Quantum Communication in Rindler Spacetime

A state that an inertial observer in Minkowski space perceives to be the vacuum will appear to an accelerating observer to be a thermal bath of radiation. We study the impact of this Davies-Fulling-Unruh noise on communication, particularly quantum communication from an inertial sender to an accelerating observer and private communication between two inertial observers in the presence of an accelerating eavesdropper. In both cases, we establish compact, tractable formulas for the associated communication capacities assuming encodings that allow a single excitation in one of a fixed number of modes per use of the communications channel. Our contributions include a rigorous presentation of the general theory of the private quantum capacity as well as a detailed analysis of the structure of these channels, including their group-theoretic properties and a proof that they are conjugate degradable. Connections between the Unruh channel and optical amplifiers are also discussed.     

Breaking Data Encryption Standard with a Reduced Number of Rounds Using Metaheuristics Differential Cryptanalysis

This article presents the author’s own metaheuristic cryptanalytic attack based on the use of differential cryptanalysis (DC) methods and memetic algorithms (MA) that improve the local search process through simulated annealing (SA). The suggested attack will be verified on a set of ciphertexts generated with the well-known DES (data encryption standard) reduced to six rounds. The aim of the attack is to guess the last encryption subkey, for each of the two characteristics Ω. Knowing the last subkey, it is possible to recreate the complete encryption key and thus decrypt the cryptogram. The suggested approach makes it possible to automatically reject solutions (keys) that represent the worst fitness function, owing to which we are able to significantly reduce the attack search space. The memetic algorithm (MASA) created in such a way will be compared with other metaheuristic techniques suggested in literature, in particular, with the genetic algorithm (NGA) and the classical differential cryptanalysis attack, in terms of consumption of memory and time needed to guess the key. The article also investigated the entropy of MASA and NGA attacks.     

Long-Range Electron Transfer in Rigid 310-Helical Oligopeptides Containing Redox Cyclic a-Amino Acids

Intrahelical photoinduced electron transfer processes (ET) in conformationally restricted oligopeptides have been studied by nanosecond time-resolved transient spectroscopy. The helical peptides were constructed from sterically hindered alpha-aminoisobutyric acid (Aib) and two cyclic alpha-amino acids (Aib class) bearing electron acceptor and donor side chains (DkNap, ThQx). This helical backbone design provides high conformation stability, as previously demonstrated, and yields reliable 3(10)-helical architectures in solution. The forward ET between ThQx and 3DkNap is followed by a slow back ET thus giving rise to an accumulation of the charge-separated ion pairs for hundreds of nanoseconds. We demonstrate the modulation of electronic interactions by the number of intervening Aib residues separating acceptor-donor side chains and propose modifications of the peptide framework by inclusion of a non-Aib amino acid residue. These well-defined and sterically stable frameworks are suited for the precise evaluation of intrahelical electron transfer processes mediated by peptides.     

From a Well-Defined Organozinc Precursor to Diverse Luminescent Coordination Polymers Based on Zn(II)-Quinolinate Building Units Interconnected by Mixed Ligand Systems

Introduction of photoactive building blocks into mixed-ligand coordination polymers appears to be a promising way to produce new advanced luminescent materials. However, rational design and self-assembly of the multi-component supramolecular systems is challenging from both a conceptual and synthetic perspective. Here, we report exploratory studies that investigate the potential of [Zn(q)₂]₂[tBuZn(OH)]₂ complex (q = deprotonated 8-hydroxyquinoline) as an organozinc precursor as well as a mixed-ligand synthetic strategy for the preparation of new luminescent coordination polymers (CPs). As a result we present three new 2D mixed-ligand Zn(II)-quinolinate coordination polymers which are based on various zinc quinolinate secondary building units interconnected by two different organic linker types, i.e., deprotonated 4,4′-oxybisbenzoic acid (H₂obc) as a flexible dicarboxylate linker and/or selected bipyridines (bipy). Remarkably, using the title organozinc precursors in a combination with H₂obc and 4,4′-bipyridine, a novel molecular zinc quinolinate building unit, [Zn₄(q)₆(bipy)₂(obc)₂], was obtained which self-assembled into a chain-type hydrogen-bonded network. The application of the organometallic precursor allowed for its direct reaction with the selected ligands at ambient temperature, avoiding the use of both solvothermal conditions and additional base reagents. In turn, the reaction involving Zn(NO₃)₂, as a classical inorganic precursor, in a combination with H₂obc and bipy led to a novel 1D coordination polymer [Zn₂(q)₂(NO₃)₂(bipy)]. While the presence of H₂obc was essential for the formation of this coordination polymer, this ditopic linker was not incorporated into the isolated product, which indicates its templating behavior. The reported compounds were characterized by single-crystal and powder X-ray diffraction, elemental analysis as well as UV-Vis and photoluminescence spectroscopy.     

Front Cover: A Highly Sterically Congested Bis-Zinc-Porphyrin Containing a Single Buta-1,3-diyne Linkage: From a Serendipitous Finding to Supramolecular Encapsulation (Eur. J. Org. Chem. 35/2023)

A unique example of a bis-zinc-porphyrin chemical system in which both macrocycles are covalently connected with a single, short buta-1,3-diyne linkage placed at the ortho sites of the meso phenyl rings is presented. This dimeric compound resulted from an homo-coupling side-reaction taking place during a copper-catalyzed click reaction between an alkyne porphyrin and 2-azidopyridine derivatives. Its unexpected formation was rationalized by control experiments and an improved synthesis was achieved under copper-catalyzed Glaser-Hay coupling reaction conditions. This highly sterically congested bis-zinc-porphyrin derivative behaved as a supramolecular host for encapsulating ditopic molecular guests such as 1,4-diazabicyclo[2.2.2]octane (DABCO) with association constant K_1.1 in the order of 10⁶ M⁻¹. This value is comparable to current systems that typically feature several connecting linkages between the two zinc-porphyrin sites resulting in (supra)molecular cages ensuring a high pre-organization. As such, the requirements to take benefit from supramolecular encapsulation can be reduced to a highly rigid, minimal covalent linkage of four atoms between zinc-porphyrins as herein described.     

Synthesis of [60]Fullerene Hybrids Endowed with Steroids and Monosaccharides: Theoretical Underpinning as Promising anti-SARS-CoV-2 Agents

Cyclopropanation reactions between C₆₀ and different malonates decorated with monosaccharides and steroids using the Bingel-Hirsch methodology have allowed the obtention of a new family of hybrid compounds in good yields. A complete set of instrumental techniques has allowed us to fully characterize the hybrid derivatives and to determine the chemical structure of monocycloadducts. Besides, the proposed structures were investigated by cyclic voltammetry, which evidenced the exclusive reductive pattern of fullerene Bingel-type monoadducts. Theoretical calculations at the DFT-D3(BJ)/PBE 6-311G(d,p) level of the synthesized conjugates predict the most stable conformation and determine the factors that control the hybrid molecules′ geometry. Some parameters such as polarity, lipophilicity, polar surface area, hydrophilicity index, and solvent-accessible surface area were also estimated, predicting its potential permeability and capability as cell membrane penetrators. Additionally, a molecular docking simulation has been carried out using the main protease of SARS-CoV-2 (Mpro) as the receptor, thus paving the way to study the potential application of these hybrids in biomedicine.     

Convergent Assembly of the Tricyclic Labdane Core Enables Synthesis of Diverse Forskolin-like Molecules

We report a new synthetic strategy for the flexible preparation of forskolin-like molecules. The approach is different from the previously published works and employs a convergent assembly of the tricyclic labdane-type core from pre-functionalized cyclic building blocks. Stereoselective Michael addition enabled the fragment coupling with excellent control over three newly created contiguous stereocenters, all-carbon quaternary centers included. Silyl enol ether-promoted ring-opening metathesis paired with ring closure were the other key steps enabling concise assembly of the tricyclic core. Late-stage functionalization sequences transformed the tricyclic intermediates into a set of different forskolin-like molecules. The modular nature of the synthetic scheme described herein has the potential to become a general platform for the preparation of analogs of forskolin and other complex tricyclic labdanes.