DMAs

Bustamente C, Vesenka J, Tang C L, Rees W, Guthold M and Keller R 1992 Circular DMA molecules imaged in air by scanning force microscopy Biochemistry 22... 

Allen M J, Hud N V, Balooch M, Tench R J, Siekhaus W J and Balhorn R 1992 Tip-radius-induced artifacts in AFM images of protamine-complexed DMA fibers Ultramicroscopy 42-A4 1095... 

Hansma H G, Vesenka J, Siegerist C, Kelderman G, Morrett H, Sinsheimer R L, Elings V, Bustamente C and Hansma P K 1992 Reproducible imaging and dissection of plasmid DMA under liquid with the atomic force microscope Science 256 1180... 

Hansma H G, Sinsheimer R L, Li M-Q and Hansma P K 1992 Atomic force microscopy of single- and double-stranded DMA Nucleic Acids Res. 20 3585... 

Rees WA, Keller R W, Vesenka J P, Yang G and Bustamente C 1993 Evidence of DMA bending in transcription complexes imaged by scanning force microscopy Sc/e/ ce 260 1646... 

Hansma H G, Sinsheimer R L, Groppe J, Bruice T C, Elings V, Gurley G, Bezanilla M, Mastrangelo I A, Hough P V C and Hansma P K 1993 Recent advances in atomic force microscopy of DMA Scanning 15 296... 

Ramsden J J and Dreier J 1996 Kinetics of the interaction between DMA and the type 1C restriction enzyme SfyR 124/31 Biochemistry Z5 3746-53... 

Figure C3.2.13. Orientation in a photoinitiated electron transfer from dimetliylaniline (DMA) solvent to a coumarin solute (C337). Change in anisotropy, r, reveals change in angle between tire pumped and probed electronic transition moments. From [46],...

We will make real progress in understanding the structure, the properties, and the function of proteins, DMA, and RNA only if bioinformatics and chemoinformatics work together ... 

Molecular mechanics calculations are a very useful tool for the spatial and energetic description of small molecules as well as macroscopic systems like proteins or DMA. 

Potts et al. (333) condensed dipolarophiles (DMA, dibenzoylacetylene, ethyl propiolate) with ylides (81) obtained by quaternization of 4-methyl-thiazole with an a-bromoketone or ester and subsequent deprotonation. In fact the 1 1 molar adduct obtained (82) rearranged to a pyr-rolothiazine (83). One example of this reaction is described Scheme 49. 

The same reaction performed in ether at 0°C (336) gives the same major adduct, but the structure proposed by Acheson et al. corresponds to 86, although such a structure is hardly compatible with the presence of an isolated low-field proton. Very recently, in a reinvestigation of these cyclo-additions of DMA to azoles (338, 339), Acheson et al. were able to establish the correct structure of the adducts on the base of CNMR spectra and X-ray diffraction studies. The adduct of thiazole is represented by formula 87, and it results from the rearrangement of the... 

The three monomethylthiazoles and 2,5-dimethylthiazole undergo the same type of cyclo addition with rearrangement when condensed with DMA in DMF (Scheme 54) (335, 339). 

Acheson et al. (336) by the condensation of DMA with 2,4-dimethyl-thiazole in THF (Scheme 56). As Reid et al. (335) first proposed, the adduct of 2,4-dimethylthiazole with DMA in DMF (93) results from the normal cyclo-addition with rearrangement (Scheme 57). The conclusive demonstration of this structure was recently given by Acheson et al. (339)... 

Until 1990 the EPA maintained a Hst of chemicals suitable for potable water treatment ia the United States. Siace then the entire question of certification and standards has been turned over to a group of organi2ations headed by the National Sanitation Eoundation, which has issued voluntary standards. As of January 1992, standards had been issued for most of the principal inorganic products, but only for two polymers, poly(DADMAC) and Epi-DMA (epichl orohydrin dimethyl amine) polymers (78). Certifications for commercial products meeting specified standards are issued by the National Sanitation Eoundation, Underwriter Laboratories, and Risk Eocus/Versar (79). 

Table 4 lists the specifications set by Du Pont, the largest U.S. producer of DMF (4). Water in DMF is deterrnined either by Kad Fischer titration or by gas chromatography. The chromatographic method is more rehable at lower levels of water (<500 ppm) (4). DMF purity is deterrnined by gc. For specialized laboratory appHcations, conductivity measurements have been used as an indication of purity (27). DMF in water can be measured by refractive index, hydrolysis to DMA followed by titration of the Hberated amine, or, most conveniendy, by infrared analysis. A band at 1087 cm is used for the ir analysis. 

Aromatic diacyl peroxides such as dibenzoyl peroxide (BPO) [94-36-0] may be used with promoters to lower the usehil decomposition temperatures of the peroxides, although usually with some sacrifice to radical generation efficiency. The most widely used promoter is dimethylaniline (DMA). The BPO—DMA combination is used for hardening (curing) of unsaturated polyester resin compositions, eg, body putty in auto repair kits. Here, the aromatic amine promoter attacks the BPO to initially form W-benzoyloxydimethylanilinium benzoate (ion pair) which subsequentiy decomposes at room temperature to form a benzoate ion, a dimethylaniline radical cation, and a benzoyloxy radical that, in turn, initiates the curing reaction (33) ... 

Wheieas the BPO—DMA ledox system works well for curing of unsaturated polyester blends, it is not a very effective system for initiating vinyl monomer polymerizations, and therefore it generally is not used in such appHcations (34). However, combinations of amines (eg, DMA) and acyl sulfonyl peroxides (eg, ACSP) are very effective initiator systems at 0°C for high conversion suspension polymerizations of vinyl chloride (35). BPO has also been used in combination with ferrous ammonium sulfate to initiate emulsion polymerizations of vinyl monomers via a redox reaction (36). 

The fate of the ion pair iatermediate depends on the stmcture of the amine and the reaction conditions. Certain tertiary amines, eg, dimethylaruline (DMA), react with specific diacyl peroxides such as diben2oyl peroxide (BPO) to generate free radicals at ca 20°C. Some reactions, eg, DMA—BPO, are explosive when neat reactants are mixed. Primary and secondary amines do not yield free radicals. 

The principal techniques for determining the microstmcture of phenoHc resins include mass spectroscopy, proton, and C-nmr spectroscopy, as well as gc, Ic, and gpc. The softening and curing processes of phenoHc resins are effectively studied by using thermal and mechanical techniques, such as tga, dsc, and dynamic mechanical analysis (dma). Infrared (ir) and electron spectroscopy are also employed. 

Fig. 3. Programmed dma scan of a resole phenoHc resin heating rate is 5°C/min.

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

---