Bertha C Valle

Texas Southern University, Houston, Texas, United States

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Publications (9)42 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Fluorescence, Phosphorescence, and Chemiluminescence cover a wide array of topics. One can simply examine the number of topics that arise from photon induced excitation and emission as summarized in Figure 1 to understand the magnitude of this overall topic. Thus, as in previous years, we are not able to provide extensive coverage of all developments of relevance to this extremely broad area of research. Instead, we have attempted to focus on important advances of general interest and relevance to the field of analytical chemistry. In addition, rather than cover extensions of previous advances, we have attempted to balance inclusion of a sufficient number of highly relevant, high-impact references to adequately survey the field with ample descriptions of individual citations for better clarification. If you feel that we have omitted an important article published during the above referenced time period, please forward the reference to the journal for inclusion in the next review.
    Analytical Chemistry 11/2015; DOI:10.1021/acs.analchem.5b04109 · 5.64 Impact Factor
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    ABSTRACT: As a result of change in due date, this review covers the one and two third-year period since our last review (1) from January 2010 through August 2011. Manuscripts outside this review period are only included if they have not been previously cited in the review. A computer search of Chemical Abstracts provided most of the references for this review. A search for documents written in English containing the terms "fluorescence or phosphorescence or chemiluminescence" published in 2010 to August 2011 resulted in more than 75,000 hits. An initial screening reduced this number to approximately 18,000 publications that were considered for inclusion in this review. Key word searches of this subset provided sub-topics of manageable sizes. Other citations were found through individual searches by the various authors who wrote a particular section of this review. In an effort to more effectively accomplish this goal, we have included authors who are knowledgeable in the various sub-topics of this review. Coverage is limited to articles that describe new developments in the theory and practice of molecular luminescence for chemical analysis in the ultraviolet, visible, and near-infrared region. We have included two new sections in this review on fluorescence nanoparticles and green chemistry. Discussions of cited work are intended to be more critical and focused than in previous reviews. In general, citations are limited to journal articles and do not include patents, proceedings, reports, and dissertations. In an effort to reduce the length of this review we have attempted to limit duplicate citations between sections by retaining the same reference number for a given citation which is cited under more than one heading. As in previous years, we are not able to provide extensive coverage of all developments of relevance to the extremely broad field of molecular fluorescence, phosphorescence, and chemiluminescence. Instead, we have focused on important advances of general interest and relevance to the field of analytical chemistry, rather than extensions of previous advances. In addition, we have attempted to balance inclusion of a sufficient number of highly relevant, high-impact references to adequately survey the field with ample descriptions of individual citations for better clarification. If you feel that we have omitted an important article published during the above referenced time period, please forward the reference to one of us and we will be certain to consider it for the next review.
    Analytical Chemistry 11/2011; 84(2):597-625. DOI:10.1021/ac202904n · 5.64 Impact Factor
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    ABSTRACT: Chiral separations employing four diastereomers of poly sodium N-undecanoyl leucylvalinate (p-SULV) as chiral selectors are probed by use of MEKC, steady-state fluorescence anisotropy, and NMR. By employing diastereomers and thus altering the stereochemistry of a single amino acid in a systematic way, one may control the enantiorecognition ability of the chiral selector. As a result, one can gain a better understanding of the mechanisms of chiral recognition for the two classes of neutral or anionic chiral analytes studied. Evaluation of the chiral interactions leading to chiral separations confirmed our earlier observation of a strong relationship between the selectivity (alpha) observed using a chromatographic separation technique (MEKC) and that determined from the spectroscopic parameter, beta. A linear alpha versus beta relationship was observed for the molecular micelle p-(L)-SULV with all eight analytes included in this study. However, as we earlier predicted, different groups of analytes had different slopes, i.e., values of m, suggesting different chiral separation mechanisms. Evaluation of the data allowed a grouping of the analytes according to the primary site of chiral interaction with the leucine or valine moiety of molecular micelle chiral headgroup.
    Langmuir 02/2007; 23(2):425-35. DOI:10.1021/la0612623 · 4.46 Impact Factor
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    ABSTRACT: NMR spectroscopy was used to investigate the association of four chiral molecules with the molecular micelle poly(sodium N-undecanoyl-l-leucylvalinate) (poly(SULV)). Adding poly(SULV) to the background electrolyte in electrokinetic chromatography (EKC) allows enantiomeric resolution to be achieved because enantiomers interact differentially with the chiral centers on the micelle headgroups as they both move in the electric field. Pulsed field gradient diffusion experiments were used to measure molecular micelle association constants for enantiomers of each analyte. These association constants were consistent with EKC elution order for the compounds 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BNP), 1,1'-bi-2-naphthol (BOH), and Troger's base. In addition, nuclear Overhauser enhancement spectroscopy, nuclear Overhauser effect difference, and intermolecular cross relaxation diffusion experiments were used to generate binding interaction maps for each chiral analyte. These maps showed that BNP and BOH inserted into the surfactant headgroup's major chiral groove and interacted predominately with the leucine chiral center. (+)-Troger's base was also found to insert into the major chiral groove. However, this compound instead interacted with the valine chiral atom. In diffusion experiments with long diffusion times, the linearized diffusion plots for each analyte-molecular micelle mixture showed curvature characteristic of intermolecular cross relaxation. The magnitude of this effect scaled linearly with the analytes' free energies of binding.
    The Journal of Physical Chemistry B 10/2006; 110(35):17359-69. DOI:10.1021/jp0627224 · 3.30 Impact Factor
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    ABSTRACT: A cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) method was applied to the enantioseparation of three binaphthyl derivatives using neutral CDs (i.e., beta- and gamma-CD) in combination with various chiral amino acid-based polymeric surfactants (PSs). Both the D- and L-configurations of poly(sodium N-undecanoyl alaninate), poly(sodium N-undecanoyl leucinate), and poly(sodium N-undecanoyl valinate) (poly(L-SUV)) were synthesized. The retention behavior of the three binaphthyl derivatives under optimum electrophoretic conditions using a single chiral additive (PS or CD) is discussed. In addition, the effect of CD cavity size and stereochemical configuration of polymeric surfactants on selectivity (alpha) and resolution (Rs) was investigated. The enantioseparation of (+/-)1,1'-binaphthyl-2,2'-diamine gave a reversal of enantiomeric order when using beta-CD in combination with any of the three D-configuration PS. However, better enantioseparation is obtained when using the corresponding L-configuration PS with beta-CD. A reversal of migration order (RMO) for the enantiomers of (+/-)1,1'-bi-2-naphthol was observed upon the addition of 10 mM gamma-CD to poly(L-SUV). However, no RMO of (+/-)1,1'-bi-2-naphthol was seen when either beta-CD or gamma-CD was combined with D-PS. The enantiomers of (+/-)1,1'-binaphthyl-2,2'-diyl hydrogen phosphate showed little enantioselective behavior toward the PS alone. However, combined D- or L-PS and beta-CD or gamma-CD systems gave increased Rs and alpha values. The chiral recognition of binaphthyl derivatives observed resulting from the various combinations of two chiral selectors is discussed.
    Electrophoresis 02/2004; 25(4-5):743-52. DOI:10.1002/elps.200305726 · 3.03 Impact Factor
  • Constantina P Kapnissi · Bertha C Valle · Isiah M Warner ·
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    ABSTRACT: In this study, fused-silica capillaries are modified using a polyelectrolyte multilayer (PEM) coating procedure in open-tubular capillary electrochromatography. The PEM coating was constructed in situ with alternating rinses of positively and negatively charged polymers. The quaternary ammonium salt poly (diallyldimethylammonium chloride) was used as the cationic polymer, and the polymeric surfactant poly (sodium N-undecanoyl-l-leucylvalinate) was used as the anionic polymer. Previous studies have shown that the PEM-coated capillaries used for achiral separations have excellent reproducibilities and high stabilities against extreme pH values. In the current study, this PEM coating approach was applied to chiral separations of 1,1'-binaphthyl-2,2'-dihydrogenphosphate (BNP), 1,1'-bi-2-naphthol, secobarbital, pentobarbital, and temazepam. However, the PEM coating procedure used in the achiral studies needed to be significantly modified in order to achieve chiral separations. Optimal conditions were established by varying the additives (sodium chloride, 1-ethyl-3-methyl-1H-imidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate) in the polymer deposition solutions, the salt concentration, the column temperature, and the bilayer number. Reproducibilities were evaluated by use of the relative standard deviation (RSD) values of the electroosmotic flow (EOF) and the first peak ((R)-(+)-BNP). In all cases, the run-to-run and capillary-to-capillary RSD values of EOF were less than 0.5%, and the run-to-run RSD values of the (R)-(+)-BNP peak were less than 1%. In addition, more than 230 runs were performed on a single PEM-coated capillary.
    Analytical Chemistry 12/2003; 75(22):6097-104. DOI:10.1021/ac034452g · 5.64 Impact Factor
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    ABSTRACT: This study examines the role of steric hindrance near the stereogenic centers of four glutamic acid based polymeric surfactants. The single amino acid surfactants of glutamic acid, glutamic acid methyl ester, glutamic ethyl ester, and glutamic acid tert-butyl ester were investigated. The micellar electrokinetic chromatography (MEKC) separation of three binaphthyl derivatives and three benzodiazepines were used to study these steric factors. In addition, the hydrophobicity of these polymers as a function of pH was investigated by use of fluorescence measurements.
    Electrophoresis 03/2003; 24(6):1077-82. DOI:10.1002/elps.200390125 · 3.03 Impact Factor
  • Shahab A Shamsi · Bertha C Valle · Fereshteh Billiot · Isiah M Warner ·
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    ABSTRACT: Dipeptide micelle polymers are a new class of polymeric surfactants of which the polysodium undecanoyl-L-leucylvalinate (poly-L-SULV) was found to be a broadly applicable chiral selector for micellar electrokinetic chromatography. This negatively charged dipeptide micelle polymer is a high molecular weight compound with large countercurrent mobility, zero critical micelle concentration, low aggregation number, and high solubility in water or water-organic solvents. In an extensive chiral screening program, enantioseparation of 75 racemic compounds was tested with poly-L-SULV as chiral pseudostationary phase in neutral pH and basic pH background electrolytes. A total of 58 out of 75 racemic compounds could be resolved after choosing an appropriate concentration of poly-L-SULV. Although anionic chiral analytes are difficult to resolve using poly-L-SULV, the percent success rate for chiral resolution of cationic (77%) and neutral (85%) racemates was very high. Aspects regarding electrostatic, steric, hydrophobic, and hydrogen-bonding interactions of this dipeptide micelle polymer with various classes of chiral analytes are discussed.
    Analytical Chemistry 03/2003; 75(3):379-87. DOI:10.1021/ac020386r · 5.64 Impact Factor
  • Xiaofeng Zhu · Serigne Thiam · Bertha C Valle · Isiah M Warner ·
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    ABSTRACT: A colloidal graphite-coated emitter is introduced for sheathless capillary electrophoresis/nanoelectrospray ionization time-of-flight mass spectrometry (CE/ESI-TOFMS). The conductive coating can be produced by brushing the capillary tip to construct a fine layer of 2-propanol-based colloidal graphite. The fabrication involves a single step and requires less than 2 min. Full cure properties develop in approximately 2 h at room temperature and then the tip is ready for use. The coated capillary tip is applied as a sheathless electrospray emitter. The emitter has proven to bear stable electrospray and excellent performance for 50 microm i.d. x 360 microm o.d. and 20 microm i.d. x 360 microm o.d. capillaries within the flow rate of 80-500 nL/min; continuous electrospray can last for over 200 h in positive mode. Baseline separation and structure elucidation of two clinically interesting basic drugs, risperidone and 9-hydroxyrisperidone, are achieved by coupling pressure-assisted CE to ESI-TOFMS using the described sheathless electrospray emitter with a bare fused-silica capillary at pH 6.7. It is found that the signal intensity of m/z in sheathless CE/ESI-TOFMS at pH 6.7 is approximately 50 times higher than that at pH 9.0 for the two analytes, although the electroosmotic flow (EOF) at pH 9.0 provides sufficient flow rate (approximately 150 nL/min) to maintain electrospray.
    Analytical Chemistry 11/2002; 74(20):5405-9. DOI:10.1021/ac025877q · 5.64 Impact Factor