Synthesis and nonlinear optical properties of new symmetrically substituted stilbenes

Three new chromophores and trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(dimethyl amino) stilbene (DMANHAS) have been synthesized and whose chemical structures have been characterized by ¹H NMR, IR, and elemental analyses. Linear absorption, single-photon-induced fluorescence and two-photon-induced fluorescence are experimentally studied. Trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(dimethyl amino)stilbene (DMAHAS) and trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(diethyl amino)stilbene (DEAHAS) have effective two-photon absorption cross-sections of σ₂=0.91×10⁻⁴⁶ cm⁴ s/photon and σ₂=1.19×10⁻⁴⁶ cm⁴ s/photon at 532 nm by using an open aperture Z-scan technique, respectively. When pumped with 800 nm laser irradiation, DMAHAS and DEAHAS indicate strong two-photon-induced blue fluorescence of 436 and 440 nm, respectively, while trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(diethyl amino) stilbene (DEANHAS) and DMANHAS exhibit no fluorescence.     

Synthesis and evaluation of new fluorescent derivatization reagents for resolution of chiral amines by RP-HPLC

New fluorescent chiral derivatization reagents (i.e., DBD-trans-4-hydroxy-l-proline, DBD-cis-4-hydroxy-l-proline, DBD-cis-4-hydroxy-d-proline, and DBD-trans-3-hydroxy-l-proline) were synthesized from the reaction of 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole with corresponding hydroxy-prolines. These reagents reacted with chiral amine to produce a couple of diastereomers. The labeling efficiently proceeded in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and pyridine as the activation reagents. The reaction conditions are mild and no racemization occurred during both the reagent synthesis and the diastereomer formation (<0.4%). The resulting diastereomers fluoresce at around 560 nm (excitation at around 450 nm). Good linearity of the calibration curves was obtained in the range of 1-75 pmol and the detection limits on chromatogram were less than 1 pmol. The separability of the diastereomers was evaluated in terms of separation factor (α) and resolution value (Rs). DBD-trans-4-hydroxy-l-proline was efficient for the resolution of dl-phenylalanine methylester; while DBD-cis-4-hydroxy-d(or l)-proline was excellent for the separation of 1-(1-naphtyl)ethylamines, as comparing with trans-4-hydroxy isomer. The reagents of cis-isomer seemed to be predominant for the resolution of hydrophobic enantiomers. On the other hand, trans-isomers were suitable for the separation of the racemic amines containing ester in the structure. With respect to the position of OH group, the effect seems to be less, judging from the results of DBD-trans-4-hydroxy-l-proline and DBD-trans-3-hydroxy-l-proline toward phenylalanine methylester. The results suggest that the separation is dependent upon both structures of the amines and the reagent used. Thus, the stereostructure, hydrophobicity and hydrogen bonding of the diastereomer, etc. seem to be affecting the separation.     

Liquid chromatographic determination of cis-platin as platinum(II) in pharmaceutical preparation, serum and urine samples of cancer patients

Spectrophotometric and high performance liquid chromatographic (HPLC) methods have been developed for the determination of cis-platin and carboplatin based on the pre-column derivatization of platinum(II) with 2-acetylpyridine-4-phenyl-3-thiosemicarbazone. The complex was extracted in chloroform with molar absorptivity of 2.2 × 10⁴ L mol⁻¹ cm⁻¹ at 380 nm. The complex eluted from a Phenomenex C-18 (150 mm × 4.6 mm i.d.) column with methanol:water:acetonitrile:tetrabutyl ammonium bromide (1 mM) (44:30:25:1, v/v/v/v) with a flow rate of 1 ml/min and UV detection at 260 nm. Ruthenium(IV) and selenium(IV) also separated completely. The linear calibration curve was with 0.5-12.5 μg/ml and detection limit of 10 ng/ml platinum(II).The analysis of cis-platin and carboplatin injections by spectrophotometric and HPLC methods indicated relative standard deviation (R.S.D.) of 0.66-2.1%. The method was used for the determinations of cis-platin in serum and urine of cancer patients after chemotherapy and platinum contents were found 148-444 and 50-90 ng/ml with R.S.D. of 0.3-3.0 and 0.6-2.4% for the serum and urine, respectively. The recovery of platinum(II) from serum was 97% with R.S.D. 2.2%.     

Heterobimetallic [Ru(II)/Fe(II)] complexes: On the formation of trans- and cis-[RuCl2(dppf)(diimines)]

The synthesis and characterization of trans/cis-[RuCl₂(dppf)(diimines)], dppf = 1,1′-bis(diphenylphosphino)ferrocene; diimines = 2,2′-bipyridine (trans/cis-(1)), the new complexes with 4,4′-dimethyl-2,2′-bipyridine (trans/cis-(2)) and 1,10-phenanthroline (cis-(3)) are presented. The complexes were synthesized using two routes and the trans/cis-isomer formation is dependent upon conditions and the precursor applied. The trans-isomer (kinetic) readily isomerizes to the cis-isomer (thermodynamic) when exposed to light (fluorescent) and this process was followed by cyclic voltammetry and UV-vis. The electrochemical studies on these complexes reveal that Fe^(III)/Fe^(II) couples are insensitive to the isomer (trans/cis) formed, but the Ru^(III)/Ru^(II) couples are dependent on the isomer. Transfer-hydrogenation reactions for reduction of acetophenone were conducted using complexes cis-(1) and cis-(2) and the results are compared with that obtained for similar complexes. X-ray structure for cis-(3) are presented and discussed.     

Solid-phase extraction of organic compounds in atmospheric aerosol particles collected with the particle-into-liquid sampler and analysis by liquid chromatography-mass spectrometry

Atmospheric aerosol particles, collected with the particle-into-liquid sampler at SMEARII station in Finland in mid-August 2007, were analysed for biogenic acids. The sample pretreatment method, comprising solid-phase extraction with anion exchange and hydrophilic-lipophilic balance materials, was optimized. Extraction efficiencies of solid-phase extraction from 10 and 20 ml samples were about 100%, with average relative standard deviation of 8.9%, in concentration range from 12.5 to 50 ng/ml of the acid. Extraction of aldehydes was less successful, with efficiencies from 69 to 163% and average 10% deviation. Pretreated samples were analysed by reversed phase high performance liquid chromatography with ion trap mass spectrometric detection. Limits of detection achieved for organic acids with the analytical procedure developed ranged from 9 to 27 μg/l of extracted sample, while limits of quantitation were from 31 to 90 μg/l. Oxidation with ozone was used for the preparation of the acid of β-caryophyllene (β-caryophyllinic acid), which was also studied in aerosol samples. MS² experiments were used to confirm the identification of trans-pinic, trans-pinonic and β-caryophyllinic acids. Azelaic, hexadecanoic, cis-pinonic, and cis- and trans-pinic acids were quantitated in the samples with use of authentic standards, while the concentrations of trans-pinonic and β-caryophyllinic acids were determined with cis-pinonic acid as surrogate. Also, the contribution of β-caryophyllene oxidation products to aerosol organic carbon was evaluated. Aldehydes could not be analysed in real samples due to the insufficient extraction. The particle-into-liquid sampler proved to be suitable for the collection of aerosol particles for the elucidation of daily and diurnal variation of selected species. The optimized sample pretreatment, together with the analysis method, offer a promising approach for the study of aerosol chemical composition, where artifact formation is minimal and time resolution is good.     

cis- and trans-Bis(pyridine)chromium(III) complexes containing mixed-valence chrysenesemiquinonate–chrysenecatecholate ligands: Synthesis,characterization and interpretation of the electronic absorption spectra using ZINDO/S method

Two new geometrical isomers of [Cr(py)₂(chrySQ)(chryCat)] (chrySQ = chrysenesemiquinonate; chryCat = chrysenecatecholate; py = pyridine) were synthesized by two different synthetic procedures. In the first, an acetonitrile solution containing a stoichiometric mixture of Cr(CO)₆, chrysenequinone and pyridine was photolyzed with a Hg-lamp. The second procedure was based on substituting one of the chrysenesemiquinonate ligand in the tris-[Cr(chrySQ)₃] complex with two pyridine ligands. In both procedures two isomeric forms of [Cr(py)(chrySQ)(chryCat)] were isolated with the trans-isomer obtained in higher yield. The structures of the two isomers have been modeled using parameterized PM3 semiempirical method. Theoretical harmonic vibrational frequencies of the cis- and trans-isomers have been computed and compared with the experimental vibrational frequencies. Variable-temperature magnetic susceptibility has been studied for the two isomers in the 10–300 K temperature range. Theoretical modeling of the magnetic data indicated strong antiferromagnetic exchange interaction between Cr^III (S = 3/2) and chrySQ (S = 1/2) with J = −365 ± 6 and −395 ± 4 cm⁻¹ for the cis- and trans-isomers, respectively. The electrochemical behavior of cis- and trans-[Cr(py)₂(chrySQ)(chryCat)] complexes were studied by cyclic voltammetry in acetonitrile solvent. Both complexes showed two one-electron redox processes attributable to reversible reduction and oxidation of the chrySQ and chryCat ligands. Reduction of the Cr(III) to Cr(II) was observed for both complexes near−1300 mV. The electronic spectra of the two isomers were dominated by charge-transfer (LMCT, MLCT and ILCT) transitions. In addition, a low-energy intervalence charge-transfer (IVCT) transition was observed for the cis-isomer at 1085 nm. Theoretical studies of the electronic spectra by ZINDO/S-CI method were useful in interpreting the observed electronic transitions.     

Facile stereoselective synthesis of cis- and trans-3-alkoxyazetidin-2-ones

A highly stereoselective synthesis of cis- and trans-3-alkoxy-3-phenyl/benzylthioazetidin-2-ones is described. The reaction of α-chlorosulfide-β-lactams with various alcohols catalyzed by a Lewis acid such as ZnCl₂ in the presence of molecular sieves (3-4 Å) leads to cis-3-alkoxy-3-phenyl/benzylthio-β-lactams whereas treatment of potassium 2-alkoxy-2-phenylthioethanoate with appropriate Schiff's base using POCl₃ in the presence of triethylamine leads to the formation of trans-3-alkoxy-3-phenylthioazetidin-2-ones as major products.     

Structure and redox behavior of Ru(II)-diene complexes

A series of Ru(acac)₂(η⁴-diene) complexes containing cis- and trans-diene coordination have been investigated by cyclic voltammetry to correlate structural bonding and conformation patterns of diene ligands with redox behaviors. The solid-state structure of Ru(acac)₂(2,3-dimethyl-1,3-butadiene) has been determined by single crystal X-ray diffraction methods. Ru(acac)₂(2,3-dimethyl-1,3-butadiene) crystallizes in the monoclinic space group C2/c with a = 12.368(2) Å, b = 17.0600(2) Å, c = 16.0110(2) Å, β = 98.4405(10)° and V = 3341.38(10) ų for Z = 8. A structural comparison between several Ru-trans-η⁴-diene complexes and Ru-η⁴-1,3-cyclohexadiene revealed no difference in the Ru-C(diene) bond distances. However, through cyclic voltammetry experiments these species demonstrated different redox behavior, as function of the coordinated diene ligand.     

Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

Isolation of the retinal isomers from the isomerization of all-trans-retinal by flash countercurrent chromatography

The isolation of the retinal isomers from all-trans-retinal was performed by flash countercurrent chromatography. In each separation, isomerization reaction solution of 200 mg all-trans-retinal could be loaded on a 1200 mL of high-speed countercurrent chromatographic column with 5 mm bore, eluted by a mobile phase flow rate of 25 mL/min, resulting in 63 mg of 11-cis-retinal, 24 mg of 13-cis-retinal and 26 mg of 9-cis-retinal with purities more than 95%. n-Hexane–acetonitrile (3:1) was used as the solvent system which possesses the advantages of simplicity, re-use of the solvent and multiple injections. This method could be used to prepare 13-cis-retinal, 11-cis-retinal and 9-cis-retinal for the photoisomerization investigation, such as the effect of 11-cis-retinal in the visual system.     

Application of a chiral copper-1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane catalyst for asymmetric cyclopropanation of styrene

The structural effects of the bridge moiety and 5-position on bisoxazoline ligands were studied for the copper-catalyzed asymmetric cyclopropanation of styrene with ethyl diazoacetate. The 1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane ligand showed a remarkable enhancement in the stereoselectivities (trans/cis = 84/16, >99.9% ee for the trans product) compared with the previously reported best ligand, 2,2-bis{2-[(4S)-tert-butyloxazolinyl]}propane (trans/cis = 75/25, 99.0% ee for the trans product).     

Fast,sensitive and highly discriminant gas chromatography–mass spectrometry method for profiling analysis of fatty acids in serum

A method for the determination of fatty acids in serum based on GC–MS (micro-SIS detection mode) has been developed and the separation and cis/trans isomers have been identified. A prior two-step extraction/derivatization procedure accelerated by ultrasound allows individual determination of esterified (EFAs) and non-esterified fatty acids (NEFAs), and shortening of the derivatization steps to 5 min for EFAs and 15 min for NEFAs. The total analysis time for 39 fatty acids was 61 min. The minimum LOD and LOQ values were 0.002 and 0.006 μg/ml, respectively. The proposed method was validated for EFAs and NEFAs using two different methods and the results show no statistical differences between the proposed method and those used as reference. The proposed derivatization–extraction methodology is suitable for fatty-acid analysis of human serum, and can be applied to nutritional and epidemiological studies.     

Alkyl and dialkylammonium tetrafluoroborate catalyzed cis-trans isomerization of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane

Alkyl and dialkylammonium tetrafluoroborate promoted cis-trans isomerization of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane (1) in DMSO-d₆ were studied. The isomerization equilibrium constant K are within the range of 3.74-3.30 from 22 to 47 °C. Thermodynamic parameters of ΔH° and ΔS° for the isomerization were −0.95 kcal/mol and −0.59 cal/mol-K respectively. The isomerization rate is first order in [cis-1] and second order in [R_nNH_4−nBF₄]. Both components of R_nNH_4−n⁺ and BF₄⁻ are essential for the catalytic cis-trans isomerization. The catalytic strength follows the decreasing order of ⁺H₃N(CH₂)₆NH₃⁺>n-C₈H₁₇NH₃⁺>n-C₁₆H₃₃NH₃⁺>Me₃CNH₃⁺>PhCH₂NH₃⁺>Et₂NH₂⁺?Ph₂CHNH₃⁺, Et₃NH⁺. Inversion region was observed in the plot of ln(k_f/T) versus (1/T) with the ceiling located at around 38 °C. The positive activation enthalpy of 9 kcal/mol was estimated at 22-32 °C. The activation enthalpy turns to be slightly negative at T>38 °C.     

Catalytic activity of Mn(III) and Fe(III) complexes of meso-tetra(n-propyl)porphyrin in oxidation of olefins: Meso-alkyl substituent in comparison with the alkenyl and aryl ones

Catalytic activity of Mn(III) and Fe(III) complexes of meso-tetra(n-propyl)porphyrin, MnT(n-Pr)P(X) and FeT(n-Pr)P(X) (X = Cl, SCN, OAc) in oxidation of olefins with tetra-n-butylammonium periodate at room temperature has been studied. The influence of different parameters including the molar ratio of catalyst to imidazole, type of counter ion (X) and oxidative stability of metalloporphyrins on the efficiency of the catalysts was investigated. The results of competitive oxidation of cis- and trans-stilbene suggest the presence of a high-valent Mn-oxo as the predominant oxidant species in equilibrium with a six coordinate complex, MnT(n-Pr)P(ImH)(IO₄) in the case of MnT(n-Pr)P(OAc). An unusual preference for trans-stilbene over cis-stilbene was observed in the reaction catalyzed by FeT(n-Pr)P(OAc). Control reaction indicated a significant cis- to trans-isomerization (81%) in oxidation of cis-stilbene catalyzed by FeT(n-Pr)P(OAc) which may explain the observed unusual cis to trans-stilbene oxide ratio. While oxidation of cyclooctene and styrene led to the exclusive formation of the corresponding epoxides, oxidation of cyclohexene gave 2-cyclohexe-1-ol and cyclohexene oxide as the products. However, the results of this study clearly demonstrate the key role played by the group substituted at the meso positions of metalloporphyrins on their catalytic activity, apart from the electron-donating or electron-withdrawing properties of the substituents.     

A novel and efficient method for the conversion of a trans-hexahydronaphthoxazine to a cis-isomer using boron tribromide

A novel and efficient method for the conversion of a trans-hexahydronaphthoxazine to a cis-isomer was achieved in high yield by utilizing boron tribromide in methylene chloride at −20 °C.     

Enhancement of the photochromic switching speed of bithiophene azo dyes

A series of heteroaryl substituted bithiophene azo dyes in solution were irradiated with visible light to promote the azo E-Z isomerization and then the kinetics of the thermal Z-E back reaction was studied. The speed of this process is strongly influenced by the nature of the aromatic ring linked to the NN function. While thiazole bithiophene azo dyes exhibit high switching speeds between the two isomers, but limited interconversion, for benzothiazole and substituted thiadiazole bithiophene azo dyes the switching between the two photoisomers can be performed in 3 s with a significant conversion of the trans-isomer to the thermal unstable cis-isomer (19-21%) and therefore a notable variation of the visible spectrum is observed.     

RP-LC Determination of the cis-Isomer of Glimepiride in a Bulk Drug Substance

A rapid reversed-phase high-performance liquid chromatographic procedure is developed and validated for the resolution of the cis-isomer of 1-[[p-[2-(3-ethyl-4-methyl-2-oxo-3-pyrroline-1-carboxamido) ethyl] phenyl] sulfonyl]-3-(trans-4-methylcyclohexyl) urea, a dopamine agonist in bulk drugs. The cis-isomer and glimepiride were baseline resolved on a Waters Symmetry column (50 × 4.6 mm, 3.5 μm) using a mobile phase system containing water: tetrahydrofuran (75:25; v/v. The chromatographic resolutions between cis-isomer and glimepiride were found to be greater than two. The developed method was extensively validated and proved to be robust. The limit of detection and the limit of quantification of cis-isomer were 500 and 1,500 ng mL⁻¹, respectively, for 10 μL injection volume. The percentage recovery of the cis-isomer ranged from 97.3 to 102.0 in bulk drug samples of glimepiride. Glimepiride sample solution and mobile phase were found to be stable for at least 48 h. The proposed method was found to be suitable and accurate for the quantitative determination of the cis-isomer in bulk drugs.     

Solid-state cis-trans isomerization reaction of (η-MeC5H4)W(CO)2P(OPr)3I

cis-(η⁵-MeC₅H₄)W(CO)₂P(OⁱPr)₃I (1) was converted to the trans isomer 2 in the solid state (90-110 °C). The reaction was monitored by heating 1 in NMR tubes for periods of time (2-60 min), cooling the tubes to room temperature and determining the conversion by solution ³¹P and ¹H NMR spectroscopy. The data were consistent with a first-order reaction and yielded an activation energy of 59 ± 3 kJ mol⁻¹. Comparative kinetic data were obtained from an in situ analysis of a powder-XRD study of 1. The powder-XRD study was conducted at 80-100 °C (10-60 min), yielding an activation energy of 52 ± 2 kJ mol⁻¹ (first-order reaction). The reaction could not be monitored by single crystal X-ray diffraction as the crystal disintegrated over time on heating. This disintegration process was monitored by optical microscopy and revealed that while the bulk crystal morphology was retained the crystal surface roughened with time. The compounds 1 and 2 were also structurally characterised by X-ray crystallographic techniques.     

Quantification of tripdiolide in human whole blood by liquid chromatography coupled with atmospheric pressure chemical ionization tandem mass spectrometry

A liquid chromatographic-tandem mass spectrometric (LC-MS/MS) assay was developed and validated to determine tripdiolide in human whole blood using dexamethasone acetate as an internal standard (I.S.). Liquid-liquid extraction with ethyl acetate was used to isolate them from the biological matrix. Detection was performed on a mass spectrometer coupled with a negative atmospheric pressure chemical ionization (APCI) in the multiple-reaction monitoring (MRM) mode. The calibration curve was linear (r² = 0.9973) in the concentration range of 0.5-100.0 ng/mL in human whole blood with a lower limit of quantification of 0.5 ng/mL. Intra-day and inter-day relative standard deviations (R.S.D.s) were less than 7.0 and 10.1%, respectively. Extraction recoveries of tripdiolide ranged from 80.5 to 90.1%. This assay can be used to determine trace tripdiolide in human whole blood.