Interactions of thorium isotopes with colloidal organic matter in oceanic environments

The phase speciation of thorium and consequences for the residence times of colloids have been examined in seawater of the Middle Atlantic Bight (MAB) and the Gulf of Mexico. Two fractions of colloidal organic matter (COM), 0.2 μm > COM₁ > 1 kD and 0.2 μm > COM₁₀ > 10 kD, were sampled using cross-flow ultrafiltration techniques and measured for their ²³⁴Th activity and organic carbon concentration. The ratios of mass concentrations of COM₁ to those of suspended particulate matter were as high as 10 in the MAB and 6–34 in the Gulf of Mexico. Higher concentrations of colloids may be of great importance in the biogeochemical cycling of many particle-reactive nuclides or trace elements owing to their high specific surface area and complexation capacity. A significant fraction of ²³⁴Th in the traditionally defined “dissolved” pool was found to be associated with colloids. On average, about 10% of “dissolved” ²³⁴Th was in the colloidal fraction of sizes between 10 kDa and 0.2 μm, and 50% was in the 1 kDa-0.2 μm fraction. Values of the partition coefficients [K_c: (0.5−4) × 10⁶ ml g⁻¹ for K_c1 and (0.5−7) × 10⁶ ml g⁻¹ for K_c10] of ²³⁴Th between truly dissolved (<1 kDa) and colloidal fractions approximated those for Th-particle interactions [K_p: (0.3−10) × 10⁶ ml g⁻¹], indicating that colloid and suspended particle surface sites are similar. The distribution of ²³⁴Th between dissolved, colloidal, and particulate phases was broadly similar to that of organic carbon in these oceanic environments. Thus, thorium isotopes might be used as tracers of marine organic carbon cycling. Residence times of colloids derived from ²³⁴Th:²³⁸U disequilibria were consistently short, ranging from 1 to 14 days for COM₁₀ and from 5 to 65 days for COM₁, suggesting that marine colloids are highly reactive in marine biogeochemical processes. The discrepancy between apparent turnover times of colloids (1 kDa) derived from Th scavenging and ¹⁴C measurements suggest that ²³⁴Th and ¹⁴C may trace different geochemical pathways of colloids in the ocean.     

Simultaneous derivative spectrophotometric determination of thorium and uranium in a micellar medium

Derivative photometric methods for trace analysis of Th(IV) and UO₂(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO₂(II) complexes at their λ_max, 614.5 nm and 637.0 nm are, 1.19 × 10⁴ 1/mol/cm and 1.12 × 10⁴ 1/mol/cm and 1.95 × 10⁻² μg/cm² and 2.13 × 10⁻² μg/cm² μg/cm², respectively. Calibration graph is linear over the range 9.28 × 10⁻²−18.56 μg/ml of Th(IV) and 9.52 × 10⁻²−19.04 μg/ml of UO₂(II). Though presence of Th(IV) and UO₂(II) causes interference in each others determination, 9.28 × 10⁻¹−9.28 μg/ml Th(IV) and 9.52 × 10⁻¹−9.52 μg/ml UO₂(II) when present together, can be simultaneously determined using derivative spectra.     

Extraction and spectrophotometric determination of cobalt(II) with isonitroso-5-methyl-2-hexanone

A simple and selective method is proposed for the extraction of cobalt(II) for its spectrophotometric determination using (HIMH) as an extractant. Cobalt(II) forms a yellow coloured complex with HIMH which can be extracted into chloroform. The calibration curve is rectilinear in the concentration range 0.1–5.0 μg ml⁻¹ of cobalt(II). The extracted species shows an absorption maximum at 400 nm with molar absorptivity of 1.135×10⁴ l mol⁻¹ cm⁻¹. The method has been applied for the determination of cobalt in synthetic mixtures, pharmaceutical, biological and high speed steel samples.     

Third-order nonlinear optical properties of azo dye attached polymers

Third-order nonlinear optical properties of a disazo dye attached polymer (3R) were evaluated and compared with that of a monoazo (Disperse Red 1) dye attached polymer (2R). The third-order nonlinear optical coefficient (ξ⁽³⁾) of the 3R is more than three times higher than that of the 2R over the fundamental wavelengths between 1.5 and 2.0 μm. This is explained by π-conjugation elongation. For both polymers, the ξ⁽³⁾ dependence on the fundamental wavelength corresponds to their absorption spectra. This is attributable to a three-photon resonance effect. At the 1.50 μm resonant wavelength, the maximum ξ⁽³⁾ of 4.8 × 10^-11 esu is obtained for 3R at a dye content of 17 mol%.     

Carbon ion irradiation induced surface modification of polypropylene

Polypropylene was irradiated with ¹²C ions of 3.6 and 5.4 MeV energies in the fluence range of 5×10¹³–5×10¹⁴ ions/cm² using 3 MV tandem accelerator. Ion penetration was limited to a few microns and surface modifications were investigated by scanning electron microscopy. At the lowest ion fluence only blister formation of various sizes (1–6 μm) were observed, but at higher fluence (1×10¹⁴ ions/cm²) a three-dimensional network structure was found to form. A gradual degradation in the network structure was observed with further increase in the ion fluence. The dose dependence of the changes on surface morphology of polypropylene is discussed.     

Packed-column hydrodynamic chromatography using 1-μm non-porous silica particles

150×3 mm I.D. columns, packed with 1-μm non-porous spherical silica particles, were used to separate soluble synthetic polymers by hydrodynamic chromatography. The columns exhibited a plate height of about 1.4 μm allowing very fast and efficient separations of polymers in the molecular mass range 10³−2·10⁶ g/mol. The migration behaviour of polymers could be well described by a simple theoretical model. The applicability of packed bed HDC for the fast separation of polymers was illustrated with separations of polystyrene and poly(methyl methacrylate) mixtures.     

The second and third order non-linear optical properties of liquid crystalline polymers

The second and third order non-linear optical susceptibilities of several donoracceptor substituted side chain polymers, some of which exhibit mesophases, will be reported. The susceptibilities were measured by harmonic generation from thin films, typically 0·5 μm thick, at a fundamental wavelength of 1064 nm and 1579 nm. For second harmonic generation, the spin coated films were contact poled on a glass substrate with an interdigited electrode pattern. Typical values obtained were χ⁽²⁾₃₁ = 1 × 10^-9 esu and χ⁽²⁾₃₃ = 3 × 10^-9 esu, the largest value was χ⁽²⁾₃₃ = 6·3 × 10^-9 esu. The difficulty in deriving reliable second order structure-property relations because of the large effect which the contact poling process has on the non-linear optical susceptibility of the films will be highlighted. The highest χ⁽³⁾ value of 5·8 × 10^-12 esu obtained from an amorphous film of a polymer with an asymmetrically substituted azo side group is comparable with the susceptibility of more typical third order non-linear materials such as the main chain polymers polyphenylacetylene and poly-p-phenylenebenzobisthiazole.     

Far-UV laser flash photolysis in solution. A study of the chemistry of 1,1-dimethylsilene in hydrocarbon solvents

The far-UV (193 nm) laser flash photolysis of nitrogen-saturated isooctane solutions of 1,1-dimethylsiletane allows the direct detection of 1,1-dimethylsilene as a transient species, which (at low laser intensities) decays with pseudo-first-order kinetics (τ 10 μs) and exhibits a UV absorption spectrum with λ_max 255 nm. Characteristic rapid quenching is observed for the silene with methanol (k_McOH = (4.9 ± 0.2) × 10⁹ M⁻¹ s⁻¹), tert-butanol (k_BuOH = (1.8 ± 0.1) × 10⁹ M⁻¹ s⁻¹) and oxygen (k_O2 = (2.0 ± 0.5) × 10⁸ M⁻¹ s⁻¹). The Arrhenius activation parameters for the reaction with methanol have been determined to be E_a = −2.6 ± 0.6 kcal mol⁻¹ and log A = 7.7 ± 0.3.     

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli.

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ_p=3 × 10⁻¹³ s, f_p = 0.5 Hz, E_p = 1.1 × 10⁻³J cm⁻², I_av = 5.5 × 10⁻⁴ W cm⁻², I_p = 10⁹ W cm⁻²) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm⁻²). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10³ lower for pulsed radiation than for CW radiation (3.3 × 10⁻¹ and 7.8 × 10² J cm⁻² respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.     

Calorimetric comparison of the interactions between salivary proteins and Streptococcus mutans with and without antigen I/II

Antigen I/II can be found on streptococcal cell surfaces and is involved in their interaction with salivary proteins. In this paper, we determine the adsorption enthalpies of salivary proteins to Streptococcus mutans LT11 and S. mutans IB03987 with and without antigen I/II, respectively, using isothermal titration calorimetry. In addition, protein adsorption to the cell surfaces was determined spectrophotometrically. S. mutans LT11 with antigen I/II, yielded a much higher, exothermic adsorption enthalpy at pH 6.8 (ranging from −2073 × 10⁻⁹ to −31707 × 10⁻⁹ μJ per bacterium) when mixed with saliva than did S. mutans IB03987 (−165 × 10⁻⁹ to −1107 × 10⁻⁹ μJ per bacterium) at all bacterial concentrations studied (5 × 10⁹, 5 × 10⁸, and 5 × 10⁷ ml⁻¹), largest effects per bacterium being observed for the lowest concentration. However, the enthalpy of salivary protein adsorption to S. mutans LT11 became smaller at pH 5.8. Adsorption isotherms for the S. mutans LT11 showed considerable protein adsorption at pH 6.8 (1.2–2.1 mg/m²), that decreased only slightly at pH 5.8 (1.1–1.6 mg/m²), with the largest amount adsorbed at the lowest bacterial concentration. This suggests that the protein(s) in the saliva with the strongest affinity for antigen I/II is (are) readily depleted from saliva. In conclusion, antigen I/II surface proteins on S. mutans play a determinant role in adsorption of salivary proteins through the creation of enthalpically favorable adsorption sites.     

One-electron oxidation of mitomycin C and its corresponding peroxyl radicals. A steady-state and pulse radiolysis study

The one-electron oxidation of Mitomycin C (MMC) as well as the formation of the corresponding peroxyl radicals were investigated by both steady-state and pulse radiolysis. The steady-state MMC-radiolysis by OH-attack followed at both absorption bands showed different yields: at 218 nm G_i (-MMC) = 3.0 and at 364 nm G_i (-MMC) = 3.9, indicating the formation of various not yet identified products, among which ammonia was determined, G(NH₃) = 0.81. By means of pulse radiolysis it was established a total κ (OH + MMC) = (5.8 ± 0.2) × 10⁹ dm³ mol⁻¹ s⁻¹. The transient absorption spectrum from the one-electron oxidized MMC showed absorption maxima at 295 nm (ε = 9950 dm³ mol⁻¹ cm^t-1), 410 nm (ε = 1450 dm³ mol⁻¹ cm⁻¹) and 505 nm ( ε = 5420 dm³ mol⁻¹ cm⁻¹). At 280–320 and 505 nm and above they exhibit in the first 150 μs a first order decay, κ₁ = (0.85 ± 0.1) × 10³ s⁻¹, and followed upto ms time range, by a second order decay, 2κ = (1.3 ± 0.3) × 10⁸ dm³ mol^-1 s⁻¹. Around 410 nm the kinetics are rather mixed and could not be resolved.

The steady-state MMC-radiolysis in the presence of oxygen featured a proportionality towards the absorbed dose for both MMC-absorption bands, resulting in a G_i (-MMC) = 1.5. Among several products ammonia-yield was determined G(NH₃) = 0.52. The formation of MMC-peroxyl radicals was studied by pulse radiolysis, likewise in neutral aqueous solution, but saturated with a gas mixture of 80% N₂O and 20% O₂. The maxima of the observed transient spectrum are slightly shifted compared to that of the one-electron oxidized MMC-species, namely: 290 nm (ε = 10100 dm³ mol⁻¹ cm⁻¹), 410 nm (ε = 2900 dm³ mol⁻¹ cm⁻¹) and 520 nm (ε = 5500 dm³ mol⁻¹ cm⁻¹). The O₂-addition to the MMC-one-electron oxidized transients was found to be at 290 to 410 nm gk(MMC·OH + O₂) = 5 × 10⁷ dm³ mol⁻¹ s⁻¹, around 480 nm κ = 1.6 × 10⁸ dm³ mol⁻¹ s⁻¹ and at 510 nm and above, κ = 3 × 10⁸ dm³ mol⁻¹ s⁻¹. The decay kinetics of the MMC-peroxyl radicals were also found to be different at the various absorption bands, but predominantly of first order; at 290–420 nm κ₁ = 1.5 × 10³ s⁻¹ and at 500 nm and above, κ = 7.0 × 10³ s⁻¹.

The presented results are of interest for the radiation behaviour of MMC as well as for its application as an antitumor drug in the combined radiation-chemotherapy of patients.     

Radiation resistance of GaAs–AlGaAs heterostructures doped with isovalent and rare-earth elements

When GaAs–Si and GaAs–AlGaAs heterostructures are exposed to γ-quanta, radiation stimulated ordering is observed. However, the gettering efficiency in such systems falls for layer widths more than 1 μm. For this reason we seek effective methods of radiation resistance improvement of materials in which one would expect point radiation defects to be gettered not only at defect boundaries, but also in the active layer volume.

S.i.GaAs–s.i.Al_xGa_1−xAs–nGaAs : Te heterostructures are presented with epitaxial layers (doped with Yb or undoped), obtained by means of LPE (liquid-phase epitaxy). The electron concentration in nGaAs was found to be (1–3)×10¹⁸ cm⁻³ for widths 1–3 μm. The samples were exposed to ⁶⁰Co γ-quanta with doses of 10⁵–10⁷ rad.

Investigations of irradiated samples by means of low-temperature (4.2 K) photoluminescence have shown considerable decrease of exciton halfwidth in the boundary spectra of nGaAs : Te : Yb epitaxial layers in comparison with nGaAs : Te layer spectra. This is caused by background impurity gettering which happens on the s.i.Al_xGa_1−xAs–nGaAs heteroboundaries as well as in deformed regions in the epitaxial layer volume. Formation of such regions is caused by the difference between the covalent radii of Yb atoms and GaAs lattice atoms. The maximum effect of radiation stimulated gettering of dopants in nGaAs epitaxial layers is observed for Yb concentrations which are equal to 10⁻⁴–10⁻⁵ atomic fractions in a solution-melt.

It is determined that the deformed regions in epitaxial layer volumes and heteroboundaries could be efficient drains for point radiation defects which form under radiation exposure. The investigations carried out showed that the doping of an epitaxial layers by rare-earth impurities provides considerable improvement in forming radiation resistant III–V materials.     

Solid-phase extraction of metal ions and their estimation in vitamins, steel and milk using 3-hydroxy-2-methyl-1,4-naphthoquinone-immobilized silica gel

3-Hydroxy-2-methyl-1,4-naphthoquinone-immobilized silica gel has been used for the adsorption and estimation of copper, cobalt, iron and zinc by both batch and column techniques. The distribution coefficient D determined for each metal ion was as follows (ml g¹): Fe, 3.6 × 10²; Cu, 3.9 × 10²; Co, 3.8 × 10²; Zn, 4.1 × 10². Methods have been developed to estimate zinc, copper and cobalt in milk, steel and vitamin samples respectively.     

Pulse radiolysis studies of 4,7-phenanthroline(II)

The one-electron reduction of 4,7-phenanthroline (P) in aqueous solutions at neutral pH has been further studied by pulse radiolysis. The spectral and kinetic properties of the transient formed due to the reaction of 4,7-phenanthroline with hydrated electron were investigated. The transient absorption spectrum obtained 5μs after the pulse exhibits a broad band with a λ_max at 420 nm. The λ_max is 10 nm blue shift compared with the absorption spectrum obtained at pH 2.9 where the reactant was the protonated form. The bimolecular'rate constant of the reaction of 4,7-phenanthroline with hydrated electron was 0etermined to be (2.2±0.1)×10¹⁰ dm³ mol⁻¹ s⁻¹. It was found that the decay of the transient was mainly following a first-order kinetics. The first-order decay rate constant was determined to be (1.25±0.1)×10⁴s⁻¹.     

Selective spectrophotometric determination of palladium(II) with 2(5-nitro-2-pyridylazo)-5-(N-propyl-N-3-sulfopropylamino)phenol(5-NO(2).PAPS) and tartaric acid with 5-NO(2).PAPS-niobium(V) complex

Spectrophotometric determinations of palladium(II) and tartaric acid were respectively investigated by using the color reactions between 2(5-nitro-2-pyridylazo)-5-(N-propyl-N-3-sulfopropylamino)phenol(5-NO₂.PAPS) and palladium(II) in strong acidic media, and between 5-NO₂.PAPS, niobium(V) tartaric acid in weak acidic media. The calibration graphs were linear in the range of 0–25 μg/10 ml palladium(II), with an apparent molecular coefficient () of 6.2×10⁴ l mol⁻¹ cm⁻¹ at 612 nm, and 0–23 μg/10 ml tartaric acid with =1.08×10⁶ l mol⁻¹ cm⁻¹ at 612 nm, respectively. The proposed methods were selective and sensitive in comparison with other chelating pyridylazo dyes–palladium(II) or metavanadic acid–tartaric acid method, and the effect of foreign ions such as copper(II) was negligible for the assay of palladium(II) with 5-NO₂.PAPS.     

Study of the mixed-metal lanthanummagnesium-purpurin complex: spectrophotometric determination of yttrium and lanthanides

Mixtures of La(III) and Mg(II) form with purpurin (P; 1,2,4-trihydroxyanthraquinone) the mixed-metal complex LaMg₂P₅, which is extracted with methyl isobutyl ketone at pH 7.5. The molar absorptivity of the complex is 6.1 × 10⁴ l.mole⁻¹.cm⁻¹ at 570 nm and its conditional extraction constant 5 × 10¹³ l⁴.mole⁻⁴. Similar complexes have been found to be formed with yttrium, cerium, praseodymium, neodymium and samarium. The use of these complexes for the spectrophotometric determination of yttrium and lanthanides up to 15 μg has been investigated.     

Transients and cooperative action of β-carotene, vitamin E and C in biological systems in vitro under irradiation

Using N^•₃ species as specific electron acceptor a defined ascorbate radical: AH^•↔A^•−+H⁺ (λ_max=360 nm, =3400 dm³ mol⁻¹ cm⁻¹) is observed. The attack of DMSO^•+ on vit.E results in a vit.E^• radical (k=1×10⁹ dm³ mol⁻¹ s⁻¹; λ_max=425 nm, =2400 dm³ mol⁻¹ cm⁻¹; 2k=4.7×10⁸ dm³ mol⁻¹ s⁻¹). Vit.E-acetate leads to the formation of a radical cation (vit.E-ac^•+). β-carotene reacts also with DMSO^•+ forming a radical cation, β-car^•+ (k=1.75×10⁸ dm³ mol⁻¹ s⁻¹; λ_max=942 nm, =14 600 dm³ mol⁻¹ cm⁻¹), which probably leads to the formation of a dimer radical cation, (β-car)^•+₂ (k=2.5×10⁷ dm³ mol⁻¹ s⁻¹).

Using E.coli bacteria (AB1157) as a model system in vitro it was found that all three vitamins are rather efficient radiation protecting agents. They can also increase the activity of cytostatica, e.g., mitomycin C (MMC), by electron transfer process. The mixture of vit.E-ac and β-car acts contradictory, but adding vit.C to it a strong cooperative enhancement of the MMC activity is observed once again. A relationship between the pulse radiolysis and the radiation biological data is found and discussed. A possible explanation of the previously reported trials concerning the role of vit.E and β-car on the increased occurence of lung and other types of cancer in smokers and drinkers is presented.     

New aspects of the reaction of silver(I) cations with the ethylenediaminetetraacetate ion

The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y⁴⁻ anion) precipitates with Ag⁺ cations to form the Ag₄Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y⁴⁻ to form a complex, AgY³⁻. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO₃) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β₁ = (1.93 ± 0.07) × 10⁵ M⁻¹ and the solubility products are K_S0 = [Ag +]⁴[Y⁴⁻] = (9.0 ± 0.4) × 10⁻¹⁸ M⁵ and K_S1 = [Ag +]³[AgY³⁻] = (1.74 ± 0.08) × 10⁻¹² M⁴. The presence of Na⁺, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β₁ = (1.19 ± 0.03) × 10⁶ M⁻¹, K_S0 = (1.6 ± 0.4) × 10⁻¹⁹ M⁵ and K_S1 = (1.9 ± 0.5) × 10⁻¹³ M⁴; at ionic strength tending to zero; β₁ = (1.82 ± 0.05) × 10⁷ M⁻¹, K_S0 = (2.6 ± 0.8) × 10⁻²² M⁵ and K_S1 = (5 ± 1) × 10⁻¹⁵ M⁴. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO₃. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag₄Y salt.     

Fast and highly selective determination of cyanide with 2,2-dihydroxy-1,3-indanedione

A very simple, accurate, fast, selective and sensitive assay of cyanide based on its reaction with 2,2-dihydroxy-l,3-indanedione at basic pH is proposed. As little as 0.01 μg ml⁻¹ of cyanide can be determined. The molar absorptivity may reach 5.1–8.0×10⁴ l mol⁻¹ cm⁻¹ depending on the reaction conditions. Thus, 1 ml of sample solution is mixed with 500 μl of 5 mg ml⁻¹ solution of 2,2-dihydroxy-1,3-indanedione monohydrate in 2% sodium carbonate. The absorbance of the purple color is measured at 510 nm in 1-cm glass cuvettes, 10–15 min after mixing the reagents. The procedure could also be used to identify free CN⁻ in natural waters and hydrocyanic acid in the environment.     

Spectrophotometric investigation of the nature and stability of silver(II) in acidic sulphate media

A spectrophotometric study of silver(II) in sulphuric acid solution indicates the formation of two sulphate complexes, in the range 4–18M H₂SO₄, with absorbance peak maxima at 361 and 260 mμ, respectively. In 15M H₂SO₄ the molar absorptivity of silver(II) is 3.11 × 10⁴ at 361 mμ. Kinetic studies of the reduction of silver(II) by the solvent suggest a rate-determining step first order in silver(II) and yield a pseudo first-order rate constant of 1.9 × 10⁻¹min⁻¹. Further studies as a function of H₂SO₄ concentration show that the specific decomposition rate of the two complexes is identical and that changes in H₂SO₄ concentration only serve to shift the concentration equilibrium between the two complexes.