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Item Open Access CONTROLLING THE STEREOCHEMISTRY IN 2-OXO-ALDEHYDE-DERIVED UGI ADDUCTS THROUGH THE CINCHONA ALKALOID-PROMOTED ELECTROPHILIC FLUORINATION(Beilstein Journal of Organic Chemistry, 2020-08) Wang, Yuqing; Wang, Gaigai; Peshkov, Anatoly A.; Yao, Ruwei; Hasan, Muhammad; Zaman, Manzoor; Liu, Chao; Kashtanov, Stepan; Pereshivko, Olga P.; Peshkov, Vsevolod A.In this report, we introduce a new strategy for controlling the stereochemistry in Ugi adducts. Instead of controlling stereochemistry directly during the Ugi reaction we have attempted to stereodefine the chiral center at the peptidyl position through the post-Ugi functionalization. In order to achieve this, we chose to study 2-oxo-aldehyde-derived Ugi adducts many of which partially or fully exist in the enol form that lacks the aforementioned chiral center. This in turn led to their increased nucleophilicity as compared to the standard Ugi adducts. As such, the stereocenter at the peptidyl position could be installed and stereodefined through the reaction with a suitable electrophile. Towards this end, we were able to deploy an asymmetric cinchona alkaloid-promoted electrophilic fluorination producing enantioenriched post-Ugi adducts fluorinated at the peptidyl position.Item Open Access Nano-Mole Scale Side-Chain Signal Assignment by 1H-Detected Protein Solid-State NMR by Ultra-Fast Magic-Angle Spinning and Stereo-Array Isotope Labeling(Public Library of Science, 2015-04) Wang, Songlin; Parthasarathy, Sudhakar; Nishiyama, Yusuke; Endo, Yuki; Nemoto, Takahiro; Yamauchi, Kazuo; Asakura, Tetsuo; Takeda, Mitsuhiro; Terauchi, Tsutomu; Kainosho, Masatsune; Ishii, YoshitakaWe present a general approach in 1H-detected 13C solid-state NMR (SSNMR) for side-chain signal assignments of 10-50 nmol quantities of proteins using a combination of a high magnetic field, ultra-fast magic-angle spinning (MAS) at ~80 kHz, and stereo-array-isotope-labeled (SAIL) proteins [Kainosho M. et al., Nature 440, 52–57, 2006]. First, we demonstrate that 1H indirect detection improves the sensitivity and resolution of 13C SSNMR of SAIL proteins for side-chain assignments in the ultra-fast MAS condition. 1H-detected SSNMR was performed for micro-crystalline ubiquitin (~55 nmol or ~0.5mg) that was SAIL-labeled at seven isoleucine (Ile) residues. Sensitivity was dramatically improved by 1H-detected 2D 1H/13C SSNMR by factors of 5.4-9.7 and 2.1-5.0, respectively, over 13C-detected 2D 1H/13C SSNMR and 1D 13C CPMAS, demonstrating that 2D 1H-detected SSNMR offers not only additional resolution but also sensitivity advantage over 1D 13C detection for the first time. High 1H resolution for the SAIL-labeled side-chain residues offered reasonable resolution even in the 2D data. A 1H-detected 3D 13C/13C/1H experiment on SAIL-ubiquitin provided nearly complete 1H and 13C assignments for seven Ile residues only within ~2.5 h. The results demonstrate the feasibility of side-chain signal assignment in this approach for as little as 10 nmol of a protein sample within ~3 days. The approach is likely applicable to a variety of proteins of biological interest without any requirements of highly efficient protein expression systems.Item Open Access Detection of Paracetamol in Water and Urea in Artificial Urine with Gold Nanoparticle@Al Foil Cost-efficient SERS Substrate(Nihon Bunseki Kagakkai, 2018) Mukanova, Zhansaya; Gudun, Kristina; Elemessova, Zarina; Khamkhash, Laura; Ralchenko, Ekaterina; Bukasov, RostislavWe demonstrated that a cost-efficient, easy to prepare, hybrid SERS substrate-gold nanoparticles (AuNPs) on untreated Al foil (AlF) can effectively detect pharmaceuticals, such as paracetamol and clinical biomarkers, like urea in artificial urine. The limit of detection (LOD) for paracetamol on AuNPs on AlF is superior (0.1 vs. 1 mM ) to the LOD reported for SERS detection of paracetamol in the literature. For SERS detection of urea in urine, AuNPs on both Al foil and Au film performed much better than AuNPs on glass, in terms of the concentration range, linearity and LOD. However, assay on AuNPs on AlF showed a better semi-logarithmic trendline with R2 = 0.98 than an assay on AuNPs on Au film with R2 = 0.94. They have comparable sensitivity with LOD 0.024 and 0.017 M, respectively. The limit of quantification (LOQ) of the former is 0.026 M, which makes it sufficient for the quantification of urea in urine at both normal and pathophysiological (0.03 – 0.15 M) concentration.Item Open Access Monitoring of vegetation drying by Brillouin and Raman spectroscopies(Nazarbayev University School of Science and Technology, 2017-05-01) Rakymzhan, Adiya; Yakupov, Talgat A.; Yelemessova, Zarina; Bukasov, Rostislav; Yakovlev, Vladislav V.; Utegulov, Zhandos N.Raman and Brillouin spectroscopic provide with a powerful way to non-invasively assess both chemical and physical (viscoelastic) properties. In this report, Brillouin microspectroscopy was used for real time analysis of elastic properties of Populus and Geranium leaves, while Raman spectroscopy and imaging were employed for assessment of their chemical variation during drying. When used together, those techniques can improve our understanding of mechanochemical changes of plants in response to environmental stress and pathogens at microscopic (cellular) level. Our results have demonstrated for the first time the ability of multimodal assessment of elasticity modulus, hydraulic conductance and interatomic vibrational modes in plants as emerging new markers for real time quantitative assessment of agricultural crops.Item Open Access Turbulence Generation by Shock-Acoustic-Wave Interaction in Core-Collapse Supernovae(MDPI, 2018-05-07) Abdikamalov, Ernazar; Huete, César; Nussupbekov, Ayan; Berdibek, ShapagatConvective instabilities in the advanced stages of nuclear shell burning can play an important role in neutrino-driven supernova explosions. In our previous work, we studied the interaction of vorticity and entropy waves with the supernova shock using a linear perturbations theory. In this paper, we extend our work by studying the effect of acoustic waves. As the acoustic waves cross the shock, the perturbed shock induces a field of entropy and vorticity waves in the post-shock flow. We find that, even when the upstream flow is assumed to be dominated by sonic perturbations, the shock-generated vorticity waves contain most of the turbulent kinetic energy in the post-shock region, while the entropy waves produced behind the shock are responsible for most of the density perturbations. The entropy perturbations are expected to become buoyant as a response to the gravity force and then generate additional turbulence in the post-shock region. This leads to a modest reduction of the critical neutrino luminosity necessary for producing an explosion, which we estimate to be less than 5%.Item Open Access Carbon Dots Doped with Dysprosium: A Bimodal Nanoprobe for MRI and Fluorescence Imaging(MDPI, 2018-05-18) Atabaev, Timur; Piao, Zhonglie; Molkenova, AnaraIn recent years, functional nanoprobes with multiple imaging modalities have become an emerging field of biomedical research. In this preliminary study, we utilized a facile hydrothermal method for the preparation of magneto-fluorescent bimodal carbon dots doped with dysprosium (Dy-CDs). The prepared Dy-CDs have shown a good colloidal stability in a water solution and strong blue–green fluorescence, with a maximum at 452 nm. In addition, the excellent transverse relaxivity of the prepared Dy-CDs (r2 = 7.42 ± 0.07 mM−1 s −1 ) makes them also suitable for T2-weighted magnetic resonance imaging (MRI). Thus, synthesized Dy-CDs could be potentially utilized for both MRI and fluorescence imaging of living cells.Item Metadata only Selective oxidation of styrene catalyzed by cerium-doped cobalt ferrite nanocrystals with greatly enhanced catalytic performance(Journal of Catalysis, 2016-12-01) Tong, Jinhui; Li, Wenyan; Bo, Lili; Wang, Huan; Hu, Yusen; Zhang, Zhixia; Mahboob, Abdulla; Jinhui, TongAbstract The rare earth metal Ce-doped cobalt ferrite samples CexCo1−xFe2O4 (x=0.1, 0.3, 0.5) were prepared by the sol–gel autocombustion route. The as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, ICP–atomic emission spectroscopy, and N2 physisorption. Their catalytic performance was evaluated in oxidation of styrene using hydrogen peroxide (30%) as oxidant. Compared with pristine CoFe2O4, the Ce-doped samples were found to be more efficient catalysts for the oxidation of styrene to benzaldehyde, with greatly enhanced catalytic performance. Especially, when Ce0.3Co0.7Fe2O4 was used as catalyst, 90.3% styrene conversion and 91.5% selectivity for benzaldehyde were obtained at 90°C for 9h reaction. The catalyst can be magnetically separated easily for reuse, and no obvious loss of activity was observed when it was reused in five consecutive runs.Item Metadata only The hows and whys of peculiar coordination of 4-amino-2,1,3-benzothiadiazole(Polyhedron, 2018-01-08) Sukhikh, T.S.; Komarov, V.Yu.; Konchenko, S.N.; Benassi, E.; T.S., SukhikhAbstract 4-Amino-2,1,3-benzothiadiazole (L) and its model complexes with Cu+, Zn2+, Ag+ and Cd2+ have been computationally investigated in order to reveal the origins of coordination preferences of this multidentate ligand. The computational description is consistent with the analysis of experimental crystal structures of the coordination compounds described earlier and of two new complexes viz. [ZnL(H2O)Cl2] and [CdL2(H2O)2(NO3)2]. Possible coordination types of L are discussed by means of rotational hindrance of NH2 group, relative thermodynamic stability of the complexes and intramolecular interaction analysis. On the basis of our findings, molecular structure – spectral properties relationships of the complexes are revealed. The results obtained for L are compared with those obtained for 8-aminoquinoline, which is structurally similar to L and is known to form a number of metal complexes.Item Metadata only Synthesis, crystal and electronic structure of the quaternary sulfides Ln2CuMS5 (Ln=La, Ce; M=Sb, Bi)(Journal of Solid State Chemistry, 2016-01-01) Kussainova, Ardak M.; Akselrud, Lev G.; Suen, Nian-Tzu; Voss, Leonard; Stoyko, Stanislav; Bobev, Svilen; Ardak M., KussainovaAbstract The series of quaternary sulfides with general formula Ln2CuMS5 (Ln=La, Ce; M=Sb, Bi) have been synthesized by solid-state reactions. Three representative members have been structurally characterized by single-crystal X-ray diffraction. La2CuSbS5 crystallizes in a new structure type (space group Ima2 (no. 46), Z=4, a=13.401(2)Å, b=7.592(1)Å, c=7.598(1)Å, V=773.1(3)Å3). The bismuth analogs of composition La2CuBiS5 and Ce2CuBiS5 crystallize with the La2CuInSe5 structure type (space group Pnma (no. 62), Z=4). Lattice parameters for La2CuBiS5: a=11.9213(5)Å, b=3.9967(2)Å, c=17.0537(8)Å, V=812.56(7)Å3; lattice parameters for Ce2CuBiS5: a=11.9179(15)Å, b=3.9596(5)Å, c=16.955(2)Å, V=800.13(17)Å3). The similarities and the differences between the two structures are discussed. Electronic structure calculations for La2CuSbS5 and La2CuBiS5 are also presented; they suggest semiconducting behavior with energy gaps exceeding 1.7eV.Item Metadata only Synthesis of Hierarchical Porous Sulfur/Polypyrrole/Multiwalled Carbon Nanotube Composite Cathode for Lithium Batteries(Electrochimica Acta, 2014-10-10) Zhang, Yongguang; Zhao, Yan; Bakenov, Zhumabay; Tuiyebayeva, Madina; Konarov, Aishuak; Chen, P.; Yongguang, ZhangAbstract A novel porous sulfur/polypyrrole/multiwalled carbon nanotube composite (S/PPy/MWNT) was synthesized via in situ polymerization of pyrrole monomer with nano-sulfur and MWNT aqueous suspension followed by a low temperature heat-treatment. Scanning electronic microscopy revealed the formation of a highly hierarchical mesoporous and macroporous structure. High resolution transmission electronic microscopy confirmed homogeneous dispersion of S, PPy and MWNT in the composite. In this composite, polypyrrole with its high adhesion ability to MWNT acts as a conductive binder to connect sulfur and MWNT matrix, as well as absorbs polysulfides into its porous structure positively affecting the composite performance as a cathode in a Li/S cell. The resulting S/PPy/MWNT composite cathode exhibited greatly enhanced cyclability and delivered a reversible discharge capacity of 751 mAh g−1 after 100 cycles at 0.2C.Item Metadata only Synthesis and Characterization of Silicon Based Anode Materials(Materials Today: Proceedings, 2017-01-01) Ould Ely, T.; Batyrbekuly, D.; Sugurbekov, Y.; Stambekova, D.; Doherty, M.F.; Bakenov, Z.; T., Ould ElyAbstract We have synthesized amorphous silicon-nanomaterials displaying high capacity and stable cyclability using an original organometallic approach. The method is based on the decomposition of silicon compounds 1Si-P1-U-2016 and 1Si-P2-C-2016, where silicon is bound to four atoms bearing an electron-withdrawing group on the β-position. These compounds decompose under argon at temperature below 500 °C. Scanning Electron Microscopy displays particles with size less than 50 nm, considerably smaller than the critical size above which silicon nanostructures will pulverize [1]. The nanosilicon particles, remain amorphous upon sintering under argon at 1150 °C, and crystallize only above 1400 °C in air, yielding SiO2 (Tetragonal, space group P41212). The silicon nanoparticles show excellent cycling performance, retaining a specific capacity of 1000 mAh g-1, and maintain more than 98% of its initial reversible capacity after 150 cycles. High specific capacity and stable cycle performance of the synthesized silicon makes it a promising anode material for lithium ion batteriesItem Metadata only Synthesis and anodic electrochemistry of cymanquine and related complexes(Journal of Organometallic Chemistry, 2016-08-15) Lam, Kevin; Geiger, William E.; Kevin, LamAbstract Three compounds have been prepared in which a 4-aminochloroquinoline moiety is covalently linked to a cyclopentadienyl manganese tricarbonyl moiety. One of these (“cymanquine”, 4) is the analogue of the potent antimalarial drug ferroquine in which an FeCp group has been replaced by a Mn(CO)3 group. The anodic electrochemistry of the new compounds was investigated in dichloromethane, using [NBu4][B(C6F5)4] as the supporting electrolyte. Compared to ferroquine, oxidations of the new compounds occur at considerably more positive potentials and are highly irreversible, being located at their amine groups rather than at the organometallic center.Item Metadata only One-electron oxidation of chloroquine, cymanquine, and related aminoquinolines in nonaqueous media(Journal of Electroanalytical Chemistry, 2017-08-15) Lam, Kevin; Van Wyck, Stephen J.; Geiger, William E.; Kevin, LamAbstract The anodic oxidation of a series of secondary-amine-substituted chloroquinoline derivatives, 1–5, has been studied in dichloromethane/0.05M [NBu4][B(C6F5)4]. Compounds 4 and 5 contain organometallic moieties of the cymantrene family as part of the amine group. All five compounds undergo an electrochemically irreversible one-electron oxidation. For compounds 2–4, this occurs at the secondary amine group (0.86 to 0.98V vs ferrocene). The oxidations of others occur at tertiary amines located either in the side chain of the quinoline secondary amine (1, 0.68V) or in the cyclopentadienyl ring of the cymantrene moiety (5, 0.82V). The anodic reaction products have been isolated and shown to be ring-nitrogen protonated aminochloroquinolinium ions. Abstraction of a hydrogen atom from the solvent by the putative aminochloroquinoline radical cation is thought to be responsible for formation of the protonated oxidation product. Cathodic reduction of the latter regenerates the neutral starting material in an overall chemically reversible process that mimics a simple acid/base reaction at the quinoline ring nitrogen.Item Metadata only Synthesis and antibacterial activity of silver@carbon nanocomposites(Journal of Inorganic Biochemistry, 2017-01-01) Wang, Kunjie; Ji, Qingjuan; Li, Hongxia; Guan, Feng; Zhang, Deyi; Feng, Huixia; Fan, Haiyan; Kunjie, WangAbstract In this work, hollow multiple-Ag-nanoclustes- C-shell nanocomposites (Ag@C) were synthesized by using silane coupling agent to graft carbon dots (CDs) with silver nanoparticles (AgNPs). CDs act as coating and stabilizing agent, protecting AgNPs from aggregation and oxidation. The resulting Ag@C nanocomposites demonstrate strong bactericidal effect against both gram-negative and gram-positive bacteria in the disk diffusion test. Cellular toxicity evaluation was performed using MTT assay. Meanwhile, the as-prepared Ag@C nanocomposites show a good biocompatibility.Item Metadata only Lipase-mediated regioselective modifications of macrolactonic sophorolipids(Tetrahedron, 2017-04-06) Sembayeva, Aliya; Berhane, Beniam; Carr, Jason A.; Aliya, SembayevaAbstract Chemoenzymatic synthesis and modification of well-defined macrolactonic sophorolipid (SLML) analogues via a series of successive regioselective de-esterification/transesterification reactions is investigated. Of the lipases screened, Candida antartica lipase- B (Novozyme-435) successfully deacylated the C-6′ acetoxy group of natural and peracylated SLMLs. Subsequent transesterification with acylating agents (esters of fatty acids) was successful only with the C-6′ deacetylated natural SLML providing an avenue to well-defined analogues of varying amphilicity. The macrolactonic motif was essential for enzymatic recognition of the sophorose rings of these complex glycolipids. In the absence of the lactonic motif, the peracylated sophorose rings are not deacylated, rather the carboxyl end of the non-lactonic forms that was preferentially transesterified. All macrolactonic derivatives were characterized by IR, 1H, 13C, 1H-1H and 1H-13C NMR spectroscopy, as well as HRMS where applicable.Item Metadata only Corrigendum to “Synthesis and anodic electrochemistry of cymanquine and related complexes” [J. Organomet. Chem. 817 (15 August 2016) 15–20](Journal of Organometallic Chemistry, 2017-05-15) Lam, Kevin; Geiger, William E.; Kevin, LamThe authors regret that the oxidation potentials given for compound 5 in the paper are incorrect. The correct values, referenced to ferrocene, are 0.88 V for the first oxidation and 1.14 V for the second oxidation.Item Metadata only Reaction barrier heights for cycloreversion of heterocyclic rings: An Achilles’ heel for DFT and standard ab initio procedures(Chemical Physics, 2015-09-08) Yu, Li-Juan; Sarrami, Farzaneh; O’Reilly, Robert J.; Karton, Amir; Li-Juan, YuAbstract We introduce a database of 20 accurate cycloreversion barrier heights of 5-membered heterocyclic rings (to be known as the CRBH20 database). In these reactions, dioxazole and oxathiazole rings are fragmented to form isocyanates, isothiocyanates, and carbonyls. The reference reaction barrier heights are obtained by means of the high-level, ab initio W1-F12 and W1w thermochemical protocols. We evaluate the performance of 65 contemporary density functional theory (DFT) and double-hybrid DFT (DHDFT) procedures. The CRBH20 database represents an extremely challenging test for these methods. Most of the conventional DFT functionals (74%) result in root-mean-square deviations (RMSDs) between 10 and 81kJmol−1. The rest of the DFT functionals attain RMSDs=5−10kJmol−1. Of the 12 tested DHDFT functionals, only five result in RMSDs<10kJmol−1. The CRBH20 dataset also proves to be a surprisingly challenging target for composite and standard ab initio procedures.Item Metadata only Theoretical design of triphenylamine-based derivatives with asymmetric D–D–π–A configuration for dye-sensitized solar cells(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2015-04-05) Balanay, Mannix P.; Enopia, Camille Marie G.; Lee, Sang Hee; Kim, Dong Hee; Mannix P., BalanayAbstract The use of theoretical techniques in the structural development of dye-sensitized solar cells helps in the efficient screening of the dyes. To properly rationalize the dye’s design process, benchmark calculations were conducted using long-range corrected exchange–correlation (xc) functionals with varying separation parameters to be able to predict the excited-state energies of triphenylamine-based dyes, namely: PPS, PSP, and PSS, wherein they differ at the π-conjugated bridge using thiophene and/or phenyl moieties. The results show that LC-ωPBE xc functional with an optimized parameter provided better correlation with the experimental results compared to the other functionals. The relative shifts of the absorption spectra, light harvesting efficiency, normal dipole moments, as well as the ionization potentials and electron affinities of the dyes were well-correlated with the experimental data. A new set of dyes was designed in an effort to increase its solar cell efficiency that was patterned after PSS with an additional donor moiety such as fluorene, cyclopentaindole, and pyrene attached asymmetrically at the triphenylamine ring. Among the newly designed dyes, analogs that contain 4-phenyl-1,2,3,4-tetrahydrocyclopenta[b]indole (I) and pyrido[2,3,4-5-imn]phenanthridine-5,10(4H,9H)-dione (P2) as the additional donor moiety produced the best photophysical properties and charge-transfer characteristics for a promising dye for solar cell applications.Item Metadata only Molecular engineering of donor–acceptor co-polymers for bulk heterojunction solar cells(Computational and Theoretical Chemistry, 2015-03-01) Balanay, Mannix P.; Kim, Dong Hee; Mannix P., BalanayAbstract We report a computational modeling, based on DFT and TD-DFT methodologies, on the structural, electronic, and optical properties of different donor–acceptor co-polymer system in bulk heterojunction solar cells. The donor moieties that were considered were the derivatives of thienocyclopentathiophene, fluorene, and thienobenzothiophene. We utilized for the acceptor groups the moieties of thieno[3,4-b]pyrrole-4,6-dione; thieno[3,4-b] thiophene-4,6-dione; tetrafluoro-1,3-dihydrothieno[3,4-c]thiophene and its non-fluorinated counterpart; various electron-donating substituents within the fused π-conjugated polymer system; and 3-fluoroselenophenothiophene. Among the donor–acceptor combination, the best in terms of molecular energy levels, energetic driving force, maximum absorption, calculated open-circuit voltage, reorganization energies, ionization potential, and electron affinity are poly[(bisthieno(bisthieno[3,2-b:2′,3′-d]thiophene)- alt-(5-alkyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione)] and poly[(4,8-dimethyl[1,3] oxazolo[5,4-f][1,3]benzoxazole)- alt-(thieno[3,4-d]pyrimidine)].Item Metadata only Homolytic C–Br bond dissociation energies obtained by means of the G4 thermochemical protocol(Chemical Data Collections, 2016-05-01) Kazakbayeva, Zhanna; Zhumagali, Shingis; Mahboob, Abdulla; O'Reilly, Robert J.; Zhanna, KazakbayevaAbstract Knowledge of the energies required to induce homolytic cleavage of the C–Br bonds of brominated organic molecules, a process that affords carbon-centered radicals and Br•, is of fundamental importance. Although some data pertaining to the strength of C–Br bonds can already be found in the literature, the chemical diversity of the species for which bond dissociation energies (BDEs) are available is somewhat limited. In this data article, we report a comprehensive set of homolytic C–Br BDEs, obtained using the G4 thermochemical protocol, for brominated organic molecules with wide structural diversity. The species in this set have C–Br BDEs (at 298K) that differ by as much as 188.3kJmol–1, with α-bromoalanine having the lowest BDE (214.1kJmol–1) and 1-bromobut-1-yne having the largest (402.4kJmol–1). Of particular relevance to biological systems are the BDEs of 8-bromoguanine (345.3kJmol–1), 8-bromoadenine (345.6kJmol–1), 5-bromocytosine (348.8kJmol–1) and 5-bromouracil (350.3kJmol–1).