Fe(III)-Based Fluorescent Probe for High-Performance Recognition, Test Strip Analysis, and Cell Imaging of Carbon Monoxide.

Fluorescence sensing and imaging techniques are being widely studied for detecting carbon monoxide (CO) in living organisms due to their speed, sensitivity, and ease of use to biological systems. Most fluorescent probes used for this purpose are based on heavy metal ions like Pd, with a few using elements like Ru, Rh, Ir, Os, Tb, and Eu. However, these metals can be expensive and toxic to cells. There is a need for more affordable and biologically safe fluorescent probes for CO detection. Drawing inspiration from the robust affinity exhibited by heme iron toward CO, in this work, a rhodamine derivative called RBF was developed for imaging CO in living cells by binding to Fe(III) and could be used for CO sensing. A Fe(III)-based fluorescent probe for CO imaging in living cells offers advantages of cost effectiveness, low toxicity, and ease of use. The fluorescence detection using the RBF-Fe system showed a direct correlation with increasing levels of CORM-3 (LOD = 146 nM) or the exposure time of CO gas, displaying reduced fluorescence. A CO test paper based on RBF-Fe was created for simple on-site CO detection, where fluorescence would diminish in response to CO exposure, allowing rapid (2 min) visual identification. Imaging of CO in living cells was successfully conducted using the probe system, showing a decrease in fluorescence intensity as CORM-3 concentrations increased, indicating its effectiveness in monitoring CO levels accurately within living cells.

Photoisomerization and thermal reconstruction induced supramolecular chirality inversion in nanofiber determined by minority isomer.

Here, amphiphile GCH based on glutamide-cyanostilbene is designed and synthesized, it is found that it can assembly in acetonitrile, and shows circular dichroism signals. After Z-E isomerizaition by UV irradiation, the CD signal of the assembly can be inverted. Unexpectedly, after another heating and cooling process, the circular dichroism signals can be totally inverted even though the E-isomers are in minority. Finally, the molecular dynamics (MD) simulations deeply elucidate the supramolecuar chirality inversion mechanism. This work brings some new insights into the control of chirality inversion, which may provide a perspective for the smart chiroptical materials construction.

Living Self-Assembly of Metastable and Stable Two-Dimensional Platelets from a Single Small Molecule.

This study reports the design of a donor-acceptor (D-A) molecule with two fluorene units on each side of a benzothiadiazole moiety, which allows multiple intermolecular interactions to compete with one another so as to induce the evolution of the metastable 2D platelets to the stable 2D platelets during the self-assembly of the D-A molecule. Importantly, the living seeded self-assembly of metastable and stable 2D structures with precisely controlled sizes can be conveniently achieved using an appropriate supersaturated level of a solution of the D-A molecule as the seeded growth medium that can temporarily hold the almost-proceeding spontaneous nucleation from competing with the seeded growth. The stable 2D platelets with smaller area sizes exhibit higher sensitivity to gaseous dimethyl sulfide, illustrating that the novel living self-assembly method provides more available functional structures with controlled sizes for practical applications. The key finding of this study is that the new living methodology is separated into two independent processes: the elaborate molecular design for various crystalline structures as seeds and the application of a supersaturated solution with appropriate levels as the growth medium to grow the uniform structures with controlled sizes; this would make convenient and possible the living seeded self-assembly of rich 1D, 2D, and 3D architectures.

Emergent Photostability Synchronization in Coassembled Array Members for the Steady Multiple Discrimination of Explosives.

The design of sensor array members with synchronous fluorescence and photostability is crucial to the reliable performance of sensor arrays in multiple detections and their service life. Herein, a strategy is reported for achieving synchronous fluorescence and photostability on two coassemblies fabricated from carbazole-based energy donor hosts and a photostable energy acceptor. When a small number of the same energy acceptors are embedded into two carbazole-based energy donor hosts, the excitation energy of the donors can be efficiently harvested by the acceptors through long-range exciton migration and Förster resonance energy transfer (FRET) to achieve synchronous fluorescence and photostability in both coassemblies. More intriguingly, the synchronous photostability substantially improves the multiple discrimination capacity (e.g., 10 times more discriminations of TNT in two coassemblies have been achieved compared to the sensor array comprising two individual donor assemblies) and the working lifetime of the sensor array. The concept of optical synchronization (i.e., emission and photostability) of sensor array members can be extended to other sensor arrays for the steady multiple detection of certain hazardous chemicals.

Development of a Fluorophore with Enhanced Unorthodox Chalcogen Bonding for Highly Sensitive Detection of Trimethyl Arsine Vapor.

In this work, we report the design of novel fluorophores that bear three benzothiadiazole and benzoselenadiazole groups, respectively, for sensitive detection of trimethyl arsine vapor. In particular, the fluorophore with the benzoselenadiazole groups can form stronger chalcogen bonding with trimethyl arsine than the fluorophore with the benzothiadiazole groups, which in turn triggers much faster and more sensitive fluorescence responses. On the basis of this novel mechanism, fluorescence detection of trimethyl arsine vapor with rapid response (∼3 s), high sensitivity (the theoretical LOD is 0.44 ppb), and high selectivity is achieved on bundled nanofibers from the fluorophore with the benzoselenadiazole groups. Here, the new fluorescence sensor may find wide applications in health and environmental monitoring, arsenic distribution recognition in soil, and arsenic mines exploration.

Highly Photostable and Luminescent Donor-Acceptor Molecules for Ultrasensitive Detection of Sulfur Mustard.

Real-time, high signal intensity, and prolonged detection is challenging because of the rarity of fluorophores with both high photostability and luminescence efficiency. In this work, new donor-acceptor (D-A) molecules for overcoming these limitations are reported. A hybridized local and an intramolecular charge-transfer excited state is demonstrated to afford high photoluminescence efficiency of these D-A molecules in solution (≈100%). The twisted molecular structure and bulky alkyl chains effectively suppress π-π and dipole-dipole interactions, enabling high luminescence efficiency of 1 and 2 in the solid state (≈94% and 100%). Furthermore, two D-A aggregates exhibit high photostability as evidenced by 4% and 8% of the fluorescence decreasing after 6 h of continuous irradiation in air, which is in sharp contrast to ≈95% of fluorescence decreasing in a reference compound. Importantly, with these molecules, ultrasensitive detection of sulfur mustard (SM) with a record limit of 10 ppb and selective detection of SM in complex matrices are achieved.

Long-Range Exciton Migration in Coassemblies: Achieving High Photostability without Disrupting the Electron Donation of Fluorene Oligomers.

In this work, photostable coassemblies from a nonphotostable fluorene oligomer (the energy donor) and a photostable oligomer (the energy acceptor) are fabricated. Long-range exciton migration over a net distance of about 370 energy-donor molecules to energy acceptors is demonstrated in such coassemblies. The fast and long energy migration allows harvesting of the excitation energy of energy donors by embedding a small number of energy acceptors for photostability enhancement. Importantly, embedding a small number of energy acceptors in coassemblies causes a negligible negative influence on the electron donation of energy donors that are desired in practical applications. The advantages of the coassemblies fabricated, that is, high photostability without disrupting the electron donation of energy donors, are well illustrated in fluorescence detection of trace explosives where prolonged working life and improved detection capacity are achieved.

Universal Strategy for Improving the Sensitivity of Detecting Volatile Organic Compounds by Patterned Arrays.

The diffusion of target analytes is a determining factor for the sensitivity of a given gas sensor. Surface adsorption results in a low-concentration region near the sensor surface, producing a concentration gradient perpendicular to the surface, and drives a net flux of molecules toward solid reactive reagents on the sensor surface, that is, vertical diffusion. Here, organic semiconductor supramolecules were patterned into micromeshed arrays to integrate vertical and horizontal diffusion pathways. When used as a gas sensor, these arrays have an order of magnitude higher sensitivity than traditional film-based sensors. The sensor sensitivity ramp down with the increase in coverage density of reactive reagents, yielding two linear regions demarcated by 0.3 coverage, which are identified by the experimental results and simulations. The universal nature of template-assisted patterning allows adjustments in the composition, size, and shape of the constituent material, including nanofibers, nanoparticles, and molecules, and thus serves to improve the sensitivity of gas sensors for detecting various volatile organic compounds.

Highly Selective Detection of Benzene, Toluene, and Xylene Hydrocarbons Using Coassembled Microsheets with Förster Resonance Energy Transfer-Enhanced Photostability.

In this work, highly photostable and fluorescent coassembled microsheets were fabricated from molecules 1 and 2 for sensitive and selective detection of BTX. We demonstrate that Förster resonance energy transfer (FRET) from nonphotostable 1 to photostable 2 gives rise to the high photostability of 1-2 coassembled microsheets. Furthermore, the combined properties of 1 and 2 components in coassembled microsheets allow distinct responses to BTX and other VOC vapors and thereby yield highly sensitive and selective detection of BTX hydrocarbons via FRET. These findings provide a new approach for the development of photostable fluorescence sensors for hazardous chemicals.

Asymmetric Fluorination of α-Branched Aldehydes by Chiral Primary Amine Catalysis: Reagent-Controlled Enantioselectivity Switch.

Asymmetric fluorination of α-branched aldehydes catalyzed by chiral primary amines under mild conditions has been developed. Both enantiomers could be obtained with good yields (up to 96%) and a high enantioselectivity (up to 90% ee) by a simple swap of the fluorination reagents.

Groundwater Microbial Communities Along a Generalized Flowpath in Nomhon Area, Qaidam Basin, China.

Spatial distribution (horizonal and vertical) of groundwater microbial communities and the hydrogeochemistry in confined aquifers were studied approximately along the groundwater flow path from coteau to plain in the Nomhon area, Qinghai-Tibet plateau, China. The confined groundwater samples at different depths and locations were collected in three boreholes through a hydrogeological section in this arid and semi-arid area. The phylogenetic analysis of 16S rRNA genes and multivariate statistical analysis were used to elucidate similarities and differences between groundwater microbial communities and hydrogeochemical properties. The integrated isotopic geochemical measurements were applied to estimate the source and recharge characteristics of groundwater. The results showed that groundwater varied from fresh to saline water, and modern water to ancient water following the flowpath. The recharge characteristics of the saline water was distinct with that of fresh water. Cell abundance did not vary greatly along the hydrogeochemical zonality; however, dissimilarities in habitat-based microbial community structures were evident, changing from Betaproteobacteria in the apex of alluvial fan to Gammaproteobacteria and then to Epsilonproteobacteria in the core of the basin (alluvial-lacustrine plain). Rhodoferax, Hydrogenophaga, Pseudomonas, and bacterium isolated from similar habitats unevenly thrived in the spatially distinct fresh water environments, while Sulfurimonas dominanted in the saline water environment. The microbial communities presented likely reflected to the hydrogeochemical similarities and zonalities along groundwater flowpath.

Catalytic Asymmetric Mannich Reaction with N-Carbamoyl Imine Surrogates of Formaldehyde and Glyoxylate.

N,O-acetals (NOAcs) were developed as bench stable surrogates for N-carbamoyl, (Boc, Cbz and Fmoc) formaldehyde and glyoxylate imines in asymmetric Mannich reactions. The NOAcs can be directly utilized in the chiral primary amine catalyzed Mannich reactions of both acyclic and cyclic ß-ketocarbonyls with high yields and excellent stereoselectivity. The current reaction offers a straightforward approach in the asymmetric synthesis of α- or ß-amino carbonyls bearing chiral quaternary centers in a practical and highly stereocontrolled manner.