Diagram of State of Stiff Amphiphilic Macromolecules

Summary: We studied coil-globule transitions in stiff-chain amphiphilic macromolecules via computer modeling and constructed phase diagrams for such molecules in terms of solvent quality and persistence length. We showed that the shape of the phase diagram essentially depends on the macromolecule degree of polymerization. Relatively short amphiphilic molecules always form a spherical globule in a poor solvent, and the coil-globule transition includes one or two intermediate conformations, depending on the chain's stiffness. These are a disk-like globule in case of high enough Kuhn segment length, and a pearl necklace-like structure of spherical micelles and a disk-like globule in case of relatively flexible chains. The phase diagram of a long stiff amphiphilic chain was found to be more complex still. Thus three specific regions can be distinguished in the poor solvent region, depending on the chain stiffness. These correspond to a cylindrical globule without any specific backbone ordering, a cylindrical globule containing blobs with collagen-like ordering of the chain, and co-existence of collagen-like and toroidal globules. In the intermediate transition region in this case, apart from the pearl necklace-like conformations with spherical micelles, necklace conformations can be also observed where the polymeric chain has collagen-like ordering within each bead.     

A new class of non-classical azapentalenes. Synthesis and c-13/n-15 NMR characterization of 2H-imidazo[1, 5-d]tetrazoles

The title compounds 6 (as well as the oxazoles 5 ) were obtained by thermolysis of 2-alkyl-5-(methoxycarbon-yldiazomethyl)tetrazoles 3 in benzonitrile. They were fully characterized by ¹H, ¹³C and ¹⁵N nmr spectroscopy.     

Analytical methods for parameter-space delimination and application to shallow-lake phytoplankton-dynamics modeling

The first step in parameter estimation is to reduce the dimensionality of the problem by deriving estimates from independent experimentation and from the literature. In addition, insensitive parameters are either removed or fixed. In the remaining lower-dimensional problem, parameter-space delimitation is possible by analytical means. Three conjunctive methods are derived: period-average analysis, extremum analysis, and quasisteady-state analysis. The basic idea is to find conditions for the parameters that must be fulfilled in order to comply with average and extreme values in the observations. The approach is applied to the modeling of the phytoplankton dynamics of Lake Balaton. The analytical techniques prove to supply valuable insight into parameter interrelationships and model adequacy, and can serve as satisfactory substitutes for formal parameter-estimation techniques in the early stages of model development.     

Towards logistics systems parameter optimisation through the use of response surfaces

Logistics systems have to cope with uncertainties in demand, in lead times, in transport times, in availability of resources and in quality. Management decisions have to take these uncertainties into consideration. An evaluation of decisions may be done by means of simulation. However, not all stochastic phenomena are of equal importance. By design of simulation experiments and making use of response surfaces, the most important phenomena are detected and their influence on performance estimated. Once the influence of the phenomena is known, this knowledge may be used to determine the optimal values of some decision parameters. An illustration is given on how to use response surfaces in a real-world case. A model is built in a logistics modelling software. The decision parameters have to be optimised for a specific objective function. Experiments are run to estimate the response surface. The validity of the response surface with few observations is also tested.     

A rare case of three rearrangements during the cycloaddition-elimination reaction of 4-methyl-5-phenylimino-Δ2-1,2,3,4-thiatriazoline with 2-pyridyl isothiocyanate

2-Pyridyl isothiocyanate ( 7 ), with its electrophilic and basic properties, gives a series of ring-transformation reactions with 4-methyl-5-phenylimino-1,2,3,4-thiatriazoline ( 1 ) at 60°. Two dithiazolidines, 8 and 10 , are formed as major products at an early stage of the reaction, whereas two thiadiazolidines, 9 and 11 , predominate at the end. The mechanism (Schemes II and III) has been elucidated by following the reaction course under a variety of conditions and by analyzing the products by ¹³C nmr spectroscopy.     

Spectra of Liouville operators

Spectra of the generators of time translations (Liouville operators) on representation spaces determined by thermodynamic equilibrium states are compared and their nature is investigated.     

Molecular rearrangements of 5-azido substituted 1,2,3-triazoles

5-Azido-4-methoxycarbonyl-1-phenyl-1,2,3-triazole ($\text{8a}$) and its phenyl substituted derivatives $\text{8b}$,$\text{c}$ rearrange at 60–80°C to give tetrazolyldiazoacetates $\text{9}$, which have been isolated. When the reactions are allowed to go to completion, products derived from the diazo compounds are obtained; i.e. norcaradienes ($\text{10}$) from benzene solutions and imidazotetrazoles ($\text{12}$) from nitrite solutions. The latter decompose photochemically into diazacyclopentadienonimines ($\text{13}$). A kinetic study of the rearrangement $\text{8}$ → $\text{9}$ has been carried out and the mechanism (Scheme VI) is discussed in comparison with the Dimroth rearrangement.     

Ab initio computed diabatic potential energy surfaces of OH-HCl

The two four-dimensional diabatic potential energy surfaces (DPESs) for OH-HCl are computed that correlate with the twofold degenerate (2)Pi ground state of the free OH radical. About 20 000 points on the surface are obtained by the ab initio coupled-cluster and multi-reference configuration interaction methods. Analytic forms for the diabatic potential energy surfaces are derived as expansions in complete sets of orthogonal functions depending on the three intermolecular angles. The numeric computation of the angular expansion coefficients is discussed. The distance-dependence of the angular coefficients is represented by the reproducing kernel Hilbert space method. It is checked that both diabatic potentials converge for large intermolecular separations to the values computed directly from the electrostatic multipole expansion. The final DPESs are discussed and illustrated by some physically meaningful one- and two-dimensional cuts through them.