Fourier-transform spectroscopy

Fourier-transform spectroscopy is a measurement technique whereby spectra are collected based on measurements of the coherence of a radiative source, using time-domain or space-domain measurements of the radiation, electromagnetic or not. It can be applied to a variety of types of spectroscopy including optical spectroscopy, infrared spectroscopy (FTIR, FT-NIRS), nuclear magnetic resonance (NMR) and magnetic resonance spectroscopic imaging (MRSI), mass spectrometry and electron spin resonance spectroscopy. There are several methods for measuring the temporal coherence of the light (see: field-autocorrelation), including the continuous-wave and the pulsed Fourier-transform spectrometer or Fourier-transform spectrograph. The term "Fourier-transform spectroscopy" reflects the fact that in all these techniques, a Fourier transform is required to turn the raw data into the actual spectrum, and in many of the cases in optics involving interferometers, is based on the Wiener–Khinchin theor

Preparation and characterization of Poly(Ethylene Glycol)/gamma-CD Polyrotaxanes using beta-CD derivatives as a capping reagent

Blaise Tardy

As living systems understanding got better, as life could be modeled in a batch, using immortalized cells, researches in fundamental sciences found startling applications of advanced techniques on living systems. As the biomaterial field developed various molecules were found to have very interesting applications on living systems. Polyrotaxane is one of these particularly interesting molecules. It is a non covalently bonded molecular necklace produced by the threading of cyclic molecules onto a linear polymer in order to form a pseudopolyrotaxane, the capping of this pseudopolyrotaxane to avoid de-threading of the cyclic compounds forms a polyrotaxane. This compound has already proven its versatility through various application including drug delivery systems, DNA delivery agent, molecular machine, hydrogel building block, resin stabilizer and a lot more. Cyclodextrins (CDs) and Polyester are known to form a pseudopolyrotaxane. CDs are composed of 6 to 8 glucopyranose forming a toroid shaped molecule that can contain different molecules depending on the solvent, experimental conditions and the number of sugar subunits. In this project an attempt has been made to synthesize a special type of polyrotaxane that would allow the whole complex to bare a higher degree of freedom compared to the ones currently documented. In order to do so the widest CD has been used (Gamma-CD, GCD), the chosen host has been poly(ethylene glycol) (PEG) chains of varying molecular weight and the capping reagent used was beta-CD derivatives. Furthermore since current literature hasn't documented it so well and its properties are essential to this study, some more characterization of the PEG/GCD pseudopolyrotaxane has been made. The Macromolecules have been characterized by maldi tof mass spectroscopy(MALDI-T-MS), electro spray ionization (ESI) mass detection, X-ray diffraction(XRD), gel phase chromatography (GPC) and liquid Nuclear magnetic resonance (NMR). The beta CD and poly(ethylene glycol) derivatives have been characterized using Fourier transform infra red spectroscopy (FTIR), NMR, MALDI-Toff MS, ESI and thin layer Chromatography (TLC)

2009

Characterisation of Living Matter Using Advanced Spectroscopy Techniques

Markus Bonda

In the context of an ageing society neurodegenerative disease have become more and more frequent among humans. Opposing the benefits of a longer life, these diseases have thus triggered research on neurons and how they interact with each other. In vitro as well as in vivo experiments are comparably involved. Due to the complex mechanisms occurring at the neuronal level there is a need for developing suitable techniques. Such techniques are required to provide high resolution in several respects in order to track cellular properties: Fourier transform infrared spectroscopy (FTIR) along with high-brilliance synchrotron radiation matches the requirements of high spectral and spatial resolution for chemical distinction perfectly. We have investigated a rat model of Huntington's disease (HD) with synchrotron-assisted Fourier transform infrared microspectroscopy (SIRMS). Several neurodegenerative diseases, ranging from Alzheimer's to prion disease, have now been identified to be caused by proteins which auto-assemble into high molecular weight amyloid aggregates or fibrils. HD is related to abnormal polyglutamine (polyQ) repeats. Its symptoms are progressive deterioration of cognitive and motor functions, along with extensive loss of neurons. In our model, one brain hemisphere was infected with HD while keeping the second one as a control. The two types of matter in the striatum are affected in different manners: in neuron-rich gray matter exposed to the disease, a higher content of aggregated protein is detected, but no signs of cell death. In contrast, myelin-rich white matter did not show any aggregates, but surprisingly showed a significant increase in phosphorylation. We interpret this result as the activation of the cellular response to stress which leads in the end to cell death. The drastic changes in the white matter were detected in the case of multiple sclerosis. We have studied its animal model, the experimental autoimmune encephalomyelitis (EAE). EAE is characterized by heavy loss of the insulating lipid-layer, the myelin around axons. This has been clearly confirmed by SIRMS and FTIR. Analysis of spatially resolved maps by both unsupervised principal component analysis and chemical signatures showed additional features of EAE. Both studies indicate that SIRMS is a powerful tool of detecting complex chemical processes in biological tissue in a relatively easy way. In addition to nanometer spatial resolution, the photonic force microscope (PFM) provides microsecond temporal resolution. A PFM tracks the Brownian motion of micron-sized beads embedded in solutions. Thanks to the high resolutions, we can calculate velocity auto-correlation functions (vacf) of the beads that are extremely sensitive on the short-time scale. We found that they depend in solutions containing polymers on the mesh size. The narrower the polymer mesh size, the earlier perturbations occur in the bead's motion. Polymer solutions possess a very interesting feature which is their viscoelasticity. Based on the mean square displacements of the beads, the complex shear modulus is obtained describing in a frequency-dependent manner viscosity and elasticity. In this way we could distinguish different polymers and also a pathologically relevant fibril: α-synuclein involved in Parkinson's disease.

EPFL2011

Effect of Humic Substance Photoalteration on Lead Bioavailability to Freshwater Microalgae

Pascal Miéville, Julian Spierings

The present study provides results on the influence of humic substance (HS) photoalteration on lead availability to the freshwater microalga Chlorella kesslerii. The evolution of the free lead-ion concentrations measured by the ion exchange technique Pb and intracellular lead contents was explored in the presence of Suwannee River humic: (SRHA) and fulvic (SRFA) acids, as well as Aldrich humic acid (AHA) exposed at increasing radiance doses under a solar simulator. Modifications of HS characteristics highly relevant to Pb complexation and accumulation of HS to algal surfaces, including Fourier transform infrared spectroscopy, were followed. It was demonstrated that simulated sunlight exposure of HS increased Pb, in the medium for SRFA and SRHA, but had no effect for AHA. No clear relationship was observed between the changes in free lead-ion concentrations and intracellular content in alga for all studied HS, suggesting that HS photodegradation products also exhibit Pb complexation properties, and that direct interactions between HS and alga are affected. Indeed, photoalteration of humic substances reduced the adsorption of HS to the algal surface; the effect was more pronounced for SRFA and AHA and less significant for SRHA. The bioavailability results were consistent with the characterization of the phototransformation of humic substances: Pb speciation changes followed the modification of the relative abundance of the carboxylic groups and their molecular environment, while the reduced HS adsorption to the alga correlated with losses of the double bond abundance and aromaticity.

2011