Small molecules with modalities for a variety of imaging techniques as well as therapeutic activity are essential, as such molecules render opportunities to simultaneously conduct diagnosis and targeted therapy, so called theranostics. In this regard, glycoporphyrins have proven useful as theranostic agents towards cancer, as well as noncancerous conditions. Herein, the synthesis and characterization of heterobifunctional glycoconjugated porphyrins with two different sugar moieties, a common monosaccharide at three sites, and a 2-fluoro-2-deoxy glucose (FDG) moiety at the fourth site are presented. The fluoro-glycoconjugated porphyrins exhibit properties for multimodal imaging and photodynamic therapy, as well as specificity towards cancer cells. We foresee that our findings might aid in the chemical design of heterobifunctional glycoconjugated porphyrins that could be utilized as theranostic agents.
Fluorescent probes identifying protein aggregates are of great interest, as deposition of aggregated proteins is associated with many devastating diseases. Here, we report that a fluorescent amyloid ligand composed of two distinct molecular moieties, an amyloidophilic pentameric oligothiophene and a porphyrin, can be utilized for spectral and lifetime imaging assessment of recombinant A 1-42 amyloid fibrils and A deposits in brain tissue sections from a transgenic mouse model with Alzheimers disease pathology. The enhanced spectral range and distinct lifetime diversity of this novel oligothiopheneporphyrin-based ligand allow a more precise assessment of heterogeneous amyloid morphology compared with the corresponding oligothiophene dye.
The technique of using luminescent oligo-thiophenes and luminescent conjugated poly-thiophenes to monitor biological processes has gained increased interest from scientists within different research areas, ranging from organic chemistry and photo-physics to biology since its introduction. The technique is generally straightforward and requires only standard equipment, and the result is available within minutes from sample preparation. In this review, the syntheses of oligo and polythiophenes developed over the last decades are discussed. Furthermore, the utilization of these molecular agents for exploring biological events, e.g., DNA hybridization or protein misfolding events, are covered.
The orientations of ligands bound to the transthyretin (TTR) thyroxine (T4) binding site are difficult to predict. Conflicting binding modes of resveratrol have been reported. We previously reported two resveratrol based trans-stilbene fluorescent ligands, (E)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (SB-11) and (E)-4-(2-(naphthalen-2-yl)vinyl)-benzene-1,2-diol (SB-14), that bind native and misfolded protofibrillar TTR. The binding orientations of these two analogous ligands to native tetrameric TTR were predicted to be opposite. Herein we report the crystal structures of these TTR:ligand complexes. Opposite binding modes were verified but were different than predicted. The reverse binding mode (SB14) placing the naphthalene moiety toward the opening of the binding pocket renders the fluorescent ligand pH sensitive due to changes in Lys15 amine protonation. Conversely, the forward binding mode (SB-11) placing the naphthalene inward mediates a stabilizing conformational change, allowing intersubunit H-bonding between Ser117 of different monomers across the dimer interface. Our structures of TTR complexes answer important questions in ligand design and interpretation of trans-stilbene binding modes to the TTR T4 binding site.
A set of oligo( ethylene glycol)-terminated and globotriose-terminated self-assembled monolayers (SAMs) has been prepared on gold substrates. Such model surfaces are well defined and have good stability due to the strong binding of thiols and disulfides to the gold substrate. They are thus very suitable for addressing questions related to effects of surface composition on wetting properties, surface interactions, and surfactant adsorption. These issues are addressed in this report. Accurate wetting tension measurements have been performed as a function of temperature using the Wilhelmy plate technique. The results show that the nonpolar character of oligo( ethylene glycol)-terminated SAMs increases slightly but significantly with temperature in the range 20-55 degrees C. On the other hand, globotriose-terminated SAMs are fully wetted by water at room temperature. Surface forces measurements have been performed and demonstrated that the interactions between oligo( ethylene glycol)-terminated SAMs are purely repulsive and similar to those determined between adsorbed surfactant layers with the same terminal headgroup. On the other hand, the interactions between globotriose-terminated SAMs include a short-range attractive force component that is strongly affected by the packing density in the layer. In some cases it is found that the attractive force component increases with contact time. Both these observations are rationalized by an orientation- and conformation-dependent interaction between globotriose headgroups, and it is suggested that hydrogen-bond formation, directly or via bridging water molecules, is the molecular origin of these effects.
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.
The syntheses of alpha-D-GlcpNAc-(1-->4)-beta-D-Galp-(1-->4)-beta-D-GlcNAc-(1-->O)-(CH2)(15)CH3 (1) and fragments thereof, corresponding to structures found in human ovarian cyst fluid, are described. Silver triflate promoted coupling of 3.4,6-tri-O-acetyl-2-azido-2-deoxy-beta-D-glucopyranosyl bromide (12) and galactose acceptor (11) gave a disaccharide donor (13), which was readily transformed into the corresponding bromo-derivative 18. For the synthesis of disaccharide beta-D-Galp-(1-->4)-D-GlcNAc, several differently protected glucosamine accepters were prepared. It was found that cetyl alcohol needed to be introduced after the formation of the P-galactoside bond. Glycosylation of pent-4-enyl 3,6-di-O-benzyl-2-deoxy-2-tetrachlorophthalimido-beta-D-glucopyranoside (30) with (3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-glucopyranosyl)-(1-->4)-2,3,6-tri-O-benzoyl-alpha-D-galactopyranosyl bromide (18) by use of silver triflate as promoter gave the desired trisaccharide 31. Finally 31 was transformed via coupling to the long alkyl chain aglycon and deprotection into the title compound 1.
Di-, tri-and tetramers of ß-(1?3)-linked N-acetyllactosamine residues have been synthesised as their methyl glycosides, to be used in ITC binding studies to various galectins. The synthetic strategy involves two types of regioselective glycosylations: couplings of a galactosyl donor to 3,4-diol N-tetrachlorophthalimido glucose acceptors to give the lactosamine monomer building blocks, and subsequent formation of the oligomers through consecutive couplings of lactosamine donors to 2',3',4'-lactosamine acceptors, with high selectivity for the desired products.
Pent-4-enyl ß-D-glucopyranoside and its peracetylated and perbenzylated derivatives are shown to be excellent substrates for preparation of a wide variety of spacer functionalities. The spacer derivatives so obtained are promising substrates for preparing agents such as neo-glycoconjugates, micelies, and liquid crystalline phases, which are of interest for studying various biological and physiological phenomena of carbohydrates.
Accumulation of misfolded transthyretin (TTR) as amyloid fibrils causes various human disorders. Native transthyretin is a neurotrophic protein and is a putative extracellular molecular chaperone. Several fluorophores have been shown in vitro to bind selectively to native TTR. Other compounds, such as thioflavin T, bind TTR amyloid fibrils. The probe 1-anilinonaphthalene-8-sulfonate (ANS) binds to both native and fibrillar TTR, becoming highly fluorescent, but with indistinguishable emission spectra for native and fibrillar TTR. Herein we report our efforts to develop a fluorescent small molecule capable of binding both native and misfolded protofibrillar TTR, providing distinguishable emission spectra. We used microwave synthesis for efficient production of a small library of trans-stilbenes and fluorescence spectral screening of their binding properties. We synthesized and tested 22 trans-stilbenes displaying a variety of functional groups. We successfully developed two naphthyl-based trans-stilbenes probes that detect both TTR states at physiological concentrations. The compounds bound with nanomolar to micromolar affinities and displayed distinct emission maxima upon binding native or misfolded protofibrillar TTR (>100 nm difference). The probes were mainly responsive to environment polarity providing evidence for the divergent hydrophobic structure of the binding sites of these protein conformational states. Furthermore, we were able to successfully use one of these probes to quantify the relative amounts of native and protofibrillar TTR in a dynamic equilibrium. In conclusion, we identified two trans-stilbene-based fluorescent probes, (E)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (11) and (E)-4-(2-(naphthalen-2-yl)vinyl)benzene-1,2-diol (14), that bind native and protofibrillar TTR, providing a wide difference in emission maxima allowing conformational discrimination by fluorescence spectroscopy. We expect these novel molecules to serve as important chemical biology research tools in studies of TTR folding and misfolding.
The use of hyphenated analytical techniques in forensic drug screening enables simultaneous identification of a wide range of different compounds. However, the appearance of drug seizures containing new substances, mainly new psychoactive substances (NPS), is steadily increasing. These new and other already known substances often possess structural similarities and consequently they exhibit spectral data with slight differences. This situation has made the criteria that ensure indubitable identification of compounds increasingly important. In this work, 6 new synthetic cathinones that have not yet appeared in any Swedish drug seizures were synthesized. Their chemical structures were similar to those of already known cathinone analogs of which 42 were also included in the study. Hence, a total of 48 synthetic cathinones making up sets of homologous and regioisomeric compounds were used to challenge the capabilities of various analytical techniques commonly applied in forensic drug screening, ie, gas chromatography-mass spectrometry (GC-MS), gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR), nuclear magnetic resonance (NMR), and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Special attention was paid to the capabilities of GC-MS and GC-FTIR to distinguish between the synthetic cathinones and the results showed that neither GC-MS nor GC-FTIR alone can successfully differentiate between all synthetic cathinones. However, the 2 techniques proved to be complementary and their combined use is therefore beneficial. For example, the structural homologs were better differentiated by GC-MS, while GC-FTIR performed better for the regioisomers. Further, new spectroscopic data of the synthesized cathinone analogs is hereby presented for the forensic community. The synthetic work also showed that cathinone reference compounds can be produced in few reaction steps.
Self-assembled monolayers (SAMs) of galactoside-terminated alkanethiols have protein-resistance properties which can be tuned via the degree of methylation [Langmuir 2005, 21, 2971-2980]. Specifically, a partially methylated compound was more resistant to nonspecific protein adsorption than the hydroxylated or fully methylated counterparts. We investigate whether this also holds true for resistance to the attachment and adhesion of a range of marine species, in order to clarify to what extent resistance to protein adsorption correlates with the more complex adhesion of fouling organisms. The partially methylated galactoside-terminated SAM was further compared to a mixed monolayer of omega-substituted methyl- and hydroxyl-terminated alkanethiols with wetting properties and surface ratio of hydroxyl to methyl groups matching that of the galactoside. The settlement (initial attachment) and adhesion strength of four model marine fouling organisms were investigated, representing both micro- and macrofoulers; two bacteria (Cobetia marina and Marinobacter hydrocarbonoclasticus), barnacle cypris larvae (Balanus amphitrite), and algal zoospores (Ulva linza). The minimum in protein adsorption onto the partially methylated galactoside surface was partly reproduced in the marine fouling assays, providing some support for a relationship between protein resistance and adhesion of marine fouling organisms. The mixed alkanethiol SAM, which was matched in wettability to the partially methylated galactoside SAM, consistently showed higher settlement (initial attachment) of test organisms than the galactoside, implying that both wettability and surface chemistry are insufficient to explain differences in fouling resistance. We suggest that differences in the structure of interfacial water may explain the variation in adhesion to these SAMs.
An approach based on electrochemistry to differentiate between phosphorylated and nonphosphorylated amino acid analogues adsorbed on gold is presented. Analogues of serine, threonine, and tyrosine, containing thiohexadecyl headgroups, were synthesized and assembled on gold, and the surface capacitance was evaluated using electrochemical impedance spectroscopy. A procedure for deprotection of tert-butyl phosphate protecting groups, on the monolayer, is also described. Characterizations of the assembled analogues by cyclic voltammetry, infrared spectroscopy, and ellipsometry are used to confirm the insulating properties of the monolayers and the outcome of surface modifications. The results from cyclic voltammetry show good insulating properties for the monolayers even after phosphate deprotection. The infrared measurements reveal well-ordered monolayers, and the thickness from ellipsometry is in good agreement with expectations from molecular modeling. The impedance experiments show a capacitance increase up to 0.6 μF/cm2 as phosphate groups are introduced. The results in this study indicate the possibility of using a surface chemical and impedance spectroscopy approach to detect the kinase/phosphatase activity and kinetics involved in phosphorylation reactions.
The synthesis of a series of thiols containing phosphorylated and non-phosphorylated serine, threonine, and tyrosine amino acid residues is described. The synthesized molecules, based on 3-mercaptopropionic acid, were assembled onto gold and subsequently characterized using infrared reflection-absorption spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and contact angle goniometry. The ellipsometric analysis indicates that they form densely packed and well-oriented monolayers on gold, with thicknesses that are in good agreement with estimated values from space-filling models. The bulky and space-demanding phosphorylated threonine analog was, however, found to be an exception. The increase in layer thickness when adding a phosphate group to the threonine is only 35% of that observed for the two other analogs. A detailed infrared examination of the influence of cation coordination to the phosphorylated serine analog using calcium and magnesium reveals structural similarities to those of the inorganic phosphate compound calcium hydroxy apatite. We furthermore discuss the application of these monolayers as soft templates for biomineralization.
Electrochemical impedance spectroscopy has been used to evaluate the change in interracial capacitance upon calcium and magnesium coordination to a phosphate-modified electrode. The phosphate electrode was prepared via immobilization of phosphorylated, thiol-containing, serine analogues onto gold. Upon subjection to calcium and magnesium, a substantial drop in capacitance was observed. Magnesium displayed the largest influence on the capacitance: a 27% capacitance drop was observed upon introduction of a 1 mM solution of magnesium ions. The lowered capacitance is a result of a change in the potential and charge distribution at the film/electrolyte interface as the cations coordinate to the phosphate groups. Moreover, the relationship between electrode potential and capacitance has been investigated and reveals a significant difference between monovalent and divalent cations. As complementary information, infrared reflection absorption spectra of the phosphorylated monolayer having different counterions are presented. The results reported in this paper indicate that the phosphorylated amino acid analogue monolayers could be used in investigations of the biochemically important coordination of calcium and magnesium to phosphates and phosphorylated amino acids.
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.
In oncology and neurology the F-18-radiolabeled glucose analogue 2-deoxy-2-[F-18]fluoro-D-glucose ([F-18]FDG) is by far the most commonly employed metabolic imaging agent for positron emission tomography (PET). Herein, we report a novel synthetic route to beta-configured mannopyranoside precursors and a chemoselective F-18-fluoroglycosylation method that employ two b-configured [F-18]FDG derivatives equipped with either a terminal azide or alkyne aglycon respectively, for use as a CuAAC clickable tool set for PET. The b-configured precursors provided the corresponding [F-18]FDGs in a radiochemical yield of 77-88%. Further, the clickability of these [F-18]FDGs was investigated by click coupling to the suitably functionalized Fmoc-protected amino acids, Fmoc-N-(propargyl)-glycine and Fmoc-3-azido-L-alanine, which provided the F-18-fluoroglycosylated amino acid conjugates in radiochemical yields of 75-83%. The F-18-fluoroglycosylated amino acids presented herein constitute a new and interesting class of metabolic PET radiotracers.
We demonstrate herein the synthesis, characterization and application of a novel chelateassociated photochemistry (CAP) for oriented and robust attachment of biomolecular ligandsto sensing surfaces. The chelation agent is nitrilotriacetic acid (NTA) which is capable ofcoordinating two histidine (His) molecules in the presence of Nickel. Therefore a ligandmodified with a His-sequence can be attached to NTA to form an oriented assembly ofligands on the sensor surface. The ligand is then covalently bound to the surface via a nearbyphotolabile benzophenone (BP) which attacks C-H bonds upon UV light activation. Theligand is then available for analyte interaction. The synthesized compounds used in this studyare based on the well-known organosulphur surface chemistry for proper attachment to goldsurfaces. Besides the two BP and NTA alkane thiols/disulphides we also synthesized a fillermolecule with an oligo (ethylene glycol) (OEG) tail to fine tune the surface composition andto reduce non-specific binding. Results from surface plasmon resonance (SPR) measurementsusing a Biacore 3000 instrument indicate that up to 55% larger analyte response is obtainedwith CAP as compared to the response obtained with the random orientation achieved byphotoimmobilization alone.
This report presents a novel method for uniform orientation and covalent attachment of proteins to sensing surfaces, termed Chelation Assisted Photoimmobilization (CAP). Alkanethiols terminated with either nitrilotriacetic acid (NTA), benzophenone (BP) or oligo(ethylene glycol) were synthesized and mixed self-assembled monolayers (SAMs) were prepared on gold and thoroughly characterized by infrared reflection absorption spectroscopy (IRAS), ellipsometry and contact angle goniometry. In the process of CAP, NTA chelates Ni2+ and the complex coordinates a His-tagged ligand in an oriented assembly. The ligand is then photoimmobilized via BP, which forms covalent bonds upon UV light activation. The CAP concept was demonstrated using human IgG-Fc modified with C-terminal hexahistidine tags (His-IgGFc) as the ligand and protein A as the analyte.
In the development of affinity biosensors, uniform orientation of ligand molecules where all analyte binding sites are accessible is often preferred to random orientation. In order to monitor the effect of ligand orientation on analyte response, the ligand-analyte interaction was quantified by surface plasmon resonance analysis, both in the case of CAP and when the ligand was attached by conventional amine coupling on surfaces presenting NTA. Responses were adjusted for differences in ligand immobilization level using IRAS. The normalized analyte response with randomly oriented ligand was 2.5 times higher than that with ligand immobilized by CAP, probably due to molecular crowding effects on the surface and the fact that His-IgGFc is bivalent for protein A. This is a reminder that many other factors than orientation alone may play a decisive role in analyte binding on biosensor surfaces.
A novel strategy for site-specific and covalent attachment of proteins has been developed, intended for robust and controllable immobilization of histidine (His)-tagged ligands in protein microarrays. The method is termed chelation assisted photoimmobilization (CAP) and was demonstrated using human IgG-Fc modified with C-terminal hexahistidines (His-IgGFc) as the ligand and protein A as the analyte. Alkanethiols terminated with either nitrilotriacetic acid (NTA), benzophenone (BP); or oligo(ethylene glycol) were synthesized and mixed self-assembled monolayers (SAMs) were prepared on gold and thoroughly characterized by infrared reflection absorption spectroscopy (IRAS), ellipsometry, and contact angle goniometry. In the process of CAP, NTA chelates Ni2+ and the complex coordinates the His-tagged ligand in an oriented assembly. The ligand is then photoimmobilized via BP, which forms covalent bonds upon UV light activation. In the development of affinity biosensors and protein microarrays, site-specific attachment of ligands in a fashion where analyte binding sites are available is often preferred to random coupling. Analyte binding performance of ligands immobilized either by CAP or by standard amine coupling was characterized by surface plasmon resonance in combination with IRAS. The relative analyte response with randomly coupled ligand was 2.5 times higher than when site-specific attachment was used. This is a reminder that also when immobilizing ligands via residues far from the binding site, there are many other factors influencing availability and activity. Still, CAP provides a valuable expansion of protein immobilization techniques since it offers attractive microarraying possibilities amenable to applications within proteomics.
In the context of surface chemistry for affinity biosensor chips, it is widely accepted that uniform orientation of the immobilized recognition element (ligand) is preferred over random orientation. However, this assumption has often been based on studies where differences in ligand immobilization level have not been taken into account. In this contribution, we present a novel two-step method for homogenous orientation and covalent attachment of proteins to sensing surfaces, called Chelation Assisted Photoimmobilization (CAP). Careful quantification of the effect of ligand orientation on analyte responses was performed by comparing this strategy to immobilization by conventional amine coupling.
In CAP, the chelation agent is nitrilotriacetic acid (NTA) which chelates Ni2+. A His-tagged ligand forms an oriented assembly when binding Ni2+-NTA and is then covalently bound to the surface via photolabile benzophenone (BP), which attacks C-H bonds upon UV light activation. We relied on a surface chemistry based on self-assembled monolayers (SAMs) of oligo(ethylene glycol) (OEG)-containing alkanethiolates on gold. Alkanethiols terminated with either NTA, BP or OEG were synthesized and mixed SAMs were characterized by infrared reflection absorption spectroscopy (IRAS), ellipsometry and contact angle goniometry. IRAS was also used to quantify ligand immobilization levels obtained either by CAP or by amine coupling via the carboxyl groups of an NTA-presenting surface. The model ligand was human IgG-Fc modified with a C-terminal 6xHis-tag and the analyte was Protein A. The ligand-analyte interaction was quantified by a surface plasmon resonance biosensor.
Analyte responses were normalized with respect to the ligand amounts obtained by the two immobilization strategies. Interestingly, the normalized analyte response with randomly oriented ligand was >2 times higher than that with ligand immobilized by CAP. This shows that oriented ligand immobilization is not necessarily a means of increasing the sensitivity of a biosensor. Factors that may influence performance include the valency of the ligand and constraints related to the surface chemistry used for orientation.
The ability to produce monomolecular coatings with well-defined structural and functional properties is of key importance in biosensing, drug delivery, and many recently developed applications of nanotechnology. Organic chemistry has proven to be a powerful tool to achieve this in many research areas. Herein, we present the synthesis of three oligo(lactosides) glycosylated in a (1 → 3) manner, and which are further functionalized with amide-linked short alkanethiol spacers. The oligosaccharides (di-, tetra-, and hexasaccharide) originate from the inexpensive and readily available lactose disaccharide. These thiolated derivatives were immobilized onto gold surfaces, and the thus formed self-assembled monolayers (SAMs) on planar gold were characterized by wettability, ellipsometry and infrared reflection–absorption spectroscopy. Further, the ability of these SAMs to stabilize gold nanoparticles in saline solutions was also demonstrated, indicating that the oligosaccharides may be used as stabilizing agents in gold nanoparticle-based assays.
The ability of fabricating surfaces with low non-specific protein adhesion is of great interest in material science. Studies have shown that self-assembled monolayers (SAMs) covered with carbohydrates moieties have protein resistant characteristics and even marine anti-fouling properties.[1,2]The presented results describe the synthesis of oligosaccharides originating from lactose and mannose. We have also set out to investigate if these orthogonally protected oligosaccharides can be used as spacer molecules and their performance in protein adsorption studies. Using the selected divergence enables incorporation into various surface systems e.g. gold nanoparticles, vesicles or as a conjugate between different macromolecules.
[1] Hederos, M.; Konradsson, P.; Liedberg, B.; Langmuir, 2005, 21, 2971-2980.[2] Fyrner, T.; Konradsson, P.; et. al.; Submitted, 2010.
We describe the synthesis of a series of mono-, di-, and trisaccharide-functionalized alkanethiols as well as the formation of fouling-resistant self-assembled monolayers (SAMs) from these. The SAls,,Is were characterized using ellipsometry, wetting measurements, and infrared reflection absorption spectroscopy (WAS). We show that the structure of the carbohydrate moiety affects the packing density and that this also alters the alkane chain organization. Upon increasing the size of the sugar moieties (from mono- to di- and trisaccharides), the structural qualities of the monolayers deteriorated with increasing disorder, and for the trisaccharide, slow reorganization dynamics in response to changes in the environmental polarity were observed. The antifouling properties of these SAMs were investigated through protein adsorption experiments from buffer solutions as well as settlement (attachment) tests using two common marine fouling species, zoospores of the green macroalga Ulva linza and cypris larvae of the barnacle Balanus amphitrite. The SAMs showed overall good resistance to fouling by both the proteins and the tested marine organisms. To improve the packing density of the SAMs with bulky headgroups, we employed mixed SAMs where the saccharide-thiols are diluted with a filler molecule having a small 2-hydroxyethyl headgroup. This method also provides a means by which the steric availability of sugar moieties can be varied, which is of interest for specific interaction studies with surface-bound sugars. The results of the surface dilution study and the low nonspecific adsorption onto the SAMs both indicate the feasibility of this approach.
When cross-linking biomolecules to surfaces or to other biomolecules, the use of appropriate spacer molecules is of great importance. Mimicking the naturally occurring spacer molecules will give further insight into their role and function, possibly unveil important issues regarding the importance of the specificity of carbohydrate-based anchor moieties, in e.g., glycoproteins and glycosylphosphatidylinositols. Herein, we present the synthesis of a lactoside-based trisaccharide, potentially suitable as a heterobifunctional bioorthogonal linker molecule whereon valuable chemical handles have been conjugated. An amino-derivative having thiol functionality shows promise as novel SPR-surfaces. Furthermore, the trisaccharide has been conjugated to a cholesterol moiety in combination with a fluorophore which successfully assemble on the cell surface in lipid microdomains, possibly lipid-rafts. Finally, a CuI-catalyzed azide-alkyne cycloaddition reaction (CuAAC) confirms the potential use of oligosaccharides as bioorthogonal linkers in chemical biology.
The synthesis of four bifunctionalized orthogonally N-protected oligosaccharides derived from lactose and mannose, intended as cross-linking derivatives, is described. The amino sugar at the non-reducing end is derivatized with an N-Boc-protected glycine moiety, and further connected to either a mannose (1→6) disaccharide or (1→3) lactose units (one, two or three) resulting in tri-, penta-, or heptasaccharides. All of the synthesized oligosaccharides have an Nbenzyloxycarbonyl-aminoethyl residue at the reducing end. The fully orthogonal N-Boc/N-Cbz protection group pattern enables further conjugation/derivatization and results in a hydrophilic cross-linking molecule. It was found that the order of the final synthetic steps were crucial to avoid acyl migration. A suitable amide coupling protocol has been applied to introduce the NBoc-protected glycine moiety in alcoholic solvent. The synthesized oligosaccharides will provide a model system to investigate the influence of length, structure and flexibility. The function of the cross-linked substituents thereby provide valuable insights into the role as a spacer molecule.
The aim of this work is to extend the knowledge of the mechanism of electropolymerization of pyrrole and PEDOT-S by means of in situ electrochemical quartz microbalance with dissipation studies (EQCM-D), which allow us to evaluate the chemical and physical processes during electrochemical deposition of these conductive polymer composites. Meanwhile, the relationship between the morphology of the films and the mechanism of the electropolymerization of pyrrole in presence of PEDOT-S will be discussed. The resulting material is electroactive, black and conducting. This material is a polymer composite where doped polypyrrole chains are found in an environment of doped PEDOT-S chains. They can be identified through the cyclic voltammetry studies of the composite, through element composition and through their optical signatures in electrochromism. The composite has properties suitable for a supercapacitor electrode, and capacitance of up to 650 F/g has been obtained.
The transglucosidations of methyl 4-O-methyl-a- and -ß-D-glucopyranoside in ethanolic camphor-10-sulfonic acid, and of ethyl 4-O-methyl-a- and -ß-D-glucopyranoside in methanolic camphor-10-sulfonic acid, have been studied. Samples were removed at intervals and the proportions of the glucosides determined by GC of their acetates. The results show that the anomer with the inverted configuration predominates in the initially formed product (˜59-70%). This indicates that all the studied reactions proceed via the same mechanism, involving exocyclic C-O cleavage and formation of a glucopyranosylium ion, but that the eliminated alcohol exerts some steric hindrance, which favors the approach of the other alcohol from the opposite side. © 2002 Published by Elsevier Science Ltd.
Protein aggregation is associated with a wide range of diseases, and molecular probes that are able to detect a diversity of misfolded protein assemblies are of great importance. The identification of prefibrillar states preceding the formation of well-defined amyloid fibrils is of particular interest both because of their likely role in the mechanism of fibril formation and because of the growing awareness that these species are likely to play a critical role in the pathogenesis of protein deposition diseases. Herein, we explore the use of an anionic oligothiophene derivative, p-FTAA, for detection of prefibrillar protein aggregates during in vitro fibrillation of three different amyloidogenic proteins (insulin, lysozyme, and prion protein). p-FTAA generally detected prefibrillar protein aggregates that could not be detected by thioflavine T fluorescence and in addition showed high fluorescence when bound to mature fibrils. Second, the kinetics of protein aggregation or the formation of amyloid fibrils of insulin was not extensively influenced by the presence of various concentrations of p-FTAA. These results establish the use of p-FTAA as an additional tool for studying the process of protein aggregation.
Short synthetic routes to protected ethyl 2-deoxy-2-phthalimido-1-β-D- thio-galactosamine derivatives via epimerization of the corresponding glucosamine compounds are described. Starting from D-glucosamine hydrochloride, the epimerizations were performed by displacement of presynthesized triflates with nitrite anions and by an oxidation/reduction route. The latter method involved Moffatt oxidation to the corresponding 4-ketohexoses and subsequent reduction using sodium borohydride/ tetrabutylammonium borohydride, zinc borohydride, or lithium tri-sec-butyl borohydride in THF. The displacement route was found to be the preferred method for epimerization of 3-O-acyl (benzoyl) derivatives. For glucosamine compounds with 3-O-etheral- (allyl or benzyl) and 6-O-benzyl protecting groups, the oxidation/reduction route was the most convenient procedure to achieve corresponding galactosamine compounds. The produced galactosamine derivatives will be useful building blocks in the synthesis of antifreeze glycoproteins substances and analogues thereof.
Synthesis of the core tetrasaccharide Manp(α1→6)-Manp(α1→4)-6-(2-aminoethylphosphonic acid)-GlcNp(α1→6)-myo-Ins-1-PO4, found in glycoinositolphospholipids of Trypanosoma cruzi parasites, is described. The key building block, 6-O-(2-azido-3-O-benzyl-6-O-((2-benzyloxycarbonylaminoethyl)phosphonic acid benzyl ester)-2-deoxy-α-d-glucopyranosyl)-1-di-O-benzylphosphoryl-4,5-O-isopropylidene-2,3-O-(d-1,7,7-trimethyl[2,2,1]bicyclohept-6-ylidene)-d-myo-inositol, was synthesized using a partially protected glucosyl d-camphorinositolphosphate and a (2-benzyloxycarbonylaminoethyl)phosphonic acid derivative in a regioselective phosphonate esterfication. Elongation with ethyl 2-O-benzoyl-3,4,6-tri-O-benzyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzyl-1-α-d-thiomannopyranoside using dimethyl(methylthio)sulfonium trifluoromethanesulfonate gave a fully protected tetrasaccharide which was successfully deprotected subsequently with sodium methoxide, sodium in liquid ammonia, and aq hydrochloric acid to give title compound.
Synthesis of the heptasaccharyl myo-inositol found in Trypanosoma cruzi lipopeptidophosphoglycan was accomplished using a convergent assembly of three building blocks. The target compound is the first complete 2-aminoethyl phosphonic acid substituted glycan related to the glycosylphosphatidylinositol anchor family to be synthesized. The order of assembly enables synthesis of phosphoinositol oligosaccharides related to other glycosylinositolphospholipids in Tr. cruzi, the protozoan parasite causing Chagas' disease, which is endemic in South America.
Synthesis of β-D-Gal-(1 → 3)-β-D-GalNAc coupled to HOC2H4NHCOC15H30SH is described. This compound was coadsorbed at various proportions with C2H5OC2H4NHCOC15H30SH to form statistically mixed self-assembled monolayers (SAMs) on gold in an attempt to mimic the properties of the active domain in antifreeze glycoproteins (AFGPs). The monolayers were characterized by null ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy, and infrared reflection−absorption spectroscopy. The disaccharide compound adsorbed preferentially, and SAMs prepared at a solution molar ratio >0.3 displayed total wetting. The mixed SAMs showed well-organized alkyl chains up to a disaccharide surface fraction of 0.8. The amount of gauche conformers in the alkyls increased rapidly above this point, and the monolayers became disordered and less densely packed. Furthermore, the generated mixed SAMs were subjected to water vapor at constant relative humidity and the subsequent ice crystallization on a cooled substrate was monitored via an optical microscope. Interestingly, rapid crystallization occurred within a narrow range of temperatures on mixed SAMs with a high disaccharide content, surface fraction >0.3. The reported crystallization temperatures and the ice layer topography were compared with results obtained for a much simpler reference system composed of −OH/−CH3 terminated n-alkanethiols in order to account for changes in topography of the water/ice layer with surface energy. Although preliminary, the obtained results can be useful in the search for the molecular mechanism behind the antifreeze activity of AFGPs.
The synthesis of two galactose-terminated alkanethiols with the structural formula X−OC2H5NHCO(CH2)15SH (X = 2,3,4,6-tetra-O-methyl-β-d-Gal or β-d-Gal) is described. Single-component and mixed self-assembled monolayers (SAMs) of the methylated and nonmethylated compounds were prepared on gold and subsequently characterized with ellipsometry, contact angle goniometry, and infraredreflection−absorption spectroscopy. Studies of the irreversible protein adsorption onto the SAMs using ex-situ ellipsometry revealed very low levels of fibrinogen and lysozyme adsorption onto mixed SAMs displaying advancing water contact angles between 24° and 45° and below 45°, respectively. A monomethylated compound (X = 6-O-methyl-β-d-Gal) was also synthesized and assembled on gold. This particular compound was found to possess wettability properties corresponding to the low adsorption regime of the mixed SAMs, and the results from the same set of fibrinogen and lysozyme adsorption experiments showed very low levels of protein adsorption. Our findings suggest that the protein rejecting properties rely on a fine balance between the surface energy and/or hydrogen bond donating/accepting properties of the SAM surface.
Changes of the optical properties of conjugated polyelectrolytes have been utilized to monitor noncovalent interactions between biomolecules and the conjugated polyelectrolytes in sensor applications. A regioregular, zwitterionic conjugated oligoelectrolyte was synthesized in order to create a probe with a defined set of optical properties and hereby facilitate interpretation of biomolecule−oligoelectrolyte interactions. The synthesized oligoelectrolyte was used at acidic pH as a novel optical probe to detect amyloid fibril formation of bovine insulin and chicken lysozyme. Interaction of the probe with formed amyloid fibrils results in changes of the geometry and the electronic structure of the oligoelectrolyte chains, which were monitored with absorption and emission spectroscopy.
There is an urgent need for simple and non-invasive identification of live neural stem/progenitor cells (NSPCs) in the developing and adult brain as well as in disease, such as in brain tumors, due to the potential clinical importance in prognosis, diagnosis, and treatment of diseases of the nervous system. Here, we report a luminescent conjugated oligothiophene (LCO), named p-HTMI, for non-invasive and non-amplified real-time detection of live human patient-derived glioblastoma (GBM) stem cell-like cells and NSPCs. While p-HTMI stained only a small fraction of other cell types investigated, the mere addition of p-HTMI to the cell culture resulted in efficient detection of NSPCs or GBM cells from rodents and humans within minutes. p-HTMI is functionalized with a methylated imidazole moiety resembling the side chain of histidine/histamine, and non-methylated analogues were not functional. Cell sorting experiments of human GBM cells demonstrated that p-HTMI labeled the same cell population as CD271, a proposed marker for stem cell-like cells and rapidly migrating cells in glioblastoma. Our results suggest that the LCO p-HTMI is a versatile tool for immediate and selective detection of neural and glioma stem and progenitor cells.
The acid catalyzed ethanolysis of methyl 5-O-methyl-a- and -ß-D-glucofuranoside and the analogous methanolysis of ethyl 5-O-methyl-a- and -ß-D-glucofuranoside have been investigated. For all four reactions, the primarily formed transglycosylation product was a single glycoside that had the opposite anomeric configuration to the starting material. This strongly indicates that a D-glucose methyl ethyl acetal is first formed and is then ring closed by a nucleophilic attack by HO-4, giving either the starting material or a transglycosylation product with the opposite anomeric configuration. Low percentages of the methyl ethyl acetals and of dimethyl acetals were also observed in the reaction product during the methanolysis reactions. © 2001 Elsevier Science Ltd.
Fucoidans are sulfated fucose-based polysaccharides that activate platelets and have pro- and anticoagulant effects; thus, they may have therapeutic value. In the present study, we show that 2 synthetic sulfated a-l-fucoside-pendant glycopolymers (with average monomeric units of 13 and 329) and natural fucoidans activate human platelets through a Src- and phosphatidylinositol 3-kinase (PI3K)-dependent and Syk-independent signaling cascade downstream of the platelet endothelial aggregation receptor 1 (PEAR1). Synthetic glycopolymers and natural fucoidan stimulate marked phosphorylation of PEAR1 and Akt, but not Syk. Platelet aggregation and Akt phosphorylation induced by natural fucoidan and synthetic glycopolymers are blocked by a monoclonal antibody to PEAR1. Direct binding of sulfated glycopolymers to epidermal like growth factor (EGF)-like repeat 13 of PEAR1 was shown by avidity-based extracellular protein interaction screen technology. In contrast, synthetic glycopolymers and natural fucoidans activate mouse platelets through a Src- and Syk-dependent pathway regulated by C-type lectin-like receptor 2 (CLEC-2) with only a minor role for PEAR1. Mouse platelets lacking the extracellular domain of GPIba and human platelets treated with GPIba-blocking antibodies display a reduced aggregation response to synthetic glycopolymers. We found that synthetic sulfated glycopolymers bind directly to GPIba, substantiating that GPIba facilitates the interaction of synthetic glycopolymers with CLEC-2 or PEAR1. Our results establish PEAR1 as the major signaling receptor for natural fucose-based polysaccharides and synthetic glycopolymers in human, but not in mouse, platelets. Sulfated a-l-fucoside-pendant glycopolymers are unique tools for further investigation of the physiological role of PEAR1 in platelets and beyond.
Olfaction may play an important role in regulating bird behavior, and has been suggested to be involved in feather-pecking. We investigated possible differences in the body odors of red junglefowl females by using an automated olfactometer which assessed the ability of trained mice to discriminate between the odors of uropygial gland secretions (the main carrier of potential individual odors in chickens) of six feather-pecked and six non-pecked birds. All mice were clearly able to discriminate between all individual red junglefowl odors, showing that each bird has an individual body odor. We analyzed whether it was more difficult to discriminate between the odors of two feather-pecked, or two non-pecked birds, than it was to discriminate between the odors of two randomly selected birds. This was not the case, suggesting that feather-pecked birds did not share a common odor signature. Analyses using gas chromatography and mass spectrometry showed that the composition of aliphatic carboxylic acids in uropygial gland secretions differed consistently between individuals. However, chemical composition did not vary according to feather-pecking status. We conclude that red junglefowl have individual body odors which appear to be largely based on differences in the relative abundance of aliphatic carboxylic acids, but there is no evidence of systematic differences between the body odors of pecked and non-pecked birds.
Chemical polymerization of a 3,4-ethylenedioxythiophene derivative bearing a sulfonate group (EDOTS) is reported. The polymer, PEDOT-S, is fully water-soluble and has been produced by polymerizing EDOT-S in water, using Na2S2O8 and a catalytic amount of FeCl3. Elemental analysis and XPS measurements indicate that PEDOT-S is a material with a substantial degree of self-doping, but also contains free sulfate ions as charge-balancing counterions of the oxidized polymer. Apart from self-doping PEDOT-S, the side chains enable full water solubility of the material; DLS studies show an average cluster size of only 2 nm. Importantly, the solvation properties of the PEDOT-S are reflected in spin-coated films, which show a surface roughness of 1.2 nm and good conductivity (12 S/cm) in ambient conditions. The electro-optical properties of this material are shown with cyclic voltammetry and spectroelectrochemical experiment reveals an electrochromic contrast (similar to 48% at lambda(max) = 606 nm).
Using a linear assembly approach a highly differentially protected derivative of the common GPI-anchor core structure (alpha-D-Man-(1-->6)-alpha-D-Man-(1-->2)-alpha-D-Man-(1-->4)-alpha-D-GlcNH(2)-(1-->6)-D-myo-inositol) has been synthesized. All mannose donors were prepared from a common thioglycoside precursor (1), and coupled to GlcN(3)-myo-inositol acceptor 5 in a linear five-step glycosylation-deprotection sequence in 49% overall yield, to give the key intermediate 10, with orthogonal temporary protecting groups at the 6", 2", 6', and 2 positions of the trimannoside motif and at the 1 and 2 positions of the inositol part. Consecutive removal of the temporary protecting groups in the trimannoside moiety followed by phosphorylation, gave a tetraphosphosphate derivative in 60% overall yield. Removal of a camphor acetal afforded a 1,2-inositol diol, which was converted to a 1,2-cyclic phosphate using commercial methyl dichlorophosphate (-->17, 95%). One-step deprotection using sodium in liquid ammonia afforded the target polyphosphorylated core structure 18 (60%), which will be tested for metabolic insulin action.
Klebsiella pneumoniae serotype KN2 is a carbapenem-resistant strain and leads to the health care-associated in-fections, such as bloodstream infections. Its capsular polysaccharide (CPS) was isolated and cleaved by a specific enzyme from a bacteriophage into a hexasaccharide-repeating unit. With GC-MS, NMR, and Mass analyses, the structure of KN2 CPS was determined to be {-> 3)-beta-D-Glcp-(1 -> 3)-[alpha-D-GlcpA-(1 -> 4)-beta-D-Glcp-(1 -> 6)]-alpha-D-Galp- (1 -> 6)-beta-D-Galp-(1 -> 3)-beta-D-Galp-(1 ->}(n). We demonstrated that 1 mu g/mL CPS could stimulate J774A.1 murine macrophages to release tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in vitro. Also, we proved that KN2 CPS induced the immune response through Toll-like receptor 4 (TLR4) in the human embryonic kidney (HEK)-293 cells. Strikingly, the hexasaccharide alone shows the same immune response as the CPS, suggesting that the hexasaccharide can shape the adaptive immunity to be a potential vaccine adjuvant. The glucuronic acid (GlcA) on other polysaccharides can affect the immune response, but the GlcA-reduced KN2 CPS and hex-asaccharide still maintain their immunomodulatory activities.
Nanotapes are formed by the co-assembly of triblock peptide copolymers with an amino acid-substituted polythiophene derivative (PTT). The driving force for the assembly is ionic interaction (complex coacervation). These nanotapes were visualized by atomic force microscopy and confocal laser scanning microscopy. The interactions between the triblock peptide copolymers and the PTT are also expressed in the steady state and time resolved fluorescence spectra. The steady-state spectra indicate that upon interaction with the peptide copolymer, the backbone of the PTT adopts a rather twisted, and definitely less, aggregated conformation. The time-resolved fluorescence decay studies further confirm this interpretation. The structure of these nanotapes at the mesoscopic scale depends, among other physical chemical parameters, on the concentrations of its constituents.
Conjugated organic nanowires have been prepared by co-assembling a carboxylate containing low-molecular weight gelator (LMWG) and an amino acid substituted polythiophene derivative (PTT). Upon introducing the zwitterionic polyelectrolyte PTT to a basic molecular solution of the organogelator, the negative charges on the LMWG are compensated by the positive charges of the PTT. As a result, nanowires form through co-assembly. These nanowires are visualized by both transmission electron microscopy (TEM) and atomic force microscopy (AFM). Depending on the concentration and ratio of the components these nanowires can be micrometers long. These measurements further suggest that the aggregates adopt a helical conformation. The morphology of these nanowires are studied with fluorescent confocal laser scanning microscopy (CLSM). The interactions between LMWG and PTT are characterized by steady-state and time-resolved fluorescence spectroscopy studies. The steady-state spectra indicate that the backbone of the PTT adopts a more planar and more aggregated conformation when interacting with LMWG. The time-resolved fluorescence decay studies confirm this interpretation.
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.
Short synthetic routes to protected derivatives of 2-amino-2-deoxy-a-D-glucopyranosyl-(1?6)-D-myo-inositol are described. Various 2-azido-2-deoxy-glucosyl donors were synthesized, starting from D-glucal or glucosamine hydrochloride. Derivatives of 1,2- and 2,3- D-myo-inositol-camphanylidene acetals were prepared to function as glycosyl acceptors. The subsequent glycosylations produced useful building blocks for the synthesis of GPI-anchor substances. © 2002 Elsevier Science Ltd. All rights reserved.