Computational approaches to design a molecular imprinted polymer for high selective extraction of 3,4-methylenedioxymethamphetamine from plasma

In this work, a molecular imprinted polymer (MIP) as a novel selective sorbent for extraction of 3,4-methylenedioxymethamphetamine (MDMA) from plasma samples was prepared. For selecting a more suitable monomer and polymerization solvent a methodology based on density functional theory calculations was developed. This computational design is based on the comparison of stabilization energies of the prepolymerization adducts between the template and different functional monomers. The effect of polymerization solvent was studied using of polarizable continuum model (PCM). The computational results revealed that the best suitable monomer and polymerization solvent for preparation of MIP is methacrylic acid (MAA) and chloroform, respectively. Also, another MIP with methacrylic acid (MAA) as monomer in acetonitrile was prepared to evaluate the validity of polarizable continuum model for selection of polymerization solvent. The performance of each polymer was evaluated by using Langmuir-Freundlich (LF) isotherm. As it is expected, the best results were obtained for the MIP which was prepared in chloroform. This MIP was used as a selective sorbent in solid-phase extraction coupled with high performance liquid chromatography-ultraviolet detector (MISPE-HPLC-UV) for rapid screening of MDMA in human plasma. For the proposed MISPE-HPLC-UV method, the linearity between responses (peak areas) and concentrations was found over the range of 3.6-11500 ng mL(-1) with a linear regression coefficient of 0.998. The limit of detection (LOD) and quantification (LOQ) in plasma were 1.0 and 3.3 ng mL(-1), respectively. The %RSD (n=5) data for five plasma samples containing 15, 25, 50, and 100 ng mL(-1) of MDMA were 1.02, 1.12, 2.05, 2.54, respectively.     

Synthesis and vibrational spectroscopic characterisation of synthetic hydrozincite and smithsonite

Hydrozincite and smithsonite were synthesised by controlling the partial pressure of CO₂. Previous crystallographic studies concluded that the structure of hydrozincite was a simple one. However both Raman and infrared spectroscopy show that this conclusion is questionable. Multiple bands are observed in both the Raman and infrared spectra in the (CO₃)²⁻ antisymmetric stretching and bending regions of hydrozincite showing that the symmetry of the carbonate anion is reduced and in all probability the carbonate anions are not equivalent in the hydrozincite structure. Multiple OH stretching vibrations centred in both the Raman and infrared spectra show that the OH units in the hydrozincite structure are non-equivalent. The Raman spectrum of synthetic smithsonite is a simple spectrum characteristic of carbonate with Raman bands observed at 1408, 1092 and 730 cm⁻¹.     

Some contribution to W(VI)-peroxo-chemistry: Synthesis,spectroscopic characterization,reactivity and DFT studies

Synthesis of white microcrystalline oxodiperoxotungstate(VI) complexes, K[WO(O₂)₂(L)(H₂O)]·H₂O, (L ?= ?salicylate, 5-chlorosalicylate, 4-hydroxybenzoate) have been achieved from reaction of Na₂WO₄·2H₂O with 30% H₂O₂ and the respective hetero-ligands at pH Ca. 7–7.5 in aqueous medium. The newly synthesized compounds were comprehensively characterized by elemental analyses, spectral studies, room temperature magnetic moment measurements and mass spectrometric studies. Infrared spectra suggest that, peroxo groups are bonded to the WO⁺⁴ center in a triangular bidentate (C_2v) fashion and the hetero-ligands benzene-core hydroxycarboxylic acids viz. salicylic acid, 5-chlorosalicylic acid, 4-hydroxybenzoic acid in anoinic form are coordinated in monodentate manner. Compounds are fairly stable in aqueous solution for sufficient period of time. The results of mass spectrometric analysis lend support to the molecular composition of the complexes ascertained on the basis of elemental analyses and spectroscopic studies. Compound potassium(aquo)(5-chlorosalicylato)oxodiperoxotungstate(VI)monohydrate, K[WO(O₂)₂(5-chlorosalicylate)(H₂O)]·H₂O, act as an oxidant of bromide ion in aqueous phase bromination of chosen organic substrates to their corresponding bromo organics. Density Functional Theory (TD-DFT) calculations were performed on the synthesized complexes substantiated the experimentally obtained results. The TD-DFT optimized structures are in excellent agreement with the results of elemental analyses, spectral as well as mass spectrometric data.     

Raman spectroscopic investigation of the antimalarial agent mefloquine

The antimalarial agent mefloquine was investigated using Fourier transform near-infrared (FT NIR) Raman and FT IR spectroscopy. The IR and Raman spectra were calculated with the help of density functional theory (DFT) and a very good agreement with the experimental spectra was achieved. These DFT calculations were applied to unambiguously assign the prominent features in the experimental vibrational spectra. The calculation of the potential energy distribution (PED) and the atomic displacements provide further valuable insight into the molecular vibrations. The most prominent NIR Raman bands at 1,363 cm⁻¹ and 1,434 cm⁻¹ are due to C=C stretching (in the quinoline part of mefloquine) and CH₂ wagging vibrations, while the most intense IR peaks at 1,314 cm⁻¹; 1,147 cm⁻¹; and 1,109 cm⁻¹ mainly consist of ring breathings and δCH (quinoline); C–F stretchings; and asymmetric ring breathings, C–O stretching as well as CH₂ twisting/rockings located at the piperidine moiety. Since the active agent (mefloquine) is usually present in very low concentrations within the biological samples, UV resonance Raman spectra of physiological solutions of mefloquine were recorded. By employing the detailed non-resonant mode assignment it was also possible to unambiguously identify the resonantly enhanced modes at 1,619 cm⁻¹, 1,603 cm⁻¹ and 1,586 cm⁻¹ in the UV Raman spectra as high symmetric C=C stretching vibrations in the quinoline part of mefloquine. These spectroscopic results are important for the interpretation of upcoming in vitro and in vivo mefloquine target interaction experiments.     

Conformational fluxionality in a palladium(II) complex of flexible click chelator 4-phenyl-1-(2-picolyl)-1,2,3-triazole: A dynamic NMR and DFT study

An experimental and theoretical DFT study was carried out on the solution behavior in [D₇]DMF for bis-chelate complex [Pd(L)₂](BF₄)₂·2CH₃CN (L = 4-phenyl-1-(2-picolyl)-1,2,3-triazole). In structure of [Pd(L)₂]²⁺, the central square-planar palladium(II) cation is trans-chelated by two L substrates, each through the pyridine and the triazole N2 nitrogen atoms, forming two six-membered metallacycles. These can adopt boat-like conformations anti-trans-[Pd(L)₂]²⁺ and syn-trans-[Pd(L)₂]²⁺ in which the picolyl methylene carbons are anti or syn, respectively, relative to the palladium coordination plane. In solution, the boat-to-boat inversion at both metallacycles takes place. The conformers are in a dynamic equilibrium, which was monitored by variable-temperature (VT) ¹H NMR spectroscopy in the temperature range of 223-353 K. The equilibrium lies on the side of the anti-trans-[Pd(L)₂]²⁺ conformer and the corresponding reaction enthalpy and entropy is estimated to be 0.6 ± 0.5 kcal mol⁻¹ and 0.8 ± 1 cal mol⁻¹ K⁻¹, respectively. From the full-line-shape analysis of resonances in the VT ¹H NMR spectra, the activation enthalpy and activation entropy was determined to be 13.0 ± 0.4 kcal mol⁻¹ and 2.7 ± 1.6 cal mol⁻¹ K⁻¹, respectively. The activation entropy close to zero suggests a nondissociative mechanism for the isomerisation. DFT investigation revealed that the isomerisation proceeds through a one step mechanism with a barrier of 11.40 kcal mol⁻¹. The structures of the syn and anti conformers as well as that of the transition state were characterized. Energy decomposition analysis was carried out in order to explore the origins of the stability difference between the syn and anti isomers.     

Lewis adducts of the side-on end-on dinitrogen-bridged complex [{(NPN)Ta}2(mu-H)2(mu-eta 1:eta 2-N2)] with AlMe3, GaMe3, and B(C6F5)3: synthesis, structure, and spectroscopic properties

Reaction of the side-on end-on dinitrogen complex [{(NPN)Ta}(2)(mu-H)(2)(mu-eta(1):eta(2)-N(2))] (1; in which NPN=(PhNSiMe(2)CH(2))(2)PPh), with the Lewis acids XR(3) results in the adducts [{(NPN)Ta}(2)(mu-H)(2)(mu-eta(1):eta(2)-NNXR(3))], XR(3)=GaMe(3) (2), AlMe(3) (3), and B(C(6)F(5))(3) (4). The solid-state molecular structures of 2, 3, and 4 demonstrate that the N-N bond length increases relative to those found in 1 by 0.036, 0.043, and 0.073 A, respectively. In solution complexes 2-4 are fluxional as evidenced by variable-temperature (1)H NMR spectroscopy. The (15)N{(1)H} NMR spectra of 2-4 are reported; furthermore, their vibrational properties and electronic structures are evaluated. The vibrational structures are found to be closely related to that of the parent complex 1. Detailed spectroscopic analysis on 2-4 leads to the identification of the theoretically expected six normal modes of the Ta(2)N(2) core. On the basis of experimental frequencies and the QCB-NCA procedure, the force constants are determined. Importantly, the N-N force constant decreases from 2.430 mdyn A(-1) in 1 to 1.876 (2), 1.729 (3), and 1.515 mdyn A(-1) (4), in line with the sequence of N-N bond lengths determined crystallographically. DFT calculations on a generic model of the Lewis acid adducts 2-4 reveal that the major donor interaction between the terminal nitrogen atom and the Lewis acid is mediated by a sigma/pi hybrid molecular orbital of N(2), corresponding to a sigma bond. Charge analysis performed for the adducts indicates that the negative charge on the terminal nitrogen atom of the dinitrogen ligand increases with respect to 1. The lengthening of the N-N bond observed for the Lewis adducts is therefore explained by the fact that charge donation from the complex fragment into the pi* orbitals of dinitrogen is increased, while electron density from the N-N bonding orbitals p(sigma) and pi(h) is withdrawn due to the sigma interaction with the Lewis acid.     

Theoretical studies of the oxidative addition of PhBr to Pd(PX3)2 and Pd(X2PCH2CH2PX2) (X = Me, H, Cl)

The density functional theory calculations were used to study the influence of the substituent at P on the oxidative addition of PhBr to Pd(PX₃)₂ and Pd(X₂PCH₂CH₂PX₂) where X = Me, H, Cl. It was shown that the C_ipso-Br activation energy by Pd(PX₃)₂ correlates well with the rigidity of the X₃P-Pd-PX₃ angle and increases via the trend X = Cl < H < Me. The more rigid the X₃P-Pd-PX₃ angle is, the higher the oxidative addition barrier is. The exothermicity of this reaction also increases via the same sequence X = Cl < H < Me. The trend in the exothermicity is a result of the Pd(II)-PX₃ bond strength increasing faster than the Pd(0)-PX₃ bond strength upon going from X = Cl to Me. Contrary to the trend in the barrier to the oxidative addition of PhBr to Pd(PX₃)₂, the C_ipso-Br activation energy by Pd(X₂PCH₂CH₂PX₂) decreases in the following order X = Cl > H > Me. This trend correlates well with the filled d_π orbital energy of the metal center. For a given X, the oxidative addition reaction energy was found to be more exothermic for the case of X₂PCH₂CH₂PX₂ than for the case of PX₃. This effect is especially more important for the strong electron donating phosphine ligands (X = Me) than for the weak electron donating phosphine ligands (X = Cl).     

Synthesis and Characterization of the Silylated Hexaphenyl Carbodiphosphorane [Me3SiC(PPh3)2][CF3SO3]

The addition of trimethylsilyl trifluoromethanesulfonate TMS‐OTf (CF₃SO₃ = OTf, triflate) to hexaphenyl carbodiphosphorane PPh₃=C=PPh₃ ( 1 ) in toluene yields the silylated carbodiphosphorane [Me₃SiC(PPh₃)₂][OTf] ( 2 ). Compound 2 represents the first silylated carbodiphosphorane characterized in solution and in the solid state. 2 is an air‐sensitive compound but stable in solution and in the solid state in an inert atmosphere as shown by heteronuclear NMR experiments and also by X‐ray diffraction analysis. Compound 2 crystallizes in the monoclinic space group P2₁/n with the cell dimensions a = 1161.7(1), b = 1714.4(1), c = 1903.3(1) pm; β = 102.74(1)° and Z = 4. Structure, frontier orbitals, and dissociation energies for 2 were determined by density functional theory‐based computations highlighting the character of 2 as a Lewis acid adduct of a carbon(0) compound.     

A NMR, X-ray, and DFT combined study on the regio-chemistry of nucleophilic addition to platinum(II) coordinated terminal olefins

The series of platinum complexes [PtCl(η²-CH₂CH-C₆H₄-X)(tmeda)](ClO₄) (X = H, 1b; 4-OMe, 1c; 3-OMe, 1d; 4-CF₃, 1e; 3-CF₃, 1f; 3-NO₂, 1g; tmeda = N,N,N′,N′-tetramethyl-1,2-ethanediamine) has been considered. In the styrene complex (1b) both solution (NMR) and solid state (X-ray) data indicate a significant difference in the Pt-C bond lengths (the longer bond being that involving the olefin carbon atom carrying the phenyl ring). Such a difference increases when X is an electron donor group (EDG, 1c) and decreases when X is an electron withdrawing group (EWG, 1d-g). The attack of a nucleophile (MeO⁻) to the substituted carbon (Markovnikov type, M) is by far the most favoured in the case of unsubstituted (1b) or EDG-substituted (1c) styrenes. The presence of an EWG (compounds 1d-g) levels off the probability of M and anti-M type of attack. DFT calculations on 1b,c and 1e were also performed. The NLMO analysis reveals the crucial role of the interaction between the filled π orbital of the olefin and the empty d orbital of platinum; the carbon with greater electron density becoming less susceptible of nucleophilic attack.     

Vibrational spectra of mixed (phthalocyaninato)(porphyrinato) yttrium(III) double-decker complexes: Density functional theory calculations

The vibrational (IR and Raman) spectra of neutral and reduced mixed (phthalocyaninato)(porphyrinato) yttrium(III) double-decker complexes Y(Pc)(Por) and [Y(Pc)(Por)]⁻ [the simplified models of mixed (phthalocyaninato)(porphyrinato) rare earth(III) complexes] are studied using density functional theory (DFT) calculations. The simulated IR and Raman spectra of Y(Pc)(Por) are compared with the experimental IR spectrum of Tb(Pc)(TClPP) and Raman spectrum of Y(Pc)(TClPP), respectively, and many bands can acceptably fit in spite of the different species. On the basis of comparison with the simulated spectra of PbPc and PbPor together with the assistance of normal coordinate analysis, the calculated frequencies in their IR and Raman spectra are identified in terms of the vibrational mode of different ligand for the first time. The calculated frequency at 1048 cm⁻¹ in the IR spectrum of [Y(Pc)(Por)]⁻ with contribution from both Pc and Por vibrational modes is the characteristic IR vibrational mode of the reduced double-decker, while the characteristic IR vibrational mode of Y(Pc)(Por) attributed from the vibration of phthalocyanine monoanion radical Pc⁻ appears at 1257 cm⁻¹. In line with our previous experimental findings that the Raman spectra of M(Pc)(TPP) and M(Pc)(TClPP) are dominated by the Pc vibrational modes, theoretical calculations indicate that most of the Raman vibrational modes contributed from Por ring are covered up by those of Pc ring and thus are hard to be recognized in the Raman spectra of [Y(Pc)(Por)]⁻ and Y(Pc)(Por) due to their much weaker intensity in comparison with that of Pc ligand. Comparison in the IR and Raman spectra between [Y(Pc)(Por)]⁻ and Y(Pc)(Por) also suggests the localization of hole on the Pc ring in the neutral double-decker Y(Pc)(Por). The present work, representing the first detailed DFT study on the vibrational spectra of mixed (phthalocyaninato)(porphyrinato) rare earth(III) double-decker complexes, is useful in helping to understand the vibrational spectroscopic properties of this series of mixed tetrapyrrole ring complexes.     

Matrix-isolation FT-IR study and theoretical calculations of the vibrational, tautomeric and H-bonding properties of hypoxanthine

The neutral compound hypoxanthine is investigated using the technique of matrix-isolation FT-IR spectroscopy combined with density functional theory (DFT) and ab initio methods. Two theoretical methods (RHF and DFT/B3-LYP) are compared for vibrational frequency prediction, and four methods (RHF//RHF, MP2//RHF, DFT//DFT and MP2//DFT) for prediction of the relative energies of the tautomers and the interaction energies of the complexes. All the possible tautomeric forms have been considered theoretically, and the results indicate that two oxo forms (O17 and O19) and one hydroxy form (H9-r1) are the three most stable forms. The experimental FT-IR spectra are consistent with this prediction, and nearly all the characteristic spectral features of these forms have been identified in the spectrum. A theoretical study of the H-bonded complexes of these three tautomers with water is also performed. Several structures have been found for each form and the results demonstrate that the closed complexes with two H-bonds are the most stable systems due to the H-bond cooperative effect.     

Vibrational Spectra and Density Functional Theory Calculations of Metallo-tetra-(tert-butyl)-tetra-azaporphyrines

The infrared absorption and 514.5 nm excited Raman spectra were measured for the metallo-tetra-(tert-butyl)-tetraazaporphyrin (MT(tBu)TAP, M=Cu, Co, Ni, Zn). The ground-state structures and vibrational spectra of MT(tBu)TAPs have been calculated at the B3LYP level of theory. The observed Raman and IR bands have been assigned based on the calculation results and by comparing with the normal metalloporphyrins. The relationship between the Raman/IR frequencies and the structures of TAP ring was investigated. The results show that the frequencies of C_βC_β′ stretch (A_g), asymmetric C_αN_m stretch (A_g), and symmetric C_αN_m stretch (B_g) modes increase linearly with the decrease of the core-sizes of TAP ring.Among the three modes, the later two are more sensitive to the core-size change.     

Unusual conformational properties of 1,3-dimethyl-1,1,3,3-tetrakis(trimethylsilyl)trisilane: A preparative, X-ray, Raman spectroscopic and ab initio study

The heptasilane Me(SiMe₃)₂SiSiH₂SiMe(SiMe₃)₂ was synthesized from Me(SiMe₃)₂SiK and H₂Si(OSO₂CF₃)₂. Crystals suitable for a X-ray single crystal analysis could be grown, with the somewhat surprising result that the two dihedral angles (H₃)CSiSi(H₂)Si are different in the crystal (24.58(10)° and 31.67(11)°). SiSiSi-bonds angles are widened, with values up to 117°. Ab initio calculations at the density functional B3LYP level employing 6-311G(d) basis sets predict minima for five conformers 1-5 with relative energies 0.0, 3.1, 8.2, 10.8 and 18.1 kJ/mol, respectively. Moreover, SiSiSiSi dihedral angles spanning the range 43.5-172.3° are predicted, reflecting the small forces which are required for distorting these angles.In the Raman spectrum of a solution in toluene, three lines at 350, 340 and 330 cm⁻¹ are observed in a wavenumber range which is typical for the SiSi-pulsation of methylated oligosilanes. The relative intensity ratio of the bands is temperature dependent, reflecting the changes in conformer concentrations that occur according to Boltzman’s law. Supported by the ab initio calculations, the Raman band at 350 cm⁻¹ is assigned to an ‘averaged’ conformer 1 and 2, because a rapid interconversion between 1 and 2 has to be assumed due to a small barrier separating them. The bands with wavenumbers 340 and 330 cm⁻¹ originate from conformers 3 and 4. From the Raman spectra, relative energies 0.0 (1 + 2), 2.2 (3) and 6.3 (4) kJ/mol are deduced, the presence of 5 is not observed. Caused by solvent effects, these values differ somewhat from the ab initio results.     

A series of ruthenium(II) organometallic complexes incorporating pyridine-2-carboxylato ligand: Detailed spectroscopic and computional studies

The reaction of Ru(κ2C,O-RL)(PPh3)2(CO)Cl, 1 with excess sodium salt of pyridine-2-carboxylic acid (Napic) furnishes the complexes of the type Ru(κ1C-RL)(PPh3)2(CO) (pic), 2(R) with excellent yield (κ2C,O-RL is C6H2O-2-CHNHC6H4R(p)-3-Me-5, κ1C-RL is C6H2OH-2-CHNC6H4R(p)-3-Me-5 and R is Me, OMe, Cl). The chelation of pic is attended with the cleavage of Ru–O and Ru–Cl bonds and iminium–phenolato→imine–phenol prototropic shift. The 1 ​→ ​2 conversion is irreversible and the type 2 species are thermodynamically more stable than the acetate, nitrite and nitrate complexes of 1. The spectral (UV–vis, IR, 1H NMR) and electrochemical data of the complexes are reported. In dichloromethane solution the complexes display one quasi–reversible RuIII/RuII cyclic voltammetric response with E1/2 in the range 0.72–0.80 ​V vs. Ag/AgCl. The crystal and molecular structure of Ru(κ1C-MeOL)(PPh3)2(CO)(pic)∙CH3CN is reported which revealed distorted octahedral RuC2P2NO coordination sphere. The pairs (P, P), (C, O) and (C, N) define the three trans directions. The electronic structures of the complexes are also scrutinized by density functional theory (DFT) and time–dependent density functional theory (TD–DFT) calculations.     

Vibrational studies of sulfamoil chloride (ClSO2NH2)

The infrared spectrum of sulfamoil chloride in the liquid phase was reinvestigated; the infrared and Raman spectra of the solid phase have also been obtained. A complete assignment of the observed bands is proposed. A subsequent normal coordinate analysis was performed. The experimental data are compared to results of ab initio and DFT (density functional theory) calculations. According to the experimental and theoretical results the main conformer of ClSO₂NH₂ possesses an anti conformation (C_s symmetry, S---Cl single bond in anti position with respect to the nitrogen lone pair).     

The Beijing four-component density functional program package (BDF) and its application to EuO, EuS, YbO and YbS

A four-component density functional program package (Beijing Density Functional), suitable for the calculation of total-energy-related chemical properties of systems containing heavy atoms, was developed. The code is based on modern sophisticated exchange-correlation functionals and was applied to calculate the spectroscopic constants of the lanthanide diatomic molecules of EuO, EuS, YbO and YbS. It is suggested that the experimental bond lengths for EuS and YbS, derived from empirical interpolations, need to be revised. Relativistic effects on the electronic structure are discussed and compared with results from previous work. The involvement of the lanthanide valence orbitals in chemical bonding is investigated with a newly developed population and bonding analysis approach. Received: 11 November 1996 / Accepted: 5 March 1997     

A density functional derived vibrational force field for β-ionone Use of the ultraviolet resonance Raman intensities to check the vibrational analysis accuracy

In the present article we aim to determine an accurate and transferable molecular force field for β-ionone in order to perform molecular dynamics calculations on the retinal isomers. For β-ionone, a force field is derived from calculations using the Density Functional Theory (DFT). The force constants expressed in the internal coordinate space were scaled fitting theoretical to experimental vibrational wavenumbers. The validity of the force field was checked using a comparison between calculated and observed resonance Raman intensities obtained from the A-term part (Franck–Condon) of the scattering tensor.     

Paramagnetic NMR shift,spectroscopic and molecular modeling studies of lanthanide(III)-morin complexes

Studies on nine-coordinate lanthanide complexes of morin are described. The complexes were characterized by elemental analysis, molar conductance, UV–Vis spectra, IR spectra, thermal analysis and NMR spectra. Molecular modeling studies were also carried out. The complexes are non-electrolytes in DMSO. TGA showed anhydrous nature of the complexes. The electronic spectra of the complexes were recorded in methanol. ¹H NMR spectra of lanthanum, praseodymium, neodymium, samarium and dysprosium complexes have been studied in DMSO-d₆. The complexes do not dissociate in DMSO and retain their coordination. ¹H NMR spectra of paramagnetic and diamagnetic complexes exhibit downfield as well as upfield shifts of morin resonances that shows change in geometry during coordination.