Catalytic-kinetic determination of copper and L-histidine with the use of a luminostat.

A luminostat, a new type of “stat”-method is described. Copper(II) catalyzes the chemiluminescent reaction between luminol and hydrogen peroxide. The intensity of the luminescence is used via a photomultiplier and a current-voltage transducer to regulate the addition of hydrogen peroxide from an automatic burette. The rate of this addition necessary to keep constant a preset luminescence is a measure of the copper(II) concentration. As L-histidine acts as an inhibitor for copper(II) in this reaction, it can be determined indirectly. Copper (II) can be determined in the range 10–100 $\text{μg}\text{20 ml}$, and L-histidine in the range 50–400 $\text{μg}\text{20 ml}$.     

Conformational Analysis of Guaianolide-Type Sesquiterpene Lactones by Low-Temperature NMR Spectroscopy and Semiempirical Calculations

Conformational analysis of 9-acetoxycumambrine A 1 and 8-O-isobutiryl-9-acetoxycumambrine B 2 was carried out by low-temperature NMR studies. Results suggested that lactones 1 and 2 are mixtures of two distinctive conformers, I and II. Based on low-temperature ¹H NMR spectra, in four solvents, the thermodynamic parameters of I II exchange process were assessed. Energy of activation of I II reaction was obtained by dynamic NMR simulations for both compounds. Results revealed that conformational exchange of lactones 1 and 2 occurs due to chair twisted chair interconversion of a heptane ring. The same PM3 semiempirical method was applied for geometry optimization of lactones 1 and 2, as well as of 9-hydroxycumambrine A 3, 9-acetoxycumambrine B 4, and cumambrine B 5.     

Inter- and intrastrand DNA crosslinks by 2-fluoro-substituted pyrrolobenzodiazepine dimers: stability, stereochemistry and drug orientation

A 2-fluoro-substituted pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimer with a 1,4-di-n-propyl piperazine linker was studied with respect to its binding and crosslinking capability towards double-helical DNA targets. Duplex thermal stabilizations upon drug binding as measured by UV melting experiments suggest that two guanine bases separated by four AT base pairs constitute the favorable binding site for the PBD dimer. Large stabilizations were observed for the self-complementary duplex d(AACAATTGTT)(2) as well as for the non-self-complementary duplex d(AAGAATTGTT)·d(AACAATTCTT) with both guanines located on the same strand. Formation of interstrand and intrastrand crosslinks by the covalent binding of both PBD moieties of the dimer to the exocyclic 2-amino group of the two guanine bases within the duplex minor groove was confirmed by NMR structural studies. In both the symmetric and non-symmetric DNA-PBD adducts the newly created stereogenic center at C11 of the tricyclic PBD subunits favors an S configuration. Different orientations of the PBD aromatic A-ring with respect to the covalently modified guanine as observed in the non-symmetric complex are shown to result in characteristic changes of PBD H11 and H11a proton chemical shifts. Based on a compilation of available NMR data on various PBD complexes, these differences may be used as valuable probes for the identification of PBD orientational preferences in DNA-PBD adducts.     

Combinatorial materials research applied to the development of new surface coatings I: a multiwell plate screening method for the high-throughput assessment of bacterial biofilm retention on surfaces

Combinatorial, high-throughput capabilities have been established to aid in the rapid development of new and effective antifouling marine coatings for naval applications. A biological screening process involving marine bacteria was developed that allows for rapid and effective quantification of bacterial biofilm growth and retention on large numbers of coating surfaces in parallel. The screening process involves (1) multiwell plate modifications for coating deposition, (2) deposition of combinatorial coating libraries via an automated liquid dispensing robot, (3) coating thickness measurements of cured coatings, (4) preconditioning of coatings via immersion in deionized water, (5) bacterial incubation, (6) plate processing, and (7) data analysis for identification of promising candidates. The details of the method developed are described in this document.     

Generalization of Hardy–Littlewood maximal inequality with variable exponent

Let $p(·)$ be a measurable function defined on ${\mathbb{R}}^d$ and $p_{-}:={inf}_{x\in {\mathbb{R}}^d}p(x)$. In this paper, we generalize the Hardy–Littlewood maximal operator. In the definition, instead of cubes or balls, we take the supremum over all rectangles the side lengths of which are in a cone-like set defined by a given function ψ. Moreover, instead of the integral means, we consider the $L_{q(·)}$-means. Let $p(·)$ and $q(·)$ satisfy the log-Hülder condition and $p(·)=q(·)r(·)$. Then, we prove that the maximal operator is bounded on $L_{p(·)}$ if and is bounded from $L_{p(·)}$ to the weak $L_{p(·)}$ if $1\le r_{-}\le \infty$. We generalize also the theorem about the Lebesgue points.