A Window into the Invisible Atomic World
By: Dr. David Aurentz, Assistant Professor of Chemistry
Perhaps it could be best described as a comic book superpower–the ability to see the invisible, my field of expertise. This ability to observe what is classically invisible through scientific analysis is critically important. Detecting changes at an atomic level can have huge effects on our understanding of the properties of all sorts of matter, ranging from materials in our homes, products found in stores, and even in our own bodies.
Throughout most of the past two decades, my research employing various spectroscopic techniques has allowed me to create windows into this amazing “invisible” world.
As Assistant Professor of Chemistry at Penn State Berks, I believe that spectroscopy, the study of the interaction of radiation and matter, is not limited only to the analysis of traditional chemicals, but can be applied to a wide range of exciting materials and disciplines.
My primary research involves the use of nuclear magnetic resonance (NMR) spectroscopy to study aluminosilicate catalysts and alumina surfaces, as well as other various chemical intermediates. Fourier transform infrared (FTIR) spectroscopy experiments are also conducted in my laboratory to analyze bacteria and fungi by studying the interaction of these biological materials with infrared laser radiation. These projects involve collaboration among chemistry, biology, and food science faculty, undergraduate students, and an industry collaborator.
The field of NMR spectroscopy was discovered roughly sixty-five years ago and involves the detection of the energy levels of magnetic nuclei, such as hydrogen (1H) and carbon-13 (13C), when placed in a magnetic field. The magnetic moment of the nuclear spin interacts with the magnetic field in such a way as to produce what is called the Zeeman splitting of the previously degenerate energy levels. Different atomic nuclei, or even similar nuclei in slightly dissimilar environments, resonate at different radio frequencies when subjected to the same magnetic field. This phenomenon allows researchers to discover fundamental structural information about the molecules of interest.
It is important to note that the “nuclear” in NMR refers only to the quantum mechanical nuclear spin within the nucleus of an atom and is not related to the radioactive decay associated with an unstable atomic nucleus. Indeed, magnetic field lines are noninvasive to humans and NMR spectroscopy is the basis of magnetic resonance imaging (MRI), which is used to provide high resolution images of the internal structure of the body.
Modern NMR spectrometers employ magnets constructed of coiled superconducting wire, which can produce strong and homogeneous fields within which samples may be analyzed. Once installed and brought to field, it is not necessary to connect these magnets to a power source. As long as the magnetic coil is kept below its critical temperature with cryogens, such as liquid helium and liquid nitrogen, a stable field is available for experiments.
The magnet currently employed at Penn State Berks produces a field strength of 7.0 tesla or roughly 140,000 times the magnetic field of the Earth. Much of the work done today to map out the conformation of proteins relies on NMR spectroscopy to determine local molecular structure. In these high-field experiments, magnetic fields over three times greater than the field produced here at the college have been used.
The NMR spectrometer was brought to Penn State Berks through a National Science Foundation grant in the amount of $134,000, which was matched by the college. The successful completion of this grant titled “Broadening Interdisciplinary Undergraduate Science through Acquisition of a Moderate Field NMR” has impacted students and faculty in a wide variety of courses and disciplines. In addition to bringing a powerful piece of instrumentation to the college, this work has enhanced my own research through the blending of the scholarship and teaching of NMR spectroscopy.
As a researcher, I came to Penn State Berks from a career in industrial chemistry as Senior Research Chemist at Air Products and Chemicals, Inc. The opportunity to transfer my experience gained at Air Products in cutting-edge materials applications to fundamental research regarding structural function has been a challenging yet extremely gratifying process.
One of the most rewarding aspects of my research here at Penn State Berks has been working with students. One student in particular, Anthony Tierno, worked in my research lab for more than three years while completing his degree as a Life Science major in 2009. Tierno has moved on to the graduate program in chemistry at Cornell University and he is a prime example of the benefits of undergraduate research at a small college.
While at Berks, Tierno and I worked on the characterization of the aluminum environments in cation-exchanged zeolites using aluminum (27Al) magic angle spinning NMR spectroscopy. This is a technique whereby a sample is spun rapidly around an axis at a certain angle relative to the magnetic field in order to drastically improve spectral resolution. The effects of cations on the local electromagnetic environments of catalytic sites in Y-zeolites were studied as a function of cation type and concentration. Knowing the effect of cations on the nature of the aluminum in these materials will allow researchers to tailor catalyst properties in a much more prescribed way.
NMR spectroscopy is a powerful and unique method to study materials. The types of information derived from NMR data include site identification, intersite correlations, dynamics and reactions, and imaging and microscopy. Observing the “invisible” atomic world using sophisticated instrumentation, such as the NMR spectrometer here at Penn State Berks, is a one of the great benefits of scientific advancement. However, determining what to do with all the observed information is entirely another superpower.