Addition of tert-butylcuprate to (2S)-N-acyl-Δ-dehydroprolinates as a diastereoselective synthetic procedure for obtaining (2S,5S)-5-tert-butylproline

The synthesis of (2S,5S)-Boc-5-tert-butylproline ethyl ester via the addition of tert-butylcuprate to (2S)-N-Boc-Δ⁵-dehydroproline ethyl ester, formed from (2S)-N-Boc-5-methoxyproline ethyl ester, gives an excellent yield of 94% and a high diastereoselectivity (2S,5S):(2S,5R) 78:22. This synthesis opens up a new synthetic route to (2S,5S)-5-tert-butylproline, which is a useful, conformationally rigid, analogue of l-proline.     

Kinetics of formation,dissociation, and redox reactions of the benzyl radical-Cu(II) ion complex in a 10% acetonitrile-90% water mixture

The rate constant of formation, dissociation, and redox reaction of the benzyl radical-copper(II) ion complex have been determined at temperatures from 274 K to 333 K by laser flash photolysis of 1,3-diphenyl-2-propanone (DBK) in a 10% acetonitrile-90% water mixture containing copper(II)perchlorate. Rate constants were calculated from time resolved absorbances of both benzyl radicals (Bz) at 315 nm and benzyl-copper complexes (BzCu²⁺) at 375 nm. Values of the rate constants of the formation of BzCu²⁺ complex were fitted to the equation and the rate constant of the reverse reaction of BzCu²⁺ complex to the equation The rate constant of the redox reaction of BzCu²⁺ complex to benzyl alcohol and copper(I) ion can be described by the equation The first order rate constant of dissociation of phenylacetyl radical formed initially in the flash photolysis of DBK is given by the equation      

The Effect of Temperature on Sorbitan Surfactant Monolayers

The effect of temperature on four sorbitan ester (Span 20, sorbitan monolaurate; Span 40, sorbitan monopalmitate; Span 60, sorbitan monostearate; and Span 80, sorbitan monooleate) monolayers was analyzed. The covered temperature range was from 22 to 42 degrees C. Surface pressure-molecular area isotherms were measured with a Langmuir-type instrument. As the temperature was increased, the monolayers expanded more. This change can also be seen from the surface compressional modulus that was lowered as the temperature was increased. Also, the collapse pressure was lowered as the temperature was increased. Copyright 2001 Academic Press.     

Development of Luminescent Europium(III) and Terbium(III) chelates of 2,2′:6′,2″- terpyridine derivatives for protein labelling

The synthesis and luminescence properties are reported for 20 different chelates composed of 2,2′:6′,2″-terpyridine as the energy-absorbing and donating group, Eu^IIIand Tb^III as the emitting ions, methylenenitrilo(acetic acids) as the stabel chelate-forming moieties, and isothiocyanato or(4,6-dichloro-1,3,5-triazin-2-yl)amino groups as the activated moieties for coupling to biomolecules.     

Novel Bioreversible Prodrugs of Clodronate

Abstract

Clodronate (1) belongs to family of bisphosphonates which are used to inhibit mineralization of soft tissues as well as bone formation and resorption disorders.[I] The clinical use of bisphosphonates is limited due to their poor bióvailability which is mostly attributed to their hydrophilic structure. More lipophilic molecules are obtained if some or all of the anionic sites are converted to covalent bonds. We herein report a new prodrug serie for clodronate: the anhydrides 2 and 3. Previously we have reported that the simple alkyl esters 4 do not release clodronate via chemical or enzymatic hydrolysis.[2] The prepared new derivatives are stable in water (pH 5–7.5) but clodronate isrelased rapidly with enzymatic hydrolysis.     

Identification of the 13/2+ isomer in 199At

The 13/2⁺ isomeric state in the ¹⁹⁹At nucleus has been identified at an excitation energy of 573 keV and its half-life measured to be 580(130) ns using the recoil-decay tagging technique. Received: 19 September 2000 / Accepted: 1 November 2000     

Synthesis of novel (1-alkanoyloxy-4-alkanoylaminobutylidene)-1,1-bisphosphonic acid derivatives

A novel strategy for the synthesis of (1-alkanoyloxy-4-alkanoylaminobutylidene)-1,1-bisphosphonic acid derivatives (1a-d) via (1-hydroxy-4-alkanoylaminobutylidene)-1,1-bisphosphonic acid derivatives (2a-d), starting from alendronate has been developed with reasonable 51-77% overall yields. Intermediate products, (1-hydroxy-4-alkanoylaminobutylidene)-1,1-bisphosphonic acid derivatives (2a-d), were prepared in water with reasonable to high yields (52-94%).     

Dependence of variables construed as an atomic formula

We define a logic D capable of expressing dependence of a variable on designated variables only. Thus D has similar goals to the Henkin quantifiers of [4] and the independence friendly logic of [6] that it much resembles. The logic D achieves these goals by realizing the desired dependence declarations of variables on the level of atomic formulas. By [3] and [17], ability to limit dependence relations between variables leads to existential second order expressive power. Our D avoids some difficulties arising in the original independence friendly logic from coupling the dependence declarations with existential quantifiers. As is the case with independence friendly logic, truth of D is definable inside D. We give such a definition for D in the spirit of [11] and [2] and [1].     

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

The present review describes the use of quantum chemical methods in estimation of structures and electronic transition energies of photosynthetic pigments in vacuum, in solution and imbedded in proteins. Monomeric Mg-porphyrins, chlorophylls and bacteriochlorophylls and their solvent 1:1 and 1:2 complexes were studied. Calculations were performed for Mg-porphyrin, Mg-chlorin, Mg-bacteriochlorin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), d and bacteriochlorophylls a, b, c, d, e, f, g, h, plus several homologues. Geometries were optimised with PM3, PM3/CISD, PM5, ab initio HF (6-31G*/6-311G**) and density functional B3LYP (6-31G*/6-311G**) methods. Spectroscopic transition energies were calculated with ZINDO/S CIS, PM3 CIS, PM3 CISD, ab initio CIS, time-dependent HF and time-dependent B3LYP methods. Estimates for experimental transition energies were obtained from linear correlations of the calculated transition energies of 1:1 solvent complexes against experimentally recorded solution energies (scaling). According to the calculations in five-coordinated solvent complexes the magnesium atom lies out of the porphyrin plane, while in six-coordinated complexes the porphyrin is nearly planar. Charge densities on magnesium and nitrogen atoms were strongly dependent on the computational method deployed. Several dark states of low oscillator strength below the main Soret band were predicted for solvent complexes and chlorophylls and bacteriochlorophylls in protein environment. Such states, though not yet identified experimentally, might serve as intermediate states for excitation energy transfer in photosynthetic complexes. Q(y), Q(x) and Soret transition energies were found to depend on the orientation of the acetyl group and external pressure. A method to estimate site energies and dimeric interaction energies and to simulate absorption and CD spectra of photosynthetic complexes is described. Simulations for the light harvesting complexes Rhodospirillum molischianum, chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, and LHC-II of Spinacia oleracea are presented as examples.     

Trees and Ehrenfeucht–Fraïssé games

Trees are natural generalizations of ordinals and this is especially apparent when one tries to find an uncountable analogue of the concept of the Scott-rank of a countable structure. The purpose of this paper is to introduce new methods in the study of an ordering between trees whose analogue is the usual ordering between ordinals. For example, one of the methods is the tree-analogue of the successor operation on the ordinals.