Kinetics and Thermodynamics of Efficient Chiral Symmetry Breaking in Nearly Racemic Mixtures of Conglomerate Crystals

Skrdla, Peter J.

doi:10.1021/cg200116e

Cited by 31 publications

(30 citation statements)

References 58 publications

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“…The positive value of β suggests that the conversion from DH to α-HH is a nucleation-limited process. 26,28 The activation energy barrier (E a ) drops down, and the reaction rate coefficient increases with time, which accounts for the faster DH−α-HH transformation with time.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…26,27 It has only two parameters endowed with physical meanings and fits well to series x−t sigmoidal transients. 28,29 Thus, this model is expected to help to explore the DH−α-HH conversion kinetics.In this paper, the solution mediated DH−α-HH transformation kinetics was studied by monitoring the solid and liquid component evolution and using dispersive kinetic model. The effect of temperature and CaCl 2 concentration on the transformation kinetics was evaluated in 2.50−3.50 m CaCl 2 solutions at 90.0−100.0°C for better transformation control from DH to α-HH.…”

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confidence: 99%

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Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl₂ Solutions at Elevated Temperature

Jiang

Wang

et al. 2013

Ind. Eng. Chem. Res.

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α-Calcium sulfate hemihydrate (α-HH), a kind of advanced cementitious material, can be prepared from calcium sulfate dihydrate (DH) in electrolyte solutions. The kinetics of the DH−α-HH transformation in CaCl 2 solutions was investigated to better understand and, hence, control the transformation process. The results showed that the DH−α-HH transformation is a nucleation−growth limited process, following a dispersive kinetic model. The α-HH nucleation and growth were both promoted significantly with the increment of CaCl 2 concentration and temperature. This is due to the enlarged activation entropy change and supersaturation, which were caused by the decreasing water activity and increasing solubility product ratio (K sp,DH /K sp,HH ), respectively. The rate of DH−α-HH transformation in aqueous solutions can be effectively controlled by regulating water activity and temperature. ■ INTRODUCTIONLarge quantities of flue gas desulfurization (FGD) gypsum produced by coal-burning power plants have continuously raised significant environmental concerns. 1,2 The recycling and utilization of these gypsums become rather important for environmental protection and gypsum industry. FGD gypsum is composed mostly by calcium sulfate dihydrate (DH), 3 which can be transformed into α-calcium sulfate hemihydrate (α-HH) in the presence of inorganic or organic additives in aqueous solutions. 3−6 Hence, the preparation of α-HH from FGD gypsum could be a potential alternative for FGD gypsum utilization 3,7 owing to the superior physical property of α-HH. 8 DH dissolution, α-HH nucleation, and growth constitute the solution mediated transformation. 7,9,10 Four principal transformation scenarios are classified on the basis of the solid and liquid component evolution, including dissolution control, 11 growth control, 12 nucleation−dissolution control, 13 and nucleation−growth control. 14 The identification of the limiting step is essential for the control of the DH transformation to α-HH.The DH−α-HH conversion is driven by their solubility difference. According to dissolution equilibrium, solubility product and water activity are two important factors affecting the solubility, which depends heavily on temperature and stock solution. 15−18 For a given temperature, there exists a critical water activity at which both DH and α-HH would reach dissolution equilibrium (i.e., having the same solubility). 19,20 Low water activity makes DH prone to dehydration, attempting to increase availability of the free water molecules. 21 The increment of temperature or acidity (hydrochloric acid concentration) could enlarge the solubility difference between DH and α-HH and, hence, accelerate the conversion. 6,21 However, the underlying relationship between the driving force and operational factors (i.e., electrolyte concentration and temperature) is still not clear.The transformation among calcium sulfate phases versus time generally presents a sigmoidal profile. 8,22,23 Many kinetic models have been proposed to describe the S-shaped transformation curve. ...

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Section: ■ Results and Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl₂ Solutions at Elevated Temperature

Jiang

Wang

et al. 2013

Ind. Eng. Chem. Res.

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“…Monte Carlo simulations 35,[42][43][44] , dispersive kinetic models 45 and population balance models [46][47][48][49] .…”

Section: Introductionmentioning

confidence: 99%

Coupling Viedma Ripening with Racemic Crystal Transformations: Mechanism of Deracemization

Xiouras

Horst

Gerven

et al. 2017

Crystal Growth & Design

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It has been recently observed that coupling Viedma ripening with a seeded in-situ metastable racemic crystal to conglomerate transformation leads to accelerated and complete deracemization: crystal transformation-enhanced deracemization. By means of a simple kinetic model, we show that the mechanistic pathway of this new process depends profoundly on the interplay between the crystal transformation and racemization processes, which in turn influence the nucleation process of the counter enantiomer. If the nucleation of the counter enantiomer is suppressed (e.g. by sufficiently fast racemization, low amount of racemic compound or gradual feed, low relative solubility between racemic compound and conglomerate), deracemization proceeds via a second order asymmetric transformation (SOAT) and is limited primarily by the dissolution rate of the racemic crystals and the growth rate of the preferred enantiomer crystals. Breakage and agglomeration accelerate the process, but contrary to conventional Viedma ripening, they are not essential ingredients to explain the observed enantiomeric enrichment. If the nucleation process of the counter enantiomer is not sufficiently suppressed, deracemization is initially controlled by the dissolution rate of the racemic crystals, but Viedma ripening is subsequently required to convert the conglomerate crystals of the counter enantiomer formed by nucleation, resulting in slower deracemization kinetics. In both cases, the combined process leads to faster deracemization kinetics compared to conventional Viedma ripening, while it autocorrects for the main disadvantage of SOAT, i.e. the accidental nucleation of the counter enantiomer. In addition, crystal transformation-enhanced deracemization extends the range of applicability of solid-state deracemization processes to compounds that form metastable racemic crystals. interplay between the crystal transformation and racemization processes, which in turn influence the nucleation process of the counter enantiomer. If the nucleation of the counter enantiomer is 3 suppressed (e.g. by sufficiently fast racemization, low amount of racemic compound or gradual feed, low relative solubility between racemic compound and conglomerate), deracemization proceeds via a second order asymmetric transformation (SOAT) and is limited primarily by the dissolution rate of the racemic crystals and the growth rate of the preferred enantiomer crystals.Breakage and agglomeration accelerate the process, but contrary to conventional Viedma ripening, they are not essential ingredients to explain the observed enantiomeric enrichment. If the nucleation process of the counter enantiomer is not sufficiently suppressed, deracemization is initially controlled by the dissolution rate of the racemic crystals, but Viedma ripening is subsequently required to convert the conglomerate crystals of the counter enantiomer formed by nucleation, resulting in slower deracemization kinetics. In both cases, the combined process leads to faster deracemization kinetics compared ...

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“…Recently, a kinetic study shows that attrition of conglomerate crystals follows a sigmoidal conversion rather than a first‐order (simple exponential) mechanism . This modeling supports that nucleation is the rate‐limiting step in Viedma‐type deracemizations and such a nucleation should be secondary, not primary.…”

Section: Deracemization By Attritionmentioning

confidence: 80%

“…Preliminary mechanistic studies have concentrated on modeling and kinetic understanding of simple systems such as that of NaClO 3 crystallization. As rightly pointed out by Skrdla recently, the literature shows that several mechanisms are possible because by altering the experimental conditions, the kinetic profiles are largely affected. The efficiency of attrition depends on parameters such as solubility, crystal size, and temperature.…”

Section: Deracemization By Attritionmentioning

confidence: 97%

On the Physical Basis of Asymmetry and Homochirality

Cintas

Viedma

2012

Chirality

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Mirror symmetry breaking is ubiquitous in our visible universe taking place in elementary particles, atoms, and molecules. Molecular chirality is not biogenic in itself, although its detection is often considered a biosignature, a conjecture inferred from the fact that we do not know life devoid of homochirality. The question of whether there is a connection between the cosmic preference for one enantiomer, as imposed by the weak force, and the single chirality displayed on Earth is vividly debated. This article gives a glimpse on the origin of asymmetry from a cosmological perspective and on physical transformations that lead to an enantiomeric imbalance, leaving chemical reactions essentially aside. These processes are more plausible as sources of prebiotic chirality than asymmetric amplifications requiring unnatural substrates and conditions and fighting against racemization. The latter may actually be a friend, not foe, and a driving force for enantioselection.

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Kinetics and Thermodynamics of Efficient Chiral Symmetry Breaking in Nearly Racemic Mixtures of Conglomerate Crystals

Cited by 31 publications

References 58 publications

Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl₂ Solutions at Elevated Temperature

Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl₂ Solutions at Elevated Temperature

Coupling Viedma Ripening with Racemic Crystal Transformations: Mechanism of Deracemization

On the Physical Basis of Asymmetry and Homochirality

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Kinetics and Thermodynamics of Efficient Chiral Symmetry Breaking in Nearly Racemic Mixtures of Conglomerate Crystals

Cited by 31 publications

References 58 publications

Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl2 Solutions at Elevated Temperature

Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl2 Solutions at Elevated Temperature

Coupling Viedma Ripening with Racemic Crystal Transformations: Mechanism of Deracemization

On the Physical Basis of Asymmetry and Homochirality

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Product

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Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl₂ Solutions at Elevated Temperature

Solution-Mediated Transformation Kinetics of Calcium Sulfate Dihydrate to α-Calcium Sulfate Hemihydrate in CaCl₂ Solutions at Elevated Temperature