Self-assembly of oligo(ethylene glycol)-terminated and amide group containing alkanethiols (HS(CH2)15CONH−EG n ; n = 1, 2, 4, 6) on gold are investigated by contact angle goniometry, ellipsometry, and infrared reflection−absorption spectroscopy. The compounds are shown to form highly ordered monolayers. The molecular conformation of the oligo(ethylene glycol) sublayer is found to depend on the oligomer chain length and intermolecular interactions within the layer, as evidenced by a sharp increase in the amount of helical conformers for n = 6.

Tumor necrosis factor-stimulated gene-6 (TSG-6) is a hyaluronan (HA)-binding protein that plays important roles in inflammation and ovulation. TSG-6-mediated cross-linking of HA has been proposed as a functional mechanism (e.g. for regulating leukocyte adhesion), but direct evidence for cross-linking is lacking, and we know very little about its impact on HA ultrastructure. Here we used films of polymeric and oligomeric HA chains, end-grafted to a solid support, and a combination of surface-sensitive biophysical techniques to quantify the binding of TSG-6 into HA films and to correlate binding to morphological changes. We find that full-length TSG-6 binds with pronounced positive cooperativity and demonstrate that it can cross-link HA at physiologically relevant concentrations. Our data indicate that cooperative binding of full-length TSG-6 arises from HA-induced protein oligomerization and that the TSG-6 oligomers act as cross-linkers. In contrast, the HA-binding domain of TSG-6 (the Link module) alone binds without positive cooperativity and weaker than the full-length protein.Both the Link module and full-length TSG-6 condensed and rigidified HA films, and the degree of condensation scaled with the affinity between the TSG-6 constructs and HA. We propose that condensation is the result of protein-mediated HA crosslinking. Our findings firmly establish that TSG-6 is a potent HA cross-linking agent and might hence have important implications for the mechanistic understanding of the biological function of TSG-6 (e.g. in inflammation). Hyaluronan (HA)3 is a structurally simple and linear polysaccharide. It is ubiquitous in the extracellular matrix of vertebrates and plays important roles in numerous physiological and pathological processes, such as inflammation, fertilization, embryogenesis, tumor development, osteoarthritis, and atherosclerosis (1, 2). HA is considered a "pericellular cue" (3) (i.e. it serves as a versatile scaffold within which other molecules are organized and regulated). A number of proteins, called hyaladherins (4), can bind to the flexible HA chains and engender self-assembly into large and hydrated multimolecular complexes (5-7).The secreted product of tumor necrosis factor-stimulated gene-6 (TSG-6) (8, 9) is of particular importance for the formation and remodeling of HA-rich pericellular coats (10, 11) and extracellular matrices (12). There is little or no constitutive expression of TSG-6 in most adult tissues (with the exception of bone marrow (13) and epidermis (14)). Expression is elevated in response to stimulation with proinflammatory mediators or certain growth factors (8, 9, 15-18), and TSG-6 is detected in the context of many inflammatory diseases (19,20) and in inflammation-like processes, such as ovulation (21,22). TSG-6 is composed mainly of two contiguous domains, a Link module and a CUB module (8,17,23,24). The Link module is conserved among members of the hyaladherin family (4) and is essential for binding to HA (23). Administration of recombinant human TSG-6 Link module (L...

We have investigated the interaction between graphene oxide and lipid membranes, using both supported lipid membranes and supported liposomes. Also, the reverse situation, where a surface coated with graphene oxide was exposed to liposomes in solution, was studied. We discovered graphene oxide-induced rupture of preadsorbed liposomes and the formation of a nanocomposite, bio-nonbio multilayer structure, consisting of alternating graphene oxide monolayers and lipid membranes. The assembly process was monitored in real time by two complementary surface analytical techniques (the quartz crystal microbalance with dissipation monitoring technique (QCM-D) and dual polarization interferometry (DPI)), and the formed structures were imaged with atomic force microscopy (AFM). From a basic science point of view, the results point toward the importance of electrostatic interactions between graphene oxide and lipid headgroups. Implications from a more practical point of view concern structure-activity relationship for biological health/safety aspects of graphene oxide and the potential of the nanocomposite, multilayer structure as scaffolds for advanced biomolecular functions and sensing applications.

A comparative study of the self-assembly and phase behavior of seven different oligo(ethylene glycol) (OEG)terminated alkanethiols on polycrystalline gold surfaces is presented. The general structure of the compounds is HS(CH 2 ) m -X-EG n , where m ) 11, 15; n ) 2, 4, 6, and the linkages X are amide (-CONH-), ester (-COO-), or ether (-O-) groups. The amide and ester groups give rise to the intermolecular hydrogen bonding and dipole-dipole interactions, respectively, whereas the ether lacks specific interactions. The results from contact angle goniometry, null ellipsometry, and infrared reflection-absorption spectroscopy (IRAS) indicate that the intermolecular interactions can be partly used to control the conformation and order of the OEG portion of the self-assembled monolayers (SAMs). It is shown that the lateral hydrogen bonding stabilizes the all-trans conformation of the EG 4 tails in the SAMs. Further on, the mechanism behind the thermal phase behavior of the OEG SAMs is investigated using temperature-programmed IRAS in ultrahigh vacuum. In the present study we show that the earlier reported helix-to-all-trans conformational transition at 60 °C in the

Cu-containing nanoparticles are used in various applications in order to e.g. achieve antimicrobial activities and to increase the conductivity of fluids and polymers. Several studies have reported on toxic effects of such particles but the mechanisms are not completely clear. The aim of this study was to investigate the interactions between cell membranes and well-characterized nanoparticles of CuO, Cu metal, a binary Cu-Zn alloy and micron-sized Cu metal particles. This was conducted via in vitro investigations of the effects of the nanoparticles on (i) cell membrane damage on lung epithelial cells (A549), (ii) membrane rupture of red blood cells (hemolysis), complemented by (iii) nanoparticle interaction studies with a model lipid membrane using quartz crystal microbalance with dissipation monitoring (QCM-D). The results revealed that nanoparticles of the Cu metal and the Cu-Zn alloy were both highly membrane damaging and caused a rapid (within 1h) increase in membrane damage at a particle mass dose of 20 μg/mL, whereas the CuO nanoparticles and the micron-sized Cu metal particles showed no such effect. At similar nanoparticle surface area doses, the nano and micron-sized Cu particles showed more similar effects. The commonly used LDH (lactate dehydrogenase) assay for analysis of membrane damage was found impossible to use due to nanoparticle-assay interactions. None of the particles induced any hemolytic effects on red blood cells when investigated up to high particle concentrations (1mg/mL). However, both Cu and Cu-Zn nanoparticles caused hemoglobin aggregation/precipitation, a process that would conceal a possible hemolytic effect. Studies on interactions between the nanoparticles and a model membrane using QCM-D indicated a small difference between the investigated particles. Results of this study suggest that the observed membrane damage is caused by the metal release process at the cell membrane surface and highlight differences in reactivity between metallic nanoparticles of Cu and Cu-Zn and nanoparticles of CuO.

Much effort is currently concentrated on research devoted to biofunctional patterned surfaces, which constitute the fundament for the development of microarrays for high-throughput gene and protein analyses. DNA microarrays have proved very successful, [1] and the concept is in the process of being applied to protein arrays. [2] However, in contrast to DNA fragments, proteins are easily denatured in contact with solid supports, and robotic printing of proteins onto chemically reactive glass slides [3] will not necessarily be applicable as a generic protocol for the preparation of protein arrays. Supported phosphatidylcholine lipid bilayers have emerged as interesting candidate substrates for protein chips, since they efficiently reduce nonspecific protein adsorption [4, 5] and, at the same time, allow different strategies for protein immobilization with biospecific water, desalted with a NAP5 column (Amersham Pharmacia, USA) according to manufacturer's protocols, and stored as working stock solutions at À 20 8C until use. Epoxy-derivatized slides were prepared from plain glass slides (Sigma, USA) as previously described. [9] Nhydroxysuccinimide slides were also used to spot the proteins but consistently gave inferior results. Proteins were prepared in NaHCO 3 buffer (0.1 M, pH 9) and arrayed on epoxy slides with a spacing of 180 mm between the spots by using an statistical microarray analysis arrayer (Engineering Services Inc., Ontario, Canada). After a 2-hour incubation period the slides were either used immediately, or stored for future use at 4 8C. The slides, if stored, were typically used within 48 h of printing.Unless otherwise indicated, probing and reactions on slides were performed as follows: Before use, the slides were quenched by treatment with phosphate-buffered saline (PBS) and glycine (0.5 M) on a shaker for 10 min. The slides were blocked with PBS, glycine (0.5 M), and bovine serum albumin (BSA; 1 % w/v) for 20 min, then washed with distilled water and air dried. The labeled probe was then applied: a mixture containing the probe (2 mM) was prepared by adding stock probe solution (0.5 mL, 200 mM) to tris(hydroxymethyl)aminomethane (Tris) buffer (49 mL, 50 mM, pH 8), and BSA (0.5 mL, 1 % w/v). The resulting mixture was applied to each slide by the coverslip method [9] and incubated for 30 min in the dark. The excess probe was washed off after incubation with distilled water, and the slides were subsequently washed with PBS that contained Tween (0.2 % v/v) for 15 minutes on a shaker. The slides were then washed with distilled water, air dried, and scanned with an ArrayWorx microarray scanner (Applied Precision, USA) at 548/595 nm. For the PMSF experiment, each slide was first incubated with freshly prepared PMSF (50 mL, 1 mM in 50 mM Tris, pH 8) for 30 minutes, rinsed extensively with distilled water to remove any free residual PMSF, and screened with FP-Cy3. The inhibition experiments were identical to the probe ± enzyme reactions, except that varying concentrations of trypsin inhibitor (original...

A strategy for the synthesis of a series of closely related oligo(ethylene glycol)-terminated alkanethiol amides (principally HS(CH(2))(m)CONH(CH(2)CH(2)O)(n)H; m = 2, 5, 11, 15, n = 1, 2, 4, 6, 8, 10, 12) and analogous esters has been developed. These compounds were made to study the structure and stability of self-assembled monolayers (SAMs) on gold in the prospect of designing new biosensing interfaces. For this purpose, monodisperse heterofunctional oligo(ethylene glycols) with up to 12 units were prepared. Selective monoacylation of the symmetrical tetra- and hexa(ethylene glycol) diols as their mesylates with the use of silver(I) oxide was performed. The synthetic approach was based on carbodiimide couplings of various oligo(ethylene glycol) derivatives to omega-(acetylthio) carboxylic acids via a terminal amino or hydroxyl function. SAM structures on gold were studied with respect to thickness, wettability (water contact angles approximately 30 degrees ), and conformation. A good fit was obtained for the relation between monolayer thickness (d) and the number of units in the oligo(ethylene glycol) chain (n): d = 2.8n + 21.8 (A). Interestingly, the corresponding infrared spectroscopy analysis showed a dramatic change in conformation of the oligomeric chains from all-trans (n = 4) to helical (n > or = 6) conformation. A crystalline helical structure was observed in the SAMs for n > 6.

A novel setup was recently developed, combining quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry for measurements on one and the same surface of, for example, biomolecular adlayers and interactions ( Rev. Sci. Instr. 2008 , 79 075107 ). This combination was chosen on the basis of prior experience of using QCM-D and optical techniques in separate instruments, which showed both the advantage of employing multiple techniques and the disadvantage of not working with the same surface and (flow) cell. The new instrument provides, for example, information about associated water and structural changes of the adlayers that would often pass unnoticed or be hard to interpret or quantify, using either technique alone. The triple response instrument (QCM-D frequency and dissipation and reflectometry) is here applied to four model systems: (A) formation of supported lipid bilayers (SLBs), (B) lipid exchange between a SLB and transiently adsorbed vesicles, (C) binding of a hydrated peptide on a functionalized SLB, and (D) streptavidin coupling to a biotinylated SLB, followed by attachment of biotinylated vesicles. The results demonstrate three major advantages of the combination instrument: (i) much faster data collection because the experiments are done on one surface for all signals, (ii) a common time axis and the same relative importance of surface kinetics and mass transport because the same liquid sample and the same transport conditions apply, and (iii) new features are discovered about the studied system that would be difficult to unravel in separate instruments.