Electric field effects on roto-vibrational transitions of13CD3OH1

We used a Stark-Optoacoustic cell and hybrid waveguide resonators to perform an Infrared and Far Infrared Stark Spectroscopy study on some transitions of¹³CD₃OH. Different behaviours of the transitions in the presence of a d.c. electric field were observed. The Stark splittings of six FIR laser lines ranging from 34 to 136 MHz/kVcm^–1 were determined. The analysis of the behaviour of the IR and FIR transitions in the presence of the external electric fields gives important and exclusive information on the levels involved in the transitions.Work Supported by FAPESP, CNPq, FAEP - Brazil, and CNR - Italy.     

The reactions of some halogenated pyridines with methoxide and methanethiolate ions in dimethylformamide

The reactions of 2,6- and 2,5-dibromopyridines and of 2,3- and 3,5-dichloropyridines with sodium isopropanethiolate and methanethiolate afforded the products of mono- or of bis-substitution depending on the experimental conditions. The same pyridines reacted with sodium methoxide to give good yields of the mono-substituted products; bis-substitution occurred easily only in the case of the 2,6-dibromo- and of the 3,5-dichloropyridine. The syntheses of some methoxy thiomethoxypyridine, starting from the halogeno methoxypyridines or from the halogeno thiomethoxypyhdines are also described. The bis-(alkylthio)pyridines can be fragmented by sodium in HMPA to give the bis(mercapto)pyridines.     

Intermolecular proton transfer in solid phase: a rare example of crystal-to-crystal transformation from hydroxo- to oxo-bridged iron(III) molecule-based magnet

Intermolecular proton transfer in solid phase from the hydroxo bridge to a water molecule occurs in a new mu-hydroxo iron(III) compound of formula {EtNH3[Fe2(ox)2Cl2(mu-OH)].2H2O}n leading to a still crystalline compound in which the mu-oxo bridge replaces the mu-hydroxo one. Both three-dimensional compounds exhibit magnetic ordering at Tc ca. 70 K due to a spin canting.     

Mechanistic studies on the asymmetric alkylation of amino ester enolates using a copper(II)salen catalyst

Hammett data indicate that the asymmetric alkylation of enolates catalysed by copper(II)salen complex 1, proceeds by an asynchronous S(N)2 reaction and that the role of the catalyst is to enhance the nucleophilicity of the enolate.     

Carotenoid triplet states associated with the long-wavelength-emitting chlorophyll forms of photosystem I in isolated thylakoid membranes

The carotenoid triplet populations associated with the long-wavelength-emitting chlorophyll forms of photosystem I (PS I)(dagger) have been investigated in isolated spinach thylakoids by means of fluorescence-detected magnetic resonance in zero field. The spectra collected in the 730-800 nm emission range can be globally fitted assuming the presence of four different carotenoid triplet states coupled to long-wavelength-emitting forms of PS I, having zero-field-splitting parameters /D/ = 0.0359 cm(-1) and /E/ = 0.00371 cm(-1), /D/ = 0.0382 cm(-1) and /E/ = 0.00388 cm(-1), /D/ = 0.0395 cm(-1) and /E/ = 0.00397 cm(-1), and /D/ = 0.0405 cm(-1) and /E/ = 0.00411 cm(-1). On the basis of the triplet-associated fluorescence emission profile, it is suggested that those triplets are associated with light-harvesting complex I, the peripheral antenna complex of PS I.     

Hyperpigmentation induced by topical 5-aminolaevulinic acid plus visible light

Photodynamic therapy (PDT) with 5-aminolaevulinic acid (ALA) is an alternative tool for the treatment of superficial non-melanoma skin cancers. Recently ALA-PDT has been employed with encouraging results also for warts, condylomata and psoriasis. In this study the effects of topical ALA plus irradiation with visible light on intact human skin have been evaluated. Five skin areas (A, B, C, D, and E) on the inner upper part of the arms of five healthy volunteers (skin types III and IV) were treated with (A) ALA 20% in base cream without irradiation, (B) only the vehicle (base cream) without ALA, (C, D and E) ALA cream at the concentrations of 5, 10 and 20%, respectively; all treatments were applied with an occlusive dressing. Four hours after ALA or vehicle application areas B, C, D and E were irradiated with a fixed dose of 40 J/cm(2). ALA penetration through the intact skin was evaluated by in vivo fluorescence determination. The effects on healthy skin were evaluated by clinical and chromometric examinations, light microscopy, immunohistochemistry and electron microscopy. RESULTS: (1) in vivo fluorescence demonstrated that ALA is able to penetrate through the intact skin, when applied with occlusive dressing and induces a classical fluorescence peak due to Protoporphyrin IX (PpIX) formation, which is the active photosensitiser. (2) Skin areas receiving ALA plus irradiation showed erythema and swelling just after the irradiative session and hyperpigmentation 48-72 h later. (3) Colourimetric data confirmed significant skin colour changes: values a* (representing the erythematous changes) increased only on the skin areas where ALA+irradiation were applied and during the 48 h after irradiation, thereafter a* began to decrease; values L* (pigmentation) increased during the 2 weeks following treatment. (4) Histopathological, immunohistochemical (S100, HMB-45) and electron microscopic findings showed an absolute increment of the number of melanocytes, which appeared clearly activated. In conclusion the application of ALA cream followed by irradiation is able to induce a pigmentation response in healthy human skin, at least in skin types III and IV. This melanocytic activation could have a potential for the treatment of skin disorders characterised by hypopigmentation.     

Metal-induced assembling/disassembling of fluorescent naphthalenediimide derivatives signalled by excimer emission

The new quadridentate bischelating ligands 2 and 3 display in solution the typical absorption and emission properties expected for naphthalenediimide derivatives. Spectrophotometric studies show that systems 2 and 3 interact with Zn(II), Cd(II) and Cu(I) in CHCl3 or MeCN according to an apparent 1:1 stoichiometry. Molecular modelling, ESI-MS and 1H NMR experiments indicate that the complex species formed in the presence of stoichiometric amounts of metal ion are nonhelical [2 + 2] adducts. The metal-induced self-assembling process is signalled by an intense excimer-type emission caused by the intramolecular interaction of two naphthalenediimide subunits that face each other in the [2 + 2] adduct, as shown by molecular modelling studies. In the presence of excess metal ion, a disassembling process takes place, leading to a dinuclear complex with a 2:1 metal/ligand stoichiometry, in which the intramolecular excimer is no longer allowed to form because the interaction between the naphthalenediimide subunits has been lost. Thus, the overall metal-induced assembling/disassembling process is signalled by the appearance and disappearance of the excimer band in the emission spectrum.     

Novel chiral three-dimensional iron(III) compound exhibiting magnetic ordering at T(c) = 40 K

The preparation and crystal structure determination of the iron(III) compound of formula [(NH(4))(2)[Fe(2)O(ox)(2)Cl(2)].2H(2)O](n) (1) (ox = oxalate dianion) are reported here. Complex 1 crystallizes in the orthorhombic system, space group Fdd2, with a = 14.956(7) A, b = 23.671(9) A, c = 9.026(4) A, and Z = 8. The structure of complex 1 consists of the chiral anionic three-dimensional network [Fe(2)O(ox)(2)Cl(2)](2-) where the iron(III) ions are connected by single oxo and bisbidentate oxalato groups. The metal-metal separations through these bridging ligands are 3.384(2) and 5.496(2) A, respectively. Ammonium cations and crystallization water molecules are located in the helical pseudohexagonal tunnels defined by iron atoms. The longest iron-iron distance in the pseudohexagonal tunnel is 15.778(2) A whereas the shortest one is 8.734(2) A. The iron atoms are hexacoordinated: a terminal chloro ligand and five oxygen atoms, that of the oxo group and four from two cis coordinated oxalate ligands, build a distorted octahedral environment around the metal atom. The Fe-O(oxo) bond distance [1.825(2) A] is significantly shorter than the Fe(III)-O(ox) [average value 2.103(4) A] and Fe(III)-Cl bond distances [2.314(2) A]. Magnetic susceptibility measurements of 1 in the temperature range 2.0-300 K reveal the occurrence of a susceptibility maximum at 195 K and a transition toward a magnetically ordered state in the lower temperature region with T(c) = 40 K. The strong antiferromagnetic coupling through the oxo bridge (J = -46.4 cm(-1), the Hamiltonian being H = -JS(A).S(B)) accounts for the susceptibility maximum whereas a weak spin canting of approximately 0.3 degrees due to the antisymmetric magnetic exchange within the chiral three-dimensional network is responsible for the magnetic ordering. The values of coercive field (H(c)) and remnant magnetization (M(r)) obtained from the hysteresis loop of 1 at 5 K are 4000 G and 0.016 micro(B).     

New far infrared laser lines from 13CH2F2 and frequency measurements

We report new FIR laser lines from ¹³CH₂F₂ molecules optically pumped by a waveguide CO₂ laser. The increased tunability (300 MHz) with respect to a conventional CO₂ laser allows the pumping of ¹³CH₂F₂ vibrational transitions of large offset. 34 new laser lines have been discovered, ranging from 113.1 m to 491.4 m in wavelength, thus increasing the number of known FIR laser lines from this important molecule to 99. For all the new lines and many (36) of those known previously, precise offset measurements through the transferred Lamb-dip technique were performed. The frequency of six new laser lines was also directly measured by heterodyne detection with known laser lines.     

Acoustooptic extension of the frequency tunability of CW CO2 lasers: New FIR lasers emissions from CH3OH and13CH3OH

We have increased the frequency tunability of our CW waveguide CO₂ lasers by means of an acoustooptic amplitude modulator, operating at the fixed frequency of 90 MHz. The up-shifted, or down-shifted, laser optical sideband can be generated independently by adjusting the orientation of the modulator. The efficiency is larger than 50%. The frequency tunability of the CO₂ laser around each laser line is thus increased by 180 MHz. To demonstrate the possibilities of this method, a source composed of the above modulator and of a CW, 300 MHz tunable waveguide CO₂ laser has been used for the search of new large offset FIR laser lines from optically pumped CH₃OH and¹³CH₃OH molecules. As a result 15 and 10 new large offset laser lines were discovered respectively. New assignments of some laser lines are also proposed. We have also measured the Stark effect, the offset, and the polarization of other already known lines. In particular a Stark effect frequency tuning of about 1 GHz is demonstrated for a laser line at 208.399 m.