Inclusion complexes of rosmarinic acid and cyclodextrins: stoichiometry,association constants,and antioxidant potential

The interaction between β-cyclodextrin (β-CD) and the polyphenol rosmarinic acid (RA) is here reported by ¹H NMR titration experiments. The formation of an aqueous soluble inclusion complex is confirmed and valuable information regarding mode of penetration of guest into β-CD, stoichiometry, and stability of the complex is obtained. The analysis by the continuous variation method shows the undoubted formation of 1:1 β-CD/RA complex. Additionally, the estimated apparent association constants reveal the importance of the asymmetry of the RA in the complexation; the incorporation of the catechol moiety closer to the carboxylic group is more favorable (K?=?2,028 M^?1) than from the other end of the RA molecule (K?=?1,184 M^?1). Finally, we have also investigated the antioxidant activity and storage stability of the β-CD/RA complexed system; the presence of β-CD was found to produce a remarkable enhancement on the antioxidant activity.     

Kinetics of the hydrogen abstraction R?OH + H → R?O• + H2 reaction class

This paper presents an application of the reaction class transition state theory (RC‐TST) to predict thermal rate constants for the hydrogen abstraction R? OH + H → R? O^? + H₂ reaction class, where R is an alkyl group. We have derived all parameters for the RC‐TST method for this reaction class from rate constants of 19 representative reactions, coupling with linear energy relationships (LERs) and the barrier height grouping (BHG) approach. Error analyses indicate that the RC‐TST/LER, where only reaction energy is needed, and RC‐TST/BHG, where no other information is needed, can predict rate constants for any reaction in this reaction class with satisfactory accuracy for combustion modeling. Specifically for this reaction class, the RC‐TST/LER method has less than 25% systematic errors in the predicted rate constants, whereas the RC‐TST/BHG method has less than 35% error when compared to explicit rate calculations. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 414–429, 2010     

Unprecedented Double aza‐Michael Addition within a Sapphyrin Core

A novel sapphyrin derivative was obtained from the reaction between a free‐base sapphyrin and dimethyl acetylenedicarboxylate (DMAD). The formation of the new compound involved a double aza‐Michael addition of two pyrrolic NH groups to a DMAD molecule, with the formation of a disubstituted ethano bridge. The NMR spectral data reveal a product with an unsymmetrical structure; DFT calculations provided support for a structure in which the ethano bridge links two adjacent pyrrole units. The present study provides a seemingly unprecedented example of an N,N′‐dinucleophile reacting with DMAD to form a heterocyclic compound in which the two N‐atoms are linked to the two sp³ carbon atoms derived from a substituted acetylene.     

On nondegenerate coupling forms

The aim of the present paper is to investigate new classes of symplectically fat fibre bundles. We prove a general existence theorem for fat vectors with respect to the canonical invariant connections. Based on this result we give new proofs of some constructions of symplectic structures. This includes twistor bundles and locally homogeneous complex manifolds. The proofs are conceptually simpler and allow for obtaining more general results.     

Solid phase synthesis of two muramyl pentapeptide derivatives

Solid phase peptide synthesis (SPPS) of two selected muramyl pentapeptide derivatives is described. The simplicity of removing the protecting groups via one-step deprotection and cleavage from the resin is the biggest advantage of SPPS. Using this method, two muramyl pentapeptide derivatives, D-MurN₃-L-Ala-D-iGlu-L-Lys-D-Ala-D-Ser (5) and D-MurN₃-L-Ala-D-iGlu-L-Lys-D-Ala-D-Ala (6), were obtained. Their chemical structures were confirmed by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) spectroscopy. To determine the absolute configuration of the carbon atom in the side chain of the muramic acid derivative, single-crystal X-ray diffraction measurements were recorded.     

Thermodynamics and infrared spectroscopy of four polymorphs of pyrithyldione

Summary The application of quantitative DSC to the determination of the thermodynamic stability over a range of temperatures is demonstrated with the four polymorphs (I–IV) of pyrithlydione. At first sight, the enthalpy of transition between I and II, calculated by means of van't Hoff isobars and the respective solubilities in n-heptane, differs from the DSC-results by a factor of 2. This is due to association of the solute, and can be established by examining the nature of different solutions of pyrithyldione by means of infrared spectroscopy. The measured densities (1.13 and 1.17 g/cm³) of I (m. p. 96.5° C) and II (m. p. 92° C) are in agreement with the enantiotropism of both forms. The very low heat of fusion (3.7 kJ/ mole) of IV (m. p. 63.5° C) suggests that this unstable form is in the plastic crystalline state. III (m. p. 87° C) can be obtained only from IV. The stability of the polymorphic phases of pyrithyldione is represented in a semi-schematic energy/temperature diagram.

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Thermodynamik und IR-Spektroskopie von vier Pyrithyldion-Modifikationen

Zusammenfassung Die Anwendung der quantitativen Differentialkalorimetrie für die Bestimmung der thermodynamischen Stabilität im gesamten Temperaturbereich wird an den vier Modifikationen (I–IV) von Pyrithyldion gezeigt. Auf den ersten Blick unterscheidet sich die Umwandlungsenthalpie zwischen Mod. I und II, welche aufgrund der van't Hoffschen Reaktionsisobare und der entsprechenden Löslichkeiten in n-Heptan berechnet wurde, von den kalorimetrischen Werten um den Faktor 2. Dieser Umstand ist auf die Assoziation des Gelösten im Lösungsmittel zurückzuführen, was sich durch die IR-Spektroskopie verschiedener Lösungen von Pyrithyldion bestätigen ließ. Die gemessenen Dichten (1,13 und 1,17 g/cm³) von Mod. I (Fp. 96,5° C) und Mod. II (Fp. 92° C) entsprechen dem enantiotropen Verhalten dieser beiden Formen. Die äußerst geringe Schmelzwärme (3,7 kJ/mol) von Mod. IV (Fp. 63,5° C) weist darauf hin, daß sich diese unstabile Form im plastisch-kristallinen Zustand befindet. Mod. III (Fp. 87° C) wird nur über Mod. IV erhalten. Die thermodynamische Stabilität der vier Pyrithyldion-Modifikationen wurde in einem halbschematischen Energie/Temperatur-Diagramm dargestellt.

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A part of this work was reported at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Experimental quantum cloning with prior partial information

When prior partial information about a state to be cloned is available, it can be cloned with a fidelity higher than that of universal quantum cloning. We experimentally verify this intriguing relationship between the cloning fidelity and the prior information by reporting the first experimental optimal quantum state-dependent cloner, using nuclear magnetic resonance techniques. Our experiments may further cast important implications into many quantum information processing protocols.