SUPPLEMENTARY INFORMATION FOR THE MANUSCRIPT
A novel approach to the measurement of surfactant parameters in arthropod digestive juice
Tea Romih a,*, Ksenija Kogej b, Damjana Drobne a
a
Department of Biology, Biotechnical Faculty, University of Ljubljana, Večna pot 111, SI-
1000 Ljubljana, Slovenia b
Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical
Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia
*Corresponding author: Tea Romih University of Ljubljana Biotechnical Faculty, Department of Biology Večna pot 111 1000 Ljubljana Slovenia Phone: +386 1 320 33 75 Fax: +386 1 257 33 90 E-mail:
[email protected]
The Supplementary Information comprises:
Supplementary Figure S1. The isolated hindgut of P. scaber with the markings of length and transversal cross-section area.
Supplementary methods: The details of calculating the equivalent volume of the titrant, including Supplementary Eq. S1–S4.
Supplementary Table S1. The schematic representation of the calculations of the first and the second differential of the potentiometric titration curves based on the Supplementary Eq. S1–S4.
Supplementary results: the titrations of commercially available synthetic surfactants as the quality control check of the performance of the surfactant ion-selective electrode.
Supplementary Figure S2. The response (E) of the surfactant ion-selective during the titration of 20 mL of 2.5 mM sodium dodecyl sulfate (SDS) solution with a 100 mM dodecylpyridinium chloride (DPC) solution.
Supplementary Figure S3. The response (E) of the surfactant ion-selective during the titration of 20 mL of 0.25 mM sodium dodecyl sulfate (SDS) solution with 4 mM dodecylpyridinium chloride (DPC) solution.
Supplementary Figure S4. The response (E) of the surfactant ion-selective electrode during the titration of 20 mL of 5 mM N-lauroylsarcosine (NLS) solution with a 100 mM dodecylpyridinium chloride (DPC) solution.
Supplementary references
Supplementary Figure S1
Figure S1. The isolated hindgut of P. scaber containing remnants of food, as seen under a stereomicroscope at 6-fold magnification. The hindgut length and the longitudinal cross-section area were measured upon calibration of the stereomicroscope with an external scale (millimeter paper). The markings of measured values in the photograph were produced automatically by the software.
Supplementary methods: The details of calculating the equivalent volume of the titrant
Given two measurements in the electrode potential vs. volume plot, (V1 , E 1 ) and (V2 , E 2 ), the first derivative is 𝜕𝐸
𝜕𝑉
≈
∆𝐸
∆𝑉
𝐸2 −𝐸1
=
𝑉2 −𝑉1
(Eq. S1),
and the second derivative is computed analogously from the differences of the first derivative values. The equivalent point is the point where the first derivative (ΔE/ΔV) reaches a maximum value, and the second derivative (Δ2E/ΔV2) equals zero or changes its sign. The equivalent volume, Ve , is equal to 𝑉𝑒 = 𝑉𝑛 + 𝑣 (Eq. S2),
where Vn is the total volume of the added titrant just below the equivalent point and v is the volume that needs to be added to reach the equivalent point, and is calculated as (∆2 𝐸/∆𝑉 2 )+
𝑣 = (∆2𝐸/∆𝑉 2 )
+ −(∆
2𝐸/∆𝑉 2 )
−
∙ ∆𝑉 (Eq. S3).
Here, (Δ2E/ΔV2) + is the last still positive value and (Δ2E/ΔV2) – is the first already negative value of the second derivative, and ΔV is the titrant volume added in the vicinity of the equivalent point.
The Eq. S3 is based on the assumption that the second derivative of the function E = f(V) depends linearly on the volume of the added titrant in the vicinity of the equivalent point. As the ΔV and consequently ΔV2 are constant, the ΔV2 parts of the Eq. S3 cancel out, so that the second derivatives of the Δ2E/ΔV2 quotients can be substituted with the differences Δ2E, which yields: (∆2 𝐸)+
𝑣 = (∆2𝐸)
+ −(∆
2 𝐸)
−
∙ ∆𝑉 (Eq. S4),
where (Δ2E) + is the last still positive value and (Δ2E) – is the first already negative value of this difference. The equivalent volume is then calculated from Eq. S2.
A schematic representation of the equivalent volume calculations based on the first and the second derivatives in the vicinity of the equivalent point of the titration curve is presented in Table S1.
Table S1. The schematic representation of the calculations of the first and the second derivative based on Eqs. S1–S4. Such calculations are possible only if the titrant volume additions are small and constant.
V [mL]
E [mV]
The first differential quotient,
The second differential quotient, Δ2E/ΔV2
ΔE/ΔV V n–1
E n–1
} Vn
En
} V n+1
E n+1
} V n+2
E n+2
𝐸𝑛 −𝐸𝑛−1 𝑉𝑛 −𝑉𝑛−1
𝐸𝑛+1 −𝐸𝑛 𝑉𝑛+1 −𝑉𝑛
∆𝐸
= �∆𝑉� ∆𝐸
= �∆𝑉�
𝐸𝑛+2 −𝐸𝑛+1 𝑉𝑛+2 −𝑉𝑛+1
∆𝑉 2
𝑛−1+
∆𝑉 2
𝑛+
∆𝐸
= �∆𝑉�
∆𝑉 2
𝑛+1+
∆𝐸 ∆𝐸 � − � � ∆𝑉 𝑛+∆𝑉 ∆𝑉 𝑛−1+∆𝑉 2 2
}
�
}
�
𝑉𝑛 −𝑉𝑛−1
∆𝐸 ∆𝐸 � − � � ∆𝑉 ∆𝑉 𝑛+1+∆𝑉 ∆𝑉 𝑛+ 2 2
𝑉𝑛+1 −𝑉𝑛
>0
(Δ2E/ΔV2) +
10 (Figure S4), but not at the natural pH of NLS, which was 7.9 (data not shown). A mathematical evaluation of titration curves was possible despite their less steep slope in comparison to the titration curves of SDS (compared with Figures S2, S3). The determined value of the NLS concentration was within 10% of the nominal value, which is in good agreement with the expected water content (~3%, determined by Karl Fischer titration; note that NLS was not dried before use!) and possible presence of impurities (as stated by Sigma Aldrich for the product no. L5125 SIGMA).
Figure S4. The response (E) of the surfactant ion-selective electrode during the titration of 20 mL of 5 mM Nlauroylsarcosine (NLS) solution with a 100 mM dodecylpyridinium chloride (DPC) solution. The DPC solution was added to the NLS solution in 100 µL increments. The two curves represent two consecutive measurements.
REFERENCES
Dowd, S.R., Little, J.M., 1976. Preparation of laurylsarcosyltaurine: a surface active constituent of crab gastric juice. Journal of Lipid Research, 17(2), 154–155.
Metrohm Application Bulletin No. 233/3 e. Titrimetric/potentiometric determination of anionic and cationic surfactants. Metrohm AG, Herisau, Switzerland.
Holwerda, D.A., Vonk, H.J., 1973. Emulsifiers in the intestinal juice of crustacea. Isolation and nature of surface-active substances from Astacus leptodactylus Esch. and Homarus vulgaris L. Comparative Biochemistry and Physiology Part B: Comparative Biochemistry, 45(1), 51–58.
van den Oord, A. et al., 1965. On the structure of the emulsifiers in gastric juice from the crab, Cancer pagurus L. Journal of Biological Chemistry, 240(5), 2242–2247.
Vonk H.J., 1969. The properties of some emulsifiers in the digestive fluids of invertebrates. Comparative Biochemistry and Physiology, 29, 361–371.
