An Inside Look at the Fundamentals and Principles of Two-Dimensional Correlation Spectroscopy

During the 21^st century, two-dimensional correlation spectroscopy (2D-COS) has emerged as a popular analysis method for data obtained using Raman and infrared (IR) spectroscopy (1). 2D-COS is an analytical technique used to enhance the interpretation of spectral data by revealing relationships between spectral features that are not easily discernible in traditional one-dimensional (1D) spectroscopy (2). By applying mathematical transformations, such as correlation analysis, 2D-COS generates two-dimensional plots that display dynamic changes in a sample's spectral response (2). These plots provide synchronous and asynchronous correlation maps that help identify co-varying signals, sequence of spectral changes, and subtle differences in molecular interactions or chemical environments (2).

Professors Isao Noda and Young Mee Jung are exploring how 2D-COS can be applied in the industry. Professor Noda is an Affiliated Professor in the Department of Materials Science and Engineering at the University of Delaware, in Newark, Delaware. Professor Jung is a Professor in the Department of Chemistry at Kangwon National University, in Chuncheon, Korea.

Recently, Spectroscopy magazine sat down with Noda and Jung to talk about their recent paper that explored the principles of 2D-COS, and how the use of 2D-COS has spurred numerous advancements in material science.

Professor Isao Noda (left) is an Affiliated Professor at the Department of Materials Science and Engineering at the University of Delaware. Professor Yung Mee Jung is a Professor at the Department of Chemistry at Kangwon National University. Photo Credit: © Isao Noda and Young Mee Jung.

Could you explain the fundamental principles of two-dimensional correlation spectroscopy (2D-COS) and how it differs from traditional spectroscopic techniques?

Traditional spectroscopy often encounters limitations when analyzing complex systems. By plotting signal intensity against a single variable (for example, the wavelength), it can lead to spectral overlap and hinder the resolution of intricate mixtures. 2D-COS addresses this by transforming 1D spectral data into a 2D correlation map. This approach essentially examines how spectral changes at one frequency are interconnected with changes at other frequencies while the system undergoes perturbation (for example, temperature, pressure). Key advantages of 2D-COS include:

• Enhanced spectral resolution: Overlapping spectral bands can be effectively separated.
• Determination of sequential spectral changes: The order in which spectral events occur can be established.
• Amplification of subtle spectral features: Features often obscured in one-dimensional spectra become more prominent.

What are some of the key applications of 2D-COS across chemistry and other scientific fields, and how has it enhanced the depth, understanding, and accuracy of analytical results?

2D-COS finds widespread application across diverse fields. It is extensively used for mechanistic studies of chemical reactions, investigating polymer structures, dynamics, and degradation, and analyzing complex solutions and mixtures. Significant research utilizing 2D-COS is evident in the life sciences field, particularly pharmaceutical drug formulations and biological interactions, and the environmental sciences for applications such as pollution monitoring, environmental control, and agricultural applications.

A comprehensive review of intriguing 2D-COS applications can be found in the accompanying paper (3).

How has 2D-COS contributed to improving the understanding of complex molecular structures and dynamics in complex materials, such as polymers and biological systems?

2D-COS excels in elucidating complex systems, such as molecular structures and dynamics of interacting processes. This is achieved without relying heavily on pre-existing models or assumptions:

• Polymer science: Understanding polymer chain dynamics, crystallinity, and the influence of processing conditions on polymer chemical and physical properties.
• Biomolecular systems: Gaining insights into protein folding, ligand-receptor interactions, and the dynamics of biomolecular assemblies.
• Investigating the impact of external factors: Studying how changes in temperature or pH affect protein structure and function.

What challenges do researchers face for interpreting the complex data generated by 2D-COS, and what technical or software advancements have been made to address these issues?

Although 2D-COS generates complex data sets, their interpretation follows a well-defined and straightforward set of rules.

• Data preprocessing: Essential steps like baseline correction and noise reduction are crucial for accurate 2D-COS analysis.
• Advancements
  • User-friendly software packages with advanced visualization and analysis tools have been developed.
  • Integration with machine learning (ML) and data mining techniques enhances information extraction.
  • The growing influence of artificial intelligence (AI)-based technologies promises to further simplify 2D-COS applications.

In your opinion, how has the development and adoption of 2D-COS influenced scientific discovery and innovation in your field of expertise for new materials and polymers?

2D-COS has significantly impacted materials science, contributing to nanomaterials characterization, polymer blend and composite design, and the development of smart materials. It provides detailed and accurate insights into the structure and properties of materials. Its enhanced efficiency enables faster and more efficient development of new materials with tailored properties. And finally, the mechanistic understanding of 2D-COSprovides insights into material degradation, aging, and processing mechanisms.

A notable example is the critical role 2D-COS played in the development of commercially available biodegradable plastics derived from vegetable oils.

What advancements or trends do you foresee in 2D-COS technology or methodologies that could further expand its impact on scientific research and development of new materials?

The future of 2D-COS holds immense promise for higher-dimensional analysis, multi-technique integration, and novel perturbation methods. For higher-dimensional analysis, extending 2D-COS to three or more dimensions, incorporating time and spatial domains, will allow for the analysis of even more complex systems. For multi-technique integration, combining 2D-COS with other analytical techniques, such as microscopy and chromatography, will provide more comprehensive insights. And finally, for novel perturbation methods, exploring diverse perturbation types (for example, electric fields and magnetic fields) in various combinations will deepen our understanding of material behavior. Our paper explores numerous emerging perturbation methods (3).

References

1. Park, Y.; Jin, S.; Noda, I.; Jung, Y. M. Continuing Progress in the Field of Two-dimensional Correlation Spectroscopy (2D-COS): Part I. Yesterday and Today. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2022, 281, 121573. DOI: 10.1016/j.saa.2022.121573
2. NIST, Advanced Spectral Analysis: Two-Dimensional Correlation Spectroscopy (2DCOS). NIST.gov. Available at: https://www.nist.gov/programs-projects/advanced-spectral-analysis-two-dimensional-correlation-spectroscopy-2dcos#:~:text=The%202DCOS%20method%20compares%20spectral,correlations%20between%20two%20spectral%20components. (accessed 2025-01-13).
3. Park, Y.; Noda, I.; Jung, Y. M. Novel Developments and Progress in Two-Dimensional Correlation Spectroscopy (2D-COS). Appl. Spectrosc. 2025, 79 (1), 13–35. DOI: 10.1177/00037028241255393