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    27Al and 31P NMR investigations of soluble aluminophosphate species in alcohol-water mixtures

    , Article Journal of Solution Chemistry ; Volume 41, Issue 5 , 2012 , Pages 888-897 ; 00959782 (ISSN) Samadi Maybodi, A ; Nejad Darzi, S. K. H ; Tafazzoli, M ; Sharif University of Technology
    In this work, phosphorus-31 and aluminum-27 nuclear magnetic resonance techniques were used to characterize the distribution of soluble aluminophosphate species in methanol + water and ethanol + water mixtures. The assignment of the peaks to alu-minate species was attempted, clarifying earlier work and producing information on the different aluminophosphate complexes. Nine peaks were observed at -0.41, -6.4, -7.5, -7.9, -13.1, -13.9, -16.6, -18.1 and -20.6 ppm. Four new peaks appeared in the 31P NMR spectra of the alcoholic aluminophosphate solutions and their intensities changed with changes of the alcohol:water volume ratio. These new peaks were observed in the presence of methanol or... 

    A methionine chemical shift based order parameter characterizing global protein dynamics

    , Article ChemBioChem ; 2020 Chashmniam, S ; Teixeira, J. M. C ; Paniagua, J. C ; Pons, M ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Coupling of side chain dynamics over long distances is an important component of allostery. Methionine side chains show the largest intrinsic flexibility among methyl-containing residues but the actual degree of conformational averaging depends on the proximity and mobility of neighboring residues. The 13C NMR chemical shifts of the methyl groups of methionine residues located at long distances in the same protein show a similar scaling with respect to the values predicted from the static X-ray structure by quantum methods. This results in a good linear correlation between calculated and observed chemical shifts. The slope is protein dependent and ranges from zero for the highly flexible... 

    Aluminum solvate complexes forming in acidic methanol-acetone mixtures studied by 27Al NMR spectroscopy

    , Article Journal of Solution Chemistry ; Volume 38, Issue 2 , 2009 , Pages 159-169 ; 00959782 (ISSN) Samadi Maybodi, A ; Pourali, S. M ; Tafazzoli, M ; Sharif University of Technology
    27Al NMR spectroscopy is a powerful tool for the study of coordination and solvation in both aqueous and nonaqueous solutions. In this study, the complexes coexisting upon dissolution of AlCl3 in acidic acetone + methanol solutions are shown to consist essentially of mixed hexacoordinated species of the general formula [Al(CH3OH) 6-n (CH3COCH3) n ]3+ (n=1,2 and 3), all exhibiting distinctly different 27Al shielding effects. The relative populations of the various mixed species are found to be highly dependent upon the acetone:methanol mole ratio that in the more acetone-rich mixtures with aluminum become appreciably coordinated by acetone. The results demonstrate that the key factor for the... 

    Dynamic NMR studies of N-benzoyl pyrrolidine and N-benzoyl piperidine derivatives

    , Article Journal of Molecular Structure ; Volume 886, Issue 1-3 , August , 2008 , Pages 24-31 ; 00222860 (ISSN) Tafazzoli, M ; Ziyaei Halimjani, A ; Ghiasi, M ; Fattahi, M ; Saidi, M. R ; Sharif University of Technology
    Variable-temperature 1H and 13C NMR spectroscopy are used to investigate barrier of C-N rotation in series of amides, such as N-benzoyl pyrrolidine, N-(4-chlorobenzoyl) pyrrolidine, N-(4-methoxybenzoyl) pyrrolidine, N-(4-chlorobenzoyl) piperidine, and N-(4-methoxybenzoyl) piperidine. Δ G298≠ of 65.2, 60.6, 58.8, 60.1, and 57.1 kJ mol-1are found for the above compounds, respectively. Theoretical studies were done for these compounds and the results showed good agreement with the experimental results. Theoretical and experimental results showed that substituted methoxy group on the para position of benzene ring decreases the rotational barrier. Increasing steric effect and therefore... 

    Conformational study of a strained tolanophane by dynamic 1H NMR spectroscopy and computational methods

    , Article Monatshefte fur Chemie ; Volume 139, Issue 10 , 2008 , Pages 1185-1189 ; 00269247 (ISSN) Darabi, H. R ; Azimzadeh Arani, M ; Tafazzoli, M ; Ghiasi, M ; Sharif University of Technology
    The existence of a short C-H⋯π (alkyl-alkyne) interaction in the structure of a strained and relatively rigid tolanophane is expected to hinder the rotation about the C-C sp3 single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl3, THF-d8, and acetone-d6) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined at coalescence (210 K) with acetone-d6 which is in good agreement with calculation result (54 kJ/mol). © 2008 Springer-Verlag  

    Synthesis and characterization of N- diethyl methyl chitosan

    , Article Iranian Polymer Journal (English Edition) ; Volume 13, Issue 5 , 2004 , Pages 431-436+437 ; 10261265 (ISSN) Avadi, M. R ; Mahdavinia, G ; Sadeghi, A. M ; Erfan, M ; Amini, M ; Tehrani, M. R ; Shafiee, A ; Sharif University of Technology
    Biodegradable polymers such as chitosan have been used extensively in biomedical fields in the form of sutures; wound dressing and as artificial skin. Colonic drug delivery for either local or systemic effects has been the subject of much research over the last decade. Chitosan exhibits poor solubility at pH values above 6 that prevent enhancing effects at sites of absorption of drugs. In the present work, N-diethyl methyl chitosan (DEMC) was prepared based on a modified two-step process via a 22 factorial design to optimize the preparative conditions. DEMC Polymer with different degrees of quaternization for pharmacological and pharmaceutical experiments was achieved. The reaction was... 

    Study of the Affecting Factors on the Stability of G-Quadruplex Structures

    , Ph.D. Dissertation Sharif University of Technology Fadaei, Elham (Author) ; Tafazzoli, Mohsen (Supervisor)
    We used spectroscopic techniques to study self-assembled structures based on nucleobases like G-quadruplexes and macrocycles. Also we used DOSY NMR technique to study hydrogen bonding network in alcohol solutions. First part of our results indicate thermodynamic stability and slow kinetic of G-quadruplexes in apolar aromatic solvents like toluene. Also our results show easy monitoring of formation of each K+ or Na+ complex by NMR, due to the low solubility of alkaline metal salts in apolar media and possibility to stop at any given time in order to control G-quadruplex yield. When combined with suitable functional units, these valuable attributes may be used for the noncovalent synthesis of... 

    Gauge invariant atomic orbital-density functional theory prediction of accurate gas phase 1H and 13C NMR chemical shifts

    , Article Concepts in Magnetic Resonance Part A: Bridging Education and Research ; Volume 38 A, Issue 6 , 2011 , Pages 269-279 ; 15466086 (ISSN) Ebrahimi, H. P ; Shaghaghi, H ; Tafazzoli, M ; Sharif University of Technology
    Hartree-Fock and density functional theory methods at gauge invariant atomic orbital approach with different simplest basis sets were employed for the computation of chemical shifts. The wave functions for calculating gas-phase 1H and 13C chemical shifts have been optimally selected using empirical models. The effects of electron correlation treatment, triple-ξ valance shell, diffuse function, and polarization function on calculated chemical shifts have been discussed. Through empirical scaling of shielding, accurate predictions of 1H chemical shifts are achieved for the molecules studied, when considering small Pople basis sets. Gas phase experimental 1H chemical shifts in alcohols, amines... 

    Calculations of gas phase1H NMR chemical shifts of alcohols: An approach to optimize basis functions using factorial design

    , Article Concepts in Magnetic Resonance Part A: Bridging Education and Research ; Volume 32, Issue 3 , 2008 , Pages 157-167 ; 15466086 (ISSN) Tafazzoli, M ; Shaghaghi, H ; Jalali Heravi, M ; Sharif University of Technology
    The wave functions for calculating gas phase 1H chemical shifts of primary and secondary alcohols have been optimized using factorial design as multivariate technique. Gas-phase experimental 1H chemical shifts of 18 alcohols were used to establish the best levels of theory for obtaining 1H chemical shift, among them the new experimental values of 1H chemical shifts of 10 alcohols were obtained in our laboratory. HF/6-31G(d,p) wave function is proposed as the best level of theory for calculating 1H chemical shifts of primary alcohols. For secondary alcohols, ONIOM(B3LYP/6-31G(d,p): HF/6-31G(d,p)) are recommended. An additional series of primary and secondary alcohols were used as test sets... 

    DFT calculations as a powerful technique to probe the crystal structure of Al(acac)3

    , Article Magnetic Resonance in Chemistry ; Volume 46, Issue 11 , 2008 , Pages 1045-1050 ; 07491581 (ISSN) Amini, S. K ; Tafazzoli, M ; Sharif University of Technology
    27Al, 17O and 13C chemical shieldings of aluminum acetylacetonate complex, Al(acac)3, were calculated at some Density Functional Theory (DFT) levels of theory. In these calculations the X-ray structures of its different polymorphs were used. Using these calculated data observed discrepancies between the X-ray crystallography and solid state NMR experiment were explained in terms of the quality of the NMR data. In this survey we resorted to the simulated spectra using our calculated chemical shifts. Inorder toconfirm our conclusions, electric field gradient (EFG) tensors of the 27Al and 17O nuclei were calculated at the same levels of theory as used in the chemical shielding calculations. On... 

    Conformation of repaglinide: a solvent dependent structure

    , Article Journal of Molecular Structure ; Volume 1143 , 2017 , Pages 388-396 ; 00222860 (ISSN) Chashmniam, S ; Tafazzoli, M ; Sharif University of Technology
    Experimental and theoretical conformational study of repaglinide in chloroform and dimethyl sulfoxide was investigated. By applying potential energy scanning (PES) at B3LYP/6-311++g** and B3LYP-D3/6-311++g** level of theory on rotatable single bonds, four stable conformers (R1-R4) were identified. Spin-spin coupling constant values were obtained from a set of 2D NMR spectra (H[sbnd]H COSY, H[sbnd]C HMQC and H[sbnd]C HMBC) and compared to its calculated values. Interestingly, from 1HNMR and 2D-NOESY NMR, it has been found that repaglinide structure is folded in CDCl3 and cause all single bonds to rotate at an extremely slow rate. On the other hand, in DMSO-d6, with strong solvent-solute... 

    Investigation of structure, vibrational and NMR spectra of oxycodone and naltrexone: A combined experimental and theoretical study

    , Article Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy ; Volume 79, Issue 3 , 2011 , Pages 574-582 ; 13861425 (ISSN) Tavakol, H ; Esfandyari, M ; Taheri, S ; Heydari, A ; Sharif University of Technology
    In this work, two important opioid antagonists, naltrexone and oxycodone, were prepared from thebaine and were characterized by IR, 1H NMR and 13C NMR spectroscopy. Moreover, computational NMR and IR parameters were obtained using density functional theory (DFT) at B3LYP/6-311++G* * level of theory. Complete NMR and vibrational assignment were carried out using the observed and calculated spectra. The IR frequencies and NMR chemical shifts, determined experimentally, were compared with those obtained theoretically from DFT calculations, showed good agreements. The RMS errors observed between experimental and calculated data for the IR absorptions are 85 and 105 cm-1, for the 1H NMR peaks are... 

    Radical chlorination of polyethylene and molecular structure characterization of reaction products

    , Article Polymer Journal ; Volume 37, Issue 9 , 2005 , Pages 661-668 ; 00323896 (ISSN) Moradi, A ; Ramazani S. A., A ; Shahrokhi, M ; Sharif University of Technology
    In this research the radical chlorination reaction of polyethylene has been carried out in perchloroethylene solvent under atmospheric pressure, using chlorine gas and UV light. In order to characterize the structural configuration of chlorinated polymer and study the reaction rate, different samples have been taken in equal periods of time during the reaction time. The FT-IR and H NMR spectra of these samples have been recorded and interpreted. The sequences of methylene groups between two subsequent chloromethylene groups in the polymeric chains have been determined through H NMR spectra and the obtained results have been confirmed with the data of some model compounds. The relative... 

    The effects of SiO 2 and K 2O on glass forming ability and structure of CaOTiO 2P 2O 5 glass system

    , Article Ceramics International ; Volume 38, Issue 4 , 2012 , Pages 3281-3290 ; 02728842 (ISSN) Ahmadi Mooghari, H. R ; Nemati, A ; Eftekhari Yekta, B ; Hamnabard, Z ; Sharif University of Technology
    The effects of SiO 2 and K 2O were investigated on the glass forming ability (GFA) and structural characteristics of CaOTiO 2P 2O 5 system. Differential thermal analyzer (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and 31P magic angle spinning NMR methods were applied for characterizations of the system. Unwanted crystallization in the initial three components base glass composition was observed by adding SiO 2 and crystalline phases such as TiP 2O 7, rutile (TiO 2) and cristobalite (SiO 2) were formed in it. The results showed that K 2O prevents crystallization of glasses and promotes the formation of glass. FT-IR and X-ray diffraction showed that the addition... 

    Structure and conformation of α-, β- and γ-cyclodextrin in solution: theoretical approaches and experimental validation

    , Article Carbohydrate Polymers ; Volume 78, Issue 1 , 2009 , Pages 10-15 ; 01448617 (ISSN) Tafazzoli, M ; Ghiasi, M ; Sharif University of Technology
    The anomeric carbon chemical shifts of α-, β- and γ-cyclodextrin in solution were studied experimentally and theoretically by NMR and two-layer ONIOM2 (B3LYP/6-31G*-GIAO: HF/6-31G*-GIAO) variant. The dependence between the anomeric carbon chemical shift and the glycosidic bond φ and ψ dihedral angles in d-Glcp-d-Glcp disaccharides with and (1 → 4) linkages in α-configurations were computed by Gauge-Including Atomic Orbital (GIAO) ab initio and ONIOM in water solvent using PCM methods. Complete chemical shift surfaces versus φ and ψ for this disaccharide were computed. We also present empirical formulas of the form 13C δ = f(φ, ψ) obtained by fitting the ab initio data to trigonometric series... 

    Five- and six-coordinated silver(I) complexes formed by a metallomacrocyclic ligand with a “Au2N2” donor group: observation of pendulum and linear motions and dual phosphorescence

    , Article Inorganic Chemistry ; Volume 59, Issue 8 , 31 March , 2020 , Pages 5702-5712 Nayeri, S ; Jamali, S ; Jamjah, A ; Shakirova, J. R ; Tunik, S. P ; Gurzhiy, V ; Samouei, H ; Shahsavari, H. R ; Sharif University of Technology
    American Chemical Society  2020
    The six-coordinated silver(I) complex [Au2Ag(μ-(PPh2)2py)2(OTf)2](OTf), 4 (py = pyridine, OTf = CF3SO3), and the five-coordinated silver(I) complex [Au2Ag(acetone)(μ-(PPh2)2py)2](PF6)3, 6, were prepared by the reaction of the precursor complexes 1(OTf)2 and 1(PF6)2, in which 1 = [Au2(μ-(PPh2)2py)2]2+, with 1 equiv of Ag(OTf) in dichloromethane and excess of Ag(PF6) in a mixture of dichloromethane/acetone, respectively. Also, the five-coordinated silver(I) complex [Au2Ag(μ-(PPh2)2py)2(py)(OTf)](OTf)2, 5, was obtained by the reaction of 4 with pyridine. The clusters 4-6 were characterized using multinuclear NMR spectroscopy and elemental microanalysis. The single-crystal X-ray diffraction... 

    NMR investigation and theoretical calculations of the solvent effect on the conformation of valsartan

    , Article Journal of Molecular Structure ; Volume 1148 , 2017 , Pages 73-80 ; 00222860 (ISSN) Chashmniam, S ; Tafazzoli, M ; Sharif University of Technology
    Structure and conformational properties of valsartan were studied by advanced NMR techniques and quantum calculation methods. Potential energy scanning using B3LYP/6-311++g** and B3LYP-D3/6-311++g** methods were performed and four conformers (V1-V4) at minimum points of PES diagram were observed. According to the NMR spectra in acetone-d6, there are two conformers (M and m) with mM = 0.52 ratio simultaneously and energy barriers of the two conformers were predicted from chemical shifts and multiplicities. While, intramolecular hydrogen bond at tetrazole ring and carboxylic groups prevent the free rotation on N6[sbnd]C11 bond in M-conformer, this bond rotates freely in m-conformer. On the... 

    Cis-trans proline isomers in the catalytic domain of calcineurin

    , Article FEBS Journal ; Volume 286, Issue 6 , 2019 , Pages 1230-1239 ; 1742464X (ISSN) Teixeira, J. M. C ; Guasch, A ; Biçer, A ; Aranguren Ibáñez, Á ; Chashmniam, S ; Paniagua, J. C ; Pérez Riba, M ; Fita, I ; Pons, M ; Sharif University of Technology
    Blackwell Publishing Ltd  2019
    Calcineurin is an essential calcium-activated serine/threonine phosphatase. The six NMR-observable methionine methyl groups in the catalytic domain of human calcineurin Aα (CNA) were assigned and used as reporters of the presence of potential cis-trans isomers in solution. Proline 84 is found in the cis conformation in most calcineurin X-ray structures, and proline 309, which is part of a highly conserved motif in phosphoprotein phosphatases, was modeled with a cis peptide bond in one of the two molecules present in the asymmetric unit of CNA. We mutated each of the two prolines to alanine to force the trans conformation. Solution NMR shows that the P84A CNA mutant exists in two forms,... 

    Experimental and theoretical study of the spectroscopic properties and the preparation of 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione

    , Article Journal of Molecular Structure ; Vol. 1065-1066, issue. 1 , May , 2014 , pp. 235-240 ; ISSN: 00222860 Moghaddam, F. M ; Foroushani, B. K ; Sharif University of Technology
    Compound 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione(3), was prepared and fully characterized. The vibrational modes (FT-IR) and NMR data ( 1H and 13C chemical shifts) were compared with the results of Density Functional Theory (DFT) method at the B3LYP/cc-PVTZ level. The calculated vibrational frequencies and NMR chemical shifts are in good agreement with the experimental results. The electronic (UV-Vis) spectrum was calculated using the TD-DFT method in CH2Cl2 with the Polarizable Continuum Model using the integral equation formalism variant (IEFPCM) and was correlated to the experimental spectra. The assignment and analysis of the frontier HOMO and LUMO orbitals indicate that... 

    Novel cationic-modified salep as an efficient flocculating agent for settling of cement slurries

    , Article Carbohydrate Polymers ; Volume 93, Issue 2 , April , 2013 , Pages 506-511 ; 01448617 (ISSN) Pourjavadi, A ; Fakoorpoor, S. M ; Hosseini, S. H ; Sharif University of Technology
    A new cationic flocculant was synthesized by graft copolymerization of acrylamide (AM) and 3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC) onto salep using free radical polymerization initiated by ammonium persulfate (APS) to produce cationic salep [S-g-P(AM-co-MAPTAC)]. Reaction parameters (monomers/salep ratio, concentration of reactants, MAPTAC/AM ratio, and APS) were optimized using a full factorial experimental design to obtain the highest settling rate for cement suspensions. The best performing product was characterized by gel permeation chromatography (GPC), FTIR, 1H NMR spectroscopy, and thermogravimetric analysis (TGA). The resulted cationic flocculant may be...