FT-IR spectra of alginic acid block fractions in three species of brown seaweeds

Sodium alginates obtained by alkaline extraction of Lessonia flavicans, Desmarestia ligulata and Desmarestia distans (Phaeophyta) from southern Chile were partially hydrolyzed with HCl. Each alginate gave three fractions that were characterized using FT-IR spectroscopy. The fractions soluble in 0.3M HCl presented in the fingerprint region four vibrations at around 960, 911, 890 and 815 cm(-1) that were assigned to heteropolymeric blocks. The fractions soluble at pH 2.85 showed bands at around 948, 888 and 820 cm(-1) attributed to homopolymannuronic acid blocks, the first band is resolved in the second-derivative spectra into two bands at 951 and 936 cm(-1). The fractions insoluble at pH 2.85 presented four bands at around 947, 903, 812 and 781 cm(-1), which were assigned to homopolyguluronic acid blocks. For some samples, the second derivative FT-IR spectra showed new bands indicating the presence of other structures, in low proportions. Structures deduced by FT-IR spectroscopy were corroborated by solution (1)H and (13)C NMR spectroscopy. Two-dimensional spectra were collected to confirm the fine structure of the hetero- and homopolymeric fractions. A geometrically optimized model for the disaccharide alpha-l-gulopyranuronosyl-(1-->4)-alpha-l-gulopyranuronic acid was calculated using density functional theory; good agreement was obtained between its corresponding calculated vibrations and the experimental bands assigned to homopolyguluronic acid blocks.     

Spring-neap cycle as a major driver of temporal variations in feeding of intertidal fishes: Evidence from the sea catfish Sciades herzbergii (Ariidae) of equatorial west Atlantic mangrove creeks

On macrotidal coasts, short- to medium term variations in feeding of intertidal fishes are influenced by several interacting time scales. To identify the driver of major variations in the feeding habits of intertidal fish, we used the pemecou sea catfish Sciades herzbergii (Ariidae), an abundant intertidal benthic second order consumer, as a model species. We analyzed the influence of the spring-neap and the day-night cycle on intertidal abundance, stomach fullness, diet composition and food consumption of S. herzbergii using block nets set at slack high tides in two mangrove creeks in north Brazil. At spring tides, intertidal abundance, stomach fullness, and total daily consumption of S. herzbergii were on average 8.8, 1.9, and 3.8 times higher than at neap tides, respectively. At spring tides, Uca spp. and Grapsidae (mostly Pachygrapsus gracilis) dominated the diet, irrespective of the time of day. Other important food items were Insecta and the semiterrestrial crab Ucides cordatus. At neap tides, Capitellidae contributed to the diet of nightly inundations while no specimens were caught at daytime. Creek location had no effect on any variable. Results from our study area and evidence from other studies suggest that the spring-neap tide pulse is likely the major driver of short- to medium term variations in feeding of intertidal fishes. This has important implications for feeding-related issues on macro- and probably also on mesotidal coasts: (i) juvenile fishes may have fortnightly growth spurts, (ii) intertidal prey populations may suffer regular fluctuations in mortality, (iii) studies of the feeding ecology of intertidal fishes should cover the combined effects of the tidal, diel, lunar and seasonal cycles, and (iv) the modeling of food webs should consider the differences between highly dynamic spring tide and quieter neap tide conditions.     

Modification with polysialic acid–PEG copolymer as a new method for improving the therapeutic efficacy of proteins

A new protein derivatization method was developed with a block copolymer to reduce the immunogenicity of therapeutic proteins. The block copolymer consisted of polyethylene glycol (PEG) and polysialic acid (PSA), a nonimmunogenic and biodegradable biopolymer. Uricase was used as a model protein. Molecular weight analysis results indicated that the uricase–PEG–PSA conjugate was linked with 2.5 copolymers for each uricase unit. The residual enzyme activity of the uricase with modification by the PEG–PSA copolymer was 72.4%. The tolerance and stability to heat, acid, alkaline, and trypsin treatments significantly improved compared with the native uricase. The immunogenicity of uricase modified with PEG–PSA copolymer was remarkably reduced. The transmission electron microscopy results of the uricase–PEG–PSA conjugate showed a spherical hydrated shell with a larger particle size. These findings proved that the PSA–PEG–protein conjugate is a formulation that can potentially be used to deliver the protein and peptide-based drugs.     

Influence of rocky landscape features and fire regime on vegetation dynamics in Appalachian Quercus forests

Question : How do interactions between rocky landscape features and fire regime influence vegetation dynamics? Location : Continental Eastern USA. Methods : We measured vegetation, disturbance and site characteristics in 40 pairs of rocky and non‐rocky plots: 20 in recently burned stands, and 20 in stands with no evidence of recent fire (‘unburned’ stands). Two‐way analysis of variance (ANOVA) was used to assess the main and interaction effects of fire and rock cover on plant community composition. Results : In burned stands, rock cover had a strong influence on vegetation. Non‐rocky ‘matrix’ forests were dominated by Quercus, and had abundant ground cover and advance regeneration of early and mid‐successional tree species. Burned rocky patches supported greater density of fire‐sensitive species such as Acer rubrum, Sassafras albidum and Nyssa sylvatica and had little advance regeneration or ground cover. Quercus had fewer fire scars and catfaces (open, basal wounds) on rocky patches, suggesting that rocky features mitigate fire severity. In unburned stands, differences between rocky and non‐rocky patches were less distinct, with both patch types having sparse ground cover, little tree regeneration, and high understorey densities of relatively shade tolerant A. rubrum, N. sylvatica and Betula lenta. Conclusion : Under a sustained fire regime, heterogeneity in rock cover created a mosaic where fire‐adapted species such as Quercus dominate the landscape, but where fire‐sensitive species persisted in isolated pockets of lower fire severity. Without fire, species and landscape richness may decline as early‐mid successional species are replaced by more shade tolerant competitors.     

Modulated Self-Organization in Complex Amphiphilic Systems

Abstract

We discuss novel simulation methods for 3D pattern formation in complex amphiphilic systems. The focus is on the supra-molecular or mesoscopic level. The building blocks consist of sequences of dissimilar monomers, connected in copolymer chain molecules. Internal factors such as composition and architecture of the polymers, but also external factors such as applied shear, embedded reactions and level of confinement control the self-organization phenomena. Specific examples include dynamical pattern formation in polymer surfactant solution, reactive polymer blends and surface directed structure formation in block copolymer liquids. The approach lives in a twilight zone between scientific disciplines. The ambitious goal is the invention of methods for the rational design of truly complex bio-mimicking materials, in which we combine principles from chemical engineering, physics, chemistry and biology. The keyword is self-organization, of course. But do not be mistaken: autonomous self-organization leads to trouble, modulated self-organization leads to beauty.     

Thermodynamic analysis of micellization in PEO–PPO–PEO block copolymer solutions from the hydrogen bonding point of view

A thermodynamic approach is suggested to study the micellization mechanism of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers solutions from the hydrogen bonding point of view. Using Flory–Huggins theory, an association model is presented to describe hydrogen bonded (HB) chains, which are bridged by hydrogen bonds between water molecules and segments of the copolymer. The entropic change due to hydrogen bonding is formulated and the individual contribution of EO–water (EO–W) and PO–water (PO–W) hydrogen bonding to the micellization are derived respectively. Fourier transform infrared (FTIR) spectroscopy is applied to obtain the information of hydrogen bonds. During the temperature-dependent micellization of P105 block copolymer solutions, rapid disruption of PO–W hydrogen bonds is observed by FTIR and the calculated entropy relating to PO–W hydrogen bonds increases drastically compared with that of EO–W hydrogen bonds. The results demonstrate that PO–W hydrogen bonds play a dominant role in micellization.     

Grouped Beating in Eisenmenger: Successful Localization and Ablation of an Accelerated Idioventricular Rhythm from Within the Purkinje System

A 33-year old female with a background of Eisenmenger syndrome secondary to multiple congenital muscular ventricular septal defects (VSD) was admitted with a recent history of frequent intermittent palpitations. It was noted that she had an independent accelerated idioventricular rhythm (AIVR), with rates varying between 85-110 bpm, which exhibited a repetitive grouped beating pattern. Although generally perceived as benign, in this case this rhythm was drug refractory, was associated with significant compromise to cardiac filling and output and progressed to haemodynamically intolerable sustained ventricular tachyarrhythmia. Successful ablation was performed at the inferior aspect of the residual VSD, from within the Purkinje network.     

Simultaneous Accessory Pathway and AV Node Mechanical Block

We report a clinical case of a 22-year-old female referred to our institution due to palpitations and preexcitation. Her ECG suggested a right superior paraseptal accessory pathway (AP), which was localised during the electrophysiological study at the superior paraseptal region in close proximity to the His recordings. Reproducible orthodromic reciprocating tachycardia was induced by atrial pacing with extrastimuli. Cryo-mapping performed in the area of earliest atrial activation was not able to terminate the tachycardia. A second attempt, slightly more posterior, caused mechanical block of the AP, which rendered the tachycardia non-inducible. More pressure with the ablation catheter determined a Wenckebach type supra-hisian AV block, which was transient but reproducible. Given this finding no ablation was done. Simultaneous block to the AP and the atrioventricular node has rarely been reported using radiofrequency energy. However, to our knowledge this phenomenon has not been previously reported in large series using cryo-thermal energy.     

Stratigraphic distribution of shallow-water benthic foraminifera from the Lower Cretaceous Taft formation,Central Iran (Yazd Block), with evidence for the importance of hiatuses

In this contribution, two stratigraphic sections are described through the Lower Cretaceous shallow-water platform sediments (Taft formation) from the northern Tethys, which are located in the Yazd Block, Central Iran. Benthic foraminifera are used to propose a biostratigraphy for these successions. They are grouped around several assemblage zones, and several genera and species are reported from the Yazd Block basin for the first time (e.g., Arenobulimina cochleata, A. meltae, Belorusiella sp., Bolivinopsis cf. labeosa, Decussoloculina barbui, Martinotiella jucunda, Myncina bulgarica, Novalesia cornucopia, Sabaudia briacensis, Simplorbitolina manasi). Their presence can provide a better understanding for the paleogeographic reconstruction of the Tethyan seaways. Furthermore, they represent candidates as potential index fossils in the Lower Cretaceous stratigraphy of the Yazd Block. The new biostratigraphic data allow to date the Lower Cretaceous successions between the probable Valanginian and the late Aptian. Based on the absence of early Barremian indicators and also late Aptian markers, two hiatuses are recognized through the Taft formation. This formation also displays a diachrony in ages at its base and top, which suggests the effect of long-term subsidence in the Yazd Block during the Early Cretaceous, following the Cimmerian phase of orogeny.