Palladium(II) complexes of oligopeptides containing aspartyl and glutamyl residues

Potentiometric and ¹H NMR spectroscopic measurements have been performed on palladium(II) complexes of di-, tri- and tetra-peptides containing aspartyl and glutamyl residues including AspAla, AlaAsp, AspAsp, AspAspAsp, GluGluGlu, GlyAspGly, AspAspAspAsp and GlyGlyAspGly. In the case of dipeptides the coordination modes are basically determined by the peptide backbone. The presence of the extra β-carboxylate residues does not result in new binding modes but these functions may slightly affect the thermodynamic stability of several species. For tripeptides the most important findings are connected to the governing role of the β-carboxylate group of internal aspartyl residues but similar effects were not observed for the peptides containing glutamic acid. Aspartic acid in the second position of a tripeptide (Xaa-Asp-Yaa sequence) promotes the binding of the preceding and prevents deprotonation and coordination of subsequent amide functions. In the case of tetrapeptides, the aspartyl residues present in the third position from the N-terminus (Xaa-Yaa-Asp-Zaa sequence) have the most pronounced effect on complex formation. In this case, the (NH₂, N⁻, N⁻, β-COO⁻)-coordination is the major binding mode and the species [PdH₋₂L] can exist in a wide pH range. The enhanced stability of these complexes was explained by the conformational changes of the coordinated ligands.     

Synthesis and gel formation of amphiphilic semicarbazones containing saccharide units

The synthesis of 4-alkyl-semicarbazones derived from reducing sugars and semicarbazides is presented as a convenient route for the preparation of amphiphilic saccharides. This semicarbazone route allows to employ a large variety of reducing sugars as hydrophilic building block for saccharide tensides. The preparation of two series of amphiphiles based on D-maltose with non-methylated and mono-N-methylated semicarbazone units is described. Then-alkyl chains were varied fromn-octyl ton-hexadecyl. Various maltotriose derivatives have also been prepared. Critical micelle concentration (CMC) as well as critical gel concentration of the derivatives were studied in dependence of then-alkyl chain length. Both values decreased with increasing length of then-alkyl chain. Self-organization of the gels was studied by transmission electron microscopy of freeze-fractured samples. Due to the supramolecular organization of the amphiphiles, the gels consisted of twisted rope-like molecular assemblies with the same helical twist sense. The helical pitch depended on the hydrophilic/lipophilic balance. In contrast to gels onn-alkylgluconamides, the gels were formed in dilute aqueous solution and exhibited striking longevity without additional stabilization by surfactants. In the solid, the amphiphiles exhibited thermotropic transitions to partially disordered mesophases.     

Nickel(II) complexes of oligopeptides containing aspartyl and glutamyl residues. Potentiometric and spectroscopic studies

Nickel(II) complexes of di-, tri- and tetra-peptides built up from Asp and/or Glu residues have been studied by potentiometric, UV–Vis and circular dichroism spectroscopic methods. The stoichiometry of the complexes are the same as in the case of common oligopeptides, but the presence of the side chain carboxylate groups results in differences in their stabilities and coordination modes. The presence of the β-carboxylate groups increases the metal binding affinity of the peptides in all cases. This is due to the coordination of the first, second and third aspartic acid residue in the case of the NiL, NiH₋₁L and NiH₋₂L complexes, respectively. The high negative charge of Asp₄ suppresses the metal ion coordination of the third amide function, therefore the NiH₋₃L complex does not form with this tetra-peptide. In the case of peptides containing glutamic acid, no stability enhancement appears because there is only a weak interaction between the nickel(II) ion and the γ-carboxylate group, which is not able to compensate the disfavoured effect of the increasing negative charge of the complexes.     

Synthesis and hydrogel formation of fluorine‐containing amphiphilic ABA triblock copolymers

Fluorine‐containing amphiphilic ABA triblock copolymers, poly(2‐hydroxyethyl vinyl ether)‐block‐poly[2‐(2,2,3,3,3‐pentafluoropropoxy)ethyl vinyl ether]‐block‐poly(2‐hydroxyethyl vinyl ether) [poly(HOVE‐b‐PFPOVE‐b‐HOVE)] (HFH), poly[2‐(2,2,3,3,3‐pentafluoropropoxy)ethyl vinyl ether]‐block‐poly(2‐hydroxyethyl vinyl ether)‐block‐poly[2‐(2,2,3,3,3‐pentafluoropropoxy)ethyl vinyl ether] [poly(PFPOVE‐b‐HOVE‐b‐PFPOVE)] (FHF), and poly(n‐butyl vinyl ether)‐block‐poly(2‐hydroxyethyl vinyl ether)‐block‐poly(n‐butyl vinyl ether) [poly(NBVE‐b‐HOVE‐b‐NBVE)] (LHL), were synthesized, and their behavior in water was investigated. The aforementioned polymers were prepared by sequential living cationic polymerization of 2‐acetoxyethyl vinyl ether (AcOVE) and PFPOVE or NBVE, followed by hydrolysis of acetyl groups in polyAcOVE. FHF and LHL formed a hydrogel in water, whereas HFH gave a homogeneous aqueous solution. In addition, the gel‐forming concentration of FHF was much lower than that of corresponding LHL. Surface‐tension measurements of the aqueous polymer solutions revealed that all the triblock copolymers synthesized formed micelles or aggregates above about 1.0 × 10^?4 mol/L. The surface tensions of HFH and FHF solutions above the critical micelle concentration were lower than those of LHL, indicating high surface activity of fluorine‐containing triblock copolymers. Small‐angle X‐ray scattering measurements revealed that HFH formed a core‐shell sperical micelle in 1 wt % aqueous solutions, whereas the other block copolymers caused more conplicated assembly in the solutions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3751–3760, 2001     

Syntheses of antibacterial peptides,gramicidin S analogs and designed amphiphilic oligopeptides

In order to clarify the relationship between antimicrobial activity and peptide-structure, gramicidin S analogs and cationic α-helical model peptides were designed and synthesized. Introduction of cationic side chains in hydrophilic side of gramicidin S increased antimicrobial activity against Gram-negative bacteria. Amphiphilic structures of the α-helical peptides were found to be effective to show antimicrobial activities against Gram positive bacteria. Increase in number of cationic amino acid residues in the α-helical peptides caused appreciable antimicrobial activities against Gram-negative bacteria, however, induced lower activities against Gram-positive ones.     

The optical rotation of oligopeptides containing L-proline and L-hydroxypyroline

Summary 1. Values of R_i for L-proline and L-hydroxyproline according to their position in the peptide chain in three different solvents have been calculated.2. The rule of additivity of the optical rotation is satisfactorily followed in the majority of cases.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 2, 120–124, 1966     

Three-membered ring formation—IV : Selective syntheses of halogenocyclopropanedicarboxylic esters possessing different alcohol residues

Selective syntheses for some 1-halogeno-2-alkyl-cis-1,2-cyclopropanedicarboxylic esters were studied. In a ring formation between α-halogenoacetic and α-propylacrylic esters, lithium hydride was a much better condensing agent than sodium hydride for the selective syntheses of cyclopropanedicarboxylic ester possessing two different alcohol residues. A greater reactivity was found at the ester group linked to carbon 1 than that linked to carbon 2 in transesterification by alkali metal t-butoxide and also in its partial hydrolysis by KOH. This is presumably ascribed to the difference in the inductive effects of alkyl group and the Cl atom.     

Synthesis of cyclic oligopeptides containing an Arg-Gly-Asp (RGD) sequence

The synthesis of cyclic RGD peptides with 8-10 residues cyclized by an amide bond and the relationship between their structure and activity (i.e. circular dichroism spectrum and inhibition of platelet aggregation) are reported. The linear peptides were synthesized by the solution method and their cyclization was performed in high dilution using DPPA.     

Some bactericidal properties of oligopeptides and regular polypeptides including lysine and ornithine residues

Summary Oligopeptides and polypeptides of the sequences Lys₆-, Ala-Lys₄-Ala, Lys₈-, Orn₂-Ala₂-, Lys₃-Pro-, Lys₃-Gly-, Orn₃-Gly-, Lys-Pro-, Lys-Pro₂-, Lys₂-Pro-, Lys₃-Ala- possess bactericidal properties in relation to a strain of the bacteriumStaphylococcus aureus.It has been shown that with an increase in the amount of lysine and ornithine residues in the polypeptide chain the bactericidal properties increase; proline residues play a fundamental part in the manifestation of these properties.Institute of Molecular Biology, Academy of Sciences of the USSR, Moscow. Institute of Chemistry, Academy of Sciences of Tadzhik SSR, Dushanbe. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 130–133, January–February, 1978.     

Preparation of polymers containing sugar residues

The synthesis of five different polymers containing sugar residues on side chain is described. 1-O-Methacryloyltetra-O-acetyl-D -glucose, 1-O-methacryloyltetra-O-acetyl-D -galactose, and 6-O-methacryloyltetra-O-acetyl-D -glucose were prepared and polymerized. The polymethacrylates obtained were converted into water-soluble polymers by removing the acetyl protective group with sodium methoxide. 6-O-Methacryloyldiisopropylidene-D -galactose was also prepared and polymerized. The isopropylidene protective group was removed by acid hydrolysis. Poly (N-methacryloylglucosamine) was prepared directly by the polymerization of N-methacryloyl-D -glucosamine without the use of any protective group.     

Electrochemical detection of oligopeptides through the precolumn formation of biuret complexes

The relatively slow kinetics of formation of the electroactive Cu(II)-peptide complexes from larger (greater than 6 amino acids) peptides requires relatively high temperature and long reaction times for a postcolumn reactor. The precolumn incubation of bradykinin, Tyr8-bradykinin and insulin A chain with biuret reagent for 20 min at 60 degrees C leads to the formation of biuret complexes which can be subjected to chromatography in acidic or basic eluents. These complexes are detected electrochemically with a sensitivity similar to the Cu(II)-(ala)3 complex (1 nC/pmol at 1.0 ml/min). The influence of the column-packing material on the electrochemical detector response of the Cu-peptide complexes has also been studied.     

Proof of delocalization-stabilization by sulfur in enolate formation during racemisation of sulfur containing amino acid residues.

The present kinetic data on the accelerating action of sulfur in the base catalyzed racemisation of cyclic dipeptides ($\text{3}$) support the explanation of Barber and Jones ($\text{4}$) for the α center and suggest further a 1,3- and 1,4-interaction of -S- with the amide N-atom ($\text{8}$) for the α′ center.     

Reactivity studies of oxo-Mo(IV) complexes containing potential hydrogen-bond acceptor/donor phenolate ligands

Reactivity studies of oxo-Mo(IV) complexes, Tp(iPr)MoO{2-OC(6)H(4)C(O)R-κ(2)O,O'} (R = Me, Et, OMe, OEt, OPh, NHPh), containing chelated hydrogen-bond donor/acceptor phenolate ligands are reported. Hydrolysis/oxidation of Tp(iPr)MoO(2-OC(6)H(4)CO(2)Ph-κ(2)O,O') in the presence of methanol yields tetranuclear [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2) (1), while condensation of Tp(iPr)MoO{2-OC(6)H(4)C(O)Me-κ(2)O,O'} and methylamine gives the chelated iminophenolate complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κ(2)O,N} (2), rather than the aqua complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κO}(OH(2)). The oxo-Mo(IV) complexes are readily oxidized by dioxygen or hydrogen peroxide to the corresponding cis-dioxo-Mo(VI) complexes, Tp(iPr)MoO(2){2-OC(6)H(4)C(O)R}; in addition, suitable one-electron oxidants, e.g., [FeCp(2)]BF(4) and [N(C(6)H(4)Br)(3)][SbCl(6)], oxidize the complexes to their EPR-active (g(iso) ≈ 1.942) molybdenyl counterparts (3, 4). Molybdenyl complexes such as Tp(iPr)MoOCl{2-OC(6)H(4)C(O)R} (5) and Tp(iPr)MoOCl(2) also form when the complexes react with chlorinated solvents. The ester derivatives (R = OMe, OEt, OPh) react with propylene sulfide to form cis-oxosulfido-Mo(VI) complexes, Tp(iPr)MoOS{2-OC(6)H(4)C(O)R}, that crystallize as dimeric μ-disulfido-Mo(V) species, [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (6-8). The crystal structures of [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2), Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe}, Tp(iPr)MoOCl{2-OC(6)H(4)C(O)NHPh}·{2-HOC(6)H(4)C(O)NHPh}, and [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (R = OMe, OEt) are reported.     

Charge control of the complex formation of phenol with unsaturated compounds containing organoelement substituents from group IV

The frequency shifts (v (OH)) of phenol and the resonance components (v_r) of these shifts in the IR spectra of forty H-complexes of phenol with furan derivatives containing organic, organosilicon, organogermanium, and organotin substituents are studied. The values of v and v_R are linearly related to quantum chemical parameters of the variation of the effective charges of the furan ring atoms affected by - and -interactions with organic substituents. The effect of the conjugation between an organoelement substituent and the furan ring on the effective charges is estimated. The resonance parameters (_R) of organoelement substituents in derivatives of benzene, thiophene, and furan and the reasons for the non-versatility of _R are considered.For report 7, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 289–295, February, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-18372).     

Sequence dependence of charge transport through DNA domains

Here we examine the photooxidation of two kinetically fast electron hole traps, N4-cyclopropylcytosine (CPC) and N2-cyclopropylamine-guanosine (CPG), incorporated in DNA duplexes of various sequence using different photooxidants. DNA oxidation studies are carried out either with noncovalently bound [Ru(phen)(dppz)(bpy')]3+ (dppz = dipyridophenazine) and [Rh(phi)2(bpy)]3+ (phi = phenanthrenequinone diimine) or with anthraquinone tethered to DNA. Because the cyclopropylamine-substituted bases decompose rapidly upon oxidation, their efficiency of decomposition provides a measure of relative hole localization. Consistent with a higher oxidation potential for CPC versus CPG in DNA, CPC decomposes with photooxidation by [Rh(phi)2(bpy)]3+, while CPG undergoes ring-opening both with photoexcited [Rh(phi)2(bpy)]3+ and with [Ru(phen)(dppz)(bpy')]3+. Anthraquinone-modified DNA assemblies of identical base composition but different base sequence are also probed. Single and double base substitutions within adenine tracts modulate CPC decomposition. In fact, the entire sequence within the DNA assembly is seen to govern CPC oxidation, not simply the bases intervening between CPC and the tethered photooxidant. These data are reconciled in the context of a mechanistic model of conformationally gated charge transport through delocalized DNA domains. Photooxidations of anthraquinone-modified DNA assemblies containing both CPC and CPG, but with varied distances separating the modified bases, point to a domain size of at least three bases. Our model for DNA charge transport is distinguished from polaron models. In our model, delocalized domains within the base pair stack form transiently based upon sequence-dependent DNA structure and dynamics. Given these results, DNA charge transport is indeed remarkably sensitive to DNA sequence and structure.     

Observation of the formation of supported bilayers by amphiphilic peptidyl-RNA

Amphiphilic peptidyl-RNA conjugates, molecules that mimic natural peptidyl-transfer RNA, are capable of self-assembling on glass substrates as vesicles and supported bilayers.