On the electrostatics of DNA in chromatin

We examine the interaction between DNA molecules immersed in an aqueous solution of oppositely charged, trivalent spermidine molecules. The DNA molecules are modeled as planar, likecharged surfaces immersed in an aqueous solution of multivalent, rod-like ions consisting of rigidly bonded point charges. An approximate field theory is used to determine the properties of this system from the weak to the intermediate through to the strong coupling regimes. In the weak coupling limit, the interaction between the charged surfaces is only repulsive, whereas in the intermediate coupling regime, the rod-like ions with spatial charge distribution can induce attractive force between the charged surfaces. In the strong coupling limit, the inter-ionic charge correlations induce attractive interaction at short separations between the surfaces. This theoretical study can give new insights in the problem of interaction between DNA molecules mediated by trivalent spermidine molecules

A field theoretic approach to the electric interfacial layer : mixture of trivalent rod-like and monovalent point-like ions between charged walls

In this paper, we study the interaction between charged macroions (surfaces) immersed in a solution of oppositely charged, rod-like counterions and point-like co-ions. The system is modeled by a field theoretic approach, which was extended to treat mixtures of rod- and point-like ions. The theory is applicable from the weak to the intermediate through to the strong coupling regimes. In the weak coupling limit, the force between the charged surfaces are only repulsive. In the intermediate coupling regime, the rod-like ions can induce attractive force between the charged surfaces. In the strong coupling limit, the inter-ionic charge correlations dominate the attractive forces at short separations between the charged surfaces

Interactions between charged surfaces mediated by stiff, multivalent zwitterionic polymers

The interaction between like-charged objects in electrolyte solutions can be heavily altered by the presence of multivalent ions which possess a spatially distributed charge. In this work, we examine the influence of stiff, multivalent zwitterionic polymers on the interaction between charged surfaces using a splitting field theory previously shown to be accurate from the weak to the intermediate through to the strong electrostatic coupling regimes. The theory is compared to Monte Carlo simulations and good agreement is found between both approaches. For surface separations shorter than the polymer length, the polymers are mainly oriented parallel to the surfaces, and the surface-surface interaction is repulsive. When the surface separation is comparable to the length of polymers, the polymers have two main orientations. The first corresponds to the polymers adsorbed to the surface with their centers located near to or in contact with the surface; the second corresponds to polymers which are perpendicular to the charged surfaces, bridging both surfaces and leading to an attractive force between them. Increasing the surface charge density leads to a more pronounced attraction via bridging. At surface separations greater than the polymer length, the polymers in the center of the system are still mainly perpendicular to the surfaces, due to "chaining" between zwitterions that enable them to bridge the surfaces at larger separations. This leads to an attractive interaction between the surfaces with a range significantly longer than the length of the polymers

Attraction between Like Charged Surfaces Mediated by Uniformly Charged Spherical Colloids in a Salt Solution

Like-charged macromolecules repel in electrolyte solutions that contain small (i.e. point-like) monovalent co- and counterions. Yet, if the mobile ions of one species are spatially extended instead of being point-like, the interaction may turn attractive. This effect can be captured within the mean-field Poisson-Boltzmann framework if the charge distribution within the spatially extended ions is accounted for. This has been demonstrated recently for rod-like ions. In the present work, we consider an electrolyte solution that is composed of monovalent point-like salt ions and uniformly charged spherical colloids, sandwiched between two planar like-charged surfaces. Minimization of the mean-field free energy yields an integral-differential equation for the electrostatic potential that we solve numerically within the linear Debye-Hückel limit. The free energy, which we calculate from the potential, indeed predicts attractive interactions for sufficiently large spherical colloids. We derive an approximate analytical expression for the critical colloid size, above which attraction between like-charged surfaces starts to emerge. (doi: 10.5562/cca1824

Adhesion of bacteria to wood coatings

Bacterial adhesion to surfaces and subsequent biofilm formation are the main causes of chronic infections with a negative impact on human health, and this is a problem in the process of manufacturing furniture. This is an important issue, relevant also to the selection and production of furniture, where there is a focus on the development of products with antibacterial surfaces to which microorganisms do not adhere. The focus of our research was to test selected wood coatings (linseed oil, water-borne stain, nitrocellulose varnish, nano-coating) with regard to the adhesion of Pseudomonas aeruginosa, where we used a beech plywood as the test surface. The topography of the test surfaces and the number of adhered bacteria were observed on SEM micrographs. The results indicate that the maximum number of bacteria adhered to the surface coated with linseed oil. In the future, extensive and in-depth studies will be needed to confirm and obtain the required results

Vpliv naravnih protimikrobnih snovi na bakterijsko hidrofobnost, adhezijo in zeta potencial

Interactions between bacterial cells and contact materials play an important role in food safety and technology. As bacterial strains become ever more resistant to antibiotics, the aim of this study was to analyse adhesion of selected foodborne bacterial strains on polystyrene surface and to evaluate the effects of natural antimicrobials on bacterial cell hydrophobicity, adhesion, and zeta potential as strategies of adhesion prevention. The results showed strain-specific adhesion rate on polystyrene. The lowest and the highest adhesion were found for two B. cereus lines. Natural antimicrobials ferulic and rosmarinic acid substantially decreased adhesion, whereas the effect of epigallocatechin gallate was neglectful. Similar results were found for the zeta potential, indicating that natural antimicrobials reduce bacterial adhesion. Targeting bacterial adhesion using natural extracts we can eliminate potential infection at an early stage. Future experimental studies should focus on situations that are as close to industrial conditions as possible.Interakcije med bakterijskimi celicami in površinami delovnih materialov imajo pomembno vlogo v živilski tehnologiji pri zagotavljanju varnih živil. Poznano je, da različni bakterijski sevi postajajo bolj in bolj odporni proti antibiotikom in drugim biocidom. Zato je bil namen naših raziskav analizirati adhezijo izbranih patogenih bakterij, ki se prenašajo z živili. Proučevali smo njihov oprijem na polistirensko površino in ovrednotili vpliv naravnih protimikrobnih snovi na bakterijsko hidrofobnost, adhezijo in zeta potencial, v smislu možnih strategij za preprečevanje adhezije. Rezultati so pokazali, da je adhezija sevno specifična lastnost, saj je bila najmanjša in največja stopnja adhezije določena za različna seva bakterij vrste Bacillus cereus. Naravni protimikrobni snovi, ferulična in rožmarinska kislina, sta zmanjšali stopnjo adhezije na polistiren, medtem ko je bil vpliv epigalokatehin galata zanemarljiv. Podobne rezultate smo dobili pri zeta potencialu, kar nakazuje na možnosti delovanja naravnih snovi kot protiadhezivnih komponent. Uporaba naravnih protimikrobnih snovi lahko prepreči oziroma zmanjša stopnjo adhezije bakterijskih celic in s tem eliminira možnosti kontaminacij ali okužb v začetni fazi. Nadaljnje eksperimentalno delo bo potrebno za ovrednotenje razmer, ki so čim bolj podobne industrijskemu okolju

Vpeljava interakcij posredovanih preko molekul topila v Poisson-Boltzmannovo teorijo

Electrostatic interactions are omnipresent in colloidal and biological systemsfor example they take place in aqueous solutions that contain mobile salt ions. Water plays a crucial role for the energetics of such systems. The ordering of water molecules changes the polarization and thus contributes to the electrostatic properties of the system. In particular, structural correlations between solvent molecules give rise to an inhomogeneous and non-local dielectric response that contributes to the energetics and the stability of biomacromolecules. This work is concerned with including solvent structures into mean-field electrostatics. It consists of three related subjects. In the first part we introduce a solvent model of interacting Langevin dipoles and incorporate that model into the Poisson-Boltzmann (PB) theory for an aqueous solution of monovalent ions in contact with a charged surface. The interplay between the electric double layer and the orientational ordering of solvent molecules determines the spatial decay of the solvent polarization. We showed that our model can result in a sign inversion of the electrostatic potential at a charged surface. The second part applies the PB model for a solvent of interacting Langevin dipoles to a mixed anionic/zwitterionic lipid layer. In the model the headgroups have ability to polarize the water in the headgroup region. The result is a positive electrostatic potential everywhere in the system. In the last part we introduce the Poisson-Helmholtz-Boltzmann theory, which adds to the electrostatic interaction potential between two ions an additional Yukawa potential. The latter accounts for solute-mediated ion-ion interactions. We demonstrate that these interactions can give rise to ion specific effects. One of the possible applications of the theory is related to the Hofmeister series. The presented analysis focuses on two systems. The first is the system of two charged surfaces embedded in a solution of only counterions, whereas the second system is one single charged surface in contact with a symmetric 1:1 electrolyte solution.Eno od pomembnejših področij celične biologije je razumevanje elektrostatskih interakcij med biološkimi strukturami (biopolimeri, membrane, celične organele). Večina bioloških struktur vsebuje prostorsko porazdeljen naboj. Elektrostatske interakcije med biomakromolekulami potekajo v vodnih raztopinah, ki vsebujejo eno in več-valentne majhne ione. V omenjenih sistemih igra voda pomembno vlogo. Le ta je močno polarizabilna in tako senči elektrostatske interakcije. Med molekulami vode delujejo vodikove vezi, katere omogočajo tvorbo lokalnih struktur. V bližini nabitih površin in ionov pride do urejanja molekul vode. Takšno urejanje spremeni polarizacijo vode in prispeva k elektrostatskim lastnostim sistema. Strukturne korelacije med vodnimi molekulami povzročijo nehomogene in nelokalne dielektričnosti. Le te so pomembne za razumevanje stabilnosti in dinamike bioloških struktur in interakcij med njimi. Prvi cilj doktorskega dela je vpeljava solvatacijskega modela interagirajočih Langevinovih dipolov v PB teorijo točkastih ionov ob naelektreni površini. Drugi cilj doktorskega dela je obravnava zwitterionsko lipidnih plast v stiku z monovaletnimi ioni in Langevinovimi dipoli, medtem ko je tretji cilj doktorskega dela je vpeljava neelektrostatskih interakcij v PB teorijo preko dodatnega odbojnega Yukawa potenciala med ioni v raztopini

Biophysical Properties of Foamed and Solid Polymers Used in Orthotics and Prosthetics

Orthotic and prosthetic materials should have good mechanical and antibacterial properties. Therefore, in our study, we consider four common foamed closed-cells and two solid polymeric materials regarding their mechanical behaviour and tendency for bacterial adhesion. For all materials, the surface roughness, hydrophobicity, zeta potential, tensile properties, hardness and CIE color parameters were measured. We found that foamed polymeric materials have higher roughness, higher hydrophobicity, lower Young’s modulus, lower maximum tensile strength and lower hardness than solid materials. Bacterial adhesion test measurements based on observation by scanning electron microscopy show much a lower adhesion extent of S. aureus on solid materials than on foamed materials. The measured biophysical properties could be the key data for users to select the optimal materials