Designing facilities for NMR spectroscopy

More and more organisations are seeing the benefit of installing NMR facilities, a move that can present many design challenges for the buildings that house them

The Cross Faculty Centre for NMR at  Imperial College London

Over the last ten years the use of NMR (nuclear magnetic resonance) spectroscopy has grown considerably to become probably the most important analytical tool available in the field of organic chemistry. This has meant that more and more research organisations, and in particular those within the major universities, have seen benefits in developing their own high-field NMR facilities. This is not a task to be undertaken lightly, NMR equipment is sensitive and demanding in terms of its location, environment and servicing and also extremely expensive.

Using two examples of recently completed projects by Berman Guedes Stretton, this article seeks to highlight some of the problems which might be encountered in designing either new or refurbished accommodation for NMR Spectroscopy.

To understand the requirements for such a facility from the outset, an appreciation of the technology is clearly important. From a scientific viewpoint the technology is complex and requires a sophisticated level of understanding and interpretation, but as an architect it is the fundamental technical requirements, directly impacting on the enclosure, which are critical. Many of you reading this will already be familiar with the function of NMR Spectroscopy, but for those who are not, a brief introduction might be helpful.

Nuclear magnetic resonance spectroscopy essentially exploits the magnetic properties of nuclei and measures their radio frequency absorptions. This can identify individual atoms in a pure molecule and in some cases how many atoms of each type exist within a given sample. Depending on the local chemical environment, different protons in a molecule each resonate at slightly different frequencies and this frequency is dependant on the strength of the magnetic field. Using a reference frequency, this allows a measurement of the ‘chemical shift’ which provides structural information about a molecule. These measurements require sophisticated analysis software, but of particular importance is that NMR technology is very reliable, predictable and reproducible. Much recent innovation in NMR spectroscopy has been within the field of protein NMR, an important technique in structural biology. These investigations can provide high resolution three dimensional computer generated structures of a protein.

The design of NMR instrumentation has been developing fast over the last ten years but because of its very specialist nature and the relatively small number of high-end users, the market tends to have been dominated by only a few key companies. The front runners, particularly in the area of ultra high-field applications, are Bruker and Varian with Oxford Instruments being one of the leading experts in the fundamental magnet technology. These companies have built up a high level of experience over a number of years in terms of the performance of their equipment over a range of enclosure types and environmental conditions and there is therefore no substitute for bringing them in at a very early stage. The problem with this is that commercial negotiations often mean that the final supplier may not be known until late in the design process, and high end NMR equipment is made to special order and has very long delivery times. Unfortunately different manufacturers often have quite different design requirements and it is prudent not to go too far before a particular manufacturer is contractually in place to avoid expensive abortive work.

The fact that the measurements being undertaken are very small means that they are very susceptible to error through all kinds of external influences such as vibration, temperature, and stray magnetic or radio interference. The enclosures within which NMR equipment is to be housed must therefore be constructed to very critical specifications and tolerances. Creating robust and reliable heating/cooling/ventilation systems to achieve ± ½º C temperature stability with very low velocity and filtered air movement, brings specific design problems and needs much larger plant space. It may also be sensible to undertake a specialist survey of the location to check for vibrations or radio waves which could affect the installation.

All NMR equipment, and particularly the new generation of super magnets, creates very powerful magnetic fields which in themselves bring design and locational problems. There are two main issues here: the influence of these fields on other adjacent equipment, processes and personnel (such as the effect on other scientific work in adjacent spaces or on pacemakers, credit cards etc), and the need to avoid any interference within the field by such things as ferrous metals and particularly moving metals (such as lifts or vehicles) which might affect the measurements achieved. This is particularly the case in existing buildings where there may be other accommodation above or even below. In any event, plotting the respective gauss radials both horizontally and vertically on to the drawings will reveal the conflicts.  Similarly avoiding ferrous metals in the construction within the critical magnetic fields is usually necessary. As the technology progresses, improved ways of shielding magnets are being incorporated by manufacturers. This certainly lessens some of the problems but there will always be issues particularly with the higher-field magnets.

The Henry Wellcome Building for Biomolecular NMR Spectroscopy at the University of Birmingham

In addition to this, magnets at the core of NMR instruments need to be kept stable at very low temperatures and therefore extreme cooling in the form of liquid nitrogen and liquid helium is necessary. Providing storage and a safe route for dewars to top up the vessels, or a piped supply system must be reviewed at an early design stage.  There are a number of risks associated with these cryogens which should be considered. Firstly their containment within equipment and the effects of spillages on finishes, secondly the danger of quenching when specific circumstances can cause them to ‘boil off’ releasing high pressure and extremely low temperature vapour into the chamber causing damage to the building and a serious safety hazard to the occupants – this is most likely during commissioning. Thirdly the build up of nitrogen gas at low level which, if undetected could cause asphyxiation.

Access for delivery, installation and future removal of equipment is an important design constraint. In particular the 800 and 900MHz spectrometers are extremely large, heavy, single piece items and early discussions with the manufacturers to establish access requirements will be necessary.

Berman Guedes Stretton has been involved in a number of facilities accommodating NMR spectrometers and the following two examples show some of the design issues in both a new-build and a refurbishment scheme.

The Henry Wellcome Building for Biomolecular NMR Spectroscopy – the University of Birmingham.
This stand-alone, new build project was designed to house a range of spectrometers from 500 to 900MHz together with the associated plant space, staff facilities, computer control area, laboratory and seminar/meeting space. The NMR equipment is accommodated in three separate chambers using dense, load bearing construction with vibration isolated floor slabs - this increased thermal mass enables close environmental control. Large vision panels allow views of the equipment and also provide the means of access for its installation and removal. Each of the chambers uses non-ferrous materials including stainless steel reinforcement and the largest chamber housing the unshielded 900MHz NMR has an uninterrupted span of 13 metres to enclose the critical five gauss radial. The five gauss radials of each NMR were carefully plotted to ensure that there was no interference between each unit and to enable circulation routes to be located to avoid passing through these fields.  Similarly the building design keeps pedestrian or vehicular movements away from any external magnetic fields. The large plant space runs the full length of the building allowing services to easily feed each chamber and providing completely independent access for maintenance.

The Cross Faculty Centre for NMR – Imperial College London
This project was funded by a joint SRIF application from the departments of medicine and chemistry, to co-locate NMR spectrometers in a shared new facility on the South Kensington Campus, which could engender collaboration between academics. The site selected for the facility was the ground floor of the old Imperial Institute Chemistry building in former workshops. To stop the harmful magnetic fields straying into the laboratory space above, the 800Mhz Ultrashield magnet needed to be set in a new pit, excavated within the building. A contemporary extension was constructed to house laboratories for preparing and analysing data, with a rooftop plant compound to house the services equipment required to create the close controlled environment within the Edwardian Building. The design was influenced to a large extent by the installation requirements for the magnet. In addition to double height doors, a large lifting beam was required to lower the 8 tonne magnet into the pit. The non-ferrous specification included stainless steel for the lifting beam and lab benching, PVC for the ducting and aluminium for the demountable access gantry and balustrades. A canvas canopy floats above the equipment to provide protection from any services leakage from the floors above.

As a growing and important tool, NMR Spectroscopy is likely to become a pre-requisite of many research institutions in the field of biosciences. Providing suitable accommodation for such complex and demanding facilities is critical and needs careful location and design considerations. As technology improves, the impact of better shielding etc. will allow high-field instruments to be located in smaller spaces but the demand for more and more powerful magnets will continue to provide design challenges for architects and services engineers.

By Roger Stretton. Roger is a director of Berman Guedes Stretton Architects and has specialised in the design of science buildings for over twenty years, particularly in the area of higher education. His clients include Imperial College London and the Universities of Birmingham, Oxford and Warwick.

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