Sizes of pentagonal clusters in fullerenes

Stability and chemistry, both exohedral and endohedral, of fullerenes are critically dependent on the distribution of their obligatory 12 pentagonal faces. It is well known that there are infinitely many IPR-fullerenes and that the pentagons in these fullerenes can be at an arbitrarily large distance from each other. IPR-fullerenes can be described as fullerenes in which each connected cluster of pentagons has size 1. In this paper we study the combinations of cluster sizes that can occur in fullerenes and whether the clusters can be at an arbitrarily large distance from each other. For each possible partition of the number 12, we are able to decide whether the partition describes the sizes of pentagon clusters in a possible fullerene, and state whether the different clusters can be at an arbitrarily large distance from each other. We will prove that all partitions with largest cluster of size 5 or less can occur in an infinite number of fullerenes with the clusters at an arbitrarily large distance of each other, that 9 partitions occur in only a finite number of fullerene isomers and that 15 partitions do not occur at all in fullerenes.     

The stochastic quasi-steady-state assumption: reducing the model but not the noise

Highly reactive species at small copy numbers play an important role in many biological reaction networks. We have described previously how these species can be removed from reaction networks using stochastic quasi-steady-state singular perturbation analysis (sQSPA). In this paper we apply sQSPA to three published biological models: the pap operon regulation, a biochemical oscillator, and an intracellular viral infection. These examples demonstrate three different potential benefits of sQSPA. First, rare state probabilities can be accurately estimated from simulation. Second, the method typically results in fewer and better scaled parameters that can be more readily estimated from experiments. Finally, the simulation time can be significantly reduced without sacrificing the accuracy of the solution.     

Angular-momentum quantization applied to the Thomas-Fermi atom

The Fermi momentum of an electron in a statistical atom can be considered as a vector sum of two components. The first represents the orbital movement of an electron and can be calculated from the quantum levels of the angular momentum. The second is the maximum progressive momentum of the same electron and can be obtained from the variational procedure given by Gombas. A new expression for the Fermi momentum leads to the modification of the Thomas-Fermi statistical equation given by Barnes and Cowan.     

氰基水解酶在有机合成中的应用

腈化物是有机合成中的重要中间体,因为其中的氰基可以通过多种方法引入,又能进一步转化成其它官能团。用氰基水解酶实现氰基降解不仅反应条件温和,少污染、易处理,更重要的是能实现一般化学转化所不能实现的优良的化学、区域及立体选择性。不管是从学术角度还是工程角度来看,氰基水解酶都是一种有巨大潜力的有机合成工具。     

DSC AS A TOOL TO PREDICT EMULSION STABILITY

The crystallization of n-Hexadecane dispersed within a suitable aqueous medium has been studied by the mean of Differential Scanning Calorimetry (DSCI. The dispersion of the oil is found to be dependent on the mixing conditions: calorimetric curves exhibit one or two exothermic signals which represent different undercoolings. n-Hexadecane can be dispersed in microscopic droplets or in both microscopic and macroscopic phases. Furthermore, during an isothermal stabilization (in a particular temperature range) one can observe an oil transfer from the microscopic droplets to the macroscopic organic phase. The same phenomenon can also be induced by thermal cycling. The effect of aging was found to be in perfect agreement with the predictions that can be drawn from the calorimetric analysis of freshly made samples.     

Effective potentials and the Gel''fand—Levitan equation

Moses et al, have derived an algorithm using the Gel'fand-Levitan equation for generating exactly solvable potentials for a particle in a box, harmonic oscillator, and Coulomb potentials by adding or subtracting a finite number of eigenvalues. We propose that their algorithm can be used to evaluate effective potentials for non exactly soluble molecular model Hamiltonians. We show that the algorithm can be used to remove bound states from the spectrum and to obtain an effective potential which supports predissociation resonances only. It can also be used to remove a specific resonance state from the spectrum, and to facilitate evaluations of excited states.     

A method for the determination of technetium in environmental waters

A method is described which can be used to determine technetium-99 levels in a range of water types. Ruthenium isotopes which may interfere in the analysis are removed from the sample by precipitation before concentration of pertechnetate onto an ion-exchange column. Other nuclides can be removed from the column using NaOH before elution of the technetium using NaSCN. The technetium in the NaSCN eluent can then be extracted into butan-2-one which can be evaporated onto a planchette. Technetium-99m is used as a yield tracer and after this has decayed away to negligible levles the amount of technetium on the planchette can be determined by measuring the rate of beta radiation emission from the final concentrate.     

Microfluidic Apps for off-the-shelf instruments

Within the last decade a huge increase in research activity in microfluidics could be observed. However, despite several commercial success stories, microfluidic chips are still not sold in high numbers in mass markets so far. Here we promote a new concept that could be an alternative approach to commercialization: designing microfluidic chips for existing off-the-shelf instruments. Such "Microfluidic Apps" could significantly lower market entry barriers and provide many advantages: developers of microfluidic chips make use of existing equipment or platforms and do not have to develop instruments from scratch; end-users can profit from microfluidics without the need to invest in new equipment; instrument manufacturers benefit from an expanded customer base due to the new applications that can be implemented in their instruments. Microfluidic Apps could be considered as low-cost disposables which can easily be distributed globally via web-shops. Therefore they could be a door-opener for high-volume mass markets.     

Interaction of hemoglobin in elevated serum total bilirubin determinations

A spectrophotometric study was carried out in an effort to elucidate how hemoglobin in serum interferes in the diazo coupling reaction used for the determination of bilirubin. Because it is difficult to see hemoglobin in neonatal specimens in which bilirubin is elevated without obtaining spectra of the mixtures, this can be a real problem when handling these specimens while using this particular reaction. From the spectrophotometric evidence described here, one can infer that hemoglobin can act in two ways. In one way, the formation of ferriprotoporphyin generates an oxidizing agent which can convert bilirubin to an oxidized product precluding it from taking part in a diazo coupling reaction. In the other way, the same ferriprotoporphyrin seems capable of oxidizing the azobilirubin complex after it has reached equilibrium again causing some lowering of the results obtained. It may be reasonable to assume that the quicker the analytical event can occur, the more accurate the result might be. If the matrix of reaction can be changed, and the reaction of diazo coupling also speeded up as a feature of the change, then it may be possible to avoid the interference from hemoglobin almost entirely. High concentrations of hemoglobin were tested here in an attempt to clearly show how the interference might take place.     

A highly selective procedure for the spectrophotometric determination of aluminium with 8-hydroxy-quinoline and its application to the determination of

Aluminium, hydroxyquinolate can be quantitatively extracted by chloroform from an ammoniacal solution containing hydroxyquinoline, complexone and cyanide. Likewise extracted are titanium, vanadium, tantalum, niobium, uranium, zirconium, gallium, antimony, bismuth, indium and traces of beryllium. Aluminium can be separated from the first five elements by an extraction in ammoniacal solution containing hydrogen peroxide.Zirconium, gallium, bismuth and antimony can be eliminated by a cupferron extraction and indium by extraction with diethyldithiocarbamate. Beryllium is eliminated by performing an extraction with hydroxyquinoline at pH 5. The proposed method enables a practically specific photometrical determination of aluminium. Applications are given of the determination of trace and higher amounts of aluminium in steels, non-ferrous alloys and in glass.     

Synthesis of alkynes and alkynyl iodides bearing a protected amino alcohol moiety as functionalized amino acids precursors

Amino acid precursors in protected amino alcohol form are important synthons that can be used as building-blocks for the hemisynthesis of non-natural amino acids. Serine can be used as a common starting material for the synthesis of such compounds differently protected. Particularly, protected amino alcohols bearing an ethynyl and/or an iodoethynyl group can be used in cross-couplings, in 1,3-dipolar cycloadditions and/or in Nozaki-Hiyama-Kishi type reactions. We thus demonstrated that the efficiently protected amino alcohols derived from serine can be coupled to a sugar derivative by an indium mediated alkynylation reaction. The conditions of this coupling are compatible with such functionalized derivatives and allow envisaging an access to C-glycosylated amino acids.     

Conversion of alpha,beta-unsaturated aldehydes into saturated esters: an Umpolung reaction catalyzed by nucleophilic carbenes

N-Heterocyclic carbenes derived from benzimidazolium salts are effective catalysts for generating homoenolate species from alpha,beta-unsaturated aldehydes. These nucleophilic intermediates can be protonated, and the resulting activated carbonyl unit is trapped with an alcohol nucleophile, thereby promoting a highly efficient conversion of an alpha,beta-unsaturated aldehyde into a saturated ester. A kinetic resolution of secondary alcohols can be achieved using chiral imidazoylidene catalysts. [reaction: see text]     

Determination of biocatalyst consumption in an aminopeptidase process using automated sample preparation and high-performance liquid chromatography

A rapid and sensitive method has been developed for the determination of the biocatalyst consumption in the chemo-enzymic production of optically pure natural and synthetic alpha-H-amino acids. It is based on automated sample preparation from an enzymic reaction mixture, reversed-phase high-performance liquid chromatographic separation, post-column reaction and fluorimetric detection. The assay procedure has been applied to the enzymic conversion of racemic norvaline amide into L-norvaline, catalysed by an L-specific aminopeptidase from Pseudomonas putida. Both norvaline amide and norvaline can be analysed in a single assay in the low nanogram range. The method yields reproducible results and requires 30 min from the time of sampling the enzymic reaction mixture to quantitation. The reaction mixture is automatically sampled and analysed several times during the course of the reaction. With the results obtained a conversion curve can be constructed from which the exact biocatalyst consumption can be calculated. By adaptation of the mobile phase, the method can also be applied to other amino acid amides used as substrates in the aminopeptidase reaction.     

Roughness-induced acoustic second-harmonic generation during electrochemical metal deposition on the quartz-crystal microbalance

This paper reports on the relation between the surface roughness and emission of compressional waves from the surface of an electrochemical quartz-crystal microbalance. The detection of the compressional waves took place with an ultrasonic microphone and the quartz crystal itself. As a model process, the electrochemical deposition of copper from an acidic copper sulfate solution has been chosen. For this system, the roughness of the layer can be tuned via the current density. Roughness may be a source of the longitudinal waves at twice the frequency of the exciting shear wave (acoustic second-harmonic generation, ASHG) if the flow profile above the quartz-crystal surface is not entirely laminar. Slight deviations from the laminar flow can be reached at high amplitudes of oscillation. Comparing the ASHG efficiency of a rough and smooth surface, we find that the rough surface is more efficient in generating second-harmonic waves. This suggests that ASHG can be used to obtain a roughness parameter independent from the resonance frequency or bandwidth (damping) of a quartz-crystal resonator. Such an independent determination of roughness should be very interesting in practical applications.     

Synthesis of a pyrrolone-type polymer containing anthraquinone units in molten antimony trichloride

1,2,5,6-Tetraaminoanthraquinone and 1,4,5,8-naphthalenetetracarboxylic acid dianhydride react in molten antimony trichloride to give a soluble polypyrrolone structure with an inherent viscosity of 0.4–0.7. Polymers having the viscosity of 0.7 can be wetspun into fibers from molten antimony trichloride or from methanesulfonic acid; also the polymer can be reduced with sodium dithionite in alkaline aqueous dimethyl sulfoxide to give a viscous solution which can be spun into brittle fibers.     

Eine thermometrisch-kinetische methode zur bestimmung von kupfer und cyanid mit hilfe der kupfer-katalysierten zersetzung von wasserstoffperoxid

The copper-catalyzed decomposition of hydrogen peroxide is retarded by cyanide. The oxidation of cyanide by hydrogen peroxide is likewise catalyzed by copper ions. The decomposition reaction of H₂O₂; can be followed thermometrically. Therefore, at a known copper concentration an unknown amount of cyanide can be determined from the retardation time; and an unknown amount of copper can be determined by adding a known amount of cyanide. Moreover, after the end of the retardation time, unknown copper concentrations can also be determined from the slope of the temperature curve (tana). Copper was determined in the range 4–40 μg, and cyanide in the ranges 3–30, 6–60 and 8–80 μg.     

REPRODUCIBLE PREPARATION OF SILVER SOLS WITH UNIFORM PARTICLE SIZE FOR APPLICATION IN SURFACE-ENHANCED RAMAN SPECTROSCOPY

Abstract This paper describes a new method for the preparation of silver colloids with a narrow range of particle size to be used in surface-enhanced Raman spectroscopy. Using malachite green as a strongly adsorbing dye, it can be shown that colloids from different preparation batches exhibit the same enhancement factor within an error margin of about 15%. By varying the number of nucleation centers, the particle size can be determined at will. An increase in particle diameter from about 38 to about 76 nm leads to an estimated five-fold increase in surface enhancement.     

Separating a mixture of egg yolk and egg white using foam fractionation

A mixture created by blending with a spatula, an egg yolk and an egg white from the same egg can serve as a binary system for testing to see how well foam fractionation can be used to separate two different groups of proteins naturally found together. This mixture of two phases is particularly attractive for such a study because the two phases can be visualized distinctly when in their separated states. It has been shown that air alone at a low flow rate and with little or no water added can effect visually clean separations of egg yolk from egg white, making this a "green" separation process. The white precedes the yolk in the process, which takes less than 10 min at a laboratory scale.     

Single-drop microextraction as a powerful pretreatment tool for capillary electrophoresis: A review

Single drop microextraction (SDME) is a convenient and powerful preconcentration and sample cleanup method for capillary electrophoresis (CE). In SDME, analytes are typically extracted from a sample donor solution into an acceptor drop hanging at the inlet tip of a capillary. The enriched drop is then introduced to the capillary for CE analysis. Since the volume of the acceptor drop can be as small as a few nanoliters, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In addition, by covering the acceptor phase with an organic layer or by using an organic acceptor phase, inorganic ions such as salts in the sample solution can be blocked from entering the acceptor phase, providing desalting effects. Here, we describe the basic principles and instrumentation for SDME and its coupling with CE. We also review recent developments and applications of SDME-CE.     

An electrochemical aptasensor for thrombin detection based on the recycling of exonuclease III and double-stranded DNA-templated copper nanoparticles assisted signal amplification

In this paper, we report an improved electrochemical aptasensor based on exonuclease III and double-stranded DNA (dsDNA)-templated copper nanoparticles (CuNPs) assisted signal amplification. In this sensor, duplex DNA from the hybridization of ligated thrombin-binding aptamer (TBA) subunits and probe DNA can act as an effective template for the formation of CuNPs on the electrode surface, so copper ions released from acid-dissolution of CuNPs may catalyze the oxidation of ο-phenylenediamine to produce an amplified electrochemical response. In the presence of thrombin, a short duplex domain with four complementary base pairs can be stabilized by the binding of TBA subunits with thrombin, in which TBA subunit 2 can be partially digested from 3′ terminal with the cycle of exonuclease III, so the ligation of TBA subunits and the subsequent formation of CuNPs can be inhibited. By electrochemical characterization of dsDNA-templated CuNPs on the electrode surface, our aptasensor can display excellent performances for the detection of thrombin in a broad linear range from 100 fM to 1 nM with a low detection limit of 20.3 fM, which can also specially distinguish thrombin in both PBS and serum samples. Therefore, our aptasensor might have great potential for clinical diagnosis of biomarkers in the future.