Effects of base pairing on the one-electron reduction rate of cytosine

Using nucleoside derivatives, which are soluble in dichloromethane, we have experimentally demonstrated that the reduction potential of cytosine is lowered by base pairing with guanine.     

alpha-Helical polypeptide microcapsules formed by emulsion-templated self-assembly

alpha-Helical peptide microcapsules were prepared by the emulsion-templated self-assembly of amphiphilic poly(gamma-benzyl L-glutamate)s (PBLG) 1. By mixing solutions of 1 in dichloromethane (in the form of a sodium salt) with water, oil-in-water emulsions were obtained. Spontaneous stripping of the dichloromethane phase caused a decrease in the diameter of the microdroplets and finally stable microcapsules formed. The microcapsules contain an inner aqueous phase as observed by confocal laser scanning microscopy (CLSM). Binding of hydrophobic pyrene molecules to the polypeptide shell was also demonstrated. The present polypeptide microcapsules are stable even after drying in air and they would serve as supramolecular vehicles for both hydrophobic and water-soluble molecules.     

Investigation of chloromethane complexes of cryptophane‐A analogue with butoxy groups using 13C NMR in the solid state and solution along with single crystal X‐ray diffraction

Host‐guest complexes between cryptophane‐A analogue with butoxy groups (cryptophane‐But) and chloromethanes (chloroform, dichloromethane) were investigated in the solid state by means of magic‐angle spinning ¹³C NMR spectroscopy. The separated local fields method with ¹³C‐¹H dipolar recoupling was used to determine the residual dipolar coupling for the guest molecules encaged in the host cavity. In the case of chloroform guest, the residual dipolar interaction was estimated to be about 19 kHz, consistent with a strongly restricted mobility of the guest in the cavity, while no residual interaction was observed for encaged dichloromethane. In order to rationalize this unexpected result, we performed single crystal X‐ray diffraction studies, which confirmed that both guest molecules indeed were present inside the cryptophane cavity, with a certain level of disorder. To improve the insight in the dynamics, we performed a ¹³C NMR spin‐lattice relaxation study for the dichloromethane guest in solution. The system was characterized by chemical exchange, which was slow on the chemical shift time scale but fast with respect to the relaxation rates. Despite these disadvantageous conditions, we demonstrated that the data could be analyzed and that the results were consistent with an isotropic reorientation of dichloromethane within the cryptophane cavity. Copyright © 2015 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.     

Herbicide activity of extracts from Ailanthus altissima (Simaroubaceae)

The purpose of the present study was to isolate and characterize ailanthone-rich materials from the bark of the deciduous tree Ailanthus altissima (Mill.) Swingle and to assess their herbicide activity on selected herbaceous species. Ailanthone-rich fractions were obtained from A. altissima bark by extraction with dichloromethane and ethyl acetate and subsequent purification of these crude extracts, and of the remaining water mixture after solvent extraction, by means of gel permeation chromatography. A number of fractions were isolated and characterized for ailanthone content. A dichloromethane fraction was shown to contain 92% w/w of ailanthone, as demonstrated by HPLC and NMR analysis. A significant pre-emergence herbicide activity was found for most of the extracts which was directly correlated to ailanthone concentration. A remarkable combined pre- and post-emergence herbicide activity was found for a specific fraction. These results indicate that the bark of A. altissima may represent an interesting source for the production of natural herbicides for use in agriculture.     

The electrochemical manipulation of apolar solvent drops in aqueous electrolytes by altering the surface polarity of polypyrrole architectures

We demonstrate an electrochemically assisted three-dimensional robotic system for the pickup, transport and release of dichloromethane drops in electrolytes using polypyrrole-coated O-rings. Changing the oxidation state of the polymer by means of cyclic voltammetry, pickup, transport and release of drops is demonstrated. Also, the drop manipulation is evaluated as a function of different doping agents in the polypyrrole coatings. Moreover, other polypyrrole-coated architectures such as chips and meshes are utilized to manipulate dichloromethane drops to successfully trap and release them on demand in moving electrolytes. These architectures are envisioned for use as microfluidic tools such as microreactors or microseparators.     

HPLC of synthetic polymers characterization of polystyrenes by high performance precipitation liquid chromatography (HPPLC)

Summary The advantages and disadvantages of high performance precipitation liquid chromatography have been demonstrated for polystyrene homopolymers. Depending on the mobile phase composition at the dissolution point of the polymeric sample and surface properties of the stationary phase, elution is governed either by a solution process or by adsorption. A contribution by adsorption was noticed on silica as well as on reversed phases based on silica with a normal phase gradient of increasing polarity (heptane to dichloromethane). Elution was solely governed by solubility of the polymers on both types of stationary phase for polystyrenes with a molecular weight above 35 000 and reversed phase gradient of decreasing polarity (methanol to dichloromethane). Under these conditions an identical dependence of elution solvent composition on sample size was found as for turbidity titrations. Due to differences in the velocity of the eluent front and the polymeric sample with porous stationary phases the polymers can be eluted as colloidal solutions Non-porous stationary phases are superior in this respect because the velocities of eluent and solutes are identical.     

Simulating the ultrathin layer structure of dichloromethane on a solid substrate by means of density functional theory and molecular dynamics

Calculations and a comparison analysis of the density profiles of an ultrathin layer of dichloromethane on three types of solid flat substrates are performed using the functional density and atomistic molecular dynamics approaches. The efficiency of using these techniques as mutually complementary ways of describing the structural properties of nanosized surface layers is demonstrated.     

Tris(pentafluorophenyl)borane: a mild and efficient catalyst for the chemoselective tritylation of alcohols

An efficient acid-catalyzed protection of alcohols as trityl ethers is described using triphenylmethanol in the presence of tris(pentafluorophenyl)borane (3 mol %) in dichloromethane at room temperature. The chemoselectivity of this protocol is demonstrated by studying the tritylation of a primary alcohol in the presence of a secondary alcohol and also the mildness of this catalyst was studied with substrates containing acid labile protecting groups.     

Capillary gas chromatography-mass spectrometry of volatile and semi-volatile compounds of Salvia officinalis

The essential oil and infusion of Salvia officinalis leaves have been widely applied in traditional medicine since ancient times and nowadays subjected to extensive research of their antibacterial, antiviral and cytotoxic properties. This paper shows chemical composition data of S. officinalis leaves essential oil isolated by steam distillation using a Clevenger-type apparatus. Also, the paper presents the chemical content of volatile and semi-volatile compounds of S. officinalis leaves infusion. The volatile and semi-volatile compounds of S. officinalis leaves infusion were isolated by solid-phase extraction (SPE) and liquid-liquid extraction with hexane and dichloromethane. SPE was carried out on 500 mg octadecylsilane (C18) cartridges and elution with dichloromethane. Liquid-liquid extraction was performed with hexane and dichloromethane. The essential oil in dichloromethane and infusion extracts in hexane and dichloromethane were analyzed by gas chromatography coupled with mass spectrometry. The quantitative results obtained by solid-phase extraction and liquid-liquid extraction showed that SPE on C18 performed the highest recovery of the volatile compounds from infusion sample.     

Design and performance of a direct-reading, multichannel spectrometer for the determination of chlorinated purgeable organic compounds by flame infrared-emission spectrometry

The feasibility of determining chlorinated, purgeable organic compounds (POCs) in aqueous samples by flame infrared-emission (FIRE) spectrometry was evaluated with a specially designed, multichannel, dispersive spectrometer having sufficient resolving power to prevent interference from large amounts of non-halogenated POCs that could also be present in the sample. The polychromator was based on a Czerny-Turner optical mounting with a 0.15-m focal length, a nominal focal ratio of f/3, and a reciprocal linear dispersion of 0.15 mum/mm in the first order. The HCl and CO(2) infrared emission bands (3.77 and 4.42 mum, respectively) were monitored in two analytical channels, while a third reference channel, used for background subtraction, monitored the H(2)O background emission at 2.8 mum. Instrumental performance was evaluated with dichloromethane, trichloromethane, trichloroethylene, 1,1,2,2-tetrachloroethane and monochlorobenzene as test compounds, and parameters such as the linear dynamic range, reproducibility, detection limit and signal-to-noise ratio, and extent of spectral crosstalk between channels were determined. The feasibility of performing a quantitative analysis of a two-component mixture of dichloromethane and trichloromethane at trace levels was demonstrated.     

Immobilized versus coated amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phases for the enantioselective separation of cyclopropane derivatives by liquid chromatography

The solvent versatility of Chiralpak IA, a new chiral stationary phase (CSP) containing amylose tris(3,5-dimethylphenylcarabamate) immobilized onto silica gel, is investigated for the enantioselective separation of a set of cyclopropane derivatives using ethyl acetate or dichloromethane (DCM) as non-standard mobile phase eluent and diluent, respectively in high-performance liquid chromatography (HPLC). A comparison of the separation of cyclopropanes on both immobilized and coated amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) in HPLC using a mixture of n-hexane/2-propanol (90/10 and 99/1, v/v) as mobile phase with a flow rate of 0.5 ml/min and UV detection at 254 nm, is demonstrated. The optimized method of separation is used for an online HPLC monitoring for the Rh(II)-catalyzed asymmetric intermolecular cyclopropanations in dichloromethane. Direct analysis techniques without further purification, workup or removal of dichloromethane were summarized. The method provides an easy and direct determination of the enantiomeric excess of the cyclopropanes and selectivity of the catalyst used without any further work up.     

涂布溶剂对涂敷型手性固定相手性识别能力的影响

以微晶纤维素为原料,在非均相乙酰化条件下反应合成了微晶纤维素三醋酸酯。分别以二氯甲烷、三氯甲烷作涂布溶剂,采用减压蒸发溶剂法将其涂布在硅胶上制备成适宜于高效液相色谱上用的涂敷型手性固定相,得到的ＣＳＰｓ对反－２,３－二苯基环氧乙烷和吡喹酮均具有较好的手性识别能力。     

Ring-opening polymerization of α,β-disubstituted oxiranes by α-methoxyphenylmethylium hexachloroantimonate

α-Methoxyphenylmethylium hexachloroantimonate was used as a novel initiator for the polymerization of α,β-disubstituted oxiranes such as cyclohexene oxide (CHO) and 2-butene oxide (trans and cis) (2-BO) at ?78°C with dichloromethane or dichloromethane-toluene mixtures as solvents. The CHO polymerization mixture became turbid and the polymer precipitated in dichloromethane. The CHO polymerization proceed quantitatively in dichloromethane–toluene mixtures. The molecular weight distribution of polyCHO obtained was bimodal regardless of the solvent used. The polymerization of trans-2-BO was heterogeneous in both dichloromethane and dichloromethane–toluene mixture. The polymerization mixtures of cis-2-BO were transparent but reached a limit yield which was less than the polymer yield of trans-2-BO. Furthermore, the microstructure of the poly2-BOs were analyzed by Vandenberg's method and the results confirmed Vandenberg's finding that inversion of configuration occurs in the propagation step.     

Iridium‐Catalyzed Asymmetric Hydrogenation of 3,3‐Disubstituted Allylic Alcohols in Ethereal Solvents

Ir‐phosphinomethyl‐oxazoline complexes have been identified as efficient, highly enantioselective catalysts for the asymmetric hydrogenation of 3,3‐disubstituted allylic alcohols and related homoallylic alcohols. In contrast to other N,P ligand complexes, which require weakly coordinating solvents, such as dichloromethane, these catalysts perform well in more ecofriendly THF or 2‐MeTHF. Their synthetic potential was demonstrated with the formal total synthesis of four bisabolane sesquiterpenes.     

Study of the preferential solvation of some betaine dyes in binary solvent mixtures

The preferential solvation (PS) in mixed binary solvents, e.g. dichloromethane/acetonitrile, dichloromethane/methanol, acetonitrile/water has been studied by monitoring the charge transfer band of some betaine dyes. Since PS accounts for dielectric as well as specific interactions while dielectric enrichment only for the former, it was shown that in the case of dichloromethane/methanol, hydrogen bonding precedes dielectric enrichment whereas in the case of acetonitrile/water the inverse is true.     

Static and dynamic quenching of Ru(II) polypyridyl excited states by iodide

The metal-to-ligand charge-transfer (MLCT) excited states of Ru(bpy)(2)(deeb)(PF(6))(2), where bpy is 2,2-bipyridine and deeb is 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-bipyridine, in dichloromethane were found to be efficiently quenched by iodide at room temperature. The ionic strength dependence of the UV-visible absorption spectra gave evidence for ion pairing. Iodide was found to quench the excited states by static and dynamic mechanisms. Stern-Volmer and Benesi-Hildebrand analysis of the spectral data provided a self-consistent estimate of the iodide-Ru(bpy)(2)(deeb)(2+) adduct in dichloromethane, K = 59 700 M(-1). Transient absorption studies clearly demonstrated an electron-transfer quenching mechanism with transient formation of I(2)(*)(-) in high yield, phi = 0.25 for 355 or 532 nm excitation. For Ru(bpy)(2)(deeb)(PF(6))(2) in acetonitrile, similar behavior could be observed at higher iodide concentrations than that required in dichloromethane. The parent Ru(bpy)(3)(2+) compound also ion pairs with iodide in CH(2)Cl(2), and light excitation gave a higher I(2)(*)(-) yield, phi = 0.50. X-ray crystallographic, IR, and Raman data gave evidence for interactions between iodide and the coordinated deeb ligand in the solid state.     

Preparation of biodegradable polymeric hollow microspheres using O/O/W emulsion stabilized by Labrafil

Biodegradable hollow microspheres were prepared by double oil and water emulsion using a lipophilic surfactant, Labrafil M 1944 CS. Olive oil was emulsified in biodegradable polymer-dissolved dichloromethane mixed with Labrafil by vigorous sonication. This oil-in-oil emulsion was directly re-emulsified in 0.1% poly(vinyl alcohol) solution, subsequently solidified by evaporating dichloromethane. Olive oil and Labrafil were extracted from the microspheres by using hexane. After vigorous washing with n-hexane, the hollow microsphere was freeze-dried and examined under scanning electron microscopy, confirming the morphology of hollow microspheres with thin walls and huge blank cores inside. The concentration of poly(l-lactide) in dichloromethane affected the size of hollow microspheres while the volume of olive oil or dichloromethane did not. This hollow microsphere is expected to be employed as an imaging contrast agent and a novel drug delivery vehicle.     

固相微萃取气相色谱法测定非那雄胺中残留的二氯甲烷和三氯甲烷

利用固相微萃取气相色谱法测定非那雄胺中的溶剂残留,对固相微萃取的萃取温度、萃取时间、解吸时间和溶液的离子强度等分析条件进行了优化.该方法具有较好的线性,相关系数:二氯甲烷为0.997,三氯甲烷为0.998;相对标准偏差:二氯甲烷为2.7%,三氯甲烷为1.8%.     

Ship-in-a-bottle synthesis of triphenylamine inside faujasite supercages and generation of the triphenylamminium radical ion

The ship-in-a-bottle synthesis of triphenylamine encapsulated within basic X zeolite has been accomplished by reacting sodium diphenylamide with bromobenzene in the presence of a bifunctional palladium (Hartwig-Buchwald conditions). The presence of incarcerated triphenylamine was demonstrated by dissolving the zeolite with concentrated HF and analyzing the organic material in the dichloromethane extract. Laser flash photolysis (266 nm) gives rise to the generation of triphenylamminium radical cation detected as a transient species decaying in hundreds of microseconds. Upon repetitive cyclic voltammograms, zeolite encapsulated triphenylamine shows a reversible oxidation-reduction process. In contrast, in solution triphenylamine undergoes irreversible oxidation with the formation of coupling dimers.     

Synthesis,characterization and computational investigation of poly(styrene-co-1-methylpyrenyl methacrylate): its efficiency as a macrophotoinitiator

Abstract

In this study, it has been demonstrated that poly(styrene-co-1-methylpyrenyl methacrylate) macro-photoinitiator (PSMM) containing side chain pyrene moieties were successfully prepared using “radical polymerization method.” Firstly, 1-pyrene methanol and methacryloyl chloride were reacted in dichloromethane for 24?h at 0?°C in order to give 1-methoxy pyrene methacrylate macromonomer. Then styrene was polymerized with this macromonomer to obtained macro-photoinitiator. The synthesized copolymer is also both computationally and experimentally demonstrated that the macro-photoinitiator obtained has similar absorption characteristics with the parent pyrene molecule. According to obtained results, the synthesized copolymer was more effective in the presence of triethyl amine as a macro-photoinitiator.