11 research outputs found
Recommended from our members
Process Applications of NMR
This thesis describes applications of NMR techniques to flowing liquid streams to
obtain quantitative information about the contents of the streams. The quantitative
accuracy of NMR spectroscopy for composition measurement of liquid mixtures is
measured as ±0.34 mol% and ±1 mol% for static and flowing mixtures respectively.
The effects of flow on NMR spectroscopy are analysed using the residence time
distributions of the streams in the magnet and the detection coil. Algorithms are
developed for automated analysis of the NMR spectra of the mixtures, in which
automatic phase and baseline correction are performed together. A peak-assignment
algorithm is written that identifies components in a mixture based on the patterns
observed in the pure-component spectra. Automated composition analysis of mixture
spectra is performed using these algorithms in less than 4 minutes with an accuracy of
±0.66 mol%. A mathematical model is derived for the NMR spectrum of a mixture
that considers the spectrum a weighted sum of pure-component spectra shifted in
frequency. The experimental lineshape observed in an inhomogeneous magnetic field
is poorly fitted by a Lorentzian lineshape, so a new model lineshape is developed
based on the distribution of resonance frequencies across the sample. Volume
selective NMR spectroscopy using the STEAM and PROJSAT pulse sequences is
optimised to give quantitative results from well-defined volumes with minimal signal
contamination. The STEAM pulse sequence is modified to include flow-compensated
slice selection gradients. The accuracy of the compositions measured from volume
selective spectra is measured as ±1 mol% and ±2 mol% for static and flowing
mixtures respectively. Pulsed field gradient NMR sequences using double echoes for
flow compensation are tested on flowing water, then used to determine the droplet
size distributions of flowing emulsions. Flow images are acquired of a vertical liquid
jets showing the narrowing and acceleration of the jet and the entrainment of the
surrounding water
Beyond the noise : high fidelity MR signal processing
This thesis describes a variety of methods developed to increase the sensitivity and resolution of liquid state nuclear magnetic resonance (NMR) experiments. NMR is known as one of the most versatile non-invasive analytical techniques yet often suffers from low sensitivity. The main contribution to this low sensitivity issue is a presence of noise and level of noise in the spectrum is expressed numerically as “signal-to-noise ratio”. NMR signal processing involves sensitivity and resolution enhancement achieved by noise reduction using mathematical algorithms. A singular value decomposition based reduced rank matrix method, composite property mapping, in particular is studied extensively in this thesis to present its advantages, limitations, and applications. In theory, when the sum of k noiseless sinusoidal decays is formatted into a specific matrix form (i.e., Toeplitz), the matrix is known to possess k linearly independent columns. This information becomes apparent only after a singular value decomposition of the matrix. Singular value decomposition factorises the large matrix into three smaller submatrices: right and left singular vector matrices, and one diagonal matrix containing singular values. Were k noiseless sinusoidal decays involved, there would be only k nonzero singular values appearing in the diagonal matrix in descending order providing the information of the amplitude of each sinusoidal decay. The number of non-zero singular values or the number of linearly independent columns is known as the rank of the matrix. With real NMR data none of the singular values equals zero and the matrix has full rank. The reduction of the rank of the matrix and thus the noise in the reconstructed NMR data can be achieved by replacing all the singular values except the first k values with zeroes. This noise reduction process becomes difficult when biomolecular NMR data is to be processed due to the number of resonances being unknown and the presence of a large solvent peak
The spatial coherence of thermal light sources
Imperial Users onl
Effet de la microstructure sur les propriétés excitoniques des polymères semi-conducteurs semi-cristallins
Les polymères semi-conducteurs semicristallins sont utilisés au sein de diodes
électroluminescentes, transistors ou dispositifs photovoltaïques organiques. Ces matériaux peuvent être traités à partir de solutions ou directement à partir de leur
état solide et forment des agrégats moléculaires dont la morphologie dicte en grande
partie leurs propriétés optoélectroniques. Le poly(3-hexylthiophène) est un des polymères semi-conducteurs les plus étudiés. Lorsque le poids moléculaire (Mw) des
chaînes est inférieur à 50 kg/mol, la microstructure est polycristalline et composée
de chaînes formant des empilements-π. Lorsque Mw>50 kg/mol, la morphologie est
semicristalline et composée de domaines cristallins imbriquées dans une matrice de
chaînes amorphes.
À partir de techniques de spectroscopie en continu et ultrarapide et appuyé
de modèles théoriques, nous démontrons que la cohérence spatiale des excitons
dans ce matériau est légèrement anisotrope et dépend de Mw. Ceci nous permet
d’approfondir la compréhension de la relation intime entre le couplage inter et
intramoléculaire sur la forme spectrale en absorption et photoluminescence. De plus,
nous démontrons que les excitations photogénérées directement aux interfaces entre
les domaines cristallins et les régions amorphes génèrent des paires de polarons liés
qui se recombinent par effet tunnel sur des échelles de temps supérieures à 10ns. Le
taux de photoluminescence à long temps de vie provenant de ces paires de charges
dépend aussi de Mw et varie entre ∼10% et ∼40% pour les faibles et hauts poids
moléculaires respectivement. Nous fournissons un modèle permettant d’expliquer
le processus de photogénération des paires de polarons et nous élucidons le rôle de
la microstructure sur la dynamique de séparation et recombinaison de ces espèces.Microstructure plays a crucial role in defining the optoelectrical properties of
conjugated polymeric semiconductors which can be used in light harvesting and
generating devices such as organic light emitting diodes, field effect transistors
or photovoltaic devices. These polymers can be processed from solution or solidstate
and form photophysical aggregates, consequently providing a complex network
which controls the fate of any photogenerated species. poly(3-hexylthiopene)
is one of the most studied polymeric semiconductor. In this material, the molecular
weight (Mw) of the polymer governs the microstructure and highly impact
the optical and electronic properties. Below Mw≈ 50 kg/mol, the polymer chains
forms polycrystalline domains of π-stacked molecules while high Mw (>50 kg/mol)
consists of a two-phase morphology of molecularly ordered crystallites that are embedded
in amorphous regions. Such morphology provides a bidimensionnal network
hosting both neutral excitations, known as Frenkel excitons, and polarons.
By means of steady-state and ultrafast spectroscopy experiment and backed up
theoretical modeling, we demonstrate that the spatial coherence of such excitations
are anisotropic in the lattice and depends on the Mw of the polymer, providing a
deep understanding of the interplay between interchain (excitonic) and intrachain
coupling in polymer aggregates. Moreover, we show that direct excitation at the
interface between molecularly ordered and amorphous regions generates tightlybound
charge pairs which decay via quantum tunneling over >10 ns. The yield
of delayed photoluminescence arising from the recombination of those charge pairs
varies between ∼10% and ∼40% for low and high Mw films respectively. We provide
a quantitative model that describes the photogeneration process of those geminate
polaron pairs and determine the role of the microstructure in the charge separation
and recombination processes
Two-dimensional spectroscopy of γ-aminobutyric acid on a clinical MRI scanner
Measurement of the cerebral metabolite y-aminobutyric acid (GABA) has been performed on
clinical MRI scanners using a variety of magnetic resonance spectroscopy (MRS)
techniques. MRS studies of GABA are difficult, especially at 1.5T due to low in-vivo
concentrations and overlapping of higher concentration metabolites. Unlike spectral editing
methods, two-dimensional (2D) MRS allows the simultaneous measurement of GABA and
other, more traditional metabolites. This work evaluates three implementations of 2D MRS
for both in-vitro and in-vivo GABA measurement on a clinical MRI scanner.Existing spectroscopy sequences were used to develop a protocol for performing 2D Jresolved MRS without a dedicated sequence. GABA was measured in-vitro at
concentrations approaching normal physiological levels and volunteer results allowed
assignment of the 3.01ppm GABA resonance at its J-coupling frequency (7.4Hz). However,
the prolonged scan time of over two hours prevented practical application of this approach.A far more efficient method of acquiring 2D J-resolved spectra is achieved with a dedicated
2D J-resolved sequence. An optimised set of acquisition parameters was produced to allow
GABA measurement with maximum SNR, and without macromolecule contamination, in 35
minutes. Since the reproducibility of the sequence must be sufficient to detect physiological
changes, a formal reproducibility study was performed acquiring three measures of
reproducibility at six concentrations of GABA, using a standard volume head coil, 3"- and
5"- surface coils. To our knowledge, this is the first such reproducibility study dedicated to
2D J-resolved GABA measurement, and as such, could have significant implications on the
interpretation of in-vivo results. In-vivo 2D J-resolved spectra were acquired and compared
well to the published results, allowing assignment of the 3.0Ippm GABA (plus
macromolecule) peak (J = 7.4Hz). In the first reported 2D J-resolved spectra specifically
designed to reduce the macromolecule contribution by optimising the echo time range,
assignment of the in-vivo 3.01 ppm GABA peak was less convincing.As an alternative to 2D J-resolved spectroscopy, preliminary testing of 2D correlation
spectroscopy (COSY) showed that it was not as sensitive or robust for either in-vitro or invivo GABA measurement. Although provisional assignment of the 3.01 ppm GABA peak
was made, in their current form, neither technique is suitable for pure GABA measurement
at 1.5T
Automated Analysis of Quantitative NMR Spectra
NMR spectroscopy is an invaluable tool for structure elucidation in chemistry and molecular biology, which is able to provide unique information not easily obtained by other analytical methods. However, performing quantitative NMR experiments and mixture analysis is considerably less common due to constraints in sensitivity/resolution and the fact that NMR observes individual nuclei, not molecules. The advances in instrument design in the last 25 years have substantially increased the sensitivity of NMR spectrometers, diminishing the main weakness of NMR, while increases in field strength and ever more intricate experiments have improved the resolving power and expanded the attainable information. The minimal need for sample preparation and its non-specific nature make quantitative NMR suitable for many applications ranging from quality control to metabolome characterization. Furthermore, the development of automated sample changers and fully automated acquisition have made high-throughput NMR acquisition a more feasible and attractive, yet expensive, possibility.
This work discusses the fundamental principles and limitations of quantitative liquid state NMR spectroscopy, and tries to put together a summary of its various aspects scattered across literature. Many of these more subtle features can be neglected in simple routine spectroscopy, but become important when extracting quantitative data and/or when trying to acquire and process vast amounts of spectra consistently.
The original research presented in this thesis provides improved methods for data acquisition of quantitative 13C detected NMR spectra in the form of modified INEPT based experiments (Q-INEPT-CT and Q-INEPT-2D), while software tools for automated processing and analysis of NMR spectra are also presented (ImatraNMR and SimpeleNMR). The application of these tools is demonstrated in the analysis of complex hydrocarbon mixtures (base oils), plant extracts and blood plasma samples.
The increased capability of NMR spectroscopy, the rising interest in metabolomics and for example the recent introduction of benchtop NMR spectrometers are likely to expand the future use of quantitative NMR in the analysis of complex mixtures. For this reason, the further development of robust, accurate and feasible analysis methods and tools is essential.NMR-spektroskopia on keskeinen mm. kemiassa ja molekyylibiologiassa käytetty analyysimenetelmä, joka perustuu atomiydinten havaitsemiseen voimakkaassa magneettikentässä radioaaltojen avulla. Menetelmä soveltuu erityisen hyvin molekyylirakenteiden selvittämiseen, ja sillä voidaan saada tietoa myös molekyylien kolmiulotteisesta rakenteesta sekä niiden välisistä interaktioista. NMR-spektroskopia on myös epäselektiivinen menetelmä, jolla on helppo tutkia erityyppisiä näytteitä ilman monimutkaista esikäsittelyä.
Perinteisesti NMR-spektroskopian heikkoutena on ollut spektrometrien kalleus ja huono herkkyys, joka on rajannut sen käyttöä laimeiden näytteiden ja etenkin seosten analysoinnissa. Laitteistojen ja analyysitekniikoiden parantuminen viimeisten 20-30 vuoden aikana on kuitenkin kohentanut tilannetta merkittävästi, ja NMR-spektroskopian käyttäminen seosten kvantitatiiviseen analyysiin on selvässä kasvussa. Etenkin metaboliittien analysoimisesta erilaisista biologisista näytteistä on muodostunut tärkeä sovellus. Tätä kehitystä on vauhdittanut myös näytteenkäsittelyn ja spektrien prosessoinnin automaation kehittyminen, joka helpottaa suurien näytemäärien tutkimista. Suurin osa NMR-spektrien käsittelyyn tarkoitetuista ohjelmistoista ei kuitenkaan vielä ole suunniteltu ensisijaisesti suurten näytesarjojen tai seosten analysointiin.
Tämä työ keskittyy kvantitatiiviseen NMR-spektroskopiaan ja sen sovelluksiin. Työssä kehitettiin kvantitatiivisia NMR-menetelmiä (pulssisarjat), sekä spektrien analyysiin soveltuvia ohjelmistotyökaluja (ImatraNMR ja SimpeleNMR), joiden tavoitteena on etenkin suurten näytesarjojen automaattisen analysoinnin helpottaminen. Kehitettyjä työkaluja käytettiin hiilivetyseosten (perusöljyt) ja kasviekstraktien analysointiin, mutta niitä voidaan soveltaa myös moniin muihin näytesarjoihin tai esimerkiksi reaktioseosten analysointiin
DEFINITION OF AN ADVANCED PROCESS FOR THE PRODUCTION OF LOW ENVIRONMENTAL IMPACT CONTAINERS AS POTENTIAL ALTERNATIVE TO PLASTICS
For decades, petroleum-based synthetic polymers, commonly known as plastics, have become one of the most appealing materials used for a wide variety of applications. Nevertheless, currently, conventional petroleum-based plastics represent a serious problem for global pollution because remain for hundreds of years in the environment when discarded. In order to reduce dependence on fossil resources, bioplastic materials are being proposed as safer and more sustainable alternatives. Bioplastics are bio-based and/or biodegradable materials, typically derived from renewable sources. Among different resources, food waste is attracting more and more attention in the research field of bioplastics’ production. The sources of food waste include household, commercial, industrial and agricultural residues. In fact, every year, around one-third of all food resources produced for human consumption are lost or wasted. Although European Union guidelines stated that food waste should preferentially be used as animal feed, in some cases, it became illegal because of disease control concerns and other times its nutritional value is very poor. On the other hand, the production of bioplastics from food waste is a renewable, sustainable process, in which materials are fabricated from carbon neutral resources, thus aligning itself with the principles of the circular bioeconomy. However, the conversion of fruit and vegetable by-products into eco-friendly materials with mechanical and hydrodynamic performances comparable to those of fuel-based plastics still remains a challenge. In this thesis, different approaches have been investigated for the valorization of fruit and vegetable wastes to produce low environmental impact materials, as a potential alternative to plastics with application in the field of food packaging. In the first section, apple waste and tomato peel by-products have been used as fillers to fabricate starch-based biocomposites. The mechanical characterization of the samples showed their suitability for covering purposes, since a ductile and soft behaviour was exhibited. In the second section, an avocado by-product extract has been incorporated to an ethyl cellulose matrix for the production of impregnated paper with enhanced durability. Since fruit wastes can contain potential pathogens and physical and chemical contaminants which can be released when used as additive for active packaging, a preliminary untargeted metabolomic characterization of the extract was conducted by LC-ESI(-)-Q Exactive-Orbitrap- MS/MS. The lipid components detected in the extract proved to be useful additives to improve paper hydrophobicity, preventing food browning and moisture loss. In general, the addition of all tested wastes (apple waste, tomato peel and avocado by-products) has proved to be useful to increase the biodegradability of the fabricated biomaterials. Hence, the environmental benefits associated with their recovery are proposed as a driving force to expand
their further use for these purposes. The upcycling of food waste through the production of value-added products is an ideal and practical end use, allowing to save huge economic and energy losses
Innovations in the Food System: Exploring the Future of Food
Innovations in Food Systems should be: Inclusive: ensuring economic and social inclusion for all food system actors, especially smallholders, women, and youth; Sustainable: minimizing negative environmental impacts, conserving scarce natural resources, and strengthening resiliency against future shocks; Efficient: producing adequate quantities of food for global needs while minimizing postharvest loss and consumer waste; Nutritious and healthy: enabling the consumption of a diverse range of healthy, nutritious, and safe foods. These are ambitious goals that will require multidisciplinary effort—from engineering to life sciences, biotechnology, medical sciences, social sciences, and economic sciences. New technologies and scientific discoveries are the solutions to the increasing demand for sufficient, safe, healthy, and sustainable foods influenced by the increased public awareness of their importance