One-step synthesis of ball-shaped metal complexes with a main absorption band in the near-IR region

The design of near-IR materials is highly relevant to energy and pharmaceutical sciences due to the high proportion of near-IR irradiation in the solar spectrum and the high penetration of near-IR light in biological samples. Here, we show the one-step synthesis of hexacoordinated ruthenium and iron complexes that exhibit a main absorption band in the near-IR region. For that purpose, novel tridentate ligands were prepared by condensation of two diimines and four cyanoaryl derivatives in the presence of ruthenium and iron template ions. This method was applied to a wide variety of cyanoaryl, diimine, and metal ion combinations. The relationship between the structure and the optical and electrochemical properties in the resulting complexes was examined, and the results demonstrated that these compounds represent novel near-IR materials whose physical properties can be controlled based on rational design guidelines. The intense absorption bands in the 700–900 nm region were assigned to metal-to-ligand charge transfer (MLCT) transitions, which should allow applications in materials with triplet excited states under irradiation with near-IR light.

Molecular Optical Switches Based on [Ru(OAC)(2MQN)2NO](H2MQN=2-methyl-8-quinolinol)

Reversible photoisomerization between the cis and trans isomer of [Ru(OAc)(2mqn)2NO] (H2mqn=2-methyl-8-quinolinol) was studied quantitatively, using 1H Nuclear magnetic resonance (NMR) spectra. The kinetic study showed that the photoisomerization from trans to cis isomer was first-order and the rate constant (k) is 0.014 (min-1) at 420 nm, 0.0034 (min-1) at 550 nm, respectively. The main absorption band in UV-Vis region for cis and trans isomer was observed from 300 nm to 550 nm, the electronic structure of these compounds was performed with DFT (Density functional theory) calculation and was discussed based on HOMO–LUMO analyses. The study provide detail information to design advance optoelectronic materials based on nitrosylruthenium(II) complexes.

Excitation spectra of the triplet states of some model lignin compounds

The triplet state excitation spectra of a number of model lignin compounds have been determined by measurements of the electron spin resonance signals associated with their triplet states in low-temperature glasses at 110 K. The optimum wavelengths for excitation of these triplet states were found to be in the tail of the main absorption band at 320-340 nm. It is postulated that excitation in the main band is inefficient in producing triplet states because of an alternative pathway for energy degradation.

Visual Pigments of Goldfish Cones

Freshly isolated retinal photoreceptors of goldfish were studied microspectrophotometrically. Absolute absorptance spectra obtained from dark-adapted cone outer segments reaffirm the existence of three spectrally distinct cone types with absorption maxima at 455 ± 3,530 ± 3, and 625 ± 5 nm. These types were found often recognizable by gross cellular morphology. Side-illuminated cone outer segments were dichroic. The measured dichroic ratio for the main absorption band of each type was 2–3:1. Rapidly bleached cells revealed spectral and dichroic transitions in regions near 400–410, 435–455, and 350–360 nm. These photoproducts decay about fivefold as fast as the intermediates in frog rods. The spectral maxima of photoproducts, combined with other evidence, indicate that retinene2 is the chromophore of all three cone pigments. The average specific optical density for goldfish cone outer segments was found to be 0.0124 ± 0.0015/µm. The spectra of the blue-, and green-absorbing cones appeared to match porphyropsin standards with half-band width Δν = 4,832 ± 100 cm–1. The red-absorbing spectrum was found narrower, having Δν = 3,625 ± 100 cm–1. The results are consistent with the notion that visual pigment concentration within the outer segments is about the same for frog rods and goldfish cones, but that the blue-, and green-absorbing pigments possess molar extinctions of 30,000 liter/mol cm. The red-absorbing pigment was found to have extinction of 40,000 liter/mol cm, assuming invariance of oscillator strength among the three cone spectra.

GEOMETRICAL ISOMERS OF RETINENE

Five crystalline retinenes have been isolated, which have every appearance of being cis-trans isomers of one another. They are all-trans retinene; three apparently mono-cis isomers: neoretinenes a and b and isoretinene a; and isoretinene b, an apparently di-cis isomer. The absorption spectra of these substances display the relations expected of cis-trans isomers. The main absorption band is displaced 5.5 to 7 mµ toward shorter wave lengths for each presumptive cis linkage. Some of the presumptive cis isomers also display a cis peak at 255 to 260 mµ. All five substances yield an identical blue product on mixing with antimony chloride. All of them are converted by light to what appears to be an identical mixture of stereoisomers. Heat isomerizes them very slowly; only neoretinene b exhibits large changes on heating at 70°C. for 3 hours. The various isomers have been extensively interconverted by gentle procedures, and all of them have been converted to all-trans retinene. The present theory of cis-trans isomerism in carotenoids predicts the existence of four stable isomers of retinene. Instead we seem to have five—specifically three mono-cis forms where two are expected. There is no doubt that all these substances are closely related isomers of one another. The only point in question is whether they differ in part by something other than cis-trans configuration. One possibility, as yet little supported by evidence, is that isomerization between ß- and α-ionone rings may be involved. If, however, as seems more likely, all these substances are geometrical isomers of one another, some modification is needed in the present theory of configurational relationships in this class of compounds.

GALLOXANTHIN, A CAROTENOID FROM THE CHICKEN RETINA

A new carotenoid has been isolated from the chicken retina for which the name galloxanthin is proposed. This substance has the properties of a hydroxy carotenoid or xanthophyll. It has not yet been crystallized. On a chromatogram of calcium carbonate it is adsorbed just below astaxanthin and above lutein. The absorption spectrum of galloxanthin lies in a region where natural carotenoids have not ordinarily been found. Its main, central absorption band falls at about 400 mµ. The position of its spectrum suggests a conjugated system of eight double bonds. This relatively short polyene structure must be reconciled with very strong adsorption affinities. With antimony trichloride, galloxanthin yields a deep blue product, possessing a main absorption band at 785 to 795 mµ, and a secondary maximum at about 710 mµ which may not be due to galloxanthin itself. Galloxanthin appears to be one of the carotenoid filter pigments associated with cone vision in the chicken. It may act as an auxiliary to the other filter pigments in differentiating colors; or its primary function may be to exclude violet and near ultraviolet radiations for which the eye has a large chromatic aberration.

SPECTROSCOPY OF CATALASE

Catalase is resistant to oxidizing agents; e.g., ferricyanide. It is also resistant to reducing agents; e.g., catalytically activated hydrogen, hydrosulfite, ferrotartrate, cysteine. The hemin group of the enzyme will combine with cyanide, sulfides, nitric oxide, fluoride. It will not combine with carbon monoxide. Catalase is therefore a ferric complex. The stability of the ferric iron in the enzyme toward reducing agents is not due to the structure of the porphyrin with which it is combined. This porphyrin is the protoporphyrin of the blood pigment. In combination with globin (methemoglobin) the ferric iron is readily reduced by the same reagents which have no effect on catalase. The stability of the ferric iron in the enzyme is therefore due to the protein component. It may be that the type of hematin-protein linkage in catalase is the reason for this phenomenon. The suggestion of Bersin (31), that sulfur may participate in this linkage, is interesting but, as yet, has no experimental basis. Hydrazine or pyridine and hydrosulfite convert catalase into hemochromogens containing ferrous iron. But in these hemochromogens the hematin is no longer attached to the protein. This has been replaced by the nitrogenous bases hydrazine and pyridine. Both hemochromogens combine reversibly with carbon monoxide. Photo-dissociation has only been demonstrated in the case of the pyridine hemochromogen. The positions of the absorption bands of catalase and its derivatives are listed in Table II. The main absorption band (Soret's band) of hemin complexes with nitrogenous substances (nitrogen bases, proteins) is situated at the border between the visible and the ultraviolet region of the spectrum. It has now been found that the spectrum of purified liver catalase has a well defined maximum of high extinction in this range, at 409 mµ. This is further evidence for the hemin nature of the enzyme.