Matthew Wallace

Kinetically Controlled Coassembly of Multichromophoric Peptide Hydrogelators and the Impacts on Energy Transport

We report a peptide-based multichromophoric hydrogelator system, wherein π-electron units with different inherent spectral energies are spatially controlled within peptidic 1-D nanostructures to create localized energy gradients in aqueous environments. This is accomplished by mixing different π-conjugated peptides prior to initiating self-assembly through solution acidification. We can vary the kinetics of the assembly and the degree of self-sorting through the choice of the assembly trigger, which changes the kinetics of acidification. The hydrolysis of glucono-δ-lactone (GdL) provides a slow pH drop that allows for stepwise triggering of peptide components into essentially self-sorted nanostructures based on subtle pKa differences, whereas HCl addition leads to a rapid formation of mixed components within a nanostructure. Using 1H NMR spectroscopy and fiber X-ray diffraction, we determine the conditions and peptide mixtures that favor self-sorting or intimate comixing. Photophysical investigations in the solution phase provide insight into the correlation of energy-transport processes occurring within the assemblies to the structural organization of the π-systems.

Low immigrant mortality in England and Wales: a data artefact?

Previous research shows low mortality for most immigrants compared to natives in host countries. This advantage is often attributed to health selection processes in migration and to protective health behaviours. Little research has examined the role of data quality, especially the registration of moves. Registration errors relating to moves between origin and host countries can mismatch deaths and risk populations, leading to denominator bias and an under-estimation of migrant mortality (data artefact). The paper investigates the mortality of immigrants in England and Wales from 1971 to 2001 using the Office for National Statistics Longitudinal Study (ONS LS), a 1% sample of the population of England and Wales. We apply parametric survival models to study the mortality of 450,000 individuals. We conduct sensitivity analysis to assess the impact of entry and exit uncertainty on immigrant mortality rates. The analysis shows that most international migrants have lower mortality than natives in England and Wales. Differences largely persist when we adjust models to entry and exit uncertainty and they become pronounced once we control for individual socioeconomic characteristics. This study supports low mortality among immigrants and shows that results are not a data artefact.

Analysis of the mesh size in a supramolecular hydrogel by PFG-NMR spectroscopy

Pulsed field gradient NMR (PFG-NMR) spectroscopy has been used to determine the network mesh size in stable hydrogels formed upon addition of Ca2+ to solutions of naphthalene diphenylalanine (2FF). At pH 12, the solutions at 0.55 wt% 2FF comprise worm-like micelles. Addition of Ca2+ results in cross-linking of these micelles. The self-diffusion of dextran guests of nominal 6, 40, 70, 100, 500, 670, 1400 and 2000 kDa, possessing hydrodynamic diameters (2Rh) similar to the expected pore sizes in these systems, was studied both in the precursor micellar solutions and in the hydrogels. The diffusivity of probes with 2Rh < 40 nm is restricted to a similar extent in both types of network with diffusion coefficients scaling as ∼Mr−0.5, where Mr is the nominal mass of the probe, consistent with relatively unrestricted diffusion. Diffusion coefficients fit well the equation Dn/Do = exp(−Rh/ξ), where Dn and Do are the diffusion coefficients in the presence and absence of network respectively and ξ is the mesh size, giving a mesh size of approximately 40 nm. The heaviest ca. 10% of the nominal 2000 kDa dextran fraction having approximate mass and hydrodynamic diameter 3300 kDa and 84 nm respectively was almost immobilised by the gel, consistent with this estimate of the mesh size. The restriction was much weaker in the micellar solution, which is attributed to the transient nature of this micellar network in the absence of Ca2+. Finally, the mesh size for micellar solutions prepared at 1.1 wt% 2FF is smaller than that of micellar solutions prepared at lower concentrations of 2FF. However, the corresponding gels have a larger mesh size than those prepared at lower concentrations of 2FF. We attribute this to increased fibre aggregation at the higher 2FF concentration. This correlates with lower rheological moduli at higher 2FF concentrations.

Magnetically Aligned Supramolecular Hydrogels

The magnetic-field-induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator, and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of CaCl2 or upon a reduction in solution pH is reported. Utilising the switchable nature of the magnetic field coupled with the slow diffusion of CaCl2, it is possible to precisely control the extent of anisotropy across a hydrogel, something that is generally very difficult to do using alternative methods. The approach is readily extended to other compounds that form viscous solutions at high pH. It is expected that this work will greatly expand the utility of such low-molecular-weight gelators (LMWG) in areas where alignment is key.

On the syneresis of an OPV functionalised dipeptide hydrogel

We describe a new dipeptide hydrogel based on an oligophenylene vinylene core. After gelation, the initial network evolves, expelling solvent and resulting in syneresis. We describe this process and the effects in the bulk properties of the material.

Mortality among immigrants in England and Wales by major causes of death, 1971–2012: A longitudinal analysis of register-based data

Recent research has found a migrant mortality advantage among immigrants relative to the UK-born population living in England and Wales. However, while all-cause mortality is useful to show differences in mortality between immigrants and the host population, it can mask variation in mortality patterns from specific causes of death. This study analyses differences in the causes of death among immigrants living in England and Wales. We extend previous research by applying competing-risks survival analysis to study a large-scale longitudinal dataset from 1971 to 2012 to directly compare causes of death. We confirm low all-cause mortality among nearly all immigrants, except immigrants from Scotland, Northern Ireland and the Republic of Ireland (who have high mortality). In most cases, low all-cause mortality among immigrants is driven by lower mortality from chronic diseases (in nearly all cases by lower cancer mortality and in some cases by lower mortality from cardiovascular diseases (CVD)). This low all-cause mortality often coexists with low respiratory disease mortality and among non-western immigrants, coexists with high mortality from infectious diseases; however, these two causes of death contribute little to mortality among immigrants. For men, CVD is the leading cause of death (particularly among South Asians). For women, cancer is the leading cause of death (except among South Asians, for whom CVD is also the leading cause). Differences in CVD mortality over time remain constant between immigrants relative to UK-born, but immigrant cancer patterns shows signs of some convergence to the cancer mortality among the UK-born (though cancer mortality is still low among immigrants by age 80). The study provides the most up-to-date, reliable UK-based analysis of immigrant mortality.

pH dependent photocatalytic hydrogen evolution by self-assembled perylene bisimides

There is growing interest in the design of supramolecular structures that are photocatalytically active. Perylene bisimides can be self-assembled to produce structures for photocatalytic hydrogen evolution. Herein we explore the role of pH in controlling self-assembly and photocatalysis. It is shown that self-assembly, which occurs as the pH of the system is decreased, is required for hydrogen evolution to occur.

Adult mortality among the descendants of immigrants in England and Wales: does a migrant mortality advantage persist beyond the first generation?

ABSTRACT Little is known about mortality among descendants of immigrants in western host countries because many descendants have not yet reached the ages of high mortality. The aim of this paper is to investigate whether the migrant mortality advantage recently observed among immigrants in England and Wales persists, converges to levels of the White England and Wales-born population or reverses among their descendants. Survival analysis is used to study mortality among over 500,000 individuals in a large, longitudinal dataset (Office for National Statistics Longitudinal Study). A recent update to this data provides a longer time series with an older sample of descendants to study. The analysis finds that, as a combined group, the descendants of immigrants have higher mortality than immigrants and White England and Wales-born. After adjusting for socioeconomic characteristics, mortality among descendants attenuates to the mortality level among the White England and Wales-born but remains high relative to immigrants. Analysis by ethnic minority group suggests there are important differences in mortality among descendants, particularly in the persistent high mortality among the descendants of Black Caribbeans. However, the age structure among descendants is still young and the estimates for ethnic minority sub-groups may not be robust. We await the further ageing of descendants to confirm or challenge these interesting sub-group findings by ethnicity.

Supramolecular nucleoside-based gel: molecular dynamics simulation and characterization of its nanoarchitecture and self-assembly mechanism

Among the diversity of existing supramolecular hydrogels, nucleic acid-based hydrogels are of particular interest for potential drug delivery and tissue engineering applications because of their inherent biocompatibility. Hydrogel performance is directly related to the nanostructure and the self-assembly mechanism of the material, an aspect that is not well-understood for nucleic acid-based hydrogels in general and has not yet been explored for cytosine-based hydrogels in particular. Herein, we use a broad range of experimental characterization techniques along with molecular dynamics (MD) simulation to demonstrate the complementarity and applicability of both approaches for nucleic acid-based gelators in general and propose the self-assembly mechanism for a novel supramolecular gelator, N4-octanoyl-2′-deoxycytidine. The experimental data and the MD simulation are in complete agreement with each other and demonstrate the formation of a hydrophobic core within the fibrillar structures of these mainly water-containing materials. The characterization of the distinct duality of environments in this cytidine-based gel will form the basis for further encapsulation of both small hydrophobic drugs and biopharmaceuticals (proteins and nucleic acids) for drug delivery and tissue engineering applications.