Search results for: Andrei Blasko

Items from 1 to 16 out of 16 results

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Two-Dimensional Liquid Chromatography (2D-LC) in Pharmaceutical Analysis: Applications Beyond Increasing Peak Capacity

Imad A. Haidar Ahmad, Andrei Blasko, Adrian Clarke, Shereen Fakih

Chromatographia > 2018 > 81 > 3 > 401-418

One-dimensional liquid chromatography (1D-LC) is not always capable of efficiently separating complex samples. This drawback is not solely due to the lack of column efficiency, but is mainly due to insufficient selectivity and the need to separate the analytes of interest with orthogonal retention mechanisms. In this regard, two-dimensional liquid chromatography (2D-LC) is currently attracting much...

article

Cleaning verification: A five parameter study of a Total Organic Carbon method development and validation for the cleaning assessment of residual detergents in manufacturing equipment

Xue Li, Imad A. Haidar Ahmad, James Tam, Yan Wang, more

Journal of Pharmaceutical and Biomedical Analysis > 2018 > 149 > C > 33-39

A Total Organic Carbon (TOC) based analytical method to quantitate trace residues of clean-in-place (CIP) detergents CIP100^® and CIP200^® on the surfaces of pharmaceutical manufacturing equipment was developed and validated. Five factors affecting the development and validation of the method were identified: diluent composition, diluent volume, extraction method, location for TOC sample preparation,...

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A simplified guide for charged aerosol detection of non-chromophoric compounds—Analytical method development and validation for the HPLC assay of aerosol particle size distribution for amikacin

Arianne Soliven, Imad A. Haidar Ahmad, James Tam, Nani Kadrichu, more

Journal of Pharmaceutical and Biomedical Analysis > 2017 > 143 > C > 68-76

Amikacin, an aminoglycoside antibiotic lacking a UV chromophore, was developed into a drug product for delivery by inhalation. A robust method for amikacin assay analysis and aerosol particle size distribution (aPSD) determination, with comparable performance to the conventional UV detector was developed using a charged aerosol detector (CAD). The CAD approach involved more parameters for optimization...

article

A 14 Parameter Study of UHPLC’s for Method Development Transfer and Troubleshooting

Imad A. Haidar Ahmad, Frank Hrovat, Arianne Soliven, Adrian Clarke, more

Chromatographia > 2017 > 80 > 8 > 1143-1159

Five ultra-high pressure liquid chromatography (UHPLC) instruments were compared to one another by examining the overall system performance and key functions of the system parts including: pump, auto-sampler, thermo-stated column compartment, and the detector. The five UHPLC systems used in this study were: ThermoFisher Vanquish, Agilent 1290 Infinity I, Agilent 1290 Infinity II, Waters Acquity I-Class,...

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Cleaning verification: Exploring the effect of the cleanliness of stainless steel surface on sample recovery

Imad A. Haidar Ahmad, James Tam, Xue Li, William Duffield, more

Journal of Pharmaceutical and Biomedical Analysis > 2017 > 134 > C > 108-115

The parameters affecting the recovery of pharmaceutical residues from the surface of stainless steel coupons for quantitative cleaning verification method development have been studied, including active pharmaceutical ingredient (API) level, spiking procedure, API/excipient ratio, analyst-to-analyst variability, inter-day variability, and cleaning procedure of the coupons. The lack of a well-defined...

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Revisiting the Solubility Concept of Pharmaceutical Compounds

Andrei Blasko, Alana Leahy-Dios, William O. Nelson, Steven A. Austin, more

Monatshefte für Chemie - Chemical Monthly > 2001 > 132 > 7 > 789-798

Summary.The kinetic and thermodynamic solubilities of Roche (Ro) pharmaceutical compounds were determined by HPLC, titrimetry, and UV/Vis spectroscopy in aqueous buffers and in non-buffered systems. For kinetic solubility, a turbidimetric method that allows the rapid determination of solubilities using small amounts of compounds (550mg) was used. Two types of precipitation were observed during the...

article

Complexation of amino sugars with cobalt(III)bis(phenanthroline)

Sergio Bunel, Carmen Ibarra, Exequiel Moraga, Jose Parada, more

Carbohydrate Research > 1998 > 312 > 4 > 191-200

Complexes of Co(III)bis(phenanthroline) with β-d-mannosamine and α-d-galactosamine can be isolated as the triiodide salts. The complex with d-mannosamine has the Δ-configuration at Co(III). Complexation with d-galactoamine gives the Δ- in excess over the Λ- complex, and the Δ-complex can be isolated chromatographically. Complexation involves cis-1-OH and 2-NH ₂ groups, eq, ax respectively...

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Design, Synthesis, and Characterization of a Novel Hexa-azacyclophane and Interactions with d(CGCA ₃ T ₃ GCG) ₂ , ctDNA and T4DNA.

Thomas C. Bruice, Yu Chi Yip, Andrei Blaskó, Felice C. Lightstone, more

Tetrahedron > 1997 > 53 > 24 > 8105-8120

A novel polyazacyclophane hexa-amine (1) has been designed, synthesized and characterized by X-ray crystallography, ¹ H NMR and fluorescence spectroscopy. 1 has the structural shape and disposition of charges complementary to the major groove of B-DNA. Acid dissociation constants for the protonated 1 were pK _a ₁ (D) = 4.8 and pK _a ₂ (D) = 8.5. Equilibrium constants...

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A Microgonotropen Branched Decaaza Decabutylamine and its DNA and DNA/Transcription Factor Interactions

Thomas C. Bruice, Dipanjan Sengupta, Andrei Blaskó, S.-Y. Chiang, more

Bioorganic & Medicinal Chemistry > 1997 > 5 > 4 > 685-692

The central pyrrole of a site-selective DNA minor groove binding tripyrrole peptide 1 has been attached to a branched decaaza decabutylamine via a -(CH ₂ ) ₃ -NHCO-(CH ₂ ) ₃ - linker to provide the decaaza-microgonotropen (8). The decaaza decabutylamine moiety of 8 was designed to have a much greater affinity to the phosphodiester linkages of the backbone of DNA. Employing...

article

Determination of acid dissociation constants of anomers of amino sugars by ¹ H NMR spectroscopy

Andrei Blaskó, Clifford A. Bunton, Sergio Bunel, Carmen Ibarra, more

Carbohydrate Research > 1997 > 298 > 3 > 163-172

Acid dissociation constants of α- and β-d-glucos-, mannos-, and galactos-ammonium ions have been determined from ¹ H NMR chemical shifts of the individual anomers in D ₂ O. Values of pK _a (D) for the α- and β-ammonium ions are, respectively: glucosamine, 8.12 and 7.87, mannosamine, 7.78 and 8.50, galactosamine, 8.49 and 8.02. The differences are ascribed largely to differences...

article

A Microgonotropen Pentaaza Pentabutylamine and its Interactions with DNA

Dipanjan Sengupta, Andrei Blaskó, Thomas C. Bruice

Bioorganic & Medicinal Chemistry > 1996 > 4 > 6 > 803-813

The central pyrrole of a site-selective DNA minor groove binding tripyrrole peptide (1) has been attached to N-protected pentaazapentacosanoic acid (17) via a --(CH ₂ ) ₃ --NHCO--(CH ₂ ) ₃ -- linker to provide19 , subsequent deprotection provided the pentaaza microgonotropen 4. The polyamine moiety of 4 reaches out of the minor groove and binds to the phosphate backbone...

article

Complexes of Co(III) with l-sorbose and phenanthroline

Andrei Blaskó, Clifford A. Bunton, Exequiel Moraga, Sergio Bunel, more

Carbohydrate Research > 1995 > 278 > 2 > 315-328

l-Sorbose and two molecules of 1,10-phenanthroline form a complex with Co(III) which has the Λ configuration about Co(III), based on CD and ORD spectra. The ¹ H NMR signals of α-l-sorbopyranose and its mixed Co(III)(phen) ₂ complex have been assigned. Signals of H-6 and H-6 of the sugar are shifted strongly upfield because of shielding by the aromatic residues, but shifts are much...

article

NMR Structure of d(CGCA ₃ T ₃ GCG) ₂ : trenmicrogonotropen-b:Zn(II) complex and solution studies of metal ion complexes of tren-microgonotropen-b interacting with DNA

Andrei Blaskó, Kenneth A. Browne, Thomas C. Bruice

Bioorganic & Medicinal Chemistry > 1995 > 3 > 11 > 1563

article

Oxidations of Organic Sulfides in Aqueous Sulfobetaine Micelles

Andrei Blaskó, Clifford A. Bunton, Houshang J. Foroudian

Journal of Colloid And Interface Science > 1995 > 175 > 1 > 122-130

Zwitterionic micelles of N -tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB3-14) inhibit oxidations of 3-chloroethyl phenyl sulfide (PhSCH ₂ CH ₂ Cl) and 1-methoxy-4(methylthio)benzene (ArSMe) by peroxymonosulfate ion (HSO ^- ₅ ) and the periodate ion oxidation of ArSMe, but there are slow residual reactions of micellar-bound substrates. Measurements of the critical...

article

NMR Structure of d(CGCA ₃ T ₃ GCG) ₂ :Tren-Microgonotropen-b:Zn(II) Complex and Solution Studies of Metal Ion Complexes of Tren-Microgonotropen-b Interacting with DNA

Andrei Blaskó, Kenneth A. Browne, Thomas C. Bruice

Bioorganic & Medicinal Chemistry > 1995 > 3 > 6 > 631-646

The solution structure of a 1:1 complex of zinc tren-microgonotropen-b {6b:Zn(II)} with d(CGCAAATTTGCG) ₂ has been determined by 2D nuclear Overhauser effect ¹ H NMR spectroscopy and restrained molecular modeling. The exchangeable and nonexchangeable proton resonances of d(CGCA ₃ T ₃ GCG) ₂ :6b:Zn(II) indicate that the Zn(II) is interacting in the A+T-rich region...

article

Complexes of cobalt(III) with d-fructose and phenanthroline

Exequiel Moraga, Sergio Bunel, Carmen Ibarra, Andrei Blaskó, more

Carbohydrate Research > 1995 > 268 > 1 > 1-15

d-Fructose and 1,10-phenanthroline form complexes with Co(III). Configurations about Co(III) are assigned from the CD and ORD spectra of the separated Λ and Δ diastereomers, and Λ strongly predominates in the mixture. Most of the ¹ H NMR signals of the complexes are shifted strongly upfield, relative to those of d-fructose, due to shielding by aromatic residues, and the effect is especially...

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