In a review of the present title, the first requirement is to ensure that the title words are understood. While the term “glass” is broadly familiar, and the origin of the “glass transition” in terms of the crossing of system and experimental time scales is generally agreed upon, there are at least three different definitions of the material property “glass transition temperature” (Tg) in current use.1,2 Furthermore, these may differ from each other by as much as 50 K in certain higher Tg cases. The difference is a consequence of the magnitude of the “glass transformation range” within which the Tg is variously defined. This magnitude, the “width of the glass transition”, can vary greatly from system to system, for reasons discussed below. Since the quantity Tg will recur frequently in this review, it is necessary to deal adequately with the definition problem, and this will be done by reference to Figures 1 and 2 below. Depending on the liquid in question, glass transitions may be observed occurring over an enormous range in temperature, from below 50 K to above 1500 K. The reason for this range is clearly to do with the strength of the interparticle interactions, i.e., the “bonds” that are being broken as the particles rearrange. However, the reason that some glass transitions are “sharp” (meaning narrow glass transformation range, or “transition width”) and others very spread out in temperature is not so clear. It is largely to do with the “fragility” of the glassformer, but may C. A. Angell was born in Canberra, Australia, and studied chemistry and metallurgy at the University of Melbourne. After working on molten salts with J. O’M Bockris at the University of Pennsylvania for two years, he became the Stanley Elmore Fellow at Imperial College of Science, London, where he completed his Ph.D. under the direction of John W. Tomlinson. There he was awarded the Armstrong medal for graduate research 1959− 1961. He returned to Australia as lecturer in chemical metallurgy but after two years came back to the U.S. as a post-doc with Dieter Gruen at Argonne National Laboratory. In 1966, he joined Purdue University as Assistant Professor, becoming full Professor in 1971. In 1989, he moved to Arizona State University where he is now Regents’ Professor of Chemistry and Biochemistry. He has enjoyed and profited from sabbatical leaves at the University of Amsterdam, the Australian National University, Institute Laue-Langevin, Grenoble, the Ecole de Physique et Chemie Industrielle, Paris, University of Rennes-Beaulieu, Sydney University, and the University of Rome. His research interests range from rechargeable lithium batteries and fuel cells, through the phenomenology of the glass transition and the origin of fragility in liquids, to the anomalous properties of water and geochemical fluids and their relation to polyamorphism. Currently, he is focusing on the annealing behavior of hyperquenched liquids and solutions, particularly denatured protein solutions, with a sideline on nanoporous network glasses as gas storage media. 2627 Chem. Rev. 2002, 102, 2627−2650

Liquid fragility and the glass transition in water and aqueous solutions.

. A new process is presented by which water soluble organics might influence ice nucleation, ice growth, chemical reactions and water uptake of aerosols in the upper troposphere: the formation of glassy aerosol particles. Glasses are disordered amorphous (non-crystalline) solids that form when a liquid is cooled without crystallization until the viscosity increases exponentially and molecular diffusion practically ceases. The glass transition temperatures, Tg, homogeneous ice nucleation temperatures, Thom, and ice melting temperatures, Tm, of various aqueous inorganic, organic and multi-component solutions are investigated with a differential scanning calorimeter. The investigated solutes are: various polyols, glucose, raffinose, levoglucosan, an aromatic compound, sulfuric acid, ammonium bisulfate and mixtures of dicarboxylic acids (M5), of dicarboxylic acids and ammonium sulfate (M5AS), of two polyols, of glucose and ammonium nitrate, and of raffinose and M5AS. The results indicate that aqueous solutions of the investigated inorganic solutes show Tg values that are too low to be of atmospheric importance. In contrast, aqueous organic and multi-component solutions readily form glasses at low but atmospherically relevant temperatures (≤230 K). To apply the laboratory data to the atmospheric situation, the measured phase transition temperatures were transformed from a concentration to a water activity scale by extrapolating water activities determined between 252 K and 313 K to lower temperatures. The obtained state diagrams reveal that the higher the molar mass of the aqueous organic or multi-component solutes, the higher Tg of their respective solutions at a given water activity. To a lesser extent, Tg also depends on the hydrophilicity of the organic solutes. Therefore, aerosol particles containing larger (≳150 g mol−1) and more hydrophobic organic molecules are more likely to form glasses at intermediate to high relative humidities in the upper troposphere. Our results suggest that the water uptake of aerosols, heterogeneous chemical reactions in aerosol particles, as well as ice nucleation and ice crystal growth can be significantly impeded or even completely inhibited in organic-enriched aerosols at upper tropospheric temperatures with implications for cirrus cloud formation and upper tropospheric relative humidity.

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Do atmospheric aerosols form glasses

We present measurements of water uptake and release by single micrometre-sized aqueous sucrose particles. The experiments were performed in an electrodynamic balance where the particles can be stored contact-free in a temperature and humidity controlled chamber for several days. Aqueous sucrose particles react to a change in ambient humidity by absorbing/desorbing water from the gas phase. This water absorption (desorption) results in an increasing (decreasing) droplet size and a decreasing (increasing) solute concentration. Optical techniques were employed to follow minute changes of the droplet's size, with a sensitivity of 0.2 nm, as a result of changes in temperature or humidity. We exposed several particles either to humidity cycles (between ∼2% and 90%) at 291 K or to constant relative humidity and temperature conditions over long periods of time (up to several days) at temperatures ranging from 203 to 291 K. In doing so, a retarded water uptake and release at low relative humidities and/or low temperatures was observed. Under the conditions studied here, the kinetics of this water absorption/desorption process is controlled entirely by liquid-phase diffusion of water molecules. Hence, it is possible to derive the translational diffusion coefficient of water molecules, DH2O, from these data by simulating the growth or shrinkage of a particle with a liquid-phase diffusion model. Values for DH2O-values as low as 10−24 m2 s−1 are determined using data at temperatures down to 203 K deep in the glassy state. From the experiment and modelling we can infer strong concentration gradients within a single particle including a glassy skin in the outer shells of the particle. Such glassy skins practically isolate the liquid core of a particle from the surrounding gas phase, resulting in extremely long equilibration times for such particles, caused by the strongly non-linear relationship between concentration and DH2O. We present a new parameterization of DH2O that facilitates describing the stability of aqueous food and pharmaceutical formulations in the glassy state, the processing of amorphous aerosol particles in spray-drying technology, and the suppression of heterogeneous chemical reactions in glassy atmospheric aerosol particles.

Ultra-slow water diffusion in aqueous sucrose glasses

Short-chain fatty acids (SCFAs), mainly acetate, propionate, and butyrate, produced by microbial fermentation of undigested food substances are believed to play a beneficial role in human gut health. Short-chain fatty acids influence colonic health through various mechanisms. In vitro and ex vivo studies show that SCFAs have anti-inflammatory and anticarcinogenic effects, play an important role in maintaining metabolic homeostasis in colonocytes, and protect colonocytes from external harm. Animal studies have found substantial positive effects of SCFAs or dietary fiber on colonic disease, but convincing evidence in humans is lacking. Most human intervention trials have been conducted in the context of inflammatory bowel disease. Only a limited number of those trials are of high quality, showing little or no favorable effect of SCFA treatment over placebo. Opportunities for future research include exploring the use of combination therapies with anti-inflammatory drugs, prebiotics, or probiotics; the use of prodrugs in the setting of carcinogenesis; or the direct application of SCFAs to improve mucosal healing after colonic surgery.

/pdf/role-of-short-chain-fatty-acids-in-colonic-inflammation-4kjcn17jz6.pdf

Role of short-chain fatty acids in colonic inflammation, carcinogenesis, and mucosal protection and healing.

The structural properties resulting from the reciprocal influence between water and three well-known homologous disaccharides, namely, trehalose, maltose, and sucrose, in aqueous solutions have been investigated in the 4-66 wt % concentration range by means of molecular dynamics computer simulations. Hydration numbers clearly show that trehalose binds to a larger number of water molecules than do maltose or sucrose, thus affecting the water structure to a deeper extent. Two-dimensional radial distribution functions of trehalose solutions definitely reveal that water is preferentially localized at the hydration sites found in the trehalose dihydrate crystal, this tendency being enhanced when increasing trehalose concentration. Over a rather wide concentration range (4-49 wt %), the fluctuations of the radius of gyration and of the glycosidic dihedral angles of trehalose indicate a higher flexibility with respect to maltose and sucrose. At sugar concentrations between 33 and 66 wt %, the mean sugar cluster size and the number of sugar-sugar hydrogen bonds formed within sugar clusters reveal that trehalose is able to form larger clusters than sucrose but smaller than maltose. These features suggest that trehalose-water mixtures would be more homogeneous than the two others, thus reducing both desiccation stresses and ice formation.

How homogeneous are the trehalose, maltose, and sucrose water solutions? An insight from molecular dynamics simulations.

c,T-dependence of the viscosity and the self-diffusion coefficients in some aqueous carbohydrate solutions.

Based on the biochemical theory of multiple ligand-receptor complexes (Klotz (1946)) a sigmoidal proceeding adsorption isotherm is derived. The special case of an arbitrarily large number of equal interaction sites and a separate one yields an equation which corresponds to the ζ-isotherm, disparately derived by Ward et al. (2007) for surface tension of solid-fluid interfaces. From the mathematical point of view it is analogous to the BET-isotherm for a limited number of adsorption layers (1938). It is shown that the isotherm maps type IV and V isotherms. The isotherm is compared with others including the type IV isotherm of Do and Do (2009). The present isotherm is unified in contrast to existing hybrid models. It is successfully applied to numerous literature data concerning the adsorption of water on microporous carbon and aluminophosphate molecular sieves.

https://pubs.rsc.org/en/content/articlepdf/2019/cp/c8cp07751g

Modeling of type IV and V sigmoidal adsorption isotherms

In the present study we describe the preparation and chemical characterization of a caramel with a high (70%) content of difructose dianhydrides (DFAs) and glycosylated derivatives (DFAs). This product was obtained by thermal activation (90 degrees C) of highly concentrated (90% w/v) aqueous D-fructose solutions using the sulfonic acid ion-exchange resin Lewatit S2328 as caramelization catalyst. DFAs represent a unique family of cyclic fructans with prebiotic properties already present in low proportions (<15%) in commercial caramel. We report the antiinflammatory activity of the new DFA-enriched caramel in the trinitrobenzenesulfonic acid (TNBS) model of rat colitis, an experimental model that resembles human inflammatory bowel disease (IBD), and compare its effects with those obtained with a commercial sucrose caramel and with linear fructooligosaccharides (FOS). For this purpose, the effects on colon tissue damage, gut microbiota, short-chain fatty acid (SCFAs) production, and different inflammatory markers were evaluated. The administration of DFA-enriched caramel to colitic rats showed intestinal antiinflammatory effect, as evidenced macroscopically by a significant reduction in the extent of the colonic damage induced by TNBS. This effect was similar to that obtained with FOS in the same experimental settings, whereas commercial caramel was devoid of any significant antiinflammatory effect. The beneficial effect was associated with the inhibition of the colonic levels of the proinflammatory cytokines, tumor necrosis factor alpha (TNF alpha) and interleukin 1beta (IL-1beta), and the reduction in colonic myeloperoxidase (MPO) activity and inducible nitric oxide synthase (iNOS) expression. The DFA-enriched caramel also promoted a more favorable intestinal microbiota, increasing lactobacilli and bifidobacteria counts as well as inducing higher concentrations of SCFAs in the luminal colonic contents. These results reinforce the concept of DFAs and glycosyl-DFAs as dietary beneficial compounds with prebiotic properties and suggest that the novel DFA-enriched caramel here reported may be an interesting candidate to be explored for the dietary treatment of human IBD.

Di-D-fructose dianhydride-enriched caramels: effect on colon microbiota, inflammation, and tissue damage in trinitrobenzenesulfonic acid-induced colitic rats.

Christoph Buttersack

Papers

c,T-dependence of the viscosity and the self-diffusion coefficients in some aqueous carbohydrate solutions.

Modeling of type IV and V sigmoidal adsorption isotherms

Di-D-fructose dianhydride-enriched caramels: effect on colon microbiota, inflammation, and tissue damage in trinitrobenzenesulfonic acid-induced colitic rats.

Determination of micropore volume and external surface of zeolites

General Cluster Sorption Isotherm