Ligand tuning

Mak D-O, McBride S, Foskett JK 1998 Inositol 1,4,5-trisphosphate activation of inositol trisphosphate receptor Ca2+ channel by ligand tuning of Ca2+ inhibition. Proc Natl Acad Sci USA 95 15821-15825... 

For all of these bond formations the right choice of catalyst is crucial for success. In other words by ligand tuning all three bond forming reactions can be realized by palladium catalysis. The following account focuses on recent work, since the subject has been already reviewed [1],... 

CAChe WorkSystem Pro, and BioMedCAChe provide the necessary tools to execute tasks involved in in silico compound screening such as docking, ligand tune-up, etc. MOPAC 2002 s MOZYME now allows the execution of semi-empir-ical calculations of large molecules (proteins, polymers, semiconductors, and crystals) in a quick yet accurate fashion. For the scientists that need to work on molecules whose parameters are either not included in MOPAC 2002 or that need to tune-up particular parameters based on ab initio or experimental data, Fujitsu offers its services to customize parameters on contractual basis. 

Kobayashi and co-workers have further extended the work of Dalcanale et al. [40, 41] to achieve selective self-assembly of a homo- or hetero-cavitand cage via metal coordination based on ligand tuning (Fig. 3) [42 -5]. The authors reported a series of tetra(4-pyridyl)-cavitand (6), tetrakis(4-pyridylethynyl)-cavitand (7), and tetrakis(4-cyanophenyl)-cavitand (8) molecules and demonstrated that addition of square-planar Pd(dppp)(OTf)2 complex (9) to cavitand 6-8 in 4 2 ratios respectively resulted in the formation of homo cavitand cages (7)2 Pd(dppp) 21 x+ 8(TfO ) (10)... 

Kobayashi K, Yamada Y, Yamanaka M, Sei Y, Yamaguchi K (2004) Complete selection of a self-assembling homo- or hetero-cavitand cage via metal coordination based on ligand tuning. J Am Chem Soc 126 13896... 

However, these catalysts suffer from the disadvantage that for a given synthetic transformation of interest, A— B, enantioselectivity may well be poor. In principle, it should be possible to apply site-directed mutagenesis [7] in order to increase enantioselectivity to an acceptable level (Fig. 11.1b), similar to ligand tuning in transition metal catalysis (Fig. 11.1a). However, this is not a straightforward process. 

Theoretically, the redox potential of the type 1 Cu(II) could provide the specificity toward a particular reductive substrate in comparison to another. Type 1 copper sites do exhibit a remarkable variability in reduction potential, from 240 mV in nitrite reductase (LaCroix et al., 1996 Suzuki et al., 1994) to >1 V for a noncatalytic type 1 copper in hCp (Machonkin et al., 1998). This variability is certainly due in part to the presence of the methionine ligand found in the four-coordinate type 1 site (as in hCp and AO) that is absent in Lac and FetSp, for example (cf. Figs. 1 and 12). Mutagenesis studies indicate that this ligand tunes ... 

As a result of the high ionic charge to radius ratio of titanium(IV), normal salts of titanium(IV) are difficult to prepare from aqueous solutions these often yield basic, hydrolyzed species. A tris-catechol species, [Ti(cat)3], prepared by Raymond etal. is one exception it is stable in aqueous solution up to pH 12. The catechol ligand is so stabilizing to Ti that the Ti ATi reduction potential is shifted from the value of -1-0.1V cited as the standard potential in acid in Scheme 1 to a value for [Ti(cat)3] of -1.14 V vs. NHE, affording a powerful example of ligand tuning of metal redox potential. 

The system was exploited by employing electronically unsymmetrical bis-(diaryl)phosphinites, giving excess of both enantiomers of naproxen nitrile in excellent yields (91 % S, 95 % R). Ligand tuning in the asymmetric hydrocyanation of vinylarenes is comprehensively surveyed by the same authors [57]. Figure 1 illustrates the tunable sites on a sugar-derived ligand. 

In the presence of less bulky 2e donors, such as H2, O2, ethylene, CO, and CH3CN, the vacant site of 17 could be occupied affording saturated 18e species [53]. However, ligand tuning with replacement of one phosphine of 17 by sterically hindered NHC ligands, such as IMes and SIMes, leads to the formation of a... 

In addition to the ligands-tuned carbonylative activation of aryl chlorides, several other catalyst systems were developed, based on the use of a nanopartical, biphasic system and Lewis acids as well. 

---