Physicochemical properties and bio-interfacial interactions of surface modified PDLLA-PAMAM linear dendritic block copolymers

Here, we demonstrate the applicability of self-assembling linear-dendritic block copolymers (LDBCs) and their nanoaggregates possessing varied surfaces as therapeutic nanocarriers. These LDBCs are comprised of a hydrophobic, linear polyester chemically coupled to a hydrophilic dendron polyamidoamine (PAMAM)—the latter of which acts as the surface of the self-assembled nanoaggregate in aqueous media. To better understand how surface charge density affects the overall operability of these nanomaterials, we modified the nanoaggregate surface to yield cationic (NH₃⁺), neutral (OH), and anionic (COO⁻) surfaces. The effect of these modifications on the physicochemical properties (i.e., size, morphology, and surface charge density), colloidal stability, and cellular uptake mechanism of the polymeric nanocarrier were investigated. This comparative study demonstrates the viability of nanoaggregates formed from PDLLA-PAMAM LDBCs to serve as nanocarriers for applications in drug delivery.     

Low-temperature hydride furnace modified for the atomic absorption spectrometric determination of metals with low appearance temperatures

The sample is vaporized from tungsten filament coils (150 W) and transported by an argon stream to the cell of a modified hydride furnace for atomic absorption spectrometry (a.a.s.). The system provides almost the same sensitivity for elements with low appearance temperatures (e.g., Bi, Cd, Pb, Tl, Zn) as graphite-furnace a.a.s. The detection limits are between 0.1 and 5 ng ml^?1, depending on the element.     

Spin Density Distribution in 2,4,6-Triphenylphenoxyl

The distribution of the unpaired electron over the oxygen and the 24 carbon atoms in the free 2,4,6-triphenylphenoxy radical was determined by electron spin resonance spectroscopy and quantum-mechanical approximation methods. The hyperfine splitting was evaluated with the aid of the spectra of triphenylphenoxyls deuterated in some or all of the substituent phenyl groups. The results of the quantum-mechanical approximations were checked by recording the ESR spectra of triphenylphenoxyls labeled with ¹³C in positions 1,2,3, or 4 of the central ring. The spin density distribution permits a first discussion of the ¹⁷O-coupling constants of correspondingly labeled triphenylphenoxyl and other organic free radicals.     

Vergleichende atomabsorptionsspektrometrische untersuchungen zur elementspurenbestimmung in Urin

When using a direct determination procedure with graphite-furnace a.a.s. (e.t.a.a.s.), it is sufficient to make an addition of nitric acid in order to arrive at the optimal reduction of the spectral background. A “matrix modifier” (NH₄NO₃, (NH₄)₂HPO₄) produces a background which often cannot be compensated completely. Detection limits of the direct determination technique are: Cd 0.1, Co 8, Cu 4, Ni 5, Pb 2 and Tl 3 (μg l^?1). A similar power of detection can be achieved as with flame-a.a.s. due to a preceding preconcentration step (trace adsorption on highly dispersed silicic acid). After preconcentration and determination with e.t.a.a.s., the detection limits are: Cd 0.002, Co 0.1, Cu 0.05, Ni 0.09, Pb 0.09 and Tl 0.06 (μg l^?1). The trace concentrations in urine of healthy persons were found to be: Cd 0.2–0.8, Co ? 0.1, Cu 4–10, Ni 1–3, Pb 6–10 and Tl 0.7–1.3 (μg l^?1). Direct e.t.-a.a.s. is, therefore, found to be suitable for the determination of Cd, Cu and Pb. For the determination of Co, Ni and Tl concentrations, a preconcentration is required. Cobalt was not found in any of the urine samples at the limit of detection of 0.1 μg l^?1.     

Isolierung und Eigenschaften der sauren Phosphatase aus Ananas comosus

Zusammenfassung Im Bromelin, einer Protease aus Ananas comosus Var. Cayenne, sind einige Fremdaktivitäten enthalten. Durch Gel-Chromatographie an Sephadex G-75 läßt sich die saure Phosphatase und eine Esterase, die N-Acetyl-l-tyrosinäthylester spaltet, von der Protease abtrennen. Durch Blektrofokussierung konnte die saure Phosphatase in mindestens zwei Isoenzyme vom isoelektrischen Punkt 4, 3 bzw. 6,1 aufgetrennt werden.Die Michaelis-Konstante der sauren Phosphatase gegenüber p-Nitrophenylphosphat beträgt 0,76 · 10^–3 M (nach Lineweaver-Burk) bzw. 0,73 · 10^–3 (nach Eadie). Das pH-Optimum in Citratpuffer liegt bei pH 5,5. Es bestehen Anzeichen dafür, daß neben der höhermolekularen Phosphatase (Mol.-Gew. > 100000) auch eine niedermolekulare saure Phosphatase in den Stengeln der Ananas comosus vorkommt.In den Strünken der Ananas lassen sich erhebliche Mengen einer pflanzlichen Ribonuclease nachweisen. Dieses Enzym läßt sich durch Ionenaustausch-Chromatographie an DEAE-Cellulose von den anderen Begleitenzymen abtrennen.Eine weitere Varietät von Ananas comosus, die in Brasilien vorkommt, enthält ebenfalls große Aktivitäten an saurer Phosphatase sowie Ribonuclease, jedoch wenig Protease und keine Aktivität gegenüber N-Acetyl-l-tyrosinäthylester.

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Isolation and properties of the acid phosphatase from ananas comosus

Bromelin, a protease from pineapple (ananas comosus var. Cayenne), contains several foreign activities. Acid phosphatase and an esterase splitting N-acetyl-l-tyrosineethyl ester can be separated from the protease by gel chromatography on Sephadex G-75. The acid phosphatase can be separated into at least two isoenzymes with isoelectric points of 4.3 and 6.1, resp., by means of electrofocusing.The Michaelis constant of acid phosphatase for p-nitrophenylphosphate is 0.76×10^–3 M (according to Lineweaver-Burk) and 0.73×10^–3M (according to Eadie). The optimum pH value in citrate buffer is about 5.5. Besides the higher-molecular phosphatase (mol.-weight > 100000) also a lower-molecular acid phosphatase seems to occur in the stems of ananas comosus.Considerable amounts of a vegetable ribonuclease can be detected in the stalks of ananas. This enzym can be separated from other accompanying enzymes by ionexchange chromatography on DEAE-cellulose. Another variety of ananas comosus, occurring in Brazil, also contains high activities of acid phosphatase and ribonuclease, but only small amounts of protease and no activity towards N-acetyl-l-tyrosineethyl ester.