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Kumar, Avvaru Praveen,Jin, Hua,Jo, Sung-Chan,Kim, Changdae,Nam, Sang-Ho,Lee, Yong-Ill Springer-Verlag 2010 Journal of the American Society for Mass Spectrome Vol.21 No.1
<P>The single ratio kinetic method is applied to the discrimination and quantification of the thyroid hormone isomers, 3,5,3′-triiodothyronine and 3,3′,5′-triiodothyronine, in the gas phase, based on the kinetics of the competitive unimolecular dissociations of singly charged transition-metal ion-bound trimeric complexes [M<SUP>II</SUP>(A)(ref*)<SUB>2</SUB>-H]<SUP>+</SUP> (M<SUP>II</SUP> = divalent transition-metal ion; A=T<SUB>3</SUB> or rT<SUB>3</SUB>; ref* = reference ligand). The trimeric complex ions are generated using electrospray ionization mass spectrometry and the ions undergo collisional activation to realize isomeric discrimination from the branching ratio of the two fragment pathways that form the dimeric complexes [M<SUP>II</SUP>(A)(ref*)-H]<SUP>+</SUP> and [M<SUP>II</SUP>(ref*)<SUB>2</SUB>-H]<SUP>+</SUP>. The ratio of the individual branching ratios for the two isomers R<SUB>iso</SUB> is found strongly dependent on the references and the metal ions. Various sets are tried by choosing the reference from amino acids, substituted amino acids, and dipeptides in combination with the central metal ion chosen from five transition-metal ions (Co<SUP>II</SUP>, Cu<SUP>II</SUP>, Mn<SUP>II</SUP>, Ni<SUP>II</SUP>, and Zn<SUP>II</SUP>) for the complexes in this experiment. The results are compared in terms of the isomeric discrimination for the T<SUB>3</SUB>/rT<SUB>3</SUB> pair. Calibration curves are constructed by relating the ratio of the branching ratios against the isomeric composition of their mixture to allow rapid quantitative isomer analysis of the sample pair. Furthermore, the instrument-dependence of this method is investigated by comparing the two sets of results, one obtained from a quadrupole ion trap mass spectrometer and the other from a quadrupole time-of-flight mass spectrometer.</P>
Azithromycin as a new chiral selector in capillary electrophoresis
Kumar, Avvaru Praveen,Park, Jung Hag Elsevier 2011 Journal of chromatography Vol.1218 No.9
<P><B>Abstract</B></P><P>In capillary electrophoresis (CE), separation of enantiomers of a chiral compound can be achieved through the chiral interactions and/or complex formation between the chiral selector and the enantiomeric analytes on leaving their diastereomeric forms with different stability constants and hence different mobilities. A great number of chiral selectors have been employed in CE and among them macrocyclic antibiotics exhibited excellent enantioselective properties towards a wide number of racemic compounds. The use of azithromycin (AZM) as a chiral selector has not been reported previously. This work reports the use of AZM as a chiral selector for the enantiomeric separations of five chiral drugs and one amino acid (tryptophan) in CE. The enantioseparation is carried out using polar organic mixtures of acetonitrile (ACN), methanol (MeOH), acetic acid and triethylamine as run buffer. The influences of the chiral selector concentration, ACN/MeOH ratio, applied voltage and capillary temperature on enantioseparation are investigated. The results show that AZM is a viable chiral selector in CE for the enantioseparation of the type of chiral drugs investigated.</P>
Synthesis and Catalytic Applications of Ruthenium(0) Nanoparticles in Click Chemistry
Avvaru Praveen Kumar,Min-Wook Baek,Chirumarry Sridhar,Begari Prem Kumar,Yong-Ill Lee 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.4
Here we report a facile synthesis of ruthenium (Ru) Nanoparticles (NPs) by chemical co-precipitation method. The calcination of ruthenium hydroxide samples at 500 oC under hydrogen atmosphere lead to the formation of Ru0 NPs. The size and aggregation of Ru NPs depends on the pH of the medium, and type of surfactant and its concentration. The X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope image (TEM) analyses of particles indicated the formation of Ru0 NPs, and have 10 to 20 nm sizes. As-synthesized Ru0 NPs are characterized and investigated their catalytic ability in click chemistry (azidealkyne cycloaddition reactions), showing good results in terms of reactivity. Interestingly, small structural differences in triazines influence the catalytic activity of Ru0 nanocatalysts. Click chemistry has recently emerged to become one of the most powerful tools in drug discovery, chemical biology, proteomics, medical sciences and nanotechnology/nanomedicine. In addition, preliminary tests of recycling showed good results with neither loss of activity or significant precipitation.
Synthesis and Catalytic Applications of Ruthenium(0) Nanoparticles in Click Chemistry
Kumar, Avvaru Praveen,Baek, Min-Wook,Sridhar, Chirumarry,Kumar, Begari Prem,Lee, Yong-Ill Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.4
Here we report a facile synthesis of ruthenium (Ru) Nanoparticles (NPs) by chemical co-precipitation method. The calcination of ruthenium hydroxide samples at $500^{\circ}C$ under hydrogen atmosphere lead to the formation of $Ru^0$ NPs. The size and aggregation of Ru NPs depends on the pH of the medium, and type of surfactant and its concentration. The X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope image (TEM) analyses of particles indicated the formation of $Ru^0$ NPs, and have 10 to 20 nm sizes. As-synthesized $Ru^0$ NPs are characterized and investigated their catalytic ability in click chemistry (azidealkyne cycloaddition reactions), showing good results in terms of reactivity. Interestingly, small structural differences in triazines influence the catalytic activity of $Ru^0$ nanocatalysts. Click chemistry has recently emerged to become one of the most powerful tools in drug discovery, chemical biology, proteomics, medical sciences and nanotechnology/nanomedicine. In addition, preliminary tests of recycling showed good results with neither loss of activity or significant precipitation.
Huy, Bui The,Kumar, Avvaru Praveen,Seo, Min-Ho,Kim, Jan-Di,Lee, Yong-Ill American Scientific Publishers 2014 Journal of nanoscience and nanotechnology Vol.14 No.10
<P>Highly luminescent CdTe quantum dots (QDs) were synthesized through a co-precipitation route in aqueous salt solutions using different thiols as stabilizers. The synthetic procedure was simple, efficient, and stable. It could also allow controlling the emission wavelength by varying the experimental conditions such as reaction time and pH values. The strong luminescence of the QDs was observed under UV-excitation and emission colors could be adjusted. The interaction between CdTe QDs and triethylenetetramine dihydrochloride (TETA) which is a candidate treatment for diabetic cardiovascular complication was investigated by fluorescence spectroscopy. Based on the quenching effect on CdTe photoluminescence intensity by TETA, a simple assay system for analyzing the content of TETA in aqueous samples was developed. The linearity was maintained in the range of 0.2 μM to 1.2 μM (R2 = 0.994) with a limit of detection (LOD; S/N = 3) at 28 nM. The results showed that CdTe QDs capped with diverse thiols has a potential for the quantitative analysis of TETA in urine samples.</P>
Lim, Jin-Yi,Kumar, Avvaru Praveen,Kim, Chang-Dae,Ahn, Chul-Jin,Yoo, Young-Jae,Lee, Yong-Ill Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.2
The complexes of $C_2-\;and\;C_6$-dihydroceramides with transition metal ions have been investigated by using Electrospray ionization-tandem mass spectrometry (ESI-MS/MS). The formation and fragmentation pathways of several doubly charged cluster ions as well as singly charged cluster ions of $C_2-\;and\;C_6$-dihydroceramides with transition metal ions have studied by ESI-MS/MS in the positive mode. Under ESI conditions, dihydroceramides form singly and doubly charged complexes with transition metal ions $(Mn^{2+},\;Fe^{2+},\;Co^{2+},\;Ni^{2+},\;and\;Zn^{2+}\;except\;Cu^{2+})$ with the compositions of $[DHCer+M+2H^2O-H]^+,\;[2DHCer+M+2H2O-H]^+,\;[3DHCer+M+2H2O-H]^+,\;[2DHCer+M]^{2+},\;[3DHCer+M]^{2+},\;[4DHCer+M]^{2+},\;[5DHCer+M]^{2+},\;and\;[6DHCer+M]^{2+}\;(DHCer\;=\;C_2-\;or\;C_6$-dihydroceramide, M = transition metal ion). The different complexation behavior of copper is responsible for relatively lower affinity of dihydroceramides to copper compared to those of other transition metals. It is also found that in the mass spectrum of the dihydroceramide complexes with copper(II), [2DHCer+Cu-H]$^+$ was observed with considerable intensity as well as [2DHCer+Cu+2$H_2O-H]^+$ due to its different geometry from those of other metals.