A probe method for studying dibromocarbene by time resolved infrared spectroscopy

Dibromocarbene reacts with tertiary-butylisocyanide to form a ketenimine. The absolute rate constant of the reaction (k_TBI = 2.3 × 10⁹ M⁻¹ s⁻¹) was determined by laser flash photolysis techniques with UV-vis detection of the dibromocarbene-pyridine ylide. The ketenimine was detected by TRIR spectroscopy at 2040 cm⁻¹. Isocyanide trapping of carbenes to form ketenimines is proposed as a general method of studying IR silent carbenes by TRIR spectroscopy.     

Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

An SFG study of interfacial amino acids at the hydrophilic SiO2 and hydrophobic deuterated polystyrene surfaces

Sum frequency generation (SFG) vibrational spectroscopy was employed to characterize the interfacial structure of eight individual amino acids--L-phenylalanine, L-leucine, glycine, L-lysine, L-arginine, L-cysteine, L-alanine, and L-proline--in aqueous solution adsorbed at model hydrophilic and hydrophobic surfaces. Specifically, SFG vibrational spectra were obtained for the amino acids at the solid-liquid interface between both hydrophobic d(8)-polystyrene (d(8)-PS) and SiO(2) model surfaces and phosphate buffered saline (PBS) at pH 7.4. At the hydrophobic d(8)-PS surface, seven of the amino acids solutions investigated showed clear and identifiable C-H vibrational modes, with the exception being l-alanine. In the SFG spectra obtained at the hydrophilic SiO(2) surface, no C-H vibrational modes were observed from any of the amino acids studied. However, it was confirmed by quartz crystal microbalance that amino acids do adsorb to the SiO(2) interface, and the amino acid solutions were found to have a detectable and widely varying influence on the magnitude of SFG signal from water at the SiO(2)/PBS interface. This study provides the first known SFG spectra of several individual amino acids in aqueous solution at the solid-liquid interface and under physiological conditions.     

Curing induced structural reorganization and enhanced reactivity of amino-terminated organic thin films on solid substrates: observations of two types of chemically and structurally unique amino groups on the surface

Infrared-visible sum frequency generation vibrational spectroscopy (SFG) was used to characterize the structure of 3-aminopropyltriethoxysilane (APTES) films deposited on solid substrates under controlled experimental conditions for the first time. Our SFG spectra in combination with complementary analytical data showed that APTES films undergo structural changes when cured at an elevated temperature. Before the films are cured, well-ordered hydrophobic ethoxy groups are dominantly present on the surface. A majority of hydrophilic surface amino groups are protonated, and they are either buried or randomly oriented at the interface. After the films are cured, chemically and structurally different neutral amino groups are detected on the surface. Unlike the protonated amino groups, a new class of neutral amino groups is ordered at the interface and shows enhanced reactivity.     

Electrochemical processes in electrospray ionization mass spectrometry

Editorial Comment Last month we presented, as a Special Feature, a set of five articles that constituted a Commentary on the fundamentals and mechanism of electrospray ionization (ESI). These articles produced some lively discussion among the authors on the role of electrochemistry in ESI. Six authors participated in a detailed exchange of views on this topic, the final results of which constitute this month's Special Feature. We particularly hope that younger scientists will find value in this month's Special Feature, not only for the science that it teaches but also what it reveals about the processes by which scientific conclusions are drawn. To a degree, the contributions part the curtains on these processes and show science in action. We sincerely thank the contributors to this discussion. The give and take of intellectual debate is not always easy, and to a remarkable extent this set of authors has maintained good humor and friendships, even when disagreeing strongly on substance. Graham Cooks and Richard Caprioli Copyright 2000 John Wiley & Sons, Ltd.     

Derivatization for electrospray ionization-mass spectrometry. 4. Alkenes and alkynes

A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd.     

Carbomethoxyfluorocarbene

Carbomethoxyfluorocarbene was studied in solution by laser flash photolysis with UV-vis and infrared detection. In contrast to expectations, carbomethoxyfluorocarbene is more reactive than carbomethoxychlorocarbene. [structure: see text]