Addition Of Polar Groups Research Articles

The Structure of Oxysterols Determines Their Behavior at Phase Boundaries: Implications for Model Membranes and Structure-Activity Relationships.

The presence of an additional polar group in the cholesterol backbone increases the hydrophilicity of resulting compounds (oxysterols), determines their arrangement at the phase boundary, and interactions with other lipids and proteins. As a result, physicochemical properties of biomembranes (i.e., elasticity, permeability, and ability to bind proteins) are modified, which in turn may affect their functioning. The observed effect depends on the type of oxysterol and its concentration and can be both positive (e.g., antiviral activity) or negative (disturbance of cholesterol homeostasis, signal transduction, and protein segregation). The membrane activity of oxysterols has been successfully studied using membrane models (vesicles, monolayers, and solid supported films). Membrane models, in contrast to the natural systems, provide the possibility to selectively examine the specific aspect of biomolecule-membrane interactions. Moreover, the gradual increase in the complexity of the used model allows to understand the molecular phenomena occurring at the membrane level. The interest in research on artificial membranes has increased significantly in recent years, mainly due to the development of modern and sophisticated physicochemical methods (static and dynamic) in both the micro- and nanoscale, which are applied with the assistance of powerful theoretical calculations. This review provides an overview of the most important findings on this topic in the current literature.

Site of the Hydroxyl Group Determines the Surface Behavior of Bipolar Chain-Oxidized Cholesterol Derivatives─Langmuir Monolayer Studies Supplemented with Theoretical Calculations.

Cholesterol oxidation products (called oxysterols) are involved in many biological processes, showing both negative (e.g., neurodegenerative) and positive (e.g., antiviral and antimicrobial) effects. The physiological activity of oxysterols is undoubtedly closely related to their structure (i.e., the type and location of the additional polar group in the cholesterol skeleton). In this paper, we focus on determining how a seemingly minor structural change (introduction of a hydroxyl moiety at C(24), C(25), or C(27) in the isooctyl chain of cholesterol) affects the organization of the resulting molecules at the phase boundary. In our research, we supplemented the classic Langmuir monolayer technique, based on the surface pressure and electric surface potential isotherms, with microscopic (BAM) and spectroscopic (PM-IRRAS) techniques, as well as theoretical calculations (DFT and MD). This allowed us to show that 24-OH behaves more like cholesterol and forms stable, rigid monolayers. On the other hand, 27-OH, similar to 25-OH, undergoes the phase transition from monolayer to bilayer structures. Theoretical calculations enabled us to conclude that the formation of bilayers from 27-OH or 25-OH is possible due to the hydrogen bonding between adjacent oxysterol molecules. This observation may help to understand the factors responsible for the unique biological activity (including antiviral and antimicrobial) of 27-OH and 25-OH compared to other oxysterols.

Synthesis of Functionalized Heteroleptic Germylene Alkoxides

AbstractN‐coordinated Ge(II) alkoxides L1(tBuO)Ge (1), L2(tBuO)Ge (2) and [L2(OtBu)Ge ⋅ BH3] (4) were prepared. Effect of either chelating ligands L1 and L2 or Ge→B interaction on strength of the Ge−OtBu bond was studied by insertion reaction of PhNCO. As a result, the Ge(II) carbamate L2{[(tBuO)OC](Ph)N}Ge (3) was isolated. Alcoholysis exchange reactions of 1 and 2 with substituted phenols were studied to find an easy synthetic protocol for a synthesis of functionalized Ge(II) alkoxides. Reactions yielded Ge(II) alkoxides L1,2(2‐Br−C6H4O)Ge (5 for L1, 8 for L2), L1,2(2‐MeNH−C6H4O)Ge (6 for L1, 9 for L2), L1,2(2‐Ph2P−C6H4O)Ge (7 for L1, 10 for L2), L2(2‐Br‐3‐OH−C6H3O)Ge (11) and L2(2‐NC5H4O)Ge (12) containing the additional polar groups Y (Y=Br, MeNH, PPh2, OH or N). Finally, phosphane decorated Ge(II) alkoxides 7 and 10 were tested as suitable ligands in reactions with (COD)W(CO)4 and BH3. As a consequence, new complexes [(κ2‐7)W(CO)4] (13) and [L1(2‐Ph2P ⋅ {BH3}‐C6H4O)Ge ⋅ {BH3}] (14) were isolated. All compounds were characterized by NMR and IR spectroscopy, and compounds 3, 4, 9 and 11 were additionally characterized by X‐ray diffraction analysis.

Ethylene-Vinyl Acetate Copolymer/Crude Gossypol Compositions as Pour Point Depressants for Waxy Oil

Wax deposition from crude oil that blocks the pipeline and increases the viscosity of the fluid is considered as a serious challenge for petroleum transportation. Employment of chemical additives, the so-called pour point depressants (PPDs), is widely used to solve this problem. Among them are the ethylene-vinyl acetate (EVA) copolymers (EVAc), containing a polyethylene segment along the backbone with vinyl acetate. To improve the performance of EVAc as PPD, the compositions of this polymer with crude gossypol (CG), isolated from the refined cottonseed oil soapstock, were prepared by joint milling in a ball mill. Prepared compositions were characterized by Fourier transform infrared (FTIR), ultraviolet (UV), and nuclear magnetic resonance (NMR) spectroscopy. The pour point and viscosity of the crude oil from the Akshabulak oil field (Kazakhstan) were studied. The compositions with 10, 20, and 25 wt% of CG demonstrate better efficiency as PPD for crude oil than EVAc at the dosage of PPD of 50, 100, 250, and 500 ppm. The improved properties of the obtained PPD in comparison with the commercial EVAc is explained by the appearance of additional nonpolar and polar groups caused by the formation of the EVAc/CG composition.

Synthesis, anticancer activity, and molecular modeling of 1,4-naphthoquinones that inhibit MKK7 and Cdc25

Cell division cycle 25 (Cdc25) and mitogen-activated protein kinase kinase 7 (MKK7) are enzymes involved in intracellular signaling but can also contribute to tumorigenesis. We synthesized and characterized the biological activity of 1,4-naphthoquinones structurally similar to reported Cdc25 and(or) MKK7 inhibitors with anticancer activity. Compound 7 (3-[(1,4-dioxonaphthalen-2-yl)sulfanyl]propanoic acid) exhibited high binding affinity for MKK7 (Kd = 230 nM), which was greater than the affinity of NSC 95397 (Kd = 1.1 μM). Although plumbagin had a lower binding affinity for MKK7, this compound and sulfur-containing derivatives 4 and 6–8 were potent inhibitors of Cdc25A and Cdc25B. Derivative 22e containing a phenylamino side chain was selective for MKK7 versus MKK4 and Cdc25 A/B, and its isomer 22f was a selective inhibitor of Cdc25 A/B. Docking studies performed on several naphthoquinones highlighted interesting aspects concerning the molecule orientation and hydrogen bonding interactions, which could help to explain the activity of the compounds toward MKK7 and Cdc25B. The most potent naphthoquinone-based inhibitors of MKK7 and/or Cdc25 A/B were also screened for their cytotoxicity against nine cancer cell lines and primary human mononuclear cells, and a correlation was found between Cdc25 A/B inhibitory activity and cytotoxicity of the compounds. Quantum chemical calculations using BP86 and ωB97X-D3 functionals were performed on 20 naphthoquinone derivatives to obtain a set of molecular electronic properties and to correlate these properties with cytotoxic activities. Systematic theoretical DFT calculations with subsequent correlation analysis indicated that energy of the lowest unoccupied molecular orbital E(LUMO), vertical electron affinity (VEA), and reactivity index ω of these molecules were important characteristics related to their cytotoxicity. The reactivity index ω was also a key characteristic related to Cdc25 A/B phosphatase inhibitory activity. Thus, 1,4-naphthoquinones displaying sulfur-containing and phenylamino side chains with additional polar groups could be successfully utilized for further development of efficacious Cdc25 A/B and MKK7 inhibitors with anticancer activity.

Sticholysin, Sphingomyelin, and Cholesterol: A Closer Look at a Tripartite Interaction

Actinoporins are a group of soluble toxic proteins that bind to membranes containing sphingomyelin (SM) and oligomerize to form pores. Sticholysin II (StnII) is a member of the actinoporin family produced by Stichodactyla helianthus. Cholesterol (Chol) is known to enhance the activity of StnII. However, the molecular mechanisms behind this activation have remained obscure, although the activation is not Chol specific but rather sterol specific. To further explore how bilayer lipids affect or are affected by StnII, we have used a multiprobe approach (fluorescent analogs of both Chol and SM) in combination with a series of StnII tryptophan (Trp) mutants to study StnII/bilayer interactions. First, we compared StnII bilayer permeabilization in the presence of Chol or oleoyl-ceramide (OCer). The comparison was done because both Chol and OCer have a 1-hydroxyl, which helps to orient the molecule in the bilayer (although OCer has additional polar functional groups). Both Chol and OCer also have increased affinity for SM, which StnII may recognize. However, our results show that only Chol was able to activate StnII-induced bilayer permeabilization; OCer failed to activate it. To further examine possible Chol/StnII interactions, we measured Förster resonance energy transfer between Trp in StnII and cholestatrienol, a fluorescent analog of Chol. We could show higher Förster resonance energy transfer efficiency between cholestatrienol and Trps in position 100 and 114 of StnII when compared to three other Trp positions further away from the bilayer binding region of StnII. Taken together, our results suggest that StnII was able to attract Chol to its vicinity, maybe by showing affinity for Chol. SM interactions are known to be important for StnII binding to bilayers, and Chol is known to facilitate subsequent permeabilization of the bilayers by StnII. Our results help to better understand the role of these important membrane lipids for the bilayer properties of StnII.

Nanodiamond Fabrication of Superhydrophilic Wool Fabrics.

Nanodiamonds (ND) have been gaining impetus in fields such as medicine and electronics. ND has been widely used to modify polymer surfaces and composites for improved functionality. However, there have been limited research on ND application in regard to textile substrates. In this study, we presented a sustainable coating method, adapted to functionalized ND particles that would be coated onto wool fabric surfaces to enhance hydrophilicity. The application of an ND coating was found to increase wool hydrophilicity because of the presence of additional polar groups, shown by Fourier transform infrared spectrometry, which increased surface energy and fiber roughness. Scanning electron microscopy images revealed that the polar ND-coated wool scales demonstrated improved fiber hydrophilicity. Water absorbency, wicking, and contact angle results for coated fabrics confirmed significant improvement in hydrophilicity, which was directly related to the concentration of ND particles. The optimal concentration of ND was therefore selected to coat the wool fabric. Furthermore, tensile strength and abrasion resistance of the coated fabrics were increased due to the exceptional mechanical properties of ND.

Self-Activated Coordination Polymerization of Alkoxystyrenes by a Yttrium Precursor: Stereocontrol and Mechanism

Coordination–insertion polymerization of polar vinyl monomers has always been a challenging subject since the Lewis basic polar groups are usually poisonous to the Lewis acidic metal centers of the catalysts. In this paper, we report the coordination polymerization of the unmasked polar alkoxystyrenes (AOS), including o-methoxystyrene (oMOS), o-ethoxystyrene (oEOS), o-n-propoxystyrene (oPOS), o-n-butoxystyrene (oBuOS), o-benzyloxystyrene (oBnOS), and 5-phenyl-2-methoxystyrene (Ph-MOS), by using the cationic quinolyl anilido yttrium alkyl species that was inert to styrene polymerization. In addition, the styrenic monomer bearing two polar groups, 4-fluoro-2-methoxystyrene (FMOS), was also polymerized since the presence of the additional polar fluorine group did not block the interaction between the ortho-oxygen and yttrium center. In contrast, the o-(tert-butyldimethyl)silyloxystyrene (oSiOS), where the ortho-oxygen atom was prevented from coordinating to the yttrium center by the sterically bulky −SiMe2tB...

Fluorine-free sulfonated aromatic polymers as proton exchange membranes

The recent progress of our research on proton exchange membranes (PEMs) for fuel cell applications is reviewed. In particular, we focus on fluorine-free sulfonated aromatic polymers as alternatives to the benchmark perfluorosulfonic acid ionomer (e.g., Nafion) PEMs. Most fluorine-free sulfonated aromatic polymers require improved proton conductivity (at high temperatures and low humidity) and chemical and mechanical stability. To address these issues, a wide range of molecular structures and their sequences were investigated. First, the effect of molecular structure on the membrane properties of sulfonated multiblock copoly(arylene ether)s is discussed. We emphasize that phosphine oxide moieties might improve chemical stability; however, aromatic ether linkages in the hydrophilic block are not suitable because oxidative degradation and excess water swelling followed by mechanical failure is essentially inevitable. We then developed a novel polymer synthetic method, an intrapolymer Heck reaction, to ladderize aromatic ether linkages in the hydrophilic block. The ladderized rigid hydrophilic structure is an effective molecular design for balancing proton conductivity and mechanical stability. We then discuss two types of segmented copolymers based on the rigid hydrophilic structural design via a Ni-mediated coupling reaction; the hydrophilic structures are sulfonated phenylene and sulfonated benzophenone. We found that the traditional multiblock structure as well as any additional polar groups (e.g., ether, sulfone, ketone) in the hydrophilic sections are not necessary for improving the membrane properties that are important for fuel cell applications, such as proton conductivity and chemical and mechanical stability. The results indicate that fluorine-free aromatic PEMs are a potentially applicable class of ionomers for the next generation of proton exchange membrane fuel cells. The recent progress of our research on proton exchange membranes for fuel cell applications is reviewed. In particular, we have focused on the effect of the molecular structures of fluorine-free sulfonated aromatic polymers on membrane properties (e.g., proton conductivity, chemical and mechanical stability). We identified an optimized hydrophilic molecular design (sulfophenylene as SPP), that is, SPP simultaneously exhibited the highest proton conductivity and excellent mechanical stability over a wide range of humidities.

Synthesis and Evaluation of QS-21-Based Immunoadjuvants with a Terminal-Functionalized Side Chain Incorporated in the West Wing Trisaccharide.

Three QS-21-based vaccine adjuvant candidates with a terminal-functionalized side chain incorporated in the west wing trisaccharide have been synthesized. The terminal polar functional group serves to increase the solubility of these analogues in water. Two of the synthetic analogues have been shown to have adjuvant activity comparable to that of GPI-0100. The stand-alone adjuvant activity of the new synthetic analogues again confirmed that it is a feasible way to develop new saponin-based vaccine adjuvants through derivatizing at the west wing branched trisaccharide domain. Inclusion of an additional polar functional group such as a carboxyl group (as in 3x) or a monosaccharide (as in 4x and 5x) is sufficient to increase the water solubility of the corresponding synthetic analogues to a level comparable to that of GPI-0100 and suitable for immunological studies and clinical application. The structure of the incorporated side chain has a significant impact on the adjuvant activity in terms of the magnitude and nature of the host's responses.

Abstract 3067: A novel tamoxifen analog, GA-11, as potential breast cancer therapeutic

Abstract Tamoxifen is the most commonly used treatment for patients with ER+ breast cancer (BC). Although many patients benefit from tamoxifen in the adjuvant and metastatic settings, resistance is an important clinical problem. We hypothesized that tamoxifen structure can be modulated to generate a more effective and a better drug-like compound. Over the past three years, extensive structure-activity relationship (SAR) studies were carried out in our laboratories to optimize tamoxifen structure. We generated over 50 tamoxifen analogs and evaluated their activity against MCF-7 (ER+) and the triple negative MDA-MB-231 (ER-, PR-, and HER2 -) human breast cancer cell lines following MTT assay. Both ER+ and triple negative cell lines were used to evaluate if the novel analogs were selectively cytotoxic to the ER+ cells similar to tamoxifen. These studies identified a novel compound GA-11 that non-selectively targeted both the ER+ and triple negative cells, interestingly being more cytotoxic to MDA-MB-231 cells. GA-11 exhibited remarkable activity with IC50 values 7 times lower against MDA-MB-231 (triple negative) and 3 times lower against MCF-7 (ER+) than tamoxifen. GA-11 contains a methoxy group in place of N,N-dimethylethyl functionality of tamoxifen, and an additional polar amine group, which makes it more cytotoxic than tamoxifen to both the cancer cell lines (ER+ and triple negative) while being non-toxic to normal mouse embryonic fibroblast (MEF) cells, suggesting that the cytotoxic response of GA-11 is selective for cancer cells. In addition, GA-11 inhibited the expression of MMP-9, c-Myc and Caveolin, the proteins associated with adhesion, migration and metastasis, in a dose-dependent manner. The response of GA-11 in triple negative MDA-MB-231 cells was more dramatic as compared to MCF-7 (ER+) cells, again suggesting its relative selectivity towards triple negative cells and its potential to target triple-negative breast cancer for which currently no effective chemotherapy options exist. Furthermore, GA-11 inhibited the migration and invasion of MDA-MB-231 cells clearly demonstrating its anti-metastatic properties. In silico evaluation showed that GA-11 with cLogP 4.8 and MW 329, fits better into the requirements of Lipinski's Rule-of-Five, formulated to determine the drug-likeness of a small molecule; than tamoxifen (cLogP 7.34). GA-11 is thus expected to have a better oral bioavailability than tamoxifen. These in vitro studies thus indicate GA-11 to be an effective agent that is superior to tamoxifen both in potency and drug-likeness. Citation Format: Gurleen Kaur, Mohinder P. Mahajan, Manoj K. Pandey, Parvesh Singh, Srinivasa R. Ramisetti, Arun K. Sharma. A novel tamoxifen analog, GA-11, as potential breast cancer therapeutic. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3067.

Cholesterol oxidation products and their biological importance

The main biological cause of oxysterols is the oxidation of cholesterol. They differ from cholesterol by the presence of additional polar groups that are typically hydroxyl, keto, hydroperoxy, epoxy, or carboxyl moieties. Under typical conditions, oxysterol concentration is maintained at a very low and precisely regulated level, with an excess of cholesterol. Like cholesterol, many oxysterols are hydrophobic and hence confined to cell membranes. However, small chemical differences between the sterols can significantly affect how they interact with other membrane components, and this in turn can have a substantial effect on membrane properties. In this spirit, this review describes the biological importance and the roles of oxysterols in the human body. We focus primarily on the effect of oxysterols on lipid membranes, but we also consider other issues such as enzymatic and nonenzymatic synthesis processes of oxysterols as well as pathological conditions induced by oxysterols.

Effect of low-temperature plasma on chitosan-coated PEEK polymer characteristics

Low-temperature plasma effect on changes of physicochemical properties of plastic polymer polyetheretherketone (PEEK) was investigated. Despite extensive use of PEEK, information about adhesion to this polymer is limited. The adhesive and energetic properties of biomaterial and after chitosan modification were studied by contact angles measurements and surface free energy evaluation using the acid-base LWAB theory and contact angle hysteresis (CAH) model. Modification by chitosan can enhance antibacterial properties, native haemostatic and the polymer biocompatibility. Plasma modification led to variation in surface chemistry and morphology determined by an optical profilometer. After air/nitrogen plasma treatment a relatively hydrophobic character of PEEK was changed into more hydrophilic, significant differences in the wettability of sample were observed. Though, practically no differences in thermal and mechanical properties were noticed. The profilometer pictures showed an increase in the surface roughness of plasma modified PEEK due to the formation of additional polar groups with oxygen and nitrogen on the surface. Plasma treated polyetheretherketone surfaces had better adhesive features. Novel and stable chitosan-coated PEEK biomaterials were prepared applicable for different industries, mainly pharmacy and reconstructive medicine.

Low-temperature air plasma modification of chitosan-coated PEEK biomaterials

Novel chitosan-coated PEEK biomaterials were prepared by air plasma modification. Low-temperature plasma effect on changes of specific thermal, mechanical and adhesive properties of polyetheretherketone (PEEK) was investigated. The topography and surface roughness of the prepared materials were determined using an optical profilometer. The wetting and energetic properties of biomaterials were studied by means of advancing and receding contact angles measurements and then apparent surface free energy (and its components) were evaluated applying the LWAB (Lifshitz–van der Waals Acid Base) theory and contact angle hysteresis model. After air plasma treatment a fairly hydrophobic character of PEEK was changed to strongly hydrophilic one. Significant differences in the wettability and thermal stability of samples were observed. However, hardly any differences in excellent mechanical properties were noticed. The profilometer images showed an increase in the surface roughness of PEEK modified surface due to the change of cross-link density, elasticity and formation of additional polar groups on the surface. Plasma treated polyetheretherketone surfaces had better adhesive features and stable chitosan coating was created. Modification by chitosan improved antibacterial properties, inherent haemostatics and polymer biocompatibility. These advantages allowed to obtain new attractive biomaterials from the same polymer differing in properties for a wide spectrum of applications, mainly regenerative medicine and orthopedic surgery.

Structure Formation Mechanisms and Electrical Properties of PVD Fluoropolymer Films

The mechanisms of forming fluoropolymer coatings on silicon substrates via condensation from an active gas phase using directed flows of accelerated electrons and ions are studied. It is demonstrated that electrical properties of the resulting fluoropolymer films strongly depend on the technological parameters of the deposition process. Their most optimal properties are reported when condensation takes place at the temperatures within ~373–386 K. It is shown that thermal annealing of the films in vacuum at 430–470 K improves their electrophysical parameters by re-evaporating the low-molecular complexes from the structure and decreasing the concentration of defects and spin-radicals, while annealing in air gives rise to formation of additional polar groups.

Reactive extraction of amino acids mixture in hydrolysate from cottonseed meal with di(2‐ethylhexyl) phosphoric acid

AbstractBACKGROUNDIn recent years there has been a noticeable growth of amino acid utilization throughout the world. How to separate and purify amino acids from fermentation broths or protein hydrolysates in an effective and low cost way is increasingly becoming an urgent problem. The utilization of solvent extraction technology for amino acids separation offers one solution.RESULTSExtractions of individual amino acids in aqueous solution with di(2‐ethyl‐hexyl)phosphoric acid (D2EPHA) are dominated by aqueous pH and their hydrophobicity. The degree of extraction of amino acids increases with increasing pH (1.0<pH<3.0), but changes only slightly in the range 3.0<pH<7.0. Amino acids with a longer carbon chain or cyclic structure have higher degrees of extraction, while those with additional polar groups have lower degrees of extraction. Protein hydrolysate from cottonseed meal was obtained by combination of microbial fermentation and HCl hydrolysis. The greatest extraction of amino acids from the hydrolysate was found at initial feed pH 6.5, and byproducts (e.g. reducing sugars and sodium chloride) were completely retained in raffinate. Amino acids loading the organic phase can be completely stripped by using an aqueous solution having an equal volume of 0.5 mol L−1 HCl.CONCLUSIONUse of D2EPHA reactive extraction enabled avoidance of a sequence of purification stages and provided purer back‐extracts. © 2014 Society of Chemical Industry

Structural Analysis of the Binding of Type I, I1/2, and II Inhibitors to Eph Tyrosine Kinases.

We have solved the crystal structures of the EphA3 tyrosine kinase in complex with nine small-molecule inhibitors, which represent five different chemotypes and three main binding modes, i.e., types I and I1/2 (DFG in) and type II (DFG out). The three structures with type I1/2 inhibitors show that the higher affinity with respect to type I is due to an additional polar group (hydroxyl or pyrazole ring of indazole) which is fully buried and is involved in the same hydrogen bonds as the (urea or amide) linker of the type II inhibitors. Overall, the type I and type II binding modes belong to the lock-and-key and induced fit mechanism, respectively. In the type II binding, the scaffold in contact with the hinge region influences the position of the Phe765 side chain of the DFG motif and the orientation of the Gly-rich loop. The binding mode of Birb796 in the EphA3 kinase does not involve any hydrogen bond with the hinge region, which is different from the Birb796/p38 MAP kinase complex. Our structural analysis emphasizes the importance of accounting for structural plasticity of the ATP binding site in the design of type II inhibitors of tyrosine kinases.

Synthesis and Gas Adsorption Properties of Tetra‐Armed Microporous Organic Polymer Networks Based on Triphenylamine

Two novel tetra-armed microporous organic polymers have been designed and synthesized via a nickel-catalyzed Yamamoto-type Ullmann cross-coupling reaction or Suzuki cross-coupling polycondensation. These polymers are stable in various solvents, including concentrated hydrochloric acid, and are thermally stable. The homocoupled polymer YPTPA shows much higher Brunauer-Emmet-Teller-specific surface area up to 1557 m(2) g(-1) than the copolymer SPTPA (544 m(2) g(-1)), and a high CO2 uptake ability of 3.03 mmol g(-1) (1.13 bar/273 K) with a CO2 /N2 sorption selectivity of 17.3:1. Both polymers show high isosteric heats of CO2 adsorption (22.7-26.5 kJ mol(-1)) because the incorporation of nitrogen atoms into the skeleton of microporous organic polymers enhances the interaction between the pore wall and the CO2 molecules. The values are higher than those of the porous aromatic frameworks, which contain neither additional polar functional groups nor nitrogen atoms, and are rather close to those of previously reported microporous organic polymers containing the nitrogen atoms on the pore wall. These data show that these materials would be potential candidates for applications in post-combustion CO2 capture and sequestration technology.

How do organic vapors contribute to new-particle formation?

Highly oxidised organic vapors can effectively stabilize sulphuric acid in heteronuclear clusters and drive new-particle formation. We present quantum chemical calculations of cluster stability, showing that multifunctional species can stabilize sulphuric acid and also present additional polar functional groups for subsequent cluster growth. We also model the multi-generation oxidation of vapors associated with secondary organic aerosol formation using a two-dimensional volatility basis set. The steady-state saturation ratios and absolute concentrations of extremely low volatility products are sufficient to drive new-particle formation with sulphuric acid at atmospherically relevant rates.

Dinucleosides with Non-Natural Backbones: A New Class of Ribonuclease A and Angiogenin Inhibitors

Ribonuclease A (RNase A) serves as a convenient model enzyme in the identification and development of inhibitors of proteins that are members of the ribonuclease superfamily. This is principally because the biological activity of these proteins, such as angiogenin, is linked to their catalytic ribonucleolytic activity. In an attempt to inhibit the biological activity of angiogenin, which involves new blood vessel formation, we employed different dinucleosides with varied non-natural backbones. These compounds were synthesized by coupling aminonucleosides with dicarboxylic acids and amino- and carboxynucleosides with an amino acid. These molecules show competitive inhibition with inhibition constant (K(i)) values of (59±3) and (155±5) μM for RNase A. The compounds were also found to inhibit angiogenin in a competitive fashion with corresponding K(i) values in the micromolar range. The presence of an additional polar group attached to the backbone of dinucleosides was found to be responsible for the tight binding with both proteins. The specificity of different ribonucleolytic subsites were found to be altered because of the incorporation of a non-natural backbone in between the two nucleosidic moieties. In spite of the replacement of the phosphate group by non-natural linkers, these molecules were found to selectively interact with the ribonucleolytic site residues of angiogenin, whereas the cell binding site and nuclear translocation site residues remain unperturbed. Docked conformations of the synthesized compounds with RNase A and angiogenin suggest a binding preference for the thymine-adenine pair over the thymine-thymine pair.