Richard M. Lemmon

Cyanamide Formation under Primitive Earth Conditions.

The dimer of cyanamide, dicyandiamide, is formed upon ultraviolet irradiation of dilute cyanide solutions, and by the electron irradiation of a mixture of methane, ammonia, and water. Thus cyanamide may have had an important role in chemical evolution.

Dicyandiamide: Possible Role in Peptide Synthesis during Chemical Evolution

Dicyandiamide promotes certain dehydration condensations under conditions possible on primitive Earth. The effect of this compound in promoting peptide syntheses was studied.

The radiation decomposition of adenine.

The radiolysis of 0.1% solutions of adenine in water leads to the formation of two major products: 4,6-diamino-5formamidopyrimidine and 8- hydroxyadenine. The two compounds account for about 80% of the decomposed adenine. Minor products are hypoxanthine and 4-amino-5formamido-6- hydroxypyrimidine. It is probable that all the reactions may occur in intact nucleic acids, and that they may therefore be of importance in radiobiology. (auth)

Simultaneous peptide and oligonucleotide formation in mixtures of amino acid, nucleoside triphosphate, imidazole, and magnesium ion

Simultaneous peptide and oligonucleotide formation was observed in reaction mixtures of amino acid, nucleoside triphosphate, imidazole, and MgCl2. At 70 degrees C in solutions that were evaporated to dryness the formation of peptide for phe and pro was greatest with CTP relative to ATP, GTP, and UTP. Lysine exhibited a preference for GTP and glycine for UTP. At ambient temperature insolution at pH 7.8, CTP was preferred by glycine, but at pH 8.7 UTP was preferred. The glycine nucleotide phosphoramidates were also detected and characterized in reactions at 40 degrees C. The glycine-reaction preference for CTP at pH 7.8 and UTP at 8.7 suggested that the basicity of the nucleoside triphosphate was involved in increasing the peptide yield. CTP near neutrality is the most basic nucleoside triphosphate and the basic anionic form UTP could facilitate peptide formation at pH 8.7. These data, together with information on the complexing of poly(C) by GTP, led to the experimentally approchable hypothesis that GTP, by forming a basic triplex between the cytosine residues adjacent to the peptidyl adenosine and aminoacyl adenosine at the termini of two proto-tRNAs, would promote peptide bond synthesis between the aminoacyl residue and peptidyl residue.

The question of the possible asymmetric polymerization of aspartic acid on kaolinite.

SummaryWe have been unable to confirm the recent report that kaolinite catalyzes the polymerization of aqueousd- andl-aspartic acid at different rates. In experiments wheredl-Asp was used, no induced optical rotation was found in the reaction solution. No evidence for polymer (or other product) formation was found whenl-Asp-2-14C was used, and products were searched by paper chromatography and X-ray film autoradiography. Asp is adsorbed by kaolinite, but no selectivity for one or the other enantiomer was observed.

A re-examination of the zeolite-promoted, clay-mediated peptide synthesis

SummaryIt has been found that, contrary to recent reports, peptides are not detectable products from alanine-ATP-Decalso-montmorillonite mixtures. The peptides appear only when pre-formed adenylates are reacted in the presence of montmorillonite.

The radiolysis and radioracemization of amino acids on clays.

L-Leucine and its hydrochloride salt have been deposited on the clay minerals kaolin and bentonite, and the amino acid/clay preparations have been irradiated in a 3000 Ci60Co γ-ray source for radiation dosages that achieved 2–89% radiolysis of the leucine. The undecomposed leucine was thereupon recovered and both percent radiolysis and percent radioracemization were determined. Similar studies were made using solid L-leucine and its hydrochloride, and L-leucine in 0.1 M aqueous solution. It has been found that radiolysis and radio-racemization in these and the previously studied leucine systems follow pseudo-first-order rate laws, and the corresponding specific rate constants are evaluated and compared. Leucine and its hydrochloride salt proved to be the most stable to both radiolysis and radioracemization, followed by leucine and its HCl salt on kaolin, followed by leucine and its HCl salt on bentonite, with leucine (and its HCl and Na salts) in aqueous solution being least stable to both radiolysis and (except for the HCl salt) radioracemization. Implications of these observations as regards the Vester-Ulbricht mechanism for the origin of optical activity are discussed.

Chemical Effect of Ionizing Radiation on Cytosine

The formation of uracil and the breakdown of the pyrimidine ring were observed when an aqueous solution of cytosine was irradiated. These two effects were investigated with the aid of radioactive tracer techniques and ultraviolet absorption studies.

Observations on Δ7-cholestenol metabolism in the rabbit☆

Abstract 1. 1. Tritium-labeled sterol appears in the free and total cholesterol pools of the serum of the rabbit following tritium-labeled Δ 7 -cholestenol feedings in a manner qualitatively similar to that occurring following tritiumlabeled cholesterol feedings. 2. 2. The conversion of Δ 7 -cholestenol to cholesterol has been demonstrated. Tritium-labeled cholesterol was isolated from the liver sterols of rabbits fed tritium-labeled Δ 7 -cholestenol.

Ionizing Energy as an Aid in Exchange Tritium Labeling

The tritium labeling of organic compounds by the Wilzbach technique—that is, by simple exposure of the compound to tritium gas—is greatly accelerated by the simultaneous exposure of the system to a silent electrical discharge. The incorporation of tritium into benzene was increased by a factor of about 104 without undue decomposition. Cobalt-60 γ-rays were found to be far less useful for increasing the tritium incorporation.