Magnetic Resonance Spectroscopy LAB

MaRS-Lab is a research laboratory devoted to the development of innovative Magnetic Resonance techniques and their application to problems in chemistry, biochemistry, materials science, and environmental science. Within the laboratory there is expertise in both Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR) spectroscopies.EPR techniques give information on geometric and electronic structures and dynamics of paramagnetic molecules in solution and in the solid state, as well as on mechanism and kinetics of radical reactions. Research activities at MaRS-Lab are particularly focused on the investigation of structural properties of transition metal complexes and organic radicals. Moreover spin labeling and spin trapping EPR techniques are applied for the study of biochemical and biophysical issues such as membrane fluidity, oxidative stress, and antioxidant properties.NMR spectroscopy is a powerful research and problem-solving tool for the physico-chemical characterization of a wide range of materials from small molecules to polymers, including inorganic, organic and composite materials, and can be applied to liquid and crystalline/amorphous solids, as well as soft materials. This technique provides detailed information on composition, chemical structure, morphology, dynamics and reaction kinetics and mechanisms; accessible spatial and time scales for structural and dynamic information are 0.1-100 nm and 10-12 to 1 s, respectively.The research activities of the MaRS-Lab encompass NMR spectroscopy studies of organic and/or inorganic materials of interest for technological or biomedical applications or in relation to environmental issues. In all cases the full breadth of the state-of-the-art solid state NMR techniques and a variety of available or purposely developed models and methodologies for data analysis are employed to tackle the issues peculiar to the different types of systems examined.

Research topics

  • Organometallic complexes.
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    X-band EPR and multi-nuclear NMR techniques are applied, both in solution and in the solid state, to determine structural and electronic properties of organometallic complexes.
  • Radicals and radical reactions.
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    X-band EPR spectroscopy is applied to investigate the structural and electronic properties of radicals, as well as the mechanism and kinetics of radical reactions. In particular, we are interested in free radicals generated in oxidative processes and on their fate in the presence of antioxidants from plant extracts. Moreover, EPR spectroscopy is applied to investigate radical polymerization reactions employed for polymer post-reactor functionalization.
  • Liquid crystals and membranes.
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    We apply multi-nuclear MR techniques to determine orientational order parameters in thermotropic liquid crystals, also as a function of temperature and phase structure. The most investigated nuclei are 2H (requiring labelled molecules) and natural abundance 13C, but less common nuclei such as 19F and 11B are also exploited. Dynamic properties of liquid crystals are investigated by analyzing spin-lattice relaxation times as a function of temperature and/or Larmor frequency. At high frequency 2H and/or 13C relaxation times are used to obtain kinetic parameters for internal and overall motions. On the other hand, 1H and, in the case of fluorinated mesogens, 19F relaxation dispersions are acquired at low frequency (0.01 to 40 MHz for 1H) using the Fast-Field-Cycling (FFC) technique to characterize collective and overall motions.31P, 2H, and 13C solid state NMR techniques and spin probing EPR techniques are applied to investigate lipid packing and dynamics in biological and phospholipid model membranes in relation to membrane composition, temperature and interaction with drug molecules.
  • Polymeric materials.
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    Up-to-date solid state NMR methods are applied to novel functional and smart polymeric materials to elucidate their main structural and dynamic features and get insight into their relationships with macroscopic properties, with the aim of optimizing their formulation in view of a better performance. For instance, several selective and non-selective high resolution 13C techniques are employed for obtaining site-specific structural and dynamic information on polymeric systems. On the other hand, low resolution 1H measurements, comprising Free Induction Decay and longitudinal relaxation time analyses, are applied to obtain global dynamic information. The acquisition of relaxation data over a wide frequency and/or temperature range, combined with the use of suitable data analysis tools and motional models, allow motions with different time regimes to be singled out and quantitatively characterized. Finally, phase separation, domain sizes and interfacial effects in polymer blends, block copolymers and composites, are investigated using techniques based on spin diffusion mediated by the dipolar interaction among the protons.
  • Materials for biomedical applications.
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    Two main classes of materials for applications in biomedicine are investigated at MaRS-Lab by means of NMR techniques: hydrogels for tissue engineering and drug delivery, and contrast agents for MRI. In the first case, solid state and solution state 1H and 13C NMR experiments are combined to get insights into the structure and dynamics of the polymeric matrix and the self-assembly mechanism of polymers in water, as well as into the state of water in hydrogels and water-polymer interactions. Both chemical and physical hydrogels are studied. In the second case, the effect of paramagnetic or super-paramagnetic systems on water proton longitudinal and transverse relaxation properties is investigated over a broad range of Larmor frequencies, using both fixed-field and FFC spectrometers, in order to explore their applicability as contrast agents for MRI. We are especially interested in understanding the mechanism of water proton relaxation enhancement in view of a guided design of contrast agents.
  • Soil organic matter and biochar.
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    Among the different techniques used to study soil organic matter (SOM) composition, solid-state NMR, and in particular the cross-polarization magic-angle spinning 13C technique, offers the major advantage of obtaining structural information in bulk soils or solid fractions without the necessity of extracting the organic material. At MaRS-Lab solid state13C NMR techniques are applied to obtain details on the distribution of molecular functional groups in SOM with the aim of studying the influence of land use and land management on the carbon stabilization in soils.
    Solid state13C NMR techniques are applied for understanding the transformation processes that take place in the carbonization of biomass to obtain biochar, a carbon-rich solid material which finds many applications in agriculture and in the chemical industry. The determination ofbiochar characteristics in dependence ofprocess parameters (feedstock composition, temperature and heating rate) will ultimately allow carbonization conditions to be optimized in view of the end-use of char. Moreover, 1H FFC relaxometry is applied to aqueous slurries of biochar to obtain information on biochar-water interactions which are fundamental for many applications.

Instruments

  • NMR Bruker AMX300-WB spectrometer (1H Larmor frequency of 300 MHz) equipped with probes for both liquid (from 109Ag to 31P, 1H) and solid state (from 2H to 31P, 1H, CPMAS 4mm probe; maximum spinning rate 15 kHz) experiments, working in the temperature range between -60 °C and 100 °C.
  • Stelar Spinmaster FFC-2000 Fast Field-Cycling NMR relaxometer working at variable 1H Larmor frequency (from 0.01 to 42.6 MHz) in the temperature range between -140 °C and 140 °C.
  • Varian E112 X-band EPR spectrometer equipped withCW and pulsed ENDOR and LOMENDOR accessories; E257 variable temperature controller; ITC4 Oxford Intelligent temperature controller; Oxford helium cryostat; Field-frequency lock; Bruker Gaussmeter and frequency meter; EIN 3200L RF power amplifier (250 kHz to 120 MHz, 200W); KALMUS RF power amplifier (100 kHz to 220 MHz,1kW).