Chemical bond imaging using torsional and flexural higher eigenmodes of qPlus sensors

Non-contact atomic force microscopy (AFM) with CO-functionalized tips allows visualization of the chemical structure of adsorbed molecules and identify individual inter- and intramolecular bonds. This technique enables in-depth studies of on-surface reactions and self-assembly processes. Herein, we analyze the suitability of qPlus sensors, which are commonly used for such studies, for the application of modern multifrequency AFM techniques. Two different qPlus sensors were tested for submolecular resolution imaging via actuating torsional and flexural higher eigenmodes and via bimodal AFM. The torsional eigenmode of one of our sensors is perfectly suited for performing lateral force microscopy (LFM) with single bond resolution. The obtained LFM images agree well with images from the literature, which were scanned with customized qPlus sensors that were specifically designed for LFM. The advantage of using a torsional eigenmode is that the same molecule can be imaged either with a vertically or laterally oscillating tip without replacing the sensor simply by actuating a different eigenmode. Submolecular resolution is also achieved by actuating the 2^nd flexural eigenmode of our second sensor. In this case, we observe particular contrast features that only appear in the AFM images of the 2^nd flexural eigenmode but not for the fundamental eigenmode. With complementary laser Doppler vibrometry measurements and AFM simulations we can rationalize that these contrast features are caused by a diagonal (i.e. in-phase vertical and lateral) oscillation of the AFM tip.

The Effect of a Citrus and Pomegranate Complex on Physical Fitness and Mental Well-Being in Healthy Elderly: A Randomized Placebo-Controlled Trial

OBJECTIVES

This study investigates whether a citrus and pomegranate complex (CPC) improves physical fitness, mental well-being, and blood biomarkers for oxidative stress and endothelial function in healthy elderly.

DESIGN

A randomized placebo-controlled cross-over trial.

PARTICIPANTS

The study included 36 healthy elderly aged 60-75 years old.

INTERVENTION AND MEASUREMENTS

Participants received four weeks of CPC supplementation and performed the handgrip strength and senior fitness test. Quality of life (QOL) was assessed and blood samples were analyzed for oxidative stress and endothelial function markers.

RESULTS

After four weeks of CPC supplementation, handgrip strength significantly improved (p=0.019), compared to placebo. Moreover, the thinking, memory, learning, and concentration facets were improved (p=0.042), compared to placebo, and plasma malondialdehyde decreased, compared to placebo (p=0.033). The intervention did not affect senior fitness and the other QOL domains and blood parameters.

CONCLUSION

Four weeks of daily CPC supplementation significantly improves handgrip strength and self-evaluated measures of psychological function in healthy older adults. Further research should focus on mechanisms associated with physical performance.

Orthogonal Catalysis for an Enantioselective Domino Inverse-Electron Demand Diels-Alder/Substitution Reaction

An enantioselective domino process for the synthesis of substituted 1,2‐dihydronaphthalenes has been developed by the combination of chiral amines and a bidentate Lewis acid in an orthogonal catalysis. This new method is based on an inverse electron‐demand Diels−Alder and a subsequent group exchange reaction. An enamine is generated in situ from an aldehyde and a chiral secondary amine catalyst that reacts with phthalazine, activated by the coordination to a bidentate Lewis acid catalyst. The absolute configuration of the product is controlled by chiral information provided by the amine. The formed ortho‐quinodimethane intermediate is then transformed via a group exchange reaction with thiols. The new method shows a broad scope and tolerates a wide range of functional groups with enantiomeric ratios up to 91 : 9. All‐in‐all, this enantioselective synthesis tool provides an easy access to complex 1,2‐dihydronaphthalenes starting from readily available phthalazine, aldehydes and thiols in a combinatorial way.

Constructing covalent organic nanoarchitectures molecule by molecule via scanning probe manipulation

Constructing low-dimensional covalent assemblies with tailored size and connectivity is challenging yet often key for applications in molecular electronics where optical and electronic properties of the quantum materials are highly structure dependent. We present a versatile approach for building such structures block by block on bilayer sodium chloride (NaCl) films on Cu(111) with the tip of an atomic force microscope, while tracking the structural changes with single-bond resolution. Covalent homo-dimers in cis and trans configurations and homo-/hetero-trimers were selectively synthesized by a sequence of dehalogenation, translational manipulation and intermolecular coupling of halogenated precursors. Further demonstrations of structural build-up include complex bonding motifs, like carbon–iodine–carbon bonds and fused carbon pentagons. This work paves the way for synthesizing elusive covalent nanoarchitectures, studying structural modifications and revealing pathways of intermolecular reactions.

Tailoring the size and connectivity of organic nanostructures is challenging but is often key in molecular electronics for tuning the properties of the quantum materials. Now an approach has been developed for building low-dimensional covalent architectures block by block on a surface by highly selective tip-induced intermolecular reactions.

Synthesis of Medium-Sized Carbocycles via a Bidentate Lewis Acid-Catalyzed Inverse Electron-Demand Diels-Alder Reaction Followed by Photoinduced Ring-Opening

The combination of a Lewis acid-catalyzed inverse electron-demand Diels-Alder (IEDDA) reaction with a photoinduced ring-opening (PIRO) reaction in a domino process has been established as an efficient synthetic method to access medium-sized carbocycles. From readily available electron-rich and electron-poor phthalazines and enamines, respectively, as starting materials, various 9- and 11-membered carbocycles were prepared. This versatile transition-metal-free tool will be valuable for broadening the structural space in biologically active compounds and functional materials.

Formation of Nucleophilic Allylboranes from Molecular Hydrogen and Allenes Catalyzed by a Pyridonate Borane that Displays Frustrated Lewis Pair Reactivity

Here we report the in situ generation of nucleophilic allylboranes from H₂ and allenes mediated by a pyridonate borane that displays frustrated‐Lewis‐pair reactivity. Experimental and computational mechanistic investigations reveal that upon H₂ activation, the covalently bound pyridonate substituent becomes a datively bound pyridone ligand. Dissociation of the formed pyridone borane complex liberates Piers borane and enables a hydroboration of the allene. The allylboranes generated in this way are reactive towards nitriles. A catalytic protocol for the formation of allylboranes from H₂ and allenes and the allylation of nitriles has been devised. This catalytic reaction is a conceptually new way to use molecular H₂ in organic synthesis.

Surface-controlled reversal of the selectivity of halogen bonds

Intermolecular halogen bonds are ideally suited for designing new molecular assemblies because of their strong directionality and the possibility of tuning the interactions by using different types of halogens or molecular moieties. Due to these unique properties of the halogen bonds, numerous areas of application have recently been identified and are still emerging. Here, we present an approach for controlling the 2D self-assembly process of organic molecules by adsorption to reactive vs. inert metal surfaces. Therewith, the order of halogen bond strengths that is known from gas phase or liquids can be reversed. Our approach relies on adjusting the molecular charge distribution, i.e., the σ-hole, by molecule-substrate interactions. The polarizability of the halogen and the reactiveness of the metal substrate are serving as control parameters. Our results establish the surface as a control knob for tuning molecular assemblies by reversing the selectivity of bonding sites, which is interesting for future applications.

Combining Bidentate Lewis Acid Catalysis and Photochemistry: Formal Insertion of o-Xylene into an Enamine Double Bond

A bidentate Lewis acid catalyzed domino inverse-electron-demand Diels-Alder reaction combined with a photoinduced ring opening formally inserts o-xylene moieties into enamine double bonds. After reduction, phenethylamines were obtained in good yields. The scope of the reaction was determined by variation of all three starting compounds: phthalazines, aldehydes, and amines.

Bond-Level Imaging of the 3D Conformation of Adsorbed Organic Molecules Using Atomic Force Microscopy with Simultaneous Tunneling Feedback

The chemical structure and orientation of molecules on surfaces can be visualized using low temperature atomic force microscopy with CO-functionalized tips. Conventionally, this is done in constant-height mode by measuring the frequency shift of the oscillating force sensor. However, this method is unsuitable for analyzing 3D objects. We are using the tunneling current to track the topography while simultaneously obtaining submolecular resolution from the frequency shift signal. Thereby, the conformation of 3D molecules and the adsorption sites on the atomic lattice can be reliably determined.

Adsorption Structure of Mono- and Diradicals on a Cu(111) Surface: Chemoselective Dehalogenation of 4-Bromo-3″-iodo- p-terphenyl

Selectivity is a key parameter for building customized organic nanostructures via bottom-up approaches. Therefore, strategies are needed that allow connecting molecular entities at a specific stage of the assembly process in a chemoselective manner. Studying the mechanisms of such reactions is the key to apply these transformations for the buildup of organic nanostructures on surfaces. Especially, the knowledge about the precise adsorption geometry of intermediates at different stages during the reaction process and their interactions with surface atoms or adatoms is of fundamental importance, since often catalytic processes are involved. We show the selective dehalogenation of 4-bromo-3″-iodo- p-terphenyl on the Cu(111) surface using bond imaging atomic force microscopy with CO-functionalized tips. The deiodination and debromination reactions are triggered either by heating or by locally applying voltage pulses with the tip. We observed a strong hierarchical behavior of the dehalogenation with respect to temperature and voltage. In connection with first-principles simulations we can determine the orientation and position of the pristine molecules as well as adsorbed mono/diradicals and the halogens. We find that the isolated radicals are chemisorbed to Cu(111) top sites, which are lifted by 16 pm ( meta-position) and 32 pm ( para-position) from the Cu surface plane. This leads to a strongly twisted and bent 3D adsorption structure. After heating, different types of dimers are observed whose molecules are either bound to surface atoms or connected via Cu adatoms. Such knowledge about the intermediate geometry and its interaction with the surface will open the way to rationally design syntheses on surfaces.

An Amine Group Transfer Reaction Driven by Aromaticity

A stereoselective domino inverse electron-demand Diels-Alder/amine group transfer reaction catalyzed by a bidentate Lewis acid provides 1-amino-1,2-dihydronaphthalenes, a core structure in many bioactive compounds. A concerted mechanism is proposed based on experimental studies as well as DFT computations demonstrating a new general reactivity scheme. The broad scope of the reaction was evaluated by variation of all three starting compounds, phthalazines, aldehydes, and amines. Scalability was demonstrated by a gram scale reaction without diminished yield.

An air-stable bisboron complex: a practical bidentate Lewis acid catalyst

We report an air-stable bisboron complex as an efficient catalyst for the inverse electron-demand Diels–Alder (IEDDA) reaction of 1,2-diazine as well as 1,2,4,5-tetrazine. Its stability towards air and moisture was demonstrated by NMR studies enabling its application in organic transformations without glovebox. A one-pot procedure for its synthesis was developed starting from 1,2-bis(trimethylsilyl)benzene greatly enhancing its practicality. Comparative reactions were carried out to evaluate its catalytic activity in IEDDA reactions of diazine including phthalazine as well as 1,2,4,5-tetrazine.

Imaging Successive Intermediate States of the On-Surface Ullmann Reaction on Cu(111): Role of the Metal Coordination

The in-depth knowledge about on-surface reaction mechanisms is crucial for the tailor-made design of covalently bonded organic frameworks, for applications such as nanoelectronic or -optical devices. Latest developments in atomic force microscopy, which rely on functionalizing the tip with single CO molecules at low temperatures, allow to image molecular systems with submolecular resolution. Here, we are using this technique to study the complete reaction pathway of the on-surface Ullmann-type coupling between bromotriphenylene molecules on a Cu(111) surface. All steps of the Ullmann reaction, i.e., bromotriphenylenes, triphenylene radicals, organometallic intermediates, and bistriphenylenes, were imaged with submolecular resolution. Together with density functional theory calculations with dispersion correction, our study allows to address the long-standing question of how the organometallic intermediates are coordinated via Cu surface or adatoms.

Synthesis of 2,3-diaza-anthraquinones via the bidentate Lewis acid catalysed inverse electron-demand Diels–Alder (IEDDA) reaction

A new synthesis of aza-anthraquinones and substituted anthraquinones via bidentate Lewis acid catalysis has been developed.

Reported weight loss and dexamethasone nonsuppression in depressed patients. A negative study

In a sample of 96 patients with DSM-III major depressive disorder and in a subset of 78 melancholic patients, there was no evidence that dexamethasone nonsuppression was more common in patients with reported weight loss.

Comparative cardiac effects of maprotiline and doxepin in elderly depressed patients

In a double-blind study, 49 elderly patients with primary major depression, with or without cardiovascular disease, were treated with maprotiline or doxepin. Holter monitors, 12-lead ECGs, and orthostatic blood pressure measurements were used. Maprotiline was associated with decreased PVCs in patients with a "high" baseline rate, while doxepin was associated with increased PVCs in this group. There were no significant differences in orthostatic blood pressure changes between treatment and nontreatment phases or between the two drugs. Small but significant increases in heart rate and prolonged PR interval were noted with both drugs. QRS interval was prolonged by maprotiline but decreased by doxepin. Neither drug produced untoward effects in patients with stable angina or an old myocardial infarction. Maprotiline may have an antiarrhythmic effect which could be beneficial in the treatment of depression with concomitant PVCs. Conversely, doxepin may be more appropriate for depressed patients with heart block or intracardiac conduction delays. Further research is necessary to confirm these suggestions.

Therapeutic superiority of maprotiline versus doxepin in geriatric depression

In a double-blind study, 49 geriatric patients suffering from primary major depression were treated with maprotiline or doxepin. Efficacy and safety were assessed by the Hamilton Depression Rating Scale and the Zung Self-Rating Depression and Anxiety scales, side effects profile, routine laboratory tests, and measurements of blood levels. Although marked improvement was obtained with both antidepressants, patients on maprotiline showed statistically greater improvement than those on doxepin. No significant differences were detected between the two drugs with respect to side effects. A significant positive correlation was obtained between dosage and blood levels of maprotiline and doxepin, but there was no correlation between blood levels and clinical response. Overall, results suggest that maprotiline may be superior to doxepin in the treatment of geriatric depression.