Spectroscopic characterization

Despite their sensitivity, electrochemical methods lack the required specificity to allow structural and electronic aspects of adsorbed species on electrode surfaces to be examined. This important complementary information can be obtained by employing spectroscopic techniques in situ, that is, with the electrode immersed in the solution under potential control. As discussed above, the number of species that can be accommodated on surfaces is of the order of only a fraction of a nmol cm 2, posing 

Rather serendipitously, transition metal macrocycles display electronic transitions in the U Vand visible spectral regions with very large cross sections. These conditions do not only lead to increased sensitivity in reflectance measurements in this energy range, but also contribute to enhance Raman signals through electronic resonances. This sub-section addresses salient aspects of in situ spectroscopy as applied to the study of macrocydic modified surfaces of relevance to the electrochemical reduction of dioxygen. 

1 Electronic Properties The spectral properties of solution phase species in 

For these experiments, the excitation wavelength, 7,exc = 532 nm, was close to the energy associated with one of the electronic transitions of Hm in the UV-visible range, a factor that contributes to further enhancements in the SERS due to resonance. Cursory inspection of these data shows marked differences between the spectral features of Hm and its reduced form. In particular, the most prominent SERS peaks found for adsorbed Hm in the range 0.0 E 0.25 V were found to be in very good agreement with those of Hm in powder form using the same excitation 

Since the mechanical properties of the composites are intimately related to the filler structure and especially to the tube surface, techniques able to bring information at a molecular level are required for a further insight into the structure/property correlation. 

Examination of the Raman spectra of EPDM filled with MWNTs, shows that the bands of MWNTs shifts to higher frequencies when carbon nanotubes are incorporated into the elastomeric matrix 

The Raman spectra were recorded in the backscattering geometry on a Labram I (Jobin-Yvon, Horiba Group, France) microspectrometer in conjunction with a confocal microscope. To avoid any thermal photochemical effect, we have used a minimum intensity laser power on sample of 370 pW with the 514.5 nm incident line from an Ar-Kr laser from Spectra Physics. Detection was achieved with an air cooled CCD detector and a 1800 grooves/mm, giving a spectral resolution of 4 cm-1. An acquisition time of 120 s was used for each spectrum. The confocal aperture was adjusted to 200 pm and a 50 X objective of 0.75 numerical aperture was used. 

Thermogravimetric analysis (TGA) is widely used to study the thermal stability of a polymer and to evaluate the effect of adding filler particles on the thermal degradation of the elastomers. 

Thermogravimetric analysis (TGA) was conducted using a TA Instrument (SDT Q600). Samples of weight around 6 and 8 mg were ramped at 10°C/mn from room temperature to 800°C under nitrogen atmosphere with a flow rate of 100 mL/min and a purge time of 20 min. 

The H NMR spectra of the parent heterocycles (cf. Table 7) each consist of two multiplets, of which the one at lower field is assigned to the a-hydrogens. Comparison of the chemical shifts of the vinylic protons of furan, H-2 7.46 and H-3 6.41, with those observed for 4,5-dihydrofuran, H-2 6.31 and H-3 4.95 (66JCS(B)127), indicates that there is ca. 1-1.5 p.p.m. downfield shift attributable to the presence of an aromatic ring current in furan. The same effect is observed for thiophene, H-2 7.35 and H-3 7.13, and 4,5-dihy-drothiophene, H-2 6.17 and H-3 5.63. The similar range of chemical shifts observed for 

Structure of Five-membered Rings with One Heteroatom 

In the case of pyrrole the ring protons are also coupled to the N—H with /i,2 = /i,5 = 2.58 Hz and /1j3 = /1i4 = 2.46Hz, while satellites due to spin-spin coupling between the a-protons and the ring heteroatom are observed for selenophene, /(77Se, H) = 47.5 Hz, and tellurophene, /(125Te, H) = 100.4 Hz 74ACS(B)175). 

Annelation of a benzene ring on to the [b] face of the heterocyclic ring does not have any pronounced effect upon the chemical shifts of the heterocyclic protons (cf. Table 8). The rather unexpected heteroatom sequence for shifts to progressively lower field for both H-2 and H-3 remains NH S 0 Se Te, as for the parent heterocycles. The chemical shift of the indolic N—H is also very solvent dependent and as in pyrrole it is also coupled to the ring protons with /12 = 2.4 Hz and /i,3 = 2.1 Hz. The assignment of the benzenoid protons H-5 and H-6 has caused some confusion in the literature as they have almost 

64JCS981, 65AJC353 65AJC353 66BCJ2316 72BSF3193 72BSF3193 

In vacuum, scanning tunneling spectroscopy (STS) has already opened new possibilities of studying the energy distribution of states at an atomic level. Owing to the necessity of scanning the tip potential over several volts, true spectroscopy has still not 

The bias dependence of STM images originates from the spatial distribution of states at the surface (see Fig. 8). The energy distribution can be derived from STS. It is easy to demonstrate from Eq. (3) that the normalized conductance T = is proportional to (E), the local density of states (LDOS) at the surface of the sample, provided that the tip-to-sample distance s is constant and (E) does not vary. The difficult question of the influence of the tip has been investigated recently. Experimentally, STS is performed by scanning the voltage during Uj while the feedback loop is interrupted hri fly. Measurements must be sufficiently fast to probe a defined site. 

STS can be performed in air, especially on materials unreactive to the surroundings, such as Ti02 [63, 64], Fc203 [63], FeS2 [65] and n-WSe2 [66]. GaAs [67] could also be studied by STS in air after stabilization of the surface with a sulfur treatment (see Sec. 5.2). On WSe2, Fan and Bard [66] combined STS with sample illumination 

At metallic surfaces, STS spectra are generally not as structured as at semiconductors. This probably explains why STS has had much less impact upon metals [69]. STS has nevertheless been successfully attempted on Au(lOO), Au(lll) and Pd(lll) [70-72]. On Au(lll), imaging the surface near the surface state gives a better contrast [73]. On Ni(lOO), islands of NiO were detected by STS [2]. Very nice results have recently been obtained on Al(lll) after adsorption of various species [74]. Hasegawa and Avouris [75] have imaged on reconstructed Au(lll) the standing wave pattern formed by the electron density. Such a phenomenon, observed at steps or around adsorbates, stems from interferences between the incident and the reflected wave functions of electrons in 2-D states on this surface. 

H2-TRP exhibits the porphyrin Soret and the four Q bands at 414, 518, 560, 584, and 642 nm, respectively and the bands of peripheral complexes at 292 (bipy 7t 7T, 356 (MLCT2 Ru (d7r) bipy( r2 )) and 470nm (MLCTl 

The vibronic coupling between the chromophores of ZnTRP has been studied by resonance Raman spectroscopy using six laser lines in the 450-515 nm range, in which there is a superposition of the Soret, Ru (dTr) (p7T )bipy and Ru (dTr) (p7T )pyP charge-transfer transitions. Intense peaks 

H2RU = [MPyP Ru(bpy)2Cl ], H2RU2 = [DPyP Ru(bpy)2Cl)2], H2RU3 = [TriPyP  

1 Divalent Metal-Binding Sites and Their Organization 

MTs cmisist of single polypeptide chains all sharing a high Cys content. These residues are present in Cys-Xaa-Cys and Cys-Xaa-Yaa-Cys motifs, where Xaa and Yaa stand for amino acids other than Cys. Besides these motifs also Cys-Cys and even Cys-Cys-Cys stretches can be found in many MT sequences (Table 1). 

ASDK —ASDk -ASDK kGGEAAEAEAEK KGEEGAKAEAEt PG------KtBdT  

IDFT 11)1 2MIIU 1MMU 2MR(i- IMkli 2MRT/JMRi 

The molar absorptivity of the 250 nm shoulder in Cd-MTs has also been used to estimate the number of cysteine ligands involved in metal binding, considering a molar extinction coefficient per cysteine ligand of about 5-6 000 cm This 

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Figure Bl.22.11. Near-field scanning optical microscopy fluorescence image of oxazine molecules dispersed on a PMMA film surface. Each protuberance in this three-dimensional plot corresponds to the detection of a single molecule, the different intensities of those features being due to different orientations of the molecules. Sub-diffraction resolution, in this case on the order of a fraction of a micron, can be achieved by the near-field scaiming arrangement. Spectroscopic characterization of each molecule is also possible. (Reprinted with pennission from [82]. Copyright 1996 American Chemical Society.)...

The initiation mechanism is well defined because of the recent isolation and spectroscopic characterization of the initial zwitterion from ethyl cyanoacrylate (ECA) and a phosphine [8,9]. Specifically, zwitterion 4 was prepared from the reaction of equimolar amounts of dimethylphenyl phosphine, 5, and ECA, 6,... 

Fig. 6-4. Minimum energy conformations of L-PA and L-phenylalanine-A -methyl-anilide (L-PMA) based on molecular mechanics calculations and UV- and NMR-spectroscopic characterizations. (From Lepisto and Sellergren [25].)...

The first example of a neutral aluminum complex of diazaphosphane, the 1,3,2,4-diazaphosphaluminetidine 50, Eq. (4), has been synthesized by the dehydrogenation reaction between Lewis acid-base adduct H3AI <— NMca and fBuP[N(H)fBu 2 49. The product fBuP(NfBu)2(H)Al [Pg.111]

Figure 5.21 Structure of tazobactam. Reprinted from Biochim. Biophys. Acta, 1547, Bonomo, R. A., Liu, J., Chen, Y., Ng, L., Hujer, A. M. and Anderson, V. E., Inactivation of CMY-2 /3-lactamase by tazobactam initial mass spectroscopic characterization , 196-205, Copyright (2001), with permission from Elsevier Science.

DeNiro, M.J. and Weiner, S. 1988 Chemical, enzymatic and spectroscopic characterization of collagen and other organic fractions in prehistoric bone. Geochimica et Cosmochimica Acta 52 2197-2206. 

Finally, also isolated from D. vulgaris was another homodimeric protein (subunit molecular mass of 27 kDa) named nigerythrin (43). Spectroscopic characterization revealed that this protein is similar to Rr. The function of nigerythrin is also unknown. It should be noted that genes coding for two similar Rr proteins were also found in Arch-aeoglobus fulgidus. 

In addition to routine spectroscopic characterization, transition metal silyls have been examined by a variety of physical methods, principally to determine (1) the definite presence of an Si—M bond, (2) the manner in which such a bond is influenced by other ligands, (3) whether such a bond possesses any w-component, and (4) the trans influence of the silyl ligand. 

X-ray Photoelectron and X-ray Absorption Spectroscopic Characterization of Cobalt Catalysts... 

IR Spectroscopic Characterization of Adsorbed Species and Processes on Surfaces... 

Adsorbed CO layers, bonding and Interactions, 559-61 Adsorbed molecules, vibrational analysis, 392-V03 Adsorbed species and processes on surfaces, IR spectroscopic characterizations, VOV-19 Adsorption... 

Spectroscopic Characterization of Organometallic Centers on Insulator Single Crystal Surfaces ... 

Rigby J, Kondratenkov M (2004) Arene Complexes as Catalysts. 7 181-204 Risse T, Freund H-J (2005) Spectroscopic Characterization of Organometallic Centers on Insulator Single Crystal Surfaces From Metal Carbonyls to Ziegler-Natta Catalysts. 16 117-149... 

A mononuclear gold complex catalyst supported on MgO spectroscopic characterization during ethylene... 

Pireaux, J.J., Chtaib, M., Delrue, J.P., Thiry, P.A., Liehr, M. and Caudino, R. (1984) Electron spectroscopic characterization of oxygen adsorption on gold surfaces I. Substrate impurity effects on molecular oxygen adsorption in ultra high vacuum. Surface Science, 141, 211-220. 

Of the group 14 elements (Si, Ge, Sn and Pb), only tin is known to form a variety of poly(pyrazoIyl)borato alkyl derivatives. For example, the reactions between K[pzTp] and the silicon derivatives Me SiCl4 (n = 1-3) have not given tractable products (115). Similarly, the reaction between K[pzTp] and Me2GeCl2 gives a complex that has been spectroscopically characterized as [pzTp]2GeMe2, but which readily decomposes. 

The products are (220), probably formed by the dimerization of (219), and the 2-alkoxy-l,2-thiaphosphole derivatives (218). Analogues of the latter are obtained with p-toluenethiol and dialkylamines. The compound (217 R=Ph) is more reactive than (217 R Me ) and will react with aniline on addition of triethylamine even at room temperature, from which the formation of (221) was observed by spectroscopic characterization. Even more reactive is cyclohexylamine which furnishes an analogue of (221) without addition of strong base. ... 

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