Youth engagement in research: exploring training needs of youth with neurodevelopmental disabilities

BACKGROUND

Authentic researcher-youth partnerships in patient-oriented research (POR) where the research responds to the needs expressed by youth themselves are essential to make research meaningful. While patient-oriented research (POR) is increasingly practiced, few training programs exist in Canada and none, to our knowledge, are tailored for youth with neurodevelopmental disabilities (NDD). Our primary objective was to explore the training needs of youth (ages 18-25) with NDD to enhance their knowledge, confidence, and skills as research partners. Our secondary objective was to identify the benefits and challenges of engaging youth with NDD in a POR approach.

METHODS

Our team of four youth and one parent with lived experience [Youth Engagement in Research (YER) partners] and six researchers engaged in POR to investigate the primary objective via two phases: (1) individual interviews with youth living with NDD and (2) a two-day virtual symposium with focus groups with youth and researchers. Collaborative qualitative content analysis was employed to synthesize the data. Our secondary objective was assessed by asking our YER partners to complete the Public and Patient Engagement Evaluation Tool (PPEET) survey and participate in reflective discussions.

RESULTS

Phase 1 participants (n = 7) identified various barriers and facilitators to their engagement in research and offered suggestions to meet their needs through minimizing barriers and integrating facilitators, which would subsequently enhance their knowledge, confidence, and skills as research partners. Informed by phase 1, phase 2 participants (n = 17) prioritized the following POR training needs: researcher-youth communication, research roles and responsibilities, and finding partnership opportunities. For delivery methods, participants stated the importance of youth representation, using Universal Design for Learning, and co-learning between youth and researchers. Based on the PPEET data and subsequent discussions, YER partners agreed that they were able to express views freely, feel that their views were heard, and that their participation made a meaningful difference. Challenges included scheduling difficulties, ensuring multiple methods for engagement, and working under short timelines.

CONCLUSION

This study identified important training needs for youth with NDD and for researchers to engage in meaningful POR, which can subsequently inform the co-production of accessible training opportunities with and for youth.

Exploring 10 years of dissemination of the F-words for Child Development: A multifaceted case study

BACKGROUND

There is growing interest in exploring how to move research findings into practice. Since 2014, a team of families and researchers has been working to promote and study the dissemination of the "F-words for Child Development" (Function, Family, Fitness, Fun, Friends, and Future). This case study describes our dissemination strategies and uses the Diffusion of Innovation theory to understand the factors contributing to the uptake of the F-words-a function-promoting, strengths-based, and family-centred innovation in child health and development.

METHODS

Between November 2011 and November 2021, we collected data from multiple sources: our dissemination strategies, including affiliated documents/artefacts (e.g., videos and presentations) and evaluation data (e.g., surveys and Google/video analytics). We used a two-step analysis: (1) a chronological time series to describe the processes involved along with indicators of dissemination over time (e.g., increase knowledge and awareness); and (2) Diffusion of Innovation theory to explore the factors that contributed to the uptake of the F-words.

RESULTS

Multifaceted dissemination strategies were essential to raise awareness and increase families' and service providers' knowledge of the F-words. These included three primary strategies: (i) development and distribution of educational materials; (ii) presentations at educational meetings; and (iii) educational outreach visits. Additional strategies, such as the use of mass media, collaboration with early adopters/champions, and the involvement of family members further supported dissemination efforts. Diffusion of Innovation factors (innovation characteristics, time, social systems, and communication channels) all contributed to the uptake of this innovation.

CONCLUSIONS

Purposeful planned dissemination practice, to increase knowledge and awareness of an innovation, is an important step in the knowledge translation process. Over a period of 10 years, through the use of multiple dissemination strategies conducted in partnership with families and service providers, the F-words have spread globally. Diffusion of Innovation theory has served to help understand how and why the F-words are being shared and adopted around the world.

Understanding the essential components and experiences of youth with autism spectrum disorders in peer mentorship programmes during the transition to adulthood: A qualitative meta-ethnography

Youth with an autism spectrum disorder (ASD) often require additional supports during the period of transition to from high school to post-secondary education or career paths. Peer mentorship (PM) programmes create opportunities to support youth with ASD in identifying their personal, academic and career goals after graduating from high school; however, there is limited insight about the components of these programmes that are valued by both participants and peer mentors and that are perceived to contribute to the overall success of a programme in achieving their goals. Our objective was to identify, describe and synthesize the components of PM programmes valued by youth with ASD and their peer mentors, as well as to document their experiences in these transitional support services. A meta-ethnography was conducted to synthesize qualitative and mixed methods studies of PM programmes for youth with ASD. A systematic search of seven databases yielded 142 nonduplicate articles. Data analysis and synthesis involved (1) extraction of raw data; (2) extraction of study authors' interpretations, followed by inductive coding; (3) synthesis of key themes and (4) schematic diagram development to illustrate the relationship of themes. Ten studies of PM programmes from Canada (2), United States (4), Australia (3) and United Kingdom (1) were included. Extracted data reflected experiences of 131 mentees and 82 mentors. The essential programme components identified were (1) mentorship, (2) skill building, (3) peer group and (4) facilitating transition. PM characterized by clear communication and connection between mentors and mentees was valuable to the success of the programme. Peer mentors played an essential role to facilitate the positive experiences that mentees had with programme components, including interactions with peer groups. Successful PM programmes created a safe environment for mentees to practice skills and helped mentees gain confidence to expand their roles to take leadership in their learning.

Knowledge translation strategies to support service providers' implementation of the "F-words in Childhood Disability"

Purpose: Service providers are adopting the "F-words" in practice as a strengths-based approach to childhood disability. This study aimed to gain insight into service providers' uses of the "F-words", associated barriers, and knowledge translation strategies needed to support implementation.Methods: Service providers were invited to participate in an interview after completing an online survey on their clinical implementation of the "F-words". Content analysis provided insight into use of the "F-words" and perceived barriers; and to identify knowledge translation strategies to facilitate implementation.Results: Twenty-one service providers from nine countries participated in interviews. Applications of the "F-words" included its use as a conceptual framework, directly in practice, and in teaching/training. Barriers included conflicting attitudes, insufficient funding, language, and misalignment with organizational/government priorities. To support the adoption of the "F-words", participants recommended knowledge translation strategies including local opinion leaders, linkage and exchange, educational outreach and meetings, and distribution of educational materials.Conclusions: Understanding uses, barriers to use, and knowledge translation strategies will inform future directions to move the "F-words" into practice. A critical step in bridging the research-to-practice gap and encouraging more widespread adoption requires collaboration with service providers to tailor knowledge translation strategies to fit the local context.Implications for RehabilitationService providers around the world are interested in the ICF-based "F-words" and are adopting them in clinical practice to support a holistic, strengths-based approach to childhood disability.While there is considerable uptake of the "F-words", service providers have experienced barriers including conflicting attitudes of families and colleagues, insufficient funding, lack of translations, and misalignment with organizational and government priorities.To further support implementation and overcome perceived barriers, service providers recommended using four knowledge translation strategies: (i) local opinion leaders; (ii) linkage and exchange; (iii) educational outreach/meetings; and (iv) the distribution of educational materials.Service providers and researchers must partner together to tailor knowledge translation strategies to the local context in order to address the needs and priorities of service providers' specific settings and bridge the gap between research evidence and practice.

Service Providers' Perspectives on Using the 'F-Words in Childhood Disability': An International Survey

AIMS

The 'F-words in Childhood Disability' - operationalizing the International Classification of Functioning, Disability and Health Framework - have attracted great interest around the world. However, we have yet to learn how service providers (SPs) are using them. The aim of this study was to explore international SPs' attitudes toward and use of the 'F-words'.

METHODS

A survey was administered, guided by the Theory of Planned Behavior, including Likert-scaled statements and an open-ended question. Ninety-one SPs working with children with impairments from 27 countries completed the survey.

RESULTS

While 82 agreed the 'F-words' are good practice, only 60 are using the 'F-words'. Similarly, 52 SPs agreed that their colleagues approved of their use and 54 felt they were easy for families to use and understand. Respondents reported three main uses: (i) support of preexisting clinical approaches, (ii) direct integration into practice, and (iii) being taught in higher education. They also identified barriers to implementation (e.g., alternative clinical approaches and limited resources).

CONCLUSIONS

Findings provide insights in how the 'F-words' are being used and the limitations thereof, which can inform future directions to support international implementation. With international SPs, we need to develop adapted dissemination tools to support uptake by individuals worldwide.

Exploring the international uptake of the "F-words in childhood disability": A citation analysis

BACKGROUND

The "F-words in childhood disability" (function, family, fitness, fun, friends, and future) were introduced in a concept paper in 2012 entitled, "The F-words in childhood disability: I swear this is how we should think!". The "F-words" are grounded in, and aim to operationalize, the World Health Organization's (World Health Organization, 2001) International Classification of Functioning, Disability and Health (ICF) framework. A citation analysis was conducted to explore the extent of research uptake of the "F-words" concepts.

METHODS

Three databases-Google Scholar, Wiley Online, and Web of Science-were searched from July 2012 to December 2018 for sources that cited the original F-words paper. Dates of publication and countries of first authors were extracted from all cited articles, and a taxonomy was developed to categorize the type of usage.

RESULTS

The search yielded 157 sources from 26 countries, and the number of citations has continued to increase since the paper's publication. Sources were placed into three categories: cited/referenced (n = 109; i.e., the paper was simply cited), integrated/informed (n = 36; i.e., the F-words were stated within the text), and non-English (n = 12). Of the 36 integrated/informed sources, 34 (94.4%) applied the F-words to the ICF framework and five themes emerged with respect to the use of the F-words: (a) support of a holistic approach to childhood disability, (b) association of the F-words to physical activity and rehabilitation, (c) application and measurement of quality of life, (d) F-words research team-related papers, and (e) "other" category.

CONCLUSION

This citation analysis shows that the F-words are mainly being used to operationalize the ICF, support a holistic approach to childhood disability, and inform physical activity and rehabilitation-based interventions. These perspectives will play an important role in informing the next steps with respect to moving the F-words into research and practice.

Is water one liquid or two?

The idea that water is a mixture of two distinct states is analyzed in some detail. It is shown that the known compressibility of water is in fact sufficiently small that for a volume of water of size 1 nm³, the density fluctuations are of order 4% of the average density. This is much smaller than the ≈25% density fluctuations that would be required for significant regions of high and low density water to occur on this volume scale. It is also pointed out that the density fluctuations in water are, if anything, smaller than those that occur in other common liquids which do not have the anomalous properties of water. It is shown that if the distribution of density fluctuations is unimodal, the system is in the one-phase region, and if bimodal, it is in the two-phase region. None of the liquid or amorphous phases of water explored in this work give any sign of being in the two-phase region. Existing neutron and X-ray scattering data on water in the amorphous phases, and in the stable liquid phases as a function pressure and temperature, are subject to a new set of empirical potential structure refinement simulations. These simulations are interrogated for their configurational entropy, using a spherical harmonic reconstruction of the full orientational pair correlation function. It is shown that the excess pair entropy derived from this function, plus the known perfect gas contributions, give a reasonable account of the total entropy of water, within the likely errors. This estimated entropy follows the expected declining trend with decreasing temperature. Evidence that higher density water will have higher entropy than lower density water emerges, in accordance with what is expected from the negative thermal expansion coefficient of water at low temperatures. However, this entropy increase is not large and goes through a maximum before declining at yet higher densities and pressures, in a manner reminiscent of what has been previously observed in the diffusion coefficient as a function of pressure. There is no evidence that ambient water can be regarded as patches of high density, high entropy and low density, low entropy liquid, as some have claimed, since high density water has a similar entropy to low density water. There is some evidence that the distinction between these two states will become more pronounced as the temperature is lowered. Extensive discussion of the use of order parameters to describe water structure is given, and it is pointed out that these indices generally cannot be used to infer two-state behavior.

Coarse-grained empirical potential structure refinement: Application to a reverse aqueous micelle

Conventional atomistic computer simulations, involving perhaps up to 10⁶atoms, can achieve length-scales on the order of a few 10s of nm. Yet many heterogeneous systems, such as colloids, nano-structured materials, or biological systems, can involve correlations over distances up 100s of nm, perhaps even 1μm in some instances. For such systems it is necessary to invoke coarse-graining, where single atoms are replaced by agglomerations of atoms, usually represented as spheres, in order for the simulation to be performed within a practical computer memory and time scale. Small angle scattering and reflectivity measurements, both X-ray and neutron, are routinely used to investigate structure in these systems, and traditionally the data have been interpreted in terms of discrete objects, such as spheres, sheets, and cylinders, and combinations thereof. Here we combine the coarse-grained computer simulation approach with neutron small angle scattering to refine the structure of a heterogeneous system, in the present case a reverse aqueous micelle of sodium-dioctyl sulfosuccinate (AOT) and iso-octane. The method closely follows empirical potential structure refinement and involves deriving an empirical interaction potential from the scattering data. As in traditional coarse-grained methods, individual atoms are replaced by spherical density profiles, which, unlike real atoms, can inter-penetrate to a significant extent. The method works over an arbitrary range of length-scales, but is limited to around 2 orders of magnitude in distance above a specified dimension. The smallest value for this dimension is of order 1nm, but the largest dimension is arbitrary. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editor: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

Neutron diffraction study of aqueous Laponite suspensions at the NIMROD diffractometer

The process of dynamical arrest, leading to formation of different arrested states such as glasses and gels, along with the closely related process of aging, is central for both basic research and technology. Here we report on a study of the time-dependent structural evolution of two aqueous Laponite clay suspensions at different weight concentrations. Neutron diffraction experiments have been performed with the near and intermediate range order diffractometer (NIMROD) that allows studies of the structure of liquids and disordered materials over a continuous length scale ranging from 1 to 300 Å, i.e., from the atomistic to the mesoscopic scales. NIMROD is presently a unique diffractometer, bridging the length scales traditionally investigated by small angle neutron scattering or small angle x-ray scattering with that accessible by traditional diffractometers for liquids. Interestingly, we have unveiled a signature of aging of both suspensions in the length scale region of NIMROD. This phenomenon, ascribed to sporadic contacts between Laponite platelets at long times, has been observed with the sample arrested as gel or as repulsive glass. Moreover, water molecules within the layers closest to Laponite platelets surface show orientational and translational order, which maps into the crystalline structure of Laponite.

Empirical potential structure refinement of semi-crystalline polymer systems: polytetrafluoroethylene and polychlorotrifluoroethylene

Empirical potential structure refinement (EPSR) simulations are performed on total neutron scattering data from powder samples of polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE), both at 300 K. Starting from single strands of polymer consisting of between 30 and 60 monomers of tetrafluoroethylene and chlorotrifluoroethylene in each case, hexagonal simulation cells are constructed consisting of an array 25 (5×5) such strands placed on a hexagonal lattice. Allowed simulation moves are polymer translation moves along all three Cartesian axes, whole polymer rotations about the polymer axis, and individual atom moves within each polymer. For PTFE a number of Bragg peaks are visible in the scattering data and these are found to be consistent with a lattice spacing a(=b) = 5.69(1) Å with a dihedral angle along the (helical) chain of 166° which gives a repeat distance along the chain (c-axis) of ~19.6 Å. The positions of the Bragg peaks are well reproduced by this model, although there is a mismatch in the amplitudes of some of the higher order reflections between simulation and data. For PCTFE there is only one visible Bragg peak (100) which is well reproduced by a hexagonal lattice of atactic parallel polymers with a spacing of a(=b) = 6.37(1) Å. In this case the absence of distinct reflections along the polymer c-axis makes characterization of the internal dihedral angle difficult, but a model with a dihedral angle of 166° was less successful at fitting the diffuse scattering than a model where this angle was set to 180°, giving a nearly straight trans (zig-zag) structure. For PCTFE little change in structure could be discerned when the material was heated to 550 K, apart from a slight increase in lattice spacing. In both cases there is substantial diffuse scattering between the Bragg peaks, and this is correctly replicated by the EPSR simulations.

Water and trehalose: how much do they interact with each other?

The observation made by early naturalists that some organisms could tolerate extreme environmental condisions and "enjoy the advantage of real resurrection after death" [ Spallanzani , M. Opuscules de Physique Animale et Vegetale 1776 (translated from Italian by Senebier , J. Opuscules de Physique Animale et Vegetale 1787 , 2 , 203 - 285 )] stimulated research that still continues to this day. Cryptobiosis, the ability of an organism to tolerate adverse environments, such as dehydration and low temperatures, still represents an unsolved and fascinating problem. It has been shown that many sugars play an important role as bioprotectant agents, and among the best performers is the disaccharide trehalose. The current hypothesis links the efficiency of its protective role to strong modifications of the tetrahedral arrangement of water molecules in the sugar hydration shell, with trehalose forming many hydrogen bonds with the solvent. Here, we show, by means of state-of-the-art neutron diffraction experiments combined with EPSR simulations, that trehalose solvation induces very minor modifications of the water structure. Moreover, the number of water molecules hydrogen-bonded to the sugar is surprisingly small.

NIMROD: The Near and InterMediate Range Order Diffractometer of the ISIS second target station

NIMROD is the Near and InterMediate Range Order Diffractometer of the ISIS second target station. Its design is optimized for structural studies of disordered materials and liquids on a continuous length scale that extends from the atomic, upward of 30 nm, while maintaining subatomic distance resolution. This capability is achieved by matching a low and wider angle array of high efficiency neutron scintillation detectors to the broad band-pass radiation delivered by a hybrid liquid water and liquid hydrogen neutron moderator assembly. The capabilities of the instrument bridge the gap between conventional small angle neutron scattering and wide angle diffraction through the use of a common calibration procedure for the entire length scale. This allows the instrument to obtain information on nanoscale systems and processes that are quantitatively linked to the local atomic and molecular order of the materials under investigation.

New sources and instrumentation for neutrons in biology

Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed.

Quantum Differences between Heavy and Light Water

The structures of heavy and light water at ambient conditions are investigated with the combined techniques of x-ray diffraction, neutron diffraction, and computer simulation. It is found that heavy water is a more structured liquid than light water. We find the OH bond length in H2O is approximately 3% longer than the OD bond length in D2O. This is a much larger change than current predictions. Corresponding to this, the hydrogen bond in light water is approximately 4% shorter than in heavy water, while the intermolecular HH distance is approximately 2% longer.

Percolation and three-dimensional structure of supercritical water

It is well established that at ambient and supercooled conditions water can be described as a percolating network of H bonds. This work is aimed at identifying, by neutron diffraction experiments combined with computer simulations, a percolation line in supercritical water, where the extension of the H-bond network is in question. It is found that in real supercritical water liquidlike states are observed at or above the percolation threshold, while below this threshold gaslike water forms small, sheetlike configurations. Inspection of the three-dimensional arrangement of water molecules suggests that crossing of this percolation line is accompanied by a change of symmetry in the first neighboring shell of molecules from trigonal below the line to tetrahedral above.

Hydration of sodium, potassium, and chloride ions in solution and the concept of structure maker/breaker

Neutron diffraction data with hydrogen isotope substitution on aqueous solutions of NaCl and KCl at concentrations ranging from high dilution to near-saturation are analyzed using the Empirical Potential Structure Refinement technique. Information on both the ion hydration shells and the microscopic structure of the solvent is extracted. Apart from obvious effects due to the different radii of the three ions investigated, it is found that water molecules in the hydration shell of K+ are orientationally more disordered than those hydrating a Na+ ion and are inclined to orient their dipole moments tangentially to the hydration sphere. Cl- ions form instead hydrogen-bonded bridges with water molecules and are readily accommodated into the H-bond network of water. The results are used to show that concepts such as structure maker/breaker, largely based on thermodynamic data, are not helpful in understanding how these ions interact with water at the molecular level.

On the uniqueness of structure extracted from diffraction experiments on liquids and glasses

There is continued interest in the problem of extracting structures from x-ray and neutron diffraction data on liquids and glasses. Traditional Fourier transform techniques, with their inherent weakness of possible systematic and truncation artefacts being introduced into the estimated distribution functions, are increasingly being complemented by computer simulation methods. These allow three-dimensional models of the scattering system to be built, at the correct atomic number density, which are consistent with both the diffraction data themselves and with other known or estimated constraints such minimum particle separations. Here the empirical potential structure refinement (EPSR) method is used to explore structure in supercooled liquid Ni, amorphous Ge and amorphous GeSe₂, and to evaluate alternative versions of the radial distribution functions which are consistent with the diffraction data. In the case of liquid Ni, it is found that there is, based on the diffraction data, some uncertainty on the hardness and shape of the repulsive core of the interatomic pair potential, and this may influence the current debate about the existence of icosahedral order in this liquid. For amorphous Ge two distinct radial distribution functions are generated, both consistent with the diffraction data, one of which has strong tetrahedral local order with the other having a predominantly triangular local coordination. For amorphous GeSe₂ it is found the SeSe and GeSe radial distribution functions can be determined well from the data, but the GeGe distribution is more uncertain, with the best fits implying both GeGe and SeSe homopolar bonds as originally proposed. The results are used to discuss the ambiguities inherent in the structural interpretation of diffraction data, even for one- and two-component systems.

Joint structure refinement of x-ray and neutron diffraction data on disordered materials: application to liquid water

X-ray diffraction data on liquids and disordered solids often provide useful complementary structural information to neutron diffraction data. Interpretation of the x-ray diffraction pattern, which is produced by scattering from the atomic electrons rather than from the atomic nuclei as in the case of neutron diffraction, is, however, complicated by the Q-dependent electronic form factors, which cause the x-ray diffraction signal to decline rapidly with increasing Q, where Q is the wave vector change in the diffraction experiment. The problem is particularly important in cases such as water where there is a significant molecular polarization caused by charge transfer within the molecule. This means that the electron form factors applicable to the molecule in the condensed environment often deviate from their free atom values. The technique of empirical potential structure refinement (EPSR) is used here to focus on the problem of forming a single atomistic structural model which is simultaneously consistent with both x-ray and neutron diffraction data. The case of liquid water is treated explicitly. It is found that x-ray data for water do indeed provide a powerful constraint on possible structural models, but that the Q-range of the different x-ray data sets (maximum Q ranges from 10.8 to ∼17.0 Å(-1) for different x-ray experiments), combined with variations between different data sets, means that it is not possible to rigorously define the precise position and height of the first peak in the OO radial distribution function. Equally, it is found that two different neutron datasets on water, although measured to a maximum Q of at least 30 Å(-1), give rise to further small uncertainties in the position of the hydrogen bond peaks. One general conclusion from the combined use of neutron and x-ray data is that many of the classical water potentials may have a core which is too repulsive at short distances. This produces too sharp a peak in r-space at too short a distance. A softer core potential is proposed here.

Structure of Aqueous Proline via Parallel Tempering Molecular Dynamics and Neutron Diffraction

The structure of aqueous L-proline amino acid has been the subject of much debate centering on the validity of various proposed models, differing widely in the extent to which local and long-range correlations are present. Here, aqueous proline is investigated by atomistic, replica exchange molecular dynamics simulations, and the results are compared to neutron diffraction and small angle neutron scattering (SANS) data, which have been reported recently (McLain, S.; Soper, A.; Terry, A.; Watts, A. J. Phys. Chem. B 2007, 111, 4568). Comparisons between neutron experiments and simulation are made via the static structure factor S(Q) which is measured and computed from several systems with different H/D isotopic compositions at a concentration of 1:20 molar ratio. Several different empirical water models (TIP3P, TIP4P, and SPC/E) in conjunction with the CHARMM22 force field are investigated. Agreement between experiment and simulation is reasonably good across the entire Q range although there are significant model-dependent variations in some cases. In general, agreement is improved slightly upon application of approximate quantum corrections obtained from gas-phase path integral simulations. Dimers and short oligomeric chains formed by hydrogen bonds (frequently bifurcated) coexist with apolar (hydrophobic) contacts. These emerge as the dominant local motifs in the mixture. Evidence for long-range association is more equivocal: No long-range structures form spontaneously in the MD simulations, and no obvious low-Q signature is seen in the SANS data. Moreover, associations introduced artificially to replicate a long-standing proposed mesoscale structure for proline correlations as an initial condition are annealed out by parallel tempering MD simulations. However, some small residual aggregates do remain, implying a greater degree of long-range order than is apparent in the SANS data.

Perturbation of water structure due to monovalent ions in solution

The ion induced modification to the tetrahedral structure of water is a topic of much current interest. We address this question by interpreting neutron diffraction data from monovalent ionic solutions of NaCl and KCl using a computer assisted structural modeling technique. We investigate the effect that these ions have on the water-water O-O, O-H and H-H radial distribution functions as a function of ionic concentration. It is found that the O-H and H-H functions are only marginally affected by ionic composition, signaling that hydrogen bonding between water molecules remains largely intact, even at the highest concentrations. On the other hand the O-O functions are strongly modified by the ions. In particular the position of the second peak in g(OO)(r), is found to move inwards with increasing salt concentration, in a manner closely analogous to what happens in pure water under pressure. Furthermore by recalculating g(OO)(r) after excluding all the water molecules in the first hydration shell of each ion, we show that this structural perturbation exists outside the first hydration shell of the ions.

The local and intermediate range structures of the five amorphous ices at 80K and ambient pressure: A Faber-Ziman and Bhatia-Thornton analysis

Using isotope substitution neutron scattering data, we present a detailed structural analysis of the short and intermediate range structures of the five known forms of amorphous ice. Two of the lower density forms--amorphous solid water and hyperquenched glassy water--have a structure very similar to each other and to low density amorphous ice, a structure which closely resembles a disordered, tetrahedrally coordinated, fully hydrogen bonded network. High density and very high density amorphous ices retain this tetrahedral organization at short range, but show significant differences beyond about 3.1 A from a typical water oxygen. The first diffraction peak in all structures is seen to be solely a function of the intermolecular organization. The short range connectivity in the two higher density forms is more homogeneous, while the hydrogen site disorder in these forms is greater. The low Q behavior of the structure factors indicates no significant density or concentration fluctuations over the length scale probed. We conclude that these three latter forms of ice are structurally distinct. Finally, the x-ray structure factors for all five amorphous systems are calculated for comparison with other studies.

Ions in water: the microscopic structure of concentrated NaOH solutions

A neutron diffraction experiment with isotopic H/D substitution on four concentrated NaOH/H(2)O solutions is presented. The full set of partial structure factors is extracted, by combining the diffraction data with a Monte Carlo simulation. These allow to investigate both the changes of the water structure in the presence of ions and their solvation shells. It is found that the interaction with the solute affects the tetrahedral network of hydrogen bonded water molecules in a manner similar to the application of high pressure to pure water. The solvation shell of the OH(-) ions has an almost concentration independent structure, although with concentration dependent coordination numbers. The hydrogen site coordinates a water molecule through a weak bond, while the oxygen site forms strong hydrogen bonds with a number of molecules that is on the average very close to four at the higher water concentrations and decreases to about three at the lowest one. The competition between hydrogen bond interaction and Coulomb forces in determining the orientation of water molecules within the cation solvation shell is visible in the behavior of the g(NaHw)(r) function

Eigen versus Zundel complexes in HCl-water mixtures

There is an ongoing debate on the nature of hydration of the hydrogen ion, H+ in solution, and the extent to which Eigen or Zundel complexes occur. Here, our previous neutron diffraction data on a solution of 1:9 HCl in water are reanalyzed using a new starting hypothesis for the Monte Carlo simulation of the data. Either bare H+ ions, all H3O+ ions, or all H5O2 + ions are allowed in the simulation box together with the water and chlorine ions. All three simulations give a satisfactory fit to the experimental data. From the simulation with simple H+ ions, it is found that all H+ ions form one strong and very short hydrogen bond with water molecules and that on average 75% of them also engage in a second, slightly longer hydrogen bond. This result can be interpreted alternatively either in terms of the formation of a high percentage of asymmetric Zundel complexes or in terms of the formation of distorted H3O+ ions, which in turn form two or three hydrogen bonds, respectively, with neighboring molecules opposite their unbonded hydrogen sites (thus forming Eigen complexes). Therefore the new analysis is not inconsistent with our previous conclusion that the solution consists primarily of Eigen complexes, but does highlight the difficulty of making a clear distinction between Eigen and Zundel complexes due to the continuous random network of hydrogen bonds formed between water and hydrated protons. The role of hydrogen ion to chloride counterion contacts is also discussed in these solutions.

The hydration of the neurotransmitter acetylcholine in aqueous solution

Neutron diffraction augmented with hydrogen isotope substitution has been used to examine the water structure around the acetylcholine molecular ion in aqueous solution. It is shown that the nearest-neighbor water molecules in the region around the trimethylammonium headgroup are located either in a ring around the central nitrogen atom or between the carbon atoms, forming a sheath around the onium group. Moreover the water molecules in this cavity do not bond to the onium group but rather form hydrogen bonds with water molecules in the surrounding aqueous environment. Given that in the bound state the onium headgroup must be completely desolvated, the absence of bonding between the onium headgroup and the surrounding water solvent may be selectively favorable to acetylcholine-binding in the receptor site. Away from the headgroup, pronounced hydrogen-bonding of water to the carbonyl oxygen is observed, but not to the ether oxygen in the acetylcholine chain.

Ions in water: The microscopic structure of concentrated hydroxide solutions

Neutron-diffraction data on aqueous solutions of hydroxides, at solute concentrations ranging from 1 solute per 12 water molecules to 1 solute per 3 water molecules, are analyzed by means of a Monte Carlo simulation (empirical potential structure refinement), in order to determine the hydration shell of the OH- in the presence of the smaller alkali metal ions. It is demonstrated that the symmetry argument between H+ and OH- cannot be used, at least in the liquid phase at such high concentrations, for determining the hydroxide hydration shell. Water molecules in the hydration shell of K+ orient their dipole moment at about 45 degrees from the K+-water oxygen director, instead of radially as in the case of the Li+ and Na+ hydration shells. The K+-water oxygen radial distribution function shows a shallower first minimum compared to the other cation-water oxygen functions. The influence of the solutes on the water-water radial distribution functions is shown to have an effect on the water structure equivalent to an increase in the pressure of the water, depending on both ion concentration and ionic radius. The changes of the water structure in the presence of charged solutes and the differences among the hydration shells of the different cations are used to present a qualitative explanation of the observed cation mobility.

Segregation in aqueous methanol enhanced by cooling and compression

Molecular segregation in methanol-water mixtures is studied across a wide concentration range as a function of temperature and pressure. Cluster distributions obtained from both neutron diffraction and molecular dynamics simulations point to significantly enhanced segregation as the mixtures are cooled or compressed. This evolution toward greater molecular heterogenity in the mixture accounts for the observed changes in the water-water radial distribution function and there are indications also of a change in the topology of the water clusters. The observed behavior is consistent with an approach to an upper critical solution point. Such a point would appear to be "hidden" below the freezing line, thereby precluding observation of the two-fluid region.

Methanol-water solutions: A bi-percolating liquid mixture

An extensive series of neutron diffraction experiments and molecular dynamics simulations has shown that mixtures of methanol and water exhibit extended structures in solution despite the components being fully miscible in all proportions. Of particular interest is a concentration region (methanol mole fraction between 0.27 and 0.54) where both methanol and water appear to form separate, percolating networks. This is the concentration range where many transport properties and thermodynamic excess functions reach extremal values. The observed concentration dependence of several of these material properties of the solution may therefore have a structural origin.

Ions in water: The microscopic structure of a concentrated HCl solution

A neutron diffraction experiment with isotopic H/D substitution on a concentrated HCl/H2O solution is presented. The full set of partial structure factors is extracted, by combining the diffraction data with a Monte Carlo simulation. This allows us to investigate both the changes of the water structure in the presence of ions and their solvation shell, overcoming the limitations of standard diffraction experiments. It is found that the interaction with the solutes affects the tetrahedral network of hydrogen bonded water molecules, in a manner similar to the application of an external pressure to pure water, although HCl seems less effective than other solutes, such as NaOH, at the same concentration. Consistent with experimental and theoretical data, the number of water molecules in the solution is not sufficient to completely dissociate the acid molecule. As a consequence, both dissociated H+ and Cl- ions and undissociated HCl molecules coexist in the sample, and this mixture is correctly reproduced in the simulation box. In particular, the hydrated H+ ions, forming a H3O+ complex, participate in three strong and short hydrogen bonds, while a well-defined hydration shell is found around the chlorine ion. These results are not consistent with the findings of early diffraction experiments on the same system and could only be obtained by combining high quality experimental data with a proper computer simulation.

Impact of urea on water structure: a clue to its properties as a denaturant?

A new investigation of the structure of urea-water solutions at a mole ratio of 1 urea to 4 water molecules is described. Neutron diffraction is used in conjunction with isotope labelling on the water and urea hydrogen atoms and on the nitrogen atom of urea. The diffraction data are analysed using the empirical potential structure refinement procedure to yield a set of site-site radial distribution functions and spatial density functions that are consistent with the diffraction data. The results are discussed in relation to recent and past X-ray and neutron diffraction experiments and theoretical studies of this system. It is found that urea incorporates readily into water, forming pronounced hydrogen bonds with water at both the amine and carbonyl headgroups. In addition the urea also hydrogen bonds to itself, forming chains or clusters consisting of up to approximately 60 urea molecules in a cluster. There, is however, little or no evidence of urea segregating itself from water, in marked contrast to a recent study of the methanol-water system. This behaviour is discussed in the context of the great propensity of urea to effect protein denaturation.

Structure of high-density amorphous ice under pressure

We report in situ neutron diffraction studies of high-density amorphous ice (HDA) at 100 K at pressures up to 2.2 GPa. We find that the compression is achieved by a strong contraction ( approximately 20%) of the second neighbor coordination shell, so that at 2.2 GPa it closely approaches the first coordination shell, which itself remains intact in both structure and size. The hydrogen bond orientations suggest an absence of hydrogen bonding between first and second shells and that HDA has increasingly interpenetrating hydrogen bond networks under pressure.

Structure of a new dense amorphous ice

The detailed structure of a new dense amorphous ice, VHDA, is determined by isotope substitution neutron diffraction. Its structure is characterized by a doubled occupancy of the stabilizing interstitial location that was found in high density amorphous ice, HDA. As would be expected for a thermally activated unlocking of the stabilizing "interstitial," the transition from VHDA to LDA (low-density amorphous ice) is very sharp. Although its higher density makes VHDA a better candidate than HDA for a physical manifestation of the second putative liquid phase of water, as for the HDA case, the VHDA to LDA transition also appears to be kinetically controlled.

Structures of high and low density amorphous ice by neutron diffraction

Neutron diffraction with isotope substitution is used to determine the structures of high (HDA) and low (LDA) density amorphous ice. Both "phases" are fully hydrogen bonded, tetrahedral networks, with local order similarities between LDA and ice Ih, and HDA and liquid water. Moving from HDA, through liquid water and LDA to ice Ih, the second shell radial order increases at the expense of spatial order. This is linked to a fifth first neighbor "interstitial" that restricts the orientations of first shell waters. This "lynch pin" molecule which keeps the HDA structure intact has implications for the nature of the HDA-LDA transition that bear on the current metastable water debate.

Molecular segregation observed in a concentrated alcohol-water solution

When a simple alcohol such as methanol or ethanol is mixed with water, the entropy of the system increases far less than expected for an ideal solution of randomly mixed molecules. This well-known effect has been attributed to hydrophobic headgroups creating ice-like or clathrate-like structures in the surrounding water, although experimental support for this hypothesis is scarce. In fact, an increasing amount of experimental and theoretical work suggests that the hydrophobic headgroups of alcohol molecules in aqueous solution cluster together. However, a consistent description of the details of this self-association is lacking. Here we use neutron diffraction with isotope substitution to probe the molecular-scale structure of a concentrated alcohol water mixture (7:3 molar ratio). Our data indicate that most of the water molecules exist as small hydrogen-bonded strings and clusters in a 'fluid' of close-packed methyl groups, with water clusters bridging neighbouring methanol hydroxyl groups through hydrogen bonding. This behaviour suggests that the anomalous thermodynamics of water alcohol systems arises from incomplete mixing at the molecular level and from retention of remnants of the three-dimensional hydrogen-bonded network structure of bulk water.

Liquid alumina: detailed atomic coordination determined from neutron diffraction data using empirical potential structure refinement

The neutron scattering structure factor S(N)(Q) for a 40 mg drop of molten alumina (Al2O3) held at 2500 K, using a laser-heated aerodynamic levitation furnace, is measured for the first time. A 1700 atom model of liquid alumina is generated from these data using the technique of empirical potential structural refinement. About 62% of the aluminum sites are 4-fold coordinated, matching the mostly triply coordinated oxygen sites, but some 24% of the aluminum sites are 5-fold coordinated. The octahedral aluminum sites found in crystalline alpha-Al2O3 occur only at the 2% level in liquid alumina.

Structures of high-density and low-density water

The three site-site partial structure factors for water have been measured as a function of pressure, using neutron diffraction, at a temperature of 268 K. It is found that the measured structure functions imply a continuous transformation with increasing pressure from a low-density form of water ( rho(L) approximately 0.0295 molecules/A(3)), with an open, hydrogen-bonded tetrahedral structure, to a high-density form of water ( rho(H) approximately 0.0402 molecules/A(3)), with nontetrahedral O-O-O angles and a collapsed second coordination shell, which implies broken hydrogen bonds between the first and second coordination shells.

Surface geochemistry of the clay minerals

Clay minerals are layer type aluminosilicates that figure in terrestrial biogeochemical cycles, in the buffering capacity of the oceans, and in the containment of toxic waste materials. They are also used as lubricants in petroleum extraction and as industrial catalysts for the synthesis of many organic compounds. These applications derive fundamentally from the colloidal size and permanent structural charge of clay mineral particles, which endow them with significant surface reactivity. Unraveling the surface geochemistry of hydrated clay minerals is an abiding, if difficult, topic in earth sciences research. Recent experimental and computational studies that take advantage of new methodologies and basic insights derived from the study of concentrated ionic solutions have begun to clarify the structure of electrical double layers formed on hydrated clay mineral surfaces, particularly those in the interlayer region of swelling 2:1 layer type clay minerals. One emerging trend is that the coordination of interlayer cations with water molecules and clay mineral surface oxygens is governed largely by cation size and charge, similarly to a concentrated ionic solution, but the location of structural charge within a clay layer and the existence of hydrophobic patches on its surface provide important modulations. The larger the interlayer cation, the greater the influence of clay mineral structure and hydrophobicity on the configurations of adsorbed water molecules. This picture extends readily to hydrophobic molecules adsorbed within an interlayer region, with important implications for clay-hydrocarbon interactions and the design of catalysts for organic synthesis.

Evidence for microscopic, long-range hydration forces for a hydrophobic amino acid

We have combined neutron solution scattering experiments with molecular dynamics simulation to isolate an excess experimental signal that is caused solely by N-acetyl-leucine-amide (NALA) correlations in aqueous solution. This excess signal contains information about how NALA molecule centers are correlated in water, and we show how these solute-solute correlations might be determined at dilute concentrations in the small angle region. We have tested qualitatively different pair distribution functions for NALA molecule centers-gas, cluster, and aqueous forms of gc(r)-and have found that the excess experimental signal is adequate enough to rule out gas and cluster pair distribution functions. The aqueous form of gc(r) that exhibits a solvent-separated minimum, and possibly longer-ranged correlations as well, is not only physically sound but reproduces the experimental data reasonably well. This work demonstrates that important information in the small angle region can be mined to resolve solute-solute correlations, their lengthscales, and thermodynamic consequences even at dilute concentrations. The hydration forces that operate on the microscopic scale of individual amino acid side chains, implied by the small angle scattering data, could have significant effects on the early stages of protein folding, on ligand binding, and on other intermolecular interactions.

Direct evidence for modified solvent structure within the hydration shell of a hydrophobic amino acid

Neutron scattering experiments are used to determine scattering profiles for aqueous solutions of hydrophobic and hydrophilic amino acid analogs. Solutions of hydrophobic solutes show a shift in the main diffraction peak to smaller angle as compared with pure water, whereas solutions of hydrophilic solutes do not. The same difference for solutions of hydrophobic and hydrophilic side chains is also predicted by molecular dynamics simulations. The neutron scattering curves of aqueous solutions of hydrophobic amino acids at room temperature are qualitatively similar to differences between the liquid molecular structure functions measured for ambient and supercooled water. The nonpolar solute-induced expansion of water structure reported here is also complementary to recent neutron experiments where compression of aqueous solvent structure has been observed at high salt concentration.