Chemical structure

A chemical structure of a molecule is a spatial arrangement of its atoms and their chemical bonds. Its determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target molecule or other solid. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together and can be represented using structural formulae and by molecular models; complete electronic structure descriptions include specifying the occupation of a molecule's molecular orbitals. Structure determination can be applied to a range of targets from very simple molecules (e.g., diatomic oxygen or nitrogen) to very complex ones (e.g., such as protein or DNA). Background Theories of chemical structure were first developed by August Kekulé, Archibald Scott Couper, and Aleksandr Butlerov, among others, from about 1858. These theories were first to state that chemical compounds are not

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications

Related people

Related units

Related concepts

Related courses

Related lectures

Summary

Official source

About this result

Related publications (100)

Related publications

Related people (15)

Related people

Related units (11)

Related units

Related concepts (30)

Related concepts

Related courses (43)

Related courses

Related lectures (63)

Related lectures

X-ray crystallography

X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into ma

Molecule

A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In q

Functional group

In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or sim

BIO-378: Physiology lab I

Le TP de physiologie introduit les approches expérimentales du domaine biomédical, avec les montages de mesure, les capteurs, le conditionnement des signaux, l'acquisition et traitement de données. Les résultats physiologiques finaux illustrent le contenu du cours de Physiologie par système.

CH-210: Biochemistry

Les constituants biochimiques de l'organisme, protéines, glucides, lipides, à la lumière de l'évolution des concepts et des progrès en biologie moléculaire et génétique, sont étudiés.

MICRO-505: Organic and printed electronics

This course addresses the implementation of organic and printed electronics technologies using large area manufacturing techniques. It will provide knowledge on materials, printing techniques, devices, systems, and applications: state of the art and current status on commercialization.

Efficiency of SPIONs functionalized with polyethylene glycol bis (amine) for heavy metal removal

Heinrich Hofmann, Yongyuth Wanna

Hybrid magnetic nanoparticles based on poly(methylmethacrylate) (PMMA) and super-paramagnetic iron oxide nanopaticles (SPIONs) with selective surface modification has been developed for heavy metal removal by applying external magnetic fields. The nanoparticles were prepared by the emulsion polymerization technique in an aqueous suspension of SPIONs. The hydrolysis of carboxyl functional group was then applied for grafting polyethylene glycol bis(amine)(PEG-bis(amine)) onto the PMMA-coated SPIONs. The morphology, the chemical structure and the magnetic properties of the grafted nano particles were investigated. The efficiency of the hybrid nanoparticles for heavy metal removal were conducted on Pb(II), Hg(II), Cu(II) and Co(II) in aqueous solutions. The metal concentration in the solutions after separation by the hybrid nanoparticles was determined by inductively coupled plasma optical emission spectrometer (ICP-OES). The results show the heavy metal uptake ratios of 0.08, 0.04, 0.03, and 0.01 mM per gramme of the grafted SPIONs for Pb(II), Hg(II), Cu(II), and Cu(II), respectively. A competitive removal of Cu(II), Pb(II), Co(II) and Hg(II) ions in mixed metal salt solutions has also been studied. The heavy metal removal efficiency of the hybrid nanoparitcles was found to depend on the cation radius, in accordance with capture of metal ions by the amine group. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier2016

Low-energy Electron Holography Microscope for Imaging of Single Molecules

Sven Alexander Szilagyi

Structure determination techniques are an essential tool to investigate and understand molecules, especially in biology, where functionality crucially depends on structure. The dominant high-resolution methods, such as transmission electron microscopy and X-ray diffraction, rely on ensemble averaging, making them unsuitable for evidencing structural variations of flexible molecules. Common single-molecule imaging techniques like scanning probe microscopy achieve high resolution but lack access to 3D objects. A possible way to overcome these limitations is offered by low-energy electron holography (LEEH). So far, LEEH achieved molecular imaging at resolutions in the range of 7-8 Å on the single-molecule level. A resolution in the range of a few Å, which would give access to atomic details of molecular structures, is in theory attainable. Obtaining a resolution near the theoretical limit requires a fully optimized LEEH setup and workflow, for which in particular sample and emitter preparation are crucial. Here, I present a novel LEEH microscope with a unique experimental workflow, which is capable of resolving molecular substructures with an unprecedented resolution for LEEH experiments. The newly constructed LEEH microscope takes advantage of an efficient vibration isolation system and is remote-controlled to minimize external perturbations. The setup is capable of low-temperature (50 K) measurements, which enhances the stability of the system. A reliable way for preparing highly coherent electron emitters constituted by sharp tungsten tips is presented along with different methods for improving their performance via functionalization and UHV treatments. I show an optimized and reliable substrate preparation protocol resulting in ultra-clean free-standing single-layer graphene (SLG) samples. Native electrospray ion beam deposition (ES-IBD) allows for the transfer of non-volatile molecules from solution into gas phase and onto the substrate. By employing a quadrupole mass selection, highly pure molecular ion beams are obtained, which are soft-landed onto the SLG substrate in a controlled and reproducible manner while retaining an intact structure. This versatile preparation method allows us to study a great variety of molecules by LEEH. Data on proteins with masses ranging from 12-820 kDa reveal molecular shapes consistent with model structures. Locally, structural details as small as 5 Å were identified, thus we are approaching our goal of a resolution in the range of a few Å. The application of our methodology to flexible proteins, exemplified by antibodies, allowed for the imaging of their conformational variability and for determining the influence of the sample preparation on their structure. This gave us the possibility to directly image gas-phase related conformations. Data of compact molecular systems with masses below 3 kDa reveal that our LEEH microscope is able to investigate small molecules, such as porphyrines, at high imaging contrast. The presented results indicate that an optimized LEEH setup and workflow in combination with ES-IBD is a versatile microscopy method, which is filling the gap between high-resolution and single-molecule techniques by elucidating structural details of various molecular species.

EPFL2022

Interaction of polyelectrolytes with oppositely charged surfaces

Vesela Malinova

Despite progress during the last decade, the behavior of charged macromolecules, polyelectrolytes, including their interactions is not yet completely understood. In particular, interactions with oppositely charged surfaces, which play a significant role in many practical applications and are of central importance in life processes, need more investigation. This situation has motivated the selection of the topic of this doctoral thesis. The study is dedicated to interactions of positively charged polyelectrolytes with negatively charged surfaces considering two types of surfaces, flat amphiphile monolayers and porous surfaces of microspheres. The research aimed at quantitative evaluation of the influence of macromolecular dimensions, chemical structure, electrostatic parameters, and surface characteristics on the adsorption process. As a prerequisite, a series of poly(vinylbenzyltrialkylammonium chloride) model polyelectrolytes has been synthesized. The characteristics were five defined contour lengths with three different types of substituents at the quaternary ammonium group each in addition to uniform charge density and narrow chain length distribution. The final polyelectrolytes were the quaternization products of precursors synthesized by controlled radical polymerization. Two experimental techniques were employed to quantify the influence of chemical, macromolecular, and electrostatic parameters as well as geometrical characteristics on the adsorption of polyelectrolytes on porous microsphere surfaces. These were adsorption on microspheres suspended in aqueous phase and microspheres packed in a chromatography column. During the first technique the total surface comes immediately in contact with the polyelectrolyte molecules, whereas the second technique followed the rules of chromatography. For the first time, the contour length of the polyelectrolyte, the Debye length, the pore dimensions, as well as the chemical structure were likewise considered in a comprehensive study to describe the interaction of polyelectrolytes with well-characterized porous surfaces. A polyelectrolyte charge to surface charge ratio was defined and served to classify different adsorption behavior. Three models have been proposed to illustrate the adsorption behavior based on experimental findings and model calculations. The first one identifies the Debye length in addition to the contour length as dominating parameter, which decides whether a polyelectrolyte molecule can enter a pore or not. The second quantifies the influence of the contour length. Finally, the third describes the concentration influence on the type of molecule organization, layer formation, on the outer surface or inside of pores with diameters exceeding considerably the contour length. For amphiphile monolayer, for the first time, the influence of chain length and substituent at the quaternary ammonium group on the adsorption process was quantified. Based on the surface pressure, pressure-area and pressure-time isotherms measured, a model describing the monolayer arrangement on polyelectrolyte solutions was proposed. A second model correlates the increase of the area per amphiphile molecule and the decrease of the surface pressure with the size and hydrophobicity of the substituents. In addition chain length influence was evident. The results of the thesis contribute to progress in basic research in the field of polyelectrolytes, while also an impact on technical applications such as surface modification, chromatographic processes or improvement of materials is expected. Precise data for comparison with theoretical model calculations are provided, which were not available before.

EPFL2005