Position Of Chlorine Research Articles

Induced Smectic-A phase at low temperatures through self-assembly

Self-assembled Smectic-A liquid crystals (LCs) are synthesized with low molar mass non-mesogenic moieties through intermolecular Hydrogen Bonding (HB) interactions. The HB complexes viz., PyBnA:xClBA (where n=10, 14 and 16; x=2, 3 and 4) are exhibiting an orthogonal Smectic-A (SmA) mesophase over a wide range of temperatures and towards ambient temperatures. The proton donors in these complexes, chloro substituted benzoic acids viz., 2-chloro, 3-chloro and 4-chloro benzoic acids (xClBA, x is the position of chlorine on the benzoic acid) are non-mesogenic. The proton acceptors, (4-pyridyl)-benzylidene-4′-n-alkyl anilines (decyl, tetradecyl and hexadecyl) (PyBnA, n is no. of carbons in alkyl chain) are also non-mesogenic. The presence of HB between the proton donor and acceptor is confirmed by Fourier Transform Infrared spectroscopy. The characteristic textures of SmA in all the complexes are observed through Polarizing Optical Microscope (POM) in conjunction with a hot stage. The enthalpy changes across the phase transitions (Isotropic – SmA; SmA – Cryst.) are determined by Differential Scanning Calorimeter (DSC). The influence of chain length of proton acceptor and the position of substituent on proton donor on the thermal stability of smectic mesomorphism are studied. The results are compared with reported linear and non-linear HBLC complexes.

Distinct mechanisms of endocrine disruption of DDT‐related pesticides toward estrogen receptor α and estrogen‐related receptor γ

Dichlorodiphenyltrichloroethane (DDT) is ubiquitous in the environment, and the exposure to DDT and its related pesticides has long been linked to endocrine disruption. The mechanism of endocrine disruption toward targeted receptors, however, remains unclear. Probing the molecular recognition of DDT analogs by targeted receptors at the atomic level is critical for deciphering this mechanism. Molecular dynamics (MD) simulations were applied to probe the molecular recognition process of DDT and its five analogs, including dichlordiphenyldichloroethylene (DDE), dichlorodiphenyldichloroethane (DDD), methoxychlor (MXC), p,p'-hydroxy-DDT (HPTE), and dicofol by human estrogen receptor (ER) α and human ER-related receptor (ERR) γ. Van der Waals interactions mainly drive the interactions of DDT analogs with ERα ligand-binding domain (LBD) and ERRγ LBD. Minor structural changes of DDT analogs in the number and position of chlorine and phenolic hydroxyl moiety cause differences in binding modes through aromatic stacking and hydrogen bonding and thus affect differently conformational changes of ERα LBD and ERRγ LBD. The binding of DDT analogs affects the helix 12 orientation of ERα LBD but causes no rearrangement of helix 12 of ERRγ LBD. These results extend our understanding of how DDT analogs exert their estrogen-disrupting effects toward different receptors via multiple mechanisms.

Nature of Isomerism of Solid Isothiourea Salts, Inhibitors of Nitric Oxide Synthases, As Studied by 1H–14N Nuclear Quadrupole Double Resonance, X-ray, and Density Functional Theory/Quantum Theory of Atoms in Molecules

Isothioureas, inhibitors of nitric oxide synthases, have been studied experimentally in solid state by nuclear quadrupole double resonance (NQDR) and X-ray methods and theoretically by the quantum theory of atoms in molecules/density functional theory. Resonance frequencies on (14)N have been detected and assigned to particular nitrogen sites in each molecule. The crystal packings of (S)-3,4-dichlorobenzyl-N-methylisothiouronium chloride with the disordered chlorine positions in benzene ring and (S)-butyloisothiouronium bromide have been resolved in X-ray diffraction studies. (14)N NQDR spectra have been found good indicators of isomer type and strength of intra- or intermolecular N-H···X (X = Cl, Br) interactions. From among all salts studied, only for (S)-2,3,4,5,6-pentabromobenzylisothiouronium chloride are both nitrogen sites equivalent, which has been explained by the slow exchange. This unique structural feature can be a key factor in the high biological activity of (S)-2,3,4,5,6-pentabromobenzylisothiouronium salts.

The carbonylation of phenyl bromide and its derivatives under visible light irradiation

Abstract The carbonylation of phenyl bromide catalyzed by Co(OAc)2 has been investigated with PhCOPh as a sensitizer under visible light in the presence of basic additive. With strong base CH3ONa, PhCOOCH3 is produced in 70% yield with 100% selectivity, the similar results are also obtained with a stronger base (CH3)3CONa. However, with another strong base NaOH, the yield of the ester is only 40%. On the other hand, with weak base NaOAc or (n-C4H9)3N, phenyl bromide cannot be carbonylated. The results of carbonylation of the six substituted phenyl bromides suggest that the activities of o, m, p-BrC6H4CH3 are similar to phenyl bromide, while the activities of o, m, p-BrC6H4Cl are higher with the high yields (≥93%) of the corresponding chloro-esters. In addition, the relative position of bromine and chlorine or methyl on phenyl ring has little effect on the activity of the carbonylation.

Work function engineering in silicides: Chlorine doping in NiSi

We present a study of the electronic properties of chlorine-doped NiSi and ClNiSi/Si contacts by means of density functional theory (DFT). Using DFT, we consider the theoretical effect of Cl doping in orthorhombic Pbnm NiSi and its impact on the work function, Schottky barrier with Si, and on the change in conductivity caused by impurity scattering. Our calculations suggest that Cl substitution on the Si site is energetically preferable. The thermodynamic analysis shows that chlorine at the surface lowers the surface energy. We find that Cl can reduce the work function of NiSi by as much as ∼100 meV, and that the Schottky barrier with Si strongly depends on the position of the substitutional chlorine. Electric conductivity of NiSi is found to be significantly reduced even for the lowest calculated Cl concentration. Both findings are validated experimentally.

Effects of Chain Length, Chlorination Degree, and Structure on the Octanol−Water Partition Coefficients of Polychlorinated n-Alkanes

Log octanol-water partition coefficients (log Kow) of 40 synthesized polychlorinated n-alkanes (PCAs) with different chlorination degrees were determined using reversed-phase high performance liquid chromatography (RP-HPLC). In addition, log Kow values of a technical mixture namely Cereclor 63L as well as 15 individual in house synthesized C10, C11, and C12 chloroalkanes with known chlorine positions were estimated. Based on these results, the effects of chain length, chlorination degree, and structure were explored. The estimated log Kow values ranged from 4.10 (polychlorinated n-decanes with 50.2% chlorine content) to 11.34 (polychlorinated n-octacosanes with 54.8% chlorine content) for PCAs and from 3.82 (1,2,5,6,9,10-hexachlorodecane) to 7.75 (1,1,1,3,9,11,11,11-octachlorododecane) for the individual chloroalkanes studied. The results showed that log Kow value was influenced linearly at a given chlorine content by chain length, while a polynominal effect was observed in dependence on the chlorination degree of an alkane chain. Chlorine substitution pattern influenced markedly the log Kow value of chloroalkanes.

The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu–Al hydrotalcite/clay composite

Liquid phase catalytic oxidation of chlorophenols (CPs) was carried out over Cu–Al hydrotalcite/clay composite at ambient temperature and pressure using hydrogen peroxide as oxidant. The results showed that the catalyst had high catalytic activity, with complete oxidation of 4-CP within 40min at 40°C. The content and position of chlorine on the aromatic ring had significantly different effects on the oxidation rate of CPs, with the rate sequence of phenol>monochlorophenol (MCP)>dichlorophenol (DCP)>trichlorophenol (TCP), 3-CP>2-CP>4-CP, and 3,5-DCP>3,4-DCP>2,5-DCP>2,4-DCP>2,6-DCP. This was ascribed to the interactions among σ-electron withdrawing conductive effect, π-electron donating conjugative effect, and steric hindrance effect of chlorine. It was evidenced that the catalytic peroxide oxidation of CPs in the first step was selective and rate-limiting, where chlorinated 1,4-benzoquinones formed.

Reactions of chlorine substituted ( E)-2,3-diphenylpropenoic acids over cinchonidine-modified Pd: Enantioselective hydrogenation versus hydrodechlorination

The effect of the chlorine position on the C–Cl bond hydrogenolysis and the enantioselective hydrogenation of Cl substituted ( E)-2,3-diphenylpropenoic acid derivatives has been studied over cinchonidine-modified Pd/Al 2O 3. In contrast to the fast hydrodechlorination of the β-phenyl- para-Cl substituted acids the Cl on the α-phenyl ring was barely hydrogenolized. These observations were interpreted by the different arrangements of the two phenyl rings on the surface, with the α- and β-phenyl rings adsorbed tilted and parallel, respectively. The results confirmed the beneficial effect of the α-phenyl- ortho-substituents on the chiral discrimination, thus the 2,3-diphenylpropionic acids substituted by Cl on the α-phenyl ring could be prepared in good yields and optical purities. The conclusions were used for the rational design of an acid, i.e. ( E)-2-(2-methoxyphenyl)-3-(3,4-difluorophenyl)propenoic acid, which afforded the best optical purity ( ee up to 95% at 295 K) described until now in this heterogeneous system.

Conceptual density functional theory study on dichloropyridines as ambiphilic molecules

Conceptual density functional theory (CDFT) has been employed to compare the electrophilic and nucleophilic characters of the given atomic sites in the complete series of dichloropyridines (DCPs) as ambiphilic molecules. Ambiphilic molecules can act either as electrophiles or as nucleophiles, depending on the reaction partner. In the present work, various chemical reactivity descriptors such as dual descriptor, local hypersoftness and multiphilic descriptor as well as electrostatic potential were computed for the carbon atoms of six position isomers of DCP. Our results show that depending on the position of chlorines in each isomer, electrophilic or nucleophilic attack may occur at the particular sites. This type of study can be used as a theoretical reference for guidance of chemists to select the appropriate reactant and so have a sightly product.

Syntheses and Phosphorescent Properties of Blue Emissive Iridium Complexes with Tridentate Pyrazolyl Ligands

Novel neutral mixed-ligand Ir(N=C=N)(N=C)X complexes (N=C=N = 1,3-bis(3-methylpyrazolyl)benzene (bpzb), 1,5-dimethyl-2,4-bis(3-methylpyrazolyl)benzene (dmbpzb), and 1,5-difluoro-2,4-bis(3-methylpyrazolyl)benzene (dfbpzb); N=C = 2-phenyl pyridine (ppy); and X = Cl or CN) have been synthesized and characterized. An X-ray single-crystal structure of the complex Ir(dmbpzb)(ppy)Cl shows that the nitrogen atom in the ppy ligand occupied the trans position to the carbon atom in the tridentate N=C=N ligand of dmbpzb with the Ir-C bond length of 1.94(1) A, whereas the coordinating carbon atom occupied the trans position of chlorine. Electrochemical data show that the complexes exhibit an oxidation Ir(III/IV) process in the potential range of +0.5 approximately 0.9 V and two irreversible reductions at approximately -2.6 and -3.0 V against Fc (0)/Fc (+), respectively. All of the Ir(III) complexes do not emit phosphorescence at room temperature, although strong phosphorescence is exhibited at 77 K with the 0-0 transition centered at around 450 nm and lifetimes of 3-14 mus. DFT calculations indicate that the HOMOs are mainly localized on iridium 5dpi and chlorine ppi*, whereas the LUMOs are mainly from the ppy ligand pi* orbitals. The phosphorescence originates from a (3)LC state mixed with the (3)MLCT and (3)XLCT ones. Temperature-dependent lifetime measurements of Ir(dfbpzb)(ppy)Cl reveal the existence of a thermal deactivation process with a low activation energy (1720 cm (-1)) and very high frequency factor (2.3 x 10 (13) s (-1)). An unrestricted density functional theory indicates that the dd state, in which both the Ir-N (pyrazolyl) bond lengths increase considerably, exists almost at the same energy as that for the phosphorescent state. A thorough analysis based on the potential energy surfaces for the T 1 and S 0 states allows us to determine the reaction pathway responsible for this thermal deactivation. The calculated activation energies of 1600 approximately 1800 cm (-1) are in excellent agreement with the observed values.

Study on the reaction of chlorophenols in room temperature ionic liquids with ionizing radiation

The effects of cations and anions of room temperature ionic liquids (RTILs) on the decomposition of chlorophenols and formation of phenol were investigated by gamma and pulse radiolyses. Absorption bands were observed for aliphatic RTILs just after pulsed electron irradiation, and were assigned as solvated electrons. The decomposition yield of chlorophenol (CP), G(-CP), and the formation yield of phenol, G(Phenol), in RTILs, in which solvated electrons were observed, were higher than those in RTILs, in which the solvated electrons were not detected. G(-CP) and G(Phenol) increased with the viscosity of the RTILs which have diethylmethyl(2-methoxyethyl)ammonium (DEMMA) as cation. G(Phenol) in DEMMA-bis(trifluoromethylsulfonyl)imide (TFSI) having high viscosity was higher than that in trimethylpropylammonium (TMPA)-TFSI having low viscosity. The ratios of G(Phenol)/ G(-CP) were not affected by the substituted position of chlorine on CP in RTILs.

Detection of Novel Reactive Metabolites of Trazodone: Evidence for CYP2D6-Mediated Bioactivation ofm-Chlorophenylpiperazine

Several new glutathione adducts (M3-M7) of trazodone were tentatively identified in human liver microsomal incubations using liquid chromatography-tandem mass spectrometry (LC/MS/MS). Following incubations with trazodone in the presence of glutathione, 1-(3'-chlorophenyl)piperazine (m-CPP), a major circulating and pharmacologically active metabolite of several antidepressants including trazodone, nefazodone, and etoperidone, was trapped with glutathione to afford the corresponding quinone imine-sulfydryl adducts M4 and M5. Two novel glutathione adducts of deschloro-m-CPP and deschloro-trazodone, M3 and M6, were also detected by tandem mass spectrometry. The identities of these m-CPP-derived glutathione adducts were further confirmed by LC/MS/MS analyses of microsomal incubations of m-CPP. To investigate the bioactivation mechanism, a regioisomer of m-CPP, 1-(4'-chlorophenyl)piperazine, was incubated in human liver microsomes. Blockage of bioactivation by 4'-chloro-substitution at least partially suggested that formation of m-CPP-derived glutathione adducts M3, M4, and M5 is mediated by a common quinone imine intermediate. A tentative pathway states that upon formation of the trazodone- and m-CPP-1',4'-quinone imine intermediates through initial 4'-hydroxylation, glutathione attacks at the chlorine position by an ipso substitution, resulting in 4'-hydroxy-3'-glutathion-deschloro-trazodone (M6) and 4'-hydroxy-3'-glutathion-deschloro-m-CPP (M3), respectively. In contrast to CYP3A4-dependent bioactivation of trazodone itself, formation of M4 was mediated specifically by CYP2D6, as evidenced by cDNA-expressed CYP2D6-catalyzing formation of M4 from m-CPP, strong inhibition of formation of M4 by quinidine, a specific CYP2D6 inhibitor, in both incubations of trazodone and m-CPP with human liver microsomes, and concentration-dependent inhibition of M4 formation by quinidine.

Numerical Method to Elucidate Likely Target Positions of Chlorine Removal in Anaerobic Sediments Undergoing Polychlorinated Biphenyl Dechlorination

Polychlorinated biphenyl (PCB) contamination in the United States is predominately from commercially manufactured Aroclor mixtures. These mixtures consist of approximately 150 congeners and are characterized by chlorination level and congener distribution profile, with some congeners maintaining a constant relative abundance across the chlorination levels. Once introduced into the environment, changes in congener profiles occur, in some cases altering the relative abundance of congeners correlated in the commercial Aroclors. The shifts in the relationships of the correlated congener pairs (trackers) are used to quantify the likelihood of natural remediation processes occurring in the anaerobic sediment and to identify positions where chlorine removal is likely. A numerical model for elucidating the most likely chlorine positions was developed, implemented, and tested on Hudson River sediment data. The model results show that flanked chlorines were most likely to have been removed, followed by meta chlorines. These results are consistent with those reported by laboratory investigation of Hudson River sediments. The findings suggest that the model can successfully determine the most likely positions of chlorine removal, even in the absence of a priori knowledge of the sediment contamination (source Aroclors) or the dechlorinating organisms. Thus the model can be applied, even where limited knowledge exists regarding the contamination source and the nature of the biogeochemical reactions affecting the fate of PCBs in a particular sediment system.

ClcR-based biosensing system in the detection of cis-dihydroxylated (chloro-)biphenyls

Polychlorinated biphenyls (PCBs) are a group of organic pollutants that are persistent when released into the environment. Among the metabolites of PCBs, dihydroxylated PCBs are also considered as toxic compounds. Various studies have shown that dihydroxylated PCBs affect the reproductive, immune, nervous, and endocrine systems. Detection of these chemicals in environmental and biological samples could provide first-hand information about their levels and lead to a better understanding of their role in toxicity. To that end, we developed a sensing system for the detection of dihydroxylated PCBs based on the clc operon. The Pseudomonas putida clc operon encodes a catabolic pathway for degradation of chlorocatechols, which are major metabolites of a large number of chlorinated compounds. In P. putida, the expression of these genes is regulated by a protein encoded by the gene clcR located upstream from the clcABD genes. We demonstrate here for the first time that dihydroxy PCBs can also induce the clc operon. Our sensing system employs P. putida bacteria harboring a plasmid in which the reporter gene, lacZ, is under the control of the regulatory protein ClcR. Consequently, when exposed to dihydroxy PCBs, the bacteria express beta-galactosidase in an amount related to the concentration of the corresponding dihydroxy PCB. Various dihydroxylated PCBs, differing in the number and position of chlorines and in the position of hydroxyls, were tested for their ability to induce expression of beta-galactosidase. Detection limits as low as 1 x 10(-6) mol L(-1) were obtained for various dihydroxylated PCBs.

Polychlorinated Biphenyls (PCBs): Routes of Exposure and Effects on Human Health

The polychlorinated biphenyls (PCBs) are synthetic organochlorine chemicals that were useful industrial products in the past, but their production was ended because they persist in both the environment and living organisms. The PCBs are mixtures of up to 209 different components (congeners), depending on the number and position of chlorines around the biphenyl ring. The PCBs are fat-soluble substances to which everyone is exposed through ingesting animal fats, inhalation, or dermal contact. Exposure to PCBs suppresses the immune system, thereby increasing the risk of acquiring several human diseases. Both ortho-substituted and coplanar (dioxin-like) congeners are tumor promoters that enhance the effects of other carcinogenic substances. PCB exposure, especially during fetal and early life, reduces IQ and alters behavior. The PCBs alter thyroid and reproductive function in both males and females and increase the risk of developing cardiovascular and liver disease and diabetes. Women are at high risk of giving birth to infants of low birth weight, who are at high lifetime risk for several diseases. As knowledge of their toxic effects has grown faster than environmental levels have declined, PCBs remain dangerous contaminants.

Polychlorinated Biphenyls (PCBs) in Mussels along the Chilean Coast

Chile signed the Stockholm Convention, which establishes measures to reduce or eliminate Persistent Organic Pollutants (POPs) release into the environment, including the prohibition of their use and reduction of secondary products release, as well as management related with waste treatment. Among POPs, PCBs are a family of 209 compounds that differ in chlorine level and position. These substances present a wide variability in their physicochemical properties such as vapor pressure, water solubility and partition coefficients that determine their behavior and mobility within the different environmental compartments. In Chile, as in other countries, the use of these compounds were and continue to occur in diverse industrial applications such as dielectric fluid in transformers and condensers, with a use in Chile of approximately 550,000 L. A sampling of bivalves was performed during the years 2000-2002 in order to obtain information on the spatial distribution of the PCB levels for the length of the long Chilean coast (18 degrees-54 degrees South latitude, 4,200 km), contributing in this way to a better understanding of the PCB trend and eventual fractionation along latitudinal gradients in Chile, using as the bivalve Perumytilus purpuratus ('Chorito Maico') bioindicator. The marine bivalves Perumytilus purpuratus were collected in 16 localities in northern and southern Chile. All samples were lyophilized, and PCBs (51 congeners) were extracted in a Soxhlet system (24 h) with n-hexane. Samples were cleaned in florisil and analyzed by GC-ECD. Blanks, certified reference materials and standards were processed along with the samples. The results obtained for P. purpuratus indicate a congeneric distribution profile associated to a latitudinal gradient, and the statistical analysis of the congeneric composition of the PCBs indicated five groups in relation to the molecular weight (number of chlorines), where the lighter congeners were observed in areas corresponding to high latitudes with total PCB values of 298 ng/g dry weight. P. purpuratus turns out to be a good bioindicator of PCB levels in the coastal areas of Chile due to its wide distribution. The highest concentrations and the more volatile congeners were found in southern Chile, which could be the result of processes of long-range transport or illegal discharge occurring in such remote areas. These results confirm previous data from the International Mussel Watch project ten years ago. Future studies are needed to confirm our findings utilizing another environmental matrix such as soil/sediments and air samples.

DFT calculation on 204 polychlorinated biphenyls: their thermodynamic function and implication of Cl substitute position

The thermodynamic function, including total energy (TE), enthalpy ( H 0), entropy ( S 0) and free energy ( G 0) for 204 polychlorinated biphenyls (PCBs), were predicted by fully optimized calculation at the B3LYP/6-31G* level. With design of isodemic reactions, the standard formation heat ( Δ H f 0 ) , standard formation free energy ( Δ G f 0 ) of PCBs were obtained. In addition, the dependences of these thermodynamic parameters on the number and position of chlorine substitute were discussed. It was suggested that TE, H 0 and G 0 of PCBs vary greatly with chlorine substitute at different positions, in which the order of increase of parameter value being position 2(6)≫position 3(5)>position 4. It was also found that the data of these thermodynamic parameters all increase in the case of the two chlorine substitutes at the same aromatic ring, compared with that at two aromatic rings, the increase effect being ortho≫ meta> para. With addition of each chlorine atom in PCB, the increase of S 0 is about 30 J/mol K, and also the relative stability of PCB congeners at 573.15 K was proposed in this work.

Catalytic oxidation of chlorinated benzenes over V 2O 5/TiO 2 catalysts

Kinetic and in situ infrared spectroscopic studies were conducted to investigate the oxidation of different chlorinated benzenes (i.e., chlorobenzene, 1,2- 1,3-, and 1,4-dichlorobenzene) over V 2O 5/TiO 2 catalysts. The oxidation of cyclohexyl chloride and that of benzene were also examined for comparison. Observed differences in the reaction rates and activation energies can be correlated to the structural differences of these compounds, in light of a common reaction mechanism. This mechanism is supported by the results of in situ FTIR studies, which indicate the presence of similar surface intermediates on the catalyst surface under reaction conditions for all the aromatic compounds examined. The results further suggest that the following two are the important mechanistic steps in the oxidation of chlorinated benzenes: (1) the adsorption of the aromatic compound on the catalyst via a nucleophilic attack on the chlorine position in the aromatic ring and (2) the subsequent oxidation of the remaining aromatic ring.

Prediction of gas phase thermodynamic function of polychlorinated dibenzo- p-dioxins using DFT

The fully optimized calculation of dibenzo- p-dioxin (DD) and 75 polychlorinated dibenzo-dioxins (PCDDs) were carried out at the B3LYP/6-311G** level. The corresponding total energy, enthalpy, entropy and free energy were calculated. In addition, the dependences of the calculated parameters on the number and the position of chlorine substitute were discussed. By designing isodemic reactions, standard formation heat and free energy were obtained, from which the order of relative stability for PCDDs was determined. Based on the comparison of the stability order with the observed percentage of PCDDs from incinerator, a predominant thermodynamic control process for formation of tetrachlorinated dibenzo-dioxins (TCDDs), pentachlorinated dibenzo-dioxins (Penta-CDDs) and hexachlorinated dibenzo-dioxins (Hexa-CDDs) in incineration was suggested.

A study of the factors affecting the diffusion of chlorinated hydrocarbons into polyisobutylene and polyethylene-co-propylene for evanescent wave sensing

Two polymers, polyisobutylene (PIB) and polyethylene-co-propylene (60% ethylene) (E/Pco), have been considered as preconcentration media for the detection of chlorinated compounds using mid-IR evanescent wave spectroscopy. In order to optimize and predict sensor response factors affecting the diffusion of analytes into the polymer films has been examined using a silver halide sensing fiber coupled to a FTIR spectrometer. A Fickian diffusion model was used to quantify the diffusion process. The diffusion model calculated a diffusion coefficient based on such parameters as refractive index of the polymer cladding and light guiding core, the polymer cladding thickness and the principal analyte wavelength of detection. The diffusion of analyte isomers was investigated. The diffusion of chlorinated benzene isomers was employed to determine whether the position of chlorines on the ring effects diffusion. Physical steric and molecular size effects were found to dominate the diffusion of these compounds. Solution composition was a fundamental issue in sensor design. The polarity of the sample stream was another diffusion determinant. The polarity of the matrix solution was altered by the addition of organic solvents. Rate of diffusion was seen to increase with decreasing matrix polarity. E/Pco was found to be less susceptible to polarity modification. The results obtained can be employed as a basis for the selection of a polymer for particular industrial applications and also as a means of improving the speed of sensor response.