Vesicle Wall Research Articles

Photo- and Thermo-Dual-Responsive Organic/Inorganic Hybrid Materials

Organic/inorganic hybrid materials based upon stimuli-responsive copolymers have attracted an inceasing attention. Compared with the polymeric materials, these hybrid materials can form aggregates in aqueous solution with much more stable shape-persistance due to the inorganic structure, which facilitate the mass delivery and long-term life. A novel hybrid material based on a new reactive block copolymer, poly(ethylene oxide)-block-poly{3-(trimethoxysilyl)propyl methacrylate-co-N-isopropylacrylamide-co-6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate} [PEO-P(TMSPMA-NIPAM-AzoMA)] was synthesized via atom transfer radical polymerization (ATRP). The vesicles were obtained by self-assembly of the resulting block copolymer in a selective solvent, and then the PTMSPMA block was subjected to hydrolysis and polycondensation reaction to fix vesicle wall in the presence of triethylamine as a catalyst. The photo- and thermo- dual-responsive properties of the vesicles were investigated.

Imaging Diagnosis, Transurethral Endoscopic Observation, and Management of 43 Cases of Persistent and Refractory Hematospermia

The goal of this study was to explore minimally invasive transurethral imaging and surgery for the treatment of severe, persistent hematospermia in cases that were refractory to conservative treatments. The study included 43 patients (aged 22-77 years; average, 44.6 years) with long-lasting, severe hematospermia, accompanied by discomfort or pain in the lumbosacral or perineal region, dysuria, frequent micturition, decreased semen volume, and/or azoospermia. Patient symptoms had persisted for 1 to 10 years (average, 5.3 years). Computed tomography or magnetic resonance imaging of each patient was evaluated, and transurethral surgery was performed. The causes of hematospermia were identified in all 43 patients, and their ejaculatory duct obstruction or seminal vesiculitis was successfully treated. No serious intraoperative or postoperative complications occurred. Pathologic analyses revealed that all of the resected or biopsied seminal vesicle tissues had chronic nonspecific inflammation in the seminal vesicle wall, and no tumors were identified. Preoperative symptomology of hematospermia disappeared in all patients followed up for 2 to 30 months (average, 16 months). A single patient experienced recurrence at 11 months and had a second minimally invasive surgery that was curative. A total of 95.3% (41 of 43) of the patients experienced normal orgasmic intensity after surgery. Magnetic resonance imaging is a valuable and accurate diagnostic method for the identification of causative factors underlying hematospermia. Transurethral dilation of ejaculatory ducts, incision of the verumontanum or the distal end of the ejaculatory ducts, and incision or resection of the relevant cysts represent simple, safe, and reliable approaches for the management of refractory cases of hematospermia that do not respond to conservative treatments.

Nonlinear elastic model for faceting of vesicles with soft grain boundaries

We use an elastic model to explore faceting of solid-wall vesicles with elastic heterogeneities. We show that faceting occurs in regions where the vesicle wall is softer, such as areas of reduced wall thicknesses or concentrated in crystalline defects. The elastic heterogeneities are modeled as a second component with reduced elastic parameters. Using simulated annealing Monte Carlo simulations we obtain the vesicle shape by optimizing the distributions of facets and boundaries. Our model allows us to reduce the effects of the residual stress generated by crystalline defects, and reveals a robust faceting mechanism into polyhedra other than the icosahedron.

Modeling of the major gas vesicle protein, GvpA: From protein sequence to vesicle wall structure

The structure and assembly process of gas vesicles have received significant attention in recent decades, although relatively little is still known. This work combines state-of-the-art computational methods to develop a model for the major gas vesicle protein, GvpA, and explore its structure within the assembled vesicle. Elucidating this protein's structure has been challenging due to its adherent and aggregative nature, which has so far precluded in-depth biochemical analyses. Moreover, GvpA has extremely low similarity with any known protein structure, which renders homology modeling methods ineffective. Thus, alternate approaches were used to model its tertiary structure. Starting with the sequence from haloarchaeon Halobacterium sp. NRC-1, we performed ab initio modeling and threading to acquire a multitude of structure decoys, which were equilibrated and ranked using molecular dynamics and mechanics, respectively. The highest ranked predictions exhibited an α-β-β-α secondary structure in agreement with earlier experimental findings, as well as with our own secondary structure predictions. Afterwards, GvpA subunits were docked in a quasi-periodic arrangement to investigate the assembly of the vesicle wall and to conduct simulations of contact-mode atomic force microscopy imaging, which allowed us to reconcile the structure predictions with the available experimental data. Finally, the GvpA structure for two representative organisms, Anabaena flos-aquae and Calothrix sp. PCC 7601, was also predicted, which reproduced the major features of our GvpA model, supporting the expectation that homologous GvpA sequences synthesized by different organisms should exhibit similar structures.

Lipid‐Containing Polymer Vesicles with pH/Ca2+‐Ion‐Manipulated, Size‐Selective Permeability

AbstractPolymeric vesicles attained from the self‐assembly of distearin (a diacylglycerol lipid)‐conjugated poly(acrylic acid) (PAAc) with various distearin contents in the aqueous phase show the capability of control over the vesicular‐wall permeability to hydrophilic solutes of varying sizes by a simple manipulation of the external pH. The pH sensitivity of the vesicle membranes in size‐selective permeability is largely dependent upon the lipid content of copolymer. By the addition of CaCl2 in aqueous vesicle suspensions, the pH‐evolved assembly structure and the membrane permeability can be immobilized with promoted resistance to further pH alteration, along with an additional counterion screening effect that reduces the pH required for the onset of polar solutes of certain sizes to pass through the membranes. Small‐angle X‐ray scattering (SAXS) measurements of the vesicle structure in the aqueous phase indicate that the pH‐regulated permeability to polar solutes is virtually governed by the extent of hydration and swelling of the vesicle membranes, and the lipid residues within each vesicle wall are packed into the ≈4–5 repeating lamellar islet structure surrounded by PAAc segments.

Poly(lactide-co-glycolide)–Laponite–F68 Nanocomposite Vesicles through a Single-Step Double-Emulsion Method for the Controlled Release of Doxorubicin

Poly(lactide-co-glycolide) (PLGA)-laponite-F68 nanocomposite (PNC) vesicles were prepared through a technically facile, single-step water/oil/water double-emulsion method using ethyl acetate/water mixture. Vesicles of diameter 100 nm to 1.2 μm and average membrane thickness 30 nm were produced. Encapsulation with chemotherapeutic drug doxorubicin revealed unilamellar nature of the vesicle wall. PNC exhibited exfoliated morphology, enhanced thermal stability over neat PLGA, and a glass transition temperature of 54.29 °C. The zeta potential of -14.1 ± 0.231 for the vesicles revealed that the negatively charged PLGA surface is covered with neutral F68 in the vesicle wall. F68-Assisted formation of water/oil/water double emulsion of PNC in ethyl acetate/water mixture is proposed for the formation of the vesicles. Release characteristics of doxorubicin in phosphate-buffered saline (pH 7.4), cytotoxicity of bare and drug-loaded PNC vesicles with L929 cells, and uptake of doxorubicin with C6 fibroblast glioma cell line were also investigated.

Transcriptional programs regulating seed dormancy and its release by after‐ripening in common wheat (Triticum aestivum L.)

Seed dormancy is an important agronomic trait in wheat (Trticum aestivum). Seeds can be released from a physiologically dormant state by after-ripening. To understand the molecular mechanisms underlying the role of after-ripening in conferring developmental switches from dormancy to germination in wheat seeds, we performed comparative transcriptomic analyses between dormant (D) and after-ripened (AR) seeds in both dry and imbibed states. Transcriptional activation of genes represented by a core of 22 and 435 probesets was evident in the dry and imbibed states of D seeds, respectively. Furthermore, two-way ANOVA analysis identified 36 probesets as specifically regulated by dormancy. These data suggest that biological functions associated with these genes are involved in the maintenance of seed dormancy. Expression of genes encoding protein synthesis/activity inhibitors was significantly repressed during after-ripening, leading to dormancy decay. Imbibing AR seeds led to transcriptional activation of distinct biological processes, including those related to DNA replication, nitrogen metabolism, cytoplasmic membrane-bound vesicle, jasmonate biosynthesis and cell wall modification. These after-ripening-mediated transcriptional programs appear to be regulated by epigenetic mechanisms. Clustering of our microarray data produced 16 gene clusters; dormancy-specific probesets and abscisic acid (ABA)-responsive elements were significantly overrepresented in two clusters, indicating the linkage of dormancy in wheat with that of seed sensitivity to ABA. The role of ABA signalling in regulating wheat seed dormancy was further supported by the down-regulation of ABA response-related probesets in AR seeds and absence of differential expression of ABA metabolic genes between D and AR seeds.

An Amyloid Organelle, Solid-state NMR Evidence for Cross-β Assembly of Gas Vesicles

Functional amyloids have been identified in a wide range of organisms, taking on a variety of biological roles and being controlled by remarkable mechanisms of directed assembly. Here, we report that amyloid fibrils constitute the ribs of the buoyancy organelles of Anabaena flos-aquae. The walls of these gas-filled vesicles are known to comprise a single protein, GvpA, arranged in a low pitch helix. However, the tertiary and quaternary structures have been elusive. Using solid-state NMR correlation spectroscopy we find detailed evidence for an extended cross-β structure. This amyloid assembly helps to account for the strength and amphiphilic properties of the vesicle wall. Buoyancy organelles thus dramatically extend the scope of known functional amyloids.

Mechanics of lipid bilayer junctions affecting the size of a connecting lipid nanotube

In this study we report a physical analysis of the membrane mechanics affecting the size of the highly curved region of a lipid nanotube (LNT) that is either connected between a lipid bilayer vesicle and the tip of a glass microinjection pipette (tube-only) or between a lipid bilayer vesicle and a vesicle that is attached to the tip of a glass microinjection pipette (two-vesicle). For the tube-only configuration (TOC), a micropipette is used to pull a LNT into the interior of a surface-immobilized vesicle, where the length of the tube L is determined by the distance of the micropipette to the vesicle wall. For the two-vesicle configuration (TVC), a small vesicle is inflated at the tip of the micropipette tip and the length of the tube L is in this case determined by the distance between the two interconnected vesicles. An electrochemical method monitoring diffusion of electroactive molecules through the nanotube has been used to determine the radius of the nanotube R as a function of nanotube length L for the two configurations. The data show that the LNT connected in the TVC constricts to a smaller radius in comparison to the tube-only mode and that tube radius shrinks at shorter tube lengths. To explain these electrochemical data, we developed a theoretical model taking into account the free energy of the membrane regions of the vesicles, the LNT and the high curvature junctions. In particular, this model allows us to estimate the surface tension coefficients from R(L) measurements.

Structural model of the gas vesicle protein GvpA and analysis of GvpA mutants in vivo

Gas vesicles are gas-filled protein structures increasing the buoyancy of cells. The gas vesicle envelope is mainly constituted by the 8 kDa protein GvpA forming a wall with a water excluding inner surface. A structure of GvpA is not available; recent solid-state NMR results suggest a coil-α-β-β-α-coil fold. We obtained a first structural model of GvpA by high-performance de novo modelling. Attenuated total reflection (ATR)-Fourier transform infrared spectroscopy (FTIR) supported this structure. A dimer of GvpA was derived that could explain the formation of the protein monolayer in the gas vesicle wall. The hydrophobic inner surface is mainly constituted by anti-parallel β-strands. The proposed structure allows the pinpointing of contact sites that were mutated and tested for the ability to form gas vesicles in haloarchaea. Mutations in α-helix I and α-helix II, but also in the β-turn affected the gas vesicle formation, whereas other alterations had no effect. All mutants supported the structural features deduced from the model. The proposed GvpA dimers allow the formation of a monolayer protein wall, also consistent with protease treatments of isolated gas vesicles.

Bladder paraganglioma in adults: MR appearance in four patients

To document the magnetic resonance imaging (MRI) characteristics of paraganglioma of the urinary bladder in adults. The MRI findings and clinical features of pathologically-proven bladder paraganglioma in four patients (three men, one woman; age range, 39-62 years; mean age, 46.8 years) were reviewed retrospectively. All patients underwent MRI in a 1.5 T instrument. The MRI features of the lesions were analyzed, with emphasis on the size, shape, location, margin, signal intensity, degree of MRI enhancement, and apparent diffusion coefficient (ADC) values. The bladder paragangliomas were located in the posterior vesicle wall (n=2), in the dome of the bladder wall (n=1), or the inferoanterior wall (n=1). On MR images, the tumors were round (n=1) or oval-shaped (n=3) and all exhibited well-circumscribed margins and broad-based attachment to the bladder wall. On T1-weighted images, the lesions demonstrated homogeneous hyperintensity (n=4) compared to the gluteus maximus muscle; while on T2-weighted images, they showed slight hyperintensity (n=4). On contrast-enhanced MR images, all lesions showed intense enhancement. On diffusion-weighted imaging (DWI), the lesions showed hyperintensity (n=4) and the mean ADC value was 0.973×10(-3) mm2/s. Bladder pheochromocytoma appears as a round or oval-shaped intensely enhancing lesion with T1 hyperintensity; these characteristics may facilitate the preoperative determination.

Fully Collapsed (Kippah) Vesicles: Preparation and Characterization

A study is presented of the formation of a kippah or hemispherical dome structure, a new morphology generated when a vesicle completely collapses to a hollow hemisphere. Justification for the new name is given in the Introduction. Relatively large vesicles of ca. approximately 500 nm in diameter were prepared from poly(acrylic acid)-block-polystyrene (PAA-b-PS) amphiphilic copolymer in the dioxane/water system. The vesicle specimens for transmission electron microscopy (TEM) were prepared using four different methods: drying under ambient conditions, freeze-drying, freeze-drying and subsequent resuspension in water, and drying under vacuum. The formation of the kippah was found to be strongly influenced by the method of preparation. When the vesicles were allowed to dry on the grid, either by drying under ambient conditions or by direct freeze-drying, "normal" vesicles (i.e., not kippah) with the classical indentation pattern were the only structures to be observed. Kippah vesicles, on the other hand, were obtained only by freeze-drying and subsequent rehydration in water or by direct drying under vacuum where no freezing is involved. The cause of the kippah vesicle formation is not yet completely understood for all methods of preparation; however, it was postulated to be strongly influenced by one or more of the following parameters: the relative flexibility of the vesicle wall, pressure gradient, and surface tension. Unlike "normal" vesicles, which exhibit, in TEM, a classical indentation pattern, kippah vesicles appear nearly round but with average wall thickness twice as large as in the "normal" vesicles. The study illustrates also the usefulness of specimen tilting in the analysis of the kippah. In addition, specimen tilting was found to allow the unambiguous determination of the orientation of the kippah on the surface (i.e., open-side-up or open-side-down).

Cell ultrastructure changes accompanying the annual life cycle of the cyanobacterium Microcystis aeruginosa

All the year round, a benthic vegetation of the cyanobacterium Microcystis aeruginosa lives in the sedimented swampy mud on the bottom of a water basin. Its cell metabolism, directed by heterotrophy, is slow. The ratio of dividing cells in this population falls beneath 20 %, though its cells permanently keep their division ability. The cells of the benthic population are completely devoid of gas vesicles. Bended fibrils of the gas vesicle wall protein mark the previous position of aerotopes. As soon as in March, a pelagic (planktic) population starts to get established; cells are shifted up from the benthos to the surface of the water column, due to reconstruction of gas vesicles and aerotopes thereof, which reconstitutes their much more intensive autotrophic metabolism. The ratio of dividing cells is increased to its summer standard gradually, reaching nearly 95 % in July. Nevertheless, a typical benthic cell can exceptionally be found in plankton, too.

Single Molecule Nanocontainers Made Porous Using a Bacterial Toxin

Encapsulation of a biological molecule or a molecular complex in a vesicle provides a means of biofriendly immobilization for single molecule studies and further enables new types of analysis if the vesicles are permeable. We previously reported on using DMPC (dimyristoylphosphatidylcholine) vesicles for realizing porous bioreactors. Here, we describe a different strategy for making porous vesicles using a bacterial pore-forming toxin, α-hemolysin. Using RNA folding as a test case, we demonstrate that protein-based pores can allow exchange of magnesium ions through the vesicle wall while keeping the RNA molecule inside. Flow measurements indicate that the encapsulated RNA molecules rapidly respond to the change in the outside buffer condition. The approach was further tested by coencapsulating a helicase protein and its single-stranded DNA track. The DNA translocation activity of E. coli Rep helicase inside vesicles was fueled by ATP provided outside the vesicle, and a dramatically higher number of translocation cycles could be observed due to the minuscule vesicle volume that facilitates rapid rebinding after dissociation. These pores are known to be stable over a wide range of experimental conditions, especially at various temperatures, which is not possible with the previous method using DMPC vesicles. Moreover, engineered mutants of the utilized toxin can potentially be exploited in the future applications.

“Breathing” Vesicles

A vesicle system is described that possesses a pH-induced "breathing" feature and consists of a three-layered wall structure. The "breathing" feature consists of a highly reversible vesicle volume change by a factor of ca. 7, accompanied by diffusion of species into and out of the vesicles with a relaxation time of ca. 1 min. The triblock copolymer poly(ethylene oxide)(45)-block-polystyrene(130)-block-poly(2-diethylaminoethyl methacrylate)(120) (PEO(45)-b-PS(130)-b-PDEA(120)) was synthesized via ATRP. Self-assembly into vesicles was carried out at a pH of ca.10.4. The vesicle wall was shown by cryo-TEM to consist of a sandwich of two external ca. 4 nm thick continuous PS layers and one ca. 17 nm thick PDEA layer in the middle. As the pH decreases, both the vesicle size and the thickness of all three layers increase. The increase of the thickness of the intermediate PDEA layer arises from the protonation and hydration, but the swelling is constrained by the PS layers. The increase of the thickness of the two PS layers is a result of an increasing incompatibility and an accompanying sharpening of the interface between the PS layers and the PDEA layer. Starting at a pH slightly below 6, progressive swelling of the PDEA layer with decreasing pH induces a cracking of the two PS layers and also a sharp increase of the vesicle size and the wall thickness. By pH 3.4, the vesicle size has increased by a factor of approximately 1.9 and the wall shows a cracked surface. These changes between pH 10.4 and 3.4 are highly reversible with the relaxation time of ca. 1 min and can be performed repeatedly. The change in the wall structure not only increases dramatically the wall permeability to water but also greatly expands the rate of proton diffusion from practically zero to extremely rapid.

Moganite and quartz inclusions in the nano-structured Anatolian fire opals from Turkey

Red, orange, yellow and colorless chick-pea shaped Anatolian fire opals with massive translucent zoned inclusions, from the Kütahya–Şaphane–Yeni Karamanca region in Turkey, investigated using optical microscopy (gemmoscope and polarizing), X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric spectroscopy (TGA), and thermoluminescent spectroscopy (TL). Hydrothermally deposited Anatolian fire opals are found as nodules within the shrinkage and dehydration cracks of rhyolitic lavas and siliceous cemented tuffs. Initially, the opal bearing zone and its surroundings were geologically mapped. Then, different colored fire opal samples were obtained from the field, and finally, tests were carried out on the representative samples to determine their texture, crystalline phases, crystallinity ratios, and the formation temperatures of the silica phases. The gemmoscope and polarizing microscope investigations show the presence of two different sized textures in Anatolian fire opals: a nano-sized matrix (opal-CT and opal-C) and micron-sized inclusions (moganite and quartz). The analyses of the XRD patterns of the Anatolian fire opals using a comparative matching technique show that there are two pseudo-crystalline and three crystalline silica phases in addition to the amorphous phase. The pseudo-crystalline phases are opal-CT and opal-C. The three crystalline phases are moganite, quartz, and also orthorhombic-silica inclusions. The analyses of the XRD patterns of Anatolian fire opals using the graphical modelling technique reveal that the crystallite sizes of the pseudo-crystalline phases are between 23 nm (red and colorless) and 27 nm (orange and yellow), and the crystallite sizes of the inclusions range between 125 and 600 nm (average 225 nm). Additionally, the amounts of tridymite present in the opal-CT are estimated to be 30–35% (for red), 45–50% (for orange and yellow), and 55–60% (for colorless). The SEM images magnified up to 100.000× confirm the presence of different crystallite sizes in Anatolian fire opals. Thermo gravimetric (TGA) patterns support the presence of a higher crystallinity ratio in Anatolian fire opals, as their total weight loss percentages are found to be fewer than 8%. Infrared (IR) patterns of the Anatolian fire opals define the vibration areas of the water species (both molecular (H 2O) and silanol (SiOH) groups) of the main silica phases, structural point defects, structural bonds, and impurities. Thermoluminescent (TL) patterns indicate the formation temperatures of the silica phases in Anatolian fire opals. The maximum crystallization peaks are recorded at 45 °C for opal-A, 165 °C for opal-CT and opal-C, and 215 °C for moganite and o-silica, and at 255 °C and over for quartz inclusions. These findings show that the colloidal formation order of the chick-pea shaped opal nodules in host rock cavities is firstly rapid opal-A precipitation on the vesicle wall, then opal-CT and opal-C poor crystallization on the opal-A over a longer time, and lastly o-silica, moganite, and quartz crystallization in the central part of the vesicle over the longest time. Thus, the crystallite sizes decrease from the centre to the cavity wall.

A study on reconstruction of ossicular chain by an in situ bone tissue engineering technique

Conclusion. The acellular cancellous bone with recombinant bone morphogenetic proteins 2 (rhBMP-2) could induce osteogenesis in the acoustic vesicle; this material might be used to reconstruct defects of the ossicular chain. Objective. In recent years, the in situ tissue engineering technique has improved rapidly, especially in bone regeneration. The aim of this study was to make an ossicular prothesis using columnar acellular cancellous bone combined with rhBMP-2, implant this prosthesis into the acoustic vesicle of rabbits, and then observe the osteogenesis in situ. Materials and methods. We prepared the acellular cancellous bone combined with rhBMP-2 as an ossicular prothesis, while the same material without rhBMP-2 was used in the control group. From the retroauricular approach, we made a hole in the posterolateral bone wall of the acoustic vesicle, and the prepared materials were implanted. After 3 months, we observed the osteogenesis of the prothesis by macroscopic anatomic and histologic methods. Results. The rabbits recovered soon after surgery. The implanted acellular cancellous bones were connected tightly with the bone of the acoustic vesicle wall. The surfaces of all materials were covered with mucosa, and osteogenesis was observed in the material with rhBMP-2.

Transformation of Vesicles in Aqueous Two‐Phase System of an Anionic Gemini Surfactant and a Cationic Conventional Surfactant Mixture

AbstractTransformation of vesicles formed in DTAB/C11‐p‐PhCNa aqueous surfactant two‐phase (ASTP) was observed by the transmission electron microscopy (TEM). The trans‐conformation of the gemini surfactant in the aggregates was considered to be the important factor for constructing the multi‐lamellar structure of the vesicle wall. The cation‐π interaction between the quaternary ammonium cation and the aromatic ring in the spacer was determined by the UV‐Vis spectrum analysis, which, as well as the general electrostatic attraction and hydrophobic force, contributes to the stability of the multi‐lamellar structure. The concentrations of the surface‐active ions were measured for understanding the mechanism of vesicle transformation. The results show that isoelectric mixing of the two components benefits the growth of vesicles both in size and wall thickness.

Dendrimer Influenced Supramolecular Structure Formation of Block Copolymers: II. Dendrimer Concentration Dependence

The dendrimer concentration dependence of the supramolecular structure formation of polystyrene-block-poly(acrylic acid) in dioxane/THF was investigated as a function of water content. The distribution as well as the localization of the dendrimer units inside the formed aggregates were determined by comparative studies of turbidity measurements and transmission electron microscopy. The strong and specific interactions present between the amine groups of the dendrimer (PAMAM) and the carboxylic acid residues of PAA in the copolymer have a strong influence on the structure formation. The PAMAM concentration as well as the character of the terminal groups of the dendrimer influence the strength of these interactions and consequently affect the structure formation process. As shown by fluorescence quenching experiments, on all supramolecular hierarchical structure levels, and specifically in vesicles, the dendrimer is coated by the PAA chains of the block copolymer due to the strong interactions; since the PAA blocks are connected to the PS blocks, which form the corona, the dendrimer is surrounded by PS chains and is thus encapsulated into the hydrophobic regions of the block copolymer aggregates. A high-resolution transmission electron microscopy image of a micelle is shown, in which the individual dendrimer cores are seen to be localized in the center of these aggregates, and thus, the structure proposed in the previous publication (Kroeger, A.; Li, X.; Eisenberg, A. Langmuir 2007, 23, 10732) is confirmed. Furthermore, the sizes of the resulting aggregates depend on the relative concentration of dendrimer, expressed as RAm/Ac (the ratio of amine to acid groups). With increasing RAm/Ac values, not only the sizes of the micelles but also the vesicle dimensions, especially vesicle wall thicknesses, increase, and this effect suggests the encapsulation of the dendrimer into the vesicle walls. Thus, the constitution of the vesicle structure is determined precisely. This feature allows the potential incorporation of a wide range of species into the vesicle walls or the center of the micelle cores.

TAPHONOMY OF EDIACARAN ACRITARCHS FROM AUSTRALIA: SIGNIFICANCE FOR TAXONOMY AND BIOSTRATIGRAPHY

A diverse assemblage of Australian Ediacaran (late Neoproterozoic) acritarchs from the Centralian Superbasin and Adelaide Rift Complex demonstrates a range of taphonomic degradation. Recognition of taphonomic variants is critical for taxonomic studies and biostratigraphic interpretation. Taphonomic features observed include compression features, folding and tearing of vesicle walls, pitting, perforation, abrasion, exfoliation, shrinking, twisting, splitting, curling, shredding, pyritization, particle entrapment, and thermal maturation effects. The physical and chemical structure of the vesicle wall is instrumental in determining the degree of taphonomic damage. Consistent associations allow identification of degradation series that incorporate previously described individual species and provide a framework for taxonomic revision. Taphonomic associations may also characterize taphofacies, providing an additional tool for basin analysis.