The natural turnover of free hyaluronic acid (HA) is predominantly based on its CD44-mediated internalisation in leukocytes. In a phagocytic cell model (RAW 264.7 murine macrophages) we here provide conclusive evidence that this receptor-mediated mechanism endocytosis is responsible also of the uptake of materials where HA is used as a coating agent, in this case chitosan/triphosphate nanoparticles on whose surface HA is electrostatically adsorbed. Alginate-coated nanoparticles were used as a control and they appeared to undergo a qualitatively similar endocytic process, which was mediated by a different scavenging receptor yet to be identified. In this general picture, an important, modulating role appears to be played by how receptors can cluster around individual nanoparticles. The CD44 slow representation (24-48 h) enforces a limit in the amount of available HA internalisation receptors; therefore a higher affinity, and hence a higher degree of clustering, would yield a lower number of internalised nanoparticles. HA presentation can be varied by acting on nanoparticle structure/morphology, and our data suggest that a better presentation may be linked to both higher affinity and lower capacity/uptake rate. Paradoxically, this result would suggest that particles with a lower affinity for CD44 may allow a more efficient HA-mediated delivery of payloads.

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Here, we describe the synthesis of the single amino acid chelator DOTAlaP and four of its derivatives. The corresponding gadolinium(III) complexes were investigated for their kinetic inertness, relaxometric properties at a range of fields and temperatures, water exchange rate, and interaction with human serum albumin (HSA). Derivatives with one inner-sphere water (q = 1) were determined to have a mean water residency time between 8 and 6 ns in phoshate-buffered saline at 37 °C. The corresponding europium complexes were also formed and used to obtain information on the hydration number of the corresponding coordination complexes. Two complexes capable of binding HSA were also synthesized, of which one, Gd(5b), contains no inner-sphere water, while the other derivative, Gd(4b), is a mixture of ca. 15% q =1 and 85% q = 0. In the presence of HSA, the latter displayed a very short mean water residency time (τM310 = 2.4 ns) and enhanced relaxivity at intermediate and high fields. The kinetic inertness of Gd(4b) with respect to complex dissociation was decreased compared to its DOTAla analogue but still 100-fold more inert than [Gd(BOPTA)(H2O)]2–. Magnetic resonance imaging in mice showed that Gd(4b) was able to provide 38% better vessel to muscle contrast compared to the clinically used HSA binding agent MS-325.

Water exchange kinetics of [Ln(L)(H2O)2](x) complexes (Ln = Pr, Nd, Dy, Tm, and Yb; L = DO3A and DTTA-Me) were studied by (17)O NMR spectroscopy as a function of temperature, pressure, and frequency and by (1)H nuclear magnetic relaxation dispersion. Water exchange rate constants of both complexes show a maximum at dysprosium. Water exchange on negatively charged complexes of the acyclic DTTA-Me ligand is much faster than on the neutral complexes of the macrocyclic DO3A. Small activation volumes |ΔV(⧧)| < 1 cm(3) mol(-1) measured for water exchange on [Ln(DO3A)(H2O)2] indicate an interchange type of mechanism (I) for the lanthanide complexes studied. In the case of [Ln(DTTA-Me)(H2O)2](-), a change in mechanism is detected from a dissociative mechanism (D, ΔV(⧧) = 7 cm(3) mol(-1)) for complexes with larger ions (Pr to Gd) to an interchange mechanism (Id, I; ΔV(⧧) = +1.8 and +0.4 cm(3) mol(-1)) for complexes with smaller ions (Dy and Tm).

In this study, the effect of human serum albumin (HSA) in a concentration range of 0 to 4 g L−1 in phosphate buffered saline (PBS) on the electrochemical corrosion behavior of AISI 316L, wrought Co-28Cr-6Mo and Ti-6Al-4 V was investigated by advanced electrochemical corrosion experiments such as cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The cyclic voltammetry results showed that the dissolution rate of iron from 316L and cobalt from Co-28Cr-6Mo alloy decreased in the presence of HSA. HSA also increased the oxidation of adsorbed hydrogen on Ti-6Al-4 V alloy by the external donation of hydrogen atoms. These results implied the formation of an adsorbed layer of protein on the oxide layer which was confirmed by the result of the EIS experiments. Furthermore, the increase of HSA concentration increased the surface coverage of HSA. The comparison of the BSA (bovine serum albumin) as an animal serum albumin with HSA showed that the surface coverage and the cathodic inhabitation of BSA were higher than HSA.

The need for magnetic resonance imaging (MRI) contrast agents with improved relaxivity maintains the development of new GdIII chelates as an intensive and demanding field of research. In this work, we introduce the new dimeric chelators bis{1,4,7,10‐tetraazacyclododecane‐1‐[(6‐amino)hexanoic]‐4,7,10‐triacetic acid}adipate [L2, bis(DOTA‐AHA)adipate] and bis{1,4,7,10‐tetraazacyclododecane‐1‐[(6‐amino)hexanoic]‐4,7,10‐triacetic acid}1,3‐phenyldiacetate [L3, bis(DOTA‐AHA)1,3‐phenyldiacetate], which are based on the bifunctional ligand 1,4,7,10‐tetraazacyclododecane‐1‐[(6‐amino)hexanoic]‐4,7,10‐triacetic acid (L1, DOTA‐AHA). Their GdIII chelates were studied by variable‐temperature 1H nuclear magnetic relaxation dispersion (NMRD) and 17O NMR spectroscopy to measure their relaxivities and the parameters that govern them. The rates of exchange of inner‐sphere water from the monomer GdL1 and from the two dinuclear chelates Gd2L2 and Gd2L3 are very similar (298kex ≈ 6.5 × 106 s–1) and slightly faster than that for [Gd(DOTA)H2O]– (298kex = 4.1 × 106 s–1). All three compounds form weakly bound aggregates with equilibrium constants 298K of 2.9, 15.6, and 14.6 for GdL1, Gd2L2, and Gd2L3, respectively. Even though the aggregates contain only 10 to 15 % of the total amount of GdIII ions, a marked increase in relaxivity between 30 and 100 MHz is observed. Furthermore, the distance between the two GdIII centers in the dinuclear compounds has been determined by double electron–electron resonance (DEER) spectroscopy experiments and by molecular modeling studies, which afforded comparable distances. The linkers between the chelating moieties allow GdIII–GdIII distances of ca. 3.0 nm for the completely stretched linker conformation and less than 1.9 nm for the conformation with the metal centers at a closer distance. These metal‐to‐metal distances by themselves cannot explain the considerably long tumbling times of the chelates in solution. Only a model consistent with some level of aggregation for the dinuclear chelates in aqueous solution could satisfactorily explain our results.

The displacement of water molecule(s) from the inner coordination sphere of [Gd(DTTA−Me)(H 2 O) 2 ] − (DTTA = ethylenetriamine-N,N,N″,N″-tetraacetate) by fluoride has been studied by multinuclear NMR relaxation ( 1 H, 17 O, 19 F) and DFT calculations. Fluoride anions can replace only one of the coordinated water molecules. The thermodynamic stability constant (K GdLF,298 0 = 11.6 ± 0.3) and thermodynamic parameters characterizing the formation of [Gd(DTTA−Me)(H 2 O)F] 2− were determined (ΔH 0 = +6.3 ± 0.1 kJ mol −1 ; ΔS 0 = +41.5 ± 3.4 J mol −1 K −1 ; ΔV 0 = +4.5 ± 1.2 cm 3 mol −1 ). Fluoride binding causes a marked acceleration of the water exchange, which is seven times faster for [Gd(DTTA−Me)(H 2 O)F] 2− (k ex,1 298 = 177 × 10 6 s −1 ) than for [Gd(DTTA−Me)(H 2 O) 2 ] − (k ex,2 298 = 24.6 × 10 6 s −1 ). Water exchange on both compounds is faster than formation of the fluoride complex. The analysis of the Gd−O water distances, electron density, and electron localization function (ELF) at the bond critical points using DFT calculations reveals that F − binding weakens the Gd−O water bonds, thereby facilitating the departure of the coordinated water molecule following a dissociative mechanism. The water exchange on both Gd(DTTA−Me) complexes follow dissociative reaction pathways as shown by the positive activation volumes ΔV ⧧ = +8 ± 2 cm 3mol −1 and +15 ± 4 cm 3 mol −1 for the bis-aqua complex and the monofluoro complex, respectively.