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The present study investigates the impact of biomass origin on the properties of biochar and its interaction with different treatment conditions, CO2 adsorption, and regeneration ability. The bioch...

The main objective of a series of our researches is to develop a novel acoustic-based method for activation of biochar. This study investigates the capability of biochar in adsorbing Ni(II) as a hazardous contaminant and aims at enhancing its adsorption capacity by the addition of extra nitrogen and most probably phosphorous and oxygen containing sites using an ultrasono-chemical modification mechanism. To reach this objective, biochar physically modified by low-frequency ultrasound waves (USB) was chemically treated by phosphoric acid (H3PO4) and then functionalized by urea (CO(NH2)2). Cavitation induced by ultrasound waves exfoliates and breaks apart the regular shape of graphitic oxide layers of biochar, cleans smooth surfaces, and increases the porosity and permeability of biochar’s carbonaceous structure. These phenomena synergistically combined with urea functionalization to attach the amine groups onto the biochar surface and remarkably increased the adsorption of Ni(II). It was found that the modified biochar could remove > 99% of 100 mg Ni(II)/L in only six hours, while the raw biochar removed only 73.5% of Ni(II) in twelve hours. It should be noted that physical treatment of biochar with ultrasound energy, which can be applied at room temperature for a very short duration, followed by chemical functionalization is an economical and efficient method of biochar modification compared with traditional methods, which are usually applied in a very severe temperature (>873 K) for a long duration. Such modified biochars can help protect human health from metal-ion corrosion of degrading piping in cities with aging infrastructure.

The present study examined the effect of pyrolysis temperature on the physicochemical properties of biochar, activation process and carbon capture. Two different categories of biochars were synthesized from herbaceous (miscanthus and switchgrass) or agro-industrial (corn stover and sugarcane bagasse) feedstock under four different pyrolysis temperatures- 500, 600, 700 and 800 oC. The synthesized biochars underwent sono-amination activation comprising low-frequency acoustic treatment followed by amine functionalization to prepare adsorbents for CO2 capture. As per the elemental analysis, the elevated pyrolysis temperature resulted in increased %C and %ash contents and reduced %N contents of biochar. The textural analysis exhibited almost 3-times enhancement of micro surface area and pore volume upon increasing the pyrolysis temperature from 500 to 700 oC, though further increase to 800 oC reduced the micro-porosity and the surface area. The intermediate temperatures of 600 and 700 oC revealed the highest interactions with ultrasound-amination, which significantly intensified CO2 adsorption. Accordingly, the CO2 capture capacity of sono-aminated biochars synthesized at 600 and 700 oC were almost 200% greater than that of raw biochars. There were 127-159% and 115-151% increases in adsorption capacity of biochars synthesized at 800 and 500 oC upon ultrasono-amine functionalization. Miscanthus biochar synthesized at 700 oC and treated sono-chemically demonstrated the highest adsorption ability of 2.89 mmol/g at 70 oC and 0.10 atm partial pressure, which is 211% higher than its pristine condition. The superior adsorption capacity of miscanthus (at 700 oC) can be attributed to its large surface area (324.35 m2/g), high carbon content (84%), and low ash content (4.9%), as well as its %N content after sono-amination that was twice that of raw char.

The present study discusses a novel biochar activation technique consisting of physical modification using low frequency ultrasound and chemical functionalization with individual amines and their b...

The scope of solid-state transitions, from melting temperatures down to 4.2 K, is described for six systems: KxVF3, RbxVF3, CsxVF3, KxCrF3, RbxCrF3, and CsxCrF3 (for x = 0.0 to 1.0). Connections are drawn between the compounds’ compositions and structures with the various transitions and ordering events. Upon solidification from the melt and gradual cooling to room temperature, a sequential descent of symmetry appears to occur, from high-symmetry perovskite phases, through possible reconstructive transitions, to phases designated α, β, and δ, within which ionic ordering finally sets in, forming many new lower-symmetry structures. Many stable new structures are seen at room temperature. Finally, at cryogenic temperatures, magnetic ordering sets in. Other anomalies for these systems are also described. The analysis underscores the overall correspondence of structure, composition, and magnetic properties in these compounds. This lowering of symmetry mirrors what has been chronicled for oxygen-bearing perovskites that have yielded so many high-temperature ceramic superconductors.

The objectives of a series of our researches are to determine the feasibility of applying ultrasonic pretreatment prior to biochar gasification. As per the initial results, the heating value (HV) of biochar significantly increased after acoustic treatment in water with dissolved CO2 (AIChE Journal, 2014;60:1054–1065). Accordingly, emphasis of the current work is placed on the parameters governing the HV of biochar in the early stage of the treatment. Switchgrass and miscanthus biochars were treated under different conditions. The reactant ratio, biochar:water:CO2, exhibited profound impacts on the synergism. The highest (but not yet systematically optimized) ratio of HV increase (or HV Gain, HG) to ultrasound energy supplied (ES) takes place when biochar-to-water ratio, or BC:W, equals 0.06 g/ml. The observed HG/ES is about 10, suggesting that the energy consumption is only a fraction of the acoustic energy supplied. Miscanthus biochar’s HV increases by up to 4.6% after treatment at 5% amplitude for 135 s (HG = 33 cal/g). For the same run, miscanthus biochar's H content increased by 42.7%. Changes in HV can be mediated by mineral leaching, C or H fixation, or O content loss. Mineral leaching is influenced by pH and CO2 concentration. CO2 and water are the sole contributors to C and H gains, respectively. CO2 concentration in the solution during the treatment is also affected by mass transfer limitations, ultrasound power, and design of the three-phase reactor. Increasing the BC:W ratio initially enhances the cavitation nuclei on the fluid/solid surface, and therefore sonolysis. The subsequent decrease in HV with increasing BC:W may be due to the limitation in ultrasound penetration and H supply from water. Carbon and hydrogen fixation may be connected to the formation of H2, CO, formic acid, formaldehyde, and associated radicals during sonolysis of aqueous CO2.

Generation of hydroxyl radicals (⋅OH) is the basis of advanced oxidation process (AOP). This study investigates the catalytic activity of microporous carbonaceous structure for in-situ generation of ⋅OH radicals. Biochar (BC) was selected as a representative of carbon materials with a graphitic structure. The work aims at assessing the impact of BC structure on the activation of H2O2, the reinforcement of the persistent free radicals (PFRs) in BC using heavy metal complexes, and the subsequent AOP. Accordingly, three different biochars (raw, chemically- and physiochemically-activated BCs) were used for adsorption of two metal ions (nickel and lead) and the degradation of phenol (100 mg/L) through AOP. The results demonstrated four outcomes: (1) The structure of carbon material, the identity and the quantity of the metal complexes in the structure play the key roles in the AOP process. (2) the quantity of PFRs on BC significantly increased (by 200%) with structural activation and metal loading. (3) Though the Pb-loaded BC contained a larger quantity of PFRs, Ni-loaded BC exhibited a higher catalytic activity. (4) The degradation efficiency values for phenol by modified biochar in the presence of H2O2 was 80.3%, while the removal efficiency was found to be 17% and 22% in the two control tests, with H2O2 (no BC) and with BC (no H2O2), respectively. Overall, the work proposes a new approach for dual applications of carbonaceous structures; adsorption of metal ions and treatment of organic contaminants through in-situ chemical oxidation (ISCO).

This paper describes a two-stage biochar activation process for CO2 capture, which includes acoustic treatment and amination. Contrarily to traditional carbon activation at temperatures above 700 °C, both stages of the current process are conducted at or near room temperature. It is known that CO2 can be fixed on the edge carbons of polycyclic aromatics hydrocarbons (PAHs) through thermal and reductive photo-carboxylation. Our previous work on biochar suggested that carbon of CO2 could be chemically fixed on biochar through acoustic or photochemical treatment of biochar in water/CO2 systems under ambient conditions. Separately, the graphene oxide (GO) literature reveals that carboxylic acids, epoxy and hydroxyl groups on biochar surface often serve as the active sites for converting GO to a new family of chemicals; amines are commonly grafted on these groups in the functionalization. Biochar has graphite and graphitic oxide clusters that consist of the oxygen functional groups mentioned above. These oxygen functionalities can be utilized for CO2 adsorption when functionalized with amine. Thus, the present study focuses on maximizing the CO2 capture capacity by manipulating the physicochemical structure of a pinewood-derived biochar. In this two-stage process, 30 s sonication at ambient temperature was applied to physically activate biochar prior to functionalization. Low-frequency ultrasound irradiation exfoliates and breaks apart the irregular graphitic layers of biochar, and creates new/opens the blocked microspores, thus enhancing the biochar’s porosity and permeability that are the keys in functionalization and subsequent CO2 capture. The sono-modified biochar was then functionalized with tetraethylenepentamine (TEPA) in the presence of two activating agents. The changes in surface characteristics, functional groups, graphene-like structure, and functionalization using activating agents were examined in detail and the capacity of the final products in CO2 removal was tested. The experimental results revealed that CO2 capture capacity, from a flow containing 10 and 15 vol% CO2, was almost 7 and 9 times higher, respectively, for ultrasound-treated amine-activated biochar, compared to raw biochar. The optimum capacity was 2.79 mmol/g at 70 °C and 0.15 atm CO2 partial pressure. Cyclic adsorption and desorption tests revealed that the CO2 capture capacity decreased 44% after 15 cycles.

Magnetization facilitates the separation and reuse of adsorbents, but significantly reduces the adsorption capacity. In this study, a double layer magnetized/functionalized biochar composite was synthesized through a hybrid post-pyrolysis magnetization which sustained and even significantly increased the adsorption capacity of microporous carbonaceous biochar (BC). The developed process included i) structural modification of biochar under ultrasound waves, ii) magnetization with magnetite (Fe3O4) nanoparticles, and iii) functionalization with 3-aminopropyltriethoxysilane (TES). Ultrasound irradiation exfoliates and breaks apart the irregular graphite layers of biochar, and creates new, or opens blocked, micropores, thus enhancing the BC’s porosity. For its part, TES stabilizes the magnetic nanoparticles on the biochar surface, while it participates in water decontamination through the strong chelation ability of its amino groups toward metal ions. Scanning electron microscopy demonstrated the stable and uniform distribution of Fe3O4 nanoparticles on the surface of microporous biochar, and Fourier-transform infrared spectroscopy indicated effective surface functionalization. In addition, although magnetization usually reduces the porosity of carbonaceous adsorbents, the ultraviolet–visible spectroscopic analysis showed that double layer magnetic biochar composite exhibited a much greater ability to remove Ni(II) and Pb(II), with 139 % and 38 % higher adsorptions than raw biochar. Almost complete removal of Pb (91 %) was observed by magnetic-BC and the adsorbent could easily be separated using a neodymium magnet. This high performance can be attributed to the synergistic effect of ultrasound activation on increasing the porosity and surface area of biochar along with enhanced chelation imparted by amine functionalization. The developed technique can be used for synthesizing advanced adsorbents for removal of nuclear waste-related metal ions from aqueous environments.

Conventional carbon activation requires heating carbon at a temperature greater than 700 °C for over 3 h, consuming 18,600 kcal/kg of activated biochar. In contrast, the ultrasound treatment method is conducted at ambient condition for a very short duration (∼30 s, which requires about 1135 kcal/kg of activated BC produced. The advanced low-temperature acoustic-based surface modification method not only increases the porosity and surface functionality of raw biochar, but also is economically feasible and environmentally friendly. As a sequel of our previous works, this study aims to investigate the interaction between ultrasonic-structural modification with four different pre-treatments including i) control with no pretreatment, ii) EDC/HBOt, iii) alkali using KOH, iv) acid using HNO3 or H3PO4. The process was then followed by amine functionalization with DEA (diethanolamine) for nickel removal. The results demonstrated that all acoustic-based amine-functionalized biochar samples, without any exception, had more amine- and oxygen-containing functional groups as well as micro porosity, compared to those aminated without acoustic-activation, particularly in samples pretreated with HNO3 and H3PO4. Despite an increase in porosity by ultrasonication, metal leaching from US-only samples and those activated with EDC/HOBt was observed during longer adsorption durations. However, the synergism created by the combined effect of ultrasound and KOH and H3PO4, not only enhanced the adsorption capacity of biochar but also significantly reduced the adsorption duration from 8 to 3 h. The highest nickel adsorptions were observed for ultrasonic-amine samples activated with H3PO4 > HNO3 ∼ KOH, which were far higher (60 %, 49 %, and 46 % more adsorption, without any leaching) than raw or US-biochar, or biochar aminated with EDC/HOBt or without pretreatment.

A critical literature review suggests that carbonaceous compounds react with (CO2 +H2O) mixture through thermal, photochemical, and sonochemical/sonophysical routes. A biochar was selected for studying these effects at 60°C and 1 atm for its potential benefits on power generation and CO2 capture. All treatments remove sizable minerals (K, Na, and Si) detrimental in power generation, and introduce carbon (up to 16% of original carbon in biochar) into the biochar matrix. Most treatments show increased hydrogen (up to 24%). Treatments lead to notable increased heating value of biochar (up to 50%). Treated biochars show increase (up to 19 fold) in internal surface area. The ultrasound energy output is a fraction of the increased heating value. Thus, pretreatment is potentially attractive for increasing the energy efficiency in combustion and gasification. Moreover, better understandings of the salient reactions of these processes will be advantageous for the development of advanced adsorbents for CO2 capture. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1054–1065, 2014

A molecule containing an electron donor (pyrene, Py), an insulating tetramethylene bridge, an electron acceptor (perylenebisimide, PBI) and a bis-decyl swallowtail with two terminal thioesters was studied for its electrical rectification as a Langmuir–Blodgett (LB) monolayer between two Au electrodes at room temperature (over a 8 month period, the thioester terminations chemisorbed partially (about 15%) onto the bottom Au electrode). At lower bias (

Sandwiches "EGaIn|Ga2O3|LB monolayer of 2|Au" and "EGaIn|Ga2O3|LB monolayer of 3|Au" rectify. They are formed from a Langmuir-Blodgett (LB) monolayer of 2 or 3 transferred onto thermally evaporated gold. Molecules 2 and 3 are of the donor-sigma-acceptor (D-σ-A) type and have the same perylenebisimide (PBI) acceptor as previously studied molecule 1. Molecule 1 has the weak donor pyrene, 2 has the good donor ferrocene, and 3 has the very strong donor N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). All three molecules have a long swallowtail ending in a thioacetyl group, which ensures slow chemisorption onto the Au electrode. These molecules were contacted directly by a gallium indium eutectic (EGaIn) drop, covered by a defective oxide Ga2O3 layer. As before for 1, the direction of rectification for 2 is bias-dependent. In the ±1.0 V range, the rectification is at positive V, with a rectification ratio (RR) that is initially greater than 5 and then decreases on successive scans to 2, while the currents decrease by as much as 2 orders of magnitude. In the ±2.5 V range, the rectification direction for 2 reverses, while upon repeated scanning the rectification ratio (in the negative direction) increases and the currents decrease. For molecule 3, both directions have a charge-trapped state (Coulomb blockade) leading to Voffset in both biases, but at high potentials rectification set is, with large RR (up to 2,800) at ±2.5 V.

The active, potent, and selective Farnesoid X Receptor (FXR) agonist 6α-ethylchenodeoxycholic acid (6ECDCA) has been synthesized in improved yield compared to the published methodologies. The synthesis employed selective oxidation of one of the two hydroxyls of the readily-available starting material chenodeoxycholic acid (CDCA) as a key step. After protection of the remaining hydroxyl, LDA/HMPA/EtI/PPTS provided an efficient deprotonation/ethylation/deprotection sequence. The two synthetic improvements that allow a productive yield are the use of PCC in the oxidation step, and the use of HMPA/ethyl iodide in the stereoselective alkylation step. This synthesis offers an economical and efficient strategy which provides a simple and cost-effective procedure for potential large-scale production of this promising FXR agonist, which is a research tool and potential drug substance of current interest.

Single molecule spectroscopic characteristics of two organic molecular rectifiers are reported. Composed of pyrene as the donor and perylenebisimide (PBI) as the acceptor, these groups are separated by bridges of one or four carbon atoms. Whereas the solution phase absorption and fluorescence spectra are similar, spectra are much more diverse and exhibit different degrees of photostability at the single molecule level. It was found that the addition of pyrene affects the stability of PBI’s emission and analysis of dipole emission patterns reveal that pyrene functions as an orientational directing group for PBI in polymer thin films.

In the presence of a mixture of n -BuLi and Me 2 S CH 2 reagents, aryl epoxides underwent a novel ring-opening α-methylenation providing conjugated allyl alcohols with an unusual regioselective pattern.

The compounds KZnTiF6, KZnVF6, KVScF6, KCrScF6, and KMnScF6 are fluoride analogs of Tetragonal Tungsten Bronze. M2+–M3+ ionic ordering in these fluorides provided systems which contained linear trinuclear complexes of their respective paramagnetic ions. Magnetic coupling within these linear trimers occurred below 100 K in each of the five systems. Derived magnetic susceptibility equations were fitted to observed magnetic susceptibilities for each of the possible spin systems: KZnTiF6 (S=1/2), J/k=−114 K; KZnVF6 (S=1), J/k=−39 K; KVScF6 (S=3/2), J/k=−16 K; KCrScF6 (S=2), J/k=−4 K; and KMnScF6 (S=5/2), J/k=−7.5 K.

A number of N,N′-disubstituted perylenetetracarboxylic diimides have been reported to bind effectively to DNA that adopts G-quadruplex motifs. In some cases, this binding may actively drive the transition from single-strand DNA to the quadruplex form. The perylenediimides in the reported cases all have amine-containing side chains, which are thought to interact with the grooves of the quadruplex and help dictate the selectivity of these compounds for quadruplex versus duplex DNA. We synthesized a polyethyleneglycol-swallowtailed (PEG-tailed) perylenediimide that is water-soluble even though it is uncharged. Binding to duplex and quadruplex DNA of this perylenediimide was studied by fluorescence quenching titrations under a variety of salt conditions, and the compound’s effect on quadruplex formation was studied by non-denaturing gel electrophoresis. Our results indicate that while the molecule binds to single-stranded DNA quite effectively and with selectivity, it does not drive the transition of the DNA to the tetrameric quadruplex structure, supporting the idea that charge neutralization is a key component of perylene compounds that stabilize tetrameric quadruplexes.

A{sub x}VF{sub 3} (A=K, Rb, Cs; x=0-1.0) and A{sub x}CrF{sub 3} compounds were sealed inside high-temperature DTA molybdenum sample cups using electron beam welding techniques. Melting temperatures of the A{sub x}VF{sub 3} compounds ranged from 1050 to 1400 deg. C; those of A{sub x}CrF{sub 3} from 850 to 1200 deg. C. Reconstructive transitions were observed for A{sub x}VF{sub 3} compounds between 650 and 950 deg. C, and for A{sub x}CrF{sub 3} compounds between 550 and 825 deg. C. A displacive transition was observed to occur in VF{sub 3} at 490 deg. C. Order-disorder transitions were determined by X-ray diffraction techniques. In the A{sub x}VF{sub 3} compounds, electronic ordering and ordering of partially filled A{sup +} sites were observed to occur between 100 and 300 deg. C. Ordering phenomena in the A{sub x}CrF{sub 3} compounds (in addition to electronic ordering and ordering of partially filled A{sup +} sites) included Jahn-Teller cooperative ordering. These compounded transitions occurred between 300 and 500 deg. C.

The isomerization of tricyclo[3.1.0.02,6]hexane to 1,3-cyclohexadiene was studied using ab initio calculations at the multiconfiguration and single-configuration levels of theory. Single-point energy calculations were also performed using the MCQDPT2 and CCSD(T) methods. The isomerization process was found to proceed through an (E,Z)-1,3-cyclohexadiene intermediate following a concerted, asynchronous pathway characterized as a conrotatory ring opening of the bicyclobutane moiety. The second step involves rotation about the trans double bond resulting in the (Z,Z)-1,3-cyclohexadiene product. The rate determining step is the first one, with an activation barrier of about 43 kcal mol-1. The activation barrier of the second step was found to be only 3 kcal mol-1. A second concerted pathway was found leading directly to (Z,Z)-1,3-cyclohexadiene but with an activation barrier of 54 kcal mol-1. A multiconfiguration based wave function is necessary to properly describe the potential energy surface of the reaction.

GP-BAR1 (also known as TGR5), a novel G-protein coupled receptor regulating various non-genomic functions via bile acid signaling, has emerged as a promising target for metabolic disorders, including obesity and type II diabetes. However, given that many bile acids (BAs) are poorly tolerated for systemic therapeutic use, there is significant need to develop GP-BAR1 agonists with improved potency and specificity and there also is significant impetus to develop a stereoselective synthetic methodology for GP-BAR1 agonists. Here, we report the development of highly stereo-controlled strategies to investigate a series of naturally occurring bile acid derivatives with markedly enhanced GP-BAR1 activity. These novel GP-BAR1 agonists are evaluated in vitro using luciferase-based reporter and cAMP assays to elucidate their biological properties. In vivo studies revealed that the GP-BAR1 agonist 23(S)-m-LCA increased intestinal GLP-1 transcripts by 26-fold. Additionally, computational modeling studies of selected ligands that exhibit enhanced potency and specificity for GP-BAR1 provide information on potential binding sites for these ligands in GP-BAR1.

Efficient preparations of 2,3-dichloro-1,4-benzoquinone (1) and 2,3-dibromo-1,4-benzoquinone (2) from 1,4-benzoquinone are reported, as is the synthesis of the previously unknown 2,3-diiodo-1,4-benzoquinone (3) from 2.

Five unsymmetrical sulfides and one unsymmetrical disulfide were synthesized for self-assembled monolayer (SAM) formation on gold electrodes. Each compound contained a dinitrobenzyl ester group at the end of a primary alkyl chain as one sulfide arm, with an allyl, methyl, or cyanobenzyl group for the other arm. Cyclic voltammetry (CV) of the resulting SAMs showed no evidence for differential cleavage of allyl or cyanobenzyl sulfide groups relative to methyl, contrary to expectations if sulfide cleavage accompanied the self-assembly process.

Pyrenes undergo initial electrophilic substitution in the 1 position; a second substitution typically occurs in the 3, 6, or 8 positions. We sought a pyrene with synthetically useful handles in the unusual 2,7 substitution pattern. To that end, 7-amino-2-pyrenecarboxylic acid was prepared by partial reduction of pyrene to 4,5,9,10-tetrahydropyrene, Friedel−Crafts acylation in the 2 position, and conversion to 2-carbethoxytetrahydropyrene through the haloform reaction and esterification. Nitration of the ester proceeded in the 7 position; rearomatization, reduction of the nitro group, and saponification gave the title compound.

Donor-σ-Acceptor (D-σ-A) molecules, arrayed in a monolayer between electrodes, can serve as molecular rectifiers. Using perylene-3,4,9,10-tetracarboxylic bisimide (PBI) as the acceptor allows the attachment of the donor group to one imide nitrogen and a solubilizing swallowtail, normally a long (e.g., C(19)) alkane connected at midchain, on the other. Such an alkyl tail facilitates the formation of Langmuir-Blodgett (LB) monolayers. We have employed several modified swallowtails to make new D-σ-A molecules: poly(ethylene glycol) (PEG) swallowtails with 6 ether oxygens or with 4 ether oxygens to promote hydrophilicity in orienting LB monolayers, and alkyl swallowtails ending with sulfur anchors (thioacetate, thiol, or methyl disulfide) to stabilize attachment of the D-σ-A molecules to gold electrodes. The preparation and characterization of D-σ-A molecules containing combinations of these swallowtails with pyrene, ferrocene, and tetramethylphenylenediamine donor groups is described.

Several amphiphilic D-σ-A molecules were synthesized with three interlocked design criteria: They are potential rectifiers of electrical current, they possess one or two sturdy polymerizable diacetylene tails, and they may have interesting nonlinear optical properties. Most of the molecules afforded good self-assembling monolayers, one transferred well as a Langmuir-Blodgett film, and a few gave polymers that may be topotactic

A systematic study of cross-linking chemistry of the Au(25)(SR)(18) nanomolecule by dithiols of varying chain length, HS-(CH(2))(n)-SH where n = 2, 3, 4, 5, and 6, is presented here. Monothiolated Au(25) has six [RSAuSRAuSR] staple motifs on its surface, and MALDI mass spectrometry data of the ligand exchanged clusters show that propane (C3) and butane (C4) dithiols have ideal chain lengths for interstaple cross-linking and that up to six C3 or C4 dithiols can be facilely exchanged onto the cluster surface. Propanedithiol predominately exchanges with two monothiols at a time, making cross-linking bridges, while butanedithiol can exchange with either one or two monothiols at a time. The extent of cross-linking can be controlled by the Au(25)(SR)(18) to dithiol ratio, the reaction time of ligand exchange, or the addition of a hydrophobic tail to the dithiol. MALDI MS suggests that during ethane (C2) dithiol exchange, two ethanedithiols become connected by a disulfide bond; this result is supported by density functional theory (DFT) prediction of the optimal chain length for the intrastaple coupling. Both optical absorption spectroscopy and DFT computations show that the electronic structure of the Au(25) nanomolecule retains its main features after exchange of up to eight monothiol ligands.

The first active electronic components used vacuum tubes with appropriately-shaped electrodes, then junctions of appropriately-doped Ge, Si, or GaAs semiconductors. Electronic components can now be made with appropriately-designed organic molecules. As the commercial drive to make ever-smaller and faster circuits approaches the 3-nm limit, these unimolecular organic devices may become more useful than doped semiconductors. Here we discuss the electrical contacts between metallic electrodes and organic molecular components, and survey representative organic wires composed of conducting groups and organic rectifiers composed of electron-donor and -acceptor groups, and the Aviram-Ratner proposal for unimolecular rectification. Molecular capacitors and amplifiers are discussed briefly. Molecular electronic devices are not only ultimately small (3 nm in all directions) and fast, but their excited states may be able to decay by photons, avoiding the enormous heat dissipation endured by Si-based components that decay by phonons. An all-organic computer is an ultimate, but more distant, goal.

Tetracyanoanthraquinodimethane (TCAQ, 1) is distorted from planarity into a bent «butterfly» shape due to steric repulsion between its cyano groups and the encroaching peri hydrogens. An X-ray structure determination of perdeuterated TCAQ (TCAQ-d 8 , 4) showed smaller b and c unit cell dimensions compared to TCAQ. The shortening along the b axis (which is roughly perpendicular to the central ring) from 10.022 A for TCAQ to 9.992 A for TCAQ-d 8 indicates a combination of closer packing of the TCAQ-d 8 molecules and/or flattening of the butterfly shape

Efficient preparations of 2,3-dichloro-1,4-benzoquinone (1) and 2,3-dibromo-1,4-benzoquinone (2) from 1,4-benzoquinone are reported, as is the synthesis of the previously unknown 2,3-diiodo-1,4-benzoquinone (3) from 2.

Self-assembled monolayers of electroactive molecules can form on gold electrodes if the molecules include a sulfur-containing group to coordinate with the gold surface. We have prepared a molecule with a tripod of sulfur groups that has the potential of fixing the geometry of the molecule relative to the gold surface. The target (3) contained the good one-electron donor ferrocene connected through a benzene spacer to an isobutane tripod, with each arm of the tripod ending in a methylthio group. Analogous compounds with one (1) and two (2) coordinating arms were also prepared.

Pockels-Langmuir and Langmuir-Blodgett monolayer films have been found for the 2-(4-nitrophenyl)ethyl esters of N-(4-dodecoxyphenyl)carbamic acid (DDOP-C-ENP, 7) and N-(3,4,5-tridodecoxyphenyl)carbamic acid (TDDOP-C-ENP, 9) and also for the (2-hydroxyethoxy)-7,7,8,8-tetracyanoquinodimethane ester of N-(3,4,5-tridodecoxyphenyl)carbamic acid (TDDOP-C-HETCNQ, 10). The pressure-area isotherms vary greatly depending on the number of dodecoxy groups attached to these donor-{sigma}-acceptor molecules. The film strength improves dramatically by lowering the subphase temperature.

We report spectroscopic characterization and unimolecular rectification (asymmetric electrical conduction) measurements of three donor-sigma-acceptor (D-sigma-A) compounds N-(10-nonadecyl)-N-(1-pyrenylmethyl)perylene-3,4,9,10-bis(dicarboximide) (1), N-(10-nonadecyl)-N-(4-[1-pyrenyl]butyl)perylene-3,4,9,10-bis(dicarboximide) (2), and N-(10-nonadecyl)-N-(2-ferrocenylethyl)perylene-3,4,9,10-bis(dicarboximide) (3). These molecules were arranged as one-molecule thick Langmuir-Blodgett monolayers between Au electrodes. In such an "Au | D-sigma-A | Au" sandwich, molecule 1 is a unimolecular rectifier, with rather small rectification ratios (between 2 and 3 at +/-1 V) that decrease upon cycling. Molecule 2 does not rectify. Molecule 3 rectifies, with a rectification ratio of between 14 and 28 at +/-1 V; the through-film rectification and currents persist, even with scans of +/-2 V, for up to 40 cycles of measurement. Qualitative arguments, based on a two-level rectification mechanism, are consistent with the current asymmetries observed in the monolayers of 1 and 3.

Donor-sigma-acceptor-lipid molecules were prepared by using perylenetetracarboxylic diimide as the acceptor, starting from perylenetetracarboxylic dianhydride. One imide nitrogen was attached to a "swallowtail" lipid (a long alkyl tail connected at midchain), which imparts enough solubility to make the system tractable and provides a lipophilic region suitable for promoting Langmuir-Blodgett monolayer formation. The other imide link was to a donor group (pyrene, ferrocene, tetramethylphenylenediamine, phenyl) through a short alkyl sigma bridge. Features of the 1H and 13C NMR spectra of swallowtailed perylenediimides are interpreted as resulting from restricted rotation about the imide C-N bond; the 13C NMR spectra and stereochemistry of these molecules are contrasted with the case of the related bis-(2,5-di-tert-butylphenyl)perylenetetracarboxylic diimide.

A diterpene hydrocarbon and diterpene ketone isolated from the paracloacal gland secretions of the Chinese alligator (alligator sinensis) were examined by GC-MS and 1H-NMR, 13C-NMR, and IR spectroscopy, and identified as 4,8,12-trimethyl-1-(1-methylethenyl)-3,7,11-cyclotetradecatrien e (cembrene A, 1) and its congeneric ketone, 4,8,12-trimethyl-1-(1-methylethenyl)-3,7-cyclotetradecadien- 10-one (2), respectively. This is the first report of cembrene A from a vertebrate; the ketone has not been described previously.

Closed geometrical shapes may be obtained from a hexagonal tiling by substituting 12 pentagons for hexagons and fusing the appropriate edges. Such geometrical shapes describe the fullerenes, demonstrating that this mathematical rule has utility in structural chemistry. Closure from a hexagonal tiling may also be obtained by substituting six squares; or four triangles; or combinations of pentagons (one point each), squares (two points each), and triangles (three points each) so that the total is 12 points. Similar recipes exist for obtaining closed shapes from tetragonal or trigonal tilings. Structures thus obtained may evolve into additional structures having the same symmetry in a manner similar to the evolution of the Archimedean solids from the Platonic solids. Important examples include the deltahedra, a group of eight convex polyhedra consisting of all triangles and belonging to high-symmetry point groups. These polyhedra evolve into additional high symmetry shapes, many of which have already found u...

The reader is invited to solve a dozen anagrams in which plausible names of people are actually scrambled names of elements.

The circadian rhythm of conidiation (spore formation) in Neurospora crassa is known to be temperature compensated, that is, the period is only slightly affected by the incubation temperature. Thus, the Q10 (the relative rate enhancement corresponding to a 10 degrees C rise in temperature) of the rhythm of the bd csp strain from 14 to 30 degrees C was 1.1, whereas the Q10 of the uncompensated growth rate in the same interval was 2.4. A mutation at the cel locus resulted in loss of the temperature-compensation property in cultures grown below 22 degrees C. The Q10 of the rhythm below 22 degrees C was 2.2, and periods of about 40 hr were observed. In contrast, the Q10 of the rhythm above 22 degrees C was 1.1, with circadian periods of 18-21 hr. Thus, cel displayed a threshold temperature or "break point" for the temperature compensation of its rhythm. Supplementation of cel strains, which require fatty acids, with unsaturated or short-chain fatty acids raised the threshold temperature to 26 degrees C, whereas supplementation with long-chain saturated fatty acids lowered it to 18 degrees C. These data suggest a role for fatty acids, as liquid components or as cellular metabolites, in the mechanism of temperature compensation.

Periodation par l'acide periodique et l'iode dans H 2 SO 4 de benzene, nitro- et -chloro-benzenes, acide benzoique, anhydride phtalique et toluene

The fatty acids oleic, linoleic, and linolenic, each of which has a cis double bond at the delta 9 position, are known to lengthen the circadian period of conidiation (spore formation) of strains of Neurospora crassa carrying the cel mutation. cel confers a partial fatty acid requirement on the organism and has been used to promote incorporation of exogenous fatty acids. To test whether a physical effect imparted by the cis double bonds, such as increased membrane fluidity, is critical for the perturbation of the rhythm, various isomers of these fatty acids were supplemented to the bd csp cel strain. Positional isomers of oleic acid, such as petroselinic (delta 6) and vaccenic (delta 11) acids, and longer-chain isomers, such as eicosenoic (delta 11) and erucic (delta 13) acids, did not lengthen the rhythm. The shorter-chain palmitoleic (delta 9) acid did not give a consistent lengthening of the rhythm; it may be elongated to vaccenic acid. In contrast, gamma-linolenic acid (delta 6,9,12) dramatically lengthened the period. Linoelaidic acid (the trans,trans isomer of linoleic acid) lengthened the period at 22 degrees C, but elaidic acid (the trans isomer of oleic acid) did not. Elaidic acid was shown to exert a lengthening effect, but only at lower temperatures. The data do not support a direct physical action as the source of the fatty acids' "chronobiotic" ability.

Employing a fatty acid-requiring strain (bd csp cel) of Neurospora crassa, the 21.5-h period of the circadian spore-forming rhythm was manipulated by fatty acid supplementation. The addition to the medium of an unsaturated fatty acid (oleic, linoleic, or linolenic acid) lengthened the period to 26, 40, or 33 h, respectively. Ther period-lengthening effect of linoleic acid was proportional to its concentration up to 1.3 X 10(-4) M, and also was reversed by the addition to the medium of a saturated fatty acid, palmitic acid. None of these period-lengthening effects was observed in the prototrophic strain (bd csp cel+).