Mark B. Masthay

A theoretical investigation of the one‐ and two‐photon properties of porphyrins

The one‐ and two‐photon properties of free base porphin, free base porphin dianion, and the 2,4‐substituted diformyl and divinyl analogs of these molecules are studied using a semiempirical SCF‐MO formalism (CNDO‐π‐SCF‐MO‐PSDCI) including extensive single and double configuration interaction. Strongly two‐photon allowed states are predicted to lie in the Soret region as well as in the region between the Soret and visible bands. A number of the two‐photon allowed states in the Soret region are predicted to have two‐photon absorptivities exceeding 100×10−50 cm4 s molecule−1 photon−1. The calculations indicate that the visible (Q) states are well characterized by the four orbital model, whereas the Soret (B) states contain significant contributions from configurations comprised of other orbitals. The inclusion of extensive double configuration interaction significantly reduces the Soret‐visible (B–Q) splitting, increases the Qx–Qy splitting, and yields calculated oscillator strengths for the Q bands in bette...

Nonlinear Optical Properties of Bacteriorhodopsin: Assignment of Second Order Hyperpolarizabilities of Randomly Oriented Systems Using Two-Photon Spectroscopy

Abstract We demonstrate that the second order hyperpolarizability of a randomly oriented molecule can be determined directly from two-photon spectroscopic measurements on the low-lying excited state manifold. Equations are derived which allow not only a determination of β, but also a determination of the error associated with the numerical method. We apply our two-photon technique to an analysis of the second order hyperpolarizability of light adapted bacteriorhodopsin. Our analysis of this protein in D2O at ambient temperature yields a value of β (= βxxx + (1/3)[βxyy + 2βyyx + βxzz + 2βzzx]) of (2250 ± 240) × 10−30 cm5/esu for a laser wavelength of 1.06μ (Nd:YAG fundamental). The large second-order nonlinear properties of bacteriorhodopsin are due primarily to the large change in dipole moment associated with excitation into the lowest-lying strongly allowed “1Bu +” π, π* state (Δμ = 13.5 ± 0.8 D). We derive an equation which estimates Ωβδ, the ratio of the number of second harmonic photons generated by ...

Human exposure to selamectin from dogs treated with revolution: methodological consideration for selamectin isolation.

This study was undertaken to determine selamectin residue in dogs blood and in gloves worn while petting dogs after Revolution™ application. Revolution™ contains the active ingredient selamectin (a semisynthetic avermectin), which controls endoparasites and ectoparasites, including adult fleas, flea eggs, ticks, heartworms, ear mites, and sarcoptic mange in dogs, for 30 days. Revolution™ was applied topically on a group of six adult house hold dogs (240 mg selamectin/dog). The gloves worn for 5 min while petting the dogs were collected in glass jars and the blood samples (5 mL/dog) were collected in EDTA tubes at 0 h, 24 h, and 72 h, and at 1, 2, 3, 4, and 5 weeks post-Revolution™ application for selamectin residue determination. At no time during the study did the dogs show any signs of toxicity, weight loss, or change in body temperature. Extracts of the blood and the gloves were analyzed for selamectin residue using RP-HPLC coupled with a UV detector (246 nm). Selamectin standard used for peak identification and quantitation was purified from Revolution™. Selamectin residue was detected in the blood (10.26 ± 1.06 ng/mL) only at 72 h post-Revolution™ application, probably due to its poor dermal absorption and rapid elimination from the circulation. In the glove extracts, the highest concentration of selamectin (518.90 ± 66.80 ppm) was detected 24 h after Revolution™ application. Transferable residue of selamectin in gloves from dogs coat was detected at a lesser magnitude after 1 week of Revolution™ application, and that was followed by a further descending trend during the second, third, and fourth weeks. No selamectin residue was detected in the glove extracts after the fifth week. In spite of selamectins binding to the sebaceous glands of the skin, gloves contained significant transferable residue. Thus, these findings suggest that repeated exposure to selamectin can pose potential health risks, especially to veterinarians, veterinary technologists, dog trainers/handlers, and pet owners.

Color Changes Induced by Pigment Granule Aggregation in Chromatophores: A Quantitative Model Based on Beer's Law

Abstract— A model is presented that quantitatively relates changes in the Beers Law absorbance of light‐absorbing chromatophores (melanophores, erythrophores and xanthophores) of cephalopods to changes in the extent of pigment granule aggregation in these cells. Assuming a circular chromatophore of uniform thickness is initially in its dispersed state, and using a pigment granule aggregation index (PGAI) that specifies the extent of pigment granule aggregation, we find that for a given PGAI, the increase in the photon flux through the chromatophore induced by pigment granule aggregation is directly proportional to the dispersed state absorbance. That is, for a given PGAI, darkly colored chromatophores experience greater clearing responses than weakly colored chromatophores. Color changes are also found to be induced as effectively by a small number of large chromatophores or a large number of small chromatophores provided the total skin surface area covered by pigment in the dispersed states are equivalent in the two cases. These results are related to the morphologies and pigment aggregation behaviors of melanophores, erythrophores and xanthophores, based on the light absorption properties of the melanin, pteridine and carotenoid pigments found in these cells. The relative utility and limitations of this model for studying cephalopod (nonden‐dritic) and vertebrate (dendritic) chromatophores are also discussed.

Effects of mono- versus di-substitution of conjugating groups on the electronic structure of porphyrins

Abstract Mono- and adjacent-pyrrole disubstituted porphin dianions (substituents either formyl or vinyl groups) are examined with a semi-empirical SCF MO formalism (CNDO π SCF PSDCI) which includes extensive single and double CI. Calculations predict that the presence of the second conjugating group on an adjacent pyrrole ring enhances the asymmetry introduced by the first group and that the magnitude and orientation of the transition-dipole moments are strongly dependent on the substituent groups.

Nonlinear Optical Properties of Bacteriorhodopsin: Assignment of the Third-order Polarizability Based on Two-Photon Absorption Spectroscopy.

The third-order (pi) -electron polarizability, (gamma) (pi), of bacteriorhodopsin in the 0.0 - 1.2 eV optical region is assigned based on an analysis of the experimental two-photon properties of the low-lying singlet state manifold. The following selected values of (gamma) (pi) (units of 10-36 esu) are observed: (gamma) (0;0,0,0) equals 2482 +/- 327; (gamma) (-3(omega) ;(omega) ,(omega) ,(omega) ) equals 2976 +/- 385 ((omega) equals 0.25 eV), 5867 +/- 704 ((omega) = 0.5 eV), 14863 +/- 1614 ((omega) = 0.66 eV), 15817 +/- 2314 ((omega) equals 1.0 eV), 10755 +/- 1733 ((omega) equals 1.17 eV). The third-order polarizability of this protein which contains an all-trans retinyl protonated Schiff base chromophore with six double bonds, is comparable to that observed for much longer chain polyenes (for example, dodecapreno (beta) -carotene, a polyene with 19 double bonds, exhibits a third-order (pi) -electron polarizability at 0.66 eV of 17000 +/- 6000 X 10-36 esu. The authors attribute the enhanced third-order nonlinearity associated with the protein bound chromophore of bacteriorhodopsin to two mutually enhancing origins. First, the chromophore is protonated, and the resultant charge reorganization enhances the polarizability in a fashion that is similar to that known to occur for polaronic and bipolaronic chromophores. It is estimated that protonation generates a five-fold enhancement in (gamma) (pi). Second, the protein bound chromophore exhibits a large change in dipole moment upon excitation into the lowest-lying, strongly-allowed 1B*u+-like state ((Delta) (mu) = 13.5 D). The latter property is responsible for a Type III enhancement of the third-order polarizability, and yields at least a 20-fold increase in (gamma) (pi).

Origins Of The Quantum Efficiency Duality In The Primary Photochemical Event Of Bacteriorhodopsin

Experimental and theoretical evidence is presented which suggests that two distinct forms of light-adapted bacteriorhodopsin may exist. We propose that these two forms have characteristic photocycles with significantly different primary quantum yields. INDO-PSDCI molecular orbital procedures and semiempirical molecular dynamics simulations predict that one ground state geometry of bR undergoes photochemistry with a primary quantum yield, Φ1, of ~ 0.27, and that a second ground state geometry, with a slightly displaced counterion, yields Φ1 ~ 0.74. This theoretical model is supported by the observation that literature measurements of Φ1 tend to fall into one of two categories- those that observe Φ1 ~ 0.33 or below, and those that observe Φ1 ~ 0.6 or above. The observation that all photostationary state measurements of the primary quantum yield give values near 0.3, and all direct measurements of the quantum yield result in values near 0.6, suggests that photochemical back reactions may select the bacteriorhodopsin conformation with the lower quantum yield. The two photocycles may have developed as a natural biological requirement that the bacterium have the capacity to adjust the efficiency of the photocycle in relation to the intensity of light and/or membrane electrochemical gradient