The effect of salt additives on the glycine crystallization pathway revealed by studying one crystal nucleation at a time

Molecular-level understanding of the early stage of crystallization remains a significant challenge. For a wide range of fundamental research and applications, it is of great importance to understand the mechanism of crystal polymorph selections in different solvents or in the presence of additives. We studied glycine crystallization in aqueous solution with or without the addition of sodium chloride (NaCl), one crystal nucleation at a time, using the recently developed single-crystal nucleation spectroscopy (SCNS). It has been reported that glycine forms γ-glycine when salt is added to aqueous solution, and the mechanism has been considered as a classical nucleation where γ-glycine forms directly as a crystal nucleus. Our study shows that metastable polymorph β-glycine forms first in aqueous solution both with or without NaCl through a nonclassical nucleation pathway. NaCl can stabilize the metastable β-glycine over several hours and also prevent it from converting to α-glycine. Eventually γ-glycine nucleates on the surface of β-glycine and then grows while dissolving the mother β-glycine. The crystal habit of β-glycine suggests that the stabilization by NaCl occurs at its polar face. SCNS provides crucial information to accelerate the investigation of the early stage of crystallization toward the rational control of polymorphisms.

From Preformulative Design to In Vivo Tests: A Complex Path of Requisites and Studies for Nanoparticle Ocular Application. Part 1: Design, Characterization, and Preliminary In Vitro Studies

Ocular pathologies are widely diffused worldwide, and their effective treatment, combined with a high patient compliance, is sometimes challenging to achieve due to the barriers of the eye; in this context, the use of nanoparticles for topical ophthalmic application could represent a successful strategy. Aiming to develop nanoplatforms with potential clinical applications, great attention has to be paid to their features, in relation to the route of administration and to the pharmacopoeial requirements. This review (part 1) thus embraces the preliminary steps of nanoparticle development and characterization. At the beginning, the main barriers of the eye and the different administration routes are resumed, followed by a general description of the advantages of the employment of nanoparticles for ocular topical administration. Subsequently, the preformulative steps are discussed, deepening the choice of raw materials and determining the quantitative composition. Then, a detailed report of the physicochemical and technological characterization of nanoparticles is presented, analyzing the most relevant tests that should be performed on nanoparticles to verify their properties and the requisites (both mandatory and suggested) demanded by regulatory agencies. In conclusion, some preliminary noncellular in vitro evaluation methods are described. Studies from in vitro cellular assays to in vivo tests will be discussed in a separate (part 2) review paper. Hence, this overview aims to offer a comprehensive tool to guide researchers in the choice of the most relevant studies to develop a nanoplatform for ophthalmic drug administration.

Polymorphism and Microstructural Changes in Avocado Pulp (Persea americana Mill.) After Scraped-Surface Heat Exchanger Processing

Avocado (Persea americana Mill.) is a fruit with a high content of unsaturated fatty acids and bioactive compounds, whose consumption has considerably increased in the USA and Europe. Thus, the conservation of the avocado mesocarp (pulp) has become more relevant. Avocado pulp was processed using a scraped-surface heat exchanger (SSHE) system to extend the shelf-life of the mesocarp. Through analysis with X-ray diffraction and HRTEM, it was possible to identify crystalline-type structures in the avocado pulp processed and stored at 4 °C. The 2θ-angles and d-spacing of the structures that reported the highest diffraction intensity are comparable to the polymorphs β' reported in the literature for fatty acid mixtures processed under similar conditions. Furthermore, the X-ray signals suggest the presence of polymorphs α and β in all samples processed and stored at different temperatures. Calorimetry analysis showed curves with first-order phase changes as indicative of crystallization-type transitions. The shelf-life evaluation of the avocado pulp showed that the crystallization process minimized the losses of antioxidant capacity and prevented color change, while the enzyme polyphenol oxidase remained inactivated. The changes induced by the SSHE continuous processing applied might represent an alternative to obtaining avocado products that preserve avocado's properties and extend its shelf-life.

Optical trapping-induced crystallization promoted by gold and silicon nanoparticles

This study investigates the promotion of sodium chlorate (NaClO3) crystallization through optical trapping, enhanced by the addition of gold nanoparticles (AuNPs) and silicon nanoparticles (SiNPs). Using a focused laser beam at the air-solution interface of a saturated NaClO3 solution with AuNPs or SiNPs, the aggregates of these particles were formed at the laser focus, the nucleation and growth of metastable NaClO3 (m-NaClO3) crystals were induced. Continued laser irradiation caused these m-NaClO3 crystals to undergo repeated cycles of growth and dissolution, eventually transitioning to a stable crystal form. Our comparative analysis showed that AuNPs, due to their significant heating due to higher photon absorption efficiency, caused more pronounced size fluctuations in m-NaClO3 crystals compared to the stable behavior observed with SiNPs. Interestingly, the maximum diameter of the m-NaClO3 crystals that appeared during the size fluctuation step was consistent, regardless of nanoparticle type, concentration, or size. The crystallization process was also promoted by using polystyrene nanoparticles, which have minimal heating and electric field enhancement, suggesting that the reduction in activation energy for nucleation at the particle surface is a key factor. These findings provide critical insights into the mechanisms of laser-induced crystallization, emphasizing the roles of plasmonic heating, particle surfaces, and optical forces.

Enhancing physicochemical and functional properties of myo-inositol in crystallization with edible sugar additives

Myo-inositol, referred to as vitamin B8, is an essential nutrient for maintaining human physiological functions. However, the morphology of myo-inositol products is predominantly powder or needle shaped, leading to poor food properties. In this work, three edible sugar additives, i.e. d-glucose, l-arabinose and d-fructose, are adopted in the crystallization of myo-inositol to improve its food properties. The results show that these additives change the morphology of myo-inositol crystals. d-glucose and l-arabinose reduced the aspect ratio of myo-inositol crystals, and d-glucose transformed elongated lamellar myo-inositol crystals into diamond-shaped lamellar crystals. The diamond-shaped lamellar myo-inositol products exhibited outstanding functional food properties. It offered a smoother texture and more pleasant mouthfeel when the products were added to infant formulas and nutraceuticals. When they were applied to functional beverages, the dissolution rate was increased by 35 %. This work provides a theoretical guidance for improving food properties through crystallization and possesses considerable potential for industrialization.

Using singular value decomposition to analyze drug/β-cyclodextrin mixtures: insights from X-ray powder diffraction patterns

The article discusses the use of mathematical models and linear algebra to understand the crystalline structures and interconversion pathways of drug complexes with β-cyclodextrin (β-CD). It involved the preparation and analysis of mixtures of indomethacin, diclofenac, famotidine, and cimetidine with β-CD using techniques such as differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and proton nuclear magnetic resonance (1H-NMR). Singular value decomposition (SVD) analysis is used to identify the presence of different polymorphs in the mixtures of these drugs and β-CD, determine interconversion pathways, and distinguish between different forms. In general, linear algebra or artificial intelligence (AI) is used to approximate the contribution of distinguishable entities to various phenomena. We expected linear algebra to completely reveal all eight entities present in the diffractogram dataset. However, after performing the SVD procedure, we found that only six independent basis functions were extracted, and the entities of the INM α-form and the CIM B-form were not included. It is considered that this is due to that data processing is limited to revealing only six or seven independent factors, as it is a small world. The authors caution that these may not always reproduce or approach reality in complicated real-world situations.

Predicting crystal form stability under real-world conditions

The physicochemical properties of molecular crystals, such as solubility, stability, compactability, melting behaviour and bioavailability, depend on their crystal form1. In silico crystal form selection has recently come much closer to realization because of the development of accurate and affordable free-energy calculations2-4. Here we redefine the state of the art, primarily by improving the accuracy of free-energy calculations, constructing a reliable experimental benchmark for solid-solid free-energy differences, quantifying statistical errors for the computed free energies and placing both hydrate crystal structures of different stoichiometries and anhydrate crystal structures on the same energy landscape, with defined error bars, as a function of temperature and relative humidity. The calculated free energies have standard errors of 1-2 kJ mol-1 for industrially relevant compounds, and the method to place crystal structures with different hydrate stoichiometries on the same energy landscape can be extended to other multi-component systems, including solvates. These contributions reduce the gap between the needs of the experimentalist and the capabilities of modern computational tools, transforming crystal structure prediction into a more reliable and actionable procedure that can be used in combination with experimental evidence to direct crystal form selection and establish control5.

Crystallization Behavior and Physical Properties of Monoglycerides-Based Oleogels as Function of Oleogelator Concentration

Oleogels have been shown as a promising replacer of hydrogenated vegetable oil. Fatty acid glycerides, including some typical mono- and di-glycerides, were used to form oleogels. The concentration effects of fatty acid glycerides on the crystallization behavior and physical properties of oleogels were investigated by using different analysis techniques. The results showed that all the oleogels formed by saturated fatty acid glycerides (glyceryl monostearate (GMS), glyceryl monolaurate (GML), glycerol monocaprylate (GMC)) exhibited a solid-like behavior and were thermally reversible systems, while a higher amount of unsaturated fatty acid glycerides (monoolein (GMO), diolein (GDO)) were needed to form oleogels. The onset gelation concentration of GMS and GMC was found to be 2 wt% (w/w), while that of GML was 4 wt% by the inverted tube method. The crystallization results illustrated that the GMS and GMC formed small needle-like crystals with the presence of β and β' crystals, while GML formed large flake-like crystals with α crystals in oleogels, and faster cooling rates caused smaller crystals. GMS- and GMC-based oleogels had higher crystallinity, resulting in higher thermal stability and better mechanical properties than GML-based ones at the same monoglyceride (MAG) level. With the increasing MAG content, the oleogels showed a more compact three-dimensional network leading to higher mechanical properties and better thermal stability and resistance to deformations. Hence, MAG-based oleogels, especially GMC ones with medium chain fatty acid, could be a promising replacer for hydrogenation vegetable oils.

Effects of natural waxes on the interfacial behavior, structural properties and foam stabilization of aerated emulsions

Aerated emulsions have widespread applications in food industry. However, the poor stability of aerated emulsions remains a major challenge due to their inherent thermodynamic instability. Herein, a novel strategy to...

Challenges associated with spray drying of lactic acid bacteria: Understanding cell viability loss

Lactic acid bacteria (LAB) cultures used in food fermentation are often dried to reduce transportation costs and facilitate handling during use. Dried LAB ferments are generally lyophilized to ensure high cell viability. Spray drying has come to the forefront as a promising technique due to its versatility and lower associated energy costs. Adverse conditions during spray drying, such as mechanical stress, dehydration, heating, and oxygen exposure, can lead to low LAB cell viability. This reduced viability has limited spray drying's industrial applications thus far. This review aims to demonstrate the operations and thermodynamic principles that govern spray drying, then correlate them to the damage suffered by LAB cells during the spray-drying process. The particularities of spray drying that might cause LAB cell death are detailed in this review, and the conclusion may enhance future studies on ways to improve cell viability.

Surface-Induced Crystallization of Sodium Dodecyl Sulfate (SDS) Micellar Solutions in Confinement

We investigate the role of confinement on the onset of crystallization in subcooled micellar solutions of sodium dodecyl sulfate (SDS), examining the impact of sample volume, substrate surface energy, and surface roughness. Using small angle neutron scattering (SANS) and dynamic light scattering (DLS), we measure the crystallization temperature upon cooling and the metastable zone width (MSZW) for bulk 10-30 wt% SDS solutions. We then introduce a microdroplet approach to quantify the impact of surface free energy (18-65 mN/m) and substrate roughness (R_α ≃ 0-60 μm) on the kinetics of surface-induced crystallization through measurements of induction time (t_i) under isothermal conditions. While t_i is found to decrease exponentially with decreasing temperature (increasing subcooling) for all tested surfaces, increasing the surface energy could cause a significant further reduction of up to ∼40 fold. For substrates with the lowest surface energy and longest t_i, microscale surface roughness is found to enhance crystal nucleation, in particular for R_α ≥ 10 μm. Finally, we demonstrate that tuning the surface energy and microscopic roughness can be effective routes to promote or delay nucleation in bulk-like volumes, thus greatly impacting the stability of surfactant solutions at lower temperatures.

Exploration of the natural waxes-tuned crystallization behavior, droplet shape and rheology properties of O/W emulsions

Lipid crystallization in O/W emulsions is essential to control the release of nutrients and to food structuring. While few information is involved in adjusting and controlling the performance of emulsions by adjusting oil phase crystallization behavior. We herein developed a novel strategy for designing lipid crystallization inside oil droplets by natural waxes to modify the O/W emulsion properties. Natural waxes, the bio-based and sustainable materials, displayed a high efficiency in modifying the crystallization behavior, droplet surface and shape, as well as the overall performance of emulsions. Specifically, waxes induced the formation of a new hydrocarbon chain distances of 3.70 and 4.15 Å and slightly decreased the lamellar distance (d₀₀₁) of the single crystallites, thus forming the large and rigid crystals in droplets. Interestingly, these large and rigid crystals in droplets tended to penetrate the interface film, forming the crystal bumps on the droplet surface and facilitating non-spherical shape transformation. The presence of rice bran wax (RW) and carnauba wax (CW) induced the droplet shape into ellipsoid and polyhedron shape, respectively. Furthermore, the uneven interface and non-spherical shape transformation promoted the crystalline droplet-droplet interaction, fabricating a three-dimensional network structure in O/W emulsions. Finally, both linear and nonlinear rheology strongly supported that waxes enhanced the crystalline droplet-droplet interaction and strengthened the network in O/W emulsions. Our findings give a clear insight into the effects of adding natural waxes into oil phase on the crystalline and physical behavior of emulsions, which provides a direction for the design and control of emulsion performance.

Changes in the physical properties of frozen cooked rice depending on thermal insulation levels of packaging during freeze-thaw

Frozen cooked rice, a common commercially available product, has become the food of convenience in different parts of the world. Frozen foods that are well made in factories often experience quality deterioration due to temperature fluctuation during distribution. This study aimed to evaluate the impact of repeated freeze-thaw, which may occur during distribution, on the physical quality of frozen cooked rice. Additionally, the effect of the thermal insulation levels of the packaging on the quality change of frozen cooked rice as a result of repeated freeze-thaw was analyzed. The repeated freeze-thaw treatment of frozen cooked rice resulted in moisture loss, microstructure destruction, increase in hardness, increase in adhesiveness, decrease in the L^* -value, increase in the a^* -value, increase in the b^* -value, and increase in the ΔE-value. In particular, the quality of frozen cooked rice quickly deteriorated in samples stored in packaging with low thermal insulation. On the contrary, the higher the thermal insulation of the packaging, the longer the changes in the physical properties of the frozen cooked rice were delayed. The findings of the present study show that the deterioration of quality induced by the repeated freeze-thaw treatment of frozen cooked rice could be suppressed by thermal insulated packaging. PRACTICAL APPLICATION: The present study indicates that thermal insulated packaging can be used for industrial packaging of frozen cooked rice, as it delays the quality deteriorating effects of repeated freeze-thaw. This can help maintain the quality of frozen cooked rice and improve consumer satisfaction despite temperature fluctuations during distribution.

Effect of processing conditions as high-intensity ultrasound, agitation, and cooling temperature on the physical properties of a low saturated fat

The objective of this work was to evaluate the effect that agitation rate, crystallization temperature, and sonication have on the physical properties of a soybean-based fat with low levels of saturated fatty acids crystallized in a scraped surface heat exchanger (SSHE). The sample was crystallized at two temperatures (20 and 25 °C) and agitation rates (344/208 rpm in the barrels/pin worker-high agitation HA and 185/71 rpm barrels/pin worker-low agitation LA), and a constant flow of 11 L/hr. High-intensity ultrasound (HIU - 12.7 mm-diameter tip, 50% amplitude, 5 s pulses) was coupled to a water jacketed flow-cell and placed at three different positions within the SSHE. The combination of all those parameters affected samples' physical properties. Higher oil binding capacity (OBC) and elasticity (G') were obtained at 20 °C compared to 25 °C (77% vs. 63.78% for OBC and 30.4 kPa vs. 6 kPa for G', respectively) due to the smaller crystals formed at 20 °C. Fewer or no differences were observed due to agitation alone, but LA conditions allowed for more secondary nucleation to form due to sonication and resulted in a higher improvement on the properties of the fat. PRACTICAL APPLICATION: Fat crystallization in a scrapped surface heat exchanger (SSHE) combined with a high-intensity ultrasound (HIU) gives a realistic idea of how the HIU would work in an industrial line under continuous flow, shaved shear, and different supercooling. Results from this research will provide industry with tools on how and where to incorporate HIU in their processing line. Moreover, will give information on how to combined crystallization conditions and sonocrystallization in order to obtain improved physical properties.

Milk fat: opportunities, challenges and innovation

Milk fat is a high-value milk component that is processed mainly as butter, cheese, cream and whole milk powder. It is projected that approximately 35 million tonnes of milk fat will be produced globally by 2025. This surplus, enhances the need for diversification of milk fat products and the milk pool in general. Infant milk formula producers, for instance, have incorporated enzyme modified ("humanised") milk fat and fat globule phospholipids to better mimic human milk fat structures. Minor components like mono- and di-glycerides from milk fat are increasingly utilized as emulsifiers, replacing palm esters in premium-priced food products. This review examines the chemistry of milk fat and the technologies employed for its modification, fractionation and enrichment. Emerging processing technologies such as ultrasound, high pressure processing, supercritical fluid extraction and fractionation, can be employed to improve the nutritional and functional attributes of milk fat. The potential of recent developments in biological intervention, through dietary manipulation of milk fatty acid profiles in cattle also offers significant promise. Finally, this review provides evidence to help redress the imbalance in reported associations between milk fat consumption and human health, and elucidates the health benefits associated with consumption of milk fat and dairy products.

Synthesis, physicochemical properties, and health aspects of structured lipids: A review

Structured lipids (SLs) refer to a new type of functional lipids obtained by chemically, enzymatically, or genetically modifying the composition and/or distribution of fatty acids in the glycerol backbone. Due to the unique physicochemical characteristics and health benefits of SLs (for example, calorie reduction, immune function improvement, and reduction in serum triacylglycerols), there is increasing interest in the research and application of novel SLs in the food industry. The chemical structures and molecular architectures of SLs define mainly their physicochemical properties and nutritional values, which are also affected by the processing conditions. In this regard, this holistic review provides coverage of the latest developments and applications of SLs in terms of synthesis strategies, physicochemical properties, health aspects, and potential food applications. Enzymatic synthesis of SLs particularly with immobilized lipases is presented with a short introduction to the genetic engineering approach. Some physical features such as solid fat content, crystallization and melting behavior, rheology and interfacial properties, as well as oxidative stability are discussed as influenced by chemical structures and processing conditions. Health-related considerations of SLs including their metabolic characteristics, biopolymer-based lipid digestion modulation, and oleogelation of liquid oils are also explored. Finally, potential food applications of SLs are shortly introduced. Major challenges and future trends in the industrial production of SLs, physicochemical properties, and digestion behavior of SLs in complex food systems, as well as further exploration of SL-based oleogels and their food application are also discussed.

Potential of Milk Fat to Structure Semisolid Lipidic Systems: A Review

Food production and consumption patterns have changed dramatically in recent decades. The universe of oils and fats, in particular, has been changed due to the negative impacts of trans fatty acids produced industrially through the partial hydrogenation of vegetable oils. Regulations prohibiting its use have led the industry to produce semisolid lipid systems using chemical methods for modification of oils and fats, with limitations from a technological point of view and a lack of knowledge about the metabolization of the modified fats in the body. Milk fat is obtained from the complex biosynthesis in the mammary gland and can be a technological alternative for the modulation of the crystallization processes of semi-solids lipid systems, once it is naturally plastic at the usual processing, storage, and consumption temperatures. The natural plasticity of milk fat is due to its heterogeneous chemical composition, which contains more than 400 different fatty acids that structure approximately 64 million triacylglycerols, with a preferred polymorphic habit in β', besides other physical properties. Therefore, milk fat differs from any lipid raw material found in nature. This review will address the relationship between the chemical behavior and physical properties of semisolid lipids, demonstrating the potential of milk fat as an alternative to the commonly used modification processes.

Manipulation of Recrystallization and Network Formation of Oil-Dispersed Micronized Fat Crystals

A detailed investigation was carried out on the modulation of the coupling between network formation and the recrystallization of oil-dispersed micronized fat crystal (MFC) nanoplatelets by varying oil composition, shear, and temperature. Sunflower (SF) and bean (BO) oils were used as dispersing media for MFC nanoplatelets. During MFC dispersion production at high shear, a significant increase in the average crystal thickness (ACT) could be observed, pointing to recrystallization of the MFC nanoplatelets. More rapid recrystallization of MFC occurred in the SF dispersion than in the BO dispersion, which is attributed to higher solubility of MFC in the SF oil. When the dispersions were maintained under low shear in narrow gap Couette geometry, we witnessed two stages of recrystallization (measured via rheo-SAXD) and the development of a local yield stress (measured via rheo-MRI). In the first stage, shear-enabled mass transfer induces rapid recrystallization of randomly distributed MFC nanoplatelets, which is reflected in a rapid increase in ACT (rheo-SAXD). The formation of a space-filling weak-link MFC network explains the increase in yield stress (assessed in real time by rheo-MRI). In this second stage, recrystallization slows down and yield stress decreases as a result of the formation of MFC aggregates in the weak link network, as observed by confocal Raman imaging. The high fractal dimension of the weak-link network indicates that aggregation takes place via a particle-cluster mechanism. The effects of oil type and shear on the recrystallization rate and network strength could be reproduced in a stirred bowl with a heterogeneous shear stress field, which opens perspectives for the rational manipulation of MFC thickness and network strength under industrial processing conditions.

Effects of crystallisation of native phytosterols and monoacylglycerols on foaming properties of whipped oleogels

Different formulations and crystallising conditions were employed to vary the bulk phase structuring of oleogels. The oleogels were formed only at monoacylglycerol:native phytosterol (MAG:NPS) ratios of 10:0, 7:3 and 5:5. NPS co-crystallised with MAG in the oleogel mixtures and influenced the growth of lipidic crystal network. Faster cooling rates caused smaller crystals whereas thermal history affected the rigidity of oleogel samples. The oleogel samples were whipped and characterised for whipping time, foam overrun, microstructure, rheology and half-life of foam. The whipped oleogels were structured by layer(s) of lipidic crystals surrounding the air bubbles, which had non-spherical shapes and rough textures. The whipping time was remarkably reduced by 80% in the oleogel samples containing smaller lipidic crystals. All whippable oleogel samples had similar foam overrun values and extremely stable against foam collapse. The obtained oil foams exhibited liquid-like behaviour at low frequency as measured by the frequency sweep test.

Influence of low-frequency ultrasound on the physico-chemical and structural characteristics of milk systems with varying casein to whey protein ratios

Casein and whey proteins respond differently to ultrasound treatment depending on the individual protein fraction and the delivered energy density. The main aim of this study was to determine the sonication-induced physiochemical and structural changes of protein solutions with varying casein to whey protein ratios as a function of processing time at 20 kHz ultrasound. Four different casein:whey protein ratios (80:20, 60:40, 50:50, 40:60) were prepared. Upon sonication, there was a reduction in particle size of the 80:20 and 60:40 ratios, but the particle size of 50:50 and 40:60 increased. Milk protein solutions with higher portion of caseins produced more hydrophobically driven aggregates while whey protein-rich milk protein solutions produced more disulphide mediated aggregates during sonication. Primarily, β-lactoglobulin was involved in the hydrophobic aggregation process and β-lactoglobulin, bovine serum albumin and κ-casein participated in the disulphide aggregation process at all ratios.

Networks of micronized fat crystals grown under static conditions

Dispersions of micronized fat crystals (MFCs) in oil form a weak-interaction network organized by crystal aggregates in a continuous net of crystalline nanoplatelets.

Superchilling of muscle foods: Potential alternative for chilling and freezing

Superchilling is an attractive technique for preservation of muscle foods which freezes part of the water and insulate the food products from temperature fluctuations thereby enhancing the shelf-life during storage, transportation and retailing. Superchilling process synergistically improves the product shelf-life when used in combination with vacuum or modified atmospheric packaging. The shelf-life of muscle foods was reported to be increased by 1.5 to 4.0 times relative to traditional chilling technique. Advantages of superchilling and its ability to maintain the freshness of muscle foods over freezing has been discussed and its potential for Industrial application is highlighted. Present review also unravel the mechanistic bases for ice-crystal formation during superchilling and measures to ameliorate the drip loss. The future challenges especially automation in superchilling process for large scale Industrial application is presented.

Computer simulation of epitaxial nucleation of a crystal on a crystalline surface

We present results of computer simulations of crystal nucleation on a crystalline surface, in the Lennard-Jones model. Motivated by the pioneering work of Turnbull and Vonnegut [Ind. Eng. Chem. 44, 1292 (1952)], we investigate the effects of a mismatch between the surface lattice constant and that of the bulk nucleating crystal. We find that the nucleation rate is maximum close to, but not exactly at, zero mismatch. The offset is due to the finite size of the nucleus. In agreement with a number of experiments, we find that even for large mismatches of 10% or more, the formation of the crystal can be epitaxial, meaning that the crystals that nucleate have a fixed orientation with respect to the surface lattice. However, nucleation is not always epitaxial, and loss of epitaxy does affect how the rate varies with mismatch. The surface lattice strongly influences the nucleation rate. We show that the epitaxy observed in our simulations can be predicted using calculations of the potential energy between the surface and the first layer of the nucleating crystal, in the spirit of simple approaches such as that of Hillier and Ward [Phys. Rev. B 54, 14037 (1996)].

Molecular recognition of methyl α-D-mannopyranoside by antifreeze (glyco)proteins

Antifreeze proteins and glycoproteins [AF(G)Ps] have been well-known for more than three decades for their ability to inhibit the growth and recrystallization of ice through binding to specific ice crystal faces, and they show remarkable structural compatibility with specific ice crystal faces. Here, we show that the crystal growth faces of methyl α-D-mannopyranoside (MDM), a representative pyranose sugar, also show noteworthy structural compatibility with the known periodicities of AF(G)Ps. We selected fish AFGPs (AFGP8, AFGP1-5), and a beetle AFP (DAFP1) with increasing antifreeze activity as potential additives for controlling MDM crystal growth. Similar to their effects on ice growth, the AF(G)Ps can inhibit MDM crystal growth and recrystallization, and more significantly, the effectiveness for the AF(G)Ps are well correlated with their antifreeze activity. MDM crystals grown in the presence of AF(G)Ps are smaller and have better defined shapes and are of higher quality as indicated by single crystal X-ray diffraction and polarized microscopy than control crystals, but no new polymorphs of MDM were identified by single crystal X-ray diffraction, solid-state NMR, and attenuated total reflectance infrared spectroscopy. The observed changes in the average sizes of the MDM crystals can be related to the changes in the number of the MDM nuclei in the presence of the AF(G)Ps. The critical free energy change differences of the MDM nucleation in the absence and presence of the additives were calculated. These values are close to those of the ice nucleation in the presence of AF(G)Ps suggesting similar interactions are involved in the molecular recognition of MDM by the AF(G)Ps. To our knowledge this is the first report where AF(G)Ps have been used to control crystal growth of carbohydrates and on AFGPs controlling non-ice-like crystals. Our finding suggests MDM might be a possible alternative to ice for studying the detailed mechanism of AF(G)P-crystal interactions. The relationships between AF(G)Ps and carbohydrate binding proteins are also discussed. The structural compatibility between AF(G)Ps and growing crystal faces demonstrated herein adds to the repertoire of molecular recognition by AF(G)Ps, which may have potential applications in the sugar, food, pharmaceutical, and materials industries.