Number Of Methylene Groups Research Articles

Adjusting Fermi Level of Graphene by Controlling the Linker Lengths of Dipolar Molecules.

Graphene modified by azo molecules has attracted much attention due to its promising graphene-enhanced Raman scattering (GERS) effect. Herein, we achieved the shortened distance between the dipole moment and graphene, by reducing the number of methylene groups and the chain length, and studied the Raman scattering in dipolar molecules/graphene hybrids. Whether for low or high concentrations, a more significant GERS signal can be observed, which can be attributed to the effective modulation of the dipole moment on interface energy level matching. Further, by fabricating FET devices, we demonstrate more obvious p-type and n-type doping in graphene that is affected by the chain length of the azobenzene molecule. On the basis of the dependence of the G band shift on the Fermi surface change, we further reveal the important role of dipole moment distance in dipolar molecules/graphene hybrids. These studies provide a new approach to optimize the interface matching between azobenzene and graphene and may help achieve more sensitive GERS detection.

A molecular dynamics study combining with entropy calculation on the packing state of hydrophobic chains in micelle interior

Micelle plays an important role both in scientific research and practical applications. However, the problem about the state of micelle interior has not been completely solved. Based on the molecular dynamics (MD) simulation, absolute configurational entropies of hydrophobic chain are calculated to give a correct description of micelle hydrophobic interior. N-dodecyl betaine (NDB) and n-tridecane (C13), which have the same number of methylene group, are investigated in the present study. Results including total entropy, translational entropy, rotational entropy as well as vibrational entropy are calculated and compared between alkyl chains of NDB micelle and liquid C13. Local entropies along NDB alkyl chain and those between micelle and C13 are also considered. Through these comparisons, we explicitly propose that innermost groups of hydrophobic chains, where carbon number is no more than two, are identical to pure alkane whilst the outer core in the micelle shows the liquidlike state at the molecular level. The detailed information of micelle interior is the foundation for understanding micelle applications, such as solubilization, drug delivery and catalysis.

Crystalline Structures and Structural Transitions of Copolyamides Derived from 1,4-Diaminobutane and Different Ratios of Glutaric and Azelaic Acids.

Copolyamides derived from even 1,4-butanediamine and different mixtures of odd dicarboxylic acids with a great difference in the number of methylene groups (i.e., glutaric and azelaic acids with 3 and 7 groups, respectively) have been synthesized, characterized and structurally studied. Calorimetric analyses revealed a complex behavior with multiple melting peaks associated to lamellar reordering and the presence of defective crystals. Equilibrium melting temperatures were evaluated and showed a eutectic behavior with composition. Copolymers were able to crystallize even for samples with comonomer percentages close to 50%. Negative and ringed spherulites from the melt state and small lath-like lamellar crystals from dilute solution crystallizations were attained. Furthermore, calorimetric data pointed out the exclusion of the less abundant monomer from the lattice of the predominant structure. All samples at room temperature showed a similar crystalline structure (form I) defined by two predominant reflections at spacings close to 0.430 and 0.380 nm, which has been related for even-odd nylons with a two-hydrogen bonded structure. Real time synchrotron experiments showed that melt crystallized samples have two polymorphic transitions on heating, which were practically reversible and consequently were also detected during cooling from the melt state. Interestingly, a different behavior was detected among solution crystallized samples and specifically the transition to the intermediate structure (form II) was not detected during heating for samples enriched on the azelate component or more precisely when they were exclusively crystallized in the form I.

Oligomeric odd–even effect in liquid crystals

We demonstrate a novel oligomeric odd–even effect of mesogenic segments connected by flexible chains with an odd number of methylene groups.

Solvatochromism as a new tool to distinguish structurally similar compounds

It is here reported a new concept based on solvatochromism to distinguish structurally similar compounds in aqueous solutions by the analysis of the stabilization of electronic excited states. The sensitivity of this approach to differentiate similar organic compounds, such as structural isomers or compound differing in the number of methylene groups, or proteins with conformational changes induced by being or not bound to cofactors, differing in two amino acids substitutions, or differing in their glycosylation profile, is demonstrated. The sensitivity of the proposed approach, based on the solvatochromic method, opens the path to its use as an auxiliary analytical tool in biomedical diagnosis/prognosis or in quality control of biologic-based drugs.

Modeling the Dynamics of the Integral Dielectric Permittivity of a Porous Low-K Organosilicate Film during the Dry Etching of a Photoresist in O2 Plasma

Using an imitational cellular-automaton model, the structural degradation of a interlayer low-K dielectric during the plasma etching etching of a photoresist is studied. The dielectric represents a porous material based on SiOCH, whose integral dielectric permittivity depends on the percentage of carbon atoms on the pore walls and in the dielectric matrix. The period of etching is such that the removal of carbon (and, accordingly, degradation) is incomplete. The simulation is performed for 2 million steps of the automaton, which correspond to 2 s in the real process. During this period, the number of methyl groups does not exceed 20% of the initial value at the dielectric pore depth of 40 nm; in this case, the permittivity e increases from 2.5 to 2.84. Extrapolating to a longer time period (nearly 1 min) shows that the total fraction of СН3-groups is 9% of the initial value through the full depth of the material, while the final value of dielectric permittivity would correspond to 3.0–3.1. The results of the modeling agree with the experimental data described in the literature.

Synthesis and liquid crystal properties of new cyclic carbonate monomers functionalised with cholesteryl moiety

ABSTRACTFour new liquid crystal cyclic carbonate monomers M1–M4, with cholesteryl moiety and flexible spacer of different lengths, were synthesised through coupling reaction. The chemical structures, mesophase properties and thermal behaviour of the monomers were characterised with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy (1H NMR), polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. Based on these results, the relationship between the number of methylene groups into flexible chain and the mesomorphism of the monomers was investigated. It was found that all the monomers showed a focal conic texture of a smectic A phase and exhibited an interdigitated molecular arrangement. Moreover, the glass transition temperature and the isotropisation temperature of the monomers except M1 decreased, and the mesophase range narrowed as the number of methylene units into the flexible chain increased.

Synthesis, characterization & cytocompatibility of poly (diol-co-tricarballylate) based thermally crosslinked elastomers for drug delivery & tissue engineering applications

The aim of this study was to investigate the synthesis and in vitro characterization of thermoset biodegradable poly (diol-co-tricarballylate) (PDT) elastomeric polymers for the purpose of their use in implantable drug delivery and tissue engineering applications. The synthesis was based on thermal crosslinking technique via a polycondensation reaction of tricarballylic acid with aliphatic diols of varying chain lengths (C6-C12). PDT prepolymers were synthesized at 140 °C for 20 min. After purification, the prepolymers were molded and kept at 120 °C for 18 h under vacuum to complete the crosslinking process. PDT prepolymers were characterized by DSC, FT-IR, 1H NMR and GPC. The PDT elastomers were also subjected to thermal and structural analysis, as well as sol content, mechanical testing, in vitro degradation and cytocompatibility studies. The mechanical properties and sol content were found to be dependent on synthesis conditions and can be controlled by manipulating the crosslinking density and number of methylene groups in the chain of precursor aliphatic diol. The family of thermally crosslinked PDT biodegradable polyesters were successfully prepared and characterized; besides they have promising use in drug delivery and other biomedical tissue engineering applications.

Tuning the Conformation and Color of Conjugated Polyheterocyclic Skeletons by Installing ortho-Methyl Groups.

ortho-Methyl effects are exploited to tune steric hindrance between side-chain N,N'-diaryls and polycyclic dihydrodibenzo[a,c]phenazine, and in turn control the conformations of N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC) and its ortho-methyl derivatives Mx-My (x=0, 1 or 2, y=1 or 2, x and y correlate with the number of methyl groups in the ortho-positiond of N,N'-diphenyl). The magnitude of steric hindrance increases as x and y increase, and the V-shaped dihydrodibenzo[a,c]phenazine skeleton is gradually tuned from a bent (DPAC) to planar (M2-M2) structure in the ground state. As a result, the relaxation of the excited-state structure of DPAC and its numerous analogues could be mimicked by model structures Mx-My, demonstrating for the first time the the conformation change from bent-to-planar and hence a large range of energy-gap tuning of polycyclic conjugated structures controlled by the steric hindrance.

Tuning the Conformation and Color of Conjugated Polyheterocyclic Skeletons by Installing ortho‐Methyl Groups

Abstractortho‐Methyl effects are exploited to tune steric hindrance between side‐chain N,N′‐diaryls and polycyclic dihydrodibenzo[a,c]phenazine, and in turn control the conformations of N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazine (DPAC) and its ortho‐methyl derivatives Mx‐My (x=0, 1 or 2, y=1 or 2, x and y correlate with the number of methyl groups in the ortho‐positiond of N,N′‐diphenyl). The magnitude of steric hindrance increases as x and y increase, and the V‐shaped dihydrodibenzo[a,c]phenazine skeleton is gradually tuned from a bent (DPAC) to planar (M2‐M2) structure in the ground state. As a result, the relaxation of the excited‐state structure of DPAC and its numerous analogues could be mimicked by model structures Mx‐My, demonstrating for the first time the the conformation change from bent‐to‐planar and hence a large range of energy‐gap tuning of polycyclic conjugated structures controlled by the steric hindrance.

Synthesis and characterization of poly(ester amide amide)s of different alkylene chain lengths

In this work, a series of aliphatic biodegradable poly(ester amide amide) polymers was synthesized by melt polycondensation of a tailor-made amide-containing monomer based on 1,4-diaminobutane and e-caprolactone and different dicarboxylic acid methyl esters with even number of methylene groups. The synthesized polymers were characterized by 1H NMR, FT-IR spectroscopy, GPC, SAXS and WAXS. DSC results show that the melting point is located at about 150 °C for all polymers. X-ray scattering experiments in small and wide angles reveal formation of crystals with extended-chain conformation resulting in strict periodicity of electron density along the main chain. TGA data indicate the high thermal stability of polymers to temperatures above 350 °C, which are much above the melting point. The obtained characteristics of the newly synthesized PEAAs can open new perspectives for melt processing to fabricate films, highly oriented fibers and injection-molded parts with good thermal stability and mechanical performance.

Study on TICT emission of TPE-BODIPY derivatives mediated by methyl group on BODIPY

A series of tetraphenylethene-borondipyrromethene (TPE-BODIPY) derivatives with different numbers of methyl groups on BODIPY cores were designed and synthesized. The intramolecular charge transfer behaviors from donor TPE to accepter BODIPY were investigated. Aggregation-induced emission (AIE), theoretical calculation, single crystal structure and solvent effect all proved that the introduction of methyl group to BODIPY can inhibit the intramolecular charge transfer behavior. Red organic luminescent material 8-TPEBODIPY (TPB) with no methyl groups showing twisted intramolecular charge transfer (TICT) emission peak both in solution and in film state, presents obviously AIE and solvatochromic properties and a large Stokes shifts over 100 nm, which can be employed as a fluorescent sensor for the detection of water in THF.

Microscopic Insight into the Protein Denaturation Action of Urea and Its Methyl Derivatives.

We employ site-specific, linear and nonlinear infrared spectroscopic techniques as well as fluorescence spectroscopy and molecular dynamics simulations to investigate the binding interactions of urea and three of its derivatives, methylurea, 1,3-dimethylurea, and tetramethylurea, with protein aromatic and polar side chains. We find that (1) urea methylation leads to preferential interactions between the cosolvent molecules and aromatic side chains with an affinity that increases with the number of methyl groups; (2) interactions with tetramethylurea cause significant dehydration of aromatic side chains and the effect is most pronounced for tryptophan; and (3) while neither urea nor tetramethylurea shows preferential accumulation around a polar side chain, the number of hydrogen-bond donors around this side chain is significantly decreased in the presence of tetramethylurea. Taken together, our findings suggest that these urea derivatives, especially tetramethylurea, can effectively disrupt hydrophobic interactions in proteins. Additionally, tetramethylurea can promote intramolecular hydrogen-bond formation and hence induce α-helix folding in peptides, as observed.

Odd-even effect on the formation of aqueous biphasic systems formed by 1-alkyl-3-methylimidazolium chloride ionic liquids and salts.

This work provides a comprehensive evaluation of the effect of the cation alkyl side chain length of the 1-alkyl-3-methylimidazolium chloride series ([C n C1im]Cl, n = 2-14) of ionic liquids (ILs) on their capability to form aqueous biphasic systems (ABSs) with salts and self-aggregation derived properties. The liquid-liquid phase behavior of ternary systems composed of [C n C1im]Cl, water, and K3PO4 or K2CO3 and the respective Setschenow salting-out coefficients (ks ), a quantitative measure of the two-phase formation ability, were determined. An odd-even effect in the ks values along the number of methylene groups of the longest IL cation alkyl side chain was identified for the ABS formed by K2CO3, a weaker salting-out agent where the phenomenon is clearly identified. In general, cations with even alkyl side chains, being likely to display higher molar volumes, are more easily salted-out and thus more prone to undergo phase separation. The odd-even effect in the ks values is, however, more significant in ILs up to n = 6, where the nanostructuration/nanosegregation of ILs plays a less relevant role. Still, with the [C n C1im]Cl (n = 7-14) series of ILs, an odd-even effect was also identified in the ILs' ionization degree, molar conductivity, and conductivity at infinite dilution. In summary, it is shown here that the ILs' odd-even effect occurs in IL aqueous solutions and not just in neat ILs, an already well-established phenomenon occurring in a series of ILs' properties described as a result of the orientation of the terminal methyl groups to the imidazolium ring cation and consequent effect in the ILs' cohesive energy.

Effect of Solvent and Functionality on the Physical Properties of Hydroxyl-Terminated Polybutadiene (HTPB)-Based Polyurethane.

The present article reports the investigation on the effects of solvent and position of functionality on various physical properties of polyurethanes (PUs) based on hydroxyl-terminated polybutadiene (HTPB). The PU films (curative) were prepared by coupling HTPB (P0) with isophorone diisocyanate (IPDI) in various solvent media. The PUs obtained in different solvent media displayed similar thermal profile and glass transition temperature (Tg), but their tensile properties varied significantly. Optimized tensile properties were observed when tetrahydrofuran was used as the solvent media. In the course, the investigation of the functionality effect, tetrazole (M1, M2, and M3) were covalently attached at the terminal carbon of HTPB to obtain three modified HTPBs (P1, P2, and P3), thereby coupling with IPDI to obtain the corresponding tetrazole functional PUs films. Pristine (P0–PU) and functional PU (P1–PU, P2–PU, and P3–PU) films have similar thermal profile and Tg (−76 °C), but they have a notable enhancement in tensile properties; for example, tensile strength and elongation at break of P0–PU were found to be 3.21 MPa and 727%, respectively, whereas these values were 4.84 MPa and 958%, respectively, in the case of P3–PU. It was observed that on increasing the number of methylene group from 1 to 3 between HTPB and tetrazole moiety, the strength of hydrogen bonding increases, which facilitates better packing of urethane network in the PU and hence improves the tensile properties. Also, modification of pristine HTPB with tetrazole derivatives enhanced the calorific values of the resulting PUs.

Influence of Parabens on Bacteria and Fungi Cellular Membranes: Studies in Model Two-Dimensional Lipid Systems.

Langmuir monolayers were used to study the influence of four commercially applied parabens on multicomponent systems composed of lipid species characteristic of the cellular membrane of microorganisms found in carbohydrates and proteins reaching products, including food and cosmetics. The aim of the undertaken studies was to shed new light on the problem of parabens' interactions with membrane lipids and their affinity for monolayers differing with regard to the composition, mutual lipid ratios, and physicochemical properties. The discussion is based on the π-A isotherm characteristics, surface morphology observation performed with BAM, and analysis of the diffraction data collected for the periodically ordered lipid domains present in the investigated multicomponent films. Our studies revealed that the selected parabens are capable of surface film modification and that the magnitude of this effect increases with the number of methylene groups in the ester part of paraben molecules. We found that the strongest destructive effect was observed for model 1 (Staphylococcus aureus), a lower effect was observed for model 2 (Pseudomonas aeruginosa), and the lowest effect was observed for model 3 (Candida albicans). It was inferred that such a trend appears due to the composition of the artificial membranes, i.e., above all, in the presence or lack of sterol molecules and the content of negatively charged lipids.

Hydration of urea and alkylated urea derivatives.

Compressibility data and broadband dielectric spectra of aqueous solutions of urea and some of its alkylated derivatives have been evaluated to yield their numbers Nh of hydration water molecules per molecule of solute. Nh values in a broad range of solute concentrations are discussed and are compared to hydration numbers of other relevant molecules and organic ions. Consistent with previous results, it is found that urea differs from other solutes in its unusually small hydration number, corresponding to just one third of the estimated number of nearest neighbor molecules. This remarkable hydration behavior is explained by the large density φH of hydrogen bonding abilities offered by the urea molecule. In terms of currently discussed models of reorientational motions and allied dynamics in water and related associating liquids, the large density φH causes a relaxation time close to that of undisturbed water with most parts of water encircling the solute. Therefore only a small part of disturbed ("hydration") water is left around each urea molecule. Adding alkyl groups to the basic molecule leads to Nh values which, within the series of n-alkylurea derivatives, progressively increase with the number of methyl groups per solute. With n-butylurea, Nh from dielectric spectra, in conformity with many other organic solutes, slightly exceeds the number of nearest neighbors. Compared to such Nh values, hydration numbers from compressibility data are substantially smaller, disclosing incorrect assumptions in the formula commonly used to interpret the experimental compressibilities. Similar to other series of organic solutes, effects of isomerization have been found with alkylated urea derivatives, indicating that factors other than the predominating density φH of hydrogen bond abilities contribute also to the hydration properties.

Single‐step solution polymerization of poly(alkylene terephthalate)s: synthesis parameters and polymer characterization

AbstractPoly(alkylene terephthalate)s represent one of the most frequently used polymer classes worldwide. Well‐known examples include poly(ethylene terephthalate) (n = 2) and poly(butylene terephthalate) (n = 4). The conventional synthesis method for these polymers is based on melt polycondensation, a two‐stage process performed under harsh conditions that includes the synthesis of an intermediate prepolymer and the presence of a catalyst, which may induce toxicity issues. The present work reports on a straightforward single‐step solution polycondensation method performed under mild conditions and in the absence of a catalyst. A homologous series of poly(alkylene terephthalate)s (n = 5 − 10) of molar masses up to 20 000 g mol−1 and dispersity <2.4 was synthesized and characterized thoroughly. Great attention was given to the thermal properties assessment by using state‐of‐the‐art techniques and a highly sensitive prototype technique called rapid heat − cool DSC. Similar to melt‐synthesized polyesters, a particular odd − even trend of the thermal properties versus the number of methylene groups within the monomer unit was revealed. To the best of our knowledge, this is the first report covering a single‐step solution‐based polycondensation performed in the absence of a catalyst that results in highly reproducible polyesters possessing unaltered thermal properties compared to polyesters synthesized through industrially applied conventional routes. © 2017 Society of Chemical Industry

Ruthenium-based PACT compounds based on an N,S non-toxic ligand: a delicate balance between photoactivation and thermal stability

In photoactivated chemotherapy, the photocleavable protecting group that prevents the bioactive compound from interacting with biomolecules in the dark is sometimes cytotoxic, which makes interpretation of phototoxicity challenging. For ruthenium polypyridyl complexes new, non-toxic protecting ligands that prevent a toxic metal complex from binding to biomolecules in the dark, but that can be efficiently photosubstituted upon visible light irradiation to recover the high toxicity of the metal complex, are necessary. In this work, we report on the synthesis, stereochemical characterization and cytotoxicity of a series of polypyridyl complexes; [Ru(bpy)2(mtpa)](PF6)2 ([1](PF6)2, bpy = 2,2’-bipyridine), [Ru(bpy)(dmbpy)(mtpa)](PF6)2 ([2](PF6)2, dmbpy = 6,6’-dimethyl-2,2’-bipyridine), and [Ru(dmbpy)2(mtpa)](PF6)2 ([3](PF6)2) based on the non-toxic 3-(methylthio)propylamine protecting ligand (mtpa). The number of methyl groups had a crucial effect on the photochemistry and cytotoxicity of these complexes. The non-strained complex [1]2+ was not capable of fully releasing mtpa and was not phototoxic in lung cancer cells (A549). In the most strained complex [3]2+, thermal stability was lost, leading to poor photoactivation in vitro and a generally high toxicity also without light activation. The heteroleptic complex [2]2+ with intermediate strain showed, upon blue light irradiation, efficient mtpa photosubstitution and increased cytotoxicity in cancer cells, but photosubstitution was not selective. Overall, fine-tuning of the lipophilicity and steric strain of ruthenium complexes appears as an efficient method to obtain phototoxic ruthenium-based photoactivated chemotherapeutic prodrugs, at the cost of synthetic simplicity and photosubstitution selectivity.

Critical Role of the Spacer Length of Gemini Surfactants on the Formation of Ionic Liquid Crystals and Thermotropic Behavior.

Numerous reports have shown that the self-assembling properties of 12-s-12 bis(quaternary ammonium) gemini surfactants in aqueous solution are significantly influenced by s, the number of methylene groups in the covalent spacer. However, the role played by s on the phase behavior of the single compounds has not been investigated in a similarly systematic way. Here, we report on the thermotropic phase behavior of the anhydrous compounds with s = 2-6, 8, 10, and 12, resorting to differential scanning calorimetry (DSC), polarized light microscopy (PLM), and X-ray diffraction (XRD). All of the compounds show a stepwise melting behavior, decomposing at 200 °C. As the spacer length increases, nonmonotonic trends are observed for the thermodynamic parameters of the thermotropic phase transitions, mesophase formation, and solid-state d00l spacings. In particular, the number and type of mesophases (ordered smectic phases and/or fluid smectic liquid crystals) depend critically on s. Further, upon heating molecules with s < 8 decompose before the liquid phase, while those with long spacers, s = 8-12, reach the isotropization (clearing) temperature, hence forming both ionic liquid crystals and ionic liquid phases. We demonstrate that the melting behavior and type of ionic mesophases formed by gemini molecules can be usefully manipulated by a simple structural parameter like the length of the covalent linker.