Alternating behavior in furan-acetylene macrocycles reveals the size-dependency of Hückel's rule in neutral molecules

Aromaticity can be assigned by Hückel's rule, which predicts that planar rings with delocalized (4n + 2) π-electrons are aromatic, whereas those with 4n π-electrons are antiaromatic. However, for neutral rings, the maximal value of "n" to which Hückel's rule applies remains unknown. Large macrocycles exhibiting global ring current can serve as models for addressing this question, but the global ring current are often overshadowed in these molecules by the local ring current of the constituent units. Here, we present a series of furan-acetylene macrocycles, ranging from the pentamer to octamer, whose neutral states display alternating contributions from global aromatic and antiaromatic ring currents. We find that the odd-membered macrocycles display global aromatic characteristics, whereas the even-membered macrocycles display contributions from globally antiaromatic ring current. These factors are expressed electronically (oxidation potentials), optically (emission spectra), and magnetically (chemical shifts), and DFT calculations predict global ring current alternations up to 54 π-electrons.

Transformation of π-conjugated macrocycles: from furanophanes to napthalenophanes

Applying sequential Diels-Alder cycloaddition and deoxygenation to small π-conjugated furan macrocycles fully converts them to 1,4-naphthalophanes with either ethylene or acetylene spacers, depending on the reaction conditions. 1,4-Napthalenophane tetraene exhibits a 1,3-alternating conformation in the solid state, inclusion of solvent molecules within the macrocycle, and low reduction potentials.

Extending the scope of the carbonyl facilitated triplet excited state towards visible light excitation

A series of extended π-conjugated benzophenone analogs was synthesized through a facile Lewis-acid catalyzed Friedel–Crafts reaction in order to exploit the integral triplet state properties of benzophenone.

Enhanced intersystem crossing in carbonylpyrenes

Photoexcited state relaxation of carbonylpyrenes displays ultrafast intersystem crossing to generate near-unity triplet formation.

Non-natural G-quadruplex in a non-natural environment

The biocompatibility as well as the sustainability of a deep eutectic solvent makes it a good substitute for aqueous media in studying biomolecules. Understanding the structure and stability of natural and non-natural G-quadruplexes in aqueous and highly viscous media will be useful in biological and nanodevice applications. We report the synthesis and conformational analysis of a model G-rich oligonucleotide G3T3 and non-natural G-rich sequences Pyr1-Pyr3 in aqueous and highly viscous media. Progressive increases in the loop replacement with a non-natural pyrene linker leads to a systematic increase of the thermal denaturation temperature of the modified G-rich oligonucleotides Pyr1-Pyr3 in 10 mM cacodylate buffer (pH 7.2) containing 100 mM KCl, as monitored using UV-Vis spectroscopy. A circular dichroism signal clearly revealed the formation of a predominantly anti-parallel vs. parallel conformation in the natural G-rich oligonucleotide G3T3 as well as the non-natural G-rich oligonucleotides Pyr1-Pyr3 in 10 mM cacodylate buffer (pH 7.2) containing 100 mM KCl. On the other hand, we observed thermodynamic destabilization of G-rich oligonucleotides in a deep eutectic solvent (DES; 1 : 2 choline chloride-urea) containing 100 mm KCl with an increase in loop replacements. Interestingly, we observed an exclusively parallel G-quadruplex conformation in the case of G3T3 in DES containing 100 mm KCl. While pyrene containing G-rich oligonucleotides Pyr1-Pyr3 exhibited a predominantly parallel vs. anti-parallel G-quadruplex conformation in DES containing 100 mM KCl.

Progressive acylation of pyrene engineers solid state packing and colour via C-H···H-C, C-H···O and π-π interactions

Quantum theory of atoms-in-molecules and Hirshfeld surface analyses indicated an increase in the extent of (i) C-H···H-C; (ii) C-H···O, (iii) π-π interactions and a decrease in the extent of (i) σ-π interaction, (ii) an interplanar angle between the vicinal pyrene units in a series of acetylpyrene derivatives offering blue-green-orange emissive crystals.

C–H⋯H–C and C–H⋯π contacts aid transformation of dimeric to monomeric anthracene in the solid state

C–H⋯H–C and C–H⋯π interaction assisted formation of thermodynamically stable blue emissive AP-I from kinetically stable green emissive AP-II of 1-(anthracen-9-yl)pyrene (AP).

A risk-prediction model for in-hospital mortality after heart transplantation in US children

We sought to develop and validate a quantitative risk-prediction model for predicting the risk of posttransplant in-hospital mortality in pediatric heart transplantation (HT). Children <18 years of age who underwent primary HT in the United States during 1999-2008 (n = 2707) were identified using Organ Procurement and Transplant Network data. A risk-prediction model was developed using two-thirds of the cohort (random sample), internally validated in the remaining one-third, and independently validated in a cohort of 338 children transplanted during 2009-2010. The best predictive model had four categorical variables: hemodynamic support (ECMO, ventilator support, VAD support vs. medical therapy), cardiac diagnosis (repaired congenital heart disease [CHD], unrepaired CHD vs. cardiomyopathy), renal dysfunction (severe, mild-moderate vs. normal) and total bilirubin (≥ 2.0, 0.6 to <2.0 vs. <0.6 mg/dL). The C-statistic (0.78) and the Hosmer-Lemeshow goodness-of-fit (p = 0.89) in the model-development cohort were replicated in the internal validation and independent validation cohorts (C-statistic 0.75, 0.81 and the Hosmer-Lemeshow goodness-of-fit p = 0.49, 0.53, respectively) suggesting acceptable prediction for posttransplant in-hospital mortality. We conclude that this risk-prediction model using four factors at the time of transplant has good prediction characteristics for posttransplant in-hospital mortality in children and may be useful to guide decision-making around patient listing for transplant and timing of mechanical support.