Host-guest Interaction at Molecular Interfaces: Binding of Cucurbit[7]uril on Ferrocenyl Self-assembled Monolayers on Gold

Ferrocene (Fc) encapsulated cucurbit[7]uril (CB[7]) supramolecular host-guest complex  (Fc@CB[7]) as a synthetic recognition pair has been widely adapted for coupling biomolecules and nanomaterials due to its ultra-high binding affinity. In this paper, we have explored the binding of CB[7] on binary ferrocenylundecanethiolate/octanethiolate self-assembled monolayer on gold  (FcC11S-/C8S-Au), a model system to deepen our understanding of host-guest chemistry at molecular interfaces. It has been shown that upon incubation with CB[7] solution, the redox behavior FcC11S-/C8S-Au changes remarkably, i.e., a new pair of peaks appeared at more positive potential with narrowed widths. The ease of quantitation of surface bound-redox species (Fc+/Fc and  Fc+@CB[7]/ Fc@CB[7]) enabled us to determine the thermodynamic formation constant of  Fc@CB[7] at FcC11S-/C8S-Au (7.3±1.8 × 104 M-1). With time-dependent redox responses, we were able to, for the first time, deduce both the binding and dissociation rate constants, 2.8±0.3 × 103  M-1s-1 and 0.08±0.01 s-1, respectively. These results showed substantial differences both thermodynamically and kinetically for the formation of host-guest inclusion complex at molecular interfaces with respect to solution-diffused, homogenous environments

Host–Guest Interaction at Molecular Interfaces: Cucurbit[7]uril as a Sensitive Probe of Structural Heterogeneity in Ferrocenyl Self-Assembled Monolayers on Gold

Herein, we combine host–guest recognition chemistry and electrochemical analysis to demonstrate that the nanometer-size, supramolecular hosts can be adapted as sensitive probes for structural heterogeneity in organized molecular assemblies on a surface. In particular, we carried out thorough cyclic voltammetric (CV) studies to evaluate the binding of cucurbit[7]­uril on mixed ferrocenylundecanethiolate/n-alkanethiolate self-assembled monolayers (SAMs) on gold (FcC11S-/CmS-Au) prepared with different methods (coadsorption vs postassembly exchanges) and with varied diluting n-alkanethiols. On the basis of the distinct CV responses of CB[7]@Fc complex and free Fc on the SAM surfaces, we were able to determine the conversion ratio from Fc to CB[7]@Fc, a direct indication of its overall density and uniformity. We have shown that the FcC11S-/C8S-Au prepared by coadsorption in a binary solution with low mole fraction of FcC11SH (5%) and by exchanging preassembled C8S-Au SAM with FcC11SH for a short time (1 min) has the “ideal” structure with isolated and uniformly distributed Fc groups on the surface. In contrast, with similar Fc surface coverage, the FcC11S-/C8S-Au prepared by exchanging FcC11S-Au with C8SH for a prolonged time (20 h) has clustered and nonuniformly distributed Fc groups at the surface. While consistent with previous observations based on conventional electrochemical or microscopic studies, the present finding expands the capability of host–guest chemistry as a new tool to probe the structures of organized molecular assemblies at the nanometer scale

Reborn Three-Dimensional Graphene with Ultrahigh Volumetric Desalination Capacity

The constructing of 3D materials with optimal performance is urgently needed to meet the growing demand of advanced materials in the high-tech sector. A distinctive 3D graphene (3DG) is designed based on a repeated rebirth strategy to obtain a better body and performance after each round of rebirth, as if it is Phoenix Nirvana. The properties of reborn graphene, namely 3DG after Nirvana (NvG), has been dramatically upgraded compared to 3DG, including high density (3.36 times) together with high porosity, as well as better electrical conductivity (1.41 times), mechanical strength (32.4 times), and ultrafast infiltration behavior. These advantages of NvG make it a strong intrinsic motivation for application in capacitive deionization (CDI). Using NvG directly as the CDI electrode, it has an extremely high volumetric capacity of 220 F cm(-3) at 1 A cm(-3) and a maximum salt absorption capacity of 8.02 similar to 9.2 mg cm(-3) (8.9-10.2 times), while the power consumption for adsorption of the same mass of salt is less than a quarter of 3DG. The Phoenix Nirvana-like strategy of manufacturing 3D structures will undoubtedly become the new engine to kick-start the development of innovative carbon materials through an overall performance upgrade

Hormone therapy and Alzheimer disease dementia: New findings from the Cache County Study

Objectives: Observational studies suggest reduced risk of Alzheimer disease (AD) in users of hormone therapy (HT), but trials show higher risk. We examined whether the association of HT with AD varies with timing or type of HT use. Methods: Between 1995 and 2006, the population-based Cache County Study followed 1,768 women who had provided a detailed history on age at menopause and use of HT. During this interval, 176 women developed incident AD. Cox proportional hazard models evaluated the association of HT use with AD, overall and in relation to timing, duration of use, and type (opposed vs unopposed) of HT. Results: Women who used any type of HT within 5 years of menopause had 30% less risk of AD (95% confidence interval 0.49-0.99), especially if use was for 10 or more years. By contrast, AD risk was not reduced among those who had initiated HT 5 or more years after menopause. Instead, rates were increased among those who began opposed estrogen-progestin compounds within the 3 years preceding the Cache County Study baseline (adjusted hazard ratio 1.93; 95% confidence interval 0.94-3.96). This last hazard ratio was similar to the ratio of 2.05 reported in randomized trial participants assigned to opposed HT. Conclusions: Association of HT use and risk of AD may depend on timing of use. Although possibly beneficial if taken during a critical window near menopause, HT (especially opposed compounds) initiated in later life may be associated with increased risk. The relation of AD risk to timing and type of HT deserves further study. © 2012 American Academy of Neurology

Electrochemical Quantification of Intermolecular Hydrogen Bonding between Ferrocenemethanol and 3‑Mercaptopropanoic Acid on Gold

Quantification of the amount of intermolecular hydrogen bonding between ferrocenemethanol and 3-mercaptopropanoic acid on gold was performed by cyclic voltammetry as well as by the finite element simulation, displaying a proof-of-concept that the slight changes of cyclic voltammetry features are used potentially for interpreting the weak molecular interactions. Ferrocenemethanol at a bulk concentration level of 0.5 mM adsorbs on the 3-mercaptopropanoic acid surface by hydrogen bonding, with the fractional surface coverage ranging from 0% to 14% of a monolayer in accordance with the surface coverage of 3-mercaptopropanoic acid which was explored by electrochemical quartz crystal microbalance. The intermolecular hydrogen bonding between ferrocenemethanol and the mercaptopropanoic acid was found to exhibit a Langmuir-type adsorption with the average value of <i>K</i> being 0.24 mM^–1. The intermolecular hydrogen bonding between FcCH₂OH and the artificial self-assembled monolayer (3-mercaptopropanoic acid) is evident, and the study on quantification of intermolecular hydrogen bonding with this artificial model is meaningful for understanding the molecular recognition events involved in the cell membrane

Spontaneous, Straightforward Fabrication of Partially Reduced Graphene Oxide–Polypyrrole Composite Films for Versatile Actuators

A facile one-step approach has been developed to fabricate partially reduced graphene oxide–polypyrrole (prGO-PPy) film <i>via</i> self-oxidation–reduction strategy, in which graphene oxide acts as the oxidant to polymerize pyrrole into PPy leading to the spontaneous partial reduction of GO and cross-linking between prGO and PPy <i>via</i> π–π interaction. With the convenient preparation method, a well controlled designed asymmetric actuator based on GO (or G)/prGO-PPy film with excellent humidity and electrochemical responses has been achieved for versatile stimulated actuations that will also play essential roles in advanced actuators for many important intelligent applications