Raman spectra study hydrogen bonds network in ice Ih with cooling

A study on the relationship between the crystallization characteristics of quenched droplets and the effect of cell cryopreservation with Raman spectroscopy

The cryopreservation method of microdroplets has steadily become widely employed in the cryopreservation of microscale biological samples such as various types of cells due to its fast cooling rate, significant reduction of the concentration of cryoprotectants, and practical liquid handling method. However, it is still necessary to consider the corresponding relationship between droplet size and concentration and the impact of crystallization during the cooling process on cell viability. The key may be a misunderstanding of the influencing factors of crystallization and vitrification behavior with concentration during cooling on the ultimate cell viability, which may be attributable to the inability to analyze the freezing state inside the microdroplets. Therefore, in this work, an in situ Raman observation system for droplet quenching was assembled to obtain Raman spectra in the frozen state, and the spectral characteristics of the crystallization and vitrification processes of microdroplets with varied concentrations and volumes were investigated. Furthermore, the degree of crystallization inside the droplets was quantitatively analyzed, and it was found that the ratio of the crystalline peak to hydrogen bond shoulder could clearly distinguish the degree of crystallization and the vitrified state, and the Raman crystallization characteristic parameters gradually increased with the decrease of concentrations. By obtaining the cooling curve and the overall cooling rate of quenching droplets, the vitrification state of the microdroplets was confirmed by theoretical analysis of the cooling characteristics of a DMSO solution system. In addition, the effect of cell cryopreservation was investigated using the microdroplet quenching device, and it was found that the key to cell survival during the quenching process of low-concentration microdroplets was dominated by the cooling rate and the internal crystallization degree, while the main influencing factor on high concentration was the toxic effect of a protective agent. In general, this work introduces a new nondestructive evaluation and analysis method for the cryopreservation of quenching microdroplets.

Influence of protic ionic liquids on hydration of glycine based peptides

The structure of water, especially around the solute is thought to play an important role in many biological and chemical processes. Water-peptide and cosolvent-peptide interactions are crucial in determining the structure and function of protein molecules. In this work, we present the H-bonding analysis for model peptides like glycyl-glycine (gly-gly), glycine-ւ-valine (gly-val), glycyl-ւ-leucine (gly-leu) and triglycine (trigly) and triethylammonium based carboxylate protic ionic liquids (PILs) in aqueous solutions as well as for peptides in ∼0.2 mol·L^-1 of aqueous PIL solutions in the spectral range of 7800-5500 cm^-1 using Fourier transform near-infrared (FT-NIR) spectroscopy at 298.15 K. The hydration numbers for peptides and PILs were obtained using NIR method of simultaneous estimation of hydration spectrum and hydration number of a solute dissolved in water. The H-bond of water molecules around peptides and PILs are found to be stronger and shorter than those in pure liquid water. We observe that the hydration shell around zwitterions is a clathrate-like cluster of water in which ions entrap. Watery network analysis confirms that singly H-bonded species or NHBs changes to partial or distorted ice-like structures of water in the hydration shell of PILs. The overall water H-bonding in the hydration sphere of PILs increases in the order TEAF < TEAA < TEAG < TEAPy ≈ TEAP < TEAB. The influence of PILs on hydration behavior of peptides is explored in terms of H-bonding, cooperativity, hydrophobicity, water structural changes, ionic interactions etc.

Study of hydrogen bonding interactions in ethylene glycol-water binary solutions by Raman spectroscopy

EG (ethylene glycol) is a good model system for the study of the fundamental hydrogen bonds in aqueous solutions. Using Raman spectroscopy, we have investigated the EG volume fraction induced variation in the hydrogen bonding interactions and conformations of EG-H₂O (water) binary solutions. New hydrogen bonding networks is evidenced by the appearance of remarkable changes in Raman spectra and the full width at half maximum (FWHM) when the mixing volume ratio is 0.5. The H-bond in water molecules firstly strengthened and then weakened with the increasing concentration of EG. Meanwhile, the dominant association structure also changed from H₂O-H₂O to EG-H₂O in binary solutions in this process. We provide a simple but effective method for studying EG-H₂O binary solutions. It also has exciting potential prospects and can be easily extended to other mixing situations.

Determination of temperature-dependent Fermi resonance in acetonitrile-water binary solution by two-dimensional correlation Raman spectroscopy

Acetonitrile (AN), as an organic solvent, has a wide range of applications. The C≡N stretching vibration mode (ν₂) and the combination mode (ν₃ + ν₄) are coupled by Fermi resonance (FR). In this work, the phase transition and the interaction mechanism of the 60% AN-water binary solution (AN-Water) were analyzed by calculating FR parameters and two-dimensional correlation Raman spectroscopy (2DCRS). The change in the ν₂ band and the base bands ν₃ and ν₄ caused energy transfer by anharmonic interaction, which led to a change in FR parameters. With a reduced temperature, the energy transfer was caused by microheterogeneity and the energy transfer effect (293-273 K), the phase separation (263-233 K), and the phase transition of AN (223-173 K). The 2DCRS and Gaussian deconvolution provided more information on FR, which revealed the interaction mechanism of the Fermi doublet. The polarity and binding modes of molecules provided a new perspective for analyzing the transmission of electrons and ions in the electrolyte at different temperatures.

Multiscale analysis of the hydrate based carbon capture from gas mixtures containing carbon dioxide

To reveal the kinetic performance of gas molecules in hydrate growth, hydrate formation from pure CO₂, flue gas, and biogas was measured using in-situ Raman and macroscopic methods at 271.6 K. In the in-situ Raman measurements, Raman peaks of gases in the hydrate phase were characterised and normalised by taking the water bands from 2800 to 3800 cm^-1 as a reference, whose line shapes were not found to have a noticeable change in the conversion from Ih ice to sI hydrate. The hydrate growth was suggested to start with the formation of unsaturated hydrate nuclei followed by gas adsorption. In hydrate formed from all tested gases, CO₂ concentrations in hydrate nuclei were found to be 23-33% of the saturation state. In the flue gas system, the N₂ concentration reached a saturation state once hydrate nuclei formed. In the biogas system, competitive adsorption of CH₄ and CO₂ molecules was observed, while N₂ molecules hardly evolved in hydrate formation. Combined with micro- and macroscopic analysis, small molecules such as N₂ and CO₂ were suggested to be more active in the formation of hydrate nuclei, and the preferential adsorption of CO₂ molecules took place in the subsequent gas adsorption process.

Spectroscopic Determination of Ice-Induced Interfacial Strain on Single-Layer Graphene

Reliably determining the physical properties of ice (e.g., crystal structure, adhesion strength, interfacial state, and molecular orientation) has proven to be both challenging and highly dependent on experiment-specific conditions, including surface roughness, ice formation, water purity, and measurement method. Here, non-destructive measurements of single-layer graphene (SLG) interfaced with bulk ice are used to determine temperature-dependent, ice-induced strain and estimate ice-created strain elastic density in SLG. The use of SLG enables the precise study of interfacial strain by monitoring the 2D Raman mode. Upon ice formation, a clear, ≈2 cm^-1 decrease in the 2D mode frequency is observed, which is ascribed to a 0.012% biaxial tensile shear strain at the ice-SLG interface. From this shear strain value, the ice-created SLG elastic strain energy density is estimated to be 2.4 μJ m^-2 . In addition to these Raman strain measurements, intentionally ionized water is used to show that water-mediated charging of the SLG surface manifests itself in a distinctly different manner than ice-induced strain. Finally, the localized nature of the Raman probe is used to map SLG regions with and without ice, suggesting that this method cannot only determine ice-induced interfacial strain, but also correlate ice adhesion properties with surface roughness and topology.