DNA Sequence and Ancillary Ligand Modulate the Biexponential Emission Decay of Intercalated [Ru(L)2dppz]2+ Enantiomers

The bi‐exponential emission decay of [Ru(L)₂dppz]²⁺ (L=N,N′‐diimine ligand) bound to DNA has been studied as a function of polynucleotide sequence, enantiomer, and nature of L (phenanthroline vs. bipyridine). The lifetimes (τ_i) and pre‐exponential factors (α_i) depend on all three parameters. With [poly(dA‐dT)]₂, the variation of α_i with [Nu]/[Ru] has little dependence on L for Λ‐[Ru(L)₂dppz]²⁺ but a substantial dependence for Δ‐[Ru(L)₂dppz]²⁺. With [poly(dG‐dC)]₂, by contrast, the Λ‐enantiomer α_i values depend strongly on the nature of L, whereas those of the Δ‐enantiomer are relatively unaffected. DNA‐bound linked dimers show similar photophysical behaviour. The lifetimes are identified with two geometries of minor‐groove intercalated [Ru(L)₂dppz]²⁺, resulting in differential water access to the phenazine nitrogen atoms. Interplay of cooperative and anti‐cooperative binding resulting from complex–complex and complex–DNA interactions is responsible for the observed variations of α_i with binding ratio. [Ru(phen)₂dppz]²⁺ emission is quenched by guanosine in DMF, which may further rationalise the shorter lifetimes observed with guanine‐rich DNA.     

Probabilistic Inductive Classes of Graphs

A unifying framework—probabilistic inductive classes of graphs (PICGs)—is defined by imposing a probability space on the rules and their left elements from the standard notion of inductive class of graphs. The rules can model the processes creating real-world social networks, such as spread of knowledge, dynamics of acquaintanceships or sexual contacts, and emergence of clusters. We demonstrate the characteristics of PICGs by casting some well-known models of growing networks in this framework. Results regarding expected size and order are derived. For PICG models of connected and 2-connected graphs order, size and asymptotic degree distribution are presented. The approaches used represent analytic alternative to computer simulation, which is mostly used to obtain the properties of evolving graphs.     

The steady-state thermal stress field in an isotropic sphere with temperature dependent properties

Conclusion For many purposes, the infinite series can be neglected in equations (29) and (30) for the stress field in a hollow sphere and in equations (47) and (48) for a solid sphere. The error estimate from equation (42) or equation (46) may be used as a criterion for deciding whether or not this is permissible. Finally, the method outlined in preceeding discussion is applicable to any one-dimensional thermoelastic problem with only very mild requirements on the variation of Young's Modulus as specified by equation (39). As would be suspected, the use of the procedure for higher dimensional problems entails the specific assumption that second order variations in Young's Modulus are negligibly small if any degree of calculational simplicity is to be retained. Still, this does not require small variations of first order.     

Infrared identification of matrix isolated H2O.O2

Theoretical studies of the H2O.O2 complex have been carried out over the past decade, but the complex has not previously been experimentally identified. We have assigned IR vibrations from an H2O.O2 complex in an inert rare gas matrix. This identification is based upon theoretical calculations and concentration dependent behavior of absorption bands observed upon co-deposition of H2O and O2 in argon matrixes at 11.5 +/- 0.5 K. To aid assignment, we have used a harmonically coupled anharmonic oscillator local mode model with an ab initio calculated dipole moment function to calculate the OH-stretching and HOH-bending frequencies and intensities in the complex. The high abundance of H2O and O2 makes the H2O.O2 complex likely to be significant in atmospheric and astrophysical chemistry.     

Z4-Kerdock Codes, Orthogonal Spreads, and Extremal Euclidean Line-Sets

When m is odd, spreads in an orthogonal vector space of type⁺(2m + 2,2) are related to binary Kerdock codes and extremalline-sets in 2^{m + 1} with prescribed angles. Spreads in a 2m-dimensionalbinary symplectic vector space are related to Kerdock codesover Z₄ and extremal line-sets in with prescribed angles. These connections involve binary, realand complex geometry associated with extraspecial 2-groups.A geometric map from symplectic to orthogonal spreads is shownto induce the Gray map from a corresponding Z₄-Kerdock codeto its binary image. These geometric considerations lead tothe construction, for any odd composite m, of large numbersof Z₄-Kerdock codes. They also produce new Z₄-linear Kerdockand Preparata codes. 1991 Mathematics Subject Classification:primary 94B60; secondary 51M15, 20C99.     

Determination of non-aminoid nitrogen by the micro-Kjeldahl method I. aromatic nitro compounds

Summary A program has been initiated to evaluate the various modifications of the micro-Kjeldahl method and study their application and limitations for the determination of nitrogen in non-aminoid compounds. This paper describes a procedure for aromatic nitro compounds. The sample (3 to 8 mg) is weighed directly into a 30-ml micro-Kjeldahl flask, dissolved in 1 ml acetic acid and 1.5 ml methanol, and reduced with 100 mg zinc metal and 0.4 ml hydrochloric acid. Two drops of concentrated sulfuric acid are added and the organic solvents are removed by heating. The product is then incinerated with 2 ml sulfuric acid, 700 mg potassium sulfate, and 25 mg selenium catalyst. Regular micro-Kjeldahl distillation follows, the ammonia being absorbed in 2% boric acid and titrated with 0.01N potassium biniodate using methyl red-bromcresol green mixed indicator. More than 100 mono- and poly-nitro compounds have been tested by this method; no difficulty has been encountered. Precision and accuracy are within ± 0.3% nitrogen.

---

Zusammenfassung Es wurde begonnen, die verschiedenen Ausführungsformen der Mikro-Kjeldahl-Bestimmung für Stickstoff in nichtaminoider Bindung zu prüfen. Diese Mitteilung beschreibt ein Verfahren für die Behandlung aromatischer Nitroverbindungen. Die Probe von 3 bis 8 mg wird unmittelbar in einen 30-ml-Kjeldahlkolben eingewogen, in 1 ml Essigsäure und 1,5 ml Methyl-alkohol gelöst und mit 100 mg metallischem Zink und 0,4 ml Salzsäure reduziert. Zwei Tropfen konz. Schwefelsäure werden zugesetzt und hierauf die organischen Lösungsmittel abgedampft. Zur Verbrennung der organischen Substanz werden 2 ml konz. Schwefelsäure, 700 mg Kaliumsulfat und 25 mg Selenkatalysator zugefügt. Bei der dann folgenden üblichen Kjeldahl-Destillation wird 2%ige Borsäurelösung vorgelegt, die dann mit 0,01-nKaliumbijodatlösung gegen eine Mischung von Methylrot und Bromkresolgrün titriert wird.Die Anwendung auf mehr als 100 Mono- und Polynitroverbindungen begegnete keinerlei Schwierigkeiten. Präzision und Genauigkeit liegen innerhalb ± 0,3% Stickstoff.

---

Résumé Mise au point d'un programme de travail pour évaluer les différentes modifications de la méthode de Kjeldahl, étudier leur application et leurs limitations dans le cas du dosage de l'azote dans les composés non aminoides. Dans la présente communication on décrit un mode opératoire pour les composés aromatiques nitrés. L'échantillon (3 à 8 mg) est directement pesé dans un micro-matras de Kjeldahl de 30 ml, dissous en 1 ml d'acide acétique et 1,5 ml de méthanol et réduit par 100 mg de zinc métallique et 0,4 ml d'acide chlorhydrique. On ajoute deux gouttes d'acide sulfurique concentré et élimine les solvants organiques par chauffage. Le produit est alors attaqué par 2 ml d'acide sulfurique en présence de 700 mg de sulfate de potassium et 25 mg de sélénium catalyseur. On effectue ensuite une distillation classique de micro-Kjeldahl, absorbe l'ammoniac dans une solution d'acide borique à 2% et titre avec du biiodate de potassium 0,01 N en présence de l'indicateur mixte rouge de méthyle vert de bromocrésol. Plus de cent dérivés mono et polynitrés ont été analysés par cette méthode sans difficulté apparente. La précision et l'exactitude correspondent à moins de ± 0,3% d'azote.

---

---

To Prof. Dr.Hans Lieb at his 70th birthday.     

A pericyclic cascade to the stereocontrolled synthesis of 9-cis-retinoids

A domino reaction that is pericyclic in nature is thought to be triggered upon treatment of alkenynol 10 with arylsulfenyl chlorides. The process comprises an ordered sequence of sigmatropic rearrangements: a reversible [2,3]-allyl sulfenate to allyl sulfoxide shift, followed by a [2,3]-propargyl sulfenate to allenyl sulfoxide rearrangement, and last a stereodifferentiating [1,5]-sigmatropic hydrogen migration leading to polyene 13. The occurrence of the C7 to C11 hydrogen migration has been demonstrated by labeling experiments. The double diastereoselection of the [1,5]-sigmatropic hydrogen shift to afford a single isomer of the final polyene 13 is thought to arise from a combination of the electronic effect of the sulfoxide at one terminus, and the steric effect imparted by the bulky trimethylcyclohexenyl substituent at the other terminus. The overall process thus constitutes a stereoselective synthesis of an E,Z,Z-triene fragment from an alkenynol and, in particular, a retinoid with the 7E,9Z,11Z,13E configuration on the conjugated polyenic side chain. Application of this method to the synthesis of retinoids, including labeled analogues, is straightforward.     

Magnetorheology in an aging, yield stress matrix fluid

Field-induced static and dynamic yield stresses are explored for magnetorheological (MR) suspensions in an aging, yield stress matrix fluid composed of an aqueous dispersion of Laponite? clay. Using a custom-built magnetorheometry fixture, the MR response is studied for magnetic field strengths up to 1?T and magnetic particle concentrations up to 30?v%. The yield stress of the matrix fluid, which serves to inhibit sedimentation of dispersed carbonyl iron magnetic microparticles, is found to have a negligible effect on the field-induced static yield stress for sufficient applied fields, and good agreement is observed between field-induced static and dynamic yield stresses for all but the lowest field strengths and particle concentrations. These results, which generally imply a dominance of inter-particle dipolar interactions over the matrix fluid yield stress, are analyzed by considering a dimensionless magnetic yield parameter that quantifies the balance of stresses on particles. By characterizing the applied magnetic field in terms of the average particle magnetization, a rheological master curve is generated for the field-induced static yield stress that indicates a concentration–magnetization superposition. The results presented herein will provide guidance to formulators of MR fluids and designers of MR devices who require a field-induced static yield stress and a dispersion that is essentially indefinitely stable to sedimentation.