D.A. Aikens

TRANSIENT PHOTOCHEMISTRY OF SAFRANIN‐O

Abstract— We have characterized the spectra, acidity constants and decay kinetics of the triplet and semireduced radical species of Safranin‐O. Between pH 3.0 and 10.6, there are three triplet species denoted 3DH2 +2, 3DH+ and 3D, the pKas being 7.5 and 9.2. All three triplet species exhibit first order decay, the rate constant for 3DH+ being ca. 5‐fold lower than the rate constants of 3DH+ and 3D. Ascorbic acid and ethylenediaminetetraacetic acid (EDTA) quench the triplet state under appropriate pH conditions and the pH dependencies of the yield of semireduced dye indicate that 3DH+ is more reactive than 3DH+ or 3D. With EDTA as the reducing agent, there is the additional requirement that at least one of the amino nitrogens be deprotonated to obtain a significant yield of semireduced dye. In these reactions, ascorbic acid is oxidized reversibly, but EDTA is oxidized irreversibly, so that with the latter reducing agent photolysis causes buildup of the leucodye, which on subsequent photolysis can reduce triplet state dye. With ascorbic acid as the reducing agent, the regeneration of the ground state dye is reversible, the decay of the semireduced radical being second order. In general, the transient photochemistry of Safranin‐O resembles that of Thionine, the major difference being that the lifetimes of 3DH2 +2 and 3DH+ are much longer for Safranin‐O than for Thionine.

The interactions between nucleic acids and polyamines. II. Protonation constants and 13C-NMR chemical shift assignments of spermidine, spermine, and homologs.

Abstract Macroscopic protonation constants have been determined by pulentiometric titration for spermidine, spermine and for the four pulyamines. 3,5-Spd, 4,4-Spd, 4,3,4-Spm and 4,4,4-Spm. which are homologs of spermidine and spermine. A method for calculation of microscopic protonation constants of polyamines based on data for mono- and diamines gives results for spermidine that agree well with the experimental macroscopic protonation constants and the protonation sequence of Kimberly and Goldstein. 13 C-NMR spectra of spermidine, spermine and six homologs have been obtained and used to assign specific resonances, correcting some ambiguity in the assignments for spermidine and some errors in the assignments for spermine.

TRANSIENT PHOTOCHEMISTRY OF NEUTRAL RED

Abstract— Flash photolysis of neutral red between pH 1.3 and pH 11 yields the triplet species 3DH2+23DH+ and 3D. Both 3DH2+2 and 3D exhibit first order decay with rate constants of 1.6 ± 0.3 × 104 s‐1 but 3DH+ decays within the lifetime of the flash. Over the entire pH range, ascorbic acid quenches the triplet, forming the semireduced radicals DH3+2 DH2+ and DH, all of which exhibit second order decay with k= 1.8 ± 0.4 ± 108M‐1s‐1 most probably by recombination with semioxidized ascorbic acid. The dependence of the rate of decay of radical neutral red on the identity of reversible reductants supports the back‐electron transfer mechanism, as does digital simulation of complex radical disproportionation schemes. In contrast to the efficient reduction of triplet neutral red by ascorbic acid, its reduction by EDTA is quite inefficient.

The interactions between nucleic acids and polyamines. III. Microscopic protonation constants of spermidine.

Changes in the NMR chemical shifts of protons adjacent to the nitrogen atoms of Spermidine which are undergoing protonation have been measured by two-dimensional heteronuclear coupled NMR. Data thus obtained measure the dependence of the state of protonation of individual nitrogens on the pH, and permit calculation of the microprotonation constants of Spermidine and the concentrations of all of the variously protonated Spermidine species present at any pH.

Linear Sweep Voltammetry of Adsorbed Neutral Red.

Abstract The strong adsorption of neutral red on mercury causes its linear sweep voltammetry to be adsorption controlled over a wide range of conditions. At pH 4.5 or below, the surface coverage of DH + increases monotonically from 1 monlayer in 3×10 −7 M solution to ca. 3 monolayers in 3×10 −4 M solution, and to a good approximation the monomeric, dimeric and tetrameric forms of the dye are adsorbed equally strongly. The morphology of the adsorption peak indicates that interactions between adsorbed molecules are substantial and that the nature of these interactions changes from moderately repulsive below pH 4 to strongly attractive above pH 6. Over this pH range the voltammograms of 2×10 −4 M dye narrow progressively and ultimately split into two extremely sharp peaks. The first of these corresponds to the single voltammetric peak observed for dilute dye solutions, wheres the second represents the reduction of an electrochemically distinguishable phase of adsorbed dye. Above pH 9 the isotherm for adsorption of D exhibits an abrupt increase when the bulk concentration exceeds the equilibrium solubility.

Mechanism and kinetics of the stepwise voltammetric reduction of pertechnetate in alkaline solution to Tc(VI, Tc(V) and Tc(IV)

Abstract The mechanism of the stepwise reduction of TcO−14 to Tc(VI), Tc(V) and Tc(IV) from pH 9.2 to pH 13.6 was studied by normal pulse polarography and dc polarography. In low ionic strength media normal pulse polarography yields TcO2−4 as the primary product. This species gains a proton by hydrolysis and reacts with water to form a 5- or 6-coordinate species which then is reduced to Tc(V) by an ECE/DISP1 mechanism. The rapid increase of the rate of the chemical reaction with increasing ionic strength is attributed to a specific ionic strength effect arising from intramolecular repulsion of charged ligands. Above pH 12 in high ionic strength media, Tc(V) is reduced to Tc(IV) in an unusual step whose rate increases with increasing pH. The rate is second order in Tc, suggesting a DISP 2 process or the formation of dimeric Tc(IV).

Interference by polyamines in the measurement of magnesium ion at physiological pH with the divalent cation-selective electrode.

Abstract The liquid ion exchange divalent cation-selective electrode responds in a non-Nernstian manner to a number of protonated amines and polyamines of biochemical interest. This electrode response is characterized for a number of amines and the interference of protonated amines in measurement of magnesium ions at physiological pH is discussed.

Two-dimensional n.m.r. investigation of the protonation sequence in spermidine

Proton–carbon-13 two-dimensional correlation n.m.r spectroscopy resolves the four protons adjacent to the nitrogen atoms of spermidine and permits determination of the protonation sequence.