Photophysical characterization of pyrazino[2,3-c]-1,2,6-thiadiazine 2,2-dioxides in DMSO and acetonitrile solutions

Photophysical characterization of some pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides derivatives in DMSO and acetonitrile has been carried out. Acid-base processes have been found to occur in the ground and excited states. In DMSO and acetonitrile equilibrium between the neutral and deprotonated molecules is established in the ground state. In acetonitrile, a second equilibrium between the neutral and protonated form is also present at a lower pH, and can be treated independently of the first one. Absorption, emission, and excitation spectra of the species involved have been measured; data analysis allows us to calculate pK _aand quantum efficiencies. The change of the decay lifetimes with pH, along with steady state fluorescence measurements show the existence of communication between the excited states and enable us to estimate the excited state kinetic rate constants.A discussion about their possible use as laser dyes based on the energy threshold condition is also given.     

Reactor comparisons for the biodegradation of thiodiglycol,a product of mustard gas hydrolysis

Applied Biochemistry and Biotechnology - An environmentally benign method for the mineralization of sulfur mustard has been proposed involving chemical hydrolysis of sulfur mustard to thiodiglycol,...     

Influence of the thermal boundary layer on the contact layer between a liquid and a cold plate in a solidification process

In this paper, the influence of both the hydrodynamic and the thermal boundary layer on the solidification process of the flowing liquid on a cold plate is theoretically analyzed. Heat transfer between a frozen layer which is created and a laminar flowing liquid over that layer is considered. The development of the boundary layers and the relation between them on the solidification process are studied. An integral method for the solution of the boundary layer equations was used to obtain approximative solutions. The influence of the Prandtl and Reynolds number on the formation of the solid crust is shown and discussed for time dependent and steady-state solutions.     

A discrete approach to the concept of derivative

The concept of derivative is a basic concept of calculus. It is closely related to the concept of function, the idea of rate of change, and the limit concept. In recent decades, teaching the concept of derivative in mathematics classrooms has changed: a quite formal approach—closely linked to the teaching of calculus at university and based on the sequence concept—has been transformed to or substituted by a new one. This means working with rates of change, an intuitive access to the concepts of limit and derivative. It includes working with real functions right from the beginning, a great emphasis on graphs, and the use of digital technologies. The meaning of sequences has decreased to a point where they are sometimes no longer even taught in the calculus course. In recent years this concept has been criticized for not developing adequate perceptions of the basic concepts of calculus and not sufficiently preparing the students for scientific courses at university. In this paper we present an alternative discrete step-by-step approach to the basic concepts of calculus by working with sequences and difference sequences, functions defined on \( \mathbb{Z}\) and discrete domains of \( \mathbb{Q}\) , and by subsequently developing the concept of rate of change in a discrete learning environment. The paper is based on general theoretical considerations and empirical investigations by the author and is meant as a contribution to classroom design-research or “design science” (Wittmann, Educ Stud Math 29(4):355–374, 1995).     

1,3-Diphosphacyclobutene Cobalt Complexes

The synthesis and characterization of rare 1,3-diphosphacyclobutene transition-metal complexes is described. Reactions of the cobalt-hydride complex [Co(P₂C₂tBu₂)₂H] ( G ) with nBuLi, tBuLi, or PhLi afforded [Li(solv)_x{Co(η³-P₂C₂tBu₂HR)(η⁴-P₂C₂tBu₂)}] ( 1 : R=nBu, (solv)_x=(Et₂O)₂; 2 : R=tBu, (solv)_x=(thf)₂; 3 : R=Ph, (solv)_x=(Et₂O)(thf)₂), with an η³-coordinated 1,3-diphosphacyclobutene ligand as a result of organyl-anion attack at one of the phosphorus atoms of the bis(1,3-diphosphacyclobutadiene) backbone. In contrast to the reactions with PhLi, the aryl-magnesium compounds p-tolyl magnesium chloride and p-fluorophenyl magnesium bromide deprotonate [Co(P₂C₂tBu₂)₂H] to give the magnesium salt [Mg(MeCN)₆][Co(η⁴-P₂C₂tBu₂)₂]₂ ( 4 ), which contains a bis(1,3-diphosphacyclobutadiene)-cobaltate anion. The [Co(η⁴-P₂C₂tBu₂)₂]⁻ anions are well separated from the octahedral [Mg(MeCN)₆]²⁺ cation in the molecular structure of 4 . Compound 1 reacts with Me₃SiCl to give neutral [Co(η³-P₂C₂tBu₂HnBu)(η⁴-P₂C₂tBu₂SiMe₃)] ( 5 , 52 % yield) with an SiMe₃ group attached to one of the P atoms of the previously unfunctionalized backbone.     

Multifunctional iron thiocarboxylate complexes: synthesis,reactivity and structure of CpFe(CO)<Subscript>2</Subscript>SCO-3,5-C<Subscript>6</Subscript>H<Subscript>4</Subscript>(COCl)<Subscript>2</Subscript>

A controlled substitution reaction of the chlorine atoms of 1,3,5-benzenetricarbonyl trichloride by the organoiron fragment (CpFe(CO)₂S) has been achieved. The complexes CpFe(CO)₂SCO-3,5-C₆H₃(COCl)₂ (1), 1,3-[CpFe(CO)₂SCO]₂-5-C₆H₃COCl (2) and 1,3,5-[CpFe(CO)₂SCO]₃C₆H₃ (3) were prepared from the reaction of (μ-S _x )[CpFe(CO)₂]₂ (x = 3, 4) with 1,3,5-C₆H₃(COCl)₃ in a 1:1, 2:1, or 3:1 metal to ligand molar ratio. The reactions of (1) with amines, thiols, and carboxylic acids produce the trifunctional mono-iron complexes CpFe(CO)₂SCO-3,5-C₆H₃(COY)₂ [Y = NR₂ (4), SR (5), OCOR (4)]. The X-ray structure determination of (1) is reported.     

Das Lösen realitätsorientierter Aufgaben zu periodischen Vorgängen mit Computeralgebra

There is a new chance in teaching and learning the relationships between mathematics and the real world while using computers and especially computer-algebra-systems in mathematics education. We discuss three real life problems in the area of periodic actions which can be handled with basic knowledge of trigonometry. First we analyse the motion of the twine of a sewing-machine. Geometrical software (Euklid and Cabri) allows the simulation of the motion and Derive gives us the analytical representation of this curve. The second example tries to answer the question how the stroke of an engine can be described mathematically. The last example shows, how a computer-algebra-system (Mathplus) helps to get an analytical expression for the relationship between the time and the monthly found out average values of the air temperature for Munich. On the one hand computer-algebra-systems are an essential help for modelling real life situations, on the other hand the given results allow to understand the situation.     

Economic comparison of calcium fumarate and sodium fumarate production byRhizopus arrhizus

The economics of using Na₂CO₃ rather than CaCO₃ as the neutralizing agent in fumaric acid production byRhizopus arrhizus is investigated and compared with the benzene route. Because sodium fumarate, unlike calcium fumarate, is soluble, downstream processing is simplified by requiring less equipment and no heat, and also allows the reuse of cells. In spite of a fumaric acid productivity (g/L/h) 2.4 x lower than the CaCO₃ case, the Na₂CO₃ alternative with cell reuse has a higher rate of return. However, with the current cost of petroleum, the selling price of fumaric acid from the benzene route is half as much as from an idealized Na₂CO₃ fermentation.