Dynamic Interplay between Defective UiO-66 and Protic Solvents in Activated Processes

UiO-66, composed by Zr-oxide inorganic bricks [Zr₆(μ₃-O)₄(μ₃-OH)₄] and organic terephthalate linkers, is one of the most studied metal–organic frameworks (MOFs) due to its exceptional thermal, chemical, and mechanical stability. Thanks to its high connectivity, the material can withstand structural deformations during activation processes such as linker exchange, dehydration, and defect formation. These processes do alter the zirconium coordination number in a dynamic way, creating open metal sites for catalysis and thus are able to tune the catalytic properties. In this work, it is shown, by means of first-principle molecular-dynamics simulations at operating conditions, how protic solvents may facilitate such changes in the metal coordination. Solvent can induce structural rearrangements in the material that can lead to undercoordinated but also overcoordinated metal sites. This is demonstrated by simulating activation processes along well-chosen collective variables. Such enhanced MD simulations are able to track the intrinsic dynamics of the framework at realistic conditions.     

Enantioselective separation of amino acids as biomarkers indicating life in extraterrestrial environments

Traces of prebiotic amino acids, i.e., the building blocks of proteins, are excellent biomarkers that could provide evidence of extinct or extant life in extra-terrestrial environments. In particular, characterization of the enantiomeric excess of amino acids gives relevant information about the biotic or abiotic origin of molecules, because it is generally assumed that life elsewhere could be based on either l or d amino acids, but not both. The analytical procedures used in in-situ space missions for chiral discrimination of amino acids must meet severe requirements imposed by flight conditions: short analysis time, low energy consumption, robustness, storage for long periods under extreme conditions, high efficiency and sensitivity, automation, and remote-control operation. Such methods are based on gas chromatography, high-pressure liquid chromatography, and capillary electrophoresis, usually coupled with mass spectrometry; of these, gas chromatography–mass spectrometry (GC–MS) is the only such combination yet used in space missions. Preliminary in-situ sample derivatization is required before GC–MS analysis to convert amino acids into volatile and thermally stable compounds. The silylation reagent most commonly used, N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide, is unsuitable for detection of homochirality, and alternative derivatization techniques have been developed that preserve the stereochemical configuration of the original compounds and are compatible with spaceflight conditions. These include the reagent N,N-dimethylformamide dimethylacetal, which has already been used in the Rosetta mission, a mixture of alkyl chloroformate, ethanol, and pyridine, a mixture of perfluorinated anhydrides and perfluoro alcohols, and hexafluoroacetone, the first gaseous derivatizing agent. In all the space instruments, solvent extraction of organic matter and chemical derivatization have been combined in a single automatic and remote-controlled procedure in a chemical reactor. Liquid-based separation systems have been used in space missions. In particular, microchip capillary electrophoresis, based on microfluidic lab-on-a-chip systems, enables high-performance chemical analysis of amino acids with low mass and volume equipment and low power and reagent consumption. Coupling with laser-induced fluorescence detectors results in ultra-low limits of detection. This critical review describes applications of the on-board instruments used in the Rosetta mission to comets and in the more recent Mars exploration program, i.e., the Mars Science Laboratory and ExoMars missions.

Proteome investigation of the non-model plant pomegranate (Punica granatum L.)

A gel-free, shotgun proteomics approach was used to characterize pomegranate aril proteome by nanoliquid chromatography–high-resolution tandem mass spectrometry. To identify both high-abundance and low-abundance proteins, we applied two distinct sample preparation protocols, i.e., a classical one widely applied in literature and a second one able to reduce the dynamic range of protein concentration of the sample, based on combinatorial hexapeptide ligand library technology. However, the proteins identified with the latter protocol were only a small minority. Because pomegranate is a non-model plant species, i.e., information of its genome sequence are lacking, only a few protein sequences are included in the most widely known protein sequence databases. To improve both the number of identified proteins and data reliability, identification was performed integrating the results obtained with three distinct plant protein databases, since the majority of proteins could only be attributed by homology with other plant species. Nevertheless, many proteins had assigned only one unique peptide, because of the phylogenetic distance of pomegranate from the main model plants. After manual revision of the identified proteins to eliminate the redundant or ambiguous identifications, a list of 1,488 proteins was obtained, only six of which belonging to pomegranate species. To the author's best knowledge, this is the first work aimed at the proteomic characterization of Punica granatum.     

Electrostatic immobilisation of copper(I) and copper(II) bis(oxazolinyl)pyridine catalysts on silica: application to the synthesis of propargylamines via direct addition of terminal alkynes to imines

Copper(I) and copper(II) complexes of two bis(oxazolinyl)pyridines were immobilized on silica via electrostatic interactions. The catalytic activity of the immobilized catalysts in the direct addition of terminal alkynes to imines leading to propargylamines was investigated under a variety of reaction conditions. The performance of the immobilized catalysts compares very well with their homogeneous equivalents. When used in toluene, the catalysts could be recycled a number of times and maintained activity. This study is the first such report of the immobilization on silica in this manner of any bis(oxazolinyl)pyridine (pybox) complex.     

Electroanalytical Determination of Some Phenolic Acids by High‐Performance Liquid Chromatography at Gold Electrodes

The electrochemical and amperometric behavior of a gold electrode was investigated towards the oxidation of several common phenolic acids in neutral phosphate solutions. Au electrodes show an appreciable stability and reproducibility of the amperometric signals by using a constant applied potential of 1.0 V vs. Ag/AgCl. Separations of selected phenolic acids using a reverse phase C₁₈ analytical column with a mobile phase containing 10 mM NaH₂PO₄ plus 10 mM Na₂HPO₄ (pH 7) and methanol as organic modifier, are achieved isocratically in less than 30 min. The detection limits at the level of nmol/L and linear ranges of four‐five orders of magnitude are generally achieved. The proposed chromatographic strategy coupled with the electrochemical detection at the Au electrode was successful tested for the quantitative determination of phenolic acids in beer, red wine and brandy with good sensitivity and recovery.     

Development of a multiresidue method for analysis of major Fusarium mycotoxins in corn meal using liquid chromatography/tandem mass spectrometry

A sensitive and reliable liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method has been developed to determine, in a single run, eight trichothecenes, three fumonisins, zearalenone and alpha-zearalenol, in corn meal samples. LC and MS conditions were varied to find the best compromise in terms of sensitivity and separation. An acceptable compromise was obtained using a C18 column thermostatted at 45 degrees C and a mobile phase gradient of methanol/water with 10 mmol/L formate buffer (pH 3.8). A multiple reaction monitoring program, in which fumonisins and trichothecenes (except nivalenol and deoxynivalenol) are acquired in positive ESI as [M+H]+ or [M+NH4]+, and all other compounds in negative ESI, was developed to match appropriate retention time windows. Sample preparation used a simple homogenization of the corn meal sample with acetonitrile/water (75:25, v/v) followed by extraction on a C18 cartridge and clean-up on a cartridge containing graphitized carbon black. Method detection limits were in the range 2-14 ng/g, with the exception of nivalenol (27 ng/g), deoxynivalenol (40 ng/g) and 15-acetyldeoxynivalenol (30 ng/g). Good accuracy (recoveries 81-104%) and precision (RSD 4-11%) were obtained by performing calibration using a spiked analyte-free extract.     

New diazadi(and tri)thia‐21‐crown‐7 ethers containing 8‐hydroxyquinoline side arms

A series of macrocyclic diazadi(and tri)thiacrown ethers containing two 5‐substituent‐8‐hydroxyquinoline side arms have been synthesized from the corresponding macrocyclic diazadi(and tri)thiacrown ethers. The crown ethers were obtained by reduction of the proper macrocyclic di(and tri)thiadiamides by borane‐tetrahydrofuran or by sodium borohydride‐boron trifluoride ethyl etherate‐tetrahydrofuran. The yields for the reduction of diamides by sodium borohydride‐boron trifluoride ethyl etherate‐tetrahydrofuran were higher than those by borane‐tetrahydrofuran. The following four methods were used to prepare macrocycles bearing two 8‐hydroxyquinoline side arms: (1) Mannich reaction with 8‐hydroxyquinoline; (2) Reductive animation with 8‐hydroxyquinoline‐2‐carboxaldehyde using sodium triacetoxyborohydride as the reducing agent; (3) Cyclization of N,N'‐bis(8‐hydroxyquinolin‐2‐ylmethyl)‐1,2‐bis(2‐aminoethoxy)ethane (38) with bis(α‐chloroamide) 5 ; and ( 4 ) A step‐by‐step process wherein macrocyclic trithiadiamide 11 was reduced by lithium aluminum hydride‐tetrahydrofuran to the cyclic monoamide 36 , which smoothly reacted with 5‐chloro‐8‐hydroxyquinoline to produce monosubstituted‐macrocyclic monoamide 39 .     

Quotients of the unit ball of ℂn for a free action of ℤ

LetB _n be the unit ball of ℂⁿ and ℤ ≅ Γ ⊂ AutB _n be generated by a parabolic element of AutB _n. We show that the quotientB _n/Γ is biholomorphic to a holomorphically convex domain of ℂⁿ, whose automorphism group is explicity described. It follows thatB _n/ℤ is Stein for any free action of ℤ. Investigation partially supported by University of Bologna. Funds for selected research topics. The second author was supported by an Instituto Nazionale di Alta Matematica grant.