Does arginine aggregate formation in aqueous solutions follow a two-step mechanism?

The formation of aggregates was studied in arginine aqueous solutions using light scattering. The main driving force for aggregate formation is hydrogen bonding between the arginine (Arg) amino acids, which is partially verified using density functional theory calculations. The measurement of energy loss during this process, coupled with Cryo-EM morphology data, indicates that these aggregates are in the solid state. The aggregation occurs in two steps, with a liquid intermediate stage. The investigation of the effect of pH and solute concentration on aggregate formation for other amino acid aqueous solutions verifies that aggregate formation is amino-acid specific, while small-sized clusters formed by weak interactions lead to large-sized aggregation. The water structure around amino acid molecules sheds light on the prediction of their aggregate formation. Homochirality is observed in the aggregates; its existence sheds light on the origin of protein homochirality.

Amorphous aggregates with a very wide size distribution play a central role in crystal nucleation

There is mounting evidence that crystal nucleation from supersaturated solution involves the formation and reorganization of prenucleation clusters, contradicting classical nucleation theory. One of the key unresolved issues pertains to the origin, composition, and structure of these clusters. Here, a range of amino acids and peptides is investigated using light scattering, mass spectrometry, and in situ terahertz Raman spectroscopy, showing that the presence of amorphous aggregates is a general phenomenon in supersaturated solutions. Significantly, these aggregates are found on a vast range of length scales from dimers to 30-mers to the nanometre and even micrometre scale, implying a continuous distribution throughout this range. Larger amorphous aggregates are sites of spontaneous crystal nucleation and act as intermediates for laser-induced crystal nucleation. These results are shown to be consistent with a nonclassical nucleation model in which barrierless (homogeneous) nucleation of amorphous aggregates is followed by the nucleation of crystals from solute-enriched aggregates. This provides a novel perspective on crystal nucleation and the role of nonclassical pathways.

Exploring the Potential of Nonclassical Crystallization Pathways to Advance Cementitious Materials

Understanding the crystallization of cement-binding phases, from basic units to macroscopic structures, can enhance cement performance, reduce clinker use, and lower CO2 emissions in the construction sector. This review examines the crystallization pathways of C-S-H (the main phase in PC cement) and other alternative binding phases, particularly as cement formulations evolve toward increasing SCMs and alternative binders as clinker replacements. We adopt a nonclassical crystallization perspective, which recognizes the existence of critical intermediate steps between ions in solution and the final crystalline phases, such as solute ion associates, dense liquid phases, amorphous intermediates, and nanoparticles. These multistep pathways uncover innovative strategies for controlling the crystallization of binding phases through additive use, potentially leading to highly optimized cement matrices. An outstanding example of additive-controlled crystallization in cementitious materials is the synthetically produced mesocrystalline C-S-H, renowned for its remarkable flexural strength. This highly ordered microstructure, which intercalates soft matter between inorganic and brittle C-S-H, was obtained by controlling the assembly of individual C-S-H subunits. While large-scale production of cementitious materials by a bottom-up self-assembly method is not yet feasible, the fundamental insights into the crystallization mechanism of cement binding phases presented here provide a foundation for developing advanced cement-based materials.

Rapid high-resolution size distribution protocol for adeno-associated virus using high speed SV-AUC

Simulated SV-AUC data for an adeno-associated virus (AAV) sample consisting of four components having closely spaced sedimentation coefficients were used to develop a high-speed protocol that optimized the size distribution analysis resolution. The resulting high speed (45K rpm) SV-AUC (hs-SV-AUC) protocol poses several experimental challenges: 1) the need for rapid data acquisition, 2) increased potential for optical artifacts from steep and fast moving boundaries and 3) the increased potential for convection. To overcome these challenges the protocol uses interference detection at low temperatures and data that are confined to a limited radial-time window. In addition to providing higher resolution AAV SV-AUC data and very short run times (<20 min after temperature equilibration), the need to match the sample and reference solvent composition and meniscus positions is relaxed making interference detection as simple to employ as absorbance detection. Finally, experimental data comparing hs-SV-AUC (at 45K rpm) with standard low-speed (15K rpm) SV-AUC on the same AAV sample demonstrate the size distribution resolution improvement. These experiments also validate the use of a radial-time window and show how quickly data can be acquired using the hs-SV-AUC protocol.

Organic Nucleation: Water Rearrangement Reveals the Pathway of Ibuprofen

The organic nucleation of the pharmaceutical ibuprofen is investigated, as triggered by the protonation of ibuprofen sodium salt at elevated pH. The growth and aggregation of nanoscale solution species by Analytical Ultracentrifugation and Molecular Dynamics (MD) simulations is tracked. Both approaches reveal solvated molecules, oligomers, and prenucleation clusters, their size as well as their hydration at different reaction stages. By combining surface-specific vibrational spectroscopy and MD simulations, water interacting with ibuprofen at the air-water interface during nucleation is probed. The results show the structure of water changes upon ibuprofen protonation in response to the charge neutralization. Remarkably, the water structure continues to evolve despite the saturation of protonated ibuprofen at the hydrophobic interface. This further water rearrangement is associated with the formation of larger aggregates of ibuprofen molecules at a late prenucleation stage. The nucleation of ibuprofen involves ibuprofen protonation and their hydrophobic assembly. The results highlight that these processes are accompanied by substantial water reorganization. The critical role of water is possibly relevant for organic nucleation in aqueous environments in general.

Amino acid chiral amplification using Monte Carlo dynamic

This study investigates the stability of chiral-molecule solution phases, with a specific focus on amino acids. The model framework is based on a two-dimensional square lattice model, where individual sites may be occupied by oriented chiral molecules or structureless solvent particles. Utilizing the Glauber dynamics and statistical mechanical formalism, as previously introduced and examined by Lombardo et al., we explore the influence of temperature, amino acid concentration, enantiomeric excess, and homochiral interaction strength on nucleation mechanisms, equilibrium phase behavior, and crystal composition. Our findings offer thermodynamic insights into the chiral amplification process of amino acids, contributing to a deeper understanding of the underlying processes.

The nucleation of C-S-H via prenucleation clusters

The nucleation and growth of calcium-silicate-hydrate (C-S-H) is of fundamental importance for the strength development and durability of the concrete. However, the nucleation process of C-S-H is still not fully understood. The present work investigates how C-S-H nucleates by analyzing the aqueous phase of hydrating tricalcium silicate (C₃S) by applying inductively coupled plasma-optical emission spectroscopy as well as analytical ultracentrifugation. The results show that the C-S-H formation follows non-classical nucleation pathways associated with the formation of prenucleation clusters (PNCs) of two types. Those PNCs are detected with high accuracy and reproducibility and are two species of the 10 in total, from which the ions (with associated water molecules) are the majority of the species. The evaluation of the density and molar mass of the species shows that the PNCs are much larger than ions, but the nucleation of C-S-H starts with the formation of liquid precursor C-S-H (droplets) with low density and high water content. The growth of these C-S-H droplets is associated with a release of water molecules and a reduction in size. The study gives experimental data on the size, density, molecular mass, and shape and outlines possible aggregation processes of the detected species.

Molecular Mechanism of Organic Crystal Nucleation: A Perspective of Solution Chemistry and Polymorphism

Crystal nucleation determining the formation and assembly pathway of first organic materials is the central science of various scientific disciplines such as chemical, geochemical, biological, and synthetic materials. However, our current understanding of the molecular mechanisms of nucleation remains limited. Over the past decades, the advancements of new experimental and computational techniques have renewed numerous interests in detailed molecular mechanisms of crystal nucleation, especially structure evolution and solution chemistry. These efforts bifurcate into two categories: (modified) classical nucleation theory (CNT) and non-classical nucleation mechanisms. In this review, we briefly introduce the two nucleation mechanisms and summarize current molecular understandings of crystal nucleation that are specifically applied in polymorphic crystallization systems of small organic molecules. Many important aspects of crystal nucleation including molecular association, solvation, aromatic interactions, and hierarchy in intermolecular interactions were examined and discussed for a series of organic molecular systems. The new understandings relating to molecular self-assembly in nucleating systems have suggested more complex multiple nucleation pathways that are associated with the formation and evolution of molecular aggregates in solution.

Mesoscale clusters of organic solutes in solution and their role in crystal nucleation

It is becoming evident that primary nucleation of crystals of organic molecules from solution is often anything but ‘classical’ in its complexity. It is also becoming increasingly clear that mesoscopic...

Pre-Nucleation Clusters Predict Crystal Structures in Models of Chiral Molecules

Kinetics can play an important role in the crystallization of molecules and can give rise to polymorphism, the tendency of molecules to form more than one crystal structure. Current computational methods of crystal structure prediction, however, focus almost exclusively on identifying the thermodynamically stable polymorph. Kinetic factors of nucleation and growth are often neglected because the underlying microscopic processes can be complex and accurate rate calculations are numerically cumbersome. In this work, we use molecular dynamics computer simulations to study simple molecular models that reproduce the crystallization behavior of real chiral molecules, including the formation of enantiopure and racemic crystals, as well as polymorphism. A significant fraction of these molecules forms crystals that do not have the lowest free energy. We demonstrate that at high supersaturation crystal formation can be accurately predicted by considering the similarities between oligomeric species in solution and molecular motifs in the crystal structure. For the case of racemic mixtures, we even find that knowledge of crystal free energies is not necessary and kinetic considerations are sufficient to determine if the system will undergo spontaneous chiral separation. Our results suggest conceptually simple ways of improving current crystal structure prediction methods.

Homogeneous nucleation of sheared liquids: advances and insights from simulations and theory

One of the most ubiquitous and technologically important phenomena in nature is the nucleation of homogeneous flowing systems. The microscopic effects of shear on a nucleating system are still imperfectly understood, although in recent years a consistent picture has emerged. The opposing effects of shear can be split into two major contributions for simple atomic and molecular liquids: increase of the energetic cost of nucleation, and enhancement of the kinetics. In this perspective, we describe the latest computational and theoretical techniques which have been developed over the past two decades. We collate and unify the overarching influences of shear, temperature, and supersaturation on the process of homogeneous nucleation. Experimental techniques and capabilities are discussed, against the backdrop of results from simulations and theory. Although we primarily focus on simple systems, we also touch upon the sheared nucleation of more complex systems, including glasses and polymer melts. We speculate on the promising directions and possible advances that could come to fruition in the future.

Probing Self-Assembly in Arginine-Oleic Acid Solutions with Terahertz Spectroscopy and X-ray Scattering

A study of the formation of microstructures in the reaction of oleic acid with arginine elucidates dynamical self-assembly processes at the molecular level. Terahertz spectroscopy combined with density functional calculations reveals the initial hydrogen-bonding motifs in the assembly process, leading to the formation of micelles and vesicles. Small-angle X-ray scattering measurements allow for kinetic analysis of the growth processes of these nanostructures, revealing a prenucleation pathway of vesicles and micelles which lead to spongelike structures. This final stage of the assembly into spongelike aggregates is investigated with optical microscopy. The formed structures only occur at pH > 8 and are resistant to extreme acidic and basic conditions. A mechanistic pathway to the formation of the spongelike aggregates is described.

From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy

Synchrotron radiation provides insight into spectroscopy and dynamics in clusters and nanoparticles.

To Be or Not To Be a Molecular Ion: The Role of the Solvent in Photoionization of Arginine

Application of photoionization mass spectroscopy, a technique capable of assessing protonation states in complex molecules in the gas phase, is challenging for arginine due to its fragility. We report photoionization efficiencies in the valence region of aqueous aerosol particles produced from arginine solutions under various pH and vaporization conditions. By using ab initio calculations, we investigate the stability of different conformers. Our results show that neutral arginine fragments upon ionization in the gas phase but solvation stabilizes the molecular ion, resulting in different photoionization dynamics. We also report the valence-band photoelectron spectra of the aerosol solutions obtained at different pH values.

From Solute, Fluidic and Particulate Precursors to Complex Organizations of Matter

The organization of matter from its constitutive units recruits intermediate states with distinctive degrees of self-association and molecular order. Existing as clusters, droplets, gels as well as amorphous and crystalline nanoparticles, these precursor forms have fundamental contributions towards the composition and structure of inorganic and organic architectures. In this personal account, we show that the transitions from atoms, molecules or ionic species to superstructures of higher order are intertwined with the interfaces and interactions of precursor and intermediate states. Structural organizations distributed across different length scales are explained by the multistep nature of nucleation and crystallization, which can be guided towards functional hybrid materials by the strategic application of additives, templates and reaction environments. Thus, the non-classical pathways for material formation and growth offer conceptual frameworks for elucidating, inducing and directing fascinating material organizations of biogenic and synthetic origins.

Optical glucose sensing using ethanolamine–polyborate complexes

An optical glucose sensor based on polyborate–amine complexes with an aggregation-induced emission mechanism.

Persistent Self-Association of Solute Molecules in Solution

The structural evolvement of a solute determines the crystallization outcome. The self-association mechanism leading to nucleation, however, remains poorly understood. Our current study explored the solution chemistry of a model compound, tolfenamic acid (TFA), in three different solvents mainly by solution NMR. It was found that hydrogen-bonded pairs of solute-solute or solute-solvent stack with each through forming a much weaker π-π interaction as the concentration increases. Depending on the solvent, configurations of the solution species may be retained in the resultant crystal structure or undergo rearrangement. Yet, the π-π stacking is always retained in the crystal regardless of the solvent used for the crystallization. The finding suggests that nucleation not only involves the primary intermolecular interaction (hydrogen bonding) but also engages the secondary forces in the self-assembly process.

A non-classical view on calcium oxalate precipitation and the role of citrate

Although calcium oxalates are relevant biominerals, their formation mechanisms remain largely unresolved. Here, we investigate the early stages of calcium oxalate formation in pure and citrate-bearing solutions. Citrate is used as a well-known oxalate precipitation inhibitor; moreover, it resembles the functional domains of the biomolecules that modulate biomineralization. Our data suggest that calcium oxalate forms after Ca²⁺ and C₂O₄^2- association into polynuclear stable complexes that aggregate into larger assemblies, from which amorphous calcium oxalate nucleates. Previous work has explained citrate inhibitory effects according to classical theories. Here we show that citrate interacts with all early stage CaC₂O₄ species (polynuclear stable complexes and amorphous precursors), inhibiting calcium oxalate nucleation by colloidal stabilization of polynuclear stable complexes and amorphous calcium oxalate. The control that citrate exerts on calcium oxalate biomineralization may thus begin earlier than previously thought. These insights provide information regarding the mechanisms governing biomineralization, including pathological processes (e.g., kidney stone formation).The formation mechanism of abundant calcium oxalate biomaterials is unresolved. Here the authors show the early stages of calcium oxalate formation in pure and citrate-bearing solutions by using a titration set-up in conjunction with solution quenching, transmission electron microscopy and analytical ultracentrifugation.

Growth of organic crystals via attachment and transformation of nanoscopic precursors

A key requirement for the understanding of crystal growth is to detect how new layers form and grow at the nanoscale. Multistage crystallization pathways involving liquid-like, amorphous or metastable crystalline precursors have been predicted by theoretical work and have been observed experimentally. Nevertheless, there is no clear evidence that any of these precursors can also be relevant for the growth of crystals of organic compounds. Herein, we present a new growth mode for crystals of DL-glutamic acid monohydrate that proceeds through the attachment of preformed nanoscopic species from solution, their subsequent decrease in height at the surface and final transformation into crystalline 2D nuclei that eventually build new molecular layers by further monomer incorporation. This alternative mechanism provides a direct proof for the existence of multistage pathways in the crystallization of molecular compounds and the relevance of precursor units larger than the monomeric constituents in the actual stage of growth.

Multistage crystallization pathways involving nanoscopic precursors or intermediates have been proposed for various systems. Here, the authors find compelling evidence that nanoscopic species participate in the crystallization of glutamic acid monohydrate, extending this non-classical growth mechanism to organic crystals.

A general strategy for colloidal stable ultrasmall amorphous mineral clusters in organic solvents

A general gas diffusion strategy using 10,12-pentacosadiynoic acid as a ligand and ethanol as a solvent was developed to fabricate stable amorphous mineral clusters with a core size of less than 2 nm.

While nature exerts precise control over the size and chemical composition of minerals, this is still a challenging task for artificial syntheses. Despite its significance, until now, there are still no reports on colloidal mineral nanoparticles in the subnanometer range. Here we developed a general gas diffusion strategy using 10,12-pentacosadiynoic acid as a ligand and ethanol as a solvent to fabricate stable amorphous mineral clusters with a core size of less than 2 nm. First discovered for CaCO₃, the method was successfully extended to produce monolayer protected clusters of MgCO₃, SrCO₃, Eu₂(CO₃)₃, Tb₂(CO₃)₃, Ce₂(CO₃)₃, Ca_x(PO₄)_y, CaC₂O₄ and their hybrid minerals, Ca_xMg_y(CO₃)_z and Ca_x(CO₃)_y(PO₄)_z. All the mineral clusters can be well dispersed in organic solvents like toluene, and are stable for a long period without further crystallization. Our work paves a way for the artificial synthesis of colloidal mineral clusters, which may have various uses in both fundamental research and industry.

Shape Analysis of DNA-Au Hybrid Particles by Analytical Ultracentrifugation

Current developments in nanotechnology have increased the demand for nanocrystal assemblies with well-defined shapes and tunable sizes. DNA is a particularly well-suited building block in nanoscale assemblies because of its scalable sizes, conformational variability, and convenient self-assembly capabilities via base pairing. In hybrid materials, gold nanoparticles (AuNPs) can be assembled into nanoparticle structures with programmable interparticle distances by applying appropriate DNA sequences. However, the development of stoichiometrically defined DNA/NP structures is still challenging since product mixtures are frequently obtained and their purification and characterization is the rate-limiting step in the development of DNA-NP hybrid assemblies. Improvements in nanostructure fractionation and characterization techniques offer great potential for nanotechnology applications in general. This study reports the application of analytical ultracentrifugation (AUC) for the characterization of anisotropic DNA-linked metal-crystal assemblies. On the basis of transmission electron microscopy data and the DNA primary sequence, hydrodynamic bead models are set up for the interpretation of the measured frictional ratios and sedimentation coefficients. We demonstrate that the presence of single DNA strands on particle surfaces as well as the shape factors of multiparticle structures in mixtures can be quantitatively described by AUC. This study will significantly broaden the possibilities to analyze mixtures of shape-anisotropic nanoparticle assemblies. By establishing insights into the analysis of nanostructure mixtures based on fundamental principles of sedimentation, a wide range of potential applications in basic research and industry become accessible.

Revealing microheterogeneities and second order phase transitions in aqueous mixtures of 1-propoxypropan-2-ol at 298 K

Second-order phase transitions, identified by Kirkwood–Buff integrals, assigned to solution microheterogeneities are corroborated by ESI-MS, surface tension and solvatochromic parameters.

High-resolution insights into the early stages of silver nucleation and growth

Nucleation and growth of silver nanoparticles has already been investigated with various experimental and computational tools. However, owing to inherent problems associated with the analytical characterization of nucleation processes, there is a general lack of experimental data regarding the earliest precursors and smallest Ag(0) clusters. Here, we address this problem by the application of Synthetic Boundary Crystallization Ultracentrifugation, utilizing a multiwavelength detector for the first time, complemented by a specialized titration assay. These techniques shed new light on silver nanoparticle precursors existing in the pre-nucleation regime, and the initially nucleated ensemble of nanoclusters. For the first time, we present experimental data of UV-Vis spectra for fractionated silver clusters. These allow for unsurpassed insights into the sequence of nucleation and early growth species as well as their optical properties.

Formation of nanoparticles and nanostructures--an industrial perspective on CaCO3 , cement, and polymers

Nanotechnology enables the design of materials with outstanding performance. A key element of nanotechnology is the ability to manipulate and control matter on the nanoscale to achieve a certain desired set of specific properties. Here, we discuss recent insight into the formation mechanisms of inorganic nanoparticles during precipitation reactions. We focus on calcium carbonate, and describe the various transient stages potentially occurring on the way from the dissolved constituent ions to finally stable macrocrystals-including solute ion clusters, dense liquid phases, amorphous intermediates, and nanoparticles. The role of polymers in nucleating, templating, stabilizing, and/or preventing these structures is outlined. As a specific example for applied nanotechnology, the properties of cement are shown to be determined by the formation and interlocking of calcium-silicate-hydrate nanoplatelets. The aggregation of these platelets into mesoscale architectures can be controlled with polymers.

Pre-nucleation clusters as solute precursors in crystallisation

Crystallisation is at the heart of various scientific disciplines, but still the understanding of the molecular mechanisms underlying phase separation and the formation of the first solid particles in aqueous solution is rather limited. In this review, classical nucleation theory, as well as established concepts of spinodal decomposition and liquid-liquid demixing, is introduced together with a description of the recently proposed pre-nucleation cluster pathway. The features of pre-nucleation clusters are presented and discussed in relation to recent modifications of the classical and established models for phase separation, together with a review of experimental work and computer simulations on the characteristics of pre-nucleation clusters of calcium phosphate, calcium carbonate, iron(oxy)(hydr)oxide, silica, and also amino acids as an example of small organic molecules. The role of pre-nucleation clusters as solute precursors in the emergence of a new phase is summarized, and the link between the chemical speciation of homogeneous solutions and the process of phase separation via pre-nucleation clusters is highlighted.

Clustering of simple aminosulfonic acids--electrospray ionization mass spectrometric study

RATIONALE

Aminosulfonic acids are structurally related to amino acids as bifunctional compounds. Some of them like taurine and homotaurine play important roles in biology. Although there is a vast literature devoted to the electrospray ionization mass spectrometric (ESI-MS) study of amino acid aggregation, no such study has been performed so far for aminosulfonic acids.

METHODS

A gas-phase clustering study was performed for aminomethanesulfonic acid (AMS), taurine (Tau), homotaurine (HT), and cysteic acid (CA) from water and methanol/water solutions, using a Bruker TOF-Q spectrometer equipped with an ESI source, in the negative-ion mode. For selected anionic clusters the tandem mass (MS/MS) spectra were recorded and the breakdown curves were obtained. The cluster formation abilities (ACS parameter) of the studied molecules were calculated.

RESULTS

Both singly and doubly charged clusters were formed when the acids were electrosprayed from water solutions; they may be described as [(H3N-R-SO3)n-zH](z-), where z = 1 or 2. The largest identified clusters are built of 20, 22, 20 and 4 monomers of AMS, Tau, HT and CA, respectively. The doubly negatively charged clusters were observed for n ≥9, 12, 14 in the case of AMS, Tau and HT. AMS pentamers and Tau, HT tetramers and hexamers show higher stabilities than the other clusters.

CONCLUSIONS

The results indicate that aminosulfonic acids form large stable clusters, similarly to aminocarboxylic acids. The cluster formation ability decreases with an increase in CH2 chain length within the series of the studied compounds. The large singly and doubly charged aggregates are formed under the conditions of the experiment, possibly in the droplets. Taurine dissolved in water seems to be a good calibrant for electrospray instruments in negative ion mode.