DEPENDENCE OF THE TRIPLET YIELD ON EXCITATION ENERGY IN ALL-TRANS AND 11-CIS RETINAL*

Abstract. The triplet-triplet absorption of all-trans and 11- cis retinal was measured as a function of the exciting radiation from 423 nm to 365 nm in a glass of 3-methylpentane at 77 K. This experiment was also accomplished with all-trans retinal in hexane at ambient temperature. The relative triplet formation quantum yields of all-trans and 11-cis retinal at 77 K were found to be independent (±10%) of the frequency of the exciting radiation. At room temperature we measured an increase in this relative quantum yield for all- trans retinal from 1.0 at 365 nm to 1.82 at 423 nm [Bensasson et al. (1975) measured an absolute quantum yield of 0.45 at 353 nm]. These results are used to evaluate previous interpretations for photophysical decay processes in all-trans retinal, and previous suggestions for wavelength dependent radiationless transitions are shown to be unacceptable. High energy excitation of 300 K solutions of all- trans retinal produce excited states that result in less efficient intersystem crossing. These states appear to be inaccessible in the 77 K matrices. We suggest that steric restrictions introduced by the retinal matrix interaction at 77 K are able to block this new internal conversion pathway back to the ground state.     

ON THE STATE OF CHROMOPHORE PROTONATION IN RHODOPSIN: IMPLICATION FOR PRIMARY PHOTOCHEMISTRY IN VISUAL PIGMENTS

Resonance Raman multicomponent spectra of bovine rhodopsin, isorhodopsin, and bathorhodopsin are obtained at low temperature. Application of the double beam, 'pump-probe' technique allows an extraction of the rhodopsin and bathorhodopsin spectra in both protonated and deuterated media. Our results show that the Schiff bases of both rhodopsin and bathorhodopsin are fully protonated and the degree of protonation is unaffected by the rhodopsin-bathorhodopsin transformation. Further, the data support the concept or cis-trans isomerization as occurring in this transition. The effect of these results on various models for the primary photochemical event in vision is discussed.     

LOW TEMPERATURE RESONANCE RAMAN STUDY OF THE L INTERMEDIATE OF BACTERIORHODOPSIN

Abstract— Resonance Raman spectra of photostationary state mixtures at — 80°C of bR568, L, L', and M for light-adapted bacteriorhodopsin were obtained. The approximate Raman spectrum of L + L' was obtained by computer, subtracting the known Raman spectra of bR568 and M from the photostationary state spectra. Several new species not previously observed with the bacteriorhodopsin photocycle have been proposed recently. We compare our results to these studies in order to investigate the photoreaction scheme of bacteriorhodopsin.     

Vibrational analyses,vibronic coupling and identification of electronic origins in the lower 1nπ* and 1ππ* states of phenazine and acrid

The spectra of the lowest ¹ nπ2 and ¹ ππ2 singlets of phenazine and acridine were studied in a biphenyl matrix at 2 K. The major findings are: (1) The lowest ππ2 singlets L^a and L^b in phenazine and acridine are clearly located and the vibrational analysis of these states support their assignments. (2) Good evidence is presented that a ¹ nπ2 state is the lowest excited singlet in acridine. The ¹nπ2 origin. The fact that the ¹L^a spectrum of acridine is twenty times broder than the ¹ L^a spectrum of antharacone which is otherwise very similar, is additional evidence that the nπ2 is the lowest excited singlet. (3) Three b^2g and three b^1g out-of-plane modes act as false origins for the long- and short-axis nπ2 spectra of phenazine. (4)Sharp lines in the region of phenazine's second singlet are shown to come from the lower ¹B^3u state and appear to be the same type of vibration interference as described by Wessel. (5) The vibrational analysis of the pure crystal spectra of phenazine published previously has been resigned.     

A possible role for MRI in polyarteritis nodosa: The “creeping fat” sign

We describe a case of polyarteritis nodosa with diffuse abnormalities in subcutaneous fat by magnetic resonance imaging. These abnormalities returned to normal following treatment. Magnetic resonance imaging may have a role in the identification and diagnosis of systemic vasculitis.     

The n-π transitions of the pyrazine molecule: II. Polarized spectrum in benzene crystal,and anharmonicity in the upper singlet state potential function

The polarized absorption spectra of pyrazine (h₄ and d₄) in single benzene crystals have been measured at high resolution at 2 K. Vibrational assignments in the ¹Ag → ¹B_3u (nπ^*) transition have been confirmed and considerably extended. The quartic potential component of hydrogen bending mode :Oa has been found to originate primarily from vibronic coupling with the nearby ¹B_2u (ππ^*). The coupling between in-plane 6a and out-of-plane 10a modes is described theoretically, and leads to further spectral assignments. Other out-of-plane modes 4 and 5 are identified and shown to have combination defects with 6a. A quartic component found for the out-of-plane ring bending mode 4 could not be explained by vibronic coupling.     

Design,Synthesis, and Biological Evaluation of 2‐(4‐Aminophenyl)benzothiazole Analogues as Antiproliferative Agents

A series of 28 novel 2‐(4‐aminophenyl)benzothiazole analogues have been synthesized and characterized using various analytical techniques like ¹H NMR, ¹³C NMR, electrospray ionization mass spectrometry, and IR and bioevaluated for their antiproliferative activity over a group of three human cancer cell lines, namely, lung cancer (A549), cervical cancer (HeLa), and breast cancer (MDA‐MB‐231), using sulforhodamine B assay method. Few synthesized molecules ( 5a , 5c , 5d , 5f , 7b , and 7j ) displayed effective growth inhibition (GI₅₀) activity against the tested human cancer cell lines at lower micromolar concentration (GI₅₀) values in the range 0.2–1.7 μM. Noticeably, compound 7b exhibited reasonable activity in all three cancer cell lines in the GI₅₀ range 0.55–1.2 μM. Further, when 7b was screened for tubulin polymerization inhibition, it exhibited more than 55% inhibition at concentration of 5.0 μM. The molecular docking simulations supported the molecular interactions of the derivatives with the targeted receptor. These derivatives may serve as lead structures for development of potential anticancer drug candidates, and 7b might act as a potential microtubule polymerization inhibitor.     

Synthesis of 3,5-diarylisoxazoles under solvent-free conditions using iodobenzene diacetate

A simple and efficient method has been developed for conversion of chalcone oximes to 3,5-diaryl isoxazoles in excellent yields under solvent-free conditions. The synthesized compounds were characterized by infrared spectroscopy, ^1H NMR, ^13C NMR and HRMS.