Exploring Negative Chemical Ionization of Per- and Polyfluoroalkyl Substances via a Liquid Electron Ionization LC-MS Interface.

Per- and polyfluoroalkyl substances (PFASs) are a class of aliphatic manufactured compounds comprising fluoro-chemicals with varied functional groups and stable carbon-fluorine bonds. They are defined as "forever chemicals" due to their persistent and bioaccumulative character. These substances have been detected in various environmental samples, including water, air, soil, and human blood, posing significant health hazards. High-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) is typically employed for the analysis of PFASs. Negative chemical ionization (NCI) is generally coupled to gas chromatography (GC) and offers high selectivity and sensitivity for compounds containing electronegative atoms, such as PFASs. The liquid electron ionization (LEI) interface is an efficient mechanism developed to robustly couple a liquid flow rate from an LC system to an EI or a CI source. This interface has been successfully utilized for pesticide determination in UHPLC-LEI-CI in negative ion mode (NCI). This work aims to evaluate different parameters involved in the ionization of PFASs analyzed in LC-LEI-NCI and subsequently develop a method for their detection in real samples. The parameters considered for this study include (i) a comparison of different CI reagent gases (methane, isobutane, and argon); (ii) the use of acetonitrile as both the chromatographic solvent and CI reagent gas; (iii) the presence of water and formic acid as chromatographic mobile phase components; and (iv) the mobile phase flow rate. The optimal combination of these parameters led to promising results. Tentative fragmentation pathways of PFASs in NCI mode are proposed based on the dissociative electron capture mechanism.

Oxetan-3-ols as 1,2-bis-Electrophiles in a Brønsted-Acid-Catalyzed Synthesis of 1,4-Dioxanes.

Annulations that combine diacceptors with bis-nucleophiles are uncommon. Here, we report the synthesis of 1,4-dioxanes from 3-aryloxetan-3-ols, as 1,2-bis-electrophiles and 1,2-diols. Brønsted acid Tf2NH catalyzes both the selective activation of the oxetanol, to form an oxetane carbocation that reacts with the diol, and intramolecular ring opening of the oxetane. High regio- and diastereoselectivity are achieved with unsymmetrical diols. The substituted dioxanes and fused bicyclic products present interesting motifs for drug discovery and can be further functionalized.

Mitoxantrone, pixantrone and mitoxantrone (2-hydroxyethyl)piperazine are toll-like receptor 4 antagonists, inhibit NF-κB activation, and decrease TNF-alpha secretion in primary microglia.

Toll-like receptor 4 (TLR4) recognizes various endogenous and microbial ligands and is an essential part in the innate immune system. TLR4 signaling initiates transcription factor NF-κB and production of proinflammatory cytokines. TLR4 contributes to the development or progression of various diseases including stroke, neuropathic pain, multiple sclerosis, rheumatoid arthritis and cancer, and better therapeutics are currently sought for these conditions. In this study, a library of 140 000 compounds was virtually screened and a resulting hit-list of 1000 compounds was tested using a cellular reporter system. The topoisomerase II inhibitor mitoxantrone and its analogues pixantrone and mitoxantrone (2-hydroxyethyl)piperazine were identified as inhibitors of TLR4 and NF-κB activation. Mitoxantrone was shown to bind directly to the TLR4, and pixantrone and mitoxantrone (2-hydroxyethyl)piperazine were shown to inhibit the production of proinflammatory cytokines such as tumor necrosis factor alpha (TNFα) in primary microglia. The inhibitory effect on NF-κB activation or on TNFα production was not mediated through cytotoxity at ≤ 1 µM concentration for pixantrone and mitoxantrone (2-hydroxyethyl)piperazine treated cells, as assessed by ATP counts. This study thus identifies a new mechanism of action for mitoxantrone, pixantrone, and mitoxantrone (2-hydroxyethyl)piperazine through the TLR4.

Mass Spectrometry Based Approach for Organic Synthesis Monitoring.

Current mass spectrometry-based methodologies for synthetic organic reaction monitoring largely use electrospray ionization (ESI), or other related atmospheric pressure ionization-based approaches. Monitoring of complex, heterogeneous systems may be problematic because of sampling hardware limitations, and many relevant analytes (neutrals) exhibit poor ESI performance. An alternative monitoring strategy addressing this significant impasse is condensed phase membrane introduction mass spectrometry using liquid electron ionization (CP-MIMS-LEI). In CP-MIMS, a semipermeable silicone membrane selects hydrophobic neutral analytes, rejecting particulates and charged chemical components. Analytes partition through the membrane, and are then transported to the LEI interface for sequential nebulization, vaporization, and ionization. CP-MIMS and LEI are both ideal for continuous monitoring applications of hydrophobic neutral molecules. We demonstrate quantitative reaction monitoring of harsh, complex reaction mixtures (alkaline, acidic, heterogeneous) in protic and aprotic organic solvents. Also presented are solvent-membrane compatibility investigations and, in situ quantitative monitoring of catalytic oxidation and alkylation reactions.

Anaerobic digestion of orange peel in a semi-continuous pilot plant: An environmentally sound way of citrus waste management in agro-ecosystems.

The management of residues of citrus processing involves economic and environmental problems. In particular, the uncontrolled disposal of citrus processing waste near production sites can have heavy impacts on air, soil, surface water bodies and groundwater. Anaerobic digestion has been proposed as a viable alternative for citrus waste valorisation, if some problems, linked to the biochemical processes, are overcome. Although many experimental tests have studied the inhibitory effects of the high essential oil content of orange peel on biomethanisation processes, fewer experiences have been carried out in continuous or semi-continuous pilot digesters, more similar to the full-scale biogas plants, using real orange peel. This study has evaluated the methane production through anaerobic digestion of industrial orange peel using a pilot plant (84L) with semi-continuous feeding at increasing Organic Loading Rates (OLR) and essential oil (EO) supply rates (EOsr) until the complete process inhibition. Under mesophilic conditions, the highest daily specific methane yield was achieved at OLR of 1.0gTVSL-1 d-1 and EOsr of 47.6mgL-1d-1. Partial inhibition of the anaerobic digestion was detected at OLR and EOsr of 1.98gTVSL-1d-1 and 88.1mgL-1 d-1, respectively and the process irreversibly stopped when OLR and EOsr reached 2.5gTVS L-1 d-1 and 111.2mgL-1 d-1, respectively. Under thermophilic conditions, the cumulative methane production (0.12LgTVS-1) was about 25% of that under mesophilic conditions (0.46LgTVS-1). The thermophilic digestion was completely inhibited at lower OLR (1.98gTVSL-1 d-1) and EOsr (88.1mgL-1 d-1) compared to mesophilic conditions. This study confirmed the suitability of anaerobic digestion of orange peel for biomethane production (provided that the right management of the process is set), in view of an environmentally sound way of agricultural residues management in agro-ecosystems.

Occurrence of Enantioselectivity in Nature: The Case of (S)-Norcoclaurine.

This review article is aimed at providing a monographic overview on (S)-norcoclaurine (NC) alkaloid from three diverse points of view, collected all together for the first time: 1) the synthetic one, where the compound is seen as a target chiral molecule to be obtained in the highest optical purity and as a starting point for the development of biocatalytic asymmetric syntheses of tetrahydroisoquinoline alkaloids; 2) the chromatographic one, which addresses the HPLC separation of the two NC enantiomers; and 3) the biochemical one, for which a thorough understanding of the topology and mechanism of action of norcoclaurine synthase (NCS) enzyme is still a matter of debate. Special emphasis on the most recent studies in the field is given by discussing the results published by the main research groups who are working on NC and NCS.

Antioxidants in the prevention of UVB-induced keratynocyte apoptosis.

Skin cells can respond to UVB-induced damage by counteracting it through antioxidant activation and DNA repair mechanisms or, when damage is massive by undergoing programmed cell death. Antioxidant factors, and, in particular, food compounds, have attracted much interest because of their potential use in new protective strategies for degenerative skin disorders. Melatonin, creatine and hydroxytyrosol show a variety of pharmacological and clinical benefits including anti-oxidant and anti-inflammatory activities. Here, the potential protective actions of antioxidant compounds against UVB-induced apoptosis were investigated in human keratinocytes. The cells were pre-treated with antioxidants before UVB exposure and their effect evaluated by means of ultrastructural and molecular analyses. After UVB radiation typical morphological apoptotic features and in situ DNA fragmentation after TUNEL reaction, appeared. A significant numerical decrease of apoptotic patterns could be observed when antioxidants were administrated before cell death induction. Moreover, both the intrinsic and extrinsic apoptotic pathways appeared activated after UVB radiation, and their down-regulation has been shown when antioxidants were added to cells before death induction. In conclusion, these compounds are able to prevent apoptotic cell death in human keratinocytes exposed to UVB, suggesting, for these molecules, an important role in preventing skin damage.

Anti-apoptotic activity of hydroxytyrosol and hydroxytyrosyl laurate.

Hydroxytyrosol (HyT) is a polyphenol primarily released in olive mill wastewater and in olive oil. In animal and cell model studies, HyT and its metabolites have strong antioxidant and antimicrobial activities, as well as beneficial effects on the cardiovascular system and in several human diseases. Differently, many researchers reported that HyT down-regulates tumor cell viability and cell cycle progression, and induces reactive oxygen species (ROS) production and apoptosis. In this study we have investigated the effects of HyT and the corresponding ester hydroxytyrosyl laurate in U937 cells, a human monocytoid cell line, and in C2C12 myoblasts, a murine proliferating muscle cell model, after apoptotic death induction. Inverted, light and transmission electron microscopy have been utilized to characterize cell death patterns. H2O2, at the concentrations known to induce apoptosis, was utilized as cell death trigger. The results obtained show that laur-HyT has a protective antioxidant effect against H2O2 treatment, greater than HyT, so having a role in the prevention of apoptotic death in normal and tumor cells. These data suggest these compounds as good candidate for novel therapeutic strategies.

Hybrid polyacrylamide chiral stationary phases for HPLC prepared by surface-initiated photopolymerization.

Two hybrid polyacrylamide chiral stationary phases (CSPs) for HPLC have been synthesized by a new surface-initiated photo-induced radical polymerization approach of enantiopure N,N'-diacryloyl derivatives of (1R,2R)-diaminocyclohexane (CSP1) and (1R,2R)-diphenylethylenediamine (CSP2). This system is based on the activation of mesoporous silica microparticles by chemically bonded trichloroacetyl groups and dimanganese decacarbonyl as catalyst. UV irradiation was performed using a lab-made quartz photochemical reactor, ad hoc designed for the photo-induced polymerization process on the surface of microparticles. The two phases were evaluated and compared as chromatographic supports for the enantioselective HPLC of model chiral compounds. Their physico-chemical properties and chromatographic performances were also evaluated in comparison with those exhibited by the homologue CSPs obtained by the grafting-from thermal-induced process (CSP3 and CSP4). The new photopolymerization approach yielded higher grafting density than the thermal-induced one, especially in the case of the less reactive monomer (the diacryloyl derivative of (1R,2R)-diphenylethylenediamine), good chromatographic efficiency and a broad application field under normal phase and polar organic mode conditions.

A new versatile solvatochromic amino-macrocycle. From metal ions to cell sensing in solution and in the solid state.

A new fluorescent NBD-polyaza-macrocycle sensor (L) was synthesized. The coordination of Cu(ii) and Zn(ii) in acetonitrile switches on the fluorescence with different emission wavelengths. Cu(ii) complexes showed solid-state fluorescence. Both L and Cu-complex interact with human cell line (U937) highlighting the cell membrane by fluorescence microscopy.

Prenylated isoflavonoids: Botanical distribution, structures, biological activities and biotechnological studies. An update (1995-2006).

In contrast with the parent class of flavonoids, the distribution of the isoflavonoid class in the plant kingdom is relatively limited, probably owing to the sporadic occurrence of isoflavone synthase. Isoflavonoids have been mostly found in the subfamily Fabaceae/Papilionoideae of the Leguminosae family. Isoprenoid-substituted (also called complex) isoflavonoids are expressed from a smaller number of plants, as a result of the similarly restricted distribution of prenyltransferases (PT-ase). After the reviews of Tanara & Ibrahim (1995), Boland & Donnelly (1997), the Handbook of Flavonoids by Harborne & C ( Handbook of Flavonoids, 1999), and the paper by Harborne and Williams (2000) few other reports concern the distribution and the biological activity of complex isoflavonoids, except a list of isoflavonoids produced from non leguminous plants. This review deals with an update of the literature on isoprenylated isoflavonoids in the years 1995-2006 and is focused on the following highlights. 1. Natural sources of complex isoflavonoids (2000-2006); 2. Chemical structure variety: new entries (2000-2006) 3. Biological activities and a possible structure-activity relationship (1995-2006) 4. In vitro production and microbial metabolism (1995-2006).

Direct preparation of unsymmetrical difunctionalized cyclen derivatives by an Ugi multicomponent reaction.

A new and efficient synthetic protocol for the preparation of unsymmetrical difunctionalized cyclen and its close derivatives using a modified Ugi reaction (N-split Ugi) is described. The scope of this methodology is further extended by the successful use of various isocyanides, highly functionalized carboxylic acids, and aldehydes.

Dynamic HPLC of stereolabile iron(II) complexes on chiral stationary phases.

A series of chiral tris-(1,10)-phenanthroline iron(II) complexes have been resolved by HPLC on chiral stationary phases based on either cellulose tris-(3,5-dimethylphenylcarbamate) or teicoplanin. At sub ambient temperatures, baseline separation of the enantiomers was observed for five different iron(II) complexes featuring substituted phenanthroline ligands. Dynamic HPLC profiles were observed near or above room temperature, indicating on-column Delta/Lambda enantiomerization. Rate constants for the Delta/Lambda interconversion in free solution and during chromatography were obtained by thermal racemization experiments and by computer simulation of the HPLC dynamic plots, respectively.

The contribution of oxazolidinone frame to the biological activity of pharmaceutical drugs and natural products.

The development of resistance by the antibiotics in the Gram-positive pathogenic bacteria over the last twenty years and continuing today has created a need for new antibiotic classes, which may be unaffected by existing bacterial resistance. The oxazolidin-2-ones represent not only a new class with a novel mechanism of action, but also satisfy the requirement for overcoming the resistance mechanisms. Both linezolid and eperozolid, the first chemical candidates, arose from the piperazine subclass, with the first one being chosen further development because of its enhanced pharmacokinetic properties. The main attractive traits of the oxazolidinone series has encouraged further work in the area, and the patent literature reveals that extensive chemical investigation is currently being made. The unexpected early resistance development emphasizes the need for further exploration of features of the oxazolidinone to eliminate these deficiencies. Recently, several changes, involving the C5 side chain as well the N-phenyl heterocyclic ring, give promise for such improvement. Oxazolidinone antibacterial agents comprise also ketolides, derivatives of macrolides, such as erythromycin A, with a newly formed carbamate cycle, with a largely unexplored potential. The oxazolidinone nucleus does not appear only in the structures of antimicrobial drugs, but a number of biological activities are connected with frameworks including the oxazolidinone ring. A partial list of these activities comprises enzyme inhibitors, agonists and antagonists, with a particular citation for a new generation of selective monoamino oxidase inhibitors (befloxatone). The oxazolidinone moiety was found in the structure of few biologically active natural products, such as (-)-cytoxazone and streptazolin. Moreover, in some cases the oxazolidinone ring has been chosen for the preparation of isosteric aza analogues of natural compounds (podophyllotoxin, pilocarpine) that can be more easily synthesised and more hardly inactivated. Finally, the participation of oxazolidinone chiral auxiliaries to several syntheses of natural products must be acknowledged.

Dynamic HPLC on chiral stationary phases: a powerful tool for the investigation of stereomutation processes.

Dynamic HPLC on enantioselective stationary phases has become a well-established technique to investigate chiral molecules with internal motions that result in stereoinversion and occur on the time scale of the separation process. Kinetic parameters for the on-column interconversion phenomena can be extracted from experimental peak profiles by computer simulation or by direct calculation methods. The technique has been used in a wide range of temperatures and is complementary in scope to dynamic NMR spectroscopy.

Coordination behavior toward copper(II) and zinc(II) ions of three ligands joining 3-hydroxy-2-pyridinone and polyaza fragments.

The synthesis and characterization of new polydentate ligand 2-(N),2'-(N')-bis[2-(3-hydroxy-2-oxo-2H-pyridin-1-yl)acetamido]-1(N'),2(N),2'(N')-trimethyl-2,2'-diaminodiethylamine (L3) is reported. The coordination properties of L3 and of two analogous macrocyclic ligands (L1 and L2) toward Cu(II) and Zn(II) metal ions are reported. All three ligands show the 3-hydroxy-2(1H)-pyridinone (HPO) groups attached as sidearms to a polyaza fragment, which is a macrocyclic framework in the case of L1 and L2 while it is an open chain in the case of L3. The role of the polyaza fragments in preorganizing the two sidearms was investigated. The basicity of L3 and the binding properties of L1-L3 were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). UV-vis spectra as well 1H and 13C NMR experiments were used to understand the role of the HPO and of the polyaza fragments in the stabilization of the cations. While L1 forms stable mono- and dinuclear complexes, L2 and L3 can form only mononuclear species with each of the metal ions investigated. In the main mononuclear species of L2 and L3, the two HPO moieties stabilize the M(II) in a square planar geometry due to the two oxygen atoms of each HPO. The coordination sphere of the metal is completed by adding a secondary ligand such as water molecules in the case of Cu(II) systems or OH- in the Zn(II) systems. These results are confirmed by the crystal structures of the [CuH(-1)L2]+ and [CuH(-1)L3]+ species reported herein. Two conformations of L1 can be hypothesized in the formation of the dinuclear species, as suggested by NMR experiments on the [ZnH(-2)L1] species, which shows two conformers slowly interchanging on the NMR time scale, one of which was found to be more insoluble.

A macrocyclic ligand able to bind gallium(III) by preorganized pendant arms; coordination and kinetic studies.

The equilibria and kinetics of the binding of gallium(III) to 4-(N),10-(N)-bis[2-(3-hydroxo-2-oxo-2-H-pyridine-1-y1)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) were investigated in acidic medium at ionic strength 1 M (NaClO4). Spectrophotometric titrations in the UV region revealed that L is able to bind Ga3+ also at high H+ concentration. The kinetic (stopped-flow) experiments are interpreted on the basis of three parallel reaction paths (i) M3+ + H2L2+ = M(H2L)5+ where M(H2L)5+ is in a steady state, (ii) M(OH)2+ + H2L2+ = M(HL)4+ + H2O and (iii) M(OH)2+ + HL+ = ML3+ + H2O. The first-order rate constants for conversion of the outer-sphere into the inner-sphere complexes are similar to those of the Ga(III)/tropolone system which is known to react according to the dissociative Id mechanism and to the relevant rate constants for water exchange at the metal ion. The effects of pH on the UV-Vis absorption, fluorescence emission properties and NMR spectral features on the Ga(III)/L system were also investigated. Spectrophotometric titrations in the UV region reveal that, in acid medium the prevailing species is M(HL)4+ whereas the chelate ML3+ prevails for [H+] < 0.01 M. The results indicate metal coordination at the oxygen atoms of the 3-hydroxo-2-oxopyridine residues.

Synthesis and interaction with copper(II) cations of cyano- and aminoresorcin[4]arenes.

Following our studies on resorcin[4]arenes, we synthesized new macrocycles containing cyanomethyl and aminomethyl side chains. Three stereoisomers (2a-c) of the former were obtained by BF3*Et2O tetramerization of the corresponding trans-cinnamic acid derivative and were shown to be in the 1,2-alternate, cone, and 1,3-alternate conformations. Conversely, the tetraamino derivative 6a in the cone conformation was prepared from the corresponding tetrabromide 3a. The interactions with Cu(II) cations of the new compounds were analyzed by measurements of 1H NMR and EPR spectra in parallel with molecular modeling calculations.