Direct determination of cadmium in placenta. Comparison with a destruction atomic absorption spectrometric method

Summary A comparison of performance characteristics of a destruction ETA-AAS method and the solid sampling ETA-AAS method experienced in analyzing cadmium in placenta is described. The accuracy of both methods is good; the precision of the destruction method was better. It was concluded that the direct method was preferable for the determination of cadmium in placenta and other tissues as it has a higher speed of analysis and is less sensitive to contamination. Problems with both methods are mentioned and homogenization of samples is shortly described.

---

Direkte Bestimmung von Cadmium in Placenta. Vergleich mit einer AAS-Methode mit Aufschluß

Zusammenfassung Die Leistungsfähigkeit einer ETA-AAS-Methode mit Aufschluß wird verglichen mit derjenigen einer Feststoff-ETA-AAS-Methode. Die Richtigkeit beider Verfahren ist gut, während die Präzision bei der Methode mit Aufschluß besser ist. Es wurde der Schluß gezogen, daß die direkte Methode zur Cadmiumbestimmung in Placenta und anderen Geweben vorzuziehen ist, da sie eine größere Analysengeschwindigkeit bietet und geringere Störanfälligkeit gegenüber Verunreinigungen aufweist. Probleme, die bei beiden Verfahren auftauchen, werden aufgezeigt. Die Homogenisierung der Probe wird kurz beschrieben.

---

---

Lecture given at the colloquium on the Analysis of Solids by AAS, Wetzlar, October 8–10, 1984

---

These investigations were supported in part by the Netherlands Technology Foundation (STW).     

Estimated subglottal pressure in six professionalcountry singers

Estimates of subglottal pressure in six professional male country singerswere obtained during the /p/ occlusion while the subjects spoke, sang a country tune, and sang the tune of the United States national anthem. The subglottal pressure values, which were very similar in both the speech-like and singing-mode syllables, usually measured below 45 cm of water column, but they ranged as high as 59 cm. The sound pressure level in singing was also measured and was lower than that discovered in classically trained singers at high subglottal pressures.     

Optimisation and validation of an automated solid phase extraction technique coupled on-line to enzyme-based biosensor detection for the determination of phenolic compounds in surface water samples

Summary A fully integrated screening system for phenolic compounds was developed incorporating on-line solid phase extraction, fractionation and biosensor detection. Two different types of biosensors, solid graphite and carbon paste electrodes incorporating the enzyme tyrosinase, were compared and used in the screening system. Interfacing of the solid phase extraction and fractionation with the biosensor detection was given special attention since the biosensors were not compatible with the organic modifier used for desorption of phenols from the solid phase extraction step. The system was validated with conventional analytical techniques. Surface water samples from the Ebro river were spiked with 1,10, and 25 μg L⁻¹ of catechol, phenol,p-cresol, respectively. Three out of seven samples were spiked and the correct samples were identified, containing phenols equivalent to the spiked concentrations.     

Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells

Hydrogenases (H₂ases) are benchmark electrocatalysts for H₂ production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p‐type Si photocathode for optimal loading and wiring of H₂ase through the introduction of a hierarchical inverse opal (IO) TiO₂ interlayer. This proton‐reducing Si|IO‐TiO₂|H₂ase photocathode is capable of driving overall water splitting in combination with a photoanode. We demonstrate unassisted (bias‐free) water splitting by wiring Si|IO‐TiO₂|H₂ase to a modified BiVO₄ photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si|IO‐TiO₂|H₂ase to a photosystem II (PSII) photoanode provides proof of concept for an engineered Z‐scheme that replaces the non‐complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode.     

Methyl side-chain dynamics in proteins using selective enrichment with a single isotopomer

13C relaxation studies on side-chain methyl groups in proteins typically involve measurements on (13)CHD(2) isotopomers, where the (13)C relaxation mechanism is particularly straightforward in the presence of a single proton. While such isotopomers can be obtained in proteins overexpressed in bacteria by use of (13)C enriched and fractionally deuterated media, invariably all possible (2)H isotopomers are obtained. This results in a loss of both resolution and sensitivity, which becomes particularly severe for larger proteins. We describe an approach that overcomes this problem by chemical synthesis of amino acids containing a pure (13)CHD(2) isotopomer. We illustrate the benefits of this approach in (13)C side-chain relaxation measurements on the mouse major urinary protein selectively enriched with [gamma(1),gamma(2)-(13)C(2),alpha,beta,gamma(1),gamma(1),gamma(2),gamma(2)-(2)H(6)] valine. Relaxation measurements in the absence and presence of pyrazine-derived ligands suggest that valine side-chain dynamics do not contribute significantly to binding entropy.     

Photochemical charge separation within aromatic hydrazines and the effect of excited-state intervalence in dihydrazines

Photolysis into the longest wavelength absorption band of 2-tert-butyl-2,3-diazabicyclo[2.2.2]oct-3-yl hydrazine (Hy) substituted naphthalenes causes aryl group reduction electron transfer to give (+)Hy-Ar(-). Electrooptical absorption measurements characterize the charge separation properties from these bands. Emission studies demonstrate that the separation between absorption and emission maxima for symmetrically disubstituted compounds is smaller than that for monosubstituted compounds, which is attributed to excited-state intervalence. The excited-state diabatic surfaces may be described as a Hy(+)-NA(- )-Hy(0), Hy(0)-NA(-)-Hy(+) pair, for which electronic interaction produces a double minimum that qualitatively resembles that in the ground state of the disubstituted intervalence radical cations.     

Electrochemical studies of tris(cyclopentadienyl)thorium and uranium complexes in the +2, +3, and +4 oxidation states

Electrochemical measurements on tris(cyclopentadienyl)thorium and uranium compounds in the +2, +3, and +4 oxidation states are reported with C₅H₃(SiMe₃)₂, C₅H₄SiMe₃, and C₅Me₄H ligands. The reduction potentials for both U and Th complexes trend with the electron donating abilities of the cyclopentadienyl ligand. Thorium complexes have more negative An(iii)/An(ii) reduction potentials than the uranium analogs. Electrochemical measurements of isolated Th(ii) complexes indicated that the Th(iii)/Th(ii) couple was surprisingly similar to the Th(iv)/Th(iii) couple in Cp′′-ligated complexes. This suggested that Th(ii) complexes could be prepared from Th(iv) precursors and this was demonstrated synthetically by isolation of directly from UV-visible spectroelectrochemical measurements and reactions of with elemental barium indicated that the thorium system undergoes sequential one electron transformations.

Electrochemical determination of the reduction potentials for a variety of tris(cyclopentadienyl)uranium and thorium complexes, including data on U(ii) and Th(ii) complexes.     

Excited-state electronic coupling and photoinduced multiple electron transfer in two related ligand-bridged hexanuclear mixed-valence compounds

The synthesis, characterization, electrochemical, photophysical, and photochemical properties of two hexanuclear mixed-valence compounds are reported. Each supramolecular species consists of two cyano-bridged [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(3)L-NC-Fe(II)(CN)(5)] triads that are linked to each other through a Pt(IV)-L-Pt(IV) bridge, where L = 4,4'-dipyridyl (bpy) or 3,3'-dimethyl-4,4'-dipyridyl (dmb). The major difference between the two compounds is the electronic nature of the bridging ligand between the two Pt atoms. Both species exhibit a broad Fe(II) --> Pt(IV) intervalent (IT) absorption band at 421 nm with an oscillator strength that is approximately four times that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(5)] and twice that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) When L = bpy, the resonance Raman spectrum obtained by irradiating the IT band at 488 nm exhibits several dipyridyl ring modes at 1604, 1291, and 1234 cm(-1) which are not present in the spectrum when L = dmb. In addition, femtosecond pump-probe spectroscopy performed at 400 nm yields a transient bleach of the IT absorption band with a single exponential decay of 3.5 ps for L = bpy, compared with only 1.8 ps for L = dmb and 2.1 ps for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) Last, prolonged irradiation of the complexes at 488 nm leads to the formation of 4 equiv of ferricyanide with a quantum efficiency of 0.0014 for L = bpy and 0.0011 for L = dmb. The transient absorption, resonance Raman, and photochemical data suggest that the degree of excited electronic coupling in these compounds is tunable by changing the electronic nature of the Pt-L-Pt bridging ligand.     

Fermentation and costs of fuel ethanol from corn with quick-germ process

The Quick-Germ process developed at the University of Illinois at Urbana-Champaign is a way to obtain corn oil, but with lower capital costs than the traditional wet-milling process. Quick-Germ has the potential to increase the coproduct credits and profitability of the existing dry-grind fuel ethanol process, but the fermentability of the corn remaining after oil recovery has not been tested. Therefore, a series of pilot scale (50 L) fermentations was carefully controlled and monitored with unique methods for standard inoculation and automatic sampling. It was found that the concentration of suspended solids was significantly reduced in the Quick-Germ fermentations. When compared at the same concentration of fermentable sugars, the fermentation rate and yield were not statistically different from controls. When Quick-Germ was integrated into a state-of-the-art dry-grind fuel ethanol process, computer simulation and cost models indicated savings of approx $0.01/L of ethanol ($0.04/gal) with the Quick-Germ process. Additional savings associated with the lower suspended solids could not be quantified and were not included. However, the savings are sensitive to the price of corn oil. Mention of brand or firm name does not constitute an endorsement by the U.S. Department of Agriculture over others of a similar nature not mentioned.