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Hydroxocobalamin is a form of vitamin B12, which is an essential nutrient for the human body. It is an intermediate in the synthesis of Nitritocobalamin and Hydroxocobalamin Acetate, and it exists in aqueous solution as an equilibrium mixture of the hydroxy isomer and the ionic aqua isomer (aquacobalamin). Hydroxocobalamin serves as a precursor for the coenzymes methylcobalamin and cobamamide, and it is involved in various biological processes, including hematopoiesis.

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  • 13422-51-0 Structure
  • Basic information

    1. Product Name: Hydroxocobalamin
    2. Synonyms: alpha-(5,6-dimethylbenzimidazolyl)hydroxocobamide;alphacobione;alpharedisol;axion;axlon;ciplaminh;cobalex;cobinamide,dihydroxide,dihydrogenphosphate(ester),mono(innersalt),3’-e
    3. CAS NO:13422-51-0
    4. Molecular Formula: C62H89CoN13O15P
    5. Molecular Weight: 1382.82
    6. EINECS: 236-534-8
    7. Product Categories: pharmaceutical intermediate
    8. Mol File: 13422-51-0.mol
  • Chemical Properties

    1. Melting Point: >300 °C
    2. Boiling Point: N/A
    3. Flash Point: N/A
    4. Appearance: dark red crystal or crystalline powder
    5. Density: N/A
    6. Refractive Index: N/A
    7. Storage Temp.: 2-8°C
    8. Solubility: methanol: 10 mg/mL at 20 °C, clear, dark r
    9. Stability: Hygroscopic
    10. CAS DataBase Reference: Hydroxocobalamin(CAS DataBase Reference)
    11. NIST Chemistry Reference: Hydroxocobalamin(13422-51-0)
    12. EPA Substance Registry System: Hydroxocobalamin(13422-51-0)
  • Safety Data

    1. Hazard Codes: Xi
    2. Statements: 36/37/38
    3. Safety Statements: 26-36
    4. WGK Germany: 3
    5. RTECS: GG3820000
    6. F: 3-8-10
    7. HazardClass: N/A
    8. PackingGroup: N/A
    9. Hazardous Substances Data: 13422-51-0(Hazardous Substances Data)

13422-51-0 Usage

Uses

Used in Pharmaceutical Industry:
Hydroxocobalamin is used as a synthetic intermediate for the production of Hydroxocobalamin Acetate, a physiological analog of vitamin B12 where the CN group is replaced with OH. This analog is essential for various biological processes and can be used in the development of pharmaceutical products.
Used in Nutritional Supplements:
Hydroxocobalamin is used as a vitamin (hematopoietic) in the formulation of nutritional supplements. It plays a crucial role in the production of red blood cells and maintaining overall health.
Used in Coordination Compounds:
Hydroxocobalamin is used as a coordination compound in various chemical reactions and processes. Its unique structure allows it to form stable complexes with other molecules, making it a valuable component in coordination chemistry.
Used in Precursor for Coenzymes:
Hydroxocobalamin serves as a precursor for the coenzymes methylcobalamin and cobamamide, which are essential for various enzymatic reactions in the body. These coenzymes are involved in the metabolism of certain amino acids and the synthesis of nucleic acids, making Hydroxocobalamin an important compound in biochemistry and molecular biology.

Originator

Alpha-Redisol,MSD,US,1962

Manufacturing Process

A solution containing 26.3 mg of vitamin B12 in 15 ml of water was shaken with 78 mg of platinum oxide catalyst and hydrogen gas under substantially atmospheric pressure at 25°C for 20 hours. Hydrogen was absorbed. During the absorption of hydrogen the color of the solution changed from red to brown. The solution was separated from the catalyst and evaporated to dryness in vacuo. The residue was then dissolved in 1 ml of water and then diluted with about 6 ml of acetone. After standing for several hours a small amount of precipitate (about 2 to 3 mg) was formed and was then separated from the solution. This solution was diluted with an additional 2 ml of acetone and again allowed to stand for several hours. During this time about 4 to 5 mg of noncrystalline precipitate formed. This solid was separated from the solution and an additional 2 ml of acetone was added to the solution. On standing, vitamin B12a began to crystallize in the form of red needles. After standing for 24 hours, the crystalline material was separated, yield 12 mg. By further dilution of the mother liquor with acetone additional crystalline precipitate formed (from US Patent 2,738,302).

Therapeutic Function

Hematopoietic vitamin

Check Digit Verification of cas no

The CAS Registry Mumber 13422-51-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,3,4,2 and 2 respectively; the second part has 2 digits, 5 and 1 respectively.
Calculate Digit Verification of CAS Registry Number 13422-51:
(7*1)+(6*3)+(5*4)+(4*2)+(3*2)+(2*5)+(1*1)=70
70 % 10 = 0
So 13422-51-0 is a valid CAS Registry Number.
InChI:InChI=1S/C62H90N13O14P.Co.H2O/c1-29-20-40-41(21-30(29)2)75(28-70-40)56-52(84)53(42(27-76)87-56)89-90(85,86)88-31(3)26-69-49(83)19-15-36-50-32(4)54-58(6,7)34(12-16-43(63)77)38(71-54)22-39-35(13-17-44(64)78)59(8,23-46(66)80)55(72-39)33(5)51-37(14-18-45(65)79)61(10,25-48(68)82)62(11,74-51)57(73-50)60(36,9)24-47(67)81;;/h20-22,28,31,34-37,42,52-53,56-57,76,84H,12-19,23-27H2,1-11H3,(H15,63,64,65,66,67,68,69,71,72,73,74,77,78,79,80,81,82,83,85,86);;1H2/q;+3;/p-3

13422-51-0 Well-known Company Product Price

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  • (H1428000)  Hydroxocobalamin  European Pharmacopoeia (EP) Reference Standard

  • 13422-51-0

  • H1428000

  • 1,880.19CNY

  • Detail

13422-51-0SDS

SAFETY DATA SHEETS

According to Globally Harmonized System of Classification and Labelling of Chemicals (GHS) - Sixth revised edition

Version: 1.0

Creation Date: Aug 17, 2017

Revision Date: Aug 17, 2017

1.Identification

1.1 GHS Product identifier

Product name hydroxocobalamin

1.2 Other means of identification

Product number -
Other names Hydroxocobalamin

1.3 Recommended use of the chemical and restrictions on use

Identified uses For industry use only.
Uses advised against no data available

1.4 Supplier's details

1.5 Emergency phone number

Emergency phone number -
Service hours Monday to Friday, 9am-5pm (Standard time zone: UTC/GMT +8 hours).

More Details:13422-51-0 SDS

13422-51-0Synthetic route

aquocob(III)alamine

aquocob(III)alamine

sodium hydroxide
1310-73-2

sodium hydroxide

hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

Conditions
ConditionsYield
In water vitamin B12a reacted with NaOH in H2O;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

water-d2
7789-20-0

water-d2

acetylene
74-86-2

acetylene

vinylcobalamin-d3

vinylcobalamin-d3

Conditions
ConditionsYield
With titanium (III) citrate In water-d2 Schlenk technique; C2H2 was allowed to equilibrate for 4 h under Tris buffer in D2O (pD 9.4) and soln. of Ti(III) citrate in D2O; Co complex wasreacted with Ti(III) citrate (60 equiv.) in Tris buffer in D2O and inje cted; soln. was stirred for 1 h; extd. (phenol/CH2Cl2, 1/1); phenol extracts washed (distd. H2O); dild. with 1-butanol/CH2Cl2 (1/1); extd. (distd. H2O); lyophilized; dissolved in ammonium acetate buffer (pH 4); chromd. (buffer/MeCN, 95/5 to 70/30);85%
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

water
7732-18-5

water

aquocob(III)alamine

aquocob(III)alamine

Conditions
ConditionsYield
With acetate or citrate buffer or aq. HClO4 In not given (N2); dissolving hydroxocobalamin in buffer or aq. HClO4;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

9-(2-chloroethyl)adenine
19255-48-2

9-(2-chloroethyl)adenine

(adenylethyl)cobalamine
59209-78-8

(adenylethyl)cobalamine

Conditions
ConditionsYield
With NaBH4 In ethanol; water Soln. of NaBH4 in water was added to a soln. of hydroxocobalamine in water and 9-(2-chloroethyl)adenine in ethanol, mixt. was stirred for 30 min under N2;; excess NaBH4 was quenched with acetone, excess of the ligand was filtered; soln. was desalted on an Amberlite XAD-2 column; product was purified with a SP-Sephadex column, eluent - H2O; eluate was concd., product was pptd. by addn. of acetone;;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

9-(3-chloropropyl)-9H-purin-6-amine
19255-49-3

9-(3-chloropropyl)-9H-purin-6-amine

(adenylpropyl)cobalamine
34502-77-7

(adenylpropyl)cobalamine

Conditions
ConditionsYield
With NaBH4 In ethanol; water Soln. of NaBH4 in water was added to a soln. of hydroxocobalamine in water and 9-(3-chloropropyl)adenine in ethanol, mixt. was stirred for 30 min under N2;; excess NaBH4 was quenched with acetone, excess of the ligand was filtered; soln. was desalted on an Amberlite XAD-2 column; product was purified with a SP-Sephadex column, eluent - H2O; eluate was concd., product was pptd. by addn. of acetone;;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

N9-(4-chlorobutyl)adenine
69293-19-2

N9-(4-chlorobutyl)adenine

(adehylbutyl)cobalamine
21806-90-6

(adehylbutyl)cobalamine

Conditions
ConditionsYield
With NaBH4 In ethanol; water Soln. of NaBH4 in water was added to a soln. of hydroxocobalamine in water and 9-(4-chlorobutyl)adenine in ethanol, mixt. was stirred for 30 min under N2;; excess NaBH4 was quenched with acetone, excess of the ligand was filtered; soln. was desalted on an Amberlite XAD-2 column; product was purified with a SP-Sephadex column, eluent - H2O; eluate was concd., product was pptd. by addn. of acetone;;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

N9-(5-chloropentyl)adenine
53359-09-4

N9-(5-chloropentyl)adenine

(adenylpentyl)cobalamine
56226-23-4

(adenylpentyl)cobalamine

Conditions
ConditionsYield
With NaBH4 In ethanol; water Soln. of NaBH4 in water was added to a soln. of hydroxocobalamine in water and 9-(5-chloropentyl)adenine in ethanol, mixt. was stirred for 30 min under N2;; excess NaBH4 was quenched with acetone, excess of the ligand was filtered; soln. was desalted on an Amberlite XAD-2 column; product was purified with a SP-Sephadex column, eluent - H2O; eluate was concd., product was pptd. by addn. of acetone;;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

4-bromo-but-1-ene-2,3-dicarboxylic acid
56575-56-5

4-bromo-but-1-ene-2,3-dicarboxylic acid

Co(C19H6N4(CH3)8(C2H4C(O)NH2)3(CH2C(O)NH2)3(C2H4C(O)NHC2H3(CH3)PO4(C4H4O(CH2OH)(OH)(C7H3N2(CH3)2))))(CH2CH(COOH)2CCH2)

Co(C19H6N4(CH3)8(C2H4C(O)NH2)3(CH2C(O)NH2)3(C2H4C(O)NHC2H3(CH3)PO4(C4H4O(CH2OH)(OH)(C7H3N2(CH3)2))))(CH2CH(COOH)2CCH2)

Conditions
ConditionsYield
With zinc In methanol complex reduced with Zn dust in anaerobic MeOH contg. 10% NH4I in a centrifuge tube, injection of soln. of organic compd.;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

dimethyl β-bromomethylitaconate
56575-59-8

dimethyl β-bromomethylitaconate

Co(C19H6N4(CH3)8(C2H4C(O)NH2)3(CH2C(O)NH2)3(C2H4C(O)NHC2H3(CH3)PO4(C4H4O(CH2OH)(OH)(C7H3N2(CH3)2))))(CH2CH(COOCH3)2CCH2)

Co(C19H6N4(CH3)8(C2H4C(O)NH2)3(CH2C(O)NH2)3(C2H4C(O)NHC2H3(CH3)PO4(C4H4O(CH2OH)(OH)(C7H3N2(CH3)2))))(CH2CH(COOCH3)2CCH2)

Conditions
ConditionsYield
With zinc In methanol complex reduced with Zn dust in anaerobic MeOH contg. 10% NH4I in a centrifuge tube, injection of organic compd.;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

chloroacetylene
593-63-5

chloroacetylene

cis-chlorovinylcobalamin

cis-chlorovinylcobalamin

Conditions
ConditionsYield
With NaBH4; Co nitrate In water Schlenk technique; aq. soln. of NaBH4 was added to aq. soln. of hydroxocobalamin, Co nitrate under Ar; ClCCH was distd. at 25°C for 2 h; extd. (phenol/CH2Cl2, 1/1); phenol extracts washed (distd. H2O); dild. with 1-butanol/CH2Cl2 (1/1); extd. (distd. H2O); lyophilized; dissolved in ammonium acetate buffer (pH 4); chromd. (Vydec C18 protein and peptidecolumn; buffer/MeCN, 95/5 to 70/30);
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

acetylene
74-86-2

acetylene

vinylcobalamin

vinylcobalamin

Conditions
ConditionsYield
With NaBH4; Co nitrate In water Schlenk technique; aq. soln. of NaBH4 was added to aq. soln. of hydroxocobalamin, Co nitrate under Ar; HCCH was added at 25°C for 2 h; extd. (phenol/CH2Cl2, 1/1); phenol extracts washed (distd. H2O); dild. with 1-butanol/CH2Cl2 (1/1); extd. (distd. H2O); lyophilized; dissolved in ammonium acetate buffer (pH 4); chromd. (Vydec C18 protein and peptidecolumn; buffer/MeCN, 95/5 to 70/30);
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

(Z)-1-{N-methyl-N-[6-(N-methylammoniohexyl)amino]}diazen-1-ium-1,2-diolate

(Z)-1-{N-methyl-N-[6-(N-methylammoniohexyl)amino]}diazen-1-ium-1,2-diolate

nitrosylcobalamin

nitrosylcobalamin

Conditions
ConditionsYield
In H2O Co complex react. with (CH3NH2C6H12)N(CH3)N(O)NO(1+) at 25°C. (pH=10.8);
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

1-(N,N-diethylamino)-diazen-1-ium-1,2-dienolate

1-(N,N-diethylamino)-diazen-1-ium-1,2-dienolate

nitrosylcobalamin

nitrosylcobalamin

Conditions
ConditionsYield
In H2O byproducts: N-nitrosodiethylamine; Co complex react. with 1.2 equiv. of (C2H5)2NN(O)NO(1-) at 25°C. in alkaline soln.;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

A

cob(II)alamine

cob(II)alamine

C62H88CoN13O16PS

C62H88CoN13O16PS

Conditions
ConditionsYield
With sodium dithionite; ascorbic acid In water at 25℃; Kinetics; Acidic conditions;
hydroxocob(III)alamin
13422-51-0

hydroxocob(III)alamin

C62H88CoN13O16PS

C62H88CoN13O16PS

Conditions
ConditionsYield
With sodium dithionite; sodium hydroxide In water at 25℃; Kinetics;

13422-51-0Relevant articles and documents

Sterically Induced, Spontaneous Co-C Bond Homolysis and β-Elimination Reactions of Primary and Secondary Organocobalamins

Schrauzer, Gerhard N.,Grate, John H.

, p. 541 - 546 (1981)

Sterically hindered secondary alkylcobalamins carrying hydrogen in the β-position decompose in neutral aqueous solutions spontaneously by way of β-elimination.The cleavage of the Co-C bond in these compounds is caused by "upward" distortions of the corrin

Vitamin B12 and redox homeostasis: Cob(II)alamin reacts with superoxide at rates approaching superoxide dismutase (SOD)

Suarez-Moreira, Edward,Yun, June,Birch, Catherine S.,Williams, John H. H.,McCaddon, Andrew,Brasch, Nicola E.

, p. 15078 - 15079 (2009)

(Graph Presented) We report a kinetic study of the reaction between superoxide and an important intracellular form of vitamin B12, cob(II)alamin. Superoxide is implicated in the pathophysiology of many inflammatory diseases, whereas vitamin Bs

Cobalamins and the spectrochemical series

Chemaly, Susan M.

, p. 5766 - 5773 (2008)

UV-visible-NIR spectra of a variety of cobalamins were run in water and methanol. A broad absorption band (band A) with extinction coefficients of about an order of magnitude less than those of the αβ bands was found in the red and NIR regions for Cl-cobalamin (Cl-cbl), Br-cbl, I-cbl, SC(NH 2)2-cbl+ and SeCN-cbl. OCrO3- cbl-, which also has a broad absorption band in the NIR was prepared for the first time. After deconvolution, similar broad bands were seen in the visible region for many other cobalamins. The wavelengths for band A placed the cobalamins in an order similar to the spectrochemical series but different from that of the αβ and γ bands (π-π* transitions), which follow the nephelauxetic series. Band A was ascribed to a ligand-to-metal charge transfer (LMCT) transition from a π orbital in the corrin ring to Co(iii). This is the first systematic study of LMCT bands in cobalamins.

Synthesis, spectroscopic characterization, axial base coordination equilibrium and photolytic kinetics studies of a new coenzyme B12 analogue-3′-deoxy-2′,3′-anhydrothymidylcobalamin

Zhang, Xin,Shen, Xujie,Yan, Hong,Chen, Huilan

, p. 2336 - 2342 (2007/10/03)

A new coenzyme B12 (AdoCbl) analogue, 3′-deoxy-2′, 3′-didehydrothymidylcobalamin (2′,3′-anThyCbl) was prepared by the reaction of 5′-iodo-3′-deoxy-2′,3′-dihydrothymidine with reduced B12a, and characterized by UV-Vis, CD, ESI-MS and NMR spectroscopies. Its axial base (dbzm) coordination equilibria with pH's and temperatures were investigated and showed similar features to those of coenzyme B12. Photolytic dynamics studies under homolytic and heterolytic conditions demonstrated that the Co-C bond of the analogue is slightly more photolabile relative to coenzyme B12. The Royal Society of Chemistry.

Thermal Decomposition and Cobalt-Carbon Bond Dissociation Energies of Organocobalamins: Neopentyl-, (Cyclopentylmethyl)-, (Cyclohexylmethyl)-, (Tetrahydrofurfuryl)- and ((Tetrahydro-2H-pyryl)methyl)cobalamin

Kim, Sook-Hui,Chen, Hui Lan,Feilchenfeld, Natalie,Halpern, Jack

, p. 3120 - 3126 (2007/10/02)

The title compounds were prepared and characterized and their thermal decomposition reactions were studied in aqueous solutions of varying pH and containing varying concentrations of cob(II)alamin (B12) and of bis(dimethylglyoximato)cobalt(II), .

Electron transfer. 90. Further oxidations of vitamin B12r (Cob(II)alamin)

Balasubramanian,Chithambarathanu Pillai,Carlson,Linn Jr.,Gould

, p. 780 - 783 (2008/10/08)

Vitamin B12r (cob(II)alamin), the Co(II) derivative of vitamin B12, reduces FeIII (to FeII), VV (to VIV), and BrO2- (to Br-) in aqueous solution. The rate law for reaction with FeIII(aq) features an inverse-[H+] term and, in the presence of added Cl- or Br-, a sizable halide-proportional term as well. These kinetic dependencies point to specific redox bridging roles for Fe(III)-bound hydroxide and halide. The very high specific rates for oxidations by Fe(NCS)2+ (1.1 × 105) and Fe(N3)2+ (>1 × 107 M-1 s-1) are in accord with this assignment. Oxidation by FeIII(aq) is inhibited by fluoride, reflecting the conversion of Fe(III) to inactive FeF2+. The specific rate pertaining to the [H+]-independent component in the oxidation by FeIII(aq) corresponds to a self-exchange rate for the cob(II,III)alamin couple of 10-4.5 M-1 s-1, or about 10-8 times the corresponding value for cob(I,II)alamin. The acidity pattern for oxidation by vanadium(V) is consistent with partition of V(V) into a reactive protonated form (pKA = 3.5) and an unreactive deprotonated species. The limiting specific rate (4.4 × 105 M-1 s-1) points to a predominant inner-sphere path for this reaction. Oxidations by bromite (BrO2-) exhibit a prominent [H+]-proportional term, attributed to reaction of B12r with HBrO2, proceeding at a specific rate of 4 × 106 M-1 s-1, i.e. about as rapidly as the analogous reaction with HClO2. Oxidations of B12r by IrCl62-, Fe(CN)63-, and Fe(bpy)33+ are too rapid to measure (k > 7 × 106 M-1 s-1 at 25°C and μ = 1.0 M) by our methods.

Electron transfer. 92. Reductions of vitamin B12a (hydroxocobalamin) with formate and related formyl species

Linn Jr.,Gould

, p. 1625 - 1628 (2008/10/08)

Vitamin B12a (hydroxocobalamin) is reduced to B12r (cob(II)alamin) with formate in aqueous media. One unit of formate consumes nearly two molecules of B12a. At formate concentrations below 0.1 M, reactions are first order in both reagents. Rates vary with pH, approach a maximum in the range pH 5-7, and conform to eq 4 in the text, indicating that the active species are the formate anion and the protonated form of B12a. At formate concentrations exceeding 0.1 M, the formate dependence exhibits kinetic saturation, pointing to the formation of a B12a-formate complex having Kassn = 4.6 M-1. The reaction is inhibited moderately by acetate and thiocyanate but severely by imidazole. The observed deuterium isotope effect, kHCOO-/kDCOO- = 1.8, is very close to that reported for the Cannizzaro reaction of benzaldehyde and is thus consistent with a path entailing migration of hydride from a formyl carbon to cobalt. The proposed mechanism for this reaction (sequence (6) - (9)) then features an internal hydride shift (k = 0.016 s-1) within a B12a-formate complex to yield a protonated CoI (B12s-like) intermediate, which very rapidly undergoes a comproportionation reaction with unreacted B12a. The reduction proceeds inconveniently slowly, or not at all, with a number of formyl-substituted carboxylic acids in which the aldehydo group is not properly positioned for hydride migration to carboxyl-bound CoIII or, in the case of glyoxylic acid, is nearly completely converted by hydration to its less reactive gem-diol form.

Electron transfer. 93. Further reactions of transition-metal-center oxidants with vitamin B12s (Cob(I)alamin)

Pillai, G. Chithambarathanu,Ghosh,Gould

, p. 1868 - 1871 (2008/10/08)

Vitamin B12, (cob(I)alamin) reduces europium(III), titanium(IV) (TiO(C2O4)22-), and uranium(VI) in aqueous solution. These oxidants undergo one-electron changes, leading in each case to the cobalt product cob(II)alamin (B12r). The reduction of Eu3+, which is inhibited by TES buffer, but not by glycine, is outer sphere. Its limiting specific rate (1 × 102 M-1 s-1), incorporated in the Marcus treatment, yields a B12s,B12r self-exchange rate of 104.8±0.5 M-1 s-1. Reductions of TiO(C2O4)22- are accelerated by H+ and by acetic acid. Kinetic patterns suggest three competing reaction paths involving varying degrees of protonation of the Ti(IV) center or its association with acetic acid. The very rapid reduction of U(VI) (k = 4 × 106 M-1 s-1) yields U(V) in several buffering media, even when B12s is taken in excess. The much slower conversion of U(V) to U(IV), although thermodynamically favored, appears to be retarded by the extensive reorganization of the coordination sphere of oxo-bound U(V) that must accompany its acceptance of an additional electron. The observed specific rate for the B12s-U(VI) reaction is in reasonable agreement, in the framework of the Marcus formalism, with reported values of the formal potential and the self-exchange rate for U(V,VI).

Acid-base properties of α-ribazole and the thermodynamics of dimethylbenzimidazole association in alkylcobalamins

Brown, Kenneth L.,Hakimi, Janette M.,Nuss, Debra M.,Montejano, Yolanda D.,Jacobsen, Donald W.

, p. 1463 - 1471 (2008/10/08)

1-α-D-Ribofuranosyl-5,6-dimethylbenzimidazole (α-ribazole) has been prepared by cerous hydroxide catalyzed hydrolysis of cyanocobalamin, purified, and characterized by elemental analysis and 1H and 13C NMR and UV-visible spectroscopy. Values of the pKa of N-3-protonated α-ribazole have been determined at several temperatures (ionic strength 1.0 M) and the pKa of N-1-protonated α-ribazole has been estimated to be -7.2 from UV-visible spectral changes in sulfuric acid-water mixtures. Seven alkylcobalamins have been synthesized by standard reductive alkylation procedures and purified chromatographically. It has been found that reductive alkylation with CF3Br produces mixtures of (trifluoromethyl)cobalamin and (difluoromethyl)cobalamin because the former is reductively converted to the latter by reducing agents commonly employed for reduction of cobalt(III) cobalamins to cob(I)alamin. The pKa's for the base-on-base-off transition of these seven alkylcobalamins and methylcobalamin have been determined at the same temperatures as the α-ribazole pKa's. From these values the apparent binding constants for ligation of the free-base benzimidazole nucleotide and the enthalpy and entropy changes for this ligand substitution have been calculated. The enthalpy change has been found to be quite insensitive to the nature of the organic ligand while the entropy change is quite sensitive. These results are discussed in terms of the probable importance of steric effects of the organic ligands on the base-on-base-off pKa's of alkylcobalamins.

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