Heterometallic 3d–4f coordination polymers: Synthesis,characterization and magnetic properties of 1D zigzag chains containing samarium and terbium

Reaction of the copper precursor [Cu(MeOsaltn)(H₂O)] (H₂MeOsaltn = N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane) with Ln(NO₃)₃·6H₂O (Ln = Sm and Tb) and pyrazine-2,3-dicarboxylic acid (H₂pyrdic) results in the formation of 1D zigzag chains with the general formula of [Cu(MeOsaltn)Ln(NO₃)(pyrdic)]_n·nDMF. X-ray crystal structures reveal that the samarium and terbium compounds are isostructural and crystalize in the orthorhombic space group Pbcn. The chains are composed of heterodinuclear copper–lanthanide building blocks which are linked by the pyrazine-2,3-dicarboxylate bridging units. Temperature-dependent susceptibility measurements indicate antiferromagnetic exchange interactions for the samarium–copper chain whereas for the terbium–copper compound ferromagnetic interactions are observed.     

Therapeutic Potential of Highly Selective A3 Adenosine Receptor Ligands in the Central and Peripheral Nervous System

Ligands of the G_i protein-coupled adenosine A₃ receptor (A₃R) are receiving increasing interest as attractive therapeutic tools for the treatment of a number of pathological conditions of the central and peripheral nervous systems (CNS and PNS, respectively). Their safe pharmacological profiles emerging from clinical trials on different pathologies (e.g., rheumatoid arthritis, psoriasis and fatty liver diseases) confer a realistic translational potential to these compounds, thus encouraging the investigation of highly selective agonists and antagonists of A₃R. The present review summarizes information on the effect of latest-generation A₃R ligands, not yet available in commerce, obtained by using different in vitro and in vivo models of various PNS- or CNS-related disorders. This review places particular focus on brain ischemia insults and colitis, where the prototypical A₃R agonist, Cl-IB-MECA, and antagonist, MRS1523, have been used in research studies as reference compounds to explore the effects of latest-generation ligands on this receptor. The advantages and weaknesses of these compounds in terms of therapeutic potential are discussed.     

Polymeric bidimensional self-assembling of [Hg(RC6H4NNNC6H4R)2Py] (R = m-acetyl) through metal-η,η-arene π-interactions and non classical C-H?O bonding: Synthesis and X-ray characterization of a bis diaryl symmetric-substituted triazenide complex of Hg(II)

Deprotonated 1,3-bis(3-acetylphenyl)triazene reacts with Hg(CH₃COO)₂ and pyridine to give light-yellow crystals of {[Hg^II(RC₆H₄NNNC₆H₄R)₂Py]}_n (R = acetyl). The tectons [Hg^II(RC₆H₄NNNC₆H₄R)₂Py] [R = CH₃C(O)] are linked to pairs as centrosymmetric dimers through reciprocal metal-η²-arene π-interactions. The dimeric units are operated by a screw axis 2₁ parallel to the crystallographic direction [0 1 0], also through a reflection-translation plane parallel to the c-axis, resulting a supramolecular bidimensional (2D) assembling of the dimeric tectons through non classical C-H?(O)CCH₃ bonding.     

Irradiation of the porphyrin causes unfolding of the protein in the protoporphyrin IX/beta-lactoglobulin noncovalent complex

Porphyrins such as protoporphyrin IX (PPIX) are known to occasionally cause conformational changes in proteins for which they are specific ligands. It has also been established that irradiation of porphyrins noncovalently intercalated between bases or bound to one of the grooves can cause conformational effects on DNA. Conversely, there is no evidence reported in the literature of conformational changes caused by noncovalently bound PPIX to globular proteins for which the porphyrin is not a specific ligand. This study shows that the irradiation of the porphyrin in the PPIX/lactoglobulin noncovalent complex indeed causes a local and limited (approximately 7%) unfolding of the protein near the location of Trp19. This event causes the intrinsic fluorescence spectrum of the protein to shift to the red by 2 nm and the average decay lifetime to lengthen by approximately 0.5 ns. The unfolding of lactoglobulin occurs only at pH >7 because of the increased instability of the protein at alkaline pH. The photoinduced unfolding does not depend on the presence of O2 in solution; therefore, it is not mediated by formation of singlet oxygen and is likely the result of electron transfer between the porphyrin and amino acid residues.     

Relaxation response of polymers containing highly flexible side groups monitored by broadband dielectric spectroscopy

The relaxation behavior of poly(5-acryloxymethyl-5-methyl-1,3-dioxacyclohexane), a polymer containing highly flexible side groups, is studied by broadband dielectric spectroscopy in the frequency and temperature ranges 10(-1)-10(9) Hz and 123-473 K, respectively. Above the glass transition temperature T(g) the dielectric loss in the frequency domain exhibits a prominent alpha absorption, followed in increasing order of frequencies by two secondary absorptions called beta and gamma. At temperatures slightly higher than T(g), the a relaxation is well separated from the beta, but as temperature increases overlapping between both relaxations augments forming an alphabeta absorption in the vicinity of 420 K. This latter absorption displays a shoulder on its high-frequency side corresponding to the y relaxation. The strength of the a relaxation decreases with increasing temperature, eventually vanishing at the temperature at which the alphabeta absorption is formed. The time retardation spectra of the isotherms are calculated and further used to facilitate the deconvolution of the overlapping relaxations. The fact that the temperature dependence of the beta relaxation also describes that of the alphabeta absorption suggests that both relaxations have the same nature. It seems that as temperature increases, the a relaxation feeds on the beta absorption until its complete disappearance. The gamma relaxation, in turn, seems to increase at the expense of the alphabeta process at high temperature.     

Optical Activity in the Near‐IR Region: The λ=980 nm Multiplet of Chiral Yb3+ Complexes

We used a very simplified electrostatic model based on charge and polarizability of atoms and groups on an organic ligand around a lanthanide ion to predict the near‐infrared electronic circular dichroism (NIR ECD) spectra of Yb³⁺ (a monoelectronic ion). We tuned our method by using two widely different complexes. The first was the heterobimetallic species CsYb(hfbc)₄ [hfbc=(?)‐3‐heptafluorobutyrylcamphorate], in which the ligand is a diketonate and, as such, is endowed with a chromophore with strong UV absorption (π–π^*). Its oxygen atoms define a square antiprism, which provides a symmetric coordination polyhedron. The second system was Yb DOTMA [DOTMA=(1R,4R,7R,10R)‐α,α′,α′′,α′′′‐tetramethyl‐1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid], a chiral Yb analogue of Gd DOTA (DOTA=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid), in which the ligand lacks relevant electronic transitions and provides a dissymmetric cage. The relative weights of dynamic (ligand polarization) and static contributions to Yb NIR ECD were evaluated, and the spectra appear to have been well predicted by theory through the introduction of a heuristic weight factor. To validate the approach and to confirm the value of the weight factor, we applied it to two other compounds, namely, Na₃Yb(BINOLate)₃ and Yb(BINOLAM)₃ [BINOLate=2,2′‐dihydroxy‐1,1′‐binaphthyl; BINOLAM=3,3′‐bis(diethylaminomethyl)‐1‐1′‐bi‐2‐naphthol].     

Azido‐Substituted BODIPY Dyes for the Production of Fluorescent Carbon Nanotubes

A series of azido‐dyes were synthesized through Knoevenagel reactions of an azido‐BODIPY with aromatic aldehydes. The nature of the substituents allowed the fine tuning of their spectroscopic properties. The dyes were used to decorate oxidized multiwalled carbon nanotubes (ox‐MWCNTs), bearing terminal triple bond groups, by CuAAC reactions, affording fluorescent materials. This decoration allowed the efficient determination of the internalization of the ox‐MWCNT derivatives by different model cancer cells, such as MCF7.     

Retention effects of oxidized polyphenols during analytical extraction of phenolic compounds of virgin olive oil

The hydrophilic extract of virgin olive oil contains several phenolic compounds such as simple phenols, lignans, and secoiridoids that have been widely studied in recent years. Interest in the hydrophilic extract has also been extended to the fraction of oxidized phenols that form during storage as a consequence of oxidative stress. The present investigation compares the two most commonly used extraction methods, namely liquid-liquid extraction and SPE, on fresh virgin olive oil and that kept at different temperatures in the presence of oxygen to promote the formation of oxidative products. The selective retention of these natural and oxidized phenolic compounds in relation to the extraction method was assessed. Quantification of eight identified phenolic molecules and 11 unknown peaks was performed by HPLC-DAD/MSD.     

Microwave-assisted extraction followed by headspace solid-phase microextraction and gas chromatography with mass spectrometry detection (MAE-HSSPME-GC-MS/MS) for determination of polybrominated compounds in aquaculture samples

This paper describes the first validated method for the extraction, purification and determination of trace levels of a number of pollutants of growing concern, including polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs), in aquaculture feeds and products. The new procedure comprises microwave-assisted extraction (MAE; optimized, using a central composite experimental design, to 15 min at 85 °C in 14 mL of 1:1 hexane/dichloromethane), and concentration by headspace solid-phase microextraction (HSSPME), and separation/quantification by gas chromatography with mass spectrometry detection (GC-MS/MS). The method was validated on the reference materials IAEA-406 and WMF-01. Limits of detection for fourteen of the fifteen analytes considered range from 10 to 600 pg g⁻¹, and limits of quantification from 50 pg g⁻¹ to 1.9 ng g⁻¹. Linear ranges, accuracies and precisions are reported.