Ab initio X‐ray structural characterization of an inclusion compound with a compositionally disordered chiral guest: no prior knowledge of the crystal composition

The crystal structure and absolute configuration of a molecular host/guest/impurity inclusion complex were established unequivocally in spite of our having no prior knowledge of its chemical composition. The host (4R,5R)‐4,5‐bis(hydroxydiphenylmethyl)‐2,2‐dimethyl‐1,3‐dioxolane, (I), displays expected conformational features. The crystal‐disordered chiral guest 4,4a,5,6,7,8‐hexahydronaphthalen‐2(3H)‐one, (II), is present in the crystal 85.1 (4)% of the time. It shares a common site with 4a‐hydroperoxymethyl‐4,4a,5,6,7,8‐hexahydronaphthalen‐2(3H)‐one, (III), present 14.9 (4)% of the time, which is the product of autoxidation of (II). This minor peroxide impurity was isolated, and the results of nuclear magnetic resonance, mass spectrometry, and X‐ray fluorescence studies are consistent with the proposed structure of (III). The complete structure was therefore determined to be (4R,5R)‐4,5‐bis(hydroxydiphenylmethyl)‐2,2‐dimethyl‐1,3‐dioxolane–4,4a,5,6,7,8‐hexahydronaphthalen‐2(3H)‐one–4a‐hydroperoxymethyl‐4,4a,5,6,7,8‐hexahydronaphthalen‐2(3H)‐one (1/0.85/0.15), C₃₁H₃₀O₄·0.85C₁₀H₁₄O·0.15C₁₀H₁₄O₃, (IV). There are host–host, host–guest, and host–impurity hydrogen‐bonding interactions of types S and D in the solid state. We believe that the crystals of (IV) were originally prepared to establish the chirality of the guest (II) by means of X‐ray diffraction analysis of host/guest crystals obtained in the course of chiral resolution during cocrystallization of (II) with (I). In spite of the absence of `heavy' elements, the absolute configurations of all anomeric centres in the structure are assigned as R based on resonant scattering effects.     

Photochemically-Driven CO2 Release Using a Metastable-State Photoacid for Energy Efficient Direct Air Capture

One of the grand challenges underlying current direct air capture (DAC) technologies relates to the intensive energy cost for sorbent regeneration and CO₂ release, making the massive scale (GtCO₂/year) deployment required to have a positive impact on climate change economically unfeasible. This challenge underscores the critical need to develop new DAC processes with substantially reduced regeneration energies. Here, we report a photochemically-driven approach for CO₂ release by exploiting the unique properties of an indazole metastable-state photoacid (mPAH). Our measurements on simulated and amino acid-based DAC systems revealed the potential of mPAH to be used for CO₂ release cycles by regulating pH changes and associated isomers driven by light. Upon irradiating with moderate intensity light, a ≈55 % and ≈68 % to ≈78 % conversion of total inorganic carbon to CO₂ was found for the simulated and amino acid-based DAC systems, respectively. Our results confirm the feasibility of on-demand CO₂ release under ambient conditions using light instead of heat, thereby providing an energy efficient pathway for the regeneration of DAC sorbents.     

Phase Separation of DNA-Encoded Artificial Cells Boosts Signal Amplification for Biosensing

Life-like hierarchical architecture shows great potential for advancing intelligent biosensing, but modular expansion of its sensitivity and functionality remains a challenge. Drawing inspiration from intracellular liquid-liquid phase separation, we discovered that a DNA-encoded artificial cell with a liquid core (LAC) can enhance peroxidase-like activity of Hemin and its DNA G-quadruplex aptamer complex (DGAH) without substrate-selectivity, unlike its gelled core (GAC) counterpart. The LAC is easily engineered as an ultrasensitive biosensing system, benefiting from DNA′s high programmability and unique signal amplification capability mediated by liquid-liquid phase separation. As proof of concept, its versatility was successfully demonstrated by coupling with two molecular recognition elements to monitor tumor-related microRNA and profile cancer cell phenotypes. This scalable design philosophy offers new insights into the design of next generation of artificial cells-based biosensors.     

Optimization of electrochemical aptamer-based sensors via optimization of probe packing density and surface chemistry

Electrochemical, aptamer-based (E-AB) sensors, which are comprised of an electrode modified with surface immobilized, redox-tagged DNA aptamers, have emerged as a promising new biosensor platform. In order to further improve this technology we have systematically studied the effects of probe (aptamer) packing density, the AC frequency used to interrogate the sensor, and the nature of the self-assembled monolayer (SAM) used to passivate the electrode on the performance of representative E-AB sensors directed against the small molecule cocaine and the protein thrombin. We find that, by controlling the concentration of aptamer employed during sensor fabrication, we can control the density of probe DNA molecules on the electrode surface over an order of magnitude range. Over this range, the gain of the cocaine sensor varies from 60% to 200%, with maximum gain observed near the lowest probe densities. In contrast, over a similar range, the signal change of the thrombin sensor varies from 16% to 42% and optimal signaling is observed at intermediate densities. Above cut-offs at low hertz frequencies, neither sensor displays any significant dependence on the frequency of the alternating potential employed in their interrogation. Finally, we find that E-AB signal gain is sensitive to the nature of the alkanethiol SAM employed to passivate the interrogating electrode; while thinner SAMs lead to higher absolute sensor currents, reducing the length of the SAM from 6-carbons to 2-carbons reduces the observed signal gain of our cocaine sensor 10-fold. We demonstrate that fabrication and operational parameters can be varied to achieve optimal sensor performance and that these can serve as a basic outline for future sensor fabrication.     

Cooperative calcium phosphate nucleation within collagen fibrils

Although "chaperone molecules" rich in negatively charged residues (i.e., glutamic and aspartic acid) are known to play important roles in the biomineralization process, the precise mechanism by which type I collagen acquires intrafibrillar mineral via these chaperone molecules remains unknown. This study demonstrates a mechanism of cooperative nucleation in which three key components (collagen, chaperone molecules, and Ca(2+) and PO(4)(3-)) interact simultaneously. The mineralization of collagen under conditions in which collagen was exposed to pAsp, Ca(2+), and PO(4)(3-) simultaneously or pretreated with the chaperone molecule (in this case, poly(aspartic acid)) before any exposure to the mineralizing solution was compared to deduce the mineralization mechanism. Depending on the exact conditions, intrafibrillar mineral formation could be reduced or even eliminated through pretreatment with the chaperone molecule. Through the use of a fluorescently tagged polymer, it was determined that the adsorption of the chaperone molecule to the collagen surface retarded further adsorption of subsequent molecules, explaining the reduced mineralization rate in pretreated samples. This finding is significant because it indicates that chaperone molecules must interact simultaneously with the ions in solution and collagen for biomimetic mineralization to occur and that the rate of mineralization is highly dependent upon the interaction of collagen with its environment.     

A Pd/C‐CeO2 Anode Catalyst for High‐Performance Platinum‐Free Anion Exchange Membrane Fuel Cells

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM‐FCs). The anion exchange membrane fuel cell (AEM‐FC) has long been proposed as a solution as non‐Pt metals may be employed. Despite this, few examples of Pt‐free AEM‐FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt‐free AEM‐FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt‐free AEM‐FC that employs a mixed carbon‐CeO₂ supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM‐FC tests run on dry H₂ and pure air show peak power densities of more than 500 mW cm^?2.     

A Study on Relationship Between Gas Chromatographic Retention Value and Atomic Hydrophobic Parameters

A study on relationship between molecular structure and chromatographic retention values for realizing the identification and prediction of chromatographic retention values has been the major task of chromatographic thermodynamics. In 1964, Prof. Lu Peizhang established the relationship between molecular structural parameters and chromatographic retention values in gas-liquid chromatography by using statistical thermodynamical methods. Based on his work, some Chinese researchers have performed the prediction of chromatographic retention values.     

Stereochemical Definition of the Natural Product (6R,10R,13R, 14R,16R,17R,19S,20S,21R,24S,25S,28S,30S,32R,33R,34R,36S,37S,39R)‐Azaspiracid‐3 by Total Synthesis and Comparative Analyses

The previously accepted structure of the marine toxin azaspiracid‐3 is revised based upon an original convergent and stereoselective total synthesis of the natural product. The development of a structural revision hypothesis, its testing, and corroboration are reported. Synthetic (6R,10R,13R,14R,16R,17R,19S,20S,21R,24S,25S,28S,30S,32R, 33R,34R,36S,37S,39R)‐azaspiracid‐3 chromatographically and spectroscopically matched naturally occurring azaspiracid‐3, whereas the previously assigned 20R epimer did not.