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Experimental studies of vibrational modes in a two-dimensional amorphous solid.

ABSTRACT: The boson peak, which represents an excess of vibrational states compared to Debye's prediction at low frequencies, has been studied extensively, and yet, its nature remains controversial. In this study, we focus on understanding the nature of the boson peak based on the spatial heterogeneity of modulus fluctuations using a simple model system of a highly jammed two-dimensional granular material. Despite the simplicity of our system, we find that the boson peak in our two-dimensional system shows a shape very similar to that of three-dimensional molecular glasses when approaching their boson peak frequencies. Our finding indicates a strong connection between the boson peak and the spatial heterogeneity of shear modulus fluctuations.The low-frequency collective vibrational modes, known as the boson peak, characterize many glasses at low temperature, yet its origin remains elusive. Zhang et al. show a correlation between the boson peak and the spatial heterogeneity of shear modulus fluctuation in a two-dimensional granular system.

SUBMITTER: Zhang L

PROVIDER: S-EPMC5503991 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Experimental studies of vibrational modes in a two-dimensional amorphous solid.

Zhang Ling L Zheng Jie J Wang Yinqiao Y Zhang Lei L Jin Zhaohui Z Hong Liang L Wang Yujie Y Zhang Jie J

Nature communications 20170710 1

The boson peak, which represents an excess of vibrational states compared to Debye's prediction at low frequencies, has been studied extensively, and yet, its nature remains controversial. In this study, we focus on understanding the nature of the boson peak based on the spatial heterogeneity of modulus fluctuations using a simple model system of a highly jammed two-dimensional granular material. Despite the simplicity of our system, we find that the boson peak in our two-dimensional system show ...[more]

PMID: 28694525

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Project description:Proteins, enzymes, and other biological molecules undergo structural dynamics as an intrinsic part of their biological functions. While many biological processes occur on the millisecond, second, and even longer time scales, the fundamental structural dynamics that eventually give rise to such processes occur on much faster time scales. Many decades ago, chemical kineticists focused on the inverse of the reaction rate constant as the important time scale for a chemical reaction. However, through transition state theory and a vast amount of experimental evidence, we now know that the key events in a chemical reaction can involve structural fluctuations that take a system of reactants to its transition state, the crossing of a barrier, and the eventual relaxation to product states. Such dynamics occur on very fast time scales. Today researchers would like to investigate the fast structural fluctuations of biological molecules to gain an understanding of how biological processes proceed from simple structural changes in biomolecules to the final, complex biological function. The study of the fast structural dynamics of biological molecules requires experiments that operate on the appropriate time scales, and in this Account, we discuss the application of ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy to the study of protein dynamics. The 2D IR vibrational echo experiment is akin to 2D NMR, but it operates on time scales many orders of magnitude faster. In the experiments, a particular vibrational oscillator serves as a vibrational dynamics probe. As the structure of the protein evolves in time, the structural changes are manifested as time-dependent changes in the frequency of the vibrational dynamics probe. The 2D IR vibrational echo experiments can track the vibrational frequency evolution, which we then relate to the time evolution of the protein structure. In particular, we measured protein substate interconversion for mutants of myoglobin using 2D IR chemical exchange spectroscopy and observed well-defined substate interconversion on a sub-100 ps time scale. In another study, we investigated the influence of binding five different substrates to the enzyme cytochrome P450(cam). The various substrates affect the enzyme dynamics differently, and the observed dynamics are correlated with the enzyme's selectivity of hydroxylation of the substrates and with the substrate binding affinity.

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Experimental studies of vibrational modes in a two-dimensional amorphous solid.

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Experimental studies of vibrational modes in a two-dimensional amorphous solid.

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