Substitution, degree

The sufficient selectivity to a principal component is the most important condition determining the possibility of ion-selective electrodes (ISEs) practical appliances. In this work, the relationship between the potentiometric selectivity of alkylammonium-selective electrodes and factors such as the nature of plasticizer, ion-exchanger and substitution degree of cationic nitrogen atoms of the principal and foreign ions, is discussed. 

It has been found that the influence of the membrane composition on the ISE selectivity is mainly governed by substitution degree of the nitrogen atom, but virtually does not depend upon the length of hydrocarbon substituents. The key factor in the selectivity of DBP-plasticized membranes with both kinds of ion-exchangers and of the o-NPOE-TNOBS-membrane is the ionic... 

Hydrazine is hardiy stabie (see on p.166). Stabiiity increases with the substitution degree and the hydrocarbon group size. The tabie beiow iiiustrates this typicai property. 

Permeability is also as reported in Barrier, one Barrier being equal to 1X10 1°P. It can be seen from Table I that no change either in permeability for C02 or C02/CH4 selectivity was obtained when the degree of bromination for PPO is low (6.5 mole%). However, at higher levels of bromination, there were increases in both permeability for C02 and C02/CH4 selectivity. The maximum effects (an increase of 2.47 times for C02 permeability and 1.45 times for C02/CH4 selectivity to that of PPO) were reached at 100% substitution degree of the aromatic ring. 

Chemical modifications of PPO by electrophilic substitution of the aromatic backbone provided a variety of new structures with improved gas permeation characteristics. It was found that the substitution degree, main chain rigidity, the bulkiness and flexibility of the side chains and the polarity of the side chains are major parameters controlling the gas permeation properties of the polymer membrane. The broad range of solvents available for the modified structures enhances the possibility of facile preparation of PPO based membrane systems for use in gas separations. 

DSm = substitution degree in mole, or molar fraction of B units 2 in the copolymer... 

The limiting molar substitution degree (DSm obtained for [RCH2Li] /[ester]Q=3 and reaction time = 20 hours) depends on the RCH2Li / polymer or model system as shown in table 2. 

Table 2 - Limiting molar substitution degree for various RCH2Li /...

We thus elucidated that three of the four cellulase components are endo- or random-type and the other is exo-type. However, it is difficult to distinguish between the components of least or lowest random-type and those of exo-type. It is rather easy to identify an endo-type cellulase component. In contrast, it is very difficult to determine a cellulase to be exo-type because if the enzyme has a glycosyl-transferring activity the hydrolysis product is not a single sort, which is one of the necessary conditions to be an exo-type. Based on our experiments, measurement of the time course of CMC using a sample of medium substitution degree seems to be the best method of diagnosis to determine a cellulase component to be endo- or exo-type. With some enzymes, direction of mutarotation of reaction products is useful to resolve this problem, as is illustrated by the classic example of the starch hydrolysis by a- and /3-amylases. If this is true for our cellulases, the mutarotation of reaction products would be a... 

The second shell substitution effect (SSSE) is operative when the reactivity of a group depends not only on the substitution degree of the unit it belongs to, but on the substitution degree of all units that are first neighbors to that unit. Unless stated otherwise, we shall assume for simplicity that all the unreacted groups of a unit have an equal chance of reacting. 

Furthermore, we can assume that the contributions to the activation energy of reaction from the substitution degree of reacting units are additive. Thus, the activation energy for the reaction between i substituted unit A and j substituted unit B (z,j=0,l) is... 

For simplicity, we start with a single tri-functional monomer RA3, the functional groups of which react with each other with the first shell substitution effect. It is now convenient to write down six types of reactions [44], one for each pair of reacting units of substitution degree 0,1, and 2. They are presented in Table 6 together with the appropriate rate constants. Similarly as in previous sec-... 

An interesting new model is provided by Eq. (97) with Kr= 1 for all r. In the limit off—> 00 it becomes the RAC model, fully equivalent to that described by Eq. (3) with Kij=ij. At bounded/it describes the evolution of/-trees, i.e., a process similar to that dealt with by Erdos and Renyi [20, 34], but with substitution degree restriction imposed on the vertices (units) and cycle formation disallowed. 

Zia, V., Rajewski, R., Bomancini, E. R., Luna, E. A., and Stella, V. J. (1997), Effect of alkyl chain length and substitution degree on the complexation of sulfoalkyl ether P-cyclodex-trins with steroids,/. Pharm. Sci., 86, 220-224. 

Liu,FY.,Kildsig,D. O., and Mitra,A. K. (1992),Complexation of 6-acyl-O-P-cyclodextrin derivatives with steroids, effects of chain length and substitution degree, Drug Del. Ind. Pharm., 18,1599-1612. 

The azo-polysiloxanes were obtained in a two-step reaction, starting from a polysiloxane containing chlorobenzyl groups iu the side-chaiu. Iu the first step, the polysiloxane was modified [21] with 4-hydroxyazobenzene (50-75% substitution degree) and, in the second one, the uiueacted chlorobenzyl groups were substituted with nucleobases or douor/acceptor groups. 

In the second step (Scheme 1), 0.5 g azo-polysiloxane was dissolved in 7ml DMSO under stirring the necessary quantity of nucleobase (as a function of the imposed substitution degree) and -0.1 g K COj were added and then the reaction mixture was heated 9 h at 55°C (under nitrogen atmosphere). The polymer was precipitated in methanol and washed 3 times with methanol to eliminate the unreacted products and dried under vacuum. In the case of donor/acceptor groups, 0.5 g azo-polysiloxane was dissolved in 7 ml DMSO under stirring the necessary quantity of sodium phenoxide and 0.1 g Bu NHSO were added and then the reaction mixture was heated 4-5 h at 80°C. The polymer purification was similar. 

Fatty acids are used in preparation of microspheres for controlled drug delivery. For example, poly(vinyl alcohol), substituted with lauric, myristic, palmitic, and stearic acids at different substitution degrees was employed for the preparation biodegradable microspheres containing progesterone or indo-... 

The log Kow values of Chloralkylene-12 components determined by reversed phase thin layer chromatography ranged from 4.56 to 9.53 with increasing chlorine and alkyl substitution degree [68]. Accordingly, isopropyl-PCBs could have a high bioconcentration potential. However, the first accumulation and excretion study of Chloralkylene-9-14C showed rapid metabolism in rats [69]. 

The increasing order of photocrosslinking efficienties of polymers is nearly the same for each type of irradiation. Poly 2 is the most sensitive polymer with a low presure lamp since in THF solution, 92% of polymer is precipitated in one minute. To obtain the same result with Poly 1, it is necessary to wait for five times more, while this result is not reached after 7 minutes with Poly 3 solution. These results are in agreement with the substitution degrees of the cinnamic double bond on one hand and with absorption characteristics of Poly-2 X max = 312 nm), Poly-1 (290 nm) and Poly-3 (288,5 nm) on the other hand. 

Crystals are always of good quality and the size exceeds generally the values observed in alkaline-type synthesis. Addition of seeds decreases the crystallization time and allows tailoring of the size. The morphology is the same as for crystals obtained by the usual alkaline route. The length/width ratio decreases with x in the template and the substitution degree of Si (16). The substitution by trivalent elements leads generally to crystals with less flat faces which indicates that crystallization occured in a more super-saturated medium. 

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