Use Of Alkanes Research Articles

Limits imposed by liquid/surface interactions in the determination of tortuosity in mesopores

Abstract The restricted mobility of different liquids, polar and non-polar, were studied by means of 1H NMR diffusion and Larmor frequency dependent relaxation measurements, upon confinement in mesoporous silica with mean pore sizes ranging from 3–30 nm. The use of alkanes as a reference in the determination of the true tortuosity value was observed to be accurate for pores larger than 6 nm, while for smaller pore sizes geometrical restrictions affect the diffusion even for short chain linear alkanes. 1H NMR fast field cycling relaxometry was used to measure the relaxation times as a function of the Larmor frequency. We observed that the total observable dispersion (TOD), which is a measure of the surface/liquid interaction, is mainly driven by the liquid polarity for pores larger than 10 nm, while less dependence on polarity is observed for smaller pore sizes. Our results indicate that as confinement increases, liquid/surface interactions become more relevant than the structural properties of the porous network, imposing a limit to the use of alkanes to probe the geometrical tortuosity.

Potential enthalpic energy of water in oils exploited to control supramolecular structure.

Water directs the self-assembly of both natural1,2 and synthetic3-9 molecules to form precise yet dynamic structures. Nevertheless, our molecular understanding of the role of water in such systems is incomplete, which represents a fundamental constraint in the development of supramolecular materials for use in biomaterials, nanoelectronics and catalysis 10 . In particular, despite the widespread use of alkanes as solvents in supramolecular chemistry11,12, the role of water in the formation of aggregates in oils is not clear, probably because water is only sparingly miscible in these solvents-typical alkanes contain less than 0.01 per cent water by weight at room temperature 13 . A notable and unused feature of this water is that it is essentially monomeric 14 . It has been determined previously 15 that the free energy cost of forming a cavity in alkanes that is large enough for a water molecule is only just compensated by its interaction with the interior of the cavity; this cost is therefore too high to accommodate clusters of water. As such, water molecules in alkanes possess potential enthalpic energy in the form of unrealized hydrogen bonds. Here we report that this energy is a thermodynamic driving force for water molecules to interact with co-dissolved hydrogen-bond-based aggregates in oils. By using a combination of spectroscopic, calorimetric, light-scattering and theoretical techniques, we demonstrate that this interaction can be exploited to modulate the structure of one-dimensional supramolecular polymers.

Effect of feeding protocol on intake by Angus bulls

<h2>ABSTRACT</h2> Individual intakes are required to evaluate rate and efficiency of gain in young bulls. The objectives were to confirm use of alkanes as acceptable markers to calculate DMI of corn silage–based diets and to assess changes in DMI by Angus bulls (288 to 402kg of BW) in response to individual feeding or group feeding. An 80:20 corn silage:supplement TMR was offered to 12 Angus bulls in each of 2yr. The bulls were housed together and fed individually (period 1), group fed in a bunk (period 2), then again fed individually (period 3). Periods lasted 21 d. In addition to the TMR, each bull consumed 0.908 g/d of 50:50 corn grain:soybean hulls. Feed intake was recorded daily. Fecal grab samples were collected during the last 5 d of each period to calculate TMR DMI from feed and fecal content of hentriacontane and dotriacontane. Measured and calculated TMR DMI did not differ (P < 0.16) in period 3. Although average daily TMR DMI of the bulls did not change from period 2 (2.58kg of DM/kg of BW, calculated with markers) to 3 (2.42kg of DM/kg of BW, P < 0.11), 21 of the 24 bulls gained or lost DMI rank by 2 or more positions among pen mates as the method of feeding changed among periods. Changes in DMI for a given bull ranged from 0.15 to 3.2 kg/d. Feeding method may not affect DMI of the top-ranked or bottom-ranked bulls, but intermediate bulls may change rank in response to individual or bunk feeding.

An Altered Mycobacterium tuberculosis Metabolome Induced by katG Mutations Resulting in Isoniazid Resistance

The most common form of drug resistance found in tuberculosis (TB)-positive clinical samples is monoresistance to isoniazid. Various genomics and proteomics studies to date have investigated this phenomenon; however, the exact mechanisms relating to how this occurs, as well as the implications of this on the TB-causing organisms function and structure, are only partly understood. Considering this, we followed a metabolomics research approach to identify potential new metabolic pathways and metabolite markers, which when interpreted in context would give a holistic explanation for many of the phenotypic characteristics associated with a katG mutation and the resulting isoniazid resistance in Mycobacterium tuberculosis. In order to achieve these objectives, gas chromatography-time of flight mass spectrometry (GCxGC-TOFMS)-generated metabolite profiles from two isoniazid-resistant strains were compared to a wild-type parent strain. Principal component analyses showed clear differentiation between the groups, and the metabolites best describing the separation between these groups were identified. It is clear from the data that due to a mutation in the katG gene encoding catalase, the isoniazid-resistant strains experience increased susceptibility to oxidative stress and have consequently adapted to this by upregulating the synthesis of a number of compounds involved in (i) increased uptake and use of alkanes and fatty acids as a source of carbon and energy and (ii) the synthesis of a number of compounds directly involved in reducing oxidative stress, including an ascorbic acid degradation pathway, which to date hasn't been proposed to exist in these organisms.

Evaluation of very long-chain fatty acids and n-alkane epicuticular compounds as markers for estimating diet composition of sheep fed heathland vegetation species

Application of very long-chain fatty acids (VLCFA) as an alternative or a complement to the alkane markers to estimate diet composition of sheep offered six different diets was evaluated. Twenty-four adult crossbred sheep were housed in metabolic crates and fed with diets composed of different proportions of herbaceous ( Lolium perenne and Trifolium repens) and woody species ( Erica spp., Calluna vulgaris and Ulex gallii). Diet composition was estimated from VLCFA (i.e., C 22–C 34) and alkane (i.e., C 25–C 33) concentrations in diet and faeces, by least-squares procedures, considering the plant species effectively offered to the animals (C1) or these plant species plus feeds that were not part of the diets but were available in the field at each experimental period (C2). Prior to this, faecal VLCFA and alkane concentrations were uncorrected for incomplete faecal recovery (FC0), corrected using recovery data for each individual ewe (FC1), corrected using mean recovery rate of the dietary treatment that the animal belonged to (FC2), or corrected using mean recovery rate across all experimental diets (FC3). For all diet components, total VLCFA concentrations were higher ( P<0.01) than those observed for alkanes, with a predomination of even-chain ( P<0.001) over odd-chain. Faecal recovery was incomplete and tended to increase with carbon-chain length in a curvilinear ( P<0.001) fashion for the even-chain VLCFA, and a linear ( P<0.001) one for odd-chain VLCFA and alkanes. Diet composition had an effect ( P<0.001) on faecal recovery of both markers. Estimates of diet composition obtained using alkanes alone were more accurate ( P<0.05) than those obtained with VLCFA alone while their combination resulted in an improvement ( P<0.05) of the accuracy. Estimates obtained when considering plant species offered effectively to the animals were more accurate ( P<0.001) than those obtained when considering more plant species as possible diet components. In general, use of faecal marker concentrations corrected with FC2 and FC3 provided equally accurate estimates of diet composition, indicating that an overall recovery data can be applied to these markers in grazing studies without losing accuracy in the estimation. Although the use of alkanes resulted in more accurate estimates of diet composition, results obtained in this study showed that VLCFA can be useful markers for studying diet selection of sheep grazing on shrubland vegetation communities. However, a suitable adjustment of their faecal concentrations prior to their application is recommended. It is also concluded that use of VLCFA in combination with alkanes could result in more accurate estimates of diet composition.

Sustainability in Catalytic Oxidation: An Alternative Approach or a Structural Evolution?

This Review documents some examples of recent innovations in the field of catalytic selective oxidation from an industrial point of view. The use of alkanes as building blocks for the synthesis of bulk chemicals and intermediates is discussed, along with the main properties that catalysts should possess in order to efficiently catalyse the selective oxidation of these hydrocarbons. The currently developed processes for propene oxide and new processes under investigation for the synthesis of adipic acid are also described, highlighting innovative aspects for a better sustainability of the chemical industry.

An Improved Cryogen for Plunge Freezing

The use of an alkane mixture that remains liquid at 77 K to freeze specimens has advantages over the use of a pure alkane that is solid at 77 K. It was found that a mixture of methane and ethane did not give a cooling rate adequate to produce vitreous ice, but a mixture of propane and ethane did result in vitreous ice. Furthermore, the latter mixture produced less damage to specimens mounted on a very thin, fragile holey carbon substrate.

DEVELOPING SELECTIVE OXIDATION CATALYSTS OF LIGHT ALKANES: FROM FUNDAMENTAL UNDERSTANDING TO RATIONAL DESIGN

Selective oxidation of light alkanes remains to be a great challenge for the wider use of alkanes as feedstocks. To achieve high activity and at the same time high selectivity, some key issues have to be addressed: (1) the stability of the desired products with respect to the reactants; (2) the roles of the active components in the catalysts, the structure and the functionality of the active centers; (3) the reducibility of the metal cations, the Lewis acid sites and their synergic effects with the basic sites of the lattice oxygen anions; (4) spatial isolation of the active centers; and (5) the mechanisms for the formation and transformation of the intermediates and their kinetic controls. In this contribution, we took selective oxidation of propane to acrolein as our target reaction, and reviewed mainly our own work, trying to provide some thinking and answers to these five questions.

On the use of methane as a reductant in the synthesis of transition metal phosphides

Methane has been shown to be an effective reductant in the synthesis of binary transition metal phosphides. By following gas-phase product distribution with time on stream, carbon monoxide and hydrogen have been observed to be significant products of transformation. An additional observation is that is possible to obtain good quality powder diffraction patterns, comparable to those in the literature, for materials in which the transformation may not be totally complete. This implies that phases cannot be assigned as being “pure” simply on the basis of diffraction pattern. The data presented indicate that reduction using methane could be a viable route to the preparation of high surface area phosphide catalysts. The use of alkanes as reductants in phosphide synthesis is interesting, since they are generally the source of the hydrogen which is most commonly employed for this purpose. Hydrogen is, in fact, a major product of the process, rather than a reactant, when employing methane.

The use of alkanes as markers for estimating diet composition in sheep and goats

SummaryAn experiment was carried out to evaluate the use of alkanes for estimating diet composition of goats and sheep offered three different dietary treatments. Twelve animals as two groups of 4 crossbred goats (G1, 24 kg live weight; G2, 22 kg) and 4 crossbred sheep (S, 26 kg live weight), were housed in metabolism pens. Animals were offered daily a total of 1 kg DM/100 kg live weight. G1 received 70% ryegrass (Lolium perenne) and 30% gorse (Ulex gallii), G2 received 70% ryegrass and 30% heather (Erica sp.) and S group ate 100% ryegrass. Diet composition was estimated from the alkane concentrations (using all alkanes from C23 to C36 or only odd-chain alkanes C27, C29, C31 and C33) in diet and faeces (with or without correction for incomplete faecal recoveries) using least-squares procedures.Dietary treatment and animal species significantly affected alkane faecal recoveries, except for C24 and C36. When applying the faecal recovery corrections, there were no significant differences between measured proportions of dietary components and those estimated using all alkanes or odd-chain alkanes. In contrast, the proportions calculated without faecal recovery correction differed significantly (P&lt;0.05) from the actual proportions and over-estimated the amount in the diet of those plant components with higher concentrations of long-chain alkanes (Erica sp. and Lolium perenne). The results indicate that alkanes are useful markers to estimate diet composition, however, it was observed that animal species and diet composition influenced the faecal recovery of alkanes. This suggests that the use of the alkane methodology for estimating the diet selection of grazing animals should be preceded by a calculation of the actual alkane faecal recoveries for each experimental condition.

Alkanes are not innocuous vehicles for hydrophobic reagents in membrane studies

Alkanes (C6–C16) are often used as vehicles for hydrophobic reagents, e.g. long-chain ceramides, in cell biology studies. It is generally understood that they are inert solvents, particularly when added in small volumes. However, simple calculations show that, under standard experimental conditions in cell studies, alkane: phospholipid molar ratios in excess of 1000:1 may be found. Even at much smaller ratios (close to 1:1) our studies with liposomes show that alkanes induce vesicle aggregation. Differential scanning calorimetry shows marked changes in both the gel–fluid and the lamellar–hexagonal transitions. Alkanes inhibit bacterial sphingomyelinase when acting on large unilamellar vesicles, and activate bacterial phospholipase C under the same conditions. Thus, the use of alkanes in cell studies requires strict control experiments to avoid artefactual results.

The reactions of nitroalkanes over Cu-MFI and Fe-MFI catalysts under hydrocarbon-selective catalytic reduction conditions

The reactions of 2-nitropropane (2NP) and 2-methyl-2-nitropropane (2M2NP), typical of secondary and tertiary nitroalkanes, respectively, have been investigated over Cu-MFI and Fe-MFI catalysts under conditions relevant to the selective catalytic reduction (SCR) of NO with the use of alkanes. With both catalysts the primary reaction is decomposition to form NO and the alkene, propene from 2NP, and isobutene from 2M2NP. If O 2 is present, then some N 2 is formed by the subsequent SCR reaction between the alkene and NO x . Production of N 2 is greater when the feed contains NO, but this is largely due to enhancement of the alkene SCR reaction rather than a direct reaction between the nitroalkane and NO x . The alkene also reacts partly through deposition of carbonaceous material, which causes deactivation. In the absence of O 2 propene is also formed, through cracking of the oligomers derived from isobutene produced by 2M2NP decomposition. The reduction of NO/O 2 by propene and isobutene over Fe-MFI proceeds in a manner similar to that of the reduction with propane and isobutane, except for a lower production of HCN. With mixed alkane/alkene feeds, the alkene reacts in preference to the alkane. Overall the data show that secondary and tertiary nitroalkanes are less reactive than primary nitroalkanes over transition-metal zeolites because of the absence of the two α-hydrogens necessary for tautomerism to an aci form and its subsequent dehydration to a reactive isocyanate. Thus secondary and tertiary nitroalkanes are unlikely to be a major source of N 2 during alkane SCR over these catalysts but could play a part through the generation of alkenes that are more reactive than alkanes.

Effect of time of feeding carbohydrate supplements and pasture on production of dairy cows

The productivity and rumen status of Friesian cows grazing short rotation Italian ryegrass ( Lolium multiflorum) pastures was examined in relation to the time of grazing and of feeding cereal-based concentrates. In experiment 1, 42 cows grazed as seven separate groups of six cows on ryegrass pasture over a 2-day period, and were fed 2 kg crushed barley grain/cow at morning and evening milking on the first day. On the second day, no concentrates were fed at morning milking and a different group of cows was removed at random from grazing and a rumen sample collected by stomach tube at 0, 1, 2, 3, 4, 5, 7 and 9 h after commencement of grazing at 07:00 h. Sampling concluded before afternoon milking at 17:00 h. Rumen ammonia (NH 3) concentration peaked and pH fell to its lowest value between 7 and 9 h after cows commenced grazing. In experiment 2, 42 cows were stratified into three groups of 14 cows on the basis of milk and component yield, age, liveweight and calving date and randomly allocated within blocks to one of three treatments. Over a 10-day adjustment period and a 21-day experimental period, cows were given their daily pasture allocation of 13.5 kg DM/cow (above 5 cm stubble height) either after morning milking, and fed crushed barley grain at morning and evening milking in the ratio of 3:1 kg/cow (Synch) or 1:3 kg (Asynch) or given their daily allocation of pasture after afternoon milking with barley fed at a ratio of 3:1 kg/cow (PM) in the morning and evening milking. Based on the results of experiment 1, the feeding schedule for the Synch group was predicted to more closely synchronise the availability of N from pasture and readily fermentable carbohydrates (RFC) from concentrates, in the rumen, compared to the Asynch cows. The comparison between Synch and PM groups was to determine the relative importance of ‘synchrony’ compared to feeding pasture (afternoon) high in water soluble carbohydrates (WSC) content. The WSC content of ryegrass pasture sampled after morning milking (when the Asynch and Synch groups received their new pasture allocation) was 70 and 74 g/kg DM, respectively, compared to 124 g/kg DM for samples taken after afternoon milking (when the PM group received a new pasture allocation). Pasture dry matter intake (DMI) and in vivo digestibility of individual cows was determined by use of alkanes as inert markers, whilst group DMI was determined from pre- and post- grazing pasture mass estimated by rising plate meter. Rumen samples were taken by stomach tube at 0, 3, 7 and 11 h after grazing commenced in the morning on the last day of the experiment. On this same day the % of cows grazing was recorded at 10-min intervals. Nitrogen intake (733 g N/cow/day) was 280% above requirements and this resulted in rumen NH 3 concentrations being three times higher than the concentration at which microbial protein synthesis (MPS) would be expected to become limited. Milk (25.1, 24.3 and 26.8 l/cow/day; ( P=0.05)) and protein (809, 794 and 850 g/cow/day; P<0.05) yield for the Asynch, Synch and PM groups, respectively, differed significantly. Pasture DMI was not significantly different ( P>0.05) but DM digestibility was ( P<0.001) at 84% for the mean of the Asynch and Synch cows compared to 88% for the PM cows, respectively. The results of the present study indicate a substantial benefit of feeding cows pasture with a high WSC content. This can be achieved by giving the cows their daily allocation of pasture after afternoon milking in the knowledge that WSC accumulates during the day and that over 70% of the intake of pasture by cows will be consumed in the first 3–4.5 h of grazing a fresh pasture allocation. Under the conditions of this study there was no production benefit from attempting to synchronise the availability of N and RFC in the rumen by timing of WSC supplementation. This presumably indicates that MPS was not limiting the daily milk yield of 25–26 l/cow when these cows consumed high N ryegrass pastures.

Comparison of methods for the measurement of microbial protein supply in sheep

The excretion of purine derivatives (PD) in urine has been used as an index for the estimation of microbial nitrogen (N) supply in ruminants. This method is simple and does not require surgical intervention of the animal. However, there have been few attempts to compare the results of this method with other methods for the measurement of microbial N supply. In the present study, two experiments were performed. The main experiment (Experiment 2) compared the estimated duodenal microbial N flow based on urinary PD excretion, with the more direct measurement based on duodenal RNA flow rates obtained from cannulated sheep using n-alkanes as the digesta flow marker. However, a preliminary experiment (Experiment 1) was needed to validate the use of alkane as a digesta marker in comparison with the commonly accepted dual phase marker method of Faichney (1975).

Paper chromatography of nitrate and tosylate esters

Three water-insoluble diastereoisomeric nitrate esters were cleanly separated on untreated filter paper by the use of alkane—methanol solvents. Addition of benzene to the solvent system permitted a similar separation of the corresponding ditosylates. The effects on the R F values of variations in the solvent compositions were readily explained on the basis of the ester solubilities. The method should be applicable to a wide range of hydrophobic substances. A photochemical reaction of diphenylamine with the esters has been developed as a convenient method for detecting them on chromatograms.