Past, present and future of nucleic acids electrochemistry

Electrochemistry of nucleic acids was discovered about 40 years ago. During the first 15 years electrochemistry brought early evidence of DNA premelting and polymorphy of the DNA double helix. At present electrochemical methods working with stationary electrodes are able to detect DNA at attomol and in some cases, even at lower levels. A great progress in the development of electrochemical sensors for DNA hybridization and DNA damage achieved in recent years suggests that these sensors may soon become important tools in medicine and other areas of practical life of the 21st century.     

Die Veresterungsgeschwindigkeiten der Nitrobenzoesäuren in Äthylenglykol und der Naphtoesäuren in Glyzerin

Zusammenfassung Es werden die monomolekuren Geschwindigkeitskonstanten der durch Chlorwasserstoff katalysierten Veresterung der Nitrobenzoesäuren in Glykol und der Naphthoesäuren in Glyzerin bei 25° gemessen und als Funktionen der Wasser- (w) und Salzsäurekonzentration (c) des Mediums durch Intrapolationsformeln dargestellt.Diese Konstanten nehmen in wasserwarmem Glyzerin und Glykol und in wasserreicherem Glyzerin proportional der Chlorwasserstoffkonzentration zu, in wasserreicherem Glykol aber rascher, was mit früheren Beobachtungen übereinstimmt. Fürc=1/6 undw=0.065 ist das Verhältnis der monomolekularen Konstanten der Benzoesäure zu jenen dero-,m- undp-Nitrobenzoesäure und der- und-Naphthoesäure in Äthylalkohol 10.0540.570.700.391.00, in Glykol 10·0380·690·79, in Glyzerin 10·0680·630·800·610·93. Die sterische Hinderung durch die Orthosubstitution ist somit hier in Glyzerin kleiner, in Glykol größer als in Äthylalkohol. Daher wird auch die Orthonitrobenzoesäure in Glyzerin rascher als in Glykol verestert, während sonst meist das umgekehrte Verhältnis besteht.Bei geringem Wassergehalt sind die Veresterungsgeschwindigkeiten in beiden Medien kleiner als in Äthylalkohol, bei größerem aber größer wegen der weitaus stärkeren verzögernden Wirkung des Wassers in letzterem.Unter den Versuchsbedingungen findet praktisch vollständige Veresterung statt, so daß die Wiederverseifung nicht zu berücksichtigen ist.Bei 183° verläuft die Selbstveresterung der Naphthoesäuren in Glyzerin ebenso wie die der bisher gemessenen Säuren nach der Gleichung für sesquimolekulare Reaktionen, deren Konstanten in Glyzerin, das etwa zwei Mole Wasser im Liter enthält, um rund 20% kleiner sind als in ursprünglich absolutem. In letzterem sind sie bei der-Naphthoesäure neunmal, bei der-Naphthoesäure elfmal kleiner als bei der Benzoesäure, woraus geschlossen wird, daß diese in Glyzerin von 183° nicht nur stärker als die-, sondern auch als die-Naphthoesäure dissoziiert sein muß, falls es sich bei der Selbstveresterung hauptsächlich um eine Wasserstoffionenkatalyse handelt.In Glyzerin und Glykol bei 25° über die Geschwindigkeit der Chlorhydrinbildung ausgeführte Versuche bestätigen den Befund von Kailan und Goitein.     

Investigation of the electrokinetic properties of paraffin suspension. 2. In cationic and anionic surfactant solutions

Electrical phenomena at nonionogenic hydrophobic surfaces (solid or liquid) in water, electrolyte, and/or surfactant solutions still attract research. In part 1 of this paper we described the electrokinetic behavior of paraffin wax suspension in water and electrolyte solutions (NaCl or LaCl3). On the basis of the latest data of water structure near hydrophobic surfaces it was concluded that immobilized water dipoles at the interface can play an essential role in the zeta potential formation. In this paper were investigated the zeta potentials of paraffin wax in cationic surfactants cetyltrimethylammonium bromide, C16H33(CH3)3NBr, and octadecyltrimethylammonium chloride, C18H37(CH3)3NCl, and anionic surfactant sodium dodecyl sulfate, C12H25SO4Na. Also changes in wettability of the paraffin surface due to the surfactant's adsorption were studied via wetting contact angle measurements and calculation of the surface free energy. It was concluded that at a low surfactant concentration (10(-6) M) the water dipole structure still contributes to the zeta potential, but at a higher one the zeta potential is determined by the surfactant molecules' adsorption. A special role of OH- ions is also clearly seen. Moreover, a functional relationship was found between the surface free energy of the surfactant-covered paraffin surface and the zeta potential.     

A further study of the cytotoxic constituents of a milnamide-producing sponge

A reinvestigation of Auletta sp. yielded the novel compound milnamide C (3) plus the known compounds milnamide A (1), milnamide B (hemiasterlin) (2), jasplakinolide (5), and geodiamolides A (6), D (7), E (8), and G (9). The isolation work was guided by cytoskeletal bioactivity data. Compounds 2 and 3 were shown to cause microtubule depolymerization, and 6-9 were shown to cause microfilament disruption. This biological activity and the structural elucidation of 3, including X-ray analysis, are reported here. [structure: see text]     

Surface free energy of a solid from contact angle hysteresis

Nature of contact angle hysteresis is discussed basing on the literature data (Colloids Surf. A 189 (2001) 265) of dynamic advancing and receding contact angles of n-alkanes and n-alcohols on a very smooth surface of 1,1,2,-trichloro-1,2,2,-trifluoroethane (FC-732) film deposited on a silicon plate. The authors considered the liquid absorption and/or retention (swelling) processes responsible for the observed hysteresis. In this paper hysteresis is considered to be due to the liquid film left behind the drop during retreating of its contact line. Using the contact angle hysteresis an approach is suggested for evaluation of the solid surface free energy. Molecular spacing and the film structure are discussed to explain the difference in n-alkanes and n-alcohols behaviour as well as to explain the difference between dispersion free energy gamma(s)(d) and total surface free energy gamma(s)(tot) of FC-732, as determined from the advancing contact angles and the hysteresis, respectively.     

Interpretation of negative values of the interaction parameter in the adsorption equation through the effects of surface layer heterogeneity

The problem of the negative values of the interaction parameter in the equation of Frumkin has been analyzed with respect to the adsorption of nonionic molecules on energetically homogeneous surface. For this purpose, the adsorption states of a homologue series of ethoxylated nonionic surfactants on air/water interface have been determined using four different models and literature data (surface tension isotherms). The results obtained with the Frumkin adsorption isotherm imply repulsion between the adsorbed species (corresponding to negative values of the interaction parameter), while the classical lattice theory for energetically homogeneous surface (e.g., water/air) admits attraction alone. It appears that this serious contradiction can be overcome by assuming heterogeneity in the adsorption layer, that is, effects of partial condensation (formation of aggregates) on the surface. Such a phenomenon is suggested in the Fainerman-Lucassen-Reynders-Miller (FLM) "Aggregation model". Despite the limitations of the latter model (e.g., monodispersity of the aggregates), we have been able to estimate the sign and the order of magnitude of Frumkin's interaction parameter and the range of the aggregation numbers of the surface species.     

μSR Investigation of ethyl radicals adsorbed on silica

SR spectra of the ethyl radical adsorbed on porous silica were observed in transverse and in longitudinal magnetic fields in the temperature range 190–298 K. The line widths reflect the dynamic partial averaging of the hyperfine anisotropy due to reorientation and surface diffusion.     

Theoretical study of some heterocyclic amines with applications to the chemistry of 9-amino-1,2,3,4-tetrahydroacridine

9-Amino-1,2,3,4-tetrahydroacridine (THA ), a potent cholinesterase inhibitor, was recently used in the treatment of Alzheimer's disease. On attempting to prepare a dihydropyridine ? pyridinium salt-based redox chemical delivery system (CDS ) to enhance brain delivery of THA , several of the practical synthetic challenges were examined by using a theoretical MO approach. The structures, reactivities and stability of THA , derivatives of THA and a model compound, 4-aminopyridine, a simple dibasic heterocyclic amine, were studied in the framework of the AM -1 approximation. The study included the possible protonated forms of THA and 4-aminopyridine. The calculated heats of formation showed that ring nitrogen protonated forms are more stable for both THA and 4-aminopyridine. The calculated heats of formation showed that ring nitrogen protonated forms are more stable for both THA and 4-aminopyridine, consistent with experimental results. Electron delocalization is responsible for the remarkable stability of these molecules and for the observed lack of reactivity of the amino group, both in the basic and protonated forms. The site of N-alkylation of the 9-nicotinamide derivative of THA (an intermediate in the synthesis of THA -CDS ) is controlled by electronic, thermodynamic, and steric factors.