Synthetic and Nanotechnological Approaches for a Diagnostic Use of Manganese

The development of multimodal imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) allows the contemporary obtaining of metabolic and morphological information. To fully exploit the complementarity of the two imaging modalities, the design of probes displaying radioactive and magnetic properties at the same time could be very beneficial. In this regard, transition metals offer appealing options, with manganese representing an ideal candidate. As nanosized imaging probes have demonstrated great value for designing advanced diagnostic/theranostic procedures, this work focuses on the potential of liposomal formulations loaded with a new synthesized paramagnetic Mn(II) chelates. Negatively charged liposomes were produced by thin-layer hydration method and extrusion. The obtained formulations were characterized in terms of size, surface charge, efficiency of encapsulation, stability over time, relaxivity, effective magnetic moment, and in vitro antiproliferative effect on human cells by means of the MTT assay. The negatively charged paramagnetic liposomes were monodisperse, with an average hydrodynamic diameter not exceeding 200 nm, and they displayed good stability and no cytotoxicity. As determined by optical emission spectroscopy, manganese complexes are loaded almost completely on liposomes maintaining their paramagnetic properties.     

Simulated Gastric and Intestinal Fluid Electrolyte Solutions as an Environment for the Adsorption of Apple Polyphenols onto β-Glucan

Interactions with dietary fibers in the gastrointestinal tract might affect the potential bioactivities of phenolic compounds. In this study, the interactions between apple phenolic compounds and β-glucan (a dietary fiber) were studied by studying the adsorption process in simulated gastric and intestinal fluid electrolyte solutions. Phenolic compounds were extracted from apples, adsorbed onto β-glucan (2 h, 37 °C, in gastric or intestinal fluid electrolyte solutions), and determined using high performance liquid chromatography. Phenolic compounds (flavan-3-ols, flavonols, phenolic acids, and dihydrochalcone) were stable in the gastric fluid (pH 3). In the intestinal fluid (pH 7), flavan-3-ols were not found and chlorogenic acid isomerized. Polyphenols from the apple peel (up to 182 and 897 mg g⁻¹) and flesh (up to 28 and 7 mg g⁻¹) were adsorbed onto β-glucan in the gastric and intestinal fluids, respectively. The adsorption was affected by the initial concentration of the polyphenols and β-glucan and by the environment (either gastric or intestinal fluid electrolyte solution). By increasing the initial polyphenol amount, the quantity of adsorbed polyphenols increased. Increasing the amount of β-glucan decreased the amount adsorbed. The results can be helpful in explaining the fate of phenolic compounds in the gastrointestinal tract.     

Union carbide polymerization catalysts: from uncovering active site structures to designing molecularly-defined analogs

The Union Carbide (UC) ethylene polymerization catalysts, based on chromocene dispersed on silica, show distinct features from the Phillips catalysts, but share the same heated debate regarding the structure of their active sites. Based on a combination of IR, EPR spectroscopies, labeling experiments, and DFT modeling, we identified monomeric surface-supported Cr(iii) hydrides, ( SiO)Cr(Cp)–H, as the active sites of the UC catalyst. These sites are formed in the presence of grafted and adsorbed chromocene as well as residual surface OH groups, only possible at high Cr loading, and involve a C–H activation of the Cp ring. These Cr-hydrides initiate polymerization, yielding Cr(iii) alkyl species that insert ethylene through a Cossee–Arlman-type mechanism, as evidenced by spectroscopic studies. These insights inspired the design of a well-defined analog, CpCr(CH(SiMe₃)₂)₂ grafted on partially dehydroxylated silica, that shows similar spectroscopic and polymer structure to the UC catalyst, further supporting the proposed active site structure.

A combined SOMC and DFT studies on the Union Carbide catalyst enable to propose that Cr(iii)-H, formed at high-loading, are active in ethylene polymerization. We therefore design a well-defined supported CpCr(iii)-R ethylene polymerization catalyst.     

Interrogation of the Effect of Polymorphism of a Metal-Organic Framework Host on the Structure of Embedded Pd Guest Nanoparticles

Metal-organic frameworks (MOFs) are very promising host materials for nanoscale guest materials. However, some MOFs such as MIL-53 are known to undergo phase transitions which can complicate the guest particle size control. In this study, Pd nanoparticles embedded in Al-MIL-53 were synthesised via (a) electrodeposition and (b) gas-phase reduction. A thorough structural investigation revealed that each synthesis method most likely favoured a different phase of Al-MIL-53, presenting the possibility of MOF phase selection as a technique for size control of embedded nanoparticles. For the first time, we hereby report the use of pair distribution function analysis to successfully investigate the structure and morphology of guest particles embedded in a MOF host.     

Borylated N-Heterocyclic Carbenes: Rearrangement and Chemical Trapping

This study details attempts to access N-heterocyclic carbenes (NHCs) featuring the diazaborolyl group, {(HCNDipp)₂B}, as one or both of the N-bound substituents, to generate strongly electron-donating and sterically imposing new carbene ligands. Attempts to isolate N-heterocyclic carbenes based around imidazolylidene or related heterocycles, are characterized by facile N-to-C migration of the boryl substituent. In the cases of imidazolium precursors bearing one N-bound diazaborolyl group and one methyl substituent, deprotonation leads to the generation of the target carbenes, which can be characterized in situ by NMR measurements, and trapped by reactions with metal fragments and elemental selenium. The half-lives of the free carbenes at room temperature range from 4–50 h (depending on the pattern of ancillary substituents) with N-to-C2 migration of the boryl function being shown to be the predominant rearrangement pathway. Kinetic studies show this to be a first-order process that occurs with an entropy of activation close to zero. DFT calculations imply that an intramolecular 1,2-shift is mechanistically feasible, with calculated activation energies of the order of 90–100 kJ mol⁻¹, reflecting the retention of significant aromatic character in the imidazole ring in the transition state. Trapping of the carbene allows for evaluation of steric and electronic properties through systems of the type LAuCl, LRh(CO)₂Cl, and LSe. A highly unsymmetrical (but nonetheless bulky) steric profile and moderately enhanced σ-donor capabilities (compared with IMes) are revealed.     

Loading of Vesicles into Soft Amphiphilic Nanotubes using Osmosis

The facile assembly of higher‐order nanoarchitectures from simple building blocks is demonstrated by the loading of vesicles into soft amphiphilic nanotubes using osmosis. The nanotubes are constructed from rigid interdigitated bilayers which are capped with vesicles comprising phospholipid‐based flexible bilayers. When a hyperosmotic gradient is applied to these vesicle‐capped nanotubes, the closed system loses water and the more flexible vesicle bilayer is pulled inwards. This leads to inclusion of vesicles inside the nanotubes without affecting the tube structure, showing controlled reorganization of the self‐assembled multicomponent system upon a simple osmotic stimulus.     

Synthesis and Characterisation of Luminescent [CrIII2L(μ-carboxylato)]3+ Complexes with High-Spin S=3 Ground States (L=N6S2 donor ligand)

The synthesis, structure, magnetic, and photophysical properties of two dinuclear, luminescent, mixed-ligand [Cr^III₂L(O₂CR)]³⁺ complexes (R=CH₃ ( 1 ), Ph ( 2 )) of a 24-membered binucleating hexa-aza-dithiophenolate macrocycle (L)²⁻ are presented. X-ray crystallographic analysis reveals an edge-sharing bioctahedral N₃Cr(μ-SR)₂(μ_1,3-O₂CR)CrN₃ core structure with μ_1,3-bridging carboxylate groups. A ferromagnetic superexchange interaction between the electron spins of the Cr³⁺ ions leads to a high-spin (S=3) ground state. The coupling constants (J=+24.2(1) cm⁻¹ ( 1 ), +34.8(4) cm⁻¹ ( 2 ), H=−2JS₁S₂) are significantly larger than in related bis-μ-alkoxido-μ-carboxylato structures. DFT calculations performed on both complexes reproduce both the sign and strength of the exchange interactions found experimentally. Frozen methanol-dichloromethane 1 : 1 solutions of 1 and 2 luminesce at 750 nm when excited into the ⁴LMCT state on the ⁴A₂ → ²T₁ (ν₂) bands (λ_exc=405 nm). The absolute quantum yields (Φ_L) for 1 and 2 were found to be strongly temperature dependent. At 77 K in frozen MeOH/CH₂Cl₂ glasses, Φ_L=0.44±0.02 (for 1 ), Φ_L=0.45±0.02 (for 2 ).     

A formal theory of generalized intermediate syllogisms

In this paper, we continue developing the formal theory of intermediate quantifiers (expressions such as most, few, almost all, a lot of, many, a great deal of, a large part of, a small part of). The theory is a fuzzy-logic formalization of the concept introduced by Peterson in his book. We will syntactically prove that 105 generalized Aristotle's syllogisms introduced in this book are valid in our theory. At the same time, we will also prove that syllogisms listed there as invalid are invalid also in our theory. Therefore, we believe that our theory provides a reasonable mathematical model of the generalized syllogistics.