Molecular characteristics of some commercial high-molecular-weight hyaluronans

Commercially available hyaluronan (HA) samples were investigated by the method of size exclusion chromatography (SEC). The fractions eluted from the SEC column were on-line molecularly characterized by using a multi-angle laser light scattering (MALLS) photometer. Along with the SEC-MALLS technique, the high-molecular-weight HA biopolymers were (off-line) analyzed by capillary viscometry.     

Structural characterisation of trimethylsilyl-protected DNA bases

The structures of the silylated DNA bases, bis(trimethylsilyl)thymine (1), bis(trimethylsilyl)cytosine (2), bis(trimethylsilyl)adenine (3) and tris(trimethylsilyl)guanine (4), have been determined. 1 is O-silylated and displays no intermolecular interactions. 2 is silylated at both exocylic O, N positions and forms a chain structure through intermolecular NH…O and NH…N hydrogen bonds. 3 contains two SiMe₃ groups, on the exocylic NH and endocyclic N⁹ position, respectively; of two independent molecules in the asymmetric unit, one dimerises through complementary NH…N hydrogen bonds, while the other forms a strained intramolecular hydrogen bond through the same pair of donor and acceptor centres. 4 incorporates N, N, O–SiMe₃ moieties and forms chains via bifurcated CH…O/N hydrogen bonds, while the NH function remains unexploited. The effects of silylation on these pyrimidine and purine ring structures are also discussed in comparison with the native bases.

The structures of the silylated DNA bases, bis-(trimethylsilyl)thymine (1), bis-(trimethylsilyl)cytosine (2), bis-(trimethylsilyl)adenine (3) and tris-(trimethylsilyl)guanine (4), have been determined. While 1 displays no intermolecular interactions. 2 forms a chain structure through intermolecular NH…O and NH…N hydrogen bonds, 3 incorporates two independent molecules in the asymmetric unit, one dimerises through complementary NH…N hydrogen bonds while the other forms a strained intramolecular hydrogen bond through the same pair of donor and acceptor centres and 4 forms chains via bifurcated CH…O/N hydrogen bonds while the NH function remains unexploited.     

Structural characterisation of a red phthalocyanine

Metal 1,4,8,11,15,18,22,25-octakis(hexylsulfanyl)phthalocyanines exhibit a weak absorption band in the 450-600 nm region, leading to novel dyes that include the red lead metallated derivative that has been characterised by X-ray crystallography.     

Structural characterisation of the first mononuclear bismuth porphyrin

A single carboxylate picket bismuth porphyrin has been characterised in the solid state as the first instance of a non-dimeric structure; the carboxylate picket, bent over the macrocycle, is coordinated to the bismuth, inducing a significant distortion of the porphyrin core.     

Structural characterisation of micro- and mesoporous materials by electron microscopy

Zeolites are one of the most important materials currently used in the petroleum industry for a wide variety of catalytic transformations. However, they are increasingly being considered for other applications such as for designing quantum-confined materials in their spaces. With such applications in mind, precise characterisation of zeolites and related porous materials has never been more necessary. Here we show how electron diffraction coupled with high-resolution imaging can reveal the detailed fine structure in both the bulk and at the surface of these materials. A variety of case studies are considered which include ETS-10, FAU, LTL and FSM-16.     

Structural characterisation and ACE-inhibitory activities of polysaccharide from Gastrodia elata Blume

The structural properties and Angiotensin-I converting enzyme (ACE) inhibition activities of a polysaccharide (PGE) extracted from Gastrodia elata Blume were investigated. PGE was extracted using hot water and purified by Sephadex G-200 followed by ultra-filtration. The structural characterisation of PGE was analysed by FT–IR, NMR spectroscopy, specific rotation determination, periodate oxidation-smith degradation, methylation analysis, GC–MS and Congo red test. The results revealed that PGE was composed by glucose, with an average molecular weight of 1.54 × 10³ kDa. The structure of PGE was 1→3 and 1→4,6-branched-glucopyranose that had a linear backbone of (1 → 4)-linked-d-glucopyranose (Glcp). ACE-inhibitory activity results showed that PGE was efficient to inhibit ACE and the IC₅₀ value was 0.66 mg/mL.     

Structural characterisation by ESI-MS of feruloylated arabino-oligosaccharides synthesised by chemoenzymatic esterification

The chemoenzymatic synthesis of feruloylated arabino-oligosaccharides has been achieved, using a feruloyl esterase type C from Sporotrichum thermophile (StFaeC).The structure of the feruloylated products was confirmed by ESI-MS(n).     

Structural FTIR analysis and thermal characterisation of lyocell and viscose-type fibres

The microstructure and thermal properties of lyocell and other regenerated cellulose fibres (viscose and modal) were analysed using DSC, TG and FTIR. The FTIR spectral analysis showed that lyocell is the most crystalline fibre and is composed principally of crystalline cellulose II and amorphous cellulose. Likewise, the thermal analysis showed that lyocell has a higher thermal stability than viscose and modal fibres, as the difference between the onset temperature for its decomposition process was as high as 20 °C.     

Synthesis of thiol-modified peptide nucleic acids designed for post-assembly conjugation reactions

Two orthogonally protected PNA monomers were prepared having the mercaptomethyl moiety attached to the PNA backbone. These building blocks were employed in solid-phase PNA synthesis and it was shown that Boc/S-p-methoxybenzyl protection scheme was only satisfactory for the introduction of N-terminal thiol modification while the Fmoc/S-butylthio protected monomer proved to be amenable to elongation. The mercaptomethyl modification did not influence the thermal stability of a PNA/RNA duplex. The feasibility of PNA-PNA native ligation was demonstrated.     

Gold electroless reduction in nanosized channels of thiol-modified SBA-15 material

A new procedure for the preparation of high aspect ratio Au nanowires utilizing gold electroless reduction in the hexagonally ordered, thiol-modified nanosized channels of the SBA-15 material is reported. Two different Au precursors were adsorbed onto pedant thiol groups, covalently bonded to the mesoporous silica surface, and used as seeds to grow extended Au nanostructures by treatment in Au electroless reduction bath. It is shown that the dimensions and the assembly of the Au seeds are important parameters for the subsequent electroless reduction process. The [AuCl4]- ions complexed to the TOAB molecules assembled on the thiol-modified mesoporous surface of the SBA-15 material are suitable precursors for the subsequent gold electroless reduction. The resulting structures are several micrometer long Au nanowires with uniform diameters of about 5 nm, having large single-crystalline domains. The TEM results clearly show that the growth of the Au nanowires is templated by the channel structure of the SBA-15 material.     

Unexplored capabilities of chemiluminescence and thermoanalytical methods in characterization of intact and degraded hyaluronans

Three intact and four degraded hyaluronans were investigated by using chemiluminometry, differential scanning calorimetry, and thermogravimetry. Degradation of hyaluronan was induced by a system containing H₂O₂ alone (882 mM); 55 mM H₂O₂plus 1.25 μM CuCl₂; NaOCl alone (10 mM); and NaOCl plus CuCl₂ and ascorbic acid (10 mM, 0.1 μM, and 100 μM, respectively). The four different oxidative systems yielded biopolymer fragments represented by similar viscosity characteristics. The results obtained by using chemiluminescence and thermoanalytical methods indicate that hyaluronans of similar rheological properties could be distinguished from each other.     

Structural characterisation of heat-treated anodic alumina membranes prepared using a simplified fabrication process

A facile method for forming porous anodic alumina membranes based on one-step anodising in sulphuric acid is reported. A flat and well-ordered basal surface incorporating uniformly sized pores was obtained without the need for electrolytic polishing. Excess metallic aluminium was removed from the film using a saturated solution of iodine in methanol. The high-temperature properties of the oxide ceramic membranes were investigated using thermal analysis, mass spectrometry, X-ray diffraction and solid-state nuclear magnetic resonance. At 970 °C the amorphous alumina crystallises to γ-Al₂O₃ with the release of SO₂ and O₂. Finally at 1228 °C the alumina converts into the thermodynamically preferred phase, corundum. The pore structure of the oxide membrane was found to be very stable at elevated temperatures, suggesting applications in materials synthesis, catalysis and gas separation.     

Fast-scan cyclic voltammetry with thiol-modified mercury electrodes distinguishes native from denatured BSA

We studied native and denatured bovine serum albumin (BSA) at bare and dithiothreithol (DTT)-modified hanging mercury drop electrode (HMDE) by fast-scan cyclic voltammetry (fsCV) and chronopotentiometric stripping (CPS) to compare these methods for their ability to recognize changes in BSA structure. Using fsCV and bare HMDE, denatured BSA could be distinguished from its native form only between 10 and 20 V/s but at lower resolution than with CPS. At DTT-HMDE denatured BSA was recognized from native BSA in a wider range of scan rates suggesting new possibilities in development of voltammetric protein structure-sensitive sensing.     

Anisotropic orientation of horseradish peroxidase by reconstitution on a thiol-modified gold electrode

Horseradish peroxidase (HRP) was reconstituted on the surface of a gold electrode that was modified first with a hemin-carbon-chain-thiol derivative followed by addition of the apo protein to the contacting solution. To facilitate the reconstitution of the holo enzyme, the hemin needs to be immobilised on a carbon-chain spacer arm. To achieve this, an immobilisation protocol was developed that is based on the initial formation of a mixed self-assembled monolayer on the gold surface consisting of 3-carboxypropyl disulphide and an activated disulphide (3,3'-dithiodipropionic acid di-(N-succinimidyl ester)) followed by binding of a diaminoalkane to the activated disulphide. The hemin was then coupled to the second amino group of the diaminoalkane by means of a carbodiimide coupling reagent. Finally, the enzyme was reconstituted on the hemin-modified surface by immersion of the electrode in a solution containing apo-HRP. The advantage of this method is that the length of the spacer arm can be changed easily, because diaminoalkanes of different chain lengths are available. The electrochemistry of the hemin and the reconstituted HRP electrodes was studied by means of cyclic voltammetry and differential-pulse voltammetry. The catalytic ability for reduction of hydrogen peroxide was investigated for both direct and mediated electrochemistry with a soluble electron donor (ortho-phenylenediamine).     

Structural characterisation of Baltic amber and its solvent extracts by several mass spectrometric methods

A sample of Baltic amber ( approximately 40 million yrs old) has been extracted using pentane, toluene and 1-methyl-2-pyrrolidinone (NMP). The relationship between solubility characteristics of the extracts in relation to molecular mass and chemical makeup has been investigated. The extracts were first characterised by (13)C-NMR spectrometry, size exclusion chromatography (SEC) and UV-fluorescence spectroscopy. The fractions differed less in terms of chemical structural features than they did in terms of molecular mass. This contrasts markedly with data on fractions of coal-derived liquids, but parallels results from petroleum-derived vacuum residues. In SEC, the toluene soluble/pentane insoluble fraction gave a peak for high mass material at about 67 000 u. Material excluded from the column porosity in this fraction and in NMP solubles eluted between 8 and 11 min, corresponding to polystyrene masses between 200 000 and several million u. A column with a larger pore size distribution was calibrated using polystyrene and polymethylmethacrylate standards with detection by a light-scattering evaporative analyser. The largest polystyrene standard (15.4 million u) eluted at 13.4 min, similar to that of the earliest eluting amber-derived material in the NMP solubles fraction. Results from probe-MS and pyrolysis-GC/MS have been used to confirm the similarity of chemical structures of the three solubility fractions. Broadly, low mass ions appear to correspond to the various monomeric units of structures present in the amber, the higher mass ions to dimer units and the molecular ions to the different combinations of three or more monomeric units. The main monomer groups have been identified in detail, showing a situation very different from that of coal-derived materials, where the sizes of aromatic ring systems increase with molecular size.     

Structural characterisation of poly(amidoamine) networks via high-resolution magic angle spinning NMR

A comprehensive structural characterisation of cross-linked insoluble poly(amidoamine) (PAA) networks was performed by high-resolution magic angle spinning (HRMAS) NMR spectroscopy. Model samples with 20%, 40% and 80% cross-linking degrees were prepared and the best conditions to obtain high-resolution spectra in the gel phase determined. Whereas the samples with 20% and 40% cross-linking degrees could be exhaustively resolved and described, the sample with 80% cross-linking degree could not be characterised by this technique owing to insufficient mobility of the polymer segments. Even with this limitation, the method developed in this study can be reasonably considered as a general one, which enables exhaustive characterisation of cross-linked PAA networks of biomedical interest.     

Structural and chemical characterisation of titanium deuteride films covered by nanoscale evaporated palladium layers

Thin titanium deuteride (TiD_y) films, covered by an ultra-thin palladium layer, have been compared with the corresponding titanium and palladium films using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TiD_y layers were prepared under ultra-high vacuum (UHV) conditions by precisely controlled deuterium sorption at 298 K on a Ti film evaporated onto a Si(100) substrate. Both Ti and TiD_y films were then covered in situ by a nanoscale Pd layer. It was found that a 10- to 12-nm-thick Pd layer protects the TiD_y films efficiently against extensive air interaction. The morphology of both the surface and bulk Pd/TiD_y (Ti) films have been observed using SEM and cross-sectional TEM analysis, respectively. A polycrystalline bulk morphology in both Ti and TiD_y films accompanied by a fine-grained Pd surface was observed. High-magnification cross-sectional TEM images reveal the TiD_y film to be plastically deformed leading to an increase in the roughness of the top Pd layer. Complex structures, including Moiré patterns, have been identified within the Pd/TiD_y interface. The chemical nature of this interface has been analysed after partial sputtering of the Pd top layer using XPS. Besides TiD_y and Pd, TiO and PdO were found to be the main chemical species in the interface region of the Pd/TiH_y film. The XPS valence-band spectra of the Pd/TiD_y interface reveal electronic features characteristic of a Pd–Ti bimetallic structure.     

Structural characterisation of some fatty acids from the brain as biomarkers of BSE risk material

Identification of bovine and ovine tissue from the central nervous system (CNS: brain and spinal cord) in meat products is possible by using certain CNS fatty acids as biomarkers in GC–MS analysis. Furthermore, the relationship between the isomers of the tetracosenic acid (C24:1) is important for differentiation of the species and age of the CNS in view of the legal definition of specified risk material (SRM). This has so far been referred to as the cis/trans ratio of the isomers of nervonic acid; however, structural analysis was not performed. Here we present results from GC–MS structural analysis by retention time and DMDS adduct profiling of the even numbered monoenoic fatty acids from C18:1 to C26:1. Retention times and mass spectra of the FAME standards indicated that the so far designated trans-nervonic acid has a different isomeric structure in the tetracosenic acid from brain-sample extracts. By performing GC–MS analysis of DMDS adducts we have shown that this isomer was actually cis-17-tetracosenic acid in all species so far tested, not trans-15-tetracosenic acid (trans-nervonic acid). The tetracosenic acid isomer ratio proved to be species-specific in accordance with previous results. Thus, instead of the ratio of cis/trans isomers of nervonic acid, the ratio of 9/7-tetracosenic acid (15c-C24:1/17c-C24:1) will have to be used as a correct reference in future publications. Although trans isomers were not detectable in sheep and cattle brain, porcine brain contained, in addition to cis-17-tetracosenic acid, small amounts of the trans isomers of the C18:1, C20:1, C24:1, and C26:1 fatty acids, in decreasing quantities. In future, this might be useful as another means of differentiation between porcine CNS (non-SRM) and ovine or bovine CNS (SRM). Extensive follow-up studies must be performed to elucidate the extent to which this GC–MS approach will facilitate the detection of CNS according to the legal SRM definition.     

Monitoring of Saccharomyces cerevisiae cell proliferation on thiol-modified planar gold microelectrodes using impedance spectroscopy

An impedance spectroscopic study of the interaction between thiol-modified Au electrodes and Saccharomyces cerevisiae of strain EBY44 revealed that the cells formed an integral part of the interface, modulating the capacitive properties until a complete monolayer was obtained, whereas the charge transfer resistance ( R ct) to the redox process of [Fe(CN)6] 3-/4- showed a linear relationship to the number of cells even beyond the monolayer coverage. R ct showed strong pH dependence upon increasing the pH of the utilized buffer to 7.2. Upon addition of S. cerevisiae cells at pH 7.2, the obtained value of R ct showed over 560% increase with respect to the value obtained on the same thiol-modified electrode without cells. It was demonstrated that real-time monitoring of S. cerevisiae proliferation, with frequency-normalized imaginary admittance (real capacitance) as the indicator, was possible using a miniaturized culture system, ECIS Cultureware, with integrated planar cysteamine-modified Au microelectrodes. A monolayer coverage was reached after 20-28 h of cultivation, observed as an approximately 15% decrease in the real capacitance of the system.