bluuebunny/crossref_metadata_2025 huggingface dataset:
Associations of ajmaline and homatropine with bromocresol green and bromophenol blue in dichloromethane: thermodynamic and kinetic parameters
Authors: Gaínza Alberto Hernández
Published: May 2006

Ajmaline (AJ) and homatropine (HM) react with bromocresol green (BCG) and bromophenol blue (BPB) in dichloromethane forming 1:1 and 1:2 ion pairs clearly in a chemical equilibrium. Thermodynamic parameters ΔG0, ΔH0, and ΔS0 are calculated using the Van't Hoff equation. In a large excess of HM a product P is formed from the 1:2 ion pair in a pseudo-first order kinetic process which fits Arrhenius' equation. The P product has been identified as a type of charge transfer complex. The thermodynamic parameters corresponding to the formation of the ion pairs BPB—(AJ)2, BCG—(AJ)2, BPB—(HM)2, and BCG—(HM)2 are, respectively: ΔG0 at 294 K, −26, −21, −26, and −19 kJ/mol; ΔH0, −63, −39, −63, and −61 kJ/mol; ΔS0, −125, −62, −125, and −138 J/K mol (ΔH0 and ΔS0 determined in a 288 to 313 K range). The values of the activation energy, Ea, for the reaction of HM (in large excess) with BCG and BPB are 58 and 91 kJ/mol.
Microanalytical determination of calcium, phosphate, and arsenate including kinetics of formation of molybdenum blue from reduction of molybdoarsenic acid by ferrous ammonium sulphate
Authors: Rat U. S. , Narasaraju T. S. B.
Published: May 2006

A method for the microdetermination of calcium, phosphate, and arsenate in mixtures of the three has been developed. In an aliquot of the mixture calcium was determined complexometrically using EDTA. Phosphate and arsenate were determined in second and third aliquots, respectively, using spectrophotometric methods. The interference of arsenate in the determination of phosphate was avoided by masking arsenate with thiosulphate. The kinetics of formation of molybdenum blue from molybdoarsenic acid by reduction with ferrous ammonium sulphate was also studied. The rate-determining step was found to be the reduction of molybdoarsenic acid with iron(II); the reaction was first order in iron(II) and arsenate over the concentration ranges studied. Values found for the enthalpy, entropy, and free energy of activation were 22, 0.05, and 7.5 kcal, respectively.
N-Allyloxycarbonyl derivatives of D-glucosamine as promotors of 1,2-trans-glucosylation in Koenigs–Knorr reactions and in Lewis acid catalyzed condensations
Authors: Boullanger Paul , Banoub Joseph , Descotes Gérard
Published: May 2006

The use of suitably blocked D-glucosamine derivatives possessing the N-allyloxycarbonyl protective group of the amino function represents potential new routes to 1,2-trans-glucosylations. Both 3,4,6-tri-O-acetyl-2-N-allyloxycarbonyl-2-amino-2-deoxy-α-D-glucopyranosyl bromide (2) and 1,3,4,6-tetra-O-acetyl-2-N-allyloxycarbonyl-2-amino-2-deoxy-β-D-glucopyranose (3) could be used in Koenigs–Knorr reactions or Lewis acid catalyzed condensations, respectively. Glucosides of simple alcohols and disaccharides were synthesized in good to excellent yields. The N-allyloxycarbonyl protective group was, moreover, easy to remove with Pd(0) complexes, thus affording, after acetylation, the corresponding N-acetyl-β-D-glucosamine glucosides under very smooth conditions.
The reaction of chloro(triphenylphosphine)gold(I) with 1-methylthymine
Authors: Faggiani R. , Howard-Lock H. E. , Lock C. J. L. , Turner M. A.
Published: May 2006

1-Methylthyminato-N3-triphenylphosphinegold(I) was prepared by reacting chloro(triphenylphosphine)gold(I) with 1-methylthymine in aqueous methanol at pH 11. The product was examined by X-ray crystallography and was found to have the orthorhombic space group C2221 (no. 20) with cell dimensions a = 12.760(7) Å, b = 11.530(2) Å, c = 31.893(5) Å, and eight formula units in the unit cell. Data were collected with use of MoKα radiation and a Syntex P21, diffractometer. The crystal structure was determined by standard methods and refined to R = 0.112 and Rw = 0.076 on the basis of 4760 unique reflections. Bond lengths and bond angles are normal. Packing in the crystal lattice is dominated by the triphenylphosphine rings which arrange roughly as blades of a propellor and are the source of the crystal's chirality. The title and related compounds were also examined by 1H nmr, 13C nmr, and vibrational spectroscopy.
Electron transfer reactions. Reaction of Δ2-oxazoline-5-ones and related substrates with potassium
Authors: Muneer Mohammed , Tikare Ravindra K. , Kamat Prashant V. , George Manapurathu V.
Published: May 2006

The reaction of several Δ2-oxazolin-5-ones (1a–c, 12) and bioxazolinones (17, 26) with potassium in THF has been investigated. Treatment of 1a with potassium in THF gave a mixture of dibenzamide (11a), N-benzoyl-C-phenylglycine (6a), and C-phenylglycine (10a). A higher yield of 11a was obtained, together with benzoic acid (9), when the reaction of 1a was carried out in THF saturated with oxygen. The reaction of 1b gave a mixture of β-phenylalanine (10b) and 9, whereas 1c gave a mixture of N-benzoyl-C,C-diphenylglycine (6c) and N-benzoyl-C,C-diphenylmethylamine (5c). Similarly, the reaction of 12 gave a mixture of α-benzamidocinnamic acid (15) and 9. The reaction of the bioxazolinone 17 with potassium gave a mixture of 11a, 6a, and 10a, along with an appreciable yield of 2,3,5,6-tetraphenylpyrazine (25), whereas 26 under analogous conditions gave a mixture of 15, 6b, and benzamide (29). Reasonable mechanisms, involving the initial formation of radical anion intermediates and their subsequent transformation to give the observed products, have been suggested. Potassium superoxide oxidation of some of these substrates gives similar product mixtures. Cyclic voltammetric studies have been carried out to measure the reduction potentials of 1a–c, 12, 17, and 26 in the generation of their radical anions. The radical anions of these substrates were also generated pulse radiolytically in methanol and their spectra showed absorption maxima in the region 295–350 nm.
Effect of mercerization on the crystallite size and crystallinity index in cellulose from different sources
Authors: Revol J. F. , Dietrich A. , Goring D. A. I.
Published: May 2006

Native cellulose samples having a wide range of crystallinity and crystallite size were mercerized by treatment with sodium hydroxide. The resultant cellulose II samples showed only a narrow range of crystallinity and an essentially constant crystallite size. For the low-crystallinity samples, crystallinity and crystallite size actually increased on mercerization. These results are in line with the proposal that mercerization involves the mingling of chains from adjacent and antiparallel cellulose I microfibrils to form cellulose II crystals of antiparallel chains.
Phase transitions and molecular motions in adamantane derivatives: 1-adamantanol
Authors: Harvey Pierre D. , Gilson Denis F. R. , Butler Ian S.
Published: May 2006

An order–disorder transition occurs in 1-adamantanol at 359 K on heating and at 342 K on cooling, with transition entropies of 36 and 34 J K−1 mol−1, respectively. FT-ir spectra show that free hydroxyl groups exist in the high temperature phase, but the majority of the O—H groups remain hydrogen bonded. The barrier to adamantyl group rotation in the low-temperature phase, determined from proton spin–lattice relaxation time measurements, is 20.9 Kj mol−1, and the barrier to rotation in the high-temperature phase is 35.0 kJ mol−1.
Pulse cyclic voltammetry. II. Flowing solutions
Authors: Eccles Gordon N. , Purdy William C.
Published: May 2006

By the use of pulse cyclic chronovoltammetry, better analytical data are sometimes obtained during the reverse scans. This is demonstrated by a chronovoltammetric FIA study of the quinone–hydroquinone couple. A quantitative FIA pulse cyclic chronovoltammetric investigation of the ferri–ferrocyanide reversible couple showed linearity for time-integrated fourier-smoothed data for reduction scan currents as well as the total of the forward and reverse scan peak currents. The detection limit was found to be 2 × 10−6 M.
Intramolecular rearrangements: Epimerization of bicyclic vinyl tertiary alcohols via a [2,3] sulfoxide sigmatropic rearrangement
Authors: Brown William L. , Fallis Alex G.
Published: May 2006

A general method for inverting the stereochemistry of bicyclic vinyl endo alcohols such as 6 and 12 to give the corresponding exo isomers 10 and 18 is described. The procedures employ a [2,3] sulfoxide rearrangement as a key step. In the case of the norbornene alcohol 12 the intermediate sulfenate ester 13 gives the oxetane 14 rather than the expected sulfoxide 17. It was therefore prepared by thionyl chloride induced rearrangement of 12 to the allylic chloride 15 followed by displacement (PhSNa) and oxidation (m-chloroperbenzoic acid). The exo alcohol thus obtained underwent smooth anionic oxy-Cope rearrangement (KH, THF) to the cis-hydrindenone 19.
Catalytic hydrolysis of cAMP
Authors: Chin Jik , Zou Xiang
Published: May 2006

[Co(trien)(OH2)(OH)]Cl2 is highly efficient in catalyzing the hydrolysis of cAMP to adenosine in neutral water (6 × 10−6 M−1 s−1 at 50 °C). The cobalt complex promoted hydrolysis of cAMP is estimated to be about a hundred million times faster than the uncatalyzed hydrolysis of cAMP. In the time that [Co(trien)(OH2)(OH)]Cl2 produces 50% cleavage of cAMP, [Co(en)2(NH3)(OH)]Cl2 or ZnCl2 has no observable effect on the hydrolysis of cAMP. A detailed mechanism is presented for the cobalt complex promoted hydrolysis of the phosphodiester.
Surface adsorption at low coverage of n-alkanes on bleached kraft papers using gas chromatography
Authors: Gurnagul N. , Gray D. G.
Published: May 2006

The adsorption at low surface coverage of a series of n-alkanes on various bleached kraft paper surfaces was measured by gas chromatography. Differences in surface area of the paper samples were readily measured from the gas chromatographic retention volumes. The standard free energy, the enthalpy, and the entropy of adsorption varied linearly with the number of carbon atoms in the n-alkanes. The heats of adsorption were close to the heats of liquefaction, indicating the non-specific interactions of the hydrocarbons with the bleached kraft surfaces. The London component of the surface free energy was estimated from the gas chromatographic results to be 47.9 mN/m.
Electroionization study of ethane: structures in the ionization and appearance curves
Authors: Plessis Pierre , Marmet Paul
Published: May 2006

Ionization efficiency curves of very high signal-to-noise ratio are presented for ethane and most fragment ions containing at least one carbon atom. These curves, which are produced by monoenergetic electron impact, extend up to 10 eV above the initial onsets. Novel structures are observed in most curves. Certain features appear at the same energy in several of the curves indicating that they belong to a common progenitor, either [Formula: see text] or [Formula: see text], and not directly to the detected ions. These sets of structure are attributed to negative ion states (Feshbach resonances) and/or to Rydberg autoionizing states.
Structural properties of modified deoxyadenosine structures in solution. Impact of the gauche and anomeric effects on the furanose conformation
Authors: Koole Leo H. , Buck Henk M. , Nyilas Agnes , Chattopadhyaya Jyoti
Published: May 2006

A variable temperature high resolution 1H nuclear magnetic resonance study (at 300 or 500 MHz) of the two modified nucleosides 9-(2′-deoxy-β-D-threo-ribofuranosyl)-adenine (1) and 9-(3′-deoxy-β-D-threo-ribofuranosyl)-adenine (2) has been performed. It was found that the furanose conformation in 1 and 2 can be best described as a rapid North (N) [Formula: see text] South (S) equilibrium that is biased toward the N-form. For 1, a marked temperature dependence of the [Formula: see text] equilibrium was found, whereas the furanose conformation in 2 is virtually insensitive to temperature changes. Comparison of these results with the well-known conformational properties of the natural nucleosides 2′-deoxyadenosine (2′-dA) and 3′-deoxyadenosine (3′-dA) revealed that the net result of the gauche effect and the anomeric effect is of major importance in determining the furanose conformation. A brief discussion in terms of the thermodynamic parameters that govern the [Formula: see text] equilibria in the investigated nucleosides is given.
Influence of steric hindrance in molecules of substituted 2-phenyl-1,1,3,3-tetramethylguanidines on the kinetics and isotope effects of their proton transfer reactions with 4-nitrophenylnitromethane in acetonitrile solvent
Authors: Pruszynski Przemyslaw
Published: May 2006

Rate constants have been determined for the proton and deuteron transfer reactions of 4-nitrophenylnitromethane, NO2C6H4CH2NO2, with three phenyl substituted derivatives of 2-phenyl-1,1,3,3-tetramethylguanidine, X—C6H4—N=C[N(CH3)2]2, where X = 4-Cl, 2-Cl, and 2-Br, in the temperature range 278–308 K in acetonitrile solvent. In the concentration ranges used, the reaction to form an ion-paired product is first order in acid and first order in base. The reaction was followed spectrophotometrically using the stopped-flow technique. The reaction is fastest for the 4-Cl substituted base and slowest for the 2-Br analogue. The observed deuterium kinetic isotope effects show a clear dependence on the position and the size of the substituent in the base molecule. Kinetic isotope effects at 25 °C, kH/kD = 9.7 ± 0.3, 12.5 ± 0.3, and 15.6 ± 0.3, were observed for 4-Cl, 2-Cl, and 2-Br substituted bases respectively. The appropriate ratios of Arrhenius preexponential factors, AH/AD = 0.98 ± 0.10, 0.87 ± 0.10, and 0.77 ± 0.10, may indicate increasing importance of tunnelling of the proton when the substituent is moved from the para to the ortho position or when the size of ortho substituent increases. Values of tunnelling correction factors were calculated using Bell's equation by means of the Caldor and Saunders method.
Deuterium isotope effects on nuclear shielding constants and spin–spin coupling constants in the ammonium ion, ammonia, and water
Authors: Wasylishen Roderick E. , Friedrich Jan O.
Published: May 2006

Deuterium isotope effects on 15N chemical shifts have been investigated for the ammonium ion, ammonia, and aniline; 1Δ15N(2/1H) equals −293.3, −622.9, and −714.6 ppb respectively. Deviations from additivity are noted for NH4−nDn+ and NH3−nDn; these deviations follow the predictions of Jameson and Osten. For ammonia, examination of the proton nuclear magnetic resonance spectrum yields 1Δ1H(15/14N) = −2.0 ± 0.4 ppb and [Formula: see text]. An accurate value of −1545 ± 5 ppb was obtained for 1Δ17O(2/1H) in water. Derivatives of the heavy atom shielding constants with respect to extensions in the equilibrium bond length have been estimated for NH4+, NH3, and H2O; these derivatives are compared with the recent calculations of Chesnut. Deuterium isotope effects on 1J (15N,H) in ammonia and aniline have been measured for the first time. For the ammonium ion, deuterium isotope effects on 1J (15N,H) are in good agreement with the less accurate values we previously observed on 1J (14N,H). In the case of water, both primary and secondary deuterium isotope effects on 1J (17O,H) are less than 2%. The isotope effects on the spin–spin coupling constants observed here are compared with those previously reported for other hydrides in the literature.
Terpenoid metabolites from skin extracts of the dendronotid nudibranch Tochuinatetraquetra
Authors: Williams David E. , Andersen Raymond J.
Published: May 2006

The skin chemistry of specimens of the dendronotid nudibranch Tochuinatetraquetra collected at Port Hardy and Bamfield, British Columbia, has been examined. Port Hardy animals yielded tochuinyl acetate (1) and dihydrotochuinyl acetate (2), two new cuparane sesquiterpenoids, as well as rubifolide (3) and pukalide (4), two previously known cembrane diterpenoids. Bamfield animals yielded the known briarein-type diterpenoid ptilosarcenone (5) and the previously unreported butanoate analogue 6. The T. tetraquetra metabolites are sequestered from coelenterates in the nudibranch's diet.
Additivity of the partial molar volumes of organic compounds
Authors: Nishimura Norio , Tanaka Tohru , Motoyama Takushi
Published: May 2006

A critical test of additivity for partial molar volume has been made at 25 °C in CCl4 with polyethylene glycol dimethyl ethers, crown ethers, cycloalkanes, n-alkanes, and others. Plots of partial molar volume at infinite dilution [Formula: see text] against the properly chosen number of repeating unit (n) are linear except for small cyclic molecules, and the slopes of homologous straight chain and ring compounds are the same. The values of [Formula: see text] extrapolated to n = 0 for cycloalkanes and crown ethers support the validity of the contribution due to the translational kinetic energy that has been predicted recently on a theoretical basis. The importance of packing efficiencies around the solute molecules has been examined by means of simple models.
An 1H nuclear magnetic resonance study of derivatives of 3-hydroxy-12,13-epoxytrichothec-9-enes
Authors: Savard Marc E. , Blackwell Barbara A. , Greenhalgh Roy
Published: May 2006

The 250-MHz 1H nuclear magnetic resonance spectra of 36 natural and synthetic trichothecenes have been analyzed and the chemical shifts as well as the vicinal and long-range coupling constants determined. Knowledge of the 16-CH3 chemical shift enables the substitution pattern of the A ring to be defined. Similarly, oxygenation in the C ring results in easily identifiable resonances. The J2,3 and J3,4 values define the configuration of substituents at C-3 and C-4, while the configuration at C-7 and C-8 can be defined by the J7,8, J7α,11, and J7β,15 values. The trichothecene ring system adopts the most stable A-half-chair, B-chair conformation in solution. The correlations obtained allow easy structural determination of unknown trichothecenes.
Model compounds for poly(oligomethylene glycol-4,4′-biphenyl dicarboxylates). An X-ray diffraction study
Authors: Deguire Suzanne , Gagné Johanne , Dugas Hermann , Brisse François
Published: May 2006

To provide the necessary parameters required for the conformational analysis of poly(oligomethylene glycol-4,4′-biphenyl dicarboxylates), two model compounds related to the above polyesters have been synthesized and their structures established by X-ray diffraction. The crystal structures of ethylene glycol di-para-phenylbenzoate (2DPPB) and 1,4-butylene glycol di-para-phenylbenzoate (4DPPB) have been solved by direct methods. 2DPPB is monoclinic with a = 7.174(2) Å, b = 8.101(2) Å, c = 19.183(4) Å, β = 102.48(2)°, Z = 2, space group P21/c. 4DPPB is triclinic with a = 9.978(2) Å, b = 11.172(3) Å, c = 11.437(2) Å, α = 85.46(2)°, β = 79.40(2)°, γ = 71.03(2)°, Z = 2, space group [Formula: see text]. The weighted least-squares refinements converged to Rw = 0.054 (2DPPB) and Rw = 0.057 (4DPPB). The values of ε, the tilt angle of the carboxylate group with respect to the phenylene ring, are 3.5° for 2DPPB and 1.5° and 1.4° for 4DPPB. A systematic study of this dihedral angle showed that the values of ε remain in the vicinity of 0°–10° and the value observed most frequently is 5°. The values of Φ, the dihedral angle between the two six-membered rings, are 36.2° in 2DPPB and 14.7° and 31.0° for 4DPPB. A systematic study with 71 biphenyl molecular fragments showed that distribution of Φ presents two maxima: one around 30° – 40° and the other in the range of 0°–10°. The conformation of the methylenic sequence is all-trans for 2BPPB and gtttt for 4DPPB.
Atomization efficiency of a graphite furnace in atomic absorption spectrometry at high heating rates
Authors: Chakrabarti C. L. , Ferrarotto D. , Cathum S. J. , Rademeyer C. J.
Published: May 2006

not available
The formation of (CH3)7Si2+ in (CH3)4Si/CH4 mixtures and CH3− exchange reactions between (CH3)4Si, (CH3)4Ge, and (CH3)4Sn studied by high pressure mass spectrometry
Authors: Wojtyniak Anastasia C. M. , Li Xiaoping , Stone John A.
Published: May 2006

The association equilibrium [Formula: see text] has been studied in a high pressure mass spectrometer ion source using tetramethylsilane/methane mixtures. Measurement of the equilibrium constant over a range of temperatures yields ΔH0 = −22.3 ± 0.4 kcal mol−1 and ΔS0 = −35.2 ± 0.9 cal mol−1 K−1. Collision-assisted dissociation experiments suggest that the methyl groups retain their integrity in (CH3)7Si2+. Mixed ions such as (CH3)7SiGe+ and (CH3)7GeSn+ were not observed in mixtures of (CH3)4X and (CH3)4Y(X ≠ Y = Si, Ge, Sn). Instead CH3− transfer equilibrium reactions were observed viz. [Formula: see text] (ΔH0 = −10.2 ± 1.2 kcal mol−1, ΔS0 = −3.7 ± 2.4 cal K−1 mol−1) and [Formula: see text], ΔS0 = −0.9 ± 1.6 cal K−1 mol−1. These are in excellent agreement with some published differences in appearance potentials for (CH3)3X+ from (CH3)4X (X = Si, Ge, Sn).
Ruthenium (II) complexes of 4-nitroimidazoles: their characterization, solution chemistry, and radiosensitizing activity
Authors: Chan Peter K. L. , Chan Paul K. H. , Frost David C. , James Brian R. , Skov Kirsten A.
Published: May 2006

A series of ruthenium(II) complexes of formulation RuCl2(dmso)2Ln, where dmso = S-bonded dimethylsulfoxide, L is a 4-nitroimidazole derivative, and n = 1 or 2, have been synthesized and characterized by spectroscopic methods, particularly 1H nmr and X-ray photoelectron spectroscopy. With L = 4-nitroimidazole itself (4-NO2Im), RSU-1170, -3083 or -3100, n = 2 and the six-coordinate complexes are considered to be of cis,cis,cis-geometry. The N-methyl-4-nitroimidazole (NMe-4-NO2Im) ligand (n = 1) chelates through the imidazole-N and the oxygen of NO2. The RSU-3159 ligand (n = 1) binds through the sulfur and may be chelated. The complexes are of interest because of their radiosensitizer properties toward hypoxic tumour cells; the RuCl2(dmso)2(NMe-4-NO2Im) complex has a higher sensitizing enhancement ratio than the free imidazole ligand, and shows no cytoxicity in vitro, and these data are compared to those reported previously for RuCl2(dmso)2(4-NO2Im)2. Some aspects of the aqueous solution chemistry of the complexes (aquation via loss of chloride, pKa of coordinated water) are discussed in relation to their biological activities.
Physical and structural studies of N-substituted-3-hydroxy-2-methyl-4(1H)-pyridinones
Authors: Nelson William O. , Karpishin Timothy B. , Rettig Steven J. , Orvig Chris
Published: May 2006

A series of 3-hydroxy-2-methyl-4(1H)-pyridinones has been prepared with the substituents H, CH3, n-C6H11, and CH2CH2NH2 at the ring N. The dipyridinone 1,6-bis(3-hydroxy-2-methyl-4(1H)-pyridinon-1-yl)hexane has also been synthesized. The products with H and CH3 substituents have been studied by single crystal X-ray diffraction. Crystals of 3-hydroxy-2-methyl-4-pyridinone are monoclinic, a = 6.8351(4), b = 10.2249(4), c = 8.6525(4) Å, β = 105.215(4)°, Z = 4, space group P21/n and those of 3-hydroxy-1,2-dimethyl-4-pyridinone are orthorhombic, a = 7.3036(4), b = 13.0490(6), c = 13.7681(7) Å, Z = 8, space group Pbca. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.037 and 0.044 for 914 and 857 reflections with I ≥ 3σ(I), respectively. Bond lengths and angles in the two compounds were normal. All the compounds have been studied by mass spectrometry, and by infrared and proton nmr spectroscopies. The importance of hydrogen bonding to both the solution and solid state properties of these compounds has been confirmed by these techniques.
Cell growth inhibitory dihydrophenanthrene and phenanthrene constituents of the african tree Combretum caffrum
Authors: Pettit George R. , Singh Sheo Bux , Niven Margaret L. , Schmidt Jean M.
Published: May 2006

Combretum caffrum, a tree in the family Combretaceae, has been found to contain three 9,10-dihydrophenanthrenes (6,7-dihydroxy-2,3,4-trimethoxy; 7-hydroxy-2,3,4,6-tetramethoxy; and 2,7-dihydroxy-3,4,6-trimethoxy) that inhibit (ED50 2.2, 2.8, and 2.6 μg/mL) growth of the murine lymphocytic leukemia cell line. One phenanthrene (7-hydroxy-2,3,4,6-tetramethoxy) was also isolated with similar (ED50 2.0 μg/mL) activity. Structures for each of these substances, including a dihydrophenanthrene (2-hydroxy-3,4,6,7-tetramethoxy-9,10-dihydrophenanthrene), were determined by detailed high resolution nuclear magnetic resonance and mass spectral studies and (or) X-ray crystal structure analysis.
Effect of ring substituents on the fluorescence spectra of substituted diarylcarbenes
Authors: Scaiano J. C. , Weir D.
Published: May 2006

The fluorescence spectra of a series of ring-substituted diarylcarbenes have been examined. The solution spectra are generally red shifted by 25–30 nm with respect to the band positions in matrices at 77 K. The difference is believed to reflect emission from non-relaxed conformations at 77 K. Both electron-withdrawing and -donating substituents lead to red shifts in the emission. These shifts are essentially additive, and the carbene emission data show an excellent correlation with free radical fluorescence data for the corresponding diarylmethyl radicals. The temperature dependence of excited carbene lifetimes have been examined for a few representative examples.
The thermodynamics of orientational disorder in a molecular solid: (CH3)3CCHO
Authors: White Mary Anne , Perrott Allyson
Published: May 2006

The heat capacity of tert-butylaldehyde, (CH3)3CCHO, has been measured as a function of temperature from 29 to 298 K, to investigate solid-state polymorphism. There are two solid–solid phase transitions in this material, Ttr = 158.5 and 183.9 K, ΔStr = 0.402 R and 3.153 R respectively. The thermodynamic parameters for the transitions are consistent with mechanisms proposed on the basis of recent nuclear magnetic resonance investigations of this material.
Dynamics of a one-dimensional classical hindered rotor
Authors: Yasuda Hideo , Raich John C.
Published: May 2006

The dynamic susceptibility of a one-dimensional rotor in crystal fields of various symmetry is calculated within the framework of classical mechanics. The contributions from oscillatory and rotary motions are treatable separately. This approach serves to clarify the structure of the spectrum. The nature and magnitude of the quantum effect are investigated and a comparison with earlier quantum mechanical calculations is made.
Heats of vaporization and gaseous molar heat capacities of ethanol and the binary mixture of ethanol and benzene
Authors: Dong Jin-Quan , Lin Rui-Sen , Yen Wen-Hsing
Published: May 2006

A combined system of the Newsham vaporization calorimeter and the Pitzer gaseous heat capacity flow calorimeter were reconstructed with modifications. Both calorimeters were calibrated with benzene, the liquid standard, and were found to be acceptable for measurements, with deviations of 0.4% and 0.9%, respectively. Heats of vaporization of pure ethanol under five pressures and binary mixtures of ethanol and benzene under normal pressure were determined. Gaseous molar heat capacities of pure ethanol under three pressures and of binary mixture of ethanol and benzene at two temperatures were also determined, with anomalies due to association noted. Association of ethanol molecules in the vapor phase was discussed and analyzed, with heats of association and entropy change of association calculated.
Infrared spectroscopic characterization of the interaction of ascorbyl palmitate with phospholipid bilayers
Authors: Köhler U. , Mantsch H. H. , Casal H. L.
Published: May 2006

The interaction of ascorbyl palmitate (AP) with phospholipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) has been studied by variable temperature infrared spectroscopy. The incorporation of AP into these lipid bilayers induces a considerable increase in the gel to liquid-crystal phase transition temperature of the lipid. The increase in this temperature is dependent on the nature of the lipid head group, on the relative concentration of AP, and on its degree of ionization; i.e., smaller temperature increases are observed when AP is ionized, forming salts with cations (NH4+, Li+, K+, and Ca2+). The stabilizing effect of the long chains in the bilayers plays an important role in inducing temperature increases. However, in the case of AP the present data also demonstrate that specific interactions at the polar head group serve to further stabilize the incorporation of AP into lipid bilayers. The infrared spectra demonstrate that in the case of DPPC:AP mixtures there are changes compatible with the formation of hydrogen bonds between the OH group at position 3 in AP and the ester carbonyl group at the sn-2 chain in DPPC. in the case of PE:AP mixtures the spectra are compatible with AP intercalated between PE head groups acting as a hydrogen bond bridge linking the phosphate and ammonium groups of two different PE molecules.
Surface photochemistry: Semiconductor mediated reactions of some saturated strained hydrocarbons
Authors: Baird N. Colin , Draper Anthony M. , Mayo Paul de
Published: May 2006

Quadricyclane (1) and 1,8-bishoniocubane (2) have been found to undergo valence isomerization to norborndiene and tricyclo[4.2.2.02,5]deca-3,7-diene, respectively, on illuminated CdS and ZnO. An electron transfer mechanism is proposed. Quantum yield, solvent effects, the role of oxygen, and the quenching of the reaction were investigated, and were consistent with this interpretation. The thermal reaction of 1 on CdS was also suggested to be an electron transfer process involving, in this case, defects or trapped holes on the surface of the semiconductor. An examination of a series of strained hydrocarbons structurally related to 1 (tetracyclo[3.3.0.02,8.04,6]octane 3, pentacyclo[4.3.0.02,4.03.805,7]nonane 4 and pentacyclo[4.4.0.02,4.03,8.05,7]decane 5) resulted, largely, in a demonstration of the resistance of their respective radical cations to rearrangement prior to back electron transfer. Calculations by MNDO, in combination with a modified version of MM2, were used to explore the differences in the reactivity of the radical cations of 1, 3, 4, 5, and an interpretation is presented.
Études des propriétés adsorbantes des fibres d'amiante modifiées et de fibres proposées comme substitut à l'amiante par chromatographie en phase gazeuse
Authors: Lefebvre Yves , Lambert Maryse , Khorami Jaleh , Ménard Hugues
Published: May 2006

A study, by vapor phase chromatography, of the adsorption isotherms of benzene on raw and modified asbestos fibers as well as on fibers proposed as substitutes for asbestos shows that there is a marked difference in the behaviour of the various fibers examined. A comparison of the adsorbing power of raw and phosphorylated asbestos fibers, as well as asbestos fibers heated to 700 °C, has been made regarding their behaviour toward solutes bearing various functional groups, and it has shown the existence of physical adsorption as well as chemisorption. The presence of hydroxyl groups in the surface of the asbestos fibers favors the adsorption of organic molecules through hydrogen bonding. [Journal translation]
Effect of solvent structure on electron reactivity: 2-propanol/water mixtures
Authors: Maham Yadollah , Freeman Gordon R.
Published: May 2006

The reactivity of solvated electrons [Formula: see text] with efficient (nitrobenzene, acetone) and inefficient (phenol, toluene) scavengers is affected greatly by the solvent composition in 2-propanol/water mixed solvents. 2-Propanol is the only secondary alcohol that is completely miscible with water. The variation of the nitrobenzene rate constant k2 with solvent composition displays four viscosity zones, as in primary and tertiary alcohol/water mixtures. In zone (c), where the Stokes–Smoluchowski equation applies, the nitrobenzene k2 values in the secondary alcohol/water mixtures are situated between those in the primary and tertiary alcohols, due to the relative values of the dielectric permittivity ε. The charge–dipole attraction energy varies as ε−1.The two water-rich zones (c) and (d) are characterized by a large change of viscosity η and a small change in [Formula: see text] solvation energy (trap depth) Er; here k2 for all the scavengers correlates with the inverse of the viscosity. In the two alcohol-rich zones (a) and (b) the change of η is small but that of Er is large; here k2 of inefficient scavengers correlates with the inverse of Er, due to the difficulty of electron transfer out of deeper traps. Activation energies E2 and entropies [Formula: see text] also show composition zone behaviour. The value of [Formula: see text] is more negative for less efficient scavengers; E2 varies less and does not correlate with reactivity or Er. Electron transfer from solvent to inefficient scavenger is driven by solvent rearrangement around the reaction center, reflected in [Formula: see text].
1H and 14N ENDOR spectra of tert-butylphenylnitroxide
Authors: Yamauchi Jun , Deguchi Yasuo
Published: May 2006

1H and 14N ENDOR spectra of tert-butylphenylnitroxide were observed in ethylbenzene solution. The experimental conditions for detecting optimum 1H and 14N ENDOR lines were quite different. The 1H hyperfine coupling constants and their signs are discussed from the viewpoints of molecular orbital calculations, general triple resonance, CRISP (cross relaxation intensity sequence pattern) method, and steric hindrance. In view of the large anisotropic hyperfine interaction between the nitrogen and the unpaired electron, detection of 14N ENDOR in nitroxide radicals is rather difficult, so that a TM110 mode cavity was utilized in this experiment. The observed 14N hyperfine coupling constant 11.86 G at −80 °C is one of the smallest values observed to date for nitroxide radicals.
N-14 ENDOR study of micellar solutions of sodium dodecylsulfate using small spin probes
Authors: Kotake Yashige , Janzen Edward G.
Published: May 2006

ENDOR (electron nuclear double resonance) spectroscopy has been applied to the study of the state of solubilization of small nitroxide spin probes in micelles produced in sodium dodecylsulfate solution. The intensity ratio of the pair of N-14 ENDOR lines observed by fixing the field on the low-field ESR (electron spin resonance) line was monitored as a measure of the motion of spin probes. Neutral spin probes, when solubilized in micelles, show a discontinuous change of ENDOR spectral parameters such as hyperfine splitting constant and peak intensity ratio. Above the critical micelle concentration, the spectrum features change only gradually as the number of solubilized probes is increased. Spin probes in micelles appear to experience environments that are less polar than those met in aqueous solutions. However, the solubilized state is stable and is insensitive to changes in the concentration of the amphiphile. An anionic spin probe, Fremy's salt, shows no indication of interaction with the micelles. The applicability of the use of ENDOR peak intensities for the study of spin probe motion is discussed.
Applications of enzymes in the synthesis and hydrolytic study of 2-deoxy-α-D-glucopyranosyl phosphate
Authors: Percival M. David , Withers Stephen G.
Published: May 2006

The labile sugar phosphate 2-deoxy-α-D-glucopyranosyl phosphate has been synthesized enzymically in a two-step process from 2-deoxy-D-glucose-6-phosphate via an intermediate uridine 5′-diphospho-2-deoxy-D-glucose. Rate constants for acid-catalysed (1 M HClO4) hydrolysis at several temperatures were determined by using an enzymic assay to measure remaining substrate. The values obtained were consistent with that anticipated on the basis of known hydrolysis rates for alkyl- and aryl-2-deoxy-D-glucopyranosides.
The infrared spectrum of aminodifluoroborane, NH2BF2: Partial assignment of the fundamentals and analysis of the band near 1608 cm−1
Authors: Jemson H. M. , Lewis-Bevan W. , Gerry M. C. L.
Published: May 2006

The infrared spectrum of gas phase aminodifluoroborane, NH2BF2, has been observed for the first time. A partial assignment to the fundamental vibrations has been made. The [Formula: see text] band has been recorded at high resolution, and the rotational and centrifugal distortion constants of NH211F2 have been obtained in both the ground and 21 levels. A small rotational perturbation in the 21 level has been attributed to a perpendicular Coriolis interaction. Using a newly written least-squares fitting program, spectroscopic constants of the unseen level have been evaluated, including its band origin and the Coriolis coupling coefficient. Possible identities of the unseen level are suggested.
Ion chemistry of transition metals in hydrocarbon flames. II. Cations of Sc, Ti, V, Cr, and Mn
Authors: Goodings John M. , Tran Quang , Karellas Nicholas S.
Published: May 2006

The same fuel-rich, premixed, conical, methane–oxygen flame at 2200 K and atmospheric pressure used for studies of Fe, Co, Ni, Cu, and Zn in Part I (1) is doped with the same concentration (~1 ppm) of Sc, Ti, V, Cr, and Mn to complete the first row of ten transition metals. Metallic ions of these metals and their compounds formed by chemical ionization reactions with H3O+ are observed by sampling the flame through a nozzle into a quadrupole mass spectrometer. Concentration profiles of individual and total cations are measured as a function of distance along the flame axis, and also mass spectra at a fixed point in the burnt gas. If A is the metal atom, the observed ions can be represented by four hydrate series including (a) A+•nH2O, (b) AOH+•nH2O, (c) AO+•nH2O, and (d) AO2H+•nH2O with n = 0–3 or 4, giving a maximum of four ligands around the metal atom. However, alternative isomeric structures are possible for each of the four basic series (e.g. AO+•2H2O ~ A(OH)2+•H2O ~ A(OH)3H+). The ions observed with Cr and Mn, in common with those of Fe, Co, Ni, and Cu, strongly favour series (a). On the other hand, Sc is completely different; the ions of series (c) are dominant. All four series are observed with each of Ti and V. Series (b) dominates for Ti and series (c) for V; ions from series (d) were observed for the first time. The ion chemistry of these metals is discussed in detail with emphasis on the probable chemical ionization reactions responsible for metallic ion formation. The pre-eminent role of proton transfer processes is apparent.
Molar volumes and refractivities of highly concentrated solutions of ammonium and potassium thiocyanates in water and dimethylsulphoxide
Authors: Pacák Petr , Kodejš Zdenĕk
Published: May 2006

Densities and refractive indices of highly concentrated solutions of ammonium and potassium thiocyanates in water and dimethylsulphoxide have been measured at 333.2 K in the composition range from xs = 0.01 up to saturated solutions. Molar volumes and apparent molar volumes have been calculated from density measurements and their concentration dependences are discussed. All the systems are volumetrically non-ideal and exhibit negative deviations from additivity. The molar refractivities were calculated from the refractive indices using the Lorentz–Lorenz equation. The refractivity values of individual ions were estimated in infinitely dilute solutions and were used for discussion of ion–solvent interactions.
Bridged-ring steroids. V. The total synthesis of 1,4-methano steroids by a modified Torgov sequence
Authors: Yates Peter , Douglas Stephen P. , Datta Sushil K. , Sawyer Jeffrey F.
Published: May 2006

The Diels–Alder adduct, 17, of cyclopentadiene and 2-methoxy-5-methyl-1,4-benzoquinone was reduced with sodium borohydride to the ketol 18, whose acetate 19 was further reduced with zinc amalgam to the monoketone 20. Reaction of 20 with vinyllithium gave the allylic alcohol 21, which underwent very ready dehydration with rearrangement to give the tricyclic enol ether 27, which was hydrolyzed to ketone 28a. Hydrogenation of 19 gave the dihydro product 30, which was reduced with zinc amalgam to the ketone 31. Treatment of the latter with vinyllithium gave the allylic alcohol 32. This was more stable than its analogue 21, but underwent hydrolysis and dehydration to the dienone 33. Treatment of 32 with 2-methyl-1,3-cyclo-pentanedione (5) in the presence of Triton B gave the tricyclic intermediate 35, its hydrolysis product 36, and the hydroxy derivative of the latter, 37. In the absence of base, 32 and 5 gave largely product 36. Hydrogenation of 36 gave the dihydro product 38, which on treatment with methanolic potassium hydroxide gave (±)-(1β,4β,5β,8α,9β,10β,13β,14β)-14-hydroxy-1,4-methanoandrostane-7,17-dione (39). Dehydration of 39 with p-toluenesulfonic acid gave first (±)-(1β,4β,5β,9β,10β,13β)-1,4-methanoandrost-8(14)-ene-7,17-dione (40), which was converted in turn to (±)-(1β,4β,5β,8α,9β,10β,13β,14β)-1,4-methanoandrost-15-ene-7,17-dione (41). Similar dehydration of 36 gave (±)-(1β,4β,5β,10β,13β,14β)-1,4-methanoandrosta-8,15-diene-7,17-dione (45).
15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. I. Protonation of deoxycytidylyl-(3′,5′)-guanosine in dimethylsulfoxide
Authors: Barbarella Giovanna , Capobianco Massimo Luigi , Carcuro Antonio , Colonna Francesco Paolo , Garbesi Anna , Tugnoli Vitaliano
Published: May 2006

The 15N and 13C chemical shifts of the sodium salt of deoxycytidylyl-(3′,5′)-guanosine have been measured in dimethylsulfoxide in the presence of variable amounts of CF3COOH. N3(cyt) is protonated first, followed by N7(gua) and the phosphate anion. These results vary from those reported for the binding of the methylmercuric cation to d(CpG).
(Ph3P)2Rh(SPCy2): A complex containing a side-on bonded η2-secondary phosphine sulfide anion
Authors: Gelmini Lucio , Stephan Douglas W.
Published: May 2006

The reaction of Cp2Zr(SPCy2)2 with either (Ph3P)3RhH(CO) or (Ph3P)4RhH led not to the expected heterobimetallic species but rather to a novel Rh species (Ph3P)2Rh(SPCy2), 4. The 31P{1H} NMR spectrum of this complex is an ABCX pattern. The molecular geometry of 4 was confirmed by a crystallographic study. Compound 4 crystallizes in the space group P21/c with a = 10.912(1) Å, b = 12.335(2) Å, c = 32.346(7) Å, β = 96.17(1)°, V = 4328(1) Å3 and Z = 4, The coordination sphere about Rh in 4 is pseudo-square planar, containing three phosphorus and a sulfur atom from the two coordinated phosphines and a side-on bonded SPCy2 moiety. This structural study confirms that the secondary phosphine chalcogenide is bonded to Rh in an η2 fashion. The complex 4 is only the fourth example in which this mode of binding has been crystallographically confirmed and is the first such species to involve one of the Pt group metals.
Theoretical conformational analysis of peptides. Evolution of a strategy and its application to cholecystokinin analogs
Authors: Wolfe Saul , Bruder Stephen , Weaver Donald Fredric , Yang Kiyull
Published: May 2006

Scheraga's ECEPP program has been used to determine the relationship between one-point energies and the energies minimized by a quadratic procedure, for different sized [Formula: see text] dihedral angle grid searches of simple peptides. Based on these trials, a new subroutine, INIT, has been written and incorporated into the program. This subroutine calculates the one-point ECEPP energies of up to 200,000 random permutations of [Formula: see text], 180 and (χ1) = −60, 180 with all ω = χ≠1 = 180; after each 40,000 permutations, the structures having the 10 lowest energies are ordered and selected for minimization. The ECEPP program has been modified further to provide an MMP2(85) input file as part of its normal output. This allows structures located by INIT to be minimized automatically, and then refined by the Newton–Raphson minimization and MMPEP parameters of MMP2(85).During the development of this protocol, it has been found that MMPEP correctly reproduces the C7 conformational preference of the alanyl dipeptide in nonpolar media, and also the experimentally observed shift to αR and PII conformations in polar solvents, when the dielectric constant ε = 78.5 D. This dielectric constant has, therefore, been selected for a conformational analysis, using INIT/MMPEP, of the peptides Gly-Trp-Met-Asp-Phe-NH2 (GLMAP), Gly-D-Trp-Met-Asp-Phe-NH2 (GDMAP), and Gly-Gly-Met-Asp-Phe-NH2 (GGMAP); GLMAP is CCK-5, a cholecystokinin fragment possessing anticonvulsant activity, which is found in the brain. The analogs GDMAP and GGMAP are not active, or much less so than GLMAP. One strongly preferred structure has been found, in each case, for GLMAP (GLMAP3) and GDMAP (GDMAP39). These structures are very similar, in the nature of the edge-to-face stacking of their Trp and Phe aromatic rings, but the C-terminal regions differ. The conformation of the C-terminal tetrapeptide of GLMAP3 is identical to a previously calculated structure of CCK-4. A comparison of the C-terminal regions of GLMAP3 and GDMAP39 with the structure of 5,5-diphenylhydantoin suggests that the mechanisms of anticonvulsant action of phenytoin and CCK-5 are not the same. In the absence of an aromatic–aromatic interaction, no clear-cut conformational preference is found for GGMAP. The structure of GGMAP whose C-terminal region is the same as that of GLMAP3 (GGMAP20) is 1.51 kcal/mol higher in energy than the lowest energy structure, and lacks the hydrophobic wall provided by the Trp residue of GLMAP3.
MMPEN: Development and evaluation of penicillin parameters for Allinger's MMP2(85)programme
Authors: Wolfe Saul , Khalil Maged , Weaver Donald Fredric
Published: May 2006

A set of parameters, termed MMPEN, has been determined for the bicyclic nucleus of penicillin, which, in conjunction with the appropriate parameters from MMPEP and the internally stored parameters of the program, allow Allinger's force field and MMP2(85) program to be applied to the molecular mechanics treatment of penicillins. The MMPEN parameters are based on crystallographic heavy atom bond lengths and bond angles, vibrational spectra, and molecular orbital calculations. The parameters reproduce the experimental crystal structures of several penicillins, including penicillin G and penicillin V, with an average deviation of 0.005 Å in bond lengths, 0.5° in bond angles, and 3° in dihedral angles. Conformational analyses of penicillin G and penicillin V, for a dielectric constant, ε = 78.5 D suggest that neither penicillin retains the crystal structure in solution. In both cases, the global minima have the C3-carboxyl group antiperiplanar to the 2β-methyl group in the thiazolidine ring, and the side chains are oriented so that the amide N-H occupies the convex face of the molecule. The predicted conformations of the methyl esters of penicillin G and bisnorpenicillin G, for a dielectric constant of 4.8 D, are consistent with the nuclear magnetic resonance spectra obtained for these compounds in chloroform solvent.
Structural investigation of water-hyacinth (Eichhornia crassipes) polysaccharides. Part I. Water-soluble polysaccharides
Authors: Issa Mohamady A.
Published: May 2006

A galactomannan and a branched (1 → 3)-β-D-glucan were isolated from the water hyacinth plant. The galactomannan, purified from the cold water extract, is composed of D-galactose and D-mannose in a ratio of 1.0:2.8. It has a (1 → 4)-linked D-mannose backbone, one out of three D-mannose residues being substituted with a single α-D-galactosyl unit. The branched (1 → 3)-β-D-glucan isolated from the hot water extract has a main chain composed of β-(1 → 3)-linked D-glucopyranosyl residues, and two single β(1 → 6)-D-glucopyranosyl groups attached as side chains to, on average, every 5 sugar units of the main chain. In addition, the branching of the β-glucan occurs regularly at O-6 of the β-(1 → 3)-linked backbone.