Molecular Structure of HS

FIGURE 10.18 Humic structures proposed by Stevenson (1994) (a) fulvic acid (b) humic acid. 

FIGURE 10.19 Humic acid structure proposed by (With kind permission from Springer Science+Business Media, Naturwissenschaften, Schulten, H.-R., and M. Schnitzer, 80,1993, 

FIGURE 10.20 The Steelink (a) and TLB (b) monomer structures in the polymeric models of HS. 

FIGURE 10.21 Typical TM-AFM image of isolated Suwannee River humic acid macromolecules adsorbed on mica. Scan size is 600 nm x 600 nm. (Reprinted with permission from Balnois, E. et ah, Environmental Science and Technology 33, no. 21, 3911-3917. Copyright 1999 American Chemical Society.) 

FIGURE 10.23 An illustration, after Clapp et al. (2005) of how components of soil HS associate in aqueous environments in the presence of metal cations to form aggregates. The M labeled spheres represent cations, the dashed lines indicate H bonds and the wide dashed lines represent hydrophobic associations, following Simpson et al. (2002). (Reprinted from Clapp et al.. Chemical Processes in Soils, Soil Science Society of America, Madison, Wl, 2005, with kind permission.) 

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Infrared (IR) spectroscopy and Fourier transform IR (FT-IR) have been very useful in studying the molecular structure of HS from organic amendments and unamended soils, as well as the effects of organic amendment on native soil HS (Senesi et al.,... 

Thus, spin-label methodology can provide useful data for better understanding the structure of HS, independent of an existing consensus regarding molecular structures of HS (Burdon, 2001 Hayes and Clapp, 2001 Piccolo, 2001 MacCarthy, 2001 Sutton and Sposito, 2005). 

Fig. 1. Molecular structure of (ri-Cr>Hs)Re(NO)(PPh3)(CHO) (39). Reprinted with permission from Wong el al. (39).

The presence of acidic functional groups, mostly carboxyl and phenolic OH groups, in the molecular structure of soil HS renders them major players in the acid-base buffering capacity of soils and in the fate, bioavailability, and physico-chemical behavior of macro- and micronutrients, toxic metal ions, and several xenobiotic organic compounds in soil (Ritchie and Perdue, 2003 Senesi and Loffredo, 2005). Consequently, the effects of amendment on the acid-base properties of soil HAs and FAs is a subject of considerable interest. 

Fig. 5. DFT-optimized molecular structure of high-spin (HS) [Mn(taa)]. Two solid arrows mean the longitudinal and transverse electric dipole moment. Spin-density isosurface at 0.005e/a.u.3 is also shown. 

Figure 9. Molecular structure of cation 20 in the salt 20 [CBnH(Br(J. Thermal ellipsoids are drawn at the50% probability level. Important bond ler hs [in picometer] and bond angles [°J Cf-C = 122.1, C -C = 145.2, Si -(J= 198.4, Si -Cf= 194.6 Cf-C-C = 178.8, S Cf-Cf =115.5, Si - C -C =133.0. (Reproduced with permission from reference 36. Copyright 2004, VCH- Wiley.)...

Calculation of molecular size and its distribution of HS, and their characterization Identification of chemical structure of HS... 

The combination of analytical pyrolysis, molecular modeling, and computational chemistry has also been stressed in investigating the structure of HS. It was reported that computational chemistry which allows to draw, construct and optimize in 3D space biomacromolecules, e.g., aquatic and terrestrial humic substances, with precise bond distances, bond angles, torsion angles, nonbonded distances, hydrogen bonds, charges, and chirality is a powerful tool, and molecular visualization and simulation can also be used to further understand the structure and dynamics of humic and dissolved organic matter. 

Figure 5.31. Molecular structures of polymers and schematic diagrams of the LEDs (a) single-layer structure and (b) double-layer structure. PdPhQx = P(5,8-diArQx) (Ar=C Hs).

Reifif et al. have studied the linear two-coordinate HS Fe compound Bis (tris(trimethylsilyl)methyl) Fe with Mossbauer spectroscopy and observed an enormously large effective magnetic field at the Fe° site of 152 T [74]. This is the largest field ever observed in an iron containing material. The molecular structure of the compound is shown in Fig. 2.41 [75]. 

Fig. 2.41 Molecular structure of Bis(tris(trimethylsilyl) methyl)Fe , a rigorously linear two-coordinate compound of Fe in HS state with ideal staggered Dsd symmetry [75]. Fe Mossbauer spectmm of Bis(tris(trimethylsilyl) methyl)Fe , recorded at 4.2 K in zero applied magnetic field [74]. The internal magnetic field derived from the distance between the two outermost resonance lines, S1-S2, is 152 T, the largest field ever observed in an iron compound...

Fig. 3.14. Two views of the molecular structure of (CO)3CoAs3. Reproduced with permission from Foust AS, Foster HS, Dahl LF (1969) J. Am. Chem. Soc. 91 5631...

Figure 22, Proposed molecular arrangement and defect structure of HS-(CH2)n-T3-H on gold (lower panel). The tilt and rotation angles for the alkyl chains are 35° and 45°, respectively. The tilt and rotation angles for the Ts-unit are -14° and 33°, respectively. The top panels show the space-filling models of the crystalline parts of the assembly [168].

The general molecular structure of the PTMG-based ionomers is shown in Scheme 3. The length of the PU HS, which is proportional to the weight fraction of HS, W2, increases in each series of samples, e.g., in the Na series, from MlBONa to MlB5Na. 

The low molecular weight polysulphides have found somewhat greater use. Of general structure HS—R—SH and with molecular weights of approximately 1000 they will react with the epoxy group to cause chain extension but not cross-linking. The normal hardeners must therefore be employed in the usual amounts (Figure 26.20). 

Another example of the shape similarity effect on molecular recognition involves the similarity between the structures of the binding sites. Investigation was made for four reaction systems I-IV each consisting of a 1 1 mixture of thiols HS—X and HS—Y... 

An interesting Mossbauer study has been reported on the dinuclear SCO complex [Fe2 (PMAT)2](BF4)4-DMF (PMAT 4-amino-3,5-bis [(2-pyridylmethyl) amino]methyl -4H-1,2,4-triazole), where thermal ST occurs from [HS-HS] to the stable endproduct [HS-LS] [32]. The molecular structure and magnetic behavior of this complex was reported earlier by Brooker et al. [33, 34] (Fig. 8.15). At ca. 225 K, the complex undergoes a sharp half ST from the HS state, T2, to a state containing 50% HS and 50% LS, Af, isomers. The single-crystal structural analysis... 

Fig. 8.15 Molecular structure and magnetic properties, XmT versus T, of [Fe2 (PMAT)2] (BF4)4-DMF. Only half of the Fe(II) sites undergo thermal SCO from HS to LS (from [33, 34])...

In the MOVB method, we use one Slater determinant with block-localized molecular orbitals to define individual VB configuration, called diabatic state. For example, the reactant state of the Sn2 reaction between HS- and CH3CI is defined as the Lewis bond structure of the substrate CH3CI ... 

High resolution negative resists are needed for masked ion beam lithography (MIBL) and for the fabrication of MIBL masks by E-beam lithography (EBL). The MOTSS copolymer resists were developed to obtain the resolution of fine features that a bilevel resist can best provide. The flexibility afforded by choosing the structure of the HS, the copolymer composition, and the molecular weight allows a resist to be tailored by simple synthesis adjustments to have the particular sensitivity and etch protection which best suits the application. 

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