Towards dielectric relaxation at a single molecule scale

Dielectric relaxation lies at the heart of well-established techniques of dielectric spectroscopy essential to diverse fields of research and technology. We report an experimental route for increasing the sensitivity of dielectric spectroscopy ultimately towards the scale of a single molecule. We use the method of radio frequency scanning tunneling microscopy to excite a single molecule junction based on a polar substituted helicene molecule by an electric field oscillating at 2–5 GHz. We detect the dielectric relaxation of the single molecule junction indirectly via its effect of power dissipation, which causes lateral displacement. From our data we determine a corresponding relaxation time of about 300 ps—consistent with literature values of similar helicene derivatives obtained by conventional methods of dielectric spectroscopy.publishedVersio

Growth kinetics of racemic heptahelicene-2-carboxylic acid nanowires on calcite (104)

Einax M, Richter T, Nimmrich M, et al. Growth kinetics of racemic heptahelicene-2-carboxylic acid nanowires on calcite (104). Journal of Chemical Physics. 2016;145(13):134702.Molecular self-assembly of racemic heptahelicene-2-carboxylic acid on a dielectric substrate at room temperature can be used to generate wire-like organic nanostructures consisting of single and double molecular rows. By means of non-contact atomic force microscopy, we investigate the growth of the wire-like pattern after deposition by experimental and theoretical means. From analyzing the time dependence of the mean row length, two distinct regimes were found. At the early post-deposition stage, the mean length grows in time. Subsequently, a crossover to a second regime is observed, where the mean row length remains nearly constant. We explain these findings by a mean-field rate equation approach providing a comprehensive picture of the growth kinetics. As a result, we demonstrate that the crossover between the two distinct regimes is accomplished by vanishing of the homochiral single rows. At later stages only heterochiral double row structures remain. Published by AIP Publishing

Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)

Hauke CM, Rahe P, Nimmrich M, et al. Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014). Journal of Physical Chemistry C. 2012;116(7):4637-4641.Chirality can have a decisive influence on the molecular structure formation upon self-assembly on surfaces. In this paper, we study the structures formed by enantiopure (M)-heptahelicene-2-carboxylic acid ((M)-[7]HCA) on the calcite (10 (1) over bar4) cleavage plane under ultrahigh vacuum conditions. Previous noncontact atomic force microscopy studies have revealed that the racemic mixture of (M)-[7]HCA and (P)-[7]FICA (1:1) self-assembles into well-defined molecular double rows that are oriented along the calcite [01 (1) over bar0] direction. Here, we investigate the enantiopure (M)[7]HCA compound, resulting in distinctly different molecular structures upon deposition onto calcite (10 (1) over bar4). In sharp contrast to the racemate, the (M)-[7]HCA enantiomer forms molecular islands with a (2 x 3) superstructure. Comparison of the results presented here for the enantiopure compound with the results previously obtained from the racemate indicates that heterochiral recognition is responsible for the formation of the unidirectional double row structures formed by the racemate

Toward Molecular Nanowires Self-Assembled on an Insulating Substrate: Heptahelicene-2-carboxylic acid on Calcite (1014)

Rahe P, Nimmrich M, Greuling A, et al. Toward Molecular Nanowires Self-Assembled on an Insulating Substrate: Heptahelicene-2-carboxylic acid on Calcite (1014). Journal of Physical Chemistry C. 2010;114(3):1547-1552.Molecular self-assembly is employed for creating unidirectional molecular nanostructures on a truly insulating substrate, namely the (10 (1) over bar4) cleavage plane of calcite. The molecule used is racemic heptahelicene-2-carboxylic acid, which forms structures, well-aligned along the [010] crystallographic direction and stable at room temperature. Precise control of both molecule-substrate and molecule-molecule interaction is required, leading to the formation of such wire-like structures of well-defined width and lengths exceeding 100 nm. This subtle balance is governed by the heptahelicene-2-carboxylic acid used in this study, allowing for both hydrogen bond formation as well pi-pi stacking

Increased expression of endothelial lipase in symptomatic and unstable carotid plaques

The aim of this study was to evaluate endothelial lipase (EL) protein expression in advanced human carotid artery plaques (HCAP) with regard to plaque (in)stability and the incidence of symptoms. HCAP were collected from 66 patients undergoing carotid endarterectomy (CEA). The degree of plaque (in)stability was estimated by ultrasound and histology. In HCAP sections, EL expression was determined by immunostaining and the intensity was assessed on a semi-quantitative scale (low: <25%, high: >25% positive cells). Monocytes and macrophages in adjacent HCAP sections were stained with a CD163 specific antibody. High EL staining was more prevalent in histologically unstable plaques (in 33.3% of fibrous plaques, 50% of ulcerated non-complicated plaques and 79.2% of ulcerated complicated plaques; χ2 test, p = 0.004) and in the symptomatic group (70.8 vs. 42.9% in the asymptomatic group; χ2 test, p = 0.028). The majority of EL immunostaining was found in those HCAP regions exhibiting a strong CD163 immunostaining. EL in HCAP might be a marker and/or promoter of plaque instability and HCAP-related symptomatology

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Areopraon chaitophori n. sp (Hymenoptera: Braconidae: Aphidiinae) associated with Chaitophorus leucomelas Koch on poplars, with a key for European Areopraon Mackauer species

Areopraon chaitophori n. sp. associated with Chaitophorus leucomelas Koch on Populus nigra is described and illustrated. The main diagnostic characters of Areopraon species are discussed, and a key for identification of European species is provided. The distal dorsal part of the second metasomal tergite of Areopraon species has a very prominent horizontal longitudinal protuberance, which represents a new diagnostic character for Areopraon

[11]Anthrahelicene on TiO2 surface

Helicenes are carbon-rich materials with an ordered structure that possess interesting and remarkable electronic, chiroptical, mechanical and magnetic properties either in bulk or as single molecule devices. We report on the first attempt to anchor and organize {[}11]anthrahelicene ({[}11]AH) molecules onto a metal oxide surface. Molecular structures obtained on the (110) and (011) faces of rutile titania are characterized using scanning probe microscopy. On the (110) surface, {[}11]AH molecules form islands that are comprised of small domains of two types that are mirror reflections of each other and have an ordered quasi-hexagonal lattice. In contrast, molecules form unordered clusters on the (011) surface. Single molecules on both faces are imaged with sub-molecular resolution. (C) 2012 Elsevier B.V. All rights reserve

On the Identity of Cereal Aphid Parasitoid Wasps Aphidius uzbekistanicus, Aphidius rhopalosiphi, and Aphidius avenaphis (Hymenoptera: Braconidae: Aphidiinae) by Examination of COI Mitochondrial Gene, Geometric Morphometrics, and Morphology

In this study, the relationships among and the taxonomic status of three closely related parasitic wasps that are widely used as biological control agents of cereal aphids, Aphidius uzbekistanicus Luzhetzki, Aphidius rhopalosiphi De Stefani Perez, and Aphidius avenaphis (Fitch), were examined. Genetic divergence at an average of 6% was recorded between A. uzbekistanicus and A. rhopalosiphi by using the mitochondrial (mt) gene cytochrome oxidase I (COI) barcoding region. Identical mtCOI gene sequences were observed in A. uzbekistanicus specimens that originated from Eurasia and in the North American species A. avenaphis. The haplotype fluctuation in A. rhopalosiphi specimens that originated from the west Palaearctic was an average of 1.5% (maximum, 2.4%). In contrast, specimens of A. uzbekistanicus from central and western parts of Eurasia were largely homogenous, with only a single mutation recorded in a specimen from eastern Europe (Serbia). The morphological and genetic diversity found in A. rhopalosiphi may suggest the existence of cryptic species, especially for lineages that have a large degree of mtCOI diversity and sympatric occurrence. The geometric morphometric analysis of stigma shape presented in this study demonstrated that members of A. uzbekistanicus have a shorter forewing r vein and a more elongated stigma, relative to those of A. avenaphis. Our research validates the use of stigma shape and flagellomere 1 color for morphological discrimination between wasp species