Noam Lahav

The emergence of life on Earth.

Combined top-down and bottom-up research strategies and the principle of biological continuity were employed in an attempt to reconstruct a comprehensive origin of life theory, which is an extension of the coevolution theory (Lahav and Nir, Origins of Life Evol. Biosphere (1997) 27, 377-395). The resulting theory of emergence of templated-information and functionality (ETIF) addresses the emergence of living entities from inanimate matter, and that of the central mechanisms of their further evolution. It proposes the emergence of short organic catalysts (peptides and proto-ribozymes) and feedback-loop systems, plus their template-and-sequence-directed (TSD) reactions, encompassing catalyzed replication and translation of populations of molecules organized as chemical-informational feedback loop entities, in a fluctuating (wetting-drying) environment, functioning as simplified extant molecular-biological systems. The feedback loops with their TSD systems are chemically and functionally continuous with extant living organisms and their emergence in an inanimate environment may be defined as the beginning of life. The ETIF theory considers the emergence of bio-homochirality, a primordial genetic code, information and the incorporation of primordial metabolic cycles and compartmentation into the emerging living entities. This theory helps to establish a novel measure of biological information, which focuses on its physical effects rather than on the structure of the message, and makes it possible to estimate the time needed for the transition from the inanimate state to the closure of the first feedback-loop systems. Moreover, it forms the basis for novel laboratory experiments and computer modeling, encompassing catalytic activity of short peptides and proto-RNAs and the emergence of bio-homochirality and feedback-loop systems.

A thermo-XRD study of Al-pillared smectites differing in source of charge, obtained in dialyzed, non-dialyzed and washed systems

The mechanism of Al-pillaring of the following smectites: montmorillonite, beidellite, saponite, hectorite and Laponite was investigated. For this purpose the products of three different preparation techniques that had been applied on the Keggin-ion smectite suspensions were studied by thermo-XRD analysis. These techniques included: (a) dialysis of the clay-Keggin ion suspensions; (b) aging of the smectites in the Keggin ion solution, and (c) separation between the clay and the supernatant after 24 h and washing the smectite to remove excess Na, Al and Cl. In the first stage after treating the smectite with the Keggin ion solution, the Keggin ion dissociated into smaller units. The adsorption of Al by the smectites took place in the first 24 h, but was very high relative to the cation exchange capacity of the smectites, indicating that the adsorbed species were hydroxy and/or chloro Al complexes. Thermo-XRD analysis showed that these adsorbed cations were monomers or very small oligomers. Large three-dimensional oligomers, which are essential for the formation of thermally stable pillared clays, were obtained inside the interlayer space after 7 days of dialysis or after thoroughly washing the smectites. At 600°C, the Al oxocation condensed with the silicate layer and the heated smectite did not swell in water. Pillared clays were obtained with montmorillonite, beidellite and saponite after 7 days of dialysis or repeated washings (in 5 days). Under the conditions used in the present study ([OH]/[Al] ratio of 2.3 and final Al concentration 0.07 M) Laponite and hectorite did not form thermally stable pillared clays.

Thermal treatment of the kaolinite/CsCl/H2O intercalation complex

Abstract Four kaolinite/CsCl intercalation complexes were prepared by different methods and characterized using X-ray diffraction, photoacoustic and diffuse reflectance infrared spectroscopy, and simultaneous DTA—TG. Sample A was obtained by wet grinding a mixture consisting of equal amounts of CsCl and kaolinite: in this complex the kaolin-like layers were not arranged in any preferred orientation. This sample contained a great amount of intercalated water which could be eliminated below 250°C. Sample B was derived from sample A by heating it at 250°C. In sample B, the kaolin-like layers were parallel with a c -spacing of 1.065 nm. Samples C and D were obtained by ageing sample A or untreated kaolinite, respectively, in a concentrated CsCl solution. Both of the latter samples were similar to sample B.

The RNA-world and co-evolution hypotheses and the origin of life: Implications, research strategies and perspectives

The applicability of the RNA-world and co-evolution hypotheses to the study of the very first stages of the origin of life is discussed. The discussion focuses on the basic differences between the two hypotheses and their implications, with regard to the reconstruction methodology, ribosome emergence, balance between ribozymes and protein enzymes, and their major difficulties. Additional complexities of the two hypotheses, such as membranes and the energy source of the first reactions, are not treated in the present work.A central element in the proposed experimental strategies is the study of the catalytic activities of very small peptides and RNA-like oligomers, according to existing, as well as to yet-to-be-invented scenarios of the two hypotheses under consideration. It is suggested that the noveldirected molecular evolution technology, andmolecular computational modeling, can be applied to this research. This strategy is assumed to be essential for the suggested goal of future studies of the origin of life, namely, the establishment of a ‘Primordial Darwinian entity’.

Thermal analysis study of heat of dehydration of tributylammonium smectites

Abstract The dehydration of laponite and montmorillonite treated with tributylammonium chloride was studied by DSC, TG and X-ray diffraction. Dehydration of the organo-laponite took place in one stage at 320–475 K, whereas that of the organo-montmorillonite occurred in two stages, at 320–435 and 435–485 K. The first stage was attributed to loss of water of the hydrophobic hydration zone. The second stage was specific for montmorillonite and was attributed to water molecules forming hydrogen bonds with the oxygen planes of the silicate layers. Hydrogen bond formation was attributed to the tetrahedral substitution of Al for Si. The organo-laponite has a lower molar heat of dehydration than laponite, indicating that the interlayer water clusters of the organo-clay are smaller than those of the untreated clay. The molar heat of dehydration of untreated montmorillonite is less than that of untreated laponite, indicating that water clusters in the interlayer of the former are smaller. The molar heat of dehydration of organo-montmorillonite is higher at the second dehydration stage than at the first, because at this stage water molecules which form hydrogen bonds with atoms from the oxygen plane are evolved. In organo-montmorillonite, water molecules from the non-structured zone form water bridges between adjacent oxygen planes, thus preventing crystalline swelling. In organo-laponite, non-structured water molecules do not form strong hydrogen bonds with atoms from the oxygen plane, water bridges between adjacent oxygen planes are weak, and crystalline swelling is thus prevented to a limited extent only.

X-ray study of the thermal intercalation of alkali halides into kaolinite

Intercalation complexes of kaolinite with a series of alkali halides (NaCl (trace amounts), KCl, RbCl, CsCl, NaBr, KBr, CsBr, Kl, Rbl and Csl) were obtained by a thermal solid state reaction between the kaolinite-dimethylsulfoxide intercalation complex and the appropriate alkali halide. The ground mixtures (1∶1 weight ratio) were pressed into disks that were gradually heated up to 250 °C for different times. X-ray diffractograms of the disks were recorded after each thermal treatment. At the end of the thermal treatment the disks were ground and basal spacings of the powders obtained. As a result of thermal treatment, alkali halide ions diffuse into the interlayers, replacing the intercalated dimethylsulfoxide molecules. Such a replacement may take place only if the thermal diffusion of the penetrating species is faster than the evolution of the intercalated organic molecule. With increasing temperature the intercalated salt diffused outside the interlayer space or underwent a thermal hydrolysis which resulted in the evolution of hydrogen halides from the interlayer space. Consequently, the amounts of intercalation complexes decreased at elevated temperatures.

Polymerization of alanine in the presence of a non-swelling montmorillonite.

SummaryAlanine, starting from alanine-adenylate, has been polymerized in the presence of non-swelling Al-montmorillonite. The yield of polymerization is much lower than that obtained in the presence of swelling Na-montmorillonite. The possibility that the changing interlayer spacing in Na-montmorillonite might be responsible for its catalytic properties, is discussed.

INFRARED STUDY OF THE INTERCALATION OF POTASSIUM HALIDES IN KAOLINITE

KCl-, KBr-, and KI-kaolinite intercalation complexes were synthesized by gradually heating potassium-halide discs of the dimethylsulfoxide (DMSO)-kaolinite intermediate at temperatures to 330°C. Two types of complexes were identified by infrared spectroscopy: almost non-hydrous, obtained during thermal treatment of the DMSO complex; and hydrated, produced by regrinding the disc in air. The former showed basal spacings with integral series of 00l reflections indicating ordered stacking of parallel 1:1 layers. Grinding resulted in delamination and formation of a disordered “card-house” type structure. The frequencies of the kaolinite OH bands show that the strength of the hydrogen bond between the intercalated halide and the inner-surface hydroxyl group decreases as Cl > Br > I. The positions of the H2O bands imply that halide-H2O interaction decreases in the same order. Consequently, the strength of the hydrogen bond between H2O and the oxygen atom plane increases in the opposite sequence.In the non-hydrous KCl-kaolinite complex the inner hydroxyl band of kaolinite at 3620 cm-1 is replaced by a new feature at 3562 cm-1, indicating that these OH groups are perturbed. It is suggested that Cl ions penetrate through the ditrigonal hole and form hydrogen bonds with the inner OH groups. In contrast, Br and I ions are too large to pass into the ditrigonal holes and do not form hydrogen bonds with the inner hydroxyls.

Soluble minerals in chemical evolution. II: Characterization of the adsorption of 5'-AMP and 5'-CMP on a variety of soluble mineral salts

The adsorption of 5′-AMP and 5′-CMP was studied in saturated solutions of several soluble mineral salts (NaCl, Na2SO4, MgCl2·6H2O, MgSO4·7H2O, CaCl2·2H2O, CaSO4·2H2O, SrCl2·6H2O, SrSO4, and ZnSO4·7H2O) as a function of pH, ionic strength, and surface area of the solid salt. The adsorption shows a pH dependence; this can be correlated with the charge on the nucleotide molecule which is determined by the state of protonation of the N-1 nitrogen of 5′-AMP or N-3 nitrogen of 5′-CMP and the phosphate oxygens. The adsorption which results from the binding between the nucleotide molecule and the salt surface is proposed as being due to electrostatic forces. It was concluded that the adsorption was reversible in nature. The adsorption shows a strong dependence upon ionic strength and decreases with increasing ionic strength. Surface area is shown to be an important factor in evaluating and comparing the magnitude of adsorption of nucleotides onto various mineral salts. The implications of the results of the study are discussed in terms of the importance of soluble mineral salts as adsorption sites in the characterization of the adsorption reactions of an adsorbed template in biogeochemical cycles.

The biogeochemical cycle of the adsorbed template. I: Formation of the template.

Experimental results are presented for the verification of the first adsorption step of the ‘adsorbed template’ biogeochemical cycle, a simple model for a primitive prebiotic replication system. The adsorption of Poly-C, Poly-U, Poly-A, Poly-G, and 5′-AMP, 5′-GMP, 5′-CMP and 5′-UMP onto gypsum was studied. It was found that under the conditions of the experiment, the polymers have a very high affinity for the mineral surface, while the monomers adsorb much less efficiently.