Thioglycolic Acid FTIR Spectra on Ag2S Quantum Dots Interfaces

The mechanism features of colloidal quantum dots (QDs) passivation with thioglycolic acid molecules (TGA) for cases of different luminescent properties is considered using FTIR. This problem is considered based on FTIR spectra analysis for various ionic forms of TGA. Experimental TGA molecules FTIR spectra is interpreted, basing on the data on modeling of TGA vibrational modes, realized in the framework of density functional method (DFT /B3LYP/6-31+G(d)) taking into account the vibrations anharmonicity of every functional group. This approach provides a significant improvement in the agreement between the experimental and calculated data. FTIR spectra of Ag 2 S/TGA QDs with exciton and recombination luminescence are differ from each other and B “freeB” TGA molecules. The ν ( S − H ) TGA peak (2559 cm − 1 ) disappears in FTIR spectra of Ag 2 S/TGA QD samples. This fact indicates the interactions between TGA thiol group and dangling bonds of Ag 2 S nanocrystals. Ag 2 S QDs passivation with TGA molecules leads to emergence ν a s (COO − ) (1584 cm − 1 ) and ν s (COO − ) (1387 cm − 1 ) peaks. It indicates TGA adsorption in ionic form. For Ag 2 S/TGA QDs with exciton luminescence we observed (a) significant low-frequency shift of ν s (COO − ) peak from 1388 cm − 1 to 1359 cm − 1 and high-frequency shift of ν a s (COO − ) peak from 1567 cm − 1 to 1581 cm − 1 ; (b) change in the ratio of intensities of ν a s (COO − ) and ν s (COO − ) vibrations. This feature is caused by the change in the symmetry of TGA molecules due to passivation of Ag 2 S quantum dots.For Ag 2 S/TGA QDs with recombination luminescence, the insignificant high-frequency shift of 7–10 cm − 1 for ν a s (COO − ) at 1567 cm − 1 and low-frequency shift of 3–5 cm − 1 for ν s (COO − ) at 1388 cm − 1 , probably caused by the interaction of thiol with Ag 2 S surface is observed. Using FTIR spectra, it was found that IR luminescence photodegradation is also accompanied by changes in the thioglycolic acid molecules, which capped Ag 2 S QDs. In the case of Ag 2 S QDs with exciton luminescence, the degradation process is non-reversible. It is accompanied by TGA photodegradation with the formation of α -thiol-substituted acyl radical (S-CH 2 -CO • ) TGA.

Комбинационное рассеяние света в эвтектическом композите InSb-MnSb

Raman spectra of bulk samples of the InSb-MnSb eutectic composite and their thin films prepared by the flash evaporation method have been studied. In the Raman spectra observed TO and LO modes at frequencies of 179.5 cm-1 and 192.4 cm-1 correspond to InSb compound and also the peaks at frequencies 122 cm-1, 127 cm-1, 167 cm-1, 211 cm-1, 245.5 cm-1 correspond to theoretical data for MnSb as is well known from literature. The TO mode in the Raman spectra for films is shifted toward lower energies (178 cm-1), but the LO mode is higher (196 cm-1). The high-frequency shift of the LO mode in the composite with compared its value for InSb is probably due to the presence of deformation at the matrix-inclusion interface, as well as the contribution by surface phonons scattering.

Femtosecond stimulated Raman spectroscopy of the dark S1 excited state of carotenoid in photosynthetic light harvesting complex.

Vibrational dynamics of the excited state in the light-harvesting complex (LH1) have been investigated by femtosecond stimulated Raman spectroscopy (FSRS). The native and reconstituted LH1 complexes have same dynamics. The ν(1) (C=C stretching) vibrational mode of spirilloxanthin in LH1 shows ultrafast high-frequency shift in the S(1) excited state with a time constant of 0.3 ps. It is assigned to the vibrational relaxation of the S(1) state following the internal conversion from the photoexcited S(2) state.

13C NMR and crystallographic evidence of push-pull effects in furoindolic β-enamino esters

A series of cyclic enamine derivatives, stabilized through conjugation with an electron-attracting CO2Me group at the β-carbon of the enamine system, has been prepared. The influence of substituents at the vinylogous donor NH2 group on 13C chemical shifts has been investigated, and the results analyzed on the basis of resonance and steric effects on the dipolar charge distribution in the molecule. Intramolecular H-bonding was established for the N-methylated enamines 4a and 4b based on the high-frequency shift of the NH proton and its solvent immutability. Several deuterium-induced isotope effects on 13C chemical shift [nΔC(ND)] due to deuteration at the enamine nitrogen have been measured. The crystal structures of the enamine 1b and the N,N-diacetylated enamine 3a, determined by X-ray analyses, show that these compounds, in the solid state, adopt an s-trans disposition around the C-C=O bond, with the carbonyl ester group and the C=C double bond in an almost coplanar conformation. Comparison of bond lengths of 1b and 3a in the crystalline state provides information on changes in the extent of n-π delocalization arising from the nature of the N-substituent.Key words: β-enamino esters, furo[2,3-b]indoles, push-pull effects, 13C NMR, X-ray.

Recombinant two-iron rubredoxin of Pseudomonas oleovorans: overexpression, purification and characterization by optical, CD and 113Cd NMR spectroscopies

The gene (alk G) encoding the two-iron rubredoxin of Pseudomonas oleovorans was amplified from genomic DNA by PCR and subcloned into the expression vector pKK223-3. The vector directed the high-level production of rubredoxin in Escherichia coli. A simple three-step procedure was used to purify recombinant rubredoxin in the 1Fe form. 1Fe-rubredoxin was readily converted to the 2Fe, apoprotein and cadmium forms after precipitation with trichloroacetic acid and resolubilization in the presence or absence of ferrous ammonium sulphate or CdCl2 respectively. Recombinant 1Fe and 2Fe rubredoxins are redox-active and able to transfer electrons from reduced spinach ferredoxin reductase to cytochrome c. The absorption spectrum and dichroic features of the CD spectrum for the cadmium-substituted protein are similar to those reported for cadmium-substituted Desulfovibrio gigas rubredoxin [Henehan, Poutney, Zerbe and Vasak (1993) Protein Sci. 2, 1756-1764]. Difference absorption spectroscopy of cadmium-substituted rubredoxin revealed the presence of four Gaussian-resolved maxima at 207, 228, 241 and 280 nm; the 241 nm band is attributable, from J⊘rgensen's electronegativity theory, to a CysS-CdII charge-transfer excitation. The 113Cd NMR spectrum of the 113Cd-substituted rubredoxin contains two 113Cd resonances with chemical shifts located at 732.3 and 730 p.p.m. The broader linewidth and high frequency shift of the resonance at 730 p.p.m. indicates that the Cd2+ ion is undergoing chemical exchange and, consistent with the difference absorption spectra, is bound less tightly than the Cd2+ ion, giving rise to the chemical shift at 732.3 p.p.m.

Cl NQR Spectra of Some New Iridium Chlorochalcogenide Complexes

The 35C1 NQR spectra of the chlorochalcogenide complexes of iridium (SCl3)2 [IrCl6] 1, (TeCl3)2 [IrCl6] 2, (SeCl3) [IrCl6] 3, [IrCl3(SCl2)2]2 4, (SCl3) [IrCl4(SCl2)2] 5 and [IrCl3(SeCl2)2]2 6 have been studied. The spectra were recorded by pulse spectrometry. They consist of two mul tiplets, widely separated in frequency. The high-frequency multiplet belongs to the chlorine atoms bonded to sulfur, selenium and tellurium, respectively, in the ligand. A high-frequency shift is observed, which is typical for the coordination of the molecules ACl2(A=S, Se) and ACl4(A=S, Se, Te). The low frequencies in the multiplets of 4 and 6 are attributed to additional bonds formed between chalcogen atom and chlorine in the coordination environment of iridium.In the spectral region 18-24 MHz lie the NQR frequencies of 35Cl bonded to iridium. For 2 the frequencies are close to those of [IrCl6]2-, which confirms the Ir oxidation state IV. The unexpectedly high frequencies for IrIII in the case of 4 and 5 are explained by the influence of ACl2 molecules, which are weaker σ-donors than the chloro ligands. This promotes electron density transfer from neighbouring chlorine atoms. The 18 MHz frequency is assigned to the bridge chlorine atoms in dimeric molecule 4. This assignment is confirmed by the positive value of d v/dT = +0,2.

A nitrogen-15 nuclear magnetic resonance study of the tetracycline antibiotics

Natural abundance 15N NMR has been used to study several tetracycline antibiotics in the solid state and in solution. In the solid state, the 15N chemical shifts of the tetracycline free bases are sensitive to the site of protonation in the "A" ring. A high frequency shift of 14 ppm is observed for the keto form of oxytetracycline (N protonated) relative to the enol form of oxytetracycline (O protonated). Comparison of 15N chemical shifts in the solid and solution states indicates for the first time that the structural integrity (site of protonation and hence conformation) of the tetracyclines is maintained in (CD3)2SO solutions. In addition, the solid state 15N CP/MAS NMR spectra are sensitive to subtle conformational changes of the "A" ring amide substituent. Key words: antibiotics, tetracyclines, 15N NMR, molecular structure.

Darstellung und Schwingungsspektren von Alkyl-und Rhodanohydrohexaboraten / Preparation and Vibrational Spectra of Alkyl and Rhodano Hydrohexaborates

Treatment of B6H62- with iodoalkanes and (SCN)2 in organic solvents affords the monosubstituted protonated hexaborates RB6H6-, R = CH3, C2H5< C3H7, C4H9, C8H17 and SCN, respectively. The acidity constants of these weak Brönsted acids range for the alkylated species from 8.8 to 9.6, and for R = SCN the pka value is ~5. From basic solutions the salts Cs2RB6H5 can be precipitated, which show band patterns in the IR and Raman spectra typical for monosubstituted hydrohexaborates. The protonated compounds RB6H6- are distinguished from the corresponding Brönsted bases RB6H52- by a high frequency shift of the BH stretching vibrations in the order of 100 cm-1. For Cs2(SCN)B6H5, S coordination of SCN- is supposed because of the high frequency of νCN: 2144 cm-1.

closo-Halogenohydrohexaborate, IV Protonierung, Deuterierung und Schwingungsspektren von claso-Hexaboraten / closo-Halogenohydrohexaborate, IV Protonation, Deuteration and Vibrational Spectra of closo-Hexaborates

The weak Brönsted acids B6H7- and XB6H6-, X = Cl, Br, I; pka : 7-4,75, are formed by protonation of B6H62- and XB6H52- respectively. The deuteration rates, evaluated from integrated IR band intensities of the BH and BD stretching vibrations, are linearly dependent on the mole fractions of the protonated species, and decrease with increasing degree of halogenation in the series Cl>Br>I. H atoms trans-positioned to halogens are exchanged 100 times more rapidly than the remaining ones. The activation energy for the H/D exchange amounts to 76 ± 1,5 kJ/mol for B6H7-. The lower symmetry of the protonated borates is evident from additional IR and Raman bands. They are distinguished from the corresponding Brönsted bases by a high frequency shift of the BH stretching vibrations in the order of 100 cm-1. Due to the pH dependent equilibrium B6H62-/B6H7- and different solubilities of the tetrabutylammonium salts, the separation of B6H62-/B12H122- mixtures is achievable. In alkaline solutions the very soluble B6H62- is present, whereas (TBA)2B12H12 precipitates quantitatively. By subsequent cautious acidification of the supernatant, insoluble (TBA)B6H7 is obtained.