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Figure: IR-dosy spectra of a mixture of acetone and dialanine, showing which IR peak belongs to which compound
Researchers at the University of Amsterdam have developed a new infrared spectroscopy method that can simultaneously characterize the structure and size of
molecules.
This method, known as infrared diffusion ordered spectroscopy (IR-dosy), works well to separate molecules of different sizes into different infrared peaks
.
In a paper just published in Applied Chemistry in the United States, researchers foresee analytical applications
in different fields such as proteins, polymers, pharmaceuticals and biomedicine.
They are currently developing a first version of a practical chemical probe that realizes the concept
of infrared multi-dose analysis.
Infrared spectroscopy is an important means of
analyzing compounds.
It helps to identify molecules
based on their functional groups and spatial conformation.
In general, the infrared spectrum is an insensitive size of molecules
.
Inspired by the already existing methods in NMR spectroscopy, researchers in Amsterdam now apply the principle of diffusion ordered spectroscopy to infrared spectroscopy
.
Here, the molecules present in the sample are separated
according to their diffusion behavior prior to spectral analysis.
IR-DOSY relies on the fact that the diffusion of molecules is determined entirely by their size – a concept originally proposed
by Albert Einstein in his classic 1905 paper on the motion of microscopic particles in Brown.
IR-DOSY spectrometers use a simple yet efficient flow method to transport mixtures and pure solvents to the sample chamber, creating a spatial non-uniform distribution of
solute molecules.
After stopping the flow, the solute molecules begin to diffuse into the pure solvent region, and their diffusion rate depends on their diffusion coefficient
.
Infrared absorption is measured at the location of only the solvent initially in the
chamber.
Over time, diffused solute molecules begin to appear in the
infrared spectrum.
In this way, the infrared spectra
of all types of molecules are recorded at different time points, depending on the size of the molecules.
Thus, IR-dosy produces a two-dimensional spectrum with an infrared frequency along one axis and a diffusion constant (or equivalent size) along the other
.
In their Angewandte paper, the researchers argue that although IR-DOSY has a lower resolving power than typical chromatographic methods, it has the advantage of not requiring prior knowledge of the chemical structure
of the compounds present in the sample.
Species in the sample solution can be actively separated by adding an electrophoresis device, and even the separation force
can be improved.
The applications presented in this paper are the analysis of
protein aggregates and fibrils.
Here, IR-DOSY can simultaneously study monomers, oligomers and fibers, which typically coexist in the
sample.
Polymers and plastic nanoparticles constitute another interesting area of research, as samples often contain many different molecules
of different sizes.
The size selectivity and structural sensitivity of IR-DOSY also make it useful
in the pharmaceutical and biomedical fields.
For example, it has the potential to detect trace amounts of small molecules
in pharmaceutical products.
For example, in the biomedical field, it can be used to detect and structurally characterize low molecular weight species
in human serum.
In all cases, IR-DOSY analysis provides valuable information about the size or distribution of molecules or molecular aggregates in the sample
.
The IR-DOSY method was jointly developed
by the university's Institute of Physics and Van 't Hoff Institute for Molecular Sciences.
In the latter, Prof.
Sander Woutersen and Dr Giulia Giubertoni collaborated with Dr.
Saer Samanipour to further develop the method as a cost-effective device that could be used
as an analytical or diagnostic tool in any laboratory by researchers from different disciplines.
For this, they were recently awarded a €160,000 "Demonstration Grant"
by the Dutch Research Council NWO.
The development of the detector is a joint effort
in collaboration with the university's Technology Center, the Technology Transfer Office IXA and the Demonstration Lab Science Park.
