Synthetic spectra for radioactive strontium production QA/QC

Radioactive ⁸²Sr/⁸²Rb produced at Los Alamos National Laboratory is routinely used in generators for hospitals and medical laboratories to support cardiac imaging. The proper quantification of strontium radioisotopes in a sample is important to ensure quality and regulatory compliance. However, the quantification of the impurity ⁸⁵Sr is difficult, because its primary gamma-ray at 514 keV interferes with the annihilation peak at 511 keV from ⁸²Rb. Synthetic spectra were created as a quality test of several gamma-ray spectral analysis tools’ ability to resolve peaks in the 511/514 keV multiplet. The peak fitting results from the spectroscopy tools (RAYGUN, SPECANAL, GammaVision, UNISAMPO, and GAMANAL) are presented. These spectra can also be useful for other programs to test their annihilation peak analysis procedures.     

Methods and software for predicting germanium detector absolute full-energy peak efficiencies

High-purity germanium (HPGe) and lithium drifted germanium (Ge(Li)) detectors have been the detector of choice for high resolution gamma-ray spectroscopy for many years. This is primarily due to the superior energy resolution that germanium detectors present over other gamma-ray detectors. In order to perform quantitative analyses with germanium detectors, such as activity determination or nuclide identification, one must know the absolute full-energy peak efficiency at the desired gamma-ray energy. Many different methods and computer codes have been developed throughout history in an effort to predict these efficiencies using minimal or no experimental observations. A review of these methods and the computer codes that utilize them is presented.     

The effect of channeling on MeV ion-induced auger electron production in silicon

We have measured Auger electron emission from single crystal targets of Si(111) bombarded with H⁺ and ⁴He⁺ beams in the 0.5 to 1.8 MeV range under channeled and random directions of incidence. Under channeling conditions (monitored by simultaneous measurement of the Rutherford backscattering yield), a significant reduction is observed in the intensity and also in the energy width of the KLL Auger line. These two characteristics of the Auger signal are influenced by channeling of the incident beam as evidenced by their angular dependence. The measured ratio of the channeled to random Auger signals correlates well with a simple model based on the shadow cone radius for the channeled ion, the lattice vibrational amplitude, the adiabatic K-shell excitation distance, and the electron inelastic mean free path, λ, for the 1620 eV Auger line. We derive a value for the latter quantity of 34 Å.     

The 1H NMR spectra of exo- and endo-3-thiatricylo[4.2.1.02,5]non-7-ene 3,3-dioxide. The shielding effect of the sulfone group

The proton spectra of exo- and endo-3-thiatricyclo[4.2.1.0^2,5]non-7-ene 3,3-dioxide have been analysed and completely assigned. Considerations of coupling constants indicate that the thietane ring is nonplanar and that the norbornene residue is significantly distorted from the geometry of norbornene itself. The sulfone group induces significant changes in the shielding of the proximate olefinic proton in the endo isomer and the bridge protons in the exo isomer. These shifts appear to be the result of the electrostatic effects and effects associated with the diagmagnetic anisotropy of the sulfone group.     

Plant callus as a source of biochemicals

This article presents a review of the recent literature describing the use of plant callus for the production of biochemicals, as well as specific examples of work done in our laboratory to analyze the production of ribosome inactivating proteins fromTrichosanthes kirilowii callus. The article discusses research advances in the development, characterization, and improvement of plant callus cell lines, including new cell lines and potentially useful products, influence of media composition, and environmental conditions on growth and product distribution, cell line selection strategies, and long-term stability.     

Synthesis and biological properties of 3-methyl-10-propargyl-5,8-dideazafolic acid

The synthesis of N³-methyl-10-propargyl-5,8-dideazafolic acid ( 1b ) is described. Ring closure of methyl-5-methylanthranilate with chloroformamidine hydrochloride gave a high yield of pure 2-amino-4-hydroxy-6-methylquinazoline treatment of which with iodomethane/sodium hydroxide provided the corresponding 3-methylquinazoline (6) which was converted to its 2-pivaloylamino derivative. This synthetic approach, next involving functionalisation of the 6-methyl group, was not further pursued because of difficulty encountered in removing the pivaloyl group. Methyl 5-methylanthranilate was treated with p-toluenesulfonyl chloride and the product then N-methylated. The tosyl group was cleaved with hydrogen bromide/phenol and the resulting methylamine ring-closed with chloroformamidine hydrochloride to provide 2-amino-1,4-dihydro-1,6-dimethyl-4-oxoquinazoline ( 11 ). The 2-pivaloylamino derivative of 11 was prone to hydrolytic deamination when attempts were made to remove the pivaloyl group and further elaboration of this heterocycle, with the intention of obtaining N¹-methyl-10-propargyl-5,8-dideazafolic acid was, too, not attempted. Di-t-butyl N-(4-propargylamino)benzoyl)-L-glutamate was therefore prepared and coupled with 2-amino-6-bromomethyl-4-hydroxyquinazoline hydrobromide. The resulting antifolate diester was N-monomethylated. Removal of the t-butyl groups with trifluoracetic acid afforded the target compound 1b and its structure was proved by degradation to the quinazoline 6 . Its IC₅₀ for L1210 thymidylate synthase (TS) was 26 μM; the control value for 10-propargyl-5,8-dideazafolic acid ( 1a ) was 0.02 μM. Thus the substitution of the lactam hydrogen in 1a by a methyl group reduced the TS inhibition by 1300-fold. Compound 1b was poorly cytotoxic to L1210 cells in culture (ID₅₀ > 100 μM). An unperturbed lactam group in this class of antifolate is important for binding to TS.     

Electronic absorption and fluorescence of cinchophen, cinchoninic acid and their methyl esters; biprotonic phototautomerism of the singly-protonated species

The pH and Hammett acidity dependences of the absorption and fluorescence spectra of cinchoninic acid (quinoline-4-carboxylic acid), cinchophen (2-phenylquinoline-4-carboxylic acid) and their methyl esters, were studied. The predominant uncharged ground-state species derived from the free acids are zwitterions. Prototropic equilibria are too slow to compete with fluorescence for deactivation of the excited state at hydrogen ion concentrations represented by the pH scale. However, fluorescence shifts accompanying protonation indicate that the carboxyl group is more basic than the ring nitrogen atom in the excited state. In the Hammett acidity range the singly-charged cations of all the compounds studied undergo phototautomerism in the lowest excited singlet state. The rate of this process is acidity dependent. In very concentrated sulphuric acid solutions doubly-charged cations are formed in the excited state but not in the ground state. The intense emissions of these compounds in moderately concentrated sulphuric acid may be suitable for quantitative analysis if great care is taken to control solution acidity.     

Ion pairing and the reaction of group IIA metal hexacyanoferrates(II) and peroxodisulfates

The rate of the reaction 2Fe(CN) ₆ ^4– +S ₂ O ₈ ^2– 2Fe(CN) ₆ ^3– + 2SO ₄ ^2– in the presence of Group IIA cations in aqueous solution has been studied over the range of ionic strength from 0.006 to 0.20 M at three temperatures between 5 and 35°C. The results are interpreted by means of the Brønsted⁽²⁾ equation, and it is concluded that the actual reacting species are MFe(CN) ₆ ^2– , and S₂O ₈ ^2– , where M is a Goup IIA metal. The contribution from the nonion-paired species seems to be negligibly small. Rate constants and activation parameters are reported for the observed reaction pathway, and these are compared with those for the same reaction carried out in the presence of alkali metal cations. The results are considered in terms of a mechanism involving cation bridging, and qualitatively this model is consistent with the trends in the results.