Small-angle X-ray and nuclear-magnetic resonance study of siloxane-PMMA hybrids prepared by the sol-gel process

Transparent siloxane-polymethylmethacrylate (PMMA) hybrids were synthesized by the sol-gel process through hydrolysis of methacryloxyproyltrimethoxysilane (TMSM), tetramethoxysilane (TMOS) and polymerization of methylmethacrylate (MMA) using benzol peroxide (BPO) as catalyst. These composites have a good chemical stability due to the presence of covalent bonds between the inorganic (siloxane) and organic (PMMA) phases. The effects of siloxane content, pH of the initial sol and BPO content on the structure of the dried gels were analyzed by small-angle X-ray scattering (SAXS). SAXS results revealed the presence of an interference (or correlation) peak at medium q-range for all compositions, suggesting that siloxane groups located at the ends of PMMA chains form isolated clusters that are spatially correlated. The average intercluster distance - estimated from the q-value corresponding to the maximum in SAXS spectra - decreases for samples prepared with increasing amount of TMSM-TMOS. This effect was assigned to the expected increase in the number density of siloxane groups for progressively higher siloxane content. The increase of BPO content promotes a more efficient polymerization of MMA monomers but has no noticeable effect on the average intercluster distance. High pH favors polycondensation reactions between silicon species of both TMOS and TMSM silicon alcoxides, leading to a structure in which all siloxane clusters are bonded to PMMA chains. This effect was confirmed by Si-29 nuclear-magnetic resonance (NMR) measurements.

β-lactam antibiotics epitope mapping with STD NMR spectroscopy: A study of drug-human serum albumin interaction

Molecular recognition events are key issues in many biological processes. STD NMR (saturation transfer difference nuclear magnetic resonance spectroscopy) is one of the techniques used to understand such biological interactions. Herein, we have investigated the interactions of four β-lactam antibiotics belonging to two classes (cephalosporins and penicillins) with human serum albumin (HSA) by 1H STD NMR revealing that the interaction between the aromatic moiety and HSA is responsible for the binding efficiency. Thus, the structural differences from the five to six-membered thio ring in penicillins and cephalosporins do not seem to influence antibiotic-albumin interactions. © 2012 Sociedade Brasileira de Química.

Caracterização da contribuição da albumina para a formação do espectro de ressonância magnética nuclear (RMN) do plasma sanguíneo

The plasma represents a average of the information referring biochemists to the physiology of the organism as a whole, therefore it indirectly or directly interacts with all tissues of the body. In such a way the plasma can be considered as a metabolic “soup”. Using the Nuclear Magnetic Resonance Spectroscopy sanguineous plasma spectra had been generated and using deconvolution techniques it was possible to know the contribution of the albumin for the formation of the spectra of the sanguineous plasma

Classification of intact fresh plums according to sweetness using time-domain nuclear magnetic resonance and chemometrics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measuring the solubility product constant of paramagnetic cations using time-domain nuclear magnetic resonance relaxometry

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nuclear magnetic relaxation for the spin-degenerate Anderson model

A renormalization-group calculation of the temperature-dependent nuclear spin relaxation rate for a magnetic impurity in a metallic host is reported. The calculation follows a simplified procedure, which produces accurate rates in the low-temperature Fermi-liquid regime, although yielding only qualitatively reliable results at higher temperatures. In all cases considered, as the temperature T diminishes, the rates peak before decaying linearly to zero in the Fermi-liquid range. For T → 0, the results agree very well with Shiba's expression relating the low-temperature coefficient of the relaxation rate to the squared zero-temperature susceptibility. In the Kondo limit, the enhanced susceptibility associated with the Kondo resonance produces a very sharp peak in the relaxation rate near the Kondo temperature. © 1991.

Theoretical and Experimental Studies in Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) is a tool used to probe the physical and chemical environments of specific atoms in molecules. This research explored small molecule analogues to biological materials to determine NMR parameters using ab initio computations, comparing the results with solid-state NMR measurements. Models, such as dimethyl phosphate (DMP) for oligonucleotides or CuCl for the active site of the protein azurin, represented computationally unwieldy macromolecules. 31P chemical shielding tensors were calculated for DMP as a function of torsion angles, as well as for the phosphate salts, ammonium dihydrogen phosphate (ADHP), diammonium hydrogen phosphate, and magnesium dihydrogen phosphate. The computational DMP work indicated a problem with the current standard 31P reference of 85% H3PO4(aq.). Comparison of the calculations and experimental spectra for the phosphate salts indicated ADHP might be a preferable alternative as a solid state NMR reference for 31P. Experimental work included magic angle spinning experiments on powder samples using the UNL chemistry department’s Bruker Avance 600 MHz NMR to collect data to determine chemical shielding anisotropies. For the quadrupolar nuclei of copper and scandium, the electric field gradient was calculated in diatomic univalent metal halides, allowing determination of the minimal level of theory necessary to compute NMR parameters for these nuclei.

High-throughput non-destructive nuclear magnetic resonance method to measure intramuscular fat content in beef

High intake of saturated fat from meats has been associated with cardiovascular disease, cancer, diabetes, and others diseases. In this paper, we are introducing a simple, high-throughput, and non-destructive low-resolution nuclear magnetic resonance method that has the potential to analyze the intramuscular fat content (IMF) in more than 1,000 beef portions per hour. The results can be used in nutritional fact labels, replacing the currently used average value. The method is based on longitudinal (T(1)) and transverse (T(2)) relaxation time information obtained by a continuous wave-free precession (CWFP) sequence. CWFP yields a higher correlation coefficient (r=0.9) than the conventional Carr-Purcell-Meiboom- Gill (CPMG) method (r=-0.25) for IMF in beef and is just as fast and a simpler pulse sequence than CPMG. The method can also be applied to other meat products.

On the quantumness of correlations in nuclear magnetic resonance

Nuclear magnetic resonance (NMR) was successfully employed to test several protocols and ideas in quantum information science. In most of these implementations, the existence of entanglement was ruled out. This fact introduced concerns and questions about the quantum nature of such bench tests. In this paper, we address some issues related to the non-classical aspects of NMR systems. We discuss some experiments where the quantum aspects of this system are supported by quantum correlations of separable states. Such quantumness, beyond the entanglement-separability paradigm, is revealed via a departure between the quantum and the classical versions of information theory. In this scenario, the concept of quantum discord seems to play an important role. We also present an experimental implementation of an analogue of the single-photon Mach-Zehnder interferometer employing two nuclear spins to encode the interferometric paths. This experiment illustrates how non-classical correlations of separable states may be used to simulate quantum dynamics. The results obtained are completely equivalent to the optical scenario, where entanglement (between two field modes) may be present.

Valorisation of organic waste: new developments from proton nuclear magnetic resonance characterization

The last half-century has seen a continuing population and consumption growth, increasing the competition for land, water and energy. The solution can be found in the new sustainability theories, such as the industrial symbiosis and the zero waste objective. Reducing, reusing and recycling are challenges that the whole world have to consider. This is especially important for organic waste, whose reusing gives interesting results in terms of energy release. Before reusing, organic waste needs a deeper characterization. The non-destructive and non-invasive features of both Nuclear Magnetic Resonance (NMR) relaxometry and imaging (MRI) make them optimal candidates to reach such characterization. In this research, NMR techniques demonstrated to be innovative technologies, but an important work on the hardware and software of the NMR LAGIRN laboratory was initially done, creating new experimental procedures to analyse organic waste samples. The first results came from soil-organic matter interactions. Remediated soils properties were described in function of the organic carbon content, proving the importance of limiting the addition of further organic matter to not inhibit soil processes as nutrients transport. Moreover NMR relaxation times and the signal amplitude of a compost sample, over time, showed that the organic matter degradation of compost is a complex process that involves a number of degradation kinetics, as a function of the mix of waste. Local degradation processes were studied with enhanced quantitative relaxation technique that combines NMR and MRI. The development of this research has finally led to the study of waste before it becomes waste. Since a lot of food is lost when it is still edible, new NMR experiments studied the efficiency of conservation and valorisation processes: apple dehydration, meat preservation and bio-oils production. All these results proved the readiness of NMR for quality controls on a huge kind of organic residues and waste.

Noninvasive assessment of exercise-related intramyocellular acetylcarnitine in euglycemia and hyperglycemia in patients with type 1 diabetes using ¹H magnetic resonance spectroscopy: a randomized single-blind crossover study

Intramyocellular acetylcarnitine (IMAC) is involved in exercise-related fuel metabolism. It is not known whether levels of systemic glucose influence IMAC levels in type 1 diabetes.

Effect of Acute Psychological Stress on Prefrontal GABA Concentration Determined by Proton Magnetic Resonance Spectroscopy

Objective Impaired function of the central gamma-aminobutyric acid (GABA) system, which provides the brain’s major inhibitory pathways, is thought to play an important role in the pathophysiology of anxiety disorders. The effect of acute psychological stress on the human GABA-ergic system is still unknown, however. The purpose of this study was to determine the effect of acute stress on prefrontal GABA levels. Method A recently developed noninvasive magnetic resonance spectroscopy method was used to measure changes in the GABA concentration of the prefrontal cortex in 10 healthy human subjects during a threat-of-shock condition and during a safe condition (two sessions on different days). The main outcome measure was the mean GABA concentration within a 3×3×2-cm3 voxel selected from the medial prefrontal cortex. Results Prefrontal GABA decreased by approximately 18% in the threat-of-shock condition relative to the safe condition. This reduction was specific to GABA, since the concentrations of N-acetyl-aspartate, choline-containing compounds, and glutamate/glutamine levels obtained in the same spectra did not change significantly. Conclusions This result appeared compatible with evidence from preclinical studies in rodents, which showed rapid presynaptic down-regulation of GABA-ergic neurotransmission in response to acute psychological stress. The molecular mechanism and functional significance of this reduced inhibitory effect of acute psychological stress in relation to impaired GABA-ergic function in anxiety disorders merit further investigation.

Magnetization exchange observed in human skeletal muscle by non-water-suppressed proton magnetic resonance spectroscopy

Many metabolites in the proton magnetic resonance spectrum undergo magnetization exchange with water, such as those in the downfield region (6.0-8.5 ppm) and the upfield peaks of creatine, which can be measured to reveal additional information about the molecular environment. In addition, these resonances are attenuated by conventional water suppression techniques complicating detection and quantification. To characterize these metabolites in human skeletal muscle in vivo at 3 T, metabolite cycled non-water-suppressed spectroscopy was used to conduct a water inversion transfer experiment in both the soleus and tibialis anterior muscles. Resulting median exchange-independent T(1) times for the creatine methylene resonances were 1.26 and 1.15 s, and for the methyl resonances were 1.57 and 1.74 s, for soleus and tibialis anterior muscles, respectively. Magnetization transfer rates from water to the creatine methylene resonances were 0.56 and 0.28 s(-1) , and for the methyl resonances were 0.39 and 0.30 s(-1) , with the soleus exhibiting faster transfer rates for both resonances, allowing speculation about possible influences of either muscle fibre orientation or muscle composition on the magnetization transfer process. These water magnetization transfer rates observed without water suppression are in good agreement with earlier reports that used either postexcitation water suppression in rats, or short CHESS sequences in human brain and skeletal muscle.

Optimized quantitative magnetic resonance spectroscopy for clinical routine

Several practical obstacles in data handling and evaluation complicate the use of quantitative localized magnetic resonance spectroscopy (qMRS) in clinical routine MR examinations. To overcome these obstacles, a clinically feasible MR pulse sequence protocol based on standard available MR pulse sequences for qMRS has been implemented along with newly added functionalities to the free software package jMRUI-v5.0 to make qMRS attractive for clinical routine. This enables (a) easy and fast DICOM data transfer from the MR console and the qMRS-computer, (b) visualization of combined MR spectroscopy and imaging, (c) creation and network transfer of spectroscopy reports in DICOM format, (d) integration of advanced water reference models for absolute quantification, and (e) setup of databases containing normal metabolite concentrations of healthy subjects. To demonstrate the work-flow of qMRS using these implementations, databases for normal metabolite concentration in different regions of brain tissue were created using spectroscopic data acquired in 55 normal subjects (age range 6-61 years) using 1.5T and 3T MR systems, and illustrated in one clinical case of typical brain tumor (primitive neuroectodermal tumor). The MR pulse sequence protocol and newly implemented software functionalities facilitate the incorporation of qMRS and reference to normal value metabolite concentration data in daily clinical routine. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.