Dual-responsive degradable core–shell nanogels with tuneable aggregation behaviour

Core–shell nanogels with a poly(N-isopropylmethacrylamide) core and poly(N-isopropylacrylamide) shell display tuneable thermoresponsive behaviour and high degradability.

A Density Functional Theory Study on the Water Aggregation Behaviour of Fatty-Acid Based Anionic Surface Active Ionic Liquids

The hydrogen bond interactions between methyl-imidazolium cation (MIM+) and fatty-acid anions (CmHnCOO–, where m=1–6; n-3–13) of ionic liquids are studied in both gas phase and water phase using density functional theory. The structural properties show that the presence of N–H···O and C–H···O hydrogen bonds between [MIM]+ and [CmHnCOO]– (m=1–6;n-3–13) ionic liquids. From the vibrational frequency analysis it was found that the hydrogen bond interaction between [MIM]+ and [CmHnCOO]– (m=1–6;n-3–13) ionic liquids are red-shifted in frequency. The natural bond orbital analysis show that the N–H···O hydrogen bond associated with the large charge transfer which has the higher stabilization energy (i.e. E(2) ~ 38 kcal/mol). Further, the cation/anion–water cluster (H2O)1-3 interactions show that the water molecules are preferred to interact with anions. In the case of ionic liquids–water cluster interaction, the water molecules occupies the interstitial space between cation and anion of ionic liquids which results in weakening the cation-anion interaction.

Organosolv lignin aggregation behaviour of soluble lignin extract from Miscanthus x giganteus at different ethanol concentrations and its influence on the lignin esterification

Background Lignin is the second most abundant naturally occurring biopolymer from lignocellulosic biomass. While there are several lignin applications, attempts to add value to lignin are hampered by its inherent complex and heterogenous chemical structure. This work assesses the organosolv lignin aggregates behaviour of soluble lignin extract derived from Miscanthus × giganteus using different ethanol concentrations (50%, 40%, 30%, 20%, 10% and 1%). The effect of two different lignin concentrations using similar ethanol concentration on the efficacy of esterification was studied. Results Overall, particle size of lignin analysis showed that the particle size of lignin aggregates decreased with lower ethanol concentrations. 50% ethanol concentration of soluble lignin extract showed the highest particle size of lignin (3001.8 nm), while 331.7 nm of lignin particle size was recorded at 1% ethanol concentration. Such findings of particle size correlated well with the morphology of the lignin macromolecules. The lignin aggregates appeared to be disaggregated from population of large aggregates to sub-population of small aggregates when the ethanol concentration was reduced. Light microscopy images analysis by ImageJ shows that the average diameter and circularity of the corresponding lignin macromolecules differs according to different ethanol concentrations. The dispersion of lignin aggregates at low ethanol concentration resulted in high availability of hydroxyl group in the soluble lignin extract. The efficacy of the lignin modification via esterification was evidenced directly via FTIR using the similar ethanol concentration of soluble lignin extract at different lignin concentrations. Conclusion This study provided the understanding of detail analysis on particle size determination, microscopic properties and structural insights of lignin aggregates at wider ethanol concentrations. The esterified lignin derived at 5 mg/mL is suggested to expand greater lignin functionality in the preparation of lignin bio-based materials.

Principles governing control of aggregation and dispersion of aqueous graphene oxide

Controlling the structure of graphene oxide (GO) phases and their smaller analogues, graphene (oxide) quantum dots (GOQDs), is vitally important for any of their widespread intended applications: highly ordered arrangements of nanoparticles for thin-film or membrane applications of GO, dispersed nanoparticles for composite materials and three-dimensional porous arrangements for hydrogels. In aqueous environments, it is not only the chemical composition of the GO flakes that determines their morphologies; external factors such as pH and the coexisting cations also influence the structures formed. By using accurate models of GO that capture the heterogeneity of surface oxidation and very large-scale coarse-grained molecular dynamics that can simulate the behaviour of GO at realistic sizes of GOQDs, the driving forces that lead to the various morphologies in aqueous solution are resolved. We find the morphologies are determined by a complex interplay between electrostatic, $${\pi }$$ π –$${\pi }$$ π and hydrogen bonding interactions. Assembled morphologies can be controlled by changing the degree of oxidation and the pH. In acidic aqueous solution, the GO flakes vary from fully aggregated over graphitic domains to partial aggregation via hydrogen bonding between hydroxylated domains, leading to the formation of planar extended flakes at high oxidation ratios and stacks at low oxidation ratios. At high pH, where the edge carboxylic acid groups are deprotonated, electrostatic repulsion leads to more dispersion, but a variety of aggregation behaviour is surprisingly still observed: over graphitic regions, via hydrogen bonding and “face-edge” interactions. Calcium ions cause additional aggregation, with a greater number of “face-face” and “edge-edge” aggregation mechanisms, leading to irregular aggregated structures. “Face-face” aggregation mechanisms are enhanced by the GO flakes possessing distinct domains of hydroxylated and graphitic regions, with $${\pi }$$ π –$${\pi }$$ π and hydrogen bonding interactions prevalent between these regions on aggregated flakes respectively. These findings furnish explanations for the aggregation characteristics of GO and GOQDs, and provide computational methods to design directed synthesis routes for self-assembled and associated applications.

The Photochemistry of Organic Materials for Photonic Devices

<p>Optically active organic chromophores have attracted much interest in recent years for their potential for use in photonic devices. Chromophores such as compound (1) have been found to have a very high second order nonlinear susceptibility ( β ) value of 650 × 10⁻³⁰esu in dimethyl formamide.¹ The performance of 1 in a polymer film is much lower than this due to the formation of aggregates which hinder the poling process necessary to ensure a noncentrosymmetric arrangement of the molecules in order to display second order nonlinear behaviour. The molecular aggregation behaviour of a set of second order nonlinear compounds based on compound 1 have been studied in this thesis. These compounds share the backbone shown in figure 1 with pendant groups added to the R₁ R₂ and R₃ positions, with the aim of finding substituent groups that can be added to the optically active merocyanine backbone that reduce the aggregation and increase the solubility of the compounds. This in turn will make them more suitable for use in photonics devices. It was found that a C₁₁H₂₃ alkyl chain added to the R₃ position made the largest contribution to decreasing aggregation. Bulky groups on the R₁ and R₂ positions also reduced aggregation. As a result compounds 5 and 8, with R₃ = C₁₁H₂₃ and bulky groups attached displayed the least aggregation of the compounds studied. ¹ See Figure 1 (pg. i): Merocyanine backbone with substituent positions marked.</p>

The Photochemistry of Organic Materials for Photonic Devices

<p>Optically active organic chromophores have attracted much interest in recent years for their potential for use in photonic devices. Chromophores such as compound (1) have been found to have a very high second order nonlinear susceptibility ( β ) value of 650 × 10⁻³⁰esu in dimethyl formamide.¹ The performance of 1 in a polymer film is much lower than this due to the formation of aggregates which hinder the poling process necessary to ensure a noncentrosymmetric arrangement of the molecules in order to display second order nonlinear behaviour. The molecular aggregation behaviour of a set of second order nonlinear compounds based on compound 1 have been studied in this thesis. These compounds share the backbone shown in figure 1 with pendant groups added to the R₁ R₂ and R₃ positions, with the aim of finding substituent groups that can be added to the optically active merocyanine backbone that reduce the aggregation and increase the solubility of the compounds. This in turn will make them more suitable for use in photonics devices. It was found that a C₁₁H₂₃ alkyl chain added to the R₃ position made the largest contribution to decreasing aggregation. Bulky groups on the R₁ and R₂ positions also reduced aggregation. As a result compounds 5 and 8, with R₃ = C₁₁H₂₃ and bulky groups attached displayed the least aggregation of the compounds studied. ¹ See Figure 1 (pg. i): Merocyanine backbone with substituent positions marked.</p>

Rhinella icterica and Rhinella ornata (Anura: Bufonidae) tadpoles do not recognise siblings

Benefits conferred to animals living in groups may be greater if groups are formed by relatives rather than non-relatives, because cooperating with relatives increases the probability of their own genes being passed on to group offspring (inclusive fitness). Non-social aggregations are formed in response to environmental characteristics, while social aggregations are formed from the attraction among individuals. The attraction or repulsion between individuals is mediated by recognition mechanisms, which mediate important ecological processes and behaviours. Here, we conducted laboratory experiments to test if tadpoles of two sympatric bufonids, Rhinella icterica and R. ornata, are able to recognise siblings. We collected eggs of the two species in the field and raised them in laboratory settings, according to three different methods: siblings and non-siblings reared in separated containers; siblings and non-siblings reared in the same container separated by a plastic net; and eggs from the same spawn reared separately, each one in an individual container. Later, we tested if tadpoles could choose between groups of siblings and non-siblings. The results indicate that tadpoles of neither species were able to discriminate between siblings and non-siblings, regardless of the rearing methods. Therefore, kinship is less important than environmental factors in tadpole aggregation behaviour of these species, and it may be dependent on the balance between costs and benefits. Our results can be used as a start point to better understand tadpole aggregation behaviour and recognition mechanisms in these species.

The social shape of sperm: using an integrative machine-learning approach to examine sperm ultrastructure and collective motility

Sperm is one of the most morphologically diverse cell types in nature, yet they also exhibit remarkable behavioural variation, including the formation of collective groups of cells that swim together for motility or transport through the female reproductive tract. Here, we take advantage of natural variation in sperm traits observed across Peromyscus mice to test the hypothesis that the morphology of the sperm head influences their sperm aggregation behaviour. Using both manual and automated morphometric approaches to quantify their complex shapes, and then statistical modelling and machine learning to analyse their features, we show that the aspect ratio of the sperm head is the most distinguishing morphological trait and statistically associates with collective sperm movements obtained from in vitro observations. We then successfully use neural network analysis to predict the size of sperm aggregates from sperm head morphology and show that species with relatively wider sperm heads form larger aggregates, which is consistent with the theoretical prediction that an adhesive region around the equatorial region of the sperm head mediates these unique gametic interactions. Together these findings advance our understanding of how even subtle variation in sperm design can drive differences in sperm function and performance.