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The anions C |$_7$| N |$^-$| and C |$_{10}$| H |$^-$| are the two longest of the linear (C,N)-bearing and (C,H)-bearing chains that have so far been detected in the interstellar medium (ISM). In order to glean information on their collision-induced rotational state-changing processes, we analyse the general features of new ab initio potentials describing the interaction of both linear anions with H |$_2$|⁠ , one of the most abundant partners in their ISM environment. We employ an artificial neural network fit of the reduced-dimensionality potential energy surface for C |$_7$| N |$^-$|⁠...H |$_2$| interaction and discuss in detail the spatial features in terms of multipolar radial coefficients. For the C |$_{10}$| H |$^-$|⁠...H |$_2$| interaction, we use the initial grid of two-dimensional raw points to generate by quadrature the Legendre expansion directly, further including the long-range terms as discussed in the main text. Quantum scattering calculations are employed to obtain rotationally inelastic cross-sections, for collision energies in the range of 10 |$^{-4}$| to 400 cm |$^{-1}$|⁠. From them we generate the corresponding inelastic rate coefficients as a function of temperature covering the range from 10 to 50 K. The results for the rate coefficients for the longest cyanopolyyne are compared with the earlier results obtained for the smaller terms of the same series, also in collision with H |$_2$|⁠. We obtain that the inelastic rate coefficients for the long linear anions are all fairly large compared with the earlier systems. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are illustrated in our conclusions. [ABSTRACT FROM AUTHOR]

By extending an earlier study [Gianturco et al., J. Chem. Phys. 154, 054311 (2021)] on the purely rotational excitation of HeH+ by He atoms, we report in this paper integral cross sections and rate coefficients for rovibrational excitation and de-excitation processes in HeH+ due to collisions with He. The data were obtained using a new ab initio potential energy surface that includes the vibrational degree of freedom. The results are compared with those computed using the earlier potential energy surface by Panda and Sathyamurthy [J. Phys. Chem. A 107, 7125 (2003)] that additionally accounts for the proton-exchange reaction between HeH+ and He. It is shown that the exchange channel contributes nearly as much as the inelastic channel to the vibrational excitation and de-excitation processes and that the total rate constants pertaining to the purely inelastic processes are largely of the same magnitude as those obtained when both inelastic and reactive channels are included in the dynamics. The inelastic rovibrational rate coefficients involving this astrophysical cation are also found to be much larger than those obtained for anions present in similar interstellar environments. [ABSTRACT FROM AUTHOR]

Two different ab initio potential energy surfaces are employed to investigate the efficiency of the rotational excitation channels for the polar molecular ion HeH+ interacting with He atoms. We further use them to investigate the quantum dynamics of both the proton-exchange reaction and the purely rotational inelastic collisions over a broad range of temperatures. In current modeling studies, this cation is considered to be one of the possible cooling sources under early universe conditions after the recombination era and has recently been found to exist in the interstellar medium. The results from the present calculations are able to show the large efficiency of the state-changing channels involving rotational states of this cation. In fact, we find them to be similar in size and behavior to the inelastic and reaction rate coefficients obtained in previous studies, where H atoms were employed as projectiles. The same rotational excitation processes, occurring when free electrons are the collision partners of this cation, are also compared with the present findings. The relative importance of the reactive, proton-exchange channel and the purely inelastic channels is also analyzed and discussed. The rotational de-excitation processes are also investigated for the cooling kinetics of the present cation under cold trap conditions with He as the buffer gas. The implications of the present results for setting up more comprehensive numerical models to describe the chemical evolution networks in different environments are briefly discussed. [ABSTRACT FROM AUTHOR]

The anion C5N− is one of the largest linear (C,N)-bearing chains detected in the interstellar medium. Here we present and discuss the general features of new ab initio potential energy surfaces describing the interaction of this linear anion with He and H2. We employ a Legendre Polynomials expansion representation for the former and an artificial neural network fit for the latter. We then carry out quantum scattering calculations to yield rotationally inelastic cross-sections for collisions with He and H2, using relative translational energy values in the range of 0.1–300 cm−1. We then obtained the corresponding inelastic rate coefficients as a function of temperature covering the range from 1 to 100 K. The results for these two systems are compared with each other, as well as with the earlier results on the C3N− colliding with the same partners. We found that the final inelastic rate coefficients for this anion are all fairly large, those from collisions with H2 being the largest. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are discussed in our conclusions. [ABSTRACT FROM AUTHOR]

Using accurate ab initio calculations of the interaction forces, we employ a quantum mechanical description of the collisional state-changing processes that occur in a cold ion trap with He as a buffer gas. We generate the corresponding inelastic rates for rotational transitions involving three simple molecular anions OH−(1Σ), MgH−(1Σ), and C2H−(1Σ) colliding with the helium atoms of the trap. We show that the rotational constants of these molecular anions are such that within the low-temperature regimes of a cold ion trap (up to about 50 K), a different proportion of molecular states are significantly populated when loading helium as a buffer gas in the trap. By varying the trap operating conditions, population equilibrium at the relevant range of temperatures is reached within different time scales. In the modeling of the photodetachment experiments, we analyze the effects of varying the chosen values for photodetachment rates as well as the laser photon fluxes. Additionally, the changing of the collision dynamics under different buffer gas densities is examined and the best operating conditions, for the different anions, for yielding higher populations of specific rotational states within the ion traps are extracted. The present modeling thus illustrates possible preparation of the trap conditions for carrying out more efficiently state-selected experiments with the trapped anions. [ABSTRACT FROM AUTHOR]

We have measured the spectrum of laser photodissociation of OH+ molecular ions to O + H+ and O+ + H fragments for photon energies of 38 100–40 900 cm−1. The OH+ ions were stored as a fast beam (5.50 MeV) in the storage ring TSR for several seconds to achieve rovibrational cooling into the lowest rotations N′′ = 0–11 of the vibrational ground state X3Σ−(v ′′ = 0), close to room temperature (≈300 K). The many resonances in the spectra reveal the energies, widths, and O/O+ branching ratios of 44 predissociating quasibound levels (Feshbach resonances) that lie between the fine-structure states of the O fragment and belong to the last, near-threshold vibrational states v ′ = 9 and 10 of the A3Π electronic state. For the A3Π0,1 substates, isolated levels with v ′ = 11 are observed and attributed to double-well distortions of these curves due to nonadiabatic interactions. Another five isolated levels are assigned to the v ′ = 0 and 1 states of the shallow 15Σ− electronic state, borrowing oscillator strength from nearby A3Π levels. Together, the near-threshold levels deliver a new value D0 = 40 253.8(1.1) cm−1 for the dissociation energy of OH+. Through a two-step photodissociation process, 72 levels from the lower bound states A3Π(v ′ = 7–8) appear as well and are rotationally analyzed. The level energies are used to construct improved A3Π and 15Σ− Born-Oppenheimer potentials. The totality of the spectral data (energies, widths, intensities, and branching ratios) can provide tight constraints for the potentials and nonadiabatic interactions assumed in future coupled-channel calculations of OH+ photodissociation or of the related charge-exchange reaction O + H+ → O+ + H. [ABSTRACT FROM AUTHOR]

The nucleophilic substitution reaction CN- + CH3I allows for two possible reactive approaches of the reactant ion onto the methyl halide, which lead to two different product isomers. Stationary point calculations predict a similar shape of the potential and a dominant collinear approach for both attacks. In addition, an H-bonded pre-reaction complex is identified as a possible intermediate structure. Submerged potential energy barriers hint at a statistical formation process of both CNCH3 and NCCH3 isomers at the experimental collision energies. Experimental angle- and energy differential cross sections show dominant direct rebound dynamics and high internal excitation of the neutral product. No distinct bimodal distributions can be extracted from the velocity images, which impedes the indication of a specific preference towards any of the product isomers. A forward scattering simulation based on the experimental parameters describes accurately the experimental outcome and shows how the possibility to discriminate between the two isomers is mainly hindered by the large product internal excitation. [ABSTRACT FROM AUTHOR]

The possibility of attaching near-threshold electrons to N-terminated carbon chains, like those observed in the outer envelopes of carbon-rich stars, is examined via accurate quantum chemistry orbital structures evaluation and quantum scattering analysis of the corresponding extra-electron wavefunctions at meV energies. It is shown that the differences in the signs and sizes of the permanent dipole moments which exist for both the neutral and anionic species of the CnN series of molecules play a significant role in suggesting or excluding possible energy paths to permanent anion formations of cyanopolyynes, for which the cases with n from 1 to 7 are examined in more detail. [ABSTRACT FROM AUTHOR]

Differential cross sections for the charge transfer reaction between Ar+ and CO have been measured using three-dimensional velocity map imaging in a crossed beam setup at the two relative collision energies 0.55 and 0.74 eV. We find dominant forward scattering with CO+ product ions predominantly in the vibrational levels ν ′ =6,7 of the electronic ground state X 2 Σ + . This is indicative of a direct resonant mechanism for the two argon spin-orbit states. At both collision energies also an isotropic distribution with product ions exhibiting high internal excitation is observed. This is more pronounced at the higher collision energy, where the first electronically excited state A 2 Π + becomes accessible. We conclude that the A-state is partially populated by the product ions at 0.74 eV collision energy and suggest that the isotropic distribution stems from the formation of a charge-transfer complex, in concurrence with previously performed studies. [ABSTRACT FROM AUTHOR]

Adiabatic alignment of CH3I, induced by the anisotropic interaction of this symmetric top molecule with the intense field of a nonresonant infrared laser pulse, has been studied using velocity map imaging. We are using photodissociation imaging with pulsed nanosecond lasers to probe the distribution of the molecular axis in the laboratory space. In contrast to the commonly used probing with femtosecond laser pulses, this technique directly yields the degree of alignment over an extended space-time volume. This will be relevant for future reactive scattering experiments with laser-aligned molecules. The obtained degree of alignment, , measured as a function of the infrared laser intensity, agrees well with a quantum calculation for rotationally cold methyl iodide. The strong infrared laser is also found to modify the photofragmentation dynamics and open up pathways to CH3I+ formation and subsequent fragmentation. [ABSTRACT FROM AUTHOR]

We present an accurate potential energy curve of the B 1Π state in the LiCs molecule for which vibrational levels between v′=0 and v′=35 (bound by 11.4 GHz) were measured by photoassociation spectroscopy in an ultracold ensemble of 7Li and 133Cs atoms. By the combination of conventional spectroscopic data of the B-X system and the new photoassociation measurements a very precise value of the dissociation energy of the ground state X 1Σ+ of LiCs was determined to be D0=5783.495(5) cm-1. [ABSTRACT FROM AUTHOR]

Absolute total photodetachment cross sections of O- and OH- anions stored in a multipole radio frequency trap have been measured using a novel laser depletion tomography method. For OH- the total cross sections of 8.5(1)stat(3)syst and 8.1(1)stat(7)syst×10-18 cm2, measured at 662 and 632 nm, respectively, were found constant in the temperature range of 8–300 K. The O- cross sections 5.9(1)stat(2)syst and 6.3(1)stat(2)syst×10-18 cm2 measured at 170 K at 662 and 532 nm, respectively, agree within error estimations with preceding experiments and increase the accuracy of the widely used calibration standard for relative photodetachment measurements of diverse atomic and molecular species. [ABSTRACT FROM AUTHOR]

We have measured the photodissociation spectrum of CH+ and CD+ molecular ions, stored as fast (MeV) ion beams in the heavy-ion storage ring TSR. Several b 3Σ--a 3Π bands were observed as strong resonances because a large fraction of the ions in the metastable a 3Π(v=0) state were pumped to b 3Σ- levels and predissociated via the c 3Σ+ state into C+ and H(D) fragments. From a rotational analysis of the 2-0, 3-0, and 4-0 bands in CH+ and the 3-0 and 4-0 bands in CD+, we derive spectroscopic constants for these levels and also revise a previous analysis of the 0-0 and 1-0 bands in CH+. Combining all data delivers new, significantly adjusted equilibrium constants for the b 3Σ- and a 3Π electronic states. Apart from the spectroscopic analysis, we estimate the predissociation rates of the upper b 3Σ- vibrational levels in CH+ and compare them to a model. For the initial rovibrational distribution of the stored metastable CH+ molecules, the data indicate a faster vibrational cooling than derived before, and rotational cooling at a rate similar to the X 1Σ+ ground state. New aspects of the spin-forbidden a 3Π-X 1Σ+ radiative decay are discussed. Finally, we predict b 3Σ--a 3Π absorption and a 3Π-X 1Σ+ emission lines through which CH+ in the metastable a 3Π(v=0) state might be detectable in astrophysical environments. [ABSTRACT FROM AUTHOR]

Infrared absorption spectroscopy of few hundred H3+ ions trapped in a 22-pole ion trap is presented using chemical probing as a sensitive detection technique down to the single ion level. By exciting selected overtone transitions of the (v1=0,v2l=31)←(0,00) vibrational band using an external cavity diode laser an accurate diagnostics measurement of the effective translational and rotational temperatures of the trapped ions was performed. The absolute accuracy of the measured transition frequencies was improved by a factor of four compared to previous plasma spectroscopy measurements using velocity modulation [Ventrudo et al., J. Chem. Phys. 100, 6263 (1994)]. The observed buffer gas cooling conditions in the ion trap indicate how to cool trapped H3+ ions into the lowest ortho and para rotational states. Future experiments will utilize such an internally cold ion ensemble for state-selected dissociative recombination experiments at the heavy ion storage ring Test Storage Ring (TSR). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Vibrational relaxation and isomerization of internally excited deuterated formyl and isoformyl cations has been investigated on the time scale of 2 ms to 12 s using the nearly interaction-free environment of an ion storage ring. De-excitation of the v[sub 2] bending modes of DCO[sup +] and DOC[sup +] due to spontaneous radiative transitions was observed as a function of the storage time by measuring their foil-induced Coulomb explosion using three-dimensional coincident fragment imaging. No isomerization of low-lying vibrational levels of DOC[sup +] ions was observed on the time scales considered. By comparing the Coulomb explosion data to molecular bond angle distributions obtained from vibrational wave function calculations, the time evolution of the mean v[sub 2] population is deduced for both isomers. The stored DOC[sup +] ions are found to thermalize with the 300 K black-body radiation, while relaxation of the DCO[sup +] bending vibrations was found to require considerably longer times, in agreement with a predicted very small transition moment of the v[sub 2]=1 level. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Measures the radiative lifetime of the NO[sup +](a[sup 3]Sigma[sup +]) metastable state using an ion trap. Linear ion trap; Measurement of metastable state lifetimes; Effect on the results of the presence of vibrationally excited states with different lifetimes.

Presents a study which investigated the influence of the excitation frequency on the development of the thermal volume instabilities in high frequency discharges within the scope of an analytical discharge model. Information on the field reduction and the time averaged recombination coefficient; Description of the discharge model; Details of eigensolutions and eigenvalues related to the study.

Multichannel scattering calculations are presented for the low-energy collisions of the OH+ cation and He atoms, using an ab initio evaluation of the interaction potential, which had been obtained in earlier work, and a time-independent, multichannel treatment of the quantum dynamics carried out in this study using our in-house scattering code ASPIN. Given the presence of spin-rotation coupling effects, within an essentially electrostatic formulation of the interaction forces with He atoms in the trap, the ensuing propensity rules which control the relative size of the state-changing cross sections and of the corresponding inelastic rates, also computed at the most likely temperatures in an ion trap, are presented and analysed in detail. [ABSTRACT FROM AUTHOR]

Absolute photodetachment cross sections of two anions of astrophysical importance CN– and C3N– were measured to be (1.18 ± (0.03)stat(0.17)sys) × 10–17 cm2 and (1.43 ± (0.14)stat(0.37)sys) × 10–17 cm2, respectively, at the ultraviolet (UV) wavelength of 266 nm (4.66 eV). These relatively large values of the cross sections imply that photodetachment can play a major role in the destruction mechanisms of these anions particularly in photon-dominated regions. We have therefore carried out model calculations using the newly measured cross sections to investigate the abundance of these molecular anions in the cirumstellar envelope of the carbon-rich star IRC+10216. The model predicts the relative importance of the various mechanisms of formation and destruction of these species in different regions of the envelope. UV photodetachment was found to be the major destruction mechanism for both CN– and C3N– anions in those regions of the envelope, where they occur in peak abundance. It was also found that photodetachment plays a crucial role in the degradation of these anions throughout the circumstellar envelope. [ABSTRACT FROM AUTHOR]

Solvents have a profound influence on chemical reactions in solution and have long been used to control their outcome. Such effects are generally considered to be governed by thermodynamics; however, little is known about the steric effects of solvent molecules. Here, we probe the influence of individual solvent molecules on reaction dynamics and present results on the atomistic dynamics of a microsolvated chemical reaction-the fundamentally important nucleophilic substitution reaction. We study the reaction of OH? with CH3I using a technique that combines crossed-beam imaging with a cold source of microsolvated reactants. Our results reveal several distinct reaction mechanisms for different degrees of solvation; surprisingly, the classical co-linear substitution mechanism only dominates the dynamics for mono-solvated reactants. We analyse the relative importance of the different mechanisms using ab initio calculations and show that the steric characteristics are at least as relevant as the energetics in understanding the influence of solvent molecules in such microsolvated reactions. [ABSTRACT FROM AUTHOR]

Absolute photodetachment cross sections have been measured for the hydrocarbon chain anions CnH-, n = 2, 4, and 6, which are relevant for an understanding of molecular clouds in the interstellar medium. Data have been obtained for different photon energies within approximately 1 eV of the detachment threshold. With our recently developed method we have achieved a precision of better than 25% on these absolute cross sections. The experiments have been carried out by means of photodetachment tomography of the mass-selected molecular anions in a multipole radio-frequency ion trap. The measured absolute cross sections are in accordance with the empirical scaling law of Millar et al. and have allowed us to determine its free parameters. These results are important for predicting the photostability and thus the abundance of carbon chain anions in planetary atmospheres, in circumstellar envelopes, and in photon-dominated regions of interstellar molecular clouds. [ABSTRACT FROM AUTHOR]

We investigate the rovibrational population redistribution of polar molecules in the electronic ground state induced by spontaneous emission and blackbody radiation. As a model system we use optically trapped LiCs molecules formed by photoassociation in an ultracold two-species gas. The population dynamics of vibrational and rotational states is modeled using an ab initio electric dipole moment function and experimental potential energy curves. Comparison with the evolution of the v″ = 3 electronic ground state yields good qualitative agreement. The analysis provides important input to assess applications of ultracold LiCs molecules in quantum simulation and ultracold chemistry. [ABSTRACT FROM AUTHOR]

We present spectrally resolved pump-probe experiments on the photoassociation of ultracold rubidium atoms with shaped ultrashort laser pulses. The pump pulse causes a free-bound transition leading to a coherent transient signal of rubidium molecules in the first excited state. In order to achieve a high frequency resolution the bandwidth of the pump pulse is reduced to a few wavenumbers. The frequency dependence of the transient signal close to the D1 atomic resonance is investigated for characteristic pump-probe delay times. The observed spectra, which show a pronounced dip for pump-probe coincidence, are interpreted using quantum dynamical calculations. [ABSTRACT FROM AUTHOR]

We have realized a high-resolution time-of-flight mass spectrometer combined with a magneto-optical trap. The spectrometer enables excellent optical access to the trapped atomic cloud using specifically devised acceleration and deflection electrodes. The ions are extracted along a laser beam axis and deflected onto an off-axis detector. The setup is applied to detect atoms and molecules photoassociated from ultracold atoms. The detection is based on resonance-enhanced multi-photon ionization. Mass resolution up to m/Δmrms=1000 at the mass of 133Cs is achieved. The performance of this spectrometer is demonstrated in the detection of photoassociated ultracold 7Li133Cs molecules near a large signal of 133Cs ions. [ABSTRACT FROM AUTHOR]

Synopsis The in vitro absorption of panthenol into and through the human nail was examined in this study. Panthenol, the alcohol form of pantothenic acid (vitamin B5), is believed to act as a humectant and improve the flexibility and strength of nails. A liquid nail treatment formulated with panthenol (2%) was compared to a solution of panthenol (2%) in water. Fingernail specimens were dosed daily for 7 days with either the nail treatment (non-lacquer film forming) formulation or aqueous solution with sampling performed every 24 h. Panthenol concentrations were determined in the dorsal surface, interior (by drilling and removal) and in the supporting bed under the human nail. Panthenol levels in the dorsal nail ( R2 = 0.87; P < 0.001), nail interior ( R2 = 0.94; P < 0.001) and nail supporting bed ( R2 = 0.79; P < 0.003) showed a significant linear increase with each day of dosing. Significantly more panthenol was delivered into the interior nail and supporting bed by a nail treatment formulation than from an aqueous solution. The film acts not only as a reservoir of panthenol, but also acts to increase the hydration of the nail and the thermodynamic activity of panthenol as well, thereby enhancing diffusion. [ABSTRACT FROM AUTHOR]

Purpose: Crotamiton is a topical drug used in the treatment of scabies and pruritus. We determined its percutaneous absorption following single and multiple dosing in normal skin. Methods: We used in vivo measurement of percutaneous absorption of [ 14 C] crotamiton in a multidose regimen by measuring urinary excretion and liquid scintillation counting in three groups of four healthy volunteers. The Feldmann urinary excretion method was utilized to ascertain percutaneous absorption. Our results showed that tape stripping does not increase percutaneous absorption of crotamiton; upon repeated application. [ABSTRACT FROM AUTHOR]

We present quantitative measurements of the photoassociation of cesium molecules inside a far-detuned optical dipole trap. A model of the trap-depletion dynamics is derived which allows us to extract absolute photoassociation rate coefficients for the initial single-photon photoassociation step from measured trap-loss spectra. The sensitivity of this approach is demonstrated by measuring the Franck-Condon modulation of the weak photoassociation transitions into the low-vibrational levels of the outer well of the Og- state that correlates to the 6s+6p3/2 asymptote. The measurements are compared to theoretical predictions. In a magneto-optical trap, these transitions have previously only been observed indirectly through ionization of ground-state molecules. [ABSTRACT FROM AUTHOR]

Deals with a study which developed a technique for the measurement of dissociative recombination (DR) reaction for selected vibrational states of molecular ions. Rate coefficient for the DR of HD+ for selected vibrational states; Results; Outlook of the study.

An overview is given of the types of lasers dominating the field of laser materials processing. The most prominent lasers in this field are the CO and the Nd: YAG laser. The domain of CO lasers is applications which demand high laser powers (up to 30 kW are available at present), whereas the domain of Nd:YAG lasers is micro-machining applications. In the kilowatt range of laser output power, the two types of lasers are in competition. New diffusion-cooled CO laser systems are capable of output laser powers of several kilowatts, with good beam qualities, while still being quite compact. The output power and beam quality of Nd:YAG lasers has been improved in recent years, so that Nd:YAG lasers are now an alternative to CO lasers even in the kilowatt range. This is especially true for applications that demand optical fibre transmission of the laser beam, which is possible with Nd:YAG laser light but not with the longerwavelength light emitted by CO lasers. The main problem in solid-state lasers such as Nd:YAG is the thermal lensing effect and damage due to thermal stresses. In order to reduce thermal loading, cooling has to be enhanced. Several alternative geometries have been proposed to reduce thermal loading and, by this, thermal lensing effects. There are now slab and tube geometries which allow much higher output powers than the conventionally used laser rods. A very new scheme proposes a thin slab whose cooled side is also used as one of the laser mirrors, so that thermal gradients occur mainly in the direction of the beam propagation and not perpendicular to it, as is the case in the other geometries. As well as CO and Nd:YAG lasers, semiconductor laser diodes are very promising for direct use of the emitted light or as pump sources for Nd:YAG and other solid-state lasers. When packaging together thousands of single laser diodes, output powers of several kilowatts can be realized. Major problems are collimation of the highly divergent laser beams and cooling of the laser diode bars. [ABSTRACT FROM AUTHOR]

The influence of anatomic site on the relationship between total penetration of a molecule and its quantities present in the stratum corneum (SC) 30 min after application was quantified in an in vivo study. For each site, six male volunteers received two symmetrical applications of 1,000 nmol benzoic acid C to an area of 1 cm for 30 min. The first application permitted measurement of total absorption of benzoic acid within 4 days (urinary excretion method), while the second enabled determination of the quantity of benzoic acid in the SC at the end of the application time. Total penetration according to site is: back < arm < chest < thigh < abdomen < forehead, (with the forehead being three times more permeable than the back). Whatever the sites and the origin of the differences observed, the results show that the single measurement of the amounts of a compound present in the SC at 30 min postapplication appears sufficient to predict its total penetration, these two parameters being linearly correlated ( r=0.97, P<0.001). [ABSTRACT FROM AUTHOR]

Human autopsy skin was sliced into three sections; an outer epidermis-rich layer, a middle dermis layer, and an inner dermis and subcutaneous fat layer. Each slice was bathed in lindane solutions over a 50-fold concentration range for 48 h at 37°C. Lindane uptake by the skin was extensive (< 90%) for all concentrations and all skin slices. Equilibrium dialysis with lindane at 37°C for 24 h showed binding affinities by the skin sections to exceed 98%. The binding constants of the outer skin section (epidermis-rich) were higher than those of the middle and inner sections. The binding attraction for lindane by United States Pharmacopeia (USP) human plasma protein fraction (mean 90.5% bound) resulted in its competitive extraction from the skin slices in a three-compartment dialytic procedure. Since the least binding constants were in the middle and inner layers, and since lindane has a preference for plasma over skin, the two (inner skin and plasma) may combine to create the sink conditions necessary for lindane percutaneous absorption into the body. This plus the high epidermis capacity for lindane explains why in some instances (such as occlusion) high levels of lindane can be percutaneously absorbed. [ABSTRACT FROM AUTHOR]

Human autopsy skin was sliced into three sections: an outer epidermis-rich layer, a middle dermis layer, and an inner dermis and subcutaneous fat layer. Each skin slice was bathed in malathion solutions over a 100-fold concentration range of 0.02-3.0 μM/g skin for 48 h at 37° C. Malathion uptake approximated 50% for each skin layer over the total concentration range. Skin capacity for malathion is thus large. Single and double compartment dialysis was used to determine free and bound malathion. Isotherm calculations gave a partition coefficient intercept for epidermis-rich and dermis tissues with aqueous buffer of 2.72 and 2.74, respectively. That of the inner layer of skin was less at 1.70. When malathion was dialyzed against simulated plasma, the binding decreased 2-fold. Since the least partition coefficient (less bound malathion) was in the inner layer of skin, and since malathion has a preference for plasma over water, the two (inner skin and plasma) may combine to create the sink conditions necessary for malathion percutaneous absorption into the body. [ABSTRACT FROM AUTHOR]

The effect of skin delipidization in humans on the percutaneous penetration of hydrocortisone was investigated in a cross-over trial. The delipidizing agent was 1:1:1 trichlorethane, a common industrial organic solvent. The findings do not show any significant difference in the topical absorption of hydrocortisone with and without skin delipidization. It was postulated that the natural skin barrier was reestablished by the metabolic cutaneous lipid regeneration concomitant with the absorption of the fatty ingredients from the cream. [ABSTRACT FROM AUTHOR]

Individual differences exist between patients, and, for topical therapy, differences in skin due to race may be a consideration. Pharmacological response depends upon the percutaneous absorption and the inherent activity of the chemical once absorbed into the biological system. Our objective was to determine the in vivo percutaneous absorption of three test chemicals in human subjects with Asian (A), black (B) and Caucasian (C) ethnic skin. Following a 30 min topical application on the upper outer arm of 1 Μmol/cmC-labeled chemical, percutaneous absorption was determined by both urinary excretion and the stripping technique. Amounts absorbed were: for benzoic acid 1.43 ± 0.27% (SD) (A), 1.07 ± 0.18% (B), 1.2 ± 0.19% (C); for caffeine 1.06 ± 0.17% (A), 1.01 ± 0.19% (B) and 0.96 ± 0.12% (C); for acetylsalicylic acid 1.8 ± 0.31% (A), 1.59 ± 0.31% (B) and 2.12 ± 0.36% (C). No statistical difference ( P>0.05) was found in percutaneous absorption of benzoic acid, caffeine or acetylsalicylic acid between Asian, black and Caucasian subjects. [ABSTRACT FROM AUTHOR]