The Level of Hydrophobic Substitution and the Molecular Weight of Amphiphilic Poly-L-lysine-Based Polymers Strongly Affects Their Assembly into Polymeric Bilayer Vesicles

With the aim of producing new materials for drug and gene delivery, the variables associated with the preparation of poly-L-lysine-based vesicles were investigated. Amphiphilic poly-L-lysine graft copolymers with varying levels of grafted methoxypolyethylene glycol (mPEG) and palmitic acid were synthesized using two-step grafting reactions of the macromonomer, mPEG-p-nitrophenyl carbonate (mPEG, MW=5,000), and palmitic acid N-hydroxysuccinimide ester onto poly-L-lysine hydrobromide (MW=4,000 and 19,600). Polymers were characterized by gel permeation chromatography/light scattering. (1)H NMR, and an assay for unreacted varepsilon-amino groups. Polymeric unilamellar vesicles were produced by probe sonication of the amphiphilic poly-L-lysine-based polymers in the presence of cholesterol. Vesicles were characterized by electron microscopy and photon correlation spectroscopy. Vesicle formation was favored by a low molecular weight and a low level of palmitoyl substitution. A vesicle formation index has been derived, F ~ H/L DP, where H is the %molar level of unreacted L-lysine units, L is the %molar level of substituted palmitoyl units, and DP is the square root of the degree of polymerization of the polymer. Additionally, the size of these vesicles may be controlled by controlling the initial molecular weight of the parent poly-L-lysine/resulting amphiphilic polymer. Hence, amphiphilic poly-L-lysine-based polymers of molecular weight=89,000 and 25,000 produced polymeric vesicles of z-average mean diameter 570 nm and 252 nm, respectively. Vesicle encapsulation efficiency for the hydrophilic macromolecule, fluorescein isothiocyanate-dextran (MW=4,400), increased with vesicle size. Copyright 2001 Academic Press.     

Insertion of C50 into single-walled carbon nanotubes: Selectivity in interwall spacing and C50 isomers

The structures and electronic properties of nanoscale "peapods," i.e., C(50) fullerenes inside single-walled carbon nanotubes (SWCNTs), were computationally investigated by density functional theory (DFT). Both zigzag and armchair SWCNTs with diameters larger than 1.17 nm can encapsulate C(50) fullerenes exothermically. Among the SWCNTs considered, (9,9) and (16,0) SWCNTs are the best sheaths for both D(3) and D(5h) isomers of C(50), corresponding to 0.32-0.34 nm tube-C50 distances. The orientation of C(50) inside nanotubes also affects the insertion energies, which depend on the actual tube-fullerene distances. The insertion of D(3) and D(5h) isomers of C(50) is somewhat selective; the less stable D(5h) isomer can be encapsulated more favorably inside SWCNTs at same tube-C(50) spacing. Because of the weak tube-C(50) interaction, the geometric and electronic structures of the peapods do not change greatly for the most stable configurations, but the selectivity in the interwall spacing and isomer encapsulation can be useful in separating various carbon fullerenes and their isomers.     

One‐Pot,Direct Incorporation of [11C]CO2 into Carbamates

Why beat about the bush? An operationally simple and mild reaction based on the direct fixation of ¹¹CO₂ with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) has been developed for the synthesis of ¹¹C‐labeled carbamates at 75 °C within 10 minutes in radiochemical yields above 70 % (see scheme). This strategy should be immediately useful for the construction of new radiotracers for positron emission tomography and other applications.

     

Incorporation of Znq2 complexes into mesoporous silica and their transparent polymer luminescent nanocomposites

Znq₂-functionalized colloidal mesoporous silicas (Znq₂-CMS)/polymer transparent nanocomposites were prepared by in situ bulk polymerization. CMS nanoparticles or nanorods with hydroxyl-, mercapto- and sulfonic-functionalized interiors were obtained by different synthetic routes in the nanosize dimensions between 50 and 500 nm. The luminescent Znq₂ complex was successfully introduced in the pores of different mesoporous silicas by chemical adsorption as the driving force. The different internal circumstances of mesoporous silicas had an obvious effect on the luminescence and lifetime of Znq₂ complex. The transparent fluorescent nanocomposites were fabricated from different Znq₂-CMS and suitable monomers. The Znq₂-CMS were uniformly dispersed in the polymer matrix without evident aggregation. The photoluminescence properties of Znq₂-CMS in the transparent matrix exhibited a dependence on the inner surrounding of CMS due to the interaction between Znq₂-CMS and polymers. The maximum emission peak of the nanocomposites had a red-shift of 28 nm as compared to pure Znq₂-CMS.     

Conformationally constrained purine mimics. Incorporation of adenine and guanine into spirocyclic nucleosides

Directed syntheses of spirocyclic nucleosides featuring adenine and guanine as the nucleobases have been successfully developed. The key starting materials are the enantiomerically pure spiro lactones 4, 15, and 28, which have proven amenable to conversion to anomeric mixtures of chloro sugars. The latter can enter into glycosidation by SN2 displacement with the sodium salts of 6-chloropurine or 2-amino-6-chloropurine. In the saturated series, the chromatographic separation of 18 from 19 was possible. Where 33 and 34 are concerned, their relatively rapid rate of epimerization precluded this. Mimics 35-37 resisted isolation as pure anomers. The configurational assignments are based on the thermal interconversions and supporting MM3 steric energy calculations. Added corroboration was gained from a crystallographic analysis of 8. Although removal of the TBS protecting groups in all late-stage guanine intermediates proved to be problematical, the pair of hydroxyl groups in 37 could be introduced by proper recourse to the oxidation of 36 with ruthenium tetraoxide.     

Incorporation of transition metals into Mg-Al layered double hydroxides: Coprecipitation of cations vs. their pre-complexation with an anionic chelator

A comparative study on two different methods for preparing Mg-Al layered double hydroxides (LDH) containing various divalent transition metals M (M=Co, Ni, Cu) has been carried out. The first (conventional) method involved coprecipitation of divalent metals M(II) with Mg(II) and Al(III) cations using carbonate under basic conditions. The second approach was based on the ability of transition metals to form stable anionic chelates with edta⁴⁻ (edta⁴⁻=ethylenediaminetetraacetate) that were synthesized and further introduced into LDH by coprecipitation with Mg and Al. The synthesized LDHs were characterized by X-ray diffraction (XRD) and X-ray fluorescence (XRF) methods, thermogravimetry with mass-selective detection of decomposition products (TG-MSD), Fourier transform infrared (FTIR) and Raman spectroscopy techniques. The results obtained were discussed in terms of efficiency of transition metal incorporation into the LDH structure, thermal stability of materials and the ability of metal chelates to intercalate the interlayer space of Mg-Al LDH. Vibrational spectroscopy studies confirmed that the integrity of the metal chelates was preserved upon incorporation into the LDH.     

HLB number of Vitamins C,E, coenzyme Q10 derivatives and their transportation efficiency into skin

We have been proposing a new delivery system of medicines and supplements. Derivatives of vitamin C, E and coenzyme Q₁₀ were examined regarding the relationship between the hydrophile-lipophile balance (HLB) number and the transdermal transportation efficiency into the skin. Non-invasive vibrational spectroscopies, infrared attenuated total reflection (IR-ATR) and near-infrared diffusive reflection (NIR-DR) methods were used in order to evaluate transported materials in the skin. Vitamin C derivatives of sodium l-ascorbyl-2-phosphate (hereafter abbreviated as APS) and sodium l-ascorbyl-2-phosphate-6-palmitate (APPS) were examined. APPS contains both a hydrophilic group and a hydrophobic group, since APS has been modified to APPS by deriving palmitic acid ester in the 6-OH position. APPS has the value of HLB around 9.0, while APS has that of 20. The iontophoretic efficiency of APPS is higher than APS. Vitamin E derivatives of DL-α-tocopheryl N,N-dimethylglycinate (TDMG) and α-tocopheryl acetate (TA) were examined regarding the transdermal transportation effect. Those HLB numbers are 2.3 and 0, respectively. TA is hydrophobic, while TDMG has a hydrophilic terminal group of dimethylglycine HCl materials. Coenzyme Q₁₀ (CoQ₁₀) is hydrophobic and a portion of benzoquinone is also hydrophobic, thus, HLB = 0. CoQ₁₀ has been modified to a reduced form of CoQ₁₀ (CoH₂Q₁₀) by NaBH₄. CoH₂Q₁₀ has a hydroquinone structure of hydrophilic property and HLB = 3.9. Supersonic perforation transported a greater amount of CoH₂Q₁₀ into the skin than CoQ₁₀. The balance of the hydrophilic group and the hydrophobic group in the transported material is an important factor for the effective transportation into the skin.     

Biosynthesis of highly modified meroterpenoids in aspergillus variecolor. Incorporation of 13C-labelled acetates and methionine into anditomin and andilesin C

Incorporations of [1-¹³C]?, [2-¹³C]?, [1,2-¹³C₂]-acetates and [¹³C]-methionine into anditomin, a metabolite of $\text{Aspergillus variecolor}$, indicate its formation by a mixed polyketide-terpenoid biosynthetic pathway similar to that elucidated for andibenin; observations are made on the possible biosynthetic relationship of the $\text{A. variecolor}$ metabolites with austin and terretonin, mycotoxins recently isolated from $\text{A. ustus}$ and $\text{A. terreus}$ respectively.     

Incorporation of Sulfate or Selenate Groups into Oxotellurates(IV): I. Calcium,Cadmium, and Strontium Compounds

Seven new mixed oxochalcogenate compounds in the systems M^II/X^VI/Te^IV/O/(H), (M^II = Ca, Cd, Sr; X^VI = S, Se) were obtained under hydrothermal conditions (210 °C, one week). Crystal structure determinations based on single‐crystal X‐ray diffraction data revealed the compositions Ca₃(SeO₄)(TeO₃)₂, Ca₃(SeO₄)(Te₃O₈), Cd₃(SeO₄)(Te₃O₈), Cd₃(H₂O)(SO₄)(Te₃O₈), Cd₄(SO₄)(TeO₃)₃, Cd₅(SO₄)₂(TeO₃)₂(OH)₂, and Sr₃(H₂O)₂(SeO₄)(TeO₃)₂ for these phases. Peculiar features of the crystal structures of Ca₃(SeO₄)(TeO₃)₂, Ca₃(SeO₄)(Te₃O₈), Cd₃(SeO₄)(Te₃O₈), Cd₃(H₂O)(SO₄)(Te₃O₈), and Sr₃(H₂O)₂(SeO₄)(TeO₃)₂ are metal‐oxotellurate(IV) layers connected by bridging XO₄ tetrahedra and/or by hydrogen‐bonding interactions involving hydroxyl or water groups, whereas Cd₄(SO₄)(TeO₃)₃ and Cd₅(SO₄)₂(TeO₃)₂(OH)₂ crystallize as framework structures. Common to all crystal structures is the stereoactivity of the Te^IV electron lone pair for each oxotellurate(IV) unit, pointing either into the inter‐layer space, or into channels and cavities in the crystal structures.     

Incorporation of Cadmium Ions and Cadmium Sulfide Particles into Sol-gel Zirconium Phosphate. Synthesis,thermal behavior and X-ray characterization

The inorganic ion-exchanger α-zirconium phosphate was synthesized by the sol-gel method and its properties relating to the exchange of Cd²⁺ and the intercalation of CdS particles were studied. The Cd²⁺-exchange process is a fast process and the material obtained exhibits an increased interlayer distance d with respect to its precursor (9.56 vs. 7.56 Å). The resulting Cd-containing material was exposed to aH₂S gas flow to give CdS particles in the exchanger. The zirconium phosphate containing CdS particles still possesses a layered structure, with a pattern almost identical to that of the initial ion-exchanger precursor. Moreover, the material may exchange further Cd²⁺ and hence lead to a higher CdS particle content. The thermal behavior of this ion-exchangers containing Cd²⁺ or CdS particles was studied.     

Biosynthesis of verrucarins and roridins. 3. Incorporation of 3R)-(5-14C)-and at C(2)stereospecific tritiated mevalonate into verrucarol]

Separate experiments, involving incorporation of either (3R)-[5-¹⁴C]-mevalonate or each enantiomer of [2-³H]-mevalonate into verrucartin A and roridin A, indicate that hydroxylation at C(4) of the tricothecane skeleton, to yield verrucarol (4), proceeds with an overall retention of configuration; they confirm that C(8) and not C(10) is derived specifically from C(2) or mevalonate.     

Identification of Newly Zeaxanthin-Producing Bacteria Isolated from Sponges in the Gulf of Thailand and their Zeaxanthin Production

Sponge-associated bacteria have been found to produce a variety of bioactive compounds including natural pigments. Here, we report the molecular identification of zeaxanthin-producing sponge-associated bacteria isolated from sponges in the Gulf of Thailand and the effect of environmental factors on zeaxanthin production from a bacterium. Three colorful sponge-associated bacteria (CHOB06-6, KODA19-6, and MAKB08-4) were identified based on the 16S rDNA profile. The 16S rDNA sequence-based analyses revealed that CHOB 06-6 and MAKB 08-4 were the closest relatives to Sphingomonas phyllosphaerae FA2^T, and KODA19-6 was a relative of Shingomonas (Blastomonas) natatoria DSM 3183^T. After all bacteria were cultivated in a modified Zobell medium, S. natatoria KODA19-6 was found to produce the highest zeaxanthin at 0.62?mg/l. pH and temperature considerably affected its zeaxanthin production. Its optimal condition for zeaxanthin production was found at a pH of 7 and 30?°C. The bacterium had a maximum specific growth rate (?? _max) of 0.06?1/h with zeaxanthin productivity (Q _p) of 6.27???g/l·h. Therefore, this newly zeaxanthin-producing bacterium has a potential to produce natural zeaxanthin for the food, feed, pharmaceutical, and cosmetic industries.     

NMR analysis of lignins in CAD-deficient plants. Part 1. Incorporation of hydroxycinnamaldehydes and hydroxybenzaldehydes into lignins

Peroxidase/H2O2-mediated radical coupling of 4-hydroxycinnamaldehydes produces 8-O-4-, 8-5-, and 8-8-coupled dehydrodimers as has been documented earlier, as well as the 5-5-coupled dehydrodimer. The 8-5-dehydrodimer is however produced kinetically in its cyclic phenylcoumaran form at neutral pH. Synthetic polymers produced from mixtures of hydroxycinnamaldehydes and normal monolignols provide the next level of complexity. Spectral data from dimers, oligomers, and synthetic polymers have allowed a more substantive assignment of aldehyde components in lignins isolated from a CAD-deficient pine mutant and an antisense-CAD-downregulated transgenic tobacco. CAD-deficient pine lignin shows enhanced levels of the typical benzaldehyde and cinnamaldehyde end-groups, along with evidence for two types of 8-O-4-coupled coniferaldehyde units. The CAD-downregulated tobacco also has higher levels of hydroxycinnamaldehyde and hydroxybenzaldehyde (mainly syringaldehyde) incorporation, but the analogous two types of 8-O-4-coupled products are the dominant features. 8-8-Coupled units are also clearly evident. There is clear evidence for coupling of hydroxycinnamaldehydes to each other and then incorporation into the lignin, as well as for the incorporation of hydroxycinnamaldehyde monomers into the growing lignin polymer. Coniferaldehyde and sinapaldehyde (as well as vanillin and syringaldehyde) co-polymerize with the traditional monolignols into lignins and do so at enhanced levels when CAD-deficiency has an impact on the normal monolignol production. The implication is that, particularly in angiosperms, the aldehydes behave like the traditional monolignols and should probably be regarded as authentic lignin monomers in normal and CAD-deficient plants.