Chemical modification of lignocelluloses - their accessibility in selected reaction systems for the preparation of hydrogels

The world population is growing exponentially. At the same time, the availability of natural resources decreases dramatically – an alarming trend which demands for a sustainable use of our resources in a circular economic framework and hence, for the valorization of wastes and by-products. Owing to its high annual abundance, lignocellulosic biomass has a promising potential as renewable resource for the development of high-value products, covering fuels, platform chemicals, and specialty polymers. Besides, lignocelluloses offer an attractive basis for material applications, considering their peculiarity as natural composites and their inherent modifiability. Therefore, targeted chemical modifications have been widely used to exploit this potential and to further increase their spectrum of characteristics and application prospects. The objective of this study was to fabricate lignocellulose-based hydrogels, with the prospect to be used as soil conditioners in agriculture. Considering this application, this study was striving for the development of a simple synthetic pathway that ideally guarantees non-toxic and biodegradable products. Besides, two key factors were involved in the development of the synthetic route and constitute the center of this study: the accessibility of lignocelluloses towards chemical modifications – in view of their inherent recalcitrance – and the envisaged properties of the hydrogel, including high swelling rates and structural stability. To comply with both key factors, three basic processing steps were carried out: (1) feedstock activation by chemical or mechanical pretreatments, (2) introduction of ionic groups to induce swelling properties and (3) gel network formation via chemical crosslinking. Furthermore, to elucidate the behavior of different biomass types, wheat straw and beech sawdust were exemplarily surveyed. In the first step, different chemical (ozonolysis, alkaline and sulfite pulping) or mechanical (short-time ball milling) pretreatment approaches were used to activate the feedstocks by inducing compositional and/or structural alterations. In the second processing step, two modification reactions – carboxymethylation and phosphorylation (with phosphoric acid/molten urea) – were examined with emphasis on their ability to access lignocellulosic matrices and to realize high contents of ionic groups. In the final step, covalently crosslinked gel networks were formed using either citric acid or electron beam irradiation. Both crosslinking approaches were evaluated in detail with respect to yield and properties of the resulting hydrogels. In view of the two key factors proposed for this study – the accessibility of lignocelluloses and the final hydrogel properties – and amongst the approaches examined, the following synthetic pathway delivered the most promising results: ball milling ⟶ carboxymethylation ⟶ citric acid crosslinking. In this process, the promoting effect of ball milling can be attributed to particle size reduction, a breakdown of plant cell structures, and a decline of the cellulose crystallinity. The effectivity of carboxymethylation was particularly based on its alcoholic-alkaline media. Therefore, the uptake of alkali induced a partial disintegration of the lignocellulosic matrix, facilitating both the introduction of ionic groups and high swelling rates of the final gels. Overall, this path delivered promising results for straw-based gels, whereas beech sawdust was hardly accessible

Challenges in synthesis and analysis of asymmetrically grafted cellulose nanocrystals via atom transfer radical polymerization

When cellulose nanocrystals (CNCs) are isolated from cellulose microfibrils, the parallel arrangement of the cellulose chains in the crystalline domains is retained so that all reducing end-groups (REGs) point to one crystallite end. This permits the selective chemical modification of one end of the CNCs. In this study, two reaction pathways are compared to selectively attach atom-transfer radical polymerization (ATRP) initiators to the REGs of CNCs, using reductive amination. This modification further enabled the site-specific grafting of the anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) from the CNCs. Different analytical methods, including colorimetry and solution-state NMR analysis, were combined to confirm the REG-modification with ATRP-initiators and PSS. The achieved grafting yield was low due to either a limited conversion of the CNC REGs or side reactions on the polymerization initiator during the reductive amination. The end-tethered CNCs were easy to redisperse in water after freeze-drying, and the shear birefringence of colloidal suspensions is maintained after this process.Peer ReviewedPostprint (author's final draft

Spatioselective surface chemistry for the production of functional and chemically anisotropic nanocellulose colloids

Maximizing the benefits of nanomaterials from biomass requires unique considerations associated with their native chemical and physical structure. Both cellulose nanofibrils and nanocrystals are extracted from cellulose fibers via a top-down approach and have significantly advanced materials chemistry and set new benchmarks in the last decade. One major challenge has been to prepare defined and selectively modified nanocelluloses, which would, e.g., allow optimal particle interactions and thereby further improve the properties of processed materials. At the molecular and crystallite level, the surface of nanocelluloses offers an alternating chemical structure and functional groups of different reactivity, enabling straightforward avenues towards chemically anisotropic and molecularly patterned nanoparticles via spatioselective chemical modification. In this review, we will explain the influence and role of the multiscale hierarchy of cellulose fibers in chemical modifications, and critically discuss recent advances in selective surface chemistry of nanocelluloses. Finally, we will demonstrate the potential of those chemically anisotropic nanocelluloses in materials science and discuss challenges and opportunities in this field.Peer reviewe

Investigation of the Complexation and the Migration Behavior of Actinides and Non-Radioactive Substances with Humic Acids under Geogenic Conditions - Complexation of Humic Acids with Actindies in the Oxidation State IV Th, U, Np

Objective of this project was the study of basic interaction and migration processes of actinides in the environment in presence of humic acids (HA). To obtain more basic knowledge on these interaction processes synthetic HA with specific functional properties as well as 14C-labeled HA were synthesized and applied in comparison to the natural HA Aldrich. One focus of the work was on the synthesis of HA with distinct redox functionalities. The obtained synthetic products that are characterized by significantly higher Fe(III) redox capacities than Aldrich HA were applied to study the redox properties of HA and the redox stability of U(VI) humate complexes. It was confirmed that phenolic OH groups play an important role for the redox properties of HA. However, the results indicate that there are also other processes than the single oxidation of phenolic OH groups and/or other functional groups contributing to the redox behavior of HA. A first direct-spectroscopic proof for the reduction of U(VI) by synthetic HA with distinct redox functionality was obtained. The complexation behavior of synthetic and natural HA with actinides (Th, Np, Pu) was studied. Structural parameters of Pu(III), Th(IV), Np(IV) and Np(V) humates were determined by X-ray absorption spectroscopy (XAS). The results show that carboxylate groups dominate the interaction between HA and actinide ions. These are predominant monodentately bound. The influence of phenolic OH groups on the Np(V) complexation by HA was studied with modified HA (blocked phenolic OH groups). The blocking of phenolic OH groups induces a decrease of the number of maximal available complexing sites of HA, whereas complex stability constant and Np(V) near-neighbor surrounding are not affected. The effects of HA on the sorption and migration behavior of actinides was studied in batch and column experiments. Th(IV) sorption onto quartz and Np(V) sorption onto granite and its mineral constituents are affected by the pH value and the presence of HA. HA exhibits a significant influence on the transport of U(IV) and U(VI) in a laboratory quartz sand system. In order to provide the basis for a more reliable modeling of the actinide transport, the metal ion complexation with HA has to be integrated into existing geochemical speciation codes. Within this project the metal ion charge neutralization model was embedded into the geochemical modeling code EQ3/6. In addition to that, a digital data base was developed which covers HA complexation data basing on the charge neutralization model

The prevalence of exposure to domestic violence and the factors associated with co-occurrence of psychological and physical violence exposure: a sample from primary care patients

<p>Abstract</p> <p>Background</p> <p>Since many health problems are associated with abuse and neglect at all ages, domestic violence victims may be considered as a group of primary care patients in need of special attention.</p> <p>Methods</p> <p>The aim of this multi-centre study was to assess the prevalence of domestic violence in primary care patients, and to identify those factors which influence the co-occurrence of psychological and physical violence exposure and their consequences (physical, sexual and reproductive and psychological) as obtained from medical records.</p> <p>A study was carried out in 28 family practices in Slovenia in 2009. Twenty-eight family physicians approached every fifth family practice attendee, regardless of gender, to be interviewed about their exposure to domestic violence and asked to specify the perpetrator and the frequency. Out of 840 patients asked, 829 individuals, 61.0% women (n = 506) and 39.0% men (n = 323) were assessed (98.7% response rate). They represented a randomised sample of general practice attendees, aged 18 years and above, who had visited their physician for health problems and who were given a physical examination. Visits for administrative purposes were excluded.</p> <p>Multivariate binary logistic regression analysis was used to determine the factors associated with exposure to both psychological and physical violence.</p> <p>Results</p> <p>Of 829 patients, 15.3% reported some type of domestic violence experienced during the previous five years; 5.9% reported physical and 9.4% psychological violence; of these 19.2% of men and 80.8% of women had been exposed to psychological violence, while 22.4% of men and 77.6% of women had been exposed to physical violence. The domestic violence victims were mostly women (p < 0.001) aged up to 35 years (p = 0.001). Exposure to psychological violence was more prevalent than exposure to physical violence. Of the women, 20.0% were exposed to either type of violence, compared to 8.0% of male participants, who reported they were rarely exposed to physical violence, while women reported often or constant exposure to physical violence. Their partners were mostly the perpetrators of domestic violence towards women, while amongst men the perpetrators were mostly other family members.</p> <p>In univariate analysis female gender was shown to be a risk factor for domestic violence exposure. Regression modelling, explaining 40% of the variance, extracted two factors associated with psychological and physical violence exposure: the abuse of alcohol in the patient (OR 4.7; 95% CI 1.54-14.45) and their unemployment (OR 13.3; 95% CI 1.53-116.45).</p> <p>Conclusions</p> <p>As far as the study design permits, the identified factors associated with both psychological and physical violence exposure could serve as determinants to raise family physicians' awareness when exploring the prevalence of domestic violence. The results of previous research, showing at least 15% prevalence of exposure to domestic violence among primary care patients in Slovenia, and the female gender as a risk factor, were confirmed.</p

Motor-Cortical Interaction in Gilles de la Tourette Syndrome

BACKGROUND: In Gilles de la Tourette syndrome (GTS) increased activation of the primary motor cortex (M1) before and during movement execution followed by increased inhibition after movement termination was reported. The present study aimed at investigating, whether this activation pattern is due to altered functional interaction between motor cortical areas. METHODOLOGY/PRINCIPAL FINDINGS: 10 GTS-patients and 10 control subjects performed a self-paced finger movement task while neuromagnetic brain activity was recorded using Magnetoencephalography (MEG). Cerebro-cerebral coherence as a measure of functional interaction was calculated. During movement preparation and execution coherence between contralateral M1 and supplementary motor area (SMA) was significantly increased at beta-frequency in GTS-patients. After movement termination no significant differences between groups were evident. CONCLUSIONS/SIGNIFICANCE: The present data suggest that increased M1 activation in GTS-patients might be due to increased functional interaction between SMA and M1 most likely reflecting a pathophysiological marker of GTS. The data extend previous findings of motor-cortical alterations in GTS by showing that local activation changes are associated with alterations of functional networks between premotor and primary motor areas. Interestingly enough, alterations were evident during preparation and execution of voluntary movements, which implies a general theme of increased motor-cortical interaction in GTS

Temperature dependence of mitochondrial function and production of reactive oxygen species in the intertidal mud clam Mya arenaria.

Mitochondrial respiration, energetic coupling to phosphorylation and production of reactive oxygen species (ROS) were studied in mitochondrial isolates of the eurythermal bivalve Mya arenaria (Myoidea) from a low shore intertidal population of the German Wadden Sea. Measurements were conducted within the range of the habitat temperatures (5 to 15°C), as well as under heat exposure at 20 and 25°C. Experimental warming resulted in an increase of state 3 and state 4 respiration in mitochondrial isolates. Highest respiratory coupling ratios (RCR) were found at 15°C, while at higher temperatures mitochondrial coupling decreased significantly and ROS release doubled between 15 and 25°C. ROS production amounted to between 2 and 3% of total oxygen consumption in state 3 (0.3-0.5 nmol ROS /mg protein min) at habitat temperature, and to a maximum of 4.3% of state 3 respiration, and 7% of oligomycin induced state 4+ respiration under heat stress. Thus, state 4 respiration, previously interpreted exclusively as a measure of protron leakage, was found to involve significant contribution of ROS formation in this animal, especially under heat stress conditions. Oxygen radical formation was directly dependent on temperature controlled respiration rates in states 3 and 4, and moreover inversely related to mitochondrial coupling (RCR+) in state 4. Mitochondrial ROS formation is obviously involved in cellular heat stress in this eurythermal marine ectotherm