ABSTRACT
We have studied the interaction of water with the lipid head group by gravimetrically measuring the lipid water adsorption and the lateral dc electrical conductivity increase resulting from this hydration. We have done this for dimyristoyl phosphatidylcholine (DMPC) having protonated or deuterated hydrocarbon chains. These studies were also done for two cationic lipids having rather different polar head groups. All three lipids behave as strong water adsorbers and all three display a steep, logarithmic increase in the conductivity as the first 1-3 waters per lipid are adsorbed. This increase is usually 5-6 orders of magnitude. After the initial 1-3 waters are adsorbed, the conductivity increases much more gradually, upon additional water adsorption. This electrical behavior is also found for weak water adsorbers and appears to be independent of the head group composition. The conductivity behavior suggests two types of water interacting with the head group. Our studies also indicate that a choline-like component is responsible for the strong water binding nature of the lipids, although, both phosphate and choline make significant contributions to the total amount of adsorbed water. The conductivity behavior, however, does not depend on the presence of both these head group components.
Subject(s)
Dimyristoylphosphatidylcholine/chemistry , Electric Conductivity , Fatty Acids, Monounsaturated/chemistry , Quaternary Ammonium Compounds/chemistry , Thermodynamics , Water/chemistry , Deuterium/chemistry , Lipid Bilayers/chemistry , Models, Chemical , Phosphatidylcholines/chemistry , Phospholipids/chemistryABSTRACT
This study examines the impact of H. influenzae type b (Hib) conjugate vaccine on sociodemographic risk factors for invasive H. influenzae disease in the 2 years before and immediately after the introduction of Hib conjugate vaccine. An ecological study design was used and cases were identified using active surveillance employing several surveillance systems. The study population comprised all children aged < 5 years resident in the West Midlands, an English health region, with laboratory confirmed invasive disease 2 years before (1990-1992) and 2 years after (1992-1994) the introduction of Hib conjugate vaccine. Selected sociodemographic variables derived from the UK census were obtained for all census enumeration districts in the region. Each variable was then ranked and divided into six categories. Linear associations between disease rates and sociodemographic variables were examined. Overall, there was a significant reduction in the incidence of invasive H. influenzae disease. In the pre-conjugate vaccine era there were trends of decreasing disease incidence with increasing child population density (p = 0.012) and total population density (p = 0.0023). In the post-conjugate vaccine period, total population density (p = 0.0275) remained significant and a trend of increasing disease incidence with increasing population mobility (p = 0.0012) was seen. Although Hib conjugate vaccine has resulted in a dramatic reduction in disease incidence changes in sociodemographic risk factors were identified in the post-conjugate vaccine period, particularly population mobility. Our results may have implications for current and future vaccine strategies.
