Preparation, properties and metabolism of retinoic acid anhydride.

A new analogue of vitamin A, viz., retinoic acid anhydride was prepared, for the first time, by the action of thionyl chloride on retinoic acid in benzene containing pyridine. The amhydride was charcterised by its chromatographic properties, elemental analysis, ultraviolet absorption, infrared and nuclear magnetic resonance spectral characteristics. The compound could be readily hydrolysed to retinoic acid both by acid and alkali treatments and reduced by lithium aluminium hydride to vitamin A alcohol (retinol). The spectral changes with antimony trichloride reagent were similar to those observed for retinoic acid. The metabolism of retinoic acid anhydride was found to be similar to that of retinoic acic. When administered either orally or intraperitoneally, the compound promotes growth in vitamin A-deficient rats. Time-course experiments revealed that retinoic acid anhydride is converted into retinoic acid by non-enzymatic hydrolysis and thereby exerts its biological activity. The biopotency of the anhydride was found to be nearly the same as that of the acid. A new method of preparing esters of retinoic acid employing retinoic acid anhydride as an intermediate, has been described.

Investigations on the preparation, oxidation and reduction reactions of thiophosphoryl fluoride

Pure thiophosphoryl fluoride has been prepared by the fluorination of thiophosphoryl chloride by sodium fluoride in acetonitrile medium. Oxidation of this phosphoryl fluoride by acidified chloramine-T ruptures the phosphorus-sulphur bond and oxidises the sulphur present to the hexavalent state. Anhydrous hydrogen iodide reduces the sulphur to hydrogen sulphide and phosphorus to the trivalent state.

Photodecomposition of ammonium oxalate

The ultraviolet induced photodecomposition of ammonium oxalate has been studied. The rate-time plots show an initial deceleration region which leads to a final constant value. The intensity dependence of the photorate can be represented by an equation of the type R = AI + BP. The photolysis was found to be sensitized by precompression and desensitized by ageing. Similarly the photolytic rate of ammonium oxalate crystallized from solutions containing phosphate ion and chloride ion impurity showed a sensitization and desensitization, respectively.

Factors influencing kinetic and equilibrium behaviour of sodium ion exchange with strong acid cation resin

This study reports an investigation of the ion exchange treatment of sodium chloride solutions in relation to use of resin technology for applications such as desalination of brackish water. In particular, a strong acid cation (SAC) resin (DOW Marathon C) was studied to determine its capacity for sodium uptake and to evaluate the fundamentals of the ion exchange process involved. Key questions to answer included: impact of resin identity; best models to simulate the kinetics and equilibrium exchange behaviour of sodium ions; difference between using linear least squares (LLS) and non-linear least squares (NLLS) methods for data interpretation; and, effect of changing the type of anion in solution which accompanied the sodium species. Kinetic studies suggested that the exchange process was best described by a pseudo first order rate expression based upon non-linear least squares analysis of the test data. Application of the Langmuir Vageler isotherm model was recommended as it allowed confirmation that experimental conditions were sufficient for maximum loading of sodium ions to occur. The Freundlich expression best fitted the equilibrium data when analysing the information by a NLLS approach. In contrast, LLS methods suggested that the Langmuir model was optimal for describing the equilibrium process. The Competitive Langmuir model which considered the stoichiometric nature of ion exchange process, estimated the maximum loading of sodium ions to be 64.7 g Na/kg resin. This latter value was comparable to sodium ion capacities for SAC resin published previously. Inherent discrepancies involved when using linearized versions of kinetic and isotherm equations were illustrated, and despite their widespread use, the value of this latter approach was questionable. The equilibrium behaviour of sodium ions form sodium fluoride solution revealed that the sodium ions were now more preferred by the resin compared to the situation with sodium chloride. The solution chemistry of hydrofluoric acid was suggested as promoting the affinity of the sodium ions to the resin.

A kinetic model for heterogeneous acetalisation of poly(vinyl alcohol)

A model for heterogeneous acetalisation of poly(vinyl alcohol) with limited solution volume is proposed based on the grain model of Sohn and Szekely. Instead of treating the heterogeneous acetalisation as purely a diffusion process, as in the Matuzawa and Ogasawara model, the present model also takes into account the chemical reaction and the physical state of the solid polymer, such as degree of swelling and porosity, and assumes segregation of the polymer phase at higher conversion into an outer fully reacted zone and an inner zone where the reaction still proceeds. The solution of the model for limited solution volume, moreover, offers a simple method of determining the kinetic parameters and diffusivity for the solid-liquid system using the easily measurable bulk solution concentration of the liquid reactant instead of conversion-distance data for the solid phase, which are considerably more difficult to obtain.

Knoevenagel condensation of 2-carbethoxycyclohexanone and malononitrile: Synthesis of 4-cyano-3-ethoxy-1-hydroxy-5,6,7,8-tetrahydroisoquinoline, an isomer of the abnormal product

The structure of the abnormal product 1a formed in the Knoevenagel condensation of 2-carbethoxycyclohexanone and malononitrile has been further confirmed. Oxidation of the tetrahydroisoquinoline 3b using Na2Cr2O-AcOH-H2SO4 gave the keto isoquinoline 3d and the isoquinoline-1-carboxylic acid 5a. The acid chloride of 5a was condensed with diethyl ethoxymagnesiomalonate to afford after decarbethoxylation the methyl ketone 5d which on Baeyer-Villiger oxidation gave a mixture of the acetate 1g and the title compound 1b. The unambiguous synthesis of 1b confirms the structure assigned earlier to the title compound also formed during the partial hydrolysis of the diethoxy compound 1c. Condensation of 2-acetylcyclohexane-1,3-dione with malononitrile gave the quinoline derivative 4c which on ethylation yielded the ketoquinoline 4d. The present studies have confirmed that the quinoline compound 4a is also formed in the condensation of 2-acetylcyclohexanone and cyanoacetamide.

A New Method for the Preparation of Sulphuryl Chloro Fluoride

It has been observed that a suspension of sodium fluoride in boiling acetonitrile could be used for the preparation of fluorine compounds such as silicon tetrafluoride [1], thiophosphoryl fluoride [2], sulphur tetrafluoride [3,4], and fluorocyclophosphazenes [5]. This method, when adopted for the fluorination of sulphuryl chloride [6], it is observed that a mixture of sulphuryl fluoride and sulphuryl chloro fluoride is obtained. On the other hand, when lead fluoride is substituted for sodium fluoride, pure sulphuryl chloro fluoride is evolved. Based on this observation, a new method has been standardised for the preparation of a pure sample of sulphuryl chlorofluoride by fluorinating sulphuryl chloride by lead fluoride in acetonitrile medium.

Characterisation and source identification of pollution episodes caused by long-range transported aerosols

Aerosol particles can cause detrimental environmental and health effects. The particles and their precursor gases are emitted from various anthropogenic and natural sources. It is important to know the origin and properties of aerosols to efficiently reduce their harmful effects. The diameter of aerosol particles (Dp) varies between ~0.001 and ~100 μm. Fine particles (PM2.5: Dp < 2.5 μm) are especially interesting because they are the most harmful and can be transported over long distances. The aim of this thesis is to study the impact on air quality by pollution episodes of long-range transported aerosols affecting the composition of the boundary-layer atmosphere in remote and relatively unpolluted regions of the world. The sources and physicochemical properties of aerosols were investigated in detail, based on various measurements (1) in southern Finland during selected long-range transport (LRT) pollution episodes and unpolluted periods and (2) over the Atlantic Ocean between Europe and Antarctica during a voyage. Furthermore, the frequency of LRT pollution episodes of fine particles in southern Finland was investigated over a period of 8 years, using long-term air quality monitoring data. In southern Finland, the annual mean PM2.5 mass concentrations were low but LRT caused high peaks of daily mean concentrations every year. At an urban background site in Helsinki, the updated WHO guideline value (24-h PM2.5 mean 25 μg/m3) was exceeded during 1-7 LRT episodes each year during 1999-2006. The daily mean concentrations varied between 25 and 49 μg/m3 during the episodes, which was 3-6 times higher than the mean concentration in the long term. The in-depth studies of selected LRT episodes in southern Finland revealed that biomass burning in agricultural fields and wildfires, occurring mainly in Eastern Europe, deteriorated air quality on a continental scale. The strongest LRT episodes of fine particles resulted from open biomass-burning fires but the emissions from other anthropogenic sources in Eastern Europe also caused significant LRT episodes. Particle mass and number concentrations increased strongly in the accumulation mode (Dp ~ 0.09-1 μm) during the LRT episodes. However, the concentrations of smaller particles (Dp < 0.09 μm) remained low or even decreased due to the uptake of vapours and molecular clusters by LRT particles. The chemical analysis of individual particles showed that the proportions of several anthropogenic particle types increased (e.g. tar balls, metal oxides/hydroxides, spherical silicate fly ash particles and various calcium-rich particles) in southern Finland during an LRT episode, when aerosols originated from the polluted regions of Eastern Europe and some open biomass-burning smoke was also brought in by LRT. During unpolluted periods when air masses arrived from the north, the proportions of marine aerosols increased. In unpolluted rural regions of southern Finland, both accumulation mode particles and small-sized (Dp ~ 1-3 μm) coarse mode particles originated mostly from LRT. However, the composition of particles was totally different in these size fractions. In both size fractions, strong internal mixing of chemical components was typical for LRT particles. Thus, the aging of particles has significant impacts on their chemical, hygroscopic and optical properties, which can largely alter the environmental and health effects of LRT aerosols. Over the Atlantic Ocean, the individual particle composition of small-sized (Dp ~ 1-3 μm) coarse mode particles was affected by continental aerosol plumes to distances of at least 100-1000 km from the coast (e.g. pollutants from industrialized Europe, desert dust from the Sahara and biomass-burning aerosols near the Gulf of Guinea). The rate of chloride depletion from sea-salt particles was high near the coasts of Europe and Africa when air masses arrived from polluted continental regions. Thus, the LRT of continental aerosols had significant impacts on the composition of the marine boundary-layer atmosphere and seawater. In conclusion, integration of the results obtained using different measurement techniques captured the large spatial and temporal variability of aerosols as observed at terrestrial and marine sites, and assisted in establishing the causal link between land-bound emissions, LRT and air quality.

Methicillin-resistant Staphylococcus aureus in Finland: recent changes in the epidemiology, long-term facility aspects, and phenotypic and molecular detection of isolates

Staphylococcus aureus is one of the most important bacteria that cause disease in humans, and methicillin-resistant S. aureus (MRSA) has become the most commonly identified antibiotic-resistant pathogen in many parts of the world. MRSA rates have been stable for many years in the Nordic countries and the Netherlands with a low MRSA prevalence in Europe, but in the recent decades, MRSA rates have increased in those low-prevalence countries as well. MRSA has been established as a major hospital pathogen, but has also been found increasingly in long-term facilities (LTF) and in communities of persons with no connections to the health-care setting. In Finland, the annual number of MRSA isolates reported to the National Infectious Disease Register (NIDR) has constantly increased, especially outside the Helsinki metropolitan area. Molecular typing has revealed numerous outbreak strains of MRSA, some of which have previously been associated with community acquisition. In this work, data on MRSA cases notified to the NIDR and on MRSA strain types identified with pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec (SCCmec) typing at the National Reference Laboratory (NRL) in Finland from 1997 to 2004 were analyzed. An increasing trend in MRSA incidence in Finland from 1997 to 2004 was shown. In addition, non-multi-drug resistant (NMDR) MRSA isolates, especially those resistant only to methicillin/oxacillin, showed an emerging trend. The predominant MRSA strains changed over time and place, but two internationally spread epidemic strains of MRSA, FIN-16 and FIN-21, were related to the increase detected most recently. Those strains were also one cause of the strikingly increasing invasive MRSA findings. The rise of MRSA strains with SCCmec types IV or V, possible community-acquired MRSA was also detected. With questionnaires, the diagnostic methods used for MRSA identification in Finnish microbiology laboratories and the number of MRSA screening specimens studied were reviewed. Surveys, which focused on the MRSA situation in long-term facilities in 2001 and on the background information of MRSA-positive persons in 2001-2003, were also carried out. The rates of MRSA and screening practices varied widely across geographic regions. Part of the NMDR MRSA strains could remain undetected in some laboratories because of insufficient diagnostic techniques used. The increasing proportion of elderly population carrying MRSA suggests that MRSA is an emerging problem in Finnish long-term facilities. Among the patients, 50% of the specimens were taken on a clinical basis, 43% on a screening basis after exposure to MRSA, 3% on a screening basis because of hospital contact abroad, and 4% for other reasons. In response to an outbreak of MRSA possessing a new genotype that occurred in a health care ward and in an associated nursing home of a small municipality in Northern Finland in autumn 2003, a point-prevalence survey was performed six months later. In the same study, the molecular epidemiology of MRSA and methicillin-sensitive S. aureus (MSSA) strains were also assessed, the results to the national strain collection compared, and the difficulties of MRSA screening with low-level oxacillin-resistant isolates encountered. The original MRSA outbreak in LTF, which consisted of isolates possessing a nationally new PFGE profile (FIN-22) and internationally rare MLST type (ST-27), was confined. Another previously unrecognized MRSA strain was found with additional screening, possibly indicating that current routine MRSA screening methods may be insufficiently sensitive for strains possessing low-level oxacillin resistance. Most of the MSSA strains found were genotypically related to the epidemic MRSA strains, but only a few of them had received the SCCmec element, and all those strains possessed the new SCCmec type V. In the second largest nursing home in Finland, the colonization of S. aureus and MRSA, and the role of screening sites along with broth enrichment culture on the sensitivity to detect S. aureus were studied. Combining the use of enrichment broth and perineal swabbing, in addition to nostrils and skin lesions swabbing, may be an alternative for throat swabs in the nursing home setting, especially when residents are uncooperative. Finally, in order to evaluate adequate phenotypic and genotypic methods needed for reliable laboratory diagnostics of MRSA, oxacillin disk diffusion and MIC tests to the cefoxitin disk diffusion method at both +35°C and +30°C, both with or without an addition of sodium chloride (NaCl) to the Müller Hinton test medium, and in-house PCR to two commercial molecular methods (the GenoType® MRSA test and the EVIGENETM MRSA Detection test) with different bacterial species in addition to S. aureus were compared. The cefoxitin disk diffusion method was superior to that of oxacillin disk diffusion and to the MIC tests in predicting mecA-mediated resistance in S. aureus when incubating at +35°C with or without the addition of NaCl to the test medium. Both the Geno Type® MRSA and EVIGENETM MRSA Detection tests are usable, accurate, cost-effective, and sufficiently fast methods for rapid MRSA confirmation from a pure culture.

Mechanisms of KCC2 upregulation during development

Gamma-aminobutyric acid (GABA) acting through ionotropic GABAA receptors plays a crucial role in the activity of the central nervous system (CNS). It triggers Ca2+ rise providing trophic support in developing neurons and conducts fast inhibitory function in mature neuronal networks. There is a developmental change in the GABAA reversal potential towards more negative levels during the first two postnatal weeks in rodent hippocampus. This change provides the basis for mature GABAergic activity and is attributable to the developmental expression of the neuron-specific potassium chloride cotransporter 2 (KCC2). In this work we have studied the mechanisms responsible for the control of KCC2 developmental expression. As a model system we used hippocampal dissociated cultures plated from embryonic day (E) 17 mice embryos before the onset of KCC2 expression. We showed that KCC2 was significantly up-regulated during the first two weeks of culture development. Interestingly, the level of KCC2 upregulation was not altered by chronic pharmacological blockage of action potentials as well as GABAergic and glutamatergic synaptic transmission. By in silico analysis of the proximal KCC2 promoter region we identified 10 candidate transcription factor binding sites that are highly conserved in mammalian KCC2 genes. One of these transcription factors, namely early growth response factor 4 (Egr4), had similar developmental profile as KCC2 and considerably increased the activity of mouse KCC2 gene in neuronal cells. Next we investigated the involvement of neurotrophic factors in regulation of Egr4 and KCC2 expression. We found that in immature hippocampal cultures Egr4 and KCC2 levels were strongly up-regulated by brain derived neurotrophic factor (BDNF)and neurturin. The effect of neurotrophic factors was dependent on the activation of a mitogen activated protein kinase (MAPK) signal transduction pathway. Intact Egr4-binding site in proximal KCC2 promoter was required for BDNF-induced KCC2 transcription. In vitro data were confirmed by several in vivo experiments where we detected an upregulation of KCC2 protein levels after intrahippocampal administration of BDNF or neurturin. Importantly, a MAPK-dependent rise in Egr4 and KCC2 expression levels was also observed after a period of kainic acid-induced seizure activity in neonatal rats suggesting that neuronal activity might be involved in Egr4-mediated regulation of KCC2 expression. Finally we demonstrated that the mammalian KCC2 gene (alias Slc12a5) generated two neuron-specific isoforms by using alternative promoters and first exons. A novel isoform of KCC2, termed KCC2a, differed from the previously known KCC2b isoform by 40 unique N-terminal amino acid residues. KCC2a expression was restricted to CNS,remained relatively constant during postnatal development, and contributed 20 50% of total KCC2 mRNA expression in the neonatal mouse brainstem and spinal cord. In summary, our data provide insight into the complex regulation of KCC2 expression during early postnatal development. Although basal KCC2 expression seems to be intrinsically regulated, it can be further augmented by neurotrophic factors or by enhanced activity triggering MAPK phosphorylation and Egr4 induction. Additional KCC2a isoform, regulated by another promoter, provides basal KCC2 level in neonatal brainstem and spinal cord required for survival of KCC2b knockout mice.

Structural and functional roles of KCC2 in developing cortex

Cation chloride cotransporters (CCCs) are critical for controlling intracellular chloride homeostasis. The CCC family is composed of four isoforms of K-Cl cotransporters (KCC1-4), two isoforms of Na-K-2Cl cotransporters (NKCC1-2), one Na-Cl cotransporter (NCC) and two the structurally related proteins with unknown function, CCC8 also known as cation-chloride cotransporter interaction protein, CIP, and CCC9. KCC2 is a neuron-specific isoform, which plays a prominent role in controlling the intracellular Cl- concentration in neurons and is responsible for producing the negative shift of GABAA responses from depolarizing to hyperpolarizing during neuronal maturation. In the present studies we first used in situ hybridization to examine the developmental expression patterns of the cation-chloride cotransporters KCC1-4 and NKCC1. We found that they display complementary expression patterns during embryonic brain development. Most interestingly, KCC2 expression in the embryonic central nervous system strictly follows neuronal maturation. In vitro data obtained from primary and organotypic neuronal cultures support this finding and revealed a temporal correlation between the expression of KCC2 and synaptogenesis. We found that KCC2 is highly expressed in filopodia and mature spines as well as dendritic shaft and investigated the role of KCC2 in spine formation by analyzing KCC2-/- neurons in vitro. Our studies revealed that KCC2 is a key factor in the maturation of dendritic spines. Interestingly, the effect of KCC2 in spine formation is not due to Cl- transport activity, but mediated through the interaction between KCC2 C-terminal and intracellular protein associated with cytoskeleton. The interacting protein we found is protein 4.1N by immunoprecipitation. Our results indicate a structural role for KCC2 in the development of functional glutamatergic synapses and suggest KCC2 as a synchronizer for the functional development of glutamatergic and GABAergic synapses in neuronal network. Studies on the regulatory mechanisms of KCC2 expression during development and plasticity revealed that synaptic activity of both the glutamatergic and GABAergic system is not required for up-regulation of KCC2 during development, whereas in acute mature hippocampal slices which undergo continuous synchronous activity induced by the absence of Mg2+ solution, KCC2 mRNA and protein expression were down-regulated in CA1 pyramidal neurons subsequently leading to a reduced capacity for neuronal Cl- extrusion. This effect is mediated by endogenous BDNF-TrkB down-stream cascades involving both Shc/FRS-2 and PLCγ-CREB signaling. BDNF mediated changes in KCC2 expression indicate that KCC2 is significantly involved in the complex mechanisms of neuronal plasticity during development and pathophysiological conditions.

Field-Effect and Frequency Dependent Transport in Semiconductor-Enriched Single-Wall Carbon Nanotube Network Device

The electrical and optical response of a field-effect device comprising a network of semiconductor-enriched single-wall carbon nanotubes, gated with sodium chloride solution is investigated. Field-effect is demonstrated in a device that uses facile fabrication techniques along with a small-ion as the gate electrolyte-and this is accomplished as a result of the semiconductor enhancement of the tubes. The optical transparency and electrical resistance of the device are modulated with gate voltage. A time-response study of the modulation of optical transparency and electrical resistance upon application of gate voltage suggests the percolative charge transport in the network. Also the ac response in the network is investigated as a function of frequency and temperature down to 5 K. An empirical relation between onset frequency and temperature is determined.

GABAa Receptor Mediated Signalling in the Brain: Inhibition, Shunting and Excitation

Within central nervous system, the simple division of chemical synaptic transmission to depolarizing excitation mediated by glutamate and hyperpolarizing inhibition mediated by γ-amino butyric acid (GABA), is evidently an oversimplification. The GABAa receptor (GABAaR) mediated responses can be of opposite sign within a single resting cell, due to the compartmentalized distribution of cation chloride cotransporters (CCCs). The K+/Cl- cotransporter 2 (KCC2), member of the CCC family, promotes K+ fuelled Cl- extrusion and sets the reversal potential of GABA evoked anion currents typically slightly below the resting membrane potential. The interesting ionic plasticity property of GABAergic signalling emerges from the short-term and long-term alterations in the intraneuronal concentrations of GABAaR permeable anions (Cl- and HCO3-). The short-term effects arise rapidly (in the time scale of hundreds of milliseconds) and are due to the GABAaR activation dependent shifts in anion gradients, whereas the changes in expression, distribution and kinetic regulation of CCCs are underlying the long-term effects, which may take minutes or even hours to develop. In this Thesis, the differences in the reversal potential of GABAaR mediated responses between dopaminergic and GABAergic cell types, located in the substantia nigra, were shown to be attributable to the differences in the chloride extrusion mechanisms. The stronger inhibitory effect of GABA on GABAergic neurons was due to the cell type specific expression of KCC2 whereas the KCC2 was absent from dopaminergic neurons, leading to a less prominent inhibition brought by GABAaR activation. The levels of KCC2 protein exhibited activity dependent alterations in hippocampal pyramidal neurons. Intense neuronal activity, leading to a massive release of brain derived neurotrophic factor (BDNF) in vivo, or applications of tyrosine receptor kinase B (TrkB) agonists BDNF or neurotrophin-4 in vitro, were shown to down-regulate KCC2 protein levels which led to a reduction in the efficacy of Cl- extrusion. The GABAergic transmission is interestingly involved in an increase of extracellular K+ concentration. A substantial increase in interstitial K+ tends to depolarize the cell membrane. The effects that varying ion gradients had on the generation of biphasic GABAaR mediated responses were addressed, with particular emphasis on the novel idea that the K+/Cl- extrusion via KCC2 is accelerated in response to a rapid accumulation of intracellular Cl-. The KCC2 inhibitor furosemide produced a large reduction in the GABAaR dependent extracellular K+ transients. Thus, paradoxically, both the inefficient KCC2 activity (via increased intracellular Cl-) and efficient KCC2 activity (via increased extracellular K+) may promote excitation.

Oxidation of spiroketones with DDQ - synthesis of tropone derivatives and DDHQ diesters

Oxidation of spiroketones 3a–f with DDQ in dry benzene gave tropone derivatives 4a–f and DDHQ esters 5a–f (cis -cis isomer 6a–f, (cis -cis isomer 7a–f). While the aryl substituted spirokeone 17a gave a 2:1 mixture of 19a and the corresponding trans -trans isomer, the aryl substituted spiroketones 17b–d gave exclusively trans-trans isomers 19b–d. Heating acid chloride of acid 9c with DDHQ resulted in compounds 4a and 7a, thus confirming the structures assigned. Mechanism of formation of these compounds has been rationalised. A detailed study of 2D 1H-1H COSY, 1H-13C COSY, HMBC and 2D NOESY of compound 7d led to complete assignment of 1H and 13C NMR signals and its solution conformation.

Interaction of surfactants with DNA. Role of hydrophobicity and surface charge on intercalation and DNA melting

A probe, 9-(anthrylmethyl)trimethylammonium chloride, 1, was prepared. 1 binds to calf-thymus DNA or Escherichia coli genomic DNA with high affinity, as evidenced from the absorption titration. Strong hypochromism, spectral broadening and red-shifts in the absorption spectra were observed. Half-reciprocal plot constructed from this experiment gave binding constant of 5±0.5×104 M−1 in base molarity. We employed this anthryl probe-DNA complex for studying the effects of addition of various surfactant to DNA. Surfactants of different charge types and chain lengths were used in this study and the effects of surfactant addition to such probe-DNA complex were compared with that of small organic cations or salts. Addition of either salts or cationic surfactants led to structural changes in DNA and under these conditions, the probe from the DNA-bound complex appeared to get released. However, the cationic surfactants could induce such release of the probe from the probe-DNA complex at a much lower concentration than that of the small organic cations or salts. In contrast the anionic surfactants failed to promote any destabilization of such probe-DNA complexes. The effects of additives on the probe-DNA complexes were also examined by using a different technique (fluorescence spectroscopy) using a different probe ethidium bromide. The association complexes formed between the cationic surfactants and the plasmid DNA pTZ19R, were further examined under agarose gel electrophoresis and could not be visualized by ethidium bromide staining presumably due to cationic surfactant-induced condensation of DNA. Most of the DNA from such association complexes can be recovered by extraction of surfactants with phenol-chloroform. Inclusion of surfactants and other additives into the DNA generally enhanced the DNA melting temperatures by a few °C and at high [surfactant], the corresponding melting profiles got broadened.