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Natural light harvesting systems absorb sunlight and transfer its energy to the reaction centre, where it is used for photosynthesis. Synthetic chromophore arrays provide useful models for understanding energy migration in these systems. Research has focussed on mimicking rings of chlorophyll molecules found in purple bacteria, known as ‘light-harvesting system 2’. Linear meso-meso linked porphyrin chains mediate rapid energy migration, but until now it has not been possible to bend them into rings. Here we show that oligo-pyridyl templates can be used to bend these rod-like photonic wires, to create covalent nanorings. The macrocycles consist of 24 porphyrin units, with a single butadiyne link. Their elliptical conformations have been probed by scanning tunnelling microscopy (STM). This system exhibits two types of excited state energy transfer processes: (a) from the central template to the peripheral porphyrins and (b) from the 24 light-absorbing porphyrin units to the π-conjugated butadiyne-linked porphyrin dimer segment.

© 2022 American Academy of Hospice and Palliative MedicineContext: The COVID-19 pandemic has highlighted variability in intensity of care. We aimed to characterize intensity of care among hospitalized patients with COVID-19. Objectives: Examine the prevalence and predictors of admission code status, palliative care consultation, comfort-measures-only orders, and cardiopulmonary resuscitation (CPR) among patients hospitalized with COVID-19. Methods: This cross-sectional study examined data from an international registry of hospitalized patients with COVID-19. A proportional odds model evaluated predictors of more aggressive code status (i.e., Full Code) vs. less (i.e., Do Not Resuscitate, DNR). Among decedents, logistic regression was used to identify predictors of palliative care consultation, comfort measures only, and CPR at time of death. Results: We included 29,923 patients across 179 sites. Among those with admission code status documented, Full Code was selected by 90% (n = 15,273). Adjusting for site, Full Code was more likely for patients who were of Black or Asian race (ORs 1.82, 95% CIs 1.5–2.19; 1.78, 1.15–3.09 respectively, relative to White race), Hispanic ethnicity (OR 1.89, CI 1.35–2.32), and male sex (OR 1.16, CI 1.0–1.33). Of the 4951 decedents, 29% received palliative care consultation, 59% transitioned to comfort measures only, and 29% received CPR, with non-White racial and ethnic groups less likely to receive comfort measures only and more likely to receive CPR. Conclusion: In this international cohort of patients with COVID-19, Full Code was the initial code status in the majority, and more likely among patients who were Black or Asian race, Hispanic ethnicity or male. These results provide direction for future studies to improve these disparities in care.

A switchable solvatochromic fluorescent dyad can be used to map ordering of lipids in vesicle membranes at a resolution better than the diffraction limit. Combining a Nile Red fluorophore with a photochromic spironaphthoxazine quencher allows the fluorescence to be controlled using visible light, via photoswitching and FRET quenching. Synthetic lipid vesicles of varying composition were imaged with an average 2.5-fold resolution enhancement, compared to the confocal images. Ratiometric detection was used to probe the membrane polarity, and domains of different lipid ordering were distinguished within the same membrane.

Cyclic porphyrin oligomers have been studied as models for photosynthetic light-harvesting antenna complexes and as potential receptors for supramolecular chemistry. Here, we report the synthesis of unprecedented β,β-directly linked cyclic zinc porphyrin oligomers, the trimer (CP3) and tetramer (CP4), by Yamamoto coupling of a 2,3-dibromoporphyrin precursor. Their three-dimensional structures were confirmed by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and single-crystal X-ray diffraction analyses. The minimum-energy geometries of CP3 and CP4 have propeller and saddle shapes, respectively, as calculated using density functional theory. Their different geometries result in distinct photophysical and electrochemical properties. The smaller dihedral angles between the porphyrin units in CP3, compared with CP4, result in stronger π-conjugation, splitting the ultraviolet–vis absorption bands and shifting them to longer wavelengths. Analysis of the crystallographic bond lengths indicates that the central benzene ring of the CP3 is partially aromatic [harmonic oscillator model of aromaticity (HOMA) 0.52], whereas the central cyclooctatetraene ring of the CP4 is non-aromatic (HOMA –0.02). The saddle-shaped structure of CP4 makes it a ditopic receptor for fullerenes, with affinity constants of (1.1 ± 0.4) × 105 M–1 for C70 and (2.2 ± 0.1) × 104 M–1 for C60, respectively, in toluene solution at 298 K. The formation of a 1:2 complex with C60 is confirmed by NMR titration and single-crystal X-ray diffraction.

Aromaticity is one of the most deeply rooted concepts in chemistry. But why, if two-thirds of existing compounds can be classified as aromatic, is there no consensus on what aromaticity is? σ−, π−, δ−, spherical, Möbius, or all-metal aromaticity… why are so many attributes needed to specify a property? Is aromaticity a dubious concept? This perspective aims to reflect where the aromaticity community is and where it is going.

Background Although specific interventions previously demonstrated benefit in patients with ARDS, use of these interventions is inconsistent, and patient mortality remains high. The impact of variability in center management practices on ARDS mortality rates remains unknown. Research Question What is the impact of treatment variability on mortality in patients with moderate to severe ARDS in the United States? Study Design and Methods We conducted a multicenter, observational cohort study of mechanically ventilated adults with ARDS and Pa o 2 to F io 2 ratio of ≤ 150 with positive end-expiratory pressure of ≥ 5 cm H2O, who were admitted to 29 US centers between October 1, 2016, and April 30, 2017. The primary outcome was 28-day in-hospital mortality. Center variation in ventilator management, adjunctive therapy use, and mortality also were assessed. Results A total of 2,466 patients were enrolled. Median baseline Pa o 2 to F io 2 ratio was 105 (interquartile range, 78.0-129.0). In-hospital 28-day mortality was 40.7%. Initial adherence to lung protective ventilation (LPV; tidal volume, ≤ 6.5 mL/kg predicted body weight; plateau pressure, or when unavailable, peak inspiratory pressure, ≤ 30 mm H2O) was 31.4% and varied between centers (0%-65%), as did rates of adjunctive therapy use (27.1%-96.4%), methods used (neuromuscular blockade, prone positioning, systemic steroids, pulmonary vasodilators, and extracorporeal support), and mortality (16.7%-73.3%). Center standardized mortality ratios (SMRs), calculated using baseline patient-level characteristics to derive expected mortality rate, ranged from 0.33 to 1.98. Of the treatment-level factors explored, only center adherence to early LPV was correlated with SMR. Interpretation Substantial center-to-center variability exists in ARDS management, suggesting that further opportunities for improving ARDS outcomes exist. Early adherence to LPV was associated with lower center mortality and may be a surrogate for overall quality of care processes. Future collaboration is needed to identify additional treatment-level factors influencing center-level outcomes. Trial Registry ClinicalTrials.gov; No.: NCT03021824; URL: www.clinicaltrials.gov

ConspectusThe ring currents of aromatic and antiaromatic molecules are remarkable emergent phenomena. A ring current is a quantum-mechanical feature of the whole system, and its existence cannot be inferred from the properties of the individual components of the ring. Huckel's rule states that when an aromatic molecule with a circuit of [4n + 2] π electrons is placed in a magnetic field, the field induces a ring current that creates a magnetic field opposing the external field inside the ring. In contrast, antiaromatic rings with 4n π electrons exhibit ring currents in the opposite direction. This rule bears the name of Erich Huckel, and it grew from his molecular orbital theory, but modern formulations of Huckel's rule incorporate contributions from others, particularly William Doering and Ronald Breslow. It is often assumed that aromaticity is restricted to small molecular rings with up to about 22 π electrons. This Account outlines the discovery of global ring currents in large macrocycles with circuits of up to 162 π electrons. The largest aromatic rings yet investigated are cyclic porphyrin oligomers, which exhibit global ring currents after oxidation, reduction or optical excitation but not in the neutral ground state. The global aromaticity in these porphyrin nanorings leads to experimentally measurable aromatic stabilization energies in addition to magnetic effects that can be studied by NMR spectroscopy. Wheel-like templates can be bound inside these nanorings, providing excellent control over the molecular geometry and allowing the magnetic shielding to be probed inside the nanoring. The ring currents in these systems are well-reproduced by density functional theory (DFT), although the choice of DFT functional often turns out to be critical. Here we review recent contributions to this field and present a simple method for determining the ring current susceptibility (in nA/T) in any aromatic or antiaromatic ring from experimental NMR data by classical Biot-Savart calculations. We use this method to quantify the ring currents in a variety of aromatic rings. This survey confirms that Huckel's rule reliably predicts the direction of the ring current, and it reveals that the ring current susceptibility is surprisingly insensitive to the size of the ring. The investigation of aromaticity in even larger molecular rings is interesting because ring currents are also observed when mesoscopic metal rings are placed in a magnetic field at low temperatures. The striking similarity between the ring currents in molecules and mesoscopic metal rings arises because the effects have a common origin: a field-dependent phase shift in the electronic wave function. The main difference is that the magnetic flux through mesoscopic rings is much greater because of their larger areas, so their persistent currents are nonlinear and oscillatory with the applied field, whereas the flux through aromatic molecules is so small that their response is approximately linear in the applied field. We discuss how nonlinearity is expected to emerge in large molecular nanorings at high magnetic fields. The insights from this work are fundamentally important for understanding aromaticity and for bridging the gap between chemistry and mesoscopic physics, potentially leading to new functions in molecular electronics.

A recent Research Article in this journal by Matito and co-workers claimed that none of the oxidation states of a butadiyne-linked six-porphyrin nanoring exhibit global aromaticity or antiaromaticity. Here we show that this conclusion is incorrect. Experimental data from NMR spectroscopy for a whole family of nanorings provide strong evidence for global ring currents. The NMR data reveal these ring currents directly, without needing analysis by density functional theory (DFT). Furthermore, DFT calculations reproduce the experimental results when a suitable functional is used.

Enhanced thermodynamic stability is a fundamental characteristic of aromatic molecules, yet most previous studies of aromatic stabilization energy (ASE) have been limited to small rings with up to 18 π-electrons. Here we demonstrate that ASE can be detected experimentally in π-conjugated porphyrin nanorings with Hückel circuits of 76-108 π-electrons. This conclusion is supported by analyzing redox potentials to calculate the energy change for isodesmic reactions that convert an aromatic ring to an antiaromatic ring or vice versa. It is also supported by analyzing the energy barriers to conformational equilibria that disrupt aromaticity in the transition state. Both types of experiment indicate that cationic porphyrin nanorings display ASEs of 1-5 kJ mol-1. Density functional theory calculations reproduce the results for both types of experiment and predict ASEs in the range of 1-16 kJ mol-1. The experimental ASEs in porphyrin nanorings are compared with an experimental ASE of [18]annulene of ∼11 kJ mol-1, deduced from analysis of the energy barriers to conformational equilibria in [16], [18], and [20]annulene. Calculated energies of isodesmic reactions give an ASE of ∼37 kJ mol-1 in [18]annulene. This work contributes to a fundamental understanding of aromaticity in large macrocycles.

Polyyne polyrotaxanes, encapsulated cyclocarbon catenanes and other fascinating mechanically interlocked carbonrich architectures should become accessible if masked alkyne equivalents (MAEs) can be developed that are large enough to prevent unthreading of a macrocycle, and that can be cleanly unmasked under mild conditions. Here we report the synthesis of a new bulky MAE based on a t-butylbicyclo[4.3.1]decatriene. This MAE was used to synthesize a polyyne [2]rotaxane and a maskedpolyyne [3]rotaxane by Cadiot-Chodkiewicz coupling. Glaser cyclooligomerization of the [2]rotaxane gave masked cyclocarbon catenanes. The unmasking behavior of the catenanes and rotaxanes was tested by photolysis at a range of UV wavelengths. Photochemical unmasking did not proceed cleanly enough to prepare extended encapsulated polyyne polyrotaxanes. We highlight the scope and challenges involved with this approach to interlocked carbon-rich architectures.

The melamine·barbiturate H-bonded rosette motif is of comparable dimensions and symmetry to the cavity of a butadiyne-linked 6-porphyrin nanoring. Functionalisation of each of the barbiturate components and the pyrimidine components of a H-bonded rosette with a pyridine ligand leads to a self-assembled hexapyridine ligand, which binds cooperatively to the zinc porphyrin nanoring. UV-vis-NIR and 1H NMR experiments show that the 7-component assembly forms at concentrations at which neither the H-bonding interactions nor the zinc porphyrin–pyridine interactions are formed in the absence of one of the three components. The mean effective molarities of these rosette complexes are around 200 mM in chloroform at 298 K., Mixing barbiturates and pyrimidines equipped with pyridine ligands to leads to self-assembly of a hexadentate rosette ligand, which is complementary to a hexameric zinc porphyrin macrocycle.

In photosynthesis nature exploits the distinctive electronic properties of chromophores arranged in supramolecular rings for efficient light harvesting. Among synthetic supramolecular cyclic structures, porphyrin nanorings have attracted considerable attention as they have a resemblance to naturally occurring light-harvesting structures but offer the ability to control ring size and the level of disorder. Here, broadband femtosecond transient absorption spectroscopy, with pump pulses in resonance with either the high or the low energy sides of the inhomogeneously broadened absorption spectrum, is used to study the population dynamics and ground and excited state vibrational coherence in large porphyrin nanorings. A series of fully conjugated, alkyne bridged, nanorings constituted of between ten and forty porphyrin units is studied. Pump-wavelength dependent fast spectral evolution is observed. A fast rise or decay of the stimulated emission are observed when large porphyrin nanorings are excited on, respectively, the high or low energy side of the absorption spectrum. Such dynamics are consistent with the hypothesis of a variation in transition dipole moment across the inhomogeneously broadened ground state ensemble. Oscillatory dynamics on the sub-ps time domain are observed in both pumping conditions. A combined analysis of the excitation wavelength-dependent transient spectra along with the amplitude and phase evolution of the oscillations allows assignment to vibrational wavepackets evolving on either ground or excited states electronic potential energy surfaces. Even though porphyrin nanorings support highly delocalized electronic wavefunctions, with coherence length spanning tens of chromophores, the measured vibrational coherences remain localised on the monomers. The main contributions to the beatings are assigned to two vibrational modes localised on the porphyrin cores: a Zn-N stretching mode and a skeletal methinic/pyrrolic C-C stretching and in-plane bending mode.

What started as a cluster of patients with a mysterious respiratory illness in Wuhan, China, in December 2019, was later determined to be coronavirus disease 2019 (COVID-19). The pathogen severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel Betacoronavirus, was subsequently isolated as the causative agent. SARS-CoV-2 is transmitted by respiratory droplets and fomites and presents clinically with fever, fatigue, myalgias, conjunctivitis, anosmia, dysgeusia, sore throat, nasal congestion, cough, dyspnea, nausea, vomiting, and/or diarrhea. In most critical cases, symptoms can escalate into acute respiratory distress syndrome accompanied by a runaway inflammatory cytokine response and multiorgan failure. As of this article's publication date, COVID-19 has spread to approximately 200 countries and territories, with over 4.3 million infections and more than 290,000 deaths as it has escalated into a global pandemic. Public health concerns mount as the situation evolves with an increasing number of infection hotspots around the globe. New information about the virus is emerging just as rapidly. This has led to the prompt development of clinical patient risk stratification tools to aid in determining the need for testing, isolation, monitoring, ventilator support, and disposition. COVID-19 spread is rapid, including imported cases in travelers, cases among close contacts of known infected individuals, and community-acquired cases without a readily identifiable source of infection. Critical shortages of personal protective equipment and ventilators are compounding the stress on overburdened healthcare systems. The continued challenges of social distancing, containment, isolation, and surge capacity in already stressed hospitals, clinics, and emergency departments have led to a swell in technologically-assisted care delivery strategies, such as telemedicine and web-based triage. As the race to develop an effective vaccine intensifies, several clinical trials of antivirals and immune modulators are underway, though no reliable COVID-19-specific therapeutics (inclusive of some potentially effective single and multi-drug regimens) have been identified as of yet. With many nations and regions declaring a state of emergency, unprecedented quarantine, social distancing, and border closing efforts are underway. Implementation of social and physical isolation measures has caused sudden and profound economic hardship, with marked decreases in global trade and local small business activity alike, and full ramifications likely yet to be felt. Current state-of-science, mitigation strategies, possible therapies, ethical considerations for healthcare workers and policymakers, as well as lessons learned for this evolving global threat and the eventual return to a 'new normal' are discussed in this article.

Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum. In short, a unidirectional flow of excited state energy from the HBC termini to the (metallo)porphyrin focal points enables concentrating light at the latter. Control over excitonic interactions within, for example, the electron-donating porphyrin dimers was realized by complexation of bidentate ligands to set up panchromatic absorption that extends all the way into the near-infrared range. The bidentate binding motif was then exploited to create a supramolecular electron donor–acceptor assembly based on a HBC-ethynyl-porphyrin dimer and an electron accepting bis(aminoalkyl)-substituted fullerene. Of great relevance is the fact that charge separation from the photoexcited HBC-ethynyl-porphyrin dimer to the bis(aminoalkyl)-substituted fullerene is activated not only upon photoexciting the HBCs in the UV as well as the (metallo)porphyrins in the visible but also in the NIR. Implicit is the synergetic interplay of energy and charge transfer in a photosynthetic mimicking manner. The dimer and bis-HBC-ethynyl-porphyrin monomers, which serve as references, were probed by means of steady-state as well as time-resolved optical spectroscopies, including global target analyses of the time-resolved transient absorption data., Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum.

Break down of the Born–Oppenheimer approximation is caused by mixing of electronic and vibrational transitions in the radical cations of some conjugated polymers, resulting in unusually intense vibrational bands known as infrared active vibrations (IRAVs). Here, we investigate the mechanism of this amplification, and show that it provides insights into intramolecular charge migration. Spectroelectrochemical time-resolved infrared (TRIR) and two-dimensional infrared (2D-IR) spectroscopies were used to investigate the radical cations of two butadiyne-linked conjugated porphyrin oligomers, a linear dimer and a cyclic hexamer. The 2D-IR spectra reveal strong coupling between all the IRAVs and the electronic π–π* polaron band. Intramolecular vibrational energy redistribution (IVR) and vibrational relaxation occur within ∼0.1–7 ps. TRIR spectra show that the transient ground state bleach (GSB) and excited state absorption (ESA) signals have anisotropies of 0.31 ± 0.07 and 0.08 ± 0.04 for the linear dimer and cyclic hexamer cations, respectively. The small TRIR anisotropy for the cyclic hexamer radical cation indicates that the vibrationally excited polaron migrates round the nanoring on a time scale faster than the measurement, i.e. within 0.5 ps, at 298 K. Density functional theory (DFT) calculations qualitatively reproduce the emergence of the IRAVs. The first singlet (S1) excited states of the neutral porphyrin oligomers exhibit similar IRAVs to the radical cations, implying that the excitons have similar electronic structures to polarons. Our results show that IRAVs originate from the strong coupling of charge redistribution to nuclear motion, and from the similar energies of electronic and vibrational transitions., Break down of the Born–Oppenheimer approximation is caused by mixing of electronic and vibrational transitions in the radical cations of some conjugated polymers, resulting in unusually intense vibrational bands known as infrared active vibrations (IRAVs).

New strategies for synthesizing polyyne polyrotaxanes are being developed as an approach to stable carbyne “insulated molecular wires”. Here we report an active metal template route to polyyne [3]rotaxanes, using dicobalt carbonyl masked alkyne equivalents. We synthesized two [3]rotaxanes, both with the same C28 polyyne dumbbell component, one with a phenanthroline-based macrocycle and one using a 2,6-pyridyl cycloparaphenylene nanohoop. The thermal stabilities of the two rotaxanes were compared with that of the naked polyyne dumbbell in decalin at 80 °C, and the nanohoop rotaxane was found to be 4.5 times more stable.

The interplay between nuclear and electronic degrees of freedom strongly influences molecular charge transport. Herein, we report on transport through a porphyrin dimer molecule, weakly coupled to graphene electrodes, that displays sequential tunneling within the Coulomb-blockade regime. The sequential transport is initiated by current-induced phonon absorption and proceeds by rapid sequential transport via a non-equilibrium vibrational distribution. We demonstrate this is possible only when the vibrational dissipation is slow relative to sequential tunneling rates, and obtain a lower bound for the vibrational relaxation time of 8 ns, a value that is dependent on the molecular charge state., Comment: 8 pages, 7 figures

A recent Research Article published in this journal by Matito and coworkers claimed that none of the oxidation states of a butadiyne-linked six-porphyrin nanoring exhibit global aromaticity or antiaromaticity. Here we show that this conclusion is incorrect. A combination of density functional theory (DFT) calculations and experimental NMR data provides compelling evidence for global (anti)aromaticity in a variety of six-porphyrin nanorings in their 2+, 4+ and 6+ oxidation states. The strength of the predicted ring current depends on the choice of DFT functional, so it is crucial to use a functional that reproduces the experimental 1H NMR chemical shifts in these cations.

Supplemental Digital Content is available in the text., Objectives: Multicenter data on the characteristics and outcomes of children hospitalized with coronavirus disease 2019 are limited. Our objective was to describe the characteristics, ICU admissions, and outcomes among children hospitalized with coronavirus disease 2019 using Society of Critical Care Medicine Discovery Viral Infection and Respiratory Illness Universal Study: Coronavirus Disease 2019 registry. Design: Retrospective study. Setting: Society of Critical Care Medicine Viral Infection and Respiratory Illness Universal Study (Coronavirus Disease 2019) registry. Patients: Children (< 18 yr) hospitalized with coronavirus disease 2019 at participating hospitals from February 2020 to January 2021. Interventions: None. Measurements and Main Results: The primary outcome was ICU admission. Secondary outcomes included hospital and ICU duration of stay and ICU, hospital, and 28-day mortality. A total of 874 children with coronavirus disease 2019 were reported to Viral Infection and Respiratory Illness Universal Study registry from 51 participating centers, majority in the United States. Median age was 8 years (interquartile range, 1.25–14 yr) with a male:female ratio of 1:2. A majority were non-Hispanic (492/874; 62.9%). Median body mass index (n = 817) was 19.4 kg/m2 (16–25.8 kg/m2), with 110 (13.4%) overweight and 300 (36.6%) obese. A majority (67%) presented with fever, and 43.2% had comorbidities. A total of 238 of 838 (28.2%) met the Centers for Disease Control and Prevention criteria for multisystem inflammatory syndrome in children, and 404 of 874 (46.2%) were admitted to the ICU. In multivariate logistic regression, age, fever, multisystem inflammatory syndrome in children, and pre-existing seizure disorder were independently associated with a greater odds of ICU admission. Hospital mortality was 16 of 874 (1.8%). Median (interquartile range) duration of ICU (n = 379) and hospital (n = 857) stay were 3.9 days (2–7.7 d) and 4 days (1.9–7.5 d), respectively. For patients with 28-day data, survival was 679 of 787, 86.3% with 13.4% lost to follow-up, and 0.3% deceased. Conclusions: In this observational, multicenter registry of children with coronavirus disease 2019, ICU admission was common. Older age, fever, multisystem inflammatory syndrome in children, and seizure disorder were independently associated with ICU admission, and mortality was lower among children than mortality reported in adults.

Electron–electron interactions are at the heart of chemistry and understanding how to control them is crucial for the development of molecular-scale electronic devices. Here, we investigate single-electron tunneling through a redox-active edge-fused porphyrin trimer and demonstrate that its transport behavior is well described by the Hubbard dimer model, providing insights into the role of electron–electron interactions in charge transport. In particular, we empirically determine the molecule's on-site and inter-site electron–electron repulsion energies, which are in good agreement with density functional calculations, and establish the molecular electronic structure within various oxidation states. The gate-dependent rectification behavior confirms the selection rules and state degeneracies deduced from the Hubbard model. We demonstrate that current flow through the molecule is governed by a non-trivial set of vibrationally coupled electronic transitions between various many-body ground and excited states, and experimentally confirm the importance of electron–electron interactions in single-molecule devices., Experimental studies of electron transport through an edge-fused porphyrin oligomer in a graphene junction are interpreted within a Hubbard dimer framework.

Direct imaging of single molecules has to date been primarily achieved using scanning probe microscopy, with limited success using transmission electron microscopy due to electron beam damage and low contrast from the light elements that make up the majority of molecules. Here, we show single complex molecule interactions can be imaged using annular dark field scanning TEM (ADF-STEM) by inserting heavy metal markers of Pt atoms and detecting their positions. Using the high angle ADF-STEM Z1.7 contrast, combined with graphene as an electron transparent support, we track the 2D monolayer self-assembly of solution-deposited individual linear porphyrin hexamer (Pt-L6) molecules and reveal preferential alignment along the graphene zigzag direction. The epitaxial interactions between graphene and Pt-L6 drive a reduction in the interporphyrin distance to allow perfect commensuration with the graphene. These results demonstrate how single metal atom markers in complex molecules can be used to study large scale packing and chain bending at the single molecule level.

Background While specific interventions have previously demonstrated benefit in patients with the Acute Respiratory Distress Syndrome (ARDS), use of these interventions is inconsistent, and patient mortality remains high. The impact of variability in center management practices on ARDS mortality rates remains unknown. Research Question What is the impact of treatment variability on mortality in patients with moderate-to-severe ARDS in the United States (US)? Study Design and Methods We conducted a multicenter, observational cohort study of mechanically ventilated adults with ARDS and PaO2/FiO2< 150 on positive end expiratory pressure (PEEP) > 5 cm H2O, who were admitted to 29 US centers between October 1, 2016 and April 30, 2017. The primary outcome was 28-day in-hospital mortality. Center variation in ventilator management, adjunctive therapy use, and mortality were also assessed. Results A total of 2,466 patients were enrolled. Median baseline PaO2/FiO2 was 105 (IQR 78.0, 129.0). In-hospital 28-day mortality was 40.7%. Initial adherence to lung protective ventilation (tidal volume < 6.5 ml/kg predicted body weight, plateau pressure and/or peak inspiratory pressure < 30mm H2O) was 31.4% and varied between centers (0%-65%), as did rates of adjunctive therapy use (27.1%-96.4%), types of modalities used (neuromuscular blockade, prone positioning, systemic steroids, pulmonary vasodilators, and extracorporeal support), and mortality (16.7-73.3%). Center standardized mortality ratios (SMRs), calculated using baseline patient-level characteristics to derive expected mortality rate, ranged from 0.33 to 1.98. Of the treatment-level factors explored, only center adherence to early lung protective ventilation (LPV) was correlated with SMR. Interpretation Substantial center-to-center variability exists in ARDS management, suggesting that further opportunities for improving ARDS outcomes exist. Early adherence to LPV was associated with lower center mortality and may be a surrogate for overall quality of care processes. Future collaboration is needed to identify additional treatment-level factors influencing center-level outcomes. Clinical Trial Registration ClinicalTrials.gov Identifier: NCT03021824

The cyclocarbons constitute a family of molecular carbon allotropes consisting of rings of two-coordinate atoms. Their high reactivities make them difficult to study, but there has been much progress towards understanding their structures and properties. Here we provide a short account of theoretical and experimental work on these carbon rings, and highlight opportunities for future research in this field. The cyclocarbons constitute a family of molecular carbon allotropes consisting of rings of two-coordinate atoms. Their high reactivities make them difficult to study, but there has been much progress towards understanding their structures and properties. Here we provide a short account of theoretical and experimental work on these carbon rings, and highlight opportunities for future research in this field.

The ability to control the charge state of individual molecules wired in two-terminal single-molecule junctions is a key challenge in molecular electronics, particularly in relation to the development of molecular memory and other computational componentry. Here we demonstrate that single porphyrin molecular junctions can be reversibly charged and discharged at elevated biases under ambient conditions due to the presence of a localised molecular eigenstate close to the Fermi edge of the electrodes. In particular, we can observe long-lived charge-states with lifetimes upwards of 1–10 seconds after returning to low bias and large changes in conductance, in excess of 100-fold at low bias. Our theoretical analysis finds charge-state lifetimes within the same time range as the experiments. The ambient operation demonstrates that special conditions such as low temperatures or ultra-high vacuum are not essential to observe hysteresis and stable charged molecular junctions.

Molecules capable of mediating charge transport over several nanometers with minimal decay in conductance have fundamental and technological implications. Polymethine cyanine dyes are fascinating molecular wires because up to a critical length, they have no bond-length alternation (BLA) and their electronic structure resembles a one-dimensional free-electron gas. Beyond this threshold, they undergo a symmetry-breaking Peierls transition, which increases the HOMO–LUMO gap. We have investigated cationic cyanines with central polymethine chains of 5–13 carbon atoms (Cy3+–Cy11+). The absorption spectra and crystal structures show that symmetry breaking is sensitive to the polarity of the medium and the size of the counterion. X-ray crystallography reveals thatCy9·PF6andCy11·B(C6F5)4are Peierls distorted, with high BLA at one end of the π-system, away from the partially delocalized positive charge. This pattern of BLA distribution resembles that of solitons in polyacetylene. The single-molecule conductance is essentially independent of molecular length for the polymethine salts ofCy3+–Cy11+with the large B(C6F5)4–counterion, but with the PF6–counterion, the conductance decreases for the longer molecules,Cy7+–Cy11+, because this smaller anion polarizes the π-system, inducing a symmetry-breaking transition. At higher bias (0.9 V), the conductance of the shorter chains,Cy3+–Cy7+, increases with length (negative attenuation factor, β = −1.6 nm–1), but the conductance still drops inCy9+andCy11+with the small polarizing PF6–counteranion.

Dyads consisting of a photochromic switch covalently linked to a fluorescent dye allow the emission from the dye to be controlled by reversible photoisomerization of the switch; one form of the switch quenches fluorescence by accepting energy from the dye. Here we investigate the use of dyads of this type for super-resolution imaging of lipid bilayers. Giant unilamellar vesicles stained with the dyads were imaged with about a two-fold resolution-enhancement compared with conventional confocal microscopy. This was achieved by exciting the fluorophore at 594 nm, using a switch activated by violet and red light (405/640 nm)., A photoswitchable quencher can be used to reversibly turn off the emission from a fluorescent dye, generating a small molecule dyad that is effective for super-resolution RESOLFT microscopy.

The electronic structure of a molecular quantum ring (stacks of 40-unit cyclic porphyrin polymers) is characterized via scanning tunneling microscopy and scanning tunneling spectroscopy. Our measurements access the energetic and spatial distribution of the electronic states and, utilizing a combination of density functional theory and tight-binding calculations, we interpret the experimentally obtained electronic structure in terms of coherent quantum states confined around the circumference of the $\ensuremath{\pi}$-conjugated macrocycle. These findings demonstrate that large (53 nm circumference) cyclic porphyrin polymers have the potential to act as molecular quantum rings.

Template-directed synthesis has been used to prepare a fully π-conjugated cyclic porphyrin octamer, composed of both β,meso,β-edge-fused porphyrin tape units and butadiyne-linked porphyrins. The UV-vis-NIR spectra of this partially fused nanoring show that π-conjugation extends around the whole macrocycle, and that it has a smaller HOMO-LUMO gap than its all-butadiyne-linked analogue, as predicted by TD-DFT calculations. The 1H NMR shifts of the bound templates confirm the disrupted aromaticity of the edge-fused porphyrins in the neutral nanoring. NMR oxidation titrations reveal the presence of a global paratropic ring current in its 4+ and 8+ oxidation states and of a global diatropic ring current in the 6+ state of the partially fused ring. The paratropic ring current in the 4+ oxidation state is about four times stronger than that in the all-butadiyne-linked cyclic octamer complex, whereas the diatropic current in the 6+ state is about 40% weaker. Two isomeric K-shaped tetrapyridyl templates with trifluoromethyl substituents at different positions were used to probe the distribution of the ring current in the 4+, 6+, and 8+ oxidation states by 19F NMR, demonstrating that the ring currents are global and homogeneous.

The photophysical behavior of natural and artificial cyclic supramolecular structures has been intensively investigated in the past decade. Among the artificial structures, large fully π-conjugated porphyrin nanorings are of particular interest because of their electronic, structural, and topological features, which make them suitable candidates for light-harvesting applications. A number of factors affect the efficiency with which such structures harvest and transmit energy. For instance, under intense irradiation conditions, the efficiency of light harvesting can be quenched by competing processes, such as exciton–exciton annihilation. Here, we investigate the pump fluence dependence of the transient absorption spectra of a series of porphyrin nanorings ranging in circumference between 13 and 52 nm (10–40 porphyrin units). This allowed the isolation of a fluence-dependent fast-decaying component in all but the smallest nanorings studied. This effect has been assigned to exciton–exciton annihilation and fit to a one-dimensional exciton diffusion model, which confirms that the exciton size and/or its mobility are inversely proportional to the nanoring size.

Cyclo[18]carbon (C18, a molecular carbon allotrope) can be synthesized by dehalogenation of a bromocyclocarbon precursor, C18Br6, in 64% yield, by atomic manipulation on a sodium chloride bilayer on Cu(111) at 5 K, and imaged by high-resolution atomic force microscopy. This method of generating C18gives a higher yield than that reported previously from the cyclocarbon oxide C24O6. The experimental images of C18were compared with simulated images for four theoretical model geometries, including possible bond-angle alternation:D18hcumulene,D9hpolyyne,D9hcumulene, andC9hpolyyne. Cumulenic structures, with (D9h) and without (D18h) bond-angle alternation, can be excluded. Polyynic structures, with (C9h) and without (D9h) bond-angle alternation, both show a good agreement with the experiment and are challenging to differentiate.

A nanoring‐rotaxane supramolecular assembly with a Cy7 cyanine dye (hexamethylindotricarbocyanine) threaded along the axis of the nanoring was synthesized as a model for the energy transfer between the light‐harvesting complex LH1 and the reaction center in purple bacteria photosynthesis. The complex displays efficient energy transfer from the central cyanine dye to the surrounding zinc porphyrin nanoring. We present a theoretical model that reproduces the absorption spectrum of the nanoring and quantifies the excitonic coupling between the nanoring and the central dye, thereby explaining the efficient energy transfer and demonstrating similarity with structurally related natural light‐harvesting systems., Colorful to the core: Rotaxane formation was used to lock a cyanine dye along the axis of a porphyrin nanoring to form a complex that mimics the photophysical behavior of the light‐harvesting complex LH1 and the reaction center in purple photosynthetic bacteria. Energy is transferred rapidly between the axial dye and the surrounding nanoring.

Bulky photolabile masked alkyne equivalents (MAEs) are needed for the synthesis of polyyne polyrotaxanes, as insulated molecular wires and as stabilized forms of the linear polymeric allotrope of carbon, carbyne. We have synthesized a novel MAE based on phenanthrene and compared it with an indane-based MAE. Photochemical unmasking of model compounds was studied at different wavelengths (250 and 350 nm), and key products were identified by NMR spectroscopy and X-ray crystallography. UV irradiation at 250 nm leads to unmasking of both MAEs. Irradiation of the phenanthrene system at 350 nm results in quantitative dimerization via [2 + 2] cycloaddition to form a [3]-ladderane; irradiation of this ladderane at 250 nm generates a dihydrotriphenylene, which can be oxidized easily to a triphenylene. Irradiation of the indane-based MAE at 350 nm in the presence of traces of oxygen forms an endoperoxide and a bisepoxide. Both MAEs have been incorporated into rotaxanes via copper-mediated active metal template Glaser or Cadiot–Chodkiewicz coupling. The identity of the rotaxanes was confirmed by NMR spectroscopy and mass spectrometry. The phenanthrene rotaxane decomposes during attempted photochemical unmasking, whereas photolysis of the indane rotaxane results in unmasking of the polyyne thread to form a rotaxane with a chain of 16 sp-hybridized carbon atoms. This approach opens avenues toward the synthesis of encapsulated carbon allotropes.

Charge transport is strongly suppressed by destructive quantum interference (DQI) in meta-connected 1,1’-biphenyl-containing molecules, resulting in low electrical conductance. Surprisingly, we have found that DQI is almost entirely overcome by adding a bridging carbonyl, to yield a cross-conjugated fluorenone. This contrasts with other π-systems, such as para-connected anthraquinone, where cross-conjugation results in low conductance. &nbsp

We present molecular magnetic systems that contain all elements necessary for spin-valve control in molecular spintronic devices in a single molecule., We present the design, synthesis and magnetic properties of molecular magnetic systems that contain all elements necessary for spin-valve control in molecular spintronic devices in a single molecule. We investigate the static and dynamic magnetic properties and quantum spin properties of butadiyne-linked homo- and hetero-nuclear lanthanide-porphyrin dimers. A heterometallated porphyrin dimer containing both TbIII and DyIII centres is created rationally by the stepwise oxidative homocoupling of distinct lanthanide-porphyrin monomers. TbIII and DyIII mononuclear porphyrin complexes, homodimers and heterodimers all exhibit slow magnetic relaxation below 10 kelvin under a static magnetic field. The coherence times for GdIII porphyrin monomers and dimers are found to be in excess of 3.0 μs at 2 K, allowing distinct magnetic manipulations in low temperature transport experiments.

We thank the EPSRC (EP/I035536/1; EP/J015067/1), The Royal Society (University Research Fellowship to JEL) and Wellcome Trust (099149/Z/12/Z) for funding and the EPSRC UK National Mass Spectrometry Facility at Swansea University for mass spectra. Paramagnetic endohedral fullerenes with long spin coherence times, such as N@C60 and Y@C82, are being explored as potential spin quantum bits (qubits). Their use for quantum information processing requires a ways to hold them in fixed spatial arrangements. Here we report the synthesis of a porphyrin-based two-site receptor 1 , offering a rigid structure that binds spin-active fullerenes (Y@C82) at a center-to-center distance of 5.0 nm, predicted from molecular simulations. The spin-spin dipolar coupling was measured with the pulsed EPR spectroscopy technique of double electron electron resonance (DEER) and analysed to give a distance of 4.87 nm with a small distribution of distances. Postprint