bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of bis(ferrocenylcarboxylato)telluranes
Authors: Srivastava Prakash C , Bajpai Sangeeta , Kumar Rajesh , Srivastava Shikha , Singh Vikas , Dwivedi Shrinkhala , Butcher Ray J
Published: April 2011

A convenient route to the synthesis of the first bis(ferrocenyl carboxylato) telluranes has been developed. Reactions of 1,1,2,3,4,5,6-heptahydro-1,1-(dihydroxo)tellurane and 1,1,2,3,4,5-hexahydro-1,1-(dihydroxo)tellurophene with ferrocene carboxylic acid give 1,1,2,3,4,5,6-heptahydro-1,1-bis(ferrocenyl carboxylato)tellurane (3) and 1,1,2,3,4,5,-hexahydro-1,1-bis(ferrocenyl carboxylato)tellurophene (5), respectively. The X-ray structure of 3 shows that it contains a tellurium heterocycle (C5H10Te), present in a chair conformation, sandwiched between two ferrocene units with carboxylate groups acting as spacers. Compound 3 also exhibits modest second harmonic generation (SHG) efficiency. The electrochemical studies of 3 and 5 through cyclic voltammetry show only one oxidation wave, indicating the presence of independent redox centers leading to reversible single-step two-electron redox systems.Key words: tellurane, ferrocenylcarboxylate, SHG efficiency, electrochemistry.
CALCULATIONS OF KINETIC ISOTOPE EFFECTS FOR THE IODIDE EXCHANGE AND FOR THE SOLVOLYSIS OF METHYL IODIDE
Authors: Willi Alfred V.
Published: April 2011

Kinetic deuterium and carbon-13 isotope effects are calculated for the SN2 exchange reaction of CH3I with *I−(131) and for the CH3I solvolysis in water. The normal vibrational frequencies of CH3I and of the transition state [Formula: see text] (X = I or OH2) are evaluated from force constants by solving the secular equation with an IBM 7094 computer. Values for force constants of the planar CH3moiety (with an sp2C atom) in the transition state are obtained by comparison with suitable stable molecules. For the iodide exchange reaction, there is not much dependence of the calculated D isotope effect on the particular choice of ƒCIand ƒ12(interaction between CI stretches) if these force constants are within reasonable limits. The bending force constantƒHCI(≠) may then be adj usted to reproduce the experimental D isotope effect.Based on the simple transition state model [Formula: see text] it is not possible to obtain agreement with the experimental D effect in the solvolysis reaction without assuming an extremely high value of ƒHCI. If must be concluded that a water molecule is probably involved in the transition state. On the basis of the model [Formula: see text] the experimental D effect may be reproduced with a suitable choice of ƒHCIand ƒHCO. It is shown that, under favorable circumstances, experimental temperature dependence data may be applied for a distinction between different sets of, ƒCH, ƒHCH, and ƒHCI(or ƒHCO) which reproduce the experimental isotope effect at one temperature.
13C n.m.r. studies. IX. Carbonyl carbon shieldings of some cyclopropyl ketones
Authors: Marr D. H. , Stothers J. B.
Published: April 2011

The 15.1 Mc/s 13C nuclear magnetic resonance spectra of 15 aliphatic and alicyclic ketones having a three-membered ring alpha to the carbonyl group have been obtained and the shieldings of their carbonyl carbon nuclei are reported. A number of derivatives of bicyclo-[4.1.0]heptan-2-one, bicyclo[3.1.0]hexan-2-one, spiro[2.5]octan-4-one, and spiro[2.4]heptan-4-one have been included. The primary objective was to investigate the question of conjugation of the cyclopropyl ring with a carbonyl grouping, since we had shown previously that 13C shieldings of carbonyl carbons are significantly affected by conjugative interactions. The 13C data for several related compounds were obtained to aid in our assessment of the cyclopropyl results. Some evidence of cyclopropyl conjugation is presented.
Lignans of western red cedar (Thuja plicata Donn). VI. Dihydroxythujaplicatin methyl ether
Authors: MacLean Harold , Murakami Koji
Published: April 2011

Proof of structure is presented for another lignan of the thujaplicatin series, 2,3-dihydroxy-2-(4″-hydroxy-3″,5″-dimethoxybenzyl)-3-(4′-hydroxy-3′-methoxybenzyl)-butyrolactone (I) (dihydroxythujaplicatin methyl ether). Analytical and spectral (ultraviolet, infrared, and nuclear magnetic resonance) data on derivatives and degradation products, in addition to the parent compound, are presented.
Low-temperature pyrolysis. II. An isotope study of the pyrolysis of the hydrogen phthalate ester of trans-1,2-dimethylcyclohexanol
Authors: Rutherford K. G. , Ottenbrite R. M.
Published: April 2011

The hydrogen phthalate ester of trans-l,2-dimethylcyclohexanol was prepared by using phthalic anhydride enriched in 18O. The ester was partially decomposed at 128°. An observed enrichment of 18O in the alcohol portion of the undecomposed ester supports an earlier postulate that an ion pair is involved in the thermal decomposition of this sterically hindered ester.
Synthesis of fused heterocyclic compounds with polyphosphoric acid
Authors: Dennler E. B. , Frasca A. R.
Published: April 2011

Several heterocycles with fused pyrazole rings were obtained by treatment of the p-nitrophenylhydrazones of several acylated hydrocarbons and thiophene with polyphosphoric acid.
Further reactions of secondary amines and arsines with fluorocycloolefins
Authors: Cullen W. R. , Dhaliwal P. S.
Published: April 2011

The generality of the reaction

[Formula: see text] has been investigated, and examples are given when M = N, X = F or Cl, Y = F, Cl, H, or As(CH3)2, and n = 1, 2, or 3; and when M = As, X = F or Cl, Y = F, Cl, H, or C2H5, and n = 1 or 2. When M = N, Y = OCH3, and X = Cl, the butenone

[Formula: see text] is obtained; the corresponding reaction with (CH3)2AsH gives only a trace of a butenone. When M = N, Y = C2H5, X = Cl, and n = 1, the simple product is not obtained. The nuclear magnetic resonance spectra of the compounds

[Formula: see text] (Y = H or F) show similar features, notably a shift to high field of the Y resonance when Z is a dialkylamino group.
Lignans of western red cedar (Thuja plicata Donn). VII. Dihydroxythujaplicatin
Authors: MacLean Harold , MacDonald B. F.
Published: April 2011

The structure of a seventh lignan from the hot-water extractive of western red cedar, which was partially separated in a previous paper, has been determined as 2,3-dihydroxy-2-(3″,4″-dihydroxy-5″-methoxybenzyl)-3-(4′-hydroxy-3′-methoxybenzyl)-butyrolactone (I). This lignan is the fifth member of the thujaplicatin series and is trivially named dihydroxythujaplicatin. Methylation, ethylation, and degradation studies provide proof of structure by comparison with known compounds.
Chalcogenides of the transition elements. V. Crystal structures of the disulfides and ditellurides of ruthenium and osmium
Authors: Sutarno  , Knop Osvald , Reid K.I.G.
Published: April 2011

The crystal structures of RuS2, OsS2, RuTe2, and OsTe2were refined isotropically by least squares from powder diffractometer data using individual temperature factors. The resulting positional parameters of the chalcogen atoms in these C2-type structures are 0.3879 ± 14, 0.3865 ± 19, 0.3739 ± 9, and 0.3725 ± 18 respectively (for meaning of the uncertainty limits see Table II and text). The structure of Ir3Te8was refined from Hockings and White's published data to give x(Te) = 0.3702 ± 18. The shortest metal–chalcogen distances in these structures are Ru—S 2.351 ± 3 Å, Os—S 2.352 d ± 5 Å, Ru–Te 2.647 ± 3 Å, Os–Te 2.647 ± b 3 Å, and Ir—Te 2.651 ± 4 Å (not corrected for thermal motion). The shortest S–S distances (in the S2groups) are 2.179 ± 30 Å in RuS2and 2.210 ± 46 Å in OsS2. The corresponding shortest Te—Te distances are 2.791 ± fc 35 Å in RuTe2, 2.826 ± 38 Å in OsTe2, and 2.872 ± 30 Å in Ir3Te8(not corrected for thermal motion). Within the stated uncertainty limits the shortest metal–chalcogen distances are independent of the nature of the metal. The shortest chalcogen–chalcogen distances are so sensitive to variations in x that even the above relatively narrow uncertainty limits preclude meaningful statements to be made about the effect of the metal on these distances, with the possible marginal exception of the nonstoichiometric C2 structure Ir3Te8.
Studies in terpenoids. IV. Synthetic studies in juvabiones and analogues. Conversion of ar- (+)-turmerone to ar- (+)-juvabione
Authors: Ayyar K. Subrahmania , Rao G. S. Krishna
Published: April 2011

Synthetic work leading to the preparation of todomatuic acids (2a), juvabiones (2b), and ar-(±)-juvabione (8d) and the successful conversion of ar-(+)-turmerone (9) to ar-(+)-juvabione (3b) is presented. The synthetic compounds 2b and 3b exhibit juvenile hormone activity.
Thermal and photolytic decomposition reactions of diazo compounds in the bicyclo[4 •1•0]heptane series
Authors: Still Ian W. J. , Wang D. T.
Published: April 2011

The photochemical and thermal decomposition reactions of 5-diazo-3-caren-2-one have been studied. Thermal decomposition led to the corresponding azine (93 %), while photochemical decomposition in aqueous dioxan led to the azine (7%) and to 3-carene-2,5-dione (9%). Photochemical decomposition in methanol led to a third product C20H24O4 (3%). Experiments on the photochemical decomposition of the isomeric 2-diazo-3-caren-5-one are also described.
Solvation of sodium ions studied by 23Na nuclear magnetic resonance
Authors: Bloor E. G. , Kidd R. G.
Published: April 2011

The 23Na chemical shifts, extrapolated to infinite dilution, of solutions containing sodium iodide dissolved in 14 different oxygen or nitrogen donor organic solvents have been determined. The observed range of chemical shifts can be successfully related to changes in the paramagnetic term of the general nuclear screening equation. A fair correlation between the magnitude of the paramagnetic term and the Lewis basicity of the solvent has been drawn. Those solvents showing anomalous behavior are the ones for which large magnetic anisotropies are to be expected. The 23Na chemical shifts for two mixed solvent systems containing sodium iodide have been obtained, and these support the conclusion that preferential solvation of the sodium ion occurs.
Transition metal acetates
Authors: Edwards D. A. , Hayward R. N.
Published: April 2011

Some anhydrous transition metal acetates (Mn(II), Co(II), Cu(II), Ni(II), Zn(II), Ag(I), Mo(II), Ce(III), La(III)) have been prepared and their infrared spectra measured in the solid state. The infrared spectra have been related to established modes of bonding of the acetate group to metals. Thermal decompositions of the anhydrous acetates have been investigated by thermogravimetric analysis; magnetic moments and visible spectra have been measured.
Velocity of sound isotherms in liquid krypton and xenon
Authors: Lim C. C. , Bowman D. H. , Aziz Ronald A.
Published: April 2011

The velocity of sound was measured with a precision of 0.1% in liquid krypton and xenon at pressures between the vapor pressure and about 65 atm, from near their triple points to near their critical points.A corresponding states treatment of these measurements and previous results in argon showed that, with a suitable choice of relative molecular parameters (σ,ε), the W*(P*,T*) surfaces were coincident to within the experimental error, except for argon near the critical temperature.The relative values of the effective atomic radii σ obtained from this analysis were somewhat lower than those obtained from other thermodynamic properties.
Yields of some light-mass nuclides produced in the proton-induced fission of 238U
Authors: Khan A. H. , Saha G. B. , Yaffe L.
Published: April 2011

The formation cross sections of cumulatively formed 66Ni, 67Cu, 72Zn, and 73Ga, and of independently formed 68Ga, 70Ga, and 72Ga produced in fission of 238U, induced by protons of energy 20–85 MeV, have been determined. The measured yields correlate well with the data obtained by others at higher energies. From the ratios of the independent and cumulative formation cross sections of 72Ga and 72Zn respectively, a value of Zp, the most probable nuclear charge, for A = 72 was determined for different widths of the charge dispersion curves.
Hydrogen bonding in sulfanes
Authors: Muller E. , Hyne J. B.
Published: April 2011

The position of the proton signals in the nuclear magnetic resonance spectrum of sulfanes (H2Sx) is dependent on the sulfur chain length, the sulfane concentration, and the temperature. These proton chemical shifts are interpreted in terms of sulfane–sulfane interactions and intramolecular hydrogen bonding in sulfanes. Supporting evidence is provided by the position and appearance of the SH-absorption bands of the sulfanes in the infrared, which also establishes the existence of sulfane–solvent interactions.It is concluded that sulfanes participate in hydrogen bonding interactions and it is suggested that there may be a special type of intramolecular hydrogen bonding operative in H2S3.
Magnetic study of the hexachlororhodate(IV) ion
Authors: Westland A. D.
Published: April 2011

The magnetic susceptibilities and electron spin resonance spectra of solid solutions of cesium hexachlororhodate(IV) in a diamagnetic host lattice were examined over a range of temperatures. The Landé splitting parameter, g, was found to be 1.7545 ± 0.0005. This led to an orbital delocalization factor of 0.81 and a spin-orbit coupling parameter of 554 cm−1. The susceptibility measurements failed to reveal any superexchange in the lattice but the electron spin resonance spectra gave some evidence for such coupling. Powder samples only were examined and these exhibited no hyperfine structure.
Effets ioniques spécifiques sur le taux de formation du ClO2 par la réaction chlorure–chlorate
Authors: Lenzi F. , Rapson W. H.
Published: April 2011

not available
Aminodideoxy sugars. Methyl 3-acetamido-2,3-dideoxy-α-D-arabino-hexopyranoside and methyl 2-acetamido-2,3-dideoxy-α-D-ribo-hexopyranoside
Authors: Rosenthal Alex , Catsoulacos P.
Published: April 2011

Oxidation of methyl 4,6-O-benzylidene-3-deoxy-α-D-arabino-hexopyranoside (2) with methyl sulfoxide and acetic anhydride yielded methyl 4,6-O-benzylidene-3-deoxy-α-D-erythro-hexopyranosid-2-ulose (3) in an 80% yield. Reduction of the oximino derivative of 3 with lithium aluminium hydride in tetrahydrofuran or with diborane afforded, after acetylation, methyl 2-acetamido-4,6-O-benzylidene-2,3-dideoxy-α-D-ribo-hexopyranoside (6) in a 44% yield. The latter was also debenzylidenated with aqueous acetic acid. In a parallel reaction, methyl 4,6-O-benzylidene-2,3-dideoxy-3-oximino-α-D-erythro-hexopyranoside yielded mainly methyl 3-acetamido-4,6-O-benzylidene-2,3-dideoxy-α-D-arabino- (and a minor amount of the ribo-epimer)-hexopyranoside.
Photochemical behavior of some α, β-unsaturated lactams. Dependence of reaction path on multiplicity
Authors: Cavalieri E. , Horoupian S.
Published: April 2011

Whereas direct irradiation (2537 Å) of 5,6-dihydro-4,6,6-trimethyl-2(1H)-pyridone 1 (1a) produced almost exclusively the cleavage products 2 and 3, the acetophenone sensitized reaction (3500 Å) gave a single cyclobutane dimer. In contrast, direct (2537 Å) or sensitized (acetophenone, 3500 Å) irradiation of the homo derivative 7 of compound 1 gave approximately the same mixture of two cyclobutane dimers. It was thus demonstrated that dimer formation proceeded by way of a triplet excited state and that the cleavage reaction most probably occurred via an excited singlet state.A structure for each cyclobutane dimer in the seven-membered series was proposed on the basis of its spectral properties.
Reactions of nitro sugars. XII. A novel type of disaccharide synthesis
Authors: Baer Hans H. , Kienzle Frank
Published: April 2011

Nitro disaccharide methyl glycosides were obtained by base-catalyzed addition of partially blocked sugar derivatives having one free hydroxyl group, across the ethylenic bond in methyl 4,6-O-benzylidene-2,3-dideoxy-3-nitro-β-D-erythro-hex-2-enopyranoside (1) and its α-anomer (2). Thus, the addition of 2,3,4,6-tetra-O-acetyl-β-D-glucopyranose (3) gave blocked derivatives of sophorose, namely methyl 2-O-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-4,6-O-benzylidene-3-deoxy-3-nitro-β-D-glucopyranoside (4) and -α-D-glucopyranoside (5). Similarly, the use of methyl 4,6-O-benzylidene-3-deoxy-3-nitro-β-D-glucopyranoside (10) and its α-anomer (13) as addends led to 2 → 2 linked bisglycosidyl ethers; these were the methyl 4,6-O-benzylidene-3-deoxy-2-O-(methyl 4,6-O-benzylidene-2,3-dideoxy-3-nitro-D-gluco-pyranosid-2-yl)-3-nitro-D-glucopyranosides with the anomeric configurations β,β, α,α, and α,β (11, 14, and 15, respectively). Methyl 4,6-O-benzylidene-3-deoxy-3-nitro-β-D-mannopyranoside (12) was found to epimerize to 10 under the reaction conditions; therefore, interaction of 12 and 1 also gave the bis-β-D-glucosidyl ether (11). The L-enantiomer of 12 gave with 1 an optically inactive meso compound (16) possessing a β-L- and a β-D-glucosidyl moiety.
Electron spin resonance studies of the reactions of sorbate with nitrite in the presence of a spin trap
Authors: Joshi Avinash , Hinton Dennis M , Yang George C
Published: April 2011

An esr spectrum was generated when a spin trap, t-nitroso butane (tNB), was added to potassium sorbate solution at pH of 6.4. This spectrum can be explained by the abstraction of allylic hydrogen by NO2, generated by the decomposition of tNB, followed by spin trapping of the radical product. With increasing concentration of NO2, which was accomplished by either the addition of sodium nitrite or by lowering the pH to cause rapid decomposition of tNB, a different esr spectrum was observed. This spectrum can be accounted for by a radical formed by addition of NO2 to the 4,5 double bond of the sorbate and subsequent trapping by tNB.
Ultrasonic velocity, excess adiabatic compressibility, apparent molar volume, and apparent molar compressibility properties of binary liquid mixtures containing 2-butoxyethanol
Authors: Rao N. P. , Verrall Ronald E.
Published: April 2011

Ultrasonic velocity and density data of binary systems of water–2-butoxyethanol (BE), 2-butoxyethanol-benzene, and 2-butoxyethanol–decane are reported for temperatures of 25, 40, and 55 °C. Adiabatic compressibility coefficients, apparent molar volumes, and apparent molar compressibilities were calculated from these data. Excess adiabatic compressibility properties were evaluated using volume fraction weighting of the individual component properties to estimate ideal mixture behavior. These results are compared with the data obtained based on the use of mole fraction weighting of the individual component properties for the ideal behavior value. A sharp ultrasonic velocity maximum and compressibility minimum is observed at low BE concentration in mixtures of water–BE at all temperatures. These maxima in ultrasonic velocity and minima in adiabatic compressibility are attributed to the formation of "clathrate-like" structures of water and alcohol. A shift of the velocity maximum towards lower concentrations of BE was observed with increase of temperature. A minimum in the ultrasonic velocity and a maximum in adiabatic compressibility coefficient values are observed in systems of BE–benzene and BE–decane. These results are discussed in terms of the breakdown of associated alcohol structures and the interstitial location of hydrocarbon molecules in alcohol aggregates.
Structure cristalline et moléculaire de l'acétoxy-3β ursane olide-28,20βa
Authors: Druet Danielle , Comeau Louis Claude , Viani Robert , Baldy André , Estienne Jacques , Pierrot Marcel
Published: April 2011

An X-ray crystallographic study of the triterpene C32H50O4, isolated from Opiliaceltidifolia, confirms the chemical analysis of the molecular structure. The rings A, B, C, and D are in the chair conformation, but ring E, due to a bridging lactone between the C(17) and C(20) carbon atoms, adopts a boat conformation. All five six-membered rings are trans-fused.
Dimerisation of mononuclear and binuclear cobalt phthalocyanines
Authors: Nevin W. A. , Liu Wei , Lever A. B. P.
Published: April 2011

The aggregation of mononuclear [2,9,16,23-tetra(neopentoxy)phthalocyanato]cobalt(II) and of some related binuclear cobalt(II) phthalocyanine derivatives, in o-dichlorobenzene, has been studied by electronic absorption spectroscopy. Dimerisation constants and the calculated aggregate dimer spectra are reported.
Charge transfer complexes of diquat and paraquat with halide anions
Authors: Bertolotti S. G. , Cosa J. J. , Gsponer H. E. , Previtali C. M.
Published: April 2011

The association of methylviologen, 1,1′-dimethyl-4,4′-bipyridynium (PQ2+), with halide and pseudo-halide ions was studied in water at 25 °C by ultraviolet spectrophotometry. A charge transfer band could be observed in the region around 300 nm. From difference absorption measurements the first association constant (K1,) was obtained as 1.7 (Cl−), 3.3 (Br−), 3.9 (I−), 0.7 (CN−), and 2.0(SCN−) M−1. Similar results were obtained for the dication, 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinium (DQ2+), with first association constants 3.3 (Cl−), 4.1 (Br−) and 4.6 (I−) M−1. First and second (K2) association constants were also determined by a potentiometric technique using ion selective electrodes: K1 = 2.0 M−1; K2 = 0.4 M−1 for the system PQ2+–Cl− and K1 = 5.3 M−1; K2 = 0.3 M−1 for DQ2+Br−.
Complexes of vanadium(V) with α-hydroxycarboxylic acids studied by 1H, 13C, and 51V nuclear magnetic resonance spectroscopy
Authors: Caldeira M. Madalena , Ramos M. Luísa , Oliveira Nuno C. , Gil Victor M. S.
Published: April 2011

A proton, carbon-13, and vanadium-51 nuclear magnetic resonance study is reported on the number, stoichiometry, geometry, and relative stability of the complexes that form when vanadate(V) solutions are mixed with each one of the following organic α-hydroxyacids in the pH range ~2.5 – ~7: glycolic, lactic, chloro-3- and phenyl-3-lactic, mandelic, glyceric, and malic acids. The predominant complexes have 1:1 composition (almost certainly in a polymeric structure) in contrast with the 1:2 (metal:ligand) stoichiometry of the corresponding Mo(VI) and W(VI) complexes.
Viscosity and density of isomeric butanol/water mixtures as functions of composition and temperature
Authors: Senanayake P. Chandani , Gee Norman , Freeman Gordon R.
Published: April 2011

Viscosity and density of 27 binary mixtures of sec-, iso-, and tert-butanol with water were measured at 273 ≤ T/K ≤ 353 and the results summarized using polynomials. At fixed T the density depended strongly but monotonically on mole fraction. The excess volume VE was large and negative. In H2O/tert-butanol as T increased VE increased, while in H2O/sec- or iso-butanol VE decreased with increasing T. The excess viscosity was large and positive in all cases.
Complexes of the dimethylgallium-1-pyrazolyl-o-aminophenolato ligand, [Me2Ga(pz)(o-NH2C6H4O)]−. Formation and crystal structure of the molybdenum amidine complex, Mo(CO)2Br(η3-C3H5)[η2-HN=CMe(pz)] (where pz = pyrazolyl, N2C3H3)
Authors: Gracey G. D. , Rettig Steven J. , Storr Alan , Trotter James
Published: April 2011

The synthesis, characterization, and structures of complexes containing the o-aminophenolato ligand are detailed. A novel molybdenum amidine complex is also described. Crystals of (o-aminophenolato)dimethylgallium are monoclinic, a = 10.1970(9), b = 9.7597(7), c = 18.778(2) Å, β = 100.810(7)°, Z = 8, space group C2/c, those of bis(dimethylgallium-1-pyrazolyl-o-aminophenolato)nickel(II) benzene solvate are monoclinic, a = 20.491(1), b = 11.789(1), c = 15.789(1) Å, β = 103.413(7)°, Z = 4, space group C2/c, and those of η3-allyl(bromo)[2-(1-pyrazolyl)ethylidenarnino]dicarbonylmolybdenum(II) are monoclinic, a = 11.0278(4), b = 8.4461(2), c = 15.3747(5) Å, β = 109.208(3)°, Z = 4, space group P21/c. The structures were solved by conventional heavy atom methods and refined by full-matrix least-squares procedures to R = 0.030, 0.053, and 0.038 for 1980, 1684, and 1901 reflections, respectively. Reaction of the [Me2Ga(pz)(OC6H4NH2)]− ligand, L−, with [Re(CO)4Cl]2 results in the formation of LRe(CO)3 whose physical properties indicate a fac arrangement of the organogallate ligand.
Facile preparations of 4-fluororesorcinol
Authors: Bélanger Patrice C. , Lau C. K. , Williams Haydn W. R. , Dufresne C. , Scheigetz John
Published: April 2011

Two facile methods for preparing 4-fluororesorcinol have been developed. In the first method, the direct fluorination of 1,3-dimethoxybenzene with trifluoromethyl hypofluorite carried out in Freon 11 at −78 °C afforded 2,4-dimethoxyfluorobenzene. Demethylation by heating under reflux in 48% HBr in acetic acid gave 4-fluororesorcinol in an overall yield of 60%. The second method involved the fluorination of 2,6-dimethoxyacetophenone by trifluoromethyl hypofluorite in Freon 11 at −78 °C, leading to 2,6-dimethoxy-3-fluoroacetophenone. On heating under reflux in 48% HBr in acetic acid, 4-fluororesorcinol was obtained in an overall yield of 74%. The latter is the method of choice for preparing 4-fluororesorcinol.
Thiophenophane–metal complexes. I. Preparation, X-ray structure, and cyclic voltammetry of 2,5,8-trithia[9](2,5)thiophenophane, L, and of its metalcomplexcation bis(2,5,8-trithia[9](2,5)thiophenophane-S2,S3]copper(I),[CuL2]+1
Authors: Lucas C. Robert , Shuang Liu , Newlands Michael J. , Charland Jean-Pierre , Gabe Eric J.
Published: April 2011

Preparation of the thiophenophane C10H14S4, (L), and syntheses of its copper(I) complex [CuL2]ClO4 or [CuL2]BF4 are described. The 13C and 1H nmr spectra of L and the ir spectra (4000–200 cm−1) of [CuL2]ClO4 and [CuL2]BF4 are reported. The molecular structures of L and [CuL2]ClO4 have been determined. For L: space group P21/a, a = 7.9347(2) Å, b = 18.7479(3) Å, c = 8.8596(2) Å, β = 108.446(2)°, Z = 4, Rf = 0.048, and Rw = 0.034. For [CuL2]ClO4: space group P21/c, a = 9.4363(1) Å, b = 18.2768(3) Å, c = 16.2157(3) Å, β = 96.520(2)°, Z = 4, Rf = 0.056, and Rw = 0.037. The Cu(I) complex has distorted tetrahedral coordination geometry; its perchlorate anion is non-coordinating and disordered. The Cu—S bond lengths lie in the range 2.301–2.392 Å and the S—Cu—S angles in the range 92.43—150.26°. Cyclic voltammetry of [CuL2]ClO4 (10−3 mol/L in dimethylsulfoxide, 0.1 mol/L Et4NClO4, glassy carbon working electrode, platinum counter electrode, aqueous saturated calomel reference electrode against which the ferrocenium/ferrocene potential under similar conditions was 400 mV) shows a quasi-reversible oxidation (E1/2 = 0.150 V, ΔEp = 170 mV at 50 mV/s). Thiophene's effect as a sub-unit in a small macrocycle upon properties of the latter is discussed.
Experimental and theoretical estimates of the internal rotational barrier of benzyl fluoride in the vapor phase
Authors: Schaefer Ted , Beaulieu Christian , Sebastian Rudy , Penner Glenn H.
Published: April 2011

The twofold barrier to rotation about the [Formula: see text] bond in benzyl fluoride is deduced from the long-range 1H,1H; 1H,19F; and 13C,19F nuclear spin–spin coupling constants in solution. The barrier changes from 3.2(2) kJ/mol in the polar solvent, acetonitrile-d3, to 0.7(2) kJ/mol in the nonpolar environment provided by cyclohexane-d12. In all solutions the conformer of greatest stability has the C—F bond in a plane perpendicular to that of the phenyl group. Extrapolation of the barrier to the vapor phase, using a simple reaction field model, indicates that the most stable conformer for the free (unclustered) molecule is now that with the C—F bond in the phenyl plane and that the barrier to internal rotation is 1.1(7) kJ/mol. Molecular orbital calculations with the basis sets STO-3G, 4-21G, 4-31G, 6-31G, and 6-31G* all predict the latter conformer as that of lowest energy. However, they disagree significantly among themselves as to the height of the internal barrier. The complete geometries are given for both conformers, as computed with the 6-31G basis, and the side-chain geometries are tabulated for the planar and perpendicular conformers, as given by all the bases. Keywords: benzyl fluoride, internal rotational potential; 13C,19F spin–spin coupling constants in benzyl fluoride; benzyl fluoride, molecular orbital computations.
Mild hydrolysis or alcoholysis of amides. Ti(IV) catalyzed conversion of primary carboxamides to carboxylic acids or esters
Authors: Fisher Lawrence E. , Caroon Joan M. , Stabler S. Russell , Lundberg Scott , Zaidi Shahid , Sorensen Carole M. , Sparacino Mark L. , Muchowski Joseph M.
Published: April 2011

Reaction of primary amides (e.g., 1a or 6–13) or O-methylhydroxamates (1b and 1c) with a catalytic amount of TiCl4 and one equivalent of aqueous HCl converts these compounds in good yields to carboxylic esters (when an alcohol is used as solvent) or to carboxylic acids (when 9:1 dioxane:H2O is used as solvent). These conversions are chemoselective for primary amides: mono- and dialkyl amides are not affected by the reaction conditions. The hydrolysis conditions described do not compromise the stereochemical integrity of an adjacent chiral center. This is exemplified by the hydrolysis of naproxen amide (34) to naproxen (33) without detectable racemization as determined by chiral HPLC.
Molecular recognition XIII. The binding of the H-type 2 human blood group determinant by a winged bean (Psophocarpus tetragonolobus) acidic lectin
Authors: Lemieux Raymond U. , Du Ming-Hui , Spohr Ulrike , Acharya Shreeta , Surolia Avadhesha
Published: April 2011

The winged bean acidic lectin (WBA II) binds the H-type 2 human blood group related trisaccharide (α-L-Fuc-(1c → 2b)-β-D-Gal-(1b → 4a)-β-D-GlcNAc-OMe, 1). Interactions that importantly contribute to the specificity of the complex formation are provided by CH2-6b, OH-4b, OH-3b, and OH-2c of 1. On the basis of the relative activities of the monodeoxy and mono-O-methyl derivatives of 1, the hydroxyl groups at the 3a, 6a, and 4c positions become located at the periphery of the combining site, whereas the CH3O-1a, NHAc-2a, and CH3-5c groups are more remote from the protein surface and fully exposed to bulk water. Whereas the WBA II lectin marginally recognizes the H-type 1 related trisaccharide (α-L-Fuc-(1c → 2b)-β-D-Gal-(1b → 3a)-β-D-GlcNAc-OMe, 23), the de-N-acetyl derivative (24) is bound 3.4 times more strongly than 1. This and other results, which are related to changes in interaction between the ligand and the apron of the combining site, are attributed to changes in hydration that lead to enthalpy–entropy compensation. In certain cases, the interactions are found to stabilize the complex.
Use of aromatic thia fatty acids as active site mapping agents for a yeast Δ9 desaturase
Authors: Buist Peter H. , Marecak Dale M.
Published: April 2011

The Δ9 desaturating system of Saccharomyces cerevisiae can sulfoxidize methyl S-benzyl-8-mercaptooctanoate as well as its naphthyl analogue but the corresponding isomers where sulfur is bonded to the aromatic ring do not function as substrates. We have accounted for these results in terms of a conformational model. We have also accumulated some evidence that suggests that dealkylation of these thia analogues does not compete with sulfoxidation. Our recently discovered chiral shift reagent (S)-(+)-α-methoxyphenylacetic acid (MPAA) can be used to determine the optical purity and absolute configuration of all sulfoxides prepared in this work.
Biosynthesis of naphthomycin A in Streptomyces collinus
Authors: Lee Jonathan P. , Tsao Sheng-Wan , Chang Ching-Jer , He Xian-Guo , Floss Heinz G.
Published: April 2011

The biosynthesis of naphthomycin A (1) in Streptomyces collinus was studied in feeding experiments with single and multiple 13C-labeled precursors followed by 13C NMR analysis of the labeling and 13C–13C coupling patterns in the product. The results indicate that 1 is assembled via the polyketide pathway from 3-amino-5-hydroxybenzoic acid (2) as the starter unit (mC7N unit) plus seven propionate and six acetate chain extension units. 2 is synthesized via the shikimate pathway by a process that attaches the nitrogen to the carbon derived from C1 of erythrose 4-phosphate, consistent with a new branch of the shikimate pathway recently discovered to operate in the biosynthesis of the mC7N unit of rifamycin B.
Reactions of the ambident super-electrophile series: the 2-(nitroaryl)-4,6-dinitrobenzotriazole 1-oxides with isopropoxide ion. Pathways of decomposition of the anionic σ-adducts
Authors: Dust Julian M. , Buncel Erwin
Published: April 2011

To elucidate the reactivity of super-electrophiles such as 4,6-dinitrobenzofuroxan as compared to normal electrophiles such as 1,3,5-trinitrobenzene, reaction of isopropoxide ion (iPrO−) with a series of ambident super-electrophiles was studied by 400 MHz 1H nuclear magnetic resonance spectroscopy. The 2-(nitroaryl)-4,6-dinitrobenzotriazole 1-oxides, 1–3, possess both a super-electrophilic (C-7) site and a normal electrophilic (C-1′) site. Nucleophiles can demonstrate selectivity for attack at C-7, which leads to formation of persistent anionic σ-adducts (Meisenheimer complexes), as compared to C-1′, which leads to N-2:C-1′ bond scission. The most reactive substrate, 2-(2′,4′,6′-trinitrophenyl)-4,6-dinitrobenzotriazole 1-oxide (Pi-DNBT, 1) was found to be the least selective substrate in C-7 adduct formation, while 2-(2′,4′-dinitrophenyl)- and 2-(4′-nitrophenyl)-4,6-dinitrobenzotriazole 1-oxides (DNP-DNBT, 2, and NP-DNBT, 3, respectively) showed increasing selectivity towards iPrO−, in turn. These results are discussed on the basis of overall selectivity for C-7 adduct formation and the relative selectivity of iPrO− as compared to methoxide and tert-butoxide ions. The conclusions are illustrated using comparative energy profiles. In terms of pathways for decomposition of the adducts, the C-7 adducts decompose via dissociation back to substrate and nucleophile and, thence, through C-1′ adduct formation to the scission products. However, for 1, the C-7 adduct 1a has now been found to decompose to 7-isopropyl-2-picryldinitrobenzotriazole, 1c. The possible mechanism of this formal internal redox will be discussed.
NMR and molecular modeling study of active and inactive taxol analogues in aqueous and nonaqueous solution
Authors: Williams Howard J. , Scott A. Ian , Dieden Reiner A. , Swindell Charles S. , Chirlian Lisa E. , Francl Michelle M. , Heerding Julia M. , Krauss Nancy E.
Published: April 2011

The conformations of the biologically active taxol analogs Taxotere®, 3R, 4R, and 4S, and the biologically inactive analog 3S were evaluated in CDCl3 and DMSO–water solution using 1H NMR coupling constant and NOESY data and molecular modeling. The solution structures of Taxotere® were very similar to those detected previously for taxol. The A-ring side chain conformations of analogs 3 and 4 could not be defined with the same precision as had been possible for taxol, but the conformational possibilities could be significantly limited by the data. Analogs 3R, 4R, and 4S (but not 3S) can mimic the dominant conformation of taxol in chloroform, but no logical relationship between biological activity and aqueous solution conformation could be detected.
Evidence for the pathway to pantothenate in plants
Authors: Jones Carol E. , Dancer Jane E. , Smith Alison G. , Abell Chris
Published: April 2011

A protocol to separate the intermediates on the biosynthetic pathway to pantothenate on HPLC is described. Feeding experiments with L-[U-14C]valine to pea leaf disks result in incorporation of radioactivity into 2-ketoisovalerate, ketopantoyl lactone, and pantoyl lactone, providing the first experimental evidence that the biosynthetic pathway to pantothenate is the same in plants and bacteria.
Salt effect on the solubility of mer-(+)-tris(L-alaninato)cobalt(III)
Authors: Yoshimura Yasuki
Published: April 2011

The effect of NaF, NaCl, NaBr, NaI, NaNO3, CH3COONH4, NaH2PO4, and (NH4)2SO4 on mer-(+)-tris(L-alaninato)cobalt(III) (mer-(+)-[Co(L-ala)3]) was examined by determining the solubility of the chelate. While the solubility of mer-(+)-[Co(L-ala)3] (salting-in effect) increased with the addition of NaCl, NaBr, NaI, and NaNO3, the solubility (salting-out effect) decreased with the addition of NaF, CH3COONH4, and NaH2PO4. In low salt concentration (NH4)2SO4 caused slight salting-in, but in salt concentration >0.5 mol dm-3 (NH4)2SO4 brought about salting-out. The magnitude of the salting-in effect increased in the order of NaCl < NaNO3 < NaBr < NaI. The standard enthalpy (Δ Hos) and entropy (Δ Sos) of dissolution for mer-(+)-[Co(L-ala)3] were estimated from the temperature dependence of the solubility. When Δ Hos was plotted against T Δ Sos , a single-correlation straight line was obtained for the salts that brought about the salting-in effect. On the basis of these findings, the origin of the salting-in effect was discussed. Furthermore, while NaF, NaCl, and NaBr showed larger salting-in effect on fac-tris(glycinato)cobalt(III) (fac-[Co(gly)3]) than on mer-(+)-[Co(L-ala)3], NaI greatly decreased the solubility of fac-[Co(gly)3]. At the present stage, an explanation for this anomalous salting-out effect of NaI cannot be presented.Key words: salt effect, solubility, thermodynamic parameters of dissolution, mer-tris(L-alaninato)cobalt(III), fac-tris(glycinato)cobalt(III).
Time-resolved structures of electrical discharges in gases: experiment and stochastic model
Authors: Bawagan A DO , Fell L , Logan J
Published: April 2011

The time-resolved discharge patterns generated in a gaseous dielectric breakdown (DB) are imaged using a fast optical imaging system ( approx 40 ns exposure time). The discharge patterns from various gases (He, air, and SF6) show general features consistent with their known dielectric strength. A new stochastic pattern-forming model that explicitly includes time is presented and is shown to produce theoretical DB patterns in qualitative agreement with the present experimental discharge patterns for air (N2). The stochastic DB model (with time) also provides an approximation to the discharge current, which is in good agreement with published current wave forms.Key words: gas discharge, electron scattering, fractal.
Synthesis, electrochemistry, structure, and magnetic susceptibility of 5-tert-butyl-1,3-bis- (1,2,3,5-dithiadiazolyl)benzene. Structural effect of the bulky substituent
Authors: Beekman Richard A , Boeré René T , Moock Klaus H , Parvez Masood
Published: April 2011

The crystal structure of the title compound was determined at 250 K in space group I 4 bar 2m, a = 20.661(5) Å , c = 6.764(7) Å , Z = 8. The individual dithiadiazole rings form two sets of contrarotatory 4-member pinwheels clustered around a 4-fold rotation-inversion axis located halfway along the unit cell edges, describing an infinite channel lined with sulfur atoms but in which there are short intra-stack contacts through only one S atom of each CN2S2 group. The double-layer stacking occurs in order to accommodate the bulk of the tBu group, and the spacing between layers is very regular, with short and long S cdot cdot cdot S contacts of 3.48(2) and 3.61(2) Å and considerable thermal motion in the c direction. The title compound and its SbF6- salt are oxidized at + 0.81 V (in CH2Cl2) and at + 0.61 V (in CH3CN), while a reduction process is observed only in CH2Cl2 at -0.73 V vs. SCE. Magnetic susceptibility data between 5 and 400 K demonstrate at very low temperature that the sample follows the Curie-Weiss law, θ = 0 K, and χ 0= -156 ppm emu mol-1. The free-spin concentration at T = 0 K is approx 1.3%, due to paramagnetic defects in an essentially diamagnetic structure. The diamagnetism starts to lift above 210 K; above 260 K, a strong antiferromagnetic exchange is operative. These results are consistent with the lifting of the Peierls distortion in this structure, starting above approx 200 K. The crystal structure of the parent diamidine 5-tert-butyl-1,3-[(Me3Si)2NCNSiMe3]2C6H3 was determined in C2/c with a = 10.0788(3), b = 21.328(5), c = 20.876(5) Å , β = 99.41(2)°, Z = 4. The two amidine functional groups are equivalent by crystal symmetry.Key words: dithiadiazole, diradical, magnetic susceptibility, crystal structure, bulky substituent.
Stereoelectronic effects in sulfonyl compounds: axial orientation of an N-methyl group in a six-membered sultam
Authors: King James Frederick , Yuyitung Gay , Gill Manjinder Singh , Stewart Jeffrey Charles , Payne Nicholas Charles
Published: April 2011

The trans form of octahydro-1-methyl-1H-2,1-benzothiazine 2,2-dioxide, in which a six-membered sultam unit is trans-fused to cyclohexane, has been synthesized. The single-crystal X-ray structure shows the molecule to have the N-methyl group in the axial orientation. The generalized anomeric effect believed to be responsible for the axial preference is estimated at =>2 kcal mol-1.Key words: generalized anomeric effect, negative hyperconjugation, sulfonamides, sultams, X-ray crystallography.
Hydration of the carbonyl group. Further evidence for a cooperative mechanism from experimental and theoretical studies of the hydrations of formaldehyde, acetaldehyde, acetone, and cyclohexanone
Authors: Wolfe Saul , Shi Zheng , Yang Kiyull , Ro Stephen , Weinberg Noham , Kim Chan-Kyung
Published: April 2011

The experimental pseudo-first-order rate constant for the neutral hydration of acetone by H218O has been determined by taking advantage of the 18O isotope shift in the 13C NMR spectrum of 2-13C-labelled acetone. With the inclusion of this result, a previously reported computational procedure has been extended, with some refinements, to the neutral hydrations of formaldehyde, acetaldehyde, acetone, and cyclohexanone by different-sized water clusters in water solvent. Excellent agreement has been achieved between the experimental free energies of activation and the free energies of activation calculated for a cyclic mechanism in which the principal reaction channel contains four nonspectator water molecules. The computational procedure predicts that the cyclic water tetramer and the cubic water octamer are the principal constituents of bulk water, in agreement with Benson's tetramer-octamer model.Key words: isotope shift, basis set superposition error (BSSE), self-consistent reaction field (SCRF), water clusters, hydration.
Synthesis of trans-2,3-dimethoxy-3- (phenylamino)flavanones and related compounds
Authors: De Surya K , Dhara Mrinal G , Mallik Asok K
Published: April 2011

trans-2,3-Dimethoxy-3-(phenylamino)flavanones (2), a new type of flavanone derivatives, are synthesized from flavanones or 2'-hydroxychalcones in two steps, the first one being a condensation with nitrosobenzenes (Ehrlich-Sachs reaction) and the second an oxidation with (diacetoxyiodo)benzene in methanol. Nitrone formation, an important side reaction of the Ehrlich-Sachs reaction, has also been exploited to synthesize 2 simply by use of an excess of nitrosobenzene in aqueous methanol. Syntheses of several analogues of 2 are also reported.Key words: trans-2,3-dimethoxy-3-(phenylamino)flavanones, 2'-hydroxychalcones, nitrosobenzenes, 3-(phenylamino)flavones, (diacetoxyiodo)benzene.
Control of relative migration of small inorganic and organic anions with cyclodextrins in capillary electrophoresis (CE)
Authors: Stathakis Costas , Cassidy Richard M
Published: April 2011

The capillary electrophoretic separation of iodide, nitrate, perchlorate, thiocyanate, bromate, iodate, and ethane-, butane-, pentane-, and octanesulphonate was examined in sodium chromate or potassium hydrogen phthalate electrolytes and in the presence of α -, γ -, (0-40 mmol/L) and β -cyclodextrin (0-10 mmol/L). Largest decreases in electrophoretic mobility were observed for iodide, perchlorate, and thiocyanate, probably due to inclusion of these anions in the cyclodextrin (CD) cavity. Changes in migration patterns and electroosmotic flow were observed, which depended on cyclodextrin type and concentration and on electrolyte-cyclodextrin interactions. Thus for larger cavity cyclodextrins ( β-or γ-cyclodextrin) or in the presence of chromate, relatively small decreases in electrophoretic mobilities for all the anions were observed, indicating that a good match between analyte and cavity size and minimal cyclodextrin affinity for electrolyte ions are essential for different migration patterns. Separation efficiencies were between 50 000 and 400 000 theoretical plates, and calibration plots for iodide and octanesulphonate were linear; R2 = 0.998 and 0.9999, respectively, in the concentration range (5 x 10-5)-(5 x 10-3) mol/L.Key words: capillary electrophoresis, inorganic and organic anions, cyclodextrins, inclusion complex, electroosmotic flow control.
Crystal structure, spectroscopic and magnetic studies, and antioxidative properties of catena-[diaqua(dihydro-orotato)manganese(II)]
Authors: Castan Paule , Viala Christine , Fabre Paul-Louis , Nepveu Françoise , Souchard Jean-Pierre , Bernardinelli Gérald
Published: April 2011

The polynuclear manganese(II) complex of L-dihydroorotic acid has been synthesized and characterized by X-ray crystallography, UV-visible spectroscopy, and magnetic susceptibility measurements. Crystal data: triclinic, space group P1 bar , a = 4.7239(5) Å, b = 7.902(1) Å, c = 10.552(2) Å, α = 105.80(1)°, β = 98.864(7)°, γ = 104.69(1)°, V = 355.9(1) D 3, Z = 1, R = 0.035, Rw = 0.028. This complex consists of polymer chains of manganese atoms that are bound together via carboxylate bridges with a Mn...Mn distance in the chain of 4.724 D . The radical scavenging properties of the complex have been evaluated by ESR spectroscopy and cyclic voltammetry methods and compared to those of vitamin E and BHT (2,6-di-tert-butyl-4-methylphenol).Key words: orotic acid, L-dihydroorotic acid, manganese(II) complex, antioxidative properties.
Kinetics and mechanism of hydroxylamine oxidation by [Fe2III(µ-O)(phen)4(H2O)2]4+ in aqueous media
Authors: Chaudhuri Beauty , Banerjee Rupendranath
Published: April 2011

Equilibrium studies show that in aqueous solutions containing excess 1,10-phenanthroline (phen) in the range pH 3-9, the complex ion [Fe2III ( μ-O)(phen)4(H2O)2]4+ (1) undergoes rapid but partial hydrolysis and coexists with [Fe2III ( μ-)(phen)3(H2O)4]4+ (1d),[Fe2 III ( μ-O)(phen)4(H2O)(OH)]3+ (2), and [Fe2III ( μ-O)(phen)4(OH)2]2+ (3). The solution oxidizes hydroxylamine quantitatively to N2O and is itself reduced to [Fe(phen)3]2+. The reactions in the range pH 3-6 are first-order in concentrations of complex and hydroxylamine but exhibits complex [H+] dependence, suggesting kinetic contributions from 1, 1d, and 2 but not from 3. Rapid formation of inner-sphere adducts between NH2OH and different {Fe2O}4+ species followed by rate-determining one-electron transfer to produce NHOH and {Fe2O}3+ is proposed. All subsequent steps are rapid. Ambient light does not affect kinetics and reaction products.Key words: kinetics, equilibrium, oxo bridge, iron (III), hydroxylamine.
Surface plasmon resonance sensors using molecularly imprinted polymers for sorbent assay of theophylline, caffeine, and xanthine
Authors: Lai Edward PC , Fafara Ania , VanderNoot Victoria A , Kono Mari , Polsky Brandee
Published: April 2011

A sensor system based on the optical phenomenon of surface plasmon resonance (SPR), which employs either photothermal deflection spectroscopy (PDS) or a photodiode array (PDA) for detection, was developed to use molecularly imprinted (MI) polymethacrylic acid - ethylene glycol dimethacrylates (PMAA-EDMA) as the sensing element. The MI polymers were first processed by Soxhlet extraction to remove the print molecules (theophylline, caffeine, and xanthine), yielding the specific anti-polymers. Each anti-polymer was layered over a silver film to serve as the analysis surface for the molecularly imprinted sorbent assay (MIA) of one target drug. This surface was exposed for 60 min to an aqueous standard drug solution, dried in air, and the uptake of the print molecule into the anti-polymer was monitored by shifts in the SPR angle θ r (and hence the SPR-PDS signal measured at constant θ ). The linear dynamic range of the MIA was found to extend up to 6 mg/mL, with a concentration detection limit estimated at 0.4 mg/mL for theophylline in aqueous solution. A cross-reactivity study of the anti-theophylline and anti-caffeine polymers, using eight other drugs structurally similar to theophylline and caffeine, showed none or very slight shifts in θ r. This implies that the anti-polymers were selective only for their original print molecules and had no affinity for the other drug molecules. Similar molecular recognition characteristics were observed for the anti-xanthine polymer.Key words: surface plasmon resonance, molecular imprinting, theophylline, caffeine, xanthine, sensor.