The search for a potentially prebiotic synthesis of nucleotides via arabinose-3-phosphate and its cyanamide derivative.

For the RNA world hypothesis to be accepted, the constitutional self-assembly of RNA will have to be demonstrated. Conceptually, the simplest route to RNA involves nucleotide polymerisation. Activated pyrimidine nucleotides can be derived from arabinose-3-phosphate under potentially prebiotic conditions, but the prebiotic synthesis of this sugar phosphate has not hitherto been investigated. The results of synthetic approaches involving phosphorylation, phosphate migration and 2,3-C--C bond construction are described herein.

On the prebiotic synthesis of ribonucleotides: photoanomerisation of cytosine nucleosides and nucleotides revisited.

Recent work has emphasised the importance of D-ribose aminooxazoline 1 in the synthesis of cytidine ribonucleosides under potentially prebiotic conditions. Upon treatment with cyanoacetylene, 1 is transformed into alpha-D-cytidine (alpha-2), and if an efficient means of anomerising this nucleoside or a derivative thereof were to be found, then the synthesis of one of the key beta-D-nucleosides required to make RNA would be realised. Photoanomerisation of alpha-2 has previously been described, but the yield was extremely low. Therefore, the present study was initiated to determine whether this low yield was the result of a low conversion or competing reaction pathways.

The N-alkyldithiocarbamato complexes [M(S2CNHR)2] (M=Cd(II) Zn(II); R=C2H5, C4H9, C6H13, C12H25); their synthesis, thermal decomposition and use to prepare of nanoparticles and nanorods of CdS.

A series of N-alkyldithiocarbamato complexes [M(S2CNHR)2] (M=Cd(II), Zn(II); R=C2H5, C4H9, C6H13, C12H25) have been synthesised and characterized. The decomposition of these complexes to sulfates has been investigated, and a mechanism proposed. The structures of [Zn(S2CNHHex)2], [Cd(SO4)2(NC5H5)4)]n and [Cd(SO4)2(NC5H5)2(H2O)2)]n have been determined by X-ray single crystal method. The cadmium complex [Cd(S2CNHC12H25)2] and zinc complex [Zn(S2CNHC6H13)2] were used as single-source precursors to synthesize CdS and ZnS nanoparticles, respectively. The synthesis of CdS nanoparticles was carried under various thermolysis conditions and changes in the shape of derived nanoparticles were studied by transmission electron microscope (TEM).

Exploratory studies to investigate a linked prebiotic origin of RNA and coded peptides. 4th Communication. Further observations concerning pyrimidine nucleoside synthesis by stepwise nucleobase assembly.

As part of an ongoing investigation into a possible linked origin of RNA and coded peptides, we have (further) investigated the potentially prebiotic synthesis of pyrimidine ribonucleosides (ribonucleotides), by stepwise nucleobase assembly on sugar (sugar phosphate) scaffolds. In this paper, we complete our description of this assembly process on aldopentose scaffolds. Treatment of D-ribose (14) and D-xylose (20) with cyanamide smoothly produces the furanosylamino-oxazolines 15 and 21, respectively (Schemes 1 and 3). Similar treatment of D-lyxose (26) also produces the furanosylamino-oxazoline 29, but as a minor component of an equilibrating mixture in which the pyranosylamino-oxazoline 28 predominates (Scheme 4). Treatment of the various amino-oxazolines with cyanoacetylene gives furanosylcytidines 16, 25, and 31, and the lyxopyranosylcytidine 30 (Schemes 1-4). Minor by-products of the cyanoacetylene reaction include imino lactone 17, acetals 19, 22, and 24, and cyanovinyl adducts 22 and 23 resulting from initial addition of nucleoside OH groups to the terminal acetylenic C-atom of cyanoacetylene (Schemes 2-4).

A family of manganese rods: syntheses, structures, and magnetic properties.

The reaction of the mixed-valent metal triangles [Mn(3)O(O(2)CR)(6)(py)(3)] (R = CH(3), Ph, C(CH(3))(3)) with the tripodal ligands H(3)thme (1,1,1-tris(hydroxymethyl)ethane) and H(3)tmp (1,1,1-tris(hydroxymethyl)propane) in MeCN, produces a family of manganese rodlike complexes whose structures are all derived from a series of edge-sharing triangles. Variable temperature direct current (dc) magnetic susceptibility data were collected for all complexes in the 1.8-300 K temperature range in fields up to 7.0 T. Complex 1, [Mn(12)O(4)(OH)(2)(PhCOO)(12)(thme)(4)(py)(2)], has an S = 7 ground state with the parameters g = 1.98 and D = -0.13 K. Complex 2, [Mn(8)O(4)((CH(3))(3)CCO(2))(10)(thme)(2)(py)(2)] has a ground state of S = 6, with g = 1.81 and D = -0.36 K. Complex 3, [Mn(7)O(2)(PhCO(2))(9)(thme)(2)(py)(3)], has a spin ground states of S = 7 with the parameters g = 1.78 and D = -0.20 K. The best fit for complex 4, [Mn(6)((CH(3))(3)CCO(2))(8)(tmp)(2)(py)(2)], gave a spin ground state of S = 3 with the parameters g = 1.73 and D = -0.75 K, but was of poorer quality than that normally obtained. The presence of multiple Mn(2+) ions in the structure of 4 leads to the presence of low-lying excited states with energy levels very close to the ground state, and in the case of complex 5, [Mn(6)(CH(3)CO(2))(6)(thme)(2)(H(2)tea)(2)], no satisfactory fit of the data was obtained. DFT calculations on 4 and 5 indicate complexes with spin ground states of S = 4 and S = 0 respectively, despite their topological similarities. Single-crystal hysteresis loop and relaxation measurements show complex 1 to be a SMM.

New routes to polymetallic clusters: fluoride-based tri-, deca-, and hexaicosametallic MnIII clusters and their magnetic properties.

The syntheses, structures and magnetic properties of three new MnIII clusters, [Mn26O17(OH)8(OMe)4F10(bta)22(MeOH)14(H2O)2] (1), [Mn(0O6(OH)2(bta)8(py)8F8] (2) and [NHEt3]2[Mn3O(bta)6F3] (3), are reported (bta=anion of benzotriazole), thereby demonstrating the utility of MnF3 as a new synthon in Mn cluster chemistry. The "melt" reaction (100 degrees C) between MnF(3) and benzotriazole (btaH, C6H5N3) under an inert atmosphere, followed by dissolution in MeOH produces the cluster [Mn26O17(OH)8(OMe)4F10(bta)22(MeOH)14(H2O)2] (1) after two weeks. Complex 1 crystallizes in the triclinic space group P1, and consists of a complicated array of metal tetrahedra linked by mu3-O2- ions, mu3- and mu2-OH- ions, mu2-MeO- ions and mu2-bta- ligands. The "simpler" reaction between MnF3 and btaH in boiling MeOH (50 degrees C) also produces complex 1. If this reaction is repeated in the presence of pyridine, the decametallic complex [Mn10O6(OH)2(bta)8(py)8F8] (2) is produced. Complex 2 crystallizes in the triclinic space group P1 and consists of a "supertetrahedral" [Mn(III)10] core bridged by six mu3-O2- ions, two mu3-OH- ions, four mu2-F- ions and eight mu2-bta- ions. The replacement of pyridine by triethylamine in the same reaction scheme produces the trimetallic species [NHEt3]2[Mn3O(bta)6F3] (3). Complex 3 crystallises in the monoclinic space group P2(1)/c and has a structure analogous to that of the basic metal carboxylates of general formula [M3O(RCO2)6L3]0/+, which consists of an oxo-centred metal triangle with mu2-bta- ligands bridging each edge of the triangle and the fluoride ions acting as the terminal ligands. DC magnetic susceptibility measurements in the 300-1.8 K and 0.1-7 T ranges were investigated for all three complexes. For each, the value of chi(M)T decreases with decreasing temperatures; this indicates the presence of dominant antiferromagnetic exchange interactions in 1-3. For complex 1, the low-temperature value of chi(M)T is 10 cm(3) K mol(-1) and fitting of the magnetisation data gives S=4, g=2.0 and D=-0.90 cm(-1). For complex 2, the value of chi(M)T falls to a value of approximately 5.0 cm(3) K mol(-1) at 1.8 K, which is consistent with a small spin ground state. For the triangular complex 3, the best fit to the experimental chi(M)T versus T data was obtained for the following parameters: Ja = -5.01 cm(-1), Jb = +9.16 cm(-1) and g=2.00, resulting in an S=2 spin ground state. DFT calculations on 3, however, suggest an S=1 or S=0 ground state with J(a)=-2.95 cm(-1) and J(b)=-2.12 cm(-1). AC susceptibility measurements performed on 1 in the 1.8-4.00 K range show the presence of out-of-phase AC susceptibility signals, but no peaks. Low-temperature single-crystal studies performed on 1 on an array of micro-SQUIDS show the time- and temperature-dependent hysteresis loops indicative of single-molecule magnetism behaviour.

Exploratory studies to investigate a linked prebiotic origin of RNA and coded peptides. 2nd communication. Derivation and reactivity of xylose phosphates.

The potentially prebiotic synthesis of ribo-nucleotides by stepwise pyrimidine nucleobase assembly on arabinose-3-phosphate derivatives has been demonstrated in previous work. Consideration of the provenance of pentose phosphates, by aldolisation or sugar phosphorylation, suggested that 2-phosphate derivatives might be generated more easily than 3-phosphate derivatives. In the 2-phosphate series, nucleobase-assembly chemistry to give ribo-nucleotides/nucleic acid can be envisaged from xylo-configured starting materials. In this paper, the derivation of xylose-2-phosphate derivatives by aldol chemistry and attempts to demonstrate subsequent pyrimidine nucleobase assembly are reported.

Exploratory studies to investigate a linked prebiotic origin of RNA and coded peptides.

An introduction to the premise that RNA and genetically coded proteins should not be viewed as etiologically discrete entities in the origin of life is presented. This premise follows from the mutual interdependence of RNA and coded proteins in biology and the lack of prebiotically plausible constitutional self-assembly processes leading to either polymeric species. The RNA:coded peptides subsystem and its informational core, the genetic code, are then analysed retrosynthetically to suggest a (replicative) synthesis involving the intermediacy of aminoacyl-RNA trimers (cf. Scheme 5). A number of potential candidate aminoacyl-RNA trimers are identified (23-26; Scheme 6) and a chemical strategy to assess their validity is outlined. Experimental investigation of potential aminoacylation chemistry, nucleobase assembly and phosphate activation rules out three of the trimers but suggests that 26 is worthy of further investigation.