Pick and Choose the Spectroscopic Method to Calibrate the Local Electric Field inside Proteins

We report here the first mesoscale characterization of solvent environments in the metal-organic framework (MOF) Cu(BTC) using infrared imaging. Two characteristic populations of the MOF structures corresponding to the carboxylate binding to the Cu(II) (metal) ions were observed, which reflect a regular solvated MOF structure with axial solvents in the binuclear copper paddlewheel and an unsolvated defect mode that lacks axial solvent coordination. Infrared imaging also shows strong correlation between solvent localization and the spatial distribution of the solvated population within the MOF. This is a vital result as any remnant solvent molecules adsorbed inside of MOFs can render them less effective. We propose fast IR imaging as a potential characterization technique that can measure adsorbate and defect distributions in MOFs.

Section: Introductionsupporting

confidence: 88%

Mapping Solvation Environments in Porous Metal–Organic Frameworks with Infrared Chemical Imaging

Ghosh

Mukherjee

Deb

et al. 2017

“…However, β-sheet absorption frequencies are variable and can shift significantly depending on the exact molecular structure. − Furthermore, the values in literature are typically from condensed-phase measurements with protein aggregates suspended in solution. Our measurements are in dehydrated, fixed tissues and do not contain any solvent, and that can further shift the vibrational frequencies, as it is well-known that amide vibrational frequencies are sensitive to the solvent environment. − Therefore, our observations do not preclude the presence of intermolecular β-sheets.…”

mentioning

confidence: 99%

Label-Free Infrared Spectroscopic Imaging Reveals Heterogeneity of β-Sheet Aggregates in Alzheimer’s Disease

Confer

Holcombe

Foes

et al. 2021

The aggregation of the amyloid beta (Aβ) protein into plaques is a pathological feature of Alzheimer's disease (AD). While amyloid aggregates have been extensively studied in vitro, their structural aspects and associated chemistry in the brain are not fully understood. In this report, we demonstrate, using infrared spectroscopic imaging, that Aβ plaques exhibit significant heterogeneities in terms of their secondary structure and phospholipid content. We show that the capabilities of discrete frequency infrared imaging (DFIR) are ideally suited for characterization of amyloid deposits in brain tissues and employ DFIR to identify nonplaque β-sheet aggregates distributed throughout brain tissues. We further demonstrate that phospholipid-rich β-sheet deposits exist outside of plaques in all diseased tissues, indicating their potential clinical significance. This is the very first application of DFIR toward a characterization of protein aggregates in an AD brain and provides a rapid, label-free approach that allows us to uncover β-sheet heterogeneities in the AD, which may be significant for targeted therapeutic strategies in the future.

“…The peak maxima of both the populations shift to higher frequencies with increase in χ DMSO . The first moments of the CO absorption frequencies, which correspond to the ensemble average electric field along the carbonyl bond (see Table S1 for details), , when plotted against DMSO mole fractions, show a linear correlation over the entire DMSO concentration range encompassing the critical mole fraction of 0.15 (Figure a). The linear trend in average CO frequencies indicates a monotonic change in the solute–solvent interactions in terms of electric fields exerted on the solute by the different binary solvent mixtures.…”

mentioning

confidence: 99%

Two-Dimensional Infrared Spectroscopy Reveals Cosolvent-Composition-Dependent Crossover in Intermolecular Hydrogen-Bond Dynamics

Kashid

Jin

Chakrabarty

et al. 2017

Self Cite

Cosolvents have versatile composition-dependent applications in chemistry and biology. The simultaneous presence of hydrophobic and hydrophilic groups in dimethyl sulfoxide (DMSO), an industrially important amphiphilic cosolvent, when combined with the unique properties of water, plays key roles in the diverse fields of pharmacology, cryoprotection, and cell biology. Moreover, molecules dissolved in aqueous DMSO exhibit an anomalous concentration-dependent nonmonotonic behavior in stability and activity near a critical DMSO mole fraction of 0.15. An experimental identification of the origin of this anomaly can lead to newer chemical and biological applications. We report a direct spectroscopic observation of the anomalous behavior using ultrafast two-dimensional infrared spectroscopy experiments. Our results demonstrate the cosolvent-concentration-dependent nonmonotonicity arises from nonidentical mechanisms in ultrafast hydrogen-bond-exchange dynamics of water above and below the critical cosolvent concentration. Comparison of experimental and theoretical results provides a molecular-level mechanistic understanding: a distinct difference in the stabilization of the solute through dynamic solute-solvent interactions is the key to the anomalous behavior.