Recent Advances in Supramolecular Analytical Chemistry Using Optical Sensing.

Mono- and di-quaternized 4,4'-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4'-bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium- and environment-responsive 4,4'-bipyridine derivatives. Two important classes of 4,4'-bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N,N'-disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4'-bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure-property relations are discussed in connection to the role of these derivatives in various novel applications.

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Mono- and Di-Quaternized 4,4'-Bipyridine Derivatives as Key Building Blocks for Medium- and Environment-Responsive Compounds and Materials

Synthesis and Applications of Boronic Acid-Containing Polymers: From Materials to Medicine.

Catalytic enantioselective allylation of carbonyl compounds and imines.

The reversible boronic acid–diol interaction empowers boronic acid receptors' saccharide binding capacities, rendering them a class of lectin mimetic, termed “boronlectins”. Boronic acids follow lectin functions not just in being able to bind saccharides, but in multivalent saccharide binding that enhances both affinity and selectivity. For almost a decade, efforts have been made to achieve and improve selectivity for given saccharide targets, most notably glucose, by using properly positioned boronic acids, offering multivalent interactions. Incorporation of several boronic acid groups into a covalent framework or non-covalent assembly of boronic acid are two general methods used to create such smart sensors, of which the latter resembles lectin oligomerisation that affords multivalent saccharide-binding architectures. In this review, we discuss supramolecular selective sensing of saccharides by using simple boronic acids in their aggregate forms, after a brief survey of the general aspects of boronic acid-based saccharide sensing.

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Selective sensing of saccharides using simple boronic acids and their aggregates

Several novel diboronic acid-substituted bipyridinium salts were prepared and, using a fluorescent reporter dye, were tested for their ability to selectively bind various monosaccharides and α-hydroxycarboxylates in an aqueous medium. The fluorescence sensing mechanism relies on the formation of a ground-state charge-transfer complex between the dye and bipyridinium. An X-ray crystal structure of this complex is described herein. Glucose selectivity over fructose and galactose was achieved by designing the bipyridinium-based receptors to be capable of attaining a 1:1 receptor/substrate stoichiometry via cooperative diboronic acid binding.

Boronic Acid-Based Bipyridinium Salts as Tunable Receptors for Monosaccharides and α-Hydroxycarboxylates

We report a simple, efficient, and general method for the indium-mediated enantioselective propargylation of aromatic and aliphatic aldehydes under Barbier-type conditions in a one-pot synthesis affording the corresponding chiral alcohol products in very good yield (up to 90%) and enantiomeric excess (up to 95%) The extension of this methodology to ketones demonstrated the need for electrophilic ketones more reactive than acetophenone as the reaction would not proceed with just acetophenone Using the Lewis acid indium triflate [In(OTf)(3)] induced regioselective formation of the corresponding homoallenic alcohol product from acetophenone However, this methodology demonstrated excellent chemoselectivity in formation of only the corresponding secondary homopropargylic alcohol product in the presence of a ketone functionality Investigation of the organoindium intermediates under our reaction conditions shows the formation of allenylindium species, and we suggest that these species contain an indium(III) center In addition, we have observed the presence of a shiny, indium(0) nugget throughout the reaction, irrespective of the stoichiometry, indicating disproportionation of indium halide byproduct formed during the reaction

Indium-mediated asymmetric Barbier-type propargylations: additions to aldehydes and ketones and mechanistic investigation of the organoindium reagents

Asymmetric indium-mediated synthesis of homopropargylic alcohols

The anionic fluorescent dye, aminopyrene trisulfonic acid (APTS), was synthesized and used in a solution-based two-component glucose-sensing system comprising the dye and a boronic acid-appended viologen. The fluorescence of the dye was quenched in the presence of the viologen and the fluorescence restored upon glucose addition. An important feature of this fluorophore is that it can be covalently bonded to a polymer through the amine group without a significant effect on optical properties. Two APTS derivatives, functionalized with polymerizable groups, were synthesized and immobilized in hydroxyethyl methacrylate (HEMA)-based hydrogels. The latter were used to continuously monitor glucose. The fluorescence signal modulation, signal stability, reversibility, reproducibility, and pH sensitivity of the hydrogels were evaluated. The APTS dyes described herein are insensitive to pH changes within the physiological range, both in solution and when immobilized in a hydrogel. When APTS is used in conjunction with boronic acid-appended viologens to sense glucose, the system displays some pH sensitivity because of the presence of the boronic acid.

Exploring the use of APTS as a fluorescent reporter dye for continuous glucose sensing.

Enantioselective alkynyl zinc additions to aromatic and aliphatic aldehydes have been studied using terpene derived chiral amino alcohol ligands. The limonene derived amino alcohol (1 R ,2 R ,5 S )-2-methyl-5-(1-methylethenyl)-2-(1-pyrrolidinyl)cyclohexanol gave the most promising results. Chiral propargylic alcohols were obtained in good yields and moderate enantioselectivities (up to 60%).

Lacie C. Hirayama

Papers

Boronic Acid-Based Bipyridinium Salts as Tunable Receptors for Monosaccharides and α-Hydroxycarboxylates

Indium-mediated asymmetric Barbier-type propargylations: additions to aldehydes and ketones and mechanistic investigation of the organoindium reagents

Asymmetric indium-mediated synthesis of homopropargylic alcohols

Exploring the use of APTS as a fluorescent reporter dye for continuous glucose sensing.

Enantioselective alkynylations of aromatic and aliphatic aldehydes catalyzed by terpene derived chiral amino alcohols