Spectral Graph Analyses of Water Hydrogen-Bonding Network and Osmolyte Aggregate Structures in Osmolyte–Water Solutions

Recently, it was shown that the spectral graph theory is exceptionally useful for understanding not only morphological structural differences in ion aggregates but also similarities between an ion network and a water H-bonding network in highly concentrated salt solutions. Here, we present spectral graph analysis results on osmolyte aggregates and water H-bonding network structures in aqueous renal osmolyte solutions. The quantitative analyses of the adjacency matrices that are graph-theoretical representations of aggregates of osmolyte molecules and water H-bond structures provide the ensemble average eigenvalue spectra and degree distribution. We show that urea molecules form quite different morphological structures compared to other protecting renal osmolyte molecules in water, particularly sorbitol and trimethylglycine, which are well-known protecting osmolytes, and at high concentrations exhibit a strong propensity to form morphological structures that are graph-theoretically similar to that of the water H-bond network. Conversely, urea molecules, even at similarly high concentrations, form separated clusters instead of extended osmolyte–osmolyte networks. This difference in morphological structure of osmolyte–osmolyte aggregates between protecting and destabilizing osmolytes is considered to be an important observation that led us to propose a hypothesis on the osmolyte aggregate growth mechanism via either osmolyte network formation or segregated osmolyte cluster formation. We anticipate that the present spectral graph analyses of osmolyte aggregate structures and their interplay with the water H-bond network structure in highly concentrated renal osmolyte solutions could provide important information on the osmolyte effects of not only water structures but also protein stability in biologically relevant osmolyte solutions

Computational Vibrational Spectroscopy of HDO in Osmolyte–Water Solutions

The IR absorption and time-resolved IR spectroscopy of the OD stretch mode of HDO in water was successfully used to study osmolyte effects on water H-bonding network. Protecting osmolytes such as sorbitol and trimethylglycine (TMG) make the vibrational OD stretch band red-shifted, whereas urea affects the OD band marginally. Furthermore, we recently showed that, even though sorbitol and TMG cause a slow-down of HDO rotation in their aqueous solutions, urea does not induce any change in the rotational relaxation of HDO in aqueous urea solutions even at high concentrations. To clarify the underlying osmolyte effects on water H-bonding structure and dynamics, we performed molecular dynamics (MD) simulations of a variety of aqueous osmolyte solutions. Using the vibrational solvatochromism model for the OD stretch mode and taking into account the vibrational non-Condon and polarization effects on the OD transition dipole moment, we then calculated the IR absorption spectra and rotational anisotropy decay of the OD stretch mode of HDO for the sake of direct comparisons with our experimental results. The simulation results on the OD stretch IR absorption spectra and the rotational relaxation rate of HDO in osmolyte solutions are found to be in quantitative agreement with experimental data, which confirms the validity of the MD simulation and vibrational solvatochromism approaches. As a result, it becomes clear that the protecting osmolytes like sorbitol and TMG significantly modulate water H-bonding network structure, while urea perturbs water structure little. We anticipate that the computational approach discussed here will serve as an interpretive method with atomic-level chemical accuracy of current linear and nonlinear time-resolved IR spectroscopy of structure and dynamics of water near the surfaces of membranes and proteins under crowded environments

High-Performance MoS₂/CuO Nanosheet-on-One-Dimensional Heterojunction Photodetectors

van der Waals heterostructures based on stacked two-dimensional (2D) materials provide novel device structures enabling high-performance electronic and optoelectronic devices. While 2D–2D or 2D–bulk heterostructures have been largely explored for fundamental understanding and novel device applications, 2D–one-dimensional (1D) heterostructures have been rarely studied because of the difficulty in achieving high-quality heterojunctions between 2D and 1D structures. In this study, we introduce nanosheet-on-1D van der Waals heterostructure photodetectors based on a wet-transfer printing of a MoS₂ nanosheet on top of a CuO nanowire (NW). MoS₂/CuO nanosheet-on-1D photodetectors show an excellent photocurrent rectification ratio with an ideality factor of 1.37, which indicates the formation of an atomically sharp interface and a high-quality heterojunction in the MoS₂/CuO heterostructure by wet-transfer-enhanced van der Waals bonding. Furthermore, nanosheet-on-1D heterojunction photodetectors exhibit excellent photodetection capabilities with an ultrahigh photoresponsivity (∼157.6 A/W), a high rectification ratio (∼6000 at ±2 V), a low dark current (∼38 fA at −2 V), and a fast photoresponse time (∼34.6 and 51.9 ms of rise and decay time), which cannot be achievable with 1D-on-nanosheet heterojunction photodetectors. The wet-transfer printing of nanosheet-on-1D heterostructures introduced in this study provides a robust platform for the fundamental study of various combinations of 2D-on-1D heterostructures and their applications in novel heterojunction devices

Whole cell recovery after photobleaching.

<p>A) Fluorescence before photobleaching (pre-bleach). B) Fluorescence after 30 min recovery (post recovery). C) Combined image (Green: pre-bleach, Red: post recovery). Overlaid cell boundaries have been added to guide the eye. D) Initial fluorescence of cells 1, 2, and 3 in Panels A. E) Fluorescence of cells 1, 2, and 3 after photobleaching and 30 min. recovery showing fast recovery of one pole and slow recovery of other pole. F) and G) Fluorescence profiles showing asymmetric recovery after 30 min and 1 hour, respectively.</p

Single pole photobleach and recovery.

<p>A) 1. Initial fluorescence, 2. Image immediately after shutter (red dashed area) removed, 3. Image after 15 min recovery, 4. Image after 25 min recovery. B) Intensity profiles along yellow dashed line in A1 showing fast recovery of the brighter, sheltered pole.</p

Localization imaging of the nascent new pole.

<p>A) Representative integrated image and filmstrip showing escape of molecules from the brighter old pole and diffusion toward the new pole region. B-C) Localization images of the propensity of Tsr-Venus to reside in the entire cell. The sharp bright dots show an artefactually small localization of the bright stable old pole cluster. At the opposite poles, the areas where the new pole forms show no indication of cluster formational though bulk fluorescence imaging (insets).</p

Creating Strategic Partner Acquisition Project Guideline for Duara Travels

With increasing scientific understanding and felt negative effects across the world, people are more concerned on sustainability issues than ever before. The notion that everyone has their share to do for better tomorrow is starting to be accepted. Corporations realize their role by launching Corporate Social Responsibility programs that aim to increase their positive impact. Some companies take this aim even further by placing the social mission as their sole purpose that is to be accomplished by commercial means. These kinds of companies are called social enterprises. The thesis is commissioned by Duara Travels, which is a for-profit social enterprise operating in travel industry. The company’s aim is to create positive social and economic impact in rural communities of developing economies with an underlying mission to shape the income distribution in tourism industry. The company provides authentic travel experiences to its customers by providing three- and six-night village-experiences in communities aimed to foster cultural exchange and community empowerment. The thesis is conducted as a project that produces a product. The final product is a guideline for strategic partner acquisition in Duara Travels’ destination for Duara Travels. The guideline is based on knowledge that is accumulated in theoretical and operational phases of the thesis. The theoretical part of the thesis consists of two main themes. First theme examines issues of corporations acting as drivers for sustainable development. Concepts such as Corporate Social Responsibility and Social Entrepreneurship are examined. The second theme examines is strategic collaboration between organizations. The issues are examined with an emphasis on tourism industry. In the operational part of the thesis, the author conducts a partner acquisition project for Duara Travels. The project is conducted as a pilot, providing knowledge base for the final product. The author conducts a trip to Bali, Duara Travels’ most popular destination, as a part of the project. In the destination various methods of acquiring partners are put into practice. The project is described in detail, laying out the plan, execution as well as reflection in each part of the project. The discussion gathers the knowledge accumulated in theoretical and operational part. Based on the knowledge acquired, the guideline is built. The guideline is built as a check-list. Its purpose is to act as a roadmap rather than strict manual, leaving space for contextual appliance and future improvement

Modulation of the Hydrogen Bonding Structure of Water by Renal Osmolytes

Osmolytes are an integral part of living organism, e.g., the kidney uses sorbitol, trimethylglycine, taurine and myo-inositol to counter the deleterious effects of urea and salt. Therefore, knowing that the osmolytes’ act either directly to the protein or mediated through water is of great importance. Our experimental and computational results show that protecting osmolytes, e.g., trimethylglycine and sorbitol, significantly modulate the water H-bonding network structure, although the magnitude and spatial extent of osmolyte-induced perturbation greatly vary. In contrast, urea behaves neutrally toward local water H-bonding network. Protecting osmolytes studied here show strong concentration-dependent behaviors (vibrational frequencies and lifetimes of two different infrared (IR) probes), while denaturant does not. The H-bond donor and/or acceptor (OH/NH) in a given osmolyte molecule play a critical role in defining their action. Our findings highlight the significance of the alteration of H-bonding network of water under biologically relevant environment, often encountered in real biological systems

Modulation of the Hydrogen Bonding Structure of Water by Renal Osmolytes

Osmolytes are an integral part of living organism, e.g., the kidney uses sorbitol, trimethylglycine, taurine and myo-inositol to counter the deleterious effects of urea and salt. Therefore, knowing that the osmolytes’ act either directly to the protein or mediated through water is of great importance. Our experimental and computational results show that protecting osmolytes, e.g., trimethylglycine and sorbitol, significantly modulate the water H-bonding network structure, although the magnitude and spatial extent of osmolyte-induced perturbation greatly vary. In contrast, urea behaves neutrally toward local water H-bonding network. Protecting osmolytes studied here show strong concentration-dependent behaviors (vibrational frequencies and lifetimes of two different infrared (IR) probes), while denaturant does not. The H-bond donor and/or acceptor (OH/NH) in a given osmolyte molecule play a critical role in defining their action. Our findings highlight the significance of the alteration of H-bonding network of water under biologically relevant environment, often encountered in real biological systems