Revisiting Hafner's Azapentalenes: The Chemistry of 1,3-Bis(dimethylamino)-2-azapentalene

Stable azaheterocyclic derivatives of pentalene have been reported by the group of Hafner in the 1970s. However, these structures remained of low interest until recently, when they started to be investigated in the context of organic light-emitting diodes' (OLEDs') development. Herein, we revisit the synthesis of stable azapentalene derivative 1,3-bis(dimethylamino)-2-azapentalene and further explore its properties both computationally and experimentally. Beyond the reproduction and optimization of some previously reported transformations, such as formylation and amine substitution, the available scope of reactions was expanded with azo-coupling, selective halogenations, and cross-coupling reactions.

An Exploration of Substituent Effects on the Photophysical Properties of Monobenzopentalenes

Monobenzopentalenes have received moderate attention compared to dibenzopentalenes, yet their accessibility as stable, non-symmetric structures with diverse substituents could be interesting for materials applications, including molecular photonics. Recently, monobenzopentalene was considered computationally as a potential chromophore for singlet fission (SF) photovoltaics. To advance this compound class towards photonics applications, the excited state energetics must be characterized, computationally and experimentally. In this report we synthesized a series of stable substituted monobenzopentalenes and provided the first experimental exploration of their photophysical properties. Structural and opto-electronic characterization revealed that all derivatives showed 1H NMR shifts in the olefinic region, bond length alternation in the pentalene unit, low-intensity absorptions reflecting the ground-state antiaromatic character and in turn the symmetry forbidden HOMO-to-LUMO transitions of ~2 eV and redox amphotericity. This was also supported by computed aromaticity indices (NICS, ACID, HOMA). Accordingly, substituents did not affect the fulfilment of the energetic criterion of SF, as the computed excited-state energy levels satisfied the required E(S1)/E(T1)>2 relationship. Further spectroscopic measurements revealed a concentration dependent quenching of the excited state and population of the S2 state on the nanosecond timescale, providing initial evidence for unusual photophysics and an alternative entry point for singlet fission with monobenzopentalenes.

Salicylideneaniline/Dithienylethene Hybrid Molecular Switches: Design, Synthesis, and Photochromism

A hybrid molecular switch comprising salicylideneaniline (SA) and dithienylethene (DTE) moieties around a single benzene ring is reported. Due to an interplay between solvent-assisted enol-keto tautomerization in the former moiety and photochromic electrocyclization in the latter, this dithienylbenzene derivative was found to be photoresponsive at room temperature with a thermally stable closed form. The main photoproduct featuring ring-closed DTE and keto-enamine SA structures could be isolated and converted back to the starting material by irradiation with visible light. The optical properties of the potential structures involved in the overall process were characterized by using density functional theory (DFT) calculations in good agreement with the measured data. The reversibility of the conversion could be tuned by the presence of donor and acceptor substituents, while the introduction of the imine in the form of a benzothiazole moiety enabled photochemistry even in nonprotic solvents.

Stable Monoareno-pentalenes with Two Olefinic Protons

A novel class of stable monoareno-pentalenes is introduced that have an olefinic proton on each five-membered ring of the pentalene subunit. Their synthesis was accomplished via a regioselective carbopalladation cascade reaction between ortho-arylacetyleno gem-dibromoolefins and TIPS-acetylene. These molecules could be experimental probes of magnetic (anti)aromaticity effects.

Photoswitching of Local (Anti)Aromaticity in Biphenylene-Based Diarylethene Molecular Switches

Photoinduced tuning of (anti)aromaticity and associated molecular properties is currently in the focus of attention for both tailoring photochemical reactivity and designing new materials. Here, we report on the synthesis and spectroscopic characterization of diarylethene-based molecular switches embedded in a biphenylene structure composed of rings with different levels of local (anti)aromaticity. We show that it is possible to modulate and control the (anti)aromatic character of each ring through reversible photoswitching of the aryl units of the system between open and closed forms. Remarkably, it is shown that the irreversible formation of an annulated bis(dihydro-thiopyran) side-product that hampers the photoswitching can be efficiently suppressed when the aryl core formed by thienyl groups in one switch is replaced by thiazolyl groups in another.

Unsymmetrical Thienopentalenes: Synthesis, Optoelectronic Properties, and (Anti)aromaticity Analysis

The synthesis and properties of a series of unsymmetrical thienopentalenes are explored, including both monoareno and diareno derivatives. For the synthesis of monoareno pentalenes, a carbopalladation cascade reaction between alkynes and gem-dibromoolefins was applied. Diareno pentalene derivatives were accessed via gold-catalyzed cyclization of diynes. Thiophene was fused to pentalene in two different geometries via its 2,3 and 3,4 bonds. 2,3-Fusion resulted in increased antiaromaticity of the pentalene unit compared to the 3,4-fusion both in the monoareno and diareno framework. Monothienopentalenes that contained the destabilizing 2,3-fusion could not be isolated. For diareno derivatives, the aromatic character of the different aryl groups fused to the pentalene was not independent. Destabilizing fusion on one side resulted in alleviated aromaticity on the other side and vice versa. The synthesized molecules were characterized experimentally by ¹H NMR and UV-vis spectroscopies, cyclic voltammetry, and X-ray crystallography, and their aromatic character was assessed using magnetic (NICS and ACID) and electronic indices (MCI and FLU).

A photoresponsive palladium complex of an azopyridyl-triazole ligand: light-controlled solubility drives catalytic activity in the Suzuki coupling reaction

Herein, the design and synthesis of a click-derived Pd-complex merged with a photoswitchable azobenzene unit is presented. While in the trans-form of the switch the complex showed limited solubility, the photogenerated cis-form rendered the molecule soluble in polar solvents. This light-controllable solubility was exploited to affect the catalytic activity in the Suzuki coupling reaction. The effect of the substrate and catalyst concentration and light intensity on the proceeding and outcome of the reaction was studied. Dehalogenation of the aryl iodide starting material was found to be a major side reaction; however, its occurrence was dependent on the applied light intensity.

Construction and Properties of Donor-Acceptor Stenhouse Adducts on Gold Surfaces

The construction of a donor-acceptor Stenhouse adduct molecular layer on a gold surface is presented. To avoid the incompatibility of the thiol surface-binding group with the donor-acceptor polyene structure of the switch, an interfacial reaction approach was followed. Poly(dopamine)-supported gold nanoparticles on quartz slides were chosen as substrates, which was expected to facilitate both the interfacial reaction and the switching process by providing favorable steric conditions due to the curved particle surface. The reaction between the surface-bound donor half and the CF3-isoxazolone-based acceptor half was proved to be successful by X-ray photoelectron spectroscopy (XPS). However, UV-vis measurements suggested that a closed, cyclopentenone-containing structure of the switch formed on the surface irreversibly. Analysis of the wetting behavior of the surface revealed spontaneous water spreading that could be associated with conformational changes of the closed isomer.

Photoinduced Changes in Aromaticity Facilitate Electrocyclization of Dithienylbenzene Switches

The concepts of excited-state aromaticity and antiaromaticity have in recent years with increasing frequency been invoked to rationalize the photochemistry of cyclic conjugated organic compounds, with the long-term goal of using these concepts to improve the reactivities of such compounds toward different photochemical transformations. In this regard, it is of particular interest to assess how the presence of a benzene motif affects photochemical reactivity, as benzene is well-known to completely change its aromatic character in its lowest excited states. Here, we investigate how a benzene motif influences the photoinduced electrocyclization of dithienylethenes, a major class of molecular switches. Specifically, we report on the synthesis of a dithienylbenzene switch where the typical nonaromatic, ethene-like motif bridging the two thienyl units is replaced by a benzene motif, and show that this compound undergoes electrocyclization upon irradiation with UV-light. Furthermore, through a detailed quantum chemical analysis, we demonstrate that the electrocyclization is driven jointly and synergistically by the loss of aromaticity in this motif from the formation of a reactive, antiaromatic excited state during the initial photoexcitation, and by the subsequent relief of this antiaromaticity as the reaction progresses from the Franck–Condon region. Overall, we conclude that photoinduced changes in aromaticity facilitate the electrocyclization of dithienylbenzene switches.

Structure-Property Relationships in Unsymmetric Bis(antiaromatics): Who Wins the Battle between Pentalene and Benzocyclobutadiene?†

According to the currently accepted structure–property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8π antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by ¹H NMR, UV–vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]π subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure–antiaromaticity relationship when compared to aceno-pentalenes was achieved.

Photoswitchable Macroscopic Solid Surfaces Based On Azobenzene-Functionalized Polydopamine/Gold Nanoparticle Composite Materials: Formation, Isomerization and Ligand Exchange

The facile preparation of dynamic interfaces is presented based on the combination of photoisomerizable azobenzenes and polydopamine (PDA)/Au nanoparticle composite materials. Azobenzenes with different spacer lengths (C₃ , C₆ ) and surface-binding groups (SH, NH₂ ) were synthesized. The polymer layer on macroscopic quartz surface was prepared by the facile aerobic autopolymerisation of dopamine hydrochloride under basic conditions. The presence of redox-active catechol moieties meant that gold nanoparticles were formed on the polymer surface. The obtained UV-Vis spectroscopic results confirmed that following their successful assembly, the switching of azobenzenes on PDA/Au was not affected by the surface binding group and the spacer length of the azobenzene molecules under the measurement conditions. Furthermore, facilitated by the curved nature of the Au particles, the surface-bound azobenzene layer could be reconstructed by ligand-exchange processes, and the photochemical characterization of the mixed layer was performed.

P1584The prognostic significance of the blood pressure-pulse wave velocity association for cardiovascular outcomes and mortality in hemodialysis patients

Introduction and purpose

Hemodialysis patients have premature arterial stiffness, and the relationship between pulse wave velocity (PWV) and blood pressure (BP) may be different than in other hypertensives. Previous studies showed that when BP decrease is accompanied by PWV decrease the survival is improved. The aim of this study is to examine the prognostic significance of BP sensitivity of PWV for major cardiovascular outcomes and all-cause mortality in hemodialysis patients.

Methods

This is a prospective cohort study including 242 hemodialysis patients [age, 62.6±14.2 years; female, 91 (37.6%); hemodialysis vintage, 41.53±43.46]. All subjects underwent 48-hour-ABPM with Mobil-O-Graph-NG and followed-up for 33.17±19.68 months. The within-individual MBP-PWV association (MBP, dependent and PWV independent variable) was evaluated using the beta-coefficient value from simple linear regression analysis for each patient. The primary end-point was first occurrence of all-cause death, non-fatal myocardial infarction or non-fatal stroke. Secondary end-points were: (i) all-cause mortality; (ii) cardiovascular mortality; (iii) a combination of cardiovascular events.

Results

Patients who experienced the primary end-point during follow-up had significantly lower beta-coefficient levels (primary end-point: 19.877±3.975 vs 18.483±3.550, p=0.008). Higher quartiles of beta-coefficients (indicating dependency of PWV on MBP) were associated with higher cumulative freedom from the primary end-point (50.8%, 60.0%, 70.0% and 80.3% for quartiles 1 to 4 respectively; logrank-p=0.001), higher overall survival (60.7%, 61.7%, 73.3%, 86.9%; logrank-p=0.002) and higher cardiovascular survival (78.7%, 75.0%, 81.7%, 91.8% for quartiles 1 to 4; logrank-p=0.044). The future risk for the primary end-point, all-cause and cardiovascular mortality and the combined outcome was progressively increasing for lower quartiles of beta-coefficients (HR for all-cause mortality 3.395; 95% CI: 1.524–7.563, p=0.003 for quartile 1 vs quartile 4). Age (OR: 1.046, 95% CI: 1.016–1.077 per year increase, p=0.003) and 48h heart rate (OR: 0.949, 95% CI: 0.916–0.982 per bpm increase, p=0.003) were independently associated with weaker relationship between 48h-MBP and 48h-PWV.

Conclusions

Lower within-individual MBP-PWV association, based on AMBP recordings, is associated with higher risk of death and cardiovascular events in hemodialysis. These findings support that BP-independent arterial stiffness may be the underlying factor for adverse outcomes in these individuals.

P2640The effect of dry-weight reduction guided by lung ultrasound on ambulatory aortic blood pressure and arterial stiffness parameters in hemodialysis patients

Introduction and purpose

Arterial stiffness and aortic blood pressure (BP) augmentation are significantly increased in hemodialysis patients. Recent studies suggest that the prognostic significance of ambulatory recordings of arterial stiffness is high in hemodialysis. This study examines for the first time the effect of dry weight reduction with a standardized lung-ultrasound-guided strategy on ambulatory aortic BP and arterial stiffness parameters in hypertensive hemodialysis patients.

Methods

A total 71 hemodialysis patients with hypertension (mean home BP ≥135/85 mmHg), that were clinically euvolemic, were included in this single-blind randomized clinical trial. Patients were randomized in a 1:1 ratio in the active group (n=35), following a strategy for dry-weight reduction guided by the total number of US-B lines (US-B lines score) prior to a mid-week dialysis session and the control group (n=), following standard-of-care treatment. All patients underwent 48-hour ABPM with the Mobil-O-Graph monitor (IEM, Stolberg, Germany) and PWV measurement in office with SphygmoCor (ArtCor, Sydney, Australia) at baseline and after 8-weeks.

Results

Overall, the US-B lines change during follow-up were −5.3±12.5 in active versus +2.2±7.6 in control group (p<0.001), which corresponded to dry-weight changes of −0.71±1.39 versus +0.51±0.98 kg (p<0.001). The change in 48-hour cSBP was significantly greater in the active group (−6.30±8.90 vs −0.50±12.46, p=0.027); the relevant cDBP fall was marginally greater (−3.85±6.61 vs −0.63±8.36, p=0.077) in the active group. 48-hour cPP (41.51±9.63 vs 39.06±9.61 mmHg, p=0.004) and 48-hour PWV (9.30±2.00 vs 9.08±2.04 m/sec, p=0.032) were significantly reduced from baseline to study-end in the active group but remained unchanged in controls. In contrast, 48-hour AIx and AIx(75) did not change between baseline and study-end in both groups; changes in AIx(75) were similar in the two groups (−0.97±3.51 vs −0.36±4.25, p=0.517). PWV measured in office was decreased from baseline to study-end in the active (10.07±2.66 vs 9.79±2.81, p=0.038) but not in the control group.

Conclusions

A lung-ultrasound-guided strategy for dry-weight reduction reduces ambulatory aortic BP and ambulatory or office PWV, but not ambulatory AIx(75). These results suggest that dry-weight reduction can primarily reduce aortic BP levels and large arteries stiffness but not wave reflections from the periphery.

Effect of Particle Restructuring During Reduction Processes Over Polydopamine-Supported Pd Nanoparticles

The effect of catalyst restructuring on the polydopamine-supported Pd catalyzed transfer hydrogenation of ethyl 4-nitrobenzoate and the catalytic hydrogenation of (E)-2-methyl-2-butenoic acid is reported. Transmission electron microscopy investigation of different catalyst pre-treatment and reaction conditions revealed high catalytic activity in both reactions unless drastic aggregation of the active metal occurred. In the transfer hydrogenation reaction aggregation was primarily dependent on the H-source used, while in the catalytic hydrogenation additives in combination with the reductive environment led to extensive Pd aggregation and thus decreased catalytic activity. The enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid showed increased enantioselectivity and decreased conversion with increased particle size.

Polydopamine: An Emerging Material in the Catalysis of Organic Transformations

Polydopamine, a ‘mussel-inspired’ polymer, has been explored extensively in materials science as a universal coating. However, as an easily available, stable and environmentally benign material, it has recently been discovered to demonstrate catalytic applications. In this short review, we briefly discuss the main approaches employing polydopamine in the catalysis of organic transformations. These include metal/polydopamine-type systems and metal-free approaches that exploit the acid/base properties of this versatile polymer.

1 Introduction

2 PDA and Metal Catalysis

2.1 Reduction of Nitroaryl Compounds to Anilines

2.2 Reduction of Carbonyl Compounds to Alcohols

2.3 Suzuki and Heck Coupling Reactions

2.4 Other Reactions Catalyzed by M/PDA-Type Systems

3 PDA as a Catalyst Itself

4 Conclusion

Reversible switching of a supramolecular morphology driven by an amphiphilic bistable [2]rotaxane

A supra-amphiphilic [2]rotaxane-based switch could self-assemble into spherical vesicles in aqueous solution and transform into worm-like micelles in a basic environment.

Pd/Al2O3-catalysed redox isomerisation of allyl alcohol: application in aldol condensation and oxidative heterocyclization reactions

The application of the Pd/Al₂O₃ catalyst in allyl alcohol isomerization and subsequent aldol-condensation and heterocyclization reactions is described.

The Impact of Antiaromatic Subunits in [4n+2] π-Systems: Bispentalenes with [4n+2] π-Electron Perimeters and Antiaromatic Character

Three series of stable, neutral, π-extended bispentalene derivatives, with two pentalenes fused to a central benzene or naphthalene moiety, have been prepared through a modified double carbopalladation cascade reaction. While these chromophores feature skeletons with [4n+2] π-electron perimeters, the two 8 π-electron pentalene subunits strongly influence bonding and spectral properties. (1)H NMR spectra showed large upfield shifts of the protons in the pentalene moieties, comparable to antiaromatic monobenzopentalenes. Further investigations on magnetic ring currents through NICS-XY-scans suggest a global paratropic current and a local diatropic current at the central benzene ring in two of the series, while the third series, with a central naphthalene ring, showed more localized ring currents, with stronger paratropic ring currents on the pentalene moieties. X-ray diffraction analyses revealed planar bispentalene cores with large double- and single-bond alternation in the pentalene units, characteristic for antiaromaticity, and small alternation in the central aromatic rings. In agreement with TD-DFT calculations, both optical and electrochemical data showed much smaller HOMO-LUMO energy gaps compared to other neutral, acene-like hydrocarbons with the same number of fused rings. Both experimental and computational results suggest that the molecular properties of the presented bispentalenes are dominated by the antiaromatic pentalene-subunits despite the [4n+2] π-electron perimeter of the skeletons.

Structure and dynamics of molecular networks: a novel paradigm of drug discovery: a comprehensive review

Despite considerable progress in genome- and proteome-based high-throughput screening methods and in rational drug design, the increase in approved drugs in the past decade did not match the increase of drug development costs. Network description and analysis not only give a systems-level understanding of drug action and disease complexity, but can also help to improve the efficiency of drug design. We give a comprehensive assessment of the analytical tools of network topology and dynamics. The state-of-the-art use of chemical similarity, protein structure, protein-protein interaction, signaling, genetic interaction and metabolic networks in the discovery of drug targets is summarized. We propose that network targeting follows two basic strategies. The "central hit strategy" selectively targets central nodes/edges of the flexible networks of infectious agents or cancer cells to kill them. The "network influence strategy" works against other diseases, where an efficient reconfiguration of rigid networks needs to be achieved by targeting the neighbors of central nodes/edges. It is shown how network techniques can help in the identification of single-target, edgetic, multi-target and allo-network drug target candidates. We review the recent boom in network methods helping hit identification, lead selection optimizing drug efficacy, as well as minimizing side-effects and drug toxicity. Successful network-based drug development strategies are shown through the examples of infections, cancer, metabolic diseases, neurodegenerative diseases and aging. Summarizing >1200 references we suggest an optimized protocol of network-aided drug development, and provide a list of systems-level hallmarks of drug quality. Finally, we highlight network-related drug development trends helping to achieve these hallmarks by a cohesive, global approach.

Silanization of quartz, silicon and mica surfaces with light-driven molecular motors: construction of surface-bound photo-active nanolayers

The attachment of molecular rotary motors containing triethoxysilane functional groups to quartz, silicon and mica surfaces is described. Motors containing silane coupling agents in their structure form stable molecular layers on quartz and silicon surfaces. Motors attached to these surfaces were found to undergo photochemical and thermal isomerization steps similar to those observed in solution. Additionally, successful formation of molecular "carpets" on atomically flat mica extending micrometer-sized length scales is presented. These "carpets" were found to undergo morphological changes upon irradiation with UV-light.

[Incidence of arterial hypertension in French population after 60 years]

OBJECTIVE

To evaluate incidence and determinants of arterial hypertension after 60 years.

METHODS

Four thousand nine hundred and forty one subjects aged 60 years or above (2505 men: 64.2±4.2 years; 2436 women: 64.8±4.3 years) were explored two times at the IPC center, Paris, between 1992 and 2007, and were normotensive at the first visit (V1): systolic BP (SBP) less than 140mmHg and diastolic BP (DBP) less than 90mmHg without treatment. The delay between the two visits was 5.8±2.2 years. At the second visit, population was analysed as normotensives and hypertensives. An age-adjusted Anova compared groups.

RESULTS

In men, incidence of hypertension is 41.5% and 25.9% for isolated systolic hypertension. In women, incidences were 37.8% and 27.8% respectively. Baseline characteristics for V2-hypertensives showed higher SBP, DBP, BMI, heart rate, glycemia, ECG abnormalities thanV2-normotensives but they had lower physical activity. The determinants of hypertension were: SBP, age, BMI, DBP, glycemia, and lack of physical activity for this age class.

CONCLUSION

From 60 years old, 6-year incidence of hypertension is about 40% and 26% for isolated systolic hypertension, this latter being higher in women. Regular physical activity is protective.

Adhesion of photon-driven molecular motors to surfaces via 1,3-dipolar cycloadditions: effect of interfacial interactions on molecular motion

We report the attachment of altitudinal light-driven molecular motors to surfaces using 1,3-dipolar cycloaddition reactions. Molecular motors were designed containing azide or alkyne groups for attachment to alkyne- or azide-modified surfaces. Surface attachment was characterized by UV-vis, IR, XPS, and ellipsometry measurements. Surface-bound motors were found to undergo photochemical and thermal isomerizations consistent with unidirectional rotation in solution. Confinement at a surface was found to reduce the rate of the thermal isomerization process. The rate of thermal isomerization was also dependent on the surface coverage of the motors. In solution, changes in the UV-vis signal that accompany thermal isomerization can be fit with a single monoexponential decay. In contrast, thermal isomerization of the surface-bound motors does not follow a single monoexponential decay and was found to fit a biexponential decay. Both one- and two-legged motors were attached to surfaces. The kinetics of thermal isomerization was not affected by the valency of attachment, indicating that the changes in kinetics from solution to surface systems are related to interactions between the surface-bound motors.

The new kidney disease: improving global outcomes (KDIGO) guidelines - expert clinical focus on bone and vascular calcification

Chronic kidney disease-mineral and bone disorder (CKD-MBD) defines a triad of interrelated abnormalities of serum biochemistry, bone and the vasculature associated with chronic kidney disease (CKD). The new kidney disease: improving global outcomes (KDIGO) guidelines define the quality and depth of evidence supporting therapeutic intervention in CKD-MBD. They also highlight where patient management decisions lack a strong evidence base. Expert interpretation of the guidelines, along with informed opinion, where evidence is weak, may help develop effective clinical practice. The body of evidence linking poor bone health and reservoir function (the ability of bone to buffer calcium and phosphorus) with vascular calcification and cardiovascular outcomes is growing. Treating renal bone disease should be one of the primary aims of therapy for CKD. Evaluation of the biochemical parameters of CKD-MBD (primarily phosphorus, calcium, parathyroid hormone and vitamin D levels) as early as CKD Stage 3, and an assessment of bone status (by the best means available), should be used to guide treatment decisions. The adverse effects of high phosphorus intake relative to renal clearance (including stimulation of hyperparathyroidism) precede hyperphosphatemia, which presents late in CKD. Early reduction of phosphorus load may ameliorate these adverse effects. Evidence that calcium load may influence progression of vascular calcification with effects on mortality should also be considered when choosing the type and dose of phosphate binder to be used. The risks, benefits, and strength of evidence for various treatment options for the abnormalities of CKD-MBD are considered.