Terminal group

N-terminal amino acids can be determined by treating a protein with l-fluoro-2,4-dinitrobenzene Sanger s reagent cf. 1.2.4.2.2) or 5-dimethy laminonaphthalene-1 - sulfony 1 chlor- 

The C-terminal amino acid is then separated from the amino acid hydrazides, e. g., by a cation exchange resin, and identified. It is possible to mark the C-terminal amino acid through selective titration via oxazolinone  

The C-terminal amino acids can be removed enzymatically by carboxypeptidase A which preferentially cleaves amino acids with aromatic and large aliphatic side chains, carboxypeptidase B which preferentially cleaves lysine, arginine and amino acids with neutral side chains or carboxypeptidase C which cleaves with less specificity but cleaves proline. 

Giupponi and Buzza (2005) explored how the magnitude of the monomer-solvent interactions impacted the dendrimer stmcture using a lattice-based 

Generation 6 Internal poor solvent Terminal athermal solvent normal micelle  

Generation 6 Internal athermal solvent Terminal poor solvent loopy micelle  

Experimental Systems. Experimentally, amphiphUic Frechet-type poly(aryl ether) dendrimers displaying poly(ethylene glycol) (PEG) peripheral arms were shown to form monomolecular micellar structures exhibiting solvent-sensitive conformational changes (Fig. 11.7 Gitsov and Frechet 1996). 

Similarly, a poly( propylene imine) (PPl) dendrimer fitted with triethyleneoxy methyl ether and octyl groups at every terminal position was soluble in both organic and aqueous solvents, indicating sufficient structural flexibUity to present either the hydrophilic or hydrophobic termini toward the solvent (Fig. 11.8 Pan and Ford 1999, 2000). 

Direct alkyl coupling to aryl systems is complicated by P-elimination in the alkyl-metal but procedures have been reported for cross-coupling of secondary and primary alkyl Grignard reagents and alkylzinc reagents with aryl or alkenyl halides [120]. 

Isothiocyanates are readily made by reaction of a primary aromatic amine with carbon disulfide/triethylamine followed by ethyl chloroformate/triethylamine and by treatment of the amine either with thiophos-gene, calcium carbonate, chloroform, water [138, 139] or with carbon disulfide, N,N -dicyclohexylcarbodiimide, pyridine [140, 141], 

Compounds with alkenyl terminal groups have been extensively studied ([142-144] and references therein) and their synthesis is quite varied, depending upon the position of the double bond and its stereochemistry, but Wittig-based routes are generally used. 

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The terminal groups of a polymer chain are different in some way from the repeat units that characterize the rest of the molecule. If some technique of analytical chemistry can be applied to determine the number of these end groups in a polymer sample, then the average molecular weight of the polymer is readily evaluated. In essence, the concept is no different than the equivalent procedure applied to low molecular weight compounds. The latter is often included as an experiment in general chemistry laboratory classes. The following steps outline the experimental and computational essence of this procedure ... 

Miscellaneous Curing Reactions. Other functional groups can react with the thiol terminal groups of the polysulfides to cross-link the polymer chains and build molecular weight. For example, aldehydes can form thioacetals and water. Organic and inorganic acids or esters can form thioesters. Active dienes such as diacrylates can add to the thiols (3). Examples of these have been mentioned in the Hterature, but none have achieved... 

A great number of different heterocycHc residues have been used as the terminal groups of PMDs. Examples appear throughout this article. PMDs containing residues with quaternary nitrogen atoms are traditionally called cyanine dyes (qv). 

The piC values of polymethine dyes depend on terminal group basicity (64) thus the protonation abHity diminishes if the basic properties of the residues decrease, passing from benzimidazole, quinoline, benzothiazole, to indolenine. On the other hand, the piC of higher homologues increases with chain lengthening. The rate constant of protonation is sensitive to other features, for example, substituents and rings in the chain and steric hindrance for short-chain dyes. 

The manufacture of siHcone polymers via anionic polymerization is widely used in the siHcone industry. The anionic polymerization of cycHc siloxanes can be conducted in a single-batch reactor or in a continuously stirred reactor (94,95). The viscosity of the polymer and type of end groups are easily controUed by the amount of added water or triorganosUyl chain-terminating groups. 

Constmction of multilayers requires that the monolayer surface be modified to a hydroxylated one. Such surfaces can be prepared by a chemical reaction and the conversion of a nonpolar terminal group to a hydroxyl group. Examples of such reactions are the LiAlH reduction of a surface ester group (165), the hydroboration—oxidation of a terminal vinyl group (127,163), and the conversion of a surface bromide using silver chemistry (200). Once a subsequent monolayer is adsorbed on the "activated" monolayer, multilayer films may be built by repetition of this process (Fig. 8). 

The stmcture of SAMs is affected by the si2e and chemical properties of surface functionahties. Indeed, the introduction of any surface functionaUty reduces monolayer order. The impetus toward disorder may result from stericaHy demanding terminal groups, eg, —O—Si(CH2)2(C(CH2)3) (245) and —C H N Ru(NH2)5 (345,346), or from very polar surface groups, eg, OH, COOH, etc. In both cases, the disorder introduced may be significant and not confined only to the surface. 

C rb myl tion. Modification of the amino-terminal groups of hemoglobin (Hb) by the carbamylation reaction using isocyanic acid [75-13-8]... 

The color and constitution of cyanine dyes may be understood through detailed consideration of their component parts, ie, chromophoric systems, terminal groups, and solvent sensitivity of the dyes. Resonance theories have been developed to accommodate significant trends very successfully. For an experienced dye chemist, these are useful in the design of dyes with a specified color, band shape, or solvent sensitivity. More recendy, quantitative values for reversible oxidation—reduction potentials have allowed more complete correlation of these dye properties with organic substituent constants. 

Fig. 3. Examples of nuclei occurring in important cyanine dyes, (a) = basic terminal groups for cyanines and merocyanines (b) = acidic terminal groups...

Acidic Heterocycles. A similar classification is made for the acidic electron-accepting terminal groups used in dipolar (merocyanine) chromophores. The unsymmetrical dyes again incorporate the -dimethylarninophenyl group, coimected to the acidic group (Fig. 3) by one or three methine carbon atoms as in the merocyanine(9), n = 0 [23517-90-0]-, n = 1 [42906-02-5]-, n = 2 [66037-49-8]-, n = 3 [66037-48-7]. 

Dyes derived from these fundamental basic and acidic terminal groups are in current use today as photographic spectral sensiti2ers [100471-81 -6] (10), chemotherapeutic dyes [54444-00-7] (11), laser dyes [53655-17-7] (12), and biological stains [7423-31-6] (13) (Fig. 4). 

The degree of polymerization is dictated by the ratio of Hquid resin (cmde DGEBPA) to bisphenol A an excess of the former provides epoxy terminal groups. The actual molecular weights attained depend on the purity of the starting material. Reactive monofunctional groups act as chain terrninators. 

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