There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

9.2. Protein-Based Hg(II) Detectors 3467 9.3. Oligonucleotide-Based Hg(II) Detector 3467 9.4. DNAzyme-Based Hg(II) Detectors 3469 9.5. Antibody-Based Hg(II) Detector 3469 10. Mercury Detectors Based on Materials 3469 10.1. Soluble and Fluorescent Polymers 3469 10.2. Membranes, Films, and Fibers 3471 10.3. Micelles 3473 10.4. Nanoparticles 3473 11. Perspectives 3474 12. Addendum 3475 12.1. Small Molecules 3475 12.2. Biomolecules 3477 12.3. Materials 3477 13. List of Abbreviations 3477 14. Acknowledgments 3478 15. References 3478

Tools and tactics for the optical detection of mercuric ion.

Azobenzene undergoes trans → cisisomerization when irradiated with light tuned to an appropriate wavelength. The reverse cis →transisomerization can be driven by light or occurs thermally in the dark. Azobenzene's photochromatic properties make it an ideal component of numerous molecular devices and functional materials. Despite the abundance of application-driven research, azobenzene photochemistry and the isomerization mechanism remain topics of investigation. Additional substituents on the azobenzene ring system change the spectroscopic properties and isomerization mechanism. This critical review details the studies completed to date on the 3 main classes of azobenzene derivatives. Understanding the differences in photochemistry, which originate from substitution, is imperative in exploiting azobenzene in the desired applications.

Photoisomerization in different classes of azobenzene

Yuming Yang,†,§ Qiang Zhao,‡,§ Wei Feng,† and Fuyou Li*,† †Department of Chemistry and State Key Laboratory of Molecular Engineering of Polymers and Institutes of Biomedical Sciences, Fudan University, Shanghai 200433, P. R. China ‡Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, Nanjing 210046, P. R. China.

Luminescent chemodosimeters for bioimaging.

Two new fluorescent sensors for Zn2+ that utilize fluorescein as a reporting group, Zinpyr-1 and Zinpyr-2, have been synthesized and characterized. Zinpyr-1 is prepared in one step via a Mannich reaction, and Zinpyr-2 is obtained in a multistep synthesis that utilizes 4‘,5‘-fluorescein dicarboxaldehyde as a key intermediate. Both Zinpyr sensors have excitation and emission wavelengths in the visible range (∼500 nm), dissociation constants (Kd1) for Zn2+ of <1 nM, quantum yields approaching unity (Φ = ∼0.9), and cell permeability, making them well-suited for intracellular applications. A 3- to 5-fold fluorescent enhancement is observed under simulated physiological conditions corresponding to the binding of the Zn2+ cation to the sensor, which inhibits a photoinduced electron transfer (PET) quenching pathway. The X-ray crystal structure of a 2:1 Zn2+:Zinpyr-1 complex has also been solved, and is the first structurally characterized example of a complex of fluorescein substituted with metal binding ligands.

/pdf/fluorescent-sensors-for-zn2-based-on-a-fluorescein-platform-4zf923v7ks.pdf

Fluorescent Sensors for Zn2+ Based on a Fluorescein Platform: Synthesis, Properties and Intracellular Distribution

Although Zn2+ is abundant in eukaryotes and most is tightly bound, pools of chelatable Zn 2+ have been imaged in living cells with concentrations ranging from sub-nM in undifferentiated mammalian cells 10 to ∼0.3 mM in hippocampal nerve synaptic vesicles. 11 Currently, the most widely applied probes for cellular zinc are aryl sulfonamides of 8-aminoquinoline such as 6-methoxy-(8-p-toluenesulfonamido)quinoline (TSQ), 12 Zinquin4,13 and TFLZn11 (TSQ analogues). The distinction between chelatable and free Zn2+ is problematic due to the fact that these quinolinebased dyes can form mixed complexes, sensing Zn 2+ that is already partially coordinated. Recent studies have clarified some of the details regarding the aqueous Zn 2+-binding equilibria of such dyes, enhancing their value as quantitative probes. 14 Quinoline probes require ultraviolet excitation ( ∼350 nm), however, which can be damaging to cells, and have relatively dim fluorescence with quantum yields ≈ 0.1 and extinction coefficients ≈ 10 × 103 M-1 cm-1.15 Because the availability of better Zn 2+-specific probes would provide additional insight into the cell biology of Zn 2+, interest in the field remains high. Several fluorescent sensors for Zn 2+

/pdf/a-new-cell-permeable-fluorescent-probe-for-zn2-k73u7n5m2u.pdf

A New Cell-Permeable Fluorescent Probe for Zn2+

A second-generation fluorescent sensor for Zn2+ from the Zinpyr family, ZP4, has been synthesized and characterized. ZP4 (Zinpyr-4, 9-(o-carboxyphenyl)-2-chloro-5-[2-{bis(2-pyridylmethyl)aminomethyl}-N-methylaniline]-6-hydroxy-3-xanthanone) is prepared via a convergent synthetic strategy developed from previous studies with these compounds. ZP4, like its predecessors, has excitation and emission wavelengths in the visible range (∼500 nm), a dissociation constant (Kd) for Zn2+ of less than 1 nM and a high quantum yields (Φ = ∼0.4), making it well suited for biological applications. A 5-fold fluorescent enhancement is observed under simulated physiological conditions corresponding to the binding of the Zn2+ cation to the sensor, which inhibits a photoinduced electron transfer (PET) quenching pathway. The metal-binding stereochemistry of ZP4 was evaluated through the synthesis and X-ray structural characterization of [M(BPAMP)(H2O)n]+ complexes, where BPAMP is [2-{bis(2-pyridylmethyl)aminomethyl}-N-methylani...

ZP4, an Improved Neuronal Zn2+ Sensor of the Zinpyr Family

Metalloneurochemistry is the study of metal ion function in the brain and nervous system at the molecular level. Research in this area is exemplified through discussion of several forefront areas where significant progress has been made in recent years. The structure and function of ion channels have been elucidated through high-resolution x-ray structural work on the bacterial K+ ion channel. Selection of potassium over sodium ions is achieved by taking advantage of key principles of coordination chemistry. The role of calcium ions in neuronal signal transduction is effected by several Ca2+-binding protein such as calmodulin, calcineurin, and synaptotagmin. Structural changes in response to calcium ion concentrations allow these proteins to function in memory formation and other neurochemical roles. Metallochaperones help to achieve metal ion homeostasis and thus prevent neurological diseases because of metal ion imbalance. Much detailed chemical information about these systems has become available recently. Zinc is another important metal ion in neuroscience. Its concentration in brain is in part controlled by metallothionein, and zinc is released in the hippocampus at glutamatergic synapses. New fluorescent sensors have become available to help track such zinc release.

https://www.pnas.org/content/pnas/100/7/3605.full.pdf

Shawn C. Burdette

Papers

Photoisomerization in different classes of azobenzene

Fluorescent Sensors for Zn2+ Based on a Fluorescein Platform: Synthesis, Properties and Intracellular Distribution

A New Cell-Permeable Fluorescent Probe for Zn2+

ZP4, an Improved Neuronal Zn2+ Sensor of the Zinpyr Family

Meeting of the minds: Metalloneurochemistry