Search

The growth of calcium oxalate monohydrate in the presence of Tamm-Horsfall protein (THP), osteopontin, and the 27-residue synthetic peptides (DDDS) 6DDD and (DDDG)6DDD (D = aspartic acid, S = serine, and G = glycine) was investigated via in situ atomic force microscopy. The results show that these four growth modulators create extensive deposits on the crystal faces. Depending on the modulator and crystal face, these deposits can occur as discrete aggregates, filamentary structures, or uniform coatings. These proteinaceous films can lead to either the inhibition of or an increase in the step speeds (with respect to the impurity-free system), depending on a range of factors that include peptide or protein concentration, supersaturation, and ionic strength. While THP and the linear peptides act, respectively, to exclusively increase and inhibit growth on the (101} face, both exhibit dual functionality on the (010) face, inhibiting growth at low supersaturation or high modulator concentration and accelerating growth at high supersaturation or low modulator concentration. Based on analyses of growth morphologies and dependencies of step speeds on supersaturation and protein or peptide concentration, we propose a picture of growth modulation that accounts for the observations in terms of the strength of binding to the surfaces and steps and the interplay of electrostatic and solvent-induced forces at the crystal surface.

Aqueous corrosion of metals is governed by formation and dissolution of a passivating, multi-component surface oxide. Unfortunately, a detailed atomistic description is challenging due to the compositional complexity and the need to consider multiple kinetic factors simultaneously. To this end, we combine experiments with a first-principles-derived, multiscale computational framework that transcends thermodynamic descriptions to explicitly simulate the kinetic evolution of surface oxides of Ni-Cr alloys as a function of composition, temperature, pH, and applied voltage. In the absence of pitting, we identify three distinct voltage regimes, which are kinetically dominated by oxide growth, dissolution, and competitive dissolution and reprecipitation. Evolving compositional gradients and oxide thickness are revealed, including a transition between a metastable Ni-Cr mixed oxide and a thick, porous Ni-dominated oxide. Beyond elucidating the underlying physics, we highlight the need for competing kinetics in models to properly predict the transition from passivation to corrosion. Our results provide a key step towards co-design of alloy composition alongside environmental conditions for sustainable use across a variety of critical energy and infrastructure applications., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Nanomaterial-mediated antibacterial photodynamic therapy (aPDT) emerges as a promising treatment against antibiotic-resistant bacterial biofilms. Specifically, titanium dioxide nanoparticles (TiO 2 NPs) are being investigated as photosensitizers in aPDT to address biofilm related diseases. To enhance their photocatalytic performance in the visible spectral range for biomedical applications, various strategies have been adopted, including reduction of TiO 2 NPs. However, despite improvements in visible-light photoactivity, reduced TiO 2 NPs have yet to reach their expected performance primarily due to the instability of oxygen vacancies and their tendency to reoxidize easily. To address this, we present a two-step approach to fabricate highly visible-light active and stable TiO 2 NP photocatalysts, involving nitrogen doping followed by a magnesium-assisted reductive annealing process. X-ray photoelectron spectroscopy analysis of the synthesized reduced nitrogen-doped TiO 2 NPs (H:Mg-N-TiO 2 NPs) reveals that the presence of nitrogen stabilizes oxygen vacancies and reduced Ti species, leading to increased production of reactive oxygen species under visible-light excitation. The improved aPDT efficiency translates to a 3-fold enhancement in the antibiofilm activity of nitrogen-doped compared to undoped reduced TiO 2 NPs against both Gram-positive ( Streptococcus mutans ) and Gram-negative ( Porphyromonas gingivalis , Fusobacterium nucleatum ) oral pathogens. These results underscore the potential of H:Mg-N-TiO 2 NPs in aPDT for combating bacterial biofilms effectively.

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Ion (de)hydration is a key rate-determining step in interfacial processes from corrosion to electrochemical energy storage. However, predicting the kinetics of ion (de)hydration remains challenging, prompting the use of static proxies such as hydration energy and valence. While useful for assessing thermodynamic preferences, such descriptors cannot fully capture the dynamical softness of the hydration shell that dictates kinetics. Accordingly, we use first-principles molecular dynamics to analyze hydration shell softness for a diverse set of metal cations. Three dynamic metrics are introduced to intuitively describe the bond rigidity, shape deformability, and exchange fluidity of the solvation shell. Together, these metrics capture the relevant physics in the static descriptors, while offering a far more complete and efficient representation for the overall propensity for (de)hydration. Application to the hydrated ion set demonstrates a weak connection between dynamical softness and hydration energy, confirming that dynamical descriptors of hydration are key for correctly describing ion transfer processes.

We investigate the interaction of 355-nm and 1064-nm nanosecond laser pulses with nominally spherical metallic particles dispersed on the input surface of transparent substrates or high-reflectivity (HR) multilayer dielectric coatings, respectively. The objective is to elucidate the interaction mechanisms associated with contaminant-induced degradation and damage of transparent and reflective optical elements for high-power laser systems. The experiments involve time-resolved imaging capturing the dynamics of the interaction pathway, which includes plasma formation, particle ejection, and secondary contamination by droplets originating from the liquefied layer of the particle. The results suggest that HR coatings are more susceptible to secondary contamination by liquid droplets produced by the particles because of the different geometry of excitation and the location of plasma initiation. Modeling results focus on better understanding the melting of the particle surface, leading to ejections of liquid droplets and the pressure applied to the substrate, leading to mechanical damage.

We herein show the chiral recognition and separation of aspartic acid (Asp) enantiomers by achiral brushite due to the asymmetries of their dynamical steps in its nonequilibrium states. Growing brushite has a higher adsorption affinity to d-Asp, while l-Asp is predominant on the dissolving brushite surface. Microstructural characterization reveals that chiral selection is mainly attributed to brushite [101] steps, which exhibit two different configurations during crystal growth and dissolution, respectively, with each preferring a distinct enantiomer due to this asymmetry. Because these transition step configurations have different stabilities, they subsequently result in asymmetric adsorption. By varying free energy barriers through solution thermodynamic driving force (i.e., supersaturation), the dominant nonequilibrium intermediate states can be switched and chiral selection regulated. This finding highlights that the dynamic steps can be vital for chiral selection, which may provide a potential pathway for chirality generation through the dynamic nature.

High dielectric constant multilayer coatings are commonly used on high-reflection mirrors for high-peak-power laser systems because of their high laser-damage resistance. However, surface contaminants often lead to damage upon laser exposure, thus limiting the mirror's lifetime and performance. One plausible approach to improve the overall mirror resistance against laser damage, including that induced by laser-contaminant coupling, is to coat the multilayers with a thin protective capping (absentee) layer on top of the multilayer coatings. An understanding of the underlying mechanism by which laser-particle interaction leads to capping layer damage is important for the rational design and selection of capping materials of high-reflection multilayer coatings. In this paper, we examine the responses of two candidate capping layer materials, made of SiO 2 and Al 2 O 3 , over silica-hafnia multilayer coatings. These are exposed to a single oblique shot of a 1053 nm laser beam (fluence ∼10  J/cm 2 , pulse length 14 ns), in the presence of Ti particles on the surface. We find that the two capping layers show markedly different responses to the laser-particle interaction. The Al 2 O 3 cap layer exhibits severe damage, with the capping layer becoming completely delaminated at the particle locations. The SiO 2 capping layer, on the other hand, is only mildly modified by a shallow depression. Combining the observations with optical modeling and thermal/mechanical calculations, we argue that a high-temperature thermal field from plasma generated by the laser-particle interaction above a critical fluence is responsible for the surface modification of each capping layer. The great difference in damage behavior is mainly attributed to the large disparity in the thermal expansion coefficient of the two capping materials, with that of Al 2 O 3 layer being about 15 times greater than that of SiO 2 .

Many transition metal complexes exhibit infrared or visible optical absorption arising from d-d transitions that are the key to functionality in technological applications and biological processes. The observed spectral characteristics of the absorption spectra depend on several underlying physical parameters whose relative contributions are still not fully understood. Although conventional arguments based on ligand-field theory can be invoked to rationalize the peak absorption energy, they cannot describe the detailed features of the observed spectral profile such as the spectral width and shape, or unexpected correlations between the oscillator strength and absorption peak position. Here, we combine experimental observations with first-principles simulations to investigate origins of the absorption spectral profile in model systems of aqueous Cu(2+) ions with Cl(-), Br(-), NO2(-) and CH3CO2(-) ligands. The ligand identity and concentration, fine structure in the electronic d-orbitals of Cu(2+), complex geometry, and solvation environment are all found to play key roles in determining the spectral profile. Moreover, similar physiochemical origins of these factors lead to interesting and unexpected correlations in spectral features. The results provide important insights into the underlying mechanisms of the observed spectral features and offer a framework for advancing the ability of theoretical models to predict and interpret the behavior of such systems.

Fe-doped lithium sodium silicate glasses codoped with Sn and C to promote the Fe²⁺ redox state are investigated under simultaneous excitation at the first and third harmonics of a nanosecond Nd:YAG laser. The aim is to evaluate critical parameters associated with the potential use of this material as an optical filter that transmits the third harmonic but blocks the fundamental frequency. Estimations of the excited-state absorption coefficient and photobleaching (reduction of absorption at the fundamental) are provided. The results provide insight on the design and expected operational parameters of this type of Fe-doped materials.

We investigate defects forming in Ce³⁺-doped fused silica samples following exposure to nanosecond ultraviolet laser pulses and their relaxation as a function of time and exposure to low intensity light at different wavelengths. A subset of these defects are responsible for inducing absorption in the visible and near infrared spectral range, which is of critical importance for the use of this material as ultraviolet light absorbing filter in high power laser systems. The dependence of the induced absorption as a function of laser fluence and methods to most efficiently mitigate this effect are presented. Experiments simulating the operation of the material as a UV protection filter for high power laser systems were performed in order to determine limitations and practical operational conditions.

Calcite crystals were grown in the presence of full-length amelogenin and during its proteolysis by recombinant human matrix metalloproteinase 20 (rhMMP-20). Recombinant porcine amelogenin (rP172) altered the shape of calcite crystals by inhibiting the growth of steps on the {104} faces and became occluded inside the crystals. Upon co-addition of rhMMP-20, the majority of the protein was digested resulting in a truncated amelogenin lacking the C-terminal segment. In rP172-rhMMP-20 samples, the occlusion of amelogenin into the calcite crystals was drastically decreased. Truncated amelogenin (rP147) and the 25-residue C-terminal domain produced crystals with regular shape and less occluded organic material. Removal of the C-terminal diminished the affinity of amelogenin to the crystals and therefore prevented occlusion. We hypothesize that HAP and calcite interact with amelogenin in a similar manner. In the case of each material, full-length amelogenin binds most strongly, truncated amelogenin binds weakly and the C-terminus alone has the weakest interaction. Regarding enamel crystal growth, the prevention of occlusion into maturing enamel crystals might be a major benefit resulting from the selective cleavage of amelogenin at the C-terminus by MMP-20. Our data have important implications for understanding the hypomineralized enamel phenotype in cases of amelogenesis imperfecta resulting from MMP-20 mutations and will contribute to the design of enamel inspired biomaterials.

Aberrant protein aggregation causes numerous neurological diseases including Creutzfeldt-Jakob disease (CJD), but the aggregation mechanisms remain poorly understood. Here, we report AFM results on the formation pathways of β-oligomers and nonfibrillar aggregates from wild-type full-length recombinant human prion protein (WT) and an insertion mutant (10OR) with five additional octapeptide repeats linked to familial CJD. Upon partial denaturing, seeds consisting of 3-4 monomers quickly appeared. Oligomers of ~11-22 monomers then formed through direct interaction of seeds, rather than by subsequent monomer attachment. All larger aggregates formed through association of these β-oligomers. Although both WT and 10OR exhibited identical aggregation mechanisms, the latter oligomerized faster due to lower solubility and, hence, thermodynamic stability. This novel aggregation pathway has implications for prion diseases as well as others caused by protein aggregation.

Femtosecond laser machining is used to create mitigation pits to stabilize nanosecond laser-induced damage in multilayer dielectric mirror coatings on BK7 substrates. In this paper, we characterize features and the artifacts associated with mitigation pits and further investigate the impact of pulse energy and pulse duration on pit quality and damage resistance. Our results show that these mitigation features can double the fluence-handling capability of large-aperture optical multilayer mirror coatings and further demonstrate that femtosecond laser macromachining is a promising means for fabricating mitigation geometry in multilayer coatings to increase mirror performance under high-power laser irradiation.

Growing laser damage sites on multilayer high-reflector coatings can limit mirror performance. One of the strategies to improve laser damage resistance is to replace the growing damage sites with predesigned benign mitigation structures. By mitigating the weakest site on the optic, the large-aperture mirror will have a laser resistance comparable to the intrinsic value of the multilayer coating. To determine the optimal mitigation geometry, the finite-difference time-domain method was used to quantify the electric-field intensification within the multilayer, at the presence of different conical pits. We find that the field intensification induced by the mitigation pit is strongly dependent on the polarization and the angle of incidence (AOI) of the incoming wave. Therefore, the optimal mitigation conical pit geometry is application specific. Furthermore, our simulation also illustrates an alternative means to achieve an optimal mitigation structure by matching the cone angle of the structure with the AOI of the incoming wave, except for the p-polarized wave at a range of incident angles between 30° and 45°.

We have designed and built a microfluidic liquid cell capable of high-resolution atomic force microscope (AFM) imaging and force spectroscopy. The liquid cell was assembled from three molded poly(dimethylsiloxane) (PDMS) pieces and integrated with commercially purchased probes. The AFM probe was embedded within the assembly such that the cantilever and tip protrude into the microfluidic channel. This channel is defined by the PDMS assembly on the top, a PDMS gasket on all four sides, and the sample substrate on the bottom, forming a liquid-tight seal. Our design features a low volume fluidic channel on the order of 50 nl, which is a reduction of over 3-5 orders of magnitude compared to several commercial liquid cells. This device facilitates testing at high shear rates and laminar flow conditions coupled with full AFM functionality in microfluidic aqueous environments, including execution of both force displacement curves and high resolution imaging.

In vitro observations have revealed major effects on the structure, growth, and composition of biomineral phases, including stabilization of amorphous precursors, acceleration and inhibition of kinetics, and alteration of impurity signatures. However, deciphering the mechanistic sources of these effects has been problematic due to a lack of tools to resolve molecular structures on mineral surfaces during growth. Here we report atomic force microscopy investigations using a system designed to maximize resolution while minimizing contact force. By imaging the growth of calcium-oxalate monohydrate under the influence of aspartic-rich peptides at single-molecule resolution, we reveal how the unique interactions of polypeptides with mineral surfaces lead to acceleration, inhibition, and switching of growth between two distinct states. Interaction with the positively charged face of calcium-oxalate monohydrate leads to formation of a peptide film, but the slow adsorption kinetics and gradual relaxation to a well-bound state result in time-dependent effects. These include a positive feedback between peptide adsorption and step inhibition described by a mathematical catastrophe that results in growth hysteresis, characterized by rapid switching from fast to near-zero growth rates for very small reductions in supersaturation. Interactions with the negatively charged face result in formation of peptide clusters that impede step advancement. The result is a competition between accelerated solute attachment and inhibition due to blocking of the steps by the clusters. The findings have implications for control of pathological mineralization and suggest artificial strategies for directing crystallization.

Using in situ atomic force microscopy (AFM), we investigate the inhibition of calcium oxalate monohydrate (COM) step growth by aspartic acid-rich peptides and find that the magnitude of the effect depends on terrace lifetime. We then derive a time dependent step-pinning model in which average impurity spacing depends on the terrace lifetime as given by the ratio of step spacing to step speed. We show that the measured variation in step speed is well fit by the model and allows us to extract the characteristic peptide adsorption time. The model also predicts that a crossover in the timescales for impurity adsorption and terrace exposure leads to bistable growth dynamics described mathematically by a catastrophe. We observe this behavior experimentally both through the sudden drop in step speed to zero upon decrease of supersaturation as well as through fluctuations in step speed between the two limiting values at the point where the catastrophe occurs. We discuss the model's general applicability to macromolecular modifiers and biomineral phases.

Calcium oxalate monohydrate (COM) is the primary constituent of the majority of renal stones. Osteopontin (OPN), an aspartic acid-rich urinary protein, and citrate, a much smaller molecule, are potent inhibitors of COM crystallization at levels present in normal urine. Current concepts of the role of site-specific interactions in crystallization derived from studies of biomineralization are reviewed to provide a context for understanding modulation of COM growth at a molecular level. Results from in situ atomic force microscopy (AFM) analyses of the effects of citrate and OPN on growth verified the critical role of site-specific interactions between these growth modulators and individual steps on COM crystal surfaces. Molecular modeling investigations of interactions of citrate with steps and faces on COM crystal surfaces provided links between the stereochemistry of interaction and the binding energy levels that underlie mechanisms of growth modification and changes in overall crystal morphology. The combination of in situ AFM and molecular modeling provides new knowledge that will aid rationale design of therapeutic agents for inhibition of stone formation.

Calcium oxalate monohydrate (COM) kidney stone formation is prevented in most humans by urinary crystallization inhibitors. Urinary osteopontin (OPN) is a prototype of the aspartic acid-rich proteins (AARP) that modulate biomineralization. Synthetic poly(aspartic acids) that resemble functional domains of AARPs provide surrogate molecules for exploring the role of AARPs in biomineralization. Effects of linear aspartic acid-rich peptides on COM growth kinetics and morphology were evaluated by the combination of constant composition (CC) analysis and atomic force microscopy (AFM). A spacer amino acid (either glycine or serine) was incorporated during synthesis after each group of 3 aspartic acids (DDD) in the 27-mer peptide sequences. Kinetic CC studies revealed that the DDD peptide with serine spacers (DDDS) was more than 30 times more effective in inhibiting COM crystal growth than the DDD peptide with glycine spacers (DDDG). AFM revealed changes in morphology on (010) and (-101) COM faces that were generally similar to those previously described for OPN and citrate, respectively. At comparable peptide levels, the effects of step pinning and reduced growth rate caused by DDDS were remarkably greater. In CC nucleation studies, DDDS caused a greater prolongation of induction periods than DDDG. Thus, nucleation studies link changes in interfacial energy caused by peptide adsorption to COM to the CC growth and AFM results. These studies indicate that, in addition to the number of acidic residues, the contributions of other amino acids to the conformation of DDD peptides are also important determinants of the inhibition of COM nucleation and growth.

The majority of human kidney stones are composed primarily of calcium oxalate monohydrate (COM) crystals. Thus, determining the molecular modulation of COM crystallization by urinary constituents is crucial for understanding and controlling renal stone disease. A comprehensive molecular-scale view of COM shape modification by citrate, obtained through a combination of in situ atomic force microscopy and molecular modeling, is presented here. We find that while the most important factors determining binding strength are coordination between COO- groups on citrate and Ca ions in the lattice, as well as H-bonds formed between the OH group of citrate and an oxalate group, the nonplanar geometry of the steps provides the most favorable environment due to the ability of the step-edge to accommodate all Ca-COO- coordinations with minimal strain. However, binding to all steps and terraces on the (010) face is much less favorable than on the (101) face due to electrostatic repulsion between oxalate and COO- groups. For example, the maximum binding energy, -166.5 kJ mol(-1), occurs for the [101] step on the (101) face, while the value for the [021] step on the (010) face is only -56.9 kJ mol(-1). This high selectivity leads to preferential binding to steps on the (101) face that pins step motion. Yet anisotropy in interaction strength on this face drives anisotropic changes in step kinetics that are responsible for shape modification of macroscopic COM crystals. Thus, the molecular scale growth kinetics and the bulk crystal habit are fully consistent with the simulations.

Calcium oxalate monohydrate (COM), which plays a functional role in plant physiology, is a source of chronic human disease, forming the major inorganic component of kidney stones. Understanding molecular mechanisms of biological control over COM crystallization is central to development of effective stone disease therapies and can help define general strategies for synthesizing biologically inspired materials. To date, research on COM modification by proteins and small molecules has not resolved the molecular-scale control mechanisms. Moreover, because proteins directing COM inhibition have been identified and sequenced, they provide a basis for general physiochemical investigations of biomineralization. Here, we report molecular-scale views of COM modulation by two urinary constituents, the protein osteopontin and citrate, a common therapeutic agent. Combining force microscopy with molecular modeling, we show that each controls growth habit and kinetics by pinning step motion on different faces through specific interactions in which both size and structure determine the effectiveness. Moreover, the results suggest potential for additive effects of simultaneous action by both modifiers to inhibit the overall growth of the crystal and demonstrate the utility of combining molecular imaging and modeling tools for understanding events underlying aberrant crystallization in disease.

FeF (2) films are grown by the reaction of XeF (2) and SeF (6) with iron foil. The growth initially follows the Mott-Cabrera parabolic rate law, indicating that the process is diffusion limited. At a certain film thickness, however, the growth abruptly stops, with the thickness using XeF (2) being nearly double that with SeF (6). It is suggested that the shutdown is due to the inability of the molecules to dissociate when too far from the substrate and that SeF (6) must approach more closely than XeF (2). This work suggests the use of molecular precursors to grow thin films via a self-limiting chemical process.