Blends as a strategy towards tailored hydrolytic degradation of poly(?-caprolactone-co-d,l-lactide)-poly(ethylene glycol)-poly(?-caprolactone-co-d,l-lactide) co-polymers

Binary blends were prepared from poly(?-caprolactone) (PCL), and P(CL-co-d,l-lactic acid)-P(ethylene glycol)-P(CL-co-d,l-lactic acid) co-polymers, where the d,l-LA content in the side chains varied from 0 to 70 mol%. Blend discs were fabricated by melt-molding, and the effect of blend composition on hydrolytic degradation was studied. Variations in medium pH were monitored, and morphological changes were observed using scanning electron microscopy. Blending of these co-polymers was found to constitute a simple means by which intermediate rates of water absorption and mass loss were obtained, compared to those observed in pure co-polymer preparations. In one of the blends, prepared from the two components containing 70 or 0 mol% d,l-LA in the side chains and thereby exhibiting large differences in degradation rate, hydrolysis resulted in the formation of a porous material over time. Furthermore, all blend samples maintained their initial shape throughout the study. Such materials may be interesting for further investigations for applications in cellular therapy and controlled release.     

Synthesis of quercetin 3-O-β-d-apiofuranosyl-(1→2)-[α-l-rhamnopyranosyl-(1→6)]-β-d-glucopyranoside

A concise method to construct a unique 2,6-branched trisaccharide was established by regioselective glycosylation of three free hydroxyl groups on a 3-O-protected glucose moiety, and successfully used in the synthesis of quercetin 3-O-β-d-apiofuranosyl-(1→2)-[α-l-rhamnopyranosyl-(1→6)]-β-d-glucopyranoside, a flavonol O-glycoside isolated from glandless cotton seeds which showed notable antidepressant activities.     

A convenient new route to protected and free 2,6-anhydro-d-glycero-d-gulo-heptoses (1-formyl-β-d-glucopyranosides)

A new and efficient process has been developed for the synthesis of 1-formyl-β-d-glucopyranosides from d-glucose.     

Synthesis of d-fructopyranosides with 2-O-acyl-β-d-fructopyranosides

Glycosylation of 2-O-acyl fructopyranosides was investigated, which were shown to be effective glycosyl donors for d-fructopyranoside synthesis with good β-selectivity and yields. For bulky acceptor 4e, α-anomer 5e was obtained with α/β = 65:23. Unexpected ring-opening was observed during acetylation of 9, indicating the sensitivity of the fructopyranosyl ring.     

Supramolecular structures from self-assembled poly(γ-benzyl-l-glutamate)-polydimethylsiloxane-poly(γ-benzyl-l-glutamate) triblock copolypeptides in thin films

We describe the self-assembly of A-B-A triblock copolymers in thin films composed of a soft polydimethylsiloxane (PDMS) central block (B) and two polypeptidic (A) blocks, poly(γ-benzyl)-l-glutamate (PBLG). The PBLG segment exhibits depending on the chain length two distinct secondary conformations either a β-sheet or a α-helical conformation. The direct relationship between the surface morphology and the secondary conformation of the polypeptide segment has been evidenced by atomic force microscopy. For chain lengths below 20 U the polypeptide segments adopt preferentially a β-sheet secondary structure and the triblock copolymer self-assembled in fibers. Moreover, the fiber diameters increased with the chain length of the triblock copolymer. For chain lengths above 20, the α-helical structure is stabilized and a lamellar morphology is formed driven by rod-rod interactions in spite of the very asymmetric composition of the triblock copolymer. However, decreasing the film thickness from 25 to 8 nm, i.e., below the L/2 and due to the preferential attraction of the polypeptide block for the hydrophilic substrate employed, instead of a lamellar morphology a rod-like morphology could be found. Thus, the use of hybrid block copolymer containing polypeptides with particular secondary structures offers novel alternatives to control the self-assembly in thin films compared to traditional amorphous block copolymers.     

New organotin(IV) complexes with l-Arginine, Nα-t-Boc-l-Arginine and l-Alanyl-l-Arginine: Synthesis, structural investigations and cytotoxic activity

Novel diorganotin(IV) derivatives of l-Arginine (HArg), N_α-(tert-Butoxycarbonyl)-l-Arginine (Boc-Arg-OH) and l-Ala-l-Arg (H₂Ala-Arg), H₂NC(NH)NH(CH₂)₃CH(NHR′)CO₂H, where R′ = H in HArg, R′ = C(O)OC(CH₃)₃ in Boc-Arg-OH, R′ = H₂NCH(CH₃)CO in H₂Ala-Arg and triorganotin(IV) derivatives of Boc-Arg-OH have been synthesized and structurally characterized. The complexes were investigated by FT-IR and ¹¹⁹Sn Mössbauer in the solid state and by ¹H, ¹³C, ¹¹⁹Sn and ¹H-¹H COSY NMR spectroscopy, in solution. The spectroscopic characterization leading to the proposed molecular structures was accomplished on the basis of these experiments. l-Arginine appears to behave as a chelating ligand through carboxylate and -NH₂ groups in Me₂Sn(Arg)₂, while in N_α-t-Boc-l-Arginine complex, the N_α-protected amino group being exempted from coordination, only the carboxylate groups are effectors of bonding to the organometallic moieties. FT-IR spectra give a clear indication that guanidino groups in all the complexes are not involved in coordination, since ν(CN-H) frequency of the terminal guanidino group is fairly constant and unshifted relative to the free ligand. The biological activity of organotin(IV)-complexes was also investigated by use of human HT29 colorectal carcinoma cells. The cytotoxic activity of the compounds was determined by the MTT quantitative colorimetric assay, capable of detecting viable cells in comparison with that exerted by cisplatin. A marked cytotoxic activity for nearly all complexes, is evident being higher than that exerted by cisplatin, while no significant improvement of activity was observed for Me₂Sn(Arg)₂ and Me₂Sn(Ala-Arg), which was confirmed by IC₅₀ values. Then, we assessed whether the cytotoxicity induced by organotin(IV) complexes was associated with the induction of apoptosis. Light microscopy analysis, performed to study the morphological changes induced in HT29 cells, confirmed the results obtained with MTT test. No significant morphological alterations were observed in HT29 cells after treatment with Me₂Sn(Ala-Arg) and Me₂Sn(l-Arg)₂. Cells treated with ⁿBu₂Sn(Boc-Arg)₂, ⁿBu₂Sn(Ala-Arg), ⁿBu₃Sn(Boc-Arg) and Me₃Sn(Boc-Arg), appeared rounded, isolated and detached from culture substrate, indicating the commitment to apoptotic cell death.     

溶剂工程调控钙钛矿薄膜中PbI2和PbI2(DMSO)的形成(英文)

钙钛矿太阳能电池以其高效、低成本的特点备受关注。到目前为止,钙钛矿太阳能电池的最高光电转换效率已经超过25%,显示出良好的应用前景。钙钛矿薄膜的结晶性能是决定器件性能的关键,因此,调控钙钛矿薄膜的生长过程至关重要。本工作中,我们发现通过简单调节前驱体溶剂,即调节二甲基亚砜：1,4-丁内酯:N,N-二甲基甲酰胺(DMSO:GBL:DMF)的三种混合溶剂的比例,可实现钙钛矿薄膜中PbI₂和PbI₂(DMSO)含量的调节,从而调节电池的器件性能。此外,本工作系统研究了PbI₂和PbI₂(DMSO)的含量对器件性能的影响。结果表明,PbI₂(DMSO)的形成会导致300–425nm波长范围内电池的外量子效率(EQE)降低,从而导致器件性能下降。相反,通过在前驱体溶液中添加额外的碘化亚甲基铵(MAI),可以抑制PbI₂和PbI₂(DMSO)的形成。     

(l)- or (d)-Valine tert-butylamide grafted on permethylated β-cyclodextrin derivatives as new mixed binary chiral selectors: Versatile tools for capillary gas chromatographic enantioseparation

This work deals with the synthesis of two mixed binary chiral selectors prepared by grafting (l)- or (d)-valine tert-butylamide on permethylated cyclodextrin macrocycle. The enantioselective properties of the new chiral selectors diluted in OV11 polysiloxane (35% phenyl- and 65% methylsiloxane) were investigated by means of injections of 117 racemic mixtures. The mixed chiral selectors with (l)-valine and, to a lesser extent with (d)-valine, were found to have an improved enantioselectivity toward amino acid derivatives by comparison to permethylated cyclodextrin. The enantioseparation capability of these new chiral selectors has proven to be slightly less efficient than Chirasil-l-Val (Alltech) for amino acid derivatives, but it has been extended to include terpenes, lactones, esters, aliphatic compounds and aryl alcohols.     

Synthesis of 2′-O-α-d-ribofuranosyladenosine, monomeric unit of poly(ADP-ribose)

The first chemical synthesis of 2′-O-α-d-ribofuranosyladenosine, monomeric unit of poly(ADP-ribose), has been achieved starting from 3′,5′-O-bis protected 9-(2-O-α-d-arabinofuranosyl-β-d-ribofuranosyl)-adenine. Configurational inversion of 2′-hydroxyl group of arabinose moiety was performed by oxidation-reduction sequence.     

Stereoselective syntheses of heptaprenylphosphoryl β-d-arabino-and β-d-ribo-furanoses

The stereoselective syntheses of heptaprenylphosphoryl β-d-arabinofuranose and heptaprenylphosphoryl β-d-ribofuranose are described. In the synthesis of the d-arabino product, the stereoselectivity was achieved by the coupling of a suitably protected β-d-arabinofuranosyl phosphate intermediate with an activated form of heptaprenol and subsequent deprotection. In the case of the ribo-analog, the desired β-anomer could be obtained by the more convenient phosphoramidite method. The products were successfully employed in the mycobacterial epimerase assay.     

Direct access to new β-d-galactofuranoconjugates: application to the synthesis of galactofuranosyl-l-cysteine and l-serine

Galactofuranose post-translational modifications, although quite rare, were detected in some biomolecules produced by parasites. While hexopyranosides were already linked to various peptides and proteins, few hexofuranosides have been artificially conjugated to amino acids. We thus report herein a robust glycosylation methodology to obtain S-alkyl, O-serine and S-cysteine-β-d-galactofuranosides starting from readily available galactofuranose donors. O-Acetyl, thioimidoyl and acetimidoyl donors were compared in terms of yields and selectivity when reacted with mercaptans, l-cysteine and l-serine. Acetimidates turned out to be the best notably for amino acids glycosylation.     

水对甲醇在Rutile-TiO2(110)-(1 ×1)表面光催化解离的影响简

采用程序升温脱附方法研究了甲醇分子吸附在真空退火后的二氧化钛（110）表面的光催化过程,对比分析了单独吸附甲醇分子以及甲醇分子与水分子共吸附情况下的光催化解离过程. 结果表明,在二氧化钛（110）表面吸附的甲醇分子对共吸附水分子的光催化解离过程并没有直接的帮助作用. 共吸附状态下的水分子也同样没有影响到甲醇的光致解离过程,但是水分子的存在抑制了甲醇光解产物甲醛的光致脱附过程,同时促进了甲酸甲酯的形成.     

An unprecedented N-transacylation reaction on 2-acetamido-2-deoxy-α-d-glucopyranosides

An unprecedented N-transacylation reaction on 2-acetamido-2-deoxy-α-d-glucopyranosides was disclosed in the presence of acyl chloride and DMAP under reflux in pyridine.     

Effect of partial crosslinking on morphology and properties of the poly(β-hydroxybutyrate)/poly(d,l-lactic acid) blends

Poly(β-hydroxybutyrate) (PHB) is a bio-based and biodegradable aliphatic polyester, however its application is limited by some disadvantages such as high price, brittleness, poor processability and low melt-strength due to serious thermal degradation. Partial crosslinking initiated by dicumyl peroxide (DCP) was applied in this work to improve the performance of poly(β-hydroxybutyrate)/poly(d,l-lactic acid) (PHB/PDLLA) blends. The partial crosslinking of the blends and its effect on the properties, morphology, rheology and thermal behavior of the blends were investigated. The tensile strength and impact toughness of the PHB were increased by incorporation of the PDLLA, which were improved further after the partial crosslinking because of an increased compatibility between the PHB and the PDLLA phases. The rheological study revealed that the storage modulus (G′) and complex viscosity (η*) of the blends were increased after addition of the DCP. On the other hand, the crystallization of PHB in the blends was restricted to a certain extent by the formation of partially crosslinked network while its crystal form was not modified.     

Increasing the inhibitory potency of l-arabino-imidazolo-[1,2]-piperidinose towards β-d-glucosidase and β-d-galactosidase

The synthesis of some potent inhibitors of two retaining β-glycosidases was achieved by introducing aglycon-mimics into the imidazole moiety of l-arabino azasugar 1. The strongest inhibition was observed with the phenyl-ethyl substituent at C(2) of 1 against β-d-galactosidase and β-d-glucosidase, whereas the hydroxymethyl group at C(2) increased only slightly the inhibitory properties.     

[Zn(μ-l)Cl2]∞: a one-dimensional (1-D) zigzag coordination chain exhibiting unique two-dimensional (2D) hydrogen-bonding supramolecular architecture

Self-assembly of the versatile bridging ligand 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (l) with ZnCl₂ in CHCl₃-H₂O medium affords a neutral one-dimensional zigzag coordination polymer [Zn(μ-l)Cl₂]_∞ (1), which has been characterized by IR, elemental analyses, thermogravimetric analysis (TGA) and X-ray diffraction techniques. The crystal structure of 1 reveals that the ligand molecules bridge the tetrahedral Zn^II centers (ZnN₂Cl₂) in the unprecedented transoid conformation, forming a one-dimensional zigzag coordination chain. The inter-chain C-H···Cl hydrogen bonds between the pyridine rings and the coordinated chloride anions extend these 1-D coordination frameworks to result in a novel 2-D supramolecular architecture, and there exist significant edge-to-edge π-π stacking interactions between the inter-chain neighboring pyridyl rings of the ligand, which may further stabilize this structure.     

Electrospinning of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide-graft-polylactic acid to produce a fibrillar scaffold

α,β-Poly(N-2-hydroxyethyl)-dl-aspartamide grafted with polylactic acid (PHEA-g-PLA) is a biocompatible and biodegradable amphiphilic copolymer that has been already employed to prepare a drug delivery system.In this study we have prepared for the first time a fibrillar scaffold from PHEA-g-PLA by the electrospinning of a solution of this copolymer in a mixture of N,N-dimethyl formamide (DMF) and acetone (80:20 vol/vol). The average diameter and the morphology of electrospun fibers were detected by scanning electron microscopy.Chemical degradation studies in phosphate buffer solution pH 7.4 have been performed until 15 days in order to obtain a preliminary information about the hydrolytic resistance of the prepared scaffold.     

Rh(Ⅱ)-catalyzed intermolecular carboamination of pyridines via double Csp2–H bond activations

We disclose the development of the Rh-catalyzed amine-directed remote 5,6-carboamination protocol of pyridines via dual Csp²–H functionalizations. A variety of readily available 2-aminopyridines and 1,2,3-triazoles are allowed for coupling cyclization to access polyfunctionalized azaindoles. Mechanistic studies including DFT calculations unveil that relay carbenoidelectrophilic addition to pyridines and the sequential pyridyl Csp²–H amination are involved in this transforma...     

Synthesis of analogues of naturally occurring 3-O-(β-d-glucopyranosyl)-fagomine

Stereoselective synthesis of 3-α-C-glucosides of d- and l-fagomine from the corresponding C-disaccharides is reported. The ethyl glycoside of perbenzylated C-disaccharide 8 was converted via the corresponding thioglycoside 10 and reducing C-disaccharide 11, into substituted alditol 12 which, upon oxidation and double reductive amination stereoselectively afforded pure perbenzylated d-fagomine C-glucoside 14. In the same manner, the ethyl glycoside of perbenzylated C-disaccharide 9 was stereoselectively converted into perbenzylated l-fagomine C-glucoside 15.