On a diffusion model of a catalytic reaction

A model to describe a catalytic reaction with simultaneous diffusion is analyzed. The possibility of formation of periodic structures in space is shown.

---

, . .

     

Photoinduced switch of a DNA/RNA inactive molecule into a classical intercalator

Spectroscopic titrations and thermal denaturation experiments show that "acyclic" analogue 1 does not bind to ds-DNA, but under same conditions "cyclic" 2 strongly interacts with ds-DNA and ds-RNA by intercalation into the double helix. Besides, 2 is significantly more effective in inhibition of the tumor cell growth in vitro than 1. We have shown that it is possible to efficiently and irreversibly convert "DNA inactive" compound 1 into "DNA active" compound 2 by light irradiation of the aqueous solutions of the former. This strategy offers a new and attractive approach to photoinduced anticancer therapy.     

Exploration of a proposed biomimetic synthetic route to plumarellide. Development of a facile transannular Diels-Alder reaction from a macrocyclic enedione leading to a new 5,6,7-tricyclic ring system

A concise synthesis of the macrocyclic vinylbutenolide 19 is described, based on a facile RCM reaction of the substrates 16/18. Treatment of 19 with TFA containing water led to the 5,6,7-tricyclic compound 27, in a single step, in >90% yield, rather than to the alternative ring system 23 found in plumarellide (1). A rationale for the formation of 27 is presented, involving initial acid-catalysed hydrolysis of the furanmethanol intermediate 20 to the furanoxonium ion 21, which is next hydrolysed to the enol ether cyclic hemiketal 22. The intermediate 22 undergoes rapid tautomerisation and isomerisation producing enedione 24, which then takes part in a transannular Diels-Alder cyclisation to 26. Dehydration of 26 finally produces the tricyclic compound 27.     

Coupling between a fluorinated olefin and a perfluorinated iodide: a model study on the reaction mechanism of perfluorinated polymer cross-linking

In a model study, , , - and - correlated NMR techniques confirm a Markovnikov type reaction intermediate for the major coupling products between a short, low MW perfluorinated iodide C₂F₅I (I) and a short, low MW fluorinated olefin CF₃(CF₂)₇CHCH₂ (II). The reaction is peroxide induced (di-t-butyl peroxide, DTBP) and is conducted at 140 °C for a 3 h reaction time in a sealed glass ampoule. Side reaction products due to the reaction of DTBP with radical reaction intermediates were also observed and identified. The study aimed to mimic as closely as possible the peroxide-initiated coupling reaction between an iodine terminated fluoropolymer (model compound I) and its fluorinated di-olefin coupling agent (model compound II). A mono-olefin was chosen to simplify the model reaction.     

Wetting of a drop on a sphere

In this work, the equilibrium morphology of a drop on a sphere is analyzed as a function of the contact angle and drop volume experimentally and with analytical effective interfacial energy calculations. Experimentally, a drop on a sphere geometry is realized in an oil bath by placing a water drop on a sphere coated with a dielectric, of which the radii of curvature are comparable with that of the drop. Electrowetting (EW) is used to change the contact angle of the water drop on the sphere. To validate the applicability of EW and the Lippman-Young equation on nonflat surfaces, we systematically investigate the response of the contact angle to the applied voltage (EW response) for various drop volumes and compared the results with the case of a planar surface. The effective interfacial energy of two competing morphologies, namely, the spherically symmetric "completely engulfing" and "partially engulfing" morphologies are calculated analytically. The analytical calculations are then compared to the experimental results to confirm which morphology is energetically more favored for a given contact angle and drop volume. Our findings indicate that the "partially engulfing" morphology is always the energetically more favorable morphology.     

Pulse microcatalytic setup with a reactor inside a flow calorimeter

A pulse microcatalytic setup, whose reactor is placed inside a Thiane-Calvet microcalorimeter is suggested. This setup permits to carry out simultaneous measurements of thermal effect and kinetic parameters of heterogeneous catalytic experiments during one experiment.

---

, -. - .

     

Ideal Conductivity Profile of a Porous Matrix for a Flow-through Porous Electrode with a High Conversion Degree of the Electroactive Component

The possibility of designing an equally accessible, in electric respect ( const), porous electrode (PE) is considered. The design involves creating a special conductivity profile of the solid phase, _s(x), in conditions of considerable variations of current density inside the electrode. A generalized expression for an ideal profile _s(x) at any current distribution is derived, and some concrete solutions for different PE operation modes at the limiting current of the target reaction are obtained. The profiles are exponential over a major fraction of PE and change to hyperbolic at a low conversion degree of the electroactive component. Similarities and differences of the profiles are analyzed. At a high conversion degree, only the exponential profile ensures effective operation of the entire surface of PE and selectivity of the target reaction.     

The sTOF,a Favorable Geometry for a Time-of-Flight Analyzer

A new geometry for the flight region in a time-of-flight mass spectrometer is presented. It consists of two opposing electrostatic sectors of about 255° each and straight sections with a length appropriate to the turns. The resulting geometry folds into a compact space. The first-order aberrations for position, angle, and energy are all zero. The transverse focusing properties are also excellent. For an energetic, high-divergence ion source such as laser ablation, the sTOF has higher resolution and ion transmission than a reflectron of similar physical size.

Open image in new window

Graphical Abstract ?

     

Potential distribution around a charged spherical colloidal particle in a medium containing its counterions and a small amount of added salts

A theory is developed for the potential distribution around a charged spherical colloidal particle carrying ionized groups on the particle surface in a medium containing its counterions (i.e., counterions produced from dissociation of the particle surface groups) and a small amount of added salts on the basis of the theory of Imai and Oosawa. Numerical solutions to the Poisson–Boltzmann equation for the potential distribution are obtained for the case of dilute (but not infinitely dilute) particle suspensions of volume fraction 1 for a1 (where is the Debye–Hückel parameter and a is the particle radius). Here we have taken into account the effects of (i) counterions from the particle surface groups, and (ii) the finite particle volume fraction. These effects, which are usually neglected in the conventional Poisson–Boltzmann equation, are found to be important. It is found that, as in the case of completely salt-free media, there is a certain critical value of the particle charge (which is the same as that for the completely salt-free case). When the particle charge is lower than the critical value, the potential is given by a Coulomb potential. If the particle charge is higher than the critical value, then counterions are accumulated in the vicinity of the particle surface (counterion condensation) and the potential becomes less dependent on the particle charge. The above behaviors can be observed even for the case where the electrolyte concentration is higher than the concentration of counterions from the particle surface groups, if the conditions 1 and a1are both satisfied.     

Mesostructured chitosan-silica hybrid as a biodegradable carrier for a pH-responsive drug delivery system

A biodegradable mesoporous chitosan-silica hybrid has been synthesized by self-assembly of non-toxic F127 Pluronic non-ionic surfactant, biodegradable chitosan and silica source through a real liquid-crystal templating route. On the basis of these biodegradable hybrids, we developed a facile one-pot pH-responsive drug delivery system relying on the coordinate bonding of a "host-metal-guest" architecture. Here, the "host", "metal" and "guest" represent amino groups of chitosan units, metal ions and drug molecules, respectively. Here, daunorubicin (DNR) was chosen as a typical anti-cancer drug molecule, the release of which can be achieved through the cleavage of the coordination bonds that are sensitive to variations in external pH at weak acidic conditions. The successful release of DNR has been observed at pH 5-6, while negligible release has been observed under physiological conditions. The existence of chitosan in the mesoporous silica enhanced both the biodegradability and the strength of the "host-metal-guest" coordination bond.     

The variance of a consensus

In proficiency tests the consensus of the participants' results is often used as the assigned value to calculate z-scores. Where the consensus is quantified as the robust mean of n results, the standard error of the assigned value is often taken to be , where is the robust standard deviation estimated from the same data ¹ . As some of the results are downweighted in robust estimation, is too large a denominator, so that tends to have a somewhat low bias. This bias is shown to be inconsequential for proficiency testing purposes. However, an unbiased estimate can be obtained by using the bootstrap.

---

     

Weakening of amide conjugation with a nitrogen atom included in a four-membered ring

The barriers to amide rotation about the N-N bond in 1-nitrosoazetidine, dimethylnitrosamine, 1-formylazetidine, 1,1-carbonylbisazetidine, 1-dimethylcarbamoylazetidine, and dimethylformamide were measured by dynamic NMR spectroscopy. 1,1-Carbonylbisazetidine and 1-dimethylcarbamoylazetidine, the structures of which were confirmed by data from the PMR and ¹³C NMR spectra, were obtained.Translated from Khimiya Geterotsiklicheskikh Soedenenii, No. 7, pp. 912–194, July, 1987.     

Steps in a minefield

This paper is a review of some of the controversial kinetic aspects of thermal analysis, starting from the esták questions posed in 1979 and looking at developments in some areas since that time. Aspects considered include: temperature programmes and variations, models and mechanisms, kinetic parameters, distinguishability and extent of fit of kinetic models, complementary evidence for kinetic models, the Arrhenius equation and the compensation effect. The value of the ideas of non-isothermal kinetics in chemical education is emphasized.On an occasion such as this, I should like to acknowledge the early inspiration and training of Professor E. G. Prout; the encouragement and help of Professor Leslie Glasser in acquiring our first thermal analysis equipment; the friendship of, and many fruitful years of collaboration with Dr. Andrew Galwey, who has made many contributions to the topic of this lecture; and Professor Patrick K. Gallagher for so much encouragement, interest and support. I am also deeply grateful to Mettler for sponsoring this award and to NATAS for administering it.     

Turn conformations in a metallacyclictripeptide and a metallacyclictetrapeptide induced by tungsten-alkyne coordination

Tungsten-alkyne coordination was employed for the preparation of a metallacyclictripeptide and a metallacyclictetrapeptide. First, the dialkynyltripeptide 7 and the dialkynyltetrapeptide 9 were prepared using solution phase peptide synthesis. In both 7 and 9 the two alkynes were attached to the peptide at the N- and C-termini. Reaction of 7 with W(CO)₃(dmtc)₂ yielded the metallacyclictripeptide 10, while reaction of 9 with W(CO)₃(dmtc)₂ yielded the metallacyclictetrapeptide 11. The identities of 10 and 11 were established using ¹H NMR spectroscopy and positive ion electrospray mass spectrometry. The ¹H NMR spectra of 10 and 11 show that these species exist as a complex mixture of isomers that differ in how the ligands are arranged around the tungsten center. Interconversion between these isomers is slow at 23 °C, but the rate of interconversion increases as the temperature is raised. With 10, all the alkyne hydrogen signals coalesce at 95 °C. However, with 11 the alkyne hydrogen signals do not fully coalesce, even at 105 °C. Related to this is the behavior of 10 and 11 during HPLC analysis; 10 elutes as a single peak, but 11 elutes as two overlapping peaks. The overlapping peaks and the high isomer interconversion temperature of 11 as compared to 10 are attributed to the presence of additional intramolecular hydrogen bonding interactions between the two ends of the peptide in 11.     

Coupling of a sheep anti-T3 IgG to a solid phase for a triiodothyronine radioimmunoassay

Optimal conditions for coupling sheep anti-T₃ IgG to a solid phase are presented. We found that the optimal activation of microcrystalline cellulose was achieved with 0.15M 1,1-carbonyldiimidazol (CDI) in acetone. We also found that using a 25 mg/cm³ anti-T₃ IgG solution, in barbitone buffer 0.05M, pH 8.0, we could get a reasonable yield of coupling and a remaining solution of anti-T₃ IgG (first supernatant) with a suitable concentration (10 mg/cm³) for another coupling. The solid phase anti-T₃ obtained in these two couplings present similar characteristics which make possible their use in a total T₃ RIA.