Dynamic 13C NMR studies of ligand exchange in linear (d10) silver(I) and gold(I) and square-planar (d8) rhodium(I) homoleptic metal carbonyl cations in superacidic media.

The dynamic CO exchange of the monovalent metal carbonyl cations [Ag(13CO)]+, [Au(13CO)2]+-Au(13CO) SO3F and [Rh(12CO)4-x(13CO)x]+ (x < or = 1) in superacidic solutions was studied by variable-temperature 13C NMR methods. The exchange rates are strongly dependent on the acidity of the solvent, the concentration of metal carbonyl cations and temperature. Whereas a suitable exchange rate of the Ag(I) system is only accessible in magic acid (HSO3F-SbF5), the more stable Au(I) and Rh(I) systems were studied in the less acidic fluorosulfuric acid. Selected solutions of Ag(I), Rh(I) and Au(I) yielded activation barriers deltaG* of 42.7, 43.5, and 56.2 kJ mol(-1) respectively.

Alginate overproduction affects Pseudomonas aeruginosa biofilm structure and function.

During the course of chronic cystic fibrosis (CF) infections, Pseudomonas aeruginosa undergoes a conversion to a mucoid phenotype, which is characterized by overproduction of the exopolysaccharide alginate. Chronic P. aeruginosa infections involve surface-attached, highly antibiotic-resistant communities of microorganisms organized in biofilms. Although biofilm formation and the conversion to mucoidy are both important aspects of CF pathogenesis, the relationship between them is at the present unclear. In this study, we report that the overproduction of alginate affects biofilm development on an abiotic surface. Biofilms formed by an alginate-overproducing strain exhibit a highly structured architecture and are significantly more resistant to the antibiotic tobramycin than a biofilm formed by an isogenic nonmucoid strain. These results suggest that an important consequence of the conversion to mucoidy is an altered biofilm architecture that shows increasing resistance to antimicrobial treatments.

Phenotype characterization of genetically defined microorganisms and growth of bacteriophage in biofilms.

Phenotypic characterization will be a pivotal aspect of future research in understanding the biofilm mode of growth. We hope that the concepts and techniques presented in this chapter will benefit other investigators in this field. Although initial studies will necessarily involve monocultures, eventually mixed culture work will have to be performed to understand biofilm growth in the natural environment. As the study of biofilm-phage interactions is new, there is considerable fundamental work that needs to be addressed. Here, we anticipate that some phage are better adapted to growth in biofilms, some are adept in growing in mixed culture biofilms, and others are better adapted to infecting planktonic organisms. Whereas biofilms are now widely accepted as a fundamental aspect of microbial growth in nature, the field of phage ecology is quite new and an exciting challenge for the future.

Retinal toxicity associated with cisplatin and etoposide in pediatric patients.

Cisplatin is an effective chemotherapeutic agent used in the treatment of many pediatric solid tumors. Retinal toxicity is a side effect of the drug reported in adults, but is not well described in pediatric patients. We present the cases of two children treated with cisplatin and etoposide who experienced retinal toxicity documented by visual evoked response (VER) and electroretinogram (ERG). significantly, both patients had abnormal renal function. The mechanism of visual toxicity induced by cisplatin is unknown but may result from central nervous system (CNS) accumulation of drug after repeated doses, especially with high-dose platinum (HDP) containing regimens. Because clearance of platinum is related to adequate renal-function, patients with any decrease in glomerular filtration rate (GFR) may have delayed platinum excretion. We propose that the patients at greatest risk of cisplatin-induced toxicity are those pretreated with nephrotoxic therapy or those with impairment of renal function from other causes. These patients should have prospective ophthalmologic evaluation especially when treated with HDP containing regimens.

Balance function test correlates of the Dizziness Handicap Inventory.

Balance Function test data alone cannot capture the reaction that a patient has to balance system disease. The present investigation examined the relations among components of the balance function examination (electronystagmography, rotational testing, and platform posturography) and self-perceived dizziness handicap, as quantified by the Dizziness Handicap Inventory (DHI). The DHI is a 25-item self-assessment scale designed to quantify the functional, emotional, and physical effects of dizziness and unsteadiness. The DHI was administered to 367 patients seen consecutively for balance function evaluations. The results indicated that the largest proportion of significant correlations existed between DHI and the sensory organization subtests of platform posturography. Further, greater perceived handicap was documented for patients with (1) spontaneous nystagmus and (2) decreased postural stability quantified by evaluating the inter-relations among vestibular, visual, and proprioceptive systems (posturography).

Auditory adaptation: notes on power and parabolic curve fitting across intensity: II.

The classic Simultaneous Dichotic Loudness Balance (SDLB) procedure for the study of auditory adaptation was used by Weiler and Hood (1977) in a successful test of a model for predicting adaptation in db at intensities above the initial baseline values, using a linear approximation across levels. When Balzer et al (Brit. J. Audiol., 1984, 18, 49-50) fitted curves for simple baseline adaptation data from four studies based on SDLB data, they reported good fits for the Gompertz technique and for a parabolic formula, but did not test the relative goodness of fit for the linear formula, nor for power approximations as Stevens (1975) might have proposed. The present study makes use of the data used by Balzer et al but examines a linear fit as well as two approximations to Stevens' power law. The present finding that the linear approximation is the least efficient examined would suggest that the Weiler and Hood model should be re-examined to determine the degree to which the model can be improved by use of a curvilinear baseline fit. In addition, it might be noted that the curvilinear formulae, of necessity, involve two or more stages. It is the the current effort of this laboratory to determine whether this reflects a multifactor basis to the classic SDLB adaptation, as well as results from other adaptation techniques.

Auditory adaptation: notes on power and parabolic curve fitting across intensity and time. I.

The classic procedure for the study of auditory adaptation has been the method of Simultaneous Dichotic Loudness Balance ( SDLB ). Data from four publications ( Jerger , 1957; Palva and Karja , 1969; Weiler , Loeb and Alluisi , 1972 and Weiler and Hood, 1977) were combined to yield values extending from 20 dB to 80 dB average sensation level. A growth curve was fitted to the data by means of the Gompertz curve-fitting technique. A close fit was obtained, and a somewhat closer fit was found using a parabolic curve. In addition to the average data for SDLB adaptation across test intensities, the Gompertz method was used to fit the course of adaptation over time for one additional study ( Thwing , 1955).