Lynn F. Gladden

Tuning the acid/base properties of nanocarbons by functionalization via amination

The surface chemical properties and the electronic properties of vapor grown carbon nanofibers (VGCNFs) have been modified by treatment of the oxidized CNFs with NH(3). The effect of treatment temperature on the types of nitrogen functionalities introduced was evaluated by synchrotron based X-ray photoelectron spectroscopy (XPS), while the impact of the preparation methods on the surface acid-base properties was investigated by potentiometric titration, microcalorimetry, and zeta potential measurements. The impact of the N-functionalization on the electronic properties was measured by THz-Time Domain spectroscopy. The samples functionalized via amination are characterized by the coexistence of acidic and basic O and N sites. The population of O and N species is temperature dependent. In particular, at 873 K nitrogen is stabilized in substitutional positions within the graphitic structure, as heterocyclic-like moieties. The surface presents heterogeneously distributed and energetically different basic sites. A small amount of strong basic sites gives rise to a differential heat of CO(2) adsorption of 150 kJ mol(-1). However, when functionalization is carried out at 473 K, nitrogen moieties with basic character are introduced and the maximum heat of adsorption is significantly lower, at approximately 90 kJ mol(-1). In the latter sample, energetically different basic sites coexist with acidic oxygen groups introduced during the oxidative step. Under these conditions, a bifunctional acidic and basic surface is obtained with high hydrophilic character. N-functionalization carried out at higher temperature changes the electronic properties of the CNFs as evaluated by THz-TDS. The functionalization procedure presented in this work allows high versatility and flexibility in tailoring the surface chemistry of nanocarbon material to specific needs. This work shows the potential of the N-containing nanocarbon materials obtained via amination in catalysis as well as electronic device materials.

Fast Multidimensional NMR Spectroscopy Using Compressed Sensing

Multidimensional NMR spectroscopic techniques form part of the standard tool kit for the structure determination of macromolecules and, increasingly, solid-state materials, such as catalysts. Advances in NMR spectroscopy have extended its applicability to large biomolecules, including protein complexes 8] and membrane proteins. 9, 10] NMR spectroscopy is also a key tool in structural-genomics projects. Such NMR spectroscopic studies rely on 3D or even higher-dimensional techniques. Limiting for all these studies are the large demands on time for the realization of sufficient experimental sensitivity and resolution. For an n-dimensional experiment processed using discrete Fourier transform (DFT), data points on an (n 1)-dimensional grid must be sampled, which leads to prohibitively long experiment times. Consequently, many systems remain beyond the reach of NMR spectroscopy, including, for example, the important family of mammalian G-protein-coupled receptors (GPCRs). There is a pressing need to develop new techniques to enable more efficient data acquisition and processing. Herein we describe the use of compressed sensing (CS) 13] as an alternative reconstruction technique for multidimensional NMR spectroscopy. In an initial step, representative of a situation in which the signal-to-noise (S/N) ratio is high, we quantify the accuracy of the technique when applied to multidimensional NMR spectroscopy with 2D [H,N]-HSQC data recorded for the model protein ubiquitin. Subsequently, we demonstrate the performance of the technique on nonuniformly sampled (NUS) 3D HNCA and HN(CO)CA data sets of pSRII, a large transmembrane protein, for which high resolution is required but, owing to slow molecular tumbling, the S/N ratio is low. However, the generality of the CS method means it could also be applied to other undersampled multidimensional experiments used, for example, in solid-state NMR spectroscopy, 14] fast metabolomics studies, and chemical-shift imaging. For decaying data, sparse or nonuniform sampling ensures that the majority of the experiment time is used to sample the signal at low evolution times at which the S/N ratio is highest, to maximize sensitivity, while increasingly sparse sampling at long evolution times, at which the S/N ratio is low, ensures that high resolution is obtained. 18] A number of methods have been proposed for the reconstruction of spectra from NUS data. 17–21] Perhaps the most established is maximum entropy (ME) reconstruction. Other methods of speeding up multidimensional NMR spectroscopy are available. However, many of these advanced methods assume a high S/N ratio or require specialist equipment, which limits their applicability. ME has recently been used to reconstruct multidimensional spectra of large proteins, such as the T-TE fragment of EntF and pSRII. We show that CS reconstruction compares favorably with ME. CS 13] is rapidly gaining acceptance in imaging applications 29–31] and has also been proposed as a tool for the reconstruction of undersampled, multidimensional NMR spectra; however, to our knowledge, the results presented herein are the first demonstration of the application of CS to the reconstruction of real 3D NMR spectra. The application of CS requires 1) sparse representation of the desired signal in a particular basis and 2) incoherent sampling with respect to that basis. Importantly, an initial estimation of the signal location is not required. Many NMR spectra are ideally suited to CS reconstruction, as they consist of relatively few isolated peaks in the Fourier basis, and therefore are inherently sparse. Furthermore, measurements are performed in the time domain, which has been shown to be optimally incoherent with respect to the Fourier basis. A large reduction in experiment time is possible through the use of CS. By the application of an exponentially weighted sampling scheme, CS reconstruction of a 2D [H,N]-HSQC spectrum of ubiquitin was performed with only 30 % of the total 128 complex data pairs recorded in the N dimension for DFT processing. This approach reduced the experiment time from 165 min to 50 min (number of scans, ns = 32; see Methods in the Supporting Information). The spectra in Figure 1 resulting from reconstruction by the two methods are almost identical, with all peaks clearly resolved (for the full amide region, see Figure S1 in the Supporting Information). Close-up views of several regions of the spectra (see Figure S1) show that all contour levels for the CS reconstruction lie almost exactly on top of the contour levels for the fully sampled spectrum. Thus, the peak positions as well as the shape and intensity of the peaks are accurately recovered by the use of CS. To quantify the accuracy of the reconstruction, we calculated the root-mean-squared (RMS) error for the peak positions to be 0.02 ppm and that for the intensities of these peaks to be 3% (see Figure S1). Furthermore, to demonstrate [*] M. J. Bostock, Dr. D. Nietlispach Department of Biochemistry, University of Cambridge 80 Tennis Court Road, Cambridge, CB2 1GA (UK) E-mail: dn206@cam.ac.uk

Structure-flow correlations in packed beds

Magnetic resonance imaging (MRI) volume- and velocity-measurement techniques are used to probe structure-flow correlations within the interparticle space of a packed bed of ballotini. Visualisation of the z-component of the flow velocity within six slices perpendicular to the symmetry axis of the bed permit the flow to be monitored throughout the bed. Significant heterogeneity in the flow is observed; in one slice it is found that approximately 8% of the pores carry 40% of the volume flow. High volume flow through any given pore is seen to be influenced most strongly by the local geometry of the pore space; i.e. the radial position of the pore within the bed, the radius of the pore and the relative amount of interfacial surface area adjoining neighbouring pores. In contrast, the topology of the bed plays a crucial role in determining the mean flow velocity through a given pore. Correlations are found between the flow velocity within a pore and both the local Reynolds number and coordination number associated with that pore. These results are discussed with reference to a simple pore network model.

In-vitro tomography and non-destructive imaging at depth of pharmaceutical solid dosage forms

Tomographic imaging techniques offer new prospects for a better understanding of the quality, performance and release mechanisms of pharmaceutical solid dosage forms. It is only over the last fifteen years that tomography has been applied for the in-vitro characterisation of dosage forms. This review aims to introduce the concept of tomography in a pharmaceutical context, and describes the current state-of-the-art of the four most promising techniques: X-ray computed microtomography, magnetic resonance imaging, terahertz imaging and optical coherence tomography. The basic working principles of the techniques are introduced and the current pharmaceutical applications of the technologies are discussed, together with a comparison of their specific strengths and weaknesses. Possible future developments in these fields are also discussed.

Nuclear magnetic resonance in chemical engineering : principles and applications

In recent years chemical engineers have shown an increasing interest in non-invasive measurement techniques; Nuclear Magnetic Resonance (NMR) is perhaps the ultimate technique of this kind. Over the past 10 years notable developments have been made in both spectrometer hadrdware our ability to understand and manipulate nuclear spin interactions, and it is now possible to address research areas in catalysis, materials science, mass transfer and flow visualisation which are of real interest to chemical engineers. This review is divided into two sections. Part I identifies three broad categories of magnetic resonance measurements: spectroscopy, diffusion measurement and imaging, and outlines the basic principles underlying these experiments. A summary of the various nuclear spin interactions and the chemical information they yield is given. In progressing to the introduction of diffusion measurements, the application of magnetic gradients is discussed and the basic Pulsed Gradient Spin Echo (PGSE) and related measurement techniques are presented. The principles of NMR imaging are then described in the context of the two popular experimental schemes: projection—reconstruction and spin-warp imaging. The principles and application of parameter-selective imaging experiments are outlined and limitations on attainable resolution are noted. Extension of NMR imaging to the study of flow phenomena is also discussed. Part II of the review reports a number of examples of NMR methods applied to problems of direct relevance to chemical engineers. This literature survey starts with an overview of applications of NMR spectroscopy in the fields of catalysis, adsorption, measurement of phase equilibria and the consideration of NMR as a quality control technique. The use of PGSE methods to study diffusion phenomena is discussed, with particular emphasis being placed on how theoretical models in combination with NMR experiments are being used to gain insight into transport processes occurring within porous media. Recent developments in NMR imaging and their application to the study of ceramics processing, polymers, porous media, catalysis, food processing, filtration processes, and transport within reactors and packed columns are also presented. Finally, the state-of-the-art in NMR flow imaging studies is discussed and the ability of NMR to study two-phase flow phenomena is highlighted.

Molecular motion and ion diffusion in choline chloride based deep eutectic solvents studied by 1H pulsed field gradient NMR spectroscopy.

Deep Eutectic Solvents (DESs) are a novel class of solvents with potential industrial applications in separation processes, chemical reactions, metal recovery and metal finishing processes such as electrodeposition and electropolishing. Macroscopic physical properties such as viscosity, conductivity, eutectic composition and surface tension are already available for several DESs, but the microscopic transport properties for this class of compounds are not well understood and the literature lacks experimental data that could give a better insight into the understanding of such properties. This paper presents the first pulsed field gradient nuclear magnetic resonance (PFG-NMR) study of DESs. Several choline chloride based DESs were chosen as experimental samples, each of them with a different associated hydrogen bond donor. The molecular equilibrium self-diffusion coefficient of both the choline cation and hydrogen bond donor was probed using a standard stimulated echo PFG-NMR pulse sequence. It is shown that the increasing temperature leads to a weaker interaction between the choline cation and the correspondent hydrogen bond donor. The self-diffusion coefficients of the samples obey an Arrhenius law temperature-dependence, with values of self-diffusivity in the range of [10(-10)-10(-13) m(2) s(-1)]. In addition, the results also highlight that the molecular structure of the hydrogen bond donor can greatly affect the mobility of the whole system. While for ethaline, glyceline and reline the choline cation diffuses slower than the associated hydrogen bond donor, reflecting the trend of molecular size and molecular weight, the opposite behaviour is observed for maline, in which the hydrogen bond donor, i.e. malonic acid, diffuses slower than the choline cation, with self-diffusion coefficients values of the order of 10(-13) m(2) s(-1) at room temperature, which are remarkably low values for a liquid. This is believed to be due to the formation of extensive dimer chains between malonic acid molecules, which restricts the mobility of the whole system at low temperature (<30 °C), with malonic acid and choline chloride having almost identical diffusivity values. Diffusion and viscosity data were combined together to gain insights into the diffusion mechanism, which was found to be the same as for ionic liquids with discrete anions.

Magnetic resonance imaging of liquid flow and pore structure within packed beds

Magnetic resonance imaging (MRI) volume- and velocity-measurement techniques are used to probe structure-flow correlations within the interparticle space of a packed bed of ballotini. Images of the three mutually orthogonal components of the velocity field are obtained in two perpendicular slices within a bed of 5 mm diameter ballotini packed within a glass column of internal diameter 4.6 cm. Comparison of flow images obtained for two beds of identical column-to-particle diameter ratio but of differing length show that velocity enhancements at the walls of the bed are greater in the shorter, more ordered, bed. A three-dimensional volume image of each bed is also obtained and analysed to partition the interparticle space into individual pores and determine the location of pore necks. Correlations between volume flow rate and the surface area of the constrictions (pore necks) within the interparticle space lie between two limiting behaviours. For pores associated with low local Reynolds number, the volume flow rate through the constrictions scales as the square of the cross-sectional area of the constriction, whereas at the extreme of high local Reynolds number pores show volume flow rates scaling with cross-sectional area.

Three-dimensional morphology of iron oxide nanoparticles with reactive concave surfaces. A compressed sensing-electron tomography (CS-ET) approach.

In this paper, we apply electron tomography (ET) to the study of the three-dimensional (3D) morphology of iron oxide nanoparticles (NPs) with reactive concave surfaces. The ability to determine quantitatively the volume and shape of the NP concavity is essential for understanding the key-lock mechanism responsible for the destabilization of gold nanocrystals within the iron oxide NP concavity. We show that quantitative ET is enhanced greatly by the application of compressed sensing (CS) techniques to the tomographic reconstruction. High-fidelity tomograms using a new CS-ET algorithm reveal with clarity the concavities of the particle and enable 3D nanometrology studies to be undertaken with confidence. In addition, the robust performance of the CS-ET algorithm with undersampled data should allow rapid progress with time-resolved 3D nanoscale studies, 3D atomic resolution imaging, and cryo-tomography of nanoscale cellular structures.

Low-Field Permanent Magnets for Industrial Process and Quality Control

In this review we focus on the technology associated with low-field NMR. We present the current state-of-the-art in low-field NMR hardware and experiments, considering general magnet designs, rf performance, data processing and interpretation. We provide guidance on obtaining the optimum results from these instruments, along with an introduction for those new to low-field NMR. The applications of lowfield NMR are now many and diverse. Furthermore, niche applications have spawned unique magnet designs to accommodate the extremes of operating environment or sample geometry. Trying to capture all the applications, methods, and hardware encompassed by low-field NMR would be a daunting task and likely of little interest to researchers or industrialists working in specific subject areas. Instead we discuss only a few applications to highlight uses of the hardware and experiments in an industrial environment. For details on more particular methods and applications, we provide citations to specialized review articles.

Magnetic resonance imaging as a quantitative probe of gas-liquid distribution and wetting efficiency in trickle-bed reactors

Abstract The potential of magnetic resonance imaging (MRI) measurements to investigate gas and liquid distributions within a fixed-bed reactor operating in co-current downflow in the trickle-flow regime is demonstrated. Liquid holdup and wetting efficiency are studied for a range of gas (66– 356 mm / s ) and liquid (0.5– 5.8 mm / s ) superficial velocities. Two-dimensional and three-dimensional (3-D) magnetic resonance images have been acquired for flow within a packing of 5 mm diameter glass ballotini contained in a cylindrical column of internal diameter 40 mm . The images are of sufficiently high resolution to be able to characterise liquid rivulets within the bed and to detect the presence of thin water films on the surfaces of the packing elements. As expected, liquid holdup and wetting efficiency increase with increase in liquid flow rate, at a fixed gas flow rate. A transition in the holdup and wetting characteristics is observed at a liquid superficial velocity of 1.5– 2 mm / s . The number of liquid rivulets increased rapidly as the liquid superficial velocity was increased from 0.5 to 2.0 mm / s and then reached a plateau; the increase in liquid flow as the liquid flow rate was further increased was taken up in the increasing size of existing rivulets. Differences in the nature of the liquid distribution within the bed are also reported for different conditions of prewetting of the packing. Gas flow rate affected the onset of flow instabilities but not the liquid distribution. 3-D MRI data enabled the visualisation of the extent of liquid filling of individual ‘pores’ within the inter-particle space as a function of liquid flow rate, and how this depended on the ‘pore’ size. For each packing element, the fraction of the surface area that was wetted was found to correlate with the number of contact points that packing element made to other packing elements within the bed.