Glucose in dry and moist ionic liquid: vibrational circular dichroism, IR, and possible mechanisms

Blasius, Jan; Elfgen, Roman; Hollóczki, Oldamur; Kirchner, Barbara

doi:10.1039/c9cp06798a

Cited by 18 publications

(27 citation statements)

References 69 publications

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“…In order to dissolve cellulose, a solvent needs to break up the hydrogen bond network between the polymer strands [25] and replace it by hydrogen bonds to the solvent [8]. Most of the ILs proposed as cellulose solvents are based on imidazolium cations [10,[25][26][27][28], which is not surprising, as it has been known for long that many imidazolium-based ILs form very strong hydrogen bonds [29][30][31][32][33][34][35][36]. Some of these imidazolium-based ILs are able to dissolve more than 20 wt.-% of cellulose if the anions are strong hydrogen bond acceptors [3,37,38].…”

Section: Introductionmentioning

confidence: 99%

Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions

et al. 2020

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We present 1,2,3-triazolium- and imidazolium-based ionic liquids (ILs) with aromatic anions as a new class of cellulose solvents. The two anions in our study, benzoate and salicylate, possess a lower basicity when compared to acetate and therefore should lead to a lower amount of N-heterocyclic carbenes (NHCs) in the ILs. We characterize their physicochemical properties and find that all of them are liquids at room temperature. By applying force field molecular dynamics (MD) simulations, we investigate the structure and dynamics of the liquids and find strong and long-lived hydrogen bonds, as well as significant π–π stacking between the aromatic anion and cation. Our ILs dissolve up to 8.5 wt.-% cellulose. Via NMR spectroscopy of the solution, we rule out chain degradation or derivatization, even after several weeks at elevated temperature. Based on our MD simulations, we estimate the enthalpy of solvation and derive a simple model for semi-quantitative prediction of cellulose solubility in ILs. With the help of Sankey diagrams, we illustrate the hydrogen bond network topology of the solutions, which is characterized by competing hydrogen bond donors and acceptors. The hydrogen bonds between cellulose and the anions possess average lifetimes in the nanosecond range, which is longer than found in common pure ILs.

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Section: Introductionmentioning

confidence: 99%

Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions

et al. 2020

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“…Nolan and co‐workers reported that the NHC–metal complexes from imidazolium salts and metal ions can form through an analogous path, in which the preparation or even the in situ generation of an NHC is unnecessary, allowing very simple synthetic routes to these practically highly important compounds . Regarding the carbene‐like reactions of imidazolium acetate ionic liquids with glucose, we found indications that the concerted mechanism should be prevalent, as the aggregates that are required for the associative mechanism spontaneously occurred in ab initio molecular dynamics simulations, whereas the barriers of this mechanism were somewhat lower than that of the reaction through carbene intermediates . However, we found that in such an ionic liquid environment, and with the acetate anion as base the difference between these two mechanisms in barriers is lower, which implies that there might be experimental setups, in which the dissociative mechanism is more facile.…”

Section: Introductionmentioning

confidence: 73%

“…The positive charge on the azolium cations is delocalized over the whole ring, whereas on the ammonium cation it is highly localized on the N−H unit. Therefore, although azolium cations have also been shown to be hydrogen‐bond donors, ammonium cations offer an even stronger donor site. These differences are clearly observable in the electrostatic potential maps of the azolium and ammonium ions, as well as the charges of the hydrogen bond donor sites (Figure ).…”

Section: Resultsmentioning

confidence: 99%

“…Although considering this novel reaction mechanism has already given a deeper insight into the chemistry of azolium salts, and resulted in actual applications, exploiting this process in its full potential—by for example, introducing unprecedented ways to control selectivities—has not yet been achieved. To this end, hereby we aim to understand in detail the influential factors that facilitate or suppress this direct reaction mechanism, while assessing its relevance in catalytic systems.…”

Section: Introductionmentioning

confidence: 99%

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N‐Heterocyclic Carbene Organocatalysis: With or Without Carbenes?

Gehrke

Hollóczki

2020

Chemistry A European J

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In this work the mechanism of the aldehyde umpolung reactions, catalyzed by azolium cationsi nt he presence of bases,w as studied throughc omputational methods. Next to the mechanism established by Breslow in the 1950s that takes effect through the formation of af ree carbene, we have suggested that these processes can follow ac oncerted asynchronous path, in whicht he azolium cation directly reacts with the substrate, avoiding the formationo f the carbene intermediate. We hereby show that substituting the azolium cation, and varying the base or the substrate do not affect the preference for the concerted reactionm echanism. The concerted path was found to exhibit low barriers also for the reactions of thiamine with model substrates, showingt hat this path might have biological relevance. The dominance of the concerted mechanism can be explained throught he specific structure of the key transition state, avoidingt he liberation of the highly reactive,a nd thus unstable carbene lone pair,w hereas activating the substrate throughh ydrogen-bonding interactions. Polar and hydrogen-bonding solvents, as well as the presence of the counterionso ft he azolium salts facilitate the reaction through carbenes,b ringing the barriers of the two reactionm echanisms closer,i nm any cases making the concerted path less favorable. Thus, our data show that by choosing the exact components in ar eaction, the mechanism can be switched to occur with or withoutcarbenes.

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“…In this approach, the electron density is stored at each time step so that finite differences with respect to the time propagation can be applied afterwards 169 . They applied their method to the IR and VCD spectra of (R)‐2‐butanol solution in carbon disulfide 130,169 and glucose in an ionic liquid 170 …”

Section: Types Of Spectroscopymentioning

confidence: 99%

Vibrational spectroscopy by means of first‐principles molecular dynamics simulations

Ditler

Luber

2022

WIREs Comput Mol Sci

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Vibrational spectroscopy is one of the most important experimental techniques for the characterization of molecules and materials. Spectroscopic signatures retrieved in experiments are not always easy to explain in terms of the structure and dynamics of the studied samples. Computational studies are a crucial tool for helping to understand and predict experimental results. Molecular dynamics simulations have emerged as an attractive method for the simulation of vibrational spectra because they explicitly treat the vibrational motion present in the compound under study, in particular in large and condensed systems, subject to complex intramolecular and intermolecular interactions. In this context, first‐principles molecular dynamics (FPMD) has been proven to provide an accurate realistic description of many compounds. This review article summarizes the field of vibrational spectroscopy by means of FPDM and highlights recent advances made such as the simulation of Infrared, vibrational circular dichroism, Raman, Raman optical activity, sum frequency generation, and nonlinear spectroscopies. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Theoretical and Physical Chemistry > Spectroscopy Molecular and Statistical Mechanics > Molecular Mechanics Electronic Structure Theory > Density Functional Theory

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Glucose in dry and moist ionic liquid: vibrational circular dichroism, IR, and possible mechanisms

Abstract: The molecular level specification of glucose monomers in ionic liquids and their mixtures with water helps understanding cellulose processing in these liquids.

Cited by 18 publications

References 69 publications

Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions

Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions

N‐Heterocyclic Carbene Organocatalysis: With or Without Carbenes?

Vibrational spectroscopy by means of first‐principles molecular dynamics simulations

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