UV radiation as a potential driving force for zooplankton community structure in Patagonian lakes

This article explores the potential role of UV radiation (UVR) as an influence on zooplankton communities. In the first section we provide a general overview of UVR effects on freshwater zooplankton, with an emphasis on Argentine and Chilean environments. In the second section we present the results of a survey involving 53 temperate lakes across a gradient of UVR exposure to determine patterns of species richness and specific diversity. These community characteristics decreased at high potential UVR exposure (i.e. high mean water column irradiance or low lake optical density). A threshold value of mean water column irradiance of approximately 10% of the surface level seems to limit both richness and diversity to minimum values. On the basis of the collected evidence it is not possible to definitely conclude that UVR rather than another covarying factor is responsible for the decrease in specific diversity observed at the lowest end of lake optical depth. However, lakes with values above the previous threshold are likely to exhibit highly depauperate zooplankton communities regardless of the mechanism. As a cautionary note we suggest that changes in the optical characteristics (i.e. changes due to atmospheric conditions, precipitation patterns or vertical displacement of the tree line) may result in sudden shifts in zooplankton community structure.     

Why and How Much Brouwer’s Fixed Point Theorem Fails in Noncompact Setting?

The celebrated Brouwer’s Fixed Point Theorem is dated in 1912. Its extension to compact set setting in Banach spaces due to Schauder appeared in 1930. Immediately it raised the question whether the Theorem can be extended to noncompact setting. The works of Kakutani, Klee, Benyamini and Sterfeld, Sternfeld and Lim solved the qualitative part of the problem. Lack of compactness makes the statement of the theorem false. However, there are some quantitative aspects of the question. The two basic are called minimal displacement problem, and optimal retraction problem. The aim of this article is to present the historical back ground and possibly, up to date state of investigations in this field. A list of open problems with comments will be discussed.     

An efficient potassium cyanide-promoted synthesis of 2-arylbenzoxazoles from [4.3.0]boron heterobicycles

The 2-arylbenzoxazoles 3a-f were produced in moderate to excellent yields merely by stirring a potassium cyanide (3 equiv)-containing methanol solution of the borobicyclic compounds 1a-f at room temperature. These compounds were fully characterized spectroscopically [IR, ¹H, and ¹³C NMR and X-ray analysis (3a)] and by elemental analysis.     

Synthesis of water‐soluble perylenediimide‐functionalized polymer through esterification with poly(vinyl alcohol)

A new material has been prepared by covalent attachment of a perylene derivative, N‐(carboxyphenyl)‐N′‐(8‐pentadecyl)perylene‐3,4:9,10‐bis(dicarboximide) (PDI‐COOH), to poly(vinyl alcohol) (PVA) by esterification. The perylenediimide (PDI)‐modified PVA polymers are soluble in water and dimethylsulfoxide (DMSO). This solubility is conferred to the insoluble perylene derivative by the water‐soluble polymer. The materials have been characterized by hydrogen‐nuclear magnetic resonance, Fourier transform infrared spectra, X‐ray diffraction, and X‐ray photoelectron spectroscopy confirming the covalent attachment of the PDI to the polymer chains. The significant changes in the crystalline parameters and the thermal stability observed for the polymer after the esterification also confirm the covalent linkage with PDI. In addition, the PDI‐modified PVA shows good fluorescence both in solution (quantum yield ～0.2–0.25) and in solid suggesting that the PDI retains largely its photochemical and photophysical properties after immobilization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3613–3622, 2010     

Kinetic parameters relevant to repetitive determinations via transient signals in flow-through systems : Part I. Direct Sample Injection into the Detection Chamber with application to the determination of some phenothiazines by a transient redox effect

The effect of rate proportionality constants on three fundamental parameters, which limit sensitivity as well as determination rate in sample injection (for repetitive determinations) into unsegmented (single-phase) flow-through systems, is discussed. Under first order or pseudo-first order conditions, the individual values and ratios of the rate constants for the two consecutive processes leading to the transient signal control the three parameters; namely : (1) the ratio of peak height to theoretical steady-state signal, (2) the time to reach the maximum (or minimum) signal value, and (3) the time to return to baseline. A simple way of extracting the values of the rate constants from the signal profiles when the two processes cannot be isolated is presented. Application to the determination of some phenothiazines based on the transient redox effect observed in their oxidation with cerium(IV) is also illustrated. The discussion and application are limited to the case of direct sample injection into the detection chamber.     

Investigation on the isomerization of 2-amino-3-aziridino-1,4-naphthoquinones to benzo[g]quinoxalines

The course of the hydriodic acid-catalysed and iodide-catalysed isomerization of various 2-amino-3-substituted-aziridino-1,4-naphthoquinones (I) to 1,2,3,4,5,10-hexahydrobenzo[g]-quinoxaline-5,10-diones (III) is investigated, and steric aspects of the reaction are also considered. Only in the case of the phenylaziridino derivative (Ie) does hydriodic acid afford direct cyclization to the corresponding benzoquinoxalinedione (IIIe); in all other cases the hydriodides (V) of the cleavage products (II) are obtained, and liberation of the free bases (II) results in cyclization to the corresponding benzoquinoxalinediones (III) when the aziridine ring is monosubstituted or trans disubstituted, with retention of configuration in the latter case. In contrast, the free bases (II) obtained from cis disubstituted (I) are relatively stable and cyclize with excess iodide yielding trans disubstituted (III). Correspondingly, monosubstituted and trans disubstituted I undergo iodide-catalysed isomerization to III whereas cis disubstituted I do not react.     

Stereoselective addition of the titanium enolate of N-acetyl (4S)-isopropyl-1,3-thiazolidine-2-thione to five-membered N-acyl iminium ions

[reaction: see text] Addition of the chlorotitanium enolate of N-acetyl 4-isopropyl-1,3-thiazolidine-2-thione to five-membered, N-substituted N-acyl iminium ions furnished the corresponding Mannich-type addition products with good diastereoselectivity and in good yields. The synthetic utility of the addition product 8 was demonstrated in a chemospecific anti-aldol reaction with cinnamaldehyde. By using this strategy, we constructed three contiguous chiral centers with high stereocontrol employing the same chiral auxiliary. X-Ray crystallographic analysis of addition product 2 and aldol product 14 revealed their absolute stereochemistry.     

Spectrophotometric cell comprising parallel rotating and stationary bioreactors: Application to the determination of glucose in serum samples

A spectrophotometric cell comprising parallel bioreactors facing each other and containing immobilized enzyme preparations is described. The lower reactor rotates to minimize diffusional constraints, and the upper reactor is fixed to provide an integrated design for the realization of coupled enzyme-catalyzed reactions. The operating characteristics of the cell are illustrated with the determination of glucose using glucose oxidase [EC 1.1.3.4] and horseradish peroxidase [EC 1.11.1.7] as immobilized enzymes (horseradish peroxidase on the rotating reactor and glucose oxidase on the stationary one). The H₂O₂ produced in the dissolved-oxygen oxidation of β- -glucose enters into oxidative coupling in a reaction with N,N-dimethylaniline and 4-aminophenazone which is catalyzed by horseradish peroxidase; the absorbance of the colored complex formed provides the basis for monitoring. The cell was incorporated into a continuous-flow/stopped-flow/continuous-flow operation, and the determination was based on the rate of response under stopped-flow conditions. The overall approach was applied to the determination of glucose in standards of human serum and samples of bovine blood serum.     

Study of Frozen Waves’ theory through a continuous superposition of Bessel beams

This paper presents a study of a recent solution to Maxwell's equation, the so-called “Frozen Waves”, whose main characteristics are to remain static in space, and to keep an arbitrary longitudinal field pattern previously chosen. These waves could be obtained by an adequate, but discrete, superposition of monochromatic Bessel beams. Contrary to that, we have here proposed a new way to get these waves through a continuous superposition of Bessel beams, and discussed some physical aspects and then exemplified for both loss and lossless media.