Helen Petach

Helen Petach
United States Agency for International Development (USAID) | USAID

About

30
Publications
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1,169
Citations

Publications

Publications (30)
Article
Full-text available
The adoption of clean cooking technologies goes beyond mere product acquisition and requires attention to issues of cooking traditions, user engagement, gender dynamics, culture, and religion to effect correct and consistent use.
Article
Full-text available
Improvements of water, sanitation, and hygiene (WASH) infrastructure and appropriate health-seeking behavior are necessary for achieving sustained control, elimination, or eradication of many neglected tropical diseases (NTDs). Indeed, the global strategies to fight NTDs include provision of WASH, but few programs have specific WASH targets and app...
Article
Using archival data from the Spitzer and GALEX Space Telescopes we have plotted a UV-IR color-magnitude diagram for AGN. The previous difficulty in determining the IR luminosity of AGN using this technique has been that AGN have varying levels of obscuration in the UV, also they are variable and previous observations were often taken at widely diff...
Article
The NITARP (NASA IPAC Teacher Archive Research Project) program provides a link between NASA researchers and high school teachers and students. This past year the Luminous Data Miners (LDM) developed and implemented a research plan to investigate whether the UV light emitted from the accretion disk of an Active Galactic Nucleus (AGN) is correlated...
Article
Multiplexed photoaptamer-based arrays that allow for the simultaneous measurement of multiple proteins of interest in serum samples are described. Since photoaptamers covalently bind to their target analytes before fluorescent signal detection, the arrays can be vigorously washed to remove background proteins, providing the potential for superior s...
Article
Photoaptamers are single-stranded nucleic acids selected for their high affinity to specific proteins of interest. Photoaptamer microarrays capture and quantify proteins from complex samples using a unique protocol that leverages both high-affinity capture with covalent retention of analytes. The initial capture of proteins from solution is similar...
Article
The development of high-density arrays for proteomics has become a goal of SomaLogic, many other companies, and a wide variety of academic entities. Unfortunately, the word proteomics has come to mean virtually everything. We define proteomics as being derived from arrays of analyte-specific reagents (ASRs) used to measure (something about) protein...
Article
The in vitro activity of arginase (EC 3.5.3.1) was investigated in youngest-mature leaves and roots (1-3 mm diameter) of kiwifruit vines (Actinidia deliciosa var. deliciosa) during an annual growth cycle, and enzyme from root material partially purified. No seasonal trend in the specific activity of arginase was observed in roots. Measurements in l...
Article
Now that enzymes are available that are stable above 100 degrees C it is possible to investigate conformational stability at this temperature, and also the effect of high-temperature degradative reactions in functioning enzymes and the inter-relationship between degradation and denaturation. The conformational stability of proteins depends upon sta...
Article
Now that enzymes are available that are stable above 100 °C it is possible to investigate conformational stability at this temperature, and also the effect of high-temperature degradative reactions in functioning enzymes and the inter-relationship between degradation and denaturation. The conformational stability of proteins depends upon stabilizin...
Article
The use of tris(hydroxymethyl)phosphine as a coupling reagent for the immobilization of alcohol dehydrogenase onto chitosan films and for the attachment of the chitosan film to a glass support resulted in enzyme activities far above those obtained by adsorption of enzyme, and greater than those observed when using the more conventional glutaraldehy...
Article
An extracellular alpha-glucosidase from the thermophilic archaebacterium Thermococcus strain AN1 was purified 875-fold in five steps (Hiload Q-Sepharose, phenyl Sepharose, HPHT-hydroxyapatite, gel filtration and Mono Q chromatography) with a yield of 4%. It is a monomer with a molecular mass of about 60 kDa and a pI around 5. At 98 degrees C, the p...
Article
An extracellular α-glucosidase from the thermophilic archaebacterium Thermococcus strain AN1 was purified 875-fold in five steps (Hiload Q-Sepharose, phenyl Sepharose, HPHT-hydroxyapatite, gel filtration and Mono Q chromatography) with a yield of 4%. It is a monomer with a molecular mass of about 60 kDa and a pI around 5. At 98°C, the purified enzy...
Article
The condensation reactions between tris(hydroxymethyl)phosphine, P(CH2OH)3, and either 1,6-diaminohexane or the trifunctional polyetheramine Jeffamine T-403 produce polymeric aminomethyl phosphines containing excess NH2 groups. These polymers, after oxidation to the phosphine oxides, can be used as supports for enzyme immobilization. Immobilised ur...
Article
A novel polymeric phosphine oxide-derived support for enzyme immobilization was synthesized by Mannich condensation of P(CH2OH)3 with a polyetheramine. The high-surface-area particles were smooth at high magnification and resisted adsorption of protein. Urease was linked to the support by glutaraldehyde coupling onto the polyetheramine, a flexible...
Article
Polymer films formed by the condensation of polyetheramines with P(CH2OH)3 were synthesized and covalently coupled to the enzyme urease via the intrinsic reactive PCH2OH hydroxyl groups. Urease activities of 1,140 U g−1 and 5.5 U cm−2 of polymer film were achieved without any additional coupling agents. Upon oxidation of the phosphorus, the intrin...
Article
The stability of two enzymes from extreme thermophiles (glutamate dehydrogenase from Thermococcales strain AN1 and beta-glucosidase from Caldocellum saccharolyticum expressed in Escherichia coli) has been exploited to allow measurement of activity over a 175 degrees C temperature range, from +90 degrees C to -85 degrees C for the glutamate dehydrog...
Article
The synthesis of an heterogeneous peptide substrate for the assay of proteases was carried out by cleaving a protein using a protease to generate small peptides which were then coupled to a chromophore, p-nitroaniline. The chromophoric peptide product could be used to assay for the protease which produced the original peptides.
Article
The paper presents the study comparing the activity of glutamate dehydrogenase (GDH) on a variety of transparent chitosan derivatives which provide different chemical environments for the immobilized GDH. The amino group of the chitosan was modified to produce succinyl-, glutaryl-, and phthalyl-derivatives, thus changing the close association of th...
Article
Tris(hydroxymethyl)phosphine, P(CH2OH)3, can be used as an effective new type of coupling agent for the immobilisation of enzymes to amino-group-containing supports.
Article
The detection of sulfhydryl groups in proteins is limited by the inaccessibility of the sulfhydryls to the reagent, 5,5′-dithiobis(2-nitrobenzoic acid). The addition of other disulfides such as 2,2′-dithiobis(ethylamine) to the chromophoric disulfide increases both the rate and the extent of detection of “buried” sulfhydryl groups in proteins.
Article
Synthesis of a novel polymeric support by Mannich condensation of P(CH2OH)3 with a polyetheramine provides flexible side chains for enzyme immobilisation without loss of catalytic activity.
Article
This paper reports that covalently linked bipyridyl ligands (L-L) with alkyl linkages varying from (-CH[sub 2]-)[sub 2] to (-CH[sub 2]-)[sub 12] were used to prepare ruthenium oxo dimers of the form [bpy (H[sub 2]O)RuO(L-L)Ru(H[sub 2]O) (bpy)][sup 4+]. The bridging alkyl linkage increased the stability of these oxo dimers by maintaining the relativ...
Article
Adsorbed monolayers of [Ru(bpy)2(bpy-(CH2)x-bpy)]2+ (x = 4 and 5) on the unreconstructed square-root 3 x 22 reconstructed surfaces of Au(111) were imaged by scanning tunneling microscopy in dimethylformamide. On the reconstructed surface, the adsorbed films display highly ordered patterns that are commensurate with the measured corrugation patterns...
Article
The ancillary character of the 6,6-dimethylcyclohexadienyl ligand (dmCh) was examined via the syntheses of various (dmCh)MoLn derivatives. Treatment of (diglyme)Mo(CO)3 with K(dmCh) afforded [K(diglyme)n][dmCh)Mo(CO)3] (1, 85%), which was converted to (dmCh)Mo(CO)3I (2) by I2 in low yield. The addition of HgI2 to 2.0 equiv of 1 produced [(dmCh)Mo(C...

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