Fluorescence and photodissociation of rhodamine 575 cations in a quadrupole ion trap

The fluorescence and photodissociation of rhodamine 575 cations confined to a quadrupole ion trap are observed during laser irradiation at 488 nm. The kinetics of photodissociation is measured by time-dependent mass spectra and time-dependent fluorescence. The rhodamine ion signal and fluorescence decay are studied as functions of buffer gas pressure, laser fluence, and irradiation time. The decay rates of the ions in the mass spectra agree with decay rates of the fluorescence. Some of the fragment ions also fluoresce and further dissociate. The photodissociation rate is found to depend on the incident laser fluence and buffer gas pressure. The implications of rapid absorption/fluorescence cycling for photodissociation of dye-labeled biomolecular ions under continuous irradiation are discussed.     

Pyrrolizidine-Derived Alkaloids: Highly Toxic Components in the Seeds of Crotalaria cleomifolia Used in Popular Beverages in Madagascar

Seeds of Crotalaria cleomifolia (Fabaceae) are consumed in Madagascar in preparation of popular beverages. The investigation of extracts from the seeds of this species revealed the presence of high amounts of alkaloids from which two pyrrolizidine-derived alkaloids were isolated. One of them was fully characterized by spectroscopic and spectrometric methods, which was found to be usaramine. Owing to the high toxicity of these alkaloids, issuing a strong warning among populations consuming the seeds of Crotalaria cleomifolia must be considered.     

Particle-rotor-model calculations in 125I

Recent experimental data on ¹²⁵I has revealed several interesting structural features. These include the observation of a three quasiparticle band, prolate and oblate deformed bands, signature inversion in the yrast positive-parity band and identification of the unfavoured πh _11/2 band showing very large signature splitting. In the present work, particle-rotor-model calculations have been performed for the πh _11/2 band, using an axially symmetric deformed Nilsson potential. The calculations reproduce the experimental results well and predict a moderate prolate quadrupole deformation of about 0.2 for the band.     

Variation in electromagnetic radiation during plastic deformation under tension and compression of metals

This paper presents some significant variations in the intermittent electromagnetic radiation (EMR) during plastic deformation under tension and compression of some metals with selected crystal structure, viz. zinc, hexagonal closed packed (hcp), copper, face-centred cubic (fcc: stacking fault energy 0.08 J/m²), aluminium (fcc: stacking fault energy 0.2 J/m²) and 0.18 % carbon steel, body-centred cubic (bcc). The intermittent EMR signals starting near yielding are either oscillatory or exponential under both modes of deformation except a very few intermediate signals, random in nature, in zinc under compression. The number and amplitude of EMR signals exhibit marked variations under tension and compression. The smooth correlation between elastic strain energy release rate and average EMR energy release rate suggests a novel technique to determine the fracture toughness of metals. The first EMR emission amplitude and EMR energy release rate occurring near the yield increase, but maximum EMR energy burst frequency decreases almost linearly with increase in Debye temperature of the metals under tension while all EMR parameters decrease nonlinearly under compression. These results can be developed into a new technique to evaluate dislocation velocity. The EMR amplitude and energy release rate of the first EMR emission vary parabolically showing a maxima with increase in electronic heat constant of the metals under tension while they first sharply decrease and then become asymptotic during compression. However, the variation in EMR maximum energy burst frequency is apparently similar under both modes of deformation. These results strongly suggest that the mechanism of EMR emission during plastic deformation of metals involves not only the interaction of conduction electrons with the lattice periodic potential as presented in the previous theoretical models but also the interaction of conduction electrons with phonons. However, during crack propagation and fracture, charge oscillations at fractured surfaces due to breaking of atomic bonds constitute an additional factor.     

A Facile [hydroxy(tosyloxy)iodo]benzene Mediated Synthesis of Symmetrical Triazolo-[3,4-b]-1,3,4-Thiadiazines

Synthesis of the title compounds has been accomplished by a one-pot procedure involving the reaction of 3-substituted-4-amino-5-mercapto-1,2,4-triazoles and a variety of heterocyclic ketones in the presence of [hydroxy(tosyloxy)iodo]benzene.     

α,α‐Dibromoketones: A Superior Alternative to α‐Bromoketones in Hantzsch Thiazole Synthesis

Abstract

α,α‐Dibromoketones (2) have been found to be a superior alternative to the conventionally used α‐bromoketones (1) for performing the Hantzsch thiazole synthesis.1 Ahluwalia, V. K., Mehta, B. and Rawat, M. 1992. Synth. Commun., 22: 2697[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar] These crystalline, nonlachrymatory compounds are more reactive than 1 as demonstrated by their reaction with 3,5‐dimethyl‐1‐thiocarboxamide (5).     

Iodobenzene Diacetate Mediated Oxidation of N-Substituted Hydrazones of Chalcones: An Efficient Regioselective Synthesis of 1,3,5-Trisubstituted Pyrazoles

Iodobenzene diacetate, a relatively benign nonmetallic oxidant, has been utilized efficiently for the oxidation of N-substituted hydrazones of chalcones to afford 1,3,5-trisubstituted pyrazoles under mild reaction conditions.     

A novel method for correlation of substituent constants in some aromatic esters using the shift reagent Eu(fod)3

The lanthanide induced chemical shifts of the ester methyl group were studied in eighteen m-, and p-substituted aromatic methyl esters with varying amounts of added shift reagent, Eu(fod)₃. Each time the lanthanide induced shift (LIS) was plotted against the molar ratio of shift reagent (SR)/substrate and a straight line was obtained upto one mole ratio of added shift reagent. The slopes of these plots correlated well with the Hammett's σ constants and yield a value of ?4.95 for the reaction constant ?. The method is therefore one of the simplest ways of correlating the substituent constants in aromatic esters.     

Investigation of quark distributions in a family of pentaquarks using the Thomas-Fermi quark model

Using the Thomas-Fermi quark model,a collective,spherically symmetric density of states is created to represent a gas of interacting fermions with various degeneracies at zero temperature.Over a family of pentaquarks,uudcc,color interaction probabilities were obtained after averaging over all the possible configurations.Three different functions are developed for light,charm,and anti-charm quarks and are assumed to be linearly related by some proportionality constants.Interesting patterns of quark distributions are observed while analyzing the quark function consistency conditions for such constants.     

Steady state and time-resolved fluorescence study of isoquinoline: reinvestigation of excited state proton transfer

In the present work we report some hitherto unnoticed features in the steady state and time-resolved measurements of isoquinoline in water and trifluoroethanol (TFE). Absorption spectra reveal that in water, neutrals as well cationic species are present. Emission spectrum shows structured features at shorter wavelengths accompanied with a broad band around 375 nm, which correspond to neutrals and cations respectively. However, time-resolved data indicate that protonation does not take place in the excited state in water. On the contrary, in stronger hydrogen bonding solvent TFE, distribution of decay components is observed and at longer wavelengths a small rise time is present. This is ascribed to neutral and cation-like species present in the ground as well as in the excited state. The difference in the results is explained in terms of different excited state potential energy surfaces for water and TFE; particularly, the presence of a rather small barrier for protonation in case of TFE.