In this review, the chemical mechanisms behind the interactions between boronic acids and N-acetylneuraminic acids, which have been widely utilized in biomedicine in recent decades, will be examined. It will also be highlighted that the affinity of boronic acids for N-acetylneuraminic acids is dependent on pH and is complementary to their affinity for other common monosaccharides found in glycocalyces. Through various examples from the literature, the unique pH profile of the boronic – N-acetylneuraminic acids acid interaction and its uses in biomedicine will be illustrated.

Molecular recognition involving glycoprotein-mediated interactions is ubiquitous in both normal and pathological natural processes. Therefore, visualization of these interactions and the extent of expression of the sugars is a challenge in medical diagnosis, monitoring of therapy, and drug design. Here, we review the literature on the development and validation of probes for magnetic resonance imaging using carbohydrates either as targeting vectors or as a target. Lectins are important targeting vectors for carbohydrate end groups, whereas selectins, the asialoglycoprotein receptor, sialic acid end groups, hyaluronic acid, and glycated serum and hemoglobin are interesting carbohydrate targets.

The NMR relaxivities of the decatungstolanthanoate core-shell nanoparticles, prepared by encapsulating [Ln(W₅O₁₈)₂]⁹⁻ polyoxometalates (LnPOM) within amorphous silica shells (K₉[Ln(W₅O₁₈)₂]@SiO₂), were studied along the Ln series. The relaxivity of GdPOM is slightly higher than for Gd-DTPA due to second-sphere relaxation effects, but the values for the other paramagnetic LnPOMs are much smaller due to the short T_1e values of their Ln³⁺-ions. The NPs have core-shell spherical structures, with LnPOM-containing cores with 9.5–28 nm diameters, and 4.0–11.0 nm thick amorphous silica shells. In water suspensions, the NPs have negative zeta potentials (−32.5 to −40.0 mV) and time-dependent hydrodynamic diameters (31–195 nm) reflecting the formation of aggregates. The relaxivities of GdPOM@SiO₂ NPs suspensions (r₁=10.97 (mM Gd)⁻¹ s⁻¹, r₂=12.02 (mM Gd)⁻¹ s⁻¹, 0.47 T, 25 °C) are considerably larger than for the GdPOM solutions, indicating that their silica shell is significantly porous to water. This increase is limited by the agglomeration of the complexes in the NPs core, limiting their access to water to those at the core surface. Replacing half of the Gd³⁺ ions by Eu³⁺ decreases the NPs r₁ and r₂ relaxivities at 0.47 T to 20 % and 35 % of their initial values, which are still considerable, but does not affect the efficient luminescence properties of the Eu³⁺ centers. This indicates that the mixed NPs have potential as dual modality MRI/optical imaging contrast agents.

Mn(III) porphyrins have great potential as Gd-free MRI contrast agents because both the cation and the ligand have interesting properties. The redox properties of the Mn(III)-ion can be exploited for the preparation of reactive oxygen species for therapy. Moreover, the porphyrin ligand allows these complexes to have a high affinity for tumor tissues. The inherent properties of the porphyrin ligands make these systems attractive for photothermal, photodynamic, and sonodynamic therapies. Therefore, these systems are attractive for the development of theranostics for MRI-guided therapy. For the magnetic field strengths at which most clinical MRI machines operate at present (0.5–1.5 T), the longitudinal relativity of low-molecular-weight complexes is even higher than that of the classical Gd-based contrast agents. This review gives an overview of the developments in the field of Mn(III) porphyrin contrast agents during the last 30 years.

In the periodical system, the lanthanides (the 15 elements in the periodic table between barium and hafnium) are unique in the sense that their trivalent cations have their valence electrons hidden behind the 5s and 5p electrons. They show a gradual decrease in ionic radius with increasing atomic number (also known as the lanthanide contraction). The resulting steric effects determine to a large extent the geometries of complexes of these ions. Here, we discuss these effects, particularly upon the properties of the complexes in aqueous solution, for selected families of Ln³⁺-complexes of oxycarboxylate and aminocarboxylate ligands. The physical properties of the cations are very different, which is very useful for the elucidation of the configuration, conformation and the dynamics of the complexes by X-ray techniques, NMR spectroscopy, and optical techniques. Often the structural analysis is assisted by computational methods.

Manganese ferrite nanoparticles are superparamagnetic and have very high saturation magnetization, which makes them candidates for application as MRI contrast agents. Because these nanoparticles are very effective enhancers of transverse relaxation, they are particularly suitable as negative (T₂-weighted) contrast agents. The magnitude of the relaxivity of nanoparticulate Mn ferrites seems to be determined mainly by the method of preparation, their dimensions, and their saturation magnetization.

A semi-empirical equation to estimate the hydration number of Mn(II) complexes was derived from a database of 49 previously published ¹H longitudinal Nuclear Magnetic Relaxation Dispersion profiles. This equation has the longitudinal ¹H relaxivity and the molecular weight of the Mn(II) complex under consideration as parameters.

Calix[4]arene-thiourea and-tetraamide nakedeye receptors do not show any tendency to self-aggregation and are highly sensitive towards small monoanions; association constants in DMSO for halogenides (chloride to iodide) and HSO₄-are <200 m^-1. Basic anions deprotonate both receptors leading to a high and selective optical readout. Binding constants for carboxylates, fluoride, and dihydrogen phosphate are three orders of magnitude higher (∼10⁵ m^-1) in case of the tetrathiourea receptor.

Synthetic variable temperature ¹H NMRD profiles and ¹⁷O NMR relaxation and shift data were generated with a model based on the Solomon-Bloembergen-Morgan and Freed theories and then fitted simultaneously or individually. The effects of the fitting procedure and of experimental uncertainties on the resulting best-fit parameters were investigated. The most reliable best-fit parameters were obtained when all data were included in a simultaneous fitting procedure. Fitting of only NMRD and/or ¹⁷O NMR data provided considerably less accurate best-fit parameters. Very large deviations from the values of the parameters used for the construction of the datasets were obtained due to the combined effects of uncertainties resulting from the fitting and from the data. For these fittings, the accuracy of the best-fit parameters appeared to be strongly dependent on the magnitude of synthetic parameters applied. For example, the accuracy of τ_M ^C was low around τ_M ^S = 10^-8 s. The parameters τ_V and Δ² are strongly correlated in fittings of only ¹⁷O NMR data. Consequently, only the ratio of these parameters can be evaluated in this way. The observations underline the need to reduce the number of adjustable parameters by constraining as many as possible of them at values obtained by independent techniques. The inaccuracies observed in these simulations come in addition to those caused by the inadequacy of the Solomon-Bloembergen-Morgan theory, particularly at low magnetic field strengths.