Inclusion complexes of proteins: Interaction of cyclodextrins with peptides containing aromatic amino acids studied by competitive spectrophotometry

The stability constants were measured of inclusion complexes formed from aromatic amino acids and their oligopeptides with - and-cyclodextrin, hydroxypropyl-cyclodextrin, and partially methylated-cyclodextrin. The method of competitive spectrophotometry withp-nitrophenol as a competing reagent was used, and measurements were made at pH 7.4-Cyclodextrin formed complexes of higher stability than the other hosts. The stability of complexes of oligopeptides containing L-phenylalanine was invariably higher than that of L-phenylalanine itself. A model for interaction of proteins with cyclodextrins is proposed, in which the most stable complexes are formed when the native functional form of proteins is unfolded and the nonpolar residues that are buried inside the structure are exposed to water. The complexation of the unfolded structure favors its formation; thus thermal denaturation of proteins is easier in the presence of cyclodextrins. On the other hand, this complexation prevents the intermolecular association of unfolded structures by noncovalent hydrophobic bonding between the exposed nonpolar residues; furthermore, the unfolded complexed forms may revert to the native functional form. This prevention of intermolecular association may explain the stabilizing effect of cyclodextrins on solutions of proteins: a return to the native form is achieved more easily from the complexed, unfolded form than from the unfolded, aggregated forms.Dedicated to Professor József Szejtli.     

Aromastoffe der roten Passionsfrucht. Zwei neue Edulanderivate

Aroma Constituents of the Purple Passion Fruit. Two New Edulan Derivatives The isolation of (2R*, 4S*, 4aS*, 8aS*)-4,4a-epoxy-4,4a-dihydroedulan ( 1 ), and (2R*, 3S*, 8aS*)-3-hydroxyedulan ( 2 ), two new constituents of the purple passion-fruit (Passiflora edulis SIMS ), is reported. Racemic epoxide 1 was synthesized by oxidation of edulan 6 with peracidic acid, and racemate of alcohol 2 was obtained by reduction of ketone 7 , one of the chromic acid oxidation-products of edulan 6 .     

Fluorénacènes et fluorénaphènes Synthèses dans la série des indéno-fluorènes,XV [1] Méthyl-5-dihydro-10, 12-indéno [2, 1-b]fluorène

Starting from α-methylchalcone and diethyl ketone the title compound, II, has been synthesized in 6 steps (overall yield 26%). As an intermediate compound the gold yellow 10, 12-dioxoderivative of II was also obtained.     

Jodometrische Bestimmung von Antimon in Erzen

Zusammenfassung In komplizierten Erzmaterialien wird Antimon mit Hilfe des Freiberger Aufschlusses in Lösung gebracht und von vielen Begleitelementen getrennt. Die Sulfosalze werden mit Wasserstoffperoxid oxydiert und Sb^v danach mit Sulfit zu Sb^III reduziert. Nach Zugabe von Weinsäure und ÄDTA wird Sb bei p_H 9 mit Natriumdiäthyldithiocarbamidat gefällt und mit Chloroform extrahiert. Aus der organischen Phase wird Antimon(III) mit Cadmium verdrängt, rückextrahiert und in der wäßrigen Phase mit einer Jod-Maßlösung titriert.

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Summary For the determination of antimony in complicated ores the sample is fused with potassium carbonate and sulphur. In this way a separation from many accompanying elements is achieved. The thiosalts are oxidized by hydrogen peroxide, whereupon antimony is reduced from the quin quevalent to the trivalent state by means of sodium sulphite. After addition of tartaric acid and EDTA antimony is precipitated at p_H 9 with sodium diethyldithiocarbamidate and extracted with chloroform. From the organic phase antimony is reextracted by displacement with cadmium salt and titrated with a standard iodine solution.

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Ein ähnliches Verfahren zur Zinkbestimmung vgl. Jankvoský, J.: diese Z. 201, 330 (1964).     

Fundamental Aspects of Ionic Dissociations: The Fragmentation Pathways of Excited Bicyclobutane Cations

A most recently developed method to quantify the fragmentation pathways of excited radical cations is presented. Using bicyclobutane cation as an illustrative example, the RRKM analysis of the breakdown diagram determined by He-Iα photoelectron-photoion coincidence spectroscopy is outlined. The results imply complete isomerization to 1,3-butadiene cation preceding the dissociative processes. The rate-energy functions of four competitive primary fragmentation reactions, leading to C₃H, C₄H, C₄H and C₂H are established. There is compelling evidence that the production of C₂H fragment ions does not compete effectively with these four reactions. The extent of kinetic and competitive shift effects is determined. The derived enthalpies of formation are in excellent accord with the available high quality reference data. The relative importance of different fragmentation pathways which ultimately lead to fragment ions of identical mass to charge ratio is assessed.     

Concrete quantum logics with covering properties

LetL be a concrete (=set-representable) quantum logic. Letn be a natural number (or, more generally, a cardinal). We say thatL admits intrinsic coverings of the ordern, and writeL C _n , if for any pairA, BL we can find a collection {C _i iI}, where cardI<n andC _i L for anyiI, such thatA B= _il C _i . Thus, in a certain sense, ifLC _n , then the rate of noncompatibility of an arbitrary pairA,BL is less than a given numbern. In this paper we first consider general and combinatorial properties of logics ofC _n and exhibit typical examples. In particular, for a givenn we construct examples ofL C _n+1\C _n . Further, we discuss the relation of the classesC _n to other classes of logics important within the quantum theories (e.g., we discover the interesting relation to the class of logics which have an abundance of Jauch-Piron states). We then consider conditions on which a class of concrete logics reduce to Boolean algebras. We conclude with some open questions.     

Configurationally and conformationally homogeneous cyclic n-aryl sulfimides—IV : Synthesis,configuration and stereochemistry of the rearrangement of 1,3-di-thiane-1-N-p-chlorophenylimides

1,3-Dithiane-1-N-p-chlorophenylimides (1,4-9) were prepared and their configuration and conformation was determined by ¹H and ¹³C NMR. The compounds were rearranged to the corresponding 2-(2'-amino-5'-chlorophenyl)-1, 3-dithianes (1U,4U,9U). The rearrangement reactions took place with ?95% stereospecifity. The mechanism of the reaction was investigated with the aid of analogs specifically deuterated at C-2.     

Performance of the general-model-space state-universal coupled-cluster method

The capabilities of the recently developed multireference, general-model-space (GMS), state-universal (SU) coupled-cluster (CC) method have been extended in order to enable the handling of any excited state that represents a single (S) or a double (D) excitation relative to the ground state. A series of calculations concerning the ground and excited states of the CH(+), HF, F(2), H(2)O, NH(2), and CH(2) molecules were carried out so as to assess the performance of the GMS SU CCSD method. For diatomics we have computed the entire potential energy curves, while for triatomics we have focused on vertical excitation energies. We demonstrate how a systematic enlargement of the model space enables a consideration of a larger and larger number of excited states. A comparison of the CC and full configuration interaction or large-scale CI results enables an assessment of the accuracy and reliability of the GMS SU CCSD method within a given basis set. In all cases very good results have been obtained, including highly excited states and those having a doubly-excited character.     

Uranium (III) scorpionates: synthesis and structure of [(TpMe2)2U[N(C6H5)2]] and [(TpMe2)2U[N(SiMe3)2]

Reaction of [(Tp(Me)2)(2)UI] with KNR(2) (R = C(6)H(5), SiMe(3)) in tetrahydrofuran (THF) afforded the monomeric trivalent actinide amide complexes [(Tp(Me)2)(2)U[N(C(6)H(5))(2)]], 1, and [(Tp(Me)2)(2)U[N(SiMe(3))(2)]], 2. The complexes have been fully characterized by spectroscopic methods and their structures were confirmed by X-ray crystallographic studies. In the solid state 1 and 2 exhibit distorted pentagonal bipyramidal geometries. The U-NR(2) bond lengths in both complexes are the same but in complex 2 the greater steric demands of the N(SiMe(3))(2) ligand led to elongated U-N(pz) bonds, especially those opposite the amido ligand.     

Formation of two isomeric closo-[(eta5-C5H5)FePC2B8H10] phosphadicarbaborane analogues of ferrocene via isolable eta1-bonded complexes of the [7-[(eta5-C5H5)Fe(CO)2]-(eta1-nido-PC2B8H10)] type

The reaction of nido-[7,8,9-PC(2)B(8)H(11)] (1) with [[CpFe(CO)(2)](2)] (Cp=eta(5)-C(5)H(5) (-)) in benzene (reflux, 3 days) gave an eta(1)-bonded complex [7-Fp-(eta(1)-nido-7,8,9,-PC(2)B(8)H(10))] (2; Fp=CpFe(CO)(2); yield 38 %). A similar reaction at elevated temperatures (xylene, reflux 24 h) gave the isomeric complex [7-Fp-(eta(1)-nido-7,9,10-PC(2)B(8)H(10))] (3; yield 28 %) together with the fully sandwiched complexes [1-Cp-closo-1,2,4,5-FePC(2)B(8)H(10)] 4 a (yield 30%) and [1-Cp-closo-1,2,4,8-FePC(2)B(8)H(10)] 4 b (yield 5%). Compounds 2 and 3 are isolable intermediates along the full eta(5)-complexation pathway of the phosphadicarbaborane cage; their heating (xylene, reflux, 24 h) leads finally to the isolation of compounds 4 a (yields 46 and 52%, respectively) and 4 b (yields 4 and 5%, respectively). Moreover, compound 3 is isolated as a side product from the heating of 2 (yield 10%). The structure of compound 4 a was determined by an X-ray structural analysis and the constitution of all compounds is consistent with the results of mass spectrometry and IR spectroscopy. Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B]-COSY, and (1)H[(11)B(selective)] magnetic resonance measurements led to complete assignments of all resonances and are in excellent agreement with the structures proposed.