Paramagnetic Relaxation Enhancement in Hydrophilic Colloids Based on Gd(III) Complexes with Tetrathia- and Calix[4]arenes

Abstract

Hydrophilic colloids (PSS-[Ln2(TCAi)2] and PSS-[LnCAi], where i = 1, 2, or 3 and Ln = Gd or Tb) were prepared by precipitation of Gd­(III) or Tb­(III) complexes with tetrathiacalix[4]­arenes (TCAi) and calix[4]­arenes bearing two 1,3-diketone groups (CAi) from dimethylformamide to an aqueous solution of poly­(sodium 4-styrenesulfonate) (PSS). Dynamic light scattering and transmission electron microscopy demonstrated the formation of nanoparticles coated by the polymer. Luminescence decay measurements on Tb­(III)-based colloids allowed hydration numbers of 2 and 4 per metal ion to be determined for PSS-[Ln2(TCAi)2] and PSS-[LnCAi] samples, respectively. Longitudinal and transverse water proton relaxivity values measured at 20.8 MHz were remarkably high for the PSS-[GdCAi] colloids but unexpectedly low for the PSS-[Gd2(TCAi)2] ones. 1H fast field cycling nuclear magnetic resonance relaxometry was applied to shed light on the origin of the different relaxation enhancement in the investigated systems. Extremely slow exchange with the bulk of water molecules coordinated to Gd­(III) and the scarce accessibility of Gd­(III) sites to water were highlighted as the main causes of limited relaxivity.

1,3-Diketone Calix[4]arene Derivatives—A New Type of Versatile Ligands for Metal Complexes and Nanoparticles

“…This is manifested by the invariance of the lanthanide-centered luminescence of the PSS-coated nanoprecipitated terbium complexes with the cyclophanic 1,3-diketone derivatives which will be further designated as [TbL] (L is cyclophanic 1,3-diketonate) at the pH values varied within wide pH-range (4-9) [ 53 ]. The easy manipulation with the PSS-stabilized colloids through the centrifugation-induced phase separation and further re-dispersion in different solutions enables their re-usability, which, in turn, facilitates their applicability in sensing [ 53 , 61 , 101 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 ].…”

“…Our work [ 111 ] is worth mentioning as an example of sensing ability of the PSS-coated colloids based on the terbium dinuclear complexes with two thiacalix[4]arene ligands ([Tb 2 (L) 2 ]) (L = 34 , 43 ). As it has been mentioned above, the energy of the ligand’s triplet energy in [Tb 2 (L) 2 ] (L = 34 , 43 ) complexes facilitates the temperature-induced quenching resulted from the enhancement of the back energy transfer.…”

“…This fact along with the high hydration number of the Ln 3+ complexes with 1,3-diketone calix[4]arenes is the reason for high longitudinal relaxivities of the colloids based on the Gd 3+ complexes with calix[4]arene 1,3-diketonates [ 108 , 110 ]. This, in turn, is the prerequisite for efficient contrasting effect in NMR imaging [ 111 ]. The longitudinal and transverse relaxivity values (r 1 and r 2 ) measured in the aqueous colloids of the PSS-coated colloids based on the Gd 3+ complexes with the cyclophanic 1,3-diketones are within 14-20 mM −1 ∙s −1 ( 26 , 27a ) [ 108 , 110 ].…”

Terbium(III)-thiacalix[4]arene nanosensor for highly sensitive intracellular monitoring of temperature changes within the 303–313 K range

“…Similar to PSS-[Gd 2 (TCAn) 2 ] (n = 1-3) 43 , the electrokinetic potential values measured in the aqueous colloids range from − 46 to − 68 mV (Table 1), which explains their stability to aggregation manifested by the small polydispersity index and the average size below 100 nm. The TEM images of the dried colloids ( Fig.…”

“…The precipitation is induced by the pouring of 0.5 ml of the complex DMF solution under intensive stirring (2200 rpm) 2.5 ml of PSS-containing aqueous solution (1 g/L in 0.5 M solution of NaCl, pH 6.0). The complex formation in the DMF solution was achieved by mixing of the Tb(NO 3 ) 3 •6H 2 O with TCAn in the 1:1 ratio, and the solution was basified by the excess amounts of triethylamine (TEA) taken in 1:8 (TCAn:TEA) ratio 43 . The resulted colloidal solution was sonicated for 30 min (sonication bath temperature was controlled to be 20 ± 2 °C).…”