Tris solution studies

Dialkyl zinc compounds form phosphine complexes of formula RZnP(SiMe3)2 on addition of one equivalent of bis(trimethylsilyl)phosphine. Solution and solid-state studies showed that the complexes are dimeric or trimeric in solution or the solid state. Bis(trimethylsilyl)phosphido-methylzinc crystallizes as a trimeric molecule with a Zn3P3 core in the twist-boat conformation. Bis(trimethylsilyl)phosphido- -butylzinc, shows a similar central Zn3P3 fragment. The sterically more demanding trimethylsilylmethyl substituent forms a dimeric species of bis(trimethylsilyl) phosphido-trimethylsilylmethylzinc. Solution studies of bis(trimethylsilyl)phosphido- .vo-propyl-zinc demonstrate a temperature-dependent equilibrium of the dimeric and trimeric species and the crystalline state contains a 1 1 mixture of these two oligomers. A monomeric bis(trimethyl-silyl)phosphido-tris(trimethylsilyl)methylzinc has also been synthesized.313... 

Present one or two bioinorganic topics of my choice. I follow the paradigms the reader will note in Chapters 4, 5, and 6 Use the structural information gained through X-ray crystallographic and NMR solution studies to try to understand the metalloprotein s function and mechanism of activity and then design small... 

Solution Studies of Tris(pyrazolyl)methane Complexes. 118... 

The known information regarding the influence of various factors is given below. Most of the investigators have tried to study the effect of one variable at a time, but often minor variations of other variables also occur alongside. For example, variation of viscosity by the use of glycerol solution varies the surface tension by a few dynes per centimeter. 

D. AxeIson We published a paper (g. C. Levy, D. E. Axelson, R. Schwartz and J. Hochmann, J. Am. Chem. Soc., 100, ilO (19T8)) late last year on methacrylates in which we tried to interpret the side chains in terms of the effect of the backbone distribution. The side chain was governed by a combination of the distribution and the multiple internal rotations. The problem we had is that when you get to the end of the chain you still can t account for the frequency dependence. We have not proceeded to the stage of doing dilute solution studies because as you mentioned, there may be an Intermolecular effect with other chains. 

One of the most important phenomena in the polymer solvation is the change in the overall size of the polymer chain upon solvation. In fact at equilibrium the average size of isolated polymer molecules in solution is a function of solvent quality and varies from expanded conformations in good solvents to random walk conformations in poor solvents. This is referred to as collapse transition and was first predicted by Stockmayer [82] more than 45 years ago. The phenomenon was observed by Nishio et al. [83] and Swislow et al. [84] more than 25 years ago and is still a subject of much experimental, computational, and theoretical research today. So far many investigators have tried to study the chain size with solvation using a variety of methods. 

Ni (11) Ga(III) , Ca(II) (Eq. 40). Metal free polymers were produced by treating the poly-CaPc with addic solution On the other side it was shown that metal ions like Cu(II), Zn(II), Fe(n), Ni(II) may be introduced into metal free polymers very slowIy PMDA is a cheaper starting material than TCB. Therefore the structure investigation is of high interest. It was tried to study the structure of the polymers in more detail using the following procedure ... 

Kullberg [74KUL] found it impossible to study the aqueous Cu -SeCN system since a brown precipitate was immediately formed upon addition of selenocyanate ions to a copper(ll) solution. Toropova [56TOR] prepared CuSeCN(s) by adding KSeCN to a solution of copper(l) sulphite or thiosulphate complexes, and tried to study the complex formation by measuring the solubility of CuSeCN in selenocyanate solutions. The experiment failed since the complexes initially formed were found to decompose into elementary selenium and copper(l) cyanide compounds. 

The conformations of l,3,5-trinitrohexahydro-l,3,5-triazine were determined by SCF/4-21G ab initio gradient optimization. The conformation aaa was identified as the most stable, in agreement with gas phase and solution studies of the compound <9lJST(25l)2l9>. Hexahydro-l,3,5-triazines, the parent compound and its derivatives 1,3,5-trisubstituted by Me, Et, Pr, and Bu", were studied by the Allinger MM2 method. l,3,5-Tri-n-butyl-l,3,5-hexahydrotriazine, due to steric bulk, has the aae form as the most stable conformer, but in agreement with experiment the aee form still predominates in the equilibrium mixture <89JST(195)89>. 

The low molecular weight and compact structure of tRNA encouraged crystallographers to try their luck. Indeed, tRNA does crystallize, but in numerous crystalline forms. Also, different tRNA s can cocrystallize or they can crystallize with 5 S RNA. The recent X-ray study by Kim et a/. (22), which is certainly a major step forward, shows an L-shaped cRNA molecule [Fig. 8.10(a)]. This structure, however, does not account for many of the results from solution studies, like the protection of the -T- -C-G loop or of the -C-C-A terminus. Thus, the structure may not necessarily be that of native tRNA. It should not be forgotten that tRNA, in the absence of Mg, assumes an apparently stable form (20), which is biologically inactive. Also there is considerable evidence that aminoacyl-tRNA and peptidyl-tRNA have tertiary structures different from that of uncharged native tRNA. 

The pale blue tris(2,2 -bipyridine)iron(3+) ion [18661-69-3] [Fe(bipy)2], can be obtained by oxidation of [Fe(bipy)2]. It cannot be prepared directiy from iron(III) salts. Addition of 2,2 -bipyridine to aqueous iron(III) chloride solutions precipitates the doubly hydroxy-bridged species [(bipy)2Fe(. t-OH)2Fe(bipy)2]Cl4 [74930-87-3]. [Fe(bipy)2] has an absorption maximum at 610 nm, an absorptivity of 330 (Mem), and a formation constant of 10. In mildly acidic to alkaline aqueous solutions the ion is reduced to the iron(II) complex. [Fe(bipy)2] is frequentiy used in studies of electron-transfer mechanisms. The triperchlorate salt [15388-50-8] is isolated most commonly. 

Relationships connecting stmcture and properties of primary alkylamines of normal stmcture C, -C gin chloroform and other solvents with their ability to extract Rh(III) and Ru(III) HCA from chloride solutions have been studied. The out-sphere mechanism of extraction and composition of extracted associates has been ascertained by UV-VIS-, IR-, and H-NMR spectroscopy, saturation method, and analysis of organic phase. Tertiary alkylamines i.e. tri-n-octylamine, tribenzylamine do not extract Ru(III) and Rh(III) HCA. The decrease of radical volume of tertiary alkylamines by changing of two alkyl radicals to methyl make it possible to diminish steric effects and to use tertiary alkylamines with different radicals such as dimethyl-n-dodecylamine which has not been used previously for the extraction of Rh(III), Ru(III) HCA with localized charge. 

Compounds in which conformational, rather than configurational, equilibria are influenced by the anomeric effect are depicted in entries 4—6. Single-crystal X-ray dilfiaction studies have unambiguously established that all the chlorine atoms of trans, cis, ira j-2,3,5,6-tetrachloro-l,4-dioxane occupy axial sites in the crystal. Each chlorine in die molecule is bonded to an anomeric carbon and is subject to the anomeric effect. Equally striking is the observation that all the substituents of the tri-0-acetyl-/ -D-xylopyranosyl chloride shown in entry 5 are in the axial orientation in solution. Here, no special crystal packing forces can be invoked to rationalize the preferred conformation. The anomeric effect of a single chlorine is sufficient to drive the equilibrium in favor of the conformation that puts the three acetoxy groups in axial positions. 

A very significant recent development in the field of catalytic hydrogenation has been the discovery that certain transition metal coordination complexes catalyze the hydrogenation of olefinic and acetylenic bonds in homogeneous solution.Of these catalysts tris-(triphenylphosphine)-chloror-hodium (131) has been studied most extensively.The mechanism of the deuteration of olefins with this catalyst is indicated by the following scheme (131 -> 135) ... 

Extension of these studies to medium rings produced interesting results (73). The mercuric acetate oxidation of 1-methyl-1-azacyclooctane (64), when worked up in the usual manner, gave no distillable material. When an equivalent amount of hydrochloric acid was added to the solution which had been saturated with hydrogen sulfide to precipitate the excess mercuric acetate and filtered, evaporation of the solution to dryness gave a solid which was subsequently identified as 2,4,6-tris(6 -methylaminohexyl)-trithiane trihydrochloride (65). Two plausible routes to the observed... 

Hydrated forms of the hydroxide ion have been much less well characterized though the monohydrate [H302] has been discovered in the mixed salt Na2[NEt3Me][Cr PhC(S)=N-(0) 3]. NaH302.18H20 which formed when [NEt3Me]I was added to a solution of tris(thiobenzohydroximato)chromate(III) in aqueous NaOH. ° The compound tended to lose water at room temperature but an X-ray study identified the centro-symmetric [HO-H-OH] anion shown in Fig. 14.15. The central O-H-O bond is very short indeed (229 pm) and is... 

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

We set out with the idea that, in the vicinity of each ion in solution there is likely to be a certain amount of electrostriction—a certain shrinkage of the solvent caused by the attraction between the ionic charge and the polar molecules. In order to estimate from experimental data how much shrinkage, if any, has taken place, we must start with a correct idea of what would have been the volume of the solution, if no shrinkage had taken place. In making a comparative study of various solutes, we need a common basis for comparison. Since this is not provided by the volumes of the crystalline solids, we may try a different approach. We may compare the addition of any pair of ions to the solvent with the addition of a pair of solvent molecules. 

A third, and more promising, route is currently under investigation. Bromine oxidation of an aqueous solution of 2-deoxy-D-nbo-hexose gave the hitherto unreported 2-deoxy-D-nbo-hexono-l,4-lactone, which was benzoylated to yield 3,5,6-tri-0-benzoyl-2-deoxy-D-nbo-hexono-l,4-lactone. Studies are in progress to effect a reduction of the benzoylated... 

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