WO1997018243A9

WO1997018243A9 - Saccharide surfactants

Info

Publication number: WO1997018243A9
Application number: PCT/US1996/018493
Authority: WO
Filing date: 1996-11-13
Publication date: 1998-08-06
Anticipated expiration: 1998-05-14

Abstract

The present invention provides new saccharide surfactants. The saccharide surfactants include diblock and triblock saccharide surfactants. The diblock saccharide surfactants have a hydrophobic segment bonded to a hydrophilic head group, that is a saccharide chain. The triblock saccharide surfactants have a hydrophobic segment bonded to two hydrophilic saccharide chains. The hydrophobic segments of the diblick and triblock saccharide surfactants comprise at least one alkyl chain having 5 to 20 carbon atoms, preferably 6 to 18 carbon atoms, more preferably 8 to 18 carbon atoms. The saccharide head groups/chains include monosaccharides, disaccharides, and oligosaccharides and have an average weight molecular range of less than 4000. Preferably the saccharide head group/chain comprises 2 to 12 sugar residues. Preferably the saccharide head groups are linked to the alkyl chains by an amide group.

Description

SACCHARIDE SURFACTANTS

FIELD OF INVENTION

The present invention relates to surfactants, primarily saccharide surfactants .

BACKGROUND OF THE INVENTION

Surfactants are compounds which reduce the interfacial tension between a gas and a liquid, for example air and water, between two different liquids, or between a liquid and a solid. Because of their surface-active properties, surfactants are useful as detergents, wetting agents, solubilizing agents, dispersing agents, or emulsifiers.

Surfactants which are soluble in water are especially useful as wetting agents. Wetting agents enhance the ability of water or a water solution to penetrate into or to spread over the surface of another material and include surfactants which are amphophilic.

Surfactants which promote the formation of a stable mixture of two immiscible liquids are also useful as emulsifiers. The emulsion that is formed depends upon the characteristics of the particular surfactant used and can be either an oil in water-type emulsion, where water is the continuous phase and the oil is the disperse phase, or a water in oil-type emulsion in which oil forms the continuous phase and water droplets form the dispersed phase. Surfactants which are able to maintain the phase separation of the emulsion, especially at elevated temperatures, are especially useful as emulsifiers.

SUMMARY OF THE INVENTION

The present invention provides new saccharide surfactants . The saccharide surfactants include diblock saccharide surfactants and triblock saccharide surfactants . Diblock saccharide surfactants have a hydrophobic segment bonded to a hydrophilic head group, that is a saccharide chain. The triblock saccharide surfactants have a hydrophobic segment bonded to two hydrophilic saccharide chains . The hydrophobic segments of the diblock and triblock saccharide surfactants comprise at least one alkyl chain having 5 to 20 carbon atoms, preferably 6 to 18 carbon atoms more preferably 8 to 18 carbons. The saccharide head groups/chains include monosaccharides , disaccharides, and oligosaccharides. Preferably the saccharide head group/chain comprises 2 to 12 sugar residues, more preferably 2 to 10 sugar residues . The diblock and triblock saccharide surfactants typically are soluble in water and reduce the surface tension of aqueous solutions. Accordingly, the water-soluble diblock and triblock saccharide surfactants are useful as wetting agents . The diblock and triblock saccharide surfactants are also useful to form oil-in-water type emulsions. The diblock and triblock saccharide surfactants also associate with hydrophobic polymeric substrates , and are useful for modifying the surface characteristics of hydrophobic substrates. Accordingly, the diblock and triblock saccharide surfactants are useful for reducing friction and providing resistance to protein adsorption of the hydrophobic substrate. Such uses may have broad application in biomedical or bioseparation systems.

DETAILED DESCRIPTION OF THE INVENTION

The saccharide surfactants of the present invention include diblock saccharide surfactants and triblock saccharide surfactants. The diblock saccharide surfactants have a hydrophobic segment comprising at least one alkyl chain and a hydrophilic head group comprising a saccharide chain. The saccharide chains of the diblock saccharide surfactants include monosaccharides , disaccharides, and oligosaccharides. The saccharide chains have from 2 to 12 sugar residues, preferably from 2 to 10 sugar residues and have a weight average molecular weight (M ranging from about 300 to less than 4000, preferably from about 300 to about 3500, more preferably from about 300 to 2000. The alkyl chains of the diblock saccharide surfactants have from about 5 to 20 carbon atoms, preferably 6 to 18 carbon atoms, more preferably 8 to 18 carbon atoms.

The triblock saccharide surfactants comprise : a hydrophobic segment comprising at least one alkyl chain; and two hydrophilic head groups each comprising a saccharide chain. The saccharide chains of the triblock polymers include monosaccharides, disaccharides, and oligosaccharides. The saccharide chains have 2 to 12 sugar residues, preferably 2 to 10 sugar residues and a weight average molecular weight (M ranging from about 300 to less than 4000, preferably from about 300 to about 3500, more preferably from about 300 to 2000. The alkyl chains of the triblock saccharide surfactants have 5 to 20 carbon atoms, preferably 6 to 18 carbon atoms, more preferably 8 to 18 carbon atoms. The hydrophobic segment and hydrophilic head groups are joined by a linkage group. The preferred linkage group is CONH.

The present invention also provides a method for forming and isolating nonionic saccharide surfactants in which the hydrophilic saccharide chains are linked to the hydrophobic alkyl chains by an amide group, that is, a CONH group. In general, the method involves oxidation of the saccharide in an aqueous solution containing iodine and potassium hydroxide. The mixture is then passed through a cationic exchange column to convert the potassium salt form of the saccharide to the acidic form of the saccharide. The eluate from the column is then lyophilized to give the lactone form of the saccharide. To prepare the diblock form of the nonionic saccharide surfactants, the lactonized saccharide is dissolved in DMSO and an alkylamine added to the solution. The solution is heated to 60°C for a time and temperature sufficient to form the diblock saccharide surfactant. The reaction products are then precipitated with chloroform and dried under vacuum at 60°C. The resulting powder is dissolved in water and passed through a weak anionic exchange column.

To prepare the triblock form of the nonionic saccharide surfactants, the lactonized saccharide is dissolved in DMSO and an alkyldiamine added to the solution. The solution is heated to 60°C until the triblock saccharide is formed. At the end of the reaction, the products are precipitated from the solution with chloroform, dried under vacuum at 60°C, and passed through a weak anionic exchange column and a weak cationic exchange column.

The following non-limiting examples are presented to further illustrate the present invention.

Example 1 Synthesis of N-n-He-cyl-D-maltonamide (MAL-C6) .

To a 20 mL aqueous solution containing 1.8 g (5 mmol) of D-maltose monohydrate from Sigma were slowly added 2.54 g (10 mmol) of iodine in 100 mL of water and 2.24 g (40 mmol) of potassium hydroxide in 30 mL of water. The reaction mixture was stirred at ambient temperature for 2 hours and passed through a strong cationic exchange column packed with Amberlite IR-120 resin from Aldrich Chemical Co. The eluate was treated with 5.5 g (20 mmol) of silver carbonate to precipitate excess iodine as silver iodide. The eluate was filtered, and the filtrate again was passed through a regenerated Amberlite IR-120 resin column to convert silver maltonate to D-maltonic acid. The maltonic acid solution was concentrated and lyophilized to give 1.53 g (90% yield) of D-maltonolactone.

To a 10 mL DMSO solution containing 0.68 g (2.0 mmol) of D- maltonolactone was added 2.02 g (20 mmol) of hexylamine from Aldrich Chemical Co. The reaction solution was stirred at 60°C for 2 days and then concentrated to 2 mL by vacuum distillation. The product was precipitated in chloroform. The precipitate was washed with ethyl ether and dried under vacuum at 60°C overnight to give a white powder. The powder was dissolved in 40 mL of distilled water and passed through a weak anionic exchange column packed with Amberlite IRA- 94 resin from Sigma. The eluate was concentrated and lyophilized to give 0.5 g (57% yield) of N-n-Hexyl-D-maltonamide (MAL-C6) . Example 2 Synthesis of N-n-Hexyldextran Aldonamide (DEX9-C6) .

To a 10 mL aqueous solution containing 2.76 g (2 mmol) of dextran (ΛT„ = 1600, M_^/M_^ = 1.16) were slowly added 1.01 g (4 mmol) of iodine in 40 mL of water and 0.90 g (16 mmol) of potassium hydroxide in 20 mL of water. The reaction mixture was stirred at ambient temperature for 24 hours and desalted by passing the reaction mixture through a Sephadex resin G15 column. The dextran fractions were passed through a strong cationic exchange column packed with Amberlite IR-120 resin to convert dextran potassium aldonate to dextran aldonic acid. The eluate was concentrated and lyophilized to give 2.40 g (87% yield) of dextran lactone.

To a 4 mL DMSO solution containing 0.55 g (0.4 mmol) of dextran lactone was added 2.02 g (20 mmol) of hexylamine. The reaction solution was stirred at 60°C for 4 days, and the product was precipitated in chloroform. The precipitate was filtered and dried under vacuum at 60°C overnight to give a white powder. The powder was dissolved in 50 mL of water and passed through a weak anionic exchange column packed with Amberlite IRA-94 resin. The eluate was concentrated and lyophilized to give 0.30 g (50% yield) of N-n-Hexyldextran Aldonamide (DEX9-C6) .

Example 3 Synthesis of N-Dodecylqluconamide (GLU-C12) .

To a 20 mL DMSO solution containing 1.78 g (10.0 mmol) of δ-gluconolactone from Aldrich Chemical Company, was added 3.70 g (20.0 mmol) of dodecylamine . The reaction solution was stirred at 60°C for 24 hours and then concentrated to a white solid residue by vacuum distillation. The residue was recrystallized from methanol to give 3.28 g (90% yield) of N-Dodecylgluconamide (GLU-C12) .

Example 4 Synthesis of N-Dodecylmaltonamide (Mal-C12) .

To a 20 mL DMSO solution containing 1.02 g (3.0 mmol) of maltonolactone, was added 1.11 g (6.0 mmol) of dodecylamine. The reaction solution was stirred at 60°C for 24 hours and then concentrated to a light brown viscous residue by vacuum distillation. The residue was washed with chloroform to yield a slightly yellow powder. The powder was dissolved in a small amount of methanol and precipitated in ethyl ether. The precipitate was filtered and dried under vacuum at 60°C overnight to give 1.24 g (78% yield) of N-Dodecylmaltonamide (Mal-C12) .

Example 5 Synthesis of N-n-Dodecyl-dextran aldonamide (DEX9-C12) . To a 4 L DMSO solution containing 0.55 g (0.4 mmol) of dextran lactone, 1.85 g (10 mmol) of dodecylamine was added. The reaction solution was stirred at 60oc for four days and the product was precipitated in chloroform. The precipitate was filtered and dried under vacuum at 60°C overnight to give 0.56 g (89% yield) of N-n- Dodecyl-dextran aldonamide (DEX9-C12) .

Example 6 Synthesis of N,N' -Hexamethylenebis (D-maltonamide) (MAL-C6- MAP .

To a 10 mL DMSO solution containing 0.68 g (2 mmol) of maltonolactone was added 58 mg (0.5 mmol) of 1, 6-hexanediamine. The mixture was stirred at 60°C for 3 days and then concentrated to 2 mL by vacuum distillation. The product was precipitated in chloroform. The precipitate was filtered and dried under vacuum at 60°C overnight to give a slightly yellow powder. The product was dissolved in 40 L of water and passed through a weak anionic exchange column packed with Amberlite IRA-94 resin and a weak cationic exchange column packed with Amberlite IRC-50 resin. The eluate was concentrated and lyophilized to give 0.22 g (55% yield) of N, N' -Hexamethylenebis (D-maltonamide) (MAL- C6-MAL) .

Example 7 Synthesis of N,N' -Hexamethylenebis (dextran aldonamide) (DEX- C6-DEX) . To a 4 mL DMSO solution containing 0.55 g (0.4 mmol) of dextran lactone was added 11.6 mg (0.1 mmol) of 1, 6-hexanediamine. The solution was stirred at 60°C for 6 days, and the product was precipitated in chloroform. The precipitate was filtered and dried under vacuum at 60°C overnight to give a yellow powder. The powder was dissolved in 40 mL of water and passed through a weak anionic exchange column packed with Amberlite IRA- 94 resin and a weak cationic exchange column packed with Amberlite IRC-50. The eluate was concentrated and lyophilized to give 0.10 g (34% yield) of N,N' -Hexamethylenebis (dextran aldonamide) (DEX-C6-DEX) .

Example 8 Synthesis of N, N' -Dodecamethylene-bismaltonamide (MAL-C12-

MAL) .

To a 10 mL DMSO solution containing 1.70 g (5 mmol) of maltonolactone, was added 0.40 g (2 mmol) of 1, 12-dodecanediamine. The mixture was stirred at 60°C for 48 hours and then concentrated to a light brown viscous residue by vacuum distillation. The residue was washed with chloroform to yield light yellow powder. The powder was purified by flash chromatography using neutral alumina gel as packing material and a water/methanol mixture [%] as eluent to give 0.80 g (59% yield) of N, N' -Dodecamethylene-bismaltonamide (MAL-C12-MAL) .

Example 9 Synthesis of N, N' -Dodecamethylene-bis (dextran aldonamide)

(DEX-C12-DEX) . To a 4 mL DMSO solution containing 0.55 g(0.4 mmol) of dextran lactone, 20.0 mg (0.1 mmol) of 1, 12-dodecanediamine was added. The solution was stirred at 60°C for six days and the product was precipitated in chloroform. The precipitate was filtered and dried under vacuum at 60°C overnight to give yellow powder. The powder was dissolved in 50 mL water and passed through a weak cationic exchange column (2.5 cm ID x 50 cm L) packed with Amberlite IRC-50, and a weak anionic exchange column (2.5 cm ID x 50 cm L) packed with Amberlite IRA-94. The eluate was concentrated and lyophilized to give 0.15 g (51% yield) of N, N' -Dodecamethylene-bis (dextran aldonamide) (DEX-C12- DEX) .

Example 10 Synthesis of N-Qctylmaltonamide (Mal-C8) .

To prepare MAL-C8 maltonolactone was reacted with ocytlamine from Aldrich Chemical Company and isolated from the reaction mixture according to the procedures described above for N-Octylmaltonamide (Mal-C8) .

Example 11 Synthesis of N-Decylmaltonamide (Mai-CIO) .

To prepare MAL-C10 maltonolactone was reacted with decylamine from Aldrich Chemical Company and isolated from the reaction mixture according to the procedures described above for N-Decylmaltonamide (Mal-CIO) in Example 4.

Example 12 Synthesis of N-Octydecylmaltonamide (Mal-C18) .

To prepare MAL-C18, maltonolactone was reacted with octydecylamine from Aldrich Chemical Company and isolated from the reaction mixture according to the procedures described above for N-Octydecylmaltonamide (Mal-C18) as in Example 4.

Example 13 Synthesis of N-n-Octvdecyl-dextran Aldonamide (Dex 9-C18) . To prepare Dex9-C18, dextran lactone was reacted with octydecylamine and isolated from the reaction mixture according to the procedures described above for N-n-dodecyl-dextran aldonamine of example 5.

Characterization of the Saccharide Surfactants The structures of the saccharide surfactants were confirmed using fourier transform infra red (FTIR) spectroscopy and ¹H-nuclear magnetic resonance spectroscopy ^H-NMR) .

FTIR spectroscopy.

Solutions were cast on KBr disks and dried under vacuum before measurements . Powdered materials were ground with KBr powder and pressed into pellets under reduced pressure. Transmission IR spectra in the range 400-4000 cm^"1 were recorded using a Digilab FTS-40 FTIR spectrometer. For each sample, 256 scans were collected with a resolution of 8 cm^"1. FTIR spectroscopy demonstrated that the representative compound maltonic acid was converted quantitatively to D-maltonolactone by lyophilization. The carbonyl stretching peak of δ-lactone at 1740 cm"¹ was shown clearly in the IR spectrum of maltonolactone and the peak attributable to carbonyl stretching of the free acid, which appears around 1700 cm^"1, was not observed. The presence of a weak δ (0-H) peak at 1643 cm^"1 indicated that some water was associated with the maltonolactone .

The quantitative conversion of maltonolactone to N-n-Hexyl- D-maltonamide (MAL-C6) was also monitored by FTIR spectroscopy. As shown by the transmission IR spectra of the reaction product of D- maltonolactone with hexylamine at various times during the 48 hour reaction, the carbonyl stretching peak, v (C=0) in the maltonolactone at 1740 cm^"1 disappeared completely by the end of the 48 hour reaction. During this time there was an increase in the v(C=0) peak at 1650cm^"1 and δ (N-H) peak at 1544 cm ^"1, corresponding to the amide I and amide II absorptions of N-n-Hexyl-D-maltonamide (MAL-C6) .

The transmission IR spectra of dextran lactone and the products of examples 2 and 7 exhibited a v(C=0) peak of δ-lactone at 1740 cm^"1 and a v(C=0) peak of δ-lactone at 1771 cm^"1. The presence of these peaks indicate that dextran aldonic acid is converted to 1,5 dextran lactone and to 1,4 dextran lactone. In contract, there were no lactone peaks in examples 2 or 7 at the end of the reactions. The v(C=0) peak at 1646 cm^"1 and the (N-H) peak at 1547 cm^"1 which are indicative of the amide bond (CONH) were observed in the spectra for both of these examples demonstrating that dextran lactone had been converted to N-n-Hexyldextran Aldonamide (DEX9-C6) and N, N' -Hexamethylenebis (dextran aldonamide) (DEX-C6-DEX) during the reactions with hexylamine and 1,6 hexanediamine, respectively.

The IR spectra of GLU-C12 produced in example 3, MAL-C12 produced in example 4 and MAL-C6-MAL produced in example 6 demonstrated a C=0 stretching (amide I) peak at 1651 cm^"1 and N-H deformation (amide II) peak at 1547 cm^"1 from the amide linkage, whereas the IR spectra of DEX9-C12 of example 5, MAL-C12-MAL of example 8 and DEX9-C12-DEX of example 9 exhibited an amide I peak at 1646 cm^"1 and an amide II peak at 1547 cm"¹. The IR spectra of Examples 3, 4, 5, 8, and 9 also showed the C-H stretching peaks at 2924 cm ^_1 and 2853 cm ^"1 and the C-H deformation at 1467 cm ^"1 from the methylene units. Further more, the O-H stretching peak at 3380 cm ^_1 was observed in the IR spectra of examples 3 , 4 , 5 , 8 and 9. ¹H-Nuclear Magnetic Resonance Spectroscopy

^XH-NMR spectra were recorded at ambient temperature, using a 200 MHz Varian XL-200 spectrometer, in parts per million downfield from tetramethylsilane (TMS) as internal standard and DMSO-d₆ as solvent. -NMR spectroscopy was used to monitor the formation of amide between the saccharide lactones and the alkylamines and alkyldiamines of examples 1-6, 8 and 9. This analytical technique exhibits the chemical shift of protons on the carbon atom adjacent to the amine as a shift in peaks from 2.75 (CH₂NH₂) to 3.09 ppm (CH₂NHCO) upon formation of the amide bond. As expected, the peak at 2.75 ppm disappeared in each of the representative examples .

The ¹H-NMR spectra of D-maltose, shows a proton peak at 6.67 ppm which is due to the anomeric hydroxyl. The ^XH-NMR spectra of MAL-C6 (example 1) and MAL-C6-MAL (example 6) show new proton peaks due to CONH at 7.58 ppm, C0NHCH₂ at 3.09 ppm, and (CH₂)₄ at 1.20-1.40 ppm, while the proton peak related to the anomeric position in maltose is absent. These proton peaks are indicative of successful reactions and purification. The only difference between the -N R spectra of MAL-C6 and MAL-C6-MAL is proton peaks derived from the hydrocarbon segments, that is, hexamethylene vs n-hexyl.

The ^XH-NMR spectra of dextran, shows a proton peak due to the anomeric OH at 6.32-6.65 ppm. The proton peaks due to CONH at 7.82 ppm, CONHCH- at 3.09 ppm and (CH₂)₄ at 1.20-1.40 ppm, were observed in the ^λH-NMR spectra of DEX-C6 (example 2) and DEX-C6-DEX (example 7) , while the proton peak due to the anomeric OH disappeared from these ¹H- NMR spectra.

The peaks and functional groups assignable to these peaks for the remaining examples are as follows :

Example 3, δ 0.86 (3H, CH₃.) , 1.16-1.40 (20H, CH₃_ (CH₂) ₁₀ , 3.07 (2H, -CONH-CH_2-) , 3.11-4.00 (6H, C-H' S and CH₂ in glucose), 4.33-5.35 (5H, -OH's), 7.59 (1H, -CONH-);

Example 4, δ 0.86 (3H, CH₃.) , 1.25-1.40 (20H, CH₃. (CH₂) ₁₀_) , 3.03-4.00 (14H, -CONH-CH₂. and all maltose C-H's except the one at the glycosidic linkage), 4.46-5.52 (9H, C-H at glycosidic linkage and all -OH's), 7.56 (1H, -CONH-);

Example 5, δ 0.87 (CH_3-) , 1.25-1.40 (CH₃_ (CH₂) _10-) , 3.00-4.04 ( -CONH-CH₂. and all dextran C-H's except the ones at the glycosidic linkage) , 4.39- 5.32 (C-H's at glycosidic linkage and all -OH's), 7.82 (-CONH) ;

Example 8, δ 1.20-1.40 (20H, -(CH₂)₁₀-), 3.09-4.00 (28H, -CONH- CH₂- and all maltose CH's and CH₂'s except the one at glycosidic linkage), 4.48-5.56 (18H, C-H at glycosidic linkage and all -OH's), 7.58 (2H, -CONH-) ;] and Example 9, δ 1.20-1.40 (-(CH₂)₁₀ , 3.00-4.04 (-C0NH-CH_2. and all dextran C-H's except the ones at glycosidic linkage), 4.39-5.32 (C-H's at glycosidic linkage and all -OH's), 7.82 (-CO-NH-) .

Both FTIR spectroscopy and -NMR spectroscopy confirmed the formation of an amide linkage between the hydrophobic alkyl chain and the hydrophilic saccharide chain of the representative saccharide surfactants . The results of these analyses also indicate that the synthetic procedures and purification methods described above successfully prepared novel diblock and triblock saccharide surfactants.

Solubility Properties

All of the representative diblock and triblock saccharide surfactants except GLU-C12, DEX-C12 and MAL-C18 were soluble in water at of 10% concentration. DEX-C12 was soluble in water at a concentration below 2 mg/ml . GLU-C12 and MAL-C18 were not soluble in water even at a concentration of 0.01%. None of the saccharide surfactants were soluble in octane, a nonpolar organic solvent. These results indicate that the diblock and triblock saccharide surfactants are more hydrophilic than hydrophobic. To determine a cloud point temperature for the sample saccharide surfactants, all of the water soluble saccharide surfactants including DEX-C12 were dissolved in water at a concentration of 1% and heated to various temperatures up to 100°C The cloud point temperature is the temperature at which a hydrophilic surfactant forms large aggregates . The formation of aggregates is believed to be due to dehydration of the surfactant . No cloud points were observed for any of the soluble saccharide surfactants . This indicates that the degree of hydration of the saccharide chains of the block surfactants is sufficient to prevent phase separation even at high temperatures .

REDUCING SURFACE TENSION OF AQUEOUS SOLUTIONS WITH SACCHARIDE SURFACTANTS

Surface tension reduction is one of the characteristic properties that water-soluble surfactants exhibit in aqueous solution. The reduction in surface tension results from the replacement of water molecules at the water/air interface by surfactant molecules . At low concentrations, the saccharide surfactants are oriented so that the hydrophobic segments are exposed to the air at the interface and the hydrophilic head groups are in the aqueous environment. As the concentration of surfactant in the solution is increased, the surface density of the surfactant also increases until the interface becomes saturated with surfactant molecules. At this point, referred to as the critical adsorption concentration (CAC) , increasing the surfactant concentration will not further reduce the surface tension of the aqueous solution. Increasing the concentration of surfactant beyond the CAC does, however, result in the formation of micelles.

With the block saccharide surfactants , the alkyl chains form the core of the micelles and the saccharide head groups extend into the aqueous phase of the aqueous solution. Since the driving force for adsorption is also the driving force for micellization, CAC and the critical micelle concentration (CMC) are closely related.

To determine the effect of each of the saccharide surfactants on the surface tension of water, a stock solution for each water-soluble surfactant was freshly prepared in water and then diluted to the desired concentration for each measurement. The surface tension of each aqueous solution of surfactant was then measured three times at 25°C and ambient pressure using a Du Nouy Ring Tensionmeter . An average error less than 0.5 dynes/cm was obtained routinely for all measurements. The water surface tension in dynes/cm was plotted against the logarithm of surfactant concentration in the aqueous solution for each of the diblock saccharide surfactants .

The water soluble diblock saccharide surfactants of examples 1, 4, 5, 8, 10, 11, 12 and 13 exhibited classic surfactant behavior. For each of the surfactants, the surface tension decreased linearly with increasing logarithm of surfactant concentration until reaching a plateau. An inflection point, which corresponds to the critical micelle concentration, was observed for the diblock saccharide surfactants of examples 1, 4, 5, 8, 10, 11, 12 and 13.

A similar study of the ability of triblock saccharide surfactants to reduce surface tension was conducted with examples 8,

MAL-C12-MAL and Example 9, DEX-C12-DEX, and compared to the results obtained with the diblock saccharide surfactants of Example 4, MAL-C12, and Example 5, DEX-C12. The results demonstrated that the diblock and triblock maltose-based surfactants, Mal-C12-Mal and Mal-C12 both reduced the surface tension of water from 72.5 dynes/cm to less than 40 dynes/cm. The diblock and triblock dextran-based surfactants Dex-Cl2- Dex and Dex-C12 both reduced the surface tension of water from about 72.5 cynes/cm to about 45 dynes/cm.

In contrast to the single inflection point observed or the surface tension plot of the diblock saccharide surfactant MAL-C12, two inflection points were observed on the surface tension plot for the triblock surfactant MAL-C12-MAL. It is believed that the first inflection point which occurs at low concentrations of MAL-C12-MAL is related to the formation of premicelles with small aggregation number and that the second inflection point, which occurs at high concentrations of MAL-C12-MAL in the aqueous solution, is related to the formation of true micelles and, thus, represents the CMC. The surface tension plot for the triblock surfactant DEX-C12-DEX exhibited one inflection point which correlated to premicelle formation. However, no second inflection point corresponding to CMC was observed for DEX-C12-DEX even when the concentration was increased to 100 mg/ml . Thus, the CMC of triblock saccharide surfactants which form micelles are higher than the CMC values of corresponding diblock saccharide surfactants .

The CMC values for the diblock and triblock saccharide surfactants are summarized in Table 1.

Table 1

As shown in Table 1, the CMC decreases with increasing alkyl chain length. There appears to be no effect on the CMC, however, of increasing the saccharide chain length of the surfactant from two sugar residues to nine sugar residues as shown by comparing the CMC values for MAL-C12 and DEX9-C12. The logarithm of CMC for the N- alkylmaltonamides of examples 1, 10, 11 and 12 was plotted as a function of carbon number in the alkyl chain. The plot showed that the logarithm of CMC decreases linearly with increasing carbon number in the alkyl chain with a slight deviation for MAL-C6.

The surface concentration and surface area occupied by the diblock and triblock saccharide surfactants were obtained for examples 1, 4, 5, 8, 9, 10, 11 and 12 using the surface tension plots and the simplified Gibbs adsorption equation: dγ = -2.303RT r dlogC. The Gibbs adsorption equation relates the surface (excess) concentration of the surfactant, r, to the surface tension and the surfactant chemical potential. r is calculated from the slope of the dγ/dlogC plot when the concentration is below CMC. For dilute surfactant solutions, the bulk concentration is much smaller that the concentration at the interface, so r is practically the same as the surface density of the monolayer. Thus, for dilute solutions the area occupied per molecule of surfactant is approximately 1/r.

The surface concentration of the diblock and triblock saccharide surfactants , the surface area occupied by each of the diblock and triblock saccharide surfactant molecules, and the sugar density per unit of surface area of the diblock and triblock surfactants are summarized in Table 2.

Table 2

Note: Data n parent esis were o taine at premice le stage

As shown in Table 2, the triblock surfactants occupy a greater surface area than the corresponding diblock surfactants, especially at low concentrations of triblock surfactant . As the concentration of the triblock surfactant increases, the area occupied per molecule of surfactant decreases. For example, the surface area per molecule of MAL-C12-MAL at the water/air interface decreased from 71 to 49 A² as the solution went through the premicelle and micelle stages. Conversely, the sugar residues per unit area increased significantly when a second oligosaccharide segment was added to the hydrophobic segment. For example, the sugar residues per unit went from 14.8 for DEX9-C12 to 19.6 for DEX9-C12-DEX9.

Of the maltose-based disaccharide surfactants, MAL-C6 had the lowest surface concentration and largest surface area per molecule. The high surface area per molecule of MAL-6 is believed to be due to weak interactions between the hexyl chains. For the other maltose-based diblock surfactants, the surface areas occupied by each molecule are quite similar. As shown in Table 2, significant changes in surface concentration and surface area per molecule were observed when the size of the hydrophilic saccharide chain was changed while the size of the alkyl chain was kept constant . A comparison of surface area per molecule of MAL-C12 and DEX-C12 demonstrates a significant increase in surface area per molecule when the size of the saccharide chain was increased from 2 sugar residues to 9 sugar residues. Since MAL-C12 and DEX9-C12 have the same alkyl segment, the higher surface area occupied by the latter surfactant is believed to be attributed to the larger hydrophilic chain. Thus, the surfactant density at the air/water interface is decreased by increasing oligosaccharide chain length and by changing the molecular geometry of the surfactants from the diblock to triblock type. However, these same changes in surfactant structure substantially increased the overall sugar density at the air/water interface.

The surface tension reduction property of the block surfactants were usually evaluated by their efficiency and effectiveness. The efficiency of a surfactant is the concentration of surfactant required to reduce surface tension to a certain value. Effectiveness, which does not always follow the same trends as efficiency, is the maximum reduction in surface tension that a certain surfactant can achieve regardless of concentration.

The efficiencies of the diblock and triblock saccharide surfactants were evaluated by determining the pC20, or the value of the negative logarithm of the bulk concentration necessary to reduce the surface tension by 20 dynes/cm. The effectiveness of the diblock and triblock saccharide surfactants were evaluated by determining the Trcmc, which is the extent of surface tension reduction attained at the CMC.

The effectiveness of a surfactant in reducing surface tension is related to its maximum surface concentration, T , CMC and efficiency by the following equation: τrcmc=20 + 2.30RT r log(cmc/c .=20) . The efficiency and measured effectiveness for the water soluble diblock and triblock saccharide surfactants are shown in Table 3. Table 3

As shown in Table 3, the efficiency exhibited by each type of surfactant increased as the size of the alkyl chain increased. For each diblock saccharide surfactant having the same hydrophilic head group, an increase in the alkyl segment length resulted in an increase in the surface tension reduction efficiency. Similar results were observed for the triblock saccharide surfactants. A plot of the efficiency of the N-alkylmaltonamides versus the carbon number demonstrated that the efficiency increased linearly with increasing carbon number in the alkyl chain.

A comparison of the pC20 values for MAL-C12 and MAL-C12-MAL demonstrates that the triblock saccharide surfactants were less efficient at reducing water surface tension than the corresponding diblock surfactants. The concentration of DEX-C12 and DEX-C12-DEX required to reduce the surface tension of water by 50 dynes/cm was 2 mg/ml and 0.2 mg/ml, respectively. Since the molecular weight of the triblock surfactant is about twice that of the diblock surfactant, this indicates that DEX-C12 is about five times as efficient as DEX-C12-DEX in reducing surface water tension.

As shown in Table 3 , the effectiveness in reducing surface tension did not change with differences in the hydrophobic chain length. The Ttcmc is almost constant for N-alkylmaltonamides with different alkyl chain lengths because log(cmc/c_π=20) and r change in opposite directions at approximately the same rate with the change of hydrophobic chain length. In addition, the DEX-C6 is almost as effective at reducing water surface tension as DEX-C12, and the DEX-C6- DEX is almost as effective as the DEX-C12-DEX at reducing water surface tension. These results are similar to the results obtained with the maltose-based compounds. In contrast, the size of the saccharide chain length had a significant effect on the effectiveness of the diblock surfactants in reducing surface tension, as demonstrated by comparing the Trcmc values for MAL-C12 and DEX9-C12 shown in Table 3.

The effect of hydrophobic/alkyl chain length on the surface reduction properties of the saccharide surfactants is also shown by comparing the efficiencies of DEX-C6 and DEX-C12-DEX. In DEX-C6 and DEX-C12-DEX the ratio of hydrophobic/alkyl chain length to hydrophilic/saccharide chain length for each of these surfactants is the same. It was found that DEX-C12-DEX is more efficient at reducing water surface tension than DEX-C6.

These studies indicate that molecular shape and molecular size of the hydrophobic segments and the hydrophilic head groups all affect the surface tension reduction capabilities of saccharide surfactants. For saccharide surfactants having the same number of saccharide chains, increasing the length of the hydrophobic segment/alkyl chain increases the efficiency of the saccharide surfactant at reducing surface tension but does not change the effectiveness of the surfactant. Increasing the length of the saccharide chain reduces the effectiveness of the surfactant but does not change the surface tension reduction efficiency.

The triblock saccharide surfactants have higher critical micelle concentrations than diblock saccharide surfactants with the same size hydrophobic/alkyl segments and hydrophilic saccharide chains. In addition, diblock saccharide surfactants are more efficient at reducing surface water tension than the corresponding triblock surfactant, i.e., having the same size alkyl chain and saccharide chain. For saccharide surfactants with a different number of saccharide chains and a different alkyl chain length but with the same saccharide chain length to alkyl chain length ratio, the triblock is more efficient than the diblock in reducing surface tension.

EMULSIFYING OIL AND OCTANE MIXTURES WITH SACCHARIDE SURFACTANTS

Emulsions were prepared with the saccharide surfactants by vortexing a l/l volume ratio octane/water mixture containing 2% surfactant at 3000 rpm for 1 hour using a Vortex Geni II Mixer. The emulsion type was determined by the dilution method. The emulsion stability was analyzed over a one week period at room temperature by visual observation. The types and stability of the emulsions prepared using the saccharide surfactants is shown in Table 4.

Table 4

As shown in Table 4, the emulsion type formed by the saccharide surfactants is an oil in water (o/w emulsion). In all cases, the emulsion dispersed readily in water but did not disperse in octane. These results are consistent with the solubility and cloud point results which also indicate that the present saccharide surfactants are more hydrophilic than hydrophobic.

ALTERING THE HYDROPHOBICITY OF SOLID SURFACES WITH SACCHARIDE SURFACTANTS Polyethylene (PE) films were rinsed several times with distilled water and soaked in the aqueous solutions containing the diblock and triblock saccharide surfactants of examples 2, 5, 7 and 9 at a concentration of 1 mg/ml for different time periods. The polyethylene films were also immersed in aqueous solutions containing different concentrations of the surfactants for 24 hours at 25°C. The PE films were then washed with distilled water three times and air dried in a class 100 clean hood overnight. Control films were soaked in distilled water or aqueous solutions of dextran at a 1% concentration.

The adsorption of the surfactants and, hence, the ability of these compounds to alter the hydrophobicity of the polyethylene substrate, was evaluated by X-ray photon spectroscopy. Because unaltered polyethylene films lack atomic oxygen, the atomic oxygen concentration at the surface of polyethylene films can be used to determine the kinetics and extent of saccharide surfactant adsorption to the hydrophobic polyethylene substrate.

The surface oxygen and carbon concentration of the control and surfactant-treated films were measured by X-ray photon spectroscopy (XPS) using a Perkin Elmer PHI-5400 ESCA system. The X-ray source was magnesium and the pass energy was 89.75 eV. The experiments were carried out at a take-off angle of 45 degrees. At least three films were tested for each surfactant concentration and the average error is within 2%. The average values were reported. To monitor the kinetics of saccharide surfactant adsorption to the hydrophobic substrate, the polyethylene films were removed from aqueous solutions containing 1 mg/ml of the saccharide surfactants at various time points and the films examined by XPS . The results of these studies indicated that adsorption of the surfactants to the PE films reached equilibrium after several hours.

The XPS survey scans of the control polyethylene film soaked in an aqueous solution of 1 mg/ml dextran were compared to the XPS survey scans of the polyethylene films treated with aqueous solutions containing lmg/ml of the diblock and triblock surfactants DEX-C12 and DEX-C12-DEX. As expected, only about 1% oxygen was observed on the control film soaked in a dextran solution. In contrast, significantly higher oxygen concentrations were observed for the PE films treated with the dextran-based surfactants, establishing the adsorption of surfactant molecules on the PE film. The driving force for the adsorption of surfactant is most likely the hydrophobic interaction between the hydrophobic dodecamethylene segment and the hydrophobic PE surface.

The surface oxygen concentration on surfactant treated PE surfaces was plotted against surfactant concentration. For both the diblock and triblock dextran based surfactants, DEX-C12 and DEX-C12- DEX, the oxygen concentration increased with increasing concentration of surfactant until the interface became saturated with surfactant molecules. At surfactant concentrations below 0.5 mg/ml, the oxygen concentration on the polyethylene treated with the diblock surfactant was slightly greater than the oxygen concentration of the PE film treated with the triblock surfactant. This reflects the higher tendency of the diblock surfactants to adsorb at the surface/water interface from aqueous solutions than the triblock surfactants . At surfactant concentrations above 1 mg/ml, the oxygen concentration on the triblock surfactant treated PE surface was almost twice the oxygen concentration on the diblock surfactant-treated PE surface. Since the bulk oxygen concentration in DEX-C12-DEX is about twice the bulk oxygen concentration in DEX-C12, these results imply that DEX-C12 and DEX-C12- DEX have similar surface molar densities. On the basis of these results, it is believed that, the hydrophobic segments of the diblock and triblock surfactants are lying parallel to the PE surface at the PE/water interface and that the dextran hydrophilic head groups are extending out into the aqueous solution at high concentrations of surfactant . When the polyethylene films were soaked in aqueous solutions containing DEX-C6 and DEX-C6-DEX, the surface oxygen concentrations were lower than those observed when the films were soaked in aqueous solutions of diblock and triblock surfactants having longer hydrophobic chains. These results confirm that hydrophobic chain length and surfactant molecular shape are important factors in controlling adsorption to hydrophobic surfaces .

These results also show that hydrophobic surfaces can be made hydrophilic by simple adsorption of dextran surfactants to the hydrophobic surface. Since it is much easier to alter the hydrophobic surfaces by adsorption of saccharide surfactants than by surface chemical derivation, physiosorption of surfactants on hydrophobic surfaces should be a highly desirable method for altering the hydrophobicity of hydrophobic substrates . While the invention has been described to some degree of particularity, various adaptations and modifications can be made without departing from the scope of the invention as defined in the appended claims .

Claims

What is claimed is :

1. A saccharide surfactant comprising at least one hydrophobic segment linked to at least one hydrophilic head group, wherein said hydrophobic segment comprises an alkyl group comprising from about 5 to 20 carbon atoms and said hydrophilic head group comprises a saccharide chain having a weight average molecular weight range of from about 300 to less than 4000.

2. The saccharide surfactant of claim 1 wherein said alkyl group comprises from 6 to 18 carbon atoms.

3. The saccharide surfactant of claim 1 wherein said saccharide chain comprises from 2 to 12 sugar residues.

4. The saccharide surfactant of claim l wherein said saccharide surfactant is nonionic.

5. The saccharide surfactant of claim 1 wherein said saccharide head group is linked to said alkyl chain by an amide group.

6. The saccharide surfactant of claim 5 wherein said saccharide chain comprises from about 2 to 12 sugar residues and has a weight average molecular weight range of from about 300 to about 3500 and said alkyl group comprises from about 6 to about 18 carbon atoms.

7. The saccharide surfactant of claim 5 wherein said saccharide chain comprises from about 2 to 10 sugar residues and has a weight average molecular weight range of from about 300 to about 2000 and said alkyl group comprises from about 8 to about 18 carbon atoms.

8. The saccharide surfactant of claim 5 wherein said saccharide chain is selected from the group consisting of maltose and dextran and said said alkyl is selected from the group consisting of hexyl , octyl , decyl , dodecyl , and octydecyl .

9. The saccharide surfactant of claim 5 wherein said saccharide surfactant is a diblock surfactant and comprises one hydrophobic segment linked to one hydrophilic head group.

10. The saccharide surfactant of claim 9 wherein said alkyl group is a hexyl and said saccharide chain is a maltose group.

11. The saccharide surfactant of claim 9 wherein said alkyl group is a hexyl and said saccharide chain is a dextran comprising nine glucose residues.

1 . The saccharide surfactant of claim 9 wherein said alkyl group is a dodecyl and said saccharide is a maltose group .

13. The saccharide surfactant of claim 9 wherein said alkyl group is a dodecyl and said saccharide chain is a dextran comprising nine glucose residues.

14. The saccharide surfactant of claim 9 wherein said alkyl group is a decyl and said saccharide chain is a maltose group.

15. The saccharide surfactant of claim 9 wherein said alkyl group is an octydecyl and said saccharide chain is a dextran comprising nine glucose residues .

16. The saccharide surfactant of claim 9 wherein said alkyl group is an octydecyl and said saccaride is a maltose group.

17. The saccharide surfactant of claim 9 wherein said alkyl group is an octyl and said saccharide chain is a maltose group .

18. The saccharide surfactant of claim 5 wherein said saccharide surfactant is a triblock surfactant and comprises one hydrophobic segment linked to two hydrophilic head groups.

19. The saccharide surfactant of claim 18 wherein said alkyl group is a hexyl and each of said saccharide chains is a maltose group.

20. The saccharide surfactant of claim 18 wherein said alkyl group is a hexyl and each of said saccharide chains is a dextran comprising nine glucose residues.

21. The saccharide surfactant of claim 18 wherein said alkyl group is a dodecyl and each of said saccharide chains is a maltose group .

22. The saccharide surfactant of claim 18 wherein said alkyl group is a dodecyl and each of said saccharide chains is a dextran comprising nine glucose residues.

23. A method for making the saccharide surfactant of claim 5 comprising the steps of :

(a) providing a saccharide comprising from 2 to 12 sugar residues and having a reducing end group;

(b) oxidizing the reducing end group of the saccharide of step

(a) in an aqueous solution to provide a saccharide having an oxidized end group;

(c) converting the oxidized end group of the saccharide of step

(b) to a lactonized end group;

(d) reacting the lactonized saccharide of step (c) with an alkyl selected from the group consisting of an alkylamine and an alkyldiame to provide a saccharide surfactant having a linear structure.