Bare carbon electrodes as simple and efficient sensors for the quantification of caffeine in commercial beverages

This work has been supported by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 642014 (IPCOS). Ĺ.Š. would like to acknowledge the Grant Agency of the Slovak Republic (grant no. 1/0489/16)

In-Plane Hydrogen Bonds and Out-of-Plane Dipolar Interactions in Self-Assembled Melem Networks

Melem(2,6,10-triamino-s-heptazine) is the building block of melon,a carbon nitride (CN) polymer that is proven to produce H2 from water under visible illumination. With the aim of bringing additional insight into the electronic structure of CN materials, we performed a spectroscopic characterization of gas-phase melem and of a melem-based self-assembled 2D H-bonded layer on Au(111) by means of ultraviolet and X-ray photoemission spectroscopy (UPS, XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In parallel, we performed density functional theory (DFT) simulations of the same systems to unravel the molecular charge density redistribution caused by the in-plane H-bonds. Comparing the experimental results with the spectroscopic DFT simulations, we can correlate the induced charge accumulation on the N-amino atoms to the red-shift of the corresponding N 1s binding energy (BE) and of the N-amino 1s -> LUMO+n transitions. Moreover, when introducing a supporting Au(111) surface in the computational simulations, we observe a molecule-substrate interaction that almost exclusively involves the out-of-plane molecular orbitals, leaving those engaged in the in-plane H-bonded network rather unperturbed

Room-temperature on-spin-switching and tuning in a porphyrin-based multifunctional interface

Molecular interfaces formed between metals and molecular compounds offer a great potential as building blocks for future opto-electronics and spintronics devices. Here, a combined theoretical and experimental spectro-microscopy approach is used to show that the charge transfer occurring at the interface between nickel tetraphenyl porphyrins and copper changes both spin and oxidation states of the Ni ion from [Ni(II), S = 0] to [Ni(I), S = 1/2]. The chemically active Ni(I), even in a buried multilayer system, can be functionalized with nitrogen dioxide, allowing a selective tuning of the electronic properties of the Ni center that is switched to a [Ni(II), S = 1] state. While Ni acts as a reversible spin switch, it is found that the electronic structure of the macrocycle backbone, where the frontier orbitals are mainly localized, remains unaffected. These findings pave the way for using the present porphyrin-based system as a platform for the realization of multifunctional devices where the magnetism and the optical/transport properties can be controlled simultaneously by independent stimuli

Modeling lipid accumulation in oleaginous fungi in chemostat cultures. II: Validation of the chemostat model using yeast culture data from literature

A model that predicts cell growth, lipid accumulation and substrate consumption of oleaginous fungi in chemostat cultures (Meeuwse et al. in Bioproc Biosyst Eng. doi:10.1007/s00449-011-0545-8, 2011) was validated using 12 published data sets for chemostat cultures of oleaginous yeasts and one published data set for a poly-hydroxyalkanoate accumulating bacterial species. The model could describe all data sets well with only minor modifications that do not affect the key assumptions, i.e. (1) oleaginous yeasts and fungi give the highest priority to C-source utilization for maintenance, second priority to growth and third priority to lipid accumulation, and (2) oleaginous yeasts and fungi have a growth rate independent maximum specific lipid production rate. The analysis of all data showed that the maximum specific lipid production rate is in most cases very close to the specific production rate of membrane and other functional lipids for cells growing at their maximum specific growth rate. The limiting factor suggested by Ykema et al. (in Biotechnol Bioeng 34:1268–1276, 1989), i.e. the maximum glucose uptake rate, did not give good predictions of the maximum lipid production rate

Electronic properties of the boroxine–gold interface: evidence of ultra-fast charge delocalization

We performed a combined experimental and theoretical study of the assembly of phenylboronic acid on the Au(111) surface, which is found to lead to the formation of triphenylboroxines by spontaneous condensation of trimers of molecules. The interface between the boroxine group and the gold surface has been characterized in terms of its electronic properties, revealing the existence of an ultra-fast charge delocalization channel in the proximity of the oxygen atoms of the heterocyclic group. More specifically, the DFT calculations show the presence of an unoccupied electronic state localized on both the oxygen atoms of the adsorbed triphenylboroxine and the gold atoms of the topmost layer. By means of resonant Auger electron spectroscopy, we demonstrate that this interface state represents an ultra-fast charge delocalization channel. Boroxine groups are among the most widely adopted building blocks in the synthesis of covalent organic frameworks on surfaces. Our findings indicate that such systems, typically employed as templates for the growth of organic films, can also act as active interlayers that provide an efficient electronic transport channel bridging the inorganic substrate and organic overlayer

Electroanalytical overview: The electroanalytical detection of theophylline

In this overview, we explore the electroanalytical determination of theophylline. Theophylline finds use as a bronchodilator for treating diseases such as asthma and chronic obstructive pulmonary disease (COPD). There is a need to measure the concentration of theophylline in pharmaceuticals for QA/QC purposes as well as in plasma samples to ensure the doses of theophylline are at the correct therapeutic levels. If the concentration levels of theophylline deviate from the therapeutic levels (10–20 µg/mL for asthma), then patients can experience adverse effects. As such, there is a desire to progress from traditional laboratory based techniques to portable rapid testing. In this overview, we review the endeavours directed to the development of theophylline electroanalytical sensors, noting current and future trends

HETERO-INTERFACES: FUNCTIONAL MOLECULAR FILMS AND LOW DIMENSIONAL MATERIALS

The aim of this PhD work is to study the formation and the electronic and morphologic properties of complex organo-metallic and hetero-organic architectures, grown on metal surfaces via a bottom-up approach. Different systems have been investigated, in order to monitor distinct situations occurring on a surface. The largest part of this work has been focused on the boroxine-based systems. This covalently-bonded films have been explored with a multi-technique approach that allowed a deeper insight in their nature. We have prepared a novel 2D material based on the boroxine unit and consisting in boron and oxygen atoms only. Moreover, we have found interesting electronic properties, such as a channel for ultra-fast charge delocalization toward the golden substrate in all the boronic systems and a dispersion in the valence band for this 2D material. These results allow to gain a new perspective in the boroxine based systems. From material mostly known for their morphological properties, we have highlighted the presence of interesting electronic properties. In addition to the covalently bonded boroxine systems, we have focused also on the possibility of building more complex architectures upon metallic substrates via weak interactions. In particular, we have taken advantage of one of the already investigated boroxine systems to study the interplay between the boron molecule, acting as a Lewis acid, and an amine acting as a Lewis base. We have evidenced a very interesting morphological change confirming that the interaction has taken place. Similarly, we have built another complex architecture relaying on weak interactions. We have taken advantage of a H-bonding to anchor a crown ether derivative on a substrate. Then we used the interaction between sodium and crown ethers to trap an alkali metal on the surface. In this experiment, we have used the crown ether for the first time on a substrate in UHV, and we have found that the affinity toward the metal is preserved. The last investigated system is also characterized by the presence of weak interactions between the molecules deposited on the surface. Despite of this similarity with the previous scientific case, the application target was completely different. We were not interested in building structures on a substrate, but we decided to take advantage offered by the UHV to study the behavior of molecules important in catalysis. In this case, we have studied the melamine and melem molecules, precursors of the 2D carbon nitride, an interesting photocatalyst for the water splitting reaction. This approach has been successful, and we gained a deeper insight in the H-bonding properties of the monitored molecules.The aim of this PhD work is to study the formation and the electronic and morphologic properties of complex organo-metallic and hetero-organic architectures, grown on metal surfaces via a bottom-up approach. Different systems have been investigated, in order to monitor distinct situations occurring on a surface. The largest part of this work has been focused on the boroxine-based systems. This covalently-bonded films have been explored with a multi-technique approach that allowed a deeper insight in their nature. We have prepared a novel 2D material based on the boroxine unit and consisting in boron and oxygen atoms only. Moreover, we have found interesting electronic properties, such as a channel for ultra-fast charge delocalization toward the golden substrate in all the boronic systems and a dispersion in the valence band for this 2D material. These results allow to gain a new perspective in the boroxine based systems. From material mostly known for their morphological properties, we have highlighted the presence of interesting electronic properties. In addition to the covalently bonded boroxine systems, we have focused also on the possibility of building more complex architectures upon metallic substrates via weak interactions. In particular, we have taken advantage of one of the already investigated boroxine systems to study the interplay between the boron molecule, acting as a Lewis acid, and an amine acting as a Lewis base. We have evidenced a very interesting morphological change confirming that the interaction has taken place. Similarly, we have built another complex architecture relaying on weak interactions. We have taken advantage of a H-bonding to anchor a crown ether derivative on a substrate. Then we used the interaction between sodium and crown ethers to trap an alkali metal on the surface. In this experiment, we have used the crown ether for the first time on a substrate in UHV, and we have found that the affinity toward the metal is preserved. The last investigated system is also characterized by the presence of weak interactions between the molecules deposited on the surface. Despite of this similarity with the previous scientific case, the application target was completely different. We were not interested in building structures on a substrate, but we decided to take advantage offered by the UHV to study the behavior of molecules important in catalysis. In this case, we have studied the melamine and melem molecules, precursors of the 2D carbon nitride, an interesting photocatalyst for the water splitting reaction. This approach has been successful, and we gained a deeper insight in the H-bonding properties of the monitored molecules

Dioxygen at Biomimetic Single Metal-Atom Sites: Stabilization or Activation? The Case of CoTPyP/Au(111)

By means of a combined experimental and computational approach, we show that a 2D metal\u2013organic framework self-assembled at the Au(111) termination is able to mimic the O2 stabilization and activation mechanisms that are typical of the biochemical environment of proteins and enzymes. 5,10,15,20-tetra(4-pyridyl)21H,23H-porphyrin cobalt(III) chloride (CoTPyP) molecules on Au(111) bind dioxygen forming a covalent bond at the Co center, yielding charge injection into the ligand by exploiting the surface trans-effect. A weakening of the O\u2013O bond occurs, together with the development of a dipole moment, and a change in the molecule\u2019s magnetic moment. Also the bonding geometry is similar to the biological counterpart, with the O2 molecule sitting on-top of the Co atom and the molecular axis tilted by 118\ub0. The ligand configuration lays between the oxo- and the superoxo-species, in agreement with the observed O\u2013O stretching frequency measured in situ at near-ambient pressure conditions

On-Surface Synthesis of Boroxine-Based Molecules

The on-surface synthesis of boroxine-containing molecules can be a convenient method of introducing specific functionalities. Here, we show the validity of a previously described synthesis protocol on the Au (111) surface by applying it to a different molecular precursor. We study in detail the assembly of the precursor, highlighting possible intermediate stages of the condensation process. We combine scanning tunneling microscopy and X-ray spectroscopies to fully characterize both the morphology and the electronic properties of the system. DFT calculations are presented to assign the main electronic transitions originating the B K-edge absorption spectrum. The study paves the way to a facile strategy for functionalizing a surface with molecules of tailored sizes and compositions