Identifying structure-function relationships to modulate crossover in nonaqueous redox flow batteries

Nonaqueous redox flow batteries (NARFBs) offer a promising solution for large-scale storage of renewable energy. However, crossover of redox active molecules between the two sides of the cell is a major factor limiting their development, as most selective separators are designed for deployment in water, rather than organic solvents. This report describes a systematic investigation of the crossover rates of redox active organic molecules through an anion exchange separator under RFB-relevant non-aqueous conditions (in acetonitrile/KPF6) using a combination of experimental and computational methods. A structurally diverse set of neutral and cationic molecules was selected, and their rates of crossover were determined experimentally with the organic solvent-compatible anion exchange separator Fumasep FAP-375-PP. The resulting data were then fit to various descriptors of molecular size, charge, and hydrophobicity (overall charge, solution diffusion coefficient, globularity, dynamic volume, dynamic surface area, clogP). This analysis resulted in multiple statistical models of crossover rates for this separator. These models were then used to predict tether groups that dramatically slow the crossover of small organic molecules in this system.

Factors influencing the vitek gram-positive susceptibility system's detection of vanB-encoded vancomycin resistance among enterococci

Studies were conducted to identify factors contributing to the inability of the Vitek Gram-Positive Susceptibility system (GPS; bioMerieux, Vitek, Inc., Hazelwood, Mo.) to reliably detect vanB-mediated vancomycin resistance among enterococci. To some extent the accuracy of the GPS depended on a particular strain's level of resistance, as all isolates for which vancomycin MICs were > or = 128 mu g/ml were readily detected but detection of resistance expressed by several strains for which MICs were < or = 64 mu g/ml was sporadic. Factors besides the level of resistance were studied in two vanB strains. For one strain (Enterococcus faecium U8304), the ability of GPS to detect resistance was accurate and consistent, while for the other (Enterococcus faecalis V583), GPS results were inconsistent and unreliable. Using these isolates, we established that growth medium had the most notable effect on the detection of resistance. In the absence of vancomycin, Vitek GPS broth supported growth comparable to that obtained with brain heart infusion broth for both E. faecium U8304 and E. faecalis V583. However, in the presence of vancomycin the growth patterns changed dramatically so that neither VanB strain grew well in Vitek broth, and growth of V583 was barely detectable after 8 h of incubation. In contrast, good growth of both strains was observed in brain heart infusion broth supplemented with vancomycin. Additionally, the same medium effect was observed with other inducibly resistant VanB strains. In conclusion, although Vitek broth can support good enterococcal growth, this medium does not sufficiently support expression of vancomycin resistance by certain strains to allow them to be detected by the Vitek automated system. Furthermore, this observation establishes that the type of growth medium used can substantially influence the expression of vancomycin resistance and indicates that medium-based strategies should be explored for the enhancement of resistance detection among commercial systems.

Failure to detect vertical transmission of hepatitis C virus

OBJECTIVE

To search for transmission of hepatitis C virus (HCV) from infected mothers to their infants.

DESIGN

Prospective clinical, serologic, and molecular biologic follow-up (at least 3 months) of the infants of mothers with anti-HCV antibody.

SETTING

A county hospital providing primary and referral care in high-risk obstetrics (perinatology).

PATIENTS

Twenty-three mothers with anti-HCV antibody and their 24 infants.

METHODS

An enzyme-linked immunosorbent assay (EIA) and a four-antigen recombinant immunoblot assay (RIBA) were used to test for anti-HCV antibody; serum HCV RNA was measured in two independent laboratories by reverse transcription and polymerase chain reaction (PCR) using nested primers in the 5'-noncoding region. Infant samples were tested for HCV RNA by PCR at delivery and after 3 to 6 months of follow-up. Each sample was tested at least four times in two independent laboratories.

RESULTS

Twenty-nine of 648 mothers (4.5%; 95% Cl, 3.0% to 6.4%) had anti-HCV antibody; these women had 30 babies. Twenty-three mothers and their 24 babies were followed at least 3 months (mean follow-up, 52 weeks). Of the 23 mothers, 21 (91%; Cl, 72% to 99%) had a reactive RIBA; one woman had an indeterminate RIBA and was positive for HCV RNA by PCR. In 16 of 23 mothers (70%; Cl, 47% to 87%), PCR yielded a positive result in both laboratories. The mean maternal alanine aminotransferase (ALT) level was 1.6 times the normal value. All the babies had anti-HCV antibody in cord-blood samples, but antibody disappeared or diminished in strength in interval samples, and no infant had evidence of active production of anti-HCV antibody. Only 1 of 24 (4%; Cl, 0.1% to 21%) cord-blood samples was HCV RNA positive, and none of 24 (0%; Cl, 0% to 14%) follow-up samples was positive for HCV RNA by PCR in either laboratory. Four mothers and one baby had antibody to HIV.

CONCLUSIONS

Infant anti-HCV antibody is most likely acquired passively in utero, and vertical transmission of HCV is uncommon.

A long-term study of hepatitis C virus replication in non-A, non-B hepatitis

BACKGROUND

Although antibodies to the hepatitis C virus (HCV) are known to be associated with non-A, non-B hepatitis, little is known about the pattern of HCV replication, its relation to antibody levels, and the clinical course of non-A, non-B hepatitis.

METHODS

We measured HCV RNA in serial serum samples from five patients with post-transfusion non-A, non-B hepatitis who were followed for 10 to 14 years after transfusion. We also studied four chimpanzees that were experimentally infected with serum from four of these patients. Serum HCV RNA was detected by a "nested" polymerase-chain-reaction (PCR) assay that used two sets of primers derived from the third (NS3) and fourth (NS4) non-structural gene regions of the HCV genome.

RESULTS

HCV sequences were detected by PCR in only two of the five patients and two of the four chimpanzees with the set of primers corresponding to the NS3 region, but in all five patients (and in all four chimpanzees) with the primers from the NS4 region. Serum HCV RNA was first detected within three weeks of transfusion in all five patients and within one week in three patients. The viremia lasted less than 4 months in the patient (and two chimpanzees) with acute, self-limited hepatitis, whereas it persisted for 10 to 14 years in the four patients (and for 1 and 3 years in two chimpanzees) with chronic non-A, non-B hepatitis. Antibodies to HCV were first detected at week 12 to 14; they disappeared after nine years in the patient with self-limited disease and became borderline after five years in one of the patients with chronic disease.

CONCLUSIONS

During the early phase of primary HCV infection, there is a period of several months of sero-negativity during which HCV RNA is the only diagnostic marker of infection. The disappearance of HCV RNA from serum appears to correlate with the resolution of non-A, non-B hepatitis, whereas viremia persists in patients whose disease progresses to chronic hepatitis. In contrast, antibody levels do not necessarily remain elevated in patients with chronic disease.