Introduction Of Alkyl Groups Research Articles

Complex formation involving Hg2+ ions on the surface of the polysiloxane xerogels functionalized by 3-mercaptopropyl groups

The influence of parameters of the porous structure and the surface layer composition of the xerogels containing 3-marcaptopropyl and alkyl groups on their sorption properties toward the Hg2+ ions and the stability constants of the formed complexes, which are calculated using the model of chemical reactions, is studied. An increase in the overall surface concentration of the functional groups is shown to induce a change in the composition of the formed complexes. At the concentration of the functional groups lower than 0.01 mmol/m2 the [HgS(CH2)3Si≡]+ complexes are formed, and above 0.01 mmol/m2 the composition of the complexes depends on the mercury(II) content in the starting solution: at low contents the [Hg{S(CH2)3Si≡}2] complexes are formed, whereas at higher concentrations the composition of the complexes becomes simpler. Only the [Hg{S(CH2)3Si≡}2] complexes are formed on the nearly nonporous xerogel with the polymeric structure of the surface layer (the functional group concentration is 0.38 mmol/m2). This, in turn, leads to the situation that the maximum static sorption capacity (590–620 (mg of Hg2+)/(g of sorbent)) is observed for the xerogels with a rather low content of the 3-mercaptopropyl groups (3.0–3.8 mmol/g). The stability of the formed complexes also depends on the surface concentration of the functional groups: the stability constant of the 1: 1 Hg(II) complexes decreases with an increase in the concentration of thiol groups. The introduction of alkyl groups into the surface layer also decreases the stability of the complexes formed. The [Hg{S(CH2)3Si≡}2] complexes formed in the surface layer of the xerogels are characterized by similar stability constants.

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO 2–CaO nanocomposite

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO 2–CaO nanocomposite were investigated using dimethyldiethoxysilane (DMDES) and tetraethoxysilane (TEOS), which could produce two and four siloxane linkages, respectively, after a sol–gel reaction. Methyl methacrylate was co-polymerized with 3-(trimethoxysilyl)propyl methacrylate and then co-condensed with DMDES (specimen D) and TEOS (specimen T), respectively, with calcium nitrate tetrahydrate under acidic conditions. The fracture toughness of specimen D was much improved compared to that of specimen T, whereas its fracture strength, hardness, and apatite-forming ability in simulated body fluid (SBF) were slightly decreased. The improved fracture toughness of specimen D without losing apatite-forming ability was explained by the decrease of siloxane linkage numbers and the introduction of alkyl groups in silica structure because covalently bonded siloxane linkages produce hard and brittle fracture behavior in the nanocomposite while the alkyl groups help to make the silica as linear chain structure. The practical implication of these results is that this new nanocomposite can be applied to the filler materials for bone cement and dental composite resin because of its good bioactivity and improved mechanical properties.

Design and Synthesis of Near-infrared-active Heptamethine–Cyanine Dyes to Suppress Aggregation in a Dye-sensitized Porous Zinc Oxide Solar Cell

Abstract New heptamethine–cyanine dyes were synthesized and used for dye-sensitization of porous zinc oxide cells in the near-infrared region (800 nm). The introduction of alkyl groups into the cyclohexene and indolenium moieties remarkably prevented H-aggregation of the dyes. Consequently, the photovoltaic performance of the dye-sensitized zinc oxide cells with DCA was improved; a solar-to-electricity conversion efficiency (η) of 0.67%, a short-circuit current density of 2.22 mA cm−2, an open-circuit photovoltage of 0.46 V, and a fill factor of 0.66 under standard AM 1.5 irradiation (100 mW cm−2).

Extraction separation of trivalent minor actinides from lanthanides with hydrophobic derivatives of TPEN

We are developing a new MA/Ln separation process with TPEN ( N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine) and its derivatives for P&T technology of HLW from spent nuclear fuel reprocessing plants. TPEN is a hexadentate ligand that has six soft-donor sites as a kind of podand type molecule and can encapsulate a metal ion. TPEN has good selectivity of Am(III) from Ln(III) and has potential to establish partitioning of MA. However, there is a serious problem for the practical application. This is to the dissolution of a slight amount of TPEN (about 10 −4 mol/L) to water. High enrichment of Am(III) will be restricted by the dissolution of TPEN to water. In this study, the hydrophobicity of TPEN is improved by introducing alkyl groups and the effect of the introduction of alkyl groups on the separation of Am(III) and Eu(III) is examined. We tried to synthesize four hydrophobic derivatives of TPEN, and three derivatives were synthesized successfully. The derivatives were examined both the extractability and selectivity of Am(III) and Eu(III). One of them, tpdben, showed good selectivity and the maximum separation factor, SF Am/Eu, was 34 at pH 5.06. A hydrophobic derivative of TPEN that has potential of application to the MA/Ln separation process was synthesized successfully.

Development ofN-Alkyl-Substituted Bis(pyrrolo[3,4-d])tetrathiafulvalenes as Organic Semiconductors for Solution-Processible Field-Effect Transistors

A series of N-alkyl-substituted bis(pyrrolo[3,4-d])tetrathiafulvalenes (PyTTFs, alkyl = n-butyl, n-octyl, n-dodecyl, n-cetyl, and n-icosyl, 3-7) were synthesized as highly soluble tetrathiafulvalene (TTF) derivatives. Their solid-state structures were characterized by X-ray diffraction, and their suitability for use as semiconductors for solution-processible organic field-effect transistor (OFET) devices was evaluated. Whereas the solubility of the TTF derivatives was enhanced with the introduction of alkyl groups, very long alkyl groups, such as the n-icosyl group, reduced the solubility probably due to intermolecular hydrophobic interactions between the very long alkyl groups. The solid-state structure was also influenced by the length of the alkyl groups; molecules 5-7 having n-dodecyl or longer alkyl groups tended to assume two-dimensional (2-D) molecular ordering both in the bulk single crystals and in the spin-coated thin films. In contrast, 3 and 4, having short n-butyl and n-octyl groups, did not take on a 2-D interactive structure in the solid state. Consistent with the solid-state structure of the PyTTF derivatives, field-effect transistor (FET) characteristics of the solution-processed OFETs markedly depended on the length of the alkyl groups. In contrast to spin-coated thin films of 3 and 4, which were relatively inferior semiconducting layers (μ FET = ∼10 -5 cm 2 V -1 s -1 or no reproducible field effect), OFET devices consisting of spin-coated thin films of 5-7 showed typical p-channel FET characteristics, namely, hole mobilities of ∼ 10 -2 cm 2 V -1 s -1 and current on/off ratios of ∼10 4 . The results indicate that an appropriate combination of a π-conjugated core with long alkyl groups could provide soluble organic semiconductors that are applicable to solution-processible OFETs.

Chiral effects of alkyl-substituted derivatives of N,O-bismethacryloyl ethanolamine on the performance of one monomer molecularly imprinted polymers (OMNiMIPs)

New monomers were synthesized and evaluated for their molecular imprinting performance by a recently discovered methodology referred to as one monomer molecularly imprinted polymers (OMNiMIPs). The structural design of the new monomers was based on a lead compound methacrylamidoethyl methacrylate (1) used for the synthesis of OMNiMIP1, and introduced alkyl groups of various sizes at the alpha-amino position of the lead compound. Enantioselectivity, determined by liquid chromatography, was used to compare the performance of the imprinted polymers. Methyl substitution provided crosslinker 5 (2-methacrylamidopropyl methacrylate), which upon imprint polymerization afforded OMNiMIP5 with approximately the same enantioselectivity (alpha = 3.8) as OMNiMP1 (alpha = 3.7) made with the lead compound (1). The other two monomers (6 and 7) with larger alkyl substitutions (isopropyl and sec-butyl respectively) resulted in OMNiMIPs with low selectivity values (alpha = 1.0 and 1.2 respectively). Last, a strong influence of diastereomeric complexes on OMNiMIP5 selectivity was determined, with L: /L: and D: /D: monomer/template pairs giving alpha values of 3.6-3.8, while L: /D: and D: /L: monomer/template pairs had alpha values of 2.3-2.4. There is no intrinsic enantioselectivity seen for the OMNiMIP5 control polymer made without template at all, giving an alpha value of 1.03.

A Facile Synthesis of Cyclopenta[d][1,2]oxazines Through [6 + 4] Cycloaddition Reaction.

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ICONE15-10583 Am(III)/Eu(III) SEPARATION WITH TPEN

We are developing a new MA/Ln separation process with N,N,N',N'-tetrakis(2-pyridylmethyl) ethylenediamine, TPEN, and its derivatives for P&T technology. TPEN has six soft-donor sites as a kind of podand type molecule and can encapsulate a metal ion. TPEN has good selectivity of Am(III) from Ln(III) and has potential to establish partitioning of MA. We elucidated extraction behavior of Am(III) and Eu(III) using several organic solvents. The maximum separation factor of Am(III) from Eu(III), SFAm/Eu, was 270 at pH 4.80 with nitrobenzene as organic solvent. In synergistic extraction system, Am(III) was separated effectively with TPEN and decanoic acid diluted with 1-octanol. The synergistic extraction system was comfortable for reduction of secondary waste from the used organic solvent and operation management, because the organic phase of the extraction system was compatible with CHON principle and has low toxicity. The SFAm/Eu and the distribution ratios of Am(III) and Eu(III) were sufficient to establish the separation process. The extraction mechanism was considered ion-pair extraction. From the viewpoint of practical application, there is a problem in the characteristics of TPEN. One of them is hydrophilicity. The hydrophobicity of TPEN is improved by introducing alkyl groups. We synthesized the hydrophobic derivative N,N,N',N'-tetrakis(2-methylpyridyl) dibutylethylenediamine, tpdben, which has two n-butyl groups. Tpdben showed the maximum SFAm/Eu was 34 at pH 5.06. A hydrophobic derivative of TPEN which has selectivity of An(III) from Ln(III) was synthesized successfully.

Mapping the Fluorophilicity of a Hydrophobic Pocket: Synthesis and Biological Evaluation of Tricyclic Thrombin Inhibitors Directing Fluorinated Alkyl Groups into the P Pocket

In the completion of our fluorine scan of tricyclic inhibitors to map the fluorophilicity/fluorophobicity of the thrombin active site, a series of 11 new ligands featuring alkyl, alkenyl, and fluoroalkyl groups was prepared to explore fluorine effects on binding into the hydrophobic proximal (P) pocket, lined by Tyr 60A and Trp 60D, His 57, and Leu 99. The synthesis of the tricyclic scaffolds was based on the 1,3-dipolar cycloaddition of azomethine ylides, derived from L-proline and 4-bromobenzaldehyde, with N-(4-fluorobenzyl)maleimide. Introduction of alkyl, alkenyl, and partially fluorinated alkyl residues was achieved upon substitution of a sulfonyl group by mixed Mg/Zn organometallics followed by oxidation/deoxyfluorination, as well as oxidation/reduction/deoxyfluorination sequences. In contrast, the incorporation of perfluoroalkyl groups required a stereoselective nucleophilic addition reaction at the "upper" carbonyl group of the tricycles, thereby yielding scaffolds with an additional OH, F, or OMe group, respectively. All newly prepared inhibitors showed potent biological activity, with inhibitory constants (K(i) values) in the range of 0.008-0.163 microM. The X-ray crystal structure of a protein-ligand complex revealed the exact positioning of a difluoromethyl substituent in the tight P pocket. Fluorophilic characteristics are attributed to this hydrophobic pocket, although the potency of the inhibitors was found to be modulated by steric rather than electronic factors.

A Facile Synthesis of Cyclopenta[d][1,2]oxazines through [6+4] Cycloaddition Reaction

Functionalized 1,2-oxzines are known to exhibit various pharmacological properties, such as antibacterial activity, acetylcholinesterase inhibitory activity, protein tyrosine phosphatase inhibitory activity. They also occur as a key structural subunit in biologically active natural products. However, there have been only limited methods for the synthesis of cyclopenta[d][1,2]oxazines and their derivatives. Linn and Sharkey reported the first practical synthesis of cyclopenta[d][1,2]oxazine by use of benzoylated cyclopentadiene. Lloyd and co-workers also reported the synthesis of cyclopenta[d][1,2]oxazine by reaction of diaroylcyclopentadienes with hydroxylamine. The reaction of benzonitrile oxide with fulvene was known to yield both 1 : 1 and 2 : 1 adducts. Herein, we report the first example of a facile and convenient synthesis of various cyclopenta[d][1,2]oxazines starting from chlorooxime and fulvene through [6+4] cycloaddition. In an effort to pursue of PTP1B inhibitors, a convenient synthesis of functionalized cyclopenta[d][1,2]oxazine derivatives was required. Fulvenes were obtained from the reaction of dimethyl sulfate salt of dimethylamides 3 and cyclopentadienyl sodium as cited. Howe and co-workers reported a convenient synthesis of chlorooximes by the use of N-chlorosuccinimide in DMF in place of chlorine, avoiding the use of hazardous chlorine and ring chlorination as side reactions with benzaldoximes that contain electron-donating substituents. Based on this efficient synthetic methodology for chlorooximes 2, we could achieve a facile synthesis of various cyclopenta[d][1,2]oxazines 5 by the cyclocondensation of 2 with fulvene 4 in the presence of triethylamine (eq. 1). The introduction of alkyl or aromatic substituents at 1-position could be accomplished by the use of substituted fulvenes or chlorooximes as given in Table 1. Diethyl ether was the solvent of choice over dichloromethane (41% yield, 5a) for cycloaddition and all of the reaction afforded the corresponding cyclopenta[d][1,2]oxazines in moderate yields. The relatively low yields for 5c, 5i, and 5l were presumably due to the deprotection of protective group, t-butyl or acetyl group. Cycloadditions of chlorooxime with fulvene are affected by the steric factor of the substituents (5o-5r), as the introduction of substituent (R) lowered the reaction yield. This method was then applied to substituted fulvenes 6, in situ generated from the corresponding cyclopentadiene, and 10 as shown in Scheme 1. As can be seen, carbometh-

Photo‐Fries Rearrangement of Carbazol‐2‐yl Sulfonates: Efficient Tool for the Introduction of Sulfonyl Groups into Polycyclic Aromatic Compounds

AbstractSystematic studies on the photo‐Fries rearrangement of different 9H‐carbazol‐2‐yl sulfonates 2 have shown that this type of conversion can be readily used for the preparative‐scale introduction of alkyl‐ or arylsulfonyl groups into polycyclic aromatic compounds under very mild conditions. A series of new 1‐sulfonyl‐ (3) or 3‐sulfonyl‐9H‐carbazoles (4) were prepared in medium‐to‐good yields, and characterized by UV/VIS, 1H‐NMR, and 13C‐NMR spectroscopy, as well as by elemental analysis. Effects of irradiation wavelength, solvent polarity, presence or absence of O2, and photosensitizers were studied in detail.

Effect of an alkyl substituted in salen ligands on 1,4‐Cis selectivity and molecular weight control in the polymerization of 1,3‐butadiene with (salen)Co(II) complexes in combination with methylaluminoxane

AbstractThe effect of an alkyl substituted in the aromatic ring of the salen ligand on the polymerization of butadiene (Bd) with (salen)Co(II) complexes in combination with methylaluminoxane (MAO) was investigated. The activity for the polymerization of Bd was influenced significantly by the introduction of alkyl groups at the 3,3′,5,5′‐positions in the aromatic ring of the salen ligand, and both the polymerization rate and 1,4‐cis contents increased in the following order with respect to the alkyl group: H < CH3 < t‐C4H9. This is in good agreement with the bulkiness of the alkyl groups. The activity for the polymerization of the (salen)Co(II) complex possessing t‐C4H9 at the 3,3′‐positions was higher than that of the (salen)Co(II) bearing t‐C4H9 at the 5,5′‐positions. Thus, the introduction of bulky substituents at the 3,3′‐positions of the salen ligand was an important factor in achieving both high activity and high 1,4‐cis selectivity in the polymerization of Bd with (salen)Co(II) complexes in combination with MAO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4088–4094, 2006

Quantum Chemical Study of Solvent and Substituent Effects on the 1,5-Hydride Shift in 2,6-Dimethyl-2-heptyl Cations

The mechanism of the degenerate 1,5-hydride shift in 2,6-dimethyl-2-heptyl cations has been investigated using ab initio MP2 and density functional theory (DFT) hybrid (B3LYP) calculations. The potential-energy profile for the 1,5-hydride shift consists of three minima corresponding to two equivalent acyclic carbocations and one symmetrically mu-hydrido-bridged carbocation, while two equivalent unsymmetrically hydrido-bridged carbocations were located as transition-state structures. The calculated relative energy differences between acyclic carbocations and symmetrically mu-hydrido-bridged structure are significantly affected by introduction of alkyl and (CH2)n-substituents at the C4 position of the 2,6-dimethyl-2-heptyl cation structure. DFT self-consistent isodensity polarizable continuum method (SCI-PCM) and MP2 PCM continuum methods have been used to calculate the effect of solvation on geometries and relative energies of the species involved in the 1,5-hydride shift. It is found that relative energies of acyclic and mu-hydrido-bridged carbocation structures as well as the energy barriers for 1,5-hydride shifts are in accord with experimental data if solvation effects are taken into account.

Polytypic phase transition in alkyl chain-functionalized valence tautomeric complexes

A novel series of valence tautomeric (VT) complexes, [Co(Cnbpy)(3,5-DTBQ)2] (Cnbpy = 4,4'-dialkyl-2,2'-bipyridine (alkyl = (C(n)H(2n+1)) where n = 0 (CoC0bpy), 1 (CoC1bpy), 5 (CoC5bpy), 9 (CoC9bpy) and 13 (CoC13bpy); 3,5-DTBQ = 3,5-di-tert-butylsemiquinonate or catecholate), including two previously reported complexes (CoC0bpy and CoC1bpy), were systematically prepared and their properties examined. Introduction of alkyl groups into VT chromophores leads to unexpected variations in the VT process, depending on the lengths of the alkyl chains. An even more interesting observation is that significant polytypic phase transitions with crystallographic symmetry changes accompanying the abrupt VT conversion are induced for the first time in CoC9bpy and CoC13bpy.

Synthesis and antimicrobial activity of some new 1-alkyl-2-alkylthio-1,2,4-triazolobenzimidazole derivatives

Some new derivatives of 1,2,4-triazolo[2,3-a]benzimidazoles were synthesized through the reaction of 1,2-diaminobenzimidazole with carbon disulfide. The resulting 1,2,4-triazolo-[2,3-a]benzimidazole-2-thione intermediate was reacted with one equivalent of alkyl halides to give the corresponding 2-alkylthio derivatives, which were further alkylated through the reaction with another one equivalent of different alkyl halides to afford the target compounds; 1-alkyl-2-alkylthio-1,2,4-traizolo[2,3-a]benzimidazoles. On the other hand, the 1,2-disubstituted derivatives with two identical alkyl substituents were prepared by the reaction of 1,2,4-triazolo[2,3-a]benzimidazole-2-thione with two equivalents of the alkyl halides. The structures of the new compounds were assigned by spectral and elemental methods of analyses. The synthesized compounds were tested for their antibacterial and antifungal activities. Most of the tested compounds proved comparable results with those of ampicillin and fluconazole reference drugs. The study indicated that, the antibacterial as well as the antifungal activities of the test compounds were improved with increase in the bulkiness of the introduced alkyl groups. Also, some active antibacterial compounds were tested for their antimycobacterial activity. All the test compounds showed equipotent antitubercular activity as that of INH as a reference drug.

C-C Bond Formation at C-5 Position of Dimethyluracil Derivatives Using SmI2

Derivation of purine and pyrimidine nucleosides has attracted much attention because of potent antitumor or antiviral activity. (Figure 1) Pyrimidine nucleosides substituted at the C-5 position constitute a class of biologically significant molecules. The well-known cancer chemotherapeutic 5-fluorouracil and antiviral agents, such as 5-iodo-2'deoxyuridine and 5-(trifluoromethyl)-2'-deoxyuridine, have been in clinical use for several years. Meanwhile, in recent years, there have been significant interests in the potential usages of the C-5-substituted pyrimidine nucleosides in synthetic oligonucleotide probes as a tether site for linking reporter groups to nucleic acids. When the modified nucleosides are incorporated into the duplex B-DNA, C-5substituents are located in the major groove, and so do not disrupt Watson-Crick base pairing. As a result, the methodologies for constructing suitable linker arms and generating bonds to C-5 are important for the synthesis of potential therapeutic agents and synthetic oligonucleotide probes. Therefore, the 5-position of pyrimidine nucleosides has been the target of extensive studies on modifications. Generally, C-C bond formation at C-5 of uracils has been achieved by the application of photolytic reaction and palladium-catalyzed coupling reactions. Although the utilization of the lithiation methodology was developed for the introduction of a carbon functionality at the C-5 or C-6 position of uridine derivatives, the ratio (C-5/C-6) of substitution is governed by the substituents on the pyrimidine base and the protecting groups on the sugar. On the other hand, Mn(OAc)3 and Ce(NH4)2(NO3)6 gave regioselective C-C bond formation at the 5-position of pyrimidine derivatives. In the new attempts for the functionalization of pyrimidine bases and because of the biological interest of the related compounds, we became interested in the introduction of alkyl group at C-5 position of pyrimidines. Kim et al. reported that the reaction of α-bromoacrylamides with carbonyl compounds in the presence of SmI2 can provide Baylis-Hillman adducts through samarium Grignard type of anionic process, solving several problems of Baylis-Hillman reaction. (Scheme 1) It has been described that the α-carbon of the acrylamide with a phenyl group is rather electron-deficient than other moieties devoid of the phenyl group due to resonance effect. Therefore, the vinyl radical can undergo further reduction to vinylsamarium reagent by SmI2. This mechanism was supported by the fact that ethyl α-bromoacrylate and 2-bromo-2cyclohexen-1-one as well as dimethyl α-bromoacrylamide did not give the corresponding desired products. We set out to address the question of whether this samarium chemistry would be applicable to the pyrimidine case. Similar to the resonance effect of the phenyl group, it was considered that the pyrimidine structure having another amide group might be able to react with electrophiles through a vinylsamarium intermediate. We focused our initial efforts on the coupling of 5iododimethyluracil with propionaldehyde under the same condition as the previously reported one. Unfortunately, when 1 equivalent of aldehyde was used, only trace amount of coupling product (2a) was observed by TLC and H NMR, while the reduction product (3) was obtained as a major product (Table 1, entry 1). However, this result encouraged us to keep finding the appropriate condition for pyrimidine substrates. Finally, it was found that the more loading of aldehyde led to both the more desired product (2a) and the less reduced one (3) (Table 1, entries 1-3). In contrast, 5-bromodimethyluracil showed less reactivity than iodo-substrate under the same condition, it can be considered as a general trend that the reactivity of α-iodoenones is higher, especially in transition metal mediated reactions, than the corresponding bromo or chloro derivatives (Table 1, entry 4). On the other hand, the use of additive such as HMPA was not successful (Table 1, entry 6). Sterically hindered aldehydes afforded the alkylated pyrimidines in only moderate chemical yields (Table 2, entry 5-6) and Figure 1 Scheme 1

Stabilization of emulsions using polymeric surfactants based on inulin

The use of polymeric surfactants for stabilization of emulsions is described. A brief account of general classification and description of polymeric surfactants is given. This is followed by a description of the adsorption and conformation of polymeric surfactants at interfaces. The theoretical approaches for studying polymer adsorption are briefly described. This is followed by a section on the experimental techniques that can be applied to study adsorption and conformation of polymers at the interface. Examples are given to illustrate the experimental techniques. A section is devoted to the interaction between droplets containing adsorbed polymer layers (steric stabilization). The last section gives results on oil-in-water (O/W) emulsions stabilised with a novel graft copolymeric surfactant based on inulin that has been modified by introducing alkyl groups. Two oils were used, namely Isopar M (isoparaffinic oil) and cyclomethicone. Emulsions prepared using the inulin-based surfactant have large droplets, but this could be significantly reduced by addition of a cosurfactant in the oil phase, namely Span 20. The stability of the emulsions was investigated in water, in 0.5, 1.0, 1.5 and 2 mol dm −3 NaCl and in 0.5, 1.0, 1.5 and 2 mol dm −3 MgSO 4. These emulsions were stable for more than 1 year up to 50 °C in NaCl concentrations up to 2 mol dm −3 and 1 mol dm −3 MgSO 4. This high stability in high electrolyte concentrations could be attributed to the nature of the hydrophilic (stabilizing) polyfructose chain. This was confirmed using cloud point measurements, which showed high hydration of the polyfructose chain in such high electrolyte concentrations. This ensured the long-term physical stability resulting from the strong steric repulsion between the polyfructose chains.

Comparison of the Electrical Properties and Chemical Stability of Crystalline Silicon(111) Surfaces Alkylated Using Grignard Reagents or Olefins with Lewis Acid Catalysts

Four methods were used to functionalize crystalline Si(111) surfaces with alkyl groups (C_nH_(2n+1), n = 1, 2, 6, 8): chlorination with PCl_5 followed by alkylation with C_nH_(2n+1)MgX (X = Cl, Br), chlorination with Cl_2(g) followed by alkylation with C_nH_(2n+1)MgX, Lewis acid-mediated reduction of a terminal alkene, and anodization in diethyl ether containing 3.0 M CH_3MgI. The chemical properties of each surface were characterized as a function of time exposed to air using X-ray photoelectron spectroscopy, and the electrical properties of the various surfaces were probed using time-resolved radio frequency (rf) photoconductivity decay methods. Both chlorination/alkylation routes produced alkylated Si surfaces that displayed low ( 600 h of exposure to air. Surfaces functionalized through this route also displayed a significantly lower rate of oxidation than did unalkylated, H-terminated or Cl-terminated Si(111) surfaces. In contrast, surfaces modified by the Lewis acid-catalyzed reduction of 1-hexene and 1-octene exhibited high S values (S > 400 cm s^(-1)) when initially exposed to air and oxidized as rapidly as H-terminated Si(111) surfaces. Methyl-terminated Si(111) surfaces functionalized by anodization in a solution of CH_3MgI in ether exhibited stable, albeit high, S values (460 cm s^(-1)), indicating that the surface had been partially modified by the anodization process. The fractional monolayer coverage of oxide on the alkylated surface after exposure to air was determined for each functionalization technique. Although all four of the functionalization routes studied in this work introduced alkyl groups onto the Si surface, subtle changes in the extent and quality of the alkyl termination are significant factors in determining the magnitude and degree of chemical and electrical passivation of the resulting functionalized Si surfaces.

Transformation of mutagenic aromatic amines into non-mutagenic species by alkyl substituents: Part II: Alkylation far away from the amino function

Alkyl and trifluoromethyl derivatives of 4-aminobiphenyl ( 1) (4ABP) and 2-aminofluorene ( 7) (2AF) were synthesised and assayed for mutagenicity using Salmonella typhimurium tester strains TA98 and TA100 with and without the addition of S9 mix. Modification of 1 was achieved by attachment of alkyl groups (methyl, ethyl, iso-propyl, n-butyl, tert-butyl) and a trifluoromethyl group (CF 3) in the 4′-position, the 3′-position (Me, CF 3) and the 3′-, 5′-positions (DiMe, DiCF 3). Compound 7 was modified by introduction of alkyl groups (methyl, tert-butyl, adamantyl) and a trifluoromethyl group (CF 3) in the 7-position. The derivatives of 1 and 7 show for groups with growing steric demand decreased mutagenic activity. The bulkiest groups (CF 3, tert-butyl and adamantyl) induce the strongest effects on the mutagenicity. It was even possible to eliminate the mutagenicity of 1 and 7 by introduction of such substituents. In the last part of the work, we compared the experimental mutagenicities with calculated values derived from QSAR correlations. Our findings show that the predictions for aromatic amines with bulky substituents were generally too high. The strongest deviations were observed in the case of the CF 3-, tert-butyl- and the adamantyl-group. Only the parent compounds and derivatives with small alkyl groups were predicted well. These investigations show that “large” substituents have an influence on the mutagenicity caused by their steric demand. To predict the correct mutagenicities of such compounds, it is necessary to introduce steric parameters in the respective QSAR equations which will be done in a forthcoming paper.

The syntheses of 6-C-alkyl derivatives of methyl α-isomaltoside for a study of the mechanism of hydrolysis by amyloglucosidase

The epimeric (6aR)- and (6aS)-C-alkyl (methyl, ethyl and isopropyl) derivatives of methyl α-isomaltoside (1) were synthesized in order to examine the effects of introducing alkyl groups of increasing bulk on the rate of catalysis for the hydrolysis of the interunit α-glycosidic bond by the enzyme amyloglucosidase, EC 3.2.1.3, commonly termed glucoamylase (AMG). It was previously established that methyl (6aR)-C-methyl α-isomaltoside is hydrolysed about 2 times faster than methyl α-isomaltoside and about 8 times faster than its S-isomer. The kinetics for the hydrolyses of the ethyl and isopropyl analogs were also recently published. As was expected from molecular model calculations, all the R-epimers are good substrates. A rationale is presented for the catalysis based on conventional mechanistic theories that includes the assistance for the decomposition of the activated complex to products by the presence of a hydrogen bond, which connects the 4a-hydroxyl group to the tryptophane and arginine units. It is proposed that activation of the initially formed complex to the transition state is assisted by the energy released as a result of both of the displacement of perturbed water molecules of hydration at the surfaces of both the polyamphiphilic substrate and the combining site and the establishment of intermolecular hydrogen bonds, i.e., micro-thermodynamics. The dissipation of the heat to the bulk solution is impeded by a shell of aromatic amino acids that surround the combining site. Such shields are known to be located around the combining sites of lectins and carbohydrate specific antibodies and are considered necessary to prevent the disruption of the intermolecular hydrogen bonds, which are of key importance for the stability of the complex. These features together with the exquisite stereoelectronic dispositions of the reacting molecules within the combining site offer a rationalization for the catalysis at ambient temperatures and near neutral pH. The syntheses involved the addition of alkyl Grignard reagents to methyl 6-aldehydo-α-D-glucopyranoside. The addition favoured formation of the S-epimers by over 90%. Useful amounts of the active R-isomers were obtained by epimerization of the chiral centers using conventional methods. Glycosylation of the resulting alcohols under conditions for bromide-ion catalysis, provided methyl (6aS)- and (6aR)-C-alkyl-hepta-O-benzyl-α-isomaltosides. Catalytic hydrogenolysis of the benzyl groups afforded the desired disaccharides. 1H NMR studies established the absolute configurations and provided evidence for conformational preferences.Key words: amyloglucosidase (AMG), exo-anomeric effect, 6-C-alkyl-α-D-glucopyranosides and isomaltosides, mechanism of enzyme catalysis.