Study of the properties of molecularly imprinted polymers by computational and conformational analysis

In this paper, a simplified model was set up to give an insight into the properties of molecularly imprinted polymer (MIP) at molecular level using MMFF94 force field. Based on our model, the interaction energies (ΔEs) between monomers and template or its analogues were calculated, and the most possible conformations of template or its analogues interacting with monomers in the molar ratio 1/4 were found. The obtained results using the computational and conformational analysis showed that large ΔE meant more activity sites in the cavities in the resultant polymer giving high affinity and good selectivity, leading to a large imprinting factor and when the ΔE differences were small, the imprinting factors were mainly determined by the activity sites. These were well consistent with the experimental results, which confirmed the validity of the model and method proposed that were believed to benefit screening molecularly imprinted systems rapidly in an experiment-free way instead of trial-and-error approach. Considering the affinity and selectivity, 2,6-bisacrylamide pyridine was predicted to be the optimal monomer used to prepare paracetamol MIP for application in quantification of drugs from the ΔE and possible activity sites.     

A qualitative scale for the electron withdrawing effect of substituted phenyl groups and heterocycles

The electron withdrawing effect of a variety of differently substituted phenyl groups can be classified on the basis of the CO or CN distance of the corresponding phenolate or aryl amide ions (Ar-O⁻ and Ar-NH⁻), respectively, which are reliably accessible by DFT calculations on B3LYP/6-311 + G(2d,p) level of theory. An increasing electron withdrawing effect of the aromatic group leads to a shortened CO and CN distance of the corresponding ions. Within the presented model it is also possible to characterize the electronic nature of different kinds of six membered heterocycles.The defined constants Δ(E)_m,p - the difference of the E-C distances of the substituted derivatives X-C₆H₄-E and the non-substituted phenyl derivative, C₆H₅-E - exhibit the same tendency as the corresponding Hammett constants. The values of Δ(E)_m,p strongly depend on the nature of E. With E = F, the resulting values Δ(F)_m,p are found to be accidentally close to the corresponding Hammett constants. Therefore, the values of Δ(E)_m,p, which can be easily determined by DFT calculations, are useful tools to classify the electronic nature of different kinds of substituents.The different electronic nature of the groups E, for example O⁻, NH⁻ or F, gives rise to varying electronic interactions with the connected aromatic ring system. These interactions influence on their part the special interaction of a given substituent X. This is the reason why the constants Δ(E)_m,p exhibits different values, which vary depending on the different electronic nature of the groups E. As a consequence, the values Δ(E)_m,p open the possibility to classify the electronic nature of substituents X in relation to any neutral or even charged group E.     

Theoretical design and selectivity researches on the enrofloxacin imprinted polymer

In this paper, enrofloxacin (ENRO) was chosen as the template molecule, 4-vinylpyridine (4-Vpy), acrylamide (AM), trifluoromethacrylic acid (TFMAA), and 2-hydroxyethyl methacrylate (HEMA) were selected as the functional monomers, with the following cross-linking agents, ethylene glycol dimethacrylate (EDMA), pentaerythritol triacrylate (PETA), and trimethylolpropane trimethacrylate (TRIM). The stable complex configurations formed by ENRO and four monomers at the molar ratio of 1:1 were calculated using the density functional theory at the B3LYP/6-31G(d,p) level. Their natural bond orbital charges and the action sites were discussed to screen the appropriate functional monomer. The optimal molar ratio of template–monomer complex and the effects of cross-linking agent were investigated. The nature of the imprinting interaction was also researched via the infrared spectrum. The results reveal that the complex formed from ENRO and TFMAA has the strongest hydrogen bond interaction. When the molar ratio is 1:7, the complex has the most stable configuration. Owning to the weakest interaction between EDMA and ENRO, and the strongest interaction between EDMA and TFMAA, EDMA is considered as the suitable cross-linking agent, in comparison with PETA and TRIM for ENRO-MIPs. After the removal of ENRO molecule, the most stable ENRO-TFMAA complex owing to the better binding capacity to ENRO is compared with its structural analogues (ciprofloxacin, sparfloxacin, pefloxacin, ofloxacin, and sarafloxacin). This study provides a reliable theoretical guidance for the preparation of new ENRO-MIPs.     

Theoretical Researches on the Recognizing Characteristics of Atrazine Imprinted Polymers with Different Functional Monomers

As a widely used herbicide, the threat of atrazine to both environment and health of people has become the focus. Therefore, the research and analysis of atrazine are getting more important. In this work, the MIT was used to detect atrazine theoretically. Atrazine was taken as a template molecule. MAA, MMA and TFMAA were taken as the functional monomers, respectively. The geometry optimization, the nature of hydrogen bonds, the NBO charge, and the binding energies of the imprinted molecule with the functional monomers were investigated at the B3LYP/6-31g(d,p) level. Results indicated that atrazine had the strongest interaction with TFMAA. When the ratio of atrazine and TFMAA was 1:6, the amount of H-bond formed from atrazine and TFMAA was the largest. Moreover, TFMAA owned the largest binding energy with atrazine while MMA owned the smallest. The study is helpful to interpret experiment phenomena of molecular imprinting and select better functional monomers.     

Linear versus bent bonding in metal-phosphinidene complexes: Theoretical studies of the electrophilic phosphinidene complexes [(Cp)(CO)2MPMe)], [(Cp)(CO)3MPMe)] (M = Cr, Mo, W)

Density functional theory calculations have been performed for the title phosphinidene complexes using the exchange correlation functionals BP86 and B3LYP. The optimized bond lengths and angles of the model compounds are in excellent agreement with experiment. The M-P bond lengths in linear phosphinidene complexes correspond to a Pauling bond order of ∼ 3. The bent geometries at phosphorus in the bent metal phosphinidene complexes are consistent with the presence of a trivalent phosphorus(III) center which is singly bonded to carbon and doubly bonded to transition metal. The analysis of the delocalized Kohn-Sham orbitals shows the polarization of the M-P σ bonding orbitals towards the phosphorus atom in the MPMe bonds, while in the MPMe bond, the contributions of metal and phosphorus are almost the same. In the linear phosphinidene complexes the contributions of the covalent bonding ΔE_orb are more than the electrostatic interaction ΔE_elstat. The bent phosphinidene complexes have a lower degree of covalent bonding than the linear phosphinidene complexes. The major differences between the linear and bent phosphinidene complexes are found in the degree of π-bonding. The MPMe bonds show a true M-P π bond and a deviated π bond due to slight bent M-P-C bond angles. The MPMe bonds show a true M-P π bond and a lone-pair on phosphorus.     

三唑酮分子印迹预组装体系的分子模拟与吸附性能

以三唑酮为模板分子, 以丙烯酰胺(AM)、 丙烯酸(AA)、 甲基丙烯酸(MAA)和三氟甲基丙烯酸(TFMAA)为功能单体预组装了分子印迹聚合物体系, 采用半经验法和从头算法, 利用Hyperchem软件模拟了三唑酮与4种功能单体所组成的分子印迹预组装体系的构型、 能量、 反应配比及复合反应的结合能, 选择复合物结合能最高的功能单体用于分子印迹聚合物的合成. 采用密度泛函方法计算了模板与单体在不同致孔剂中的溶剂化能. 结果表明, 三唑酮与三氟甲基丙烯酸所形成复合物的作用力最强, 在非极性溶剂中溶剂化能最弱. 由预组装体系的差示紫外光谱法研究发现, 一分子三唑酮可与两分子三氟甲基丙烯酸在氯仿中形成氢键复合物, 与分子模拟的结果一致. 在最佳模拟条件下, 合成了三唑酮的印迹聚合物, 利用吸附等温线Langmuir和Freundlich模型研究了印迹聚合物的吸附行为及识别机理. 上述方法对于分子印迹体系的筛选及分子印迹聚合物性能的预测有重要的意义.     

Synthesis and characterization of bimetallic ruthenium complexes connected through linear (CH)14 chain

Treatment of RuHCl(CO)(PPh₃)₃ with (3E,5E,7E,9E,11E)-HCC-(CHCH)₅- CCH produces [RuCl(CO)(PPh₃)₂]₂[μ-(CHCH)₇]. The later complex reacts with PMe₃ to give [RuCl(CO)(PMe₃)₃]₂[μ-(CHCH)₇], the structure of which has been confirmed by X-ray diffraction. The through-space distance from one Ru to the other is 19.88 Å.     

Towards understanding monomer coordination in atom transfer radical polymerization: synthesis of [Cu(PMDETA)(π-M)][BPh4] (M = methyl acrylate, styrene, 1-octene, and methyl methacrylate) and structural studies by FT-IR and H NMR spectroscopy and X-ray crystallography

Cu^I complexes of the form [Cu^I(PMDETA)(π-M)][BPh₄] (where PMDETA = N,N,N′,N″,N″-pentamethyldiethylenetriamine, and M = vinyl monomer) were synthesized and isolated from solution as crystals with methyl acrylate (MA), styrene (Sty), and 1-octene (Oct). The interaction of the CC double bond of the vinyl monomer with Cu^I was characterized via FT-IR and ¹H NMR spectroscopy and single crystal X-ray crystallography. A fourth complex with methyl methacrylate (MMA) was synthesized and characterized spectroscopically, but no crystals suitable for X-ray structure analysis could be obtained. In all complexes, PMDETA acts as a tridentate ligand, while the pseudotetrahedral coordination geometry around Cu^I is completed by a π-interaction with the CC double bond of M in the presence of a non-coordinating counter-ion. A decrease in CC IR stretching frequencies of Δν(CC) = −110, −80, −109, and −127 cm⁻¹ for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coordination. No significant change in CC bond length was seen in the crystal structure for complexes with MA and Oct while a slight lengthening was observed for the Sty complex. The upfield shift of the vinyl proton resonances indicated the presence of significant π-back-bonding.     

Highly stereoselective and efficient synthesis of ω-heterofunctional di- and trienoic esters for Horner-Wadsworth-Emmons reaction via alkyne hydrozirconation and Pd-catalyzed alkenylation

In situ OH metalation with ⁱBu₂AlH and hydrozirconation with HZrCp₂Cl of HOCH₂CCH, (E)-HOCH₂CHCHCCH, and HOCH₂CCCH₃ followed by Pd-catalyzed alkenyl-alkenyl coupling with (E)-BrCHCHCO₂Et and (E)-BrCHC(Me)CO₂Et using PEPPSI-IPr (7) as a catalyst provides a highly efficient and selective (?98% all-E) route to ω-hydroxy di- and trienoic acid esters (1a-6a). The corresponding phosphonate esters (1c-4c) of ?98% isomeric purity can be obtained via conventional bromination-phosphonation in >80% yields. As expected, their carbonyl olefination is ca. 85-90% E-selective with alkyl aldehydes but ?98% E-selective with PhCHO and some α,β-unsaturated aldehydes under the conditions used.     

Development of a molecularly imprinted polymer for pyridoxine using an ion-pair as template

One of the main challenges in the molecularly imprinted polymers (MIP) field is the proper MIP design for water-soluble compounds because of appearance of serious drawbacks in polar solvents and insolubility of those compounds in non-polar solvents which are commonly used for MIP synthesis. In this work a novel and simple method for synthesis of molecularly imprinted polymers for a water-soluble compound was introduced. Pyridoxine was chosen as a target molecule and the ion-pair complex formed between pyridoxine ion (Py⁺) and dodecyl sulfate ion (DS⁻) was transferred into the chloroform via liquid-liquid extraction. Then polymerization was carried out in chloroform. The molecular mechanics and density functional theory were proposed to screen proper monomer. Binding energy, ΔE, of a template and a monomer as a measure of their interaction was considered. Ion-pair [Py⁺-DS⁻] was supposed as a template molecule and acrylic acid, methacrylic acid, allyamine, vinylpridine and 2-hydroxy ethyl methacrylate were as tested monomers. The MIP synthesized using acrylic acid showed the highest selectivity to pyridoxine as predicted from the ΔE calculation. The obtained MIP showed very high affinity against vitamin B6 in comparison to non-imprinted polymers (NIP). It was proved that the obtained MIP with introduced method was much better than that prepared in methanol as porogen. It was showed that the MIP prepared by this new method could be used as an adsorber for extraction and determination of pyridoxine in real and synthetic samples.     

2π + 2π cycloaddition kinetics of some fluoro olefins and fluoro vinyl ethers

The second order 2π + 2π homo- and co-dimerization between various classes of fluorinated olefins has been investigated. The fluorinated olefins examined in this study were: (1) R_fOCFCF₂ (perfluorinated vinyl ethers); (2) R_fCFCF₂ (perfluorinated terminal olefins); (3) RCH₂CFCF₂; (4) PhOCFCF₂ (aryl perfluorinated vinyl ethers).Homo-dimerizations between vinyl ethers have an E_a between 20 and 24 kcal mol⁻¹ while homo-dimerizations between terminal olefins have an average E_a between 35 and 40 kcal mol⁻¹; vinyl groups have a second order cyclodimerization rate constant of formation between 1 × 10⁻⁷ and 1 × 10⁻⁴ M⁻¹ S⁻¹ while vinyl ethers have a second order cyclodimerization rate constant of formation = 1 × 10⁻¹ M⁻¹ s⁻¹. If there is a CH₂ group α to the terminal olefin, the E_a of cyclodimerization is about 7 kcal mol⁻¹) lower with respect to those olefins with a CF₂ α to the instauration. At 270 °C co-dimerizations have an average ΔS^≠ = −45 cal K⁻¹ mol⁻¹ and a second order rate constant of cyclodimerization ranging between 0.1 × 10⁻⁴ M⁻¹ S⁻¹ and 16 × 10⁻⁴ M⁻¹ S⁻¹ while homo-dimerizations have an average ΔS^≠ = −17 cal K⁻¹ mol⁻¹ and a second order rate constant which can span from 7 × 10⁻⁷ M⁻¹ S⁻¹ to as much as 1 × 10⁻¹ M⁻¹ S⁻¹ depending on the electronic nature of the perfluorinated terminal olefin.A good correlation between the electronegativity χ and the activation energy E_a demonstrates that “polarizing” groups, O, PhO, α to the olefin play an important role in the formation and stabilization of the cyclodimerization biradical intermediate.     

Synthesis and characterization of (CHCH)n-bridged (n = 1, 2, 3) heterobimetallic and trimetallic ferrocene-ruthenium complexes

A series of heterobinuclear ferrocene-ruthenium complexes Fc(CHCH)_nRuCl(CO)(PMe₃)₃ (n = 1, 3; n = 2, 12), Fc(CHCH)RuCl(CO)(Py)(PPh₃)₂ (4), and trimetallic Fc(CHCH)RuCl(CO)(PPh₃)₂(Py-E-(CHCH)Fc) (6) have been prepared. The length of the molecular rods is extended by successive insertion of CHCH spacers in the bridging ligands or the ancillary ligands. The respective products have been fully characterized and the structures of 3 and 12 have been established by X-ray crystallography. Electrochemical studies have revealed that ethenyl heterobimetallic complexes display two successive one-electron processes, and that intermetallic electronic communication between the two endgroups is attenuated with the increase of the length of the conjugated bridge. The electrochemical behavior of the trimetallic complex reveals strong electronic communication between ruthenium and ferrocene transmitted through the ethenyl bridge, however, it also reveals a very weak interaction between ruthenium and ferrocene transmitted through the (E)-CHCH-Py bridge.     

A new mechanism for the addition of alcohols to disilenes revealed by DFT and ONIOM calculations

Density functional and ONIOM calculations of alcohol and phenol additions to two (tetramethyl and tetramesityl) disilenes were carried out. The dimer of MeOH adds to Me₂SiSiMe₂ more readily than the monomer. The trimer does not afford the adduct, but a zwitter-ionic intermediate. In the (CF₃OH)₂ addition to Me₂SiSiMe₂, H?Si bond formation is more advanced than O?Si bond formation in the transition state (TS). Addition of seven phenol derivatives to Me₂SiSiMe₂ was examined, and the dimer reactions were found to be superior to the monomer reaction regardless of the substituents on the benzene rings. (MeOH)₂ reacts also with Mes₂SiSiMes₂ favorably, and an isomer of the reactant-like complex (precursor) may afford an adduct of different stereochemistry via internal rotations. Generally, the dimer of the alcohol or phenol is the reactant toward the disilenes. Exceptionally, a monomer of p-(dimethylamino)phenol reacts with Mes₂SiSiMes₂ owing to steric congestion by the four mesityl groups.     

Effect of nanoclay and macroinitiator on the kinetics of atom transfer radical homo- and copolymerization of styrene and methyl methacrylate initiated with CCl3-terminated poly (vinyl acetate) macroinitiator

Effect of nanoclay on the kinetics of atom transfer radical bulk homo- and copolymerization of styrene (St) and methyl methacrylate (MMA) initiated with CCl₃-terminated poly (vinyl acetate) macroinitiator at 90 °C was investigated. CuCl/PMDETA was used as a catalyst system. Results showed that nanoclay significantly enhances the homopolymerization rate of MMA. It was attributed to the activated conjugated CC bond of MMA monomer via interaction between the carbonyl group of MMA monomer and the hydroxyl moiety (AlOH) of nanoclay as well as to the effect of nanoclay on the dynamic equilibrium between the active (macro)radicals and dormant species. Homopolymerization rate of St (a noncoordinative monomer with nanoclay) decreased slightly in the presence of nanoclay. It could be explained by inserting of a portion of macroinitiator into the clay galleries, where no sufficient St monomer exists due to the low compatibility or interaction of St monomer with nanoclay to react with the macroinitiator. Controlled/living characteristic of all the reactions were confirmed by GPC results. More reliable reactivity ratios of the St and MMA in the presence of nanoclay were calculated by using the cumulative average copolymer composition at the moderate to high conversion to be r_St = 0.290 ± 0.082, r_MMA = 0.443 ± 0.093 (extended Kelen-Tudos method) and r_St = 0.293 ± 0.071, r_MMA = 0.447 ± 0.080 (Mao-Huglin method). Results indicated that the rate of incorporation of MMA comonomer into the copolymer increases in the presence of nanoclay, verifying the existence of interaction between the carbonyl group of MMA comonomer and the hydroxyl moiety of nanoclay. It was found that in the presence of nanoclay, tendency of the random copolymerization of St and MMA toward an alternating copolymerization increases.     

Preparation of E-(1,2-difluoro-1,2-ethenediyl)bis(tributylstannane)

Chlorotrifluoroethene is converted in situ to [F₂CCFSiMe₃]. The crude [F₂CCFSiMe₃] solution is reduced with lithium aluminum hydride to (HFCCFSiMe₃), which (without isolation) is converted to (Z)-HFCCFSnBu₃. Subsequent metallation and trapping of the vinyllithium reagent with Bu₃SnCl gives (E)-Bu₃SnCFCFSnBu₃ in 73% overall yield. Only two isolation steps are required and the use of Me₃SiCl and F₂CCFCl provides a cheap, economical route to this useful synthon.     

Quantification of the push-pull character of azo dyes and a basis for their evaluation as potential nonlinear optical materials

The push-pull characters of a large series of donor-acceptor substituted azo dyes—71 structures in all—have been quantified by the NN double bond lengths, d_NN, the ¹⁵N NMR chemical shift differences, Δδ_15N, of the two nitrogen atoms and the quotient, π^∗/π, of the occupations of the antibonding π^∗, and bonding π orbitals of this partial NN double bond. The excellent correlation of the occupation quotients with the bond lengths strongly infers that both π^∗/π and d_NN are excellent parameters for quantifying charge alternation in the push-pull chromophore and the molecular hyperpolarizability, β₀, of these compounds. By this approach, selected compounds can be appropriately considered as viable candidates for nonlinear optical (NLO) applications.     

Stereoselective synthesis of unsymmetrical conjugated dienes and trienes utilizing silacyclobutenes

Treatment of the different kinds of alkynyl-substituted dialkynyldiarylsilanes with zirconocene-ethylene complex Cp₂Zr(CH₂CH₂) followed by acidification with 3 N HCl gave regio- and stereoselectively the corresponding silacyclobutenes in good yields. Desilylation of the silacyclobutenes with tetrabutylammonium fluoride afforded stereoselectively unsymmetrical conjugated (1E,3E)-dienes and -trienes (R¹ or R² = 1-cyclohexenyl) in excellent yields.     

Twisted molecular geometry and localized electronic structure of the triplet excited gem-diphenyltrimethylenemethane biradical: substituent effects on thermoluminescence and related theoretical calculations

Substituent effects on the energies of electronic transitions (ETs) between the triplet excited and ground states of gem-diphenyltrimethylenemethane biradicals (³2a) were explored by using thermoluminescence (TL) spectroscopy and density functional theory (DFT) including time-dependent (TD) DFT. Linear free energy (Hammett) analyses of TL energies of a variety of para-substituted aryl derivatives of ³2* gave reasonable correlations with the substituent constant, σ. The slope of Hammett plots of the data are nearly identical to one obtained from a similar analysis of the photoluminescence (PL) energies of the structurally-related 1,1-diarylethyl radicals (3*). The results suggest that TL of ³2* and PL of 3* derive from a common diarylmethyl radical fluorophore. This interpretation is also supported by the DFT and TDDFT calculated electronic structures and ET energies of ³2 and 3. Thermodynamic and kinetic analyses of the charge recombination (CR) process between 2⁺ and 1⁻, which generates ³2*, revealed that substituents not only alter the TL energies but also the TL intensities of ³2*. The observations made in this effort demonstrate that ³2* as well as ³2 and 2⁺ have greatly twisted molecular geometries and highly localized electronic structures.     

Hemilability and regioselectivity in palladium and platinum complexes of dppm(E) [E = O, S, Se] ligands

Hemilability and nonrigidity in a series of mixed P^PE donor ligands where E = O, S, or Se have been studied in palladium and platinum complexes of the type [M{κ²-(dimethylamino)ethylnaphthyl-C,N)}(P^PE)][SbF₆] where P^PE = Ph₂PCH₂P(E)Ph₂.The role of the donor in hemilability, regioselectivity and the binding preferences of particular donors trans to the metallated carbon atom were also investigated. NMR parameters including couplings to ¹⁹⁵Pt and ⁷⁷Se were investigated for cis and trans isomers. The magnitude of ²J¹³C-⁷⁷Se couplings can readily distinguish the cis and trans isomers. A large through-space ¹³C-⁷⁷Se ³J coupling was observed in one of the amino methyl groups of the dppm(Se) complexes.