Uridine Monophosphates Research Articles

CaCO3 Polymorphs as Mineral Catalysts for Prebiotic Phosphorylation of Uridine

AbstractEstablishing plausible routes for the abiotic formation of nucleotides is a challenging problem because the phosphorylation of organic molecules is thermodynamically unfavorable in water, and because common phosphorous‐containing minerals such as apatite are highly insoluble. Reactions of reduced phases such as the meteoritic mineral schreibersite with ammonia containing solutions can form stable amino‐derivatives of phosphates/phosphite, and carbonate‐rich lakes have been suggested as environments where phosphate species and organic molecules could accumulate in significant abundances, thus promoting an ideal environment for abiotic phosphorylation. This work reports the catalytic properties of three CaCO3 polymorphs—calcite, aragonite, and vaterite—on diamidophosphate (DAP)‐induced phosphorylation of the uridine nucleoside during a 24‐hr dry‐down reaction. It is shown that the phosphorylation reaction is accelerated in solutions containing CaCO3 compared to those with no mineral present. For un‐buffered solutions with no mineral present, the primary products formed are uridine monophosphates (UMPs), with yields making up 22.3 ± 3.9% of the total detected species, while solutions containing calcite and aragonite formed primarily UMP dimers (yields of 15.3 ± 1.1% and 14.8 ± 1.3%, respectively). Vaterite showed a strong preference for forming cyclic UMP (cUMP) (26.3 ± 0.3% yield), and no higher order polymers were observed using any carbonate mineral. Reactions containing CaSO4·2H2O (gypsum) showed a preference for forming cUMP, though not as strong as vaterite, while those containing CaCl2 (calcium chloride) and CaWO4 (scheelite) did not yield any phosphorylated products other than UMPs. These results suggest that CaCO3 minerals could have played an important role in facilitating prebiotic phosphorylation in aqueous environments that undergo drying cycles.

Immunity, breast milk and infant formula: finding the optimal balance

Mother's milk is a unique product for children in the first and second year of life. In addition to the components that provide the energy needs of the baby, breast milk contains many biologically active compounds, microorganisms, stem cells that influence the maturation of organs and systems, including the immune system. Even in the most advanced artificial formula, it is impossible to replicate the composition and effects of breast milk completely. Nevertheless, it is possible to introduce some components into the formula that have a positive effect on the developing immune system. These include fat components, in particular long-chain polyunsaturated fatty acids and -palmitate, nucleotides, the most valuable of which are adenosine, guanine, uridine, cytidine and inosine monophosphates, oligosaccharides, probiotics, macro- and microelements. Goat's milk is an attractive natural product for the production of quality infant formula. Enriching milk formulas based on goat's milk with components with immunomodulatory functions homologous to those of breast milk makes it possible to significantly reduce the adverse effects of artificial feeding of infants, as well as to achieve a positive immunomodulatory effect. Kabrita adapted goat milk formula contains all the beneficial natural components of goat milk, adapted by the manufacturer according to the protein, fat, carbohydrate, micro- and macronutrient composition, with the addition of probiotic complex BB-12 and lipid complex DigestX.

Silicate-, Magnesium Ion-, and Urea-Induced Prebiotic Phosphorylation of Uridine via Pyrophosphate; Revisiting the Hot Drying Water Pool Scenario.

The availability of nucleotides on the early Earth is of great significance for the origin of a self-replicating system capable of undergoing evolution. We hereby report the successful phosphorylation reactions of the nucleoside uridine under heating in the “drying pool” prebiotic model at temperatures ranging from 60–75 °C, and by using pyrophosphate as a phosphorylation agent. Uridine monophosphates (UMP) such as uridine-5′-monophosphate (5′-UMP), 2′-UMP, and 3′-UMP, as well as cyclic 2′-3′-UMP, were identified by 31P-NMR. In addition to the above-mentioned products, a dimer of uridine-phosphate-uridine (U-P-U) was also observed. The reactions were promoted by white quartz sand, Mg2+, and by using urea as a condensation agent. The reactions also proceeded without this mixture; however, the yields increased remarkably with the presence of the above-mentioned materials. The results suggest that a hot/evaporating-drying pool of water containing organics, salts, and reactive phosphorus could be sufficient to form significant phosphate esters.

Nucleotide Selectivity in Abiotic RNA Polymerization Reactions

In order to establish an RNA world on early Earth, the nucleotides must form polymers through chemical rather than biochemical reactions. The polymerization products must be long enough to perform catalytic functions, including self-replication, and to preserve genetic information. These functions depend not only on the length of the polymers, but also on their sequences. To date, studies of abiotic RNA polymerization generally have focused on routes to polymerization of a single nucleotide and lengths of the homopolymer products. Less work has been done the selectivity of the reaction toward incorporation of some nucleotides over others in nucleotide mixtures. Such information is an essential step toward understanding the chemical evolution of RNA. To address this question, in the present work RNA polymerization reactions were performed in the presence of montmorillonite clay catalyst. The nucleotides included the monophosphates of adenosine, cytosine, guanosine, uridine and inosine. Experiments included reactions of mixtures of an imidazole-activated nucleotide (ImpX) with one or more unactivated nucleotides (XMP), of two or more ImpX, and of XMP that were activated in situ in the polymerization reaction itself. The reaction products were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the lengths and nucleotide compositions of the polymerization products. The results show that the extent of polymerization, the degree of heteropolymerization vs. homopolymerization, and the composition of the polymeric products all vary among the different nucleotides and depend upon which nucleotides and how many different nucleotides are present in the mixture.

One flask synthesis of 2′,3′-cyclic nucleoside monophosphates from unprotected nucleosides using activated cyclic trimetaphosphate

The 2′,3′-cyclic nucleoside monophosphates (2′,3′-cNMPs) of adenosine, guanosine, cytidine, and uridine were prepared in good yield in a one pot reaction from unprotected ribonucleosides and activated trimetaphosphate in the presence of N-methylimidazole, 4-nitroimidazole and MgCl2.

Nucleoside monophosphate complex structures of the endonuclease domain from the influenza virus polymerase PA subunit reveal the substrate binding site inside the catalytic center.

Highly pathogenic influenza virus strains currently in circulation pose a significant risk of a global pandemic. Following the reported crystal structure of the endonuclease domain from the avian influenza virus polymerase PA subunit, here we report the results of a systematic X-ray crystallographic analysis of its complex with adenosine, uridine, and thymidine nucleoside monophosphates (NMPs). Electron density corresponding to the monophosphate moiety of each nucleotide was apparent in each NMP complex and bound to the catalytic metal. A hydrophobic site was found to contribute to nucleoside binding. The NMP complex structures should represent the conformation of the bound product after nuclease cleavage. Moreover, one solvent molecule was found to occupy an equivalent position to the second reported Mn(2+) ion, where it mediates the interaction between bound NMPs and the N-terminal PA domain in the presence of the Mg(2+) ion. The results presented here indicate a possible cleavage mechanism and identify a distinct nucleotide binding pocket. The identification of this binding pocket opens a new avenue for anti-influenza drug discovery, targeting the cap-dependent endonuclease, in response to the worldwide threat of influenza.

An insight into the phenomena involved in a multiple-function stationary phase for the capillary electrochromatographic separation of 2'-, 3'-, and 5'-monophosphorylated nucleoside isomers.

The electrochromatographic separations of 2'-, 3'- and 5'-monophosphates of adenosine, guanosine, cytidine, and uridine were carried out with an open-tubular capillary column which was wall-coated with a highly selective reagent, 28-membered macrocyclic polyamine, 4, 8, 12, 18, 22, 26-hexaaza-1,15-dioxacyclooctaeicosane ([28]ane-N6O2). The effects of pH, composition and concentration of background electrolyte (BGE), applied voltage, column length, and the additive of the BGE, such as metal ions, borate, beta-cyclodextrin and organic solvent on the separation of these monophosphorylated nucleotide isomers were investigated. The results suggested that the interactions between analytes and the bonded groups on the wall predominantly comprise anion coordination and anion exchange in addition to the electrophoresis. A well-resolved electrochromatogram was obtained with the capillary column of 100 cm (75 cm effective length) x 75 microm inside diameter (ID), citrate buffer (20 mM, pH 3.99), applied voltage of -22 kV and detection at 254 nm. Column efficiency was found with the average theoretical plate numbers of 119,500/m and a low detection limit of 0.01 microM level could be achieved for the separation of these isomers.

Determination of total potentially available nucleosides in human milk from Asian women

Objectives The objective was to measure the total potentially available nucleosides (TPAN) in breast milk from Asian women. Methods One hundred sixty milk samples were collected from 135 healthy, lactating women in Hong Kong, the Philippines, and Singapore at four stages of lactation: colostrum (1 to 3 days postpartum), transitional (7 to 10 days postpartum), early mature (28 to 35 days postpartum), and late mature (90 to 100 days postpartum). Samples were pooled by site and stage of lactation before analysis. Results The mean TPAN concentration was 203 μM/L (69.4 mg/L corrected for recovery). Average TPAN concentrations were 171.9 μM/L in colostrum, 208.1 μM/L in transitional milk, 221.6 μM/L in early mature milk, and 210.6 μM/L in late mature milk, with no notable differences between countries. The major sources of nucleosides were RNA (43.3% of TPAN) and free nucleotides (39.9% of TPAN). The average percentages of cytidine, uridine, guanosine, and adenosine monophosphates were 44.5%, 23.1%, 16.5%, and 16.1% of TPAN, respectively. The sources of nucleosides and percentages of nucleotide bases were similar for all stages of lactation. Over 91% of the TPAN was present in the non-cellular component except in colostrum. Conclusions The average TPAN level in Asian women is similar to that in European and American women, and free nucleotides in human milk represent less than half of the TPAN.

Fluid secretion by isolated malpighian tubules ofDrosophila melanogasterMeig.: effects of organic anions, quinacrine and a diuretic factor found in the secreted fluid

Para-aminohippuric acid (PAH, 0.2 and 1 mmol l(-)(1)) had no effect on the basal fluid secretion rate (FSR) of isolated Malpighian tubules of Drosophila melanogaster Meig. and did not affect stimulation of the FSR induced by adenosine 3',5'-monophosphate (cAMP). Phenol Red (phenolsulphonphthalein, PSP; 0.5 and 1 mmol l(-)(1)) slowed the FSR and abolished stimulation of the FSR by cAMP. Diodrast (1 mmol l(-)(1)) slightly, but significantly, reduced the FSR and greatly reduced the stimulation of the FSR normally provoked by cAMP and by the 3',5'-monophosphates of guanosine (cGMP), inosine (cIMP) and uridine (cUMP). However, stimulation of the FSR by the 3', 5'-monophosphate of cytidine (cCMP) was little affected by diodrast. Probenecid (0.2 or 1 mmol l(-)(1)) consistently stimulated the FSR, on average by approximately 25 %, but did not markedly inhibit the subsequent stimulation of the FSR by cAMP, cGMP or cIMP. However, the FSR of tubules stimulated by cGMP was temporarily lowered by probenecid. Quinacrine (0.1 mmol l(-)(1)) slowed basal FSR by an average of approximately 30 %, but subsequent stimulation of the FSR by cAMP was not noticeably affected. Both 0.1 mmol l(-)(1) cAMP and 1 mmol l(-)(1) probenecid stimulated adenylate cyclase activity in extracts of Malpighian tubules, but cIMP, cGMP, cUMP and diodrast were without effect in this regard. Uptake of radioactivity from a solution containing 500 nmol l(-)(1) [(3)H]cAMP and 9.5 micromol l(-)(1) cAMP was reduced by more than 90 % by 1 mmol l(-)(1) PSP, by approximately 40 % by 0.2 mmol l(-)(1) probenecid, by 36 % by 1 mmol l(-)(1) diodrast and by 30 % by 1 mmol l(-)(1) PAH. Neither 0.01 mmol l(-)(1) ouabain nor 0.1 mmol l(-)(1) quinacrine affected the uptake of [(3)H]cAMP by the Malpighian tubules. Fluid secreted by isolated Malpighian tubules of Drosophila melanogaster contains a factor that stimulated the FSR on average by approximately 50 %. The presence in the secreted fluid of cGMP at a concentration of 8.3 micromol l(-)(1) did not explain the stimulatory effect on FSR. These results support the existence of a carrier-mediated uptake of cyclic nucleotides into the Malpighian tubules of Drosophila melanogaster, possibly involving a multispecific transporter.

Stimulation of fluid secretion of malpighian tubules of drosophila melanogaster meig. by cyclic nucleotides of inosine, cytidine, thymidine and uridine

External application of the 3',5'-cyclic monophosphates of inosine, cytidine, uridine and thymidine stimulated the fluid secretion rate (FSR) of Malpighian tubules isolated from Drosophila melanogaster. The evidence suggested that the cyclic nucleotides acted intracellularly in some capacity. Receptors of the 'purinergic' type appeared not to be major contributors to fluid secretion; of three purinergic agonists tried, adenosine, adenosine 5'-monophosphate (AMP) and adenosine 5'-triphosphate (ATP), only adenosine had an effect, but this was not observed consistently. None of the purinergic agonists interfered with the stimulation of the FSR by adenosine 3',5'-cyclic monophosphate (cAMP). The maximum stimulation of the fluid-secretion rate by any cyclic nucleotide was approximately double the unstimulated (control) rate. Tubules stimulated to less than maximal FSR by one cyclic nucleotide could be stimulated maximally by an appropriate concentration of another cyclic nucleotide. Malpighian tubules bathed in solutions that contained either [3H]cAMP or [3H]cGMP accumulated radioactivity to a level many times that in the medium. Accumulation of radioactivity by tubules bathed in 430 nmol l-1 [3H]cAMP was suppressed by 1 mmol l-1 non-radioactive cyclic nucleotides in the order cAMP>>cGMP>cIMP>cCMP; neither cTMP nor cUMP suppressed the accumulation of [3H]cAMP. Approximately 35 % of the [3H]cAMP and 80 % of the [3H]cGMP that entered the Malpighian tubule cells was metabolised to compounds that were not identified. It was concluded that cyclic nucleotides enter the Malpighian tubule cells by at least one transport mechanism which is particularly sensitive to purine-based nucleotides.

Attachment of Sugar Phosphates and Nucleotide Derivatives to Pyrazolylborate-Zinc Units

Phosphate derivatives which model intermediates of enzymatic glycoside and nucleotide transformations were reacted with the hydrolytically active zinc-hydroxide species Tp*Zn−OH (Tp* = 3,5-disubstituted tris(pyrazolyl)borates). Depending on the substrate or the reaction conditions, either phosphate ester cleavage or deprotonation of a nucleobase NH was observed. As a result, the Tp*Zn units were attached to the phosphate part or/and to the nucleobase part of the substrate. Nucleobase adducts were found of three uridine monophosphate derivatives. Phosphate adducts were found of a hydroxyacetone monophosphate, of a ribose phosphate, and of uridine and N-methyluridine monophosphates. The products were identified by crystallographic and spectroscopic methods as tetrahedral Tp*Zn−X complexes. Crystals of TpCum,MeZn−OPO(OC6H4NO2)(O-hydroxyacetone dimethyl ketal) are monoclinic, space group P21/n, with a = 13.221(1) Å, b = 13.738(1) Å, c = 30.303(3) Å, β = 99.57(1)°, Z = 4; those of TpCum,MeZn−OPO(OC6H4NO2)(O-2,3-isopropylidene-5-methylribose) are monoclinic, space group P21, with a = 16.179(6), Å, b = 16.206(5) Å, c = 21.192(14) Å, β = 101.02(5)°, Z = 2; those of TpPic,MeZn(H2O)−OPO(OC6H4NO2)(O-2,3-isopropylidene-5-methylribose) are triclinic, space group P1, with a = 13.106(4) Å, b = 13.676(5) Å, c = 17.021(6) Å, α = 84.10(3)°, β = 88.37(3)°, γ = 62.43(3)°, Z = 1.

ChemInform Abstract: Hydrolytic Dethiophosphorylation and Desulfurization of the Monothioate Analogues of Uridine Monophosphates under Acidic Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hydrolytic dethiophosphorylation and desulfurization of the monothioate analogues of uridine monophosphates under acidic conditions

The hydrolytic reactions of uridine 2′-, 3′- and 5′-phosphoromonothioates (2″-, 3′- and 5′-UMPS) under acidic and neutral conditions have been followed by HPLC. Under slightly acidic conditions (pH 2–5), only pH-independent dethiophosphorylation to uridine takes place. This reaction is 200- to 300-fold as fast as dephosphorylation of the corresponding uridine monophosphates (UMP), presumably due to higher stability of the thiometaphosphate monoanion compared to metaphosphate anion. At pH > 5, i.e. at pH > pKa2 of the thiophosphate moiety, the dethiophosphorylation is retarded with increasing basicity of the solution. At pH < 1, acid-catalysed desulfurization of 2′- and 3′-UMPS to an isomeric mixture of 2′/3′-UMP competes with their dethiophosphorylation. This reaction is suggested to proceed by a nucleophilic attack of the neighbouring hydroxy group on phosphorus. No such reaction occurs with 5′-UMPS. In contrast to 2′- and 3′-UMP, no sign of interconversion of 2′- and 3′-UMPS is detected.

Interactions of nickel(II) with adenosine, uridine and cytidine monophosphates. A calorimetric study

The thermodynamic parameters of the interaction between nickel(II) and 3′AMP, 2′AMP, 5′UMP and 5′CMP in aqueous solution were determined calorimetrically (ionic strength adjusted to 0.1 with tetramethylammonium bromide, 25°C at physiological pH). The experimental conditions were carefully selected to avoid polynuclear complex formation. The calorimetric data confirm the existence of the [(Ni(NMP)) 2] 2− complexes for 3′AMP and 2′AMP, the latter previously studied by Frey and Stuehr by potentiometry. The [(Ni(NMP) 2] 2− complex formation constant (log K 2 = 1.96 and 2.16 for the 3′AMP and 2′AMP derivatives, respectively) and complex formation enthalpies ( ΔH 1 = + 4.5 kJ mol −1 and ΔH 2 = −10.0 kJ mol −1 for the 3′AMP complexes, and ΔH 1 = +2.4 kJ mol −1 and ΔH 2 = −22.3 kJ mol −1 for the 2′AMP complexes) were determined. The values of ΔH 1 for the complexes Ni(5′UMP) and Ni(5′CMP) are, respectively, 8.3 and 8.7 kJ mol −1. The degree of macrochelation indicated by Sigel after very careful potentiometric studies is confirmed by the calorimetric data, and follows the order: [Ni(5′AMP)] cl > [Ni(2′AMP)] cd > [Ni(3′AMP)] cl. These results confirm the formation of the ML 2 complex in solution and agree very well with the hypothesis of ‘stacking’ between the purine bases promoted for metal ions.

Ribonucleotide Electrolytes for Capillary Electrophoresis of Polyphosphates and Polyphosphonates with Indirect Photometric Detection

Ribonucleotide electrolytes, namely adenosine, cytidine, guanosine, and uridine monophosphates (AMP, CMP, GMP, and UMP), are investigated for capillary electrophoresis (CE) with indirect photometric detection (IPD) of polyphosphates (PR) and polyphosphonates (RPR). A separation of 12 PR and RPR components in about 30 min using 5 mM ribonucleotide with 2 mM diethylenetriamine as electroosmotic flow suppressor with negative polarity CE is possible. Although all of the ribonucleotide monophosphates seem to provide reasonable selectivity, AMP is the best electrolyte because of its high molar absorptivity, large dynamic reserve, and favorable transfer ratio required for a sensitive IPD. However, the quality of separation for some P n (particularly P 3 - and P 4 -phosphates) can be dramatically improved by incorporating Mg 2+ in the running buffer with positive polarity. Detection limits for PR and RPR range from 0.84 to 11 μM, quite comparable to those obtained with commonly used HPLC methods. The reproducibility of the migration time is between 0.5 and 1.0% RSD. One pratical application is the determination of phosphates and phosphonates in soap and various brands of toothpaste. The quantitation of glyphosate and aminomethylphosphonic acid in a commmercial herbicide is performed with an average relative error of 1.6%. The developed CE method could be applied routinely for the analysis of samples having phosphorus-containing polyvalent anions

Additional evidence for the exceptional mechanism of the acid-catalysed hydrolysis of 4-oxopyrimidine nucleosides: hydrolysis of 1-(1-alkoxyalkyl)uracils, seconucleosides, 3′-C-alkyl nucleosides and nucleoside 3′,5′-cyclic monophosphates

The rate constants for the acid-catalysed hydrolysis of 1-(1 -alkoxyethyl)uracils and 1-alkoxymethyluracils have been determined. With both series of compounds, the hydrolysis rate is rather insensitive to the polar nature of the alkoxy group, in striking contrast with the hydrolysis of the corresponding analogues of adenine and cytosine nucleosides, which react via rate-limiting formation of an oxocarbenium ion intermediate. Furthermore, it has been shown that the 3′,5′-cyclic monophosphates of thymidine and uridine undergo the hydrolysis of the N-glycosidic bond 760 and 260 times as fast as their parent nucleosides, while the cyclic monophosphates of 2′-deoxyadenosine and adenosine are depurinated much more slowly than the corresponding nucleosides. On this basis it is suggested that 4-oxopyrimidine nucleosides are hydrolysed by opening of the sugar ring. To obtain further evidence for this exceptional mechanism, comparative kinetic measurements with some seco- and 3′-C-alkyl nucleosides of uracil and adenine have been carried out.

Hydrolysis of 2'- and 3'-C-methyluridine 2',3'-cyclic monophosphates and interconversion and dephosphorylation of the resulting 2'- and 3'-monophosphates: comparison with the reactions of uridine monophosphates.

2',3'-Cyclic monophosphates of 2'- and 3'-C-methyluridines have been prepared and shown to hydrolyze to a mixture of the correaponding 2'- and 3'-monophosphates. The predominant product isomer is the one having the tertiary hydroxyl group phosphorylated, but on longer treatment a phosphate migration from the tertiary to secondary hydroxyl function takes place. Hydrolytic dephosphorylation competes with the phosphate migration, the tertiary hydroxyl group being dephosphorylated 1 order of magnitude faster than the secondary one

Carrier-mediated translocation of uridine diphosphate glucose into the lumen of endoplasmic reticulum-derived vesicles from rat liver.

Radiolabeled UDPGlc incubated with rough endoplasmic reticulum (RER)-derived microsomes from rat liver became associated with the vesicles. This microsomal uptake of nucleotide sugar was time and temperature dependent. Analysis of the molecular species containing radiolabel revealed that initial uptake represented entry of predominantly intact UDPGlc in the microsomes. Conclusive evidence for proper translocation of UDPGlc across the microsomal membrane into the intravesicular space was obtained by demonstrating that UDPGlc was transported into an osmotically sensitive compartment. Microsomal uptake of UDPGlc exhibited features characteristic of carrier-mediated transport including saturation, specificity, and countertransport. Inhibition and trans-stimulation studies showed that other uridine-containing nucleotide sugars and 5'-UMP were substrates of the postulated microsomal carrier system for UDPGlc, while cytosine- or guanosine-containing nucleotides and non-5'-uridine monophosphates were, at best, very poor substrates. UDPGlc translocation activities were lower in smooth microsomal fractions than in the RER-derived vesicles, indicating that contamination with Golgi membranes could not be responsible for microsomal transport of UDPGlc. Our findings suggest that rat liver endoplasmic reticulum possesses a carrier system mediating proper translocation of UDPGlc and 5'-uridine-substituted structural analogues across the membrane.

ChemInform Abstract: Aqueous Coordination Chemistry of Vanadocene Dichloride, V(η5‐C5H5)2Cl2, with Nucleotides and Phosphoesters. Mechanistic Implications for a New Class of Antitumor Agents.

AbstractThe mode of interaction of the organometallic antitumor agent (η5‐C5H5)2VCl2 with nucleotides such as 2'‐deoxyribonucleotide‐5'‐monophosphates of adenosine, cytidine, guanosine, thymidine, and uridine, alkylated derivatives, and phosphoesters, in aqueous solution near physiological pH, is investigated employing high‐field 1H and 31P FT NMR and EPR.

Low‐frequency vibrations (20–400 cm−1) of some mononucleotides in aqueous solutions

AbstractLow‐frequency Raman scattering (20–400 cm−1) of aqueous solutions of 5′‐monophosphates of uridine (UMP), cytidine (CMP), guanosine (GMP) and of adenosine (AMP) are studied by construction of a quantity R (ν). The frequencles for intensity maxima below 100 cm−1 depend upon the protonization or the purine and pyrimidine rings, but not upon ionization of the phosphate groups. An assignment to modes very similar to corresponding nucleoside modes is discussed.