Synthesis of Molecular Wires of Linear and Branched Bis(terpyridine)‐Complex Oligomers and Electrochemical Observation of Through‐Bond Redox Conduction

Films of linear and branched oligomer wires of Fe(tpy)₂ (tpy=2,2′:6′,2′′‐terpyridine) were constructed on a gold‐electrode surface by the interfacial stepwise coordination method, in which a surface‐anchoring ligand, (tpy? C₆H₄N?NC₆H₄? S)₂ ( 1 ), two bridging ligands, 1,4‐(tpy)₂C₆H₄ ( 3 ) and 1,3,5‐(C?C? tpy)₃C₆H₃ ( 4 ), and metal ions were used. The quantitative complexation of the ligands and Fe^II ions was monitored by electrochemical measurements in up to eight complexation cycles for linear oligomers of 3 and in up to four cycles for branched oligomers of 4 . STM observation of branched oligomers at low surface coverage showed an even distribution of nanodots of uniform size and shape, which suggests the quantitative formation of dendritic structures. The electron‐transport mechanism and kinetics for the redox reaction of the films of linear and branched oligomer wires were analyzed by potential‐step chronoamperometry (PSCA). The unique current‐versus‐time behavior observed under all conditions indicates that electron conduction occurs not by diffusional motion but by successive electron hopping between neighboring redox sites within a molecular wire. Redox conduction in a single molecular wire in a redox‐polymer film has not been reported previously. The analysis provided the rate constant for electron transfer between the electrode and the nearest redox‐complex moiety, k₁ (s^?1), as well as that for intrawire electron transfer between neighboring redox‐complex moieties, k₂ (cm² mol^?1 s^?1). The strong effect of the electrolyte concentration on both k₁ and k₂ indicates that the counterion motion limits the electron‐hopping rate at lower electrolyte concentrations. Analysis of the dependence of k₁ and k₂ on the potential gave intrinsic kinetic parameters without overpotential effects: k₁⁰=110 s^?1, k₂⁰=2.6×10¹² cm² mol^?1 s^?1 for [n Fe 3 ], and k₁⁰=100 s^?1, k₂⁰=4.1×10¹¹ cm² mol^?1 s^?1 for [n Fe 4 ] (n=number of complexation cycles).     

Über Anzahl und Verteilung der Scheitel ebener Bogen

Zusammenfassung Seit der Entdeckung des 4-Scheitel-Satzes durch S. Mukhopadhaya (1909) und A. Kneser (1912) hat sich eine umfangreiche Literatur über Scheitel- und verwandte Sätze entwickelt. Unter anderem wurden ebene Bogen auf Scheitel hin untersucht bzgl. Charakteristiken, welche von k 1 Parametern stetig abhängen. Wir legen für die wichtigsten Sätze aus diesem Teil der Theorie überarbeitete Definitionen und Beweise unter vereinfachten Voraussetzungen vor.

---

     

Reibungsdämpfung durch Scheuerleisten: Ein praxisgerechtes Auslegungskonzept

Übersicht Die Fugen zusammengesetzter Bauteile sind einerseits für eine nachteilige Steifigkeitsminderung verantwortlich, tragen aber andererseits durch Reibungsvorgänge wesentlich zum Dämpfungsvermögen einer Konstruktion bei. Merkliche Reibungsdämpfung ohne gleichzeitigen Steifigkeitsverlust bewirken zusätzliche Fugen, die durch Anbringen sogenannter Scheuerleisten entstehen. Der Autor stellt ein Näherungsverfahren zur dämpfungsoptimalen Auslegung von Scheuerleisten vor. Ausgehend von der zu dämpfenden Schwingungsform liefert dieses Verfahren Kriterien für eine günstige Scheuerleistenanordnung, geeignete Leistenabmessungen und als wichtigstes Ergebnis eine dämpfungsoptimale Fugenpressung, die zu maximaler Energiedissipation führt. Schließlich kann das zu erwartende Dämpfungsmaß berechnet und damit das Ergebnis einer vorgesehenen Dämpfungsmaßnahme abgeschätzt werden.

---

Damping by friction ledges: a practical design concept

Summary On the one hand, mating surfaces of structures are responsible for a reduction of stiffness, on the other hand relative motion produces friction, which contributes considerably to the damping. Noticeable friction damping without simultaneous stiffness reduction can be achieved by adding further mating surfaces. Such interfaces are realized by fastening additional elements (e.g. beamlike) onto the structure. An analytic approximation method for these so-called friction ledges is described in this paper. Initiating from the mode shape to be damped the procedure yields criteria for the suitable positioning and design of the ledges. Most important of all is the damping optimized interface pressure, that leads to maximum energy dissipation. Finally, the expected damping rate can be computed, and therefore the result of the proposed measure assessed.

     

Wirkungsgrade in der Welt des Lebens und der Technik

Zusammenfassung Um der oft gehörten Meinung entgegenzutreten, die energetischen Wirkungsgrade lebender Organismen seien wesentlich höher als die technischer Verfahren, werden entsprechende Werte miteinander verglichen. Der sehr niedrige Wirkungsgrad der Photosynthese zusammen mit der kleinen Energiedichte der Sonnenstrahlung erzwang ab einer kritischen Größe die Aufspaltung in Energiesammler, die Pflanzen, und Verbraucher chemischer Energie, den Tieren. Dank den 10 mal höheren Wirkungsgraden in der Technik, lassen sich Solarmobile bauen, die von der auf sie fallenden Sonnenstrahlung angetrieben werden. Wegen des Multiplikationsgesetzes der Teilwirkungsgrade ergeben sich sowohl für die Speicherung der Sonnenenergie in den fossilen Brennstoffen wie in der Nahrungskette extrem niedrige Wirkungsgrade.

---

Efficiencies in the world of life and in engineering

One often hears the opinion, that the efficiencies in the world of life are higher than in engineering. To disprove this, many values of efficiency of corresponding processes are compared. The very low efficiency of photosynthesis in living plants together with the low density of solar radiation has led the world of life to split into collectors of energy, the plants, and consumers of chemical energy, the animals. Thanks to the ten times higher efficiencies of solar cells, it is possible, to produce solar mobiles, vehicles that move driven by solar radiation.

---

---

Herrn Prof. Dr.-Ing. U. Grigull zum 75. Geburtstag gewidmet     

On the diffusion field in the neighborhood of two identical spheres

Summary Under steady state conditions the reduction in the diffusive flux into a sphere due the presence of a neighboring, identical sphere is calculated. Taking the flux into a sphere as 1 when the particles are at infinite separation, the flux decreases to a minimum value of 0.693 when the spheres are touching.

---

Zusammenfassung Unter stationären Bedingungen wird die Abnahme des Diffusionsflusses in eine Kugel, bedingt durch eine benachbarte identische Kugel, berechnet.Wird der Diffusionsfluß in eine Kugel gleich 1 gesetzt, wenn die Partikel unendlich weit voneinander entfernt sind, so nimmt der Diffusionsfluß auf einen Minimalwert von 0,693 ab, wenn sich die Kugeln berühren.

---

---

With 2 figures     

Umsetzung von hydrobromiertem 1,4-Polybutadien mit lithiumorganischen Verbindungen

Ohne ZusammenfassungMit 1 Abbildung und 1 Tabelle     

Eine semiempirische Gleichung zur Beschreibung des Lösungsmitteleinflusses auf Statik und Kinetik chemischer Reaktionen. Teil I

A model has been developed for calculating the enthalpy, entropy and free energy change associated with the creation of cavities in a liquid the size of which corresponds to the volume occupied by a solvent molecule. The molar enthalpy change H _cav equals the molar enthalpy of vaporization of the liquid, the free energy change G _cav is given by G _cav=–RT ln (V _m ·p _eq /RT) (V _m =molar volume,p _eq =equilibrium vapor pressure) and is related to the standard free energy of vaporization. This relationship provides an estimate of the free energy of cavity formation required to accomodate a substrate in the liquid. It has been shown, that the free energy of solvation of a substrate can be dissected into different contributions accounting for (1) the concentration dependence of partial molar free energy quantities, (2) the formation of holes in the solvent, (3) the existence of specific, short range solute-solvent interactions and (4) the dielectric polarization of the medium. Application of this concept leads to an equation of the general form G ^S –G ^R =a(DN ^S –DN ^R )+b(AN ^S –AN ^R )+c(G _vp ^oS –G _vp ^oR ), where G represents the free energy of reaction or activation,DN the donor number,AN the acceptor number and G _vp ^o the standard free energy of vaporization of a solventS and a reference solventR, resp.

---

---

Mit 3 Abbildungen     

K2[(UO2)As2O7] – the First Uranium Polyarsenate

Yellowish crystals of K₂[(UO₂)As₂O₇] ( 1 ) have been synthesized by solid‐state reactions method. The structure of 1 [orthorhombic, Pmmn, a = 12.601(2), b = 13.242(2), c = 5.621(1) Å, V = 937.9(3) ų, Z = 4] has been solved by direct methods and refined to R₁ = 0.049, wR₂ = 0.1060 for 1059 observed reflections. The structure of 1 is based upon [(UO₂)As₂O₇]^2? sheets formed by corner sharing between [UO₆]^6? distorted octahedra and [As₂O₇]^4? polyarsenate groups. The K⁺ cations are either in eightfold or tenfold coordination and are located between the sheets. The topology of the uranyl arsenate sheet is related to silicate minerals of the melilite group and related synthetic silicate, aluminate and germanate compounds.     

Rapid determination of sulphonamides in milk using liquid chromatographic separation and fluorescamine derivatization.

A simple and selective method is presented for the multiple residue determination of eight sulphonamides in consumers' milk. The drugs are sulphisomidine (ID), sulphadiazine (DZ), sulphamerazine, sulphadimidine, sulphamonomethoxine, sulphamethoxazole, sulphadimethoxine and sulphaquinoxaline (SQ). The milk sample was deproteinized with the same volume of 2 M hydrochloric acid and filtered. A 1-ml volume of the filtrate was mixed with 1 ml each of 1.25 M sodium acetate solution and a buffer (pH 3.0) for derivatization with 0.6 ml of 0.02% fluorescamine solution in acetone. A high-performance liquid chromatographic analysis was carried out on a C18 column with a mobile phase of acetonitrile-2% acetic acid (3:5) at 55 degrees C using a fluorescence detector at an excitation wavelength of 405 nm and an emission wavelength of 495 nm. Average recoveries at fortification levels of 2, 5 and 10 ng/ml were 114%, 109% and 106%, respectively. Relative standard deviations were 1-4% at 10 ng/ml for ID, 5 ng/ml for DZ and SQ and 2.5 ng/ml for the other five sulphonamides. The method was applied to 25 milk samples and all appeared to be free from the drugs.     

Structural and Magnetic Study of N2, NO,NO2, and SO2 Adsorbed within a Flexible Single‐Crystal Adsorbent of [Rh2(bza)4(pyz)]n

The crystalline one‐dimensional compound, [Rh^II₂(bza)₄(pyz)]_n ( 1 ) (bza=benzoate, pyz=pyrazine) demonstrates gas adsorbency for N₂, NO, NO₂, and SO₂. These gas‐inclusion crystal structures were characterized by single‐crystal X‐ray crystallography as 1 ?1.5 N₂ (298 K), 1 ?2.5 N₂ (90 K), and 1 ?1.95 NO (90 K) under forcible adsorption conditions and 1 ?2 NO₂ (90 K) and 1 ?3 SO₂ (90 K) under ambient pressure. Crystal‐phase transition to the P space group that correlates with gas adsorption was observed under N₂, NO, and SO₂ conditions. The C2/c space group was observed under NO₂ conditions without phase transition. All adsorbed gases were stabilized by the host lattice. In the N₂, NO, and SO₂ inclusion crystals at 90 K, short interatomic distances within van der Waals contacts were found among the neighboring guest molecules along the channel. The adsorbed NO molecules generated the trans‐NO???NO associated dimer with short intermolecular contacts but without the conventional chemical bond. The magnetic susceptibility of the NO inclusion crystal indicated antiferromagnetic interaction between the NO molecules and paramagnetism arising from the NO monomer. The NO₂ inclusion crystal structure revealed that the gas molecules were adsorbed in the crystal in dimeric form, N₂O₄.