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The effect of an inert phase on neck growth rates during sintering of lamellar structures is described. Sintering diagrams are constructed for an aggregate of two-phase Cu spheres with lamellar microstructure containing an inert phase. It is shown that the regions corresponding to lattice diffusion domination shrink due to the inert phase presence. As the dispersion becomes finer, the alterations in the map become substantial.
The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range (0.505 to 0.575) and compared to classical nucleation rate calculations. The experimental nucleation rate density varies with volume fraction more slowly than expected theoretically. Gravity may influence nucleation because crystal nuclei are more dense than the surrounding fluid and may be gravitationally convected. The largest observed crystal size was near volume fraction 0.52. Near the freezing point, crystals should grow to large size because nuclei are sparse and there is plenty of room to grow without contacting other crystals. Near melting the opposite is true, with crystals growing into one another shortly after nucleation. The maximum crystal size seen near 0.52 volume fraction suggests that gravitational stresses are limiting crystal growth near freezing.
Atomic Force Microscopy (AFM) has emerged as a powerful technique for investigating protein crystal growth. Earlier AFM studies were among the first to demonstrate that these crystals grew by dislocation and 2D nucleation growth mechanisms [1]. These investigations were restricted to the micron range where only surface features, such as dislocation hillocks and 2D islands are visible. Most AFM instruments can scan at higher resolutions and have the potential to resolve individual protein molecules at nanometer ranges. Such scans are essential for determining the molecular packing arrangements on crystal faces and for probing the growth process at the molecular level. However, at this resolution the AFM tip influences the image produced, with the resulting image being a convolution of the tip shape and the surface morphology [2]. In most studies this problem is resolved by deconvoluting the image to obtain the true surface morphology. Although deconvolution routines work reasonably well for simple one- dimensional shapes, for complex surfaces this approach does not produce accurate results. In this study we devised a new approach which takes advantage of the precise molecular order of crystal surfaces, combined with the knowledge of individual molecular shapes from the crystallographic data of the protein and the AFM tip shape. This information is used to construct expected theoretical AFM images by convoluting the tip shape with the constructed crystal surface shape for a given surface packing arrangement. By comparing the images from actual AFM scans with the constructed ones for different possible surface packing arrangements, the correct packing arrangement can be conclusively determined. This approach was used in this study to determine the correct one from two possible packing arrangements on (I 10) faces of tetragonal lysozyme crystals. Another novel AFM technique was also devised to measure the dimension of individual growth units of the crystal faces. Measuring these units was not attempted before and most studies have assumed that the growth unit consisted of individual protein molecules. The linescan mode of AFM instruments allows the crystal surface to be scanned along a single line. By scanning across a growth step an image showing the motion of the step is obtained. Normally such an image shows a straight line for continuous and constant step velocity. In this study by increasing the scan rate and by decreasing the step velocity (by decreasing the supersaturation), we were able to capture images of individual growth events, shown by jump discontinuities in the step line. By suitable integration of the image the growth unit dimension in the scanned direction can be obtained. Since multiple units can be involved in the growth process it is necessary to collect a statistically relevant sample before drawing conclusions about the growth mechanism. This technique was successfully employed to obtain the dimensions of growth units for the (110) face, showing that they consisted of various aggregates corresponding to the 43 helices in the crystal structure.
Distributed embedded energy conversion technology (DEEC-Tec) is a very promising - but underdeveloped - domain in marine renewable energy research. The technology utilizes small distributed embedded energy converters (DEECs) that, in aggregate, form a much larger energy harvesting-converting structure. Each DEEC is a small transducer - an individual mechanism that converts one form of energy into another. A transducer's specific mode of operation can be based upon any number of physical phenomena, including variable capacitance, variable magnetic fields, or piezoelectrics. It is the dynamic deformation of a structure made from such DEECs (a DEEC-Tec structure) that provides the needed physical phenomena (the external energy source) for the underlying transducers to intake and convert energy into another form, such as electricity. DEEC-Tec structures designed specifically to dynamically deform in the presence of ocean wave energy - for the purpose of harvesting and converting that energy - can be called flexWECs. A flexWEC's gross shape (topology) and its compliant characteristics (morphologies) are chiefly determined by how the DEECs making up its structure are arranged and implemented. In turn, those corresponding topologies and morphologies will largely determine how a flexWEC interacts with - and dynamically deforms within - the presence of ocean wave energy. FlexWECs appear to have many attractive features, including broad-banded ocean energy conversion, in situ energy conversion throughout an entire flexWEC structure, inherent redundancy, and appealing material and manufacturing costs. To this end, the design and development of any particular flexWEC or flexWEC feature is a revolutionary opportunity for how we conceptualize and envision the future of ocean wave energy conversion.
Distributed embedded energy conversion technology (DEEC-Tec) is a very promising - but underdeveloped - domain in marine renewable energy research. The technology utilizes small distributed embedded energy converters (DEECs) that, in aggregate, form a much larger energy harvesting-converting structure. Each DEEC is a small transducer - an individual mechanism that converts one form of energy into another. A transducer's specific mode of operation can be based upon any number of physical phenomena, including variable capacitance, variable magnetic fields, or piezoelectrics. It is the dynamic deformation of a structure made from such DEECs (a DEEC-Tec structure) that provides the needed physical phenomena (the external energy source) for the underlying transducers to intake and convert energy into another form, such as electricity. DEEC-Tec structures designed specifically to dynamically deform in the presence of ocean wave energy - for the purpose of harvesting and converting that energy - can be called flexWECs. A flexWEC's gross shape (topology) and its compliant characteristics (morphologies) are chiefly determined by how the DEECs making up its structure are arranged and implemented. In turn, those corresponding topologies and morphologies will largely determine how a flexWEC interacts with - and dynamically deforms within - the presence of ocean wave energy. FlexWECs appear to have many attractive features, including broad-banded ocean energy conversion, in situ energy conversion throughout an entire flexWEC structure, inherent redundancy, and appealing material and manufacturing costs. To this end, the design and development of any particular flexWEC or flexWEC feature is a revolutionary opportunity for how we conceptualize and envision the future of ocean wave energy conversion.
Abstract Molecular excitons play a central role in natural and artificial light harvesting, organic electronics, and nanoscale computing. The structure and dynamics of molecular excitons, critical to each application, are sensitively governed by molecular packing. Deoxyribonucleic acid (DNA) templating is a powerful approach that enables controlled aggregation via sub-nanometer positioning of molecular dyes. However, finer sub-Angstrom control of dye packing is needed to tailor excitonic properties for specific applications. Here, we show that adding rotaxane rings to squaraine dyes templated with DNA promotes an elusive oblique packing arrangement with highly desirable optical properties. Specifically, dimers of these squaraine:rotaxanes exhibit an absorption spectrum with near-equal intensity excitonically split absorption bands. Theoretical analysis indicates that the transitions are mostly electronic in nature and only have similar intensities over a narrow range of packing angles. Compared with squaraine dimers, squaraine:rotaxane dimers also exhibit extended excited-state lifetimes and less structural heterogeneity. The approach proposed here may be generally useful for optimizing excitonic materials for a variety of applications ranging from solar energy conversion to quantum information science.
The Basin-Scale Structural Features database provides spatial datasets of faults, fractures, folds, and earthquakes compiled from public, authoritative sources (e.g., U.S. Geological Survey and State Geological Surveys) and aggregated into derivative forms to support subsurface assessments. Recognizing that characterizing basin-scale structural features requires interpreting data that are often ambiguous or lack key information, the source data were evaluated using a knowledge-data framework and geospatial fuzzy logic method (Justman et al., 2020) to represent both measured (observed) and predicted (inferred or potential) structural features as derivative datasets. This workflow employs conceptual models for known structural features and predicted structural features, incorporating geospatial data to estimate potential, even with limited data. The aim is to aid and support an understanding of basin-scale features and identify potential gaps in data and knowledge. As of 4/30/2025, the database includes resources for nine sedimentary basins: Appalachian, Denver, U.S. Gulf Coast, Illinois, Michigan, Permian, Sacramento, San Joquin and Williston. The database is organized by basin and then data category: 1) Faults, fractures, folds, 2) Earthquakes, 3) Topographic, 4) Structural contours and isopachs, 5) Geophysical, and 6) Structural feature density assessment maps.
Nanomaterial additives have been broadly used in cement and concrete-based sensors to measure the stress and strain in the structure. Most of the studies focused on measuring the resistivity of sensors with Direct Current (DC) or relatively low-frequency. Here in this work, the impedance responses of enhanced Carbon Nano-Fiber Aggregates (CNFAs) at different frequencies are rigorously studied and utilized as a tool for real-time structural health monitoring (SHM). The CNFA impedance measurements at different measurement frequencies provide an extra dimension (frequency dimension) to allow the characterization of different phenomena and multimodal measurements simultaneously. First, a comprehensive physical model is established to understand the frequency responses of the CNFA impedance. Second, COMSOL Multiphysics is used to simulate the frequency responses of the CNFA impedance, which provides more insights into the electric field and current density distribution. The impedance of CNFAs decreased with the increased dosage of carbon nanofibers (CNFs). Third, experimental studies are reported in detail. The electrical impedance variation (EZV) of the CNFA in parallel orientation is 151% higher than that of perpendicular orientation at the frequency of 2612 Hz and uniaxial compression stress of 4.65 MPa. The strain-EZV curve obtained from the response spectrum is linear for frequencies ranging from 98 Hz to 463.9 kHz. The strain-EZV curve for 5625 Hz has a linear fit with the gauge factor of 147.78. At 1000 Hz, the CNFA exhibited a repeatable behavior up to 9.35 MPa and detection limit up to the stress of 18.62 MPa.
Alzheimer’s disease (AD) is a neurodegenerative disorder defined by the progressive formation and spread of fibrillar aggregates of Aβ peptide and tau protein. Polymorphic forms of these aggregates may contribute to disease in varying ways since different neuropathologies appear to be associated with different sets of fibrillar structures and follow distinct pathological trajectories that elicit characteristic clinical phenotypes. The molecular mechanisms underlying the spread of these aggregates in disease may include nucleation, replication, and migration all of which could vary with polymorphic form, stage of disease, and region of brain. Given the linkage between mechanisms of progression and distribution of polymorphs, mapping the distribution of fibrillar structures in situ has the potential to discriminate between mechanisms of progression. However, the means of carrying out this mapping are limited. Optical microscopy lacks the resolution to discriminate between polymorphs in situ, and higher resolution tools such as ssNMR and cryoEM require the isolation of fibrils from tissue, destroying relevant spatial information. Here, we demonstrate the use of scanning x-ray microdiffraction (XMD) to map the locations of fibrillar polymorphs of Aβ peptides and tau protein in histological thin sections of human brain tissue. Coordinated examination of serial sections by immunohistochemistry was used to aid in the interpretation of scattering patterns and to put the observations in a broader anatomical context. Scattering from lesions in tissue shown to be rich in Aβ fibrils by immunohistochemistry exhibited scattering patterns with a prototypical 4.7 Å cross-β peak, and overall intensity distribution that compared well with that predicted from high resolution structures. Scattering from lesions in tissue with extensive tau pathology also exhibited a 4.7 Å cross-β peak but with intensity distributions that were distinct from those seen in Aβ-rich regions. In summary, these observations demonstrate that XMD is a rich source of information on the distribution of fibrillar polymorphs in diseased human brain tissue. When used in coordination with neuropathological examination it has the potential to provide novel insights into the molecular mechanisms underlying disease.
Normal mammalian tissue and the culturing process has been developed for the three groups of organ, structural, and blood tissue. The cells are grown in vitro under microgravity culture conditions and form three dimensional cells aggregates with normal cell function. The microgravity culture conditions may be microgravity or simulated microgravity created in a horizontal rotating wall culture vessel.
Electrolytes comprised of polymers mixed with salts have great potential for enabling the use of Li metal anodes in batteries for increased safety. Ionic conductivity is one of the key performance metrics of these polymer electrolytes and achieving high room-temperature conductivity remains a challenge to date. For a bottom-up design of the polymer electrolytes, we must first understand how the structure of polyelectrolytes on a molecular level determines their properties. Here, we use classical molecular dynamics to study the solvation structure and ion diffusion in electrolytes composed of a short-chain perfluoroether with LiFSI or LiTFSI salts. Density functional theory is also used to provide some insights into the structures and energies of the salt interactions with the perfluoroether. We observe the formation of aggregates of salts in the fluorinated systems even at low salt concentrations. The fluorine-fluorine attraction in the solvent is the governing factor for creating the salt aggregates. The aggregates’ size and lifetime change with concentration and anion. These simulations provide an insight into the structure and dynamics of perfluoroether based electrolytes that can be used to improve Li-ion batteries.
Production of second-generation bioethanol from lignocellulosic biomass requires pretreatment to open the plant cell wall structure and improve enzyme access. Many different thermochemical pretreatments have been extensively developed and employed, but the exact nature of plant cell wall recalcitrance and the most efficient and economical approach to alter plant cell wall structure via pretreatment still remain elusive. In order to understand the role of noncellulosic switchgrass polymers on the overall efficiency of pretreatment, the structural evolution of the noncellulosic polymers of the plant cell wall were investigated during dilute acid pretreatment (DAP) by employing in-situ small-angle neutron scattering (in-situ SANS). In this study, we observed real-time structural changes not possible to observe by any other technique. To deconvolute the structural evolution of lignin and hemicellulose polymers during DAP, native switchgrass (NATV), and isolated holocellulose (HOLO) and cellulose (CELL) fractions from NATV were studied. Our results show that aggregate particles first appear around 80 °C for NATV and HOLO samples. Further, due to the low temperature and pretreatment severity condition, these particles are likely derived from hemicellulose. The formations of much larger aggregate particles, only observed in the NATV sample, were attributed to lignin. For the HOLO sample, as the temperature and pretreatment severity condition increased, hemicellulose-derived aggregate particle sizes increased, suggesting this process was the nucleation and early stage formation of pseudolignin particles. Consistent with our interpretation of structural evolutions in NATV and HOLO samples, no formation of aggregate particles was observed in CELL samples for the entire duration of the pretreatment. These results suggest that not only lignin but also hemicellulose can form aggregate particles within plant cell walls during pretreatment.
We report that noncovalent intermolecular interactions in nanomaterials, such as van der Waals effects, allow adjustment of the nanoscopic size of compounds and their conformation in molecular crystal regimes. These strong interactions permit small particle sizes to be maintained as the crystals grow. In particular, these effects can be leveraged in the confined/reinforcing phase of molecules. With this in mind, we used C 60 molecules as a core particle in single-PC60 surfactant-covered colloid in a water-processable system. Compared with our previous results based on a PC 61 BM core-PC60 shell particle, the PC60-C 60 colloid had a considerably smaller spherical structure due to the increased intermolecular interactions between C 60 (fullerene) molecules. Interestingly, the conformation of C 60 aggregates was altered depending on the mixed solvents and their volume fraction in the organic phase, which strongly affected the structural properties of the PC60-C 60 colloids. The particle facilitated strong interactions with a p-type core sphere when it was introduced as the shell part of a p-n heterojunction particle. This direct interaction provided effective electronic communication between p- and n-type particles, resulting in ultraefficient photonic properties, particularly in charge separation in aqueous heterostructured colloids. Lastly, this enabled the development of an extremely efficient photovoltaic device with a 6.74% efficiency, which could provide the basis for creating high-performance water-processable solar cells based on p-n heterostructured NPs.
With the increasing strategies aimed at repressing shuttle problems in the lithium–sulfur battery, dissolved contents of polysulfides are significantly reduced. Except for solid-state Li 2 S 2 and Li 2 S, aggregated phases of polysulfides remain unexplored, especially in well confined cathode material systems. Here, we report a series of nanosize polysulfide clusters and solid phases from an atomic perspective. The calculated phase diagram and formation energy evolution process demonstrate their stabilities and cohesive tendency. It is interesting to find that Li 2 S 6 can stay in the solid state and contains short S 3 chains, further leading to the unique stability and dense structure. Simulated electronic properties indicate reduced band gaps when polysulfides are aggregated, especially for solid phase Li 2 S 6 with a band gap as low as 0.47 eV. In conclusion, their dissolution behavior and conversion process are also investigated, which provides a more realistic model and gives further suggestions on the future design of the lithium–sulfur battery.
The study of protein aggregation, and amyloidosis in particular, has gained considerable interest in recent times. Several neurodegenerative diseases, such as Alzheimer’s (AD) and Parkinson’s (PD) show a characteristic buildup of proteinaceous aggregates in several organs, especially the brain. Despite the enormous upsurge in research articles in this arena, it would not be incorrect to say that we still lack a crystal-clear idea surrounding these notorious aggregates. In this review, we attempt to present a holistic picture on protein aggregation and amyloids in particular. Using a chronological order of discoveries, we present the case of amyloids right from the onset of their discovery, various biophysical techniques, including analysis of the structure, the mechanisms and kinetics of the formation of amyloids. We have discussed important questions on whether aggregation and amyloidosis are restricted to a subset of specific proteins or more broadly influenced by the biophysiochemical and cellular environment. The therapeutic strategies and the significant failure rate of drugs in clinical trials pertaining to these neurodegenerative diseases have been also discussed at length. At a time when the COVID-19 pandemic has hit the globe hard, the review also discusses the plausibility of the far-reaching consequences posed by the virus, such as triggering early onset of amyloidosis. Finally, the application(s) of amyloids as useful biomaterials has also been discussed briefly in this review.
Drug nanoaggregates are particles that can deleteriously cause false positive results during drug screening efforts, but alternatively, they may be used to improve pharmacokinetics when developed for drug delivery purposes. The structural features of molecules that drive nanoaggregate formation remain elusive, however, and the prediction of intracellular aggregation and rational design of nanoaggregate-based carriers are still challenging. We investigate nanoaggregate self-assembly mechanisms using small molecule fragments to identify the critical molecular forces that contribute to self-assembly. We find that aromatic groups and hydrogen bond acceptors/donors are essential for nanoaggregate formation, suggesting that both π-π stacking and hydrogen bonding are drivers of nanoaggregation. We apply structure-assembly-relationship analysis to the drug sorafenib and discover that nanoaggregate formation can be predicted entirely using drug fragment substructures. We also find that drug nanoaggregates are stabilized in an amorphous core-shell structure. These findings demonstrate that rational design can address intracellular aggregation and pharmacologic/delivery challenges in conventional and fragment-based drug development processes.
Phosphorylation is a ubiquitous protein modification that is known to play important roles in many biological phenomena including cell signaling, the opening and closing of membrane protein channels, and even triggering of amyloid protein aggregation. Despite the effects phosphorylation has on protein function, the impact phosphorylation has on the structure of proteins is not well understood. Here, to determine how phosphorylation affects the structure of proteins, top-down mass spectrometry (TD-MS) and ion mobility-mass spectrometry (IM-MS) were performed on various phosphorylated proteins and their dephosphorylated proteoforms. TD-MS with collision- and electron-based fragmentation techniques was utilized to locate phosphorylation sites on the intrinsically disordered amyloid proteins β-casein and α-synuclein. TD-MS also provided evidence that alkaline phosphatase dephosphorylates β-casein from the N-terminus to the C-terminus. Furthermore, IM-MS of common phosphorylated proteins such as β-casein, α-casein, ovalbumin, and phosvitin indicates that phosphorylation promotes compaction of protein structure in denaturing as well as native conditions. Increases in abundance of more compact conformers are also observed when the disease related amyloid protein α-synuclein is phosphorylated at serine 129. We interpret the increased abundance of more compact conformers when proteins are phosphorylated as evidence that salt bridges form between negatively charged phosphates and positively charged residues, which alters protein structure. Salt bridge formation due to phosphorylation could be a mechanism for regulating protein function and be responsible for many of the phenomena observed in nature.
Given multiple distinct deprotonation sites and flexible structural conformation in citric acid (CA), the intrinsic interaction between protons, sodium cations and citrate anions deems complicated. In this work, we address this issue by combining photoelectron spectroscopy and theoretical modeling on a series of gaseous sodium citrate anion clusters with progressive substitution of protons with sodium cations [(CA-nH)·(n-1)Na]- (n = 1-3). Despite markedly different pKa values for the central (C, 3.28), terminal carboxylic (T, 5.98) and hydroxyl group (O, 18.44), our study reveals experimental observation of all three distinct deprotomers in [CA-1H]- with deprotonation from hydroxyl energetically competitive. Upon Na+ binding to the doubly or triply deprotonated CA, only one kind of deprotonation tautomer, respectively TC or TTC, is experimentally accessible. Moreover, a dianionic dimer [(CA-3H)·2Na]22- is observed. This work displays a diverse binding landscape among protons, sodium and citrate species in the gas phase, advancing our understanding of sodium citrate chemistry.