Triple Regioselective Functionalization of Cationic [4]Helicenes via Iridium-Catalyzed Borylation and Suzuki Cross-Coupling Reactivity

In essentially one-pot, using Ir- and Pd-catalysis, tris(arene)-functionalized cationic [4]helicenes are synthesized with full regioselectivity and enantiospecificity starting from a trivial precursor (17 examples). This poly-addition of aryl groups improves key optical properties, that is, fluorescence quantum yields and lifetimes. Electronic circular dichroism and circularly polarized luminescence signatures are observed up to the far-red domain, in particular with additional arenes prone to aggregation.     

Biodegradable polymer nanocomposites: An overview

Biodegradable polymer nanocomposites, due to their biodegradability and other improved properties possess tremendous scope in the industrial sector. This current article reviews the recent studies carried out over biodegradable polymer nanocomposites that includes preparation, characterization, properties, and applications of nanocomposites based on biodegradable polymers. An orderly introduction of nanocomposites prepared by using various biodegradable aliphatic polyesters and polymers obtained from biomass products has been brought about. A wide range of organic and inorganic nanoparticles was used as additives or fillers to prepare nanocomposites with improved desired properties. Considering vast research on layered silicates/polymer nanocomposites, a special emphasis has been summarized at the end of the review.     

A Facile One‐Pot Synthesis and Anticancer Evaluation of Novel Substituted 1,2‐Dihydropyridine and 1,2,3,4‐Tetrahydropyrimidine Analogues

Current paper involves the one‐pot synthesis of various 1,2‐dihydropyridine and 1,2,3,4‐tetrahydropyrimidine analogues. The antitumor activity of the synthesized compounds has been carried out against various human cancer cell lines, and some of the analogues are found to be potent.     

Interactions of neutral and singly charged keV atomic particles with gas-phase adenine molecules

KeV atomic particles traversing biological matter are subject to charge exchange and screening effects which dynamically change this particle's effective charge. The understanding of the collision cascade along the track thus requires a detailed knowledge of the interaction dynamics of radiobiologically relevant molecules, such as DNA building blocks or water, not only with ionic but also with neutral species. We have studied collisions of keV H(+), He(+), and C(+) ions and H(0), He(0), and C(0) atoms with the DNA base adenine by means of high resolution time-of-flight spectrometry. For H(0) and H(+) we find qualitatively very similar fragmentation patterns, while for carbon, strong differences are observed when comparing C(0) and C(+) impact. For collisions with He(0) and He(+) projectiles, a pronounced delayed fragmentation channel is observed, which has not been reported before.     

HNO trapping and assisted decomposition of nitroxyl donors by ferric hemes

The role of nitric oxide (NO) as a signalling molecule in biological systems has been thoroughly studied in the last decades. More recently, there has been an increasing interest in the one-electron reduction product of NO, namely nitroxyl (HNO/NO⁻). Some studies suggest that nitroxyl can be produced by nitric oxide synthases under certain conditions, and that distinct pharmacological effects are observed for NO and nitroxyl donors. HNO is capable of react with heme proteins, thiols, molecular oxygen, NO and HNO itself. However, only recently the different reactivity patterns are being thoroughly understood. Heme model compounds offer the opportunity to study the reaction kinetics without the complexity arising from ligand interactions with the protein matrix. In this study we analyzed the reaction between the commonly used nitroxyl donors sodium trioxodinitrate and toluene sulfohydroxamic acid, with the ferric model compounds microperoxidase-11 (MP11) and the cationic metalloporphyrin [Fe^IIITEPyP]⁵⁺ (Tetrakis N-ethylpyridinium-2yl porphyne). Our results show that there are two alternative modes of reactivity for nitroxyl donors towards heme in aqueous solutions. The first one comprises the heme assisted decomposition of the donor, enhancing its decomposition rate more than 100-fold. In the second, the donor produces HNO which subsequently reacts with the porphyrin. The observed rate constants (of about 10⁵ M⁻¹ s⁻¹) are consistent with the estimated data for the HNO reaction with heme proteins, and may be controlled by the leaving water ligand. This rate constant probably represents an upper limit for the bimolecular rate constant of HNO towards these proteins.     

Synthetic route for the novel pyrimidine-substituted alkanoate,acetohydrazide, and imines: Synthon for β-lactams

A simple and efficient synthesis of novel pyrimidine-substituted alkanoate, acetohydrazide, and imines is described. The synthesis of novel ethyl 2-(2,6-dimethylpyrimidin-4-yloxy)acetate (EDMPyA) 2 was performed through S_N2 O-alkylation of 2,6-dimethyl-4-hydroxypyrimidine 1 with ethyl haloacetate. The compound EDMPyA 2 was subjected to nucleophilic substitution reaction with hydrazine hydrate to afford novel 2-(2,6-dimethylpyrimidin-4-yloxy)acetohydrazide (DMPyAH) 3. This DMPyAH 3 upon condensation with differently substituted carbonyl compounds (aldehydes/ketones) furnished DMPyAH imines (DMPyAH-I) 4a–d. These imines can be used for the preparation of unique β-lactams. The structure elucidation of all the newly synthesized compounds was performed using spectroscopy (FT-IR, ¹H and ¹³C NMR) and elemental analysis (C, H, N).     

Diastereoselective synthesis of novel 3-aryloxy/alkoxy-4-benzothiazolylpyrazolyl-β-lactams: Potential synthons for novel aminoacids/nanocopolymers

A fast, efficient, and diastereoselective synthesis of novel 3-oxo-4-benzothiazolylpyrazolyl-β-lactams is described. The reaction between 2-aryloxy/alkoxyacetic acid and novel benzothiazolylpyrazole-substituted imines afforded exclusive formation of trans-β-lactams. The scope of the reaction was investigated by varying different groups on substrates (R¹, R², R³, Z). All the novel compounds were characterized using various spectroscopic techniques such as FT-IR, ¹H NMR, ¹³C NMR, elemental analysis, and mass spectrometry in representative cases. No report has been listed in the literature for the synthesis of these types of β-lactam heterocycles so far.     

Simulation of Electronic Circular Dichroism of Nucleic Acids: From the Structure to the Spectrum

We present a quantum mechanical (QM) simulation of the electronic circular dichroism (ECD) of nucleic acids (NAs). The simulation combines classical molecular dynamics, to obtain the structure and its temperature‐dependent fluctuations, with a QM excitonic model to determine the ECD. The excitonic model takes into account environmental effects through a polarizable embedding and uses a refined approach to calculate the electronic couplings in terms of full transition densities. Three NAs with either similar conformations but different base sequences or similar base sequences but different conformations have been investigated and the results were compared with experimental observations; a good agreement was seen in all cases. A detailed analysis of the nature of the ECD bands in terms of their excitonic composition was also carried out. Finally, a comparison between the QM and the DeVoe models clearly revealed the importance of including fluctuations of the excitonic parameters and of accurately determining the electronic couplings. This study demonstrates the feasibility of the ab initio simulation of the ECD spectra of NAs, that is, without the need of experimental structural or electronic data.