Comparing demographics, clinical characteristics, and hospital outcomes by vaccine uptake status: A single-institution cross-sectional study.

Vaccination against Coronavirus disease 2019 (COVID-19) has been the cornerstone of reducing morbidity and mortality of this disease, as it has been shown to decrease the risk of viral transmission, severity of disease, hospitalization, and intubation. However, true understanding of its impact is skewed by heterogeneous vaccine administration due to lack of equitable access, vaccine hesitancy, and varying social determinants of health. Therefore, this study aims to identify groups that are less likely to be vaccinated and understand whether the resultant differences in vaccination rates affect morbidity and mortality in socially marginalized COVID-19 patients. A retrospective cohort analysis was performed on a randomized and stratified population of 939 COVID-19 patients from January 2021 to December 2021. Bivariate analysis and logistic regression were used to assess demographic and clinical characteristic trends in unvaccinated, partially vaccinated, and fully vaccinated groups. No one age (P = .21), gender (P = .9), race (P = .12), ethnicity (P = .09), or health insurance status (P = .13) group was more vaccinated than the other. Similarly, no subgroup was at increased odds of intubation (P = .08) or death. However, patients with all categories of comorbidities including cardiopulmonary disease (P = <.001, effect size .17), renal disease (P = <.001, effect size 0.138), metabolic disease (P = .04), and immunocompromised (P = .01) states were found to have significantly higher vaccination rates. Our study also shows that full vaccination protects against mortality and decreases the odds of intubation by 55% (adjusted odds ratio = 0.453, P value = .015) compared to no vaccination or partial vaccination. Findings from this study show an encouraging trend that sicker patients had higher rates of vaccination against COVID-19. This trend highlights the need for further identification of motivators that may be applied to vaccine-hesitant populations, which can help guide population-level policy, increase vaccination campaign yield, and reach for health equity.

Valoración del liderazgo enfermero en un hospital del Sistema Sanitario Público Andaluz / Leadership in a hospital of the Andalusian Public Health System

Objetivo: Analizar, con perspectiva de género, las características y la percepción de los efectos del liderazgo de las enfermeras y enfermeros de un hospital del Sistema Sanitario Público Andaluz. Metodología: Estudio cualitativo con enfoque fenomenológico. Los/as participantes fueron enfermeras asistenciales y con cargos intermedios con contrato mayor a 6 meses. Se realizó un análisis de contenido cualitativo. Se establecieron 4 fases para el análisis de datos, de donde resultaron 5 categorías. Se utilizó el software NVivo 11 para el análisis de los diálogos. Resultados: Los discursos de los participantes dotan al líder de características que lo definen como una persona referente. La contribución de los mandos intermedios es necesaria para la consecución de los objetivos de las unidades asistenciales y cohesión del grupo, aunque este grupo la perciben solo en relación al manejo de los recursos. El acceso a cargos de gestión no tiene vinculación con el género. Conclusiones: El estilo de liderazgo predominante en los cargos intermedios del Hospital de Lebrija es reconocido como un liderazgo participativo, esencial para el mantenimiento de la gestión eficiente y favorecedor de la promoción y la igualdad entre profesionales; no identificándose sesgos de género en el acceso a dichos cargos.(AU)

Objective: To analyse, from a gender perspective, the characteristics and perception of the effects of leadership of nurses in a hospital of the Andalusian Public Health System. Methodology: Qualitative study with a phenomenological approach. The participants were nurses in care and intermediate positions with a contract of more than 6 months. A qualitative content analysis was carried out. Four phases were established for data analysis, from which 5 categories resulted. NVivo 11 software was used to analyse the dialogues. Results: The participants’ discourses endow the leader with characteristics that define him as a reference person. The contribution of middle management is necessary for the achievement of the objectives of the care units and the cohesion of the group, although this group perceives it only in relation to the management of resources. Access to management positions is not linked to gender. Conclusions: The participants’ discourses endow the leader with characteristics that define him as a reference person. The contribution of middle management is necessary for the achievement of the objectives of the care units and the cohesion of the group, although this group perceives it only in relation to the management of resources. Access to management positions is not linked to gender.(AU)

Leadership in a hospital of the Andalusian Public Health System.

OBJECTIVE: To analyse, from a gender perspective, the characteristics and perception of the effects of leadership of nurses in a hospital of the Andalusian Public Health System. METHODOLOGY: Qualitative study with a phenomenological approach. The participants were nurses in care and intermediate positions with a contract of more than 6 months. A qualitative content analysis was carried out. Four phases were established for data analysis, from which 5 categories resulted. NVivo 11 software was used to analyse the dialogues. RESULTS: The participants' discourses endow the leader with characteristics that define him as a reference person. The contribution of middle management is necessary for the achievement of the objectives of the care units and the cohesion of the group, although this group perceives it only in relation to the management of resources. Access to management positions is not linked to gender. CONCLUSIONS: The participants' discourses endow the leader with characteristics that define him as a reference person. The contribution of middle management is necessary for the achievement of the objectives of the care units and the cohesion of the group, although this group perceives it only in relation to the management of resources. Access to management positions is not linked to gender.

Maize-Brachiaria intercropping: A strategy to supply recycled N to maize and reduce soil N2O emissions?

Nitrogen use in agriculture directly impacts food security, global warming, and environmental degradation. Forage grasses intercropped with maize produce feed for animals and or mulch for no-till systems. Forage grasses may exude nitrification inhibitors. It was hypothesized that brachiaria intercropping increases N recycling and maize grain yield and reduces nitrous oxide (N2O) emissions from soil under maize cropping. A field experiment was set up in December 2016 to test three cropping system (maize monocropped, maize intercropped with Brachiaria brizantha or with B. humidicola) and two N rates (0 or 150 kg ha-1). The grasses were sown with maize, but B. humidicola did not germinate well in the first year. B. brizantha developed slowly during the maize cycle because of shading but expanded after maize was harvested. The experiment was repeated in 2017/2018 when B. humidicola was replanted. N2O and carbon dioxide (CO2) emissions, maize grain yield and N content were measured during the two seasons. After the first maize harvest, the above- and below-ground biomass, C and N content of B. brizantha grown during fall-winter, and the biological nitrification inhibition potential of B. brizantha were evaluated. Maize yield responded to N fertilization (5.1 vs. 9.8 t ha-1) but not to brachiaria intercropping. B. brizantha recycled approximately 140 kg N ha-1 and left 12 t dry matter ha-1 for the second maize crop. However, the 2017/18 maize yields were not affected by the N recycled by B. brizantha, whereas N2O emissions were higher in the plots with brachiaria, suggesting that part of the recycled N was released too early after desiccation. Brachiarias showed no evidence of causing nitrification inhibition. The strategy of intercropping brachiarias did not increase maize yield, although it added C and recycled N in the system.

The Influence of Marginalization on Cultural Attitudes and Trash Disposal Practices in Esfuerzo de Paraíso of the Dominican Republic: A Qualitative Interview Study.

The inadequate management of municipal solid waste (MSW) in fast-developing nations is a major public health problem. Trash collection is often inconsistent, leaving residents to use unsafe disposal methods such as incineration or unregulated dumping. The issue is especially pronounced in marginalized communities, where public service provision is scarce. Past research has identified factors that perpetuate harmful disposal practices. The current study expanded on previous work by exploring how individuals' perceptions of political, spatial, and economic marginalization affected their agency with regards to waste management. Researchers focused on a marginalized community in the Dominican Republic known as Esfuerzo de Paraíso. There, they conducted semi-structured interviews to explore residents' perceptions of marginalization at the individual, interpersonal, community, and institutional levels, and its effects on their agency. A qualitative coding process revealed that most community members were discontent with their trash disposal practices, but that long-standing marginalization left them feeling ill equipped to generate change at the individual level. Interviewees believed that change should be initiated at the community level and implemented with the support of institutional-level actors, namely the municipal government. Residents did not identify any non-governmental organizations as possible sources of help, which may suggest a limited view of institutional support networks.

Assessment of runoff using 7Be in vineyards in the central valley of Chile.

In Chile, erosion processes (on-site and off-site impact) affect at least 36.9 million ha-1, representing 49% of the total land area. Different regions show severe soil degradation mainly caused by water erosion processes. The importance of sediment-associated transport and the key role of soil erosion affect the fertility of the land and the contamination of water bodies. The aim of this work was to estimate the erosion rate, caused by the rainfall in Apalta vineyards in the Libertador General Bernardo O'Higgins Region of Chile using isotope techniques, assessing the 7Be runoff during four years (2009-2012). The 7Be distribution mass depth at a reference site ranged from 7 to 24 kg m-2 in the first two centimetres soil layer. Even when the vineyards have been well managed, the topographic characteristics and the climatic conditions facilitated soil erosion, with average rates of 50.4, 23.5, 50.6 and 67.3 tons ha-1 y-1 in 2009, 2010, 2011 and 2012, respectively. The robustness of the 7Be technique demonstrated the advantage of a non-soil-destructive methodology to calculate soil distribution and erosion rates.

Development of a New Coarse-Grained Model to Simulate Assembly of Cellulose Chains Due to Hydrogen Bonding.

In this work, we present a new coarse-grained (CG) model that captures the directional hydrogen bonding interactions that drive cellulose chains to assemble into ordered aggregates. This CG model balances the incorporation of chemical details at the monomer level needed to represent directional interactions and the coarse-graining needed to capture large length scales and time scales associated with macromolecular assembly. We validate this CG model by first comparing the cellulose single-chain structure in the CG molecular dynamics (MD) simulations with that in atomistic MD simulations. We also compare the hydrogen bonding pattern, interchain distance, and interchain orientation seen in assembled cellulose chains observed in CG MD simulations with those seen in experimental crystal structures of cellulose. Upon validation, we present the aggregation behavior of cellulose chains with "silenced" hydrogen bonding site interactions to mimic cellulose chains that are chemically modified at the donor and acceptor hydrogen bonding sites (e.g., methylcellulose). We expect this type of CG model to be useful in predicting the morphology of cellulose chains in solution under a wide range of solution conditions and chemical modifications.

Biological Nitrification Inhibition (BNI): Phenotyping of a Core Germplasm Collection of the Tropical Forage Grass Megathyrsus maximus Under Greenhouse Conditions.

Modern intensively managed pastures that receive large external nitrogen (N) inputs account for high N losses in form of nitrate (NO3 -) leaching and emissions of the potent greenhouse gas nitrous oxide (N2O). The natural plant capacity to shape the soil N cycle through exudation of organic compounds can be exploited to favor N retention without affecting productivity. In this study, we estimated the relationship between biological nitrification inhibition (BNI), N2O emissions and plant productivity for 119 germplasm accessions of Guineagrass (Megathyrsus maximus), an important tropical forage crop for livestock production. This relation was tested in a greenhouse experiment measuring BNI as (i) rates of soil nitrification; (ii) abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA); and (iii) the capacity of root tissue extracts to inhibit nitrification in vitro. We then measured N2O emissions, aboveground biomass and forage nutrition quality parameters. Reductions on nitrification activity ranging between 30 and 70% were found across the germplasm collection of M. maximus. Accessions with low nitrification rates showed a lower abundance of AOB as well as a reduction in N2O emissions compared to accessions of high nitrification rates. The BNI capacity was not correlated to N uptake of plants, suggesting that there may be intraspecific variation in the exploitation of different N sources in this grass species. A group of accessions (cluster) with the most desirable agronomic and environmental traits among the collection was identified for further field validation. These results provide evidence of the ability of M. maximus to suppress soil nitrification and N2O emissions and their relationship with productivity and forage quality, pointing a way to develop N conservative improved forage grasses for tropical livestock production.

Computational Reverse-Engineering Analysis for Scattering Experiments on Amphiphilic Block Polymer Solutions.

In this paper, we present a computational reverse-engineering analysis for scattering experiments (CREASE) based on genetic algorithms and molecular simulation to analyze the structure within self-assembled amphiphilic polymer solutions. For a given input comprised of scattering intensity profiles and information about the amphiphilic polymers in solution, CREASE outputs the structure of the self-assembled micelles (e.g., core and corona diameters, aggregation number) as well as the conformations of the amphiphilic polymer chains in the micelle (e.g., blocks' radii of gyration, chain radii of gyration, monomer concentration profiles). First, we demonstrate CREASE's ability to reverse-engineer self-assembled nanostructures for scattering profiles obtained from molecular simulations (or in silico experiments) of generic coarse-grained bead-spring polymer chains in an implicit solvent. We then present CREASE's outputs for scattering profiles obtained from small-angle neutron scattering (SANS) experiments of poly(d-glucose carbonate) block copolymers in solution that exhibit assembly into spherical nanoparticles. The success of this method is demonstrated by its ability to replicate, quantitatively, the results from in silico experiments and by the agreement in micelle core and corona sizes obtained from microscopy of the in vitro solutions. The primary strength of CREASE is its ability to analyze scattering profiles without an off-the-shelf scattering model and the ability to provide chain and monomer level structural information that is otherwise difficult to obtain from scattering and microscopy alone.

Coarse-grained molecular dynamics simulations of α-1,3-glucan.

In this paper we present a computational study of aggregation in aqueous solutions of α-1,3-glucan captured using a coarse-grained (CG) model that can be extended to other polysaccharides. This CG model captures atomistic geometry (i.e., relative placement of the hydrogen bonding donors and acceptors within the monomer) of the α-1,3-glucan monomer, the directional interactions due to the donor-acceptor hydrogen bonds, and their effect on aggregation of multiple α-1,3-glucan chains without the extensive computational resources needed for simulations with atomistic models. Using this CG model, we conduct molecular dynamics simulations to assess the effect of varying α-1,3-glucan chain length and hydrogen bond interaction strengths on the aggregation of multiple chains at finite concentrations in implicit solvent. We quantify the hydrogen bonding strength needed for multiple chains to aggregate, the distribution of inter- and intra-chain hydrogen bonds within the aggregate and in some cases, the shapes of the aggregate. We also explore the effect of substitution/silencing of some randomly selected or specific hydrogen bonding sites in the chain on the aggregation and aggregate structure. In the unmodified α-1,3-glucan solution, the inter-chain hydrogen bonds cause the chains to aggregate into sheets. Random silencing of hydrogen bonding donor sites only increases the hydrogen bond strength needed for aggregation but retains the same aggregate structure as the unmodified chains. Specific silencing of the hydrogen-bonding site on the C6 carbon leads to the chains aggregating into planar sheets that then fold over to form hollow cylinders at intermediate hydrogen bond strength - 4.7 to 5.3 kcal mol-1. These cylindrical aggregates assemble end-to-end to form larger aggregates at higher hydrogen bond strengths.

Shear-Induced Alignment of Janus Particle Lamellar Structures.

Control over the alignment of colloidal structures plays a crucial role in advanced reconfigurable materials. In this work, we study the alignment of Janus particle lamellar structures under shear flow via Brownian dynamics simulations. Lamellar alignment (orientation relative to flow direction) is measured as a function of the Péclet number (Pe)-the ratio of the viscous shear to the Brownian forces-the particle volume fraction, and the strength of the anisotropic interaction potential made dimensionless with thermal energy. Under conditions where lamellar structures are formed, three orientation regimes are observed: (1) random orientation for very small Pe, (2) parallel orientation-lamellae with their normals parallel to the direction of the velocity gradient-for intermediate values of Pe, and (3) perpendicular orientation-lamellae with their normals parallel to the vorticity direction-for large Pe. To understand the alignment mechanism, we carry out a scaling analysis of competing torques between a pair of particles in the lamellar structure. Our results suggest that the change of parallel to perpendicular orientation is independent of the particle volume fraction and is caused by the hydrodynamic and Brownian torques on the particles overcoming the torques resulting from the interparticle interactions. This initial study of shear-induced alignment on lamellar structures formed by Janus colloidal particles also opens the door for future applications where a reversible actuator for structure orientation is required.

Phase diagram of Janus particles: The missing dimension of pressure anisotropy.

Brownian dynamics simulations of single-patch Janus particles under sedimentation equilibrium reveal that the phases found at fixed temperature and volume fraction are extremely sensitive to small changes in lateral box dimension. We trace this sensitivity to an uncontrolled parameter, namely, the pressure component parallel to the hexagonally ordered layers formed through sedimentation. We employ a flexible-cell constant-pressure scheme to achieve explicit control over this usually overlooked parameter, enabling the estimation of phase behavior under given pressure anisotropy. Our results show an increase in the stability range of an orientationally ordered lamellar phase with lateral layer compression and suggest a novel mechanism to control solid-solid phase transitions with negligible change in system volume, thus showing prospect for design of novel structures and switchable crystals from anisotropic building blocks.

Rotator-to-Lamellar Phase Transition in Janus Colloids Driven by Pressure Anisotropy.

We demonstrate through Brownian dynamics simulations a phase transition in plastic crystalline assemblies of Janus spheres through controlled pressure anisotropy. When the pressure in plane with hexagonally ordered layers is increased relative to that normal to the layers, a rapid first-order rotator-to-lamellar transition of Janus sphere orientation occurs at constant temperature. We show that the underlying mechanism closely follows the Maier-Saupe theory, originally developed for isotropic-to-nematic transition in positionally disordered materials but here applied to positionally ordered ones. Since the transition involves almost no translational diffusion or volume change, and occurs rapidly by particle rotation, the results should help guide the design of rapidly switchable colloidal crystals.

Putative binding mode of Escherichia coli exopolyphosphatase and polyphosphates based on a hybrid in silico/biochemical approach.

The exopolyphosphatase of Escherichia coli processively and completely hydrolyses long polyphosphate chains to ortho-phosphate. Genetic surveys, based on the analysis of single ppx(-) or ppk(-) mutants and on the double mutant, demonstrate a relationship between these genes and the survival capacity. The exopolyphosphatase belongs to the ASKHA protein superfamily, hence, its active site is well known; however, the knowledge of the way in which this enzyme binds polyP remains incomplete. Here we present different computational approaches, site-direct mutagenesis and kinetic data to understand the relationship between structure and function of exopolyphosphatase. We propose H(378) as a fundamental gatekeeper for the recognition of long chain polyphosphate.

Autonomía en pacientes de UCI: limitación del esfuerzo terapéutico y donación de órganos / Autonomy in ICU patients: Limitation of Therapeutic Effort and organ donation

OBJETIVOS: conocer el grado de autonomía de los pacientes ingresados en la Unidad de Cuidados Intensivos (UCI) de un hospital comarcal, con un diagnóstico de gravedad tal que pudieran ser subsidiarios de limitación del esfuerzo terapéutico (LET) y/o de donación de órganos. MÉTODO: estudio descriptivo transversal en la UCI del Servicio de Cuidados Críticos y Urgencias del Hospital San Juan de Dios del Aljarafe de Bormujos (Sevilla). Se revisaron todas las historias clínicas de los pacientes ingresados en UCI (enero 2011 hasta enero2014) para seleccionar aquellas en las que existía registro de algún tipo de LET y/o de donación de órganos (n= 146). VARIABLES: edad, sexo, tipo de LET, persona que toma la decisión de LET y/o donación, voluntades vitales anticipadas (VVA). Se utilizó el test Chi cuadrado como prueba de contraste de hipótesis. RESULTADOS: el 60,3% de los pacientes eran hombres, el 58,1%tenía entre 71 y 98 años. Hubo 79,5% casos de LET y un 10,3% de donaciones. La familia decidió en 82,5% de los hombres y en el69,2% de las mujeres subsidiarias de LET. En la donación de órganos la familia decidió en el 100% de los casos con independencia del sexo del paciente. CONCLUSIONES: la autonomía de las mujeres subsidiarias de LET es ejercida por la familia el doble de veces que por la paciente; en el caso de los hombres casi el triple. La autonomía ejercida en la donación de órganos corresponde en su totalidad a la familia. No existen casos de voluntades vitales anticipadas registradas en la historia

OBJECTIVES: to understand the level of autonomy of patients admitted to the Intensive Care Unit (ICU) of a regional hospital, with a diagnosis of severity which could make them candidate to a Limitation of Therapeutic Effort (LTE) and/or organ donation. METHOD: a descriptive transversal study in the ICU of the Critical Care and Emergencies Unit of the Hospital San Juan de Dios del Aljarafe de Bormujos (Seville). The clinical records of all patients admitted to the ICU were reviewed (from January, 2011 to January,2014) in order to select those where some type of LTE and/or organ donation had been recorded (n= 146). VARIABLES: age, gender, type of LTE, person who made the decision for LTE and/or donation, anticipated directives or living will (LW). Square Chi Test was used for hypothesis test contrast. RESULTS: a 60.3% of patients were male, 58.1% was between 71and 98-year-old. There were 79.5% cases of LTE and 10.3% of donations. The family made the decision in 82.5% of men and 69.2% of women candidate to LTE. Regarding organ donation, the family made the decision on 100% of cases, regardless of patient gender. CONCLUSIONS: the autonomy of women candidate to LTE is taken over by their family twice as often as patients; in the case of men, almost three times as often. The autonomy regarding organ donation is completely taken over by the family. There are no cases of anticipated directives or living wills registered in clinical records

Exogenous application of pectin-derived oligosaccharides to grape berries modifies anthocyanin accumulation, composition and gene expression.

Anthocyanins are secondary metabolites synthesized in grape berry skins via the phenylpropanoid pathway, with functions ranging from skin coloration to protection against pathogens or UV light. Accumulation of these compounds is highly variable depending on genetics, environmental factors and viticultural practices. Besides their biological functions, anthocyanins improve wine quality, as a high anthocyanin content in berries has a positive impact on the color, total phenolic concentration and, ultimately, the price of wine. The present work studies the effect of the pre-veraison application of pectin derived oligosaccharides (PDO) on the synthesis and accumulation of these compounds, and associates the changes observed with the expression of key genes in the phenylpropanoid pathways. To this end, pre-veraison Cabernet Sauvignon bunches were treated with PDO to subsequently determine total anthocyanin content, the anthocyanin profile (by HPLC-DAD) and gene expression (by qRT-PCR), using Ethrel and water treatments for comparison. The results show that PDO were as efficient as Ethrel in generating a significant rise in total anthocyanin content at 30 days after treatment (dat), compared with water treatments (1.32, 1.48 and 1.02 mg e.Mv-3G/g FW respectively) without any undesirable effect on berry size, soluble solids, tartaric acid concentration or pH. In addition, a significant alteration in the anthocyanin profile was observed. Specifically, a significant increase in the relative concentration of malvidin was observed for both PDO and Ethrel treatments, compared with water controls (52.8; 55.0 and 48.3%, respectively), with a significant rise in tri-hydroxylated forms and a fall in di-hydroxylated anthocyanins. The results of gene expression analyses suggest that the increment in total anthocyanin content is related to a short term increase in phenylalanine ammonia-lyase (PAL) expression, mediated by a decrease in MYB4A expression. A longer term increase in UDP-glucose flavonoid 3-O-glucosyltransferase (UFGT) expression, probably mediated by a rise in MYBA1 was also observed. Regarding the anthocyanin profile, despite the increase observed in MYB5A expression in PDO and Ethrel treatments, no changes in flavonoid 3'-hydroxylase (F-3'-H); flavonoid 3'5'-hydroxylase (F-3'5'-H) or O-methyltransferase (OMT) could be related with the profile modifications described. Overall, this study highlights that application of PDO is a novel means of altering specific grape berry anthocyanins, and could be a means of positively influencing wine quality without the addition of agrochemicals.

Rich Janus colloid phase behavior under steady shear.

We study the assembly of single-patch colloidal Janus particles under steady shear flow via Brownian dynamics simulations. In the absence of flow, by varying the Janus patch size and the range and strength of the anisotropic interaction potential, Janus colloids form different aggregates such as micelles, wormlike clusters, vesicles and lamellae. Under shear flow we observe rearrangement, deformation, and break-up of aggregates. At small and intermediate Péclet (Pe) numbers-the ratio between shear and Brownian forces-the competition between rearrangement, deformation, and break-up favors the growth of micelles and vesicles increasing mean cluster size, which is consistent with a previous numerical study of Janus particles under shear. This initial shear-induced growth causes micelles and vesicles to reach a maximum cluster size at Pe ≈ 1 and Pe ≈ 10, respectively. After this growth micelles dissociate continuously to reach a dilute colloidal "gas phase" at Pe ≈ 10 while vesicles dissociate into micelles with high aspect ratio at Pe ≈ 10 and finally break-up into a gas phase at Pe ≈ 30. Wormlike clusters initially break-up into micelles with high aspect ratio at Pe ≈ 0.1, and proceed to finally reach a gas phase at Pe ≈ 10. Lamellae initially break into smaller lamellae that align with the flow in the velocity-velocity-gradient plane and finally break-up into a gas phase at Pe ≈ 100. The different cluster sizes and morphologies observed as functions of interaction range, Janus patch size, interaction strength, and shear rate, open new actuation routes for reconfigurable materials and applications.

Kinetic modeling and design of colloidal lock and key assembly.

We investigate the kinetics of colloidal lock and key particle assembly by modeling transitions between free, non-specifically and specifically (dumbbells) bound pairs to enable the rapid formation of specific pairs. We expand on a model introduced in a previous publication (Colón-Meléndez et al., 2015) to account for the shape complementarity between the lock and the key particle. Specifically we develop a theory to predict free energy differences between specific and non-specific states based on the interaction potential between arbitrary surfaces and apply this to the interaction of a spherical key particle with the concave dimple surface. Our results show that a lock particle dimple slightly wider than the key particle radius results in optimal binding, but also show escape rates much smaller than those observed in experimental measurements described in the paper cited above. We assess the possible sources of error in experiments and in analysis, including spatial and temporal resolution of the confocal microscopy method used to measure kinetic coefficients, the polydispersity of the lock dimple size, and the sedimentation of the particles in a quasi-two-dimensional layer. We find that the largest sources of variation are in the limited temporal resolution of the experiments, which we account for in our theory, and in the quasi-two-dimensional nature of the experiment that leads to misidentification of non-specific pairs as specific ones. Accounting for these sources of variation results in very good quantitative agreement with experimental data.

Binding kinetics of lock and key colloids.

Using confocal microscopy and first passage time analysis, we measure and predict the rates of formation and breakage of polymer-depletion-induced bonds between lock-and-key colloidal particles and find that an indirect route to bond formation is accessed at a rate comparable to that of the direct formation of these bonds. In the indirect route, the pocket of the lock particle is accessed by nonspecific bonding of the key particle with the lock surface, followed by surface diffusion leading to specific binding in the pocket of the lock. The surprisingly high rate of indirect binding is facilitated by its high entropy relative to that of the pocket. Rate constants for forward and reverse transitions among free, nonspecific, and specific bonds are reported, compared to theoretical values, and used to determine the free energy difference between the nonspecific and specific binding states.

Colloidal crystal grain boundary formation and motion.

The ability to assemble nano- and micro- sized colloidal components into highly ordered configurations is often cited as the basis for developing advanced materials. However, the dynamics of stochastic grain boundary formation and motion have not been quantified, which limits the ability to control and anneal polycrystallinity in colloidal based materials. Here we use optical microscopy, Brownian Dynamic simulations, and a new dynamic analysis to study grain boundary motion in quasi-2D colloidal bicrystals formed within inhomogeneous AC electric fields. We introduce "low-dimensional" models using reaction coordinates for condensation and global order that capture first passage times between critical configurations at each applied voltage. The resulting models reveal that equal sized domains at a maximum misorientation angle show relaxation dominated by friction limited grain boundary diffusion; and in contrast, asymmetrically sized domains with less misorientation display much faster grain boundary migration due to significant thermodynamic driving forces. By quantifying such dynamics vs. compression (voltage), kinetic bottlenecks associated with slow grain boundary relaxation are understood, which can be used to guide the temporal assembly of defect-free single domain colloidal crystals.