Size distribution curves of senile plaques in patients with Alzheimer’s disease: do plaques grow according to the log-normal model?

The size frequency distributions of diffuse, primitive and cored senile plaques (SP) were studied in single sections of the temporal lobe from 10 patients with Alzheimer’s disease (AD). The size distribution curves were unimodal and positively skewed. The size distribution curve of the diffuse plaques was shifted towards larger plaques while those of the neuritic and cored plaques were shifted towards smaller plaques. The neuritic/diffuse plaque ratio was maximal in the 11 – 30 micron size class and the cored/ diffuse plaque ratio in the 21 – 30 micron size class. The size distribution curves of the three types of plaque deviated significantly from a log-normal distribution. Distributions expressed on a logarithmic scale were ‘leptokurtic’, i.e. with excess of observations near the mean. These results suggest that SP in AD grow to within a more restricted size range than predicted from a log-normal model. In addition, there appear to be differences in the patterns of growth of diffuse, primitive and cored plaques. If neuritic and cored plaques develop from earlier diffuse plaques, then smaller diffuse plaques are more likely to be converted to mature plaques.

Pd/C catalysts based on synthetic carbons with bi- and tri-modal pore-size distribution:applications in flow chemistry

Two new types of phenolic resin-derived synthetic carbons with bi-modal and tri-modal pore-size distributions were used as supports for Pd catalysts. The catalysts were tested in chemoselective hydrogenation and hydrodehalogenation reactions in a compact multichannel flow reactor. Bi-modal and tri-modal micro-mesoporous structures of the synthetic carbons were characterised by N2 adsorption. HR-TEM, PXRD and XPS analyses were performed for characterising the synthesised catalysts. N2 adsorption revealed that tri-modal synthetic carbon possesses a well-developed hierarchical mesoporous structure (with 6.5 nm and 42 nm pores), contributing to a larger mesopore volume than the bi-modal carbon (1.57 cm3 g-1versus 1.23 cm3 g-1). It was found that the tri-modal carbon promotes a better size distribution of Pd nanoparticles than the bi-modal carbon due to presence of hierarchical mesopore limitting the growth of Pd nanoparticles. For all the model reactions investigated, the Pd catalyst based on tri-modal synthetic carbon (Pd/triC) show high activity as well as high stability and reproducibility. The trend in reactivities of different functional groups over the Pd/triC catalyst follows a general order alkyne ≫ nitro > bromo ≫ aldehyde.

Living cationic polymerization

The kinetics of the polymerization of styrene iniated by 1-chloro-1-phenyltehane/tin (IV) chloride in the presence of tetrabutylammonium chloride have been studied. Dilatometry studies at 25 °C were conducted and the orders of reaction were established. Molecular weight studies were conducted for these experiments using size exclusion chromatography. These studies indicated that transfer/termination reactions were present. The observed kinetics may be explained by a polymerization mechanism involving a single propagating species which is present in low concentrations. Reactions at 0 °C and -15 °C have shown that a "living" polymerization could be obtained at low temperatures. A method was derived to study the kinetics of a "living" polymerization by following the increase in degree of polymerization with time. Polymerizations of styrene were conducted using 1,4-bis(bromomethyl)benzene as a difunctional co-catalyst. These reactions produced polymers with broad or bimodal molecular weight distributions. These observations may be explained by the rate of initiation being slower than the rate of propagation or the presence of transfer/termination reactions. Reactions were conducted using a co-catalyst using a co-catalyst produced by the addition of 1,1-diphenylethane to 1,4-bis(bromomethyl)benzene. Size exclusion chromatography studies showed that the polymers produced had a narrower molecular weight distribution than those produced by polymerizations initiated by 1,4-bis(bromomethyl)benzene alone. However the polydispersity was still observed to increase with reaction time. This may also be explained by slow initiation compared to the rate of propagation. Polymerizations initiated by both bifunctional initiators were examined using the method of studying reaction kinetics by following the change in number average degree of polymerization. The results indicated that a straight line relationship could also be obtained with a non-living polymerization.

Characterisation of a harvesting step for monoclonal antibodies from mammalian cell culture

The focus of this research was defined by a poorly characterised filtration train employed to clarify culture broth containing monoclonal antibodies secreted by GS-NSO cells: the filtration train blinded unpredictably and the ability of the positively charged filters to adsorb DNA from process material was unknown. To direct the development of an assay to quantify the ability of depth filters to adsorb DNA, the molecular weight of DNA from a large-scale, fed-batch, mammalian cell culture vessel was evaluated as process material passed through the initial stages of the purification scheme. High molecular weight DNA was substantially cleared from the broth after passage through a disc stack centrifuge and the remaining low molecular weight DNA was largely unaffected by passage through a series of depth filters and a sterilising grade membrane. Removal of high molecular weight DNA was shown to be coupled with clarification of the process stream. The DNA from cell culture supernatant showed a pattern of internucleosomal cleavage of chromatin when fractionated by electrophoresis but the presence of both necrotic and apoptotic cells throughout the fermentation meant that the origin of the fragmented DNA could not be unequivocally determined. An intercalating fluorochrome, PicoGreen, was elected for development of a suitable DNA assay because of its ability to respond to low molecular weight DNA. It was assessed for its ability to determine the concentration of DNA in clarified mammalian cell culture broths containing pertinent monoclonal antibodies. Fluorescent signal suppression was ameliorated by sample dilution or by performing the assay above the pI of secreted IgG. The source of fluorescence in clarified culture broth was validated by incubation with RNase A and DNase I. At least 89.0 % of fluorescence was attributable to nucleic acid and pre-digestion with RNase A was shown to be a requirement for successful quantification of DNA in such samples. Application of the fluorescence based assay resulted in characterisation of the physical parameters governing adsorption of DNA by various positively charged depth filters and membranes in test solutions and the DNA adsorption profile of the manufacturing scale filtration train. Buffers that reduced or neutralised the depth filter or membrane charge, and those that impeded hydrophobic interactions were shown to affect their operational capacity, demonstrating that DNA was adsorbed by a combination of electrostatic and hydrophobic interactions. Production-scale centrifugation of harvest broth containing therapeutic protein resulted in the reduction of total DNA in the process stream from 79.8 μg m1-1 to 9.3 μg m1-1 whereas the concentration of DNA in the supernatant of pre-and post-filtration samples had only marginally reduced DNA content: from 6.3 to 6.0 μg m1-1 respectively. Hence the filtration train was shown to ineffective in DNA removal. Historically, blinding of the depth filters had been unpredictable with data such as numbers of viable cells, non-viable cells, product titre, or process shape (batch, fed-batch, or draw and fill) failing to inform on the durability of depth filters in the harvest step. To investigate this, key fouling contaminants were identified by challenging depth filters with the same mass of one of the following: viable healthy cells, cells that had died by the process of apoptosis, and cells that had died through the process of necrosis. The pressure increase across a Cuno Zeta Plus 10SP depth filter was 2.8 and 16.5 times more sensitive to debris from apoptotic and necrotic cells respectively, when compared to viable cells. The condition of DNA released into the culture broth was assessed. Necrotic cells released predominantly high molecular weight DNA in contrast to apoptotic cells which released chiefly low molecular weight DNA. The blinding of the filters was found to be largely unaffected by variations in the particle size distribution of material in, and viscosity of, solutions with which they were challenged. The exceptional response of the depth filters to necrotic cells may suggest the cause of previously noted unpredictable filter blinding whereby a number of necrotic cells have a more significant impact on the life of a depth filter than a similar number of viable or apoptotic cells. In a final set of experiments the pressure drop caused by non-viable necrotic culture broths which had been treated with DNase I or benzonase was found to be smaller when compared to untreated broths: the abilities of the enzyme treated cultures to foul the depth filter were reduced by 70.4% and 75.4% respectively indicating the importance of DNA in the blinding of the depth filter studied.

Studies of the cationic polymerisation of vinylic and energetic cyclic ether monomers

The cationic polymerisation of various monomers, including cyclic ethers bearing energetic nitrate ester (-ON02) groups, substituted styrenes and isobutylene has been investigated. The main reaction studied has been the ring-opening polymerisation of 3- (nitratomethyl)-3-methyl oxetane (NIMMO) using the alcohol/BF3.0Et2 binary initiator system. A series of di-, tri- and tetrafunctional telechelic polymers has been synthesised. In order to optimise the system, achieve controlled molecular weight polymers and understand the mechanism of polymerisation the effects of certain parameters on the molecular weight distribution, as determined by Size Exclusion Chromatography, have been examined. This shows the molecular weight achieved depends on a combination of factors including -OH concentration, addition rate of monomer and, most importantly, temperature. A lower temperature and OH concentration tends to produce higher molecular weight, whereas, slower addition rates of monomer, either have no significant effect or produce a lower molecular weight polymer. These factors were used to increase the formation of a cyclic oligomer, by a side reaction, and suggest, that the polymerisation of NIMMO is complicated with endbiting and back biting reactions, along with other transfer/termination processes. These observations appear to fit the model of an active-chain end mechanism. Another cyclic monomer, glycidyl nitrate (GLYN), has been polymerised by the activated monomer mechanism. Various other monomers have been used to end-cap the polymer chains to produce hydroxy ends which are expected to form more stable urethane links, than the glycidyl nitrate ends, when cured with isocyanates. A novel monomer, butadiene oxide dinitrate (BODN), has been prepared and its homopolymerisation and copolymerisation with GL YN studied. In concurrent work the carbocationic polymerisations of isobutylene or substituted styrenes have been studied. Materials with narrow molecular weight distributions have been prepared using the diphenyl phosphate/BCl3 initiator. These systems and monomers are expected to be used in the synthesis of thermoplastic elastomers.

The study and characterisation of water-based latices used for can coating interiors

Water-based latices, used in the production of internal liners for beer/beverage cans, were investigated using a number of analytical techniques. The epoxy-graft-acrylic polymers, used to prepare the latices, and films, produced from those latices, were also examined. It was confirmed that acrylic polymer preferentially grafts onto higher molecular weight portions of the epoxy polymer. The amount of epoxy remaining ungrafted was determined to be 80%. This figure is higher than was previously thought. Molecular weight distribution studies were carried out on the epoxy and epoxy-g-acrylic resins. A quantitative method for determining copolymer composition using GPC was evaluated. The GPC method was also used to determine polymer composition as a function of molecular weight. IR spectroscopy was used to determine the total level of acrylic modification of the polymers and NMR was used to determine the level of grafting. Particle size determinations were carried out using transmission electron microscopy and dynamic light scattering. Levels of stabilising amine greatly affected the viscosity of the latex, particle size and amount of soluble polymer but the core particle size, as determined using TEM, was unaffected. NMR spectra of the latices produced spectra only from solvents and amine modifiers. Using solid-state CP/MAS/freezing techniques spectra from the epoxy component could be observed. FT-IR spectra of the latices were obtained after special subtraction of water. The only difference between the spectra of the latices and those of the dry film were due to the presence of the solvents in the former. A distinctive morphology in the films produced from the latices was observed. This suggested that the micelle structure of the latex survives the film forming process. If insufficient acrylic is present, large epoxy domains are produced which gives rise to poor film characteristics. Casting the polymers from organic solutions failed to produce similar morphology.

Some aspects of the interaction of humic substances with metal ions

Humic substances are the major organic constituents of soils and sediments. They are heterogeneous, polyfunctional, polydisperse, macromolecular and have no accurately known chemical structure. Their interactions with radionuclides are particularly important since they provide leaching mechanisms from disposal sites. The central theme to this research is the interaction of heavy metal actinide analogues with humic materials. Studies described focus on selected aspects of the characteristics and properties of humic substances. Some novel approaches to experiments and data analysis are pursued. Several humic substances are studied; all but one are humic acids, and those used most extensively were obtained commercially. Some routine characterisation techniques are applied to samples in the first instance. Humic substances are coloured, but their ultra-violet and visible absorption spectra are featureless. Yet, they fluoresce over a wide range of wavelengths. Enhanced fluorescence in the presence of luminescent europium(III) ions is explained by energy transfer from irradiated humic acid to the metal ion in a photophysical model. Nuclear magnetic resonance spectroscopy is applied to the study of humic acids and their complexes with heavy metals. Proton and carbon-13 NMR provides some structural and functionality information; Paramagnetic lanthanide ions affect these spectra. Some heavy metals are studied as NMR nuclei, but measurements are restricted by their sensitivity. A humic acid is fractionated yielding a broad molecular weight distribution. Electrophoretic mobilities and particle radii determined by Laser Doppler Electrophoretic Light Scattering are sensitive to the conditions of the supporting media, and the concentration and particle size distribution of humic substances. In potentiometric titrations of humate dispersions, the organic matter responds slowly and the mineral acid addition is buffered. Proton concentration data is modelled and a mechanism is proposed involving two key stages, both resulting in proton release after some conformational changes.

The separation of secondary oil-water dispersions in particulate beds

The literature relating to haze formation, methods of separation, coalescence mechanisms, and models by which droplets <100 μm are collected, coalesced and transferred, have been reviewed with particular reference to particulate bed coalescers. The separation of secondary oil-water dispersions was studied experimentally using packed beds of monosized glass ballotini particles. The variables investigated were superficial velocity, bed depth, particle size, and the phase ratio and drop size distribution of inlet secondary dispersion. A modified pump loop was used to generate secondary dispersions of toluene or Clairsol 350 in water with phase ratios between 0.5-6.0 v/v%.Inlet drop size distributions were determined using a Malvern Particle Size Analyser;effluent, coalesced droplets were sized by photography. Single phase flow pressure drop data were correlated by means of a Carman-Kozeny type equation. Correlations were obtained relating single and two phase pressure drops, as (ΔP2/μc)/ΔP1/μd) = kp Ua Lb dcc dpd Cine A flow equation was derived to correlate the two phase pressure drop data as, ΔP2/(ρcU2) = 8.64*107 [dc/D]-0.27 [L/D]0.71 [dp/D]-0.17 [NRe]1.5 [e1]-0.14 [Cin]0.26  In a comparison between functions to characterise the inlet drop size distributions a modification of the Weibull function provided the best fit of experimental data. The general mean drop diameter was correlated by: q_p q_p p_q /β      Γ ((q-3/β) +1) d qp = d fr  .α        Γ ((P-3/β +1 The measured and predicted mean inlet drop diameters agreed within ±15%. Secondary dispersion separation depends largely upon drop capture within a bed. A theoretical analysis of drop capture mechanisms in this work indicated that indirect interception and London-van der Waal's mechanisms predominate. Mathematical models of dispersed phase concentration m the bed were developed by considering drop motion to be analogous to molecular diffusion.The number of possible channels in a bed was predicted from a model in which the pores comprised randomly-interconnected passage-ways between adjacent packing elements and axial flow occured in cylinders on an equilateral triangular pitch. An expression was derived for length of service channels in a queuing system leading to the prediction of filter coefficients. The insight provided into the mechanisms of drop collection and travel, and the correlations of operating parameters, should assist design of industrial particulate bed coalescers.

Novel bioadhesive formulations for mucosal and parenteral delivery of vaccines

In this work we have established the efficient mucosal delivery of vaccines using absorption enhancers and chitosan. In addition, the use of chitosan was shown to enhance the action of other known adjuvants, such as CTB or Quil-A. Collectively, the results presented herein indicate that chitosan has excellent potential as a mucosal adjuvant. We have evaluated a number of absorption enhancers for their adjuvant activity in vivo. Polyornithine was shown to engender high scrum immune reasons to nasally delivered antigens, with higher molecular weight polyornithine facilitating the best results. We have demonstrated for the first time that vitamin E TPGS can act as mucosal adjuvant. Deoxycholic acid, cyclodextrins and acylcarnitines were also identified as effective mucosal adjuvants and showed enhanced immune responses to nasally delivered TT, DT and Yersinia pestis V and F1 antigens. Previously, none of these agents, common in their action as absorption enhancing agents, have been shown to have immunopotentiating activity for mucosal immunisation. We have successfully developed novel surface modified microspheres using chitosan as an emulsion stabiliser during the preparation of PLA microspheres. It was found that immune responses could be substantially increased, effectively exploiting the immunopenetrating characteristics of both chitosan and PLA microspheres in the same delivery vehicle. In the same study, comparison of intranasal and intramuscular routes of administration showed that with these formulations, the nasal route could be as effective as intramuscular delivery, highlighting the potential of mucosal administration for these particulate delivery systems. Chitosan was co-administered with polymer microspheres. It was demonstrated that this strategy facilitates markedly enhanced immune responses in both magnitude and duration following intramuscular administration. We conclude that this combination shows potential for single dose administration of vaccines. In another study, we have shown that the addition of chitosan to alum adsorbed TT was able to enhance immune responses. PLA micro/nanospheres were prepared and characterised with discreet particle size ranges. A smaller particle size was shown to facilitate higher scrum IgG responses following nasal administration. A lower antigen loading was additionally identified as being preferential for the induction of immune responses in combination with the smaller particle size. This may be due to the fact that the number of particles will be increased when antigen loading is low, which may in turn facilitate a more widespread uptake of particles. PLA lamellar particles were prepared and characterised. Adsorbed TT was evaluated for the potential to engender immune responses in vivo. These formulations were shown to generate effective immune responses following intramuscular administration. Positively charged polyethylcyanoacrylate and PLA nanoparticies were designed and characterised and their potential as delivery vehicles for DNA vaccines was investigated. Successful preparation of particles with narrow size distribution and positive surface charge (imparted by the inclusion of chitosan) was achieved. In the evaluation of antibody responses to DNA encoded antigen in the presence of alum administered intranasally, discrimination between the groups was only seen following intramuscular boosting with the corresponding protein. Our study showed that DNA vaccines in the presence of either alum or Quil-A may advantageously influence priming of the immune system by a mucosal route. The potential for the combination of adjuvants, Quil-A and chitosan, to enhance antibody responses to plasmid encoded antigen co-administered with the corresponding protein antigen was shown and this is worthy of further investigation. The findings here have identified novel adjuvants and approaches to vaccine delivery. In particular, chitosan or vitamin E TPGS are shown here to have considerable promise as non-toxic, safe mucosal adjuvants. In addition, biodegradable mucoadhesive delivery systems, surface modified with chitosan in a single step process, may have application for other uses such as drug and gene delivery.

The size frequency distributions of beta-amyloid deposit subtypes in Alzheimer's disease

The size frequency distributions of diffuse, primitive and classic beta/A4 deposits was studied in single sections in the hippocampus, parahippocampal gyrus (PHG) and lateral occipitotemporal gyrus (LOT) in five cases of Alzheimer's disease. In most brain regions, the size distribution of the diffuse deposits was significantly different from that of the primitive and classic deposits. The data suggested that larger diffuse deposits appeared to be converted less often into primitive and classic deposits. Significant differences in the size distribution of primitive deposits were commonly observed between brain regions in which there was no difference in the size distribution of the diffuse deposits. Hence, local brain factors may influence the size of diffuse deposit which can be converted into mature amyloid deposit.

Firm growth and firm size

This article analyses the growth rates of the complete population of UK-registered firms for the period 2001 to 2005. We estimate Gibrat's law – that growth rates are independent of firm size – by deciles of the firm size distribution. Whether we are able to reject Gibrat's law varies across deciles. We also show how estimates vary according to the measure of firm size, time period and sample selection.

An international cohort comparison of size effects on job growth

The contribution of different-sized businesses to job creation continues to attract policymakers’ attention; however, it has recently been recognised that conclusions about size were confounded with the effect of age. We probe the role of size, controlling for age, by comparing the cohorts of firms born in 1998 over their first decade of life, using variation across half a dozen northern European countries Austria, Finland, Germany, Norway, Sweden and the UK to pin down size effects. We find that a very small proportion of the smallest firms play a crucial role in accounting for cross-country differences in job growth. A closer analysis reveals that the initial size distribution and survival rates do not seem to explain job growth differences between countries, rather it is a small number of rapidly growing firms that are driving this result.

Design of experiments to study the impact of process parameters on droplet size and development of non-invasive imaging techniques in tablet coating

Atomisation of an aqueous solution for tablet film coating is a complex process with multiple factors determining droplet formation and properties. The importance of droplet size for an efficient process and a high quality final product has been noted in the literature, with smaller droplets reported to produce smoother, more homogenous coatings whilst simultaneously avoiding the risk of damage through over-wetting of the tablet core. In this work the effect of droplet size on tablet film coat characteristics was investigated using X-ray microcomputed tomography (XμCT) and confocal laser scanning microscopy (CLSM). A quality by design approach utilising design of experiments (DOE) was used to optimise the conditions necessary for production of droplets at a small (20 μm) and large (70 μm) droplet size. Droplet size distribution was measured using real-time laser diffraction and the volume median diameter taken as a response. DOE yielded information on the relationship three critical process parameters: pump rate, atomisation pressure and coating-polymer concentration, had upon droplet size. The model generated was robust, scoring highly for model fit (R2 = 0.977), predictability (Q2 = 0.837), validity and reproducibility. Modelling confirmed that all parameters had either a linear or quadratic effect on droplet size and revealed an interaction between pump rate and atomisation pressure. Fluidised bed coating of tablet cores was performed with either small or large droplets followed by CLSM and XμCT imaging. Addition of commonly used contrast materials to the coating solution improved visualisation of the coating by XμCT, showing the coat as a discrete section of the overall tablet. Imaging provided qualitative and quantitative evidence revealing that smaller droplets formed thinner, more uniform and less porous film coats.