-derived beverages based on soluble manganese(IV) chemiluminescence (CL) detection. It was found that mixing polyphenols with acidic soluble manganese(IV) in the presence of formaldehyde evoked chemiluminescence. Based on this finding, a new FI-CL method was developed for the estimation of the total content of phenolic compounds (expressed as milligrams of gallic acid equivalent per litre of drink) in a variety of wine, tea and fruit juice samples. The proposed method is sensitive with a detection limit of 0.02 ng mL(-1) (gallic acid), offers a wide linear dynamic range (0.5-400 ng mL(-1)) and high sample throughput (247 samples h(-1)). The relative standard deviation for 15 measurements was 3.8% for 2 ng mL(-1) and 0.45% for 10 ng mL(-1) of gallic acid. Analysis of 36 different samples showed that the results obtained by the proposed FI-CL method correlate highly with those obtained by spectrophotometric methods commonly used for the evaluation of the total phenolic/antioxidant level. However, the FI-CL method was found to be far simpler, more rapid and selective, with almost no interference from non-phenolic components of the samples examined.

Determination of phenolic compounds and their antioxidant activity in Erigeron acris L. extracts and pharmaceutical formulation by flow injection analysis with inhibited chemiluminescent detection.

It was found that the chemiluminescence (CL) produced from the reaction of luminol with iodine in the alkaline medium was strongly inhibited by plant phenolic compounds. Based on this finding, a new flow injection CL method was developed for the determination of caffeic acid and 6'-caffeoylerigeroside. The latter compound was isolated for the first time from Erigeron acris L. herb. The method was simple, rapid and sensitive with a detection limit of 4 x 10(-3) ng mL(-1) (caffeic acid) and 0.18 ng mL(-1) (6'-caffeoylerigeroside), linear range of 0.1-1.5 ng mL(-1) (caffeic acid) and 1-200 ng mL(-1) (6'-caffeoylerigeroside), relative standard deviation of 3.3% for 10 measurements of 0.45 ng mL(-1) caffeic acid and 2.9% for 40 ng mL(-1) 6'-caffeoylerigeroside. This method was successfully applied to determine the content of phenolic compounds/antioxidant activity of E. acris L. extracts and phenolic acids content in pharmaceutical formulation. A possible mechanism of the inhibition of the proposed CL system was discussed.