Molecular orbital | EPFL Graph Search

In chemistry, a molecular orbital (ɒrbədl) is a mathematical function describing the location and wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The terms atomic orbital and molecular orbital were introduced by Robert S. Mulliken in 1932 to mean one-electron orbital wave functions. At an elementary level, they are used to describe the region of space in which a function has a significant amplitude. In an isolated atom, the orbital electrons' location is determined by functions called atomic orbitals. When multiple atoms combine chemically into a molecule by forming a valence chemical bond, the electrons' locations are determined by the molecule as a whole, so the atomic orbitals combine to form molecular orbitals. The electrons from the constituent atoms occupy the molecular orbitals. Mathematically, molecular orbitals are an approximate s

Caged luciferin probes for the bioluminescence imaging of nitroreductase and hydrogen sulfide in living animals

Anzhelika Vorobyeva

Molecular imaging advances our understanding of cellular and molecular functions within complex biological systems. The development of novel imaging probes that can be applied to answer fundamental biological questions, diagnose and monitor disease progression and the efficacy of therapy in vivo is essential to the field of molecular imaging. Bioluminescence imaging is a powerful technique that allows to study and follow biological processes of interest noninvasively in real-time in living animals. Activatable bioluminescent probes can be designed according to the target of interest and can provide imaging signal in response to the specific stimuli. A strategy called "caged luciferin" can be used to design new bioluminescent probes for imaging of enzymatic activity, the presence of small molecules or metabolite uptake in vivo. In Chapter 1 we present an overview of bioluminescence imaging, with a focus on firefly luciferase-luciferin system. The caged luciferin approach is discussed and examples of existing caged luciferin probes are presented. In Chapter 2 we describe the development of a bioluminescent probe for imaging of bacterial nitroreductase activity and show the potential for its application in different areas of research. Bacterial nitroreductases have been widely utilized in the gene-directed enzyme prodrug therapy (GDEPT) approach for cancer therapy that reached clinical trials. However, both preclinical and clinical development of NTR-based GDEPT systems has been hampered by the lack of imaging tools that allow in vivo evaluation of transgene expression. We developed the NTR caged luciferin (NCL) probe and demonstrated its application for sensitive bioluminescence imaging of NTR in vitro, in bacteria and cancer cells, as well as in vivo in mouse models of bacterial infection and NTR-expressing tumor xenografts. We anticipate that this probe would significantly accelerate the development of cancer therapy approaches based on GDEPT and other fields where evaluation of NTR expression is important. In Chapter 3 we describe the development of a bioluminescent probe for imaging of hydrogen sulfide (H2S) using the caged luciferin approach. The objective of the research was to develop a probe that can detect endogenously produced H2S noninvasively in real-time in living animals. We present a series of caged luciferin probes that were evaluated on their ability to rapidly and selectively detect H2S in in vitro assays, in cells and in bacterial culture. The two selected probes were applied for imaging of exogenous H2S in the gastrointestinal tract in living mice. We anticipate further applications of the best performing probe (Az-CL) for imaging of H2S production by gut microbiota in mice. In Chapter 4 we present the overall conclusion followed by the outlook and future perspectives.

EPFL2016

The influence of external electric fields on charge reorganization energy in organic semiconductors

Weicong Huang, Hongguang Liu

Charge reorganization energies (k) of inter-ring carbon-carbon (IRCC) bond connected conjugated polycyclics are shown to exhibit an electric-field-driven anisotropic character. An external electric field parallel to the IRCC linker(s) reduces k while the field vertical to the molecular plane does the opposite. This anisotropic character can be modulated by introducing inter-ring noncovalent locks into appropriate sites.

ROYAL SOC CHEMISTRY2019

Local electronic properties and adsorption conformations of molecular nanostructures at surfaces

Ivan Pentegov

Nanoscale science is an emerging field of our time and opens a broad horizon for applications in almost every area of human activity, from medicine to energy storage. As usual, there are numerous challenges in the way of progress, which slow down the development and application of new ideas. Therefore the versatile investigation of nanostructures is of current importance for the realization of future technologies. The central aim of this thesis was to advance the field of molecular nanoscience on several crucial fronts. For that, the scanning tunneling microscopy (STM) was chosen as the principal experimental technique. It provides an unprecedented resolution at the atomic scale and can be used to reveal topographical or electronic properties of single molecules or atoms on conducting surfaces. Moreover, it gives a certain freedom to manipulate the object of interest at the nanoscale by the apex of the scanning tip. The introduction to this thesis gives a brief overview about the history of nanotechnology and its current status. In the first chapter the theory of the tunnelling effect and the working principle of the STM are presented and the experimental set-up is described. The second chapter is devoted to shot noise measurements with the STM. At first, the theory of shot noise is presented from the view point of the scattering approach. The challenges that arise on the way towards noise detection are discussed from two different sides: current and voltage amplification. Several test measurements are suggested for the approval of the amplification circuity. Afterwards, the data obtained on the copper and gold quantum point contact are shown. The third chapter presents an investigation of a purely organic radical with spin system 1/2. This molecule was previously studied on the Au(111) surface and demonstrated a Kondo effect in the weak coupling regime. In this thesis, its adsorption on Pd(111) and cobalt islands on Cu(111) is explored. The obtained data reveal electronic transport where molecular orbitals and vibration excitations are involved. The final chapter presents an investigation of the sequence controlled polymers - the oligo-triazole amide trimers, which were successfully deposited on the Cu(100) surface by means of the electrospray ion-beam deposition technique. The molecules show a large variety of adsorption conformations which are correlated with the sequence of monomers in the molecular backbone. Each chapter contains a summary and outlook, where possible improvements are discussed and future experiments suggested.

EPFL2015