Adsorption of charged diblock copolymers : effect on colloidal stability

In this thesis we present Scheutjens-Fleer (SF) calculations on the adsorption of diblock copolymers. More specifically, we restrict ourselves to adsorption at uncharged surfaces, while the specific type of block copolymers we consider have one uncharged adsorbing "anchor" block and one non-adsorbing charged "buoy" block. We compare these systems with a more simple one, that of the charged brushes. A polymer brush is the structure that is formed when polymer molecules are attached by one end to a surface, with a density high enough so that the chains are obliged to stretch away from the interface. Complementary to the numerical computations, the scaling behaviour of these systems is discussed. We study the structure of the adsorbed layer, and try to answer ultimately the question what the effect of the adsorption is on colloidal stability.In the introductory Chapter 1 we explain the most important terms and discuss the relevance of this study. Furthermore, we introduce the SF model and compare it to two other approaches: Monte Carlo and Scaling. Finally, we briefly present the available information on the two systems under consideration, and compare them to a number of related systems.The body of this work is divided in two parts. In Chapters 2 and 3 we discuss charged brushes, systems that are simpler than diblock copolymer adsorption, but still exhibit similar characteristics. In the subsequent two chapters we then proceed to the adsorption of diblock copolymers (Chapter 4) and its effect on colloidal stability (Chapter 5).In Chapter 2 we present numerical results from the SF model for the structure and sealing behaviour of charged brushes and compare these with predictions of an analytical model on the same system. The relevant parameters are the chain length N , the average anchoring density σ, the average segmental charge αon the chains, and the salt concentration φ S .At high anchoring densities, three regimes of brush behaviour may be distinguished. In the salt-free case, the behaviour of the brush is dominated by electrostatic interactions if the charges are high (the so-called Osmotic Brush) or by non-electrostatic excluded volume interactions if the charges are low (the quasi-Neutral Brush regime). Upon adding salt a third regime can be found: the Salted Brush. The behaviour in this regime, although resulting from electrostatic interactions, is very similar to that in a neutral brush and can effectively be described using an electrostatic excluded volume parameter vel ≈ φ S-1α2. We find excellent agreement regarding structure as well as scaling relations between the two theories in these three (high anchoring density ) regimes. At extremely low anchoring densities, the agreement with the analytical theory is less good. This is due to the breakdown at low densities of the mean-field approximationpresently used in the numerical model.In between, at intermediate anchoring densities, the analytical theory predicts a very peculiar regime, where the thickness H scales as H ≈N3σ-1α2. This so-called " Pincus Brush ", named after the author who originally described it, is not recovered with the numerical theory. For the wide range of parameters used, we find the Pincus regime is too small to be detected. This is probably true for any reasonable set of parameters.In Chapter 3 we consider the acid-base equilibrium of the charged brush segments, so that grafted weak polyacids may be studied. For these systems the charge of a brush segment depends on its local environment and on the pH in the solution. The scaling dependence of the thickness H on the salt concentration φ S for such a brush is very different from that for a conventional charged brush with constant charge density.In Chapter 4 we proceed to the adsorption of ionic diblock copolymers. One block, the "anchor", consists of N A uncharged adsorbing A segments, whereas the "buoy" block has N B segments which carry a fixed charge and are non-adsorbing. Upon adsorption these sorbed amount and layer thickness as a function of the block lengths N A and N B , the charge αe on the B segments, and the salt concentration φ S in each of the four regimes. The scaling relations axe checked using SF calculations.The existence of two regimes for uncharged diblock copolymer adsorption has been reported previously. We argue that those HU and LU regimes are closely related to the two regimes HC and LC we find for charged molecules. Scaling relations can be translated from the uncharged to the corresponding charged regimes by replacing the excluded volume parameter v of the buoy segments by an effective electrostatic excluded volume parameter ve = α 2/φ S .In the LC regime the chain density σscales as σ α( N A /N B ) 3/2ve-1and the layer thickness H as H α ( N A /N B ) 1/2. The latter scaling is independent of ve . Using the SF model, these relations axe found to be valid for an adsorbed amount of A segments below 10% of monolayer coverage.In the HC regime the adsorption is dominated by the anchoring block and the scaling relation σ α1/ N A for the chain density is identical to that for uncharged molecules. The SF calculations show that this regime will not be reached in practical situations.Finally, we address in Chapter 5 the effect of the adsorption of charged diblock copolymers on colloidal stability. Using again a scaling as well as the SF approach, we focus on the LC regime and find that the adsorbed layer may cause a significant repulsive interaction between two surfaces, despite the very low adsorbed amounts. The magnitude of this repulsion is well within the range that could be mea, sured using a surface force apparatus. Moreover, we estimate that the repulsive interaction may be strong enough to induce kinetic stability, provided the particle radius is large enough. Upon lowering the salt concentration, however, a critical concentration φ S * is reached eventually, below which the repulsion is no longer strong enough to effect colloidal stability. The scaling analysis predicts that this critical concentration scales as:φ S * ≈ N Bα2/ RN A3where R is the radius of the particles and the other parameters have been defined above. Thus the repulsive interaction decreases when the relative importance of charge effects increases, i.e., with decreasing salt concentration, and increasing buoy block length or buoy block charge. This counterintuitive behaviour can be explained from the effect that electrostatic interactions have on the adsorbed amount: stronger interactions lead to a lower adsorbed amount, which, in turn, leads to a weaker repulsion. The SF calculations confirm these scaling predictions

Platelet-Induced Clumping of Plasmodium falciparum–Infected Erythrocytes from Malawian Patients with Cerebral Malaria—Possible Modulation In Vivo by Thrombocytopenia

Platelets may play a role in the pathogenesis of human cerebral malaria (CM), and they have been shown to induce clumping of Plasmodium falciparum–parasitized red blood cells (PRBCs) in vitro. Both thrombocytopenia and platelet-inducedPRBCclumping are associated with severe malaria and, especially, withCM.In the present study, we investigated the occurrence of the clumping phenomenon in patients with CM by isolating and coincubating their plasma and PRBCs ex vivo. Malawian children with CM all had low platelet counts, with the degree of thrombocytopenia directly proportional to the density of parasitemia. Plasma samples obtained from these patients subsequently induced weak PRBC clumping. When the assays were repeated, with the plasma platelet concentrations adjusted to within the physiological range considered to be normal, massive clumping occurred. The results of this study suggest that thrombocytopenia may, through reduction of platelet-mediated clumping of PRBCs, provide a protective mechanism for the host during CM

A Dutch Fanconi Anemia FANCC Founder Mutation in Canadian Manitoba Mennonites

Fanconi anemia (FA) is a recessive DNA instability disorder associated with developmental abnormalities, bone marrow failure, and a predisposition to cancer. Based on their sensitivity to DNA cross-linking agents, FA cells have been assigned to 15 complementation groups, and the associated genes have been identified. Founder mutations have been found in different FA genes in several populations. The majority of Dutch FA patients belongs to complementation group FA-C. Here, we report 15 patients of Dutch ancestry and a large Canadian Manitoba Mennonite kindred carrying the FANCC c.67delG mutation. Genealogical investigation into the ancestors of the Dutch patients shows that these ancestors lived in four distinct areas in The Netherlands. We also show that the Dutch and Manitoba Mennonite FANCC c.67delG patients share the same haplotype surrounding this mutation, indicating a common founder

Diblock copolymers at a homopolymer-homopolymer-interface: a Monte Carlo simulation

The properties of diluted symmetric A-B diblock copolymers at the interface between A and B homopolymer phases are studied by means of Monte Carlo (MC) simulations of the bond fluctuation model. We calculate segment density profiles as well as orientational properties of segments, of A and B blocks, and of the whole chain. Our data support the picture of oriented ``dumbbells'', which consist of mildly perturbed A and B Gaussian coils. The results are compared to a self consistent field theory (SCFT) for single copolymer chains at a homopolymer interface. We also discuss the number of interaction contacts between monomers, which provide a measure for the ``active surface'' of copolymers or homopolymers close to the interface

Self-consistent field theory for the interactions between keratin intermediate filaments

Background: Keratins are important structural proteins found in skin, hair and nails. Keratin Intermediate Filaments are major components of corneocytes, nonviable horny cells of the Stratum Corneum, the outermost layer of skin. It is considered that interactions between unstructured domains of Keratin Intermediate Filaments are the key factor in maintaining the elasticity of the skin. Results: We have developed a model for the interactions between keratin intermediate filaments based on self-consistent field theory. The intermediate filaments are represented by charged surfaces, and the disordered terminal domains of the keratins are represented by charged heteropolymers grafted to these surfaces. We estimate the system is close to a charge compensation point where the heteropolymer grafting density is matched to the surface charge density. Using a protein model with amino acid resolution for the terminal domains, we find that the terminal chains can mediate a weak attraction between the keratin surfaces. The origin of the attraction is a combination of bridging and electrostatics. The attraction disappears when the system moves away from the charge compensation point, or when excess small ions and/or NMF-representing free amino acids are added. Conclusions: These results are in concordance with experimental observations, and support the idea that the interaction between keratin filaments, and ultimately in part the elastic properties of the keratin-containing tissue, is controlled by a combination of the physico-chemical properties of the disordered terminal domains and the composition of the medium in the inter-filament region. Keywords: Stratum corneum, Skin keratins, Intermediate filaments, Unstructured terminal domains, Bridging attractio

Pharmacogenomics of Vincristine-Induced Peripheral Neuropathy Implicates Pharmacokinetic and Inherited Neuropathy Genes

Vincristine is an effective chemotherapeutic drug for various cancers, including acute lymphoblastic leukemia (ALL). Unfortunately, clinical utility is restricted by dose-limiting vincristine-induced peripheral neuropathies (VIPN). We sought to determine the association of VIPN with a recently identified risk variant, CEP72 rs924607, and drug absorption, distribution, metabolism, and excretion (ADME) gene variants in pediatric ALL. This was followed by a meta-analysis of pharmacogenomic data from over 500 patients. CEP72 rs924607 was significantly associated with VIPN (P = 0.02; odds ratio (OR) = 3.4). ADME analyses identified associations between VIPN and ABCC1 rs3784867 (P = 5.34 × 10 −5 ; OR = 4.9), and SLC5A7 rs1013940 (P = 9.00 × 10 −4 ; OR= 8.6); genes involved in vincristine transport and inherited neuropathies, respectively. Meta-analysis identified an association with a variant related to TTPA (rs10504361: P = 6.85 × 10 −4 ; OR = 2.0), a heritable neuropathy-related gene. This study provides essential corroboratory evidence for CEP72 rs924607 and highlights the importance of drug transporter and inherited neuropathy genes in VIPN

Governors and directors: Competing models of corporate governance

Why do we use the term ‘corporate governance’ rather than ‘corporate direction’? Early British joint stock companies were normally managed by a single ‘governor’. The ‘court of governors’ or ‘board of directors’ emerged slowly as the ruling body for companies. By the nineteenth century, however, companies were typically run by directors while not-for-profit entities such as hospitals, schools and charitable bodies had governors. The nineteenth century saw steady refinement of the roles of company directors, often in response to corporate scandals, with a gradual change from the notion of the director as a ‘representative shareholder’ to the directors being seen collectively as ‘representatives of the shareholders’. Governors in not-for-profit entities, however, were regarded as having broader responsibilities. The term ‘governance’ itself suggests that corporate boards should be studied as ‘political’ entities rather than merely through economic lenses such as agency theory

Assessing proliferation, cell-cycle arrest and apoptotic end points in human buccal punch biopsies for use as pharmacodynamic biomarkers in drug development

Easily accessible normal tissues expressing the same molecular site(s) of drug action as malignant tissue offer an enhanced potential for early proof of anticancer drug mechanism and estimation of the biologically effective dose. Studies were undertaken in healthy male volunteers to assess the tolerability of single and multiple (four in 24 h) 3 mm punch biopsies of the buccal mucosa, and to determine the feasibility of detecting and quantifying a range of proliferation, cell-cycle arrest and apoptosis markers by immunohistochemistry (IHC) for use as potential pharmacodynamic (PD) end points. The biopsy procedure was well tolerated with 100% of volunteers stating that they would undergo single (n=10) and multiple (n=12) biopsies again. Total retinoblastoma protein (pRb), phosphorylated pRb (phospho-pRb), total p27, phosphorylated p27 (phospho-p27), phosphorylated-histone H3 (phospho-HH3), p21, p53, Cyclin A, Cyclin E, Ki67 all produced good signal detection, but M30, cleaved caspase 3 and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling did not. Total pRb, phospho-pRb, total p27 and phospho-p27 were quantified further in a multiple biopsy study to allow components of variability to be addressed to inform future sizing decisions on intervention studies. Neither site of biopsy within the oral cavity, nor the nominal time of biopsy had any significant impact on any of the four markers expression levels. Inter- and intrasubject coefficients of variation (CVs) that could be used to size future intervention studies for pRb, phospho-pRb, total p27 and phospho-p27 were 14, 19, 18 and 16%; and 18, 29, 25 and 19%, respectively. In conclusion, quantitation of such markers in 3 mm buccal punch biopsies would be suitable to explore as PD end points within intervention studies of drugs acting on these pathways

SIOP‐PODC adapted risk stratification and treatment guidelines: Recommendations for neuroblastoma in low‐ and middle‐income settings

Neuroblastoma is the most common extracranial solid tumor in childhood in high‐income countries (HIC), where consistent treatment approaches based on clinical and tumor biological risk stratification have steadily improved outcomes. However, in low‐ and middle‐ income countries (LMIC), suboptimal diagnosis, risk stratification, and treatment may occur due to limited resources and unavailable infrastructure. The clinical practice guidelines outlined in this manuscript are based on current published evidence and expert opinions. Standard risk stratification and treatment explicitly adapted to graduated resource settings can improve outcomes for children with neuroblastoma by reducing preventable toxic death and relapse. Pediatr Blood Cancer 2015;62:1305–1316. © 2015 The Authors. Pediatric Blood & Cancer, published by Wiley Periodicals, Inc

Pharmacological development of target-specific delocalized lipophilic cation-functionalized carboranes for cancer therapy

PURPOSE: Tumor cell heterogeneity and microenvironment represent major hindering factors in the clinical setting toward achieving the desired selectivity and specificity to malignant tissues for molecularly targeted cancer therapeutics. In this study, the cellular and molecular evaluation of several delocalized lipophilic cation (DLC)-functionalized carborane compounds as innovative anticancer agents is presented. METHODS: The anticancer potential assessment of the DLC-carboranes was performed in established normal (MRC-5, Vero), cancer (U-87 MG, HSC-3) and primary glioblastoma cancer stem (EGFRpos, EGFRneg) cultures. Moreover, the molecular mechanism of action underlying their pharmacological response is also analyzed. RESULTS: The pharmacological anticancer profile of DLC-functionalized carboranes is characterized by: a) a marked in vitro selectivity, due to lower concentration range needed (ca. 10 fold) to exert their cell growth-arrest effect on U-87 MG and HSC-3, as compared with that on MRC-5 and Vero; b) a similar selective growth inhibition behavior towards EGFRpos and EGFRneg cultures (>10 fold difference in potency) without, however, the activation of apoptosis in cultures; c) notably, in marked contrast to cancer cells, normal cells are capable of recapitulating their full proliferation potential following exposure to DLC-carboranes; and, d) such pharmacological effects of DLC-carboranes has been unveiled to be elicited at the molecular level through activation of the p53/p21 axis. CONCLUSIONS: Overall, the data presented in this work indicates the potential of the DLC-functionalized carboranes to act as new selective anticancer therapeutics that may be used autonomously or in therapies involving radiation with thermal neutrons. Importantly, such bifunctional capacity may be beneficial in cancer therapy