Showing papers by "George M. Whitesides published in 1977"

Rates of thiol-disulfide interchange reactions between mono- and dithiols and Ellman's reagent

Abstract: The rate constants for thiol-disulfide interchange between 21 mono- and dithiols and Ellman's reagent correlate with the pKu's of the thiol groups with a Bronsted coefficient of p = 0.36. The maximum rates ofreduction are observed for thiols having pK, values close to the pH of the solution in which the reactions were carried out. In the dilute solutions examined (10-4-10-6 M in each reagent), the rate of the second, intramolecular interchange step in reactions of dithiols was faster than that of the first, intermolecular interchange, regardless of the size of the cyclic disulfide formed. A convenient synthesis of a mixture of diastereomers of 1,4-dimercapto-2,3-butanediol (i.e., of a mixture of dithiothreitol, DTT, and dithioerythritol, DTE) has been developed from 1,2:,4-diepoxybutane and thiolacetic acid.

Introduction, modification, and characterization of functional groups on the surface of low-density polyethylene film

Abstract: Initial oxidation of low-density polycthytene film w'ith concentrated chromic acid solution at temperr,ur.Jbetwccn 25 and 75 oC, follovved by furthcr oxidation with 70% aqueous nitric acid at 50 oC, generatcs a surface containing a relativelr small numbcr of diffcrcnt tlpcs oi (unctional groups. The idcntities and relative numbcrs of these (unctional groups have bccrt cstablishcd using ATR lR spcctroscopy and chemical dcrivatization. The surface functionality consists primarily of carbonr'l dcrivativcs, with approximttcly 6ClX, oi thcsc prescnt as carboxylic acid groups and 40'b as kctoncs or aldchy'des. Alcohols d,r not sccm to bc prcscnt. Thc absolute numbcr of carboxylic acid groups gcneratcd at the surfa!'c rlas assrty'cd using two indepcn- dcnt fluorimctric tcchniqucs to bc approximately 2 X l0l5/cml of gcontctricrl filrn arca: sincc thc surface is rough, thc actu.rl surface dcnsity of carb,.lxyl groups is lower thrn this numbcr. Severll procedures hrve becn dcvcloped which use thesc carbor- ylic acid groups as thc basis for (urthcr chcnrical modification of the pol;-mc'r surface.

Vinylic radicals are intermediates in the oxidation of vinylic lithium reagents to lithium enolates by dioxygen, but not by lithium tert-butyl peroxide

Abstract: Abs t rac t : ( 1 : ' ) and (Z ) l l i t h i o l p ropcnc ( l ) and (C ) and (Z ) l l i t h i o l pheny l l bu tenc (2 ) r eac t w i t h d i ox l \"gen a t -7 t J oC and f ie ld the cor rcsponding l i th ium cnola tes wi th par t ia l oss o f s tcrcochemist r r around the double bond. React ions o f I and 2 wi th l i th iunt lc r t -but1, l perox ide -vie ld enola tcs wi th re tent ion o iconf igurat ion. Thesc s tcrcochemica l observat ions impl icate f rec v iny l ic rad ica ls in rcact ions o f v in l \" l ic l i th ium reagents wi th d ior rgcn. and cxc lude thcnr in react ions wi th l i th ium ter t bu t v l nc rox idc .

Large-scale ATP-requiring enzymic phosphorylation of creatine can be driven by enzymic ATP regeneration

Abstract: Slr: We have previously used the hexokinase-catalyzed conversion of glucose to glucose G-phosphate to illustrate the practicality of ATP regeneration in enzyme-catalyzed organic synthesis.2 The equilibrium constant for phosphate transfer from ATP to glucose is large (K = 1.5 X 102 at pH 6.0),3 and this reaction goes to completion. ATP is, however, only a moderately strong biological phosphorylating agent,a'5 and many ATP-requiring enzymatic transformations of potential interest in organic synthesis have unfavorable equilibrium constants. Acetyl phosphate, the ultimate phosphorylating reagent in our ATP regeneration scheme, has a significantly greater thermodynamic potential for phosphorylation than ATP, and an important advantage of an ATP regeneration scheme based on acetyl phosphate is its ability to drive to useful conversion a reaction whose equilibrium constant is unfavorable based on the phosphate-donor potential of ATP alone.a,6 Here we provide an example of a reaction of this type by the phosphorylation of creatine (C) to creatine phosphate (CP) on a practical scale (eq 1). The maximum value reported creatine hydrate (100 g, 667 mmol, only part ial ly soluble), ATP (5.0 mmol), MgSOa.TH2o(20 mmol), and dithiothreitol (5.0 mmol).r0 Polyacrylamide gel part icles containing immobilized acetate kinase (AcK, 8.C.2.7 .2.1, 980 U, 4 mL of gel) and creat ine k inase (CK, 8 .C.2.7 .3 .2 ,312 U, 160 mL of ge l ) were suspended in the mixture. l l Diammonium acetyl phosphate in 10o/o aqueous ethylene glycol solution (1 M, pH 9.0) was added continuously over 36 h at 25 mL h-r to the stirred solut ion.l2 The solut ion was maintained between pH 8.8 and 9.2 by the addition of 5.0 N NaOH solution (10o/o aeueous ethylene glycol) using an automatic pH controller. The reaction was conducted at ambient temperature, and the reaction mixture and reagent solutions were deoxygenated before use and maintained under argon. After 36 h of operation (675 mmol of AcP added), enzymatic assayl i l indicated that the reaction was close to equilibrium. The concentration of CP was 56 mM. This quantity (234 mmol in 4200 mL) corresponds to a 63o/\" yield based on dissolved C (56 g) and a 35olo yield based on AcP. The polyacrylamide gel particles and a white precipitate composed primari ly

Method for preparing adenosine triphosphate

Abstract: Acyl phosphate salts suitable for use as phosphate donors in the production of cofactors, such as adenosine triphosphate, are prepared by acylation of phosphoric acid with a ketene, followed by reaction with ammonia or an amine. The reaction product, e.g. diammonium acetyl phosphate, can normally be used directly in enzymic production of cofactors without the necessity of prior conversion to the free acid or another salt, such as the sodium salt. The acyl phosphate salts are produced in high yields, and the method allows production of cofactors for use in biosynthesis from readily available materials.