Supported phospholipid bilayers constitute a biomimetic platform for cell behavior studies and a new approach to the design of cell culture substrates. Phosphocholine bilayers are resistant to cell attachment, but can be functionalized with bioactive molecules to promote specific cell interactions. Here, we explore phosphocholine bilayers, functionalized with the laminin-derived IKVAV pentamer, as substrates for attachment, growth, and differentiation of neural progenitor cells (AHPs). By varying peptide concentration (0-10%), we discovered a strongly nonlinear relationship between cell attachment and IKVAV concentration, with a threshold of 1% IKVAV required for attachment, and saturation in cell binding at 3% IKVAV. This behavior, together with the 10-fold reduction in cell attachment when using a jumbled peptide sequence, gives evidence for a specific interaction between IKVAV and its AHP cell-surface receptor. After 8 days in culture, the peptide- functionalized bilayers promoted a high degree of cell cluster formation. This is in contrast to the predominant monolayer growth, observed for these cells on the standard laminin coated growth substrates. The peptide-functionalized bilayer did not induce differentiation levels over those observed for the laminin coated substrates. These results are promising in that peptide-functionalized bilayers can allow attachment and growth of stem cells without induction of differentiation. © 2007 Wiley Periodicals, Inc.

A biomimetic model system based on long-chain alkanethiols tailored with serine, threonine and tyrosine side-chain groups is created as a platform for the study of phosphorylated amino acids. The phosphorylated analogues are synthesized with protective tert-butyl groups that after assembly on thin polycrystalline gold films are removed in an acidic deprotection solution to form the corresponding phosphate self-assembled monolayers (SAMs). The SAMs are thoroughly characterized with null ellipsometry, contact angle goniometry, infrared reflection–absorption spectroscopy and X-ray photoelectron spectroscopy. The assembly and the subsequent deprotection process are optimized with respect to molecular orientation and chain conformation by varying the incubation time and the exposure time to the deprotection solution. The high quality of the generated SAMs suggests that the present assembly/deprotection approach is an attractive alternative when traditional synthetic routes become demanding because of solubility problems.

This contribution describes the synthesis, characterisation and evaluation of a novel biochip technology for the detection of the explosive substance 2,4,6-trinitrotoluene (TNT). Two types of thiols are self-assembled to produce the biochip on gold, namely oligo(ethylene glycol) (OEG)-alkyl thiols terminated with a hydroxyl group and a TNT-analogue (2,4-dinitrobenzene), respectively. Three different TNT-analogues are mixed in various proportions with hydroxyl-terminated OEG-thiols to obtain highly selective and sensitive biochips with a low non-specific binding. The produced self-assembled monolayers (SAMs) are thoroughly characterised with null ellipsometry, contact angle goniometry, infrared reflection absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS) and they all meet high standards in terms of molecular conformation, packing and orientation. The biochip is designed to function as a platform for a competitive label-free immunoassay and two real-time transducers – surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) – are used to monitor the dissociation of on-line immobilised monoclonal antibodies produced against TNT. The three TNT-analogues are all potential candidates for the development of a functional biochip, though one of them displayed superior properties in terms of shorter recovery/stabilisation time after antibody immobilisation and a better response/loading capacity ratio. This is particularly evident when using low antigen (TNT-analogue) content in the mixed SAM.

This paper reports on the structure and desorption dynamics of thin D 2O ice overlayers (0.2-10 monolayers) deposited on serine- and serinephosphate- (with H+, Na+, Ca2+ counterions) terminated self-assembled monolayers (SAMs). The D2O ice overlayers are deposited on the SAMs at ~85 K in ultrahigh vacuum and characterized with infrared reflection absorption spectroscopy (IRAS). Reflection absorption (RA) spectra obtained at sub-monolayer D2O coverage reveal that surface modes, e.g. free dangling OD stretch, dominate on the serine SAM surface, whereas vibrational modes characteristic for bulk ice are more prominent on the serinephosphate SAMs. Temperature programmed desorption mass spectrometry (TPD-MS) and TPD-IRAS are subsequently used to investigate the energetics and the structural transitions occurring in the ice overlayer during temperature ramping. D2O ice (~2.5 monolayers) on the serine SAMs undergoes a gradual change from an amorphous- to a crystalline-like phase upon increasing the substrate temperature. This transition is not as pronounced on the serine phosphate SAM most likely because of reduced mobility due to strong pinning to the surface. We show also that the energy of desorption for a sub-monolayer of D2O ice on serinephosphate SAM surfaces with a Na+ and Ca2+ counterions is equally high or even exceeds previously reported values for analogous high-energy SAMs. © 2006 American Chemical Society.

The influence of protein stability on the adsorption and desorption behavior to surfaces with fundamentally different properties (negatively charged, positively charged, hydrophilic, and hydrophobic) was examined by surface plasmon resonance measurements. Three engineered variants of human carbonic anhydrase II were used that have unchanged surface properties but large differences in stability. The orientation and conformational state of the adsorbed protein could be elucidated by taking all of the following properties of the protein variants into account: stability, unfolding, adsorption, and desorption behavior. Regardless of the nature of the surface, there were correlation between (i) the protein stability and kinetics of adsorption, with an increased amplitude of the first kinetic phase of adsorption with increasing stability; (ii) the protein stability and the extent of maximally adsorbed protein to the actual surface, with an increased amount of adsorbed protein with increasing stability; (iii) the protein stability and the amount of protein desorbed upon washing with buffer, with an increased elutability of the adsorbed protein with increased stability. All of the above correlations could be explained by the rate of denaturation and the conformational state of the adsorbed protein. In conclusion, protein engineering for increased stability can be used as a strategy to decrease irreversible adsorption on surfaces at a liquid-solid interface.

The control of cellular interactions with engineered materials is critical for the development of cell-integrated biochips used in cell-based sensors, "lab-on-a-chip" bioanalytical systems, and artificial neuronal networks, as well as medical implants and functional biomaterial scaffolds for tissue engineering. Supported lipid bilayers offer efficient reduction of nonspecific cell and protein binding and, if selectively functionalized, constitute one attractive approach to surface modification strategies of materials used in such devices. The present work describes the in situ modification of supported lipid bilayers through the coupling of a cysteineterminated peptide to thiol-reactive maleimido lipids incorporated in the bilayer. The accumulation of peptide at the lipid bilayer interface was monitored by the quartz crystal microbalance technique with dissipation monitoring (QCM-D). Coupling of the peptide could be detected by QCM-D with a high signal-to-noise ratio despite its low molecular weight (2 kDa), primarily because the mass uptake included both peptide and the water associated to it. Lipid bilayers that were modified with the cysteine-terminated IKVAV-containing peptide promoted the binding of anti-IKVAV antibodies, as well as the attachment of PC12 cells, which express a membrane receptor for the IKVAV sequence. Very low nonspecific binding of peptides, proteins, and the cells was observed on nonfunctionalized lipid bilayers. Similarly, IKVAV-functionalized lipid bilayers were resistant to serum protein adsorption as well as the binding of non-IKVAV-specific antibodies. QCM-D and fluorescence recovery after photobleaching revealed that the lipid bilayers persisted under all the experimental conditions used for cell attachment, including staining and fixation. Thus, the described lipid-based surface modification is highly relevant for the development of controlled cell-attachment substrates and can even be applicable for patterning cell attachment because lipid-bilayer formation by vesicle fusion is material-specific.

Lysophosphatidic acid (LPA) is a lipid mediator that, among several other cellular responses, can stimulate cells to mobilize calcium (Ca2+). LPA is known to activate at least three different subtypes of G protein-coupled receptors. These receptors can then stimulate different kinds of G proteins. In the present study, LPA and LPA analogs were synthesized from (R)- and (S)-glycidol and used to characterize the ability to stimulate Ca2+ mobilization. The cytosolic Ca2+ concentration ([Ca2+]i) was measured in fura-2-acetoxymethylester-loaded human erythroleukemia (HEL) cells. Furthermore, a reverse transcriptase polymerase chain reaction was used to characterize LPA receptor subtypes expressed in HEL cells. The results show that HEL cells mainly express LPA1 and LPA2, although LPA3 might possibly be expressed as well. Moreover, LPA and its analogs concentration-dependently increased [Ca2+]i in HEL cells. The response involved both influx of extracellular Ca2+ and release of Ca2+ from intracellular stores. This is the first time the unnatural (S)-enantiomer of LPA, (S)-3-O-oleoyl-1-O-phosphoryl-glycerol, has been synthesized and studied according to its ability to activate cells. The results indicate that this group of receptors does not discriminate between (R)- and (S)-enantiomers of LPA and its analogs. When comparing ether analogs having different hydrocarbon chain lengths, the tetradecyl analog (14 carbons) was found to be the most effective in increasing [Ca2+]i. Pertussis toxin treatment of the HEL cells resulted in an even more efficient Ca2+ mobilization stimulated by LPA and its analogs. Furthermore, at repeated incubation with the same ligand no further increase in [Ca2+]i was obtained. When combining LPA with the ether analogs no suppression of the new Ca2+ signal occurred. All these findings may be of significance in the process of searching for specific agonists and antagonists of the LPA receptor subtypes.

Two different tyrosine derivatives, one with the OH group free and one with the OH group phosphorylated, linked to 3-mercaptopropionic acid through an amide bond are adsorbed to gold surfaces. The adsorbates are studied by means of X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IRAS). The techniques are used to investigate the coordination to the surface and the molecular orientation of adsorbates relative to the surface. Molecular surface interactions, causing chemical shifts in the core level XPS spectra of the adsorbates on gold, are investigated using multilayer films as references. Angle-dependent XPS, XPS(T), and IRAS are used to estimate molecular orientation relative to the surface. The tyrosine derivatives adsorb chemically to the surface through the sulfur atoms and highly organized monolayers are formed with the OH and the PO32- exposed to the air/vacuum interface. © 2003 Elsevier Science (USA). All rights reserved.

Strategies to form supported lipid assemblies on organophosphate- and organosulfate-monolayer-modified gold surfaces are described. By varying surface treatment and the Mg2+ (Ca2+) content in a solution containing phosphatidylcholine vesicles, we demonstrate (i) efficient formation of supported phosphatidylcholine bilayers (SPBs), (ii) formation of supported nonruptured phosphatidylcholine vesicles, and (iii) reduced phosphatidylcholine vesicle adsorption. Thus, by simply varying the solution conditions, the system can be tuned to controlled formation of either a SPB, supported nonruptured vesicles, or a surface with fairly low coverage of nonruptured vesicles. The profound effects induced on the system by Mg2+ and Ca2+ are assigned to a combination of ion-coordination to the surface, ion-association to the lipid headgroups, and osmotic pressure.

New efficient routes to enantiopure phospholipids, starting from (S)-glycidol, are described. Lysophosphatidic acids and phosphatidic acids were obtained in good overall yields from (S)-glycidol, in only three and four steps, respectively. Moreover, the strategy can also be used to produce phosphatidylcholines in three steps. Using dialkylphosphoramidites, (S)-glycidol was phosphorylated to give (R)-1-O-glycidyl dialkyl phosphates. Regiospecific epoxide opening, using hexadecanol or cesium palmitate, followed by phosphate deprotection, provided lysophosphatidic acids. 2-O-Esterification prior to phosphate deprotection provided 1,2-O-diacyl and 1-O-alkyl-2-O-acyl phosphatidic acids. Phosphorylation of (S)-glycidol using phosphorus oxychloride followed by in situ treatment with choline tosylate produced (R)-glycidyl phosphocholine. Subsequent nucleophilic opening of the epoxide using cesium palmitate produced 1-O palmitoyl-sn-glycero-3-phosphocholine, which has been used in syntheses of phosphatidylcholines.