Avermectin-milbemycin studies. 4. An expedient two-step preparation of p-hydroxybenzoates

Dianions derived from a variety of 1,3-diketones react with $\text{Z}$-ethyl-3-bromopropenoate to afford unsaturated diketoesters which upon treatment with base undergo facile cyclization-dehydration to p-hydroxybenzoates.     

Aspects of plastic scintillators. II. Energy transfer studies in polymerizing media

Changes in scintillation efficiency during formation of plastic scintillator compositions have been studied. The separate roles of energy transfer and solute fluorescence efficiencies in the determination of the observed luminescence output of the systems were elucidated. Bis-1,4-2-(5-phenyloxazolyl)benzene(POPOP); 1,1′,4,4′-tetraphenylbutadiene(TPB), and 9-methyl anthracene (MAN) were employed as scintillator solutes. The increased scintillation yield of polymerizing solutions of POPOP is primarily a consequence of increased energy transfer efficiency from solvent to solute. Solutions of TPB exhibit enormous increases in luminescence output upon formation of polymers. The major contributor to the overall effect is the great enhancement of the fluorescence efficiency of TPB which occurs when the microviscosity of the medium is increased. MAN solutions exhibit a decreasing luminescence yield upon polymerization despite increasing energy transfer efficiency. Structural rearrangements of the fluor, consequent upon involvement in the polymerization kinetic chain, are responsible for the decreased scintillation efficiency.     

Hypervirial analysis of enclosed quantum mechanical systems. III. Unsymmetrical boundary conditions

New theoretical developments based upon hypervirial analysis of enclosed systems are given. Systems which obey unsymmetrical boundary conditions are analyzed. Several results which were given by the authors in two previous communications are generalized.     

Photochemische Reaktionen. 48. Mitteilung [1]. Photolytische Substitutionen von Aromaten mit α-Sulfonyloxyketonen. Vorläufige Mitteilung

Photo-excited arenes have been found to initiate a substitution reaction in which the sulfonyloxy group of α-sulfonyloxyketones is displaced, and the corresponding β-arylketones are formed. Evidence is presented that the electronically excited arene need not be involved directly in the substitution step. It would seem to be more likely that upon interaction with the sulfonyloxyketone a reactive species derived from the latter is produced which is capable of aromatic substitution.     

Gas chromatography in qualitative analysis. Part 14. Molecular retention index as an alternative system for the characterization of gas chromatographic stationary phases

Summary The limitations of methods for the characterization of stationary phases, which require the use of a base or reference stationary phase, are considered. In order to overcome these problems, a new method of column characterization, based upon measurements of molecular retention index and ΔMe values for selected functional groups, is proposed. ΔMe values are shown to be dependent upon liquid phase composition, nature of the support and liquid phase loading.     

Thallium in organic synthesis. 68. A convenient synthesis of 2-phenylindoles from anilides

Thallation of anilides with TTFA in a mixture of TFA and ether gives ortho-thallated derivatives, which yield 2-acetamido-tolanes upon reaction with copper(I) phenylacetylide in acetonitrile. Treatment of the latter compounds with palladium(II) chloride results in ring closure to give 1-acyl-2-phenylindoles, from which 2-phenyl-indoles are obtained by alkaline hydrolysis.     

Multilayered assemblies composed of brilliant yellow and poly(allylamine) for an optical pH sensor.

Multilayered thin films containing poly(allylamine) (PAA) and brilliant yellow (BY) were prepared on a quartz slide by a layer-by-layer (LBL) deposition technique. The UV-visible spectra of the PAA/BY films were sufficiently changed depending upon the pH value of the solution in which the film was immersed. The response of the PAA/BY films was very fast (within a second) upon pH change from 9.0 to 5.0, while the response time was ca. 100 s upon pH change from 5.0 to 9.0.     

Porphyrins and Related Compounds as Photoactivatable Insecticides. 2. Phototoxic Activity of Meso-Substituted Porphyrins

We have recently proposed the use of porphyrin sensitizers as photoinsecticidal agents. Our present findings show that the phototoxic efficiency of porphyrins toward the Mediterranean fruit fly Ceratitis capitata is strongly dependent on their chemical structure. Thus, two highly hydrophilic porphyrins, such as a tetraanionic and a te-tracationic meso-substituted derivative, show a very low photoactivity even upon prolonged irradiation with full-spectrum visible light. The phototoxicity increases upon increasing the hydrophobicity of the porphyrin molecule; out of the compounds examined by us, the highest pho-tocidal activity is exhibited by a dicationic amphophilic porphyrin, namely cis-(JV-methyl-piridyl), c/s-diphenyl-porphine, which causes 100% mortality upon 1 h irradiation with a fluence rate of 1220 μ.E s^-lm^-2even at a concentration as low as 0.85 mM. The differences in photoactivity are not related to differences in the photo-physical and photobiological properties or to differences in the rate of porphyrin uptake and clearance by the flies.     

Research on the aromas. On the aroma of coffee. I

The analysis of a coffee concentrate is described: 202 constituents have been identified, 154 of which for the first time. Some of these compounds are new chemicals; their synthesis is described. Most identifications are based upon mass spectrometry combined in many cases with IR. spectrometry and comparison with reference compounds. MS. and IR. data are given in detail. The analysis shows that a large number of minor constituents is present, many of which could not be identified.     

Torsional barriers in aromatic molecular clusters as probe of the electronic properties of the chromophore.

We present a computer program that is capable of fitting n-fold torsional barriers Vn (n = 2-6) and torsional constants F simultaneously to high- and low-resolution spectroscopic data of different isotopomeric internal rotors. The program has been utilized to fit independently barriers and torsional constants for both electronic states of several aromatic clusters. The constant F of the ammonia moiety in the phenol-ammonia cluster is shown to decrease upon electronic excitation, thus imaging the formation of a hydrogen-bonded complex between the phenoxy radical and the NH4 radical in the excited state. In contrast, for the naphthol-ammonia 1:1 clusters no change of F of ammonia could be found. For phenol-methanol cluster we found a decrease of F upon excitation which points to a stronger hydrogen bond between phenol and methanol in the excited state. A strong reduction of the torsional barrier upon excitation points to the formation of a methoxonium radical in a similar photoreaction as in phenol-ammonia cluster. For the phenol-water system we postulate the same mechanism, a photoreaction, which leads to a translocated hydrogen atom in the S1 state what can be deduced from the change of the torsional constant upon electronic excitation.     

Polycondensed nitrogen heterocycles. X. 5,6,7,8-Tetrahydropyrrolo[1,2-e][1,5]benzodiazocin-7-ones. A new ring system

The synthesis of a new heterocyclic ring system is described. Condensation of 1,4-diketones 1a,b with β-alanine gave the substituted propionic acids 2a,b which upon reduction with palladium on charcoal afforded compounds 3a,b . Title compounds 4a,b were obtained by refluxing 3a,b in toluene with p-toluenesulphonic acid as catalyst.     

The NCI Drug Information System. 6. System maintenance

The NCI Drug Information System (DIS) is a collection of 24 interactively searchable databases which contain all the data associated with NCI's drug screening program. Data flow into all of these databases upon a daily basis, and maintenance procedures have been developed which provide a high degree of currency to the files. An extensive security system controls both write access and read access to the DIS and matches both to the authorization possessed by each specific user. Detailed usage statistics are collected automatically. The cost of the overall system in terms of both manpower and machine time is discussed briefly.     

New ylide anions. A vinyl anion equivalent for substituted fumarate esters

A new type of ylide anion is reported which upon alkylation and elimination of triphenylphosphine serves as a vinyl anion equivalent.     

Electrochemistry of conductive polymers 40. Earlier phases of aniline polymerization studied by Fourier transform electrochemical impedance spectroscopy

Earlier stages of aniline polymerization have been studied by Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. Initial oxidation of aniline leads to the formation of a thin layer passivating the electrode surface, which is depassivated upon a further increase in potential and mediates a further electron transfer from aniline to the electrode. The charge-transfer resistance was first shown to decrease upon increasing the potential, which leads to the inductive behavior upon further increase in the overpotential. The oligomer-polymer film thus formed was shown to undergo a transition from its passive state to neutral oligomer-polymer molecules via a conducting state; its oxidation was then observed during the anodic scan. It is this transition to the conductive states that leads to the propagation of the conductive zone throughout the nonconductive film, leading to further growth of polyaniline, as was clearly shown by the FTEIS measurements.     

The allyl bonded stationary phase. II. Conversions to new phases for gas chromatography

Summary The presence of the double bond on the allyl moiety has been utilized as a site for addition reactions which could produce new stationary phases. Bromination and hydrobromination reactions have been employed to prove the feasibility of making modifications to the allyl bonded phase. Both retention volumes and thermodynamic parameters for the solutes studied change upon conversion to one of the brominated phases. Sample size studies are consistent with a bonded phase adsorption mechanism. FTIR spectra also confirm the modifications which have occurred on the allyl bonded material.     

Molecular binding at gold transport interfaces. III. Field dependence of electronic properties

The behavior of the electronic structure in a metal/molecular/metal junction as a function of the applied electric field is studied using density functional methods. Although the calculations reported here do not include the electrode bulk, or intermolecular interactions, and do not permit actual transport to occur, nevertheless they illuminate the charging, energy shift, polarization and orbital occupation changes in the molecular junction upon the application of a static electric field. Specifically, external electric fields generally induce polarization localization on the two cluster ends. The HOMO/LUMO gap usually decreases and, for large enough fields, energy levels can cross, which presages a change of electronic state and, if found in molecular electronic circuits, a change in transmission. The calculations also show changes in the geometry both of the molecule and the molecule/cluster interface upon application of the electric field. These effects should be anticipated in whole circuit studies.     

Prearranged Glycosides. Part 8. Intramolecular α-Galactosylation Via Succinoyl Tethered Glycosides

ABSTRACT

Benzyl protected phenyl 1-thio-galactopyranoside donors which were tethered by a succinoyl linker at their positions 2 and 6, respectively, to position 3 of a blocked benzyl glucopyranoside acceptor with a 4-OH group solely afforded the corresponding α-(1→4)-linked disaccharides upon intramolecular glycosylation. 4,6-Siloxane protected mannosides react with rearrangement of the siloxane group under similar conditions.     

Ion chemistry of α-diazoketones. 1. A collissional activation study of 1-diazo-3-phenoxypropan-2-one upon elecgtron impact

The gaseous ionic products of 1-diazo-3-phenoxypropan-2-one upon electron impact show that cyclization reactions, which have counterparts in condensed-phase chemistry, occur in competition with a mass spectral Wolff type rearrangement.     

Negative ion mass spectrometry of highly fluorinated compounds. 1. perhalogeno-pyridine derivatives

Perhalogenated pyridine derivatives give negative molecular ions which undergo various fragmentation processes upon negative ion chemical ionisation. The similarities between highly fluorinated negative molecular and fragment ions that are preferentially formed in the gas and solution phases are outlined. Copyright 2000 John Wiley & Sons, Ltd.     

Photocrosslinkable vinylamine copolymers. I. Synthesis and photosensitivity of cinnamoylated polyvinylamine

Vinylamine copolymers prepared by the Hofmann reaction were functionalized by amidification with cinnamoyl chloride. The resulting photosensitive polymers, which are the nitrogen analogues of poly(vinylcinnamate), can be prepared with various contents of cinnamamide side groups. The polymers exhibit a marked hydrophilicity and undergo efficient crosslinking upon exposure to 250–300 nm UV light. The sensitivity S expressed in cm²·J⁻¹ was shown to be higher for a given content, τ, in cinnamamide groups expressed in mol·g⁻¹ when the residual vinyl amine units are in the ammonium form. The dependence of S upon τ was of the second order for the free base form of the photopolymers, but a higher order with S approximately proportional to τ³ for the hydrochloride form of the photosensitive polymers. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2513–2520, 1997