Thioetherification of Br-Mercaptobiphenyl Molecules on Au(111).

Thioether polymers are fundamental for a variety of applications. Their synthesis is, however, more challenging than that of other metal-catalyzed reactions due to the reported detachment of the S atom during thermal activation. In this study, it has been demonstrated unambiguously that thermal annealing results in the thioetherification of the 4-bromo-4-mercaptobiphenyl molecule (Br-MBP) adsorbed on the surface of Au(111). Through complementary techniques, such as scanning tunneling microscopy, spectroscopy, and first-principle calculations, we have identified four reaction steps, involving sulfhydryl or bromine molecular functional groups and leading to the formation of intermolecular C-S bonds. To form the thioether polymer and to overcome the competitive formation of C-C bonds, two reaction steps, the dehalogenation, and dissociation of the S-Au bond, must occur simultaneously. We detail the electronic properties of the phenyl-sulfur bond and the polymer as a function of the ligand length. This result suggests a wider perspective of this chemical synthesis.

Entre science et engagement : les défis de la recherche communautaire au sein du réseau Coalition PLUS.

Community-based research, that is, the meaningful involvement of affected populations in the production of scientific knowledge that concerns them, is a political struggle and an ethical necessity. Coalition PLUS, an international network of organizations (most of them NGOs) fighting against HIV and hepatitis, created a community-based research laboratory (CBRL) composed of people from more than sixteen countries and various disciplinary fields. The objectives of the CBLR are to build research capacity, ensure collaboration with local and international academic research centers, and develop international research projects. The CBRL acts as a bridge between different partners, reconciling sometimes divergent interests, and must provide mediation and support to promote dialogue, transparency, and a relationship of trust between the communities and academic researchers. However, the need for scientific legitimacy obliges us to continuously seek a balance between responding to the needs of the field and using rigorous scientific methods, while optimizing and prioritizing existing resources. The permanent quest for this balance has led the CBRL to reorganize its mode of operation to optimize existing synergies with academic research laboratories, with a view to asserting its scientific legitimacy and continuing to contribute to social transformation through community-based research that is both innovative and of high quality. This paper provides a critical reflection on the issues, challenges, practices, and solutions of community-based research within the Coalition PLUS network.

Electron Paramagnetic Resonance of Alkali Metal Atoms and Dimers on Ultrathin MgO.

Electron paramagnetic resonance (EPR) can provide unique insight into the chemical structure and magnetic properties of dopants in oxide and semiconducting materials that are of interest for applications in electronics, catalysis, and quantum sensing. Here, we demonstrate that EPR in combination with scanning tunneling microscopy (STM) allows for probing the bonding and charge state of alkali metal atoms on an ultrathin magnesium oxide layer on a Ag substrate. We observe a magnetic moment of 1 µB for Li2, LiNa, and Na2 dimers corresponding to spin radicals with a charge state of +1e. Single alkali atoms have the same charge state and no magnetic moment. The ionization of the adsorbates is attributed to charge transfer through the oxide to the metal substrate. Our work highlights the potential of EPR-STM to provide insight into dopant atoms that are relevant for the control of the electrical properties of surfaces and nanodevices.

Chemsex in Barcelona: A qualitative study of factors associated with the practice, the perception of the impact on health and prevention needs. / Chemsex en Barcelona: Estudio cualitativo sobre factores asociados a la práctica, percepción del impacto en salud y necesidades de prevención.

Chemsex is defined as use of psychoactive drugs with the aim of having sexual relations between gay men, bisexuals and men who have sex with men for a long period of time. To study this phenomenon, this qualitative descriptive study was proposed with the objective of describing the practice of chemsex from the perspective of users, to determine the main factors associated with its practice, the perception of the impact on their health and to establish prevention needs. Data were obtained using conversational techniques: 12 semi-structured interviews and 3 focus groups. The purposive sample was made up of GBMSM with a mean age of 40.1 years, 78% born in Spain, and 68% with completed university studies. The qualitative analysis focused on three thematic areas: factors associated with the practice of chemsex, the impact of chemsex on health, and prevention and risk reduction needs. It is concluded that the practice of chemsex should be understood as multifactorial and multicausal, associated with the sociocultural context. Sexual satisfaction, increased libido and the search for more intense pleasure are identified as key factors among people who practice it. These men are still scared of being judged, even by specialists who may lack knowledge or training. A reanalysis and rethinking of the interventions and policies directed towards this population is necessary, putting the focus of action on shared decision-making, self-care, cultural competence and the humanization of care.

El chemsex se define como el uso de drogas psicoactivas con el objetivo de mantener relaciones sexuales entre hombres gay, bisexuales y otros hombres que tienen sexo con hombres (GBHSH), por un largo periodo de tiempo. El objetivo de este estudio cualitativo exploratorio es describir la práctica del chemsex desde la perspectiva de los usuarios, determinar los principales factores asociados a su práctica, la percepción del impacto en su salud y establecer necesidades de prevención. Se obtuvieron los datos mediante técnicas conversacionales: 12 entrevistas semiestructuradas y 3 grupos focales. El análisis cualitativo se centró en tres áreas temáticas: factores asociados a la práctica de chemsex, impacto del chemsex en la salud y necesidades prevención y reducción de riesgos. La muestra intencionada fue conformada por hombres GBHSH con una edad media de 40,1 años, 78% nacidos en España, y 68% con estudios universitarios finalizados. Los resultados del estudio ponen de manifiesto que la práctica de chemsex debe comprenderse como multifactorial y multicausal, y asociada al contexto sociocultural. La satisfacción sexual, del aumento de la libido y de la búsqueda de placer más intenso se identifican como factores clave entre las personas que lo practican. Sigue existiendo miedo en estos hombres a ser juzgados, incluso por los especialistas que pueden carecer de conocimiento o formación. Es necesario un reanálisis y replanteamiento de las intervenciones y políticas dirigidas hacia esta población, poniendo el foco de acción en la toma de decisiones compartidas, el autocuidado, la competencia cultural y la humanización del cuidado.

Doublet-Singlet-Doublet Transition in a Single Organic Molecule Magnet On-Surface Constructed with up to 3 Aluminum Atoms.

Starting from a long aza-starphene neutral and nonmagnetic organic molecule, a single-molecule magnet is on-surface constructed using up to 3 light nonmagnetic aluminum (Al) atoms. Seldom observed in solution with transition-metal atoms and going from 1 to 3 Al coordinated atoms, the doublet-singlet-doublet transition is easily on-surface accessible using the scanning tunneling microscope single-atom and single-molecule manipulations on a gold(111) surface. With 3 coordinated Al atoms, the lateral vibration modes of the Al3-aza-starphene molecule magnet are largely frozen. Using the Kondo states, this opens the observation of the in-phase Al vertical atom vibrations and out-of-phase central phenyl vibrations.

La recherche communautaire en temps de pandémie : retour sur l'étude multi-pays EPIC.

In 2020, the COVID-19 health crisis affected all regions of the world, not sparing people already vulnerable to other viral epidemics such as HIV or HCV and/or those in precarious or socially marginalized situations. This is particularly the case for drug users or sex workers.Coalition PLUS, a network of associations fighting against HIV and viral hepatitis which defends and promotes the community-based approach, and its partners, have set up a multi-country community-based research project aimed at documenting the impact of the health crisis on the fight against HIV and viral hepatitis (key populations and community workers/activists), as well as the community responses put in place (EPIC survey).The objective of this paper is to reflect on the implementation of this community-based research study during the COVID-19 health crisis, and in particular the unforeseen difficulties to which the community-based research process had to confront and adapt. The goal is to draw lessons on what worked (and what did not work) in order to capitalize on community-based research practices during this pandemic and subsequently, facilitate the implementation of new research projects in similar contexts.

Challenges in the synthesis of corannulene-based non-planar nanographenes on Au(111) surfaces.

The on-surface synthesis of non-planar nanographenes is a challenging task. Herein, with the aid of bond-resolving scanning tunneling microscopy (BRSTM) and density functional theory (DFT) calculations, we present a systematic study aiming at the fabrication of corannulene-based nanographenes via intramolecular cyclodehydrogenation on a Au(111) surface. The formation of non-planar targeted products is confirmed to be energetically unfavorable compared to the formation of planar/quasi-planar undesired competing monomer products. In addition, the activation of intermolecular coupling further inhibits the formation of the final targeted product. Although it was not possible to access the corannulene moiety by means of on-surface synthesis, partial cyclodehydrogenation of the molecular precursors was demonstrated.

The Role of Community Health Workers Within the Continuum of Services for HIV, Viral Hepatitis, and Other STIs Amongst Men Who Have Sex with Men in Europe.

Little is known about Community Health Workers (CHWs) who work in non-clinical settings to provide sexual health support around HIV, viral hepatitis, and other sexually transmitted infections (STIs) to men who have sex with men (MSM) in Europe and neighbouring countries. This article describes for the first time, who CHWs are, and how they contribute to the continuum of services for HIV, viral hepatitis, and other STIs amongst MSM. The first European Community Health Worker Online Survey (ECHOES) developed in the framework of the EU-funded ESTICOM project ( www.esticom.eu ), was available in 16 languages (October 2017-January 2018). Amongst the 1035 persons aged 18 and older reporting CHW activities in the previous 12 months, 28.2% were women, 30.7% were volunteers, 59.2% were men self-defining as gay/homosexual, bisexual or queer ('peer CHWs'), and most CHWs worked/volunteered in private not-for-profit organisations (86.4%). CHWs involvement in the continuum of services for HIV, viral hepatitis and other STIs was as follows: primary prevention (88.6%), consultation and counselling (58.0%), testing provision (50.6%), linkage to care (49.8%), and treatment and support activities (51.3%). CHWs were also involved in cross-cutting activities such as developing interventions, advocacy, and engaging in research (46.3%). CHWs as a public health workforce contribute to all steps of the continuum of services for HIV, viral hepatitis, and other STIs amongst MSM in Europe. National governments should recognise and support CHWs better in order to make their activities more visible and sustainable, and increase their impact on the continuum of services.

The Kondo Effect of a Molecular Tip As a Magnetic Sensor.

A single molecule offers to tailor and control the probing capability of a scanning tunneling microscope when placed on the tip. With the help of first-principles calculations, we show that on-tip spin sensitivity is possible through the Kondo ground state of a spin S = 1/2 cobaltocene molecule. When attached to the tip apex, we observe a reproducible Kondo resonance, which splits apart upon tuning the exchange coupling of cobaltocene to an iron atom on the surface. The spin-split Kondo resonance provides quantitative information on the exchange field and on the spin polarization of the iron atom. We also demonstrate that molecular vibrations cause the emergence of Kondo side peaks, which, unlike the Kondo resonance, are sensitive to cobaltocene adsorption.

On-Surface Atom-by-Atom-Assembled Aluminum Binuclear Tetrabenzophenazine Organometallic Magnetic Complex.

The Kondo effect results from the interactions of the conduction electrons in a metal bulk with localized magnetic impurities. While adsorbed atop a metallic surface, the on-surface nanoscale version of this effect is observed when a single magnetic atom or a single magnetic molecule (SMM) is interacting with the conduction electrons. SMMs are commonly organometallic complexes incorporating transition-metal atoms in different oxidation states. We demonstrate how a single nonmagnetic neutral tetrabenzo[a,c,j,h]phenazine molecule can be on-surface-coordinated with exactly two aluminum metal atoms (between Al(I) and Al(II) oxidation state on the Au(111) surface) by low-temperature scanning tunneling microscope (LT-STM) single-atom manipulation. It results in a Kondo measurable localized molecular magnetic moment. This opens a new way to design SMM complexes without the need for heavy transition-metal atoms and complex ligands to stabilize the molecular coordination sphere.

Bottom-up Fabrication and Atomic-Scale Characterization of Triply Linked, Laterally π-Extended Porphyrin Nanotapes*.

Porphyrin nanotapes (Por NTs) are promising structures for their use as molecular wires thanks to a high degree of π-conjugation, low HOMO-LUMO gaps, and exceptional conductance. Such structures have been prepared in solution, but their on-surface synthesis remains unreported. Here, meso-meso triply fused Por NTs have been prepared through a two-step synthesis on Au(111). The diradical character of the on-surface formed building block PorA2 , a phenalenyl π-extended ZnII Por, facilitates intermolecular homocoupling and allows for the formation of laterally π-extended tapes. The structural and electronic properties of individual Por NTs are addressed, both on Au(111) and on a thin insulating NaCl layer, by high-resolution scanning probe microscopy/spectroscopy complemented by DFT calculations. These Por NTs carry one unpaired electron at each end, which leads to magnetic end states. Our study provides a versatile route towards Por NTs and the atomic-scale characterization of such tapes.

Inducing Open-Shell Character in Porphyrins through Surface-Assisted Phenalenyl π-Extension.

Organic open-shell compounds are extraordinarily attractive materials for their use in molecular spintronics thanks to their long spin-relaxation times and structural flexibility. Porphyrins (Pors) have widely been used as molecular platforms to craft persistent open-shell structures through solution-based redox chemistry. However, very few examples of inherently open-shell Pors have been reported, which are typically obtained through the fusion of non-Kekulé polyaromatic hydrocarbon moieties to the Por core. The inherent instability and low solubility of these radical species, however, requires the use of bulky substituents and multistep synthetic approaches. On-surface synthesis has emerged as a powerful tool to overcome such limitations, giving access to structures that cannot be obtained through classical methods. Herein, we present a simple and straightforward method for the on-surface synthesis of phenalenyl-fused Pors using readily available molecular precursors. In a systematic study, we examine the structural and electronic properties of three surface-supported Pors, bearing zero, two (PorA2), and four (PorA4) meso-fused phenalenyl moieties. Through atomically resolved real-space imaging by scanning probe microscopy and high-resolution scanning tunneling spectroscopy combined with density functional theory calculations, we unambiguously demonstrate a triplet ground state for PorA2 and a charge-transfer-induced open-shell character for the intrinsically closed-shell PorA4.

Supramolecular chemistry based on 4-acetylbiphenyl on Au(111).

On a gold surface, supramolecules composed of 4-acetylbiphenyl molecules show structural directionality, reproducibility and robustness to external perturbations. We investigate the assembly of those molecules on the Au(111) surface and analyze how the observed supramolecular structures are the result of weak long-range dispersive forces stabilizing the 4-acetylbiphenyl molecules together. Metallic adatoms serve as stabilizing agents. Our analysis suggests new ways of creating complex molecular nano-objects that can eventually be used as devices or as seeds for extended hierarchical structures.

Efficient Ab Initio Multiplet Calculations for Magnetic Adatoms on MgO.

Scanning probe microscopy and spectroscopy, and more recently, single-atom electron spin resonance, have allowed the direct observation of electron dynamics at the atomic limit. The interpretation of data is strongly dependent on model Hamiltonians. However, fitting effective spin Hamiltonians to experimental data lacks the ability to explore a vast number of potential systems of interest. By using plane-wave density functional theory as starting point, we build a multiplet Hamiltonian making use of maximally localized Wannier functions. The Hamiltonian contains spin-orbit and electron-electron interactions needed to obtain the relevant spin dynamics. The resulting reduced Hamiltonian is solved by exact diagonalization. We compare three prototypical cases of 3d transition metals Mn (total spin S = 5/2), Fe (S = 2), and Co (S = 3/2) on MgO with experimental data and find that our calculations can accurately predict the spin orientation and anisotropy of the magnetic adatom. Our method does not rely on experimental input and allows us to explore and predict the fundamental magnetic properties of adatoms on surfaces.

Implementing Functionality in Molecular Self-Assembled Monolayers.

The planar heterocyclic molecules 1,6,7,12-tetraazaperylene on a Ag(111) metal substrate show different charging characteristics depending on their local environment: next to vacancies in self-assembled islands, molecules can be charged by local electric fields, whereas their charge state is fixed otherwise. This enables the activation of selected molecules inside islands by vacancy creation from scanning-probe-based manipulation. This concept allows for combining the precise mutual atomic-scale alignment of molecules by self-assembly, on one hand, and the implementation of specific functionality into otherwise homogeneous monolayers, on the other. Activated molecules in the direct neighborhood influence each other in their charging characteristics, suggesting their use as molecular quantum cellular automata. Surprisingly, only very few interacting molecules exhibit a rich spectroscopic signature, which offers the prospect of implementing complex functionality in such structures in the future.

Spin Control Induced by Molecular Charging in a Transport Junction.

The ability of molecules to maintain magnetic multistability in nanoscale-junctions will determine their role in downsizing spintronic devices. While spin-injection from ferromagnetic leads gives rise to magnetoresistance in metallic nanocontacts, nonmagnetic leads probing the magnetic states of the junction itself have been considered as an alternative. Extending this experimental approach to molecular junctions, which are sensitive to chemical parameters, we demonstrate that the electron affinity of a molecule decisively influences its spin transport. We use a scanning tunneling microscope to trap a meso-substituted iron porphyrin, putting the iron center in an environment that provides control of its charge and spin states. A large electron affinity of peripheral ligands is shown to enable switching of the molecular S = 1 ground state found at low electron density to S = 1/2 at high density, while lower affinity keeps the molecule inactive to spin-state transition. These results pave the way for spin control using chemical design and electrical means.

Spin in a Closed-Shell Organic Molecule on a Metal Substrate Generated by a Sigmatropic Reaction.

Inert metal surfaces present more chances of hosting organic intact radicals than other substrates, but large amounts of delocalized electronic states favor charge transfer and thus spin quenching. Lowering the molecule-substrate interaction is a usual strategy to stabilize radicals on surfaces. In some works, thin insulating layers were introduced to provide a controllable degree of electronic decoupling. Recently, retinoid molecules adsorbed on gold have been manipulated with a scanning tunneling microscope (STM) to exhibit a localized spin, but calculations failed to find a radical derivative of the molecule on the surface. Now the formation of a neutral radical spatially localized in a tilted and lifted cyclic end of the molecule is presented. An allene moiety provokes a perpendicular tilt of the cyclic end relative to the rest of the conjugated chain, thus localizing the spin of the dehydrogenated allene in its lifted subpart. DFT calculations and STM manipulations give support to the proposed mechanism.

On-Demand Preexposure Prophylaxis in Men at High Risk for HIV-1 Infection.

BACKGROUND: Antiretroviral preexposure prophylaxis has been shown to reduce the risk of human immunodeficiency virus type 1 (HIV-1) infection in some studies, but conflicting results have been reported among studies, probably due to challenges of adherence to a daily regimen. METHODS: We conducted a double-blind, randomized trial of antiretroviral therapy for preexposure HIV-1 prophylaxis among men who have unprotected anal sex with men. Participants were randomly assigned to take a combination of tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) or placebo before and after sexual activity. All participants received risk-reduction counseling and condoms and were regularly tested for HIV-1 and HIV-2 and other sexually transmitted infections. RESULTS: Of the 414 participants who underwent randomization, 400 who did not have HIV infection were enrolled (199 in the TDF-FTC group and 201 in the placebo group). All participants were followed for a median of 9.3 months (interquartile range, 4.9 to 20.6). A total of 16 HIV-1 infections occurred during follow-up, 2 in the TDF-FTC group (incidence, 0.91 per 100 person-years) and 14 in the placebo group (incidence, 6.60 per 100 person-years), a relative reduction in the TDF-FTC group of 86% (95% confidence interval, 40 to 98; P=0.002). Participants took a median of 15 pills of TDF-FTC or placebo per month (P=0.57). The rates of serious adverse events were similar in the two study groups. In the TDF-FTC group, as compared with the placebo group, there were higher rates of gastrointestinal adverse events (14% vs. 5%, P=0.002) and renal adverse events (18% vs. 10%, P=0.03). CONCLUSIONS: The use of TDF-FTC before and after sexual activity provided protection against HIV-1 infection in men who have sex with men. The treatment was associated with increased rates of gastrointestinal and renal adverse events. (Funded by the National Agency of Research on AIDS and Viral Hepatitis [ANRS] and others; ClinicalTrials.gov number, NCT01473472.).

Jahn-Teller Splitting in Single Adsorbed Molecules Revealed by Isospin-Flip Excitations.

Scanning tunneling spectroscopy measurements of Mn phthalocyanine (MnPc) molecules adsorbed on (sqrt[3]×sqrt[3]) surface alloys show single inelastic steps at exclusively positive or negative bias strongly depending on the tip position. This is in contrast to conventional molecular excitation thresholds, which are independent of the current direction and therefore always occur at both positive and negative bias. This polarity selectivity is found to coincide with the spatial distribution of occupied and empty orbitals. Because of the interaction with the substrate, charge transfer into the doubly degenerate d_{π} orbitals of MnPc takes place. The resulting Jahn-Teller effect lifts the degeneracy and leads to an isospin- or pseudospin-flip excitation, the inelastic analogue of an orbital Kondo resonance.

Influence of Magnetic Ordering between Cr Adatoms on the Yu-Shiba-Rusinov States of the ß-Bi_{2}Pd Superconductor.

We show that the magnetic ordering of coupled atomic dimers on a superconductor is revealed by their intragap spectral features. Chromium atoms on the superconductor ß-Bi_{2}Pd surface display Yu-Shiba-Rusinov bound states, detected as pairs of intragap excitations in tunneling spectra. By means of atomic manipulation with a scanning tunneling microscope's tip, we form Cr dimers with different arrangements and find that their intragap features appear either shifted or split with respect to single atoms. These spectral variations are associated with the magnetic coupling, ferromagnetic or antiferromagnetic, of the dimer, as confirmed by density functional theory simulations. The striking qualitative differences between the observed tunneling spectra prove that intragap Shiba states are extremely sensitive to the magnetic ordering on the atomic scale.