Matriglycan maintains t-tubule structural integrity in cardiac muscle.

Maintaining the structure of cardiac membranes and membrane organelles is essential for heart function. A critical cardiac membrane organelle is the transverse tubule system (called the t-tubule system) which is an invagination of the surface membrane. A unique structural characteristic of the cardiac muscle t-tubule system is the extension of the extracellular matrix (ECM) from the surface membrane into the t-tubule lumen. However, the importance of the ECM extending into the cardiac t-tubule lumen is not well understood. Dystroglycan (DG) is an ECM receptor in the surface membrane of many cells, and it is also expressed in t-tubules in cardiac muscle. Extensive posttranslational processing and O-glycosylation are required for DG to bind ECM proteins and the binding is mediated by a glycan structure known as matriglycan. Genetic disruption resulting in defective O-glycosylation of DG results in muscular dystrophy with cardiorespiratory pathophysiology. Here, we show that DG is essential for maintaining cardiac t-tubule structural integrity. Mice with defects in O-glycosylation of DG developed normal t-tubules but were susceptible to stress-induced t-tubule loss or severing that contributed to cardiac dysfunction and disease progression. Finally, we observed similar stress-induced cardiac t-tubule disruption in a cohort of mice that solely lacked matriglycan. Collectively, our data indicate that DG in t-tubules anchors the luminal ECM to the t-tubule membrane via the polysaccharide matriglycan, which is critical to transmitting structural strength of the ECM to the t-tubules and provides resistance to mechanical stress, ultimately preventing disruptions in cardiac t-tubule integrity.

Biology and engineering of integrative and conjugative elements: Construction and analyses of hybrid ICEs reveal element functions that affect species-specific efficiencies.

Integrative and conjugative elements (ICEs) are mobile genetic elements that reside in a bacterial host chromosome and are prominent drivers of bacterial evolution. They are also powerful tools for genetic analyses and engineering. Transfer of an ICE to a new host involves many steps, including excision from the chromosome, DNA processing and replication, transfer across the envelope of the donor and recipient, processing of the DNA, and eventual integration into the chromosome of the new host (now a stable transconjugant). Interactions between an ICE and its host throughout the life cycle likely influence the efficiencies of acquisition by new hosts. Here, we investigated how different functional modules of two ICEs, Tn916 and ICEBs1, affect the transfer efficiencies into different host bacteria. We constructed hybrid elements that utilize the high-efficiency regulatory and excision modules of ICEBs1 and the conjugation genes of Tn916. These elements produced more transconjugants than Tn916, likely due to an increase in the number of cells expressing element genes and a corresponding increase in excision. We also found that several Tn916 and ICEBs1 components can substitute for one another. Using B. subtilis donors and three Enterococcus species as recipients, we found that different hybrid elements were more readily acquired by some species than others, demonstrating species-specific interactions in steps of the ICE life cycle. This work demonstrates that hybrid elements utilizing the efficient regulatory functions of ICEBs1 can be built to enable efficient transfer into and engineering of a variety of other species.

Beneficial and detrimental genes in the cellular response to replication arrest.

DNA replication is essential for all living organisms. Several events can disrupt replication, including DNA damage (e.g., pyrimidine dimers, crosslinking) and so-called "roadblocks" (e.g., DNA-binding proteins or transcription). Bacteria have several well-characterized mechanisms for repairing damaged DNA and then restoring functional replication forks. However, little is known about the repair of stalled or arrested replication forks in the absence of chemical alterations to DNA. Using a library of random transposon insertions in Bacillus subtilis, we identified 35 genes that affect the ability of cells to survive exposure to an inhibitor that arrests replication elongation, but does not cause chemical alteration of the DNA. Genes identified include those involved in iron-sulfur homeostasis, cell envelope biogenesis, and DNA repair and recombination. In B. subtilis, and many bacteria, two nucleases (AddAB and RecJ) are involved in early steps in repairing replication forks arrested by chemical damage to DNA and loss of either nuclease causes increased sensitivity to DNA damaging agents. These nucleases resect DNA ends, leading to assembly of the recombinase RecA onto the single-stranded DNA. Notably, we found that disruption of recJ increased survival of cells following replication arrest, indicating that in the absence of chemical damage to DNA, RecJ is detrimental to survival. In contrast, and as expected, disruption of addA decreased survival of cells following replication arrest, indicating that AddA promotes survival. The different phenotypes of addA and recJ mutants appeared to be due to differences in assembly of RecA onto DNA. RecJ appeared to promote too much assembly of RecA filaments. Our results indicate that in the absence of chemical damage to DNA, RecA is dispensable for cells to survive replication arrest and that the stable RecA nucleofilaments favored by the RecJ pathway may lead to cell death by preventing proper processing of the arrested replication fork.

A CRISPR interference screen reveals a role for cell wall teichoic acids in conjugation in Bacillus subtilis.

Conjugative elements are widespread in bacteria and include plasmids and integrative and conjugative elements (ICEs). They transfer from donor to recipient cells via an element-encoded type IV secretion system. These elements interact with and utilize host functions for their lifecycles. We sought to identify essential host genes involved in the lifecycle of the integrative and conjugative element ICEBs1 of Bacillus subtilis. We constructed a library of strains for inducible knockdown of essential B. subtilis genes using CRISPR interference. Each strain expressed one guide RNA in ICEBs1. We induced partial interference of essential genes and identified those that caused an acute defect in acquisition of ICEBs1 by recipient cells. This screen revealed that reducing expression of genes needed for synthesis of cell wall teichoic acids caused a decrease in conjugation. Using three different ways to reduce their synthesis, we found that wall teichoic acids were necessary in both donors and recipients for efficient conjugative transfer of ICEBs1. Further, we found that depletion of wall teichoic acids caused cells involved in ICEBs1 conjugation to die, most likely from damage to the cell envelope. Our results indicate that wall teichoic acids help protect against envelope stress caused by active conjugation machines.

TnSmu1 is a functional integrative and conjugative element in Streptococcus mutans that when expressed causes growth arrest of host bacteria.

Integrative and conjugative elements (ICEs) are major drivers of horizontal gene transfer in bacteria. They mediate their own transfer from host cells (donors) to recipients and allow bacteria to acquire new phenotypes, including pathogenic and metabolic capabilities and drug resistances. Streptococcus mutans, a major causative agent of dental caries, contains a putative ICE, TnSmu1, integrated at the 3' end of a leucyl tRNA gene. We found that TnSmu1 is a functional ICE, containing all the genes necessary for ICE function. It excised from the chromosome and excision was stimulated by DNA damage. We identified the DNA junctions generated by excision of TnSmu1, defined the ends of the element, and detected the extrachromosomal circle. We found that TnSmu1 can transfer from S. mutans donors to recipients when co-cultured on solid medium. The presence of TnSmu1 in recipients inhibited successful acquisition of another copy and this inhibition was mediated, at least in part, by the likely transcriptional repressor encoded by the element. Using microscopy to track individual cells, we found that activation of TnSmu1 caused an arrest of cell growth. Our results demonstrate that TnSmu1 is a functional ICE that affects the biology of its host cells.

Multiple mechanisms for overcoming lethal over-initiation of DNA replication.

DNA replication is highly regulated and primarily controlled at the step of initiation. In bacteria, the replication initiator DnaA and the origin of replication oriC are the primary targets of regulation. Perturbations that increase or decrease replication initiation can cause a decrease in cell fitness. We found that multiple mechanisms, including an increase in replication elongation and a decrease in replication initiation, can compensate for lethal over-initiation. We found that in Bacillus subtilis, under conditions of rapid growth, loss of yabA, a negative regulator of replication initiation, caused a synthetic lethal phenotype when combined with the dnaA1 mutation that also causes replication over-initiation. We isolated several classes of suppressors that restored viability to dnaA1 ∆yabA double mutants. Some suppressors (relA, nrdR) stimulated replication elongation. Others (dnaC, cshA) caused a decrease in replication initiation. One class of suppressors decreased replication initiation in the dnaA1 ∆yabA mutant by causing a decrease in the amount of the replicative helicase, DnaC. We found that decreased levels of helicase in otherwise wild-type cells were sufficient to decrease replication initiation during rapid growth, indicating that the replicative helicase is limiting for replication initiation. Our results highlight the multiple mechanisms cells use to regulate DNA replication.

Impact of Surface Functionalization and Deposition Method on Cu-BDC surMOF Formation, Morphology, Crystallinity, and Stability.

For direct integration into device architectures, surface-anchored metal-organic framework (surMOF) thin films are attractive systems for a wide variety of electronic, photonic, sensing, and gas storage applications. This research systematically investigates the effect of deposition method and surface functionalization on the film formation of a copper paddle-wheel-based surMOF. Solution-phase layer-by-layer (LBL) immersion and LBL spray deposition methods are employed to deposit copper benzene-1,4-dicarboxylate (Cu-BDC) on gold substrates functionalized with carboxyl- and hydroxyl-terminated alkanethiol self-assembled monolayers (SAMs). A difference in crystal orientation is observed by atomic force microscopy and X-ray diffractometry based on surface functionalization for films deposited by the LBL immersion method but not for spray-deposited films. Cu-BDC crystallites with a strong preferred orientation perpendicular to the substrate were observed for the films deposited by the LBL immersion method on carboxyl-terminated SAMs. These crystals could be removed upon testing adhesive properties, whereas all other Cu-BDC surMOF film structures demonstrated excellent adhesive properties. Additionally, film stability upon exposure to water or heat was investigated. Ellipsometric data provide insight into film formation elucidating 7 and 14 Å average thicknesses per deposition cycle for films deposited by the immersion method on 11-mercapto-1-undecanol (MUD) and 16-mercaptohexadecanoic acid (MHDA), respectively. In contrast, the films deposited by the spray method are thicker with the same average thickness per deposition cycle (21 Å) for both SAMs. While the spray method takes less time to grow thicker films, it produces similar crystallite structures, regardless of the surface functionalization. This research is fundamental to understanding the impact of deposition method and surface functionalization on surMOF film growth and to provide strategies for the preparation of high-quality surMOFs.

Assay of the enzymes of glutathione biosynthesis.

This article is dedicated to the late long-time Editor-in-Chief of Analytical Biochemistry, William Jakoby. As a graduate student, I remember reading many articles in Analytical Biochemistry and Methods in Enzymology, both volumes that Bill edited. I first met him as a graduate student presenting at the American Society of Biochemistry (and Molecular Biology) meetings. My Ph.D. advisor, Alton Meister, would bring over well-known biochemists and introduce me as Dr. Anderson, leaving me a bit tongue-tied being that I was still actually a humble graduate student! I next met Bill at my first Analytical Biochemistry Executive Editors meeting in San Diego when he was Editor-in-Chief Emeritus; I felt honored to be on the same board with him and serving the journal to which he had brought to prominence. His eyes were piercing and he was so sharp; his knowledge was both broad and deep. Since much of the large body of Bill's research was on glutathione S-transferases, my article focuses on the assay of the enzymes that synthesize glutathione, a substrate for glutathione S-transferases.

Protective role for the N-terminal domain of α-dystroglycan in Influenza A virus proliferation.

α-Dystroglycan (α-DG) is a highly glycosylated basement membrane receptor that is cleaved by the proprotein convertase furin, which releases its N-terminal domain (α-DGN). Before cleavage, α-DGN interacts with the glycosyltransferase LARGE1 and initiates functional O-glycosylation of the mucin-like domain of α-DG. Notably, α-DGN has been detected in a wide variety of human bodily fluids, but the physiological significance of secreted α-DGN remains unknown. Here, we show that mice lacking α-DGN exhibit significantly higher viral titers in the lungs after Influenza A virus (IAV) infection (strain A/Puerto Rico/8/1934 H1N1), suggesting an inability to control virus load. Consistent with this, overexpression of α-DGN before infection or intranasal treatment with recombinant α-DGN prior and during infection, significantly reduced IAV titers in the lungs of wild-type mice. Hemagglutination inhibition assays using recombinant α-DGN showed in vitro neutralization of IAV. Collectively, our results support a protective role for α-DGN in IAV proliferation.

HNK-1 sulfotransferase modulates α-dystroglycan glycosylation by 3-O-sulfation of glucuronic acid on matriglycan.

Mutations in multiple genes required for proper O-mannosylation of α-dystroglycan are causal for congenital/limb-girdle muscular dystrophies and abnormal brain development in mammals. Previously, we and others further elucidated the functional O-mannose glycan structure that is terminated by matriglycan, [(-GlcA-ß3-Xyl-α3-)n]. This repeating disaccharide serves as a receptor for proteins in the extracellular matrix. Here, we demonstrate in vitro that HNK-1 sulfotransferase (HNK-1ST/carbohydrate sulfotransferase) sulfates terminal glucuronyl residues of matriglycan at the 3-hydroxyl and prevents further matriglycan polymerization by the LARGE1 glycosyltransferase. While α-dystroglycan isolated from mouse heart and kidney is susceptible to exoglycosidase digestion of matriglycan, the functional, lower molecular weight α-dystroglycan detected in brain, where HNK-1ST expression is elevated, is resistant. Removal of the sulfate cap by a sulfatase facilitated dual-glycosidase digestion. Our data strongly support a tissue specific mechanism in which HNK-1ST regulates polymer length by competing with LARGE for the 3-position on the nonreducing GlcA of matriglycan.

Revealing a Decisive Role for Secondary Coordination Sphere Nucleophiles on Methane Activation.

Density functional theory and ab initio calculations indicate that nucleophiles can significantly reduce enthalpic barriers to methane C-H bond activation. Valence bond analysis suggests the formation of a two-center three-electron bond as the origin for the catalytic nucleophile effect. A predictive model for methane activation catalysis follows, which suggests that strongly electron-attracting and electron-rich radicals, together with both a negatively charged and strongly electron-donating outer sphere nucleophile, result in the lowest reaction barriers. It is corroborated by the sensitivity of the calculated C-H activation barriers to the external nucleophile and to continuum solvent polarity. More generally, from the present studies, one may propose proteins with hydrophobic active sites, available strong nucleophiles, and hydrogen bond donors as attractive targets for engineering novel methane functionalizing enzymes.

Clinical utility of RNA sequencing to resolve unusual GNE myopathy with a novel promoter deletion.

INTRODUCTION: UDP N-acetylglucosamine2-epimerase/N-acetylmannosamine-kinase (GNE) gene mutations can cause mostly autosomal-recessive myopathy with juvenile-onset known as hereditary inclusion-body myopathy (HIBM). METHODS: We describe a family of a patient showing an unusual HIBM with both vacuolar myopathy and myositis without quadriceps-sparing, hindering diagnosis. We show how genetic testing with functional assays, clinical transcriptome sequencing (RNA-seq) in particular, helped facilitate both the diagnosis and a better understanding of the genotype-phenotype relationship. RESULTS: We identified a novel 7.08 kb pathogenic deletion upstream of GNE using array comparative genomic hybridization (aCGH) and a common Val727Met variant. Using RNA-seq, we found only monoallelic (Val727Met-allele) expression, leading to ~50% GNE reduction in muscle. Importantly, α-dystroglycan is hypoglycosylated in the patient muscle, suggesting HIBM could be a "dystroglycanopathy." CONCLUSIONS: Our study shows the importance of considering aCGH for GNE-myopathies, and the potential of RNA-seq for faster, definitive molecular diagnosis of unusual myopathies. Muscle Nerve, 2019.

Role of dystroglycan in limiting contraction-induced injury to the sarcomeric cytoskeleton of mature skeletal muscle.

Dystroglycan (DG) is a highly expressed extracellular matrix receptor that is linked to the cytoskeleton in skeletal muscle. DG is critical for the function of skeletal muscle, and muscle with primary defects in the expression and/or function of DG throughout development has many pathological features and a severe muscular dystrophy phenotype. In addition, reduction in DG at the sarcolemma is a common feature in muscle biopsies from patients with various types of muscular dystrophy. However, the consequence of disrupting DG in mature muscle is not known. Here, we investigated muscles of transgenic mice several months after genetic knockdown of DG at maturity. In our study, an increase in susceptibility to contraction-induced injury was the first pathological feature observed after the levels of DG at the sarcolemma were reduced. The contraction-induced injury was not accompanied by increased necrosis, excitation-contraction uncoupling, or fragility of the sarcolemma. Rather, disruption of the sarcomeric cytoskeleton was evident as reduced passive tension and decreased titin immunostaining. These results reveal a role for DG in maintaining the stability of the sarcomeric cytoskeleton during contraction and provide mechanistic insight into the cause of the reduction in strength that occurs in muscular dystrophy after lengthening contractions.

Structural basis of laminin binding to the LARGE glycans on dystroglycan.

Dystroglycan is a highly glycosylated extracellular matrix receptor with essential functions in skeletal muscle and the nervous system. Reduced matrix binding by α-dystroglycan (α-DG) due to perturbed glycosylation is a pathological feature of several forms of muscular dystrophy. Like-acetylglucosaminyltransferase (LARGE) synthesizes the matrix-binding heteropolysaccharide [-glucuronic acid-ß1,3-xylose-α1,3-]n. Using a dual exoglycosidase digestion, we confirm that this polysaccharide is present on native α-DG from skeletal muscle. The atomic details of matrix binding were revealed by a high-resolution crystal structure of laminin-G-like (LG) domains 4 and 5 (LG4 and LG5) of laminin-α2 bound to a LARGE-synthesized oligosaccharide. A single glucuronic acid-ß1,3-xylose disaccharide repeat straddles a Ca(2+) ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca(2+)-bound water molecules. The chelating binding mode accounts for the high affinity of this protein-carbohydrate interaction. These results reveal a previously uncharacterized mechanism of carbohydrate recognition and provide a structural framework for elucidating the mechanisms underlying muscular dystrophy.

L-2,3-diaminopropionate generates diverse metabolic stresses in Salmonella enterica.

Unchecked amino acid accumulation in living cells has the potential to cause stress by disrupting normal metabolic processes. Thus, many organisms have evolved degradation strategies that prevent endogenous accumulation of amino acids. L-2,3-diaminopropionate (Dap) is a non-protein amino acid produced in nature where it serves as a precursor to siderophores, neurotoxins and antibiotics. Dap accumulation in Salmonella enterica was previously shown to inhibit growth by unknown mechanisms. The production of diaminopropionate ammonia-lyase (DpaL) alleviated Dap toxicity in S. enterica by catalyzing the degradation of Dap to pyruvate and ammonia. Here, we demonstrate that Dap accumulation in S. enterica elicits a proline requirement for growth and specifically inhibits coenzyme A and isoleucine biosynthesis. Additionally, we establish that the DpaL-dependent degradation of Dap to pyruvate proceeds through an unbound 2-aminoacrylate (2AA) intermediate, thus contributing to 2AA stress inside the cell. The reactive intermediate deaminase, RidA, is shown to prevent 2AA damage caused by DpaL-dependent Dap degradation by enhancing the rate of 2AA hydrolysis. The results presented herein inform our understanding of the effects Dap has on metabolism in S. enterica, and likely other organisms, and highlight the critical role played by RidA in preventing 2AA stress stemming from Dap detoxification.

The acetaminophen metabolite N-acetyl-p-benzoquinone imine (NAPQI) inhibits glutathione synthetase in vitro; a clue to the mechanism of 5-oxoprolinuric acidosis?

1. Metabolic acidosis due to accumulation of l-5-oxoproline is a rare, poorly understood, disorder associated with acetaminophen treatment in malnourished patients with chronic morbidity. l-5-Oxoprolinuria signals abnormal functioning of the γ-glutamyl cycle, which recycles and synthesises glutathione. Inhibition of glutathione synthetase (GS) by N-acetyl-p-benzoquinone imine (NAPQI) could contribute to 5-oxoprolinuric acidosis in such patients. We investigated the interaction of NAPQI with GS in vitro. 2. Peptide mapping of co-incubated NAPQI and GS using mass spectrometry demonstrated binding of NAPQI with cysteine-422 of GS, which is known to be essential for GS activity. Computational docking shows that NAPQI is properly positioned for covalent bonding with cysteine-422 via Michael addition and hence supports adduct formation. 3. Co-incubation of 0.77 µM of GS with NAPQI (25-400 µM) decreased enzyme activity by 16-89%. Inhibition correlated strongly with the concentration of NAPQI and was irreversible. 4. NAPQI binds covalently to GS causing irreversible enzyme inhibition in vitro. This is an important novel biochemical observation. It is the first indication that NAPQI may inhibit glutathione synthesis, which is pivotal in NAPQI detoxification. Further studies are required to investigate its biological significance and its role in 5-oxoprolinuric acidosis.

Endogenous glucuronyltransferase activity of LARGE or LARGE2 required for functional modification of α-dystroglycan in cells and tissues.

Mutations in the LARGE gene have been identified in congenital muscular dystrophy (CMD) patients with brain abnormalities. Both LARGE and its paralog, LARGE2 (also referred to as GYLTL1B) are bifunctional glycosyltransferases with xylosyltransferase (Xyl-T) and glucuronyltransferase (GlcA-T) activities, and are capable of forming polymers consisting of [-3Xyl-α1,3GlcAß1-] repeats. LARGE-dependent modification of α-dystroglycan (α-DG) with these polysaccharides is essential for the ability of α-DG to act as a receptor for ligands in the extracellular matrix. Here we report on the endogenous enzymatic activities of LARGE and LARGE2 in mice and humans, using a newly developed assay for GlcA-T activity. We show that normal mouse and human cultured cells have endogenous LARGE GlcA-T, and that this activity is absent in cells from the Large(myd) (Large-deficient) mouse model of muscular dystrophy, as well as in cells from CMD patients with mutations in the LARGE gene. We also demonstrate that GlcA-T activity is significant in the brain, heart, and skeletal muscle of wild-type and Large2(-/-) mice, but negligible in the corresponding tissues of the Large(myd) mice. Notably, GlcA-T activity is substantial, though reduced, in the kidneys of both the Large(myd) and Large2(-/-) mice, consistent with the observation of α-DG/laminin binding in these contexts. This study is the first to test LARGE activity in samples as small as cryosections and, moreover, provides the first direct evidence that not only LARGE, but also LARGE2, is vital to effective functional modification of α-DG in vivo.

A failure to communicate: a qualitative exploration of care coordination between hospitalists and primary care providers around patient hospitalizations.

BACKGROUND: Care coordination between adult hospitalists and primary care providers (PCPs) is a critical component of successful transitions of care from hospital to home, yet one that is not well understood. OBJECTIVE: The purpose of this study was to understand the challenges in coordination of care, as well as potential solutions, from the perspective of hospitalists and PCPs in North Carolina. DESIGN AND PARTICIPANTS: We conducted an exploratory qualitative study with 58 clinicians in four hospitalist focus groups (n = 32), three PCP focus groups (n = 19), and one hybrid group with both hospitalists and PCPs (n = 7). APPROACH: Interview guides included questions about care coordination, information exchange, follow-up care, accountability, and medication management. Focus group sessions were recorded, transcribed verbatim, and analyzed in ATLAS.ti. The constant comparative method was used to evaluate differences between hospitalists and PCPs. KEY RESULTS: Hospitalists and PCPs were found to encounter similar care coordination challenges, including (1) lack of time, (2) difficulty reaching other clinicians, (3) lack of personal relationships with other clinicians, (4) lack of information feedback loops, (5) medication list discrepancies, and (6) lack of clarity regarding accountability for pending tests and home health. Hospitalists additionally noted difficulty obtaining timely follow-up appointments for after-hours or weekend discharges. PCPs additionally noted (1) not knowing when patients were hospitalized, (2) not having hospital records for post-hospitalization appointments, (3) difficulty locating important information in discharge summaries, and (4) feeling undervalued when hospitalists made medication changes without involving PCPs. Hospitalists and PCPs identified common themes of successful care coordination as (1) greater efforts to coordinate care for "high-risk" patients, (2) improved direct telephone access to each other, (3) improved information exchange through shared electronic medical records, (4) enhanced interpersonal relationships, and (5) clearly defined accountability. CONCLUSIONS: Hospitalists and PCPs encounter similar challenges in care coordination, yet have important experiential differences related to sending and receiving roles for hospital discharges. Efforts to improve coordination of care between hospitalists and PCPs should aim to understand perspectives of clinicians in each setting.

Fundamentals of MOF Thin Film Growth via Liquid-Phase Epitaxy: Investigating the Initiation of Deposition and the Influence of Temperature.

Thin films can integrate the versatility and great potential found in the emerging field of metal-organic frameworks directly into device architectures. For fabrication of smart interfaces containing surface-anchored metal-organic frameworks, it is important to understand how the foundational layers form to create the interface between the underlying substrate and porous framework. Herein, the formation and morphology of the first ten cycles of film deposition are investigated for the well-studied HKUST-1 system. Effects of processing variables, such as deposition temperature and substrate quality, are studied. Sequences of scanning probe microscopy images collected after cycles of alternating solution-phase deposition reveal the formation of a discontinuous surface with nucleating and growing crystallites consistent with a Volmer-Weber growth mechanism. Quantitative image analysis determines surface roughness and surface coverage as a function of deposition cycles, producing insight regarding growth and structure of foundational film layers. For carboxylic acid terminated self-assembled monolayers on gold, preferred crystal orientation is influenced by deposition temperature with crystal growth along [100] observed at 25 °C and [111] favored at 50 °C. This difference in crystal orientation results in reduced surface roughness and increased surface coverage at 50 °C. To properly fabricate and fully determine the potential of this material for industrial applications, fundamental understanding of film formation is crucial.

Multinary Tetrahedrite (Cu12-x-yMxNySb4S13) Nanoparticles: Tailoring Thermal and Optical Properties with Copper-Site Dopants.

Tetrahedrite (Cu12Sb4S13) is an earth-abundant and nontoxic compound with prospective applications in green energy technologies such as thermoelectric waste heat recycling or photovoltaic power generation. A facile, one-pot solution-phase modified polyol method has been developed that produces high-purity nanoscale tetrahedrite products with exceptional stoichiometric and phase control. This modified polyol method is used here to produce phase-pure quaternary and quintenary tetrahedrite nanoparticles doped on the Cu-site with Zn, Fe, Ni, Mn, or Co. This is the first time that Cu-site codoped quintenary tetrahedrite and Mn-doped quaternary tetrahedrite have been produced by a solution-phase method. X-ray diffraction shows phase-pure tetrahedrite, while scanning and transmission electron microscopy show the size and morphology of the nanomaterials. Energy dispersive X-ray spectroscopy confirms nanoparticles have near-stoichiometric elemental compositions. Thermal stability of quintenary codoped tetrahedrite material is analyzed using thermogravimetric analysis, finding that codoping with Mn, Fe, Ni, and Zn increased thermal stability while codoping with cobalt decreased thermal stability. This is the first systematic study of the optical properties of quaternary and quintenary tetrahedrite nanoparticles doped on the Cu-site. Visible-NIR diffuse reflectance spectroscopy reveals that the quaternary and quintenary tetrahedrite nanoparticles have direct optical band gaps ranging from 1.88 to 2.04 eV. Data from thermal and optical characterization support that codoped tetrahedrite nanoparticles are composed of quintenary grains. This research seeks to enhance understanding of the material properties of tetrahedrite, leading to the optimization of sustainable, nontoxic, and high-performance photovoltaic and thermoelectric materials.