A quantitative framework for the design of acellular hemoglobins as blood substitutes: implications of dynamic flow conditions

The delivery of oxygen to tissue by cell-free carriers eliminates intraluminal barriers associated with red blood cells. This is important in arterioles, since arteriolar tone controls capillary perfusion. We describe a mathematical model for O(2) transport by hemoglobin solutions and red blood cells flowing through arteriolar-sized tubes to optimize values of p50, Hill number, hemoglobin molecular diffusivity and concentration. Oxygen release is evaluated by including an extra-luminal resistance term to reflect tissue oxygen consumption. For low consumption (i.e., high resistance to O(2) release) a hemoglobin solution with p50=15 mmHg, n=1, D(HBO2)=3 x 10(-7) cm(2)/s delivers O(2) at a rate similar to that of red blood cells. For high consumption, the p50 must be decreased to 5 mmHg. The model predicts that regardless of size, hemoglobin solutions with higher p50 will present excess O(2) to arteriolar walls. Oversupply of O(2) to arteriolar walls may cause constriction and paradoxically reduced capillary perfusion.     

Membrane entrapped Saccharomyces cerevisiae in a biosensor-like device as a generic rapid method to study cellular metabolism

We describe a new, faster and convenient method to study some metabolic characteristics - by the successful application of immobilized yeast cells (S. cerevisiae) in a microbial biosensor-like device. Microbial biosensors consist of microorganisms immobilized on the surface of a membrane or in a gel, in close contact with a transducer. Almost all works published to date have used biosensors for analyses in which a concentration-related property of the external medium is measured. A different approach is presented here; we have successfully used S. cerevisiae and a carbon dioxide electrode as the main components of a biosensor-like device, used as a proof of concept, for a system useful to characterize metabolic parameters of the microbial cells immobilized on a carbon dioxide electrode. The biosensor-like device we are presenting allows us to calculate Michaelis-Menten parameters related to the kinetics of transport and degradation of several carbohydrates (i.e., glucose, fructose, galactose, sucrose and xylose, with K(m(app)) of 6.0, 5.8, 0.9, 2.0, and 147 mM, respectively), and the study of the kinetics of expression of non-constitutive proteins related to the transport and degradation of galactose.     

Side chain electrostatic interactions and pH‐dependent expansion of the intrinsically disordered,highly acidic carboxyl‐terminus of γ‐tubulin

Intramolecular electrostatic attraction and repulsion strongly influence the conformational sampling of intrinsically disordered proteins and domains (IDPs). In order to better understand this complex relationship, we have used nuclear magnetic resonance to measure side chain pK_a values and pH‐dependent translational diffusion coefficients for the unstructured and highly acidic carboxyl‐terminus of γ‐tubulin (γ‐CT), providing insight into how the net charge of an IDP relates to overall expansion or collapse of the conformational ensemble. Many of the pK_a values in the γ‐CT are shifted upward by 0.3–0.4 units and exhibit negatively cooperative ionization pH profiles, likely due to the large net negative charge that accumulates on the molecule as the pH is raised. pK_a shifts of this magnitude correspond to electrostatic interaction energies between the affected residues and the rest of the charged molecule that are each on the order of 1 kcal mol^?1. Diffusion of the γ‐CT slowed with increasing net charge, indicative of an expanding hydrodynamic radius (r_H). The degree of expansion agreed quantitatively with what has been seen from comparisons of IDPs with different charge content, yielding the general trend that every 0.1 increase in relative charge (|Q|/res) produces a roughly 5% increase in r_H. While γ‐CT pH titration data followed this trend nearly perfectly, there were substantially larger deviations for the database of different IDP sequences. This suggests that other aspects of an IDP's primary amino acid sequence beyond net charge influence the sensitivity of r_H to electrostatic interactions.     

Electrocatalytic Reduction of Gaseous CO2 to CO on Sn/Cu‐Nanofiber‐Based Gas Diffusion Electrodes

Earth‐abundant Sn/Cu catalysts are highly selective for the electrocatalytic reduction of CO₂ to CO in aqueous electrolytes. However, CO₂ mass transport limitations, resulting from the low solubility of CO₂ in water, so far limit the CO partial current density for Sn/Cu catalysts to about 10 mA cm^?2. Here, a freestanding gas diffusion electrode design based on Sn‐decorated Cu‐coated electrospun polyvinylidene fluoride nanofibers is demonstrated. The use of gaseous CO₂ as a feedstock alleviates mass transport limitations, resulting in high CO partial current densities above 100 mA cm^?2, while maintaining high CO faradaic efficiencies above 80%. These results represent an important step toward an economically viable pathway to CO₂ reduction.     

Amphoteric Indium Enables Carrier Engineering to Enhance the Power Factor and Thermoelectric Performance in n‐Type AgnPb100InnTe100+2n (LIST)

The Ag and In co‐doped PbTe, Ag_nPb₁₀₀In_nTe_100+2n (LIST), exhibits n‐type behavior and features unique inherent electronic levels that induce self‐tuning carrier density. Results show that In is amphoteric in the LIST, forming both In³⁺ and In¹⁺ centers. Through unique interplay of valence fluctuations in the In centers and conduction band filling, the electron carrier density can be increased from ≈3.1 × 10¹⁸ cm^?3 at 323 K to ≈2.4 × 10¹⁹ cm^?3 at 820 K, leading to large power factors peaking at ≈16.0 µWcm^?1 K^?2 at 873 K. The lone pair of electrons from In⁺ can be thermally continuously promoted into the conduction band forming In³⁺, consistent with the amphoteric character of In. Moreover, with rising temperature, the Fermi level shifts into the conduction band, which enlarges the optical band gap based on the Moss–Burstein effect, and reduces bipolar diffusion and thermal conductivity. Adding extra Ag in LIST improves the electrical transport properties and meanwhile lowers the lattice thermal conductivity to ≈0.40 Wm^?1 K^?1. The addition of Ag creates spindle‐shaped Ag₂Te nanoprecipitates and atomic‐scale interstitials that scatter a broader set of phonons. As a result, a maximum ZT value ≈1.5 at 873 K is achieved in Ag₆Pb₁₀₀InTe₁₀₂ (LIST).     

K‐Birnessite Electrode Obtained by Ion Exchange for Potassium‐Ion Batteries: Insight into the Concerted Ionic Diffusion and K Storage Mechanism

Novel and low‐cost rechargeable batteries are of considerable interest for application in large‐scale energy storage systems. In this context, K‐Birnessite is synthesized using a facile solid‐state reaction as a promising cathode for potassium‐ion batteries. During synthesis, an ion exchange protocol is applied to increase K content in the K‐Birnessite electrode, which results in a reversible capacity as high as 125 mAh g^?1 at 0.2 C. Upon K⁺ exchange the reversible phase transitions are verified by in situ X‐ray diffraction (XRD) characterization. The underlying mechanism is further revealed to be the concerted K⁺ ion diffusion with quite low activation energies by first‐principle simulations. These new findings provide new insights into electrode process kinetics, and lay a solid foundation for material design and optimization of potassium‐ion batteries for large‐scale energy storage.     

Novel K3V2(PO4)3/C Bundled Nanowires as Superior Sodium‐Ion Battery Electrode with Ultrahigh Cycling Stability

Sodium‐ion battery has captured much attention due to the abundant sodium resources and potentially low cost. However, it suffers from poor cycling stability and low diffusion coefficient, which seriously limit its widespread application. Here, K₃V₂(PO₄)₃/C bundled nanowires are fabricated usinga facile organic acid‐assisted method. With a highly stable framework, nanoporous structure, and conductive carbon coating, the K₃V₂(PO₄)₃/C bundled nanowires manifest excellent electrochemical performances in sodium‐ion battery. A stable capacity of 119 mAh g^?1 can be achieved at 100 mA g^?1. Even at a high current density of 2000 mA g^?1, 96.0% of the capacity can be retained after 2000 charge–discharge cycles. Comparing with K₃V₂(PO₄)₃/C blocks, the K₃V₂(PO₄)₃/C bundled nanowires show significantly improved cycling stability. This work provides a facile and effective approach to enhance the electrochemical performance of sodium‐ion batteries.