Numerical analysis of relaxation times of multiple quantum coherences in the system with a large number of spins

We study the decay of multiple quantum (MQ) NMR coherences in systems with the large number of equivalent spins. As being created on the preparation period of the MQ NMR experiment, they decay due to the dipole-dipole interactions (DDI) on the evolution period of this experiment. It is shown that the relaxation time decreases with the increase in MQ coherence order (according to the known results) and in the number of spins. We also consider the modified preparation period of the MQ NMR experiment [G. A. Alvarez and D. Suter, Phys. Rev. Lett. 104, 230403 (2010)] concatenating the short evolution periods under the secular DDI Hamiltonian (the perturbation) with the evolution period under the nonsecular averaged two-spin/two-quantum Hamiltonian. The influence of the perturbation on the decoherence rate is investigated for the systems consisting of 200-600 equivalent spins.     

Novel liquid crystalline resins based on MQ siloxanes

MQ siloxane resins containing Si-H functions have been made from tetramethyldisiloxane and tetraethoxysilane. Hydrosilylations with mesogenic alkenes give low molecular weight liquid crystal MQ resins with potentially useful properties.     

Enantiomeric analysis of the five major monohydroxylated metabolites of methaqualone in human urine by chiral capillary electrophoresis

Methaqualone (MQ; 2-methyl-3-o-tolylquinazolin-4(3H)-one) is a hypnotic and anticonvulsive drug in which the rotation about the nitrogen-to-aryl bond between the planar 2-methyl-quinazolin-4(3H)-one structure and the o-tolyl moiety is sterically hindered at body temperature. MQ and its five major monohydroxylated metabolites found in urine, 4'-hydroxymethaqualone (4'OH-MQ), 2'-hydroxymethaqualone (2'-OH-MQ), 3'-hydroxymethaqualone (3'OH-MQ), 2-hydroxymethaqualone (2OH-MQ) and 6-hydroxymethaqualone (6OH-MQ), are thus chiral substances whose enantiomers are shown to be separable by chiral capillary electrophoresis at pH 2.1 in the presence of 50 mM (2-hydroxypropyl)-beta-cyclodextrin (OHP-beta-CD). Other neutral derivatives of beta-CD, namely (2-hydroxypropyl)-gamma-CD, (2,3,6-trimethyl)-beta-CD, and (2,6-di-O-methyl)-beta-CD were found to be able to resolve the enantiomers of some but not all of these six components. With OHP-beta-CD, simultaneous analysis of the enantiomers of MQ and its five metabolites is hampered by the difficulty in separating MQ and 4'OH-MQ, the major urinary metabolite. A two-step solid phase extraction process is shown to permit discrimination between these two compounds and thus analysis of MQ enantiomers in unhydrolyzed urines that were collected overnight after administration of 250 mg of racemic MQ. Furthermore, analysis of liquid/liquid or solid-phase extracts of enzymatically hydrolyzed urines reveals the distribution of the enantiomers of the five hydroxymetabolites of MQ and, for the first time, insight into the stereoselectivity of the MQ metabolism. The major metabolite, 4'OH-MQ, is shown to be excreted almost exclusively as single enantiomer. The two urinary enantiomers of 6OH-MQ are present at about equal amounts, whereas unequal amounts are noted for the enantiomers of 3'OH-MQ, 2OH-MQ, and 2'OH-MQ.     

Multiple Quantum Transitions Induced by Irradiating Single Quantum Coherence in a Heteronuclear Spin System

In a heteronuclear spin system, with initially prepared single quantum (SQ) coherence of X-spin, the irradiation of the proton spins will induce all the possible transitions including those SQs and multiple quanta (MQs) available in the system to be studied. The MQs appear in a rather weak irradiation while a strong irradiation results in a complete decoupling situation. Theoretical analysis is made to explain this phenomenon and is agreed qualitatively with experiments in the CH₂ group. This phenomenon of MQ induction may happen in a decoupling experiment, when the effective irradiation strength is rather weak and it may also provide a convenient approach to create and then to manipulate MQ coherences in heteronuclear spin systems.     

新型低聚噻吩衍生物的设计、合成及其液晶性能的研究

设计、合成了一系列新型低聚噻吩衍生物N,N’-双烷烃基-5,5’-二溴基-2 ,2’：5’,2’-三噻吩-4,4’-二酰胺[N,N’-dialkyl-5,5’-dibromo-2,2’:5 ’,2’-terthiophene-4,4’-dicarboxamide](DNCnDBr3T,n=5,8,6,18)。示差扫描 量热法（DSC）测定的结果及偏光光学显微镜观察的结果显示,DNC18DBr3T, DNC16DBr3T,DNC8DBr3T具有近晶A形液晶性质,DNC5DBr3T不具有液晶性质。为了探 讨分子间氢链对液晶形成的影响,设计、合成了新型低聚噻衍生物4,4“-双烷烃 酯-5,5“-二溴基-2,2’:5’,2’-三噻吩[4,4’-bis(alkyloxycarbonyl)-5,5’ -dibromo-2,2’:5’,2’-terthiophene](DOCnDBr3T,n=5,8,16,18).测定和观察的 结果发现,DOCnDBr3T(n=5,8,16,18）不具有液晶的结果。这个结果表明,酰胺基 的存在于液晶的形成起着重要的作用。测定DNC18DBr3T在结晶状态和液晶状态下的 红外光谱,进一步证实了部分分子间氢键对于液晶的形成起着重要的作用。     

Probing aerogels by multiple quantum filtered (131)Xe NMR spectroscopy.

At the interface between solid surfaces and cavities filled with gaseous or liquid xenon, the nuclear magnetization of (131)Xe (S = (3)/(2)) is subject to quadrupolar interactions which may lead to higher rank single-quantum coherences that can be described by tensor elements T(2,)(+/-)(1) and T(3,)(+/-)(1). This can be demonstrated by multiple-quantum filtered (MQF) NMR experiments. In gaseous xenon on Pyrex surfaces, the primary source of such coherences was shown to be coherent evolution induced by a nonvanishing average quadrupolar coupling. In this contribution, MQF NMR is applied to aerogels filled with liquid xenon to demonstrate the potential of this technique for material sciences. Xenon in the liquid phase provides a sufficient spin density to obtain reasonable signal-to-noise ratios. Coherent evolution and relaxation both contribute to the creation of higher rank coherences depending on the presence or absence of water molecules on the surface. These two processes can be distinguished experimentally and provide complementary information about the surface of the host material.     

3D TEDOR NMR experiments for the simultaneous measurement of multiple carbon-nitrogen distances in uniformly (13)C,(15)N-labeled solids

We describe three-dimensional magic-angle-spinning NMR experiments for the simultaneous measurement of multiple carbon-nitrogen distances in uniformly (13)C,(15)N-labeled solids. The approaches employ transferred echo double resonance (TEDOR) for (13)C-(15)N coherence transfer and (15)N and (13)C frequency labeling for site-specific resolution, and build on several previous 3D TEDOR techniques. The novel feature of the 3D TEDOR pulse sequences presented here is that they are specifically designed to circumvent the detrimental effects of homonuclear (13)C-(13)C J-couplings on the measurement of weak (13)C-(15)N dipolar couplings. In particular, homonuclear J-couplings lead to two undesirable effects: (i) they generate anti-phase and multiple-quantum (MQ) spin coherences, which lead to spurious cross-peaks and phase-twisted lines in the 2D (15)N-(13)C correlation spectra, and thus degrade the spectral resolution and prohibit the extraction of reliable cross-peak intensities, and (ii) they significantly reduce cross-peak intensities for strongly J-coupled (13)C sites (e.g., CO and C(alpha)). The first experiment employs z-filter periods to suppress the anti-phase and MQ coherences and generates 2D spectra with purely absorptive peaks for all TEDOR mixing times. The second approach uses band-selective (13)C pulses to refocus J-couplings between (13)C spins within the selective pulse bandwidth and (13)C spins outside the bandwidth. The internuclear distances are extracted by using a simple analytical model, which accounts explicitly for multiple spin-spin couplings contributing to cross-peak buildup. The experiments are demonstrated in two U-(13)C,(15)N-labeled peptides, N-acetyl-L-Val-L-Leu (N-ac-VL) and N-formyl-L-Met-L-Leu-L-Phe (N-f-MLF), where 20 and 26 (13)C-(15)N distances up to approximately 5-6 A were measured, respectively. Of the measured distances, 10 in N-ac-VL and 13 in N-f-MLF are greater than 3 A and provide valuable structural constraints.     

Determination of mefloquine in blood, filter paper-absorbed blood and urine by 9-fluorenylmethyl chloroformate derivatization followed by liquid chromatography with fluorescence detection

We describe a method for determination of mefloquine (MQ) in 100-microliters samples of urine, whole blood, and capillary blood collected on filter paper; quantification is by liquid chromatography with fluorescence detection at 475 nm of the 9-fluorenylmethyleneoxycarbonyl derivative. Whole blood and urine samples were prepared by extraction of MQ and internal standard from aqueous base with methyl tert.-butyl ether (MTBE), separation and evaporation of the MTBE layer, and derivatization using a solution of 9-fluorenylmethyl chloroformate in acetonitrile. Filter paper spots were immersed for 16 h in 0.1 M hydrochloric acid, followed by extraction with MTBE from aqueous sodium carbonate. The separated and evaporated organic layer was treated with the derivatizing solution. An aliquot was injected onto a high-performance liquid chromatography system using a C18 reversed-phase column and acetonitrile-water (72:28) mobile phase for filter paper spot extracts as for whole blood and urine extracts. The method has a limit of determination in blood, blood spots, and urine of 50 ng/ml with 100 microliters sample size (coefficient of variation = 16%). Linearity and precision (within-day and between-day) for the method are good. The MQ derivative was isolated and characterized spectroscopically. Values for MQ concentrations in filter paper blood spots compared favorably with values found in corresponding whole blood samples analyzed by a published method.     

Molecular simulation of liquid crystal sensor based on competitive inclusion effect

With the progressive understanding of liquid crystal materials that rely on the interface interactions, optical properties of liquid crystal are attracting attention as a detector for chemicals and biomolecules. In this work, a recently reported liquid crystal sensing system based on the competitive inclusion effect of β-cyclodextrin (β-CD) was studied. Quantum mechanical calculations were applied to study different β-CD inclusion complexes of methyl blue (MB), 4-cyano-4′-pentyl biphenyl (5CB), sodium dodecyl sulfonate (SDS), dopamine (DA) and their inclusion processes. The work shows that DA cannot be an analyte for the liquid crystal sensor as it could not compete for the cavity of β-CD with SDS. However, MB molecule can push SDS out of the β-CD cavity so as to induce the change in optical appearance when MB forms a 1:2 inclusion complex. The simulated absorption spectrum is in agreement with experiment results, implying that MB molecule may exist in both 1:1 and 1:2 inclusion complexes in the system of liquid crystal sensor.     

From single to multiple atomic layers: a unique approach to the systematic tuning of structures and properties of inorganic-organic hybrid nanostructured semiconductors

In order to systematically tailor the structures and properties of a unique family of inorganic-organic hybrid nanostructured materials based on II-VI semiconductors, we have designed and engineered a new group of two-dimensional crystalline [(M2Q2)(L)] nanostreuctures (where M = Zn, Cd; Q = S, Se; and L = ethylamine, n-propylamine, n-butylamine, n-amylamine, n-hexylamine). These compounds are composed of double atomic layers of M2Q2 separated by organic monoamines. The crystal structures of 2D-[(M2Q2)(L)] are characterized by powder X-ray diffraction (PXRD) analysis. The crystal structures of these compounds are similar to the 2D-[(MQ)(L)] series that we reported earlier, in that they also contain II-VI slabs sandwiched by organic monoamines. The main difference is in the thickness of the II-VI slabs, where they are single-layer (n = 1) in 2D-[(MQ)(L)] but double-layer (n = 2) in 2D-[(M2Q2)(L)]. Optical absorption experiments show that all double-layer compounds exhibit a blue shift in their absorption edge (0.6-1.2 eV), due to the quantum confinement effect (QCE). However, the extent of such a blue shift is significantly less than that of the single-layer 2D-[(MQ)(L)] systems (1.0-2.0 eV) as a result of the difference in their layer thickness. Thermogravimetric (TG) analysis has revealed nanosized II-VI (MQ) particles as the post-TG product of all double-layer hybrids.     

Photochromic metal complexes of N-methyl-4,4'-bipyridinium: mechanism and influence of halogen atoms

Photochromism of N-methyl-4,4'-bipyridinium (MQ(+)) salts and their metal complexes has never been reported. A series of MQ(+) coordinated halozinc complexes [(MQ)ZnX(3)] (X = Cl (1), Br (2), I (3)) and [(MQ)ZnCl(1.53)I(1.47)](2)(MQ)ZnCl(1.68)I(1.32) (4), with better physicochemical stability than halide salts of the MQ(+) cation, have been found to exhibit different photochromic behaviors. Compounds 1-3 are isostructural, but only 1 and 2 show photochromism. Introduction of partial Cl atoms to nonphotochromic compound 3 yields compound 4, which also displays photochromism. The photochromic response of 1, 2, and 4 indicates the presence of their long-lived charge separation states, which originate from X → MQ(+) electron transfer according to ESR and XPS measurements. Studies on the influence of different coordinated halogen atoms demonstrate that the Cl atom may be a more suitable electron donor than Br and I atoms to design redox photochromic metal complexes.     

Mesogen-jacketed Liquid Crystal Polymers With Mesogens of Aromatic Amide Structure

The synthesis and property of a new series of "mesogen-jacketed liquid crystal polymers" are reported. These polymers have aromatic amide structures as the mesogenic groups and are represented by poly-2,5-bis(4-methoxy- benzamido)styrene. The preliminary study on properties shows that the polymers have very high glass transition temperatures as well as very low critical concentrations for the formation of the lyotropic liquid crystal phase. The results indicate a high degree of chain rigidity. However, the liquid crystalline order of molecular organization in bulk samples disappears upon heating to the glass transition temperature as revealed by polarizing microscopy and by X-ray diffractometer. Therefore, the liquid crystalline order of these polymers forms only through solution but not through heating. This behavior is different from that of the previously studied poly-2,5-bis[(4-methoxybenzoyl)oxy]styrene and its homologs. The latter polymers are liquid crystals both lyotropically and thermotropically. © 1997 John Wiley & Sons, Ltd.     

Synthesis,characterization, pharmacological,molecular modeling and antimicrobial activity evaluation of novel isomer quinoline derivatives

The structural and spectroscopic characteristics of the synthesized structurally novel compound 4-chloro-6-methylquinoline-2(1H)-one (4C6MQ) and its isomer 4-chloro-8-methylquinoline-2(1H)-one (4C8MQ) have been examined by means of experimental and computational quantum chemical methods like density functional theory (DFT). The crystal structure of the 4C6MQ compound has been brought to light by single-crystal x-ray diffraction (SCXRD) method which consists of two independent molecules (A and B) in the asymmetric unit with similar conformations. Both the isomer compounds are characterized spectroscopically by FTIR, FT-Raman, UV-Vis, and NMR spectrum and compared with DFT results. The geometries of the isomer compounds have been optimized by using DFT/B3LYP method with the 6-311G++(d,p) basis sets. From the optimized geometry of the compounds, geometric parameters (bond lengths, bond angles, and torsion angles); vibrational analysis; chemical shifts; and electronic absorption of the isomer compounds have been computed and compared with the experimental result. The detailed assignments of vibrational wave numbers have been prepared based on potential energy distribution (PED) which was carried out in the VEDA4 program. In addition, natural bonding orbital analysis, frontier molecular orbital, and molecular electrostatic potential have been explained theoretically. The in silico (absorption, distribution, metabolism, excretion and toxicity) studies were analyzed to identify the potential drug likeliness of the isomer compounds. The implications of the inhibitory activity of isomer compounds against DNA gyrase and lanosterol 14 α-demethylase enzyme by molecular docking are discussed. Further, the isomer compounds were screened for their antibacterial and antifungal activities.     

Chromatographic characterization of a bonded liquid crystal stationary phase for HPLC

Summary A chromatographic and thermodynamic study of the compound [4-(allyloxy)benzoyl]-4-methoxyphenyl (ABMP) as a model of a chemically bonded liquid crystal stationary phase for HPLC was undertaken. A number of polycyclic aromatic hydrocarbons (PAHs) and two small solutes, carvone and pulegone, were studied under varying solvent and temperature conditions. Plots of log k vs. % organic in the mobile phase were not completely linear in all cases. The van't Hoff plots revealed at least one phase transition. The enthalpies of solute transfer from the mobile phase to the ABMP phase were determined for several PAHs. All tests indicate that ABMP possess liquid crystal properties when bonded to particulate silica.     

刚性侧链型液晶高分子与含二维液晶基元的液晶高分子

提出了“刚性侧链型液晶高分子”与“含二维液晶基元的液晶高分子”两个新概念。     

Polymer-Metal Nanoparticle Complexes for Improving the Performance of Liquid Crystal Displays

Summary: Here we applied metal nanoparticles as a dopant of liquid crystals. Since liquid crystal molecules are self-assembled, it is not so easy to disperse metal nanoparticles in liquid crystal media. We first prepared metal nanoparticles protected by liquid crystal molecules by reduction of metal ions in the presence of liquid crystal molecules. This liquid crystal molecule-protected metal nanoparticles can be easily dispersed in liquid crystal media to fabricate liquid crystal sol containing metal nanoparticles. A simple liquid crystal molecule, 4′-pentylbiphenyl-4-carbonitrile (abbreviated as 5CB) was used in the present experiments at first. 5CB sol containing metal nanoparticles could construct novel twisted nematic liquid crystal devices (TN-LCDs), which revealed the electrooptic properties depending on the kind of metal of nanoparticles. During the experiments we discovered that 5CB-protected metal nanoparticles could move in liquid crystal media by applying the voltage. This phenomenon is inconvenient for liquid crystal displays, especially those driven by a matrix of thin-film transistors (TFTs). In order to avoid this phenomenon, we prepared polymer-protected metal nanoparticles and applied them to liquid crystal devices, which provided good performance as the devices, i.e., low driving voltage, rapid response at low temperature, and so on.     

Photochemically induced fluorimetric determination of the antimalarial mefloquine

Mefloquine (MQ) was determined quantitatively in pharmaceutical tablets by irradiating the MQ solution for 2–7 min with a high-pressure UV lamp, measuring simultaneously the increase in fluorescence signal at room temperature (298 K) and comparing the signal with that of a standard. The effects of several solvents (acetone, dioxane, ethanol, methanol, propan-2-ol, tetrahydrofuran, water) and “pH” on the fluorescence properties of MQ and its photochemical decomposition product were studied. The limit of detection of MQ was 50 ng ml^?1. The mean overall recovery from pharmaceutical tablets was 102.3 ± 4%.     

Reliability of liquid crystal cell and immiscibility between dual-curable adhesives and liquid crystal

The dual-curable adhesive used to attach thin film transistors (TFTs) to color filters in the construction process of liquid crystal display (LCD) panels requires fast curing by UV irradiation and strong bond strength after thermal-curing. In addition, it is necessary to consider the immiscibility of the dual-curable adhesives with the liquid crystal, because they come directly into contact with the liquid crystal without curing process in the large LCD panel production. In this study, dual-curable adhesives based on partially acrylated epoxy acrylate oligomers were prepared and investigated with nematic liquid crystals using gas chromatography (GC), polarized optical microscopy and the measurement of the transmittance of the liquid crystal.As the concentration of CC bonds was increased, the immiscibility was enhanced due to the fast curing rate of the partially acrylated epoxy acrylate oligomers and reduced visual contamination was observed in the polarized optical microscope images. Moreover, the transmittance of the liquid crystal cells was not changed before and after the dual-curing of the adhesives and was maintained for 100 h.     

Photochemistry of methoxyhydroquinone and methoxy-p-benzoquinone in solution related to the photoyellowing of the lignocellulosics.

The photoreactivity of methoxy-p-benzoquinone (MQ) and methoxyhydroquinone (MHQ) in dilute solution (10(-4)-10(-3) M) was studied using continuous irradiation and laser flash photolysis (LFP). The quinone irradiated in degassed tetrahydrofuran (THF) gives MHQ and an adduct with the solvent. Only the formation of hydroquinone is observed in ethanol, and hydroxylation is evidenced in water, whereas the compound is stable in CCl4. The bis-quinone, 4,4'-dimethoxybiphenyl-2,5,2',5'-bisquinone, and the dibenzofurane-quinone, 8-hydroxy-3,7-dimethoxydibenzofuran-1,4-quinone, are formed in the presence of MHQ, whereas the reactivity is low with ethylconiferyl alcohol. When MHQ is irradiated selectively in degassed THF, the formation of MQ and of the bis-hydroquinone, 4,4'-dimethoxy-2,5,2',5'-tetrahydroxy-biphenyl, are observed. The dimer is oxidized photochemically or thermally into the mono- or bis-quinones, the process being accelerated in alkaline medium. The formation of the dimers is strongly favored by the contiguous presence of quinone and hydroquinone. When MHQ is selectively irradiated in the presence of transethylconiferaldehyde (EtC), quinone formation and isomerization of EtC are observed. LFP experiments, performed with a selective excitation of MQ, indicate that the triplet state of the quinone is strongly quenched by MHQ to conduce to a semiquinone radical. The interaction between 3MQ* and MQ is mainly driven by an electron transfer process according to the similar value of the quenching rate constant found with another electron donor compound such as 1,4-dimethoxybenzene. By contrast, no strong quenching of 3EtC* by MHQ was observed. It is proposed that the photochemistry of the couple MQ/MHQ is governed by the formation of encounter complex between either 3MQ* and MHQ or 3MHQ* and MQ. Consequently, the fast part of the photoyellowing of lignocellulosics does not appear to involve the couple MHQ/MQ or MHQ/etherified coniferaldehyde, but more likely a combination of oxidation of the hydroquinone by ground-state oxygen and photohydration of the formed quinone from its triplet state, giving inter-alia more colored o-quinonoid type molecules.     

Molecular organization in two-dimensional films of liquid crystalline mixtures III. Langmuir films of binary mixtures of liquid crystal materials with terminal CN o r NCS group

Langmuir films of binary mixtures of the following liquid crystal materials: 4-octyl-4'-cyano'biphenyl (8CB) or 4-pentyl-4"-cyano-p-terphenyl (5CT) with 4-(trans-4'-octylcyclohexyl)isothiocyanatobenzene (8CHBT), trans-4-octyl(4'-cyanophenyl)cyclohexane (8PCH) or 4-octyl4'-isothiocyanatobiphenyl (8BT) were investigated. Surface pressure-mean molecular area isotherms were recorded at various mixture compositions. It was found that only liquid crystal materials for which the molecules have a terminal -CN group are able to form a stable monolayer at the air-water interface. Moreover, information about the miscibility or the phase separation of the two components in the mixures was obtained by using the excess area criterion and surface phase rules.