Hemiacetal-based dynamic systems: a new mechanistic insight.

The formation of hemiacetals from pyrazine trifluoromethylketone as a model receptor and four simple alcohols was studied by using quantum chemical calculations and NMR spectroscopy. Free energy profiles for four types of mechanistic pathways were calculated and discussed with respect to kinetic and thermodynamic measurements. We show that hemiacetal formation is facilitated by an assisted proton transfer process via a pseudo eight-membered transition state which brings the theory and experiment into close agreement. Also, a newly proposed mechanistic pathway for hemiacetal formation via a five-membered transition state leading to zwitterionic intermediates is discussed. Direct proton transfer in a pseudo four-membered transition state can be ruled out due to the high energy of transition states with respect to other mechanistic pathways. We also show that in the case of hemiacetals, water and alcohol molecules cannot account sufficiently for the H-transfer process via six-membered transition states.

Novel cationic coating agent for protein separation by capillary electrophoresis(†).

A novel positively charged surfactant N-dodecyl-N,N-dimethyl-(1,2-propandiol) ammonium chloride was used for the dynamic coating of the inner wall of a silica capillary. This paper covers the evaluation of dynamic coating and study of the influence of the analysis conditions for the magnitude and direction of electroosmotic flow as well as for the effective and selective separation of chosen proteins (ribonuclease A, cytochrome c, lysozyme, and myoglobin). The concentration of 0.1 mM of N-dodecyl-N,N-dimethyl-(1,2-propandiol) ammonium chloride enabled the reversal of the electro-osmotic flow, however, to separate basic as well as neutral proteins the higher concentration of the studied surfactant was necessary. The final conditions for the separation of studied proteins were set at 100 mM sodium acetate pH 5.5 with 10.0 mM of the studied surfactant. The results were also compared with those of two commercially available cationic surfactants, cetyltrimethylammonium bromide and dodecyltrimethylammonium bromide. Additionally, the developed method for protein separation was applied for the determination of lysozyme in a cheese sample. The limits of detection and quantification of lysozyme were 0.9 and 3.0 mg/L, respectively. The mean concentration of lysozyme found in the cheese sample was 167.3 ± 10.3 mg/kg.

Stabilized hemiacetal complexes as precursors for the controlled release of bioactive volatile alcohols.

Hemiacetals of pyridine-2-carbaldehyde derivatives and volatile alcohols can be stabilized in organic solution in the presence of protons or different metal cations. Despite the inherent instability of hemiacetals in H(2) O, stabilizing them with zinc(II) triflate and adding them to a cationic surfactant formulation resulted in the slow release of the alcohol from cotton surfaces being treated with the hemiacetal complex. Stabilized hemiacetals might thus be suitable delivery systems of bioactive volatiles by rapid hydrolysis in H(2) O-based media.

Hemiacetals in dynamic covalent chemistry: formation, exchange, selection, and modulation processes.

A reversible formation of hemiacetals represents a useful tool in covalent dynamic chemistry. Heterocyclic hemiacetals can be stabilized effectively via either protonation or metal cation coordination. The resulting hemiacetal systems are highly dynamic, show fast response, and display component selection.

Stereoselectivity in the formation of tris-diimine complexes of Fe(II), Ru(II), and Os(II) with a C2-symmetric chiral derivative of 2,2'-bipyridine.

A C2-symmetric enantiopure 4,5-bis(pinene)-2,2'-bipyridine ligand (-)-L was used to investigate the diastereoselectivity in the formation of [ML3]2+ coordination species (M = Fe(II), Ru(II), Os(II), Zn(II), Cd(II), Cu(II), Ni(II)), and [ML2Cl2] (M = Ru(II), Os(II)). The X-ray structures of the [ML3]2+ complexes were determined for Delta-[FeL3](PF6)2, Delta-[RuL3](PF6)2, Lambda-[RuL3](PF6)2, Delta-[OsL3](PF6)2, and Lambda-[OsL3](TfO)2. All of these compounds were also characterized by NMR, CD and UV/VIS absorption spectroscopy. The [FeL3]2+ diastereoisomers were studied in equilibrated solutions at various temperatures and in several solvents. The [RuL3]2+ complexes, which are thermally stable up to 200 degrees C, were photochemically equilibrated.

Using of S-(-)-2-hydroxymethyl-1,1-dimethylpyrrolidinium tetrafluoroborate as additive to the background electrolyte in capillary electrophoresis.

We synthesised and used new type of quaternary ammonium salt [S-(-)-2-hydroxymethyl-1,1-dimethylpyrrolidinium tetrafluoroborate] as effective additive to acidic background electrolytes. We used this quaternary ammonium salt as effective agent for capillary zone electrophoresis separation of model mixture of five tricyclic antidepressants (amitriptyline, nortriptyline, imipramine, desipramine and clomipramine) as model analytes. We observed that addition of S-(-)-2-hydroxymethyl-1,1-dimethylpyrrolidinium tetrafluoroborate ([HMDP](+) [BF(4)](-)) to acidic background electrolytes leads to suppression of magnitude of electroosmotic flow (EOF) and gradually change the direction of the EOF. Baseline separation of five TAs was achieved by using of 91.1 mmol L(-1) (20 gL(-1)) of [HMDP](+) [BF(4)](-) in 25 mmol L(-1) sodium phosphate pH 2.5, where electroosmotic mobility was -11.3 x 10(-9) m(2) V(-1) s(-1). We achieved baseline separation of five TAs with using of [HMDP](+) [BF(4)](-) as water solution too. We observed that [HMDP](+) [BF(4)](-) can be used as buffer additive, which offers relatively smaller anodic electroosmotic flow instead of cationic surfactants that are mostly used for genarating of anodic electroosmotic flow in capillary electrophoresis.