Charge Transfer Complexes of Crown Ethers with 2, 3, 5, 6 - Tetracyano Pyrazine

The interaction of five crown ethers, 15-crown-5, 18-crown-6, benzo-15-crown-5, dibenzo-l8-crown-6, and dibenzo-24-crown-8 with 2, 3, 5, 6 - tetracyano pyrazine has been studied by spectroscopic methods. The association constants and thermodynamic parameters of the 1:1 complexes formed by donor ethers with the acceptor have been evaluated. There is an indication that oxygens of the ethers and aryl part of the ether act cooperatively in binding of the acceptor.

Inter And Intramolecular Interactions Of Porphyrins With 5,5′-Dithiobis(2-Nitrobenzoic Acid)

meso-Tetraphenylporphyrin and its metal [zinc(II) and copper(II)] derivatives form both inter and intramolecular complexes with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). The nature of interaction is predominantly charge transfer (CT) in origin, with the porphyrin functioning as a II-donor and DTNB as an acceptor. Among the covalently linked intramolecular systems, the magnitude of CT interaction varies with the position (of one of the aryl groups of the porphyrin) to which DTNB is attached as ortho meta > para. Steady-state and time-resolved fluorescence studies revealed electron transfer to be the dominant pathway for the fluorescence quenching in these systems. Steady-state photolysis experiments probed using EPR and optical absorption studies have shown that electron transfer (from the excited singlet state of the porphyrin) to DTNB results in the formation of thiyl radical and production of free thiolate anion. It is found that the products of electrochemical reduction of covalently linked porphyrin-DTNB systems are different from those observed for the photochemical studies.

Structure of 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecyl 1,10-ditosylate by X-ray crystallography and F-19-NMR spectroscopy

2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecyl 1,10-ditosylate and its precursors were synthesized and characterized by H-1- and F-19-NMR spectroscopic methods and X-ray crystallography. These compounds are building blocks for the syntheses of the surfactants containing polyperfluoromethylene spacer. The molecule has extended all-trans conformation with molecular symmetry (1) over bar (C-i). There is a reasonably strong C-H ... O interaction in the crystal and there are two F ... F intermolecular contact distances less than the sum of van der Waals radii. (C) 1999 Elsevier Science B.V. All rights reserved.

Ethyl 6-methyl-2-sulfanylidene-4-[4(trifluoromethyl)phenyl]-1,2,3,4-tetrahyd ropyrimidine-5-carboxylate

The title compound, C(15)H(15)F(3)N(2)O(2)S, adopts a conformation with an intramolecular C-H center dot center dot center dot pi interaction. The dihedral angles between the planes of the 4-(trifluoromethyl) phenyl and ester groups with the plane of the six-membered tetrahydropyrimidine ring are 81.8 (1) and 16.0 (1)degrees, respectively. In the crystal structure, intermolecular N-H center dot center dot center dot S hydrogen bonds link pairs of molecules into dimers and N-H center dot center dot center dot O interactions generate hydrogen-bonded molecular chains along the crystallographic a axis.

Homo- or Heterosynthon? A Crystallographic Study on a Series of New Cocrystals Derived from Pyrazinecarboxamide and Various Carboxylic Acids Equipped with Additional Hydrogen Bonding Sites

Four new cocrystals of a well studied active pharmaceutical ingredient (API), namely, pyrazinecarboxamide (PZA), with various monocarboxylic acids equipped with additional hydrogen bonding sites such as vanillic acid (VA), gallic acid (GA), 1-hydroxy-2-naphthoic acid (1HNA), and indole-2-carboxylic acid (I2CA) have been successfully prepared and characterized by FTIR, H-1 NMR, differential scanning calorimetry (DSC), and single crystal and powder X-ray diffraction (SXRD and PXRD, respectively) techniques. In the majority of the cases, preferential occurrence amide amide and acid acid homosynthons has been observed. Since the heterosynthon is energetically preferred to homosynthon, such unusual occurrence of homosynthon in these cocrystals is intriguing.

Total synthesis and determination of the absolute configuration of 5,6-Dihydro-alpha-pyrone natural product synargentolide B

Enantiospecific total synthesis and determination of the absolute stereochemistry of the alpha-pyrone-containing natural product synargentolide B were accomplished. The absolute stereochemistry of the natural product was established by synthesizing the possible diastereomers and comparison of the data with those reported for the natural product. During the process, total synthesis of the putative structure of related natural product 6R-1S,2R,SR,6S-(tetraacetyloxy)-3E-heptenyl]-5,6-dihydro-2H-pyran-2-o ne was also accomplished and confirmed by X-ray crystal structure analysis. Wittig-Horner reaction of a chiral phosphonate derived from (S)-lactic acid and ring-closing metathesis were the key reactions during the course of the total synthesis.

Laser action from 1,3,5,7-tetramethyl-2,6-diethyl-8-n-propyl pyrromethene-BF2

We measured spectroscopic and laser action properties of a novel 8-position substituted pyrromethene-BF2, namely 1,3,5,7-tetramethyl-2,6-diethyl-8-n-propyl pyrromethene-BF2 complex. The laser action was performed with the corresponding dye solution in ethanol, which was placed in a Littman-type laser cavity pumped by the second harmonic of a Q-switched Nd:YAG laser. The spectroscopic measurements clearly indicated that the corresponding dye solution in ethanol exhibited intense absorption in the visible spectral region with large fluorescence quantum yield. It possesses rather low triplet-triplet absorption in the spectral region 460-550 nm and almost negligible triplet-triplet absorption in the lasing spectral region. As a consequence, it lases nearly as efficiently as commercially available benchmark laser dyes such as Rhodamine-6G and outperformed them in wavelength tunability in our laser cavity and pump geometry. (C) 2002 Optical Society of America.

1. Astronomical photometry at wavelengths of 8.5, 10.5, and 11.6 µm. 2. Infrared emission from asteroids at wavelengths of 8.5, 10.5, and 11.6 µm

The purpose of this thesis is to present new observations of thermal-infrared radiation from asteroids. Stellar photometry was performed to provide standards for comparison with the asteroid data. The details of the photometry and the data reduction are discussed in Part 1. A system of standard stars is derived for wavelengths of 8.5, 10.5 and 11.6 µm and a new calibration is adopted. Sources of error are evaluated and comparisons are made with the data of other observers.

The observations and analysis of the thermal-emission observations of asteroids are presented in Part 2. Thermal-emission lightcurve and phase effect data are considered. Special color diagrams are introduced to display the observational data. These diagrams are free of any model-dependent assumptions and show that asteroids differ in their surface properties.

On the basis of photometric models, (4) Vesta is thought to have a bolometric Bond albedo of about 0.1, an emissivity greater than 0.7 and a true radius that is close to the model value of 300^(+50)_(-30)km. Model albedos and model radii are given for asteroids 1, 2, 4, 5, 6, 7, 15, 19, 20, 27, 39, 44, 68, 80, 324 and 674. The asteroid (324) Bamberga is extremely dark with a model (~bolometric Bond) albedo in the 0.01 - 0.02 range, which is thought to be the lowest albedo yet measured for any solar-system body. The crucial question about such low-albedo asteroids is their number and the distribution of their orbits.

Studies on fish lipids. Pt. 2. Fatty acid composition of lipids of oil sardine (Sardinella longiceps)

Gas-liquid chromatography has been employed for the qualitative and quantitative analysis of the component fatty acids in lipids of oil sardine (Sardinella longiceps). Phospholipids and triglycerides of the lipids were previously separated by column chromatography before they were converted into the methyl esters of the fatty acids. The predominant acids present in the depot fat of the fish have been found to be C14:0=8.13%, C16:0=27.9%, C18:0=3.8%, C18:1=15.4%., C20:5=10.6% and C22:6=8.8%. Apart from the above acids the distribution of minor acids belonging to Cl8, C20 and C22 groups have also been worked out. The separated phospholipid fraction contained more than 70% polyunsaturated acids of which the important constituents were docosahexaenoic (C22:6=28%) and eicosapentaenoic (C20:5=10.6%). A marked reduction was found in the amounts of polyunsaturated acids in triglycerides, their total amount registering about 20%. This fraction recorded about 48% of C16 acids of which palmitic and palmitoleic acids amounted to 25.8% and 19.1% respectively. Occurrence of odd numbered fatty acids C15 and C17 has also been noted in the phospholipid and composite samples of the fish.

5，6-二羟基-2-（4-羟苯基）-4-酮-4H-1-苯并吡喃基-7-羟基-β-D-葡萄糖醛酸在制药中的应用

本发明提供化合物5，6-二羟基-2-(4-羟苯基)-4-酮-4H-1-苯并吡喃基-7-羟基-β-D-葡萄糖醛酸在制备抗艾滋病药物中和在制备逆转录酶抑制剂药物中的应用。

Efficient and divergent synthesis of cyclophosphamide analogues from 2-arylamino-3-acetyl-5, 6-dihydro-4H-pyrans

A facile and efficient one-pot synthesis of substituted cyclophosphamidic chlorides and their analogues has been developed from readily available enaminones, 2-arylamino-3-acetyl-5,6-dihydro4H-pyrans.

Bis(2,2 '-bipyridine)(5,6-epoxy-5,6-dihydro-[1,10] phenanthroline)ruthenium: Synthesis and electrochemical and electrochemiluminescence characterization

In this work, an electrochemiluminescence (ECL) reagent bis(2,2'-bipyridine)(5,6-epoxy-5,6-dihydro-[1,10]phenanthroline)ruthenium complex (Ru-1) was synthesized, and its electrochemical and ECL properties were characterized. The synthesis of Ru-1 was confirmed by IR spectra, element analysis, and H-1 NMR spectra. For further study, its UV-vis absorption and fluorescence emission spectra were investigated. Ru-1 also exhibited quasi-reversible Ru-II/Ru-III redox waves in acetonitrile solution. The aqueous ECL behaviors of Ru-1 were also studied in the absence and in the presence of tripropylamine.

Vilsmeier-Haack reactions of 2-arylamino-3-acetyl-5,6-dihydro-4H-pyrans toward the synthesis of highly substituted pyridin-2(1H)-ones

A facile and efficient one-pot synthesis of highly substituted pyridin-2(IH)-ones was developed via Vilsmeier-Haack reactions of readily available enaminones, 2-arylamino-3-acetyl-5,6-dihydro-4H-pyrans, and a mechanism involving sequential ring-opening, haloformylation, and intramolecular nucleophilic cyclization reactions is proposed.

Syntheses, structures and near-IR luminescent studies on ternary lanthanide (Er-III, Ho-III, Yb-III, Nd-III) complexes containing 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dionate

The ligand Hhfth [4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dione], which contains a heptafluoropropyl group, has been used to synthesize several new ternary lanthanide complexes (Ln = Er, Ho, Yb, Nd) in which the synergistic ligand is 1,10-phenanthroline (phen) or 2,2'-bipyridine (bipy). The two series of complexes are [Ln(hfth)(3)phen] [abbreviated as (Ln)1, where Ln = Er, Ho, Yb] and [Ln(hfth)(3)bipy] [abbreviated as (Ln)2, where Ln = Er, Ho, Yb, Nd]. Members of the two series have been structurally characterized. The growth morphology, diffuse reflectance (DR) spectra, thermogravimetric analyses, and photophysical studies of these complexes are described in detail. After ligand-mediated excitation of the complexes, they all show the characteristic near-infrared (NIR) luminescence of the corresponding Ln(3+) ions (Ln = Er, Ho, Yb, Nd). This is attributed to efficient energy transfer from the ligands to the central Ln(3+) ions, i.e. an antenna effect. The heptafluorinated substituent in the main hfth sensitizer serves to reduce the degree of vibrational quenching. With these NIR-luminescent lanthanide complexes, the luminescent spectral region from 1300 to 1600 nm, which is of particular interest for telecommunication applications, can be covered completely.

Resolution of 3,3 '-dioxo-1,1 '(3H,3 ' H)spirobi[isobenzofuran]-5,6,5 ' 6 '-tetracarboxylic acid and Optically active Polyimides thereof

3,3'-Dioxo-1.1'(3H.3'H)spirobi[isobenzofuran]-5,6,5',6 acid 1 was resolved successfully and the corresponding optically active polyimides PI were synthesized. The properties of the optically active PI and the racemic one were investigated. The results showed that the specific rotation of(-)-PI was about two times to that of the: (+)-PI, and the regularity of the optically active PI was higher than that of the racemic one.