Bioconjugates of PAMAM dendrimers with trans-retinal, pyridoxal, and pyridoxal phosphate.

BACKGROUND: Bioconjugates of a polyamidoamine (PAMAM) G3 dendrimer and an aldehyde were synthesized as carriers for vitamins A and B6, and the bioavailability of these vitamins for skin nutrition was investigated. METHODS: Nuclear magnetic resonance (NMR) and ultraviolet-visible methods were used to characterize the structure of the bioconjugates and for monitoring release of pyridoxal (Pyr) and pyridoxal phosphate (PLP) from these bioconjugates in vitro. A skin model permeation of bioconjugates was also studied in a Franz chamber. RESULTS: A transdermal G3 PAMAM dendrimer was used to synthesize bioconjugates with trans-retinal (Ret), pyridoxal (Pyr), or PLP. These nanomolecules, containing up to four covalently linked Ret, Pyr, or PLP (G3(4Ret), G3(4Pyr), and G3(4PLP)), were able to permeate the skin, as demonstrated in vitro using a model skin membrane. PLP and Pyr bound to a macromolecular vehicle were active cofactors for glutamic pyruvic transaminase, as shown by ¹H NMR spectral monitoring of the progress of the L-alanine + α-ketoglutarate → glutamic acid + pyruvic acid reaction. CONCLUSION: PAMAM-PLP, PAMAM-Pyr, and PAMAM-Ret bioconjugates are able to permeate the skin. PLP and Pyr are available as cofactors for glutamic pyruvic transaminase.

Solubility and in vitro transdermal diffusion of riboflavin assisted by PAMAM dendrimers.

PAMAM dendrimers of full generation (Gn) and half generation (Gn.5) were used as solubility enhancers of riboflavin (B2 vitamin) in methanol. They were found to weakly enhance solubility of B2 (7.2-10.3 times) according to the order: G2≫G2.5>G3≫G3.5>G4. The homogeneous mixtures of Gn (or Gn.5) with B2 of 1:1 molar ratio were obtained by removal of methanol to form oily host-guest complexes. The complexes were released from o/w emulsions and the transdermal permeation of B(2) through polyvinyldifluoride (PVDF) and pig ear skin (PES) membranes was estimated. PAMAM dendrimers were demonstrated to promote permeation of B2 according to the order: G2>G3≫G2.5>G3.5>G4 (none). The permeation of fluorescein labeled dendrimers is faster than B2; the diffusion of G2 dendrimer through PES was the slowest of all studied Gn dendrimers, presumably due to absorption inside the skin. On the other hand the G2 was the best permeation enhancer for B2. The water soluble PAMAM dendrimers G2 and G3 can be successfully applied in cosmetic and dermatologic emulsions for this weakly water soluble vitamin.

An integrated approach to the mid-spin state (S = 3/2) in six-coordinate iron(III) chiroporphyrins.

An intermediate-spin state very close to the mid-spin state (S = 3/2) can be stabilized in a ferric porphyrin by an integrated approach which combines the favorable effects of a weak axial field strength and of a small macrocycle hole. Axial ligand exchange by reaction of chloroiron(III)tetramethylchiroporphyrin [(TMCP)FeCl] with silver perchlorate in ethanol-chloroform leads to ethanol-ligated ferric chiroporphyrins. Two distinct crystalline products containing a bisethanol complex [[(TMCP)FeIII(EtOH)2]ClO4] and three variants of a mixed ethanol-water complex [[(TMCP)FeIII(EtOH)(H2O)]ClO4] have been structurally characterized in the solid state. The small hole of the ruffled chiroporphyrin and the weak axial oxygen ligation result in strongly tetragonally distorted complexes. The six-coordinate species exhibit long axial Fe-O bond distances (2.173(5)-2.272(4) A) and the shortest equatorial Fe-N(av) distances (1.950(5)-1.978(7) A) found as yet in a ferric porphyrin, reflecting a singly occupied dz2 orbital and a largely depopulated dx2-y2 orbital. An intriguing case of bond-stretch isomerism is seen for the axial Fe-O bonds in two crystallographically independent mixed ethanol-water species, and it is accounted for by their distinct intra- and intermolecular hydrogen-bond arrays. The Mössbauer spectrum (delta = 0.35(1) mm s-1 and delta EQ = 3.79(1) mm s-1 at 77 K) indicates a strong tetragonal distortion around the ferric ion, in agreement with the structural data. The value of the magnetic moment (mu eff = 3.8 mu B in the range 50-300 K) strongly supports a mid-spin state (S = 3/2). The EPR spectrum at 80 K (g perpendicular approximately 4.0, g parallel approximately 2.00) is consistent with a nearly pure mid-spin state (4A2) with little rhombic distortion. The 1H NMR spectra in CDCl3-EtOH exhibit upfield-shifted resonances for the pyrrole protons (delta approximately -30 ppm) which are consistent with the depopulated iron dx2-y2 orbital. Solution equilibria with water and various alcohols, and the spin state of the corresponding species, are discussed on the basis of the NMR data. The bisethanol and ethanol-water species are potential models of unknown hemoprotein ligation states such as Tyr(OH)/Tyr(OH) or Tyr(OH)/H2O that could be obtained by site-directed mutagenesis.

Palladium(II) complexes with cytidine-guanosine pair in DMSO.

Solutions containing nucleosides: cytidine and guanosine, and Pd(II) ion in dimethylsulphoxide have been investigated using 1H NMR method. It has been found that the glycylglycinate-palladium(II) complex reacts with cytidine through its N(3) nitrogen atom as the fourth donor for Pd(II) ion, and with guanosine which binds with Pd(II) through N(7) of purine ring. The primary binding site of cytidine-guanosine pair for the glycylglycinate-Pd(II) complex was N(7) of guanosine. However, in the reaction of PdCl2 with the cytidine-guanosine pair, equivalent binding sites were N(1) of guanosine and N(3) of cytidine giving CydN(3)-Pd-N(1)Guo ternary complex.

Coordination of Gly-Tyr x Pd(II) complex to GMP nucleotide.

Coordination of the glycyl-L-tyrosinate x Pd(II) complex to guanosine-5'-monophosphate (GMP) has been studied using 1H, 13CV NMR and electron spectra methods. Two kinds of monomeric ternary complexes were found in aqueous solutions: Gly-Tyr x Pd(II)-N7(GMP) complex (Pd-N7) at pH range 3 - 9 and Gly-Tyr x Pd(II)--N1(GMP) complex (Pd-N1) at pH above 5.2. The influence of the aromatic ring of tyrosine upon the chemical shifts for the -N7 bonded nucleotide molecule suggest that the plane of the purine ring and that of the Gly-Tyr x Pd(II) complex are almost perpendicular to each other.

Coordination of Gly-Tyr . Pd(II) complex to ATP and ADP nucleotides.

The coordination of the glycyl-L-tyrosinate . Pd(II) complex to adenosine 5' -diphosphate (ADP) and adenosine 5' -triphosphate (ATP) has been studied using 13C, 1H NMR and electronic spectral methods. Two dominant species have been found in solution, a monomeric ternary complex with Gly-Tyr . Pd(II) bound to the N-1 purine nitrogen and a dimer in which two dipeptide . Pd(II) complex molecules are coordinated to the nucleotide by N-1 and N-7 nitrogens. Monomeric ternary complexes having metal coordination to N-7 were not detected. The influence of the aromatic ring of tyrosine upon the chemical shifts for the bonded nucleotide molecule suggest that the plane of the purine ring and of the Gly-Tyr . Pd(II) complex are almost perpendicular to each other.