International Journal of Molecular Sciences

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10 pages, 370 KiB

Open AccessArticle

Comparing Microscopic and Macroscopic Dynamics in a Paradigmatic Model of Glass-Forming Molecular Liquid

by Giuseppe Porpora, Francesco Rusciano, Raffaele Pastore and Francesco Greco

Int. J. Mol. Sci. 2022, 23(7), 3556; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms23073556 - 24 Mar 2022

Cited by 4 | Viewed by 2089

Abstract

Glass transition is a most intriguing and long-standing open issue in the field of molecular liquids. From a macroscopic perspective, glass-forming systems display a dramatic slowing-down of the dynamics, with the inverse diffusion coefficient and the structural relaxation times increasing by orders of [...] Read more.

Glass transition is a most intriguing and long-standing open issue in the field of molecular liquids. From a macroscopic perspective, glass-forming systems display a dramatic slowing-down of the dynamics, with the inverse diffusion coefficient and the structural relaxation times increasing by orders of magnitude upon even modest supercooling. At the microscopic level, single-molecule motion becomes strongly intermittent, and can be conveniently described in terms of “cage-jump” events. In this work, we investigate a paradigmatic glass-forming liquid, the Kob–Andersen Lennard–Jones model, by means of Molecular Dynamics simulations, and compare the macroscopic and microscopic descriptions of its dynamics on approaching the glass-transition. We find that clear changes in the relations between macroscopic timescales and cage-jump quantities occur at the crossover temperature where Mode Coupling-like description starts failing. In fact, Continuous Time Random Walk and lattice model predictions based on cage-jump statistics are also violated below the crossover temperature, suggesting the onset of a qualitative change in cage-jump motion. Interestingly, we show that a fully microscopic relation linking cage-jump time- and length-scales instead holds throughout the investigated temperature range. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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19 pages, 1160 KiB

Open AccessArticle

Hydrophilic and Hydrophobic Effects on the Structure and Themodynamic Properties of Confined Water: Water in Solutions

by Francesco Mallamace, Domenico Mallamace, Sow-Hsin Chen, Paola Lanzafame and Georgia Papanikolaou

Int. J. Mol. Sci. 2021, 22(14), 7547; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22147547 - 14 Jul 2021

Cited by 8 | Viewed by 2659

Abstract

NMR spectroscopy is used in the temperature range 180–350 K to study the local order and transport properties of pure liquid water (bulk and confined) and its solutions with glycerol and methanol at different molar fractions. We focused our interest on the hydrophobic [...] Read more.

NMR spectroscopy is used in the temperature range 180–350 K to study the local order and transport properties of pure liquid water (bulk and confined) and its solutions with glycerol and methanol at different molar fractions. We focused our interest on the hydrophobic effects (HE), i.e., the competition between hydrophilic and hydrophobic interactions. Nowadays, compared to hydrophilicity, little is known about hydrophobicity. Therefore, the main purpose of this study is to gain new information about hydrophobicity. As the liquid water properties are dominated by polymorphism (two coexisting liquid phases of high and low density) due to hydrogen bond interactions (HB), creating (especially in the supercooled regime) the tetrahedral networking, we focused our interest to the HE of these structures. We measured the relaxation times (

T_{1}

and

T_{2}

) and the self-diffusion (D

_{S}

). From these times, we took advantage of the NMR property to follow the behaviors of each molecular component (the hydrophilic and hydrophobic groups) separately. In contrast, D

_{S}

is studied in terms of the Adam–Gibbs model by obtaining the configurational entropy (S

_{c o n f}

) and the specific heat contributions (C

_{P, c o n f}

). We find that, for the HE, all of the studied quantities behave differently. For water–glycerol, the HB interaction is dominant for all conditions; water–methanol, two different T-regions above and below 265 K are observable, dominated by hydrophobicity and hydrophilicity, respectively. Below this temperature, where the LDL phase and the HB network develops and grows, with the times and C

_{P, c o n f}

change behaviors leading to maxima and minima. Above it, the HB becomes weak and less stable, the HDL dominates, and hydrophobicity determines the solution. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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12 pages, 2282 KiB

Open AccessArticle

Tailoring Chitosan/LTA Zeolite Hybrid Aerogels for Anionic and Cationic Dye Adsorption

by Martina Salzano de Luna, Francesco Greco, Raffaele Pastore, Giuseppe Mensitieri, Giovanni Filippone, Paolo Aprea, Domenico Mallamace, Francesco Mallamace and Sow-Hsin Chen

Int. J. Mol. Sci. 2021, 22(11), 5535; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22115535 - 24 May 2021

Cited by 9 | Viewed by 2048

Abstract

Chitosan (CS) is largely employed in environmental applications as an adsorbent of anionic dyes, due to the presence in its chemical structure of amine groups that, if protonated, act as adsorbing sites for negatively charged molecules. Efficient adsorption of both cationic and anionic [...] Read more.

Chitosan (CS) is largely employed in environmental applications as an adsorbent of anionic dyes, due to the presence in its chemical structure of amine groups that, if protonated, act as adsorbing sites for negatively charged molecules. Efficient adsorption of both cationic and anionic dyes is thus not achievable with a pristine chitosan adsorbent, but it requires the combination of two or more components. Here, we show that simultaneous adsorption of cationic and anionic dyes can be obtained by embedding Linde Type A (LTA) zeolite particles in a crosslinked CS-based aerogel. In order to optimize dye removal ability of the hybrid aerogel, we target the crosslinker concentration so that crosslinking is mainly activated during the thermal treatment after the fast freezing of the CS/LTA mixture. The adsorption of isotherms is obtained for different CS/LTA weight ratios and for different types of anionic and cationic dyes. Irrespective of the formulation, the Langmuir model was found to accurately describe the adsorption isotherms. The optimal tradeoff in the adsorption behavior was obtained with the CS/LTA aerogel (1:1 weight ratio), for which the maximum uptake of indigo carmine (anionic dye) and rhodamine 6G (cationic dye) is 103 and 43 mg g⁻¹, respectively. The behavior observed for the adsorption capacity and energy cannot be rationalized as a pure superposition of the two components, but suggests that reciprocal steric effects, chemical heterogeneity, and molecular interactions between CS and LTA zeolite particles play an important role. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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17 pages, 705 KiB

Open AccessArticle

Glass and Jamming Rheology in Soft Particles Made of PNIPAM and Polyacrylic Acid

by Silvia Franco, Elena Buratti, Valentina Nigro, Emanuela Zaccarelli, Barbara Ruzicka and Roberta Angelini

Int. J. Mol. Sci. 2021, 22(8), 4032; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22084032 - 14 Apr 2021

Cited by 12 | Viewed by 3134

Abstract

The phase behaviour of soft colloids has attracted great attention due to the large variety of new phenomenologies emerging from their ability to pack at very high volume fractions. Here we report rheological measurements on interpenetrated polymer network microgels composed of poly(N [...] Read more.

The phase behaviour of soft colloids has attracted great attention due to the large variety of new phenomenologies emerging from their ability to pack at very high volume fractions. Here we report rheological measurements on interpenetrated polymer network microgels composed of poly(N-isopropylacrylamide) (PNIPAM) and polyacrylic acid (PAAc) at fixed PAAc content as a function of weight concentration. We found three different rheological regimes characteristic of three different states: a Newtonian shear-thinning fluid, an attractive glass characterized by a yield stress, and a jamming state. We discuss the possible molecular mechanisms driving the formation of these states. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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16 pages, 1625 KiB

Open AccessArticle

Direct Metal-Free Transformation of Alkynes to Nitriles: Computational Evidence for the Precise Reaction Mechanism

by Lucija Hok and Robert Vianello

Int. J. Mol. Sci. 2021, 22(6), 3193; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22063193 - 21 Mar 2021

Cited by 8 | Viewed by 3519

Abstract

Density functional theory calculations elucidated the precise reaction mechanism for the conversion of diphenylacetylenes into benzonitriles involving the cleavage of the triple C≡C bond, with N-iodosuccinimide (NIS) as an oxidant and trimethylsilyl azide (TMSN₃) as a nitrogen donor. The reaction [...] Read more.

Density functional theory calculations elucidated the precise reaction mechanism for the conversion of diphenylacetylenes into benzonitriles involving the cleavage of the triple C≡C bond, with N-iodosuccinimide (NIS) as an oxidant and trimethylsilyl azide (TMSN₃) as a nitrogen donor. The reaction requires six steps with the activation barrier ΔG^‡ = 33.5 kcal mol⁻¹ and a highly exergonic reaction free-energy ΔG_R = −191.9 kcal mol⁻¹ in MeCN. Reaction profiles agree with several experimental observations, offering evidence for the formation of molecular I₂, interpreting the necessity to increase the temperature to finalize the reaction, and revealing thermodynamic aspects allowing higher yields for alkynes with para-electron-donating groups. In addition, the proposed mechanism indicates usefulness of this concept for both internal and terminal alkynes, eliminates the option to replace NIS by its Cl- or Br-analogues, and strongly promotes NaN₃ as an alternative to TMSN₃. Lastly, our results advise increasing the solvent polarity as another route to advance this metal-free strategy towards more efficient processes. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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Graphical abstract

17 pages, 2810 KiB

Open AccessArticle

A Molecular Interpretation of the Dynamics of Diffusive Mass Transport of Water within a Glassy Polyetherimide

by Andrea Correa, Antonio De Nicola, Giuseppe Scherillo, Valerio Loianno, Domenico Mallamace, Francesco Mallamace, Hiroshi Ito, Pellegrino Musto and Giuseppe Mensitieri

Int. J. Mol. Sci. 2021, 22(6), 2908; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22062908 - 12 Mar 2021

Cited by 5 | Viewed by 1879

Abstract

The diffusion process of water molecules within a polyetherimide (PEI) glassy matrix has been analyzed by combining the experimental analysis of water sorption kinetics performed by FTIR spectroscopy with theoretical information gathered from Molecular Dynamics simulations and with the expression of water chemical [...] Read more.

The diffusion process of water molecules within a polyetherimide (PEI) glassy matrix has been analyzed by combining the experimental analysis of water sorption kinetics performed by FTIR spectroscopy with theoretical information gathered from Molecular Dynamics simulations and with the expression of water chemical potential provided by a non-equilibrium lattice fluid model able to describe the thermodynamics of glassy polymers. This approach allowed us to construct a convincing description of the diffusion mechanism of water in PEI providing molecular details of the process related to the effects of the cross- and self-hydrogen bonding established in the system on the dynamics of water mass transport. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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13 pages, 640 KiB

Open AccessArticle

Some Aspects of the Liquid Water Thermodynamic Behavior: From The Stable to the Deep Supercooled Regime

by Francesco Mallamace, Giuseppe Mensitieri, Domenico Mallamace, Martina Salzano de Luna and Sow-Hsin Chen

Int. J. Mol. Sci. 2020, 21(19), 7269; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21197269 - 01 Oct 2020

Cited by 4 | Viewed by 1938

Abstract

Liquid water is considered to be a peculiar example of glass forming materials because of the possibility of giving rise to amorphous phases with different densities and of the thermodynamic anomalies that characterize its supercooled liquid phase. In the present work, literature data [...] Read more.

Liquid water is considered to be a peculiar example of glass forming materials because of the possibility of giving rise to amorphous phases with different densities and of the thermodynamic anomalies that characterize its supercooled liquid phase. In the present work, literature data on the density of bulk liquid water are analyzed in a wide temperature-pressure range, also including the glass phases. A careful data analysis, which was performed on different density isobars, made in terms of thermodynamic response functions, like the thermal expansion

α_{P}

and the specific heat differences

C_{P} - C_{V}

, proves, exclusively from the experimental data, the thermodynamic consistence of the liquid-liquid transition hypothesis. The study confirms that supercooled bulk water is a mixture of two liquid “phases”, namely the high density (HDL) and the low density (LDL) liquids that characterize different regions of the water phase diagram. Furthermore, the

C_{P} - C_{V}

isobars behaviors clearly support the existence of both a liquid–liquid transition and of a liquid–liquid critical point. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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Review

Jump to: Research

21 pages, 4236 KiB

Open AccessReview

Infrared Comb Spectroscopy of Buffer-Gas-Cooled Molecules: Toward Absolute Frequency Metrology of Cold Acetylene

by Luigi Santamaria, Valentina Di Sarno, Roberto Aiello, Maurizio De Rosa, Iolanda Ricciardi, Paolo De Natale and Pasquale Maddaloni

Int. J. Mol. Sci. 2021, 22(1), 250; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22010250 - 29 Dec 2020

Cited by 4 | Viewed by 2765

Abstract

We review the recent developments in precision ro-vibrational spectroscopy of buffer-gas-cooled neutral molecules, obtained using infrared frequency combs either as direct probe sources or as ultra-accurate optical rulers. In particular, we show how coherent broadband spectroscopy of complex molecules especially benefits from drastic [...] Read more.

We review the recent developments in precision ro-vibrational spectroscopy of buffer-gas-cooled neutral molecules, obtained using infrared frequency combs either as direct probe sources or as ultra-accurate optical rulers. In particular, we show how coherent broadband spectroscopy of complex molecules especially benefits from drastic simplification of the spectra brought about by cooling of internal temperatures. Moreover, cooling the translational motion allows longer light-molecule interaction times and hence reduced transit-time broadening effects, crucial for high-precision spectroscopy on simple molecules. In this respect, we report on the progress of absolute frequency metrology experiments with buffer-gas-cooled molecules, focusing on the advanced technologies that led to record measurements with acetylene. Finally, we briefly discuss the prospects for further improving the ultimate accuracy of the spectroscopic frequency measurement. Full article

(This article belongs to the Special Issue From Molecules to Colloids: Recent Advances in Their Chemical Physics)

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