A Turn-On Fluorescent Amino Acid Sensor Reveals Chloroquine's Effect on Cellular Amino Acids via Inhibiting Cathepsin L

Is Cocaine Protonated When it Binds to the Dopamine Transporter?

There has been much controversy about whether the well-known alkaloid and tertiary amine base cocaine (pK a = 8.5) binds to the human dopamine transporter (DAT) in its protonated form. Most potent DAT inhibitors are also strong amines-yet there are some noteworthy examples where neutral cocaine analogues have high affinity, while the quaternary ammonium analog of cocaine, cocaine methiodide, is a comparatively poor inhibitor. In this paper, we show that a fluorescent cocaine analog, with a lower pK a than cocaine, becomes protonated in the DAT binding site and conclude that similar behavior must be expected from cocaine. By determining the pK a of the aspartate residue in DAT believed to interact with the amine of cocaine, we are able to explain the apparently contradictory structure-activity data of cocaine analogues.

Tailoring Chirality and Optimizing Enantioselective Recognition in Strategic Defect Engineering of Chiral Metal-Organic Frameworks

Introducing chiral molecules into metal-organic frameworks (MOFs) to obtain chiral MOFs (CMOFs), the tunability of their structures makes them a highly anticipated class of chiral materials for electrochemical sensing. However, the structure of CMOFs is often limited by synthesis challenges, and introducing chiral molecules into MOFs often leads to a decrease in their internal space. This study introduces a defect engineering strategy into the synthesis of CMOFs to obtain CMOFs with defects, which is an efficient synthesis method. The two CMOFs constructed with different structures not only have more chiral recognition sites but also greatly increase the substrate capacity due to the defects, making them have a wide range of substrates and enhancing the enantioselective recognition effect of the two defective CMOFs. In addition, using MOF as a chiral carrier greatly overcomes the problem of low conductivity of chiral molecules. Based on the advantages of defective CMOFs, we have designed a novel chiral electrochemical sensor with an excellent enantiomer recognition performance. This study provides a simple and scalable synthetic method for constructing CMOFs with defects and high stability.

High-efficiency detection of primary amine-based chiral molecules by a facile aldimine condensation reaction

Detection of chiral molecules in a high-efficiency way is very important to meet the demands for chiral analysis in drug testing, asymmetric synthesis, etc. Herein, we have developed a novel route to realize the rapid determination of concentration and configuration of primary amine-based chiral molecules. An aldehyde functionalized acid & base-sensitive fluorane dye (R-C) was used as the active agent to be reacted with the chiral molecules through an aldimine condensation reaction. After the mixing operation, concentration and configuration of the detected chiral molecule could be facilely read from the UV-vis absorption spectra and CD spectra, respectively.

Imaging Neurotransmitters with Small-Molecule Fluorescent Probes

Neurotransmitters play a crucial role in regulating communication between neurons within the brain and central nervous system. Thus, imaging neurotransmitters has become a high priority in neuroscience. This minireview focuses on recent advancements in the development of fluorescent small-molecule fluorescent probes for neurotransmitter imaging and applications of these probes in neuroscience. Innovative approaches for probe design are highlighted as well as attributes which are necessary for practical utility, with a view to inspiring new probe development capable of visualizing neurotransmitters.

Chemical and linguistic considerations for encoding Chinese characters: an embodiment using chain-end degradable sequence-defined oligourethanes created by consecutive solid phase click chemistry

Sequence-defined polymers (SDPs) are currently being investigated for use as information storage media. As the number of monomers in the SDPs increases, with a corresponding increase in mathematical base, the use of tandem-MS for de novo sequencing becomes more challenging. In contrast, chain-end degradation routines are truly de novo, potentially allowing very large mathematical bases for encoding. While alphabetic scripts have a few dozen symbols, logographic scripts, such as Chinese, can have several thousand symbols. Using a new in situ consecutive click reaction approach on an oligourethane backbone for writing, and a previously reported chain-end degradation routine for reading, we encoded/decoded a confucius proverb written in Chinese characters using two encoding schemes: Unicode and Zhèng Mă. Unicode is an internationally standardized arbitrary string of hexadecimal (base-16) symbols which efficiently encodes uniquely identifiable symbols but requires complete fidelity of transmission, or context-based inferential strategies to be interpreted. The Zhèng Mă approach encodes with a base-26 system using the visual characteristics and internal composition of Chinese characters themselves, which leads to greater ambiguity of encoded strings, but more robust retrievability of information from partial or corrupted encodings. The application of information-encoded oligourethanes to two different encoding systems allowed us to establish their flexibility and versatility for data storage. We found the oligourethanes immensely adaptable to both encoding schemes for Chinese characters, and we highlight the expected tradeoff between the efficiency and uniqueness of Unicode encoding on the one hand, and the fidelity to a scripts' particular visual characteristics on the other.

Synthesis of a Near-Infrared Fluorescent Probe for Imaging Catecholamines via a Tandem Nucleophilic Aromatic Substitution

A near-infrared (NIR) fluorescent probe NS667 was developed using a novel synthetic strategy by integrating an electron-rich 1,2,3,4-tetrahydroquinoxaline (THQ) into the scaffold from NS510, which binds to catecholamines with high affinity. The fluorophore core was constructed with a tandem nucleophilic aromatic substitution. Upon binding to catecholamines, the fluorescence of this probe shifted, with the emission in the NIR region. Live cell imaging results demonstrate that NS667 can effectively image norepinephrine in chromaffin cells with shifted fluorescence, which highlights the potential of the probe for neuroimaging in tissues.

Colorimetric Sensor Based on the Oxidase-Mimic Supramolecular Catalyst for Selective and Sensitive Biomolecular Detection

We have engineered a colorimetric sensor capable of selective and sensitive detection of amino acids. This sensor employs a supramolecular copper-dependent oxidase mimic as the probe, stemming from our prior research. The oxidase mimic is constructed through the self-assembly of commercially available guanosine monophosphate (GMP), Fmoc-lysine, and Cu2+. It catalyzes the formation of a red product with a maximum absorbance at 510 nm. The changes in color and absorbance are responsive to both the concentrations and types of amino acids present. This effect is most pronounced in the presence of histidine, with a detection limit (LOD) of 6.4 nM. Furthermore, the catalytic probe can distinguish histidine from histamine and imidazole propionate, as well as 1-methyl-histidine from 3-methyl-histidine, based on their distinct coordination capacities with copper. This underscores the high selectivity of the sensing platform. Both theoretical simulations and experimental results (including UV-vis spectra, fluorescence, and EPR) indicate that the amino acids may engage in copper center coordination, thereby impeding O2 access to copper─a pivotal aspect of the oxidase catalysis. This sensing platform, characteristic of its swift response, simple fabrication, and exceptional sensitivity and selectivity, can also be applied to detect other biological analytes such as nucleotides. It holds potential for use in environmental and biochemical analyses.