Higher Aggregation States Research Articles

Gelatinous lanthanide coordination polymer with aggregation-enhanced antenna effect for ratiometric detection of endogenous alkaline phosphatase

Aggregation-induced emission (AIE) and antenna effect (AE) are two significant behaviors that have attracted increasing attention. However, it is challenging to achieve the synergistic effect of AIE and AE in luminescent materials for more extensive applications. Here, four gelatinous Ln3+ coordination polymers (Ln-CPs) are synthesized by self-assembly of ciprofloxacin (CIP), adenosine monophosphate (AMP), and Ln3+ ions in aqueous medium. Encouragingly, a remarkable increase in the characteristic fluorescence of Ln3+ and a significant decrease in CIP are observed along with increasing concentration of Ln-CPs, which is attributed to the large aggregates formed by self-assembly that strictly constrain the intramolecular motions of antenna ligands, thereby achieving the aggregation-enhanced AE. More meaningfully, Eu-CP not only shows a rice-like morphology at high aggregation state, but also provides an opportunity for the selective detection of alkaline phosphatase (ALP). A new flower-like polymer is formed upon incubating Eu-CP with ALP, accompanied by the fluorescence quenching of Eu3+ and recovery of CIP, a ratiometric determination of ALP in the range of 0.1–6.0 U·L−1 is thus achieved. Additionally, ALP assay in human serum and bioimaging in living cells have been successfully performed. This research opens a new horizon for the fabrication of Ln3+-based luminescent materials with promising applications.

Confined Electrochemical Behaviors of Single Platinum Nanoparticles Revealing Ultrahigh Density of Gas Molecules inside a Nanobubble.

Understanding the basic physicochemical properties of gas molecules confined within nanobubbles is of fundamental importance for chemical and biological processes. Here, we successfully monitored the nanobubble-confined electrochemical behaviors of single platinum nanoparticles (PtNPs) at a carbon fiber ultramicroelectrode in HClO4 and H2O2 solution. Due to the catalytic decomposition of H2O2, a single oxygen nanobubble was formed on individual PtNPs to block the active surface of particles for proton reduction and to suppress their stochastic motion, resulting in significantly distinguished current traces. Furthermore, the combination of theoretical calculations and high-resolution electrochemical measurements allowed the nanobubble size and the oxygen gas density inside a single nanobubble to be quantified. Moreover, the ultrahigh oxygen density inside (1046 kg/m3) was revealed, indicating that gas molecules in a nanosized space existed with a high state of aggregation. Our approach sheds light on the gas aggregation behaviors of nanoscale bubbles using single-entity electrochemical measurements.

Photoluminescence of Tilapia skin collagen: Aggregation-induced emission with clustering triggered emission mechanism and its multiple applications

There is an urgent need for natural sources of aggregation-induced emission (AIE) materials which have good water solubility, biocompatibility, and can be produced in large quantities. Here, Tilapia skin collagen (Tsc) is a very abundant protein in nature, with solid-phase and solution-state fluorescence emission effect and its multiple applications was explored. Due to Tsc was in high concentration or aggregation state which shown AIE property. This obvious emission can be account for clustering-triggered emission (CTE) mechanism. The photoluminescence property of Tsc not only provide a deeper understanding of the emission characteristics of proteins, but also has important guiding significance for further elucidating the basis of fluorescence properties.

Recent Advances in Two-Photon AIEgens and Their Application in Biological Systems.

Two-photon fluorescence imaging technology has the advantages of high light stability, little light damage, and high spatiotemporal resolution, which make it a powerful biological analysis method. However, due to the high concentration or aggregation state of traditional organic light-emitting molecules, the fluorescence intensity is easily reduced or disappears completely, and is not conducive to optimal application. The concept of aggregation-induced emission (AIE) provides a solution to the problem of aggregation-induced luminescence quenching (ACQ), and realizes the high fluorescence quantum yield of luminescent molecules in the aggregation state. In addition, two-photon absorption properties can readily be improved just by increasing the loading content of AIE fluorogen (AIEgen). Therefore, the design and preparation of two-photon fluorescence probes based on AIEgen to achieve high-efficiency fluorescence imaging in vitro/in vivo has become a major research hotspot. This review aims to summarize representative two-photon AIEgens based on triphenylamine, tetraphenylethene, quinoline, naphthalene and other new structures from the past five years, and discuss their great potential in bioimaging applications.

Role of Sheet-Edge Interactions in β-sheet Self-Assembling Peptide Hydrogels.

Hydrogels’ hydrated fibrillar nature makes them the material of choice for the design and engineering of 3D scaffolds for cell culture, tissue engineering, and drug-delivery applications. One particular class of hydrogels which has been the focus of significant research is self-assembling peptide hydrogels. In the present work, we were interested in exploring how fiber–fiber edge interactions affect the self-assembly and gelation properties of amphipathic peptides. For this purpose, we investigated two β-sheet-forming peptides, FEFKFEFK (F8) and KFEFKFEFKK (KF8K), the latter one having the fiber edges covered by lysine residues. Our results showed that the addition of the two lysine residues did not affect the ability of the peptides to form β-sheet-rich fibers, provided that the overall charge carried by the two peptides was kept constant. However, it did significantly reduce edge-driven hydrophobic fiber–fiber associative interactions, resulting in reduced tendency for KF8K fibers to associate/aggregate laterally and form large fiber bundles and consequently network cross-links. This effect resulted in the formation of hydrogels with lower moduli but faster dynamics. As a result, KF8K fibers could be aligned only under high shear and at high concentration while F8 hydrogel fibers were found to align readily at low shear and low concentration. In addition, F8 hydrogels were found to fragment at high concentration because of the high aggregation state stabilizing the fiber bundles, resulting in fiber breakage rather than disentanglement and alignment.

Molecular Mechanisms of Nonphotochemical Quenching in the LHCSR3 Protein of Chlamydomonas reinhardtii.

Photosynthetic organisms possess photoprotection mechanisms from excess light conditions. The fastest response consists in the pH-triggered activation of a dissipation channel of the energy absorbed by the chlorophylls into heat, called nonphotochemical quenching. In green algae, the pigment binding complex LHCSR3 acts both as a chlorophyll quencher and as a pH detector. In this work, we study the quenching of the LHCSR3 protein in vitro considering two different protein aggregation states and two pH conditions using a combination of picosecond time-resolved photoluminescence and femtosecond transient absorption in the visible and NIR spectral regions. We find that the mechanisms at the basis of LHCSR3 quenching activity are always active, even at pH 7.5 and low aggregation. However, quenching efficiency is strongly enhanced by pH and by aggregation conditions. In particular, we find that electron transfer from carotenoids to chlorophylls is enhanced at low pH, while quenching mediated by protein–protein interactions is increased by going to a high aggregation state. We also observe a weak pH-dependent energy transfer from the chlorophylls to the S1 state of carotenoids.

Biochemical and metabolic effects of a short-term exposure to nanoparticles of titanium silicate in tadpoles of Pelophylax perezi (Seoane)

This study aimed to evaluate sublethal effects of a short-term exposure (96h) to titanium silicate nanoparticles (TiSiO4-NP) on Pelophylax perezi tadpoles. Tadpoles were exposed to five concentrations of TiSiO4-NP (8.2, 10.2, 12.8, 16 and 20mg/L) plus a control. Effect criteria were: mortality, cholinesterases, glutathione S-transferases, lactate dehydrogenase, and catalase activities, and alanine and lactate contents. Light scattering was used for physical characterization of TiSiO4-NP suspensions, revealing a high aggregation state of the NP, consistent with low z-potential values (<30mV). Mortality among TiSiO4-NP treatments was <11%. Significant differences relatively to the control were observed at the biochemical level (for CAT and LDH) and in lactate and alanine contents, which may end-up in increased oxidative stress. Overall, some of the monitored endpoints suggest metabolic alterations in TiSiO4-NP exposed tadpoles, highlighting the potential of TiSiO4-NP long-term effects on these organisms.

Carbenoid Alkene Insertion Reactions of Oxiranyllithiums

The first computational investigations of the carbenoid reactions of α-lithiated dimethyl ether (methoxymethyllithium) and the intramolecular and intermolecular reactions of lithiated epoxides with the alkene double bond to yield cyclopropane rings are presented. These reactions represent the full spectrum of known carbenoid pathways to cyclopropanation. The reaction of Li-CH(2)-O-CH(3) with ethylene proceeds exclusively through a two-step carbolithiation pathway, the intramolecular reaction of 1,2-epoxy-5-hexene follows either the carbometalation or a concerted methylene transfer pathway (the former is energetically more favorable), and the reaction of lithiated ethylene oxide (oxiranyllithium) with ethylene, the main focus of this paper, appears to proceed exclusively by the methylene transfer mechanism. In the case of these latter reactions, the free energy of activation for cyclopropanation tends to decrease with the higher aggregation states. Formation of tetramers or higher aggregates is favorable in nonpolar solvents, but in strongly coordinating solvents such as tetrahydrofuran (THF), steric factors appear to limit aggregate sizes to the dimer. In the case of 1,2-epoxy-5-hexene, consideration of competing reaction pathways provide an explanation for the observed product distribution.

Records of mantle metasomatism in the morphology of diamonds from the Slave craton

Every population of kimberlitic diamonds contains crystals with remnants of mantle-derived resorption features that carry information about diamond-destroying mantle metasomatic events. We investigated 109 octahedral and tetrahexahedral diamonds (with {111} faces) representing unresorbed, kimberlite-induced (KIM), and mantle-derived (MR) resorption morphologies selected from 630 crystals from Grizzly, Misery, Leslie, and Koala kimberlites (Ekati mine, Northwest Territories, Canada). The MR category is further subdivided into morphologies with complex features (CM-1/2/3) and with resorption-derived step-faces (SM-1/2/3a, b/4) and classification criteria are proposed. In order to test if the different morphological styles have a common residence history in the mantle we obtained cathodoluminescence (CL) images on polished surfaces of each diamond and measured content and aggregation state of nitrogen defects using Fourier transform infrared (FTIR) spectroscopy. Zoning patterns on CL images also helped to distinguish between growth and resorption for step-faced morphologies. Nitrogen data of diamond rims form two clusters: (I) total nitrogen above ~400 ppm and low state of aggregation (<30 % of B centres); (II) total nitrogen <1000 ppm (mostly <400 ppm) and high state of aggregation (~20–98 % of B centres, mostly above 30 %). The study shows a clear correlation between the mantle resorption styles and the internal properties – nitrogen data and zoning patterns on CL images. Comparison of our results with the existing experimental data on diamond dissolution at high pressure and with the published datasets of diamonds recovered from eclogitic and peridotitic xenoliths shows that, in the Slave craton, metasomatism in peridotite develops complex resorption features (CM-1) most likely in the presence of CO2-rich fluid and step-faced (SM-2) diamonds in the presence of H2O fluid, whereas metasomatic fluid in eclogite is probably H2O-rich.

Detection of Prion Protein Particles in Blood Plasma of Scrapie Infected Sheep

Prion diseases are transmissible neurodegenerative diseases affecting humans and animals. The agent of the disease is the prion consisting mainly, if not solely, of a misfolded and aggregated isoform of the host-encoded prion protein (PrP). Transmission of prions can occur naturally but also accidentally, e.g. by blood transfusion, which has raised serious concerns about blood product safety and emphasized the need for a reliable diagnostic test. In this report we present a method based on surface-FIDA (fluorescence intensity distribution analysis), that exploits the high state of molecular aggregation of PrP as an unequivocal diagnostic marker of the disease, and show that it can detect infection in blood. To prepare PrP aggregates from blood plasma we introduced a detergent and lipase treatment to separate PrP from blood lipophilic components. Prion protein aggregates were subsequently precipitated by phosphotungstic acid, immobilized on a glass surface by covalently bound capture antibodies, and finally labeled with fluorescent antibody probes. Individual PrP aggregates were visualized by laser scanning microscopy where signal intensity was proportional to aggregate size. After signal processing to remove the background from low fluorescence particles, fluorescence intensities of all remaining PrP particles were summed. We detected PrP aggregates in plasma samples from six out of ten scrapie-positive sheep with no false positives from uninfected sheep. Applying simultaneous intensity and size discrimination, ten out of ten samples from scrapie sheep could be differentiated from uninfected sheep. The implications for ante mortem diagnosis of prion diseases are discussed.

Toxicity and genotoxicity of organic and inorganic nanoparticles to the bacteria Vibrio fischeri and Salmonella typhimurium

The present work aimed at evaluating the toxicity and genotoxicity of two organic (vesicles composed of sodium dodecyl sulphate/didodecyl dimethylammonium bromide-SDS/DDAB and of monoolein and sodium oelate-Mo/NaO) and four inorganic (titanium oxide-TiO₂, silicon titanium-TiSiO₄, Lumidot-CdSe/ZnS, and gold nanorods) nanoparticles (NP), suspended in two aqueous media (Milli Q water and American Society for Testing and Materials (ASTM) hardwater), to the bacteria Vibrio fischeri (Microtox test) and Salmonella typhimurium-his⁻ (Ames test with strains TA98 and TA100). Aiming a better understanding of these biological responses physical and chemical characterization of the studied NP suspensions was carried out. Results denoted a high aggregation state of the NP in the aqueous suspensions, with the exception of SDS/DDAB and Mo/NaO vesicles, and of nanogold suspended in Milli Q water. This higher aggregation was consistent with the low values of zeta potential, revealing the instability of the suspensions. Regarding toxicity data, except for nano TiO₂, the tested NP significantly inhibited bioluminescence of V. fischeri. Genotoxic effects were only induced by SDS/DDAB and TiO₂ for the strain TA98. A wide range of toxicity responses was observed for the six tested NP, differing by more than 5 orders of magnitude, and suggesting different modes of action of the tested NP.

Insights into carbohydrate recognition by Narcissus pseudonarcissus lectin: the crystal structure at 2 Å resolution in complex with α1-3 mannobiose

Carbohydrate recognition by monocot mannose-binding lectins was studied via the crystal structure determination of daffodil (Narcissus pseudonarcissus) lectin. The lectin was extracted from daffodil bulbs, and crystallised in the presence of α-1,3 mannobiose. Molecular replacement methods were used to solve the structure using the partially refined model of Hippeastrum hybrid agglutinin as a search model. The structure was refined at 2.0 Å resolution to a final R-factor of 18.7 %, and Rfree of 26.7 %.The main feature of the daffodil lectin structure is the presence of three fully occupied binding pockets per monomer, arranged around the faces of a triangular β-prism motif. The pockets have identical topology, and can bind mono-, di- or oligosaccharides. Strand exchange forms tightly bound dimers, and higher aggregation states are achieved through hydrophobic patches on the surface, completing a tetramer with internal 222-symmetry. There are therefore 12 fully occupied binding pockets per tetrameric cluster. The tetramer persists in solution, as shown with small-angle X-ray solution scattering. Extensive sideways and out-of-plane interactions between tetramers, some mediated via the ligand, make up the bulk of the lattice contacts.A fourth binding site was also observed. This is unique and has not been observed in similar structures. The site is only partially occupied by a ligand molecule due to the much lower binding affinity. A comparison with the Galanthus nivalis agglutinin/mannopentaose complex suggests an involvement of this site in the recognition mechanism for naturally occurring glycans.

Characterization of chlorophyll a/b proteins of photosystem I from Chlamydomonas reinhardtii.

In this study we have isolated the chlorophyll a/b-binding proteins from a photosystem I preparation of the green alga Chlamydomonas reinhardtii and characterized them by N-terminal sequencing, fluorescence, and absorption spectroscopy and by immunochemical means. The results indicate that in this organism, the light-harvesting complex of photosystem I (LHCI) is composed of at least seven distinct polypeptides of which a minimum number of three are shown to bind chlorophyll a and b. Both sequence homology and immunological cross-reactivity with other chlorophyll-binding proteins suggest that all of the LHCI polypeptides bind pigments. Fractionation of LHCI by mildly denaturing methods showed that, in contrast to higher plants, the long wavelength fluorescence emission typical of LHCI (705 nm in C. reinhardtii) cannot be correlated with the presence of specific polypeptides, but rather with changes in the aggregation state of the LHCI components. Reconstitution of both high aggregation state and long wavelength fluorescence emission from components that do not show these characteristics confirm this hypothesis.

Dimeric hemoglobins from the arcid blood clam, Noetia ponderosa. Structure and functional properties.

The hemoglobin found in the nucleated erythrocytes of the arcid blood clam Noetia ponderosa is heterogeneous and consists of two electrophoretic components, Hb-Major and Hb-Minor, present in about 80% and 20% proportions, respectively. Both components are hemoglobin dimers over a wide concentration range based on light-scattering measurements. No higher aggregation states are observed. The oxygen binding by Hb-Major and Hb-Minor is characterized by p50 values of 16.8 and 8.7 mm of Hg and Hill coefficients of 1.4 and 1.2, respectively, at pH 7.0 and 25 degrees C. Neither component exhibits an alkaline Bohr effect. An unusual nonlinear Hill plot is observed for Hb-Major. Hb-Major is composed of two different polypeptide chains and thus is a heterodimer based on sodium dodecyl sulfate/urea-polyacrylamide gel electrophoresis and reverse phase high performance liquid chromatography. By the same methods, Hb-Minor is a homodimer and may share a common chain with Hb-Major. Amino acid compositions of the two hemoglobins indicate 2 histidines/polypeptide chain which are presumably involved in the coordination of the heme iron. Visible absorption spectra indicate the heme environment is normal in the oxy state but perhaps more constrained in the deoxy state. Oxygen binding as a function of temperature and concentration and binding by the intact erythrocytes indicates the absence of intracellular regulators of oxygen binding.

Mechanism of light fading of dyes on cellophane and poly(ethylene terephthalate)

Studies of relative rates of fading of dyes and Hammett σ-value of substituents in their molecules lead to further evidence that fading of azo dyes on Cellophane and poly-(ethylene terephthalate) is probably an oxidation type of reaction. Absorption spectra of the same dye on these two substrates tend to indicate a very high state of aggregation of dyes on Cellophane as compared to that on poly(ethylene terephthalate).

Mechanism of light fading of dyes on cellophane and poly(ethylene terephthalate)

AbstractStudies of relative rates of fading of dyes and Hammett σ‐value of substituents in their molecules lead to further evidence that fading of azo dyes on Cellophane and poly‐(ethylene terephthalate) is probably an oxidation type of reaction. Absorption spectra of the same dye on these two substrates tend to indicate a very high state of aggregation of dyes on Cellophane as compared to that on poly(ethylene terephthalate).

Effects of diethylzinc in alkyllithium‐initiated polymerizations

AbstractIn an alkyllithium‐initiated polymerization of butadiene or styrene, dialkylzinc complexed with the initiator and effectively increased the initiation rate. This is particularly true with initiator of low solubility due to its very high state of aggregation. Dialkylzinc also complexes with the aggregated polymer‐lithium molecules to give a lower apparent solution viscosity. In the presence of a base such as tetrahydrofuran, diethylzinc served as chain‐transfer agent.

Membrane-associated protein synthesis in Streptococcus faecalis

1. Cell-free extracts of Streptococcus faecalis were separated centrifugally into a ribosomal, a washed membrane, and several intermediate fractions. All fractions incorporate labeled amino acids into hot trichloroacetic acid-insoluble material. The requirements for amino acid incorporation are similar for all fractions, and electro-phoresis of the reaction products gives identical polypeptide peaks. 2. All particulate fractions contain phospholipid, and the level of amino acid incorporation is proportional to phospholipid content. No qualitative differences are found in the phospholipid composition of the various fractions. 3. Incorporation by cell fractions is also proportional to RNA content, except for the ribosomal fraction and a first membrane washing, where “excess” RNA appears to be present. On sucrose density gradients of ribosomal fractions the bulk of the “excess” RNA is isolated as a broad peak with a sedimentation coefficient of 80–150 S. On mild ribonuclease (EC 2.7.7.16) treatment this peak dissociates into 30-20 S ribosomal subunits. 4. In addition to large 30-20 S ribosomal aggregates, crude extracts of S. faecalis contain large polyribosomal aggregates. The polyribosomes, consisting of 30-S and 50-S subunits are released from membranes on exposure to deoxycholate. The ribosomes appear to be bound to membranes through the 50-S subunit. These membrane-bound polyribosomes are ribonuclease-sensitive, but are not degraded on incubation with a soluble fraction of S. faecalis. 5. It is concluded that in S. faecalis the bulk of the ribosomes are in a high state of aggregation. In fractionated extracts, protein synthesis is a function of the concentration of membrane-associated polyribosomes. Possible implications of this finding on mechanisms of protein synthesis are discussed.

A MINERALOGICAL STUDY OF WEATHERING AND SOIL FORMATION FROM OLIVINE BASALT IN NORTHERN IRELAND

SummaryThe composition of a soil profile derived from olivine basalt in Northern Ireland is described with the assistance of a series of diagrams of the cumulative curve type incorporating mineralogical and particle size data. The weathering sequence of primary minerals in the basalt is olivine, labradorite, augite. Olivine alters to vermiculite and labradorite to kaolin. The soil resisted all attempts to achieve complete dispersion and its high state of aggregation is considered to affect its physical properties. The presence of quartz is attributed to glacial contamination.

Título en español.

Se hicieron 52 pruebas de infiltración en seis tipos de suelos lateríticos representados por los grupos Laterita, Suelos Lateríticos Pardo Rojizos, y Suelos Lateríticos Pardo Amarillentos. La velocidad de infiltración fué muy rápida y varió entre 3.72 y 9.47 pulgadas por hora. Esta velocidad rápida de infiltración se explica a base de una agregación alta de las partículas del suelo, del contenido de sesquióxidos libres de hierro y aluminio y de la presencia de una arcilla del tipo caolín, en los suelos lateríticos.