Macrocyclic vs. dendrimeric effect. A DFT study

Macrocycles up to 15 members with different heteroatoms (N, O, and S) and dendrimeric functionalized branches were assembled, resulting in unique "collective" supramolecular hosts with several active sites for transition metal ions complexation. The nature of the interactions between these kinds of systems and metal ions of the first transition series (Fe, Ni, Cu, Zn) was evaluated by calculations of the binding energies at the B3LYP/LACVP* level of theory, resulting in a preference of metal ions for macrocyclic cavity in terms of complexation; however, there is a favorable contribution in energy due to the cooperative effect of dendrimeric branches (DBs) in the inclusion process by means of long-range interactions between metal ions and the heteroatoms present in DBs. According to calculated binding energies, even when the complexation in the middle of DBs appears as a less favored situation, still competes with the complexation occurred in several known macrocycles traditionally used in the formation of inclusion complexes. The capability of macrocycles as host entities is related to some criteria like: (1) the compatibility in orbital symmetry between host and guest molecules; (2) the cavity dimensions and the negative charge inside; and (3) the hardness-softness affinity between host and guest molecules. When DBs are included in host systems, their flexibility seems to be very important, in addition to localized negative charge, which permits the occurrence of long-range interactions.     

Cyanocalix[4]arenes: synthesis,crystal structures and reactivity studies

Abstract

Herein, we describe an improved method to synthesise mono-, di- and tetra-cyanocalix[4]arene and report their crystal structure determinations. We also report our attempts to further functionalise the cyanocalix[4]arenes into dithiadiazolyl-calix[4]arenes, and propose a hypothesis as to why the cyano group on a calix[4]arene is an extremely challenging group to modify.     

Comparative analysis of the electrogravitational Kepler problem in GRT and RTG

In the framework of Einstein's General Relativity Theory and of the Relativistic Theory of Gravitation, the equations governing the trajectories of charged particles in the field created by a charged mass point are given. An analysis of the shape of the trajectories in both theories is presented. The first and the second order approximate solutions of the electrogravitational Kepler problem are found in the two theories and the results are compared with each other. I have pointed out the differences between the predictions in the two theories.     

Modeling of Selenoprotein Nitrozation: Synthetic Approaches

Model reactions have been carried out to evaluate the question of what kind of links may exist between the biological cycles of nitrogen oxide (NO) and those of selenoproteins, especially the amino acid selenocysteine (Sec). To collect information about the properties of the as-yet unknown selenonitrites (RSeNO) in comparison with the well-known thionitrites, (RSNO), the interaction of nitrosating reagents with a choice of molecular thiols and related selenoles as model compounds have been studied. Selenol nitrosation is clearly preferred in vitro to thiol nitrosation, but selenonitrites are thermally significantly less stable than the related thionitrites, suggesting that selenonitrites may be important, but yet-undetected intermediates in selenoprotein chemistry. Chemical trapping of RSeNO was achieved for the first time by its 1,4-addition to dimethylbutadiene leading to a stable unsaturated oxime.     

Metastable P-Tellurium-Substituted Phosphaalkenes: Formation, 125Te- and 31P-NMR Spectroscopic Characterization,and Decomposition

Abstract

The formation and decomposition of P-tellurium-substituted phosphaalkenes was followed by ³¹P- and ¹²⁵Te-NMR spectroscopy. Acyclic compounds with C?P-Te moieties are in general thermally labile, but bulky substituents enhance the lifetime of a number of species. The P-chlorophosphaalkene (Me₃Si)₂C?PCl (1a) reacts with the disilyltelluride (iPrMe₂Si)₂Te (2) leading to the mixed-substituted telluride (Me₃Si)₂C?PTeSiMe₂iPr 3a which reacts with another equivalent of 1a furnishing the tellurobis(phosphaalkene) [(Me₃Si)₂C?P]₂Te (4a). 4a is a shortlived compound decomposing thermally with precipitation of elemental tellurium, leading to a known diphosphabicyclobutane 5a. In a similar way, the bulkier P-chlorophosphaalkene (iPrMe₂Si)₂C?PCl (1b) reacts with (iPrMe₃Si)₂Te furnishing [(iPrMe₂Si)₂C?P]₂Te (4b), which loses tellurium much more slowly than 4a and can be kept in cold solutions for an extended time. Reactions of in situ-prepared lithium aryltellurolates LiTeAr 6 – 9 [Ar?Ph: 6, Ar?2,4,6-Me₃Ph (?Mes): 7, Ar?2,4,6-iPr₃Ph (?TIP): 8, Ar?2,4,6-tBu₃Ph (?Mes*): 9] with 1a provide P-aryltellurophosphaalkenes 10 – 13, which decompose with the loss of diarylditellurides leading to 5a. After a 2 + 4 cycloaddition trapping experiment of 12 with cyclopentadiene, a metastable P-aryltelluro phosphanorbornene 14 was detected by ³¹P-NMR. Reactions of elemental tellurium with P-phosphanylphosphaalkenes (Me₃Si)₂C?PPR′R′;′ 15 – 17 (R′, R′′?iPr: 15; R′?iPr, R′′?tBu: 16; R′, R′′?tBu: 17) lead to metastable insertion products (Me₃Si)₂C?PTePR′R′′ 18 – 20 that decompose with formation of the tellurobisphosphanes (R′R′′P)₂Te 21 – 23, and of the bicyclic diphosphane 5a, which isomerises thermally to the diphosphabicyclooctane 24. The P-di-i-propylphosphanyl-phosphanorbornene 25 dismutates under the action of tellurium into the symmetric diphosphanes iPr₄P₂ and bis-phosphanorbornene 26. The tellurium-free products 24 and 26 were characterized by X-ray crystallography.     

Exploring Excited‐State Tunability in Luminescent Tris‐cyclometalated Platinum(IV) Complexes: Synthesis of Heteroleptic Derivatives and Computational Calculations

The synthesis, structure, electrochemistry, and photophysical properties of a series of heteroleptic tris‐ cyclometalated Pt^IV complexes are reported. The complexes mer‐[Pt(C^N)₂(C′^N′)]OTf, with C^N=C‐deprotonated 2‐(2,4‐difluorophenyl)pyridine (dfppy) or 2‐phenylpyridine (ppy), and C′^N′=C‐deprotonated 2‐(2‐thienyl)pyridine (thpy) or 1‐phenylisoquinoline (piq), were obtained by reacting bis‐ cyclometalated precursors [Pt(C^N)₂Cl₂] with AgOTf (2 equiv) and an excess of the N′^C′H pro‐ligand. The complex mer‐[Pt(dfppy)₂(ppy)]OTf was obtained analogously and photoisomerized to its fac counterpart. The new complexes display long‐lived luminescence at room temperature in the blue to orange color range. The emitting states involve electronic transitions almost exclusively localized on the ligand with the lowest π–π* energy gap and have very little metal character. DFT and time‐dependent DFT (TD‐DFT) calculations on mer‐[Pt(ppy)₂(C′^N′)]⁺ (C′^N′=thpy, piq) and mer/fac‐[Pt(ppy)₃]⁺ support this assignment and provide a basis for the understanding of the luminescence of tris‐cyclometalated Pt^IV complexes. Excited states of LMCT character may become thermally accessible from the emitting state in the mer isomers containing dfppy or ppy as chromophoric ligands, leading to strong nonradiative deactivation. This effect does not operate in the fac isomers or the mer complexes containing thpy or piq, for which nonradiative deactivation originates mainly from vibrational coupling to the ground state.     

Ladder oligophenothiazines by direct thionation of N-Arylanilino Derivatives

Ladder oligophenothiazines were synthesized by direct catalyzed insertion of elemental sulfur in anilino-substituted phenothiazines and para-oligoanilines. The starting 3- and 3,7-anilino derivatives of phenothiazine were prepared with improved selectivities and yields by new syntheses. The oxidability of the oligomers is discussed.     

NMR Spectroscopic Assignment of Backbone and Side‐Chain Protons in Fully Protonated Proteins: Microcrystals,Sedimented Assemblies,and Amyloid Fibrils

We demonstrate sensitive detection of alpha protons of fully protonated proteins by solid‐state NMR spectroscopy with 100–111 kHz magic‐angle spinning (MAS). The excellent resolution in the Cα‐Hα plane is demonstrated for 5 proteins, including microcrystals, a sedimented complex, a capsid and amyloid fibrils. A set of 3D spectra based on a Cα–Hα detection block was developed and applied for the sequence‐specific backbone and aliphatic side‐chain resonance assignment using only 500 μg of sample. These developments accelerate structural studies of biomolecular assemblies available in submilligram quantities without the need of protein deuteration.     

Catalase-peroxidase activity of iron(III)-TAML activators of hydrogen peroxide

Exceptionally high peroxidase-like and catalase-like activities of iron(III)-TAML activators of H 2O 2 ( 1: Tetra-Amidato-Macrocyclic-Ligand Fe (III) complexes [ F e{1,2-X 2C 6H 2-4,5-( NCOCMe 2 NCO) 2CR 2}(OH 2)] (-)) are reported from pH 6-12.4 and 25-45 degrees C. Oxidation of the cyclometalated 2-phenylpyridine organometallic complex, [Ru (II)( o-C 6H 4py)(phen) 2]PF 6 ( 2) or "ruthenium dye", occurs via the equation [ Ru II ] + 1/2 H 2 O 2 + H +-->(Fe III - TAML) [ Ru III ] + H 2 O, following a simple rate law rate = k obs (per)[ 1][H 2O 2], that is, the rate is independent of the concentration of 2 at all pHs and temperatures studied. The kinetics of the catalase-like activity (H 2 O 2 -->(Fe III - TAML) H 2 O + 1/2 O 2) obeys a similar rate law: rate = k obs (cat)[ 1][H 2O 2]). The rate constants, k obs (per) and k obs (cat), are strongly and similarly pH dependent, with a maximum around pH 10. Both bell-shaped pH profiles are quantitatively accounted for in terms of a common mechanism based on the known speciation of 1 and H 2O 2 in this pH range. Complexes 1 exist as axial diaqua species [FeL(H 2O) 2] (-) ( 1 aqua) which are deprotonated to afford [FeL(OH)(H 2O)] (2-) ( 1 OH) at pH 9-10. The pathways 1 aqua + H 2O 2 ( k 1), 1 OH + H 2O 2 ( k 2), and 1 OH + HO 2 (-) ( k 4) afford one or more oxidized Fe-TAML species that further rapidly oxidize the dye (peroxidase-like activity) or a second H 2O 2 molecule (catalase-like activity). This mechanism is supported by the observations that (i) the catalase-like activity of 1 is controllably retarded by addition of reducing agents into solution and (ii) second order kinetics in H 2O 2 has been observed when the rate of O 2 evolution was monitored in the presence of added reducing agents. The performances of the 1 complexes in catalyzing H 2O 2 oxidations are shown to compare favorably with the peroxidases further establishing Fe (III)-TAML activators as miniaturized enzyme replicas with the potential to greatly expand the technological utility of hydrogen peroxide.