W present the results of our work testing a version of the Expanding Photosphere Method (EPM) used by Hamuy et al. and Dessart & Hillier to calculate distances to Type II-P supernovae, accounting for the deviations of their luminosities from those of true blackbodies. This method was applied to a sample of supernovae with data sets covering different postexplosion time periods. Different spectral lines in visible wavelengths—H β , He i , Fe ii , Sc ii , Na i , and Ba ii —are used to measure the expansion velocity with the goal of determining the species that produces the most reliable distance determination when combined with the blackbody temperature of the effective photosphere. This research suggests that H β , Fe ii , and Ba ii lines are most likely to yield accurate distances when combined with blackbody temperature, and provides further evidence of EPM’s effectiveness as an indicator of distance, provided we have a minimum of three data sets covering a broad range of postexplosion phases of the supernova.

Supernova 1987A remains the most well studied supernova to date. Observations produced excellent broadband photometric and spectroscopic coverage over a wide wavelength range at all epochs. We model the observed spectra from day 1 to day 81 using a hydrodynamical model. We show that good agreement can be obtained at times up to about 60 days if we allow for extended nickel mixing. Later than about 60 days the observed Balmer lines become stronger than our models can reproduce. We show that this is likely due to a more complicated distribution of gamma rays than we allow for in our spherically symmetric calculations. We present synthetic light curves in UBVRIJHK and a synthetic bolometric light curve. Using this broad baseline of detailed spectroscopic models, we find a distance modulus of μ = 18.5 ± 0.2 using the spectral-fitting expanding atmosphere method of determining distances to supernovae. We find that the explosion time agrees with that of the neutrino burst and is constrained at 68% confidence to within ±0.9 days. We argue that the weak Balmer lines of our detailed model calculations cast doubt on the accuracy of the purely photometric expanding photosphere method. We also suggest that Type IIP supernovae will be most useful as distance indicators at early times because of a variety of effects.

Supernova 1987A remains the most well observed and well studied supernova to date. Observations have produced excellent broadband photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day 1, but by day 4, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of 56Ni into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 × 10-5 M☉ is required above 5000 km s-1 by day 4. PHOENIX models thus have the potential to be a sensitive probe for nickel mixing in the outer layers of a supernova.

A number of solute descriptors that relate to the ability of a solute to take part in solute-solvent interactions have been identified, quantified and incorporated into a multiple linear regression equation. This general solvation equation can then be used for the correlation and prediction of solute effects in transport processes, that is, processes in which the main step is either the equilibrium transfer, or the rate of transfer, of a solute from one phase to another. Examples discussed include the solubility of gases and vapours in water, various water-solvent partitions, blood-brain distribution, brain perfusion, and skin permeability. (C) 1999 Society of Chemical Industry .

Twelve measured ethylene glycol-heptane partition coefficients, Peh, have been combined with 20 measured literature values and 44 indirectly determined values to give a set of 76 values. Excluding one value for benzamide, the log Peh values are correlated through our general solvation equation, log Peh = 0.336 - 0.075R2 - 1. 201pi2H - 3.786 Sigmaalpha2H - 2.201 Sigmabeta2H + 2.085Vx with r2 = 0.966, sd = 0.28, and F = 386. The solute descriptor R2 is the excess molar refraction, pi2H is the dipolarity/polarizability, Sigmaalpha2H and Sigmabeta2H are the overall hydrogen bond acidity and basicity, and Vx is the McGowan volume. The log Peh equation has then been used to obtain descriptors for eleven peptides, all of which are end-protected. It is shown that for these end-protected peptides, hydrogen bond basicity makes a greater contribution to log Peh than does hydrogen bond acidity.

Several algorithms that use hydrogen bond descriptors have been published for the permeation of compounds from aqueous solution through human stratum corneum. In the present work, all the skin permeability coefficients, Kp in cm s(-1), used in these algorithms for non-steroids have been correlated through the Abraham equation to give a new algorithm:log Kp = -5.241 + 0.437R(2) - 0.410 pi(2)(H) - 1.631 Sigma alpha(2)(H) - 3.286 Sigma beta(2)(H) + 2.012V(x)(1)(n = 47, r(2) = 0.9567, s.d. = 0.197, F = 181)where n is the number of solutes, r is the correlation coefficient, s.d. is the standard deviation, and F is the F-statistic. The solute descriptors are: R-2 and excess molar refraction, pi(2)(H) the dipolarity/polarizability, Sigma alpha(2)(H) and Sigma beta(2)(H) the overall or effective hydrogen-bond acidity and basicity, and V-x the McGowan characteristic volume. Equation 1 is a reasonably good predictor of log Kp values for steroids as given by Johnson et al, but not for those given by Scheuplein.

A number of RP–HPLC systems have been characterized by the linear free energy relationship:(i)logSP=c+r.R2+s.πH2+a.∑αH2+b.∑β2+v.VxHere, SP is either log k′ or log kw for a series of solutes in a given system, where k′ is the capacity factor and kw is the capacity factor extrapolated to l00% water, and the solute descriptors are, R2 an excess molar refraction, π2H the dipolarity/polarizability, ∑α2H and ∑β2 the overall or effective hydrogen-bond acidity and basicity, and Vx the McGowan characteristic volume. Comparison of the coefficients in Eq. (1)with those for water-solvent partitions confirms that the modified electrostatically coated C18 phase of Pagliara et al. (J. Liq. Chromatogr., 18 (1995) 1721) can be used to obtain solute lipophilicities, as log Poct. For RP–HPLC systems based on poly(styrene–divinylbenzene), the coefficients in Eq. (i)are nearer those for the correlation of water–alkane partition coefficients, as log Palk, than for the correlation of log Poct, suggesting that the RP–HPLC systems with poly(styrene–divinylbenzene) phases could be used as a rapid method for determination of solute lipophilicity, as log Palk or as log Pcyc, where the latter is the water–cyclohexane partition coefficient. Eq. (i)has also been applied to RP–HPLC log k′ values obtained with an immobilized artificial membrane (IAM) phase. A good regression equation was obtained, but the coefficients in this equation are substantially different to those for regressions with log Poct, log Palk, or log Pcyc as the dependent variable. On the other hand, log k′ values from the RP–HPLC system of Miyake al. [J. Chromatogr., 389 (1987) 47], consisting of silica gel coated with dipalmitoyl phosphatidyl choline as a stationary phase, with aqueous acetonitrile mobile phases, yielded coefficients in Eq. (i)very similar to those for log Poct.

Partition coefficients in the water-octanol, -cyclohexane, and -dichloromethane systems were determined as a function of pH for three non-zwitterionic ampholytes (nitrazepam, albendazole sulfoxide, and sulfadimidine) and three zwitterionic ampholytes (morphine, difloxacin, and niflumic acid). From known macro- and microprotonation constants in water, the concentration of cation, anion, neutral form, and zwitterion can be found, and partition coefficients can then be calculated for the partition of the neutral form in water to the neutral form in the organic solvent for all six compounds. These micropartition coefficients were then used to obtain descriptors for the neutral form in the general linear free energy (LFER) equation of Abraham. Knowledge of the descriptors enables a number of physicochemical and biochemical properties of the neutral form to be estimated; a detailed analysis is given of the estimation of the blood-brain distribution ratio for the process of going from the neutral form in blood to the neutral form in brain. A related procedure leads to an estimation of the distribution ratio for the process of going from the zwitterion in blood to the neutral form in brain.

The infrared (IR) spectrum of vancomycin, in D2O solution, has been assigned by recording spectra at different pD values and by comparing them with the spectrum in H2O at pH 5. The effects of self-association on the spectrum of vancomycin at pD 5 have also been investigated. Details of underlying components of the broad bands in the spectra were revealed using resolution enhancement and second derivatives. The IR spectra of two peptide models, N-Ac-D-Ala-D-Ala and N,N'-Ac-2-L-Lys-D-Ala-D-Ala, have also been assigned in D2O solution. The interactions of these peptides with vancomycin, in pD 5 solution, have been studied by infrared spectroscopy and the above assignments used to interpret the observed spectral changes; the solubilities of the vancomycin-peptide complexes at pD 5 were determined to facilitate these studies. The IR spectra of the complexes show substantial increases in intensity of a component at about 1588 cm(-1). Using C-13 labelled N-Ac-D-Ala-D-Ala this was found to be due to the asymmetric stretch of the carboxylate group of the peptide, showing that this group undergoes a substantial perturbation on binding to vancomycin.

In this study, human skin permeation data are analysed using a number of physicochemical descriptors. It is shown that the equilibrium distribution of compounds between the stratum corneum and water (log K-m) can be correlated with either water-octanol partition coefficients (log P-oct) or Abraham solute descriptors. The latter reveals that partitioning of compounds is governed by solute size and hydrogen-bond acidity that favour the stratum corneum, and solute dipolarity/polarizability, and hydrogen-bond basicity that favour water.For water-skin permeation coefficient (log k(p)) data it is demonstrated that log P-oct cannot be used as a descriptor across a wide range of chemical families, but that log k(p) can be correlated using Abraham solute descriptors. These disclose that log k(p) values are increased by solute size and decreased by solute dipolarity/polarizability, hydrogen-bond acidity and hydrogen-bond basicity. It is suggested that different solutes travel through the stratum corneum by the same route, which cannot be distinguished as an intercellular or transcellular mechanism.Backward skin permeation is examined and. it is demonstrated that factors governing this process can be rationalized. Furthermore, it is shown that using the Abraham analysis, log P-oct can be corrected to correlate log k(p) over a wide range of compounds.The determination of solute descriptors is also described, indicating that Abraham solute descriptors can be obtained by substructure summation and partition coefficient measurements, so that dermatological properties can be predicted for solutes without the necessity for synthesis.

A general linear solvation energy equation has been used to analyze published partition coefficients in the systems water-octanol (613 solutes), water-hexadecane (370 solutes), water-alkane (200 solutes), and water-cyclohexane (170 solutes). The descriptors used in the equation areR2, an excess molar refraction; π2H, the solute dipolarity/polarizability; ∑α2Hand ∑β2H, the effective solute hydrogen-bond acidity and basicity; and VX, the characteristic volume of McGowan. It is shown that the water-octanol partition coefficient is dominated by solute hydrogen-bond basicity, which favors water, and by solute size, which favors octanol, but solute excess molar refraction and dipolarity/polarizability are also significant. For the water-alkane partition coefficients, the same factors are at work, together with solute hydrogen-bond acidity as a major influence that favors water. An analysis of 288 ΔlogPvalues shows that solute hydrogen-bond acidity is the major factor but that solute hydrogen-bond basicity and, to a lesser extent, solute dipolarity/polarizability and size are also significant factors that influence the ΔlogPparameter.

An equation is described that relates the equilibrium distribution of compounds between blood and brain to various solute descriptors, for 57 varied compounds. It is shown that the main factors influencing the distribution are solute size that favours brain, and solute dipolarity/ polarisability, hydrogen-bond acidity and hydrogen-bond basicity that favour blood. The descriptors can be obtained from measurements on compound substructures, so that the blood-brain distribution can be predicted for drug molecules without the necessity for synthesis.

It is shown that neither the set of directly determined blood–brain concentration ratios (BB) of Young and Mitchell nor the set of indirectly obtained values of Abraham and Weathersby are suitable for the construction of a general equation for the interpretation and prediction of log BB values. However, combination of both sets leads to the general equation log BB = -0.038 + 0.198R2- 0.687πH2- 0.715αH2- 0.698βH2+ 0.995Vx(n= 57,Q= 0.9522, sd = 0.197, F = 99.2), where the solute descriptors areR2, an excess molar refraction; πH2, the dipolarity/polarizability, αH2and βH2, the effective or summation hydrogen-bond acidity and basicity; andVx, the characteristic volume of McGowan. Thus solute dipolarity/polarizability, hydrogen-bond acidity, and hydrogen-bond basicity favor blood, and solute size, asVx, favors brain. Methods are given for the estimation of solute descriptors through fragment schemes, so that log BB values themselves may be obtained simply from knowledge of solute molecular structure.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Decomposition of the N-nitrosodipeptides obtained from N-(N'-acetyl-L-prolyl)glycine and N-(N'-acetyl-L-propyl)-L-alanine in aqueous acid at 25-degrees-C involves both deamination and denitrosation. Both reactions occur concurrently via different conjugate acid intermediates, with denitrosation being predominant at high acidity. Acidity dependences and inverse solvent deuterium isotope effects [k(H2SO4)/k(D2SO4) ca. 0.7] suggest that deamination involves rate limiting attack by H2O on an O-conjugate acid, formed in a rapid pre-equilibrium. For denitrosation, H+ transfer to the amide N-atom is considered rate limiting because of the substantial normal solvent deuterium isotope effects [k(H2SO4)/k(D2SO4) ca. 2.5] and Bunnett omega value in the range -0.1 to -0.5: the N-conjugate acid formed breaks down rapidly to products. Both the kinetics and mechanisms for decomposition of these N-nitrosodipeptides are very similar to those of alicyclic N-nitrosamides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.