Synthesis of Organosilicon Ligands for Europium (III) and Gadolinium (III) as Potential Imaging Agents

The relaxivity of MRI contrast agents can be increased by increasing the size of the contrast agent and by increasing concentration of the bound gadolinium. Large multi-site ligands able to coordinate several metal centres show increased relaxivity as a result. In this paper, an “aza-type Michael” reaction is used to prepare cyclen derivatives that can be attached to organosilicon frameworks via hydrosilylation reactions. A range of organosilicon frameworks were tested including silsesquioxane cages and dimethylsilylbenzene derivatives. Michael donors with strong electron withdrawing groups could be used to alkylate cyclen on three amine centres in a single step. Hydrosilylation successfully attached these to mono-, di-, and tri-dimethylsilyl-substituted benzene derivatives. The europium and gadolinium complexes were formed and studied using luminescence spectroscopy and relaxometry. This showed the complexes to contain two bound water moles per lanthanide centre and T1 relaxation time measurements demonstrated an increase in relaxivity had been achieved, in particular for the trisubstituted scaffold 1,3,5-tris((pentane-sDO3A)dimethylsilyl)benzene-Gd3. This showed a marked increase in the relaxivity (13.1 r1p/mM−1s−1)

Enhancement of learning for engineering students through constructivist methods

In student feedback, many students expressed difficulty with the concepts being taught. There was a difficulty with quick, in-class retrieval of information. To facilitate transfer, understanding and retention of knowledge there needs to be prior knowledge in the long-term memory. In the case of complex engineering problems, the performance outputs are a function of many input variables. Airfoil design is a good example—the engineer needs to understand the dependence of performance parameters on the input conditions along with the physical phenomena. Visual representation is a powerful means of depicting cause and effect relationships. It can be reasoned by adding relational, interpretive visuals to a lesson, a higher level of learning will occur. In the proposed interactive program the student is given control of input variables and can see the influence these have on the primary aerodynamic concepts. It creates realistic configurations from complex theoretical calculations, facilitating the storage of information in the long-term memory. This when complemented with traditional teaching methods, allows the student to develop conceptual understanding. The programme was used in second year undergraduate engineering teaching and over a three-year period was monitored and improved. Students’ performance was used to assess the effectiveness of the learning technique, as was student module feedback. The average class size for courses investigated was 26 students. The students performed better using this approach. It generated a motivation for further enquiry in the students and created an enthusiasm for student–student and student–lecturer interaction. This agrees with the constructivist theories and how social psychology affects learnin

Paleo-Pole Positions from Martian Magnetic Anomaly Data

Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor s magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed four North and 3 South poles with two at approximately 60 degrees north latitude. These results suggest that during the existence of the Martian main magnetic field it experienced several reversals

Application of the Lagrangian meshfree approach to modelling of batch crystallisation: Part I-modelling of stirred tank hydrodynamics

Crystallization phenomena in stirred reactors are influenced by local hydrodynamic conditions and these must be taken into account for successful process scale-up and optimization. This article is the first of two presenting the application of the Smoothed Particle Hydrodynamics (SPH) method to modelling of batch crystallisation in stirred tanks. The benefits of the Lagrangian meshfree methods were discussed and the SPH method was proposed as an efficient method for the rapid prediction of the global mean flow in stirred reactors. Various aspects of the simulation results were discussed such as quality of the fluid prediction, computational requirements and availability of the crystal size distribution without reconstruction. It has been shown that the computational requirements and accuracy of the fluid flow prediction can be controlled through the particle size and that the particles with a radius of 1.50-1.75 mm in the reactor of 2.65 I provide a good balance between the quality of the prediction and the computational requirements.The developed Smoothed Particle Hydrodynamics model was applied to a numerical solution of coupled computational fluid dynamics and discretised population balance equations to model a batch crystallization process. Due to the specific formulation of the SPH equations the resulting ODE system is solved using the weighted contributions rather than numerically by solving a linear system of equations. Therefore, a large number of additional transport equations resulting from the discretisation of the population balance leads to only a minor increase in computational requirements (around 60% for 200 equations). The non-idealities in the reactor result in non-uniform mixing and contribute to the dispersion of the CSD. The effect of the hydrodynamics on the local temperature/supersaturation and the resulting crystal size distribution was captured and compared to the ideal mixing case.The developed SPH method served as a basis for the Part II of the series where a methodology for solution of population balance equations using high-resolution finite volume schemes or method of characteristics computed in parallel and independently from the Navier-Stokes equations is presented. (C) 2015 Elsevier Ltd. All rights reserved

The effects of particle shape, orientation, and reynolds number on particle-wall collisions

Crystallisation is an important unit operation used in the production of Active Pharmaceutical Ingredients (APIs). Crystallisation is typically carried out using seed crystals in a process called secondary nucleation that allows for greater control of crystal quality attributes. The mechanism of secondary nucleation is still not well understood. Particle attrition is one proposed mechanism. This work examines the conditions under which particle-wall collisions occur. This is done through the simulation of free-moving particles in an impinging jet flow using an immersed-boundary lattice Boltzmann method (IB-LBM) CFD solver. Particle Reynolds numbers from 100 to 400 are examined. Particle shapes with aspect ratios from 1:1 to 8:1 are used to represent the crystal habits of APIs. Particles that start in their low-drag or high-drag orientation maintain this orientation on approach to the target surface. All other intermediate initial orientations examined cause particles to rotate toward and overshoot their high-drag form before adopting their high-drag form in proximity to the target surface. Particles in their low-drag form remain in their initial orientation due to the symmetry of the computational domain. In this orientation, a collision is most likely to occur, and the minimum critical Reynolds number at which a particle-wall collision will occur can be determined. This value is shown to increase with increasing particle frontal length. Pointed or rounded leading edges are shown to improve a particle’s ability to pierce the boundary layer adjacent to the target surface and reduce this value. In cases where a Reynolds number of 400 is insufficient to cause a particle-wall collision, the particles’ minimum distances from the target surface are reported. Using the minimum critical Reynolds number values obtained, the approach velocities required for particles to collide with a wall are shown to be larger than the impeller tip speeds typically used during crystallisation operations. This work provides for the first time the conditions under which particle-wall collisions occur for varying shape and orientation, their behaviour on approach, and the associated impact velocities.</p

Plasticity in zwitterionic drugs: the bending properties of pregabalin and gabapentin and their hydrates

The investigation of mechanical properties in molecular crystals is emerging as a novel area of interest in crystal engineering. Indeed, good mechanical properties are required to manufacture pharmaceutical and technologically relevant substances into usable products. In such endeavour, bendable single crystals help to correlate microscopic structure to macroscopic properties for potential design. The hydrate forms of two anticonvulsant zwitterionic drugs, Pregabalin and Gabapentin, are two examples of crystalline materials that show macroscopic plasticity. The direct comparison of these structures with those of their anhydrous counterparts, which are brittle, suggests that the presence of water is critical for plasticity. In contrast, structural features such as molecular packing and anisotropic distribution of strong and weak interactions seem less important