1113-41-3

Basic information

• Product Name: L-Penicillamine
• Synonyms: 3-MERCAPTO-L-VALINE;3-THIOL-VALINE;3,3-DIMETHYL-L-CYSTEINE;L-BETA,BETA-DIMETHYLCYSTEINE;L-BETA-MERCAPTOVALINE;L-(+)-PENICILLAMINE;L-PENICILLAMINE;L(+)-2-AMINO-3-MERCAPTO-3-METHYLBUTANOIC ACID
• CAS NO: 1113-41-3
• Molecular Formula: C₅H₁₁NO₂S
• Molecular Weight: 149.21
• EINECS: 214-203-9
• Product Categories: Amino Acids;Biochemistry;non-Proteinorganic Amino Acids;Amino Acids & Derivatives;Intermediates & Fine Chemicals;Pharmaceuticals
• Mol File: 1113-41-3.mol
• Article Data: 4

Chemical Properties

• Melting Point: 206 °C (dec.)(lit.)
• Boiling Point: 251.8°Cat760mmHg
• Flash Point: 106.1°C
• Appearance: White to almost white/Crystalline Powder
• Density: 1.113 (estimate)
• Refractive Index: 63 ° (C=1, 1mol/L NaOH)
• Storage Temp.: Store at RT.
• Solubility: Aqueous Base (Sparingly), DMSO (Slightly, Heated), Water (Slightly)
• PKA: 2.13±0.12(Predicted)
• Stability: Hygroscopic
• Merck: 14,7088
• BRN: 1722374
• CAS DataBase Reference: L-Penicillamine(CAS DataBase Reference)
• NIST Chemistry Reference: L-Penicillamine(1113-41-3)
• EPA Substance Registry System: L-Penicillamine(1113-41-3)

Safety Data

• Hazard Codes: Xi,Xn
• Statements: 36/37/38-40-20/21/22
• Safety Statements: 26-36-22-24/25
• WGK Germany: 2
• RTECS: YV9445500
• Hazardous Substances Data: 1113-41-3(Hazardous Substances Data)

Usage

Chemical Properties

white to almost white crystalline powder

Uses

Different sources of media describe the Uses of 1113-41-3 differently. You can refer to the following data:
1. As a Penicillin metabolite, L-Penicillamine can be used in the treatment of Wilson’s disease, Cystinuria, Scleroderma and arsenic poisoning.
2. L-Penicillamine is a metabolite of penicillin. L-Penicillamine is used in the treatment of Wilson’s disease, Cystinuria, Scleroderma and arsenic poisoning.
3. Metal-chelating agent

Definition

ChEBI: The L-enantiomer of penicillamine.

Indications

Penicillamine (Cuprimine) can be used to treat acute, severe rheumatoid arthritis, producing reductions in joint pain, edema, and stiffness.The response to penicillamine is usually delayed (4–12 weeks), and remissions can last several months after withdrawal of treatment. Radiographic evidence of this drug’s efficacy is limited; thus, penicillamine is seldom used to treat rheumatoid arthritis.

Mechanism of action

The mechanism of action of penicillamine is unknown, but some evidence suggests that it may involve the inhibition of angiogenesis, synovial fibroblast proliferation, or transcriptional activation. Because penicillamine can chelate copper and promote its excretion, it is used to treat Wilson’s disease (hepatolenticular degeneration) and has also been used in mercury and lead intoxication.

Pharmacology

Penicillamine is readily absorbed from the GI tract and is rapidly excreted in the urine, largely as the intact molecule. Gradually increasing its dose minimizes side effects, which necessitate discontinuance of penicillamine therapy in perhaps one-third of patients. The most common side effects are maculopapular pruritic dermatitis, GI upset, loss of taste sensation, mild to occasionally severe thrombocytopenia and leukopenia,and mild proteinuria, which at times may progress to the nephritic syndrome. Discontinuance of therapy usually results in a rapid disappearance of side effects.

Safety Profile

A poison by intraperitoneal route. Mutation data reported. Whenheated to decomposition it emits toxic vapors of NOx and SOx.

Purification Methods

Same as preceding entry for its enantiomer. [Beilstein 4 IV 3228.]

Synthetic route

C5H11NO2S*C4H6O6 → L-penicillamine (1113-41-3)

Conditions	Yield
With triethylamine In ethanol at 20℃;	95.2%

N-formyl-L-penicillamine (884311-05-1) → L-penicillamine (1113-41-3)

Conditions	Yield
With hydrogenchloride

N-acetyl-D-penicillamine (2510-38-5) → L-penicillamine (1113-41-3)

Conditions	Yield
With hydrogenchloride

S-benzyl-L-penicillamine (54536-38-8) → L-penicillamine (1113-41-3)

Conditions	Yield
With ammonia; sodium

propan-1-ol (71-23-8) + Penicillamine thiyl radical (58167-41-2) → L-penicillamine (1113-41-3) + 1-hydroxy-propyl (5723-77-3)

Conditions	Yield
With perchloric acid In water Rate constant; Ambient temperature;

ethanol (64-17-5) + Penicillamine thiyl radical (58167-41-2) → ethanol radical (2348-46-1) + L-penicillamine (1113-41-3)

Conditions	Yield
With perchloric acid In water Rate constant; Ambient temperature;

ethylene glycol (107-21-1) + Penicillamine thiyl radical (58167-41-2) → L-penicillamine (1113-41-3) + 1,2-dihydroxy-ethyl (3250-66-6)

Conditions	Yield
With perchloric acid In water Rate constant; Ambient temperature;

isopropyl alcohol (67-63-0) + Penicillamine thiyl radical (58167-41-2) → L-penicillamine (1113-41-3) + 2-hydroxy-2-propyl radical (5131-95-3)

Conditions	Yield
With perchloric acid In water Rate constant; Ambient temperature;

(-)(R)-2.2.5.5-tetramethyl-3-formyl-thiazolidine-carboxylic acid-(4) → L-penicillamine (1113-41-3)

Conditions	Yield
With hydrogenchloride unter CO2;

propylamine (107-10-8) + heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, complex with l-penicillamine → L-penicillamine (1113-41-3) + heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, complex with n-propylamine

Conditions	Yield
In methanol; water Kinetics;

propylamine (107-10-8) + permethylated maltoheptaose, complex with D-penicillamine → L-penicillamine (1113-41-3) + permethylated maltoheptaose, complex with n-propylamine

Conditions	Yield
In methanol; water Kinetics;

S-benzyl-N-formyl-L-penicillamine (884311-31-3) → L-penicillamine (1113-41-3)

Conditions	Yield
Multi-step reaction with 2 steps 1: sodium; liquid NH3 2: aqueous HCl View Scheme

3,3-dimethyl-D-cysteine (52-67-5) → L-penicillamine (1113-41-3)

Conditions	Yield
Multi-step reaction with 4 steps 1.1: 2 h / 55 °C 2.1: 5 h / 53 °C 3.1: acetic acid / toluene / 1 h / 98 °C 3.2: 1 h / 95 °C / Inert atmosphere 4.1: triethylamine / ethanol / 20 °C View Scheme

(4S)-2,2,5,5-tetramethylthiazolidine-4-carboxylic acid (72744-87-7) → L-penicillamine (1113-41-3)

Conditions	Yield
Multi-step reaction with 3 steps 1.1: 5 h / 53 °C 2.1: acetic acid / toluene / 1 h / 98 °C 2.2: 1 h / 95 °C / Inert atmosphere 3.1: triethylamine / ethanol / 20 °C View Scheme

(μ-1,5-bis(diphenylphosphine)pentane)bis(chlorogold) (99350-05-7) + L-penicillamine (1113-41-3) + water (7732-18-5) → C39H50Au2N2O4P2S2*3H2O

Conditions	Yield
With potassium hydroxide In ethanol at 20℃; for 2h;	97%

formaldehyd (50-00-0) + L-penicillamine (1113-41-3) → (R)-5,5-dimethyl-1,3-thiazolidine-4-carboxylic acid (72778-00-8)

Conditions	Yield
With pyridine In ethanol; water at 110℃; for 0.0833333h; Microwave irradiation;	95%
In water at 0℃; for 1h;	87%
Stage #1: formaldehyd; L-penicillamine In water at 8℃; for 14h; Stage #2: In methanol at 20℃; for 12h;	86%

6-ethoxy-2,3,4,5-tetrahydro-pyridine (15200-13-2) + L-penicillamine (1113-41-3) → (R)-3-mercapto-3,3-dimethyl-2-(piperidine-2-ylideneamino)-propanoic acid (122861-59-0)

Conditions	Yield
In methanol for 8h; Ambient temperature;	91%

1,4-bis(diphenylphosphino)butane digold(I) dichloride (63640-04-0) + L-penicillamine (1113-41-3) + water (7732-18-5) → C38H48Au2N2O4P2S2*2H2O

Conditions	Yield
With potassium hydroxide In ethanol at 20℃; for 2h;	91%

[(ClAu)]3(1,1,1-tris(diphenylphosphinomethyl)ethane) (84152-18-1) + L-penicillamine (1113-41-3) → [Au3(1,1,1-tris(diphenylphosphinomethyl))(D-penicillamininate)3]*5H2O

Conditions	Yield
In ethanol at 20℃; for 1h;	90%

L-penicillamine (1113-41-3) + 2-bromoethanol (540-51-2) + 4-but-2-ynyloxybenzenesulfonyl chloride (286459-94-7) → N-{[4-(2 butynyloxy)phenyl]-sulfonyl}-3-[(2-hydroxyethyl)sulfanyl]valine (287407-19-6)

Conditions	Yield
Stage #1: L-penicillamine With sodium hydroxide In methanol at 0℃; Stage #2: 2-bromoethanol In acetonitrile at 0 - 20℃; for 2.5h; Stage #3: 4-but-2-ynyloxybenzenesulfonyl chloride With hydrogenchloride; sodium carbonate more than 3 stages;	89.6%

L-penicillamine (1113-41-3) + 2-bromoethanol (540-51-2) + 4-but-2-ynyloxybenzenesulfonyl chloride (286459-94-7) → (2S)-2-({[4-(2-butynyloxy)-phenyl]sulfonyl}amino)-3-[(2-hydroxyethyl)thio]-3-methylbutanoic acid

Conditions	Yield
Stage #1: L-penicillamine With sodium hydroxide In methanol at 0℃; Stage #2: 2-bromoethanol In methanol at 0 - 20℃; for 2.5h; Stage #3: 4-but-2-ynyloxybenzenesulfonyl chloride With hydrogenchloride more than 3 stages;	89.6%

L-penicillamine (1113-41-3) + di-tert-butyl dicarbonate (24424-99-5) + (4Z,7Z,10Z,13Z,16Z,19Z)-N-(2-(pyridin-2-yldisulfaneyl)ethyl)-docosa-4,7,10,13,16,19-hexaenamide → (R)-2-((tert-butoxycarbonyl)amino)-3-((2-((4Z,7Z,10Z,13Z,16Z,19Z)-docosa-4,7,10,13,16,19-hexaenamido)ethyl)disulfanyl)-3-methylbutanoic acid

Conditions	Yield
Stage #1: L-penicillamine; (4Z,7Z,10Z,13Z,16Z,19Z)-N-(2-(pyridin-2-yldisulfaneyl)ethyl)-docosa-4,7,10,13,16,19-hexaenamide In methanol at 20℃; for 18h; Stage #2: di-tert-butyl dicarbonate With sodium hydroxide In methanol; water at 20℃; for 4h;	88.2%

L-penicillamine (1113-41-3) + di-tert-butyl dicarbonate (24424-99-5) → (R)-2-((tert-butoxycarbonyl)amino)-3-mercapto-3-methylbutanoic acid (110763-40-1)

Conditions	Yield
With sodium hydroxide In 1,4-dioxane; water at 20℃; for 22h; Cooling with ice;	88%
In tetrahydrofuran at 20℃; for 16h; Acylation;
In sodium carbonate; tert-butyl alcohol
With triethylamine In N,N-dimethyl-formamide for 18h;

L-penicillamine (1113-41-3) + tert-butyldicarbonate (34619-03-9) → (R)-2-((tert-butoxycarbonyl)amino)-3-mercapto-3-methylbutanoic acid (110763-40-1)

Conditions	Yield
With sodium hydroxide In 1,4-dioxane; water at 20℃; for 20h; Cooling with ice; Inert atmosphere;	88%

L-penicillamine (1113-41-3) + Trifluoro-methanesulfonate2-[(3S,8S,9S,10R,13R,14S,17R)-17-((R)-1,5-dimethyl-hexyl)-10,13-dimethyl-2,3,4,7,8,9,10,11,12,13,14,15,16,17-tetradecahydro-1H-cyclopenta[a]phenanthren-3-yldisulfanyl]-1-methyl-pyridinium; (136911-96-1) → (R)-2-Amino-3-[(3S,8S,9S,10R,13R,14S,17R)-17-((R)-1,5-dimethyl-hexyl)-10,13-dimethyl-2,3,4,7,8,9,10,11,12,13,14,15,16,17-tetradecahydro-1H-cyclopenta[a]phenanthren-3-yldisulfanyl]-3-methyl-butyric acid

Conditions	Yield
In N,N-dimethyl-formamide reaction of other N-alkylpyridyl disulfides; other substrates;	87%
In N,N-dimethyl-formamide Yield given;

L-penicillamine (1113-41-3) + di-tert-butyl dicarbonate (24424-99-5) + 3-(5-bromo-2-thienyl)-1-phenyl-1H-pyrazole-4-carboxaldehyde (274900-91-3) → (2RS,4R)-2-[3-(5-bromo-2-thienyl)-1-phenyl-1H-pyrazol-4-yl]-3-(tert-butyloxycarbonyl)-5,5-dimethylthiazolidine-4-carboxylic acid (612500-41-1)

Conditions	Yield
Stage #1: L-penicillamine; 3-(5-bromo-2-thienyl)-1-phenyl-1H-pyrazole-4-carboxaldehyde In ethanol; water for 5h; Heating; Stage #2: di-tert-butyl dicarbonate With sodium hydroxide In 1,4-dioxane; ethanol at 20℃; for 5h;	81%

potassium tetrachloroplatinate(II) (10025-99-7) + L-penicillamine (1113-41-3) → 4Pt(2+)*2(CH3)2CSCHNH2COOH(1-)*2(CH3)2CSCHNH2COO(2-)*2Cl(1-)=Pt4[(CH3)2CSCHNH2COOH]2[(CH3)2CSCHNH2COO]2Cl2

Conditions	Yield
In water heating (50-55°C, 30 min); washing (water); elem. anal.;	81%

formaldehyd (50-00-0) + L-penicillamine (1113-41-3) → 5,5-dimethylthiazolidine-4-carboxylic acid (72778-00-8)

Conditions	Yield
With pyridine In water a) water (pH 5), several h, b) 0 deg C, 3 h, c) ethanol, 0 deg C, overnight;	80%

L-penicillamine (1113-41-3) + 4-methoxy-benzaldehyde (123-11-5) → (1L)-2-imino-3-p-methoxybenzyl-4-sulfanyl-5,5-dimethyl-1-carboxylic acid

Conditions	Yield
With manganese(IV) oxide In ethanol at 70℃; for 1h;	80%

L-penicillamine (1113-41-3) + acetone (67-64-1) → (R)-4-carboxy-2,2,5,5-tetramethylthiazolidin-3-ium chloride

Conditions	Yield
With hydrogenchloride In water for 3.5h; Reflux;	76%

L-penicillamine (1113-41-3) + methyl iodide (74-88-4) → S-methyl-L-penicillamine (100217-05-8)

Conditions	Yield
Stage #1: L-penicillamine With sodium hydroxide In methanol at 0℃; Stage #2: methyl iodide In methanol at 0 - 20℃; for 1.66667h; Stage #3: With hydrogenchloride In water pH=3;	75.8%
With sodium methylate
Stage #1: L-penicillamine With sodium hydroxide In methanol at 0℃; Stage #2: methyl iodide In methanol at 0 - 20℃; for 1.66667h; Stage #3: With hydrogenchloride In water pH=3;
With sodium hydroxide In methanol; water at 0℃; for 16h;

methanol (67-56-1) + L-penicillamine (1113-41-3) → (R)-penicillamine methyl ester hydrochloride (70361-44-3)

Conditions	Yield
With thionyl chloride for 120h; in a sealed vessel;	75%
With thionyl chloride at 0℃; for 96h; Heating / reflux;	75%

L-penicillamine (1113-41-3) + 2,4,6-trimethoxybenzyl alcohol (61040-78-6) → (R)-2-amino-3-methyl-3-(2,4,6-trimethoxybenzylthio)butyric acid trifluoroacetate (1200836-59-4)

Conditions	Yield
With trifluoroacetic acid In dichloromethane at 0 - 20℃; for 17h;	75%

L-penicillamine (1113-41-3) + 7-methoxy-3-(1H-benzotriazol-1-ylcarbonyl)-2H-chromene-2-one (1286276-26-3) → (R)-2-amino-3-methyl-3-[(7-methoxy-2-oxo-2H-chromene-3-carbonyl)thio]butanoic acid (1327278-91-0)

Conditions	Yield
In water; acetonitrile at 20℃; for 12h;	75%

6-ethoxy-2,3,4,5-tetrahydro-pyridine (15200-13-2) + L-penicillamine (1113-41-3) → 2-isopropylidene-5,6,7,8-tetrahydro-2H-imidazo<1,2-a>pyridine-3-one + (R)-3-mercapto-3,3-dimethyl-2-(piperidine-2-ylideneamino)-propanoic acid (122861-59-0)

Conditions	Yield
In methanol at 80℃; for 2h;	A 15% B 74%

N-Methyl-2,2-diethoxypyrrolidine (826-41-5) + L-penicillamine (1113-41-3) → (R)-3-mercapto-3,3-dimethyl-2-(1-methyl-pyrrolidine-2-ylideneamino)-propanoic acid

Conditions	Yield
In ethanol at 80℃; for 6h;	73%

L-penicillamine (1113-41-3) + [Au(ppy)Cl2] → [Au(ppy)(D-pen)]*2H2O

Conditions	Yield
With sodium hydroxide In ethanol; water at 50℃; for 1h;	73%

6-ethoxy-2,3,4,5-tetrahydro-pyridine (15200-13-2) + L-penicillamine (1113-41-3) → 2-isopropylidene-5,6,7,8-tetrahydro-2H-imidazo<1,2-a>pyridine-3-one + (R)-5,5-dimethyl-2-<3-(piperidine-2-ylideneamino)-butyl>-4,5-dihydro-1,3-thiazole-4-carboxylic acid

Conditions	Yield
In methanol at 80℃; for 8h;	A 15% B 72%

L-penicillamine (1113-41-3) + 3-(1H-benzotriazol-1-ylcarbonyl)-2H-chromene-2-one (312929-01-4) → (R)-2-amino-3-methyl-3-[(2-oxo-2H-chromene-3-carbonyl)thio]butanoic acid (1327278-85-2)

Conditions	Yield
In water; acetonitrile at 20℃; for 12h;	72%

L-penicillamine (1113-41-3) + (3R)-3-formamido-4,4-dimethylthietan-2-one (159000-76-7) → N-(N-formyl-D-penicillaminyl)-L-penicillamine (158945-06-3)

Conditions	Yield
With sodium hydroxide In chloroform for 1h;	71%

Upstream product

• 884311-05-1 N-formyl-L-penicillamine 
• 2510-38-5 N-acetyl-L-penicillamine 
• 107-21-1 ethylene glycol 
• 58167-41-2 Penicillamine thiyl radical 
• 72744-87-7 (4S)-2,2,5,5-tetramethylthiazolidine-4-carboxylic acid 
• 52-67-5 3,3-dimethyl-D-cysteine 
• 884311-31-3 S-benzyl-N-formyl-L-penicillamine 
• 107-10-8 propylamine 
• 67-63-0 isopropyl alcohol 
• 64-17-5 ethanol 
• 71-23-8 propan-1-ol 
• 54536-38-8 S-benzyl-L-penicillamine 

Downstream Products

• 72778-00-8 (R)-5,5-dimethyl-1,3-thiazolidine-4-carboxylic acid 
• 70398-13-9 2S,4R-2-phenyl-5,5-dimethylthiazolidine-4-carboxylic acid 
• 387868-34-0 (R)-2-Amino-3-(4-methoxy-benzylsulfanyl)-3-methyl-butyric acid 
• 64-17-5 ethanol 
• 58167-41-2 Penicillamine thiyl radical 
• 71-23-8 propan-1-ol 
• 109-99-9 tetrahydrofuran 
• 123-91-1 1,4-dioxane 
• 107-21-1 ethylene glycol 
• 73466-15-6 S-nitrosopenicillamine 
• 110763-40-1 (R)-2-((tert-butoxycarbonyl)amino)-3-mercapto-3-methylbutanoic acid 
• 612500-41-1 (2RS,4R)-2-[3-(5-bromo-2-thienyl)-1-phenyl-1H-pyrazol-4-yl]-3-(tert-butyloxycarbonyl)-5,5-dimethylthiazolidine-4-carboxylic acid 
• 117081-20-6 (3S,6S,7aR)-6-Benzyloxycarbonylamino-2,2-dimethyl-5-oxo-hexahydro-pyrrolo[2,1-b]thiazole-3-carboxylic acid benzyl ester 
• 117056-61-8 (3S,6S,7aR)-2,2-Dimethyl-6-[(S)-5-(4-nitro-benzyloxycarbonyl)-5-(4-nitro-benzyloxycarbonylamino)-pentanoylamino]-5-oxo-hexahydro-pyrrolo[2,1-b]thiazole-3-carboxylic acid benzyl ester 

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Effect of L-Penicillamine (cas 1113-41-3) hydantoin, an analogue of glutathione, on rat liver glutathione peroxidase, reductase and transferase reactions08/18/2019

In soluble fractions prepared from rat liver homogenates, l-penicillamine hydantoin appeared to be, on the basis of SH consumption measurements, a substrate for glutathione peroxidase but not transferase reactions. When glutathione is incubated with rat liver soluble proteins in the presence of ...detailed

Transport of D- and L-Penicillamine (cas 1113-41-3) by mammalian cells08/16/2019

SummaryL-Penicillamine is taken up and accumulated by mammalian cells via their amino acid transport systems. Natural amino acids compete with L-penicillamine and have a higher affinity to their transport systems, as shown in the case of L-valine.D-Penicillamine is not accumulated within the cel...detailed

Relevant articles and documents

Enantiomeric analysis of pharmaceutical compounds by Ion/molecule reactions

Protonated complexes involving cyclodextrin hosts and guest compounds that are pharmacologically important are produced in the gas phase and reacted with a gaseous amine. The guest is exchanged to produce a new protonated complex with the amine. The reaction is enantioselective and is used to develop a method for determining enantiomeric excess using only mass spectrometry. The pharmaceutical compounds include DOPA, amphetamine, ephedrine, and penicillamine. The presence of more than one reacting species is observed with DOPA and penicillamine. Molecular dynamics calculations are used to understand the nature of the interactions and the possible source of the variations in the reactivities.

Determination of Absolute Rate Constants for the Reversible Hydrogen-atom Transfer between Thiyl Radicals and Alcohols or Ethers

Absolute rate constants have been determined for the reversible hydrogen-transfer process R. + RSH ->/. by pulse radiolysis, mainly through direct observation of the RS. radical formation kinetics in water-RH (1:1, v/v) mixtures.The thiols investigated were penicillamine and glutathione; the RH hydrogen donors were methanol, ethanol, propan-1-ol, propan-2-ol, ethylene glycol, tetrahydrofuran and 1,4-dioxane with the abstracted hydrogen being located α to the hydroxy or alkoxy function.Rate constants for the forward reaction of the above equilibrium (in radiation biology referred to as 'repair' reaction) were typically of the order of 1E7-1E8 dm3 mol-1 s-1 while hydrogen abstraction from RH by thiyl radicals (reverse process) occurred with rate constants of the order of 1E3-1E4 dm3 mol-1 s-1.This yields equilibrium constants of the order of 1E4.Based on these data, standard reduction potentials could be evaluated for the R'R''C.OH/H(1+)//R'R''CHOH, R'R''CO/H(1+)//R'R''C.(OH) and R'R''CO//R'R''C.O(1-) couples from methanol, ethanol and propan-2-ol.Effective hydrogen-atom abstraction by RS. required activation by neighbouring groups of the C-H bond to be cleaved in RH.No such process was observed for the RS. reaction with -CH3 groups, e.g. in 2-methylpropan-2-ol.Several halogenated hydrocarbons, including some anaesthetics (e.g. halothane) and Fe(CN)6(3-) have been tested with respect to their ability to disturb the (CH3)2C.OH + RSH ->/. equilibrium through an irreversible electron-transfer reaction with the reducing α-hydroxyl radical, thereby drawing the equilibrium to the left-hand side.The respective efficiencies are found to be related to the electronegativities of the electron acceptors.The results are briefly discussed in terms of their biological relevance.