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Impedance spectroscopy was used to probe the AC conductivity of extremely dilute colloidal suspensions (2.5 × 10–5 ≤ Φw/v ≤ 4.0 × 10–2) comprising of polystyrene microspheres (PS; κa ≫ 1 and ζ = −65 mV), gold nanoparticles (Au NPs; κa > 1 and ζ = −26 mV), and Au-coated PS metallodielectric particles (Au-PS) in HEPES buffer. When AC electric fields of strength 10 mV and 1 MHz were applied via 100 μm gap interdigitated microelectrodes across 10 μL samples, a highly resistive (θcapacitive < 1°) and nonmonotonic response was obtained with particle concentrations at steady state. While the suspensions were less resistive (than the buffer) below a critical concentration, they became more resistive above it. More interestingly, particle–particle interactions took place in suspensions with concentrations as low as 0.005% w/v. We believe this unique behavior is linked to the ion size asymmetry in the HEPES molecule that provides an ideal microenvironment for counterionic polarization around the particles. The exact mechanism of polarization in HEPES, however, still remains elusive as the current theoretical models for simple electrolytes fail to explain our data.

T~. paper describes an investigation, by the heterodyne heat method, of the dielectric polarization of mixtures of nitrobenzene and benzene and of nitrobenzene and carbon tetrachloride, of various concentrations and at various temperatures. The results are discussed on the basis of Debye'a dipole theory and the assumption of molecular association.Introduction.

Background: Cryptococcal meningoencephalitis is a life-threatening fungal infection in human immunodeficiency virus (HIV)-infected patients. Cryptococcus neoformans var. grubii and neoformans are the causative agents that usually respond well to fluconazole and amphotericin B. However, resistance/ non-responding cryptococcal meningitis cases to fluconazole and amphotericin B have been reported globally. Methods: The causative Cryptococcus was identified by phenotypic and singleplex polymerase chain reaction (PCR) targeting the putative sugar transporter (STR1) gene. In addition, the phospholipase and proteinase enzymatic activities of the isolates were determined by the plate method using egg yolk agar and bovine serum albumin agar plates, respectively. Finally, the in-vitro minimal inhibitory concentration (MIC) of fluconazole, voriconazole, and amphotericin B against isolated C. neoformans strains was determined by the broth microdilution method. Results: A total of 50 C. neoformans strains were isolated from the cerebrospinal fluid of HIV-infected patients, which were further identified as variety grubii by simplex polymerase chain reaction (PCR). All the isolated strains producing phospholipase and proteinase enzymes were determined by the calculation of Pz, a ratio of colony diameter and diameter of colony plus the precipitation zone. A comparative high proteinase enzyme activity was observed, and these strains produced medium to high phospholipase (mean Pz 0.3720±0.082, range 0.23-0.56) and proteinase activity (Mean Pz 0.3069±0.086, range 0.012- 0.54). A varied antifungal MIC was detected, and voriconazole had the lowest MIC50 and MIC90 (0.03 & 0.06 µg/mL) in comparison to fluconazole and amphotericin B. Conclusion: Cryptococcus neoformans var. grubii is the commonest cause of cryptococcal meningoencephalitis in HIV-infected patients. The isolates had varied extracellular hydrolytic enzyme activities. The emergence of C. neoformans strains with higher fluconazole MIC (≥4 mcg/mL) could have resulted in treatment failure.