Andrei Blasko

Determination of acid dissociation constants of anomers of amino sugars by 1H NMR spectroscopy

Abstract Acid dissociation constants of α- and β- d -glucos-, mannos-, and galactos-ammonium ions have been determined from 1H NMR chemical shifts of the individual anomers in D2O. Values of pKa(D) for the α- and β-ammonium ions are, respectively: glucosamine, 8.12 and 7.87, mannosamine, 7.78 and 8.50, galactosamine, 8.49 and 8.02. The differences are ascribed largely to differences in the hydration requirements of ammonium and amino groups in the axial and equatorial positions and hydration at upper and lower faces of the sugars. Acid dissociation constants of the 1-hydroxyl group of nonionic d -glucosamine and d -glucose are higher for the β than the α anomer.

HYDROLYSIS OF 2,4-DINITROPHENYL PHOSPHATE IN NORMAL AND REVERSE MICELLES

The rate of spontaneous hydrolysis of the 2,4-dinitrophenyl phosphate dianion (DNPP2–) is strongly increased by aqueous cationic micelles of cetyltrialkylammonium bromides (alkyl = Me, Pr, Bu) and tetradecylquinuclidinium bromide. First order rate constants reach limiting values in dilute surfactant where DNPP2– is fully micellar bound. Rate enhancements increase with increasing bulk of the head group and are associated with decreases in activation enthalpies. Betaine sulfonate micelles (C14H29N+R2[CH2]3SO3–, R = Me, Et, Pr, Bu) also speed hydrolysis, but first order rate constants continue to increase even up to 0.2 mol dm–3 surfactant, because DNPP2– is not strongly bound. Reverse micelles of cetyltrialkylammonium bromide (alkyl = Me, Bu) in dichloromethane give rapid hydrolysis, but rate constants decrease on addition of water approximately to the value observed with aqueous cationic micelles as ‘water pool’ reverse micelles of CTABr are formed. N,N-Dimethylhydroxylamine increases the rate of hydrolysis in water, but not in reverse micelles, and a (hypothetical) phosphoramidate is not trapped by F–.

A microgonotropen branched decaaza decabutylamine and its DNA and DNA/transcription factor interactions.

The central pyrrole of a site-selective DNA minor groove binding tripyrrole peptide 1 has been attached to a branched decaaza decabutylamine via a -(CH-2)3-NHCO-(CH2)-3 linker to provide the decaaza-microgonotropen (8). The decaaza decabutylamine moiety of 8 was designed to have a much greater affinity to the phosphodiester linkages of the backbone of DNA. Employing Hoechst 33258 (Ht) as a fluorescent titrant, the equilibrium constants for the binding for of 8 to the hexadecameric duplex d(GGCGCA3T3GGCGG)/d(CCGCCA3T3GCGCC) and to calf thymus DNA were determined. The log of the product of equilibrium constants (log Kl1Kl2) for 1:1 and 1:2 complexes formation at A3T3 is 17 (35 degrees C). Results of studies of the inhibition of the binding of several proteins to target DNA are discussed. Binding of the E2F1 transcription factor to its DNA target is 50% inhibited at approximately 2 nM concentration of 8.

Complexes of cobalt(III) with D-glucosamine and amines

Abstract d -Glucosamine and ammonia, 1,2-ethylenediamine, or 1,10-phenanthroline form complexes with Co(III) * . The complexes are: [Co(NH 3 ) 3 ·H 2 O· d -glucosamine] 3+ , [Co(en) 2 · d -glucosamine] 2+ and [Co(phen) 2 · d -glucosamine] 3+ . Formation of the last two complexes is stereospecific with Co(III) with predominance of the Δ over the Λ diastereomer. The Δ and Λ diastereomers of the ethylenediamine and phenanthroline complexes with d -glucosamine were separated and their configurations about Co(III) assigned from the CD and ORD spectra. The ethylenediamine complex has p K a ∼ 3.4 and is more acidic than the other complexes, pointing to coordination of the alkoxide residue at position 1 of glucosamine.

A microgonotropen pentaaza pentabutylamine and its interactions with DNA

The central pyrrole of a site-selective DNA minor groove binding tripyrrole peptide (1) has been attached to N-protected pentaazapentacosanoic acid (17) via a -(CH2)3-NHCO-(CH2)3- linker to provide 19, subsequent deprotection provided the pentaaza microgonotropen 4. The polyamine moiety of 4 reaches out of the minor groove and binds to the phosphate backbone of DNA. We find when employing Hoechst 33258 (Ht) as a fluorescent titrant to follow binding of 4 to the hexadecameric duplex d(GGCGCAAATTTGGCGG)/(CCGCCAAATTTGCGCC) and by 1H NMR titration of d(CGCAAATTTGCG)2 with 4 that the latter forms both 1:1 and 2:1 dsDNA complexes. Certain aspects of the structure of 4:d(CGCAAATTTGCG)2 complex derived via 1H NMR are discussed. The electrophoretic mobilities of phi X-174 DNA digested with HaeIII endonuclease restriction fragments complexed to 4 shows that the latter brings about a greater conformational change in the DNA fragments than observed previously with other microgonotropens.

Studies on a hydrocarbon capped free base tetraphenylporphyrin and its conjugate acids - first observation of a monoprotonated tetrapehylporphyrin &{;CapTPP(H3+)CF3CO2−&};

Abstract 1 H-NMR and visible absorbtion spectroscopic titrations of a unique hydrocarbon capped porphyrin 3 H 2 with trifluoroacetic acid in chloroform result in the formation of a monoprotonated porphyrin species 3 H 3 + &{;CF 3 CO 2 − &};. This represents the first observation of a monobasic tetraphenylporphyrin acid. The monocation forms the dibasic 3 H 4 2+ &{;CF 3 CO 2 −&};2 upon further addition of acid. Back-titration of 3 H 4 2+ &{;CF 3 CO 2 − &}; 2 with DMSO demonstrates that the monocation can be generated from the diacid as well as the free base porphyrin. The capping structure on one face of the tetraphenylporphyrin is suggested to diminish the extent of solvation of one proton of 3 H 4 2+ &{;CF 3 CO 2 − &};, thereby rendering the first dissocation constant (represented by C 50(1) ) considerably larger than the second dissociation (C 50(2) ). 19 F NMR chemical shifts of the counterions of −50°C show a similarity to the CF 3 CO 2 − counterions of TPP H 4 2+ &{;CF 3 CO 2 − &}; 2 and indicated a strong association with the prophyrin acid species. 2D NMR ROESY spectroscopy with Distance Geometry Refinement afforded a solution structure for 3 H 2 , from which representative structures of possible inclusion compounds 3 H 3 + &{;CF 3 CO 2 − &}; and 3 H 2 &{;CHCl 3 &}; were created by molecular modeling. Although the dome of the capping structure is predicted to be large enough to accommodate a trifluoroacetate anion on the inside, 19 F NMR spectra and FAB-mass spectra do not support the presence of an acid-base inclusion compound.

SN2 REACTIONS OF A SULFONATE ESTER IN MIXED CATIONIC/PHOSPHINE OXIDE MICELLES

Addition of the nonionic surfactant, dodecyl(dimethyl)phosphine oxide (C12PO) to aqueous cetyltrimethylammonium bromide (CTABr) inhibits the micellar-mediated reaction of Br– with fully bound methyl naphthalene-2-sulfonate (MeONs). Reaction in the micellar pseudophase depends on the concentration of Br– in the interfacial surface region, which is decreased on addition of C12PO by increases in both the fractional micellar ionization, α, and the volume of the micellar pseudophase. The inhibition of the reaction is partially offset by an increase in the second-order rate constant in the micellar pseudophase on addition of C12PO which appears to be related to a solvent-like effect at the micelle–water interface. Interactions of CTABr and C12PO in the mixed micelles were explored by using 1H and 31P NMR spectroscopy.

Structures of complexes of cobalt(III) and glucosamine. Applications of molecular mechanics and NMR spectroscopy

Abstract The 1 H NMR signals of the hydrochlorides of 2-amino-2-deoxy-α- and β- d -glucose (α- and β- d -glucosamine) have been assigned and chemical shifts and coupling constants determined from their phase-sensitive COSY spectra in D 2 O. Based on the Karplus relation the observed coupling constants fit H-H dihedral angles calculated with MM2 parameters. The COSY spectrum of the Λ isomer of [Co(en) 2 · d -glucosamine] 2+ shows that it is formed from the α anomer. The coupling constants, except for J 2,3 and J 3,4 , agree qualitatively with dihedral angles predicted by MM2 parameters. The structure of triammine-Co(III)- l -malate simulated by using MM2 parameters agrees reasonably well with that from X-ray crystallography.

OXIDATIVE HYDROLYSIS OF PHOSPHORUS(V) ESTERS OF THIOLS BY PEROXYMONOSULFATE ION. REACTIONS OF PEROXYMONOSULFATE ION WITH PHOSPHORUS(V) ESTERS OF THIOLS

Peroxymonosulfate ion, HSO−5, as Oxone, readily converts phosphorus(V) esters of thiols into the phosphorus(V) and sulfonic acids. The esters were Ph2PO·SC6H4R(p) with R=MeO (1a), Me (1b), H (1c), Cl (1d) and NO2 (1e), (EtO)2PO · SPh (2), Ph2OI · SEt (3) and PhPO(OEt)SEt (4). Reactions are first order in each reactant and second-order rate constants, k2, for 1a–e fit the Hammett equation with ρ=−0.46. The rate constants increase markedly with increasing water content of H2O–MeCN, the activation enthalpies are low and the entropies are negative. Despite the low value of −ρ, these esters are much less reactive than thiol ethers, but the rate constants of reactions of these compounds and acyl thiols qualitatively follow the ionization potentials of the ethers and the esters.

Complexation of amino sugars with cobalt(III)bis(phenanthroline)

Abstract Complexes of Co(III)bis(phenanthroline) with β - d -mannosamine and α - d -galactosamine can be isolated as the triiodide salts. The complex with d -mannosamine has the Δ -configuration at Co(III). Complexation with d -galactoamine gives the Δ - in excess over the Λ - complex, and the Δ -complex can be isolated chromatographically. Complexation involves cis -1-OH and 2-NH 2 groups, eq , ax respectively with β -mannosamine and ax , eq respectively, with α -galactosamine, as with α -glucosamine, based on 1 H NMR spectra. Galactosamine complexes in aqueous solution decompose to the free sugar, but the mannosamine complex is much more stable.