Radiofluorination of a Pre‐formed Gallium(III) Aza‐macrocyclic Complex: Towards Next‐Generation Positron Emission Tomography (PET) Imaging Agents

As part of a study to investigate the factors influencing the development of new, more effective metal‐complex‐based positron emission tomography (PET) imaging agents, the distorted octahedral complex, [GaCl(L)]?2 H₂O has been prepared by reaction of 1‐benzyl‐1,4,7‐triazacyclononane‐4,7‐dicarboxylic acid hydrochloride (H₂L?HCl) with Ga(NO₃)₃?9 H₂O, which is a convenient source of Ga^III for reactions in water. Spectroscopic and crystallographic data for [GaCl(L)]?2 H₂O are described, together with the crystal structure of [GaCl(L)]?MeCN. Fluorination of this complex by Cl^?/F^? exchange was achieved in high yield by treatment with KF in water at room temperature over 90 minutes, although the reaction was complete in approximately 30 minutes if heated to 80 °C, giving [GaF(L)]?2 H₂O in good yield. The same complex was obtained by hydrothermal synthesis from GaF₃?3 H₂O and Li₂L, and has been characterised by single‐crystal X‐ray analysis, IR, ¹H and ¹⁹F{¹H} NMR spectroscopy and ESI⁺ MS. Radiofluorination of the pre‐formed [GaCl(L)]?2 H₂O has been demonstrated on a 210 nanomolar scale in aqueous NaOAc at pH 4 by using carrier‐free ¹⁸F^?, leading to 60–70 % ¹⁸F‐incorporation after heating to 80 °C for 30 minutes. The resulting radioproduct was purified easily by using a solid‐phase extraction (SPE) cartridge, leading to 98–99 % radiochemical purity. The [Ga¹⁸F(L)] is stable for at least 90 minutes in 10 % EtOH/NaOAc solution at pH 6, but defluorinates over this time scale at pH of approximately 7.5 in phosphate buffered saline (PBS) or human serum albumin (HSA). The subtle role of the Group 13 metal ion and co‐ligand donor set in influencing the pH dependence of this system is discussed in the context of developing potential new imaging agents for PET.     

Enhanced T1 differentiation between normal and dystrophic muscles

Proton spin-lattice relaxation times (T1) of pectoralis major muscles from normal (Line 412) and homozygous dystrophic (Line 413) chicks was measured by FONAR QED 80 at 1.69 MHz. The T1 values of dystrophic muscles (216.8 +/- 17.3 ms) was two-fold higher than those of normal muscles (110.2 +/- 8.1 msec). When these values were compared with the T1 values obtained at high frequencies (20 MHz and 32 MHz), the T1 differentiation between normal and dystrophic muscles was considerably enhanced at 1.69 MHz. Based on these results, we suggest that the high resolution of T1 obtained at low frequency (1.69 MHz) could be effectively used to detect the degenerative processes in muscles by the NMR techniques.     

A thermoluminescence study of defect centres in MgO

Thermoluminescence glow curves are a fairly good representation of the different defect centres in MgO produced by γ or reactor irradiation. The glow peaks at 370, 440, 485 and 545 K have been found to be due to hole trapped centres. The 370 K peak has been found to be due to holes released from V_M centres (hole trapped at action vacancy associated with a neighbouring impurity ion). The 665 K peak in γ-irradiated MgO is due to charge transfer between the adsobred oxygen ions and surface defect centres. The F-type centres produced on reactor irradiation (neutron and γ) and on quenching from high temperatures before γ-irradiation are also found to give thermoluminescence peaks at temperatures higher than 560 K. It has also been found that reactor irradiation partially annihilates the trapping centres which are responsible for lower temperature glow peaks.     

A lattice dynamical investigation for the Raman and the infrared frequencies of Bi2W2O9

Studies on infrared and Raman-active phonons in the Aurivillius ferroelectric Bi₂W₂O₉ were performed theoretically. The Raman and infrared phonons were calculated by applying a short-range force constant model using normal coordinates having space group Pna2₁. Sixteen stretching, two repulsive and seventeen bending force constants were used for the calculations of the zone center phonons. The calculated Raman and infrared wavenumbers are in very good agreement with the experimental ones in the literature. Potential energy distribution for this compound has also been investigated for the contribution of each force constant towards the Raman and the infrared wavenumbers.     

Synthesis of 2-oxo/thioxooctahydroquinazolin-5-one derivatives and their evaluation as anticancer agents

An environment friendly method for the synthesis of 2-oxo/thioxooctahydroquinazolin-5-one derivatives has been devised using Ceric ammonium nitrate (CAN) as catalyst and polyethylene glycol (PEG) as solvent. The cytotoxic effect of these compounds was studied on U87 human glioma cells, compounds 4c, 4d and 4e are found to exhibit excellent activity at a concentration as low as 0.06 μg/ml.     

Thermoluminescence and ESR of γ-ray and pile-irradiated natural barite

Thermoluminescence (TL) and electron spin resonance (ESR) studies of γ-ray and pile-irradiated natural barite have led to the identification of centres which act as electron or hole traps. Intense pile irradiation seems to help the formation of the S₂O₃-radical. The presence of cation vacancies, as indicated by TL glow curves, makes pile-irradiated (>10¹⁸ n cm^-2 samples “immune” to further γ-irradiations as far as TL and ESR are concerned.     

Synthesis and reactivity of [18F]-N-fluorobenzenesulfonimide

A novel [18F]NF reagent and two novel radiochemical transformations have been developed: [18F]NFSi has been prepared from sodium dibenzenesulfonimide and reacted in the presence of silyl enol ethers and allylsilanes to deliver labelled fluorinated ketones and allylic fluorides respectively; the radiosynthesis of the fluorinated A ring of vitamin D3 has also been completed with success.     

Phase evolution studies of sol�Cgel derived lead zirconate titanate (PZT) nanopowder using X-ray diffraction and X-ray photoelectron spectroscopy

We report here the formation of single phase lead zirconate titanate (PZT) nanopowder with composition Pb(Zr_0.52Ti_0.48)O₃ and average crystallite size 12?C20?nm, synthesized by sol?Cgel process. The phase evolution of PZT gel powder, heat treated at temperatures 550, 650 and 800°C was monitored by X-ray diffraction (XRD) and X-ray photo-electron spectroscopy (XPS). The high resolution XPS spectra of Pb4f, Zr3d, Ti2p and O1s show that PZT with pure perovskite structure is obtained at 800°C while at lower temperatures pyrochlore phase co-exists with perovskite phase. The XRD results also support this analysis. We have also identified the pyrochlore phase using XPS by analyzing the corresponding variations in the FWHM values, peak positions and the separation between the spin doublets of Pb, Zr and Ti associated with it. The composition of the final powder obtained with pure perovskite structure is calculated and is close to the designed value.     

Mechanism of thermoluminescence in Sm- and Eu-doped barium sulphate

Thermoluminescence, TL emission spectra, ESR and optically excited luminescence of BaSO₄:Sm and BaSO₄:Eu were investigated. The optically excited luminescence studies showed that samarium ions were stabilized in the trivalent state in doped samples, and a fraction of these ions was reduced to the divalent state on γ-irradiation. These reduced ions were reoxidized on thermal annealing. Europium was found to be stabilized in the divalent form in BaSO₄:Eu phosphor, both before and after γ-irradiation. These results were further confirmed from the emission spectra of different glow peaks from BaSO₄:Sm and BaSO₄:Eu samples. The ESR spectra of these samples, recorded after γ-irradiation and various post-irradiation thermal annealings, revealed that anion radicals (such as SO₄^?, SO₃^?, SO₂⁺ and O₃^?) are formed on γ-irradiation and get annihilated at temperatures which corresponds to some of the glow peaks. An attempt is made to explain the results by a mechanism, suggested earlier for other impurity-doped BaSO₄ phosphors, in which holes released on thermal activation from anion radicals recombine with the electrons trapped at certain defect centres and the energy thus released is non-radiatively transferred to the impurity ions, which give their characteristic emission.