From Hexaoxy‐[6]Pericyclynes to Carbo‐Cyclohexadienes,Carbo‐Benzenes,and Dihydro‐Carbo‐Benzenes: Synthesis,Structure, and Chromophoric and Redox Properties

When targeting the quadrupolar p‐dianisyltetraphenyl‐carbo‐benzene by reductive treatment of a hexaoxy‐[6]pericyclyne precursor 3 with SnCl₂/HCl, a strict control of the conditions allowed for the isolation of three C₁₈‐macrocyclic products: the targeted aromatic carbo‐benzene 1 , a sub‐reduced non‐aromatic carbo‐cyclohexadiene 4 A , and an over‐reduced aromatic dihydro‐carbo‐benzene 5 A . Each of them was fully characterized by its absorption and NMR spectra, which were interpreted by comparison with calculated spectra from static structures optimized at the DFT level. According to the nucleus‐independent chemical shift (NICS) value (NICS≈?13 ppm), the macrocyclic aromaticity of 5 A is indicated to be equivalent to that of 1 . This is confirmed by the strong NMR spectroscopic deshielding of the ortho‐CH protons of the aryl substituents, but also by the strong shielding of the internal proton of the endocyclic trans‐CH?CH double bond that results from the hydrogenation of one of the C?C bonds of 3 . Both the aromatics 1 and 5 A exhibit a high crystallinity, revealed by SEM and TEM images, which allowed for a structural determination by using an X‐ray microsource. A good agreement with calculated molecular structures was found, and columnar assemblies of the C₁₈ macrocycles were evidenced in the crystal packing. The non‐aromatic carbo‐cyclohexadiene 4 A is shown to be an intermediate in the formation of 1 from 3 . It exhibits a remarkable dichromism in solution, which is related to the occurrence of two intense bands in the visible region of its UV/Vis spectrum. These properties could be attributed to the dibutatrienylacetylene (DBA) unit that occurs in the three chromophores, but which is not involved in a macrocyclic π‐delocalization in 4 A only. A versatile redox behavior of the carbo‐chromophores is evidenced by cyclic voltammetry and was analyzed by calculation of the ionization potential, electron affinity, and frontier molecular orbitals.     

A 12-connected metal-organic framework constructed from an unprecedented cyclic dodecanuclear copper cluster

A 12-connected metal-organic framework based on an unprecedented cyclic Cu(12) cluster with a large internal cavity has been prepared, and its cation exchange property was determined.     

Bridging QTAIM with vibrational spectroscopy: the energy of intramolecular hydrogen bonds in DNA-related biomolecules

Physical properties of over 8000 intramolecular hydrogen bonds (iHBs), including 2901 ones of the types OH···O, OH···N, NH···O and OH···C, in 4244 conformers of the DNA-related molecules (four canonical 2'-deoxyribonucleotides, 1,2-dideoxyribose-5-phosphate, and 2-deoxy-D-ribose in its furanose, pyranose and linear forms) have been investigated using quantum theory of atoms in molecules (QTAIM) and vibrational analysis. It has been found that for all iHBs with positive red-shift of the proton donating group stretching frequency the shift value correlates with ρ(cp)-the electron charge density at the (3,-1)-type bond critical point. Combining QTAIM and spectroscopic data new relationships for estimation of OH···O, OH···N, NH···O and OH···C iHB enthalpy of formation (kcal mol(-1)) with RMS error below 0.8 kcal mol(-1) have been established: E(OH···O) = -3.09 + 239·ρ(cp), E(OH···N) = 1.72 + 142·ρ(cp), E(NH···O) = -2.03 + 225·ρ(cp), E(OH···C) = -0.29 + 288·ρ(cp), where ρ(cp) is in e a(0)(-3) (a(0)- the Bohr radius). It has been shown that XHY iHBs with red-shift values over 40 cm(-1) are characterized by the following minimal values of the XHY angle, ρ(cp) and nubla(2)ρ(cp): 112°, 0.005 e a(0)(-3) and 0.016 e a(0)(-5), respectively. New relationships have been used to reveal the strongest iHBs in canonical 2'-deoxy- and ribonucleosides and the O(5')H···N(3) H-bond in ribonucleoside guanosine was found to have the maximum energy (8.1 kcal mol(-1)).     

From hexaoxy-[6]pericyclynes to carbo-cyclohexadienes, carbo-benzenes, and dihydro-carbo-benzenes: synthesis, structure, and chromophoric and redox properties

When targeting the quadrupolar p-dianisyltetraphenyl-carbo-benzene by reductive treatment of a hexaoxy-[6]pericyclyne precursor 3 with SnCl(2)/HCl, a strict control of the conditions allowed for the isolation of three C(18)-macrocyclic products: the targeted aromatic carbo-benzene 1, a sub-reduced non-aromatic carbo-cyclohexadiene 4A, and an over-reduced aromatic dihydro-carbo-benzene 5A. Each of them was fully characterized by its absorption and NMR spectra, which were interpreted by comparison with calculated spectra from static structures optimized at the DFT level. According to the nucleus-independent chemical shift (NICS) value (NICS≈-13 ppm), the macrocyclic aromaticity of 5A is indicated to be equivalent to that of 1. This is confirmed by the strong NMR spectroscopic deshielding of the ortho-CH protons of the aryl substituents, but also by the strong shielding of the internal proton of the endocyclic trans-CH=CH double bond that results from the hydrogenation of one of the C≡C bonds of 3. Both the aromatics 1 and 5A exhibit a high crystallinity, revealed by SEM and TEM images, which allowed for a structural determination by using an X-ray microsource. A good agreement with calculated molecular structures was found, and columnar assemblies of the C(18) macrocycles were evidenced in the crystal packing. The non-aromatic carbo-cyclohexadiene 4A is shown to be an intermediate in the formation of 1 from 3. It exhibits a remarkable dichromism in solution, which is related to the occurrence of two intense bands in the visible region of its UV/Vis spectrum. These properties could be attributed to the dibutatrienylacetylene (DBA) unit that occurs in the three chromophores, but which is not involved in a macrocyclic π-delocalization in 4A only. A versatile redox behavior of the carbo-chromophores is evidenced by cyclic voltammetry and was analyzed by calculation of the ionization potential, electron affinity, and frontier molecular orbitals.     

Conformationally locked chromophores as models of excited-state proton transfer in fluorescent proteins

Members of the green fluorescent protein (GFP) family form chromophores by modifications of three internal amino acid residues. Previously, many key characteristics of chromophores were studied using model compounds. However, no studies of intermolecular excited-state proton transfer (ESPT) with GFP-like synthetic chromophores have been performed because they either are nonfluorescent or lack an ionizable OH group. In this paper we report the synthesis and photochemical study of two highly fluorescent GFP chromophore analogues: p-HOBDI-BF2 and p-HOPyDI:Zn. Among known fluorescent compounds, p-HOBDI-BF(2) is the closest analogue of the native GFP chromophore. These irrreversibly (p-HOBDI-BF(2)) and reversibly (p-HOPyDI:Zn) locked compounds are the first examples of fully planar GFP chromophores, in which photoisomerization-induced deactivation is suppressed and protolytic photodissociation is observed. The photophysical behavior of p-HOBDI-BF2 and p-HOPyDI:Zn (excited state pK(a)'s, solvatochromism, kinetics, and thermodynamics of proton transfer) reveals their high photoacidity, which makes them good models of intermolecular ESPT in fluorescent proteins. Moreover, p-HOPyDI:Zn is a first example of "super" photoacidity in metal-organic complexes.     

Spin-parity analysis of pp¯ mass threshold structure in J/ψ and ψ(3686) radiative decays

A partial wave analysis of the ppˉ mass-threshold enhancement in the reaction J/ψ→γppˉ is used to determine its J(PC) quantum numbers to be 0(-+), its peak mass to be below threshold at M=1832(-5)(+19)(stat)(-17)(+18)(syst)±19(model) MeV/c(2), and its total width to be Γ<76 MeV/c(2) at the 90% C.L. The product of branching ratios is measured to be BR[J/ψ→γX(ppˉ)]BR[X(ppˉ)→ppˉ]=[9.0(-1.1)(+0.4)(stat)(-5.0)(+1.5)(syst)±2.3(model)]×10(-5). A similar analysis performed on ψ(3686)→γppˉ decays shows, for the first time, the presence of a corresponding enhancement with a production rate relative to that for J/ψ decays of R=[5.08(-0.45)(+0.71)(stat)(-3.58)(+0.67)(syst)±0.12(model)]%.     

First observation of η(1405) decays into f(0)(980)π0

The decays J/ψ → γ π+ π- π0 and J/ψ → γ π0 π0 π0 are analyzed using a sample of 225×10(6) J/ψ events collected with the BESIII detector. The decay of η(1405) → f(0)(980)π0 with a large isospin violation is observed for the first time. The width of the f(0)(980) observed in the dipion mass spectra is anomalously narrower than the world average. Decay rates for three-pion decays of the η' are also measured precisely.     

Rapid, one-pot synthesis of α,α-disubstituted primary amines by the addition of Grignard reagents to nitriles under microwave heating conditions

A series of α,α-disubstituted amines have been prepared in a simple and efficient one-pot procedure by the addition of Grignard reagents to a series of aliphatic, aromatic, and heteroaromatic nitriles. Key to this reported procedure is the unprecedented addition of the Grignard reagent to the nitrile under heating by microwave irradiation which both significantly improves reaction yields and reduces reaction times. In general, the Grignard addition reaction is complete within 5-10 min at 100 °C followed by rapid reduction with sodium borohydride to give the target amines.     

3-Hydroxybenzo[g]quinolones: dyes with red-shifted absorption and highly resolved dual emission

New derivatives of 3-hydroxyquinolone (3HQ) with a fused benzene ring (3-hydroxybenzo[g]quinolones) have been synthesized. They display a remarkable red shift of their absorption spectrum in comparison with other 3HQ analogs allowing their excitation by common He/Cd and Ar-ion lasers. As a result of their irreversible excited-state intramolecular proton transfer (ESIPT) reaction, they display a dual fluorescence in a series of solvents of varying polarities, starting from toluene to methanol. The dual emission of these dyes correlates well with solvent H-bond basicity, which is connected with the effect of this solvent property on the kinetics of the ESIPT reaction. In addition to their red-shifted absorption and fluorescence, these new derivatives show a larger separation of their two emission bands and a more appropriate range of their intensity ratio than the previously synthesized 3HQs. These properties allow an improved ratiometric evaluation of the local H-bond basicity of unknown environments, which will favor future applications of the new dyes in polymer and biological sciences.     

Equation of state of cubic hafnium(IV) nitride having Th3P4 -type structure

Pressure dependence of the specific volume, V(P), of the recently discovered high-pressure compound Hf₃N₄ having cubic Th₃P₄-type structure (c- Hf₃N₄) has been measured at room temperature up to 43.9 GPa in a diamond anvil cell using energy-dispersive X-ray powder diffraction combined with synchrotron radiation. A least-square fit of the Birch-Murnaghan equation of state to the experimental V(P)-data yielded for c- Hf₃N₄ the bulk modulus of and its first pressure derivative of . For fixed at 4 the bulk modulus of c- Hf₃N₄ was determined to be . The obtained B₀-value is only insignificantly below that estimated in preliminary measurements. Existing theoretical predictions for B₀ scatter around the present experimental data. The observation of a high bulk modulus of c- Hf₃N₄ supports the suggestion that this compound could have high hardness.