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The aim of this study is to analyze linear calf thymus DNA (ct DNA) nanoparticle formation with N4,N9-dioleoylspermine and N1-cholesteryl spermine carbamate.Fluorescence correlation spectroscopy (FCS) was used to determine the quality of ct DNA condensed by lipopolyamines. ct DNA was prelabeled with PicoGreen (PG) to allow fluorescence intensity fluctuation measurement and analysis.N4,N9-Dioleoylspermine efficiently condensed ct DNA into point-like molecules with diffusion coefficient (D) = 1.8 × 10−12m2/s and particle number (PN) = 0.7 [at ammonium/phosphate (N/P) charge ratio=1.0–1.5]. The determined PN values are close to the theoretical value of 0.6, providing evidence that the DNA conformation has been fully transformed, and thus a single nanoparticle has been detected. N1-Cholesteryl spermine carbamate showed (slightly) poorer DNA condensation efficiency, even at higher N/P ratios (N/P = 1.5–2.5) with D= 1.3 × 10−12m2/s and PN value of 5.2. N4,N9-Dioleoylspermine is a more efficient DNA-condensing agent than N1-cholesteryl spermine carbamate.FCS measurement using PG as the probe is a novel analytical method to detect single nanoparticles of condensed DNA in nonviral gene therapy formulation studies.

Abstract Many experimental designs, in which nucleic acid conformational changes are of interest, require reliable fluorescence labeling. The appropriate fluorescence probe should have suitable optical properties and, more importantly, should not interfere with the investigated processes. In order to avoid chemical modifications the fluorescence label needs to be associated with nucleic acid via weak non-covalent interactions. There are a number of fluorescent probes that change their fluorescent properties (i.e. their quantum yield and/or spectral characteristics) upon association with nucleic acid. Such probes are frequently used to detect, visualize and follow processes involving nucleic acid and its conformational changes. In order to obtain reliable data regarding macromolecule or aggregate topology a detailed knowledge of probe–nucleic acid interactions on the molecular level is needed. In this paper we show that the association of propidium iodide with DNA alters its conformation and that it selectively labels plasmid fragments and/or its subpopulations in a concentration-dependent meaner. Another dye, PicoGreen, exhibits better properties. It labels nucleic acid uniformly and without any concentration-dependent artifacts.

The micellization as well as the interaction with model membranes of dodecyltrimethylammonium halides (DTAX) and N-dodecyl-N,N-dimethyl-N-benzylammonium halides (DBeAX) were studied at 298K and 313K by means of titration calorimetry. The calorimetric curves reflect both the counterion and benzyl group effects on the interaction of the surfactants studied with the lipid bilayer. Bromide as counterion enhanced the interactions more than chloride of both DTAX and DBeAX compounds with model membranes.

Phenyltins are chemicals widely used in industry, hence their occurrence in the human environment is frequent and widespread. Such compounds include hydrophobic phenyl rings bonded to positively charged tin. This molecular structure makes them capable of adsorbing onto and penetrating through biological membranes, hence they are potentially hazardous. Two such compounds, diphenyltin and triphenyltin, show different steric constraints when interacting with the lipid bilayer. It has been demonstrated that these compounds are positioned at different locations within model lipid bilayers, causing dissimilarity in their ability to affect membrane properties. In this paper we present a study regarding the ability of these two phenyltins to facilitate the transport of S2O4-2ions across the lipid bilayer, evaluated by a fluorescence quenching assay. In concentration range of up-to 60 µm those compounds do not affect lipid bilayer topology, when evaluated by vesicle size distribution. Both phenyltins facilitate the transfer of S2O4-2across the model lipid bilayer, but the dependence of dithionite transport on phenyltin concentration is different for both. In principle, above 20 µm triphenyltin is more efficient in transfering ions across the lipid bilayer than diphenyltin.

Organometallic compounds and surfactants constitute a potential threat to the environment. For that reason we have embarked on a study of their joint action on membranes. Model lecithin liposome membranes were modified with the cationic surfactant trimethyldodecylammonium bromide or the anionic surfactant sodium dodecylsulfonate, and the effect of tripropyltin chloride on the process of calcium (Ca2+) and praseodymium (Pr3+) desorption from the liposome membrane was studied.

The effect of four amphiphilic cationic compounds that differ in their polar head properties on the kinetics of calcium ion desorption from unilamellar lecithin liposom e membranes has been studied. The compounds under investigation were: N-benzyl-N,N-dimethyl-N-tetradecy-lammonium chloride (BDTA), N-methyl-N-tetradecylmorpholinium bromide (MTM), N-methyl-N-dodecyloxym ethylenem orpholinium chloride (MDOM) and N,N,N-trimethyl-N-te-tradecylammonium bromide (TMTA). Kinetic constants were determined using the three-compartmental analysis for isotopic labels. For the above mentioned compounds electronic structure calculations were performed and point charges and dipole moments of the molecules determined by using quantum chemis­try methods. It was found that the rate of desorption increases with increasing concentration of the compounds studied, and effectiveness of the compounds follows the sequence: BDTA >MTM >TMTA >MDOM . For dipole moments the sequence obtained is somewhat different, namely: BDTA>MTM >MDOM >TMTA. Apparently, the differences in the effectiveness of action of the compounds in the calcium desorption process follow not only from the values of dipole moments of their polar heads but also from the values of point charges on some atoms and from steric properties.

Organometallic compounds and surfactants constitute a potential threat to the environment. For that reason we have embarked on a study of their joint action on membranes. Model lecithin liposome membranes were modified with the cationic surfactant trimethyldodecylammonium bromide or the anionic surfactant sodium dodecylsulfonate, and the effect of tripropyltin chloride on the process of calcium (Ca²⁺) and praseodymium (Pr³⁺) desorption from the liposome membrane was studied. Kinetic constants for the process of Ca²⁺ ion desorption from lecithin liposome membranes were determined using the radiotracer method. The percentage of Pr³⁺ ion desorption from liposome membranes was measured by the ¹H NMR method. Trimethyltin, triethyltin and tripropyltin alone caused increased Ca²⁺ and Pr³⁺ desorption from liposome membranes with increasing concentration of the compounds and alkyl chain length. For both the processes studied, a cationic surfactant brought about a lower effectiveness of tripropyltin and an anionic surfactant resulted in a higher effectiveness. The effect observed can be explained by changes in the surface charge of the membrane, induced by the surfactant modifiers and by the concomitant change in the partition coefficient of the organotin. The results obtained indicate a protective or harmful joint action of the surfactants used with tripropyltin on membranes. © 1997 John Wiley & Sons, Ltd.

The spermine-induced DNA condensation is a first-order phase transition. Here, we apply a novel technique fluorescence lifetime correlation spectroscopy to analyze this transition in a greater detail. We show that the method allows for the observation of the condensed and uncondensed molecules simultaneously based solely on different fluorescence lifetimes of the intercalating fluorophore PicoGreen in the folded und unfolded domains of DNA. The auto- and cross-correlation functions reveal that a small fraction of the DNA molecules is involved in the dynamic intramolecular equilibrium. Careful inspection of the cross-correlation curves suggests that folding occurs gradually within milliseconds.