C-13 and H-1 NMR Study of Alkyl and Aryl-Substituted 1-(4′-Dimethylaminobenzylideneamino)pyridinium Perchlorates

C-13 and H-1 NMR spectra of some 1-(4′-dimethylaminobenzylideneamino)pyridinium perchlorates show that the angle of twist of the pyridine ring in unsubstituted, 1, and 2-alkyl substituted compounds 2–5 is comparable. However, it is considerably increased in 2,6-dialkyl derivatives. As seen from the spectral data, pyridine and phenyl rings in 2,6-diphenyl derivative 15 are not coplanar. The effect of 4-alkyl substituent is of hyperconjugative chacter. In general, the amount of the positive charge at C-4 in 2,6-dialkyl substituted salts is higher as compared to 2-monosubstituted compounds.     

Synthesis and fluorescence study of sodium-2-(4′-dimethyl-aminocinnamicacyl)-3,3-(1′,3′-alkylenedithio) acrylate

We synthesized two new compounds: Sodium 2-(4′-dimethyl-aminocinnamicacyl)-3,3-(1′,3′- ethyl- enedithio) acrylate (STAA-1) and Sodium 2-(4′-dimethyl-aminocinnamicacyl)-3, 3-(1′,3′-propylenedithio) acrylate (STAA-2). The maximum absorption of these compounds ranges from 460 to 520 nm with different molecular structures in different solvents. Meanwhile, the emission peak of these compounds arranges from yellow (510 nm) to red (605 nm). The emission spectra show red shift according to the strength of the hydrogen bonding property of the solvent. But the absorption spectra do not show clearly relationship with the strength of the hydrogen bonding property of the solvent. The Stoke shift of the compounds ranges from 42 to 102 nm. It changes in the following order, EtOH>H₂O>DMF, and STAA-1>STAA-2 in the same solvent. The fluorescent quantum yield of STAA-1 was measured to be 7.12% with quinine sulphate as the standard compound in ethanol. Furthermore, the relationship of the fluorescence of STAA-1 with pH (ranges form 4 to 14) in water (c=∼10⁻⁴) was studied to make sure that these compounds could be used as proton sensors.     

Spectroscopic study of mono‐ and bis(styryl) dyes of the pyridinium series containing azathiacrown ether residue

Phenylazathiacrown ether monostyryl and bis(styryl) dyes were synthesized and their complex forming ability was evaluated in acetonitrile by absorption and fluorescence spectroscopy. It was found that dyes are sensitive to the presence of H⁺ and Hg²⁺, Ag⁺, Cu²⁺ cations. The most stable complexes were formed with mercury. Stability constants and UV–Vis spectra of complexes defined stoichiometry were determined with the use of HYPERQUAD program. Evidence was given for the occurrence of two stoichiometries: LM and LM₂. The pronounced optical response on complex formation was found both in absorption and emission spectra that could be used for optical detection of cations. Copyright © 2008 John Wiley & Sons, Ltd.     

7-Hydroxy-4-methyl-8-(4′-methylpiperazine-1′-yl)methyl coumarin: An efficient probe for fluorescence resonance energy transfer to a bioactive indoloquinolizine system

Solvatochromic effects on the fluorescence behavior of 7-hydroxy-4-methyl-8-(4′-methyl-piperazine-1′ yl)methylcoumarin (HMMC) was studied in different solvents. The fluorescence of HMMC was found to be highly sensitive to both the polarity and the protic character of the solvent. Exploiting the polarity-sensitive fluorescence property of HMMC, its excited-state dipole moment has been determined. Fluorescence (Förster) resonance energy transfer (FRET) process from HMMC to a potent bioactive molecule 3-acetyl-4-oxo-6,7-dihydro-12 H indolo-[2,3-a] quinolizine (AODIQ) was studied. From the determined K_SV and R₀ values, it is argued that a long-range dipole-dipole interaction is operating for the energy transfer mechanism. The energy transfer efficiency (E) and the distance between the acceptor and the donor (r₀) have been determined.     

Spectral behavior and laser activity of 3-(4′-dimethylaminophenyl)-1-(1H-pyrrol-2-yl) prop-2-en-1-one (DMAPrP). A new laser dye

The photophysical properties of DMAPrP have been investigated in different solvents. DMAPrP dye exhibits a large change in dipole-moment upon excitation due to an intramolecular charge transfer interaction. A crystalline solid of DMAPrP give an excimer like emission at 546 nm. The ground and excited state protonation constants of DMAPrP are calculated. DMAPrP acts as good laser dye upon pumping with nitrogen laser in some organic solvents. The laser parameters such as the tuning range, gain coefficient (α), emission cross section (σ_e) and half-life energy (E_1/2) are also calculated. The photoreactivity and net photochemical quantum yield of DMAPrP in chloromethane solvents are also studied.     

非线性光学晶体4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲基苯磺酸盐的制备与性能研究

采用籽晶法制备了大体积高质量的4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲基苯磺酸盐(DAST)晶体，对制备条件进行了优化，对DAST晶体X射线衍射谱图中的主要峰进行了指标化.另外，还对所制备的DAST晶体的透光性、热稳定性进行了研究， 并对265℃的焙烧产物进行了X射线衍射 (XRD)和傅里叶变换红外光谱(FT-IR)测试，证明了260℃是DAST晶体的熔化相变温度， 说明采用熔融法制备DAST晶体是可行的；同时还对DAST晶体的热失重过程进行了初步探讨. 关键词： 4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲基苯磺酸盐 晶体生长 X射线衍射 热稳定性     

Characteristic dielectric parameters of para-, ferro- and antiferro-electric phases of (S)-4-(1-methylheptyloxycarbonyl)phenyl-4′-(6-pentanoyloxyhex-1-oxy)biphenyl-4-carboxylate

Frequency and temperature dependence of dielectric parameters of a liquid crystalline compound (S)-4-(1-methylheptyloxycarbonyl)phenyl-4′-(6-pentanoyloxyhex-1-oxy)biphenyl-4-carboxylate under planar orientation of the molecules have been investigated in the frequency range 1 Hz-10 MHz. This compound possesses smectic paraelectric (SmA*), ferroelectric (SmC*) and antiferroelectric (SmC_A*) phases. Dielectric spectroscopy suggests the existence of a relaxation mechanism in the SmA* phase, which behaves as a soft mode. In the SmC* phase two relaxation modes are observed. One mode continues from the SmA* phase with decreasing dielectric strength and the other has characteristics of the Goldstone mode. Two dielectric relaxation modes have been observed for the SmC_A* phase. These two modes are related to the antiferroelectric ordering and the helical structure of the SmC_A* phase.     

Theoretical and experimental photophysical studies of the tris(4,4,4-trifluoro-1-(1-naphthyl)-1,3-butanedionate) (2,2′-bipiridyl)-europium(III)

The complexes tris(4,4,4-Trifluoro-1-(1-naphthyl)-1,3-butanedionate) (2,2′-bipiridyl) Ln(III), Ln(tan)₃bipy, where Ln(III)=Eu³⁺ and Gd³⁺ have been synthesized, characterized and their photophysical properties (absorption, excitation and luminescence spectra and emission quantum yield) investigated down to 4.2 K. The Eu(tan)₃bipy complex has its molecular structure experimentally determined using X-ray crystallography and theoretically using the SMLC/AM1 method as well as their electronic singlet and triplet states were calculated, using the INDO/S-CI method with a point charge model to represent the Eu³⁺ ion, where two values were adopted, +3.0e and +3.5e, to investigate the imperfect shielding of the 4f shells. The so calculated +3.5e model electronic absorption spectrum and low lying triplet state energies agreed very well with the experimental ones. The emission quantum yield of the Eu³⁺ complex is quite low at room temperature, namely 7%, probably due to the too low lying triplet state, 19,050 cm^-1, and increases by a factor of three when the temperature is lowered to 4.2 K. This strong thermal effect indicates the presence of a channel deactivating the main emitting state, what can be due to a LMCT state possibly lying in the same spectral region, as usually found in Eu³⁺ compounds.     

Electro-optical features of antiferroelectric liquid crystal material (S)-(+)-4-(1-methylheptyloxycarbonyl) phenyl 4′-(6-octanoyloxyhex-1-oxy) biphenyl-4-carboxylate in its ferro and antiferroelectric phases

A detailed investigation of the electro-optical switching parameters of an antiferroelectric liquid crystal (S)-(+)-4-(1-methylheptyloxycarbonyl) phenyl 4′-(6-octanoyloxyhex-1-oxy) biphenyl-4-carboxylate (abbreviated as S-7H6Bi) has been carried out. S-7H6Bi has paraelectric (SmA^?) and ferroelectric (SmC^?) phases in addition to antiferroelectric (SmC^?_A) phase. Switching parameters viz. spontaneous polarization and switching time were determined by polarization reversal method. The spontaneous polarization (P_s) is found to be highly temperature dependent and decreases with temperature. The maximum value of P_s is found to be ∼90 nC/cm² whereas the switching time (t_s) is found to be of the order 1-2 ms. The temperature dependent torsional viscosity (γ_t) is of the order 10 Pa sec. It increases with decrease in temperature.     

Theoretical and antimicrobial activity study for ethyl{4-[3-(1H-imidazole-1-yl)propyl]-3-methyl-5-oxo-4,5-dihydro-1H-1,2,4-triazol-1-yl}acetate

Ethyl{4-[3-(1H-imidazole-1-yl)propyl]-3-methyl-5-oxo-4,5-dihydro-1H-1,2,4-triazol-1-yl}-acetate (I) was synthesized as described in the literature and studied by proton and carbon-13 nuclear magnetic resonance, Fourier transform infrared spectroscopic techniques. Theoretical calculations were performed by the density functional method with 6-311G(d,p) and 6-311++G(d,p) basis sets. Structural parameters of compound I, vibrational frequencies, and chemical shift values were determined. The antimicrobial activity of compound I was tested for seven standard bacteria; Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, Yersinia enterocolitica, Listeria monocytogenes, Shigella flexneri, Pseudomonas aeruginosa, and one standard fungi isolate by microdilution broth assay with Alamar Blue Dye. The in vitro results show that compound I has antimicrobial activity against to two standard bacteria, Shigella flexneri and Listeria monocytogenes. And also, the antifungal activity was not detected against selected fungi isolate, Candida tropicalis.     

Comparative study of electrical properties of Au/n-Si (MS) and Au/Si3N4/n-Si (MIS) Schottky diodes

In this paper, the electrical parameters of Au/n-Si (MS) and Au/Si₃N₄/n-Si (MIS) Schottky diodes are obtained from the forward bias current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. Experimental results show that the rectifying ratios of MS and MIS diode at ± 5 V are found to be 1.25×10³ and 1.27×10⁴, respectively. The main electrical parameters of MS and MIS diode, such as the zero-bias barrier height (Φ _Bo) and ideality factor (n) are calculated to be 0.51 eV (I-V), 0.53 eV (C-V), and 4.43, and 0.65 eV (I-V), 0.70 eV (C-V), and 3.44, respectively. Also, the energy density distribution profile of the interface states (N_ss) is obtained from the forward bias I-V. In addition, the values of series resistance (R_s) for the two diodes are calculated from Cheung's method and Ohm's law.     

2-(N,N-二乙基苯胺-4-基)-4,6-双(3,5-二甲基比唑-1-基)-1,3,5三嗪的电子结构和光物理性质

采用量子化学计算方法研究了2-(N,N-二乙基苯胺-4-基)-4,6-双(3,5-二甲基吡唑-1-基)-1,3,5三嗪(dpbt)聚合物的电子结构和光物理性质，并且用二维实空间和三维实空间分析方法进行理论研究．结果表明, dpbt聚合物的第一激发态为分子内电荷转移激发态，存在较大的电偶极距变化和极化率，其中电偶极距变化与实验数值符合较好，理论计算所得到极化率数值与实验结果一致．S1激发态存在较大的电偶极距变化和极化率会导致非线性光学效应，促使高效的双光子吸收截面的形成．同时对外电场变化时dpbt的激发态性质进行理论研究．     

Calorimetric and computational study of 2H-1, 4-benzoxazin-3(4H)-one and of related species

The standard molar enthalpy of formation in the gas phase of 2H-1,4-benzoxazin-3(4H)-one was derived from the standard energy of combustion determined by static bomb combustion calorimetry in oxygen atmosphere and from the standard sublimation enthalpy determined by Calvet microcalorimetry. In addition, we report the results of a systematic theoretical study of the keto and enol tautomers in benzoxazinones and diones using density functional theory. The keto tautomers are computed to be more stable than the enols. Tautomerization energies are reported.     

Syntheses, structures, fluorescence and thermal properties of three lanthanide coordination polymers built by N-benzoyl-N′-(4-benzoxy)thiourea

Three novel lanthanide 1-D chain coordination polymers, namely {[Tb(μ₂-L)₂(η²-NO₃)(CH₃OH)(H₂O)]·0.5CH₃OH·0.5H₂O}_n (1), {[Dy(μ₂-L)₂(η²-NO₃)(CH₃OH)(H₂O)]·H₂O}_n (2) and {[Ce(μ₂-L)₂(η²-NO₃)(H₂O)₃]·H₂O}_n (3) (HL=N-benzoyl-N′-(4-benzoxy)thiourea), have been prepared and characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. The luminescence properties and themostabilities of polymers 1-3 have been determined as well.     

蛋白质INSM1中的锌指结构域ZF (4-5)的表达、纯化与表征

胰岛素瘤相关蛋白1（INSM1）是一类转录调节蛋白,通过其C-端的锌指结构域（氨基酸250-510）来识别序列特异性的DNA分子.INSM1的C-端包含有5个串联的锌指结构域,然而这些结构域的结构及其如何识别DNA的分子机制目前仍不清楚.通过重组构建的质粒pET-32m-INSM1（424-497）表达的蛋白质（氨基酸424-497）包含了最后两个锌指结构域4和5,简称为ZF（4-5）.该文详细研究了蛋白质ZF（4-5）的诱导表达条件,得到了较高产率的纯化蛋白.核磁共振（NMR）谱和圆二色谱（CD）揭示了Zn²⁺对稳定锌指蛋白结构的必要性,以及C2H2-Zn²⁺结合的组氨酸呈现为δ-异构方式.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-Phenyl)-3a, 4-dihydro (1,2,4) oxadiazolo(4,5-a), 1, 5-benzodiazepines Using 2D NMR Spectroscopy

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic environment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.     

MgmBn(m=1,2;n=1—4)团簇结构与性质的密度泛函理论研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G基组水平上对Mg_mB_n(m=1,2;n=1-4)团簇各种可能的构型进行几何结构优化，预测了各团簇的最稳定结构.并对最稳定结构的振动特性、电离势、成键特性、极化率和超极化率等性质进行了理论研究.结果表明，团簇的最稳定结构大多是平面结构，团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心，而其他B原子和Mg原子通常处在端位，且显正电性；团簇中通常是B-B键和B-Mg键共存，极少出现Mg-Mg键， 关键词： mB_n(m=1')" href="#">Mg_mB_n(m=1 n=1-4)团簇 密度泛函理论 结构与性质     

Resonant Auger spectroscopy study of charge transfer phenomena in N 1s core-excited acetonitrile adsorbates on Si(0 0 1)-2 × 1

Acetonitrile (CH₃CN) adsorbs on Si(0 0 1)-2 × 1 at room temperature under two forms, a cycloaddition-like adduct (Si-CN-Si) and a pendent cyano (Si-CH₂-CN) resulting from the decomposition of the molecule. Resonant Auger spectroscopy has been used to study the excited-state-dependent electron transfer from the N 1s core-excited molecular adsorbate to the silicon substrate, using the core-hole lifetime (∼6 fs) as an internal clock. It is shown that the π_CN^∗ NEXAFS state lies within the silicon bandgap because of a core-excitonic effect. Therefore no charge transfer of the excited electron to the substrate is observed. On the other hand the π_CN^∗ NEXAFS state is placed within the silicon conduction band. Excitation to this orbital leads to valence/Auger spectra in which both resonant and normal Auger contributions are observed. Therefore there is evidence for a charge transfer from the pendent CN to the silicon surface, on a timescale estimated to tens of femtoseconds.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-phenyl)-3a,4-dihydro (1,2,4) oxadiazolo(4,5-a), 1,5-benzodiazepines using 2D NMR Spectroscopy.

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic enviroment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.