2 research outputs found
New Molecular Motif for Recognizing Sialic Acid Using Emissive Lanthanide–Macrocyclic Polyazacarboxylate Complexes: Deprotonation of a Coordinated Water Molecule Controls Specific Binding
A new
molecular motiflanthanide–macrocyclic polyazacarboxylate
hexadentate complexes, Ln<sup>3+</sup>-ABNOTAî—¸was found to
specifically bind to sialic acid with strong emission enhancement
and high affinity. The selectivity toward sialic acid over other monosaccharides
was one of the highest among artificial receptors. Also, the novel
binding mechanism was investigated in detail; binding selectivity
is controlled by interactions between sialic acid and both the central
metal and a hydroxyl group produced by deprotonation of a coordinated
water molecule in the Ln<sup>3+</sup> complex
Molecular Design of Boronic Acid-Functionalized Squarylium Cyanine Dyes for Multiple Discriminant Analysis of Sialic Acid in Biological Samples: Selectivity toward Monosaccharides Controlled by Different Alkyl Side Chain Lengths
We designed a new series of boronic
acid-functionalized squarylium
cyanine dyes (SQ-BA) with different lengths of alkyl chain residues,
suitable for multiple discriminant analysis (MDA) of sialic acid (Neu5Ac)
in biological samples. The SQ-BA dyes form aggregates based on hydrophobic
interactions, which result in quenched fluorescence in aqueous solutions.
When the boronic acid binds with saccharides, the fluorescence intensity
increases as a result of dissociation to the emissive monomeric complex.
We inferred that different dye aggregate structures (<i>H</i>-aggregates and <i>J</i>-aggregates) were induced depending
on the alkyl chain length, so that monosaccharides would be recognized
in different ways (especially, multipoint interaction with <i>J</i>-aggregates). A distinctive emission enhancement of SQ-BA
dyes with shorter-alkyl-chains in the presence of Neu5Ac was observed
(2.4-fold fluorescence enhancement; with formation constant 10<sup>1.7</sup> M<sup>–1</sup>), with no such enhancement for SQ-BA
dyes with longer-alkyl-chain. In addition, various enhancement factors
for other monosaccharides were observed depending on the alkyl chain
length. Detailed thermodynamic and NMR studies of the SQ-BA complexes
revealed the unique recognition mechanism: the dye aggregate with
a shorter-alkyl-chain causes the slipped parallel structure and forms
a stable 2:1 complex with Neu5Ac, as distinct from longer-alkyl-chain
dyes, which form a 1:1 monomeric complex. MDA using the four SQ-BA
dyes was performed for human urine samples, resulting in the successful
discrimination between normal and abnormal Neu5Ac levels characteristic
of disease. Thus, we successfully controlled various responses to
similar monosaccharides with a novel approach that chemically modified
not the boronic acid moiety itself but the length of the alkyl chain
residue attached to the dye in order to generate specificity