Branched Chain Structures Research Articles

Biosynthesis of plant‐derived flavor compounds

Plants have the capacity to synthesize, accumulate and emit volatiles that may act as aroma and flavor molecules due to interactions with human receptors. These low-molecular-weight substances derived from the fatty acid, amino acid and carbohydrate pools constitute a heterogenous group of molecules with saturated and unsaturated, straight-chain, branched-chain and cyclic structures bearing various functional groups (e.g. alcohols, aldehydes, ketones, esters and ethers) and also nitrogen and sulfur. They are commercially important for the food, pharmaceutical, agricultural and chemical industries as flavorants, drugs, pesticides and industrial feedstocks. Due to the low abundance of the volatiles in their plant sources, many of the natural products had been replaced by their synthetic analogues by the end of the last century. However, the foreseeable shortage of the crude oil that is the source for many of the artificial flavors and fragrances has prompted recent interest in understanding the formation of these compounds and engineering their biosynthesis. Although many of the volatile constituents of flavors and aromas have been identified, many of the enzymes and genes involved in their biosynthesis are still not known. However, modification of flavor by genetic engineering is dependent on the knowledge and availability of genes that encode enzymes of key reactions that influence or divert the biosynthetic pathways of plant-derived volatiles. Major progress has resulted from the use of molecular and biochemical techniques, and a large number of genes encoding enzymes of volatile biosynthesis have recently been reported.

Combustion-Derived Hydrocarbons Localize to Lipid Droplets in Respiratory Cells

Combustion-generated radicals interact to form polynuclear aromatic hydrocarbons (PAHs), including carcinogens. PAHs aggregate into 20- to 50-nm particles, which extend into branched-chain structures (soots). Incomplete combustion yields black soot particles and black smoke. Many PAHs, including those in soots, fluoresce upon excitation. We have reported that butadiene soot (BDS), generated during combustion of the high-volume petrochemical 1,3-butadiene, serves as a reproducible example of combustion-derived fine and ultrafine particles, with the potential for acute or delayed health effects. Human bronchoepithelial cells (BEAS-2B) display time- and concentration-dependent responses to BDS exposure, culminating in concentration of fluorescent PAHs within discrete cytoplasmic bodies. Here we identify the cytoplasmic compartment(s) in which combustion-derived PAHs concentrate and assess the metabolic responses associated with this compartmentalization. BDS-associated fluorescence colocalized with a red fluorescent cholesterol analog and a transfected plasmid coding for a fluorescent lipid droplet surface protein within BEAS-2B cells. After BDS exposure, murine alveolar macrophages (MH-S) and adipocytes (3T3-L1) also develop fluorescence. These findings, especially within adipocytes, support the accumulation of PAHs within lipid droplets. Microarray data revealed up-regulation of aryl hydrocarbon receptor-induced Phase I biotransformation enzymes and nuclear erythroid-2 related factor 2-mediated oxidative stress responses in BEAS-2B cells. Quantitative RT-PCR results confirmed a time-dependent up-regulation of Phase I biotransformation enzymes (CYP1A1, CYP1B1, and ALDH3A1) in BDS-exposed BEAS-2B and MH-S cells. Thus, respiratory cell lipid droplets concentrate PAHs delivered by combustion-derived ultrafine particles. These PAHs, including several found in BDS and in cigarette smoke, activate xenobiotic metabolism pathways and thereby potentiate their toxicity.

Unusual one-dimensional branched-chain structures assembled by a novel imidazole-containing tripodal ligand with cadmium(II) salts and their fluorescent property

Three novel coordination polymers [Cd 3( L) 2( μ-Br)( μ-Cl)Br 3Cl] ( 1), [Cd 3( L) 2( μ-Cl) 2Cl 4] ( 2) and [Cd( L)Cl] 2[CdCl 4]·H 2O ( 3) were obtained by reactions of an imidazole-containing tripodal ligand N 1-(2-aminoethyl)- N 1-(2-imidazolethyl)-ethane-1,2-diamine (L) with Cd(II) salts. Their structures were determined by X-ray crystallography. Crystal data for 1, monoclinic system, P2 1/ c, a=7.752(4) Å, b=31.70(2) Å, c=14.012(7) Å, β=109.439(7)°, V=3247(3) Å 3, Z=4. 2, monoclinic system, P2 1/ c, a=7.6564(15) Å, b=31.433(6) Å, c=13.925(3) Å, β=109.89(3)°, V=3151.1(11) Å 3, Z=4. 3, orthorhombic system, Pbcn, a=22.950(2) Å, b=8.435(7) Å, c=17.360(2) Å, V=3360.3(51) Å 3, Z=4. Complexes 1 and 2 have similar one-dimensional (1D) branched-chain structure while complex 3 features a 1D zigzag cationic chain with [CdCl 4] 2− serving as counter anion. The photoluminescent measurements reveal that all the complexes exhibit blue fluorescence at room temperature in the solid state.

Synthesis and reactivity of nonstabilized diazo sugars

1,6-Anhydro-4-deoxy-4-diazo-2,3- O-isopropylidene-β- d- lyxo-hexopyranose ( 4) is a stable crystalline compound readily accessible by an improved synthetic procedure. It has been used as a model for evaluating the reactivity of the diazo group, when not stabilized by an adjacent carbonyl function, in a rigid chiral matrix. A range of carbene-type, electrophile-promoted, and 1,3-dipolar reactions were evaluated, leading to 4,4′-alkene dimers, 4-deoxy-3-enose and related derivatives, 4,4-dihalo compounds, 4-spirocyclopropane derivatives, 4-spiropyrazole structures, and by skeletal rearrangement, branched-chain anhydropentose structures having a bicyclo[2.2.2] skeleton.

Novel and Stereocontrolled Synthesis of (±)-Tetrodotoxin frommyo-Inositol

[reactions: see text] The novel and stereocontrolled synthesis of (+/-)-tetrodotoxin from myo-inositol is described. The key steps involve the stepwise oxidation of hydroxyl groups to the carbonyl function, followed by the addition of specific nucleophiles, including the successive spiro alpha-chloroepoxide formation and its ring-opening with the azide anion, to give the desired branched chain structures (5-->6, 17-->18-->19-->20 and 23-->24-->25) with the desired regio- and stereoselectivities in high yields. The stepwise conversion of the alpha-azido aldehyde 25 to the delta-lactone 29, followed by reduction of the azide, introduction of a guanidine moiety, aldehyde formation, and deprotection, produced the (+/-)-tetrodotoxin.

Synthesis of d-rubranitrose by using a novel method for constructing functionalized branched-chain structures

Convenient synthesis of d-rubranitrose from d-glucose was achieved by using simple and novel methods for deoxygenation and construction of functionalized branched-chain structures. The total yield of d-rubranitrose from methyl 4,6-O-benzylidene-α-d-glucopyranoside (1) was 4.9%.

Translocation of branched-chain arginine peptides through cell membranes: flexibility in the spatial disposition of positive charges in membrane-permeable peptides.

A basic peptide derived from HIV-1 Tat has been reported to have the ability to translocate through cell membranes and to bring exogenous proteins into cells. We have demonstrated that these features could be observed among many arginine-rich peptides, and the presence of a ubiquitous internalization mechanism for arginine-rich oligopeptides has been suggested. In this report, we report that these features are also applicable to the peptides having branched-chain structures. Peptides that have arginine residues on four branched chains (R(n))(4) [n (number of arginine residues)= 0-6] were prepared. Fluorescence microscopic observation revealed that the (R(2))(4) peptide exhibited the most efficient translocation. The dependence on the number of arginine residues of the translocation efficiency and cellular localization was also observed for the branched-chain peptides as was seen in the linear peptides. Quite interestingly, efficient translocation was also recognized in the (RG(3)R)(4) peptide, where three glycine residues intervened between two arginine residues on each chain of (R(2))(4). The results strongly suggested that a linear structure was not indispensable for the translocation of arginine-rich peptides and that there could be considerable flexibility in the location of the arginine residue in the molecules.

Two-dimensional ordering of inclusions in smectic C phase

The organization of inclusions nucleated in free standing films of smectic C (SmC) liquid crystal is investigated using polarized light microscopy. Anchoring on the inclusion boundaries induces distortions of the in-plane orientational order of the SmC phase, which drive the elastic interactions between inclusions. Such interactions show a quadrupolar character. At low concentration, the inclusions self-organize in linear or branched chain structures, while at high concentrations two-dimensional patterns appear in the film.

Molecular distribution of monocarboxylic acids in Asuka carbonaceous chondrites from Antarctica.

Molecular distribution of low-molecular-weight monocarboxylic acids was studied in three CM2 Asuka carbonaceous chondrites (A-881280, A-881334 and A-881458), which were recovered from Antarctica by the 29th Japanese Antarctic Research Expedition in 1988. GC and GC/MS analyses identified more than 30 monocarboxylic acids in A-881458, including aliphatic and aromatic acids with various structural isomers. Isomeric phenolic compounds were also identified. The aliphatic carboxylic acids have straight-chain structures having 2 to 12 carbon atoms (C2 to C12), and branched-chain structures (C4 to C9). The quantities of straight-chain acids decrease logarithmically with increasing carbon number. At the same carbon number, a straight-chain isomer is always predominant compared to branched-chain isomers. All of the 14 possible C4, C5 and C6 aliphatic monocarboxylic acids (not including optical isomers) have been identified, although all the isomers were not reported in Murchison and Y-791198 meteorites. Of the 17 possible isomeric C7 acids, at least 14 isomers were tentatively identified by mass spectra (EI and CI mode). At C8 or above, peaks of branched-chain isomers become obscure, probably due to the large number of isomers and small concentrations. Branched-chain monocarboxylic acids over C6 have never been reported in Muchison. Although occurrence of aliphatic acids are similar between A-881458 and Murchison at C4, C5 and C6 acids, a major difference is that A-881458 as well as Y-791198 have straight-chain predominance among isomers in contrast to Murchison being branched-chain predominant. In the case of isomeric aromatic compounds such as toluic acids and cresols, m-toluic acid and p-cresol are more abundant among their isomers, respectively. The molecular distribution may not reflect thermodynamic equilibrium but rather a kinetically controlled process for their formation mechanism. The other two CM2 chondrites (A-881280 and A-881334) were depleted in carboxylic acids in spite of similar carbon contents. The depletion is not due to weathering on ice, because the degrees of weathering are small and similar among the three chondrites. Probably those latter two chondrites may have been subjected to aqueous alteration or metamorphism on their meteorite parent bodies.

Density Functional Theory Calculations of the Structures, Binding Energies, and Infrared Spectra of Methanol Clusters

Density functional theory (DFT) calculations of the structures, binding energies, vibrational frequencies and infrared intensities of methanol clusters containing two to five molecules have been carried out using the Becke3LYP functional. Thirteen representative H-bonded structures have been studied including cyclic, chain, branched-cyclic and branched-chain hydrogen bond structures. In the methanol trimer, tetramer, and pentamer, the cyclic structure is more stable by 3.5, 8.3, and 3.6 kcal/mol over the next most strongly bound minimum. In the tetramer and pentamer, the second-most stable minimum corresponds to a branched cycle. Chain structures are destabilized from the cyclic minimum by the loss of a hydrogen bond and from a smaller cooperative strengthening of the H-bonds that remain. In all branched structures studied, the formation of the branch H-bond strengthens the “branch-point” methanol's H-bond donation to its neighbor, but weakens its two acceptor H-bonds, leading to largely compensating effe...

Fundamental features of hydrocarbon autoignition in a rapid compression machine

Results are reported for the autoignition characteristics of n-butane, n-pentane, n-hexane, and n-heptane and also of i-butane, i-octane, and toluene in stoichiometric mixtures with air following mechanical compression to gas temperatures in the range 600–950 K and pressures up to 0.9 MPa. Emphasis is placed on the dependence of ignition delay on compressed gas temperature, on the evolution of reaction as portrayed in the pressure-time records and on features of light output associated with single and two-stage ignition. Two-stage ignition is a clear feature of the n-alkane combustion at low compressed gas temperatures. Single-stage ignition is apparent at somewhat higher compressed gas temperatures, but there is evidence of the first stage reaction having occurred during the final stages of compression in some circumstances. Engine-knock related pressure waves are associated with the autoignition of the n-alkanes, to a lesser extent with the branched chain structures, but not at all with toluene under the present experimental conditions. These general features and also the relationship of the measured pressures to average gas temperatures attained during the ignition delay period are discussed. These data are relevant to the validation of numerical models for the autoignition of hydrocarbons.

ChemInform Abstract: 2‐Phenyloxazoline as Carboxylate Precursors. Application to the Synthesis of Asymmetric Branched‐Chain Structures.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

2-phenyloxazolines as carboxylate precursors - applications to the synthesis of asymmetric branched-chain structures

A synthetic approach to the title compounds is presented that features the asymmetric elaboration of a chiral, non-racemic oxazoline followed by a two-step oxidative ring cleavage of the heterocycle to a triamide for further transformation.

Optical scattering and absorption by branched chains of aerosols

We utilize the Volume Integral Equation Formulation (VIEF) and the method of moments to calculate the electromagnetic scattering and absorption of aerosol particles with branched-chain structures. Two kinds of polarization of the incident electromagnetic wave were considered: the cross- and end-fire polarizations. The numerical results of internal electric field distribution, absorbed power, and extinction and scattering cross sections, obtained from the VIEF, show excellent agreement with the Mie theory for the special case of spherical particles. Comparison between the results of the VIEF and Iterative Extended Boundary Condition Method for very long oriented (elongated) chains of particles also showed good agreement. After validating the accuracy of the VIEF, the absorption characteristics of three branched-chain structuressimulated from microscopic pictures of coagulated smoke aerosol particles were calculated. Results showed that the ratio of absorption in the two polarization cases, P(cross-fire)/P(end-fire), for very long oriented chain structures is as high as a factor of 4 at lower frequencies (lambda =10microm). While in the higher frequency (lambda = 0.5-microm) case, the ratio Of P(cross-fire)/P(end-fire) is reduced to 2.0. For branched-chain structures, the ratio Of P(cross-fire)/P(end-fire) decreased with the increase in the number of the side branches. These observations show that the frequency, polarization, and structure factors play important roles in determining the optical characteristics of branched chains of aerosol particles.

Characterization of skin-surface lipids from the monkey (Macaca fascicularis).

Skin-surface lipids from the monkey Macaca fascicularis are composed of sterol esters (38%), cholesterol (4%) and two types of wax diesters, identified as Type II (IIa and IIb, 17% and 40%, respectively). Type IIa contained diesters of 1,2-alkanediols esterified with two molecules of long-chain (C14-C34) fatty acids having straight and branched chains. In the diesters IIa, fatty acids shorter than C19 predominated in position 1, and fatty acids longer than C20 predominated in position 2. Type IIb contained diesters of 1,2-alkanediols esterified with C4 and C5 branched-chain fatty acids (predominantly isovaleric acid) at position 1 and long-chain (C14-C27) acids, having straight and branched chains, at position 2. The short-chain acids were converted to 2-nitrophenylhydrazides and analyzed by high-performance liquid chromatography (HPLC). Ammonia chemical ionization (CI)-gas chromatography (GC)-mass spectrometry (MS) resolved the intact diesters IIb into 12 peaks corresponding to molecular weights ranging from 597 to 748, and showed that the molecular species, such as C21-C16-C5 (diol, fatty acid in position 2, fatty acid in position 1), C22-C16-C5 and C23-C16-C5, were prevalent. The fatty acids from both diesters were mostly (greater than 98%) saturated. The 1,2-alkane-diols from both diesters consisted of C16-C26 saturated straight- and branched-chain components. The acyl groups of sterol esters contained 86% C14-C34 branched-chain acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural characteristics of the IHSS Suwannee River fulvic and humic acids determined by solution state C-13 NMR spectroscopy

The IHSS Suwannee River fulvic and humic acids have been examined by solution state C-13 NMR spectroscopy. C-13 NMR spectra acquired under quantitative conditions indicated proportions of sp hybridized carbons of 60 and 72 percent for the fulvic and humic acids, respectively. Attached Proton Test (APT) experiments clearly resolved the C-13 NMR spectra of both samples into methyl (0–26 ppm), methylene (26–43 ppm), methine (43–62 ppm and 62–92 ppm), protonated aromatic (105–135 ppm) and non-protonated aromatic (135–165 ppm) carbons. The APT spectra also revealed that the aliphatic moieties of the fulvic and humic acids are predominated by branched chain structures.

AN ANTIBODY TO HUMAN THYMIC HASSALL'S BODY EPITHELIUM RECOGNIZES A SUBSET OF BLOOD GROUP A ANTIGENS

TE-19, a mouse monoclonal antibody (mAb) against thymic Hassall's body epithelium, was investigated because of its cross-reactivity with human erythrocytes. Antibody TE-19 was found to react only with group A erythrocytes, though it reacted with Hassall's body epithelium from donors of all blood group phenotypes. TE-19 antibody bound preferentially to cells of subgroup A1, and reacted only weakly with A2 and Aint erythrocytes. Although it apparently bound to A antigen with both glycolipid and glycoprotein backbones, TE-19 antibody only reacted with A antigenic moieties containing long or branched chain structures. Analysis of TE-19 reactivity with erythrocyte membrane components using electroblotting and immunostaining techniques showed antibody reactivity with components migrating in the areas of band 4 X 5 and just ahead of the dye front, consistent with membrane glycolipid. It is possible that all human thymic Hassall's bodies contain epithelial cells which, irrespective of the donor's erythrocyte blood group, bear a carbohydrate antigen similar to A antigen.

Synthetic approach to glycan chains of a glycoprotein and a proteoglycan

Abstract

Minor carboxylic acids in finnish tall oil fatty acids: Aromatic, alicyclic, and branched chain aliphatic constituents

AbstractThirteen aromatic carboxylic acids in Finnish tall oil fatty acids were identified and quantified by gas chromatography‐mass spectrostereoisomeric secodehydroabeitic acids secoditerpene and dehydroabeitic acids. The other aromatic acids were various secoditerpene ando‐ alkyl‐ phenylalkanoic acids. A number of minor nonaromatic acids with mono‐ and bicyclic, and branched chain structures were also identified and quantified.

溶融FeO-Fe<SUB>2</SUB>O<SUB>3</SUB>-SiO<SUB>2</SUB>系スラグの構造

A high temperature X-ray diffraction technique has been used to determine the structure of molten FeO-Fe2O3-SiO2 from 1250 to 1350°C. The SiO2 content and oxygen partial pressure were in the range of 22.5 to 35 wt% and 2.0×10−7 to 2.0×10−3 Pa. From an analysis of the scattering intensity, the radial distribution function was calculated from which the interatomic distance and coordination numbers were estimated. The following characteristic features emerge from these results. A constant coordination number of about four and an interatomic distance of about 0.162×10−9 m are found for Si-O pairs in the composition and temperature range investigated. This supports that the fundamental local ordering unit is SiO4 tetrahedra in molten FeO-Fe2O3-SiO2. The Si-Si distance, which corresponds to the inter SiO4 distance, gradually decreases as the SiO2 content increases and then approaches a nearly constant value at composition beyond about 30 wt%SiO2. This constant value is rather comparable with the value of the Si-O-Si distance in polymerized ring and branched chain structures and suggests that some of the SiO4 tetrahedra polymerize to form silicate anions. The Fe-O distance also gradually decreases as the SiO2 content increases and becomes nearly constant beyond about 30 wt%SiO2. The coordination number of Fe-O pairs varies from six to four. This variation of the Fe-O correlation corresponds to a change in the position of Fe from an octahedral site to a tetrahedral site. The viscosity maximum near the fayalite composition has been also discussed by means of a combination of the silicate anion polymerization effect and the cation effect which are connected with the present structural information.