Template-Directed In Crystallo Photopolymerization of a Donor-Acceptor Cyclopropane: When Everything Falls into Place!

A single-crystal-to-single-crystal solid-state reaction of vinylogous donor-acceptor cyclopropanes is documented. The enantiospecific synthesis of new products, distinct from those obtained in solution, is achieved for the target compounds. Photopolymerization occurred upon X-ray exposure to the crystals. Notably, in one case, this reactivity exhibits selectivity since an ordered arrangement of polymers and unreacted cocrystallized monomeric conformers has been observed. Structural characterization of the complete transformation monitored through single-crystal X-ray diffraction and supported by molecular dynamics simulations sheds light on the subtle role of crystal packing in the reaction process. Moreover, the X-ray diffraction (XRD)-resolved structure of a donor-acceptor cyclopropane intermediate reveals an elongation in bond length that corroborates the existence of the so-called "push-pull effect".

Padlocking dihydrofurannulation for the control of small degree of helicity built on a fused-tetracyclic core.

Enantioselective construction of small molecules displaying a configurationally stable helical shape built on a fused-tetracyclic core is a daunting synthetic challenge even more pronounced when five-membered rings are incorporated in the structure. The resulting higher configurational lability strongly hampers their access, and therefore the development of new efficient methodologies is timely and highly desirable. In this context, we describe a padlocking approach via the enantioselective organocatalytic domino furannulation of appropriately designed achiral fused-tricyclic precursors resulting in the synthesis of configurationally locked helically chiral tetracyclic scaffolds featuring one or two five-membered rings with the simultaneous control of central and helical chiralities.

Two-step access to bis-meso-perfluoroalkyl-corroles towards meso-perfluoroacyl-ABC-corroles.

A solventless and acid-catalyzed condensation of meso-perfluoroalkyl-dipyrromethanes with selected benzaldehydes was used to prepare ten different bilanes that were isolated before their oxidation into trans-A2B-corroles bearing two meso-perfluoroalkyl groups. Macrocycles bearing long chains (C3F7 or C7F15) are key precursors to afford ABC-corroles having a meso-acyl substituent when subjected to a mild and basic hydrolysis affecting one of the alkyl substituents.

Internal Dynamics and Modular Peripheral Binding in Stimuli-Responsive 3 : 2 Host:Guest Complexes.

Now that the chemistry of 1 : 1 host:guest complexes is well-established, it is surprising to note that higher stoichiometry (oligomeric) complexes, especially those with excess host, remain largely unexplored. Yet, proteins tend to oligomerize, affording new functions for cell machinery. Here, we show that cucurbit[n]uril (CB[n]) macrocycles combined with symmetric, linear di-viologens form unusual 3 : 2 host:guest complexes exhibiting remarkable dynamic properties, host self-sorting, and external ring-translocation. These results highlight the structural tunability of cucurbit[8]uril (CB[8]) based 3 : 2 host:guest complexes in water and their responsiveness toward several stimuli (chemicals, pH, redox).

Conformational, Structural, and Chiroptical Properties of an Overcrowded Triply Fused Carbo[7]helicene.

Recently, the synthesis of the racemate of an overcrowded triply fused carbo[7]helicene of formula C66H36 with three carbo[7]helicenes fused within a central six-membered ring was described. This molecule was found to embed an extremely contorted central six-membered ring and two negative curvatures. We report herein the resolution of the corresponding enantiomers and their conformational, structural, photophysical, and chiroptical properties. The racemization of the triply fused carbo[7]helicene was determined to proceed at a rate of krac = 8.06 × 10-4 s-1 at 175 °C in ortho-dichlorobenzene, corresponding to a barrier to enantiomerization ΔGenant‡ = 140.4 kJ·mol-1, a value significantly lower than for pristine carbo[7]helicene. Interestingly, the crystalline structures of the racemic and enantiopure materials show some differences regarding the molecular geometry, with an increased negative curvature in the latter cases. This unusual curved delocalized π-conjugated system afforded notably green fluorescence at room temperature and far-red phosphorescence at low temperature. Finally, electronic circular dichroism and circularly polarized luminescence responses of the enantiopure compounds have been measured and showed very close absorption and emission dissymmetry factors, gabs and glum, respectively, of ca. 2.6 × 10-3, indicating a similar chiral rigid geometry for both ground and excited states.

Overcrowded Triply Fused Carbo[7]helicene.

This paper presents the synthesis and comprehensive analysis of a highly contorted and doubly negatively curved multihelicene compound, composed of three carbo[7]helicene units fused within a central six-membered ring. The synthesis of this compound involved a [2 + 2 + 2] cycloaddition reaction of 13,14-picyne, employing a Ni(0) catalyst, which exhibited superior performance compared to conventional Pd(0) catalysts. The evaluation of aromaticity in this triple carbo[7]helicene, utilizing magnetic and electronic criteria, led to noteworthy insights challenging the limitations of Clar's model of aromaticity.

Transmission and clearance of human papillomavirus infection in the oral cavity and its role in oropharyngeal carcinoma - A review.

The majority of sexually active individuals becomes infected with human papillomavirus (HPV) at least once in their lifetime. Pathways for HPV transmission vary across different mucosal sites per individual. They include autoinoculation within one host, direct transmission between individuals (including perinatal transmission and transmission during sexual activity), and indirect transmission through contact with hands. The authors aim to clarify the prevalence and route of transmission per anatomic site, inter- and intra-individually, using a narrative review of the literature. In conclusion, transmission of HPV to the oral cavity and oropharynx is hypothesised to occur mainly through sexual contact. Transmission of particles through saliva has not been proven and daily living activities are not a documented source of HPV infection. Oropharyngeal HPV related cancer survivors and their partners do not show increased risk of infection during sexual intercourse. Transmission of HPV to the oral cavity (autoinoculation with fingers or transmission through saliva in deep kissing) is probably of limited importance.

Energy-Efficient Iodine Uptake by a Molecular Host⋠Guest Crystal.

Recently, porous organic crystals (POC) based on macrocycles have shown exceptional sorption and separation properties. Yet, the impact of guest presence inside a macrocycle prior to adsorption has not been studied. Here we show that the inclusion of trimethoxybenzyl-azaphosphatrane in the macrocycle cucurbit[8]uril (CB[8]) affords molecular porous host⋅guest crystals (PHGC-1) with radically new properties. Unactivated hydrated PHGC-1 adsorbed iodine spontaneously and selectively at room temperature and atmospheric pressure. The absence of (i) heat for material synthesis, (ii) moisture sensitivity, and (iii) energy-intensive steps for pore activation are attractive attributes for decreasing the energy costs. 1 H NMR and DOSY were instrumental for monitoring the H2 O/I2 exchange. PHGC-1 crystals are non-centrosymmetric and I2 -doped crystals showed markedly different second harmonic generation (SHG), which suggests that iodine doping could be used to modulate the non-linear optical properties of porous organic crystals.

Enantiospecific Syntheses of Congested Atropisomers through Chiral Bis(aryne) Synthetic Equivalents.

The synthetic equivalents of the enantiopure binaphthyl bis(aryne) atropisomers derived from BINOL (1,1'-bi-2,2'-naphtol) featuring a stereogenic axis vicinal to the two reactive triple bonds can be generated for the first time in solution in an enantiospecific manner. Using a two-step sequence based on the bidirectional [4+2] cycloaddition of furan derivatives followed by an aromatizative deoxygenation reaction, several 9,9'-bianthracenyl-based atropisomers could be prepared enantiospecifically in high enantiomeric purity. Alternatively, bidirectional reactions with anthracene, 2-bromostyrene, and perylene as the arynophiles afforded very congested bis(benzotriptycene), bis(tetraphene) and bis(anthra[1,2,3,4-ghi]perylene) nanocarbon atropisomers in equally high enantiomeric purity. In complement, cross reactions with two different arynophiles revealed possible. The unusual atropisomer prototypes described in this study open the way to enantiopure nanographene atropisomers designed for functions.

Determination of the Rate Constant of the [4 + 2] Cycloaddition Between an Aryne Atropisomer and Furan in Solution.

Using a specially designed prototype of a nonracemic aryne atropisomer with a low barrier to enantiomerization (ca. 36 kJ·mol-1), it was possible to determine the kinetic constant of its cycloaddition with furan in solution by a combination of theoretical calculations and experimental measurements. It was found that the reaction half-life of this aryne atropisomer in solution with 100 equivalents of furan as the trapping reagent is <150 ns at temperatures above -20 °C.

Pharmacology, particle deposition and drug administration techniques of intranasal corticosteroids for treating allergic rhinitis.

This review presents an overview of the available literature regarding intranasal corticosteroids (INCs) for the treatment of allergic rhinitis (AR). Various treatment options exist for AR including INCs, antihistamines and leucotriene antagonists. INCs are considered to be the most effective therapy for moderate-to-severe AR, as they are effective against nasal and ocular symptoms and improve quality of life. Their safety has been widely observed. INCs are effective and safe for short-term use. Local adverse events are observed but generally well-tolerated. The occurrence of (serious) systemic adverse events is unlikely but cannot be ruled out. There is a lack of long-term safety data. INC may cause serious eye complications. The risk of INCs on the hypothalamic-pituitary-adrenal axis, on bone mineral density reduction or osteoporosis and on growth in children, should be considered during treatment. Pharmacological characteristics of INCs (e.g. the mode of action and pharmacokinetics) are well known and described. We sought to gain insight into whether specific properties affect the efficacy and safety of INCs, including nasal particle deposition, which the administration technique affects. However, advances are lacking regarding the improved understanding of the effect of particle deposition on efficacy and safety and the effect of the administration technique. This review emphasizes the gaps in knowledge regarding this subject. Advances in research and health care are necessary to improve care for patients with AR.

Informed consent for suspension microlaryngoscopy: what should we tell the patient? A consensus statement of the European Laryngological Society.

INTRODUCTION: Informed consent for any surgical intervention is necessary, as only well-informed patients can actively participate in the decision-making process about their care, and better understand the likely or potential outcomes of their treatment. No consensus exists on informed consent for suspension microlaryngoscopy (SML). MATERIALS AND METHODS: Informed consent procedures in nine countries on five continents were studied. RESULTS: Several risks can be discerned: risks of SML as procedure, anesthesiologic risks of SML, specific risks of phonosurgery, risks of inadequate glottic exposure or unexpected findings, risks of not treating. SML has recognized potential complications, that can be divided in temporary (minor) complications, and lasting (major) complications. CONCLUSION: SML is a safe procedure with low morbidity, and virtually no mortality. Eleven recommendations are provided.

Persulfurated Benzene-Cored Asterisks with π-Extended ThioNaphthyl Arms: Synthesis, Structural, Photophysical and Covalent Dynamic Properties.

The synthesis of regioisomeric asterisks (5) and (6) incorporating a benzene core with six 1-naphthylthio or six 2-naphthylthio arms are reported in search for new materials with optoelectronic properties. The consequences on the extension of a π system surrounding a persulfurated benzene core provide a new avenue to study the structural, photophysical, and chemical properties of such family of all-organic phosphors. It also diverts the persulfuration mechanism after two radical cyclizations for making a [5]dithiohelicene by-product (7) and favors dynamic sulfur component exchange reactions surrounding the core. These exchanges convert asterisks (5) and (6), non-phosphorescent at 20 °C to the highly phosphorescent (4) (ϕ ∼100 %, solid state at 20 °C). For asterisks (5) and (6), the absence of the typical phosphorescence of the per(phenylthio)benzene core in the solid state at 20 °C and the presence of a weak naphthalene-based phosphorescence at 77 K is attributed to an energy transfer from the triplet state of the persulfurated benzene core to the outer naphthalene moieties, resulting in an antenna system.

Synthesis and Electron Accepting Properties of Two Di(benz[f]indenone)-Fused Tetraazaanthracene Isomers.

We designed and synthesized a novel di(benz[f]indenone)-fused tetraazaanthracene derivative and isolated its two isomers, 1a and 1s, having anti and syn configurations, respectively. Their structure and that of the condensation reaction intermediates, anti-2a and syn-2s, were fully characterized using one- and two-dimensional nuclear magnetic resonance spectroscopy and single-crystal X-ray diffraction. The optical and electronic properties of 1a and 1s were investigated using ultraviolet-visible absorption and fluorescence spectroscopies, cyclic voltammetry, and time-dependent density functional theory calculations. The presence of the carbonyl and ethynyltris(isopropyl)silane groups endows the di(benzoindenone)-fused azaacene derivatives with a strong electron accepting character. With an electron affinity of approximately -3.7 eV, the two isomers represent attractive electron-deficient molecular systems for the generation of n-channel semiconducting materials. Organic field effect transistors of 1a and 1s showed electron transport, and organic solar cells gave a proof of concept of the potential of the two compounds as electron acceptor materials when they are paired with an electron donor polymer.

Chirality determination in crystals.

This tutorial review article discusses chirality determination in the solid state, both in single crystals and in crystal assemblies, with an emphasis on X-ray diffraction. The main principles of using X-ray diffraction to reliably determine absolute structure are summarized, and the complexity which can be encountered in chiral structures-kryptoracemates, scalemates, and inversion twinning-is illustrated with examples from our laboratories and the literature. We then address the problem of the bulk crystallization and discuss different techniques to determine chirality in a large assembly of crystal structures, with a special prominence given to an X-ray natural circular dichroism mapping technique that we recently reported.

A nonheme peroxo-diiron(III) complex exhibiting both nucleophilic and electrophilic oxidation of organic substrates.

The complex [FeIII2(µ-O2)(L3)4(S)2]4+ (L3 = 2-(4-thiazolyl)benzimidazole, S = solvent) forms upon reaction of [FeII(L3)2] with H2O2 and is a functional model of peroxo-diiron intermediates invoked during the catalytic cycle of oxidoreductases. The spectroscopic properties of the complex are in line with those of complexes formed with N-donor ligands. [FeIII2(µ-O2)(L3)4(S)2]4+ shows both nucleophilic (aldehydes) and electrophilic (phenol, N,N-dimethylanilines) oxidative reactivity and unusually also electron transfer oxidation.

Oral and laryngeal HPV infection: Incidence, prevalence and risk factors, with special regard to concurrent infection in head, neck and genitals.

This review focuses on the importance of oral and laryngeal HPV infection which is present in majority of sexually active individuals at least once in their lifetime. Despite testing, still little is known about prevalence rates, determinants and, especially, the concurrent HPV infection in head and neck, and genitals. The purpose of this review is to clarify some issues of oral HPV incidence, prevalence, and to demonstrate the difficulties in identification of asymptomatic oral HPV carriers. The main premise to take up this topic is the high and still increasing risk for development of oropharyngeal cancer, and potential benefit from screening strategies, education programs and HPV vaccination. Transmission of HPV to the oral cavity and oropharynx is hypothesized to occur mainly through sexual contact. The exposure of oropharyngeal mucosa to HPV infection with consequence of increased risk for oropharyngeal carcinoma depends on specific sexual behavior. Male gender, older age, race or ethnicity, oral hygiene and current cigarette smoking are independently associated with any prevalent oral HPV infection.

Hydrogen evolution reaction mediated by an all-sulfur trinuclear nickel complex.

We report the synthesis and the characterization of a trinuclear nickel complex. Solid state and solution studies using X-ray diffraction, NMR and UV-vis spectroscopy highlight the square planar geometries around the metal centers and an all-sulfur coordination sphere. It exhibits significant electrocatalytic activity for hydrogen evolution in DMF using Et3NHCl as the proton source. DFT studies suggest that sulfur atoms act as proton relay, as proposed in [NiFe] hydrogenases.

Ligand-based electronic effects on the electrocatalytic hydrogen production by thiosemicarbazone nickel complexes.

This work reports on the synthesis and characterization of a series of mononuclear thiosemicarbazone nickel complexes that display significant catalytic activity for hydrogen production in DMF using trifluoroacetic acid as the proton source. The ligand framework was chemically modified by varying the electron-donating abilities of the para substituents on the phenyl rings, which was expected to impact the capability of the resulting complexes to reduce protons into hydrogen. Over the four nickel complexes that were obtained, the one with the thiomethyl substituent, NiSCH3, was found to overtake the catalytic performances of the parent complex NiOCH3 featuring lower overpotential values and similar maximum turnover frequencies. These results confirm the electronic effects of the ligand on HER when using thiosemicarbazone nickel complexes and support that chemical modifications can tune the catalytic performances of such systems.

Stereoselective Syntheses, Structures, and Properties of Extremely Distorted Chiral Nanographenes Embedding Hextuple Helicenes.

We report a molecular design and concept using π-system elongation and steric effects from helicenes surrounding a triphenylene core toward stable chiral polycyclic aromatic hydrocarbons (PAHs) with a maximal π-distortion to tackle their aromaticity, supramolecular and molecular properties. The selective syntheses, and the structural, conformational and chiroptical properties of two diastereomeric large multi-helicenes of formula C90 H48 having a triphenylene core and embedding three [5]helicene units on their inner edges and three [7]helicene units at their periphery are reported based on diastereoselective and, when applicable, enantiospecific Yamamoto-type cyclotrimerizations of racemic or enantiopure 9,10-dibromo[7]helicene. Both molecules have an extremely distorted triphenylene core, and one of them exhibits the largest torsion angle recorded so far for a benzene ring (twist=36.9°).