No abstract

Melanins are ubiquitous in nature but their biological activities and functions have been difficult to discern. Conventional approaches to determine material function start by resolving structure and then characterize relevant properties. These approaches have been less successful for melanins because of their complex structure and insolubility, and because their relevant properties are not readily characterized by conventional methods. Here, we report a novel spectroelectrochemical reverse engineering approach that focuses on redox and radical scavenging activities. In this method, the melanin is immobilized in a permeable hydrogel film adjacent to an electrode and this immobilized melanin is probed using diffusible mediators and complex electrical inputs. Response characteristics are measured using two modalities, electrochemical currents associated with the reaction of diffusible mediators, and optical absorbance associated with the presence of diffusible free radicals. Using this method, we observed that both Sepia and fungal melanins are redox active and can repeatedly exchange electrons to be switched between oxidized and reduced states. Further, we observed that these melanins can quench radicals either by donating or accepting electrons. Finally, we demonstrate that the melanins' radical scavenging activities are dependent on their redox state such that a melanin must be reduced to have donatable electrons to quench oxidative free radicals, or must be oxidized to accept electrons from reductive free radicals. While the observation that melanin is redox-active is consistent with their well-accepted beneficial (radical-scavenging) and detrimental (pro-oxidant) activities, these observations may also support less well-accepted proposed functions for melanin in energy harvesting and redox communication.

A novel acylated flavonol tetraglycoside, kaempferol 3-O-[(E)-p-coumaroyl-(1→2)][α-l-arabinopyranosyl-(1→3)][β-d-glucopyranosyl (1→3)-α-l-rhamnopyranosyl(1→6)]-β-d-glucopyranoside (camellikaempferoside C, 1), together with 2 flavonols and 18 flavone and flavonol glycosides (FGs) (2-21) was isolated from the green tea Lu'an GuaPian (Camellia sinensis L.O. Kuntze). Their structures were identified by spectroscopic and chemical methods. Four acylated FGs (1, 7, 8, 9) were found to inhibit the proliferation and differentiation of 3T3-L1 preadipocytes at concentrations of 25, 50, and 100 μM (P < 0.05). Furthermore, we established a rapid UPLC method to quantify nine FGs in six major processing types of tea. The results showed that dark tea had the highest amount of 20 (0.70 ± 0.017 mg/g) and black tea had the highest amount of 8 (0.09 ± 0.012 mg/g), whereas the amounts of 10 and 16 basically decreased with the increasing degree of fermentation and could contribute to the discrimination of different processing types of tea.

No abstract

User-interactive electronic skin (e-skin) that could convert mechanical stimuli into distinguishable outputs displays tremendous potential for wearable devices and health care applications. However, the existing devices have the disadvantages such as complex integration procedure and lack of the intuitive signal display function. Here, we present a bioinspired user-interactive e-skin, which is simple in structure and can synchronously achieve digital electrical response and optical visualization upon external mechanical stimulus. The e-skin comprises a conductive layer with a carbon nanotubes/cellulose nanofibers/MXene nanohybrid network featuring remarkable electromechanical behaviors, and a stretchable elastomer layer, which is composed of silicone rubber and thermochromic pigments. Furthermore, the conductive nanohybrid network with outstanding Joule heating performance can generate controllable thermal energy under voltage input and then achieve the dynamic coloration of silicone-based elastomer. Especially, such an innovative fusion strategy of digital data and visual images enables the e-skin to monitor human activities with evermore intuition and accuracy. The simple design philosophy and reliable operation of the demonstrated e-skin are expected to provide an ideal platform for next-generation flexible electronics.