Dielectric behaviour and relaxation in poly(propylene glycol)–water mixtures studied by time domain reflectometry

Dielectric behaviour of poly(propylene glycol) (PPG) of number‐average molecular weight 2000 g mol^?1 and binary mixtures of PPG with water (PPG–W) of various concentrations were carried out in the frequency range 10 MHz to 4 GHz at 25 °C. The dielectric dispersion and absorption curves related to the orientational motion of these molecules in the binary mixtures are described by a single relaxation time using Debye's model. The values of static dielectric constant ε_o, high frequency limiting dielectric constant ε_∞, and dielectric relaxation time τ_o were determined for PPG and PPG–W mixtures. The values of the dielectric parameters were used to explore the nature of homogeneous and heterogeneous dynamic networks formed through hydrogen bonding in the binary mixtures of PPG and water molecules with concentration variation. The dielectric studies of PPG molecules were also carried out in the same frequency range at four temperatures, namely 25, 35, 45 and 55 °C. The temperature‐dependent relaxation times were used to evaluate the thermodynamical parameters for the dielectric relaxation processes. The dielectric relaxation free energy of activation ΔF_τ for PPG molecules was found in the range ～4.5 to 4.7 kcal mol^?1, which corresponds to the activation energy needed for the breakage of hydrogen bonds. Furthermore, the large negative value of the entropy ΔS_τ of PPG molecules confirms that the configuration involved in dipolar orientation has an activated state, which is more ordered than in the normal state. Copyright © 2004 Society of Chemical Industry     

Amplified enzyme-linked-immunofilter assays enable detection of 50-10(5) bacterial cells within 1 hour

1. The hydrolysis of organophosphate pesticides (OP) and nerve gases by serum paraoxonase (PON1) is an important factor determining their toxicity to mammals including man. The PON1 gene contains 2 polymorphic sites at amino acid positions 55 (L-->M) and 192 (G-->A, classically defined as the A and B genotypes) which result in several alloenzymes of PON1 in human serum. 2. The 192 polymorphism has previously been shown to affect PON1 activity. We have investigated the effect of both polymorphisms on the hydrolysis of paraoxon by serum from 279 healthy human subjects. 3. The 55 polymorphism significantly influenced PON1 activity. MM homozygotes had over 50% less activity towards paraoxon compared to the LL and LM genotypes regardless of the 192 genotype (P < 0.001). 4. Multiple regression analysis indicated that the 192 polymorphism, 55 polymorphism and serum PON1 concentration were responsible for 46, 16 and 13% of the variation in PON1 activity, respectively (all P < 0.001). None of the other parameters investigated significantly affected PON1 activity. 5. Therefore both PON1 polymorphisms affect the hydrolysis of paraoxon. AA/MM and AB/MM individuals may be potentially more susceptible to OP intoxication. 6. Genotyping individuals for both PON1 polymorphisms may provide a method for identifying those individuals at most risk of OP poisoning. The effect of PON1 polymorphisms on activity may also explain why some Gulf War Veterans have developed Gulf War Syndrome and some have not.     

Transmyocardial laser revascularization: current experience and future direction

Transmyocardial laser revascularization (TMR) with the CO2 laser (PLC Medical Systems, Inc., Franklin, MA) appears to improve the quality of life and event-free survival of end-stage coronary artery disease patients. Application of this technology prior to clinical instability, along with diligent anesthetic support, careful patient selection, and perioperative management, are essential to a successful outcome. Rush-Presbyterian-St. Luke's Medical Center became the fifth clinical site to investigate TMR under Phase II and Phase III U.S. Food and Drug Administration (FDA) protocols. This clinical experience includes a total of seventy-nine patients, of whom sixty-three had sole TMR utilizing a minimally invasive approach on the beating heart. Lessons learned, to optimize patient selection and operative- and postoperative management, will be delineated and the future direction of TMR will be discussed.