Total synthesis of the antitumor antibiotic (+/-)-fredericamycin A by a linear approach

A linear approach to the total synthesis of racemic fredericamycin A (1) through the oxidative intramolecular [4 + 2] cycloaddition of a (phenylthio)acetylene-cobalt complex is described, which is applicable for the asymmetric total synthesis of naturally occuring 1. The highlight of this work is the aromatic Pummerer-type reaction with 1-ethoxyvinyl chloroacetate, which effects the introduction of the oxygen functional group to the internal B-ring of the highly functionalized, congested polyaromatic ABC-ring moiety.     

Syntheses and electronic properties of the nickel and palladium complexes of the octaethylporphyrin(M1)-(dihexylbithiophene)n-octaethylporphyrin(M2) system [OEP(M1)-(DHBTh)n-OEP(M2)] connected with the diacetylene linkage. A methodology for molecular design of the particular electronic structure

The palladium complexes of highly extended π-electronic conjugation system, octaethylporphyrin(Pd)-(dihexylbithiophene)_n-octaethylporphyrin(Pd) [OEP(Pd)-(DHBTh)_n-OEP(Pd), n=1-6], were synthesized, in which all the chromophores are connected with diacetylene linkage. The unsymmetrical derivatives of OEP(Ni)-DHBTh-OEP(Pd) were also successfully synthesized. Electronic properties of these symmetrical and unsymmetrical complexes were conclusively described, as compared with those of OEP(Ni)-(DHBTh)_n-OEP(Ni). Based on the structure elements, a methodical guiding principle for molecular design of the particular electronic structure will be proposed.     

Extending the horizon: towards the efficient modeling of large biomolecular complexes in atomic detail

The application of evaluation of implicit solvent methods for the simulation of biomolecules is described. Detailed comparisons with explicit solvent are described for the modeling of peptide and proteins in continuum aqueous solvent. In addition, we are presenting new data on the simulation of DNA with implicit solvent and describe the development of a heterogeneous dielectric model for the simulation of integral membranes. The performance of implicit solvent simulations based on the GBMV generalized Born method is compared with explicit solvent simulations, and implications for the simulation of very large biomolecular complexes is discussed. We are anticipating that the work described herein will lead to new, efficient modeling tools that will allow the simulation of longer timescales and larger system sizes in order to meet current and future challenges by the experimental community.     

Strong binding between acidic guests and fluorescein modified -γ-Cyclodextrin via hydrogen bonding

-Cyclodextrin with appended fluorescein (1) has been prepared as a sensor and a charge-changeable receptor for detecting organic compounds including terpenoids, carboxylic acids and bile acids. Compound1 has cationic, neutral and anionic forms depending on the pH of the solutions. The anionic form of1 at about neutral pH exhibits the highest sensing ability for carboxylic acids and bile acids, while at alkaline pH it detects hardly any of the guests examined. The high sensitivity and selectivity of the anionic form of1 at around neutral pH for acidic guests seems to be caused by the hydrogen bond between the phenoxide anion moiety of fluorescein and acidic guests. The neutral form of1 exhibits little sensing ability for all the guests, but the cationic form shows comparatively higher sensing ability for the guests examined.     

A 2D layered spin crossover complex constructed by NH...Cl- hydrogen bonds: [FeIIH3LMe]Cl.I3 (H3LMe = tris[2-(((2-methylimidazoyl-4-yl)methylidene)amino)ethyl]amine

A 2D layered spin crossover complex, [FeIIH3L(Me)]Cl.I3, has been synthesized from the reaction of FeIIICl3, a tripod ligand (H3LMe = tris[2-(((2-methylimidazoyl-4-yl)methylidene)amino)ethyl]amine), and NaI in methanol. The compound showed an abrupt spin transition between the HS (S = 2) and LS (S = 0) states at T(1/2) = 110 K without hysteresis. The crystal structures of the HS and LS states were determined at 180 and 90 K. A 2D layered structure is composed of NH...Cl- hydrogen bonds between the Cl- ion and three neighboring imidazole groups of [FeIIH3LMe]2+. The green light irradiation at 5 K induced the LIESST effect, and the thermal relaxation process from the HS to LS state showed a sigmoid curve at T > 55 K.     

Potent and specific sialyltransferase inhibitors: imino-linked 5a'-carbadisaccharides

Methyl 5a'-carba-beta-lactoside, imino-linked, has been shown to possess potent and specific inhibitory activity (IC50 = 185 microM) toward rat recombinant alpha2,3-sialyltransferase.     

On the convergence of the kadanoff transformation towards trivial fixed points

Summary We consider the Kadanoff transformation T (depending on a positive parameter p) acting on probability measures on the space {+1, –}^d. A measure is called a non-trivial fixed point of T, if it is extremal in the set of T-invariant measures but is not a product measure. We describe the set of trivial fixed points and show that non-trivial fixed points exist provided that d2 and p large enough. A strong mixing condition on implies convergence of T ⁿ towards a trivial fixed point. In particular this applies to the two-dimensional Ising model except at the critical point. What happens at the critical point still remains unknown.Research supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 123)     

Langmuir monolayers of cerebroside originated from Linckia laevigata: binary systems of cerebrosides and phospholipid

The surface pressure (pi)-area (A), the surface potential (DeltaV)-A and the dipole moment (mu( perpendicular))-A isotherms were obtained for six cerebrosides of LLC-2, LLC-2-1, LLC-2-8, LLC-2-10, LLC-2-12, and LLC-2-15, which were isolated from Linckia laevigata, and two-component monolayers of two different cerebrosides (LLC-2 and LLC-2-8) with phospholipid of dipalmitoylphosphatidylcholine (DPPC) on a subphase of 0.15 M sodium chloride solution as a function of cerebroside compositions in the two-component systems by employing the Wilhelmy method, the ionizing electrode method, and the fluorescence microscopy. The new finding was that LLC-2 showed a stable and liquid expanded type film. Four of them (LLC-2-8, -10, -12, and -15) had the phase transition from the liquid-expanded (LE) to the liquid-condensed (LC) states at 298.2 K. The apparent molar quantity changes (Deltas(gamma), Deltah(gamma), and Deltau(gamma)) on their phase transition on 0.15M at 298.2 K were calculated. The miscibility of cerebroside and phospholipid in the two-component monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the cerebroside molar fraction (X(cerebroside)), using the additivity rule. From the A-X(cerebroside) and DeltaV(m)-X(phospholipid) plots, a partial molecular surface area (PMA) and an apparent partial molecular surface potential (APSP) were determined at the discrete surface pressure. The PMA and APSP with the mole fraction were extensively discussed for the miscible systems. Judging from the two-dimensional phase diagrams, these were found to be one type, a positive azeotropic type; all the cerebrosides were miscible with DPPC. Furthermore, assuming a regular surface mixture, the Joos equation for the analysis of the collapse pressure of two-component monolayers allowed calculation of the interaction parameter (xi) and the interaction energy (-Deltavarepsilon) between the cerebrosides and DPPC. The miscibility of cerebroside and phospholipid components in the monolayer state was also supported by fluorescence microscopy.     

Molecular design of lipophilic disalicylic acid compounds with varying spacers for selective lead(II) extraction

Lipophilic disalicylic acids 5,5'-decyl-2,2'-[1,2-ethanediylbis(oxy)]bisbenzoic acid (1), 5,5'-decyl-2,2'-[1,3-propanediylbis(oxy)]bisbenzoic acid (2), 5,5'-decyl-2,2'-[oxybis(1,2-ethanediyl-oxy)]bisbenzoic acid (3), 3,5-bis[2'-(2'-carboxyphenoxy)ethyl]-4-oxahexacyclo-[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecane (4), and 1,3-bis[2'-(2'-carboxyphenoxy)ethyl]adamantane (5) are evaluated as selective Pb(II) extractants. The solvent extraction of Pb(II) and of Cu(II) from buffered aqueous solutions of varying pH into chloroform by ligands 1-5 is examined in relation to the molecular structure of the dicarboxylic acid extractant. Ligand 1, with an ethylene spacer between two lipophilic salicylic acid units, exhibits excellent extraction selectivity for Pb(II) over Cu(II). Lengthening the spacer in ligands 2 and 3 diminishes both the extraction efficiency and selectivity. Ligands 4 and 5, with rigid spacer units, show significant reductions in both Pb(II) and Cu(II) extraction. Slope analysis reveals that ligand 1 reacts in a 2:1 stoichiometry with Pb(II) in extraction, which differs from the 1:1 stoichiometries for 2 and 3. The differences in the half extraction pH (DeltapH(1/2)) values for Pb(II) and Cu(II) extraction are 1.29, 0.49, and 0.48 for 1-3, respectively.     

Photo-responsive behavior of a monolayer composed of an azobenzene containing polypeptide in the main chain

A photoresponsive polypeptide, two -helical poly(-methyl L-glutamate)s joined with an azobenzene (MAzoM,Mn=11000), have been prepared. Monolayers of the polypeptide were formed at air-water interface and the photoresponsive behavior of the monolayer obtained was investigated. A trans to cis photo-isomerization of the azobenzene moiety in the main chain of MAzoM induced by UV light irradiation resulted in a bending structure formation in the main chain of the polypeptide via photo-induced changes in the geometry of the azobenzene chromophore. As a result, the limiting area per molecule of the MAzoM monolayer was decreased. Based on the degree of the decrease in the limiting area per molecule, it was estimated that the bending angle between the two -helical rods of MAzoM molecule under UV light irradiation was ca. 140°. The photo-responsive behavior of the MAzoM monolayer was reversible and consisted along with the photo-isomerization of azobenzene moiety.