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An etched long-period grating was used as a refractive index sensor for vapours of four volatile organic compounds, i.e. m-xylene, cyclohexane, trichloroethylene and commercial gasoline. The sensitivity to the vapours was further increased by solid-phase microextraction into a coating made of polydimethylsiloxane (PDMS)/polymethyl-octylsiloxane (PMOS) co-polymer. By further amplification of the optical loss in an optical cavity made of two identical fiber-Bragg gratings and interrogation by phase-shift cavity ring-down spectroscopy we could detect and distinguish xylene (detection limit: 134 ppm) from trichloroethylene (3300 ppm), cyclohexane (1850 ppm) and gasoline (10,500 ppm).

The contour lithography method [1] is used to improve the fabrication yield of previously demonstrated [2] microfluidic Fabry-Perot (FP) refractive index (RI) sensors. The sensors are then coated with polydimethylsiloxane (PDMS) based polymers to detect vapor analytes by solid-phase microextraction (SPME). Preliminary characterization of devices coated with two different polymers and exposed to xylenes vapors yields a maximum sensitivity of 0.015 nm/ppm and a detection limit below 120 ppm.

Herpes simplex encephalitis was diagnosed by immunofluorescence and histology of a brain biopsy on the 19th day of life in a neonate in whom symptoms had begun at 12 days. Treatment with steroid, diuretic and cytosine arabinoside was begun and initially there was dramatic improvement in the symptoms. This improvement was not sustained, however, and the infant developed evidence of severe brain-damage. Disseminated herpes simplex virus infection is discussed and available therapy for this severe disease is outlined.

An efficient method for the enantioselective 1,4-conjugate addition of amines to α,β-unsaturated esters containing an inexpensive chiral auxiliary, such as (S)-2-methyl-1-butanol and fenchyl alcohol, in solvent-free conditions mediated by solid lithium perchlorate is reported. Over 12 examples of the products are generated in excellent yields, accompanied by moderate enantioselectivity. The concentrated solution of LiClO4 in a diethyl ether system works well for the enantioselective 1,4-addition of organolithium compounds to α,β-unsaturated amides without any side reactions.

A study of the hydrolysis of formamide is reported with the aims of isolating the water reaction for hydrolysis from the acid and base hydrolysis terms and determining the solvent deuterium kinetic isotope effect (dkie) on base-catalyzed hydrolysis. Respective activation parameters (ΔH‡and ΔS‡) of (17.0 ± 0.4) kcal mol–1and (–18.8 ± 1.3) cal mol–1K–1for the acid reaction and (17.9 ± 0.2) kcal mol–1and (–11.1 ± 0.5) cal mol–1K–1for the base reaction were determined from Eyring plots of the second-order rate constants over the range of 27–120°C. Kinetic studies at the minima of the pH/rate profiles in the pH range from 5.6 to 6.2 in MES buffers at 56°C, and in the pH range of 4.25–6.87 in acetate and phosphate buffers at 120°C are reported. At 56°C the available data fit the expression k56obs= 0.00303[H3O+] + 0.032[HO–] + (3.6 ± 0.1) × 10–9, while at 120°C the data fit k120obs= (0.15 ± 0.02)[H3O+] + (3.20 ± 0.24)[HO–] + (1.09 ± 0.29) × 10–6. Preliminary experimental estimates of Ea(ln A) of 22.5 kcal mol–1(15.03) for the water rate constant (kw) are calculated from an Arrhenius plot of the 56 and 120°C data giving an estimated kwof 1.1 × 10–10s–1(t1/2= 199 years) at 25°C. Solvent dkie values of kOH/kOD= 1.15 and 0.77 ± 0.06 were determined at [OL–] = 0.075 and 1.47 M, respectively. The inverse value is determined under conditions where the the first step of the reaction dominates and is analyzed in terms of a rate-limiting attack of OL–.Key words: formamide, activation parameters, water reaction, acid and base hydrolysis, solvent kinetic isotope effect.

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen involved in normal and abnormal angiogenesis. VEGF mRNA and protein are abundant in distal epithelium of midtrimester human fetal lung. In the present study, we identified immunoreactivity for KDR, a major VEGF-specific receptor, in distal lung epithelial cells of human fetal lung tissue, suggesting a possible autocrine or paracrine regulatory role for VEGF in pulmonary epithelial cell growth and differentiation. Addition of exogenous VEGF to human fetal lung explants resulted in increased epithelium volume density and lumen volume density in the tissues, both morphometric parameters of tissue differentiation. Cellular proliferation demonstrated by bromodeoxyuridine uptake was prominent in distal airway epithelial cells and increased in the VEGF-treated explants. VEGF-treated explants also demonstrated increased surfactant protein (SP) A mRNA, SP-C mRNA, and SP-A protein levels compared with controls. However, SP-B mRNA levels were unaffected by VEGF treatment. [3H]choline incorporation into total phosphatidylcholine was increased by VEGF treatment, but incorporation into disaturated phosphatidylcholine was not affected by exogenous VEGF. Based on these observations, we conclude that VEGF may be an important autocrine growth factor for distal airway epithelial cells in the developing human lung.

The interaction of La(3+) with diphenyl phosphate, methyl p-nitrophenyl phosphate, and bis(p-nitrophenyl) phosphate (4, 5, and 3) and the ensuing catalysis of methanolysis has been studied in methanol under completely homogeneous conditions of known pH. (31)P NMR shows that phosphates 3 and 4 are each associated with La(3+) as a rapidly interconverting mixture of complexes having 2:1, 1:1 (or 2:2), and 1:2 stoichiometry. At [La(3+)]2 x 10(-4) M, the kinetically dominant species in the pH regions of interest are phosphate-bound La(3+) dimers having 2-5 associated methoxides. Potentiometric titration reveals that 4 mM La(3+) alone in MeOH exhibits two apparent pK(a)s at 7.86 and 10.44 consuming 1 and 1.5 CH(3)O(-) per metal, the suggested structures being La(3+) dimers with first two and then five associated methoxides. In the presence of 0.5 equiv of 4 the potentiometric titration reveals strong complexation of 4 to La(3+) and a profile with apparent pK(a)s at 7.8 and 11.1 consuming 1 and 1.5 CH(3)O(-) per metal corresponding to phosphate-bridged La(3+) dimers with first two and then five associated methoxides. Methanolysis of 3-5 is strongly accelerated by La(3+). At pH 8.9 or 11.1, respectively, as little as 5 x 10(-4) M La(OTf)(3) accelerates the methanolysis of 3 or 4 by 10(10)-fold relative to the background reaction. Detailed kinetic studies of the methanolysis of 5 at varying [La(3+)] and pH indicate that both La(3+) monomers and dimers with associated methoxides are reactive species. The rate constants for La(3+) monomer and dimer catalysis of the methanolysis of 5 are dependent on pH, the slopes of the log plots being 0.35 and 0.5, respectively. A scheme is proposed to account for the non-first-order dependence on [CH(3)O(-)] wherein the La(3+)(CH(3)O(-))(x) + 5--La(3+)(CH(3)O(-))(x):5 and (La(3+))(2)(CH(3)O(-))(y) + 5--5:(La(3+))(2)(CH(3)O(-))(y) equilibria are driven to the left with increasing numbers of associated methoxides and that attack on these complexes, whether by external or metal-associated methoxide, is slower due to the reduced net positive charge on the complex.

The hydrolysis of p-nitrophenyldiphenyl phosphate (PNPDPP, 7) catalyzed by N-dodecylaminoethanol (6a), N-tetradecylaminoethanol (6b), N-methyl-N-tetradecylaminoethanol (6c), and N-hexadecylaminoethanol (6d) was investigated at 25°C at various pH values in aqueous media containing additives. Added ethanol or dimethoxyethane produces very little activity of 6a, b, c toward 7. The highest activities of 6a, b were found at pH 8.0 and 8.5 in solvents containing 20% glycerol or ethylene glycol. Under no conditions was N-hexadecylaminoethanol (6d) found to be active. The kinetics of the reaction of 6b with 7 were also investigated in a medium containing various amounts of glycerol, polyethylene glycol 400 (PEG 400), and water at pH 7.6-8.5. The best catalytic system comprised 3 mM 6b in 20% aqueous ethylene glycol, pH 8.5, which accelerated the hydrolysis of 7 by 1700-fold over the blank rate. Kinetic experiments conducted using [7]/[6b] = 1 and 2 demonstrate that 6b exhibits true turnover catalysis. A mechanism for the catalyzed reaction is proposed.Key words: ß-aminoethanols, hydrolysis, p-nitrophenyldiphenyl phosphate, micelles, polyhydroxy alcohols.

The deuterium kinetic isotope effect (dkie) for the electrophilic bromination of ethylene-h4 and ethylene-d4 in methanol and dichloroethane (DCE) at 25 °C has been determined using mass spectrometr...

The electrophilic addition of Br2 to specifically deuterated cyclohexenes (1−5) was studied methanol (MeOH) by stopped-flow kinetics in order to determine a deuterium kinetic isotope effect (DKIE) ...

Two neutral cyclodextrins (CDs), hydroxypropyl-beta-CD (HP beta OD) and methyl-beta-CD (M beta CD), and two negatively charged forms, carboxymethyl-beta-CD (CM beta CD) and sulfobutylether-beta-CD (SB beta CD), were used to demonstrate the principle of separation of hydrophobic and non-charged polynuclear aromatic hydrocarbons (PAHs) by capillary electrophoresis (CE) based on differential partitioning of analytes between the CDs. The estimation of the partition coefficient (Ki) confirmed that the PAH components which partitioned most to the negative cyclodextrin (i.e. with the highest Ki) exhibited the longest migration time. The Ki values obtained for the CM beta CD-HP beta CD system are all below 1, indicating that the PAHs prefer to remain in the neutral HP beta CD. The Ki values for the SB beta CD-M beta CD buffer are all greater than 1, and cover a wider range, indicating preference of the PAHs for the anionic derivative. Methods were applied for separation of a PAH mixture containing various important PAHs on the US Environmental Protection Agency priority list. This novel procedure provided much better separation of PAH isomers, including benzo[a]pyrene and benzo[e]pyrene, than has been reported previously using CE. The system was applied to the sensitive determination of nanomolar levels of PAHs in contaminated soil.

The kinetics and products of addition of Br2 in MeOH to anti-sesquinorbornene (1) have been studied at 25 °C in the presence of varying [LiBr]. The products consist of ∼10% cis dibromide and 90% cis methoxy bromide, the amounts of these being independent of the [Br-]. The kinetics reveal that the reaction proceeds via the addition of Br2, and that Br3- is not a brominating agent for this olefin. Acetic acid is shown to add rapidly to the double bond of 1 in a spontaneous reaction and via an acid-catalyzed process in the presence of HClO4. For the spontaneous reaction a solvent deuterium kinetic isotope effect (DKIE) of 3.3 is observed. Proton inventory plots of kobs vs atom fraction of deuterium in the medium indicate that the DKIE arises from a transition state for addition involving two or more protons undergoing changes in bonding. The HClO4-catalyzed addition exhibits a large DKIE of 5.4 and is attributable to a simultaneous attack of HClO4 or ClO4- H2OAc+ and HOAc on the double bond. LiClO4 also cata...

The kinetics of the transfer of X+ from the bromonium and iodonium ions of adamantylideneadamantane (1-Br+ and 1-I+) to some 1,ω-alkenols and alkenoic acids in ClCH2CH2Cl at 25 °C was investigated. In all cases, the expected products of halocyclization were observed. For the iodonium ion transfer the reaction kinetics are second order overall, first order in both 1-I+ and acceptor olefin. Transfer of the bromonium ion from 1-Br+ to these acceptor olefins exhibits different kinetic characteristics. In most cases, the rate of the Br+ transfer is subject to strong retardation in the presence of added parent olefin (AdAd), suggestive of a common species rate depression. In some cases, such as 4-penten-1-ol (2b) and 4-pentenoic acid (4b), the reaction can be completely suppressed at high [AdAd]. In other cases, such as 3-buten-1-ol (2a), 5-hexen-1-ol (2c), cyclohexene, 4-(hydroxymethyl)cyclohexene (3), and 5-endo-carboxynorbornene (5), added AdAd does not suppress the reaction completely. In the cases of the 1...

Initial results are presented for a novel experimental arrangement which allows the successful study of laser-desorbed neutral species under matrix isolation conditions. In the current work, a pulsed carbon dioxide laser (10.6 μm) is employed for laser desorption. With the combination of a previously described cryogenic trapping technique with coaxial matrix isolation gas (xenon or argon) introduction, laser-desorbed neutrals have been matrix isolated and their Fourier transform infrared spectra recorded. Two different cinnamic acid derivatives ( p-coumaric acid and sinapinic acid) typically employed for matrix-assisted laser ionization (MALDI) mass spectrometry were utilized to demonstrate this new technique. Experimental conditions were determined for optimal matrix isolation of the laser-desorbed species. Two different desorption geometries were examined with respect to their effectiveness for matrix isolation of desorbed neutrals. A covalent dimer of p-coumaric acid produced in an external UV photoreactor and thought to be a possible photoreaction product in UV MALDI was studied by this technique. Thermal degradation of this dimer is shown to occur above threshold irradiance for laser desorption.

Inclusion complexes of 1,1'-dimethylferrocene (DMFe) with alpha-, 2-hydroxypropyl-beta- or gamma-cyclodextrins were formed in aqueous systems. For the first time, the interacting DMFe-cyclodextrin systems have been characterized using cyclic voltammetry which enabled the estimation of the complexation order, the formation constant and the diffusivity. Cyclic voltammetry was performed at a stationary electrode, yielding complexation ratios of 1:2 for DMFe with alpha-cyclodextrin and 1:1 with the other two cyclodextrins, as expected from the known cavity dimensions for the cyclodextrins. Formation constants of 4.4 x 10(4) M-2, 1.2 x 10(3) M-1 and 2.9 x 10(2) M-1 were then determined for the complexes between DMFe and the alpha-, beta- and gamma-cyclodextrins, respectively, in relative agreement with the literature. The maximum complexation efficiency, diffusivity and solubility were observed for the DMFe:2-hydroxypropyl-beta-cyclodextrin inclusion complex, which, combined with cost factors, resulted in the selection of this form for bioelectrocatalysis studies. The efficiency of the complex as a mediator for the glucose:glucose oxidase system was determined by measuring the rate constant (ks) for reaction of the oxidized DMFe with the reduced enzyme. The ks value decreased from 3.4 x 10(4) M-1 s-1 to 1.9 x 10(4) M-1 s-1 with an increase in 2-hydroxypropyl-beta-cyclodextrin concentration from 4 mM to 10 mM. In this range, the ks value is similar to that of free ferrocene, implying a high efficiency of the DMFe:2-hydroxypropyl-beta-cyclodextrin inclusion complex.

The transfer of Br+ from the bromonium ion of adamantylideneadamantane (1-Br+/CF3SO3−) to the reactive alkenes cyclohexene, ω-alken-1-ols, 3a–c, and 4-pentenoic acid, 4, in 1,2-dichloroethane at 25 °C has been investigated. 1H NMR analysis of the reactions of equimolar 1-Br+/CF3SO3− and olefin indicates the products to be the expected cyclic ones in the cases of 3a–c and 4, and trans-2-bromocyclohexyltrifluoromethane sulfonate in the case of cyclohexene, along with adamantylideneadamantane (Ad=Ad). Detailed kinetic analysis shows that the reaction rates are suppressed by the addition of free Ad=Ad, suggestive of a common species rate depression. In the case of certain of the cyclization reactions such as that of 4-penten-1-ol, 3a, the cyclization reaction is bimolecular in acceptor olefin. A primary deuterium kinetic isotope effect of 2.0 on the cyclization of 3a-OH relative to 3a-OD exists. The role of the second molecule appears to be that of a general base in assisting the cyclization of an intermediate ω-hydroxy cyclic bromonium ion. A general mechanistic scheme for Br+ transfer from 1-Br+ to the reactive alkenes is proposed.

An instrument is described which measures fluorescence intensity and lifetime properties using a single optical fiber for the development of fiber optic chemical sensors. The instrument utilizes a fast-pulse nitrogen laser for excitation and a digital storage oscilloscope to provide time-resolved fluorescence decay curves. The time-resolved measurements permitted the separation of most of the scattered excitation radiation from the sample signal and allowed for analysis of samples exposed to ordinary room lighting. A method for determination of lifetimes from the time-resolved decays was developed based on the time-correlated single-photon counting method. The new method used reference fluorophore solutions to determine the instrument response function, including the influence of the optical fiber, and multiple decays were averaged to improve signal-to-noise and to provide statistical weighting for the analysis. The accuracy of the lifetime analysis was demonstrated by comparison of results for Stern-Volmer quenching of quinine sulfate by chloride ion (slope = 0.115 ± 0.001, int. = 1.04 ± 0.04, r2 = 0.9992) with a literature study on the same system (slope = 0.118 ± 0.002, int. = 1.06 ± 0.05, r2 = 0.9986). Measurement of the lifetime of pyrene in ethanol gave 17.8 ± 0.9 ns, while the value for coumarin was 3.82 ± 0.45 ns. When mixed together, two lifetimes with values of 17.43 ± 0.73 and 3.68 ± 1.30 ns were determined.

A substrate recycling assay for phenolic compounds was developed using tyrosinase, a copper-containing enzyme, in excess NADH. The reaction of various phenols with the enzyme produced an o-quinone, which was then detected by recycling between reactions with the enzyme and NADH. The recycling of quinones by excess NADH to their original reduced forms prevented the problems of subsequent quinone polymerization and product inactivation which occur in nonrecycling assays. Absorbance measurements of the NADH consumption rate enhanced the assay sensitivity for catechol 100-fold compared to nonrecycling o-quinone detection, giving a detection limit of 240 nM. Fluorescence NADH monitoring permitted a 10-fold improvement over absorbance, with a detection limit of 23 nM. The recycling reaction was selective for o-quinones, and no interference was noted for p-quinones or quinoneimines. The two-step oxidation of phenols was observed as an initial lag phase (ca. 10 min), requiring a higher enzyme concentration to achieve the same sensitivity as that for catechol. The procedure was most useful for assaying catechol, 4-chlorocatechol, phenol, p-cresol, and 4-chlorophenol and may provide selective detection of these components in mixtures. Several other derivatives of catechols, including amine derivatives, were also detected, with relative sensitivity being related to substrate activity of the enzyme.

The hydrolyses of phthalide (2a) and thiophthalide (3) have been stu- died in highly alkaline media, T=25 o C, μ=3 (HCl). For both esters, an upward curvature in the plot of k hyd vs [OH - ] is observed, sugges- tive of the onset of a second order in [OH - ] process in the hydrolysis. Carbonyl 18 O-exchange studies indicated that no 18 O is lost from the ester recovered from the hydrolysis media at times up to 3t 1/2 hydrolysis. Solvent kinetic isotope (skie) studies indicate that for 3, (k hyd ) H2O/D2O is inverse throughout the entire range of [OL - ]

1, 1'-dimethylferricinium (DMF+), a deep blue, and stable mediator, was prepared from a water-soluble 1, 1'-dimethylferrocene(DMF):2-hydroxypropyl- beta-cyclodextrin complex via enzymatic oxidation using immobilised bilirubin oxidase. This mediator was superior to other soluble ferrocenes, notably carboxyferrocene, in terms of both solubility (110 mM vs 0.5 mM) and oxidation potential (150 mV vs 300 mV against Ag/AgCl). Although the cyclic voltammogram of DMF+ was electrochemically equivalent to DMF, the use of the former resulted in a significantly lower background current (< 10 nA vs 30 nA). Because of its higher solubility, concentrated stock solutions of DMF+ can be prepared and supplied to the electrode. This is of particular importance when the signal is severely limited by the rate at which the working electrode can oxidase DMF to DMF+. A linear response of current versus units of glucose oxidase (GOD) was obtained up to 0.5 unit/ml. The detection limit was estimated to be 0.03 unit/ml and the response time was 2.5 min or less. The amperometric system was used successfully to follow the GOD activity during the growth of Aspergillus niger a well-known GOD producer. The results obtained correlated well with a standard absorbance-based assay using dichlorophenol-indophenol (DCPIP). The KM of GOD for the glucose in the lysate was measured as 38 mM. A reduced response and higher KM (48 mM) of the cell homogenate, compared to the lysate, illustrated the requirement for the DMF+ and glucose to diffuse across the cell membrane to interact with GOD in whole cells.

The trans-2-bromotriflate of cycloherane (4) has been solvolyzed at ambient temperatures in HOAc and MeOH containing varying [Br - ] and in the presence of 0.5 M of a scavenger olefin, cyclopentene. The kinetics of solvolysis of 4 have been determined by observing the rate of change in color of an acid/base indicator that instantly responds to the production of HOTf or HBr. The kinetics show that the rate of solvolysis of 4 at constant ionic strength is independent of [Br - ]. The products of solvolysis of 4 under the various conditions have been determined by quantitative GLPC analysis. In the presence of Br - , the products consisted of the trans 1,2-dibromides and bromosolvates of cyclohexane and cyclopentane

The kinetics of bromine addition to various deuterated isotopomers of cyclohexene, namely the parent (3a), 3,3,6,6-tetradeuteriocyclohexene (3b), and cyclohexene-d 10 (3c), have been determined in HOAc (T=25 o C) as a function of added [Br - ], and the products were determined. The observed kinetic isotope effect for bromination of 3a/3b is k H /k D ≃1.0 with no added salt and indicates that deuteration of the allylic positions does not influence the kinetics

Maximum-likelihood restoration (MLR) data processing is applied to matrix-assisted laser desorption time-of-flight mass spectra of several peptide/protein samples. It is shown that this technique can enhance mass resolution for peptides (porcine insulin; MW = 5777.58 Da) sufficiently to assist in the identification of various matrix adduct ion species formed in the laser desorption process. For higher-molecular-weight proteins, mass resolution enhancement is such that peak overlap contributions from partially resolved matrix adduct ion species can be minimized. Mass accuracies are improved by approximately a factor of six for a sample of a bacterial protease (Subtilisin Carlsberg; Subtilopeptidase A) from Bacillus licheniformis (MW = 27,288.4 Da). The MLR technique also supports the contention that the mass resolution degradation observed with increasing analyte mass is at least partially due to ion signal tailing, presumably caused by secondary ion species being produced in the detection process. This factor is also postulated as being at least partially responsible for the lack of success at resolution enhancement for higher mass analytes (bovine serum albumin; MW = 66,430.3 Da) where the multiple matrix adduct ion species produced can no longer be resolved from the protonated molecular ion species, thus limiting experimental mass measurement accuracies.

The hydrolyses of phthalide (2a) and thiophthalide (3) have been stu- died in highly alkaline media, T=25 o C, μ=3 (HCl). For both esters, an upward curvature in the plot of k hyd vs [OH - ] is observed, sugges- tive of the onset of a second order in [OH - ] process in the hydrolysis. Carbonyl 18 O-exchange studies indicated that no 18 O is lost from the ester recovered from the hydrolysis media at times up to 3t 1/2 hydrolysis. Solvent kinetic isotope (skie) studies indicate that for 3, (k hyd ) H2O/D2O is inverse throughout the entire range of [OL - ]

Publisher Summary The generally accepted mechanism for electrophilic bromination of olefins in hydroxylic solutions of medium to high polarity, and at low [Br 2 ], is given in this chapter. A classical approach to assessing the behavior of ions or intermediates suspected to be present during a given reaction is to generate those ions in a completely different way, and to then study their fates under conditions relevant to the original reaction in question. With respect to Br 2 addition to olefins, it is difficult to tell whether the proposed intermediate bromonium ion is formed reversibly. This is because even if the ion reacts reversibly with Br-, this simply reforms the starting materials, the ultimate fate of which is to progress through the reaction manifold to form products. However, in principle, if a bona fide bromonium ion could be generated independently, and if this were shown to be capable of reacting with Br - to form Br 2 , then at least phenomenologically, one would have evidence that Br - was capable of attacking a bromonium ion on Br + in competition with the normal process of C-attack to form dibromide products.

Results are oresented for various instrumental configurations employed for matrix-assisted laser desorption mass spectrometry. Mass resolution is determined for a linear time-of-flight mass spectrometer for various lengths of the field-free region. A wire ion guide is utilized and is shown to improve ion transport efficiencies for longer field-free regions. It is also determined experimentally that a modest mass resolution increase is often obtained in configurations employing the wire ion guide when compared to the mass resolution obtained with the same geometr without the wire ion guide. Optimal applied potentials are determined for the wire ion guide. No mass dependence on the opitmal applied potential (−100 V) for the wire ion guide is observed for samples of equine myoglobin (MW 16 951.5 Da) and a bacterial protease (MW 27 228.4 Da). The optimal applied voltage was also found to b identical (−100 V) for the singly through quadruply charged molecular ion species of rabbit gamma globulin (MW ≈ 150 000 Da). It is shown that a 2 m flight tube with a wire ion guide provides better signal-to-noise mass spectra than a 1 m flight tube without the wire ion guide and can more than double the mass resolution obtainable. Utilization obtainable. Utilization of a 4 m flight tube gives minimal mass resolution enhancement at the expense of signal-to-noise.

A distorted anilide (4) has been shown to be remarkably susceptible to attack by thiolates containing pendant N-H + groups. Thiolates alone are not reactive nor are amines or ammonium ions. Attack of the zwitterionic form produces a thiol ester+which is isolable in the case of N,N-dimethylcysteamine. If the pendant amine is primary, as in the case of cysteamine, the isolable product is the amide formed by intramolecular S to N acyl transfer. The kinetics of the reaction of 2-(mercaptomethyl)-N-methylimidazole (1b) on 4 show a bell-shaped pH vs log k 2 profile that results from attack of the zwitterionic form on the amide

The product ratios for Br 2 or NBS additions to cyclopentene, cyclohexene, tetramethylethylene, and styrene in MeOH containing varying concentrations of added N 3 - or Br - have been determined with an aim of determining the lifetimes of the bromonium ion intermediates. On the basis of the ratio of trans bromo azide to methoxy bromide products, the partitioning rate constant ratios (K N3 /k CH3OH ) for the four olefins are 5.9, 4.9, 9.3, and 2.7 M -1 , respectively

Interest continues in the use of immobilized lipid membranes of mixed lipid composition to prepare chemically modified electrodes. Fundamental investigations of the structure and mechanism of the analytical function of such systems are scarce. In this work ion conductivities of bilayer lipid membranes formed from mixtures of egg phosphatidylcholine and dipalmitoylphosphatidic acid were evaluated to determine the effect of surface charge and phase domain formation on the process of ion translocation. Ion conductivity was controlled by the surface distribution of ions at the membrane solution interface as predicted from electrical double-layer theory. It was found that the conductivity of the membranes could be approximated as a linear function of the weight percentage composition of the charged lipid. The conductivity was observed to alter drastically at a lipid composition containing a minimum of 25% phosphatidic acid as this component within the membrane was increased. This was attributed to the presence of a phase transition induced by the phosphatidic acid. At concentrations of the acid less than 25%, ion conduction occurred through zones that were enriched in the charged lipid. At higher concentrations of the acid, the average surface charge was the predominant factor which determined the magnitude of ion conductivity. The adjustment of pH to control the degree of ionization of the phosphatidic acid had a similar effect to the variation of the amount of the acidic phospholipid within the membrane of experiments done at fixed pH. An electrochemical method based on ion permeability is proposed for the determination of the p K a value for a charged lipid within a planar bilayer lipid membrane.

Chemical selectivity of biosensors is derived from biological materials interfaced to the surface of transducing devices. Molecular recognition events lead to macroscopic function suitable for analytical measurements. The structure-function relationships of biochemical species at interfaces must be established to characterize and optimize biosensor operation. The techniques of ellipsometry, fluorescence microscopy, electron microscopy, and scanning tunneling microscopy are used to investigate the structure of monolayers and multilayers of proteins and lipids at interfaces that are prepared by Langmuir-Blodgett techniques and by self-assembly from bulk solution. The relative merits and limitations of the measurement techniques in the determination of aspects of interfacial structure are considered.

A variety of experimental parameters are evaluated which are important in maximizing the sensitivity of the combination of gas chromatography and Fourier transform infrared spectrometry (GC/FT-IR) for the detection and identification of mixtures of volatile organic compounds. Basic parameters can be optimized such as the mirror scan velocity and the detector bias current employed to reduce the overall system noise, thus improving the signal-to-noise ratio (S/N) of the resulting spectra. Quantitation of the resulting trade-off between using a lower-noise narrow-spectral-range mercury-cadmium-telluride (MCT) detector versus a wider-spectral-range MCT detector with somewhat higher noise characteristics is examined. An optical design incorporating a variable aperture to reduce the amount of unmodulated infrared radiation from the heated lightpipe which reaches the detector is evaluated. Linearity in sample absorbance is shown to be unaffected by the amount of unmodulated heat reaching the detector despite the nonlinear behavior of the detector observed as interferogram signal loss at elevated detector temperatures. By flowing a fixed concentration of isobutane in helium through the lightpipe, one can monitor the absorbance; it is observed to change significantly from ambient to operating temperature, mostly due to temperature broadening of the absorbance bands. However, no discernible change in the absorbance is observed as a function of the amount of unmodulated light reaching the detector. Finally, lightpipe dimensions are examined as they affect sensitivity. A comparison of the performance of a 1.1-mm i.d. and a 0.6-mm i.d. lightpipe shows increased chromatographic performance of the latter, as expected, but similar signal losses with temperature. Little or no evidence for the counter Jacquinot (sometimes referred to as the Hirschfeld) advantage is found, and reasons for this inconsistency are discussed.

A distorted anilide (3,4-dihydro-2-oxo-1,4-propanoquinoline (3)) has been synthesized, its structure determined by X-ray diffraction, and its hydrolysis profile from pH 0–13 investigated. The amide unit in 3 is distorted in that the N lone pair is twisted 35° and tilted 15° out of optimum conjugation with the C=O II system. Due to this distortion, 3 hydrolyses rapidly in H2O at 25 °C. The pH/rate constant profile exhibits domains consistent with OH− attack on 3[Formula: see text] and H2O attack on a protonated form of 3[Formula: see text]; pKa (3-H+) = 0.56). The kinetic pKa is most consistent with an N-protonated form. It is also shown that this mechanism of hydrolysis is common to the series of bridged anilides consisting of 3, 3,4-dihydro-2-oxo-1,4-ethanoquinoline (1), and 2,3,4,5-tetrahydro-2-oxo-1,5-ethanobenzazepine (2). Keywords: distorted amide, hydrolysis, X-ray structure.

The feasibility of using cryogenic trapping techniques combined with infrared spectrometry to study the products of laser desorption is demonstrated. A prototype system for cryogenically trapping transient species desorbed during the laser desorption process is described. The products produced by a high-power pulsed carbon dioxide laser (10.6 μm) are cryogenically trapped on an infrared transmitting substrate attached directly to a closed-cycle helium refrigerated coldhead via an OFHC copper holder whose temperature is maintained at approximately 18 K. The sample is then rotated into the beam of a Fourier transform infrared (FT-IR) spectrometer, and conventional transmission spectra are obtained. System performance is described, and representative results obtained for a sample of rhodamine B dye and a polyethylene glycol polymer are presented. The rhodamine B dye is shown to significantly fragment as a result of laser desorption (consistent with the known behavior of the ionic products studied by laser desorption mass spectrometry), while the polyethylene glycol sample produces almost exclusively intact neutral species (also in agreement with laser desorption mass spectrometry results).

The carbonyl 18 O exchange and hydrolysis kinetics of N-ethyl-N-(trifluoroethyl)toluamide (4) and N-toluoyl-3,3,b,b-tetrafluoropyrrolidine (5) have been studied in basic media as a function of temperature. For these two amides, the rate constant for 18 O=C exchange exceeds the rate constant for hydrolysis in the [OH - ] domain where both processes are first order in [OH - ]

C 23 H 34 N 2 O 2 cristallise dans P2 1 /c avec a=11,0578, b=23,740, c=8,8991 A, β=111,117 o , Z=4; affinement jusqu'a R=0,059. Les longueurs et les angles de liaison a l'interieur de la molecule sont normaux. La longueur etroite de la liaison hydrogene intermoleculaire entre O(1) et N(1) est de 2,841 A. Les angles de torsion C(1)−N(1)−C(7)−O(1) et C(8)−N(2)−C(14)−O(2) sont de −10,6 et −10,7 o respectivement

The ion detection process in a discrete-dynode electron multiplier can result in significant mass resolution losses in time-of-flight mass spectrometry (TOF-MS) for higher mass-to-charge (m/z) ion species. This resolution loss is attributed to propagation time delays and signal broadening in the ion detector. This is presumed to be due to the generation of a distribution of secondary ion species produced initially upon impact of a primary ion with the first dynode surface of the ion detector. Comparisons are made between the signals produced by a standard discrete dynode ion detector (which amplifies the negatively charged species produced by impact of a primary ion) and a detector modified to respond to only the positively charged secondary ion species produced by a primary ion impact. Ion signals for higher m/z ions with the standard detector geometry are seen to be due to a narrow signal component, most likely due to the generation of secondary electrons and/or very low mass secondary ions (H-), and a broad signal component, apparently due to secondary ions which take significant amounts of time to traverse the low potential fields between the first and second detector dynode. This results in ion signal tailing for higher m/z ion species. Numerical subtraction of the ion signal obtained with the standard and modified detector geometries (singly protonated molecular ion species of equine myoglobin) results in an improvement in mass resolution, such that a new adduct ion species (from trifluoroacetic acid) can be resolved.

The Carbonic Anhydrases (CAs) are Zn2+-containing enzymes that occur ubiquitously in Nature. They have been extensively studied with respect to their ability to hydrate CO2 and dehydrate HCO3 −. The first part of the following discussion will focus on the recent studies with the enzyme that have in total, led to the formulation of a detailed mechanism of action, namely, the “zinc hydroxide” mechanism. The second part of the discussion deals with the simpler chemical models that mimic the spectroscopic properties of cobalt CA, and others which mimic the catalytic properties.