Dimethyl phosphate molecule

Takayama and coworkers (60) introduced the h.p.l.c. separation technique for such amphiphilic molecules as lipid A, and in earlier experiments they applied paired-ion reverse-phase h.p.l.c. for the preparation of homogeneous fractions deriving from 4,-monophosphated lipid A of S. typhimur-ium. The purified preparations obtained were suitable for f.a.b. - m.s. analysis. However, monophosphated lipid A isolated in this way expressed a considerable heterogeneity with respect to the number and location of 0-acyl residues (60). In order to further improve the purification procedure, as well as to obtain lipid A derivatives suitable for n.m.r. spectroscopy, Qureshi et al. (174) prepared the dimethyl phosphate derivative of S. minnesota (R595) lipid A, which, after purification by reverse-phase h.p.l.c. (C18), could be analyzed by1 H-n.m.r. The n.m.r. spectrum of, for example, the heptaacyl lipid A dimethyl monophosphate fraction, unequivocally revealed 0-acyl substitution [14 0(3-OH)J at position 3 and a free hydroxyl group at position 4 of GlcN(I). 

In the second example, two bicyclic phosphate molecules are coupled together by an Arbuzov reaction with dimethyl methylphosphonate (Figure 6). This creates a very non-volatile material from three relatively volatile but thermally-stable molecules. 

OP.v are unstable in aqueous solution and even more so in blood owing to the presence of esterase. After ingestion, OP.v decompose in the human body to yield alkyl phosphates. Typical degradation products are dimethyl phosphate (DMP), dimethyl phosphorothionate (DMTP), dimethyl phosphorodithioate (DMDTP), diethyl phosphate (DEP), diethyl phosphorothionate (DETP) and diethylphosphorodithioate (DEDTP), which are formed by the hydrolysis of the ester bond in the OP molecule. In Figure 9.5 the chemical structures of the respective alkylphosphates are shown. ... 

Figure 4. MP2/6-31G (QM) interaction energy and new molecular mechanics (MM) interaction energy for dimethyl phosphate and dimethyl phosphorothioate with a single water molecule.

Phosphoric acid has three —OH groups and forms mono-, di-, and triesters, which are named by giving the name(s) of the alkyl or aryl group (s) bonded to oxygen followed by the word phosphate, as, for example, dimethyl phosphate. In more complex phosphoric esters, it is common to name the organic molecule and then indicate the presence of the phosphoric ester using either the word phosphate or the prefix pfiospfio-. 

Table IV summarizes the essential results obtained. Its upper part indicates the values of the energies of binding for the attachment of one water molecule to the principal sites of hydration of the gg and gt conformers. The column AE gt—gg) indicates the energy difference between the two forms in free dimethyl phosphate anion and in its different monohydrates. It is seen that following the site of the monohydration this difference, which is 3.4 kcal mole in favor of the gg form in the free molecule, oscillates between the values of 2-3.9 kcal mole in the monohydrates. Following the position of its attachment, a water molecule may thus have a stabilizing or a destabilizing effect upon the gt form with respect to the gg one.

The application of fluorogenic labeling to the determination of some organophosphate insecticides has been attempted [178,179]. Fenthion (0,0-dimethyl 0-[(4-metiiylthio)-m-tolyl] phosphorothioate), Ruelene (0-2-chloro-4-ferf.-butylphenyl O-methyl methyl-phosphoramidate), GC 6506 [dimethyl p-(methylthio)phenyl phosphate] and several other compounds which yield phenols on hydrolysis have been examined. The limits of detection for some of these labeled derivatives have been reported to be in the low nanogram range. The organophosphate Proban [0,0-dimethyl 0-(p-sulphamoylphenyl) phosphorothioate] has been determined directly without hydrolysis by dansylation of the free amino group of the molecule [180]. The derivative exhibited blue fluorescence, as compared to yellow for phenol and alkylamine dansyl derivatives. 

This vitamin possesses the most complex structure of any of the vitamins and is unique in that it has a metallic element, cobalt, in the molecule (Figure 9-19). The molecule is a coordination complex built around a central tervalent cobalt atom and consists of two major parts—a complex cyclic stmcture that closely resembles the porphyrins and a nucleotide-like portion, 5,6-dimethyl-l-(a-D-ribofuranosyl) benzimidazole-3 -phosphate. The phosphate of the nucleotide is esterified with 1-amino-2-propanol this, in turn, is joined by means of an amide bond with the propionic acid side chain of the large cyclic stmcture. A second linkage with the large stmcture is through the coordinate bond between the cobalt atom and one of the nitro-... 

The final step is a dismutation reaction between two molecules of dimethyl-lumazine, catalyzed by riboflavin synthase, yielding riboflavin and amino-ribitylaniino-pyiiniidinedione. This latter product can undergo reaction with dihydroxybutanone 4-phosphate to yield dimethyl-ribityllumazine. 

For the detection of ionic species other than protons, it is necessary to introduce receptor molecules which can selectively bind guest species on top of the gate of the ISFET. Direct attachment of ion-selective moieties to the surface, e.g. by silylation with (3-cyanopropyl)dimethyl(dimethylamino)silane resulted in some sensitivity towards Ag+ ions (20 mV decade" ), but the sensor was still sensitive towards protons (15 mV decade" ) [10]. Chemical grafting with ammonium phosphonate (1-3) and phosphate sites (4) (Figure 2) or with phthalocyanine-based ionophores bearing crown-ether moieties resulted in a sensitivity towards alkaline (earth) ions, but the pH dependency remained [11,12]. 

The conjugate base of dimethyl methylphosphonate readily reacts with alcohols and carbonyl compounds in the gas phase. (Me0)2P(0) CH2" reacts with CD3OH via three pathways, each of which proceed initially via proton transfer to form the ion-molecule complex [CD3O" (Me0)2P(0)Me], which subsequently undergoes S 2 attack at carbon (equation 56a) or addition/elimination at phosphorus (equation 56b and c). (MeO)2 P(0)CH2 reacts with methyl pyruvate via proton transfer (equation 57a), addition/ elimination (equation 57b) and also via a Horner-Emmons-Wadsworth reaction (equation 57c). The latter reaction is the dominant one for benzaldehyde. Although a consideration of the reactions of phosphate esters were not a mandate for this review, it is... 

The benzopteridines are derived from guanosine triphosphate by the pathway outlined in Fig. 178. The ribityl side chain is formed from the ribosyl residue of 5-amino-2,6-dihydroxy-4-ribosylaminopyrimidine phosphate. 6,7-Dimethyl-8-ribityllumazine is built from 4-ribitylamino-5-aminourazil phosphate and ribose-phosphate with loss of C-4 of the latter precursors. From two molecules of 6,7-dimethyl-8-ribityllumazine one molecule riboflavin is formed. In this reaction the carbon atomes 6 and 7, together with the attached methyl groups of one molecule are transferred to the other molecule in the reversed sequence. As a second product 4-ribitylamine-5-aminouracil is budt. 

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