Wagner-Meerwein skeletal rearrangement of 3-spiroannulated 6,8a-epoxy- and 6,8a;7,8-diepoxyisoquinolines (3-aza-11-oxatricyclo[6.2.1.0(1,6)]undec-9-enes). Isolation and identification of 5-aza-2-oxatricyclo[6.2.1.0(3,9)]undec-3-enes

The reactions of 3-acetyl-3-aza-11-oxatricyclo[6.2.1.0(1,6)]undec-9-ene and its 9,10-epoxy derivative with bromine and Ac(2)O/BF(3).OEt(2) under different conditions were studied. Unusual products of Wagner-Meerwein rearrangement bearing the olefin fragment (5-aza-2-oxatricyclo[6.2.1.0(3,9)]undecen-3-enes) were isolated and characterized by X-ray analysis.     

First total synthesis of trans- and cis-resorcylide: remarkable hydrogen-bond-controlled, stereospecific ring-closing metathesis

[reaction: see text] Stereospecific synthesis of the pair of natural macrolides, trans- and cis-resorcylide, was performed using ring-closing metathesis on dienes 3 and 4, which lack or feature an intramolecular H-bond, respectively. An effective Stille carbonylative coupling of benzyl chlorides 11 and 15 was employed for their preparation. The influence of intramolecular H-bonding on the interconversions of resorcylides was also studied.     

Squalenyl Hydrogen Sulfate Nanoparticles for Simultaneous Delivery of Tobramycin and an Alkylquinolone Quorum Sensing Inhibitor Enable the Eradication of P. aeruginosa Biofilm Infections

Elimination of pulmonary Pseudomonas aeruginosa (PA) infections is challenging to accomplish with antibiotic therapies, mainly due to resistance mechanisms. Quorum sensing inhibitors (QSIs) interfering with biofilm formation can thus complement antibiotics. For simultaneous and improved delivery of both active agents to the infection sites, self-assembling nanoparticles of a newly synthesized squalenyl hydrogen sulfate (SqNPs) were prepared. These nanocarriers allowed for remarkably high loading capacities of hydrophilic antibiotic tobramycin (Tob) and a novel lipophilic QSI at 30 % and circa 10 %, respectively. The drug-loaded SqNPs showed improved biofilm penetration and enhanced efficacy in relevant biological barriers (mucin/human tracheal mucus, biofilm), leading to complete eradication of PA biofilms at circa 16-fold lower Tob concentration than Tob alone. This study offers a viable therapy optimization and invigorates the research and development of QSIs for clinical use.     

Between Adamantane and Atrane: Intrabridgehead Interactions in the Cage‐Like Phosphane Related to a Novel Tris(homoadamantane) Ring System

Herein, we report unusual four‐center interactions in the novel cage‐like phosphane, 1,4,7‐triaza‐9‐phosphatricyclo[5.3.2.1^4,9]tridecane (CAP). This water‐soluble ligand, the first example of a tris(homoadamantane) ring system, can be considered a macrocyclic homologue of the well‐known PTA (1,3,5‐triaza‐7‐phosphaadamantane). However, ³¹P NMR spectroscopic anomalies of CAP follow those typical for the bi‐/tricyclic atrane systems. Another atrane‐like feature of CAP is the ability of one nitrogen atom to undergo out–in pyramidal inversion. The latter is associated with a substantial decrease in the intracage N?N and P?N distances. Analysis of electron density distribution [molecular electrostatic potential (MESP) and atoms‐in‐molecules (AIM) approaches] suggests that the P and N atoms in the pyramidally inverted CAP derivatives are involved in interactions resulting in accumulation of electron density at the center of the phosphane cage. The latter can reliably explain the stereoelectronic and NMR anomalies of the new ligand. The semi‐flexible CAP cage populates the structural niche between the rigid adamantine skeleton of PTA and flexible atrane systems and can be regarded as an alternative to PTA in aqueous coordination chemistry.     

Ion Mobility Spectrometry Reveals Duplex DNA Dissociation Intermediates

Electrospray ionization (ESI) soft desolvation is widely used to investigate fragile species such as nucleic acids. Tandem mass spectrometry (MS/MS) gives access to the gas phase energetics of the intermolecular interactions in the absence of solvent, by following the dissociation of mass-selected ions. Ion mobility mass spectrometry (IMS) provides indications on the tridimensional oligonucleotide structure by attributing a collision cross section (CCS) to the studied ion. Electrosprayed duplexes longer than eight bases pairs retain their helical structure in a solvent-free environment. However, the question of conformational changes under activation in MS/MS studies remains open. The objective of this study is to probe binding energetics and characterize the unfolding steps occurring prior to oligonucleotide duplex dissociation. Comparing the evolution of CCS with collision energy and breakdown curves, we characterize dissociation pathways involved in CID-activated DNA duplex separation into single strands, and we demonstrate here the existence of stable dissociation intermediates. At fixed duplex length, dissociation pathways were found to depend on the percentage of GC base pairs and on their position in the duplex. Our results show that pure GC sequences undergo a gradual compaction until reaching the dissociation intermediate: A-helix. Mixed AT-GC sequences were found to present at least two conformers: a classic B-helix and an extended structure where the GC tract is a B-helix and the AT tract(s) fray. The dissociation in single strands takes place from both conformers when the AT base pairs are enclosed between two GC tracts or only from the extended conformer when the AT tract is situated at the end(s) of the sequence.

Synthesis of novel 14-membered cyclic bis-semicarbazones

An efficient method for the stereoselective synthesis of novel 14-membered cyclic bis-semicarbazones based on acid-catalyzed cyclization of the hydrazones of 3-(3-oxobutyl)semicarbazides has been developed. The starting semicarbazides were prepared according to a four-step strategy involving amidoalkylation of the sodium enolate of acetylacetone with N-(α-tosylbenzyl)carbamates followed by base-promoted retro-Claisen reaction and treatment of the obtained N-(3-oxobutyl)carbamates with hydrazine.     

The Tits indices over semilocal rings

We give a simplified proof of the Tits classification of semisimple algebraic groups that remains valid over semilocal rings. We also give a new proof of the existence of all indices of exceptional inner type using the notion of canonical dimension of projective homogeneous varieties.     

Triglycerides as Novel Phase-Change Materials: A Review and Assessment of Their Thermal Properties

Latent Heat Storage (LHS) with Phase-Change Materials (PCMs) represents a high energy density storage technology which could be applied in a variety of applications such as waste heat recovery and integration of renewable energy technologies in energy systems. To increase the sustainability of these storage solutions, PCMs have to be developed with particular regard to bio-origin and biodegradability. Triglycerides represent an interesting class of esters as the main constituents of animal and vegetable fats, with attractive thermal properties. In order to be used as PCMs, the thermal behaviour of triglycerides has to be fully understood, as in some cases they have been reported to show polymorphism and supercooling. This study assesses the suitability of triglycerides as PCMs by reviewing the literature published so far on their behaviour and properties. In particular, melting points, enthalpies of fusion, polymorphism, thermal conductivities, heat capacities and thermal cycling stabilities are considered, with a focus on LHS and thermal energy storage applications. In addition, the efforts conducted regarding modelling and the prediction of melting points and enthalpies based on chemical structures are summarized and assessed.     

Isotopic Traceability (13C and 18O) of Greek Olive Oil

In recent years, isotopic analysis has been proven a valuable tool for the determination of the origin of various materials. In this article, we studied the ¹⁸O and ¹³C isotopic values of 210 olive oil samples that were originated from different regions in Greece in order to verify how these values are affected by the climate regime. We observed that the δ¹⁸O isotopic values range from 19.2 ‰ to 25.2 ‰ and the δ¹³C values range from −32.7 ‰ to −28.3 ‰. These differences between the olive oils’ isotopic values depended on the regional temperature, the meteoric water, and the distance from the sea. Furthermore, we studied the ¹³C isotopic values of biophenolic extracts, and we observed that they have same capability to differentiate the geographic origin. Finally, we compared the isotopic values of Greek olive oils with samples from Italy, and we concluded that there is a great dependence of oxygen isotopes on the climatic characteristics of the different geographical areas.