Soft-landing electrospray ion beam deposition of sensitive oligoynes on surfaces in vacuum

AbstractAdvances in synthetic chemistry permit the synthesis of large, highly functional, organic molecules. Characterizing the complex structure of such molecules with highly resolving, vacuum-based methods like scanning probe microscopy requires their transfer into the gas phase and further onto an atomically clean surface in ultrahigh vacuum without causing additional contamination. Conventionally this is done via sublimation in vacuum. However, similar to biological molecules, large synthetic compounds can be non-volatile and decompose upon heating. Soft-landing ion beam deposition using soft ionization methods represents an alternative approach to vacuum deposition. Using different oligoyne derivatives of the form of R1(CC)nR2, here we demonstrate that even sensitive molecules can be handled by soft-landing electrospray ion beam deposition. We generate intact molecular ions as well as fragment ions with intact hexayne parts and deposit them on clean metal surfaces. Scanning tunneling microscopy shows that the reactive hexayne segments of the molecules of six conjugated triple bonds are intact. The molecules agglomerate into ribbon-like islands, whose internal structure can be steered by the choice of the substituents. Our results suggest the use of ion beam deposition to arrange reactive precursors for subsequent polymerization reactions

Sequencing conjugated polymers by eye.

The solid-state microstructure of a conjugated polymer is the most important parameter determining its properties and performance in (opto)-electronic devices. A huge amount of research has been dedicated to tuning and understanding how the sequence of monomers, the nature and frequency of defects, the exact backbone conformation, and the assembly and crystallinity of conjugated polymers affect their basic photophysics and charge transporting properties. However, because of the lack of reliable high-resolution analytical techniques, all the structure-property relations proposed in the literature are based either on molecular modeling or on indirect experimental data averaged on polydisperse samples. We show that a combination of electrospray vacuum deposition and high-resolution scanning tunneling microscopy allows the imaging of individual conjugated polymers with unprecedented detail, thereby unraveling structural and self-assembly characteristics that have so far been impossible to determine

Thermally-induced chemical transformations and self-assembly of short peptides on metal surfaces

Peptides have been identified as having high potential for creating molecular building blocks for nanoscience, due to their intrinsic biocompatibility, wide availability, and chiral properties. In particular, these molecules are well suited to the fabrication of functional thin films via supramolecular self-assembly, because of their wide-ranging functionalities around a common core, in addition to chemical motifs that facilitate self-assembly, as observed abundantly in nature. However, relatively few studies of such molecules on surfaces can be found, leaving a gap in the exploration of the potential of the class. Therefore, the primary goal of this thesis is to investigate the self-assembly of short peptides, specifically on metal surfaces. However, in order to ensure high quality thin films are manufactured, peptides should ideally be deposited on a surface in vacuum via molecular beam epitaxy, a technique that can result in their decomposition. An understanding of the capabilities and limits of this technique, in particular with respect to peptides, is currently limited, and so part of this thesis focuses on tackling this shortfall in a methodical manner. Depending on the primary structure of the peptide studied, mass spectrometry data indicated a sublimation limit can be found at just a few residues (~4/5). Additionally, these investigations demonstrated the possibility for cyclisation by thermal action for aromatic dipeptides, forming diketopiperazines. Scanning tunnelling microscopy and X-ray photoelectron spectroscopy data for ultrathin films of aromatic dipeptides and diketopiperazines follow, and reveal interesting self-assembly behaviour that also sheds light on previous peptide studies in the literature. Furthermore, it proved possible to chemically modify the diketopiperazines by onsurface annealing, resulting in stark changes to their assembly, and offering a simple pathway to challenging synthetic products. Key results from the study of L-Tyr-L-Tyr are supported by computational data for a more complete picture of the nature of the observed assemblies

Confidence in predicted position error explains saccadic decisions during pursuit

A fundamental problem in motor control is the coordination of complementary movement types to achieve a common goal. As a common example, humans view moving objects through coordinated pursuit and saccadic eye movements. Pursuit is initiated and continuously controlled by retinal image velocity. During pursuit, eye position may lag behind the target. This can be compensated by the discrete execution of a catch-up saccade. The decision to trigger a saccade is influenced by both position and velocity errors and the timing of saccades can be highly variable. The observed distributions of saccade occurrence and trigger time remain poorly understood and this decision process remains imprecisely quantified. Here we propose a predictive, probabilistic model explaining the decision to trigger saccades during pursuit to foveate moving targets. In this model, expected position error and its associated uncertainty are predicted through Bayesian inference across noisy, delayed sensory observations (Kalman filtering). This probabilistic prediction is used to estimate the confidence that a saccade is needed (quantified through log-probability ratio), triggering a saccade upon accumulating to a fixed threshold. The model qualitatively explains behavioural observations on the probability of occurrence and trigger time distributions of saccades during pursuit over a range of target motion trajectories. Furthermore, this model makes novel predictions about the influence of sensory uncertainty and target motion parameters on saccade decisions. We suggest that this predictive, confidence-based decision making strategy represents a fundamental principle for the probabilistic neural control of coordinated movements

Recurrent disseminated coccidioidal meningitis in two subsequent pregnancies

Objective: Recurrent disseminated coccidioidal meningitis in two subsequent pregnancies is rare and can pose a challenge in ensuring the health of both mother and baby. In this unique case we highlight this rare occurrence and subsequent treatment. Case report: A 29-year-old G4P1021 with a history of disseminated coccidioidomycosis in a previous pregnancy presented at 8 weeks gestation with nausea, headache, and neck pain. Cerebrospinal fluid analysis was positive for recurrent coccidioidal infection. She was started on Amphotericin and discharged. She re-presented at 30 week's gestation with phonophobia and photophobia, emesis, neck pain and swelling. MRI showed evidence of ventriculomegaly with communicating hydrocephalus. She was treated with therapeutic lumbar punctures throughout her pregnancy and a ventriculoperitoneal shunt following delivery. She had a spontaneous vaginal delivery at 38 weeks and 3 days with no complications. Conclusion: This unique case highlights the susceptibility of recurrent disseminated coccidioidomycosis in subsequent pregnancies and treatment thereof

Predicted Position Error Triggers Catch-Up Saccades during Sustained Smooth Pursuit

For humans, visual tracking of moving stimuli often triggers catch-up saccades during smooth pursuit. The switch between these continuous and discrete eye movements is a trade-off between tolerating sustained position error (PE) when no saccade is triggered or a transient loss of vision during the saccade due to saccadic suppression. de Brouwer et al. (2002b) demonstrated that catch-up saccades were less likely to occur when the target re-crosses the fovea within 40–180 ms. To date, there is no mechanistic explanation for how the trigger decision is made by the brain. Recently, we proposed a stochastic decision model for saccade triggering during visual tracking (Coutinho et al., 2018) that relies on a probabilistic estimate of predicted PE (PEpred). Informed by model predictions, we hypothesized that saccade trigger time length and variability will increase when pre-saccadic predicted errors are small or visual uncertainty is high (e.g., for blurred targets). Data collected from human participants performing a double step-ramp task showed that large pre-saccadic PEpred (>10°) produced short saccade trigger times regardless of the level of uncertainty while saccade trigger times preceded by small PEpred (<10°) significantly increased in length and variability, and more so for blurred targets. Our model also predicted increased signal-dependent noise (SDN) as retinal slip (RS) increases; in our data, this resulted in longer saccade trigger times and more smooth trials without saccades. In summary, our data supports our hypothesized predicted error-based decision process for coordinating saccades during smooth pursuit

Promoting the Quality of User Generated Ideas in Online Innovation Communities: A Knowledge Collaboration Perspective

Enabled by Internet-based technologies, users are increasingly participating and collaborating in idea generation in online innovation communities. However, with the limited understanding of the phenomenon, few studies have investigated what determines the quality of ideas. This study aims at addressing the knowledge gap. We find that idea experimentation effort, i.e., the effort associated with creating the idea, and idea review, i.e., comments by other users, influence idea quality. Further, idea recombination, i.e. peer users participating in wiki-based edits, have a positive influence on idea Quality, in case idea experimentation effort was low, and a negative influence in case of high idea experimentation effort. These results contribute to idea generation, knowledge collaboration, and user generated content literature by investigating the mechanisms through which collaboration influences the quality of the collaborative outcome (i.e., idea quality) in online contexts for the first time. Advice for organizations running online innovation communities is provided

Cellular/Molecular Separate Ca2 Sources Are Buffered by Distinct Ca2 Handling Systems in

Although the contributionofCa2buffering systems canvarybetweenneuronal types and cellular compartments, it is unknownwhether distinct Ca2 sources within a neuron have different buffers. As individual Ca2 sources can have separate functions, we propose that each is handled by unique systems. Using Aplysia californica bag cell neurons, which initiate reproduction through an afterdischarge involvingmultiple Ca2-dependent processes, we investigated the role of endoplasmic reticulum (ER) andmitochondrial sequestration, as well as extrusion via the plasmamembrane Ca2-ATPase (PMCA) and Na/Ca2 exchanger, to the clearance of voltage-gated Ca2 influx, Ca2-induced Ca2-release (CICR), and store-operated Ca2 influx. Cultured bag cell neurons were filled with the Ca2 indicator, fura-PE3, to image Ca2 under whole-cell voltage clamp. A 5 Hz, 1 min train of depolarizing voltage steps elicited voltage-gated Ca2 influx followedbyEGTA-sensitive CICR from themitochondria. A compartmentmodel of Ca2 indicated the effect of EGTAonCICRwas due to buffering of released mitochondrial Ca2 rather than uptake competition. Removal of voltage-gated Ca2 influx was dominated by the mitochondria and PMCA, with no contribution from the Na/Ca2 exchanger or sarcoplasmic/endoplasmic Ca2-ATPase (SERCA). In contrast, CICR recoverywas slowed by eliminating theNa/Ca2 exchanger and PMCA. Last, store-operated influx, evoked by ER depletion, was removed by the SERCA and depended on the mitochondrial membrane potential. Our results demonstrate that distinct buffering systems are dedicated to particular Ca2 sources. In general, this may represent a means to differentially regulate Ca2-dependent processes, and for Aplysia, influence how reproductive behavior is triggered

Management Strategies for Cln2 Disease

CLN2 disease (neuronal ceroid lipofuscinosis type 2) is a rare, autosomal recessive, pediatric-onset, rapidly progressive neurodegenerative lysosomal storage disorder caused by tripeptidyl peptidase 1 (TPP1) enzyme deficiency, and is characterized by language delay, seizures, rapid cognitive and motor decline, blindness, and early death. No management guidelines exist and there is a paucity of published disease-specific evidence to inform clinical practice, which currently draws upon experience from the field of childhood neurodisability. Twenty-four disease experts were surveyed on CLN2 disease management and a subset met to discuss current practice. Management goals and strategies are consistent among experts globally and are guided by the principles of pediatric palliative care. Goals and interventions evolve as the disease progresses, with a shift in focus from maintenance of function early in the disease to maintenance of quality of life. A multidisciplinary approach is critical for optimal patient care. This work represents an initial step toward the development of consensus-based management guidelines for CLN2 disease.WoSScopu