Absence of expected side-reactions in the dehydration reaction of fructose to HMF in water over niobic acid catalyst

The catalytic dehydration of fructose (FRU) to 5-hydroxymethylfurfural (HMF) usually runs with the formation of several side products. Among these, levulinic acid (LA) is often reported as the product of a consecutive reaction of HMF re-hydration. In this work, side reactions of the dehydration of FRU performed in very green conditions (water as solvent and niobic acid as solid catalyst) are taken into account. Experimental evidences are given that, in the used conditions: i) HMF is a final stable product, ii) no formation of LA, either deriving from a consecutive reaction of HMF or directly from FRU transformation, was observed, and iii) LA does not react to give condensation products with any other chemical species present in the reaction mixture.     

Structure–Activity Relationships of Benzenesulfonamide‐Based Inhibitors towards Carbonic Anhydrase Isoform Specificity

Carbonic anhydrases (CAs) are implicated in a wide range of diseases, including the upregulation of isoforms CA IX and XII in many aggressive cancers. However, effective inhibition of disease‐implicated CAs should minimally affect the ubiquitously expressed isoforms, including CA I and II, to improve directed distribution of the inhibitors to the cancer‐associated isoforms and reduce side effects. Four benzenesulfonamide‐based inhibitors were synthesized by using the tail approach and displayed nanomolar affinities for several CA isoforms. The crystal structures of the inhibitors bound to a CA IX mimic and CA II are presented. Further in silico modeling was performed with the inhibitors docked into CA I and XII to identify residues that contributed to or hindered their binding interactions. These structural studies demonstrated that active‐site residues lining the hydrophobic pocket, especially positions 92 and 131, dictate the positional binding and affinity of inhibitors, whereas the tail groups modulate CA isoform specificity. Geometry optimizations were performed on each ligand in the crystal structures and showed that the energetic penalties of the inhibitor conformations were negligible compared to the gains from active‐site interactions. These studies further our understanding of obtaining isoform specificity when designing small molecule CA inhibitors.     

VDACs Post-Translational Modifications Discovery by Mass Spectrometry: Impact on Their Hub Function

VDAC (voltage-dependent anion selective channel) proteins, also known as mitochondrial porins, are the most abundant proteins of the outer mitochondrial membrane (OMM), where they play a vital role in various cellular processes, in the regulation of metabolism, and in survival pathways. There is increasing consensus about their function as a cellular hub, connecting bioenergetics functions to the rest of the cell. The structural characterization of VDACs presents challenging issues due to their very high hydrophobicity, low solubility, the difficulty to separate them from other mitochondrial proteins of similar hydrophobicity and the practical impossibility to isolate each single isoform. Consequently, it is necessary to analyze them as components of a relatively complex mixture. Due to the experimental difficulties in their structural characterization, post-translational modifications (PTMs) of VDAC proteins represent a little explored field. Only in recent years, the increasing number of tools aimed at identifying and quantifying PTMs has allowed to increase our knowledge in this field and in the mechanisms that regulate functions and interactions of mitochondrial porins. In particular, the development of nano-reversed phase ultra-high performance liquid chromatography (nanoRP-UHPLC) and ultra-sensitive high-resolution mass spectrometry (HRMS) methods has played a key role in this field. The findings obtained on VDAC PTMs using such methodologies, which permitted an in-depth characterization of these very hydrophobic trans-membrane pore proteins, are summarized in this review.     

Peptide-containing aggregates as selective nanocarriers for therapeutics

New nanocarriers are obtained by assembling two amphiphilic monomers: one containing the bioactive peptide CCK8 spaced, by a polydisperse poly(ethylene glycol), from two hydrophobic tails ((C18)2PEG2000CCK8), and the other containing a chelating agent able to give stable radiolabeled indium-111 complexes linked to the same hydrophobic moiety ((C18)2DTPAGlu). The size and shape of the supramolecular aggregates were structurally characterized by dynamic light scattering, small-angle neutron scattering, and cryogenic transmission electronic microscopy. Under the experimental conditions we investigated (pH 7.4 and molar ratio between monomers 30:70), there is the presence of high polydisperse aggregates: rod-like micelles with a radius of approximately 40 A and length >700 A, open bilayer fragments with thickness approximately 65 A, and probably vesicles. The presence of the bioactive peptide well exposed on the external surface of the aggregate allows selective targeting of nanocarriers towards the cholecystokinin receptors overexpressed by the cancerous cells. In vitro binding assays and in vivo biodistribution studies by nuclear medicine experiments using indium-111 are reported. Moreover, preliminary data concerning the drug loading capability of the aggregates and their drug efficiency on the target cells is reported by using the cytotoxic drug doxorubicin. Incubation of receptor-positive and control cells with peptide-containing aggregates filled with doxorubicin shows significantly lower cell survival in receptor-expressing cells relative to the control, for samples incubated in the presence of doxorubicin.     

Self‐Immobilizing Precatalysts: Norbornene‐Bridged Zirconium ansa‐Metallocenes

We report here the synthesis of new tethered biscyclopentadienyl and bisindenyl zirconocenes, bearing one unsaturation on the interannular bridge, and their use as self‐immobilizing catalysts. They proved to be active catalysts towards ethylene polymerization in solution, with activities comparable to those displayed by commercial rac‐Et(Ind)₂ZrCl₂. When tested as self‐polymerization catalysts under suitable experimental conditions, they gave colored precipitates that, once reactivated with MAO, were significantly active in ethylene polymerization, although lower than those of the corresponding catalytic systems in solution. The molecular weights of the produced polymers were similar to those obtained with the same catalysts in solution, but their distribution resulted to be broader, with values typical of heterogeneous catalytic systems. From ¹³C NMR studies we had the first spectroscopic evidence of the actual incorporation of a metallocene of this type into a polymeric chain.     

Influence of Al2O3 on the performance of CeO2 used as catalyst in the direct carboxylation of methanol to dimethylcarbonate and the elucidation of the reaction mechanism

In this paper we show that modification of ceria by loading alumina strongly reduces the oxidation of methanol and the consequent reduction of Ce(IV) to Ce(III) with increase of both the life of the catalysts and their selectivity. The combination of surface techniques (XPS and BET) with structural techniques (XRD) has allowed a good characterisation of the working catalysts. Spectroscopic analyses (DRIFT and multinuclear solid state and solution NMR) have permitted the monitoring of the species formed on the surface of the catalyst and released from it. The formation of DMC takes place in successive steps such as (i) interaction of methanol with the catalyst surface with the formation of the surface-bound OCH₃; (ii) building on the catalyst surface of the hemicarbonate moiety [–OCH₃ → –OC(O)OCH₃]; and (iii) reaction of the latter with the gas-phase methanol to afford the organic carbonate.     

Spermatozoa Transcriptional Response and Alterations in PL Proteins Properties after Exposure of Mytilus galloprovincialis to Mercury

Mercury (Hg) is an environmental pollutant that impacts human and ecosystem health. In our previous works, we reported alterations in the properties of Mytilus galloprovincialis protamine-like (PL) proteins after 24 h of exposure to subtoxic doses of toxic metals such as copper and cadmium. The present work aims to assess the effects of 24 h of exposure to 1, 10, and 100 pM HgCl₂ on spermatozoa and PL proteins of Mytilus galloprovincialis. Inductively coupled plasma–mass spectrometry indicated accumulation of this metal in the gonads of exposed mussels. Further, RT-qPCR analyses showed altered expression levels of spermatozoa mt10 and hsp70 genes. In Mytilus galloprovincialis, PL proteins represent the major basic component of sperm chromatin. These proteins, following exposure of mussels to HgCl₂, appeared, by SDS-PAGE, partly as aggregates and showed a decreased DNA-binding capacity that rendered them unable to prevent DNA damage, in the presence of CuCl₂ and H₂O₂. These results demonstrate that even these doses of HgCl₂ exposure could affect the properties of PL proteins and result in adverse effects on the reproductive system of this organism. These analyses could be useful in developing rapid and efficient chromatin-based genotoxicity assays for pollution biomonitoring programs.