Single crystals LiGaX 2 (X = S, Se, Te) of optical quality were grown, with transparency ranges at 5 cm -1 absorption level of 0.32-11.6 µm, 0.37-13.2 µm and 0.54-14.2 µm, respectively. The first two, LiGaS 2 and LiGaSe 2 , have a wurtzite-type structure whereas LiGaTe 2 is tetragonal (chalcopyrite lattice). The three refractive indices were measured in the whole transparency ranges of LiGaS 2 and LiGaSe 2 and n a and n c were found to be very close (quasi-uniaxial optical anisotropy) with a crosspoint at 6.5 µm (LiGaS 2 ) and 8 µm (LiGaSe 2 ). Sellmeier equations were fitted and phase-matching conditions for second harmonic generation (SHG) were calculated: the 1.467-11.72 µm spectral range for the fundamental is covered by LiGaS 2 and LiGaSe 2 .

Vello tõugu 1 & peep palumaa 1* it has been reported that cu(ii) ions in human blood are bound mainly to serum albumin (HSA), ceruloplasmin (CP), alpha-2-macroglobulin (α2M) and His, however, data for α2M are very limited and the thermodynamics and kinetics of the copper distribution are not known. We have applied a new LC-ICP MS-based approach for direct determination of Cu(II)-binding affinities of HSA, CP and α2M in the presence of competing Cu(II)-binding reference ligands including His. The ligands affected both the rate of metal release from Cu•HSA complex and the value of K D. Slow release and K D = 0.90 pM was observed with nitrilotriacetic acid (NTA), whereas His showed fast release and substantially lower K D = 34.7 fM (50 mM HEPES, 50 mM NaCl, pH 7.4), which was explained with formation of ternary His•cu•HSA complex. High mM concentrations of EDTA were not able to elicit metal release from metallated CP at pH 7.4 and therefore it was impossible to determine the K D value for CP. In contrast to earlier inconclusive evidence, we show that α2M does not bind Cu(II) ions. In the human blood serum ~75% of Cu(II) ions are in a nonexchangeable manner bound to CP and the rest exchangeable copper is in an equilibrium between HSA (~25%) and Cu(II)-His-Xaa ternary complexes (~0.2%).

A spectroscopic study of a variety of covalently linked thioxanthone(TX)−linker−2-(2-nitrophenyl)propoxycarbonyl(NPPOC)−substrate conjugates is presented. Herein, the TX chromophore functions as an intramolecular sensitizer to the NPPOC moiety, a photolabile protecting group used in photolithographic DNA chip synthesis. The rate of electronic energy transfer between TX and NPPOC was quantified by means of stationary fluorescence as well as nanosecond and femtosecond time-resolved laser spectroscopy. A dual mechanism of triplet−triplet energy transfer has been observed comprising a slower mechanism involving the T1(ππ*) state of TX with linker-length-dependent time constants longer than 20 ns and a fast mechanism with linker-length-dependent time constants shorter than 3 ns. Evidence is provided that the latter mechanism is due to energy transfer from the T2(nπ*) state which is in fast equilibrium with the fluorescent S1(ππ*) state. In the case of direct linkage between the aromatic rings of TX and NPPOC, the spectroscopic properties are indicative of one united chromophore which, however, still shows the typical NPPOC cleavage reaction triggered by intramolecular hydrogen atom transfer to the nitro group.

Insulin, a 51-residue peptide hormone, is an intrinsically amyloidogenic peptide, forming amyloid fibrils in vitro. In the secretory granules, insulin is densely packed together with Zn(II) into crystals of Zn(2)Insulin(6) hexamer, which assures osmotic stability of vesicles and prevents fibrillation of the peptide. However, after release from the pancreatic beta-cells, insulin dissociates into active monomers, which tend to fibrillize not only at acidic, but also at physiological, pH values. The effect of co-secreted Zn(II) ions on the fibrillation of monomeric insulin is unknown, however, it might prevent insulin fibrillation. We showed that Zn(II) inhibits fibrillation of monomeric insulin at physiological pH values by forming a soluble Zn(II)-insulin complex. The inhibitory effect of Zn(II) ions is very strong at pH 7.3 (IC(50)=3.5 microM), whereas at pH 5.5 it progressively weakens, pointing towards participation of the histidine residue(s) in complex formation. The results obtained indicate that Zn(II) ions might suppress fibrillation of insulin at its release sites and in circulation. It is hypothesized that misfolded oligomeric intermediates occurring in the insulin fibrillation pathway, especially in zinc-deficient conditions, might induce autoantibodies against insulin, which leads to beta-cell damage and autoimmune Type 1 diabetes.

Oligomers are commonly observed intermediates at the initial stages of amyloid fibril formation. They are toxic to neurons and cause decrease in neural transmission and long-term potentiation. We describe an in vitro study of the initial steps in amyloid fibril formation by human stefin B, which proved to be a good model system. Due to relative stability of the initial oligomers of stefin B, electrospray ionization mass spectrometry (ESI MS) could be applied in addition to size exclusion chromatography (SEC). These two techniques enabled us to separate and detect distinguished oligomers from the monomers: dimers, trimers, tetramers, up to decamers. The amyloid fibril formation process was followed at different pH and temperatures, including such conditions where the process was slow enough to detect the initial oligomeric species at the very beginning of the lag phase and those at the end of the lag phase. Taking into account the results of the lower-order oligomers transformations early in the process, we were able to propose an improved model for the stefin B fibril formation.