Interaction of H2@C60 and Nitroxide through Conformationally Constrained Peptide Bridges

We synthesized two molecular systems, in which an endofullerene C₆₀, incarcerating one hydrogen molecule (H₂@C₆₀) and a nitroxide radical are connected by a folded 3₁₀‐helical peptide. The difference between the two molecules is the direction of the peptide orientation. The nuclear spin relaxation rates and the para → ortho conversion rate of the incarcerated hydrogen molecule were determined by ¹H NMR spectroscopy. The experimental results were analyzed using DFT‐optimized molecular models. The relaxation rates and the conversion rates of the two peptides fall in the expected distance range. One of the two peptides is particularly rigid and thus ideal to keep the H₂@C₆₀/nitroxide separation, r, as large and controlled as possible, which results in particularly low relaxation and conversion rates. Despite the very similar optimized distance, however, the rates measured with the other peptide are considerably higher and thus are compatible with a shorter effective distance. The results strengthen the outcome of previous investigations that while the para → ortho conversion rates satisfactorily obey the Wigner's theory, the nuclear spin relaxation rates are in excellent agreement with the Solomon–Bloembergen equation predicting a 1/r⁶ dependence.     

Solid-state structure and conformation of (Z)-2-(phenylbenzylidene)-3-quinuclidinone,an intermediate in the synthesis of quinuclidine derivatives

(Z)-2-(2-phenylbenzylidene)-3-quinuclidinone, C₂₀H₁₉NO,M _r =300.47D crystallizes in the monoclinicP2₁/c space group witha = 6.9809(2) Å,b=19.0523(2) Å,c = 11.7733(1) Å,=100.92(2)°,V=1537.5(3) ų,Z=4,D _c = 1.298 g/cm³,D _x =1.29 g/cm³ (flotation). Diffractometric data, using CuK radiation,=1.54178 Å, were collected on plate-like crystals. The structure, solved by direct methods was refined to a final R value of 0.037 for the 2645 observed reflections withF _o >3.0(F _o ). The molecule shows a trans conformation around the double bond. The quinuclidine and the diphenyl moieties present deformations in their geometric and conformational parameters due to the need of releasing intramolecular strains and/or nonbonded interactions.     

Electrochemically induced electron transfer through molecular bridges

In this Opinion, we address some of the most important results obtained electrochemically in the area of intramolecular electron transfer (ET). The focus is on freely diffusing molecular systems in which a donor D and an acceptor A are separated by a well-defined bridge B (D-B-A systems). B can be a saturated spacer, a delocalized bridge, or the more complex peptide backbones. As to the acceptors, the selected examples encompass species that can be charged reversibly but a special emphasis is on ETs associated with the concerted cleavage of a sigma bond (dissociative ETs). Our goal is to showcase the essential background, the most appropriate electrochemical tools and methodologies, and a series of selected examples where molecular electrochemistry has provided invaluable information on the mechanisms of intramolecular ET and electronic communication through bridges.     

Atomically Precise Metal Nanoclusters: Novel Building Blocks for Hierarchical Structures

Atomically precise ligand-protected nanoclusters (NCs) constitute an important class of compounds that exhibit well-defined structures and, when sufficiently small, evident molecular properties. NCs provide versatile building blocks to fabricate hierarchical superstructures. The assembly of NCs indeed offers opportunities to devise new materials with given structures and able to carry out specific functions. In this Concept article, we highlight the possibilities offered by NCs in which the physicochemical properties are controlled by the introduction of foreign metal atoms and/or modification of the composition of the capping monolayer with functional ligands. Different approaches to assemble NCs into dimers and higher hierarchy structures and the corresponding changes in physicochemical properties are also described.     

Effect of the Distillation Time on the Chemical Composition,Antioxidant Potential and Antimicrobial Activity of Essential Oils from Different Cannabis sativa L. Cultivars

Within the unavoidable variability of various origins in the characteristics of essential oils, the aim of this study was to evaluate the effect of the distillation time on the chemical composition and biological activity of Cannabis sativa essential oils (EOs). The dry inflorescences came from Carmagnola, Kompolti, Futura 75, Gran Sasso Kush and Carmagnola Lemon varieties from Abruzzo region (Central Italy), the last two being new cultivar here described for the first time. EOs were collected at 2 h and 4 h of distillation; GC/MS technique was applied to characterize their volatile fraction. The EOs were evaluated for total polyphenol content (TPC), antioxidant capacity (AOC) and antimicrobial activity against food-borne pathogens and spoilage bacteria. The time of distillation particularly influenced EOs chemical composition, extracting more or less terpenic components, but generally enriching with minor sesquiterpenes and cannabidiol. A logical response in ratio of time was observed for antioxidant potential, being the essential oils at 4 h of distillation more active than those distilled for 2 h, and particularly Futura 75. Conversely, except for Futura 75, the effect of time on the antimicrobial activity was variable and requires further investigations; nevertheless, the inhibitory activity of all EOs against Pseudomonas fluorescens P34 was an interesting result.     

Organic Functionalized Carbon Nanostructures for Solar Energy Conversion

This review presents an overview of the use of organic functionalized carbon nanostructures (CNSs) in solar energy conversion schemes. Our attention was focused in particular on the contribution of organic chemistry to the development of new hybrid materials that find application in dye-sensitized solar cells (DSSCs), organic photovoltaics (OPVs), and perovskite solar cells (PSCs), as well as in photocatalytic fuel production, focusing in particular on the most recent literature. The request for new materials able to accompany the green energy transition that are abundant, low-cost, low-toxicity, and made from renewable sources has further increased the interest in CNSs that meet all these requirements. The inclusion of an organic molecule, thanks to both covalent and non-covalent interactions, in a CNS leads to the development of a completely new hybrid material able of combining and improving the properties of both starting materials. In addition to the numerical data, which unequivocally state the positive effect of the new hybrid material, we hope that these examples can inspire further research in the field of photoactive materials from an organic point of view.     

Metal bioavailability in marine sediments measured by chemical extraction and enzymatic mobilization

In this work we compared metal bioavailable fractions in marine sediments operationally measured by sequential selective extractions (in particular the labile fraction released by acetic acid) and by a biomimetic approach using a commercially available proteolytic enzyme, proteinase K, chosen because of its non-specific behaviour and because it is representative of the enzymes encountered in many deposit-feeding organisms. Different experimental conditions for enzymatic extraction were investigated and the enzyme was employed both untreated and thermally denatured to study metal release mechanisms (i.e. enzymatic hydrolysis and/or complexation). Extractable protein content was also measured to verify possible correlations with some metals.Considering the two sediments used in this work, the available fraction evaluated with a biomimetic approach was often significantly lower than the fraction released by the first step of selective extractions, as expected. Moreover a good correlation was found between the fraction of metal available to the enzyme and enrichment factors in the gut fluids of deposit-feeding organisms, suggesting that enzymatic approach is qualitatively more reliable than chemical extraction in replicating the mechanism of metal mobilization that occurs in the guts of deposit-feeders.     

Cyclochiral resorcin[4]arenes as effective enantioselectors in the gas phase

The effect of cyclochirality of rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methylresorcin[4]arene (C) on the enantiodiscrimination of a number of chiral bidentate and tridentate aromatic and aliphatic biomolecules (G) has been investigated by nano-electrospray ionization (nano-ESI)-Fourier transform ion cyclotron resonance mass spectrometry. The experimental approach is based on the formation of diastereomeric proton-bound [C·H·G](+) complexes by nano-ESI of solutions containing an equimolar amount of quasi-enantiomers (C) together with the chiral guest (G) and the subsequent measurement of the rate of the G substitution by the attack of several achiral and chiral amines. In general, the heterochiral complexes react faster than the homochiral ones, except when G is an aminoalcoholic neurotransmitter whose complexes, beyond that, exhibit the highest enantioselectivity. The kinetic results were further supported by both collision-induced dissociation experiments on some of the relevant [C(2) ·H·G](+) three-body species and Density functional theory (DFT) calculations performed on the most selective systems.     

On symplectic polar spaces over non-perfect fields of characteristic 2

Given a field 𝕂 of characteristic 2 and an integer n ≥ 2, let W(2n ? 1, 𝕂) be the symplectic polar space defined in PG(2n ? 1, 𝕂) by a non-degenerate alternating form of V(2n, 𝕂) and let Q(2n, 𝕂) be the quadric of PG(2n, 𝕂) associated to a non-singular quadratic form of Witt index n. In the literature it is often claimed that W(2n ? 1, 𝕂) ? Q(2n, 𝕂). This is true when 𝕂 is perfect, but false otherwise. In this article, we modify the previous claim in order to obtain a statement that is correct for any field of characteristic 2. Explicitly, we prove that W(2n ? 1, 𝕂) is indeed isomorphic to a non-singular quadric Q, but when 𝕂 is non-perfect the nucleus of Q has vector dimension greater than 1. So, in this case, Q(2n, 𝕂) is a proper subgeometry of W(2n ? 1, 𝕂). We show that, in spite of this fact, W(2n ? 1, 𝕂) can be embedded in Q(2n, 𝕂) as a subgeometry and that this embedding induces a full embedding of the dual DW(2n ? 1, 𝕂) of W(2n ? 1, 𝕂) into the dual DQ(2n, 𝕂) of Q(2n, 𝕂).