bluuebunny/crossref_metadata_2025_split huggingface dataset:
Copper metalorganic chemical vapor deposition reactions of hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane and bis (hexafluoroacetylacetonate) Cu(II) adsorbed on titanium nitride
Authors: Donnelly V. M. , Gross M. E. 
Published: July 2002

Cu is receiving increasing attention as a replacement for Al in future Si ultra-large-scale integrated circuits due to its lower resistivity and potentially better reliability in terms of electromigration resistance and stress-induced voiding. Metalorganic chemical vapor deposition (MOCVD) of Cu offers the advantages of conformal coverage and selective growth. Whatever the means of deposition, a diffusion barrier and adhesion layer such as TiN is required. To understand the nucleation mechanisms of Cu film growth on TiN during MOCVD, we have studied the thermal decomposition of two metalorganic precursors, hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane [CuI(hfac)(vtms)], and bis (hexafluoroacetylacetonate) Cu(II) [CuII(hfac)2] by x-ray photoelectron spectroscopy and temperature programmed desorption mass spectrometry in an ultrahigh vacuum (UHV) system.
Experiments were carried out on polycrystalline air-exposed (i.e., oxidized) TiN and N2 ion beam sputter-cleaned TiN. These surfaces are representative of those found in the traditional stand-alone and newer integrated metallization processing sequences, respectively. Room temperature dosing of TiN with CuI(hfac)(vtms) is accompanied by rapid desorption of the vtms ligand, leaving chemisorbed CuI(hfac). This CuI(hfac) decomposes upon heating to form CO, CO2 and CF4 desorption products, leaving about 90% of the Cu on the surface, along with some F and C. CII(hfac)2 also dissociatively chemisorbs at room temperature to form CuI(hfac) and an adsorbate with the stoichiometry of hfac. Unlike CuI(hfac)(vtms), a Cu(hfac)-containing species desorbs upon heating above 75 °C. Near 200 °C this process ceases and decomposition (and possibly some intact desorption) of hfac takes place, leading to desorption of CO, CO2, and CF4. After desorption of all C-containing species, about 30% of the initially deposited Cu remains on the surface, along with a submonolayer coverage of F. Regardless of the precursor, Cu begins to diffuse into the TiN film, above 280 °C. The results of our studies offer insights into the different mechanisms that may play a role in the nucleation of MOCVD film growth and incorporation of impurities at the interface. Significantly, the disproportionation reaction that dominates the deposition of pure Cu from CuI(hfac)(vtms) at the higher pressures typical of MOCVD does not occur under UHV conditions.
Acquisition of Chloramphenicol Resistance by the Linearization and Integration of the Entire Staphylococcal Plasmid pC194 into the Chromosome of
Streptococcus pneumoniae
Authors: Widdowson Carol A. , Adrian Peter V. , Klugman Keith P. 
Published: July 2002

ABSTRACT

Chloramphenicol resistance in
Streptococcus pneumoniae
was associated with
cat
, which has 100% identity with
cat
pC194
from
Staphylococcus aureus
. Inverse PCR with primers specific for pC194 confirmed that in some isolates the entire staphylococcal plasmid was present in the
S. pneumoniae
chromosome, with linearization having occurred between
cat
pC194
and the origin of replication.
Identification of
Cryptosporidium parvum
Dihydrofolate Reductase Inhibitors by Complementation in
Saccharomyces cerevisiae
Authors: Brophy Victoria Hertle , Vasquez John , Nelson Richard G. , Forney John R. , Rosowsky Andre , Sibley Carol Hopkins 
Published: July 2002

ABSTRACT

There is a pressing need for drugs effective against the opportunistic protozoan pathogen
Cryptosporidium parvum
. Folate metabolic enzymes and enzymes of the thymidylate cycle, particularly dihydrofolate reductase (DHFR), have been widely exploited as chemotherapeutic targets. Although many DHFR inhibitors have been synthesized, only a few have been tested against
C. parvum
. To expedite and facilitate the discovery of effective anti-
Cryptosporidium
antifolates, we have developed a rapid and facile method to screen potential inhibitors of
C. parvum
DHFR using the model eukaryote,
Saccharomyces cerevisiae
. We expressed the DHFR genes of
C. parvum
,
Plasmodium falciparum
,
Toxoplasma gondii
,
Pneumocystis carinii
, and humans in the same DHFR-deficient yeast strain and observed that each heterologous enzyme complemented the yeast DHFR deficiency. In this work we describe our use of the complementation system to screen known DHFR inhibitors and our discovery of several compounds that inhibited the growth of yeast reliant on the
C. parvum
enzyme. These same compounds were also potent or selective inhibitors of the purified recombinant
C. parvum
DHFR enzyme. Six novel lipophilic DHFR inhibitors potently inhibited the growth of yeast expressing
C. parvum
DHFR. However, the inhibition was nonselective, as these compounds also strongly inhibited the growth of yeast dependent on the human enzyme. Conversely, the antibacterial DHFR inhibitor trimethoprim and two close structural analogs were highly selective, but weak, inhibitors of yeast complemented by the
C. parvum
enzyme. Future chemical refinement of the potent and selective lead compounds identified in this study may allow the design of an efficacious antifolate drug for the treatment of cryptosporidiosis.
Evernimicin (SCH27899) Inhibits both Translation and 50S Ribosomal Subunit Formation in
Staphylococcus aureus
Cells
Authors: Champney W. Scott , Tober Craig L. 
Published: July 2002

ABSTRACT

The effects of the everninomicin antibiotic evernimicin (SCH27899) on growing
Staphylococcus aureus
cells were investigated. Cellular growth rates and viable cell numbers decreased with increasing antibiotic concentrations. The rate of protein synthesis, measured as
35
S-amino acid incorporation, declined in parallel with the growth rate. Significantly, the formation of the 50S ribosomal subunit was inhibited in a dose-dependent fashion as well. 30S ribosomal subunit synthesis was not affected over the same concentration range. Evernimicin did not stimulate the breakdown of mature ribosomal subunits. Pulse-chase labeling experiments revealed a reduced rate of 50S subunit formation in drug-treated cells. Two erythromycin-resistant strains of
S. aureus
that carried the
ermC
gene were as sensitive as wild-type cells to antibiotic inhibition. In addition, two methicillin-resistant
S. aureus
organisms, one sensitive to erythromycin and one resistant to the macrolide, showed similar sensitivities to evernimicin. These results suggest a use for this novel antimicrobial agent against antibiotic-resistant bacterial infections.
Phenotypic Expression of Oxacillin Resistance in
Staphylococcus epidermidis
: Roles of
mecA
Transcriptional Regulation and Resistant-Subpopulation Selection
Authors: Dickinson Tanja M. , Archer Gordon L. 
Published: July 2002

ABSTRACT

The MICs for many oxacillin-resistant (OR)
Staphylococcus epidermidis
(ORSE) strains are below the
Staphylococcus aureus
methicillin or oxacillin resistance breakpoint. The difficulty detecting the OR phenotype in
S. epidermidis
may be due to extreme heterotypy in resistance expression and/or transcriptional repression of
mecA
, the OR gene, by MecI. To determine the role of these factors in the phenotypic expression of ORSE, 17 geographically diverse
mecI
+
ORSE isolates representing 14 distinct pulsed-field gel electrophoresis pulse types (>3 band differences) were investigated. Thirteen of the 14 types contained
mecI
and
mecA
promoter-operator sequences known to be associated with maximal
mecA
repression, and in all isolates,
mecA
transcription was repressed. All 17 were heterotypic in their resistance expression. Oxacillin MICs ranged from 1 to 128 μg/ml and increased for 16 of 17 isolates after β-lactam induction. Allelic replacement inactivation of
mecI
in three isolates similarly resulted in a four- to sevenfold increase in MIC. In the two of these three isolates producing β-lactamase,
mecA
transcription was regulated by both
mecI
and β-lactamase regulatory sequences. Heterotypic expression of resistance in these three isolates was unaffected by either β-lactam induction or
mecI
inactivation. However, prolonged incubation in concentrations of oxacillin just sufficient to produce a lag in growth (0.5 to 1.0 μg/ml) converted the population resistance expression from heterotypic to homotypic. Homotypic conversion could also be demonstrated in microtiter wells during MIC determinations in one isolate for which the MIC was high. We conclude that the phenotypic expression of
S. epidermidis
OR in broth can be affected both by
mecA
transcriptional regulation and by subpopulation resistance expression.
Interactions of Ofloxacin and Erythromycin with the Multidrug Resistance Protein (MRP) in MRP-Overexpressing Human Leukemia Cells
Authors: Terashi Kenji , Oka Mikio , Soda Hiroshi , Fukuda Minoru , Kawabata Shigeru , Nakatomi Katsumi , Shiozawa Ken , Nakamura Takashi , Tsukamoto Kazuhiro , Noguchi Yuji , Suenaga Mitsuhiro , Tei Chuwa , Kohno Shigeru 
Published: July 2002

ABSTRACT
To investigate interactions between the multidrug resistance protein (MRP) and antimicrobial agents, we examined the effects of 12 agents on vincristine sensitivity and efflux of the calcein acetoxy-methyl ester (calcein-AM) of a MRP substrate in MRP-overexpressing cells. Only ofloxacin and erythromycin enhanced sensitivity with increased intracellular vincristine accumulation and inhibited the calcein-AM efflux. Our findings suggest that the two agents are possible MRP substrates and may competitively inhibit MRP function as a drug efflux pump.
Single-Oral-Dose Azithromycin Prophylaxis against Experimental Streptococcal or Staphylococcal Aortic Valve Endocarditis
Authors: Tsitsika Artemis , Pefanis Angelos , Perdikaris George S. , Donta Ismini , Karayiannakos Panayiotis , Giamarellou Helen 
Published: July 2002

ABSTRACT

Azithromycin and ampicillin protected 94 and 72% of animals challenged with
Streptococcus oralis
, respectively (
P
= 0.177), while azithromycin and vancomycin protected 59 and 94% of the methicillin-resistant
Staphylococcus aureus
(MRSA)-challenged animals, respectively (
P
= 0.018). Azithromycin is effective in preventing experimental streptococcal endocarditis, but against MRSA it is less effective than vancomycin.
In Vitro Activities of MK-826 (L-749,345) against 363 Strains of Anaerobic Bacteria
Authors: Wexler Hannah M. , Molitoris Denise , Finegold Sydney M. 
Published: July 2002

ABSTRACT

The activity of MK-826 was compared to the activities of cefoxitin, ceftriaxone, imipenem, and meropenem against 363 gram-negative and gram-positive anaerobes by using NCCLS procedures. At least 98% of the strains were susceptible to the carbapenems. All strains of
Clostridium perfringens
,
Fusobacterium nucleatum
,
Peptostreptococcus
, and
Sutterella wadsworthensis
were susceptible to all agents tested.
Antimalarial Activities of Peptide Antibiotics Isolated from Fungi
Authors: Nagaraj G. , Uma M. V. , Shivayogi M. S. , Balaram Hemalatha 
Published: July 2002

ABSTRACT

Malaria caused by
Plasmodium falciparum
is a major public health problem in the developing countries of the world. Clinical treatment of malaria has become complicated due to the occurrence of infections caused by drug resistant parasites. Secondary metabolites from fungi are an attractive source of chemotherapeutic agents. This work reports the isolation and in vitro antiplasmodial activities of peptide antibiotics of fungal origin. The three peptide antibiotics used in this study were efrapeptins, zervamicins, and antiamoebin. The high-performance liquid chromatography-purified peptides were characterized by nuclear magnetic resonance and mass spectral analysis. All three fungal peptides kill
P. falciparum
in culture with 50% inhibitory concentrations in the micromolar range. A possible mode of action of these peptide antibiotics on
P. falciparum
is presented.
Determination of Dosing Guidelines for Stavudine (2′,3′-Didehydro-3′-Deoxythymidine) in Children with Human Immunodeficiency Virus Infection
Authors: Kaul Sanjeev , Kline Mark W. , Church Joseph A. , Dunkle Lisa M. 
Published: July 2002

ABSTRACT

The results of the development of dosing guidelines for stavudine in human immunodeficiency virus (HIV)-infected children are summarized. Included in the integrated analyses were 21 and 33 HIV-infected pediatric and adult patients, respectively, from three phase I-II studies. Data for 21 children and 18 adults who received intravenous doses of 0.125 to 2 and 0.5 to 1 mg/kg of body weight, respectively, were used for the determination of dosing guidelines; exposure data for 16 children and 15 adults who received oral doses of 1 to 2 and 0.5 to 1 mg/kg/day, respectively, were used to validate the dosing recommendations for children. Significant relationships were observed between total body clearance (in milliliters per minute) in children and adults combined and demographic parameters of age, body weight, and body surface area (
R
2
= 0.77 to 0.80;
P
= 0.0001). Models of approximated pediatric dose based on clearance values and direct adult exposure yielded a stavudine dosage of 2 mg/kg/day for children of ≤30 kg of body weight and 1 mg/kg/day (adult dose) for children of >30 kg of body weight.
In Vitro Development of Resistance to Six Quinolones in
Streptococcus pneumoniae, Streptococcus pyogenes
, and
Staphylococcus aureus
Authors: Boos Mechthild , Mayer Susanne , Fischer Ansgar , Köhrer Karl , Scheuring Sibylle , Heisig Peter , Verhoef Jan , Fluit Ad C. , Schmitz F.-J. 
Published: July 2002

ABSTRACT

Streptococcus pneumoniae, Streptococcus pyogenes
, and
Staphylococcus aureus
isolates were exposed to subinhibitory MICs of ciprofloxacin, sparfloxacin, gatifloxacin, moxifloxacin, clinafloxacin, and gemifloxacin during a 10-day period. Subculturing led to resistance development, regardless of the initial potencies of the quinolones. None of the quinolones was associated with a significantly slower rate of resistance development.
Development of a Whole-Cell Assay for Peptidoglycan Biosynthesis Inhibitors
Authors: Barbosa Maria D. F. S. , Yang Gaoyun , Fang Jie , Kurilla Michael G. , Pompliano David L. 
Published: July 2002

ABSTRACT

Osmotically stabilized
Escherichia coli
cells subjected to freezing and thawing were utilized as the source of enzymes for a peptidoglycan pathway assay that can be used to simultaneously test all targets of the committed steps of cell wall biosynthesis. The use of
14
C-labeled UDP-
N
-acetylglucosamine (UDP-GlcNAc) as a substrate allows the direct detection of cross-linked peptidoglycan formed. The assay was validated with known antibiotics. Fosfomycin was the strongest inhibitor of the pathway assay, with a 50% inhibitory concentration of 1 μM. Flavomycin, bacitracin, vancomycin,
d
-cycloserine, penicillin G, and ampicillin also inhibited formation of radiolabeled peptidoglycan by the
E. coli
cells. Screening of compounds identified two inhibitors of the pathway, Cpd1 and Cpd2. Subsequent tests with a biochemical assay utilizing purified enzyme implicated UDP-GlcNAc enolpyruvyl transferase (MurA) as the target of Cpd1. This compound inhibits the first enzyme of the pathway in a time-dependent manner. Moreover, enzyme inactivation is dependent on preincubation in the presence of UDP-GlcNAc, which forms a complex with MurA, exposing its active site. Cpd1 also displayed antimicrobial activity against a panel of microorganisms. The pathway assay used in conjunction with assays for individual enzymes provides an efficient means of detecting and characterizing novel antimicrobial agents.
Characterization of Imidazo[4,5-
d
]Pyridazine Nucleosides as Modulators of Unwinding Reaction Mediated by West Nile Virus Nucleoside Triphosphatase/Helicase: Evidence for Activity on the Level of Substrate and/or Enzyme
Authors: Borowski Peter , Lang Melanie , Haag Annemarie , Schmitz Herbert , Choe Joonho , Chen Huan-Ming , Hosmane Ramachandra S. 
Published: July 2002

ABSTRACT

Compounds that interact with DNA or RNA generally act as inhibitors of enzymes that unwind DNA or RNA. In the present study we describe the synthesis and properties of some nucleoside analogues that interact with double-stranded DNA but that, in contrast, facilitate the unwinding reaction mediated by West Nile (WN) virus nucleoside triphosphatase (NTPase)/helicase. The nucleoside analogues described, 1-(2′-
O
-methyl-β-
d
-ribofuranosyl)imidazo[4,5-
d
]pyridazine-4,7(5
H
,6
H
)-dione (HMC-HO4), 1-(β-
d
-ribofuranosyl)imidazo[4,5-
d
]pyridazine-4,7(5
H
,6
H
)-dione, and 1-(2′-deoxy-α-
d
-ribofuranosyl)imidazo[4,5-
d
]pyridazine-4,7(5
H
,6
H
)dione, all contain the imidazo[4,5-
d
]pyridazine ring system. The extent of the enhancing effect on helicase activity was found to be dependent on the time of exposure of the DNA substrate to the compounds and their concentrations. The nucleoside analogues were nevertheless found to be capable of uncoupling the ATPase and helicase activities of the enzyme by a mechanism operating on the level of the enzyme. Thus, in the case of HMC-HO4, the direct interaction with the enzyme caused inhibition of its helicase activity, with a half-maximal inhibitory concentration of 30 μM. The similar potency of the compound against replication of WN virus in cell culture suggests that inhibition of the helicase activity of the viral enzyme is responsible for the observed antiviral activity of HMC-HO4 and may indeed represent an important mode of action of antiviral drugs in general. Comparative studies performed with the related NTPase/helicase from hepatitis C virus revealed that the extent of the effects mediated by imidazo[4,5-
d
]pyridazine nucleosides is enzyme specific. The substances described may represent a starting point for the development of a new class of helicase-specific antivirals.
Purification and Characterization of
Streptomyces griseus
Catechol
O
-Methyltransferase
Authors: Dhar Kajari , Rosazza John P. N. 
Published: July 2002

ABSTRACT

A soluble (100,000 ×
g
supernatant) methyltransferase catalyzing the transfer of the methyl group of
S
-adenosyl-
l
-methionine to catechols was present in cell extracts of
Streptomyces griseus
. A simple, general, and rapid catechol-based assay method was devised for enzyme purification and characterization. The enzyme was purified 141-fold by precipitation with ammonium sulfate and successive chromatography over columns of DEAE-cellulose, DEAE-Sepharose, and Sephacryl S-200. The purified cytoplasmic enzyme required 10 mM magnesium for maximal activity and was catalytically optimal at pH 7.5 and 35°C. The methyltransferase had an apparent molecular mass of 36 kDa for both the native and denatured protein, with a pI of 4.4. Novel N-terminal and internal amino acid sequences were determined as DFVLDNEGNPLENNGGYXYI and RPDFXLEPPYTGPXKARIIRYFY, respectively. For this enzyme, the

K
m

for 6,7-dihydroxycoumarin was 500 ± 21.5 μM, and that for
S
-adenosyl-
l
-methionine was 600 ± 32.5 μM. Catechol, caffeic acid, and 4-nitrocatechol were methyltransferase substrates. Homocysteine was a competitive inhibitor of
S
-adenosyl-
l
-methionine, with a

K
i

of 224 ± 20.6 μM. Sinefungin and
S
-adenosylhomocysteine inhibited methylation, and the enzyme was inactivated by Hg
2+
,
p
-chloromercuribenzoic acid, and
N
-ethylmaleimide.
In Situ Determination of Sulfide Turnover Rates in a Meromictic Alpine Lake
Authors: Lüthy Lucas , Fritz Markus , Bachofen Reinhard 
Published: July 2002

ABSTRACT
A push-pull method, previously used in groundwater analyses, was successfully adapted for measuring sulfide turnover rates in situ at different depths in the meromictic Lake Cadagno. In the layer of phototrophic bacteria at about 12 m in depth net sulfide consumption was observed during the day, indicating active bacterial photosynthesis. During the night the sulfide turnover rates were positive, indicating a net sulfide production from the reduction of more-oxidized sulfur compounds. Because of lack of light, no photosynthesis takes place in the monimolimnion; thus, only sulfide formation is observed both during the day and the night. Sulfide turnover rates in the oxic mixolimnion were always positive as sulfide is spontaneously oxidized by oxygen and as the rates of sulfide oxidation depend on the oxygen concentrations present. Sulfide oxidation by chemolithotrophic bacteria may occur at the oxicline, but this cannot be distinguished from spontaneous chemical oxidation.
Diversity of Infectious Pancreatic Necrosis Virus Strains Isolated from Fish, Shellfish, and Other Reservoirs in Northwestern Spain
Authors: Cutrin J. M. , Olveira J. G. , Barja J. L. , Dopazo C. P. 
Published: July 2002

ABSTRACT
A comparison was done of 231 strains of birnavirus isolated from fish, shellfish, and other reservoirs in a survey study that began in 1986 in Galicia (northwestern Spain). Reference strains from all of the infectious pancreatic necrosis virus serotypes were included in the comparison, which was done by neutralization tests and agarose and polyacrylamide gel electrophoresis of the viral genome. The neutralization tests with antisera against the West Buxton, Spajarup (Sp), and Abild (Ab) strains showed that most of the Galician isolates were European types Sp and Ab; however, many isolates (30%) could not be typed. Results from agarose gels did not provided information for grouping of the strains, since all were found to have genomic segments of similar sizes. Analysis of polyacrylamide gels, however, allowed six electropherogroups (EGs) to be differentiated on the basis of genome mobility and separation among segments, and a certain relationship between EGs and serotypes was observed. A wide diversity of electropherotypes was observed among the Galician isolates, and as neutralization tests showed, most of the isolates were included in EGs corresponding to European types Ab and Sp. Only 6.5% of the isolates had the electropherotype characteristic of American strains.
Production of Pectate Lyases and Cellulases by
Chryseomonas luteola
Strain MFCL0 Depends on the Growth Temperature and the Nature of the Culture Medium: Evidence for Two Critical Temperatures
Authors: Laurent P. , Buchon L. , Guespin-Michel J. F. , Orange N. 
Published: July 2002

ABSTRACT

Several extracellular enzymes that are responsible for plant tissue maceration were detected in culture supernatant of the psychrotrophic bacterium
Chryseomonas luteola
MFCL0. Isoelectrofocusing experiments showed that pectate lyase (PL) activity resulted from the cumulative action of three major isoenzymes, designated PLI, PLII, and PLIII. Cellulolytic activity was also detected in culture supernatants. These enzymes exhibited different behaviors with respect to growth temperature. PLII was not regulated by temperature, whereas PLI and PLIII were regulated similarly by growth temperature. Maximal levels of PLI and PLIII were produced at 14°C when cells were grown in polygalacturonate-containing synthetic medium and at around 20 to 24°C in nutrient broth. In contrast, thermoregulation of cellulolytic activity production differed from thermoregulation of PL. The level of cellulolytic activity was low in all media at temperatures up to 20°C, and then it increased dramatically until the temperature was 28°C, which is the optimal temperature for growth of
C. luteola
. Previously, we defined the critical temperature by using the modified Arrhenius equation to characterize bacterial behavior. This approach consists of monitoring changes in the maximal specific growth rate as a function of temperature. Our most striking result was the finding that the temperature at which maximum levels of PLI and PLIII were produced in two different media was the same as the critical temperature for growth observed in these two media.