Eugenijus Butkus

Deprotonation of β-cyclodextrin in alkaline solutions

Variable pH (13)C NMR and (1)H NMR spectroscopic studies of the beta-cyclodextrin (beta-CD) in alkaline aqueous solutions revealed that beta-CD does not deprotonate at pH<12.0. Further increase in solution pH results in the deprotonation of OH-groups adjacent to C-2 and C-3 carbon atoms of beta-CD glucopyranose units, whereas the deprotonation of OH-groups adjacent to C-6 carbon atoms is expressed less markedly. The pK(a) values for beta-CD OH-groups adjacent to C-2 and C-3 carbon atoms are rather close, pK(a1,2) being 13.5+/-0.2 (22.5 degrees C).

Stability of a Dinuclear Cu(II)–β-Cyclodextrin Complex

Cu(II) ions form a dinuclear complex with the tetraanion of β-cyclodextrin (CD4-) in alkaline solutions under conditions of metal ion excess. The spectrophotometric method of ligand displacement was used for the determination of the stability constant of this complex using EDTA and OH- ions as competitive ligands. The results obtained are in agreement with the 2:1 stoichiometry of the complex, namely Cu2CD, the logarithm of the stability constant being 39.2±0.2. This complex predominates in the pH range from 12.5 to 14.3 (3 M NaOH solution), transforming with the increase in alkalinity to

Synthesis of new SAM-forming ferrocene derivatives and their interfacial properties on gold

Abstract We report the synthesis of ferrocene-terminated (C12–C13)-alkylthiols containing an ester group removed from the ferrocene ring by 3-4 carbon atoms. The basic redox properties and some structural features of the self-assembled monolayers formed by these compounds on gold were studied by cyclic voltammetry and surface-enhanced Raman spectroscopy. The monolayers of 9-mercaptanonyl-4′-ferrocenyl butanoate ( 4c ) and -5′-ferrocenyl pentanoate ( 4d ) demonstrated exclusive stability.

Composition- and Size-Controlled Cyclic Self-Assembly by Solvent- and C60-Responsive Self-Sorting.

Synthesis, solvent-, and guest-controlled self-assembly, and self-sorting of new hydrogen-bonded chiral cavity receptors are reported. The design of the cavity is based on the cyclic self-aggregation of monomers containing the 4H-bonding ureidopyrimidinone motif fused with the bicylo[3.3.1]nonane framework. Selective formation of kinetically inert cyclic tetramers is observed in chloroform, while in toluene an equilibrium between tetrameric and pentameric forms exists. The high affinity of the tetrameric aggregates toward C60 and C70 is observed in aromatic solvents. The host-guest interaction of unconventional π-acidic supramolecular receptors for fullerenes is turned off and on by changing the solvent, whereas the selection of size and the very composition of the cavity aggregate is controlled by either the change of solvent or the addition of fullerene guest, making our systems a new type of self-sorting device.

Enantiomer separation and absolute configuration of densely functionalized 2-oxatricyclo[4.3.1.03,8]decanes by CD spectroscopy and chemical correlation

Abstract Enantiomer separation by HPLC on a swollen microcrystalline triacetylcellulose column of highly substituted 2-oxatricyclo[4.3.1.0 3,8 ]decane (2-oxaprotoadamantane) structures afforded enantiomers of this molecule. Application of the octant rule to the carbonyl chromophore to establish the absolute configuration of the enantiomers did not lead to an unequivocal conclusion. The enantioselective synthesis of 4-bromo-3-methoxy-oxaprotoadamantanone was performed from homochiral (+)-(1 S ,5 S )-bicyclo[3.3.1]nonane-2,6-dione thus permitting the assignment of the (1 R ,3 S ,4 S ,6 R ,8 R )-configuration to the title structures.

A Remarkably Complex Supramolecular Hydrogen-Bonded Decameric Capsule Formed from an Enantiopure C2-Symmetric Monomer by Solvent-Responsive Aggregation

The formation of an unprecedented decameric capsule in carbon disulfide, held together by the combination of double and triple hydrogen bonds between isocytosine units embedded in an enantiomerically pure bicyclic framework is reported. The aggregation occurs via symmetry breaking of the enantiopure intrinsically C2-symmetric monomer brought about by solvent, induced tautomerization of the hydrogen-bonding unit. We show that the topology of the aggregate is responsive to the solvent in which the assembly takes place. In this study we demonstrate that in carbon disulfide the chiral decameric cavity aggregate consisting of three forms of the same monomer, differing in their hydrogen bonding to each other is selectively formed, representing a tube-like structure capped with two C2-symmetric monomers. The large cylindrical cavity produced selectively accommodates one partially solvated C60 molecule, and molecular dynamic simulations revealed the special role of the solvent in the inclusion mechanism. The strategy described herein represents the first step toward the creation of a new class of hydrogen-bonded tubular objects from only one small symmetric building block by solvent-responsive aggregation.

Lipophilic 1,4-naphthoquinone derivatives: synthesis and redox properties in solution and entrapped in the aqueous cubic liquid-crystalline phase of monoolein

1,4-naphthoquinone derivatives (NQD) containing lipophilic alkyl chains, i.e. 2-((Z)-heptadec-8-enyl)-3-methyl 1,4-naphthoquinone (QMe), 2-((Z)-heptadec-8-enyl)-3-hydroxy-1,4-naphthoquinone (QOH) and (Z)-octadec-9-enyl 1,4-naphthoquinone-2-carboxylate (QE) were synthesized. The redox behavior of these NQD was studied in ethanol and entrapped in the reversed bicontinuous cubic phase of space group type Pn3m (Q(224)) of aqueous monoolein. In ethanol, cyclic voltammetry curves exhibit two pairs of oxidation-reduction peaks arising from the redox processes controlled by adsorption and molecular diffusion. The NQD molecules are also electrochemically active in the cubic phase, indicating the participation in the 2e(-), 2H(+)-redox cycle at pH<9. Therefore, it was concluded that the head group of the entrapped NQD reaches the lipid bilayer interface of cubic phase during the process.

Influence of Ionic Strength and Cation Nature on the Deprotonation of Methanediol in Alkaline Solution

The pKa values of methanediol deprotonation were found to decrease with increase in solution ionic strength as estimated by a 13C NMR titration method.

Interaction of (+)-Tartrate with Methanediol in AlkalineSolutions

The equilibrium of acetal-type compound formation from (+)-tartrate and methanediol in alkaline solutions has been studied and characterized quantitatively.

Homoconjugation vs. Exciton Coupling in Chiral α,β-Unsaturated Bicyclo(3.3.1)nonane Dinitrile and Carboxylic Acids

The chiroptical properties of enantiomerically pure bicyclo[3.3.1]nona-2,6-diene-2,6-dicarbonitrile and related acids were studied by circular dichroism spectroscopy and theoretical computations. A consideration of the molecular structure of the synthesized difunctional compounds revealed that chromophores are predisposed to transannular through-space interaction due to a favourable conformation of the bicyclic skeleton and a rather small interchromophoric distance. Evidence for non-exciton-type coupling between the two acrylonitrile and acrylate moieties in 3 and 4, respectively, was obtained by chiroptical spectroscopy and DFT calculations.