Ratiometric Near-Infrared Fluorescent Probes Based on Hemicyanine Dyes Bearing Dithioacetal and Formal Residues for pH Detection in Mitochondria

Ratiometric near-infrared fluorescent probes (AH+ and BH+) have been prepared for pH determination in mitochondria by attaching dithioacetal and formal residues onto a hemicyanine dye. The reactive formyl group on probe BH+ allows for retention inside mitochondria as it can react with a protein primary amine residue to form an imine under slightly basic pH 8.0. Probes AH+ and BH+ display ratiometric fluorescent responses to pH changes through the protonation and deprotonaton of a hydroxy group in hemicyanine dyes with experimentally determined pKa values of 6.85 and 6.49, respectively. Calculated pKa values from a variety of theoretical methods indicated that the SMDBONDI method of accounting for solvent and van der Waals radii plus including a water molecule located near the site of protonation produced the closest overall agreement with the experimental values at 7.33 and 6.14 for AH+ and BH+ respectively.

Apocyanine dyes

Cyanine dyes without a methine group or polymethine chain between their two terminal unsaturated heterocycles are called apocyanines. Such colorants which are yellow and red received the labels xantho-apocyanine and erythro-apocyanine dyes, respectively. Nevertheless, from time to time in the literature, the term “apocyanine dyes” is wrongly applied to various N-bridgehead heterocycles. In addition, the phenylogous zeromethine hemicyanine dyes are often incorrectly referred to with the term “apocyanine dyes”. This chapter clarifies the definition of apocyanine, describes how confusion over the term has come about, and points the ways in which it is sometimes incorrectly employed.

A caveat to common hemicyanine dye components and their resolution

Hemicyanine dyes containing typical heterocycles such as 2-indolinium have limited chemo- and photo-stability issues, which can be resolved with a 4-pyridinium derivative that also shows good two-photon imaging capability.

Synthesis of different classes of five/six membered heterocyclic cyanine dyes: A review

In this paper, synthesis of different classes of five/six membered heterocyclic cyanine dyes has been reviewed. In this paper review detailed synthesis steps were represented via equations. The synthesis covers, monomethine cyanine dyes (simple cyanine dyes), dimethine cyanine dyes, trimethine cyanine dyes (carbocyanine dyes), styryl cyanine dyes (hemicyanine dyes), aza-styryl cyanine dyes (aza-hemicyanine dyes and/or aza-cyanine dyes), merocyanine dyes (acyclic merocyanine dyes and cyclic merocyanine dyes) and apocyanine dyes. Besides, in the introduction section of this review paper some light is focused on the uses, applications and properties of cyanine dyes. This review paper is informative, useful and very readable for synthetic dye chemists, researchers and students who look for the different methods in the synthesis and preparation of various classes of five/six membered heterocyclic cyanine dyes with special emphasize in the field of heterocyclic and/or cyanine dyes chemistry. This specific type of collective review in the synthesis of different classes of only five/six membered heterocyclic cyanine dyes has been paid little attention and has great importance in the chemistry literature.