Stereochemical Inversion of Rim-Differentiated Pillar[5]arene Molecular Swings.

To investigate the dynamic stereochemical inversion behavior of pillar[5]arenes (P[5]s) in more detail, we synthesized a series of novel rim-differentiated P[5]s with various substituents and examined their rapid rotations by variable-temperature NMR (203-298 K). These studies revealed for the first time the barrier of "methyl-through-the-annulus" rotation (ΔG‡ = 47.4 kJ·mol-1 in acetone) and indicated that for rim-differentiated P[5]s with two types of alkyl substituents, the smaller rim typically determines the rate of rotation. However, substituents with terminal C═C or C≡C bonds give rise to lower inversion barriers, presumably as a result of attractive π-π interactions in the transition state. Finally, data on a rim-differentiated penta-methyl-penta-propargyl P[5] exhibited the complexity of the overall inversion dynamics.

Diagnostic utility of zinc protoporphyrin to detect iron deficiency in Kenyan pregnant women.

BACKGROUND: Iron-deficient erythropoiesis results in excess formation of zinc protoporphyrin (ZPP), which can be measured instantly and at low assay cost using portable haematofluorometers. ZPP is used as a screening marker of iron deficiency in individual pregnant women and children, but also to assess population iron status in combination with haemoglobin concentration. We examined associations between ZPP and disorders that are common in Africa. In addition, we assessed the diagnostic utility of ZPP (measured in whole blood and erythrocytes), alone or in combination with haemoglobin concentration, in detecting iron deficiency (plasma ferritin concentration <15 µg/L). METHODS: Single blood samples were collected from a population sample of 470 rural Kenyan women with singleton pregnancies, gestational age 13 to 23 weeks, and haemoglobin concentration ≥90 g/L. We used linear regression analysis to assess associations between ZPP and iron markers (including anaemia), factors known or suspected to be associated with iron status, inflammation markers (plasma concentrations of C-reactive protein and α 1-acid glycoprotein), infections (Plasmodium infection, HIV infection), and other disorders (α(+)-thalassaemia, plasma concentrations of total bilirubin, and lactate dehydrogenase). Subsequently, in those without inflammation, Plasmodium infection, or HIV infection, we used logistic discriminant analysis and examined receiver operating characteristics curves with corresponding area-under-the-curve to assess diagnostic performance of ZPP, alone and in combination with haemoglobin concentration. RESULTS: Individually, whole blood ZPP, erythrocyte ZPP, and erythrocyte protoporphyrin had limited ability to discriminate between women with and without iron deficiency. Combining each of these markers with haemoglobin concentration had no additional diagnostic value. Conventional cut off points for whole blood ZPP (>70 µmol/mol haem) resulted in gross overestimates of the prevalence of iron deficiency. CONCLUSIONS: Erythrocyte ZPP has limited value to rule out iron deficiency when used for screening in conditions with a low prevalence (e.g., 10%). ZPP is of unreliable diagnostic utility when discriminating between pregnant women with and without iron deficiency. Based on these findings, guidelines on the use of ZPP to assess iron status in individuals or populations of pregnant women need review. TRIAL REGISTRATION: NCT01308112 (2 March 2011).

Organic monolayers from 1-alkynes covalently attached to chromium nitride: alkyl and fluoroalkyl termination.

Strategies to modify chromium nitride (CrN) surfaces are important because of the increasing applications of these materials in various areas such as hybrid electronics, medical implants, diffusion barrier layers, corrosion inhibition, and wettability control. The present work presents the first surface immobilization of alkyl and perfluoro-alkyl (from C6 to C18) chains onto CrN substrates using appropriately functionalized 1-alkynes, yielding covalently bound, high-density organic monolayers with excellent hydrophobic properties and a high degree of short-range order. The obtained monolayers were characterized in detail by water contact angle, X-ray photoelectron spectroscopy (XPS), ellipsometry, and infrared reflection absorption spectroscopy (IRRAS).

SI-PET-RAFT in flow: improved control over polymer brush growth.

Surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) provides a light-dependent tool to synthesize polymer brushes on different surfaces that tolerates oxygen and water, and does not require a metal catalyst. Here we introduce improved control over SI-PET-RAFT polymerizations via continuous flow conditions. We confirm the composition and topological structure of the brushes by X-ray photoelectron spectroscopy, ellipsometry, and AFM. The improved control compared to no-flow conditions provides prolonged linear growth of the polymer brush (up to 250 nm, where no-flow polymerization maxed out <50 nm), and improved polymerization control of the polymer brush that allows the construction of diblock polymer brushes. We further show the linear correlation between the molecular weight of the polymer brush and its dry thickness by combining ellipsometry and single-molecule force spectroscopy.

Tuning UV Absorption in Imine-Linked Covalent Organic Frameworks via Methylation.

Covalent organic frameworks (COFs) are porous materials with high surface areas, making them interesting for a large variety of applications including energy storage, gas separation, photocatalysis, and chemical sensing. Structural variation plays an important role in tuning COF properties. Next to the type of the building block core, bonding directionality, and linking chemistry, substitution of building blocks provides another level of synthetic control. Thorough characterization and comparison of various substitution patterns is relevant for the molecular engineering of COFs via rational design. To this end, we have systematically synthesized and characterized multiple combinations of several methylated and non-methylated building blocks to obtain a series of imine-based COFs. This includes the experimental assignment of the COF structure by solid-state NMR. By comparing the properties of all COFs, the following trends were found: (1) upon methylation of the aldehyde nodes, COFs show increased Brunauer-Emmett-Teller surface areas, reduced pore collapse, blue-shifted absorbance spectra, and ∼0.2 eV increases in their optical band gaps. (2) COFs with dimethylated amine linkers show a lower porosity. (3) In tetramethylated amine linkers, the COF porosity even further decreases, the absorbance spectra are clearly red-shifted, and smaller optical band gaps are obtained. Our study shows that methyl substitution patterns on COF building blocks are a handle to control the UV absorbance of the resulting frameworks.

Mimicking the silicon surface: reactivity of silyl radical cations toward nucleophiles.

Radical cations of selected low molecular-weight silicon model compounds were obtained by photoinduced electron transfer. These radical cations react readily with a variety of nucleophiles, regularly used in monolayer fabrication onto hydrogen-terminated silicon. From time-resolved kinetics, it was concluded that the reactions proceed via a bimolecular nucleophilic attack to the radical cation. A secondary kinetic isotope effect indicated that the central Si-H bond is not cleaved in the rate-determining step. Apart from substitution products, also hydrosilylation products were identified in the product mixtures. Observation of the substitution products, combined with the kinetic data, point to an bimolecular reaction mechanism involving Si-Si bond cleavage. The products of this nucleophilic substitution can initiate radical chain reactions leading to hydrosilylation products, which can independently also be initiated by dissociation of the radical cations. Application of these data to the attachment of organic monolayers onto hydrogen-terminated Si surfaces via hydrosilylation leads to the conclusion that the delocalized Si radical cation (a surface-localized hole) can initiate the hydrosilylation chain reaction at the Si surface. Comparison to monolayer experiments shows that this reaction only plays a significant role in the initiation, and not in the propagation steps of Si-C bond making monolayer formation.

Chemoenzymatic synthesis of biotin-appended analogues of gangliosides GM2, GM1, GD1a and GalNAc-GD1a for solid-phase applications and improved ELISA tests.

Biotinylated analogues of gangliosides GM2, GM1, GD1a and GalNAc-GD1a were synthesized in high yields using glycosyltransferases from Campylobacter jejuni. The presence of a biotin moiety in the aglycone part of these mimics allows for attachment of these materials onto various streptavidin-coated surfaces. Analysis of the interaction of biotin-appended GM1 with the B subunit of Escherichia coli heat-labile enterotoxin performed in a modified ELISA procedure shows the potential of this compound to replace the natural GM1 in toxin detection.

Postnatal development of depth-dependent collagen density in ovine articular cartilage.

BACKGROUND: Articular cartilage (AC) is the layer of tissue that covers the articulating ends of the bones in diarthrodial joints. Adult AC is characterised by a depth-dependent composition and structure of the extracellular matrix that results in depth-dependent mechanical properties, important for the functions of adult AC. Collagen is the most abundant solid component and it affects the mechanical behaviour of AC. The current objective is to quantify the postnatal development of depth-dependent collagen density in sheep (Ovis aries) AC between birth and maturity. We use Fourier transform infra-red micro-spectroscopy to investigate collagen density in 48 sheep divided over ten sample points between birth (stillborn) and maturity (72 weeks). In each animal, we investigate six anatomical sites (caudal, distal and rostral locations at the medial and lateral side of the joint) in the distal metacarpus of a fore leg and a hind leg. RESULTS: Collagen density increases from birth to maturity up to our last sample point (72 weeks). Collagen density increases at the articular surface from 0.23 g/ml ± 0.06 g/ml (mean ± s.d., n = 48) at 0 weeks to 0.51 g/ml ± 0.10 g/ml (n = 46) at 72 weeks. Maximum collagen density in the deeper cartilage increases from 0.39 g/ml ± 0.08 g/ml (n = 48) at 0 weeks to 0.91 g/ml ± 0.13 g/ml (n = 46) at 72 weeks. Most collagen density profiles at 0 weeks (85%) show a valley, indicating a minimum, in collagen density near the articular surface. At 72 weeks, only 17% of the collagen density profiles show a valley in collagen density near the articular surface. The fraction of profiles with this valley stabilises at 36 weeks. CONCLUSIONS: Collagen density in articular cartilage increases in postnatal life with depth-dependent variation, and does not stabilize up to 72 weeks, the last sample point in our study. We find strong evidence for a valley in collagen densities near the articular surface that is present in the youngest animals, but that has disappeared in the oldest animals. We discuss that the retardance valley (as seen with polarised light microscopy) in perinatal animals reflects a decrease in collagen density, as well as a decrease in collagen fibril anisotropy.

Synthesis and optoelectronic properties of nanometer-sized and highly soluble homocoupled oligodiacetylenes.

A new series of pure, nanometer-sized and highly-soluble homocoupled oligodiacetylenes (HODA) consisting of two symmetrical oligodiacetylene units was synthesized with high yield and on a multi-milligram scale under mild, catalytic Sonogashira conditions. The lambda(max) and the epsilon(max) of absorption for these HODAs show an increase with the chain elongation. The lambda(max) converges to 450 nm for the longest members of the series at micromolar concentration and to 462 nm for thin drop-casted films. An additional red-shifted absorption is observed in the solid state and in solution at low temperatures, which is caused by aggregation. The lambda(max) of the fluorescence emission increases with the chain length and reaches 492 nm for the longest oligomer. The fluorescence quantum yield has its maximum for the shortest oligomer and decreases rapidly for the longer ones. A similar trend is found for the fluorescence lifetime with a maximum of 100 ps for the homocoupled monomer. The rotational correlation time shows a linear increase with the oligomer length. This reveals a significant persistence length and indicates that the HODA molecules are fully stretched molecular rods (up to 8.2 nm).

Hybrid conjugated organic oligomers consisting of oligodiacetylene and thiophene units: synthesis and optical properties.

Novel and highly soluble hybrid conjugated organic oligomers consisting of oligodiacetylene and thiophene units have been synthesized in high purity through iterative and divergent approaches based on a sequence of Sonogashira reactions. The series of thiophene-containing oligodiacetylenes (ThODAs) and homocoupled ThODAs (HThODAs) show--both in solution and in the solid state--a strong optical absorption, which is progressively red shifted with increasing chain length. The linear correlation of the absorption maximum (lambda(A)(max)) with the inverse of conjugation length (CL = number of double and triple bonds) shows that the effective conjugation length of this system is extended up to at least CL = 20. Furthermore, absorption measurements of dropcast thin films display not only a bathochromic shift of the absorption maxima but also a higher wavelength absorption, which is attributed to increased pi-pi interactions. The wavelength of the maximum fluorescence emission (lambda(E)(max)) also increases with CL, and emission is maximal for oligomers with CL=7-12 (fluorescence quantum yield Phi(F) = approximately 0.2). Both longer and shorter oligomers display marginal emission. The calculated Stokes shifts of these planar materials are relatively large (0.4 eV) for all oligomers, and likely due to excitation to the S(2) state, thus suggesting that the presence of enyne moieties dominates the ordering of the lowest excited states. The fluorescence lifetimes (tau(F)) are short (tau(F,max) = <<1 ns) and closely follow the tendency obtained for the fluorescence quantum yield. The anisotropy lifetimes show a near-linear increase with CL, in line with highly rigid oligomers.

Site-specific immobilization of DNA in glass microchannels via photolithography.

For the first time, a microchannel was photochemically patterned with a functional linker. This simple method was developed for the site-specific attachment of DNA via this linker onto silicon oxide surfaces (e.g., fused silica and borosilicate glass), both onto a flat surface and onto the inside of a fused silica microchannel. Sharp boundaries in the micrometer range between modified and unmodified zones were demonstrated by the attachment of fluorescently labeled DNA oligomers. Studies of repeated hybridization-dehybridization cycles revealed selective and reversible binding of cDNA strands at the explicit locations. On average, approximately 7 x 10(11) fluorescently labeled DNA molecules were hybridized per square centimeter. The modified surfaces were characterized with X-ray photoelectron spectroscopy, infrared microscopy, static contact angle measurements, confocal laser scanning microscopy, and fluorescence detection (to quantify the attachment of the fluorescently labeled DNA).

Alkyl-functionalized oxide-free silicon nanoparticles: synthesis and optical properties.

Highly monodisperse silicon nanoparticles (1.57 +/- 0.21 nm) are synthesized with a covalently attached alkyl monolayer on a gram scale. Infrared spectroscopy shows that these silicon nanoparticles contain only a few oxygen atoms per nanoparticle. XPS spectra clearly show the presence of unoxidized Si and attached alkyl chains. Owing to the relatively efficient synthesis (yields approximately 100-fold higher than of those previously reported) the molar extinction coefficient epsilon can be measured: epsilon(max) = 1.7 x 10(-4) M(-1)cm(-1), only a factor of 4 lower than that of CdS and CdSe nanoparticles of that size. The quantum yield of emission ranges from 0.12 (C(10)H(21)-capping) to 0.23 (C(16)H(33)-capping). UV/Vis absorption and emission spectroscopy show clear vibrational progressions (974 +/- 14 cm(-1); up to five vibrational bands visible at room temperature), resembling bulk SiC phonons, which support the monodispersity observed by TEM. This was also confirmed by time-resolved fluorescence anisotropy measurements, which display a strictly monoexponential decay that can only be indicative of monodisperse, ball-shaped nanoparticles.

GM3, GM2 and GM1 mimics designed for biosensing: chemoenzymatic synthesis, target affinities and 900 MHz NMR analysis.

Undec-10-enyl, undec-10-ynyl and 11-azidoundecyl glycoside analogues corresponding to the oligosaccharides of human gangliosides GM3, GM2 and GM1 were synthesized in high yields using glycosyltransferases from Campylobacter jejuni. Due to poor water solubility of the substrates, the reactions were carried out in methanol-water media, which for the first time were shown to be compatible with the C. jejuni alpha-(2-->3)-sialyltransferase (CST-06) and beta-(1-->4)-N-acetylgalactosaminyltransferase (CJL-30). Bioequivalence of our synthetic analogues and natural gangliosides was examined by binding to Vibrio cholerae toxin and to the B subunit of Escherichia coli heat-labile enterotoxin. This bioequivalence was confirmed by binding mouse and human monoclonal antibodies to GM1 and acute phase sera containing IgM and IgG antibodies to GM1 from patients with the immune-mediated polyneuropathy Guillain-Barré syndrome. The synthesized compounds were analyzed by 1D and 2D 900 MHz NMR spectroscopy. TOCSY and DQF-COSY experiments in combination with 13C-1H correlation measurements (HSQC, HMBC) were carried out for primary structural characterization, and a complete assignment of all 1H and 13C chemical shifts is presented.

One-Pot Gram-Scale Synthesis of Hydrogen-Terminated Silicon Nanoparticles.

Silicon nanoparticles (Si NPs) are highly attractive materials for typical quantum dots functions, such as in light-emitting and bioimaging applications, owing to silicon's intrinsic merits of minimal toxicity, low cost, high abundance, and easy and highly stable functionalization. Especially nonoxidized Si NPs with a covalently bound coating serve well in these respects, given the minimization of surface defects upon hydrosilylation of H-terminated Si NPs. However, to date, methods to obtain such H-terminated Si NPs are still not easy. Herein, we report a new synthetic method to produce size-tunable robust, highly crystalline H-terminated Si NPs (4-9 nm) using microwave irradiation within 5 min at temperatures between 25 and 200 °C and their further covalent functionalization. The key step to obtain highly fluorescent (quantum yield of 7-16%) green-red Si NPs in one simple step is the reduction of triethoxysilane and (+)-sodium l-ascorbate, yielding routinely ∼1 g of H-Si NPs via a highly scalable route in 5-15 min. Subsequent functionalization via hydrosilylation yielded Si NPs with an emission quantum yield of 12-14%. This approach can be used to easily produce high-quality H-Si NPs in gram-scale quantities, which brings the application of functionalized Si NPs significantly closer.

Siloxanes with pendent naphthalene diimides: synthesis and fluorescence quenching.

Cyclic siloxanes with pendent naphthalene diimide groups were synthesized via hydrosilylation to form amorphous electron-accepting compounds. Photophysical measurements and >99.9% fluorescence quenching of well-known p-type polymers by the siloxanes demonstrate that these siloxanes form a new class of highly efficient n-type materials that provide some control over intermolecular interactions.

Synthesis and optical properties of all-trans-oligodiacetylenes.

A new series of pure and highly soluble oligodiacetylenes (ODAs) was synthesized in high yield and on a multi-milligram scale by a sequence of Sonogashira reactions with a strongly reduced level of homocoupling. The lambda max and epsilon max of these ODAs show an increase with both chain elongation and solvent polarity. A plot of lambda max absorption versus 1/CL (CL=conjugation length) was shown to be linear. The lambda max converges to 435 nm for the longest members of the series at micromolar concentration. This reveals that the longest wavelength absorption observed for PDA chains (lambda max up to 700 nm) is due to aggregation effects. The fluorescence quantum yield increased from monomer to trimer and decreased for longer ODAs. A similar trend is found for the lifetime of fluorescence with a maximum of 600 ps for the trimer. The observed linearity of the rotational correlation time with the oligomer length implies that the ODA chains in solution lack significant geometrical changes. This implies that the ODAs in solution are fully stretched molecular rods of up to 4 nm in length.

Covalently attached monolayers on crystalline hydrogen-terminated silicon: extremely mild attachment by visible light.

A very mild method was developed for the attachment of high-quality organic monolayers on crystalline silicon surfaces. By using visible light sources, from 447 to 658 nm, a variety of 1-alkenes and 1-alkynes were attached to hydrogen-terminated Si(100) and Si(111) surfaces at room temperature. The presence and the quality of the monolayers were evaluated by static water contact angles, X-ray photoelectron spectroscopy, and IR spectroscopy. Monolayers prepared by thermal, UV light, or visible light initiation were compared. Additionally, the ability of infrared reflection-absorption spectroscopy to study organic monolayers on silicon was explored. A reaction mechanism is discussed on the basis of investigations of the reaction behavior of 1-alkenes with silicon wafers with varying types and levels of doping. Finally, a series of mixed monolayers derived from the mixed solutions of a 1-alkene and an omega-fluoro-1-alkene were investigated to reveal that the composition of the mixed monolayers was directly proportional to the molar ratio of the two compounds in the solutions.

An FTIR-DRIFT study on river sediment particle structure: implications for biofilm dynamics and pollutant binding.

Diffuse reflectance infrared Fourier transform (DRIFT) spectrometry was applied to a set of sediment samples collected by traps over one and a half years in a mid-mountainous river. Dynamic changes in hydrological and life-cycle conditions generated sediment particles of different C(org) content and organic composition. Periods in the midst of or shortly after flood events left particles poor in C(org) content with spectral features that were enriched in carboxylic and aromatic signals. These are characteristic of terrestrial oxidized vascular plant debris. Low-flow conditions saw the consequent build-up of amide, aliphatic, and polysaccharide moieties as expected for autochthonous biofilm derived material. A peak ratio of two bands representing the alternation of these two types of organic matter showed that flood particle C(org) had a higher affinity for metals than the high C(org) of mature biofilms, probably owing to higher COO- contents in the first. The relative dietary bioavailability of the metals from sediment C(org), which is related to the nutritional value of the substrate, is therefore probably lower in the aftermath of a flood than in prolonged low-flow situations. This needs to be accounted for in future metal speciation and bioavailability modeling approaches.

Reduced heterogeneity of a lignite humic acid by preparative HPSEC following interaction with an organic acid. Characterization of size-separates by Pyr-GC-MS and 1H-NMR spectroscopy.

Preparative high performance size exclusion chromatography (HPSEC) was used to size-fractionate a humic acid (HA) solution with 0.05 M ionic strength before and after having made the humic solution 0.5 x 10(-3) M in acetic acid (AcOH). Size-fractions were characterized by pyrolysis-gas-chromatography/mass spectrometry (Pyr-GC-MS) and 1H NMR spectroscopy. Pyr-GC-MS showed that the AcOH treatment altered the distribution of humic molecular components in the size-fractions. The unsaturated alkyl chains were moved from size-fractions of larger molecular-size into those of lower molecular-sizes. Most of the aromatic moieties, which were found in larger molecular-size fractions for the untreated HA, were spread into fractions of lower molecular size after AcOH addition to HA. Carbohydrates, which were undetectable in anyfraction of the untreated HA, appeared instead in the pyrogram of the lowest molecular-size and most hydrophilic fraction after treatment with AcOH. Our results suggested that AcOH disrupted the weakly bound association of humic supramolecularstructures and HPSEC elution separated size-fractions of different composition without losing humic matter by adsorption on the HPSEC column. The fractions with the largest apparent molecular size were the richest in alkyl chains, thereby suggesting that humic molecules were stabilized into supramolecular associations by multiple weak interactions among apolar groups such as alkyl chains and aromatic moieties. 1H NMR spectra of size-fractions were greatly simplified and more resolved after AcOH treatment. This was attributed to a less complex molecular association in the size separates which provided a larger solubility in the NMR solvent and more favorable relaxation times. Combination of the procedure used here for size-fractionation with NMR and Pyr-GC-MS methods appears to be promising to advance knowledge on the molecular composition of humic substances.