23 research outputs found
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
Diagnosed Depression Among Medicare Home Health Patients: National Prevalence Estimates and Key Characteristics
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
Carbon Dots Derived from Citric Acid and Glutathione as a Highly Efficient Intracellular Reactive Oxygen Species Scavenger for Alleviating the Lipopolysaccharide-Induced Inflammation in Macrophages
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<sup>–1</sup>. The intermolecular hydrogen bonding between FcCH<sub>2</sub>OH
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